These raps stood out in a docket crowded with the usual misdemeanours of a huge, close-packed city.
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The militants fight with mortars, guns and car bombs, often hiding among civilians in the close-packed houses and narrow streets.
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The Premier League trophy glints in the afternoon sunlight, while the players – as exhorted by their manager – wave to the close-packed throng.
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The artists Robert Gober and Donald Moffett have orchestrated the most complex, suggestive and close-packed display at Demisch Danant on a thick-topped oak refectory table, as well as the floor and adjacent walls.
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Public health authorities also should oversee the creation of temperature checkpoints outside of factories and office buildings, and in other close-packed or high-traffic places — and those measures should be increased anytime disease detectives find the hint of a brewing outbreak.
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On the shortest stage of the 104th Tour, other than the two time trials, Sky brought Mikel Landa into play — sending Froome's Spanish teammate racing off ahead on a fast and furious Stage 13 that became part chess and part a test of speed and endurance over a close-packed succession of three climbs in the Pyrenees.
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Another example is hematite on magnetite . The magnetite structure is based on close-packed oxygen anions stacked in an ABC- ABC sequence. In this packing the close-packed layers are parallel to (111) (a plane that symmetrically "cuts off" a corner of a cube). The hematite structure is based on close-packed oxygen anions stacked in an AB-AB sequence, which results in a crystal with hexagonal symmetry.
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"Introduction to Chemical and Structural Defects in Crystalline Solids", in Treatise on Solid State Chemistry Volume 1, Springer. The most common example of stacking faults is found in close-packed crystal structures. Face-centered cubic (fcc) structures differ from hexagonal close packed (hcp) structures only in stacking order: both structures have close-packed atomic planes with sixfold symmetry — the atoms form equilateral triangles. When stacking one of these layers on top of another, the atoms are not directly on top of one another.
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The double hexagonal close packed (dhcp) structure with ABAC alignment of FeH. Each sphere is an iron atom. Hydrogen are located in the interstices. The best- known high-pressure phase in the iron-hydrogen system (characterized by V. E. Antonov and others, 1989) has a double hexagonal close packed (DHCP) structure.
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NiAs structure Many chemical compounds have distorted structures. Nickel arsenide, NiAs has a structure where nickel and arsenic atoms are 6-coordinate. Unlike sodium chloride where the chloride ions are cubic close packed, the arsenic anions are hexagonal close packed. The nickel ions are 6-coordinate with a distorted octahedral coordination polyhedron where columns of octahedra share opposite faces.
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AlCl3 adopts three structures, depending on the temperature and the state (solid, liquid, gas). Solid AlCl3 is a sheet-like layered cubic close packed layers. In this framework, the Al centres exhibit octahedral coordination geometry.In contrast, AlBr3 has a more molecular structure, with the Al3+ centers occupying adjacent tetrahedral holes of the close-packed framework of Br− ions.
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226 with low mechanical strength.Liu & Pecht 2004, p. 54 It has a close-packed face-centred cubic structure (BCN 12).Donohue 1982, p.
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This is not a close packed structure. In this each metal atom is at the centre of a cube with 8 nearest neighbors, however the 6 atoms at the centres of the adjacent cubes are only approximately 15% further away so the coordination number can therefore be considered to be 14 when these are ong one 4 fold axe structure becomes face-centred cubic (cubic close packed).
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Its structure consists of chains of TiCl6 octahedra that share opposite faces such that the closest Ti—Ti contact is 2.91 Å. This short distance indicates strong metal-metal interactions (See Figure in upper right). The three violet "layered" forms, named for their color and their tendency to flake, are called alpha, gamma, and delta. In α-TiCl3, the chloride anions are hexagonal close-packed. In γ-TiCl3, the chlorides anions are cubic close-packed.
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Hexagonal close packed (hcp) unit cell Hexagonal close packed (hcp) is one of the two simple types of atomic packing with the highest density, the other being the face centered cubic (fcc). However, unlike the fcc, it is not a Bravais lattice as there are two nonequivalent sets of lattice points. Instead, it can be constructed from the hexagonal Bravais lattice by using a two atom motif (the additional atom at about (,,)) associated with each lattice point.
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Chromium hydride is important in chrome plating, being an intermediate in the formation of the chromium plate. Unit cell of hexagonal close packed form of chromium hydride Unit cell of face-centered cubic CrH2 An apparent unusual allotrope of chromium in a hexagonal crystal form was investigated by Ollard and Bradley by X-ray crystallography; however they failed to notice that it contained hydrogen. The hexagonal close packed crystalline substance they discovered actually contains CrHx with x between 0.5 and 1.
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In 1991 J. V. Badding and others analysed a sample using X-ray diffraction, as having an approximate composition FeH0.94 and double hexagonal close packed (DHCP) structure. Since then, the pressure-temperature phase diagram of the iron-hydrogen system has been intensively investigated up to 70 GPa. Two additional stable crystalline forms have been observed, denoted “ε’” (the original DHCP form), “ε” (hexagonal close packed, HPC). In these phases the packing of iron atoms is less dense than in pure iron.
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Granular Matter, 21(2), 26 . Both the face-centred cubic (fcc) and hexagonal close packed (hcp) crystal lattices have maximum densities equal to this upper limit, which can occur through the process of granular crystallisation.
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At these high temperatures, kinks may form and move by climb as well as glide. Climb of kinks is evidenced by the fact that they do not always move along the close-packed planes in CNTs, but rather along the length of a tube. When kinks do glide along close-packed planes in CNTs, they follow a helical path. It is proposed that elevated temperatures allow for the diffusion of vacancies, so that defects climb through a process similar to that observed in 3D crysalline materials.
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532 is unable to support its own weight.Schweitzer 2003, p. 695 It has a close-packed structure (BCN 12) but an abnormally large inter- atomic distance that has been attributed to partial ionisation of the lead atoms.
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The whole surface overrun by fine, close-packed, spiral threads. The aperture is linear. The anal sulcus is an almost closed tube at the top of a bold varix. The outer lip is insinuate near the base.
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If two tetrahedra are attached to opposite faces of an octahedron, the result is a rhombohedron.. The number of close-packed spheres in the rhombohedron is a cube, justifying the equation :O_n+2T_{n-1}=n^3.
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Several series of uranates(V) have been characterized. Compounds with the formula MIUO3 have a perovskite structure. Compounds MI3UO4 have a defect rock-salt structure. MI7UO6 structures are based on a hexagonally close-packed array of oxygen atoms.
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Gerard & King 1968, p. 16; Dwight 1999, p. 2 It has a close-packed structure (BCN 12) showing some evidence of partially directional bonding.Russell & Lee 2005, pp. 1–2; 359 It has a low melting point and a high thermal conductivity.
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66 Although the group 11 metals have normal close-packed metallic structuresPhillips & Williams 1965, p. 33 they show an overlap in chemical properties. In their +1 compounds (the stable state for silver; less so for copper)Wiberg, Holleman & Wiberg 2001, pp.
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Its symmetry is either hexagonal (space group P63mc) or orthorhombic (Cmcm) depending on the phase. There, close-packed Re layers alternate with puckered triangular boron layers along the (001) plane. This can be seen above on the example of osmium diboride.
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Metal single crystals are often used as substrates in graphene growth since they form a smooth and chemically uniform growth platform for graphene. Especially, the chemical uniformity is an important advantage of metal single crystal surfaces: for example in different oxide surfaces the oxidized component and the oxygen forms very different adsorption sites. A typical metal single crystal substrate surface is hexagonal close-packed surface since this geometry is also the geometry of carbon atoms in a graphene layer. Common surfaces that have hexagonal close packed geometry are for example FCC(111) and HCP(0001) surfaces.
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In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen ions with half of the octahedral sites occupied with magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions.
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Comparison of fcc and hcp lattices, explaining the formation of stacking faults in close-packed crystals. In crystallography, a stacking fault is a type of defect which characterizes the disordering of crystallographic planes. It is thus considered a planar defect.Fine, Morris E. (1921).
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Rather than adopting a close-packed structure typical of metal dihalides, e.g., cadmium chloride, molybdenum(II) chloride forms a structure based on clusters. Molybdenum(II), which is a rather large ion, prefers to form compounds with metal-metal bonds, i.e. metal clusters.
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Nesse, William (2000). Introduction to Mineralogy. Oxford University Press. Page 79 If the cations were small enough to fit into a truly close-packed structure of oxygen anions then the spacing between the nearest neighbour oxygen sites would be the same for both species.
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Like most metals it has a close-packed crystalline structure,Russell & Lee 2005, pp. 358–60 et seq and forms a cation in aqueous solution.Harding, Janes & Johnson 2002, pp. 118 It has some properties that are unusual for a metal; taken together,Metcalfe, Williams & Castka 1974, p.
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In the β phase, the molecule centres are hexagonal close packed. This means that the c/a ratio is ≈ 1.633 = /3. The nitrogen molecules are randomly tipped at an angle of 55° from the c-axis. There is a strong quadrupole-quadrupole interaction between the molecules.
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The very broad definition adopted by the International Union of Crystallography, IUCR, states that the coordination number of an atom in a crystalline solid depends on the chemical bonding model and the way in which the coordination number is calculated. Some metals have irregular structures. For example, zinc has a distorted hexagonal close packed structure. Regular hexagonal close packing of spheres would predict that each atom has 12 nearest neighbours and a triangular orthobicupola (also called an anticuboctahedron or twinned cuboctahedron) coordination polyhedron. In zinc there are only 6 nearest neighbours at 266 pm in the same close packed plane with six other, next-nearest neighbours, equidistant, three in each of the close packed planes above and below at 291 pm. It is considered to be reasonable to describe the coordination number as 12 rather than 6. Similar considerations can be applied to the regular body centred cube structure where in addition to the 8 nearest neighbors there 6 more, approximately 15% more distant, and in this case the coordination number is often considered to be 14.
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115 that is easily deformed.Goffer 2007, p. 176 It has a close-packed face-centred cubic structure (BCN 12). The chemistry of gold is dominated by its +3 valence state; all such compounds of gold feature covalent bonding,Sidgwick 1950, p. 177 as do its stable +1 compounds.
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The sodium chloride (NaCl) polymorph is most common. A cubic close-packed arrangement of chloride anions with rubidium cations filling the octahedral holes describes this polymorph. Both ions are six-coordinate in this arrangement. This polymorph's lattice energy is only 3.2 kJ/mol less than the following structure's.
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Quasi-crystals let non-space- filling coordination persist to larger size scales. However, they generally form only when the compositional makeup (e.g. of two dissimilar metals like Ti and Mn) serves as an antagonist to formation of one of the more common close- packed space-filling but twinned crystalline forms.
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Sodium bismuthate adopts an ilmenite structure, consisting of octahedral bismuth(V) centers and sodium cations. The average Bi-O distance is 2.116 Å. The ilmenite structure is related to the corundum structure (Al2O3) with a layer structure formed by close packed oxygen atoms with the two different cations alternating in octahedral sites.
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Braunović 2014, p. 244 It has a close-packed face-centred cubic structure (BCN 12).Donohue 1982, p. 222 The chemistry of silver is dominated by its +1 valence state in which it shows generally similar physical and chemical properties to compounds of thallium, a main group metal, in the same oxidation state.
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Hexagonal close-packing would result in a six-sided pyramid with a hexagonal base. Snowballs stacked in preparation for a snowball fight. The front pyramid is hexagonal close-packed and rear is face-centered cubic. The cannonball problem asks which flat square arrangements of cannonballs can be stacked into a square pyramid.
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A hexagonal close packed (HCP) form of FeH also exists at lower pressure hydrogen, also described by M. Yamakata and others in 1992. This is called the ε phase (no prime). The hcp phase is not ferromagnetic, probably paramagnetic. This appears to be the most stable form in a wide pressure range.
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Nb3Cl8 has a hexagonal close packed array of chloride ions. Triangles of niobium occur in octahedral spaces in the chloride array. The compositions with higher chloride have some niobium atoms missing from the structure, creating vacancies. NbCl4 has this pattern of vacancies stretched until the niobium atoms are in pairs rather than triangles.
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Nickel(II) hydroxide has two well-characterized polymorphs, α and β. The α structure consists of Ni(OH)2 layers with intercalated anions or water. The β form adopts a hexagonal close-packed structure of Ni2+ and OH− ions. In the presence of water, the α polymorph typically recrystallizes to the β form.
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In general, a honeycomb in n dimensions is an infinite example of a polytope in n + 1 dimensions. Tilings of the plane and close-packed space-fillings of polyhedra are examples of honeycombs in two and three dimensions respectively. A line divided into infinitely many finite segments is an example of an apeirogon.
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There are many mixed oxides containing aluminium where there are no discrete or polymeric aluminate ions. The spinels with a generic formula that contain aluminium as Al3+, such as the mineral spinel itself, MgAl2O4 are mixed oxides with cubic close packed O atoms and aluminium Al3+ in octahedral positions.Wells A.F. (1984) Structural Inorganic Chemistry 5th edition, Oxford Science Publications BeAl2O4, chrysoberyl, isomorphous with olivine, has hexagonal close-packed oxygen atoms with aluminium in octahedral positions and beryllium in tetrahedral positions."Refinement of the chysoberyl structure", E.F. Farrell, J.H. Fang, R.E. Newnham, The American Mineralogist, 1963, 48, 804 Some oxides with the general formula of MAlO3 sometimes called aluminates or orthoaluminates such as YAlO3, Yttrium ortho-aluminate are mixed oxides and have the perovskite structure.
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S. P. Efimov from Bauman Moscow State Technical University in 1978 y. found an approach to ease the restrictions for spectrum domain. He considered N identical sampling lattices to be shifted arbitrarily to each other. Optimal sampling is valid for spectrum domain that shifted versions of is close-packed N times on reciprocal lattice.
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Crystalline materials contain uniform planes of atoms organized with long-range order. Planes may slip past each other along their close-packed directions, as is shown on the slip systems page. The result is a permanent change of shape within the crystal and plastic deformation. The presence of dislocations increases the likelihood of planes.
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Even though Frenkel defects involve only the migration of the ions within the crystal, the total volume and thus the density is not necessarily conserved: in particular for close-packed systems, the lattice expansion due to the strains induced by the interstitial atom typically dominates over the lattice contraction due to the vacancy, leading to a decrease of density.
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Solid YCl3 adopts a cubic structure with close-packed chloride ions and yttrium ions filling one third of the octahedral holes and the resulting YCl6 octahedra sharing three edges with adjacent octahedra, giving it a layered structure.Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications This structure is shared by a range of compounds, notably AlCl3.
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Like most metal halides, FeBr2 adopts a polymeric structure consisting of isolated metal centers cross- linked with halides. It crystallizes with the CdI2 structure, featuring close- packed layers of bromide ions, between which are located Fe(II) ions in octahedral holes. The packing of the halides is slightly different from that for FeCl2, which adopts the CdCl2 motif.
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Below 912 °C (1,674 °F), iron has a body-centered cubic structure and is known as α-iron or ferrite. It is thermodynamically stable and fairly soft metal. α-Fe can be subjected to pressures up to ca. 15 GPa before transforming into a high- pressure form termed ε-iron, which crystallizes in a hexagonal close-packed (hcp) structure.
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The potentials can include many-body contributions. The interacting Lagrangian is then: : L_i = \int_x \psi^\dagger(x_1)\psi^\dagger(x_2)\cdots\psi^\dagger(x_n) V(x_1,x_2,\dots,x_n)\psi(x_1)\psi(x_2)\cdots\psi(x_n).\, These types of potentials are important in some effective descriptions of close-packed atoms. Higher order interactions are less and less important.
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Krypton is characterized by several sharp emission lines (spectral signatures) the strongest being green and yellow. Krypton is one of the products of uranium fission. Solid krypton is white and has a face- centered cubic crystal structure, which is a common property of all noble gases (except helium, which has a hexagonal close-packed crystal structure).
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Fe3O4 has a cubic inverse spinel group structure which consists of a cubic close packed array of oxide ions where all of the Fe2+ ions occupy half of the octahedral sites and the Fe3+ are split evenly across the remaining octahedral sites and the tetrahedral sites. Both FeO and γ-Fe2O3 have a similar cubic close packed array of oxide ions and this accounts for the ready interchangeability between the three compounds on oxidation and reduction as these reactions entail a relatively small change to the overall structure. Fe3O4 samples can be non-stoichiometric. The ferrimagnetism of Fe3O4 arises because the electron spins of the FeII and FeIII ions in the octahedral sites are coupled and the spins of the FeIII ions in the tetrahedral sites are coupled but anti-parallel to the former.
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A dense packing of spheres with a radius ratio of 0.64799 and a density of 0.74786 Many problems in the chemical and physical sciences can be related to packing problems where more than one size of sphere is available. Here there is a choice between separating the spheres into regions of close-packed equal spheres, or combining the multiple sizes of spheres into a compound or interstitial packing. When many sizes of spheres (or a distribution) are available, the problem quickly becomes intractable, but some studies of binary hard spheres (two sizes) are available. When the second sphere is much smaller than the first, it is possible to arrange the large spheres in a close-packed arrangement, and then arrange the small spheres within the octahedral and tetrahedral gaps.
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The density of this interstitial packing depends sensitively on the radius ratio, but in the limit of extreme size ratios, the smaller spheres can fill the gaps with the same density as the larger spheres filled space. Even if the large spheres are not in a close-packed arrangement, it is always possible to insert some smaller spheres of up to 0.29099 of the radius of the larger sphere. When the smaller sphere has a radius greater than 0.41421 of the radius of the larger sphere, it is no longer possible to fit into even the octahedral holes of the close-packed structure. Thus, beyond this point, either the host structure must expand to accommodate the interstitials (which compromises the overall density), or rearrange into a more complex crystalline compound structure.
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A number of designs were used, including a tetrahedron which could be close-packed without waste space, and could not be knocked over accidentally (slogan: "No more crying over spilt milk"). However, the industry eventually settled on a design similar to that used in the United States.Milk and Juice Cartons Fact Sheet, Waste Wise WA, zerowastewa.com.au. Retrieved June 21, 2009.
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The metametals are zinc, cadmium, mercury, indium, thallium, tin and lead. They are ductile elements but, compared to their metallic periodic table neighbours to the left, have lower melting points, relatively low electrical and thermal conductivities, and show distortions from close- packed forms.Wiberg, Holleman & Wiberg 2001, p. 143 Sometimes berylliumKlemm 1950 and galliumMiller GJ, Lee C & Choe W 2002, p.
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A colloidal crystal is an ordered array of colloid particles and fine grained materials analogous to a standard crystal whose repeating subunits are atoms or molecules. A natural example of this phenomenon can be found in the gem opal, where spheres of silica assume a close-packed locally periodic structure under moderate compression.Darragh, P.J., et al., Opal, Scientific American, Vol.
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The Fe3+ centers, with a high-spin d5 configuration, are ferromagnetically coupled. This area of technology is usually considered to be an application of the related fields of materials science and solid state chemistry. A related family of industrially useful "hexagonal ferrites" are known, also containing barium. In contrast to the usual spinel structure, these materials feature hexagonal close-packed framework of oxides.
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In three dimensions, close-packed structures offer the best lattice packing of spheres, and is believed to be the optimal of all packings. With 'simple' sphere packings in three dimensions ('simple' being carefully defined) there are nine possible definable packings. The 8-dimensional E8 lattice and 24-dimensional Leech lattice have also been proven to be optimal in their respective real dimensional space.
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The structure of iddingsite is difficult to characterize because of the complexity of the possible alterations that can occur from olivine. Iddingsite has the tendency to be optically homogeneous which indicates that there is some structural control. Structural rearrangements are controlled by hexagonal sequences of approximately close-packed oxygen sheets. These oxygen layers are perpendicular to the x-axis of an olivine cell.
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Zircoflex is a flexible aluminium-backed ceramic heat-shield, claimed to be the first-ever such product. Based on a derivative of Zircotec's Thermohold coating, close-packed ceramic platelets are plasma-sprayed onto an aluminium foil. This allows tight folding of the heat-shield through 180°, whilst still maintaining thermal protection. Zircoflex is 0.25mm thick and lightweight at 460g/m2.
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At standard temperature and pressure, aluminium atoms (when not affected by atoms of other elements) form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; hence aluminium (at these conditions) is a metal. This crystal system is shared by many other metals, such as lead and copper; the size of a unit cell of aluminium is comparable to that of those other metals. It is however not shared by the other members of its group; boron has ionization energies too high to allow metallization, thallium has a hexagonal close- packed structure, and gallium and indium have unusual structures that are not close-packed like those of aluminium and thallium. Since few electrons are available for metallic bonding, aluminium metal is soft with a low melting point and low electrical resistivity, as is common for post-transition metals.
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The unit cell of Cd3As2 is tetragonal. The arsenic ions are cubic close packed and the cadmium ions are tetrahedrally coordinated. The vacant tetrahedral sites provoked research by von Stackelberg and Paulus (1935), who determined the primary structure. Each arsenic ion was surrounded by cadmium ions at six of the eight corners of a distorted cube and the two vacant sites were at the diagonals.
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The metals are held together by metallic bonding, which confers distinctive physical properties such as their shiny metallic lustre, ductility and malleability, and electrical conductivity. Native elements are subdivided into groups by their structure or chemical attributes. The gold group, with a cubic close-packed structure, includes metals such as gold, silver, and copper. The platinum group is similar in structure to the gold group.
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In this context, a stacking fault is a local deviation from one of the close-packed stacking sequences to the other one. Usually, only one- two- or three-layer interruptions in the stacking sequence are referred to as stacking faults. An example for the fcc structure is the sequence ABCABABCAB. Stacking faults carry a given formation enthalpy per unit area; this is called stacking-fault energy.
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390 It has a close-packed crystalline structure (BCN 6+6) but an abnormally large interatomic distance that has been attributed to partial ionisation of the thallium atoms.Wells 1985, p. 1279–80 Although compounds in the +1 (mostly ionic) oxidation state are the more numerous, thallium has an appreciable chemistry in the +3 (largely covalent) oxidation state, as seen in its chalcogenides and trihalides.Howe 1968a, p.
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Image of a bubble raft (bubble size ~1.5 mm) showing vacancies and an edge dislocation in the bottom right corner. A bubble raft is an array of bubbles. It demonstrates materials' microstructural and atomic length-scale behavior by modelling the {111} plane of a close-packed crystal. A material's observable and measurable mechanical properties strongly depend on its atomic and microstructural configuration and characteristics.
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A 1971 study identified the mineral's structure as an array of oxygen atoms in a double hexagonal close packed pattern. However, a 1977 study discovered that all the manganese ions in arsenoclasite are six-coordinated, a constraint this structure cannot permit without severe distortion.Ruszala, p. 2420 The 1977 study identified arsenoclasite as isostructural to Co5(PO4)2(OH)4 and Mn5(PO4)2(OH)4.
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At pressures above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ε-iron or hexaferrum; the higher-temperature γ-phase also changes into ε-iron, but does so at a higher pressure. Antiferromagnetism in alloys of epsilon-Fe with Mn, Os and Ru has been observed.
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In three-dimensional Euclidean space, the densest packing of equal spheres is achieved by a family of structures called close-packed structures. One method for generating such a structure is as follows. Consider a plane with a compact arrangement of spheres on it. Call it A. For any three neighbouring spheres, a fourth sphere can be placed on top in the hollow between the three bottom spheres.
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Under gigapascals of pressure, xenon forms a metallic phase. Solid xenon changes from face-centered cubic (fcc) to hexagonal close packed (hcp) crystal phase under pressure and begins to turn metallic at about 140 GPa, with no noticeable volume change in the hcp phase. It is completely metallic at 155 GPa. When metallized, xenon appears sky blue because it absorbs red light and transmits other visible frequencies.
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One of the close-packed directions is parallel to the z-axis of an olivine cell. These ion arrangements within olivine control the structural orientation of the alteration products. X-ray diffraction patterns found that there are five structural types of iddingsite that can occur during different stages of alteration. They are: olivine-like structures, goethite-like structures, hematite structures, spinel structures and silicate structures.
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8, above left) contain minimal internal energy, retaining only that due to the ever-present background of zero-point energy. No other crystal structure can exceed the 74.048% packing density of a closest-packed arrangement. The two regular crystal lattices found in nature that have this density are hexagonal close packed (HCP) and face-centered cubic (FCC). These regular lattices are at the lowest possible energy state.
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Roentgenium is expected to be similar to its lighter homologue gold in many ways. It is expected to have a close-packed body-centered cubic structure. It should be a very dense metal, with its density of 28.7 g/cm3 surpassing all known stable elements. Roentgenium chemistry is expected to be dominated by the +3 valence state, similarly to gold, in which it should similarly behave as a transition metal.
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Four-helix bundles typically consist of four helices packed in a coiled-coil arrangement with a sterically close-packed hydrophobic core in the center. Pairs of adjacent helices are often additionally stabilized by salt bridges between charged amino acids. The helix axes typically are oriented about 20 degrees from their neighboring helices, a much shallower incline than in the larger helical structure of the globin fold.Branden C, Tooze J. (1999).
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The monoxide PaO has only been observed as a thin coating on protactinium metal, but not in an isolated bulk form. Protactinium forms mixed binary oxides with various metals. With alkali metals A, the crystals have a chemical formula APaO3 and perovskite structure, or A3PaO4 and distorted rock-salt structure, or A7PaO6 where oxygen atoms form a hexagonal close-packed lattice. In all these materials, protactinium ions are octahedrally coordinated.
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The spinels are any of a class of minerals of general formulation which crystallise in the cubic (isometric) crystal system, with the X anions (typically chalcogens, like oxygen and sulfur) arranged in a cubic close- packed lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice.Robert J. Naumann: Introduction to the Physics and Chemistry of Materials CRC Press, 2008, .
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The crystal structure of Sc2S3 is closely related to that of sodium chloride, in that it is based on a cubic close packed array of anions. Whereas NaCl has all the octahedral interstices in the anion lattice occupied by cations, Sc2S3 has one third of them vacant. The vacancies are ordered, but in a very complicated pattern, leading to a large, orthorhombic unit cell belonging to the space group Fddd.
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In the process there is a slight shift in the crystal structure, but the structure remains intact. The vanadium-oxygen bonds have not been broken and the hexagonal close-packed oxygen framework has not been disrupted. In some cases there may be an intermediate "diffuse A" phase. The process by which montroseite is altered to paramontroseite seems analogous to the magnetite → maghemite, lepidocrocite → maghemite, and goethite → hematite processes.
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The fcc structure is a close- packed structure unlike the bcc structure; thus the volume of the iron decreases when this transformation occurs. Crystallography is useful in phase identification. When manufacturing or using a material, it is generally desirable to know what compounds and what phases are present in the material, as their composition, structure and proportions will influence the material's properties. Each phase has a characteristic arrangement of atoms.
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In addition to their use as antennas, fractals have also found application in other antenna system components including loads, counterpoises, and ground planes. Fractal inductors and fractal tuned circuits (fractal resonators) were also discovered and invented simultaneously with fractal element antennas. An emerging example of such is in metamaterials. A recent invention demonstrates using close-packed fractal resonators to make the first wideband metamaterial invisibility cloak at microwave frequencies.
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With a melting point of 824 °C and a boiling point of 1196 °C, ytterbium has the smallest liquid range of all the metals. Contrary to most other lanthanides, which have a close-packed hexagonal lattice, ytterbium crystallizes in the face-centered cubic system. Ytterbium has a density of 6.973 g/cm3, which is significantly lower than those of the neighboring lanthanides, thulium (9.32 g/cm3) and lutetium (9.841 g/cm3).
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X-ray diffraction patterns taken from iddingsite vary from true olivine pattern to patterns that are very diffuse spots. This is an indication of a distorted structure caused by atomic replacement creating a distorted atomic arrangement. Goethite-like structures are common because goethite is in the same space group as olivine. This allows for goethite to grow within the olivine making the close packed planes common for both structures.
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If we do this for half of the holes in a second plane above the first, we create a new compact layer. There are two possible choices for doing this, call them B and C. Suppose that we chose B. Then one half of the hollows of B lies above the centers of the balls in A and one half lies above the hollows of A which were not used for B. Thus the balls of a third layer can be placed either directly above the balls of the first one, yielding a layer of type A, or above the holes of the first layer which were not occupied by the second layer, yielding a layer of type C. Combining layers of types A, B, and C produces various close-packed structures. Two simple arrangements within the close-packed family correspond to regular lattices. One is called cubic close packing (or face-centred cubic, "FCC")—where the layers are alternated in the ABCABC... sequence.
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The concept was enabled by the realization that engineered forms of silicon carbide and pyrolytic carbon were quite strong, even at temperatures as high as 2000 °C (3600 °F). The natural geometry of close-packed spheres then provides the ducting (the spaces between the spheres) and spacing for the reactor core. To make the safety simple, the core has a low power density, about 1/30 the power density of a light water reactor.
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A common way to determine the coordination number of an atom is by X-ray crystallography. Related techniques include neutron or electron diffraction. The coordination number of an atom can be determined straightforwardly by counting nearest neighbors. α-Aluminium has a regular cubic close packed structure, fcc, where each aluminium atom has 12 nearest neighbors, 6 in the same plane and 3 above and below and the coordination polyhedron is a cuboctahedron.
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Fe2O3 has a crystal structure that can be described as having a near close packed array of oxygen atoms with iron atoms filling two thirds of the octahedral holes. However each iron atom has 3 nearest neighbors and 3 others a little further away. The structure is quite complex, the oxygen atoms are coordinated to four iron atoms and the iron atoms in turn share vertices, edges and faces of the distorted octahedra.
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Each central sphere can have up to twelve neighbors, and in a face-centered cubic lattice these take the positions of a cuboctahedron's vertices. In a hexagonal close- packed lattice they correspond to the corners of the triangular orthobicupola. In both cases the central sphere takes the position of the solid's center. Cuboctahedra appear as cells in three of the convex uniform honeycombs and in nine of the convex uniform 4-polytopes.
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Corundum from Brazil, size about 2×3 cm. The most common form of crystalline aluminium oxide is known as corundum, which is the thermodynamically stable form. The oxygen ions form a nearly hexagonal close- packed structure with the aluminium ions filling two-thirds of the octahedral interstices. Each Al3+ center is octahedral. In terms of its crystallography, corundum adopts a trigonal Bravais lattice with a space group of Rc (number 167 in the International Tables).
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However, whereas the brucite structure can be described as a close- packed structure in gibbsite the OH groups on the underside of one layer rest on the groups of the layer below. This arrangement led to the suggestion that there are directional bonds between OH groups in adjacent layers. This is an unusual form of hydrogen bonding since the two hydroxide ion involved would be expected to point away from each other.
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This can be rationalised in terms of close packing of spheres of different sizes. For example, NaCl can be described as close-packed chloride ions (in a face-centered cubic lattice) with sodium ions in the octahedral holes. After the development of X-ray crystallography as a tool for determining crystal structures, many laboratories built models based on spheres. With the development of plastic or polystyrene balls it is now easy to create such models.
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Reacting to the violence, the police attempted to disperse the crowd using tear gas and baton charges. The crowd was pushed into the close-packed slum area of the neighborhood; 70% of the inhabitants of this area were non-Dalits. Members of the Shiv Sena followed the gathering, and began to attack them; the Dalits retaliated. Dalits and non-Dalit Hindus were reported to have attacked each other with stones and glass bottles.
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Orientational anisotropy takes the form of a difference in both diffusion rates and mechanisms at the various surface orientations of a given material. For a given crystalline material each Miller Index plane may display unique diffusion phenomena. Close packed surfaces such as the fcc (111) tend to have higher diffusion rates than the correspondingly more "open" faces of the same material such as fcc (100).Oura, Lifshits, Saranin, Zotov, and Katayama 2003, p.
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Many crystals naturally grow in faceted shapes. For instance, common table salt forms cubes and quartz forms hexagonal prisms. These characteristic shapes are a consequence of the crystal structure of the material and the surface energy, as well as the general conditions under which the crystal formed. The Bravais lattice of the crystal structure defines a set of possible "low-energy planes", which are usually planes on which the atoms are close- packed.
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Rhenium is a silvery-white metal with one of the highest melting points of all elements, exceeded by only tungsten and carbon. It also has one of the highest boiling points of all elements, and the highest among stable elements. It is also one of the densest, exceeded only by platinum, iridium and osmium. Rhenium has a hexagonal close-packed crystal structure, with lattice parameters a = 276.1 pm and c = 445.6 pm.
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Technetium is a silvery-gray radioactive metal with an appearance similar to platinum, commonly obtained as a gray powder. The crystal structure of the pure metal is hexagonal close-packed. Atomic technetium has characteristic emission lines at wavelengths of 363.3 nm, 403.1 nm, 426.2 nm, 429.7 nm, and 485.3 nm. The metal form is slightly paramagnetic, meaning its magnetic dipoles align with external magnetic fields, but will assume random orientations once the field is removed.
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It crystallizes in a monoclinic cell, and has a distorted rutile, (TiO2) crystal structure. In TiO2 the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In MoO2 the octahedra are distorted, the Mo atoms are off-centre, leading to alternating short and long Mo – Mo distances and Mo-Mo bonding. The short Mo – Mo distance is 251 pm which is less than the Mo – Mo distance in the metal, 272.5 pm.
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Gadolinium is a silvery-white, malleable, ductile rare-earth element. It crystallizes in the hexagonal close- packed α-form at room temperature, but, when heated to temperatures above , it transforms into its β-form, which has a body-centered cubic structure. The isotope gadolinium-157 has the highest thermal-neutron capture cross-section among any stable nuclide: about 259,000 barns. Only xenon-135 has a higher capture cross-section, about 2.0 million barns, but this isotope is radioactive.
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Calcium metal melts at 842 °C and boils at 1494 °C; these values are higher than those for magnesium and strontium, the neighbouring group 2 metals. It crystallises in the face-centered cubic arrangement like strontium; above 450 °C, it changes to an anisotropic hexagonal close-packed arrangement like magnesium. Its density of 1.55 g/cm3 is the lowest in its group. Calcium is harder than lead but can be cut with a knife with effort.
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Partial dislocations leave behind a stacking fault. Two types of partial dislocation are the Frank partial dislocation which is sessile and the Shockley partial dislocation which is glissile. A Frank partial dislocation is formed by inserting or removing a layer of atoms on the {111} plane which is then bounded by the Frank partial. Removal of a close packed layer is known as an intrinsic stacking fault and inserting a layer is known as an extrinsic stacking fault.
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There are other forms of metastable iron carbides that have been identified in tempered steel and in the industrial Fischer-Tropsch process. These include epsilon (ε) carbide, hexagonal close-packed Fe2-3C, precipitates in plain- carbon steels of carbon content > 0.2%, tempered at 100–200 °C. Non- stoichiometric ε-carbide dissolves above ~200 °C, where Hägg carbides and cementite begin to form. Hägg carbide, monoclinic Fe5C2, precipitates in hardened tool steels tempered at 200–300 °C.
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The crystal structure of titanium at ambient temperature and pressure is close-packed hexagonal α phase with a c/a ratio of 1.587. At about 890 °C, the titanium undergoes an allotropic transformation to a body-centred cubic β phase which remains stable to the melting temperature. Some alloying elements, called alpha stabilizers, raise the alpha-to-beta transition temperature, while others (beta stabilizers) lower the transition temperature. Aluminium, gallium, germanium, carbon, oxygen and nitrogen are alpha stabilizers.
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The higher temperature polymorphs of silica cristobalite and tridymite are frequently the first to crystallize from amorphous anhydrous silica, and the local structures of microcrystalline opals also appear to be closer to that of cristobalite and tridymite than to quartz. The structures of tridymite and cristobalite are closely related and can be described as hexagonal and cubic close-packed layers. It is therefore possible to have intermediate structures in which the layers are not regularly stacked.
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The spinel structures have a twined orientation and are controlled by close packed sheets. This twined orientation is can be described as: the a-axis of olivine is parallel to the (111) spinel face. The b-axis of olivine is parallel to +/− (112) and the c-axis of olivine is parallel to +/− (110) spinel face. These alterations tend to be rare in iddingsite but when they are present they show a sharp diffraction spot making them easily identified.
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A version of the concentric cylinder packed particles or close-packed polymer to create a three-dimensionally ordered macroporous (3DOM) carbon anode. This system is fabricated by using colloidal crystal templating, electrochemical thin-film growth, and soft sol–gel chemistry. 3DOM materials have a unique structure of nanometer thick walls that surround interconnected and closed-packed sub-micrometer voids. The 3DOM structure is coated with a thin polymer layer and then filled with second conducting phase.
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This continues until the first transition occurs and there is a proportional increase in pressure with decreasing area. Moving into the solid region is accompanied by another sharp transition to a more severe area dependent pressure. This trend continues up to a point where the molecules are relatively close packed and have very little room to move. Applying an increasing pressure at this point causes the monolayer to become unstable and destroy the monolayer forming polylayer structures towards the air phase.
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Most non- silicate mineral species are rare (constituting in total 8% of the Earth's crust), although some are relatively common, such as calcite, pyrite, magnetite, and hematite. There are two major structural styles observed in non-silicates: close-packing and silicate-like linked tetrahedra. close-packed structures is a way to densely pack atoms while minimizing interstitial space. Hexagonal close-packing involves stacking layers where every other layer is the same ("ababab"), whereas cubic close-packing involves stacking groups of three layers ("abcabcabc").
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Experiments performed in microgravity on the Space Shuttle Columbia suggest that the typical face-centered cubic structure may be induced by gravitational stresses. Crystals tend to exhibit the hcp structure alone (random stacking of hexagonally close-packed crystal planes), in contrast with a mixture of (rhcp) and face-centred cubic packing when allowed sufficient time to reach mechanical equilibrium under gravitational forces on Earth. Glassy (disordered or amorphous) colloidal samples have become fully crystallized in microgravity in less than two weeks.
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According to the traditional picture, Lonsdaleite has a hexagonal unit cell, related to the diamond unit cell in the same way that the hexagonal and cubic close packed crystal systems are related. The diamond structure can be considered to be made up of interlocking rings of six carbon atoms, in the chair conformation. In lonsdaleite, some rings are in the boat conformation instead. At the nanoscale dimensions cubic diamond is represented by diamondoids while hexagonal diamond is represented by wurtzoids.
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At low temperatures and at pressures up to around 400 GPa, hydrogen forms a series of solid phases formed from discrete H2 molecules. Phase I occurs at low temperatures and pressures, and consists of a hexagonal close-packed array of freely rotating H2 molecules. Upon increasing the pressure at low temperature, a transition to Phase II occurs at up to 110 GPa. Phase II is a broken-symmetry structure in which the H2 molecules are no longer able to rotate freely.
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It can be formed by progressive hydrogenation of scandium foil with hydrogen.Chemistry of d-block elements G. Singh (2007) In the narrow range of concentrations which make up scandium hydride, mixtures of hydrogen and scandium can form two different structures. At room temperature, the most stable form of scandium is the hexagonal close-packed (HCP) structure α-scandium. It is a fairly soft metallic material that can dissolve a moderate concentration of hydrogen, no more than 0.89 wt% at 22 °C.
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Pan-STARRS currently (2018) consists of two 1.8-m Ritchey–Chrétien telescopes located at Haleakala in Hawaii. The initial telescope, PS1, saw first light using a low-resolution camera in June 2006. The telescope has a 3° field of view, which is extremely large for telescopes of this size, and is equipped with the largest digital camera ever built, recording almost 1.4 billion pixels per image. The focal plane has 60 separately mounted close packed CCDs arranged in an 8 × 8 array.
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Redfin bullies are amphidromous – they migrate between fresh water and the sea as part of their life cycle. Over winter and spring, the male establishes and defends a ‘nest’ – usually a hollow beneath a rock. The male turns very dark, from brown to completely black, while defending the nest. When a female is ready to lay eggs, she enters the nest and turns upside-down to lay 1,000–20,000 oval eggs in a close-packed, single layer attached to the nest's ‘ceiling’.
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The waves can take the form of stripes, close-packed hexagons, or even squares or quasiperiodic patterns. Faraday waves are commonly observed as fine stripes on the surface of wine in a wine glass that is ringing like a bell. Faraday waves also explain the 'fountain' phenomenon on a singing bowl. The Faraday wave and its wavelength is analogous to the de Broglie wave with the de Broglie wavelength in De Broglie–Bohm theory in the field of quantum mechanics .
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The total energy of all particle motion translational and internal, including that of conduction electrons, plus the potential energy of phase changes, plus zero-point energy comprise the internal energy of a substance. Fig. 8 When many of the chemical elements, such as the noble gases and platinum-group metals, freeze to a solid — the most ordered state of matter — their crystal structures have a close-packed arrangement. This yields the greatest possible packing density and the lowest energy state.
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Nickel(II) titanate crystallizes at 600 °C and is stable at room temperature and normal pressure in an ilmenite structure with rhombohedral R3 symmetry. Nickel(II) titanate's rhombohedral structure has layers of Ni and Ti alternate along the rhombohedral axis with O layers between them. The XRD data supports nickel(II) titanate's ilmenite structure with its rhombohedral symmetry. Other descriptions of nickel(II) titanite's Illemite structure consists of a pseudo close packed hexagonal array of O2− ions with two thirds occupied by an ordered hexagonal like cation.
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For current density above 1800 amps per square meter and at low temperatures, the hexagonal close- packed form was made, but if the current was lower or the temperature was higher, then regular body-centered cubic chromium metal was deposited. full text available The condition for preferring the formation of face-centered cubic chromium hydride is a high pH. The fcc form of CrH has hydrogen atoms in octahedaral sites in the P63/mmc spacegroup. Chart of effect of temperature and current density on chromium plate brightness.
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For this, it gives metals their relatively high thermal and electrical conductivity as well as being characteristically ductile. Three of the most commonly used crystal lattice structures in metals are the body-centred cubic, face-centred cubic and close-packed hexagonal. Ferritic steel has a body- centred cubic structure and austenitic steel, non-ferrous metals like aluminum, copper and nickel have the face-centred cubic structure. Ductility is an important factor in ensuring the integrity of structures by enabling them to sustain local stress concentrations without fracture.
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Titanium undergoes allotropic transformation from its α-phase (hexagonal close-packed (hcp) structure at temperatures less than 882.5 °C) to its β-phase (body centered cubic, bcc) structure at temperatures above 882.3 °C). Alpha-phase titanium products typically exhibit medium to high strength with excellent creep strength, whereas beta-phase titanium products typically exhibit very high strength and low ductility. Foams created under thermal cycling conditions have been shown to exhibit increased porosity due to the density difference between allotropic phases. Davis et al.
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Phase separation is suitable for forming large-area ordered QD monolayers. A single QD layer is formed by spin casting a mixed solution of QD and an organic semiconductor such as TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine). This process simultaneously yields QD monolayers self-assembled into hexagonally close-packed arrays and places this monolayer on top of a co- deposited contact. During solvent drying, the QDs phase separate from the organic under-layer material (TPD) and rise towards the film's surface.
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Iron(II) oxide adopts the cubic, rock salt structure, where iron atoms are octahedrally coordinated by oxygen atoms and the oxygen atoms octahedrally coordinated by iron atoms. The non- stoichiometry occurs because of the ease of oxidation of FeII to FeIII effectively replacing a small portion of FeII with two thirds their number of FeIII, which take up tetrahedral positions in the close packed oxide lattice. Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.
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Repeating units will help to show how easy it is and clear it is to represent molecules through balls that represent atoms. Fig. 2. Sodium chloride (NaCl) lattice, showing close-packed spheres representing a face-centered cubic AB lattice similar to that of NaCl and most other alkali halides. In this model the spheres are equal sizes whereas more "realistic" models would have different radii for cations and anions. The binary compounds sodium chloride (NaCl) and caesium chloride (CsCl) have cubic structures but have different space groups.
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Once again there was a massive concentration of guns and ammunition: for this assault there was one 18-pounder for every of the attacking front. On II Corps' front the guns were hidden close-packed behind woods between Zillebeke and Verbrandemolen. The artillery duel went on for several weeks before the attack, with British batteries taking heavy casualties from German CB fire and gas shelling. The offensive opened on 31 July with the Battle of Pilckem Ridge, the infantry advancing behind the biggest barrage programme yet devised.
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The amount of fiber in a fiber reinforced composite directly corresponds with the mechanical properties of the composite. Theoretically the maximum fiber ratio of round fibers that can be achieved in a composite is 90.8% if the fibers are in a unidirectional hexagonal close packed configuration. Realistically the highest fiber volume ratio is around 70% due to manufacturing parameters and is usually in the range of 50% to 65%. Adding too little fiber reinforcement in the composite will actually deteriorate the properties of the material.
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Barrio Libre is a neighborhood in Tucson, Arizona notable for its existence as a relatively unchanged 19th-century Hispanic neighborhood of close-packed row houses. Houses in the barrio are typically adobe with very plain detailing, reflecting the area's history as a district of townhouses for Mexican ranching families. The district includes more than 200 contributing structures, with relatively few non-conforming buildings. The district is bounded by 14th and 18th streets to the north and south, and by Stone and Osborne to the east and west.
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There are several known solid forms of molecular dinitrogen. At ambient pressures there are two solid forms. β-N2 is a hexagonal close packed structure which exists from 35.6 K up to 63.1 5K at which point it melts. At 45 K the unit cell has a=4.050 Å and c=6.604 Å. At 4125 atmospheres pressure, and 49K the unit cell sizes have shrunk to a=3.861 Å c=6.265 Å. If the pressure is increased the c/a ratio stays the same.
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He probably split the army into three, with the knights as a cavalry reserve and the infantry arranged in schiltrons, close-packed arrays of spearmen. There is no mention of significant numbers of archers. The islanders were arranged in the traditional cuneiform or wedge shape, with Hector MacLean commanding the right wing and the chief of Clan Mackintosh on the left. At first the clansmen launched themselves at Scrymgeour's men, but failed to make much impression on the armoured column and many were slain.
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Nanosphere lithography (NSL) is an economical technique for generating single- layer hexagonally close packed or similar patterns of nanoscale features. Generally, NSL applies planar ordered arrays of nanometer-sized latex or silica spheres as lithography masks to fabricate nanoparticle arrays. NSL uses self-assembled monolayers of spheres (typically made of polystyrene, often available commercially as an aqueous suspension) as evaporation masks. These spheres can be deposited using multiple methods including Langmuir-Blodgett, Dip Coating, Spin Coating, solvent evaporation, force-assembly, and air-water interface.
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Pyknon (from ), sometimes also transliterated as pycnon (from close, close- packed, crowded, condensed; ) in the music theory of Antiquity is a structural property of any tetrachord in which a composite of two smaller intervals is less than the remaining (incomposite) interval. The makeup of the pyknon serves to identify the melodic genus (also called "genus of a tetrachord") and the octave species made by compounding two such tetrachords, and the rules governing the ways in which such compounds may be made centre on the relationships of the two pykna involved.
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Mackinawite is an iron nickel sulfide mineral with formula (Fe,Ni)1 + xS (where x = 0 to 0.11). The mineral crystallizes in the tetragonal crystal system and has been described as a distorted, close packed, cubic array of S atoms with some of the gaps filled with Fe. Mackinawite occurs as opaque bronze to grey-white tabular crystals and anhedral masses. It has a Mohs hardness of 2.5 and a specific gravity of 4.17. It was first described in 1962 for an occurrence in the Mackinaw mine, Snohomish County, Washington for which it was named.
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In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen ions with half of the octahedral sites occupied with magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions. There are three distinct oxygen sites (marked O1, O2 and O3 in figure 1), two distinct metal sites (M1 and M2) and only one distinct silicon site. O1, O2, M2 and Si all lie on mirror planes, while M1 exists on an inversion center. O3 lies in a general position.
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Today home to over 120,000 people, according to the Instituto Nacional de Estadística, Gràcia is both the smallest district by area, at 4.2 km2, and the second most densely populated neighbourhood in Barcelona. One of the hippest, most cosmopolitan areas in the city, Gràcia's intimate, close-packed streets and predominately low-rise, Mediterranean architecture give it a distinct feel. Its old, one-way streets are organized around a series of plazas, including Plaça de Vila de Gràcia, Plaça del Sol and Plaça de la Virreina. “Old-world charm” abounds.
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The Iphicratean peltast was not a skirmisher but a form of light hoplite, characterised by using a longer spear and smaller shield.Mattew, p. 119 However, the introduction of the sarissa pike in conjunction with a smaller shield seem to have been innovations devised by Philip himself, or at the very least he produced the definitive synthesis of earlier developments.Elis, p. 56 Diodorus claimed that Philip was inspired to make changes in the organisation of his Macedonian infantry from reading a passage in the writings of Homer describing a close-packed formation.Lendon, p. 11.
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Being a relatively electropositive metal, indium reacts quickly with chlorine to give the trichloride. Indium trichloride is very soluble and deliquescent.Indium Trichloride A synthesis has been reported using an electrochemical cell in a mixed methanol-benzene solution.Habeeb, J. J.; Tuck, D. G. "Electrochemical Synthesis of Indium(III) Complexes" Inorganic Syntheses, 1979, volume XIX, Like AlCl3 and TlCl3, InCl3 crystallizes as a layered structure consisting of a close-packed chloride arrangement containing layers of octahedrally coordinated In(III) centers,Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier a structure akin to that seen in YCl3.
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There are two forms of Cu2S: a low temperature monoclinic form ("low-chalcocite") which has a complex structure with 96 copper atoms in the unit cell and a hexagonal form stable above 104 °C.Wells A.F. (1984) Structural Inorganic Chemistry, 5th ed., Oxford Science Publications, In this structure there are 24 crystallographically distinct Cu atoms and the structure has been described as approximating to a hexagonal close packed array of sulfur atoms with Cu atoms in planar 3 coordination. This structure was initially assigned an orthorhombic cell due to the twinning of the sample crystal.
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Worrall senior, however, worked for a time as a blacksmith in Cheshire so was living away from the family.1891 England censuses: Church, Lancashire: piece 3409, folio 86; Cheadle, Cheshire: piece 2801, folio 61 Although the centre of Church was heavily built up, with close-packed, terraced housing and many mills, foundries and chemical works, the Worralls lived in Dill Hall Lane which was surrounded by fields and pleasant views of countryside. There was a vista from their house across the Leeds and Liverpool Canal to Dunkenhalgh Park.
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In the Renaissance, the battle became a favorite theme for artists: an excuse to display close-packed bodies in violent confrontation. The young Michelangelo executed a marble bas-relief of the subject in Florence about 1492.Art Renewal Center - The Battle of the Lapiths and Centaurs by Michelango Piero di Cosimo's panel Battle of Centaurs and Lapiths, now at the National Gallery, London, was painted during the following decade. If it was originally part of a marriage chest, or cassone, it was perhaps an uneasy subject for a festive wedding commemoration.
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The Great Fire of Warwick was a major conflagration that swept through the small town of Warwick, England, beginning at 2:00 p.m. on 5 September 1694 and lasting for six hours. The fire started from a spark from a torch that was being carried up High Street. The town's small population, the close-packed nature of the environment, and the amount of combustible building material all lead to the fire's start and spread, and the limited fire-fighting methods of the time helped transform the small torch fire into a catastrophic event.
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However, the defensive chemicals of tessaratomids (particularly that of Tessaratoma papillosa and Musgraveia sulciventris) are notable for being one of the most debilitating to vertebrates, probably a defense specifically aimed against birds. They can cause damage to human skin and even cause temporary blindness if sprayed unto the eyes. In Lyramoprha parens, nymphs are also known to be highly gregarious, forming massed feeding groups and moving to new feeding sites in close-packed groups. This behavior, along with their bright colorations and stink glands is believed to help in discouraging potential predators.
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Ferrites are usually ferrimagnetic ceramic compounds derived from iron oxides. Magnetite (Fe3O4) is a famous example. Like most of the other ceramics, ferrites are hard, brittle, and poor conductors of electricity. Many ferrites adopt the spinel structure with the formula AB2O4, where A and B represent various metal cations, usually including iron (Fe). Spinel ferrites usually adopt a crystal motif consisting of cubic close-packed (fcc) oxides (O2−) with A cations occupying one eighth of the tetrahedral holes and B cations occupying half of the octahedral holes, i.e.
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The lake is used as a breeding site for banded stilts following major flood events. The stilts nest in large close-packed colonies on low islands in ephemeral inland salt lakes such as Lake Eyre, Lake Barlee and Lake Ballard. The last recorded nesting on the lake was in 1995 following the aftermath of Cyclone Bobby. The lake, along with the neighbouring Lake Marmion some to the east, has been identified by BirdLife International as a Important Bird Area (IBA), because it has supported a high proportion of the known banded stilt mass breeding events.
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Galena belongs to the octahedral sulfide group of minerals that have metal ions in octahedral positions, such as the iron sulfide pyrrhotite and the nickel arsenide niccolite. The galena group is named after its most common member, with other isometric members that include manganese bearing alabandite and niningerite. Divalent lead (Pb) cations and sulfur (S) anions form a close-packed cubic unit cell much like the mineral halite of the halide mineral group. Zinc, cadmium, iron, copper, antimony, arsenic, bismuth and selenium also occur in variable amounts in galena.
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Alloys with zinc are magnetic at less than 35 K. The melting point of zirconium is 1855 °C (3371 °F), and the boiling point is 4371 °C (7900 °F). Zirconium has an electronegativity of 1.33 on the Pauling scale. Of the elements within the d-block with known electronegativities, zirconium has the fifth lowest electronegativity after hafnium, yttrium, lanthanum, and actinium. At room temperature zirconium exhibits a hexagonally close-packed crystal structure, α-Zr, which changes to β-Zr, a body-centered cubic crystal structure, at 863 °C.
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On September 16, 1952, Pauling opened a new research notebook with the words "I have decided to attack the problem of the structure of nuclei." On October 15, 1965, Pauling published his Close- Packed Spheron Model of the atomic nucleus in two well respected journals, Science and the Proceedings of the National Academy of Sciences. For nearly three decades, until his death in 1994, Pauling published numerous papers on his spheron cluster model. The basic idea behind Pauling's spheron model is that a nucleus can be viewed as a set of "clusters of nucleons".
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The pendant inflorescences are massive and some 3 m in length, bearing unisexual flowers – male flowers at the distal end, female flowers at proximal – with first order branches of 13–32 rachillae very close-packed in almost one plane (see illustration). Raphia spp are monocarpic or hapaxanthic, flowering and fruiting only once, followed by death. Raphia farinifera flowers when the tree is some 20–25 years old, and it takes a further 5–6 years from flowering to ripe fruit, all fruits ripening together. Fruit is oblong to ovoid, 5–10 cm in length, with imbricate, glossy, golden- brown scales.
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Praseodymium nevertheless can continue losing a fourth and even occasionally a fifth valence electron because it comes very early in the lanthanide series, where the nuclear charge is still low enough and the 4f subshell energy high enough to allow the removal of further valence electrons.Greenwood and Earnshaw, pp. 1235–8 Thus, similarly to the other early trivalent lanthanides, praseodymium has a double hexagonal close-packed crystal structure at room temperature. At about 560 °C, it transitions to a face-centered cubic structure, and a body-centered cubic structure appears shortly before the melting point of 935 °C.
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This fact is intentionally ignored in continuum mechanics, which assumes a material to have no underlying microstructure and be uniform and semi-infinite throughout. Bubble rafts assemble bubbles on a water surface, often with the help of amphiphilic soaps. These assembled bubbles act like atoms, diffusing, slipping, ripening, straining, and otherwise deforming in a way that models the behavior of the {111} plane of a close-packed crystal. The ideal (lowest energy) state of the assembly would undoubtedly be a perfectly regular single crystal, but just as in metals, the bubbles often form defects, grain boundaries, and multiple crystals.
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Crystal growth is a major stage of a crystallization process, and consists in the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice. The growth typically follows an initial stage of either homogeneous or heterogeneous (surface catalyzed) nucleation, unless a "seed" crystal, purposely added to start the growth, was already present. The action of crystal growth yields a crystalline solid whose atoms or molecules are close packed, with fixed positions in space relative to each other. The crystalline state of matter is characterized by a distinct structural rigidity and very high resistance to deformation (i.e.
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It forms alloys with lanthanide metals but little is known about the resulting materials. The element has two crystalline forms at standard atmospheric pressure: a double-hexagonal close-packed form dubbed alpha (α) and a face-centered cubic form designated beta (β). The α form exists below 600–800 °C with a density of 15.10 g/cm3 and the β form exists above 600–800 °C with a density of 8.74 g/cm3. At 48 GPa of pressure the β form changes into an orthorhombic crystal system due to delocalization of the atom's 5f electrons, which frees them to bond.
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The first beta- helix was observed in the enzyme pectate lyase, which contains a seven-turn helix that reaches 34 Å (3.4 nm) long. The P22 phage tail spike protein, a component of the P22 bacteriophage, has 13 turns and in its assembled homotrimer is 200 Å (20 nm) in length. Its interior is close-packed with no central pore and contains both hydrophobic residues and charged residues neutralized by salt bridges. Both pectate lyase and P22 tailspike protein contain right-handed helices; left-handed versions have been observed in enzymes such as UDP-N-acetylglucosamine acyltransferase and archaeal carbonic anhydrase.
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A colloidal crystal is a highly ordered array of particles which can be formed over a long range (to about a centimeter). Arrays such as this appear to be analogous to their atomic or molecular counterparts with proper scaling considerations. A good natural example of this phenomenon can be found in precious opal, where brilliant regions of pure spectral color result from close-packed domains of colloidal spheres of amorphous silicon dioxide, SiO2 (see above illustration). The spherical particles precipitate in highly siliceous pools and form highly ordered arrays after years of sedimentation and compression under hydrostatic and gravitational forces.
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Rama Rao began his research career with X-ray diffraction study of structural imperfections including development of new methods of analysis of X-ray line-broadening and prediction and experimental verification of fault configurations in double hexagonal close – packed crystals. He then turned to high temperature mechanical behaviour of metallic materials (tensile, creep, fatigue and fracture characteristics) some of which were undertaken for the first time in the country. He became involved in research- based alloy development during his tenure at the Hyderabad defence laboratory. Notable among these efforts is the development of an ultrahigh strength high fracture toughness low alloy steel.
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Pure lead has a bright, silvery appearance with a hint of blue. It tarnishes on contact with moist air and takes on a dull appearance, the hue of which depends on the prevailing conditions. Characteristic properties of lead include high density, malleability, ductility, and high resistance to corrosion due to passivation. alt=A disk of metal Lead's close-packed face-centered cubic structure and high atomic weight result in a density of 11.34 g/cm3, which is greater than that of common metals such as iron (7.87 g/cm3), copper (8.93 g/cm3), and zinc (7.14 g/cm3).
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Areas of close-packed molecules nucleate and grow until the surface of the substrate is covered in a single monolayer. Adsorbate molecules adsorb readily because they lower the surface free-energy of the substrate and are stable due to the strong chemisorption of the "head groups." These bonds create monolayers that are more stable than the physisorbed bonds of Langmuir–Blodgett films. A Trichlorosilane based "head group", for example in a FDTS molecule, reacts with a hydroxyl group on a substrate, and forms very stable, covalent bond [R-Si-O-substrate] with an energy of 452 kJ/mol.
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Fourth rank tensor properties, like the elastic constants, are anisotropic, even for materials with cubic symmetry. The Young's modulus relates stress and strain when an isotropic material is elastically deformed; to describe elasticity in an anisotropic material, stiffness (or compliance) tensors are used instead. In metals, anisotropic elasticity behavior is prevalent in all single crystals, with the exception of Tungsten, due to the fact there are only two independent stiffness coefficients in the stiffness tensor (while other cubic crystals have three). For face centered cubic materials like Copper, the elastic modulus is highest along the <111> direction, normal to the close packed planes.
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Nevertheless, the analogy is not exact due to the ease of nucleophilic attack at boron due to its deficiency in electrons, which is not possible in a wholly carbon-containing ring. The largest category of nitrides are the interstitial nitrides of formulae MN, M2N, and M4N (although variable composition is perfectly possible), where the small nitrogen atoms are positioned in the gaps in a metallic cubic or hexagonal close-packed lattice. They are opaque, very hard, and chemically inert, melting only at very high temperatures (generally over 2500 °C). They have a metallic lustre and conduct electricity as do metals.
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For an edge type, b is perpendicular to the dislocation line, whereas in the cases of the screw type it is parallel. In metallic materials, b is aligned with close-packed crystallographic directions and its magnitude is equivalent to one interatomic spacing. Dislocations can move if the atoms from one of the surrounding planes break their bonds and rebond with the atoms at the terminating edge. It is the presence of dislocations and their ability to readily move (and interact) under the influence of stresses induced by external loads that leads to the characteristic malleability of metallic materials.
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Rhenium can cause superalloys to become microstructurally unstable, forming undesirable TCP (topologically close packed) phases. In 4th- and 5th- generation superalloys, ruthenium is used to avoid this effect. Among others the new superalloys are EPM-102 (with 3% Ru) and TMS-162 (with 6% Ru), as well as TMS-138 and TMS-174. CFM International CFM56 jet engine still with blades made with 3% rhenium For 2006, the consumption is given as 28% for General Electric, 28% Rolls-Royce plc and 12% Pratt & Whitney, all for superalloys, whereas the use for catalysts only accounts for 14% and the remaining applications use 18%.
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Recent estimates (2007) allow for up to 10% nickel and 2–3% of unidentified lighter elements. According to computations by D. Alfè and others, the liquid outer core contains 8–13% of oxygen, but as the iron crystallizes out to form the inner core the oxygen is mostly left in the liquid. Laboratory experiments and analysis of seismic wave velocities seem to indicate that the inner core consists specifically of ε-iron, a crystalline form of the metal with the hexagonal close-packed (hcp) structure. That structure can still admit the inclusion of small amounts of nickel and other elements.
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Upland bullies are neither diadromous nor migratory – they remain in freshwater for their whole lives. Over spring and summer, the male establishes and defends a ‘nest’ – usually a hollow beneath a rock. Males prefer larger nests, however when in the presence of a predator, more enclosed nest sites are favoured. While defending the nest, the male turns very dark, from brown to completely black. When a female is ready to lay eggs, she enters the nest and turns upside-down to lay several hundred to a thousand oval eggs in a close-packed, single layer attached to the nest's ‘ceiling’.
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Random close packing (RCP) is an empirical parameter used to characterize the maximum volume fraction of solid objects obtained when they are packed randomly. For example, when a solid container is filled with grain, shaking the container will reduce the volume taken up by the objects, thus allowing more grain to be added to the container. In other words, shaking increases the density of packed objects. But shaking cannot increase the density indefinitely, a limit is reached, and if this is reached without obvious packing into a regular crystal lattice, this is the empirical random close- packed density.
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As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic (fcc) crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope. The physical properties of iron at very high pressures and temperatures have also been studied extensively, because of their relevance to theories about the cores of the Earth and other planets. Above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into another hexagonal close-packed (hcp) structure, which is also known as ε-iron.
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These particles align themselves as water leaves the slurry, or as clay is formed. Casting or other fluid-to-solid transitions (i.e., thin-film deposition) produce textured solids when there is enough time and activation energy for atoms to find places in existing crystals, rather than condensing as an amorphous solid or starting new crystals of random orientation. Some facets of a crystal (often the close-packed planes) grow more rapidly than others, and the crystallites for which one of these planes faces in the direction of growth will usually out-compete crystals in other orientations.
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Even in the narrow range of concentrations that make up chromium hydride, mixtures of hydrogen and chromium can form a number of different structures, with very different properties. Understanding such properties is essential to making quality chromium hydride. At room temperature, the most stable form of pure chromium is the body-centered cubic (BCC) structure α-chromium. It is a fairly hard metal that can dissolve only a small concentration of hydrogen. It can occur as a dull brown or dark grey solid in two different crystalline forms: face-centered cubic with formula CrH~2 or a close packed hexagonal solid with formula CrH~1.
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Civil inattention can lead to feelings of loneliness or invisibility, and it reduces the tendency to feel responsibility for the well-being of others. Newcomers to urban areas are often struck by the impersonality of such routines, which they may see as callous and uncaring, rather than as necessary for the peaceful co-existence of close-packed millions.Franco Moretti, Modern Epic (1996) p. 156 Goffman noted that "when men and women cross each other's path at close quarters, the male will exercise the right to look for a second or two at the female ... Civil inattention, then, can here involve a degree of role differentiation regarding obligations".
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The high number of proline residues inhibits the formation of close-packed secondary structures in such as α-helixes and β-pleated sheets. Due to κ-caseins being glycoproteins, they are stable in the presence of calcium ions so the κ-caseins are on the outer layer of the micelle to partially protect the non glycoproteins β-caseins, α(s1)-caseins, α(s2)-caseins from precipitating out in the presence of excess calcium ions. Due to the lack of a strong secondary or tertiary structure as a result of the proline residues, casein micelles are not heat sensitive particles. However, they are pH sensitive.
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Many properties of promethium rely on its position among lanthanides and are intermediate between those of neodymium and samarium. For example, the melting point, the first three ionization energies, and the hydration energy are greater than those of neodymium and lower than those of samarium; similarly, the estimate for the boiling point, ionic (Pm3+) radius, and standard heat of formation of monatomic gas are greater than those of samarium and less than those of neodymium. Promethium has a double hexagonal close packed (dhcp) structure and a hardness of 63 kg/mm2. This low- temperature alpha form converts into a beta, body-centered cubic (bcc) phase upon heating to 890 °C.
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Assuming one atom per lattice point, in a primitive cubic lattice with cube side length a, the sphere radius would be and the atomic packing factor turns out to be about 0.524 (which is quite low). Similarly, in a bcc lattice, the atomic packing factor is 0.680, and in fcc it is 0.740. The fcc value is the highest theoretically possible value for any lattice, although there are other lattices which also achieve the same value, such as hexagonal close packed (hcp) and one version of tetrahedral bcc. As a rule, since atoms in a solid attract each other, the more tightly packed arrangements of atoms tend to be more common.
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Under extremely high pressures (1.1 million atm) and high temperatures (2000 K), as produced in a diamond anvil cell, nitrogen polymerises into the single- bonded cubic gauche crystal structure. This structure is similar to that of diamond, and both have extremely strong covalent bonds, resulting in its nickname "nitrogen diamond". Solid nitrogen on the plains of Sputnik Planitia on Pluto next to water ice mountains At atmospheric pressure, molecular nitrogen condenses (liquefies) at 77 K (−195.79 °C) and freezes at 63 K (−210.01 °C) into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (−237.6 °C) nitrogen assumes the cubic crystal allotropic form (called the alpha phase).
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Shells that had been intended for the armies of the Czar burst in terrific salvos over the roofs of the houses, shattered chimneys, riddled the car repair barns of the Lackawanna Railway, and set two dwellings on fire.”Jersey Blast Demolishes Shell Plant; Rakes Town Two miles of the Delaware, Lackawanna, and Western Railroad tracks were torn up by the explosions. Commuters from New York City were delayed by up to four hours and at one point 40,000 were jammed into the Hoboken station in a "clamoring, close-packed mass." Express trains to and from Washington D.C. were disrupted and a comical dispute over rights to a diner car ensued.
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Th4+: __ / O2−: __ Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. A hypothetical metallic state of thorium that had the [Rn]6d27s2 configuration with the 5f orbitals above the Fermi level should be hexagonal close packed like the group 4 elements titanium, zirconium, and hafnium, and not face- centred cubic as it actually is. The actual crystal structure can only be explained when the 5f states are invoked, proving that thorium, and not protactinium, acts as the first actinide metallurgically. Tetravalent thorium compounds are usually colourless or yellow, like those of silver or lead, as the Th4+ ion has no 5f or 6d electrons.
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The angle-preserving effect of stereographic plots is even more obvious in the figure at right, which subtends a full 180° of the orientation space of a face-centered or cubic close packed crystal e.g. like that of Gold or Aluminum. The animation follows {220} fringe-visibility bands of that face-centered cubic crystal between <111> zones, at which point rotation by 60° sets up travel to the next <111> zone via a repeat of the original sequence. Fringe-visibility bands have the same global geometry as do Kikuchi bands, but for thin specimens their width is proportional (rather than inversely proportional) to d-spacing.
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Within the titanium-selenium system, many stoichiometries have been identified. Titanium diselenide crystallizes with the CdI2 -type structure, in which the octahedral holes between alternating hexagonal closely packed layer of Se2− layers (that is half of the total number of octahedral holes) are occupied by Ti4+ centers. The CdI2 structure is often referred to as a layer structure as the repeating layers of atoms perpendicular to the close packed layer form the sequence Se- Ti-Se…Se-Ti-Se…Se-Ti-Se with weak van der Waals interactions between the selenium atoms in adjacent layers. The structure has (6,3)-coordination, being octahedral for the cation and trigonal pyramidal for the anions.
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354 Copernicium is expected to be a liquid at room temperature, although experiments have so far not succeeded in determining its boiling point with sufficient precision to prove this. Like its lighter congener mercury, many of its singular properties stem from its closed-shell d10s2 electron configuration as well as strong relativistic effects. Its cohesive energy is even less than that of mercury and is likely only higher than that of flerovium. Solid copernicium is expected to crystallise in a close-packed body-centred cubic structure and have a density of about 14.7 g/cm3, decreasing to 14.0 g/cm3 on melting, which is similar to that of mercury (13.534 g/cm3).
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Smith enhanced the geometrical solution of four triangular prisms by adding another joint, resulting in a new form with seven triangular prisms enclosing two tetrahedra. After some time passed, he decided that the resulting form was something other than a design exercise, so titled it Throne because the symmetrical abstraction reminded him of the dense volume of an African beaded throne. Smith joined the faculty at Bennington College, Vermont. In 1960 a class project investigating close-packed cells based on D'Arcy Thompson's book Growth & Form (1918) sparked Smith's search for artistic inspiration in the natural world. The resulting agglomeration of 14-sided tetrakaidecahedrons, the ideally efficient soap-bubble cell, is known as the Bennington Structure.
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Beryllium is a steel gray and hard metal that is brittle at room temperature and has a close-packed hexagonal crystal structure. It has exceptional stiffness (Young's modulus 287 GPa) and a melting point of 1287 C. The modulus of elasticity of beryllium is approximately 50% greater than that of steel. The combination of this modulus and a relatively low density results in an unusually fast sound conduction speed in beryllium – about 12.9 km/s at ambient conditions. Other significant properties are high specific heat (1925 J·kg−1·K−1) and thermal conductivity (216 W·m−1·K−1), which make beryllium the metal with the best heat dissipation characteristics per unit weight.
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Mouse neurula tissues divide rapidly, with an average cell cycle lasting 8–10 hours. Proteoglycans in the extracellular matrix (ECM) of neurula-stage cells play an important role in promoting functional cranial neurulation and neural fold elevation; hyaluronic acid (HA) is synthesized and becomes accumulated, while the cell maintains a low level of sulfated glycosaminoglycans (GAGs). HA is involved in creation of biconvex neural folds, while sulfated GAGs are critical in manipulating the neural groove into a V-shape, as well as in neural tube closure. The ECM does not play a major role in spinal neurulation due to the close-packed nature of the mesodermal cells in the spinal region, which allows little intercellular space.
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There are however problems with the shell model when an attempt is made to account for nuclear properties well away from closed shells. This has led to complex post hoc distortions of the shape of the potential well to fit experimental data, but the question remains whether these mathematical manipulations actually correspond to the spatial deformations in real nuclei. Problems with the shell model have led some to propose realistic two-body and three-body nuclear force effects involving nucleon clusters and then build the nucleus on this basis. Three such cluster models are the 1936 Resonating Group Structure model of John Wheeler, Close- Packed Spheron Model of Linus Pauling and the 2D Ising Model of MacGregor.
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In Phase I the majority of the tiles (112) were scattered across a roughly 1.5 km core region, forming an array with very high imaging quality, and a field of view of several hundred square degrees at a resolution of several arcminutes. The remaining 16 tiles are placed at locations outside the core, yielding baseline distances of about 3 km to allow higher angular resolution observations. In Phase II the MWA operated in two configurations, a compact configuration and an extended configuration of 128 tiles each. The compact configuration consists of seven Phase I receivers and 56 tiles, plus 72 new tiles arranged in two dense hexagonal configurations each of 36 close-packed tiles.
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The spin ice model is only one subdivision of frustrated systems. The word frustration was initially introduced to describe a system's inability to simultaneously minimize the competing interaction energy between its components. In general frustration is caused either by competing interactions due to site disorder (see also the Villain model or by lattice structure such as in the triangular, face-centered cubic (fcc), hexagonal-close-packed, tetrahedron, pyrochlore and kagome lattices with antiferromagnetic interaction. So frustration is divided into two categories: the first corresponds to the spin glass, which has both disorder in structure and frustration in spin; the second is the geometrical frustration with an ordered lattice structure and frustration of spin.
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The pyknon was an important criterion in the classification of melodic genera (). The Greek word πυκνόν is an adjective meaning "close", "compact", "close-packed", or "crowded" . In Ancient Greek music theory, this term is used to describe a pair of intervals within a tetrachord, the sum of which is less than the remainder of the tetrachord . Although in modern usage, a tetrachord may be any four-note segment of a scale, or indeed any (unordered) collection of four pitch classes, in ancient Greek music theory a tetrachord consists of a four- note segment of the Greater and Lesser Perfect Systems bounded by the interval of a perfect fourth, the outer notes of which remain fixed in all genera and therefore are called "standing notes" ().
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The concept of bubble raft modelling was first presented in 1947 by Nobel Laureate Sir William Lawrence Bragg and John Nye of Cambridge University's Cavendish Laboratory in Proceedings of the Royal Society A.[1] Legend claims that Bragg conceived of bubble raft models while pouring oil into his lawn mower. He noticed that bubbles on the surface of the oil assembled into rafts resembling the {111} plane of close-packed crystals[2]. Nye and Bragg later presented a method of generating and controlling bubbles on the surface of a glycerine-water-oleic acid- triethanolamine solution, in assemblies of 100,000 or more sub-millimeter sized bubbles. In their paper [1], they go on at length about the microstructural phenomena observed in bubble rafts and hypothesized in metals.
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A material with high stacking-fault energy, such as aluminium or titanium, will be far more susceptible to galling than materials with low stacking-fault energy, like copper, bronze, or gold. Conversely, materials with a hexagonal close packed (HCP) structure and a high c/a ratio, such as cobalt-based alloys, are extremely resistant to galling.Surface Engineering for Corrosion and Wear Resistance By J. R. Davis -- ASM International 2001 Page 76 Galling occurs initially with material transfer from individual grains, on a microscopic scale, which become stuck or even diffusion welded to the adjacent surface. This transfer can be enhanced if one or both metals form a thin layer of hard oxides with high coefficients of friction, such as those found on aluminum or stainless-steel.
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Jäger around 1800, showing the relatively drab uniforms of soldiers specializing in skirmishing in Napoleonic times, as an aid in using cover During the Napoleonic Wars, skirmishers played a key role in battles; they attempted to disrupt the main enemy force by firing into their close-packed ranks and to prevent enemy skirmishers from doing the same to friendly troops. Because skirmishers generally fought in open order, they could take cover behind trees, houses, towers and similar items, thereby presenting unrewarding targets for small arms and artillery fire. Such tactics often made them vulnerable to cavalry, however. A skirmish force screening the main body of infantry became so important to any army in the field that eventually, all major European powers developed specialised skirmishing infantry.
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Precious opal consists of spheres of silicon dioxide molecules arranged in regular, closely packed planes. (Idealized diagram) Multicolor rough crystal opal from Coober Pedy, South Australia, expressing nearly every color of the visible spectrum Precious opal replacing ichthyosaur backbone; display specimen, South Australian Museum Precious opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal structure. At microscopic scales, precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice. It was shown by J. V. Sanders in the mid-1960s that these ordered silica spheres produce the internal colors by causing the interference and diffraction of light passing through the microstructure of the opal.
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The strong bonding of metals in the liquid form demonstrates that the energy of a metallic bond is not a strong function of the direction of the metallic bond; this lack of bond directionality is a direct consequence of electron delocalization, and is best understood in contrast to the directional bonding of covalent bonds. The energy of a metallic bond is thus mostly a function of the number of electrons which surround the metallic atom, as exemplified by the Embedded atom model. This typically results in metals assuming relatively simple, close-packed crystal structures, such as FCC, BCC, and HCP. Given high enough cooling rates and appropriate alloy composition, metallic bonding can occur even in glasses with an amorphous structure.
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Hematite has a triagonal crystal system and experiences twinning by having an approximately hexagonal close-packed oxygen framework and has a structural orientation similar to olivine. When twinning occurs, the orientation of hematite-like iddingsite is as follows: a-axis of olivine is parallel to the c-axis of hematite, the b-axis of olivine is parallel to the +/− [010] plane of hematite and the c-axis of olivine is parallel to the +/− [210] plane of hematite. This hematite structure is very well oriented and occurs because of the high stability of the anion framework and because the cations can be made to migrate throughout the structure. Spinel structures consist of multiple oxide structures that are cubic and have cubic close packing.
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Market-share of PV technologies since 1990 Most solar modules are currently produced from crystalline silicon (c-Si) solar cells made of multicrystalline and monocrystalline silicon. In 2013, crystalline silicon accounted for more than 90 percent of worldwide PV production, while the rest of the overall market is made up of thin-film technologies using cadmium telluride, CIGS and amorphous siliconPhotovoltaics Report, Fraunhofer ISE, 28 July 2014, pages 18,19 Emerging, third generation solar technologies use advanced thin-film cells. They produce a relatively high-efficiency conversion for the low cost compared to other solar technologies. Also, high-cost, high-efficiency, and close- packed rectangular multi-junction (MJ) cells are preferably used in solar panels on spacecraft, as they offer the highest ratio of generated power per kilogram lifted into space.
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The square continued in use into the late 19th century by European armies against irregular warriors in colonial actions, but it was different in form from the Napoleonic formation: :"The new square was not simply infantry in static defence but a large, close-packed formation of some 1,000 to 1,500 men, capable of slow movement with ranks of infantry or cavalry forming the four sides and artillery, wheeled machine guns, transport carts, baggage animals and their handlers in the centre. Such a square could only survive where the enemy were without modern firearms."Fuzzy-Wuzzy; Notes on the text (by Roger Ayers) at www.kipling.org.uk At the Battle of Custoza, during the Third Italian War of Independence, Italian bersaglieri formed squares at Villafranca to defend themselves from charging Austrian uhlans.
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Battle of Ravenna, (woodcut by unknown artist, 16th century) In the end, as proven at Marignano and Bicocca, the mass pike attack columns of the Swiss mercenaries proved to be too vulnerable to gunpowder weapons as firearms technology advanced, especially arquebusiers and artillery deployed on prepared ground (e.g., earthworks) and properly supported by other arms. These arquebusiers and heavy cannons scythed down the close-packed ranks of the Swiss squares in bloody heaps—at least, as long as the Swiss attack could be bogged down by earthworks or cavalry charges, and the vulnerable arquebusiers were backed up by melee infantry—pikemen, halberdiers, and/or swordsmen (Spanish sword-and-buckler men or the Doppelsöldner wielding the Zweihänder)—to defend them if necessary from the Swiss in close combat. Other stratagems could also take the Swiss pikemen at a disadvantage.
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A colloidal crystal is a highly ordered array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear analogous to their atomic or molecular counterparts. One of the finest natural examples of this ordering phenomenon can be found in precious opal, in which brilliant regions of pure spectral color result from close-packed domains of amorphous colloidal spheres of silicon dioxide (or silica, SiO2). These spherical particles precipitate in highly siliceous pools in Australia and elsewhere, and form these highly ordered arrays after years of sedimentation and compression under hydrostatic and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of interstitial voids, which act as a natural diffraction grating for visible light waves, particularly when the interstitial spacing is of the same order of magnitude as the incident lightwave.
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Polarized light (PL) is very useful when studying the structure of metals with non-cubic crystal structures (mainly metals with hexagonal close-packed (hcp) crystal structures). If the specimen is prepared with minimal damage to the surface, the structure can be seen vividly in cross- polarized light (the optic axis of the polarizer and analyzer are 90 degrees to each other, i.e., crossed). In some cases, an hcp metal can be chemically etched and then examined more effectively with PL. Tint etched surfaces, where a thin film (such as a sulfide, molybdate, chromate or elemental selenium film) is grown epitaxially on the surface to a depth where interference effects are created when examined with BF producing color images, can be improved with PL. If it is difficult to get a good interference film with good coloration, the colors can be improved by examination in PL using a sensitive tint (ST) filter.
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Carrollite from Katanga, specimen 11 × 6 cm The linnaeite group is a group of sulfides and selenides with the general formula AB2X4 in which X is sulfur or selenium, A is divalent Fe, Ni, Co or Cu and B is trivalent Co, Ni or, for daubréelite, Cr. The minerals are isometric, space group Fd3m and isostructural with each other and with minerals of the spinel group. The structure of the linnaeite group consists of a cubic close packed array of X (X is oxygen in the spinels and sulfur or selenium in the linnaeite group). Within the array of Xs there are two types of interstices, one type tetrahedrally co-ordinated and one type octahedrally co-ordinated. One eighth of the tetrahedal sites A are typically occupied by 2+ cations, and half of the octahedral sites B by 3+ cations.Klein and Hurlbut (1993) Manual of Mineralogy, 21st edition Charnock et al.
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During this time, the light infantry gathered what missiles they could that were lying around the battlefield and prepared for a second attack. The Gauls prepared for the assault by stationing themselves in front of the walls of their camp, as the camp itself was insufficiently built to serve as a fortification. The consul once again ordered the light infantry to commence the battle, and describes the onslaught that the Gauls faced: > They were then deluged by missiles of every kind; and since the more > numerous and close-packed the defenders were, the less did any weapons fall > harmlessly between them, they were at once forced within the rampart, > leaving strong guards only at the very approaches to the gates. A huge > number of missiles was hurled at the crowd herded into the camp, and the > shouting, mingled with the lamentations of the women and children, denoted > that many were wounded.
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The chondrodite structure is based on a slightly distorted hexagonal close packed array of anions O, OH and F with metal ions in the octahedral sites resulting in zigzag chains of octahedra. Chains are staggered so that none of the independent tetrahedral sites occupied by Si has OH or F corners.Phillips, W R and Griffen, D T (1981) Optical Mineralogy, pages 142 to 144 Half of the octahedral sites are filled by divalent cations, principally Mg, and one tenth of the tetrahedral sites are filled by Si. There are three distinct octahedra in the array: Fe is ordered in the M1 sites but not in the larger M2 and smaller M3 sites.American Mineralogist (1970): 55: 1182-1194 Ti is ordered in the M3 positions, which are the smallest, but Ti concentration appears never to exceed 0.5 atoms Ti per formula unit in natural specimens.
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Tetrahedral packing: The dihedral angle of a tetrahedron is not commensurable with 2; consequently, a hole remains between two faces of a packing of five tetrahedra with a common edge. A packing of twenty tetrahedra with a common vertex in such a way that the twelve outer vertices form an irregular icosahedron The stability of metals is a longstanding question of solid state physics, which can only be understood in the quantum mechanical framework by properly taking into account the interaction between the positively charged ions and the valence and conduction electrons. It is nevertheless possible to use a very simplified picture of metallic bonding and only keeps an isotropic type of interactions, leading to structures which can be represented as densely packed spheres. And indeed the crystalline simple metal structures are often either close packed face-centered cubic (fcc) or hexagonal close packing (hcp) lattices.
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199 Nihonium is expected to have a hexagonal close-packed crystalline structure, albeit based on extrapolation from those of the lighter group 13 elements: its density is expected to be around 16 g/cm3. A standard electrode potential of +0.6 V is predicted for the Nh+/Nh couple. The relativistic stabilisation of the 7s electrons is very high and hence nihonium should predominantly form the +1 oxidation state; nevertheless, as for copernicium, the +3 oxidation state should be reachable with highly electronegative ligands, with likely being of similar stability to (which is a strong oxidising agent, fuming in moist air and reacting with glass). Because of the shell closure at flerovium caused by spin-orbit coupling, nihonium is also one 7p electron short of a closed shell and would hence form a −1 oxidation state; in both the +1 and −1 oxidation states, nihonium should show more similarities to astatine than thallium.
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Pieces of hafnium Hafnium is a shiny, silvery, ductile metal that is corrosion-resistant and chemically similar to zirconium (due to its having the same number of valence electrons, being in the same group, but also to relativistic effects; the expected expansion of atomic radii from period 5 to 6 is almost exactly cancelled out by the lanthanide contraction). Hafnium changes from its alpha form, a hexagonal close-packed lattice, to its beta form, a body-centered cubic lattice, at 2388 K. The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity. A notable physical difference between these metals is their density, with zirconium having about one-half the density of hafnium. The most notable nuclear properties of hafnium are its high thermal neutron capture cross section and that the nuclei of several different hafnium isotopes readily absorb two or more neutrons apiece.
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Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum (Al2O3) structure. Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3,Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications although a high pressure form with the CaIrO3 structure has been reported too.High Pressure Phase transition in Mn2O3 to the CaIrO3-type Phase Santillan, J.; Shim, S. American Geophysical Union, Fall Meeting 2005, abstract #MR23B-0050 α-Mn2O3 has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol cI80, space group Ia3, #206). The bixbyite structure has been found to be stabilised by the presence of small amounts of Fe3+, pure Mn2O3 has an orthorhombic structure (Pearson symbol oP24,space group Pbca, #61). α-Mn2O3 undergoes antiferromagnetic transition at 80 K. γ-Mn2O3 has a structure related to the spinel structure of Mn3O4 where the oxide ions are cubic close packed.
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The hcp lattice (left) and the fcc lattice (right) The principles involved can be understood by considering the most efficient way of packing together equal- sized spheres and stacking close-packed atomic planes in three dimensions. For example, if plane A lies beneath plane B, there are two possible ways of placing an additional atom on top of layer B. If an additional layer was placed directly over plane A, this would give rise to the following series: :...ABABABAB... This arrangement of atoms in a crystal structure is known as hexagonal close packing (hcp). If, however, all three planes are staggered relative to each other and it is not until the fourth layer is positioned directly over plane A that the sequence is repeated, then the following sequence arises: :...ABCABCABC... This type of structural arrangement is known as cubic close packing (ccp). The unit cell of a ccp arrangement of atoms is the face-centered cubic (fcc) unit cell.
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The greater part of the development of the area occurred in two phases; until the 1870s many large Italianate villas were built, mostly in the southern part of Highbury. After this time, development went high-density with close packed mostly terraced houses being built, mainly in the north of Highbury. Available land continued to be in-filled with more housing until 1918, but little else changed until after World War II. A need for a place for Catholic residents of Highbury to worship in the 1920s led to the commissioning of St Joan of Arc's church, thought to be the first dedicated to the saint canonised in 1920, on a site on Kelross Road where the church hall is now located. The church was soon expanded, but the influx of Catholic residents after the war led to a need for a new, larger church. The new church, also dedicated to St Joan of Arc, and designed by Stanley Kerr Bate, opened on 23 September 1962 on Highbury Park.
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This shape was called a Siamese dodecahedron in the paper by Hans Freudenthal and B. L. van der Waerden (1947) which first described the set of eight convex deltahedra.. The dodecadeltahedron name was given to the same shape by , referring to the fact that it is a 12-sided deltahedron. There are other simplicial dodecahedra, such as the hexagonal bipyramid, but this is the only one that can be realized with equilateral faces. Bernal was interested in the shapes of holes left in irregular close-packed arrangements of spheres, so he used a restrictive definition of deltahedra, in which a deltahedron is a convex polyhedron with triangular faces that can be formed by the centers of a collection of congruent spheres, whose tangencies represent polyhedron edges, and such that there is no room to pack another sphere inside the cage created by this system of spheres. This restrictive definition disallows the triangular bipyramid (as forming two tetrahedral holes rather than a single hole), pentagonal bipyramid (because the spheres for its apexes interpenetrate, so it cannot occur in sphere packings), and icosahedron (because it has interior room for another sphere).
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