The rate of mass transfer per area unit is, among other factors, related to the shape of polymeric chains within the dosage form. Higher tortuosity or curviness retards mass transfer as it acts obstructively on the drug particles within the formulation. HVAC makes extensive use of tortuosity in evaporator and condenser coils for heat exchangers, whereas Ultra-high vacuum makes use of the inverse of tortuosity, which is conductivity, with short, straight, voluminous paths. Tortuosity has been used in ecology to describe the movement paths of animals.
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In Fuel Cell Seminar & Energy Exposition It is important to notice that there are different kind of tortuosity, i.e., gas-phase, ionic and electronic tortuosity. In acoustics and following initial works by Maurice Anthony Biot in 1956, the tortuosity is used to describe sound propagation in fluid-saturated porous media. In such media, when frequency of the sound wave is high enough, the effect of viscous drag force between the solid and the fluid can be ignored.
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A tortuous river (meander of Nowitna River, Alaska) Tortuosity is a property of a curve being tortuous (twisted; having many turns). There have been several attempts to quantify this property. Tortuosity is commonly used to describe diffusion and fluid flow in porous media, such as soils and snow.
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Tortuosity calculation from an x-ray tomography reconstruction of a porous sandstone (the pores are shown):Gommes, C.J., Bons, A.-J., Blacher, S. Dunsmuir, J. and Tsou, A. (2009) Practical methods for measuring the tortuosity of porous materials from binary or gray-tone tomographic reconstructions. American Institute of Chemical Engineering Journal, 55, 2000-2012 the color represents the shortest distance within the pore space from the left limit of the image to any point in the pores. Comparing this distance to the straight-line distance shows that the tortuosity is about 1.5 for this sample.
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Diffusion is controlled by other factors such as pore size and soil skeleton, tortuosity of flow path, and distribution of the solvent (water) and solutes.
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It has been demonstrated that the tortuosity increases when the porosity decreases. Usually subjective estimation is used. However, several ways to adapt methods estimating tortuosity in 2-D have also been tried. The methods include arc-chord ratio, arc-chord ratio divided by number of inflection points and integral of square of curvature, divided by length of the curve (curvature is estimated assuming that small segments of curve are planar).
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The constant a, called the tortuosity factor, cementation intercept, lithology factor or, lithology coefficient is sometimes used. It is meant to correct for variation in compaction, pore structure and grain size. The parameter a is called the tortuosity factor and clearly is related to the path length of the current flow. The value lies in the range 0.5 to 1.5, and it may be different in different reservoirs.
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AIChE J., 5: 270-271 In practice, the constrictivity together with the porosity and tortuosity are often used in models as purely empirical parameters to establish the effective diffusivities in porous media.
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E. Bullitt, G. Gerig, S. M. Pizer, Weili Lin, S. R. Aylward. Measuring tortuosity of the intracerebral vasculature from MRA images. IEEE Transactions on Medical Imaging, Volume 22, Issue 9, Sept. 2003, p.
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In this case, velocity of sound propagation in the fluid in the pores is non-dispersive and compared with the value of the velocity of sound in the free fluid is reduced by a ratio equal to the square root of the tortuosity. This has been used for a number of applications including the study of materials for acoustic isolation, and for oil prospection using acoustics means. In analytical chemistry applied to polymers and sometimes small molecules tortuosity is applied in Gel permeation chromatography (GPC) also known as Size Exclusion Chromatography (SEC). As with any chromatography it is used to separate mixtures.
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A force constant for chain extension can be estimated from the resulting change in free energy associated with this entropy change. As with regime Ia, the force model for this regime is linear and proportional to the temperature divided by the chain tortuosity.
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To this end, the propagation of the crack is controlled by the transport rate and mechanisms of the embrittler at the tip of nucleated cracks. SMIE can be mitigated by increasing the tortuosity of crack paths such that resistance to intercrystalline cracking increases.
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Tortuosity of blood vessels (for example, retinal and cerebral blood vessels) is known to be used as a medical sign. In mathematics, cubic splines minimize the functional, equivalent to integral of square of curvature (approximating the curvature as the second derivative). In many engineering domains dealing with mass transfer in porous materials, such as hydrogeology or heterogeneous catalysis, the tortuosity refers to the ratio of the diffusivity in the free space to the diffusivity in the porous medium (analogous to arc-chord ratio of path). Strictly speaking, however, the effective diffusivity is proportional to the reciprocal of the square of the geometrical tortuosityGommes, C.J., Bons, A.-J.
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Damodos's style is a pellucid, simple Greek, in strong contrast to the artificiality and archaism of Mavrokordatos, and the tortuosity of the third representative of this period, Eugenios Voulgaris.G. P. Henderson. Greek Philosophy From 1600 to 1850 e Philosophical Quarterly (0031-8094) 1955-04-01. Vol.5,Iss.19; pp.
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This limits the reactants ability to access the catalyst and significantly decreases performance. Teflon can be coated onto the GDL to limit the possibility of flooding. Several microscopic variables are analyzed in the GDLS such as: porosity, tortuosity and permeability. These variables have incidence over the behavior of the fuel cells.
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Hypertensive retinopathy with AV nicking and mild vascular tortuosity Hypertensive retinopathy is a condition characterized by a spectrum of retinal vascular signs in people with elevated blood pressure. It was first described by Liebreich in 1859.Liebreich R. Ophthalmoskopischer Befund bei Morbus Brightii. Albrecht von Graefes Arch Ophthalmol 1859; 5: 265–268.
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1163 - 1171 Another method used for quantifying tortuosity in 3D has been applied in 3D reconstructions of solid oxide fuel cell cathodes where the Euclidean distance sums of the centroids of a pore were divided by the length of the pore.Gostovic, D., et al., Three-dimensional reconstruction of porous LSCF cathodes. Electrochemical and Solid State Letters, 2007.
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The Kuban River, the longest river in the entire North Caucasian region, flows through the city. Its length is 870 km, and the basin area is 57900 km². On the flat part of the river created a lot of artificial reservoirs. In the area of the city of Kuban is characterized by the tortuosity of the channel.
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Technical difficulties are because of loops and tortuosity of the radial and the subclavian artery, anatomical variations in radial artery, and radial spasm. Major complication associated with a transradial interventions include early and late radial artery occlusion. Most of the radial artery occlusions are asymptomatic. Post PCI radial artery occlusion can be reduced by using smaller diameter catheters and anticoagulation.
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A porous medium is most often characterised by its porosity. Other properties of the medium (e.g. permeability, tensile strength, electrical conductivity, tortuosity) can sometimes be derived from the respective properties of its constituents (solid matrix and fluid) and the media porosity and pores structure, but such a derivation is usually complex. Even the concept of porosity is only straightforward for a poroelastic medium.
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Figure 2. Increase of the pressure with respect of time in steps, holding the actual pressure for a certain time before increasing it to the next value. The pressure/step stability method represents an alternative for the pressure scan method which permits a more accurate measurement of the pore sizes. It takes into account the different tortuosity and pore length of pores with the same diameter.
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Optic-disc edema will be graded based on the Frisén Scale as below: Stage 0 – Normal Optic-disc Blurring of nasal, superior and inferior poles in inverse proportion to disc diameter. Radial nerve fiber layer (NFL) without NFL tortuosity. Rare obscuration of a major blood vessel, usually on the upper pole. Stage 1 – Very early optic-disc edema Obscuration of the nasal border of the disc.
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Medical signs that can be detected from observation of eye fundus (generally by funduscopy) include hemorrhages, exudates, cotton wool spots, blood vessel abnormalities (tortuosity, pulsation and new vessels) and pigmentation.Imran Akram, Adrian Rubinstein "Common retinal signs. An overview", "Optometry Today", 28/01/05, Arteriolar constriction, seen as "silver wiring", and vascular tortuosities are seen in hypertensive retinopathy. The eye's fundus is the only part of the human body where the microcirculation can be observed directly.
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The gene TGFBR2 has been implicated in several connective tissue disorders including Marfan syndrome, arterial tortuosity, and thoracic aortic aneurysm. A study of patients with SCSFLS demonstrated no mutations in this gene. Minor features of Marfan syndrome have been found in 20% of CSF leak patients. Abnormal findings of fibrillin-1 have been documented in these CSF leak patients, but only one patient demonstrated a fibrillin-1 defect consistent with Marfan syndrome.
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Dilation is a typical characteristic of several diseases and disorders. These include diseases from metabolic and genetic disorders such as mannosidosis, myotonic dystrophy, Lowe syndrome, and Coffin–Lowry syndrome. Dilation is also a common characteristic of diseases or disorders of vascular pathologies, including CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), hereditary infantile hemiparesis, retinal arteriolar tortuosity and leukoencephalopathy, migraines, and vascular dementia. A third group disorders typically associated with VRS dilation are neuroectodermal syndromes.
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Clinical use has been limited to proximal intracranial anatomy of patient with limited tortuosity, showing the potential of OCT for the imaging of neurovascular disease. An intravascular OCT imaging catheter design tailored for use in tortuous neurovascular anatomy has been proposed in 2020. Further developments of intravascular OCT included the combination with other optical imaging modalities (multi-modality imaging). OCT has been combined with fluorescence molecular imaging to enhance its capability to detect molecular/functional and tissue morphological information at the same time.
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Historically, physicians believed that their function was to aid in the passage of bile to and from the gallbladder, as well as regulate the degree of gallbladder distension. The presence of the spiral folds, in combination with the tortuosity of the cystic duct, makes endoscopic cannulation and catheterization of the cystic duct extremely difficult. Also, the valves of Heister are susceptible to lacerations and were a serious obstacle to the surgical canalization. Thanks to newer technologies, nowadays this procedure is possible.
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Air permeability is expressed in terms of the Gurley value, the time required for a specified amount of air to pass through a specified area of the separator under a specified pressure. The Gurley value reflects the tortuosity of the pores, when the porosity and thickness of the separator is fixed. A separator with uniform porosity is vital to battery life cycle. Deviations from uniform permeability produce uneven current density distribution, which causes the formation of crystals on the anode.
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The Molecular Kink Paradigm envisions a representative network chain as a series of vectors that follow the chain contour within its tube. Each vector represents the equilibrium end- to-end distance of a kink. The actual 3-dimensional path of the chain is not pertinent, since all elastic forces are assumed to operate along the chain contour. In addition to the chain's contour length, the only other important parameter is its tortuosity, the ratio of its contour length to its end-to-end distance.
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Since these distributions (which turn out to be approximately Gaussian) are directly related to the number of states, we may associate them with the entropy of the kink at any end-to-end distance. By numerically differentiating the probability distribution, the change in entropy, and hence free energy, with respect to the kink end-to-end distance can be found. The force model for this regime is found to be linear and proportional to the temperature divided by the chain tortuosity. Fig. 2 Isoprene backbone unit.
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The cementation exponent models how much the pore network increases the resistivity, as the rock itself is assumed to be non-conductive. If the pore network were to be modelled as a set of parallel capillary tubes, a cross-section area average of the rock's resistivity would yield porosity dependence equivalent to a cementation exponent of 1. However, the tortuosity of the rock increases this to a higher number than 1. This relates the cementation exponent to the permeability of the rock, increasing permeability decreases the cementation exponent.
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Atypical Gillespie syndrome associated with bilateral ptosis, exotropia, correctopia, iris hypoplasia, anterior capsular lens opacities, foveal hypoplasia, retinal vascular tortuosity, and retinal hypopigmentation. Neurological signs are nystagmus, mild craniofacial asymmetry, axial hypotonia, developmental delay, and mild mental retardation. Mariën P did not support the prevailing view of a global mental retardation as a cardinal feature of Gillespie syndrome but primarily reflect cerebellar induced neurobehavioral dysfunctions following disruption of the cerebrocerebellar anatomical circuitry that closely resembles the "cerebellar cognitive and affective syndrome" (CeCAS). Congenital pulmonary stenosis and helix dysplasia can be associated.
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In the case of GPC the separation is based on molecular size and it works by the use of stationary media with appropriately dimensioned pores. The separation occurs because larger molecules take a shorter, less tortuous path and elute more quickly and smaller molecules can pass into the pores and take a longer, more tortuous path and elute later. In pharmaceutical sciences, tortuosity is used in relation to diffusion-controlled release from solid dosage forms. Insoluble matrix formers, such as ethyl cellulose, certain vinyl polymers, starch acetate and others control the permeation of the drug from the preparation and into the surrounding liquid.
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Despite similar failure mechanisms in both sodium-etched and plasma-etched samples, sodium etching produces much higher bond strengths than plasma etching. Sodium-etched samples exhibited 4 to 5 times the strength of plasma-etched samples when tested in tension per ASTM D4541. When tested in peel, sodium-etched samples exhibited 3 to 12 times the peel strength of plasma-etched samples, depending on the type of plasma used. One proposed explanation for the large difference in bond strengths is that chemical etching modifies the PTFE to a greater depth than plasma etching, increasing the tortuosity of the fracture path through the etched layer during adhesion testing.
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This could be of use when developing permeable gas transfer membranes where tortuosity and roughness could impede gas flow. It also turns out that z- and r-crystals do not interact with ceramic particles in the same way. The z-crystals pack particles in the x-y plane while r-crystals pack particles primarily in the z-direction. R-crystals actually pack particles more efficiently than z-crystals and because of this, the area fraction of the particle-rich phase (1 - area fraction of ice crystals) changes as the crystal population shifts from a mixture of z- and r-crystals to only z-crystals.
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It is a fast and reproducible method that is generally recommended for quality control work and for samples with all pores identical. However it is important to take into account that when the samples present a complex structure and with a considerable amount of pores of different tortuosity it is possible that during the pressure scan pores with the same diameter but longer pore path are not emptied at the pressure corresponding to their diameter (if the scan is fast there is not time to allow the gas flow to displace the wetting liquid through the pore length). As consequence, the pores with longer pore length will be report smaller pore sizes than the actual ones.
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For most fluids and some homogenous solid materials, like gels, diffusion is the same in all directions and characterized by the same diffusion coefficient number. This property is called isotropicity which gives cubosomes the ability to be used in biological tissues which are highly structured and typically have different diffusion coefficients along different directions (anisotropic). Because of advantages such as the unique structure of the cubic phase and its resemblance to biological membranes as well as biodegradability of lipids, cubosomes are a great tool for drug delivery system. In addition, the bicontinuous cubic liquid crystalline phase (cubic phase)’s tortuosity is useful for slowing down diffusion as shown by Higuchi’s square root of time release kinetics.
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The company operates across four major service areas: Drilling, Surveying, Wireline, and Support. Drilling Services encompasses a wide range of technologies designed for directional drilling applications, including performance motors, measurement-while-drilling (MWD) tools, rotary steerable systems (RSS), and gyro-while-drilling (GWD) tools, the latter of which was invented by Gyrodata in 2002 to use real-time gyro steering and surveying data while drilling. Surveying Services provides gyroscopic surveys designed to improve wellbore placement using both spinning-mass and solid-state technology, depending on the application. Wireline Services covers not only traditional wireline and cased-hole logging solutions but unique offerings in high-density wellbore tortuosity logging and cement bond logging.
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The advantages of this technology are many for both main groups of users: geoscientists and drillers. Continuous rotation of the drill string allows for improved transportation of drilled cuttings to the surface resulting in better hydraulic performance, better weight transfer for the same reason allows a more complex bore to be drilled, and reduced well bore tortuosity due to utilizing a more steady steering model. The well geometry therefore is less aggressive and the wellbore (wall of the well) is smoother than those drilled with a motor. This last benefit concerns geoscientists, because better measurements of the properties of the formation can be obtained, and the drillers, because the well casing or production string can be more easily run to the bottom of the hole.
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Over the years, the Sardinian railway network has remained largely unchanged as a route: not considering the closure of some sections, the only changes to the routes concerned mainly small / medium-sized variants and rectification works to speed up journeys. In any case, the total lack of electrification of the network and the tortuosity of the lines in certain areas mean that the average train speeds are rather low compared to the rest of Italy, which in some cases has compromised the competitiveness of the railway towards bus lines. Commonly, the Sardinian network is divided into the main ordinary gauge network (that of the FS, managed through the subsidiary Rete Ferroviaria Italiana) and the secondary narrow gauge network (of the ARST).
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This led him to apply, at the forefront of the development, Bethe and percolation networks to the description of mass transport and reaction inside catalyst particles, instead of the description in terms of a tortuosity factor. Another major area where Froment has been active is thermal cracking for olefins production, an operation of tremendous industrial importance, providing the key building blocks for the petrochemical and chemical industries. Froment started research in this area already in 1959, stressing the derivation of accurate kinetic data from experimentation in tubular flow reactors and developing the equivalent reactor volume concept introduced by Hougen and Watson. Continuing this work through the decades led to more advanced and detailed reaction kinetics integrated within reactor models with transport phenomena.
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In 2010, the company introduced several new technologies, including a new, in-house-developed gyroscope—which is the primary sensor used across a range of Gyrodata technologies and services—a new mud motor, and a new GWD system designed to provide surveys at up to 40° of inclination. GWD systems for wells with up to 70° of inclination shortly followed, establishing Gyrodata as the only provider of gyroscopic surveys above 40°. Construction began on the company’s new headquarters in Houston, Texas in 2010, and in early 2011, Gyrodata began operating from the new offices. The next several years saw a substantial amount of technology innovation, including a GWD system for wells up to 90°, a high-density tortuosity logging software to improve casing running and placement of artificial lift equipment, and two next-generation MWD systems: one that provided inclination and azimuth while drilling via mud-pulse telemetry, the other that used electromagnetic telemetry to enable compatibility with RSS and GWD tools.
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Water is by far the most commonly used suspension media, and by freeze drying is readily conducive to the step of sublimation that is necessary for the success of freeze-casting processes. Due to the hgih level of control and broad range of possible porous microstructures that freeze-casting can produce, the technique has been adopted in disparate fields such as tissue scaffolds,, Bio-materials by freeze casting photonics, metal-matrix composites, dentistry, , Freeze Casting of High Strength Composites for Dental Applications materials science,, Dispersion, connectivity and tortuosity of hierarchical porosity composite SOFC cathodes prepared by freeze-casting, Processing of Hierarchical and Anisotropic LSM-YSZ Ceramics, Lightweight and stiff cellular ceramic structures by ice templating and even food science There are three possible end results to uni-directionally freezing a suspension of particles. First, the ice-growth proceeds as a planar front, pushing particles in front like a bulldozer pushes a pile of rocks. This scenario usually occurs at very low solidification velocities (< 1 μm s−1) or with extremely fine particles because they can move by Brownian motion away from the front.
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