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Tortuosity
Selected AbstractsThe Use of 3D Contrast-Enhanced CT Reconstructions to Project Images of Vascular Rings and Coarctation of the AortaECHOCARDIOGRAPHY, Issue 1 2009Thomas G. Di Sessa M.D. Background: Aortic arch and pulmonary artery anomalies make up a group of vascular structures that have complex three-dimensional (3D) shapes. Tortuosity as well as hypoplasia or atresia of segments of the aortic arch or pulmonary artery makes the conventional two-dimensional (2D) imaging difficult. Methods: Nine patients with native coarctation or recoarctation and 4 patients with a vascular ring had a CT scan as a part of their clinical evaluation. There were 7 males. The mean age was 11.7 years. (range 19 days to 29 years) The mean weight was 22.7 kg (range 3.3,139.0 kg). The dicom data from contrast CT scans were converted by the Amira software package into a 3D image. The areas of interest were selected. The images were then projected in 3D on a standard video monitor and could be rotated 360° in any dimension. Results: Adequate CT scans and 3D reconstructions were obtained in 12 of 13 patients. There were 85,1,044 slices obtained in the adequate studies. We could not reconstruct a 3D image from a patient's CT scan that had only 22 slices. The anatomy defined by 3D was compared to 2D CT imaging and confirmed by cardiac catheterization or direct visualization in the operating room in the 12 patients with adequate 3D reconstructions. In 5 of 12 patients, 3D reconstructions provided valuable spatial information not observed in the conventional 2D scans. Conclusion: We believe that 3D reconstruction of contrast-enhanced CT scans of these complex structures provides additional valuable information that is helpful in the decision-making process. [source] Arteriovenous Fistula Leading to Severe Tortuosity and Aneurysm FormationJOURNAL OF CARDIAC SURGERY, Issue 2 2009Murat Ugurlucan M.D. In this report we present the images of a 58-year-old male patient with a 25-year history of gun shot injury and arteriovenous fistula formation at the femoral region. [source] A Simple Experimental Technique to Measure Tortuosity in Packed BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2006J. M. P. Q. Delgado Abstract In this article, a simple and inexpensive experimental technique easy to build in laboratory, for the measurement of tortuosity of a packed bed of inert particles, is described. Experimental values of the tortuosity were obtained with four different packed beds of sand. The experimental results obtained are in good agreement with the theoretical values of tortuosity in a porous media; and the data reported showed the tortuosity to increase with decrease in the void fraction of the packed bed as expected. On décrit dans cet article une technique expérimentale simple et peu coûteuse facile à concevoir en laboratoire, pour la mesure de la tortuosité d'un lit garni de particules inertes. Des valeurs expérimentales de tortuosité ont été obtenues avec quatre lits différents garnis de sable. Les résultats expérimentaux obtenus montrent un bon accord avec les valeurs théoriques de la tortuosité dans un milieu poreux; et les données signalées montrent que la tortuosité augmente avec la diminution de la fraction de vide du lit garni tel qu'attendu. [source] Branches of the splenic artery and splenic arterial segmentsCLINICAL ANATOMY, Issue 5 2003A. Daisy Sahni Abstract In 200 adult autopsy specimens, the arterial supply to the pancreas and spleen was studied radiologically and by manual dissection. The splenic artery divided into two or three lobar arteries, which supplied its corresponding lobe; each lobar artery subsequently divided into two to four lobular branches. Six to twelve lobular branches were observed entering the splenic substance at the hilum. Lobar arteries did not anastomose with each other, hence, the lobes of the spleen are also termed segments. The lobules, however, were not found to be independent segments and the arteries of one lobule anastomosed with those of other lobules. The branching pattern of the splenic artery varied from one specimen to another, so much so that a prevailing pattern could not be identified. Polar arteries, particularly to the superior pole, arose quite proximal to the hilum in 51% of cases and were occasionally missed. In 45% of males and 40% of females, the posterior gastric artery arose from about the middle of the splenic artery. The splenic artery was not found to be tortuous in fetuses, newborns, and young children. Tortuosity was seen in only 10% of adults; thus, the characteristic tortuosity of the splenic artery appears to develop with age. Clin. Anat. 16:371,377, 2003. © 2003 Wiley-Liss, Inc. [source] Practical methods for measuring the tortuosity of porous materials from binary or gray-tone tomographic reconstructionsAICHE JOURNAL, Issue 8 2009Cedric J. Gommes Abstract Two practical methods are proposed to measure the tortuosity of a porous or permeable material from its tomographic reconstruction. The first method is based on the direct measurement of the shortest distance between two points in the pores, and the second is based on the geodesic reconstruction of the pore or permeation space. Unlike the first method, the second can be directly applied to gray-tone tomograms, without the need of a segmentation step. The methods are illustrated with an electron tomogram of clay/plastic nanocomposite, an X-ray microtomogram of sandstone, and a series of model morphologies consisting of penetrable random spheres. For the latter series, the measured tortuosities compare very well with those derived independently from the theoretical effective diffusion coefficients. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Effects of variability in anatomical reconstruction techniques on models of synaptic integration by dendrites: a comparison of three internet archivesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2004Tibor Szilágyi Abstract The first step in building a realistic computational neuron model is to produce a passive electrical skeleton on to which active conductances can be grafted. For this, anatomically accurate morphological reconstructions of the desired cell type are required. In this study compartmental models were used to compare from a functional perspective three on-line archives of rat hippocampal CA1 pyramidal cell morphologies. The topological organization of cells was found to be similar for all archives, but several morphometric differences were observed. The three-dimensional size of the cells, the diameter and tortuosity of dendrites, and the electrotonic length of the main apical dendrite and of the branches in stratum lacunosum moleculare were dissimilar. The experimentally measured kinetics of somatically recorded inhibitory postsynaptic currents evoked in the stratum lacunosum moleculare (data from the literature) could be reproduced only using the archives that contained cells with an electrotonically short main apical dendrite. In the amplitude attenuation of the simulated postsynaptic currents and the voltage escape from the command potential under voltage clamp conditions, a two- to three-fold difference was observed among archives. Upon activation of a single model synapse on distal branches, cells with low dendritic diameter showed a voltage escape larger than 15 mV. The diameter of the dendrites influenced greatly the results, emphasizing the importance of methods that allow an accurate measurement of this parameter. Our results indicate that there are functionally significant differences in the morphometric data available in different archives even if the cell type, brain region and species are the same. [source] Effect of degree of fluid saturation on transport coefficients in disturbed soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2004A. Tuli Summary To improve the predictive capability of transport models in soils we need experimental data that improve their understanding of properties at the scale of pores, including the effect of degree of fluid saturation. All transport occurs in the same soil pore space, so that one may intuitively expect a link between the different transport coefficients and key geometrical characteristics of the pores such as tortuosity and connectivity, and pore-size distribution. To understand the combined effects of pore geometry and pore-size distribution better, we measured the effect of degree of water saturation on hydraulic conductivity and bulk soil electrical conductivity, and of degree of air saturation on air conductivity and gaseous diffusion for a fine sand and a sandy loam soil. To all measured data were fitted a general transport model that includes both pore geometry and pore-size distribution parameters. The results show that both pore geometry and pore-size distribution determine the functional relations between degree of saturation, hydraulic conductivity and air conductivity. The control of pore size on convective transport is more for soils with a wider pore-size distribution. However, the relative contribution of pore-size distribution is much larger for the unsaturated hydraulic conductivity than for gaseous phase transport. For the other transport coefficients, their saturation dependency could be described solely by the pore-geometry term. The contribution of the latter to transport was much larger for transport in the air phase than in the water phase, supporting the view that connectivity dominates gaseous transport. Although the relation between effective fluid saturation and all four relative transport coefficients for the sand could be described by a single functional relation, the presence of a universal relationship between fluid saturation and transport for all soils is doubtful. [source] Study of the Catalytic Layer in Polybenzimidazole-based High Temperature PEMFC: Effect of Platinum Content on the Carbon SupportFUEL CELLS, Issue 2 2010J. Lobato Abstract In this work, the effect of platinum percentage on the carbon support of commercial catalyst for electrodes to be used in a Polybenzimidazole (PBI)-based PEMFC has been studied. Three percentages were studied (20, 40 and 60%). In all cases, the same quantity of PBI in the catalyst layer was added, which is required as a ,binder'. From Hg porosimetry analyses, pore size distribution, porosity, mean pore size and tortuosity of all electrodes were obtained. The amount of mesopores gets larger as the platinum percentage in the catalytic layer decreases, which reduces the overall porosity and the mean pore size and increases the tortuosity. The electrochemical characterisation was performed by voltamperometric studies, assessing the effective electrochemical surface area (ESA) of the electrodes, by impedance spectroscopy (IS), determining the polarisation resistance, and by the corresponding fuel cell measurements. The best results were obtained for the electrodes with a content of 40% Pt on carbon, as a result of an adequate combination of catalytic activity and mass transfer characteristics of the electrode. It has been demonstrated that the temperature favours the fuel cell performance, and the humidification does not have remarkable effects on the performance of a PBI-based polymer electrolyte membrane fuel cell (PEMFC). [source] Pristine New Zealand forest soil is a strong methane sinkGLOBAL CHANGE BIOLOGY, Issue 1 2004Sally J. Price Abstract Methanotrophic bacteria oxidize methane (CH4) in forest soils that cover ,30% of Earth's land surface. The first measurements for a pristine Southern Hemisphere forest are reported here. Soil CH4 oxidation rate averaged 10.5±0.6 kg CH4 ha,1 yr,1, with the greatest rates in dry warm soil (up to 17 kg CH4 ha,1 yr,1). Methanotrophic activity was concentrated beneath the organic horizon at 50,100 mm depth. Water content was the principal regulator of (r2=0.88) from the most common value of field capacity to less than half of this when the soil was driest. Multiple linear regression analysis showed that soil temperature was not very influential. However, inverse co-variability confounded the separation of soil water and temperature effects in situ. Fick's law explained the role of water content in regulating gas diffusion and substrate supply to the methanotrophs and the importance of pore size distribution and tortuosity. This analysis also showed that the chambers used in the study did not affect the oxidation rate measurements. The soil was always a net sink for atmospheric CH4 and no net CH4 (or nitrous oxide, N2O) emissions were measured over the 17-month long study. For New Zealand, national-scale extrapolation of our data suggested the potential to offset 13% of CH4 emissions from ca. 90 M ruminant animals. Our average was about 6.5 times higher than rates reported for most Northern Hemisphere forest soils. This very high was attributed to the lack of anthropogenic disturbance for at least 3000,5000 years and the low rate of atmospheric nitrogen deposition. Our truly baseline data could represent a valid preagricultural, preindustrial estimate of the soil sink for temperate latitudes. [source] Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysisHYDROLOGICAL PROCESSES, Issue 21 2010F. Rezanezhad Abstract In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air-filled pores control the unsaturated hydraulic conductivity of peat soils using high-resolution (45 µm) three-dimensional (3D) X-ray computed tomography (CT) and digital image processing of four peat sub-samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross-sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air-filled pore hydraulic radius, tortuosity, air-filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air-filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright © 2010 John Wiley & Sons, Ltd. [source] Applicability of the Washburn theory for determining the wetting angle of soilsHYDROLOGICAL PROCESSES, Issue 17 2007Henryk Czachor Abstract The Washburn theory is frequently applied to determine the wetting angle of soils. It is based on the porous medium being characterized as a set of cylindrical, straight capillaries. It is clear that this is an oversimplification as real soil pores vary at least as regards two important features: cross-section and tortuosity. In this study, a mathematical model of meniscus movement in a tortuous, sinusoidal shaped capillary was developed and the obtained analytical expressions for the wetting angle and for the pore radius were compared with the appropriate formula concerning the Washburn theory. The results demonstrate that the wetting angle of water in soil determined on the basis of the measured wetting front kinetics and of Washburn equations is likely to have an overestimated value due to the wavy, tortuous nature of inter-soil grain pores. The above conclusion was confirmed by capillary rise experiments. Wetting angles of methyl alcohol and of water measured on flat glass were 0 and 27·4° , respectively. Apparent wetting angles calculated from capillary rise in powdered glass kinetics and Washburn equation were 70 and 83° respectively. If the pore structure characteristics of porous media are not taken into account the applicability of the Washburn theory for soil wettability estimation seems to be very limited. Copyright © 2007 John Wiley & Sons, Ltd. [source] Isolated right-sided varicocele as a salvage pathway for portal hypertensionINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 6 2005G-M. Pinggera Summary Retrograde blood flow can occur in the testicular veins and in the pampiniformis plexus in the absence of valves or if the valves are incompetent, resulting in tortuosity and dilatation of the veins. These abnormal alterations in the anatomy of the veins, termed varicoceles, are associated with infertility in the male. Most varicoceles occur on the left. We report the case of a rare isolated right-sided varicocele in a male evaluated for infertility in whom extensive work-up revealed venous anomalies and a spontaneous porto-systemic shunt. In such cases, standard approaches to infertility treatment are fruitless. [source] Movement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on BorneoJOURNAL OF ANIMAL ECOLOGY, Issue 5 2006KONSTANS WELLS Summary 1Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13 525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features. [source] Individual responses of seabirds to commercial fisheries revealed using GPS tracking, stable isotopes and vessel monitoring systemsJOURNAL OF APPLIED ECOLOGY, Issue 2 2010Stephen C. Votier Summary 1.,The large amount of discards produced by commercial fisheries can have major impacts on marine predator populations: this abundant food may increase populations of some scavengers or decrease others via accidental bycatch. Yet, despite the conservation implications of discard practices, the ecology of individual scavengers is poorly understood. 2.,Here, we assess the influence of commercial fisheries' activity on the foraging behaviour of individual breeding northern gannets Morus bassanus. Using recent developments in stable isotope mixing models (Stable Isotope Analysis in R or SIAR) we estimate individual discard consumption. Using GPS tracking and the Vessel Monitoring System (VMS), we investigate behavioural responses to trawlers. 3.,Analysis of conventional diet samples, as well as stable isotope ratios of carbon and nitrogen in blood (plasma and cells), highlight marked individual differences in the proportion of fishery discards in the diet. Individual differences in foraging behaviour revealed by stable isotopes show evidence of both short-term consistency and behavioural flexibility. 4.,At-sea path tortuosity of 25 gannets (tracked using GPS loggers) revealed scale-dependent adjustments in response to VMS-derived fishing vessel locations, as well as to sea surface temperature, chlorophyll a concentration and copepod abundance. The results also indicate individual variability in behavioural response to trawlers. 5.,Individual differences in the amount of discards estimated from SIAR were negatively correlated with differences in foraging trip length and body condition, indicating potential fitness consequences. 6.,Synthesis and applications. The management of commercial fisheries and apex predators is a daunting task. Ultimately, reducing bycatch and removing dependency on discards remain key conservation priorities, but managers should also ensure that scavenging species have sufficient alternative food to meet their energetic needs, to ameliorate potential unforeseen knock-on consequences. The results of Stable Isotope Analysis (SIAR) reveal intra-population differences in discard consumption by gannets; differences that have impacts on foraging effort and body condition. The use of GPS tracking and Vessel Monitoring Systems (VMS) reveal that gannet at-sea behaviour is influenced by fishing vessels, although this also varies among individuals. A combination of SIAR, GPS tracking and VMS can be used to study fishery/scavenger interactions in detail at the individual level, to answer fundamental questions about scavenging behaviour. [source] Mathematical modeling of solid oxide fuel cells at high fuel utilization based on diffusion equivalent circuit modelAICHE JOURNAL, Issue 5 2010Cheng Bao Abstract Mass transfer and electrochemical phenomena in the membrane electrode assembly (MEA) are the core components for modeling of solid-oxide fuel cell (SOFC). The general MEA model is simply governed with the Stefan-Maxwell equation for multicomponent gas diffusion, Ohm's law for the charge transfer and the current-overpotential equation for the polarization calculation. However, it has obvious discrepancy at high-fuel utilization or high-current density. An advanced MEA model is introduced based on the diffusion equivalent circuit model. The main purpose is to correct the real-gas concentrations at the triple-phase boundary by assuming that the resistance of surface diffusion is in series with that of the gaseous bulk diffusion. Thus, it can obtain good prediction of cell performance in a wide range by avoiding the decrement of effective gas diffusivity via unreasonable increment of the electrode tortuosity in the general MEA model. The mathematical model has been validated in the cases of H2H2O, COCO2 and H2CO fuel system. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Practical methods for measuring the tortuosity of porous materials from binary or gray-tone tomographic reconstructionsAICHE JOURNAL, Issue 8 2009Cedric J. Gommes Abstract Two practical methods are proposed to measure the tortuosity of a porous or permeable material from its tomographic reconstruction. The first method is based on the direct measurement of the shortest distance between two points in the pores, and the second is based on the geodesic reconstruction of the pore or permeation space. Unlike the first method, the second can be directly applied to gray-tone tomograms, without the need of a segmentation step. The methods are illustrated with an electron tomogram of clay/plastic nanocomposite, an X-ray microtomogram of sandstone, and a series of model morphologies consisting of penetrable random spheres. For the latter series, the measured tortuosities compare very well with those derived independently from the theoretical effective diffusion coefficients. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] ORIGINAL ARTICLE: Radiological review of intercostal artery: Anatomical considerations when performing procedures via intercostal spaceJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 4 2010S Choi Abstract Introduction: The aim of this study was to closely examine the course of the intercostal arteries within the intercostal spaces particularly with regard to where the arteries were located in relation to their adjacent ribs. The degree of tortuosity of the arteries was also examined, along with anatomical differences in different age groups. Methods: A total of 81 patients between the age of 30 and 90 years who had underwent a CT examination of the chest for any indication were included in the study. All studies were performed on a dual source 64 slice CT (Siemens Definition Erlangen Germany). Analysis of the intercostal arteries was performed on a CT workstation using volume rendered 3D reconstructions F, or each patient the 10'n intercostals pacesb ilaterally were examined for the course and tortuosity of the intercostal arteries. Results: The ICA is located relatively inferiorly in the intercostal space at costovertebral junction and it gradually becomes more superiorly positioned within the intercostal space it as courses laterally. This finding was consistent in all age groups. In addition, analysis of the data demonstrated increasing intercostal artery tortuosity with advancing age. Conclusion: In this study we have examined the course of the posterior intercostal arteries using MDCT. This study confirms the classical description of the course of ICA. We have shown that in the medial chest, posteriorly, the artery is located in the inferior half of the intercostal space. As it moves away from the costovertebral junction it travels closer to the inferior border of the rib above and reaches the intercostal groove. We have also shown that the artery tends to be more tortuous in elderly patients, decreasing the area of "safe" space for interventions. Both of these findings are relevant to radiologists and non-radiologists performing interventional procedures via the intercostal space. [source] Prediction of gas sorption kinetics for porous media using MRIAICHE JOURNAL, Issue 9 2006Matthew J. Watt-Smith Abstract Diffusion and reaction within porous media involving condensable vapors are important processes in catalysis, fuel cells, and membrane separations. In this work, 3-D maps of the spatial variation of porosity, pore size and network tortuosity within a porous solid, derived from magnetic resonance images, have been used to construct a structural model for a mesoporous catalyst pellet. Simulations of the kinetic uptake, adsorption and capillary condensation of butane vapor within the porous solid, conducted on the structural model, have successfully predicted experimental measurements of the effects of the onset of capillary condensation on mass transfer rates without the need of the various adjustable parameters prevalent in other models. These findings suggest that accurate mathematical models for both the complex void space of the porous medium, and the mass transport processes taking place within it, have been successfully developed. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Quantitative characterization of sphere-templated porous biomaterialsAICHE JOURNAL, Issue 4 2005A. J. Marshall Abstract Three-dimensional (3-D) porous hydrogels were fabricated by polymerizing 2-hydroxyethyl methacrylate around templates of random close-packed poly(methyl methacrylate) microspheres with nominal diameter of 5 or 15 ,m. The templates were leached out to create networks of interconnected spherical pores. Applications for sphere-templated porous biomaterials include scaffolds for tissue engineering and spatial control of wound healing. This study describes an approach to characterizing pore structure and predicting permeability of sphere-templated porous hydrogels. The materials were embedded in resin, and 1-,m-plane sections were digitally analyzed with fluorescence microscopy. The porosity and pore size distribution were determined from stereological interpretation, and we present novel techniques for obtaining the pore throat size distribution, the number of pore throats per pore, and the tortuosity. A simple apparatus is also introduced for measurement of the hydraulic permeability. Permeability predictions based on quantitative microscopy measurements and on stereology were found to agree closely with permeability measurements. The aptness of the Kozeny equation for spherically pored materials is also investigated. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Evaluation of hydrophilic permeant transport parameters in the localized and non-localized transport regions of skin treated simultaneously with low-frequency ultrasound and sodium lauryl sulfateJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2008Joseph Kushner IV Abstract The porosity (,), the tortuosity (,), and the hindrance factor (H) of the aqueous pore channels located in the localized transport regions (LTRs) and the non-LTRs formed in skin treated simultaneously with low-frequency ultrasound (US) and the surfactant sodium lauryl sulfate (SLS), were evaluated for the delivery of four hydrophilic permeants (urea, mannitol, raffinose, and inulin) by analyzing dual-radiolabeled diffusion masking experiments for three different idealized cases of the aqueous pore pathway hypothesis. When , and , were assumed to be independent of the permeant radius, H was found to be statistically larger in the LTRs than in the non-LTRs. When a distribution of pore radii was assumed to exist in the skin, no statistical differences in ,, ,, and H were observed due to the large variation in the pore radii distribution shape parameter (3 Å to infinity). When infinitely large aqueous pores were assumed to exist in the skin, , was found to be 3,8-fold greater in the LTRs than in the non-LTRs, while little difference was observed in the LTRs and in the non-LTRs for ,. This last result suggests that the efficacy of US/SLS treatment may be enhanced by increasing the porosity of the non-LTRs. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:906,918, 2008 [source] Prediction of steady-state skin permeabilities of polar and nonpolar permeants across excised pig skin based on measurements of transient diffusion: Characterization of hydration effects on the skin porous pathwayJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2002Hua Tang Abstract The applicability of a two-parameter Fickian diffusion model for predicting the skin steady-state permeability based on measurements of the transient transport of permeants across the skin was tested. Using five model permeants possessing different physicochemical properties and pig skin as the model membrane, the skin permeabilities predicted by the two-parameter Fickian diffusion model were compared with the measured skin permeabilities. Results show that the transient skin permeation profiles of the hydrophobic permeants, estradiol, testosterone, and dolichol, across split-thickness pig skin can be modeled adequately by the two-parameter Fickian diffusion model (with constant parameter values), and therefore, that this model can be utilized to shorten the experimental time required to determine the skin permeabilities of these compounds. However, the skin permeabilities of the highly hydrophilic permeants, mannitol and sucrose, predicted by the two-parameter Fickian diffusion model (with constant parameter values) were significantly lower than the experimentally determined values, indicating that the dominant skin pathway of polar permeants within the excised pig skin undergoes significant structural changes during the in vitro diffusion cell studies. Although the skin permeability values determined experimentally using the traditional steady-state method normally correspond to a highly hydrated skin sample, the two-parameter Fickian diffusion model enables an estimation of the skin permeability of the skin membrane at its less-hydrated state (a condition more representative of in vivo and clinical situations). Using the two-parameter Fickian diffusion model and a recently developed skin porous-pathway theory, the effects of skin hydration on the skin porous pathway within the excised pig skin were characterized. Specifically, we found that hydration leads to induction of new pores/reduction of the tortuosity of existing pores within the excised pig skin during the 48 h diffusion cell studies conducted, while the skin average pore radii remain relatively constant (,26 Å) for up to 48 h. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1891,1907, 2002 [source] Homogenizing the acoustic properties of a porous matrix containing an incompressible inviscid fluidMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2003J. L. Ferrin We undertake a rigorous derivation of the Biot's law for a porous elastic solid containing an inviscid fluid. We consider small displacements of a linear elastic solid being itself a connected periodic skeleton containing a pore structure of the characteristic size ,. It is completely saturated by an incompressible inviscid fluid. The model is described by the equations of the linear elasticity coupled with the linearized incompressible Euler system. We study the homogenization limit when the pore size ,tends to zero. The main difficulty is obtaining an a priori estimate for the gradient of the fluid velocity in the pore structure. Under the assumption that the solid part is connected and using results on the first order elliptic systems, we obtain the required estimate. It allows us to apply appropriate results from the 2-scale convergence. Then it is proved that the microscopic displacements and the fluid pressure converge in 2-scales towards a linear hyperbolic system for an effective displacement and an effective pressure field. Using correctors, we also give a strong convergence result. The obtained system is then compared with the Biot's law. It is found that there is a constitutive relation linking the effective pressure with the divergences of the effective fluid and solid displacements. Then we prove that the homogenized model coincides with the Biot's equations but with the added mass ,a being a matrix, which is calculated through an auxiliary problem in the periodic cell for the tortuosity. Furthermore, we get formulas for the matricial coefficients in the Biot's effective stress,strain relations. Finally, we consider the degenerate case when the fluid part is not connected and obtain Biot's model with the relative fluid displacement equal to zero. Copyright © 2003 John Wiley & Sons, Ltd. [source] Arteriolar Remodeling Following Ischemic Injury Extends from Capillary to Large Arteriole in the MicrocirculationMICROCIRCULATION, Issue 5 2008Alexander M. Bailey ABSTRACT Objective: Skeletal muscle vasculature undergoes arteriogenesis to restore tissue perfusion and function following loss of blood flow. This process has been shown to occur in large vessels following ischemia, although recent studies suggest this may occur in the microcirculation as well. We tested the hypothesis that ischemia induces microvascular remodeling in the skeletal muscle microcirculation on the scale of capillary to sub-35 ,m diameter arterioles. Methods: Ligations of a feeding arteriole to the caudal-half of the spinotrapezius muscle were performed on C57BL/6 mice. At 5 days, microvascular remodeling responses were quantified using intravital and whole-mount confocal microscopy. Immunohistochemistry was performed to visualize vessels, incorporated leukocytes, and regions of hypoxia. Results: Ischemic tissue underwent localized microvascular remodeling characteristic of arteriogenesis, including pronounced vessel tortuosity. In patent microvessels (diameters 15,35 ,m), we observed increases in vascular density (38%), branching (90%) and collateral development (36.5%). The formation of new arterioles (diameters 6,35 ,m) increased by 24.3%, while chronic hypoxia was absent from all tissues. Conclusions: Ischemic injury induces arteriogenesis in skeletal muscle microcirculation. Furthermore, this surgical model enables en face analysis of microcirculatory adaptations with single-cell resolution and can provide investigators with morphometric data on a microscale that is difficult to achieve using other models. [source] Modelling advection and diffusion of water isotopologues in leavesPLANT CELL & ENVIRONMENT, Issue 8 2007MATTHIAS CUNTZ ABSTRACT We described advection and diffusion of water isotopologues in leaves in the non-steady state, applied specifically to amphistomatous leaves. This explains the isotopic enrichment of leaf water from the xylem to the mesophyll, and we showed how it relates to earlier models of leaf water enrichment in non-steady state. The effective length or tortuosity factor of isotopologue movement in leaves is unknown and, therefore, is a fitted parameter in the model. We compared the advection,diffusion model to previously published data sets for Lupinus angustifolius and Eucalyptus globulus. Night-time stomatal conductance was not measured in either data set and is therefore another fitted parameter. The model compared very well with the observations of bulk mesophyll water during the whole diel cycle. It compared well with the enrichment at the evaporative sites during the day but showed some deviations at night for E. globulus. It became clear from our analysis that night-time stomatal conductance should be measured in the future and that the temperature dependence of the tracer diffusivities should be accounted for. However, varying mesophyll water volume did not seem critical for obtaining a good prediction of leaf water enrichment, at least in our data sets. In addition, observations of single diurnal cycles do not seem to constrain the effective length that relates to the tortuosity of the water path in the mesophyll. Finally, we showed when simpler models of leaf water enrichment were suitable for applications of leaf water isotopes once weighted with the appropriate gas exchange flux. We showed that taking an unsuitable leaf water enrichment model could lead to large biases when cumulated over only 1 day. [source] Effect of morphology on barrier properties of poly(ethylene terephthalate),POLYMER ENGINEERING & SCIENCE, Issue 3 2005A.A. Natu The effects of morphology on the barrier properties of poly(ethylene terephthalate) (PET) have been investigated. Various levels of crystallinity can be developed in PET as a result of thermal exposure, orientation, and heat setting. The morphologies of the crystalline phase are affected by the conditions of their formation. As a result of morphological differences, samples with equivalent levels of crystallinity have been found to exhibit different oxygen barrier properties. These differences are most apparent at low and intermediate levels of crystallinity. For thermally crystallized systems, at the same crystalline content, increasing superstructure size in the crystalline phase leads to greater tortuosity for the permeant molecules, resulting in lower permeability. For stretched and heat set PET, transport properties can be correlated with birefringence as well as overall orientation, measured in terms of fraction of molecules in the trans or extended chain conformation. At high levels of crystallinity, where the spherulites become volume filling, permeation takes place primarily through the interlamellar regions of the crystalline phase and is controlled by level of crystallinity, independent of the mode of crystallization. The barrier properties of PET, before spherulitic impingement occurs, are governed by the size and number of spherulites as well as by the amorphous orientation present in non-crystalline regions. POLYM. ENG. SCI., 45:400,409, 2005. © 2005 Society of Plastics Engineers [source] A Simple Experimental Technique to Measure Tortuosity in Packed BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2006J. M. P. Q. Delgado Abstract In this article, a simple and inexpensive experimental technique easy to build in laboratory, for the measurement of tortuosity of a packed bed of inert particles, is described. Experimental values of the tortuosity were obtained with four different packed beds of sand. The experimental results obtained are in good agreement with the theoretical values of tortuosity in a porous media; and the data reported showed the tortuosity to increase with decrease in the void fraction of the packed bed as expected. On décrit dans cet article une technique expérimentale simple et peu coûteuse facile à concevoir en laboratoire, pour la mesure de la tortuosité d'un lit garni de particules inertes. Des valeurs expérimentales de tortuosité ont été obtenues avec quatre lits différents garnis de sable. Les résultats expérimentaux obtenus montrent un bon accord avec les valeurs théoriques de la tortuosité dans un milieu poreux; et les données signalées montrent que la tortuosité augmente avec la diminution de la fraction de vide du lit garni tel qu'attendu. [source] Arteriolar network architecture and vasomotor function with ageing in mouse gluteus maximus muscleTHE JOURNAL OF PHYSIOLOGY, Issue 2 2004Shawn E. Bearden Physical diminishes with ageing, but little is known of how the microvascular supply to skeletal muscle fibres is affected. To test the hypothesis that ageing alters blood flow control, we investigated network architecture and vasomotor responses of arterioles in the gluteus maximus muscle of young (2,3 months), adult (12,14 months) and old (18,20 months) C57BL6 male mice (n= 83) (Young, Adult and Old, respectively). Microvascular casts revealed that the total number, length and surface area of arteriolar segments (diameter, 10,50 ,m) were not significantly different across age-groups. However, for arterioles with diameter of 30 ,m, tortuosity and branch angles increased with age (P < 0.05). In anaesthetized mice, second-order (2A) distributing arterioles had similar resting (17 ± 1 ,m) and maximal (37 ± 1 ,m) diameters and similar responsiveness to cumulative (10,10,10,4m) superfusion of acetylcholine or phenylephrine. With superfusate oxygen level raised from 0 to 21%, 2A arteriolar constriction in Young (11 ± 1 ,m) was greater (P < 0.05) than Adult and Old (5 ± 1 ,m). Observed 1 mm upstream from microiontophoresis of ACh (1 ,A, 1 s), conducted vasodilatation was 10 ± 1 ,m in Young, 17 ± 1 ,m in Adult and 6 ± 1 ,m in Old (P < 0.05). With muscle contractions (2, 4 and 8 Hz; 30 s) arteriolar diameter increased similarly across age-groups (6 ± 1, 11 ± 1 and 18 ± 1 ,m, respectively). Muscle mass and active tension were similar across age-groups yet postcontraction vasodilatation recovered more rapidly in Old versus Adult and Young (P < 0.05). With arteriolar network architecture maintained during ageing, the impairment in conducted vasodilatation and attenuation of postcontraction vasodilatation may compromise exercise tolerance. [source] The pitfalls of extrapolation in conservation: movements and habitat use of a threatened toad are different in the boreal forestANIMAL CONSERVATION, Issue 1 2010J. M. Constible Abstract Widely distributed species often vary geographically in their ecology. Thus, results of studies done in one part of their range cannot necessarily be extrapolated readily to populations elsewhere. This problem is particularly important for threatened species whose ecology has been studied in a few disconnected locations. The Canadian toad Bufo (Anaxyrus) hemiophrys occupies a large geographic range in western North America, but most studies of its ecology have been done in the prairies, where the species is considered to be closely associated with aquatic habitats. However, B. hemiophrys also occurs in boreal forest, where it faces threats from logging activities, especially if it uses upland habitats far from ponds and lakes. We radio-tracked 29 toads in the boreal forest of northern Alberta, Canada to determine their patterns of movement and habitat use. Most movements between fixes were <50 m, but toads sometimes made longer movements exceeding 100 m. Over time, however, these short-term movements combined into large-scale directional movements that were highly variable among toads in both tortuosity and timing, but which generally took toads into upland forested habitats. Putative hibernacula also were located in upland sites. However, despite this terrestriality, toads still were associated with wetlands, using them significantly more often than would be expected based on their proportionate areal contribution to the landscape. Nonetheless, use of upland sites and long-distance terrestrial movements differentiate this population of B. hemiophrys from those studied in prairie environments. Conservation plans based on what we know about the species elsewhere therefore would be inappropriate in this region. Management often requires site-specific information, which can be obtained only from natural-history studies of the populations in question. [source] NO and de novo mammalian angiogenesis: Further evidence that NO inhibits bFGF-induced angiogenesis while not influencing VEGF165 -induced angiogenesisAPMIS, Issue 1 2000Ingrid Näslund Using the non-surgical rat mesenteric window angiogenesis assay, we studied the systemic effect of (i) the nitric oxide (NO)-releasing vasodilator isosorbide-5-mononitrate (ISMN) and (ii) the NO-synthase inhibitor L-NAME on angiogenesis induced by the intraperitoneal injection of bFGF and VEGF165. The response was assessed objectively and quantitatively by microscopic morphometry and image analysis in terms of the vascularized area (VA; a measurement of microvessel spatial extension), the microvascular length (MVL; a composite measurement of microvessel density), the total microvascular length (TMVL=VAxMVL), the number of microvessel segments per unit tissue volume (No. MS), the length of the microvessel segments (Le. MS) and the degree of microvessel tortuosity (MVT). Additional architectural features of the network were assessed in terms of variables introduced here: the number of microvessel branching points per unit tissue volume (No. BP), the index of interconnecting microvessel loop formation (In. LF), the index of microvessel intersection (In. IS), the number of microvessel sprouts per unit tissue volume (No. SP) and their length (Le. SP). In bFGF-mediated angiogenesis, L-NAME significantly, augmented angiogenesis, whereas ISMN significantly inhibited angiogenesis. By contrast, neither L-NAME nor ISMN affected the angiogenic response to VEGF165. [source] Thoracic aneurysm repair: Managing severe tortuosity with brachiofemoral tractionCATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 7 2007Christos Lioupis MD Abstract Challenging anatomy of the thoracic aorta is often encountered, and aortic tortuosity may be a major impediment to the propulsion of the stent-graft. Traction on both ends of a guidewire, with one end exiting the right upper extremity and the other end exiting the lower extremity, is an excellent option to manage thoracic aorta tortuosity. Careful application of simple guidelines may lessen associated risks and improve safety. © 2007 Wiley-Liss, Inc. [source] | |||||||||||||||||||