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Layer Thickness (layer + thickness)
Kinds of Layer Thickness Selected AbstractsEffects of Individual Layer Thickness on the Microstructure and Optoelectronic Properties of Sol,Gel-Derived Zinc Oxide Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008Noureddine Bel Hadj Tahar Zinc oxide (ZnO) thin films were prepared under different conditions on glass substrates using a sol,gel process. The microstructure of ZnO films was investigated by means of diffraction analysis, and plan-view and cross-sectional scanning electron microscopy. It was found that the preparation conditions strongly affected the structure and the optoelectronic properties of the films. A structural evolution in morphology from spherical to columnar growth was observed. The crystallinity of the films was improved and columnar film growth became more dominant as the zinc concentration and the substrate withdrawal speed decreased. The individual layer thickness for layer-by-layer homoepitaxy growth that resulted in columnar grains was <20 nm. The grain columns are grown through the entire film with a nearly unchanged lateral dimension through the full film thickness. The columnar ZnO grains are c -axis oriented perpendicular to the interface and possess a polycrystalline structure. Optical transmittance up to 90% in the visible range and electrical resistivity as low as 6.8 × 10,3·,·cm were obtained under optimal deposition conditions. [source] Model Based Evaluation of Bridge Decks Using Ground Penetrating RadarCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2008Kimberly Belli Interpretation of the radar signal is typically performed through preliminary filtering techniques and interpretation is based on viewing numerous signals in the form of a scan. Although anomalies can be evident in the scanned image, quantification and interpretation of the main issue remain ambiguous. This article presents the ambiguity and common methods of interpretation based on response amplitude and travel time. An integrated medium is developed and used as a forward modeling tool to generate a realistic radar reflection of a reinforced concrete bridge deck with defects. A healthy deck reflection is obtained from a separate model and is combined with an inverse solution to quantifiably estimate unknown subsurface properties such as layer thickness and dielectric constants of subsurface materials evident in the realistic radar trace as well as. The forward modeling tool and associated model based assessment provides an objective computational alternative to the interpretation of scanned images. [source] Mechanisms affecting the dissolution of nonaqueous phase liquids into the aqueous phase in slow-stirring batch systemsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2001Mathias Schluep Abstract Understanding the kinetics of the exchange processes between nonaqueous phase liquids (NALs) and water is important in predicting the fate of anthropogenic compounds such as petroleum hydrocarbons, i.e., benzene, toluene, ethylbenzene, and xylene (BTEX) as well as polynuclear aromatic hydrocarbons (PAHs). Exchange processes occurring in the environment resemble the experimental setup of the slow-stirring method (SSM) designed to determine solubilities and octanol-water partition coefficients. Data obtained from SSM experiments for diesel fuel compounds are interpreted by a linear transfer model that is characterized by an aqueous molecular boundary layer and the water/NAPL equilibrium partition coefficient. For the chosen experimental setup, the boundary layer thickness is 2.42 × 10,2 cm. Typical equilibration times lie between 1 and 2 d. Due to the temperature dependence of the aqueous diffusivity, this time increases with decreasing temperature. Transport within the NAPL phase can slow down the exchange process for the more water-soluble compounds (e.g., benzene) provided that the stirring rate exceeds a critical value. [source] Three-Dimensional Printing of Complex-Shaped Alumina/Glass Composites,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Wei Zhang Abstract Alumina/glass composites were fabricated by three-dimensional printing (3DPÔ) and pressureless infiltration of lanthanum-alumino-silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600,°C for 2,h prior to glass infiltration at 1100,°C for 2,h. The influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150,µm resulted in an increase of the total porosity from ,19 to ,39,vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y -axis of the 3D-printer compared to those orientated along the X - or the Z -axis, respectively. Fabricated Al2O3/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6,MPa m1/2, 175,MPa, 228,GPa, and 12,GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process. [source] Protists with different feeding modes change biofilm morphologyFEMS MICROBIOLOGY ECOLOGY, Issue 2 2009Anne Böhme Abstract The effect of Dexiostoma (filter feeder), Vannella, Chilodonella (raptorial feeders), Spumella, and Neobodo (direct interception feeders) on the morphology of multispecies bacterial biofilms was investigated in small flow cells. The filter feeder Dexiostoma campylum did not alter biofilm volume and porosity but stimulated the formation of larger microcolonies compared with ungrazed biofilms. In contrast, the raptorial feeder Vannella sp. efficiently grazed bacteria from the biofilm surface, leading to smaller microcolonies and lower maximal and basal layer thickness compared with ungrazed biofilms. Microcolony formation was not stimulated in the presence of the sessile Spumella sp. Chilodonella uncinata rasped bacteria from the outer surface leading to mushroom-shaped microcolonies. In the presence of C. uncinata and Spumella sp., the biofilm volume was 2.5,6.3 times lower compared with ungrazed biofilms. However, the biofilm porosity and the ratio of biofilm surface area to biofilm volume were 1.5,3.7 and 1.2,1.8 times higher, respectively. Thus, exchange of nutrients and gases between the biofilm and its surrounding fluid should also be improved in deeper biofilm layers, hence accelerating microbial growth. [source] Controlling Electron and Hole Charge Injection in Ambipolar Organic Field-Effect Transistors by Self-Assembled MonolayersADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Xiaoyang Cheng Abstract Controlling contact resistance in organic field-effect transistors (OFETs) is one of the major hurdles to achieve transistor scaling and dimensional reduction. In particular in the context of ambipolar and/or light-emitting OFETs it is a difficult challenge to obtain efficient injection of both electrons and holes from one injecting electrode such as gold since organic semiconductors have intrinsically large band gaps resulting in significant injection barrier heights for at least one type of carrier. Here, systematic control of electron and hole contact resistance in poly(9,9-di- n -octylfluorene- alt -benzothiadiazole) ambipolar OFETs using thiol-based self-assembled monolayers (SAMs) is demonstrated. In contrast to common believe, it is found that for a certain SAM the injection of both electrons and holes can be improved. This simultaneous enhancement of electron and hole injection cannot be explained by SAM-induced work-function modifications because the surface dipole induced by the SAM on the metal surface lowers the injection barrier only for one type of carrier, but increases it for the other. These investigations reveal that other key factors also affect contact resistance, including i) interfacial tunneling through the SAM, ii) SAM-induced modifications of interface morphology, and iii) the interface electronic structure. Of particular importance for top-gate OFET geometry is iv) the active polymer layer thickness that dominates the electrode/polymer contact resistance. Therefore, a consistent explanation of how SAM electrode modification is able to improve both electron and hole injection in ambipolar OFETs requires considering all mentioned factors. [source] Repeated Transfer of Colloidal Patterns by Using Reversible Buckling ProcessADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Dong Choon Hyun Abstract The reversible nature of buckling is employed to repeatedly transfer colloids assembled in buckling patterns to flat surfaces. The cycle of colloidal loading,transfer,buckling is repeatedly carried out to fabricate the same colloidal patterns. The key to success is the reduction in the amplitude of the buckling patterns to a few nanometers as well as the recovery of initial buckling patterns after repeated stretching. The reduced buckling amplitude by poststretching or thermal annealing embosses the colloids assembled in the trenches of the buckling patterns, which enables the transfer regardless of the size, species, or layer thickness of the particles. This report demonstrates various transferred patterns composed of colloidal crystals, fluorescence hydrogel colloids, Au nanoparticles, and iron oxide magnetic particles. Since the process does not require surface modification of the colloids, it can be used to fabricate any colloidal patterns. [source] A thermochemical boundary layer at the base of Earth's outer core and independent estimate of core heat fluxGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2008David Gubbins SUMMARY Recent seismological observations suggest the existence of a ,150-km-thick density-stratified layer with a P -wave velocity gradient that differs slightly from PREM. Such a structure can only be caused by a compositional gradient, effects of a slurry or temperature being too small and probably the wrong sign. We propose a stably stratified, variable concentration layer on the liquidus. Heat is transported by conduction down the liquidus while the light and heavy components migrate through the layer by a process akin to zone refining, similar to the one originally proposed by Braginsky. The layer remains static in a frame of reference moving upwards with the expanding inner core boundary. We determine the gradient using estimates of co, the concentration in the main body of the outer core, and cb, the concentration of the liquid at the inner core boundary. We determine the depression of the melting point and concentrations using ideal solution theory and seismologically determined density jumps at the inner core boundary. We suppose that co determines ,,mod, the jump from normal mode eigenfrequencies that have long resolution lengths straddling the entire layer, and that cb determines ,,bod, the jump determined from body waves, which have fine resolution. A simple calculation then yields the seismic, temperature, and concentration profiles within the layer. Comparison with the distance to the C-cusp of PKP and normal mode eigenfrequencies constrain the model. We explore a wide range of possible input parameters; many fail to predict sensible seismic properties and heat fluxes. A model with ,,mod= 0.8 gm cc,1, ,,bod= 0.6 gm cc,1, and layer thickness 200 km is consistent with the seismic observations and can power the geodynamo with a reasonable inner core heat flux of ,2 TW and nominal inner core age of ,1 Ga. It is quite remarkable and encouraging that a model based on direct seismic observations and simple chemistry can predict heat fluxes that are comparable with those derived from recent core thermal history calculations. The model also provides plausible explanations of the observed seismic layer and accounts for the discrepancy between estimates of the inner core density jumps derived from body waves and normal modes. [source] Guided waves at subduction zones: dependencies on slab geometry, receiver locations and earthquake sourcesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006S. Martin SUMMARY We investigate the geometry of deep subduction zone waveguides (depth >100 km). The wavefield characteristics for up-dip profiles are described and compared with data recorded at the Chile,Peru subduction zone. Observed distorted P onsets at stations in northern Chile near 21°S can be matched by 2-D finite difference simulations of a thin low-velocity layer (LVL) atop the slab in an IASP91 velocity model. The replacement of the LVL by simple random velocity undulations in the slab in the same model cannot explain the observations. Varying slab geometries are investigated and the distribution of guided wave onsets originating in deep waveguides is predicted relative to the slab surface. Further, double couple source position and orientation is explored and found to be closely limited by the guided wave observations. Sources situated above the layer and at distances more than 2 layer widths below the subducted Moho are not suitable. For the remaining favourable source locations, a strong link between pulse shapes and fault plane dip angle is evident. We conclude that up-dip guided wave observations at subduction zones follow a simple pattern given by slab geometry and modified by source position. The resulting onsets are shaped by layer thickness and velocity contrast and further influenced by the shape of the slab surface. [source] Determining the dilation factor in 4D monitoring of compacting reservoirs by rock-physics modelsGEOPHYSICAL PROSPECTING, Issue 6 2007José M. Carcione ABSTRACT Hydrocarbon depletion and fluid injection cause compaction and stretching of the reservoir and overburden layers. 4D prestack seismic data can be used to detect these changes because compaction/stretching causes changes in traveltimes and seismic velocities. We show that, by using two different petro-elastic models at varying effective pressures, a good approximation is to assume that the fractional changes in layer thickness, ,L/L, and seismic velocity, ,v/v, are related by a linear function of ,L/L. The slope of this function (the dilation factor, ,= (,v/v)/(,L/L)) is negative and its absolute value generally decreases (shale, low porosity) or increases (sandstone, high porosity) with increasing layer thickness and decreasing effective pressure. The analysis is mainly performed for isotropic deformations. The dilation factor for uniaxial deformations is smaller in absolute value. The dilation factor, which can be calculated from time-lapse data, can be used to predict reservoir compaction/stretching as a function of depth and surface subsidence. [source] Shrub expansion may reduce summer permafrost thaw in Siberian tundraGLOBAL CHANGE BIOLOGY, Issue 4 2010D. BLOK Abstract Climate change is expected to cause extensive vegetation changes in the Arctic: deciduous shrubs are already expanding, in response to climate warming. The results from transect studies suggest that increasing shrub cover will impact significantly on the surface energy balance. However, little is known about the direct effects of shrub cover on permafrost thaw during summer. We experimentally quantified the influence of Betula nana cover on permafrost thaw in a moist tundra site in northeast Siberia with continuous permafrost. We measured the thaw depth of the soil, also called the active layer thickness (ALT), ground heat flux and net radiation in 10 m diameter plots with natural B. nana cover (control plots) and in plots in which B. nana was removed (removal plots). Removal of B. nana increased ALT by 9% on average late in the growing season, compared with control plots. Differences in ALT correlated well with differences in ground heat flux between the control plots and B. nana removal plots. In the undisturbed control plots, we found an inverse correlation between B. nana cover and late growing season ALT. These results suggest that the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw. Increased shrub growth may thus partially offset further permafrost degradation by future temperature increases. Permafrost models need to include a dynamic vegetation component to accurately predict future permafrost thaw. [source] Design of Multilayered Nanostructures and Donor,Acceptor Interfaces in Solution-Processed Thin-Film Organic Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2008Hiroaki Benten Abstract Multilayered polymer thin-film solar cells have been fabricated by wet processes such as spin-coating and layer-by-layer deposition. Hole- and electron-transporting layers were prepared by spin-coating with poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and fullerene (C60), respectively. The light-harvesting layer of poly-(p -phenylenevinylene) (PPV) was fabricated by layer-by-layer deposition of the PPV precursor cation and poly(sodium 4-styrenesulfonate) (PSS). The layer-by-layer technique enables us to control the layer thickness with nanometer precision and select the interfacial material at the donor,acceptor heterojunction. Optimizing the layered nanostructures, we obtained the best-performance device with a triple-layered structure of PEDOT:PSS|PPV|C60, where the thickness of the PPV layer was 11,nm, comparable to the diffusion length of the PPV singlet exciton. The external quantum efficiency spectrum was maximum (ca. 20%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as high as ca. 50% from a saturated photocurrent at a reverse bias of ,3,V. The power conversion efficiency of the triple-layer solar cell was 0.26% under AM1.5G simulated solar illumination with 100,mW,cm,2 in air. [source] Solidification of binary aqueous solution cooled from aboveHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2010Shigeo Kimura Abstract Freezing and melting phenomena are important in many different fields, including crystal growth, casting, metallurgy, geophysics, and oceanography. Solidification of a multi-component solution is the one often observed in nature. In order to investigate basic features of the freezing processes of binary systems, we conducted a series of laboratory experiments in a rectangular box cooled from above using aqueous NaNO3 solution. During the freezing, the solid phase always grows into many needle-like crystals called the mushy layer. We measured the growth of the mushy layer thickness, the solid fraction, the temperature, and the concentration distributions. The average solid fraction is found to increase with time in the mushy layer. This causes a slow descent of the released solute in the mushy layer and its eventual fall into the liquid region below because of gravity. We propose a one-dimensional model to explain the horizontally-averaged mushy layer growth. In the model, the estimate of a heat flux at the mushy-liquid interface due to natural convection is found essential for a correct prediction. The proposed theory predicts well the growth of the mushy-layer and the average solid fraction, once the convective heat flux is properly given. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20278 [source] Numerical analysis of the effect of boundary layer thickness on vortex structures and heat transfer in the wake behind a hillHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2009Hideki Yanaoka Abstract This study presents a three-dimensional numerical analysis of the effect of boundary layer thickness on vortex structures and heat transfer behind a hill mounted in a laminar boundary layer. When the thickness of the velocity boundary layer is comparable to the hill height, a hairpin vortex is formed symmetrically to the center of the spanwise direction in the wake. A secondary vortex is formed between the legs, and horn-shaped secondary vortices appear under the concave parts of the hairpin vortex. When the boundary layer thickness increases, the legs and horn-shaped secondary vortices move toward the center of the spanwise direction, and thus heat transport and heat transfer increase there. At this time, high-turbulence areas generated locally move toward the center of the spanwise direction with an increase in the boundary layer thickness. With a further increase in the boundary layer thickness, steady streamwise vortices are formed downstream of the hill, but the heat transfer decreases. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20261 [source] Analysis of flow and heat transfer in evaporator porous wicking structure of a flat heat pipeHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2009Congxiang Hu Abstract With a specified pressure distribution, an analytical investigation was conducted to explore the flow and heat transfer characteristics in an evaporator porous wicking structure of a flat heat pipe. The boundary effect on the flow rate is more significant than the inertia, and both the boundary and inertia effects exert very little influence on fluid layer thickness and velocity distribution. The bottom of the porous layer is at a quite uniform temperature, and the heat flux is almost normal to the solid boundary. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20237 [source] Heat transfer for Marangoni-driven boundary layer flowHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2002David M. Christopher Abstract Marangoni convection induced by variation of the surface tension with temperature along a surface influences crystal growth melts and other processes with liquid,vapor interfaces, such as boiling in both microgravity and normal gravity in some cases. This paper presents the Nusselt number for Marangoni flow over a flat surface calculated using a similarity solution for both the momentum equations and the energy equation assuming developing boundary layer flow along a surface. Solutions are presented for the surface velocity, the total flow rate, and the Nusselt number for various temperature profiles, Marangoni numbers, and Prandtl numbers. For large bubbles, the predicted boundary layer thickness would be less than the bubble diameter, so the curvature effects could be neglected and this analysis could be used as a first estimate of the effect of Marangoni flow around a vapor bubble. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 105,116, 2002; DOI 10.1002/htj.10019 [source] Vertical dynamic response of a rigid foundation embedded in a poroelastic soil layerINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2009Y. Q. Cai Abstract A simplified analytical method is presented for the vertical dynamic analysis of a rigid, massive, cylindrical foundation embedded in a poroelastic soil layer. The foundation is subjected to a time-harmonic vertical loading and is perfectly bonded to the surrounding soil in the vertical direction. The soil underlying the foundation base is represented by a single-layered poroelastic soil based on rigid bedrock while the soil at the side of the foundation is modeled as an independent poroelastic layer composed of a series of infinitesimally thin layers. The behavior of the soil is governed by Biot's poroelastodynamic theory and its governing equations are solved by the use of Hankel integral transform. The contact surface between the foundation base and the soil is smooth and fully permeable. The dynamic interaction problem is solved following standard numerical procedures. The accuracy of the present solution is verified by comparisons with the well-known solutions obtained from other approaches for both the elastodynamic interaction problem and poroelastodynamic interaction problem. Numerical results for the vertical dynamic impedance and response factor of the foundation are presented to demonstrate the influence of nondimensional frequency of excitation, soil layer thickness, poroelastic material parameters, depth ratio and mass ratio on the dynamic response of a rigid foundation embedded in a poroelastic soil layer. Copyright © 2008 John Wiley & Sons, Ltd. [source] Practical techniques for a three-dimensional FEM analysis of incompressible fluid flow contained with slip walls and a downstream tube bundleINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2001Yuzuru Eguchi Abstract Two practical techniques are proposed in this paper to simulate a flow contained in a plenum with a downstream tube bundle under a PC environment. First, a technique to impose slip wall conditions on smooth-faced planes and sharp edges is proposed to compensate for the mesh coarseness relative to boundary layer thickness. In particular, a new type of Poisson equation is formulated to simultaneously satisfy both such velocity boundary conditions on walls and the incompressibility constraint. Second, a numerical model for a downstream tube bundle is proposed, where hydraulic resistance in a tube is imposed as a traction boundary condition on a fluid surface contacting the tube bundle end. The effectiveness of the techniques is numerically demonstrated in the application to a flow in a condenser water box. Copyright © 2001 John Wiley & Sons, Ltd. [source] Microstructure,Property Relationships for Low-Voltage VaristorsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010Wen-Hsuan Pan The low-voltage varistors with various layer thickness are prepared by laminating thin ZnO-based ceramic layers and AgPd electrodes together. The breakdown voltage dose not exhibit linear relationship with layer thickness. It is due to that the presence of the AgPd electrodes enhances the growth of ZnO grains. As some ZnO grains are large enough to touch the upper and lower electrodes, the breakdown voltage of the varistor is only 3.7 V. The nonlinear coefficient of the low-voltage varistor is 33. Such nonlinear current,voltage behavior is mainly contributed by the interface between the AgPd electrode and ZnO grains. [source] Inner Electrodes for Multilayer VaristorsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2009Shu-Ting Kuo In the present study, Pt or AgPd metal is used as the inner electrode for Bi2O3 -doped ZnO multilayer varistors (MLV). The growth of the ZnO grains is constrained by the presence of the inner electrodes. The Pt inner electrodes are chemically inert to Bi2O3 -doped ZnO. The Bi2O3 could react with Pd to form PdBi2O4. The Bi2O3 -rich liquid also tends to wet the AgPd electrode. The size of ZnO grains in the MLV/AgPd specimen is larger. The ZnO grains in the MLV/AgPd specimen can even grow to a size larger than the layer thickness at the expense of electrode continuity. [source] Fabrication of a Multilayered Low-Temperature Cofired Ceramic Micro-Plasma-Generating DeviceINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2006Amanda Baker Plasma technology is currently being used in innumerable industrial applications. Some of the common uses of this technology include surface cleaning and treatment, sputtering and etching of semiconductor devices, excitation source for chemical analyses, cutting, environmental cleanup, sterilization, and phototherapy. The harsh conditions that these devices must endure require robust refractory materials systems for their fabrication and reliability. Low-temperature cofired ceramic (LTCC) material systems provide a durable and cost-effective platform for the manufacture of such devices, and allow for possible integration into meso-scale microsystems. Our designs are based on RF microstriplines that capacitively couple and ionize small gas discharge sites over the top electrode. In this paper, we have built several iterations of this micro-plasma generating device using LTCC material systems. The impact of electrode ink selection and processing, lamination methods, dielectric layer thickness, and electrode design has been investigated. Several micro-plasma-generating devices were then evaluated for power requirements, output stability, and long-term reliability. [source] Thickness and continuity of the adherent colonic mucus barrier in active and quiescent ulcerative colitis and Crohn's diseaseINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 5 2008V. Strugala Summary Background:, The colon is covered by a mucus barrier that protects the underlying mucosa and alterations in this mucus barrier have been implicated in the aetiology of inflammatory bowel disease (IBD). This study investigated the thickness and continuity of the mucus barrier in ulcerative colitis (UC) and Crohn's disease (CD) in comparison to normal controls. Methods:, Rectal biopsies were taken from 59 patients and cryostat sections stained with periodic acid-Schiff's/Alcian blue to visualise the mucus layer. Mucus thickness and continuity and goblet cell density were measured using light microscopy. Results:, An essentially continuous adherent mucus layer was observed in normal human rectum and there was no change in the mucus barrier in quiescent UC. In active UC there was a trend for the mucus layer to become progressively thinner and significantly more discontinuous as disease severity increased. In severe active UC the mucus layer thickness and goblet cell density were significantly reduced compared with normal controls while the percentage discontinuity significantly increased. Conclusion:, It is not until severe UC that there is a global change in mucosal protection as a consequence of large regions lacking mucus, a decrease in secretory potential caused by a loss of goblet cells and a thinner, less effective mucus layer even when it is present. [source] Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006A. V. S. S. K. S. Gupta Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source] Computational energy analysis of an innovative isothermal chamber for testing of the special equipment used in the transport of perishable productsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2004S. K. Chatzidakis Abstract This paper describes an improved numerical simulation study of an isothermal chamber recently constructed at Zografou Campus of the National Technical University of Athens (NTUA) for the testing of special equipment used for transporting perishable foodstuffs in accordance with the United Nations ATP agreement. Using a transient finite difference model, a simulation is developed for a modern ATP test chamber and a typical specimen refrigerated vehicle to be tested. The simulation results are compared to experimental measurements taken under real conditions by a data acquisition system and a refrigerated semi-trailer as specimen. Proportional,integral control is employed for the regulation of the cooling and heating system. The impact of various parameters on the time required to reach the set-point temperature (tset) is investigated and the energy consumption is simulated for a period of 22 h. In particular, the impact of specimen insulation thickness and the thickness of the chamber insulation floor are considered in detail. The total energy consumption increases by approximately 16% when the concrete floor layer thickness is increased from 8 to 16 cm for typical initial conditions and desired chamber and specimen temperatures of 32.5 and 7.5°C, respectively. Using a floor insulation of 6 cm extruded heavy strain-resistant polystyrene reduces the energy consumption by at least 13%. Specimen insulation thickness increase from U -value of 0.35 W m,2 K to 0.75 W m,2 K result to an increase in energy consumption by a percentage of 28%. Thermal capacity, temperature of car body and specimen dimensions are also treated as variables that affect the total duration of an ATP test and its total energy consumption. Copyright © 2004 John Wiley & Sons, Ltd. [source] Quasi-static analysis of microstrip lines with variation of substrate thickness in transverse directionINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2003S. Khoulji Abstract This article is devoted to the analysis of microstrip lines printed on dielectric substrates with transversely varying thickness using the quasi-static approximation and the method of lines. Discretization lines of varying length, according to the layer thickness, are used and only the Laplace wave equation has to be solved. The numerical results presented herein permit the illustration of the effect of arbitrarily curved substrate interfaces along the transverse direction on the characteristics of the microstrip structures under consideration. The behavior of the per unit length parameters of these structures as a function of the shape of these substrates' cross section is studied in depth. Furthermore, the effects of the finite metallization thickness and losses are also investigated in detail. The results that are obtained are consistent with those published in the literature. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 194,205, 2003. [source] Effect of Altitude on Energy Exchange Characteristics of Some Alpine Medicinal Crops from Central HimalayasJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2004S. Chandra Abstract To explore the conservation and cultivation of endangered alpine medicinal crops at comparatively lower altitudes, a study on variations in morphological parameters and energy exchange characteristics was conducted on five herbaceous medicinal crops from the alpines of Central Himalayas. Plants of same age were selected from the alpine medicinal crop nursery, Tungnath (3600 m), and were planted at the nurseries at 2100 and 550 m altitudes. After well acclimatization at lower altitudes, plants were examined for morphological and energy exchange studies during their active growth period. The energy balance sheet of these plant species indicates that most of the energy absorbed by the leaves dissipates by re-radiation, transpiration and thermal conductance across leaf surfaces. All species maintained leaf temperature below the surrounding air temperature at all altitudes and therefore gained energy by convection of heat as well as by boundary layer thermal conduction. Leaf-to-air temperature difference, gain of energy by convection of heat and boundary layer thermal conduction was maximum at an altitude of 2100 m in all the species. Boundary layer thermal conductivity, boundary layer thickness, thermal conductivity of the leaf and therefore, total energy absorbed by the leaves of these species increase significantly with decreasing altitude. Leaf thickness significantly decreases with decreasing altitude, which in turn enhances total energy absorption (r = ,0.975, P < 0.005) of the leaves in all the species. The results indicate that all these species absorb higher amount of energy at lower altitudes, which indicates their adaptability to warm temperatures at low altitudes (up to 550 m). Therefore, these species can be cultivated at relatively lower altitudes. However, a proper agronomic methodology needs to be developed for better yields. [source] Tear-film lipid layer morphology and corneal sensation in the development of blinking in neonates and infantsJOURNAL OF ANATOMY, Issue 3 2005John G. Lawrenson Abstract The aim of the study was to evaluate the role of lipid layer thickness and corneal sensation in the development of blinking in neonates. The study group comprised sixty-four neonates and infants (mean age 27.5 ± 15 (sd) weeks, range 3.4,52) whose mothers were attending a general practice healthy baby clinic. Spontaneous eye-blink activity was determined from digital videographic recordings; tear film lipid layer morphology wasexamined using interference patterns produced by the Keeler TearscopeÔ Plus over a five-point grading scale (higher grades are associated with thick and stable lipid films); corneal sensation threshold was assessed with the Non-Contact Corneal Aesthesiometer (NCCA), using the eye-blink response as an objective indication that the cooling stimulus had been felt; palpebral aperture dimensions were measured using calibrated digital still images of the eye in the primary position. The overall mean spontaneous blink-rate was found to be 3.6 (± 0.3) blinks min,1, and the mean interblink time was 21.6 (± 2.8) s. The lowest blink-rates were observed in the 0,17-week age group (average 2 blinks min,1). The blink-rate showed a highly significant correlation with age (r = 0.46, P < 0.01). The overall mean lipid layer grading was 3.6 (± 0.2 SE) arbitrary units. Higher grades were found in the newborn and the mean grading score reduced with age (P < 0.01). The mean sensation threshold to blink (TTB) was 0.69 (0.04 SE) mbar, which did not differ from a control group of older subjects (P > 0.05). There was a rapid increase in palpebral aperture length and width from birth to 1 year old, with surface area increasing by 50% over the same period. We concluded that the low rate of spontaneous eye blink activity in neonates is associated with a thick stable lipid layer that may be a function of a small palpebral aperture. Furthermore, neonates appear to have the capacity to detect ocular surface cooling, which is a major trigger for spontaneous blinking. [source] A method for the non-destructive analysis of gradients of mechanical stresses by X-ray diffraction measurements at fixed penetration/information depthsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006A. Kumar A rigorous measurement strategy for (X-ray) diffraction stress measurements at fixed penetration/information depths has been developed. Thereby errors caused by lack of penetration-depth control in traditional (X-ray) diffraction (sin2,) measurements have been annulled. The range of accessible penetration/information depths and experimental aspects have been discussed. As a practical example, the depth gradient of the state of residual stress in a sputter-deposited nickel layer of 2,µm thickness has been investigated by diffraction stress measurements with uncontrolled penetration/information depth and two controlled penetration/information depths corresponding to about one quarter and one tenth of the layer thickness, respectively. The decrease of the planar tensile stress in the direction towards the surface could be well established quantitatively. [source] Small-angle X-ray scattering studies on oxide layer thickness at the porous silicon interfaceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003M. Björkqvist We have determined the thickness of an oxide layer at the p+-type porous silicon interface as a function of oxidation time, by using a small angle X-ray scattering (SAXS). The scattering experiments were carried out using a Kratky camera with a step-scanning device. Oxidation was achieved by storing the porous silicon samples in various temperatures under high relative humidity. The negative deviations from Porod's law were observed from the scattering curves of oxidized samples. The oxide layer thickness was determined from the scattering curve using a sigmoidal-gradient approximation for the diffuse boundary. The oxide layer thickness values as a function of oxidation time, obtained using SAXS are compared to measured weight increase values, caused by the oxidation. [source] Estimation of cobalt coating layer thickness on acicular Fe3O4 powder using HR-TEMJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2001Keitarou Sakai The thicknesses of cobalt coating layers grown on four different types of acicular Fe3O4 particles were estimated from the analysis of lattice images and from the determination of the Co depth profile using high-resolution transmission electron microscopy (HR-TEM) coupled with an energy dispersive X-ray (EDX) analysis system. It was observed that the coating thickness might vary with the crystallite size resulting from the growth mechanism of the coating layer. In this study, two different layer thicknesses, 40,Å and less than 10,Å, were evidenced for crystallite sizes of 390,Å and 350,Å, respectively. [source] | |||||||||||||||||||||||||||||||||||||||||||