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Temperature Gradient (temperature + gradient)
Kinds of Temperature Gradient Terms modified by Temperature Gradient Selected AbstractsSurface Structures in Thin Polymer Layers Caused by Coupling of Diffusion-Controlled Marangoni Instability and Local Horizontal Temperature GradientMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005Lothar Weh Abstract Summary: Surface tension-driven Marangoni convection causes the formation of regular surface structures in drying polymer layers. The shape of the surface structures formed during solvent evaporation depends on layer and interfacial dynamic parameters as well as external factors. The influence of a horizontal radial temperature gradient produced by a point heat source below the polymer layer on the diffusion-controlled Marangoni instability has been studied. In the region of the lateral temperature gradient, radial surface flow coupled with the interfacial instability leads to stripe, ladder, chevron and/or labyrinthine surface structures. Stepped ladder structures in a poly(vinyl butyral) layer produced by interfacial instability and heating with an ultrasonic sonotrode below the layer substrate. [source] Directionally Integrated VLS Nanowire Growth in a Local Temperature Gradient,ANGEWANDTE CHEMIE, Issue 40 2009Geunhee Lee Dr. Ganz gerade: Ein einfacher und robuster Mechanismus richtet die Wachstumsrichtungen von Nanodrähten mithilfe eines lokalen Temperaturgradienten als lokaler kinetischer Variable während eines üblichen Dampf-flüssig-fest(VLS)-Wachstums kohärent aus (siehe Bild, Maßstab=200,,m). Die Nanodrähte wachsen gerade in die senkrechte Richtung, zeigen in der Nähe der katalytischen Spitzen aber Knicke. [source] Temperature gradient focusing in a PDMS/glass hybrid microfluidic chipELECTROPHORESIS, Issue 24 2007Takuya Matsui Abstract This paper reports the application of temperature gradient focusing (TGF) in a PDMS/glass hybrid microfluidic chip. With TGF, by the combination of a temperature gradient along a microchannel, an applied electric field, and a buffer with a temperature-dependent ionic strength, analytes are focused by balancing their electrophoretic velocities against the bulk velocity of the buffer containing the analytes. In this work, Oregon Green 488 carboxylic acid was concentrated approximately 30 times as high as the initial concentration in 45,s at moderate electric strength of 70,V/cm and a temperature gradient of 55°C across the PDMS/glass hybrid microfluidic chip with a 1,cm long capillary. [source] Microwave-Assisted Electroanalysis: A ReviewELECTROANALYSIS, Issue 2 2009Abstract Microwave-assisted electrochemistry is critically discussed with a focus on the fundamental aspects of the processes involved and its applications in electroanalysis. The concept of direct and nondirect heated electrodes is discussed, and simulation work is evaluated. Microwave-assisted electrochemistry predominantly results in higher current responses (up to 2 magnitudes higher) due to increased temperature and mass transport to the active electrodes. Temperature gradients at microwave-affected electrodes may exceed 105 K/cm, with temperature hotspots found in the thin diffusion layers set up at ultramicroelectrodes. Research into microwave-assisted electroanalysis can lead to enhanced capillary electrophoresis detection, improved stripping voltammetry and development of new high temperature methods. [source] Characteristics of preferential flow and groundwater discharge to Shingobee Lake, Minnesota, USAHYDROLOGICAL PROCESSES, Issue 10 2002Hans F. Kishel Abstract Small-scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m2 grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater-lake interaction within underlying organic-rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10,3 m day,1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater,lake interaction. These results suggest that site-specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge-dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Evidence for the Microwave Effect During the Annealing of Zinc OxideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007J. Binner A microwave/conventional hybrid furnace has been used to anneal virtually fully dense zinc oxide ceramics under pure conventional and a microwave/conventional hybrid heating regime with a view to obtaining evidence for the "microwave effect" during the resulting grain growth. In each case it was ensured that each sample within a series had an identical thermal history in terms of its temperature/time profile. The results showed that grain growth was enhanced during hybrid heating compared with pure conventional heating; the greatest enhancement, a factor of ,3 increase in average grain size, was observed in the range 1100°,1150°C. The grain growth exponent decreased from 3 during conventional heating to 1.4 during hybrid heating in this temperature range, suggesting an acceleration of the diffusional processes involved. Temperature gradients within the samples were found to be too small to explain the results. This suggests that clear evidence has been found to support the existence of a genuine "microwave effect." [source] A new piezoelectric single crystal obtained by Ge doping in the SiO2 structureCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2009M. Miclau Abstract The interest of Si1,xGexO2 single crystals with alpha-quartz structure is connected to improvement of electromechanical coefficients and rise of , , , phase transition of quartz one. Growth of an ,-SixGe1,xO2 crystal was realized by a hydrothermal method of temperature gradient in autoclaves, made from Cr,Ni alloys. Nutrient material was prepared from synthetic quartz as crashed rods and placed in the bottom of autoclaves. There was loaded GeO2 powder additive in proportions to quartz nutrient. Single crystals were investigated by electron microprobe analysis, X-ray diffraction and atomic force microscopy. The most important result, which was obtained during the investigations, is an experimental proof of growth of ,-SixGe1,xO2 single crystals under the hydrothermal conditions. The present results thus open the possibility to tune the piezoelectric properties of these materials by varying the chemical composition. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimization of control parameters of cadmium zinc telluride Bridgman single crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2007Liu Juncheng Abstract The temperature gradient within a furnace chamber and the crucible pull rate are the key control parameters for cadmium zinc telluride Bridgman single crystal growth. Their effects on the heat and mass transfer in front of the solid-liquid interface and the solute segregation in the grown crystal were investigated with numerical modeling. With an increase of the temperature gradient, the convection intensity in the melt in front of the solid-liquid interface increases almost proportionally to the temperature gradient. The interface concavity decreases rapidly at faster crucible pull rates, while it increases at slow pull rates. Moreover, the solute concentration gradient in the melt in front of the solid-liquid interface decreases significantly, as does the radial solute segregation in the grown crystal. In general, a decrease of the pull rate leads to a strong decrease of the concavity of the solid-liquid interface and of the radial solute segregation in the grown crystal, while the axial solute segregation in the grown crystal increases slightly. A combination of a low crucible pull rate with a medium temperature gradient within the furnace chamber will make the radial solute segregation of the grown crystal vanish. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Global simulation of a Czochralski furnace for silicon crystal growth against the assumed thermophysical propertiesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006Y. R. Li Abstract In order to understand the effects of the thermophysical properties of the melt on the transport phenomena in the Czochralski (Cz) furnace for the single crystal growth of silicon, a set of global analyses of momentum, heat and mass transfer in small Cz furnace (crucible diameter: 7.2 cm, crystal diameter: 3.5 cm, operated in a 10 Torr argon flow environment) was carried out using the finite-element method. The global analysis assumed a pseudosteady axisymmetric state with laminar flow. The results show that different thermophysical properties will bring different variations of the heater power, the deflection of the melt/crystal interface, the axial temperature gradient in the crystal on the center of the melt/crystal interface and the average oxygen concentration along the melt/crystal interface. The application of the axial magnetic field is insensitive to this effect. This analysis reveals the importance of the determination of the thermophysical property in numerical simulation. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of bismuth tri-iodide platelets by the physical vapor deposition methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2004A. Cuña Abstract The work reports the growth of single BI3 crystals with platelets habit. Platelets were grown by physical vapor deposition (PVD) in a high vacuum atmosphere and with argon, polymer or iodine as additives. Crystals grew in the zone of maximum temperature gradient, perpendicular to the ampoule wall. Crystals grown with argon as additive show a very shining surface, have hexagonal (0 0 l) faces, sizes up to 20 x 10 mm2 and thicknesses up to 100 ,m. They were characterized by optical microscopy and scanning electron microscopy (SEM). Dendritic-like structures were found to be their main surface defect. SEM indicates that they grow from the staking of hexagonal unities. Electrical properties of the crystals grown under different growth conditions were determined. Resistivities up to 2 x 1012 ,cm (the best reported value for monocrystals of this material) were obtained. X-ray response was measured by irradiation of the platelets with a 241Am source of 3.5 mR/h. A comparison of results according to the growth conditions was made. Properties of the crystals grown by this method are compared with the ones measured for others previously grown from the melt. Also, results for bismuth tri-iodide platelets are compared with the ones obtained for mercuric and lead iodide platelets. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature gradient focusing in a PDMS/glass hybrid microfluidic chipELECTROPHORESIS, Issue 24 2007Takuya Matsui Abstract This paper reports the application of temperature gradient focusing (TGF) in a PDMS/glass hybrid microfluidic chip. With TGF, by the combination of a temperature gradient along a microchannel, an applied electric field, and a buffer with a temperature-dependent ionic strength, analytes are focused by balancing their electrophoretic velocities against the bulk velocity of the buffer containing the analytes. In this work, Oregon Green 488 carboxylic acid was concentrated approximately 30 times as high as the initial concentration in 45,s at moderate electric strength of 70,V/cm and a temperature gradient of 55°C across the PDMS/glass hybrid microfluidic chip with a 1,cm long capillary. [source] Study of Joule heating effects on temperature gradient in diverging microchannels for isoelectric focusing applicationsELECTROPHORESIS, Issue 10 2006Brian Kates Abstract IEF is a high-resolution separation method taking place in a medium with continuous pH gradients, which can be set up by applying electrical field to the liquid in a diverging microchannel. The axial variation of the channel cross-sectional area will induce nonuniform Joule heating and set up temperature gradient, which will generate pH gradient when proper medium is used. In order to operationally control the thermally generated pH gradients, fundamental understanding of heat transfer phenomena in microfluidic chips with diverging microchannels must be improved. In this paper, two 3-D numerical models are presented to study heat transfer in diverging microchannels, with static and moving liquid, respectively. Through simulation, the temperature distribution for the entire chip has been revealed, including both liquid and solid regions. The model for the static liquid scenario has been compared with published results for validation. Parametric studies have showed that the channel geometry has significant effects on the peak temperature location, and the electrical conductivity of the medium and the wall boundary convection have effects on the generated temperature gradients and thus the generated pH gradients. The solution to the continuous flow model, where the medium convection is considered, shows that liquid convection has significant effects on temperature distribution and the peak temperature location. [source] Temperature effects on the mass flow rate in the SBI and similar heat-release rate test equipmentFIRE AND MATERIALS, Issue 1 2007Bart J. G. Sette Abstract In various medium-to-large-scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat-release rate and smoke-production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi-directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. [source] Climate change and the future for coral reef fishesFISH AND FISHERIES, Issue 3 2008Philip L Munday Abstract Climate change will impact coral-reef fishes through effects on individual performance, trophic linkages, recruitment dynamics, population connectivity and other ecosystem processes. The most immediate impacts will be a loss of diversity and changes to fish community composition as a result of coral bleaching. Coral-dependent fishes suffer the most rapid population declines as coral is lost; however, many other species will exhibit long-term declines due to loss of settlement habitat and erosion of habitat structural complexity. Increased ocean temperature will affect the physiological performance and behaviour of coral reef fishes, especially during their early life history. Small temperature increases might favour larval development, but this could be counteracted by negative effects on adult reproduction. Already variable recruitment will become even more unpredictable. This will make optimal harvest strategies for coral reef fisheries more difficult to determine and populations more susceptible to overfishing. A substantial number of species could exhibit range shifts, with implications for extinction risk of small-range species near the margins of reef development. There are critical gaps in our knowledge of how climate change will affect tropical marine fishes. Predictions are often based on temperate examples, which may be inappropriate for tropical species. Improved projections of how ocean currents and primary productivity will change are needed to better predict how reef fish population dynamics and connectivity patterns will change. Finally, the potential for adaptation to climate change needs more attention. Many coral reef fishes have geographical ranges spanning a wide temperature gradient and some have short generation times. These characteristics are conducive to acclimation or local adaptation to climate change and provide hope that the more resilient species will persist if immediate action is taken to stabilize Earth's climate. [source] Supercritical carbon dioxide separation of bergamot essential oil by a countercurrent processFLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2003Marco Poiana Abstract The ef,ciency of separation of bergamot essential oil, performed by a countercurrent column ,lled with Raschig rings and using supercritical carbon dioxide as partition solvent, is affected by various parameters. In the experiments explained in this work, the direct effect of CO2 density was shown and the ratio between the amount of oil loaded to on the column and the amount of CO2 used were discussed. The conditions that produced extracts with a similar volatile fraction composition of starting material and with a high yield (more than 80% of recovery) were those with a low feed:solvent ratio; the lowest bergaptene content was obtained at low CO2 density or at high feed:solvent ratio. A good result was observed at a CO2 density of 206 g/dm3 (8 MPa of pressure and a temperature gradient of 46,50,54 °C) and a feed:solvent ratio of 9.4,9.6; in this separation, a yield of 74,77% and a bergaptene content lower than 0.01% was measured. Copyright © 2003 John Wiley & Sons, Ltd. [source] Heat and mass transfer phenomena in magnetic fluidsGAMM - MITTEILUNGEN, Issue 1 2007Th. Völker Abstract In this article the influence of a magnetic field on heat and mass transport phenomena in magnetic fluids (ferrofluids) will be discussed. The first section is dealing with a magnetically driven convection, the so called thermomagnetic convection while in the second section the influence of a temperature gradient on the mass transport, the Soret effect in ferrofluids, is reviewed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and albitization of K-feldspar in crystalline rocks in the shallow crust: a tracer for fluid circulation during exhumation?GEOFLUIDS (ELECTRONIC), Issue 2 2003M. B. Holness Abstract A general feature of medium- to coarse-grained, sheet-silicate bearing, quartzo-feldspathic rocks of either metamorphic or igneous affinity is the retrograde development of lenses of pure K-feldspar at the grain boundaries between sheet silicate (0 0 1) faces and original feldspar grains. The growth of these lenses acts to displace and deform the sheet silicate grain by a force of crystallization, although the substrate feldspar and adjacent quartz are not deformed. Subsequent to the growth of the lenses they are replaced to variable degrees by pure albite, which grows into the lens from the substrate feldspar behind an irregular replacement front. The composition and texture of both K-feldspar and replacive albite suggest a strong affinity with authigenic feldspars, although it is considered likely that the K-feldspar of the lenses is derived from low-temperature biotite-breakdown reactions. A model is proposed whereby the lenses grow into open pores at dilatant sites in response to infiltration of aqueous fluids as the crystalline rocks are exhumed under brittle conditions. Continued circulation of infiltrating fluids in a temperature gradient results in the replacement of K-feldspar by albite via an alkali exchange process. The lenses point to a significant grain-scale permeability in crystalline rock at shallow levels in the crust. [source] Spatial Analysis of the Factors Contributing to the Relationship between the Transient, Meridional Eddy Sensible, and Latent Heat Flux in the Southern HemisphereGEOGRAPHICAL ANALYSIS, Issue 2 2000Marilyn Raphael In this paper principal component analysis (PCA) and singular value decomposition (SVD) are used to define the importance of the variables contributing to the relationship between the transient latent and sensible heat fluxes and to show their temporal and spatial variation. SVD is offered as an alternative means of isolating spatial and temporal structures in data with the advantage that it can depict simultaneous space-time variations that are aggregates of the results produced by PCA. Both methods of analysis produced two very important uncorrelated modes of variability in January and July, indicating that the transient heat fluxes are influenced by few controlling factors. We suggest that these modes of variability represent the influences of the meridional temperature gradient, atmospheric moisture, and activity within the source and sink regions of the transient heat fluxes. The physical relationships between the heat fluxes that appear to represented by the statistical modes of variability are discussed. [source] Multiyear to daily radon variability from continuous monitoring at the Amram tunnel, southern IsraelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010S. M. Barbosa SUMMARY Radon is a naturally occurring radioactive noble gas generated within mineral grains of uranium bearing rocks by alpha decay from radium. The Amram tunnel (A. Bloch Geophysical Observatory) is a particularly suitable location for the investigation of radon variability. Located in the arid environment of the Arava desert, near Elat, the 170 m tunnel that constitutes the observatory enables radon monitoring in a desert environment and under fairly stable environmental conditions. The analysis of the temporal variability of continuous measurements of radon and environmental parameters at the Amram tunnel over a period of several years shows a complex temporal pattern characterized by non-stationary and multiscale features. Radon concentrations exhibit multiyear variability in the form of a increasing trend of ,1000 Bq m,3 yr,1 in the mean and much larger trends up to ,2500 Bq m,3 yr,1 in the maximum radon levels. Radon concentrations also display strong seasonal patterns, with maxima in summer and minima in winter, ranging from 2.5 kBq m,3 in winter to 35 kBq m,3 in summer. Intraseasonal variability is characterized by very large radon anomalies, with sharp increases of more than 20 kBq m,3 relative to the base level, that occur in spring and summer and last for several days. Daily periodic variability with maxima around midnight appears also in spring and summer, being absent in the cold months. Radon variability at seasonal, intraseasonal and daily timescales is associated with the air temperature outside the tunnel, specifically the temperature gradient between the external environment and the more stable environment inside the tunnel where the measurements are performed. [source] Productivity of high-latitude lakes: climate effect inferred from altitude gradientGLOBAL CHANGE BIOLOGY, Issue 5 2005Jan Karlsson Abstract Climate change is predicted to be dramatic at high latitudes. Still, climate impact on high latitude lake ecosystems is poorly understood. We studied 15 subarctic lakes located in a climate gradient comprising an air temperature difference of about 6°C. We show that lake water productivity varied by one order of magnitude along the temperature gradient. This variation was mainly caused by variations in the length of the ice-free period and, more importantly, in the supply of organic carbon and inorganic nutrients, which followed differences in terrestrial vegetation cover along the gradient. The results imply that warming will have rapid effects on the productivity of high latitude lakes, by prolongation of ice-free periods. However, a more pronounced consequence will be a delayed stimulation of the productivity following upon changes of the lakes terrestrial surroundings and subsequent increasing input of elements that stimulate the production of lake biota. [source] Structural Transformations during Formation of Quasi-Amorphous BaTiO3,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2007D. Ehre Abstract A model of structural transformations of amorphous into quasi-amorphous BaTiO3 is suggested. The model is based on previously published data and on X-ray photoelectron spectroscopy data presented in the current report. Both amorphous and quasi-amorphous phases of BaTiO3 are made up of a network of slightly distorted TiO6 octahedra connected in three different ways: by apices (akin to perovskite), edges, and faces. Ba ions in these phases are located in the voids between the octahedra, which is a nonperovskite environment. These data also suggest that Ba ions compensate electrical-charge imbalance incurred by randomly connected octahedra and, thereby, stabilize the TiO6 network. Upon heating, the edge-to-edge and face-to-face connections between TiO6 octahedra are severed and then reconnected via apices. Severing the connections between TiO6 octahedra requires a volume increase, suppression of which keeps some of the edge-to-edge and face-to-face connections intact. Transformation of the amorphous thin films into the quasi-amorphous phase occurs during pulling through a steep temperature gradient. During this process, the volume increase is inhomogeneous and causes both highly anisotropic strain and a strain gradient. The strain gradient favors breaking those connections, which aligns the distorted TiO6 octahedra along the direction of the gradient. As a result, the structure becomes not only anisotropic and non-centrosymmetric, but also acquires macroscopic polarization. Other compounds may also form a quasi-amorphous phase, providing that they satisfy the set of conditions derived from the suggested model. [source] Molecular dynamics study on effects of surface structures in nanometer scale on energy transfer from fluid to surfaceHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2005Masahiko Shibahara Abstract Energy transfer from fluid to surface was calculated numerically by using the classical molecular dynamics method in order to investigate the effects of surface structures from 0.1 nm to 10 nm on surface energy transfer. Surface structures on a constant surface area were composed of several hundred atoms having various potential energy parameters, in other words, thermal properties. The upper region in the calculation domain was controlled at a constant temperature and one of the solid atomic layers at the lower region in the calculation domain was controlled at another constant temperature to create a temperature gradient in the calculation system. Energy transfer to the surface was very dependent on surface nanometer scale structures in that affected the static structure and the dynamic behaviors of fluid molecules in the vicinity of the surface. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(3): 171,179, 2005; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/htj.20055 [source] Estimation of rainfall from infrared-microwave satellite data for basin-scale hydrologic modellingHYDROLOGICAL PROCESSES, Issue 15 2010Oscar Anthony Kalinga Abstract The infrared-microwave rainfall algorithm (IMRA) was developed for retrieving spatial rainfall from infrared (IR) brightness temperatures (TBs) of satellite sensors to provide supplementary information to the rainfall field, and to decrease the traditional dependency on limited rain gauge data that are point measurements. In IMRA, a SLOPE technique (ST) was developed for discriminating rain/no-rain pixels through IR image cloud-top temperature gradient, and 243K as the IR threshold temperature for minimum detectable rainfall rate. IMRA also allows for the adjustment of rainfall derived from IR-TB using microwave (MW) TBs. In this study, IMRA rainfall estimates were assessed on hourly and daily basis for different spatial scales (4, 12, 20, and 100 km) using NCEP stage IV gauge-adjusted radar rainfall data, and daily rain gauge data. IMRA was assessed in terms of the accuracy of the rainfall estimates and the basin streamflow simulated by the hydrologic model, Sacramento soil moisture accounting (SAC-SMA), driven by the rainfall data. The results show that the ST option of IMRA gave accurate satellite rainfall estimates for both light and heavy rainfall systems while the Hessian technique only gave accurate estimates for the convective systems. At daily time step, there was no improvement in IR-satellite rainfall estimates adjusted with MW TBs. The basin-scale streamflow simulated by SAC-SMA driven by satellite rainfall data was marginally better than when SAC-SMA was driven by rain gauge data, and was similar to the case using radar data, reflecting the potential applications of satellite rainfall in basin-scale hydrologic modelling. Copyright © 2010 John Wiley & Sons, Ltd. [source] Tomography of temperature gradient metamorphism of snow and associated changes in heat conductivityHYDROLOGICAL PROCESSES, Issue 18 2004Martin Schneebeli Abstract Temperature gradient metamorphism is one of the dominant processes changing the structure of natural dry snow. The structure of snow regulates the thermal and mechanical properties. Physical models and numerical simulations of the evolution of the snow cover require a thorough understanding of the interplay between structure and physical properties. The structure of snow and the heat conductivity were measured simultaneously without disturbance in a miniature snow breeder. The structure was measured by microtomography, and heat conductivity by measuring heat fluxes and temperatures. A temperature gradient from 25 to 100 K m,1 was applied to the snow. The snow density range of the samples varied from 150 to 500 kg m,3. The density in the observed volume remained constant during the experiments under temperature gradient conditions. The structure was analysed with respect to the size of typical ice structures and air pores, specific surface area, curvature and anisotropy of the ice matrix. The temporal changes in structure and heat conductivity are compared. The heat conductivity changed by as much as twice its initial value, caused by changes in structure and texture, but not due to changes in density. This shows the enormous importance of structure in the evolution of the heat conductivity. The observed changes are not in good agreement with the current understanding of the metamorphic process, because heat conductivity increased during temperature gradient metamorphism, instead of the expected decrease due to a shrinking of the bonds. We also observed a plateau in the evolution of the heat conductivity coefficient, which indicates a quasi-steady state of the structural evolution with respect to thermophysical properties of snow. Copyright © 2004 John Wiley & Sons, Ltd. [source] Causes and consequences of fire-induced soil water repellencyHYDROLOGICAL PROCESSES, Issue 15 2001J. Letey Abstract A wettable surface layer overlying a water-repellent layer is commonly observed following a fire on a watershed. High surface temperatures ,burn' off organic materials and create vapours that move downward in response to a temperature gradient and then condense on soil particles causing them to become water repellent. Water-repellent soils have a positive water entry pressure hp that must be exceeded or all the water will runoff. Water ponding depths ho that exceeds hp will cause infiltration, but the profile is not completely wetted. Infiltration rate and soil wetting increase as the value of ho/hp increases. The consequence is very high runoff, which also contributes to high erosion on fire-induced water-repellent soils during rain storms. Grass establishment is impaired by seeds being eroded and lack of soil water for seeds that do remain and germinate. Extrapolation of these general findings to catchment or watershed scales is difficult because of the very high temporal and spatial variabilities that occur in the field. Copyright © 2001 John Wiley & Sons, Ltd. [source] Frost heave modelling using porosity rate functionINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2006Radoslaw L. Michalowski Abstract Frost-susceptible soils are characterized by their sensitivity to freezing that is manifested in heaving of the ground surface. While significant contributions to explaining the nature of frost heave in soils were published in late 1920s, modelling efforts did not start until decades later. Several models describing the heaving process have been developed in the past, but none of them has been generally accepted as a tool in engineering applications. The approach explored in this paper is based on the concept of the porosity rate function dependent on two primary material parameters: the maximum rate, and the temperature at which the maximum rate occurs. The porosity rate is indicative of ice growth, and this growth is also dependent on the temperature gradient and the stress state in the freezing soil. The advantage of this approach over earlier models stems from a formulation consistent with continuum mechanics that makes it possible to generalize the model to arbitrary three-dimensional processes, and use the standard numerical techniques in solving boundary value problems. The physical premise for the model is discussed first, and the development of the constitutive model is outlined. The model is implemented in a 2-D finite element code, and the porosity rate function is calibrated and validated. Effectiveness of the model is then illustrated in an example of freezing of a vertical cut in frost-susceptible soil. Copyright © 2006 John Wiley & Sons, Ltd. [source] A finite element porothermoelastic model for dual-porosity mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2004R. Nair Abstract An existing dual-porosity finite element model has been extended to include thermo-hydro-mechanical coupling in both media. The model relies on overlapping distinct continua for the fluid and solid domains. In addition, conductive and convective heat transfers are incorporated using a single representative thermodynamics continuum. The model is applied to the problem of an inclined borehole drilled in a fractured formation subjected to a three-dimensional state of stress and, a temperature gradient between the drilling fluid and the formation. A sensitivity analysis has been carried out to study the impact of thermal loading, effect of heat transport by pore fluid flow and, the effect of parameters of the secondary medium used to represent the fractures. Copyright © 2004 John Wiley & Sons, Ltd. [source] A Cartesian-grid collocation technique with integrated radial basis functions for mixed boundary value problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2010Phong B. H. Le Abstract In this paper, high-order systems are reformulated as first-order systems, which are then numerically solved by a collocation method. The collocation method is based on Cartesian discretization with 1D-integrated radial basis function networks (1D-IRBFN) (Numer. Meth. Partial Differential Equations 2007; 23:1192,1210). The present method is enhanced by a new boundary interpolation technique based on 1D-IRBFN, which is introduced to obtain variable approximation at irregular points in irregular domains. The proposed method is well suited to problems with mixed boundary conditions on both regular and irregular domains. The main results obtained are (a) the boundary conditions for the reformulated problem are of Dirichlet type only; (b) the integrated RBFN approximation avoids the well-known reduction of convergence rate associated with differential formulations; (c) the primary variable (e.g. displacement, temperature) and the dual variable (e.g. stress, temperature gradient) have similar convergence order; (d) the volumetric locking effects associated with incompressible materials in solid mechanics are alleviated. Numerical experiments show that the proposed method achieves very good accuracy and high convergence rates. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modelling and process optimization for functionally graded materialsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2005Ravi S. Bellur-Ramaswamy Abstract We optimize continuous quench process parameters to produce functionally graded aluminium alloy extrudates. To perform this task, an optimization problem is defined and solved using a standard non-linear programming algorithm. Ingredients of this algorithm include (1) the process parameters to be optimized, (2) a cost function: the weighted average of the precipitate number density distribution, (3) constraint functions to limit the temperature gradient (and hence distortion and residual stress) and exit temperature, and (4) their sensitivities with respect to the process parameters. The cost and constraint functions are dependent on the temperature and precipitate size which are obtained by balancing energy to determine the temperature distribution and by using a reaction-rate theory to determine the precipitate particle sizes and their distributions. Both the temperature and the precipitate models are solved via the discontinuous Galerkin finite element method. The energy balance incorporates non-linear boundary conditions and material properties. The temperature field is then used in the reaction rate model which has as many as 105 degrees-of-freedom per finite element node. After computing the temperature and precipitate size distributions we must compute their sensitivities. This seemingly intractable computational task is resolved thanks to the discontinuous Galerkin finite element formulation and the direct differentiation sensitivity method. A three-dimension example is provided to demonstrate the algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source] Finite element analysis and evaluation of design limits for structural materials in a cyclic state of creepINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2003M. Boulbibane Abstract In this paper a direct non-time stepping method derived from the minimum theorems given by the authors (European Journal of Mechanics , A/Solids 2002; 21:915,925) is outlined. This method can be used in the prediction of the deformation and life assessment of structures subjected to cyclic mechanical and thermal loadings. It produces accurate predictions of failure modes based on material behaviour incorporated into constitutive equations. It also can be used to define limit loads related to certain design criteria. Generally, for complex geometries and load histories, the identification of load histories that correspond to predefined design conditions, in the form of time or number of cycles to failure, can only be achieved by extensive and repeated calculations. For the Linear Matching Method, however, the representation of materially non-linear stress and strain fields by linear behaviour with spatially varying moduli, indicates the possibility that direct evaluation of loads and temperature ranges that correspond to a design restriction may be evaluated directly through the construction of the exact cyclic state and via sequence of approximations. The technique employs the finite element method combined with the cyclic state solution. The description of the material behaviour is given by a non-linear viscous model (Norton's law). It can also apply to any class of material behaviour that includes internal state variables. This technique has been applied successfully to a set of characteristics problems (Bree problem and plate containing a circular hole and subjected to radial temperature gradient). Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||