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Transport Phenomena (transport + phenomenon)
Kinds of Transport Phenomena Selected AbstractsOn the Approximation of Transport Phenomena , a Dynamical Systems ApproachGAMM - MITTEILUNGEN, Issue 1 2009Michael Dellnitz Abstract Transport phenomena are studied in a large variety of dynamical systems with applications ranging from the analysis of fluid flow in the ocean and the predator-prey interaction in jelly-fish to the investigation of blood flow in the cardiovascular system. Our approach to analyze transport is based on the methodology of so-called transfer operators associated with a dynamical system since this is particularly suitable. We describe the approach and illustrate it by two real world applications: the computation of transport for asteroids in the solar system and the approximation of macroscopic structures in the Southern Ocean (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mass fractal dimension of soil macropores using computed tomography: from the box-counting to the cube-counting algorithmEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003J.S. Perret Summary Transport phenomena in porous media depend strongly on three-dimensional pore structures. Macropore networks enable water and solute to move preferentially through the vadose zone. A complete representation of their geometry is important for understanding soil behaviour such as preferential flow. Once we know the geometrical, topological and scaling attributes of preferential flow paths, we can begin computer simulations of water movement in the soil. The box-counting method is used in three dimensions (i.e. cube-counting algorithm) to characterize the mass fractal dimension of macropore networks using X-ray computed tomography (CT) matrices. We developed an algorithm to investigate the mass fractal dimension in three dimensions and to see how it compares with the co-dimensions obtained using the box-counting technique in two dimensions. For that purpose, macropore networks in four large undisturbed soil columns (850 mm × 77 mm diameter) were quantified and visualized, in both two and three dimensions, using X-ray CT. We observed an increasing trend between the fractal dimension and macroporosity for the four columns. Moreover, similar natural logarithm functions were obtained for the four cores by a least squares fit through plots of mass fractal dimension against macroporosity. [source] On the Approximation of Transport Phenomena , a Dynamical Systems ApproachGAMM - MITTEILUNGEN, Issue 1 2009Michael Dellnitz Abstract Transport phenomena are studied in a large variety of dynamical systems with applications ranging from the analysis of fluid flow in the ocean and the predator-prey interaction in jelly-fish to the investigation of blood flow in the cardiovascular system. Our approach to analyze transport is based on the methodology of so-called transfer operators associated with a dynamical system since this is particularly suitable. We describe the approach and illustrate it by two real world applications: the computation of transport for asteroids in the solar system and the approximation of macroscopic structures in the Southern Ocean (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transport phenomena at interfaces between turbulent fluidsAICHE JOURNAL, Issue 2 2008Damon Turney First page of article [source] Introducing natural-convective chilling to food engineering undergraduate freshmen: Case studied assisted by CFD simulation and field visualizationCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2009J. A. Rabi Abstract A computational fluid dynamics (CFD)-assisted didactic activity has been applied to Food Engineering freshmen aiming at introducing basic concepts of process modeling and simulation towards the food industry. Evoking natural convection, a relatively simple case study was proposed involving two initially room temperature porous samples (identified as two fruits) that were placed inside a refrigeration chamber. Three different configurations were suggested for placing such warmer samples so that students were asked to order them with respect to their chilling capability, that is, to their ability to chill samples as fast as possible. Freshmen's written answers were collected before CFD was used to simulate and visualize each distinct chilling scenario. Accordingly, a finite-volume FORTRAN simulator for transport phenomena in domains fully or partially filled up with porous matrix was used to help compare each chilling performance. Among all possible combinations, answer distribution is presented and discussed in the light of freshmen's scholar background as well as based on the way natural convection concepts were introduced. © 2008 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 34,43, 2009; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae20161 [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] Investigations of the Morphogenesis of Filamentous Microorganisms,ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2006S. Kelly Abstract Several biotechnological production processes are based on the cultivation of filamentous microorganisms like the fungus Aspergillus niger. The morphological development plays an important role for transport phenomena and the related productivity. The description of filamentous morphogenesis of A. niger as a model organism, given here, is structured in three morphological growth processes, a very fast conidial aggregation, followed by a second slower aggregation step promoted by germination and hyphal tip growth, and the growth of pellets as the last process. [source] A Review of Mathematical Models for Hydrogen and Direct Methanol Polymer Electrolyte Membrane Fuel CellsFUEL CELLS, Issue 1-2 2004K.Z. Yao Abstract This paper presents a review of the mathematical modeling of two types of polymer electrolyte membrane fuel cells: hydrogen fuel cells and direct methanol fuel cells. Models of single cells are described as well as models of entire fuel cell stacks. Methods for obtaining model parameters are briefly summarized, as well as the numerical techniques used to solve the model equations. Effective models have been developed to describe the fundamental electrochemical and transport phenomena occurring in the diffusion layers, catalyst layers, and membrane. More research is required to develop models that are validated using experimental data, and models that can account for complex two-phase flows of liquids and gases. [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] Chemical modification of pyroclastic rock by hot water: an experimental investigation of mass transport at the fluid,solid interfaceGEOFLUIDS (ELECTRONIC), Issue 1 2009J. HARA Abstract Hydrothermal water,(pyroclastic) rock interactions were examined using flow-through experiments to deduce the effect of mass transport phenomena on the reaction process. A series of experiments were conducted over the temperature range 75,250°C, with a constant temperature for each experiment, and at saturated vapour pressure, to estimate the apparent rate constants as a function of temperature. Based on the chemistry of analysed solutions, the water,rock interaction in the experiments was controlled by diffusion from the reaction surface and by the existence of a surface layer at the rock,fluid interface, which regulated the chemical reaction rate. The reaction progress depended to a high degree on flow velocity and temperature conditions, with element abundances in the fluid significantly affected by these factors. Mass transport coefficients for diffusion from the rock surface to the bulk solution have been estimated. Ca is selectively depleted under lower temperature conditions (T < 150°C), whereas Na is greatly depleted under higher temperature conditions (T > 150°C), and K reaction rates are increased when flow velocity increases. Using these conditions, specific alkali and alkali earth cations were selectively leached from mineral surfaces. The ,surface layer' comprised a 0.5,1.8 mm boundary film on the solution side (the thickness of this layer has no dependence on chemical character) and a reaction layer. The reaction layer was composed of a Si, Al-rich cation-leached layer, whose thickness was dependent on temperature, flow velocity and reaction length. The reaction layer varied in thickness from about 10,4 to 10,7 mm under high temperature/low fluid velocity and low temperature/high fluid velocity conditions, respectively. [source] Potential and Bottlenecks of Bioreactors in 3D Cell Culture and Tissue ManufacturingADVANCED MATERIALS, Issue 32-33 2009David Wendt Abstract Over the last decade, we have witnessed an increased recognition of the importance of 3D culture models to study various aspects of cell physiology and pathology, as well as to engineer implantable tissues. As compared to well-established 2D cell-culture systems, cell/tissue culture within 3D porous biomaterials has introduced new scientific and technical challenges associated with complex transport phenomena, physical forces, and cell,microenvironment interactions. While bioreactor-based 3D model systems have begun to play a crucial role in addressing fundamental scientific questions, numerous hurdles currently impede the most efficient utilization of these systems. We describe how computational modeling and innovative sensor technologies, in conjunction with well-defined and controlled bioreactor-based 3D culture systems, will be key to gain further insight into cell behavior and the complexity of tissue development. These model systems will lay a solid foundation to further develop, optimize, and effectively streamline the essential bioprocesses to safely and reproducibly produce appropriately scaled tissue grafts for clinical studies. [source] High-Performance Organic Field-Effect TransistorsADVANCED MATERIALS, Issue 14-15 2009Daniele Braga Abstract With the advent of devices based on single crystals, the performance of organic field-effect transistors has experienced a significant leap, with mobility now in excess of 10,cm2 V,1 s,1. The purpose of this review is to give an overview of the state-of-the-art of these high-performance organic transistors. The paper focuses on the problem of parameter extraction, limitations of the performance by the interfaces, which include the dielectric,semiconductor interface, and the injection and retrieval of charge carriers at the source and drain electrodes. High-performance devices also constitute tools of choice for investigating charge transport phenomena in organic materials. It is shown how the combination of field-effect measurements with other electrical characterizations helps in elucidating this still unresolved issue. [source] Investigation of nanoscale electrohydrodynamic transport phenomena in charged porous materialsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2005P. Pivonka Abstract Depending on the permeability of porous materials, different mass transport mechanisms have to be distinguished. Whereas mass transport through porous media characterized by low permeabilities is governed by diffusion, mass transport through highly permeable materials is governed by advection. Additionally a large number of porous materials are characterized by the presence of surface charge which affects the permeability of the porous medium. Depending on the ion transport mechanism various phenomena such as co-ion exclusion, development of diffusion,exclusion potentials, and streaming potentials may be encountered. Whereas these various phenomena are commonly described by means of different transport models, a unified description of these phenomena can be made within the framework of electrohydrodynamics. In this paper the fundamental equations describing nanoscale multi-ion transport are given. These equations comprise the generalized Nernst,Planck equation, Gauss' theorem of electrostatics, and the Navier,Stokes equation. Various phenomena such as the development of exclusion potentials, diffusion,exclusion potentials, and streaming potentials are investigated by means of finite element analyses. Furthermore, the influence of the surface charge on permeability and ion transport are studied in detail for transient and steady-state problems. The nanoscale findings provide insight into events observed at larger scales in charged porous materials. Copyright © 2005 John Wiley Sons, Ltd. [source] Transport mechanisms and performance simulation of a PEM fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2008Geng-Po Ren Abstract A three-dimensional, gas,liquid two-phase flow and transport model has been developed and utilized to simulate the multi-dimensional, multi-phase flow and transport phenomena in both the anode and cathode sides in a proton exchange membrane (PEM) fuel cell and the cell performance with different influencing operational and geometric parameters. The simulations are presented with an emphasis on the physical insight and fundamental understanding afforded by the detailed distributions of velocity vector, oxygen concentration, water vapor concentration, liquid water concentration, water content in the PEM, net water flux per proton flux, local current density, and overpotential. Cell performances with different influencing factors are also presented and discussed. The comparison of the model prediction and experimental data shows a good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Thermal-fluid transport phenomena in an axially rotating flow passage with twin concentric orifices of different radiiINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2006Shuichi Torii Abstract This paper investigates the thermal fluid-flow transport phenomena in an axially rotating passage in which twin concentric orifices of different radii are installed. Emphasis is placed on the effects of pipe rotation and orifice configuration on the flow and thermal fields, i.e. both the formation of vena contracta and the heat-transfer performance behind each orifice. The governing equations are discretized by means of a finite-difference technique and numerically solved for the distributions of velocity vector and fluid temperature subject to constant wall temperature and uniform inlet velocity and fluid temperature. It is found that: (i) for a laminar flow through twin concentric orifices in a pipe, axial pipe rotation causes the vena contracta in the orifice to stretch, resulting in an amplification of heat-transfer performance in the downstream region behind the rear orifice, (ii) simultaneously the heat transfer rate in the area between twin orifice is intensified by pipe rotation, (iii) the amplification of heat transfer performance is affected by the front and rear orifice heights. Results may find applications in automotive and rotating hydraulic transmission lines and in aircraft gas turbine engines. Copyright © 2005 John Wiley & Sons, Ltd. [source] Carbon monoxide poisoning of proton exchange membrane fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2001J. J. Baschuk Abstract Proton exchange membrane fuel cell (PEMFC) performance degrades when carbon monoxide (CO) is present in the fuel gas; this is referred to as CO poisoning. This paper investigates CO poisoning of PEMFCs by reviewing work on the electrochemistry of CO and hydrogen, the experimental performance of PEMFCs exhibiting CO poisoning, methods to mitigate CO poisoning and theoretical models of CO poisoning. It is found that CO poisons the anode reaction through preferentially adsorbing to the platinum surface and blocking active sites, and that the CO poisoning effect is slow and reversible. There exist three methods to mitigate the effect of CO poisoning: (i) the use of a platinum alloy catalyst, (ii) higher cell operating temperature and (iii) introduction of oxygen into the fuel gas flow. Of these three methods, the third is the most practical. There are several models available in the literature for the effect of CO poisoning on a PEMFC and from the modeling efforts, it is clear that small CO oxidation rates can result in much increased performance of the anode. However, none of the existing models have considered the effect of transport phenomena in a cell, nor the effect of oxygen crossover from the cathode, which may be a significant contributor to CO tolerance in a PEMFC. In addition, there is a lack of data for CO oxidation and adsorption at low temperatures, which is needed for detailed modeling of CO poisoning in PEMFCs. Copyright © 2001 John Wiley & Sons, Ltd. [source] Time domain global modelling of EM propagation in semiconductor using irregular gridsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2002Hsiao-Ping Tsai Abstract A two-dimensional finite volume time domain (FVTD) method using a triangular grid is applied to the analysis of electromagnetic wave propagation in a semiconductor. Maxwell's equations form the basis of all electromagnetic phenomena in semiconductors and the drift-diffusion model is employed to simulate charge transport phenomena in the semiconductor. The FVTD technique is employed to solve Maxwell's equations on an irregular grid and the finite box method is implemented on the same grid to solve the drift-diffusion model for carrier concentration. The locations of unknowns have been chosen to allow linking coupled Maxwell's equations and transport equations in a seamless way. To achieve suitable accuracy and computational efficiency, using irregular grid topology allows a finer mesh in doped region and at junction, and a coarser mesh in substrate and insulting regions. The proposed scheme has been implemented and verified by characterizing electromagnetic wave propagation at microwave frequency in a semiconductor slab with arbitrary doping profile. Copyright © 2002 John Wiley & Sons, Ltd. [source] Modeling of transport phenomena and melting kinetics of starch in a co-rotating twin-screw extruder,ADVANCES IN POLYMER TECHNOLOGY, Issue 1 2006Lijun Wang A mathematical model was developed to simulate fluid flow, heat transfer, and melting kinetics of starch in a co-rotating intermeshing twin-screw extruder (TSE). The partial differential equations governing the transport phenomena of the biomaterial in the extruder were solved by a finite element scheme. For validating the model, the predicted product pressure, bulk temperature at the entrance of the die, and minimum residence time of the biomaterial in the extruder were compared with experimental data. Standard errors of product pressure, bulk temperature at the die entrance, and minimum residence time were about 8.8, 2.8, and 17.3%. Simulations were carried out to investigate profiles of product pressure, bulk temperature, and melt fraction within the extruder during extrusion. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 22,40, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20055 [source] An overview of the mathematical modelling of liquid membrane separation processes in hollow fibre contactorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2009E Bringas Abstract Liquid membranes have traditionally been employed for liquid/liquid mass transfer and have found applications in industrial, biomedical and analytical fields as well as in hydrometallurgical processes, wastewater treatment and remediation of polluted groundwater. However, in spite of the known advantages of liquid membranes, there are few examples of industrial application. The development of reliable mathematical models and design parameters (mass transport coefficients and equilibrium or kinetic parameters associated with the interfacial reactions) is a necessary step for design, cost estimation, process optimisation and scale-up. This work reports an overview of the different approaches that have been proposed in the literature to the mathematical modelling of liquid membrane separation processes in hollow fibre contactors providing, at the same time, a useful guideline to characterise the mass transport phenomena and a tool for the optimal design and intensification of separation processes. Copyright © 2009 Society of Chemical Industry [source] APPLICATION OF DISCRETE MODELING APPROACH TO FLUIDIZED BED YEAST DRYINGJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2010F. DEBASTE ABSTRACT Yeast drying is widely used to ease transport and conservation. In this work, baker's yeast drying in fluidized bed is modeled using a pore network model. Classical balanced equations at the reactor scale are coupled with the pore network for the grain, which takes into account diffusion in the gas phase, transport by liquid film in partially saturated region and pressure gradient effects in the liquid phase. The porous structure to be applied in the model is obtained using environmental scanning electron microscopy. Simulations are validated on a thermogravimetric analysis experiment. The model is then applied to fluidized bed drying for which experimental results obtained on a laboratory pilot are available. Finally, the model results are compared to those of a simplified receding front model. PRACTICAL APPLICATIONS The presented model allows simulation of Saccharomyces cerevisiae fluidized bed drying. Taking into account transport phenomena in the grain offers the opportunity to predict drying rate without the use of a desorption isotherm. Moreover, the model predicts roughly the critical humidity. Therefore, the model can be used for scale-up, design and optimization of dryer including the effect of changes in yeast granulation. [source] A time-dependent multiphysics, multiphase modeling framework for carbon nanotube synthesis using chemical vapor depositionAICHE JOURNAL, Issue 12 2009Mahmoud Reza Hosseini Abstract A time-dependent multiphysics, multiphase model is proposed and fully developed here to describe carbon nanotubes (CNTs) fabrication using chemical vapor deposition (CVD). The fully integrated model accounts for chemical reaction as well as fluid, heat, and mass transport phenomena. The feed components for the CVD process are methane (CH4), as the primary carbon source, and hydrogen (H2). Numerous simulations are performed for a wide range of fabrication temperatures (973.15,1273.15 K) as well as different CH4 (500,1000 sccm) and H2 (250,750 sccm) flow rates. The effect of temperature, total flow rate, and feed mixture ratio on CNTs growth rate as well as the effect of amorphous carbon formation on the final product are calculated and compared with experimental results. The outcomes from this study provide a fundamental understanding and basis for the design of an efficient CNT fabrication process that is capable of producing a high yield of CNTs, with a minimum amount of amorphous carbon. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Convection, diffusion, and exothermic zero-order reaction in a porous catalyst slab: Scaling and perturbation analysisAICHE JOURNAL, Issue 10 2009João P. Lopes Abstract The analysis of the interaction between transport phenomena and chemical reaction inside large-pore catalyst particles needs to include intraparticular convection as an additional mass/heat transfer mechanism. In this work, we describe by a 3D regime diagram the global behavior of a permeable catalyst slab, where an exothermic, zero-order reaction is occurring. An order of magnitude estimate for the maximum temperature change is obtained by scaling techniques in each regime of operation. Specific operating regimes of fast mass/heat transport, dominant reaction and strong intraparticular convection, are then studied in more detail using perturbation analysis. The results include approximate concentration and temperature profiles, which allow the estimation of both the effectiveness factor and maximum temperature attained inside the catalyst in these regimes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Modeling hydrogen spillover in dual-bed catalytic reactorsAICHE JOURNAL, Issue 4 2004John C. Weigle Abstract A semiquantitative model was developed to describe hydrogen spillover in dual-bed catalytic reactors. In previous studies it has been conclusively demonstrated that hydrogen can diffuse macroscopic distances and activate catalytic sites. The test reaction in those studies was the isomerization of 1-butene to 2-butene. The model is derived based on the fundamental principles of transport phenomena and reaction kinetics. Because many of the required values in the model are unknown, it cannot be solved quantitatively. Thus, a parametric analysis was conducted. The model successfully predicts trends observed experimentally. Specifically, the activity increases nonlinearly as the bed composition changes, the selectivity was low for all dual-bed reactors, and the selectivity was high for well-mixed catalyst beds. © 2004 American Institute of Chemical Engineers AIChE J, 50: 821,828, 2004 [source] Multi-scale modelling of two-phase,two-component processes in heterogeneous porous mediaNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 9 2006J. Niessner Abstract This work deals with flow and transport phenomena in porous media, which occur on different space and time scales. Additionally, the porous medium itself is heterogeneous where the heterogeneities occur on all spatial scales. We consider a large domain with randomly distributed heterogeneities where complex two-phase,two-component processes are relevant only in a small (local) subdomain. This subdomain needs fine resolution as the complex processes are governed by small-scale effects. For a comprehensive fine-scale model taking into account two-phase,two-component processes as well as heterogeneities in the whole (global) model domain, data collection is expensive and computational time is high. Therefore, we developed a multi-scale concept where on the one hand, the global flow field influences the local two-phase,two-component processes on the fine scale. On the other hand, a coarse-scale saturation equation is solved where the effects of the fine-scale two-phase,two-component processes in the subdomain are captured by source/sink terms and the effects of fine-scale heterogeneities by a macrodispersion term. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of ODE methods for laminar reacting gas flow simulationsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 3 2008S. van Veldhuizen Abstract Two-dimensional transient simulations are presented of the transport phenomena and multispecies, multireaction chemistry in chemical vapor deposition (CVD). The transient simulations are run until steady state, such that the steady state can be validated against the steady state solutions from literature. We compare various time integration methods in terms of efficiency and robustness. Besides stability, which is important due to the stiffness of the problem, preservation of non-negativity is crucial. It appears that this latter condition on a time integration method is much more restrictive toward the time step size than stability. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008 [source] How to design perforated polymeric films for modified atmosphere packs (MAP)PACKAGING TECHNOLOGY AND SCIENCE, Issue 6 2001Luciano ZanderighiArticle first published online: 12 APR 200 Abstract Increasing proportions of fresh produce are being sold in modified atmosphere packs (MAP) with the aim of preserving product quality longer and reducing freight costs. A rigorous theoretical analysis was made of the transport phenomena across packaging film (composite, perforated, etc.) in order to find out whether polymeric film will permit a stationary modified atmosphere (MA) inside the pack, and if so when, and to investigate the effect of the size and shape of the holes in the perforated film. The continuity equations of the pack, for all diffusing species, were written and solved for stationary conditions, with the boundary conditions that species not involved in metabolic processes do not diffuse across polymeric film. After a detailed analysis of the transport phenomena across both continuous and perforated film, and of the metabolic rate processes, it transpires that no stationary conditions compatible with any MA can be found for continuous film, owing to the permeation characteristics of the film and the rate of the metabolic processes. With perforated film it is possible to find, at least for certain metabolic process rates, a stationary state where a constant MA is maintained inside the pack. A proposal is given, provided the rate of the metabolic process is known, for the design of a pack in terms of polymeric materials and of the pinhole size. Two case studies, strawberry and cabbage, are presented and discussed, along with the optimization of the polymeric film and the size and length of the pinholes of the packs. Another point raised deals with the advantages of using perforated film and/or of making holes or openings along the edges where the polymeric film is welded. Copyright © 2001 John Wiley & Sons, Ltd. [source] Electrical transport phenomena in magnesium-doped p-type GaNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009Leszek Konczewicz Abstract In this paper we present the resistivity and Hall-effect measurements on p-type GaN doped with Mg. The experiments were carried out as a function of hydrostatic pressure up to 1200 MPa in the temperature range 260,400 K. Both bulk GaN crystals as well as GaN:Mg epilayers were studied. In the investigated samples the decrease of resistivity and increase of hole concentration under pressure was observed. Such a behavior, which is contrary to the n-type material, strongly suggests a decrease of the ionization energy of Mg acceptor (Ea = 183 meV) with pressure. This shift is very weak, less than ,2 meV/GPa. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of the correlation effects on charge transport through quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007T. Doma Abstract We study the effect of the Coulomb interactions on a charge transport through a single level quantum dot. The excitation spectrum is at low temperatures characterized by a narrow Kondo resonance (the low energy feature) formed on top of the line broadening (high energy part of the spectrum). We investigate mutual interplay between these low and high energy parts and discuss their influence on the transport phenomena for a semi-equilibrium situation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Aharonov,Bohm effects in multiwall carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006C. Strunk Abstract We investigate quantum transport phenomena in multiwall carbon nanotubes in perpendicular and parallel magnetic field. An efficient gating technique allows for a considerable tuning of the nanotube doping level. We show that the weak localization is strongly suppressed at peaks at certain gate voltages which can be linked with the bottoms of one-dimensional electronic subbands. In large parallel magnetic field, we observe a superposition of h /2e -periodic Altshuler-Aronov-Spivak oscillations and an additional h /e -periodic contribution, which we attribute to the magnetic field dependence of the band structure. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phase transitions and transport phenomena in Li0.25Cu1.75Se superionic compoundPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004M. Kh. Abstract Phase transformation points in Li0.25Cu1.75Se mixed electronic,ionic conductor have been determined by calorimetric, conductometric and thermoelectric measurements. The phase transformation (PT) from triclinic to monoclinic occurs at 403,413 K. At 503,515 K the monoclinic phase is followed by a rhombohedral modification. Both of these PTs are accompanied by drops on the calorimetric curve. At about 653 K observed anomalies in the temperature dependencies of the ionic conductivity, of the chemical diffusion coefficient and the jump of the ionic Seebeck coefficient have been induced by the PT to hexagonal phase. Neutron diffraction studies reveal the cubic structure of Li0.25Cu1.75Se compound (with space group Fm3m) at 773 K. The corresponding PT causes anomalies in the electrical and diffusion properties at 703,713 K. Cu ions are statistically distributed over tetrahedral and trigonal voids in an Fm3m cage; lithium ions randomly occupy 32(f) positions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||