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Fundamental Understanding (fundamental + understanding)
Selected AbstractsUsing Nano-Cast Model Porous Media and Integrated Gas Sorption to Improve Fundamental Understanding and Data Interpretation in Mercury PorosimetryPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2006Sean P. Rigby Abstract The mechanisms of entrapment, and the nanoscopic spatial distribution, of the residual mercury within nano-cast and amorphous porous media (pore sizes ~1,100 nm) following high-pressure penetration have been studied. It has been shown that, even at the nano-scale, one of the same two principle mechanisms that have been observed previously in mercury porosimetry experiments on macroscopic glass pore models also occur within a given amorphous, nanoporous solid. Using percolation theory to interpret novel, integrated gas sorption experiments, entrapment was shown to arise, either because of the presence of sufficiently narrow pore necks interspersed between larger voids, or due to non-random, longer-range structural heterogeneity. The threshold "snap-off" ratio parameter for the entrapment process has also been directly measured but found to be considerably smaller than seen previously for macroporous materials. The techniques employed here enable information not previously available for nanoporous systems to be determined, and therefore to be incorporated into simulations of mercury porosimetry on those materials. [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] Fundamentals of Metal-induced Crystallization of Amorphous SemiconductorsADVANCED ENGINEERING MATERIALS, Issue 3 2009Zumin Wang Abstract A general, quantitative model has been developed that provides fundamental understanding of the metal-induced crystallization (MIC) of amorphous semiconductors. Interface thermodynamics has been shown to play a decisive role for the whether or not occurrence of MIC. The model has been employed to predict the MIC temperature for various metal/amorphous-semiconductor systems. A consequence of the model is the prediction that the thickness of an ultrathin, pure Al film put on the top of an amorphous Si layer can be used as a very accurate tool to tune the crystallization temperature of amorphous Si. These theoretical predictions have been confirmed experimentally. The fundamental understanding reached may lead to pronounced technological progress in the low-temperature manufacturing of crystalline-Si-based devices deposited on cheap and flexible substrates such as glasses, plastics, and possibly even papers. [source] Cast NiTi Shape-Memory Alloys,ADVANCED ENGINEERING MATERIALS, Issue 6 2005M. Ortega The purpose of this study is to build a fundamental understanding of the relationship between the structure and properties of cast nickel-titanium (NiTi). The structure of the cast material will be analyzed at various scales and will be related to the properties of the cast material such as transformation temperatures, stress-strain behavior, and recovery properties. This study demonstrates that cast NiTi can possess excellent shape-memory properties. [source] Electronic Structure of Self-Assembled Monolayers on Au(111) Surfaces: The Impact of Backbone PolarizabilityADVANCED FUNCTIONAL MATERIALS, Issue 23 2009LinJun Wang Abstract Modifying metal electrodes with self-assembled monolayers (SAMs) has promising applications in organic and molecular electronics. The two key electronic parameters are the modification of the electrode work function because of SAM adsorption and the alignment of the SAM conducting states relative to the metal Fermi level. Through a comprehensive density-functional-theory study on a series of organic thiols self-assembled on Au(111), relationships between the electronic structure of the individual molecules (especially the backbone polarizability and its response to donor/acceptor substitutions) and the properties of the corresponding SAMs are described. The molecular backbone is found to significantly impacts the level alignment; for molecules with small ionization potentials, even Fermi-level pinning is observed. Nevertheless, independent of the backbone, polar head-group substitutions have no effect on the level alignment. For the work-function modification, the larger molecular dipole moments achieved when attaching donor/acceptor substituents to more polarizable backbones are largely compensated by increased depolarization in the SAMs. The main impact of the backbone on the work-function modification thus arises from its influence on the molecular orientation on the surface. This study provides a solid theoretical basis for the fundamental understanding of SAMs and significantly advances the understanding of structure,property relationships needed for the future development of functional organic interfaces. [source] Corn stover feedstock trials to support predictive modelingGCB BIOENERGY, Issue 5 2010DOUGLAS L. KARLEN Abstract To be sustainable, feedstock harvest must neither degrade soil, water, or air resources nor negatively impact productivity or subsequent crop yields. Simulation modeling will help guide the development of sustainable feedstock production practices, but not without field validation. This paper introduces field research being conducted in six states to support Sun Grant Regional Partnership modeling. Our objectives are to (1) provide a fundamental understanding of limiting factor(s) affecting corn (Zea mays L.) stover harvest, (2) develop tools (e.g., equations, models, etc.) that account for those factors, and (3) create a multivariant analysis framework to combine models for all limiting factors. Sun Grant modelers will use this information to improve regional estimates of feedstock availability. A minimum data set, including soil organic carbon (SOC), total N, pH, bulk density (BD), and soil-test phosphorus (P), and potassium (K) concentrations, is being collected. Stover yield for three treatments (0%, 50%, and 90% removal) and concentrations of N, P, and K in the harvested stover are being quantified to assess the impact of stover harvest on soil resources. Grain yield at a moisture content of 155 g kg,1 averaged 9.71 Mg ha,1, matching the 2008 national average. Stover dry matter harvest rates ranged from 0 to 7 Mg ha,1. Harvesting stover increased N,P,K removal by an average of 42, 5, and 45 kg ha,1 compared with harvesting only grain. Replacing those three nutrients would cost $53.68 ha,1 based on 2009 fertilizer prices. This first-year data and that collected in subsequent years is being used to develop a residue management tool that will ultimately link multiple feedstock supplies together in a landscape vision to help develop a comprehensive carbon management plan, quantify corn stover harvest effects on soil quality, and predict regional variability in feedstock supplies. [source] A Multiscale Description of the Electronic Transport within the Hierarchical Architecture of a Composite Electrode for Lithium BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Jean-Claude Badot Abstract The broadband dielectric spectroscopy technique is applied, for the first time, to a composite material used as an electrode for lithium battery. The electrical properties (permittivity and conductivity) are measured from low (a few Hz) to microwave (a few GHz) frequencies. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. This work opens up new prospects for a more fundamental understanding and more rational optimization of the electronic transport in composite electrodes for lithium batteries and other electrochemical energy storage technologies (including other batteries, supercapacitors, low- and medium-temperature fuel cells), electrochemical sensors and conductor,insulator composite materials. [source] The carrying capacity of ecosystemsGLOBAL ECOLOGY, Issue 6 2004Pablo Del Monte-Luna ABSTRACT We analyse the concept of carrying capacity (CC), from populations to the biosphere, and offer a definition suitable for any level. For communities and ecosystems, the CC evokes density-dependence assumptions analogous to those of population dynamics. At the biosphere level, human CC is uncertain and dynamic, leading to apprehensive rather than practical conclusions. The term CC is widely used among ecological disciplines but remains vague and elusive. We propose the following definition: the CC is ,the limit of growth or development of each and all hierarchical levels of biological integration, beginning with the population, and shaped by processes and interdependent relationships between finite resources and the consumers of those resources'. The restrictions of the concept relate to the hierarchical approach. Emergent properties arise at each level, and environmental heterogeneity restrains the measurement and application of the CC. Because the CC entails a myriad of interrelated, ever-changing biotic and abiotic factors, it must not be assumed constant, if we are to derive more effective and realistic management schemes. At the ecosystem level, stability and resilience are dynamic components of the CC. Historical processes that help shape global biodiversity (e.g. continental drift, glaciations) are likely drivers of large-scale changes in the earth's CC. Finally, world population growth and consumption of resources by humanity will necessitate modifications to the paradigm of sustainable development, and demand a clear and fundamental understanding of how CC operates across all biological levels. [source] An investigation on thermal-recycling of recycled plastic resin (spherically symmetric analysis of abrupt heating processes of a micro plastic-resin particle)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006Ryuji Yamakita Abstract A fundamental understanding of the physical properties of a micro plastic-resin particle subjected suddenly to hot combustion gas, such as the temperature history in the micro particle and its lifetime, is necessary for effectively realizing thermal recycling of recycled plastic resin. However, micro plastic particles have such small diameters, ranging from 100 µm to 200 µm, that the measurement of temperature histories within them is extremely difficult. In this paper, therefore, a spherically symmetric one-dimensional analysis is applied to the abrupt heating process of a micro plastic resin particle in a high temperature inert atmosphere. Variations of the temperature history and the lifetime with the ambient gas temperature and the initial particle diameter are numerically analyzed, by dividing the entire heating process into four independent periods; the solid heating period, the melting period, the liquid heating period, and the vaporization period. Effects of the Nusselt number on the particle lifetime are also discussed. It is found that, by suitably taking account of the influences of heat transfer properties, the proposed simplified analysis is useful for estimating the fundamental and overall temperature characteristics of a micro plastic resin particle under abrupt heating. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 279,293, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20113 [source] Role of the Charge Transfer State in Organic Donor,Acceptor Solar CellsADVANCED MATERIALS, Issue 37 2010Carsten Deibel Charge transfer complexes are interfacial charge pairs residing at the donor,acceptor heterointerface in organic solar cell. Experimental evidence shows that it is crucial for the photovoltaic performance, as both photocurrent and open circuit voltage directly depend on it. For charge photogeneration, charge transfer complexes represent the intermediate but essential step between exciton dissotiation and charge extraction. Recombination of free charges to the ground state is via the bound charge transfer state before being lost to the ground state. In terms of the open circuit voltage, its maximum achievable value is determined by the energy of the charge transfer state. An important question is whether or not maximum photocurrent and maximum open circuit voltage can be achieved simultaneously. The impact of increasing the CT energy,in order to raise the open circuit voltage, but lowering the kinetic excess energy of the CT complexes at the same time,on the charge photogeneration will accordingly be discussed. Clearly, the fundamental understanding of the processes involving the charge transfer state is essential for an optimisation of the performance of organic solar cells. [source] Interface Engineering of Inorganic Thin-Film Solar Cells , Materials-Science Challenges for Advanced Physical ConceptsADVANCED MATERIALS, Issue 42 2009Wolfram Jaegermann Abstract The challenges and research needs for the interface engineering of thin-film solar cells using inorganic-compound semiconductors are discussed from a materials-science point of view. It is, in principle, easily possible to define optimized device structures from physical considerations. However, to realize these structures, many materials' limitations must be overcome by complex processing strategies. In this paper, interface properties and growth morphology are discussed using CdTe solar cells as an example. The need for a better fundamental understanding of cause,effect relationships for improving thin-film solar cells is emphasized. [source] Understanding and modeling basin hydrology: interpreting the hydrogeological signatureHYDROLOGICAL PROCESSES, Issue 7 2005R. E. Beighley Abstract Basin landscapes possess an identifiable spatial structure, fashioned by climate, geology and land use, that affects their hydrologic response. This structure defines a basin's hydrogeological signature and corresponding patterns of runoff and stream chemistry. Interpreting this signature expresses a fundamental understanding of basin hydrology in terms of the dominant hydrologic components: surface, interflow and groundwater runoff. Using spatial analysis techniques, spatially distributed watershed characteristics and measurements of rainfall and runoff, we present an approach for modelling basin hydrology that integrates hydrogeological interpretation and hydrologic response unit concepts, applicable to both new and existing rainfall-runoff models. The benefits of our modelling approach are a clearly defined distribution of dominant runoff form and behaviour, which is useful for interpreting functions of runoff in the recruitment and transport of sediment and other contaminants, and limited over-parameterization. Our methods are illustrated in a case study focused on four watersheds (24 to 50 km2) draining the southern coast of California for the period October 1988 though to September 2002. Based on our hydrogeological interpretation, we present a new rainfall-runoff model developed to simulate both surface and subsurface runoff, where surface runoff is from either urban or rural surfaces and subsurface runoff is either interflow from steep shallow soils or groundwater from bedrock and coarse-textured fan deposits. Our assertions and model results are supported using streamflow data from seven US Geological Survey stream gauges and measured stream silica concentrations from two Santa Barbara Channel,Long Term Ecological Research Project sampling sites. Copyright © 2004 John Wiley & Sons, Ltd. [source] Thermally Driven AFM for NanoenergeticsIMAGING & MICROSCOPY (ELECTRONIC), Issue 2 2009A Method to Investigate the Decomposition on the Nanoscale Abstract A fundamental understanding of the decomposition of energetic nanocompounds infiltrated in porous host matrixes requires the investigation of their behavior on a nanoscale during a thermal stress. Up to now, the decomposition of pure energetic nanomaterials has only been observed on a macroscopic scale. Thermally driven AFM revealed that the decomposition of the energetic material present in the pores of a Cr2O3 matrix induces a spatial expansion of the oxide on the nanometric scale. [source] Elastohydrodynamics of tensioned web roll coating processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2003M. S. Carvalho Abstract Coating process is an important step in the manufacturing of different products, such as paper, adhesive and magnetic tapes, photographic films, and many other. The tensioned web roll coating is one the several methods used by different industries. It relies on the elastohydrodynamic action between the fluid and the tensioned substrate for transferring and applying the liquid. The main advantage of this method is its ability to apply very thin liquid layers with less sensitivity to mechanical tolerance at relative small cost. Despite its industrial application, theoretical analysis and fundamental understanding of the process are limited. This work analyses this elastohydrodynamic action by solving the differential equations that govern the liquid flow, described by the Navier,Stokes equation, and the web deformation, modelled by the cylindrical shell approximation. The goal is to determine the operating conditions at which the process is two dimensional and defect free. The equations are discretized by the Galerkin/finite-element method. The resulting non-linear system of equations is solved by Newton's method coupled with pseudo-arc-length continuation in order to obtain solutions around turning points. The theoretical results are used to construct an operating window of the process that is in agreement with limited experimental data. Copyright © 2003 John Wiley & Sons, Ltd. [source] Rational Functionalization of Carbon Nanotubes Leading to Electrochemical Devices with Striking Applications,ADVANCED MATERIALS, Issue 15 2008Jie Yan Abstract As one-dimensional carbon nanostructures, carbon nanotubes (CNTs) are a member of the carbon family but they possess very different structural and electronic properties from other kinds of carbon materials frequently used in electrochemistry, such as glassy carbon, graphite, and diamond. Although the past decade has witnessed rapid and substantial progress in both the fundamental understanding of CNT-oriented electrochemistry and the development of various kinds of electrochemical devices with carbon nanotubes, the increasing demand from both academia and industry requires CNT-based electrochemical devices with vastly improved properties, such as good reliability and durability, and high performance. As we outline here, the smart functionalization of CNTs and effective methods for the preparation of devices would pave the way to CNT-based electronic devices with striking applications. [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] Recent advances in microdevices for electrochemical energy conversion and storageINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6-7 2007Gerardo Jose La O' Abstract The application of silicon microfabrication technologies to electrochemical devices allows reduction of overall device package to potentially increase volumetric power densities. This review first focuses on some exciting developments in microfuel cells, in particular, solid oxide fuel cells (SOFCs) and proton exchange membrane fuel cells (PEMFCs). The emphasis is given to innovative 2D processing methods, novel 2D architectures of microfuel cells, and demonstrated performance in terms of area power densities. Emerging 3D fabrication techniques that are potentially promising to produce 3D electrochemical devices such as 3D cell and stack architectures on the micrometer scale will then be discussed. Lastly this paper highlights some new opportunities in electrode kinetics studies enabled by microfabricated devices,investigation of scaling relationship between microelectrodes and electrochemical responses, which has led to improved fundamental understanding of electrode reactions and rate-limiting steps. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dye,fiber interactions in PET fibers: Hydrogen bonding studied by IR-spectroscopyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Karen De Clerck Abstract Dye,fiber interactions are studied in poly (ethylene terephthalate) fibers by FT-IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye,fiber system, where the PET fibers are dyed with anthraquinone-based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1-amino anthraquinones show strong "chelate-type" intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the CO groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye,fiber systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Thermal analysis of polymer,water interactions and their relation to gas hydrate inhibitionJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Manika Varma-Nair Abstract Gas hydrates formed in oil production pipelines are crystalline solids where hydrocarbon gas molecules such as methane, propane, and their mixtures are trapped in a cagelike structure by hydrogen-bonded water molecules to form undesirable plugs. Methanol and glycol are currently used to prevent these plugs via thermodynamic inhibition. Small amounts of water-soluble polymers may provide an alternate approach for preventing gas hydrates. In this study, we expand the fundamental understanding of water,polymer systems with differential scanning calorimetry. Nonfreezable bound water was used to quantify polymer,water interactions and relate them to the chemical structure for a series of polymers, including acrylamides, cyclic lactams, and n -vinyl amides. For good interactions, the water structure needs to be stabilized through hydrophobic interactions. An increased hydrophobicity of the pendant group also appears to favor polymer performance as a gas hydrate inhibitor. Good inhibitors, such as poly(diethyl acrylamide) and poly(N -vinyl caprolactam), also show higher heat capacities, which indicate higher hydrophobicity, than poor performers such as polyzwitterions, in which hydrophilicity dominated. The phase behavior and thermodynamic properties of dilute polymer solutions were also evaluated through measurements of the heat of demixing and lower critical solution temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2642,2653, 2007 [source] Comparative studies of quantitative trait and neutral marker divergence: a meta-analysisJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2008T. LEINONEN Abstract Comparative studies of quantitative genetic and neutral marker differentiation have provided means for assessing the relative roles of natural selection and random genetic drift in explaining among-population divergence. This information can be useful for our fundamental understanding of population differentiation, as well as for identifying management units in conservation biology. Here, we provide comprehensive review and meta-analysis of the empirical studies that have compared quantitative genetic (QST) and neutral marker (FST) differentiation among natural populations. Our analyses confirm the conclusion from previous reviews , based on ca. 100% more data , that the QST values are on average higher than FST values [mean difference 0.12 (SD 0.27)] suggesting a predominant role for natural selection as a cause of differentiation in quantitative traits. However, although the influence of trait (life history, morphological and behavioural) and marker type (e.g. microsatellites and allozymes) on the variance of the difference between QST and FST is small, there is much heterogeneity in the data attributable to variation between specific studies and traits. The latter is understandable as there is no reason to expect that natural selection would be acting in similar fashion on all populations and traits (except for fitness itself). We also found evidence to suggest that QST and FST values across studies are positively correlated, but the significance of this finding remains unclear. We discuss these results in the context of utility of the QST,FST comparisons as a tool for inferring natural selection, as well as associated methodological and interpretational problems involved with individual and meta-analytic studies. [source] Glycemic Responses and Sensory Characteristics of Whole Yellow Pea Flour Added to Novel Functional FoodsJOURNAL OF FOOD SCIENCE, Issue 9 2009Christopher P.F. Marinangeli ABSTRACT:, A fundamental understanding regarding postprandial glycemic responses to foods containing whole yellow-pea flour (WYPF) remains unknown. This, alongside concerns that WYPF possesses unfavorable sensory characteristics has limited the incorporation of WYPF into new functional food products as a healthy novel ingredient. The objective of this study was to evaluate how WYPF modulates postprandial glycemic responses as well as sensory characteristics in novel foods. In a single-blind crossover trial, the present study assessed postprandial glycemic responses of banana bread, biscotti, and spaghetti containing either WYPF or whole wheat flour (WWF). Boiled yellow peas (BYP) and white bread (WB) were used as positive and negative controls, respectively. On day 1, subjects evaluated appearance, taste, texture, smell as well as overall acceptance of each WYPF and WWF food on a 5-point hedonic scale. WYPF banana bread (97.9 ± 17.8 mmol·min/L) and biscotti (83 ± 13 mmol·min/L), as well as BYP (112.3 ± 19.9 mmol·min/L), reduced (P,< 0.05) glycemic responses compared to WB (218.1 ± 29.5 mmol·min/L). The glycemic response of WYPF pasta (160.7 ± 19.4 mmol·min/L) was comparable to WB. WYPF biscotti produced a lower (P,= 0.019) postprandial glycemic response compared to WWF biscotti (117.2 ± 13.1 mmol·min/L). Hedonic responses between corresponding foods were similar except for the WYPF pasta (2.9 ± 0.9) which possessed a lower sensory score (P,= 0.02) for smell compared to WWF pasta (3.6 ± 1). WYPF can be used to produce low-glycemic functional foods possessing sensory attributes that are comparable to identical food products containing WWF. [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] Chemical engineers and the fundamental understanding of human diseaseAICHE JOURNAL, Issue 10 2008Peter G. Vekilov First page of article [source] Tocopheryl acetate disposition in porcine and human skin when administered using lipid nanocarriersJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 6 2010Mojgan Moddaresi Abstract Objectives Assessing the delivery of a drug into the skin when it has been formulated within a nanocarrier is a complex process that does not conform to the conventions of traditional semi-solid formulations. The aim of this study was to gain a fundamental understanding of drug disposition in both human and porcine skin when applied using a lipidic nanocarrier. Methods A model system was generated by loading tocopheryl acetate into a well-characterised solid lipid nanoparticle and formulating this system as a traditional aqueous hyaluronic acid gel. Franz diffusion cells fitted with a silicone or nylon membrane were used to assess drug and particle transport independently whilst human and pig skin were employed to determine skin delivery. Key findings The tocopheryl acetate, when loaded into the solid lipid nanoparticles, did not release from the particle. However, 1.65 ± 0.90% of an infinite dose of tocopheryl acetate penetrated into the stratum corneum of pig skin when delivered using a nanoparticle-containing gel. Conclusions These results suggest that hydration of the stratum corneum in pig skin could lead to the opening of hydrophilic pores big enough for 50 nm-sized particles to pass into the superficial layers of the skin, a phenomenon that was not repeated in human skin. [source] Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Paolo Colombo Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers. (2) Special microstructural features of PDCs. (3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines. (4) Processing strategies to fabricate ceramic components from preceramic polymers. (5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available. [source] Electronic Structure and Bonding of All Crystalline Phases in the Silica,Yttria,Silicon Nitride Phase Equilibrium DiagramJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Wai-Yim Ching This paper reviews the structures and properties of 10 binary, ternary, and quaternary crystals within the equilibrium phase diagram of the SiO2,Y2O3,Si3N4 system. They are binary compounds SiO2, Y2O3, Si3N4; ternary compounds Si2N2O, Y2Si2O7, and YSi2O5; and quaternary crystals Y2Si3N4O3 (M-melilite), Y4Si2O7N2, (N-YAM), YSiO2N (wallastonite), and Y10(SiO4)6N2 (N-apatite, N-APT). Although the binary compounds are well-known and extensively studied, the ternary and the quaternary crystals are not. Most of the ternary and the quaternary crystals simply have been referenced as secondary phases in the processing of nitrogen ceramics. Their crystal structures are complex and not precisely determined. In the quaternary crystals, there exists O/N disorder in that the exact atomic positions of the anions cannot be uniquely determined. It is envisioned that a variety of cation,anion bonding configurations exist in these complex crystals. The electronic structure and bonding in these crystals are, therefore, of great interest and are indispensable for a fundamental understanding of structural ceramics. We have used ab initio methods to study the structure and bonding properties of these 10 crystals. For crystals with unknown or incomplete structural information, we use an accurate total energy relaxation scheme to obtain the most likely atomic positions. Based on the theoretically modeled structures, the electronic structure and bonding in these crystals are investigated and related to various local cation,anion bonding configurations. These results are presented in the form of atom-resolved partial density of states, Mulliken effective charges, and bond order values. It is shown that Y,O and Y,N bonding are not negligible and should be a part of the discussion of the overall bonding schemes in these crystals. Spectroscopic properties in the form of complex, frequency-dependent dielectric functions, X-ray absorption near-edge structure (XANES), and the electron energy-loss near-edge structure (ELNES) spectra in these crystals also are calculated and compared. These results are discussed in the context of specific bonding configurations between cations (silicon and yttrium) and anions (oxygen and nitrogen) and their implications on intergranular thin films in polycrystalline Si3N4 containing rare-earth elements. [source] Trauma: physiology, pathophysiology, and clinical implicationsJOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE, Issue 4 2006DACVA, DACVECC, William Muir DVM Abstract Objective: To review the physiology, pathophysiology, and consequences of trauma. The therapeutic implications of hypovolemia, hypotension, hypothermia, tissue blood flow, oxygen delivery, and pain will be discussed. Data Sources: Human and veterinary clinical and research studies. Human and veterinary data synthesis: Trauma is defined as tissue injury that occurs more or less suddenly as a result of violence or accident and is responsible for initiating hyothalamic,pituitary,adrenal axis, immunologic and metabolic responses that are designed to restore homeostasis. Tissue injury, hemorrhage, pain, and fear are key components of any traumatic event. Trauma and blood loss result in centrally integrated autonomic-mediated cardiovascular responses that are designed to increase heart rate, systemic vascular resistance, and maintain arterial blood pressure (ABP) to vital organs at the expense of blood flow to the gut and skeletal muscle. Severe trauma elicits exuberant physiologic, immunologic, and metabolic changes predisposing the animal to organ malfunction, a systemic inflammatory response, infection, and multiple organ dysfunctions. The combination of both central and local influences produces regional redistribution of blood flow among and within tissue beds which, when combined with impaired vascular reactivity, leads to maldistribution of blood flow to tissues predisposing to tissue hypoperfusion and impaired oxygen delivery and extraction. Gut blood flow and viability may serve as a sentinel of patient survival. These consequences are magnified in animals suffering from pain or that become hypothermic. Successful treatment of traumatized animals goes beyond the restoration of blood pressure and urine output, is dependent on a fundamental understanding of the pathophysiologic processes responsible for the animals current physical status, and incorporates the reduction of pain, stress, and the systemic inflammatory response and methods that restore microcirculatory blood flow and tissue oxygenation. Conclusions: Severe trauma is a multifaceted event and is exacerbated by hypothermia, pain, and stress. Therapeutic approaches must go beyond the simple restoration of vascular volume and ABP by maintaining tissue blood flow, restoring tissue oxygenation, and preventing systemic inflammation. [source] The ion funnel: Theory, implementations, and applicationsMASS SPECTROMETRY REVIEWS, Issue 2 2010Ryan T. Kelly Abstract The electrodynamic ion funnel has enabled the manipulation and focusing of ions in a pressure regime (0.1,30 Torr) that has challenged traditional approaches, and provided the basis for much greater mass spectrometer ion transmission efficiencies. The initial ion funnel implementations aimed to efficiently capture ions in the expanding gas jet of an electrospray ionization interface and radially focus them for efficient transfer through a conductance limiting orifice. We review the improvements in fundamental understanding of ion motion in ion funnels, the evolution in its implementations that have brought the ion funnel to its current state of refinement, as well as applications of the ion funnel for purposes such as ion trapping, ion cooling, low pressure electrospray, and ion mobility spectrometry. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:294,312, 2010 [source] Benign cysts in the central nervous system: Neuropathological observations of the cyst wallsNEUROPATHOLOGY, Issue 1 2004Asao Hirano A diverse variety of benign cysts exist in the CNS. Advances in diagnostic radiology have facilitated diagnoses and surgical intervention in many patients with CNS cysts. However, a fundamental understanding of the pathological features of these lesions is clinically vital. From an etiological point of view, the cysts can be divided into two groups. The first includes lesions that arise from within the CNS and may be static structures such as cavities arising from infarcts and other destructive processes while other lesions such as arachnoid cysts, ependymal cysts, cystic hemangioblastoma, cystic cerebellar astrocytoma and infectious processes, are progressive. The second group of cysts arise from the intrusion of non-nervous system tissue into the neuroaxis and are usually midline. They are frequently expanding congenital lesions although some become symptomatic only in adults. Examples include teratomas, dermoid cysts, epidermoid cysts, craniopharyngiomas, Rathke's cleft cysts, and other epithelial cysts presumably derived from the upper respiratory or intestinal tract. Chick embryos exposed to lead have been used as a model of cyst formation. [source] A commentary on coastal research in New Zealand universitiesNEW ZEALAND GEOGRAPHER, Issue 2 2008Paul S. Kench Abstract: , University research in coastal geomorphology, processes and management has made a major contribution to the fundamental understanding of coastal systems in New Zealand over the past 43 years. This article examines the growth in university-based coastal research since 1964 and discusses the geographical pattern and themes of this research. Data indicate a significant geographical concentration of research effort and focus on a narrow range of research themes. Underlying reasons for these characteristics of New Zealand coastal research are explored and challenges facing university based research are discussed. Such challenges can be overcome through a more coordinated research effort to realize the huge potential to undertake coastal science of national relevance and international significance. [source] | |||||||||||||||||||||||||||||||||||||