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General Considerations (general + consideration)
Selected AbstractsSolid,liquid,air coupling in multiphase porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2003Lyesse Laloui Abstract This paper addresses various issues concerning the modelling of solid,liquid,air coupling in multiphase porous media with an application to unsaturated soils. General considerations based on thermodynamics permit the derivation and discussion of the general form of field equations; two cases are considered: a three phase porous material with solid, liquid and gas, and a two phase porous material with solid, liquid and empty space. Emphasis is placed on the presentation of differences in the formulation and on the role of the gas phase. The finite element method is used for the discrete approximation of the partial differential equations governing the problem. The two formulations are then analysed with respect to a documented drainage experiment carried out by the authors. The merits and shortcomings of the two approaches are shown. Copyright © 2003 John Wiley & Sons, Ltd. [source] Many zeros does not mean zero inflation: comparing the goodness-of-fit of parametric models to multivariate abundance dataENVIRONMETRICS, Issue 3 2005David I. Warton Abstract An important step in studying the ecology of a species is choosing a statistical model of abundance; however, there has been little general consideration of which statistical model to use. In particular, abundance data have many zeros (often 50,80 per cent of all values), and zero-inflated count distributions are often used to specifically model the high frequency of zeros in abundance data. However, in such cases it is often taken for granted that a zero-inflated model is required, and the goodness-of-fit to count distributions with and without zero inflation is not often compared for abundance data. In this article, the goodness-of-fit was compared for several marginal models of abundance in 20 multivariate datasets (a total of 1672 variables across all datasets) from different sources. Multivariate abundance data are quite commonly collected in applied ecology, and the properties of these data may differ from abundances collected in autecological studies. Goodness-of-fit was assessed using AIC values, graphs of observed vs expected proportion of zeros in a dataset, and graphs of the sample mean,variance relationship. The negative binomial model was the best fitting of the count distributions, without zero-inflation. The high frequency of zeros was well described by the systematic component of the model (i.e. at some places predicted abundance was high, while at others it was zero) and so it was rarely necessary to modify the random component of the model (i.e. fitting a zero-inflated distribution). A Gaussian model based on transformed abundances fitted data surprisingly well, and rescaled per cent cover was usually poorly fitted by a count distribution. In conclusion, results suggest that the high frequency of zeros commonly seen in multivariate abundance data is best considered to come from distributions where mean abundance is often very low (hence there are many zeros), as opposed to claiming that there are an unusually high number of zeros compared to common parametric distributions. Copyright © 2005 John Wiley & Sons, Ltd. [source] On the possibility of self-induction of drug protein bindingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2010Leonid M. Berezhkovskiy Abstract The equilibrium unbound drug fraction (fu) is an important pharmacokinetic parameter, which influences drug elimination and distribution in the body. Commonly the drug plasma concentration is substantially less then that of drug binding proteins, so that fu can be assumed constant independent of drug concentration. A general consideration of protein binding based on the mass-action law provides that the unbound drug fraction increases with the increase of drug concentration, which is also a usual experimental observation. For several drugs, though, a seemingly unusual sharp decrease of the unbound drug fraction with the increase of total drug concentration (Ro) in the interval 0,<,Ro,,,5,µM was experimentally observed. A possible explanation of this apparently strange phenomenon is presented. The explanation is based on the consideration of a two-step mechanism of drug protein binding. The first step occurs as a drug binding to the site with relatively low affinity. Consequently this binding leads to the activation of a high affinity site, which otherwise is not available for binding. The suggested binding scheme yields the curves for fu dependence on the total drug concentration that are in good agreement with experimental measurements. The interpretation of pharmacokinetic data for the drugs with such unusual concentration dependence of fu appears to be a formidable problem. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4400,4405, 2010 [source] Stoffliche und konstruktionsbezogene Besonderheiten beim Einsatz von UHFB im Brückenbau am Beispiel von drei PilotprojektenBETON- UND STAHLBETONBAU, Issue 9 2009Michael Reichel Dipl.-Ing. Brückenbau; Entwurf und Konstruktion Abstract Seit 1997 wurden weltweit ca. 30 Brücken aus UHFB (Ultrahochfester Beton) gebaut. Wegen der hohen Leistungsfähigkeit von UHFB, vor allem in Bezug auf seine Festigkeits- und Dauerhaftigkeitseigenschaften, ist er geradezu prädestiniert für Ingenieurbauwerke und damit auch für Brücken. Übliche Konstruktionsprinzipien des Betonbaus lassen sich jedoch nicht einfach auf den neuen Werkstoff übertragen. Die konsequente Einbeziehung der Eigenschaften und Besonderheiten des neuen Werkstoffes sowie die Berücksichtigung der Forderungen der Nachhaltigkeit führen zu filigranen, modularen und flexiblen Bauweisen, die sich ihrem Konstruktionsprinzip nach zwischen Beton- und Stahlkonstruktionen einordnen lassen. Bei Betrachtung der gesamten Lebenszykluskosten sind mit solchen Bauweisen wirtschaftliche Bauwerke mit eminentem Nutzen für die Volkswirtschaft möglich. Nach einer allgemeinen Betrachtung werden anhand der Erfahrungen bei Konstruktion, Bemessung und Ausführung von drei verschiedenen Pilotprojekten in Österreich die Besonderheiten und neuen Erkenntnisse beispielhaft erläutert. Special Features of Material and Structure in the Application of UHPC for Bridge Construction exemplified by three Pilot Projects Since 1997 nearly 30 bridges have been built worldwide using UHPC (Ultra High Performance Concrete). Due to the high performance of UHPC, especially owing to its strength and durability properties, this material is predestined for engineering structures and as a result also for bridges. Common design philosophies in concrete construction can not easily be adapted to this new material. The consistent incorporation of the properties and special features of this new material as well as the demands for sustainability lead to filigree, flexible and modular buildings. Therefore the design philosophy can be classified between concrete and steel constructions. Considering the complete life-cycle costs, such constructions permit economical buildings with an eminent benefit for the national economy. After general consideration, the special properties and the new insights gained are exemplified based on experiences during construction, dimensioning and implementation of three different pilot projects in Austria. [source] Electrocaloric Materials for Solid-State RefrigerationADVANCED MATERIALS, Issue 19 2009Sheng-Guo Lu Abstract The electrocaloric effect (ECE) in dielectric materials has great potential in realizing solid-state cooling devices with compact size and high efficiency, which are highly desirable for a broad range of applications. This paper presents the general considerations for dielectric materials to achieve large ECE and reviews the experimental efforts investigating ECE in various polar dielectrics. For practical cooling devices, an ECE material must possess a large isothermal entropy change besides a large adiabatic temperature change. We show that polar dielectrics operated at temperatures near order,disorder transition have potential to achieve large ECE due to the possibility of large change in polarization induced by electric field and large entropy change associated with the polarization change. We further show that indeed the ferroelectric poly(vinylidene fluoride,trifluoroethylene)-based polymers display a large ECE, i.e., an isothermal entropy change of more than 55,J,(kgK),1 and an adiabatic temperature change of more than 12,°C, at temperatures above the order,disorder transition. [source] Use of proteomics for the identification of novel drug targets in brain diseasesJOURNAL OF NEUROCHEMISTRY, Issue 2 2007Jose A. Morón Abstract In spite of the rapid advances in the development of the new proteomic technologies, there are, to date, relatively fewer studies aiming to explore the neuronal proteome. One of the reasons is the complexity of the brain, which presents high cellular heterogeneity and a unique subcellular compartmentalization. Therefore, tissue fractionation of the brain to enrich proteins of interest will reduce the complexity of the proteomics approach leading to the production of manageable and meaningful results. In this review, general considerations and strategies of proteomics, the advantages and challenges to exploring the neuronal proteome are described and summarized. In addition, this article presents an overview of recent advances of proteomic technologies and shows that proteomics can serve as a valuable tool to globally explore the changes in brain proteome during various disease states. Understanding the molecular basis of brain function will be extremely useful in identifying novel targets for the treatment of brain diseases. [source] The Management of difficult intubation in childrenPEDIATRIC ANESTHESIA, Issue 2009ROBERT W.M. WALKER FRCA Summary This article looks at the current techniques and equipment recommended for the management of the difficult intubation scenario in pediatric practice. We discuss the general considerations including preoperative preparation, the preferred anesthetic technique and the use of both rigid laryngoscopic and fiberoptic techniques for intubation. The unanticipated scenario is also discussed. [source] X-ray diffraction by a crystal in a permanent external electric field: general considerationsACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2005Semen V. Gorfman The variations of X-ray diffraction intensities from a crystal in the presence of a permanent external electric field is modeled analytically using a first-order stationary perturbation theory. The change in a crystal, induced by an external electric field, is separated into two contributions. The first one is related to a pure polarization of an electron subsystem, while the second contribution can be reduced to the displacements of the rigid pseudoatoms from their equilibrium positions. It is shown that a change of the X-ray diffraction intensities mainly originates from the second contribution, while the influence of the pure polarization of a crystal electron subsystem is negligibly small. The quantities restored from an X-ray diffraction experiment in the presence of an external electric field were analyzed in detail in terms of a rigid pseudoatomic model of electron density and harmonic approximation for the atomic thermal motion. Explicit relationships are derived that link the properties of phonon spectra with E -field-induced variations of a structure factor, pseudoatomic displacements and piezoelectric strains. The displacements can be numerically estimated using a model of independent atomic motion if the Debye,Waller factors and pseudoatomic charges are known either from a previous single-crystal X-ray diffraction study or from density functional theory calculations. The above estimations can be used to develop an optimum strategy for a data collection that avoids the measurements of reflections insensitive to the electric-field-induced variations. [source] | |||||||||||||