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Exact Calculation (exact + calculation)
Selected AbstractsCan cocaine use be evaluated through analysis of wastewater?ADDICTION, Issue 5 2009A nation-wide approach conducted in Belgium ABSTRACT Aims Cocaine is the second most-used illicit drug world-wide and its consumption is increasing significantly, especially in western Europe. Until now, the annual prevalence has been estimated indirectly by means of interviews. A recently introduced and direct nation-wide approach based on measurements of the major urinary excreted metabolite of cocaine, benzoylecgonine, in wastewater is proposed. Design Wastewater samples from 41 wastewater treatment plants (WWTPs) in Belgium, covering approximately 3 700 000 residents, were collected. Each WWTP was sampled on Wednesdays and Sundays during two sampling campaigns in 2007,08. Samples were analysed for cocaine (COC) and its metabolites, benzoylecgonine (BE) and ecgonine methylester (EME) by a validated procedure based on liquid chromatography coupled with tandem mass spectrometry. Concentrations of BE were used to calculate cocaine consumption (g/day per 1000 inhabitants) for each WWTP region and for both sampling campaigns (g/year per 1000 inhabitants). Findings Weekend days showed significantly higher cocaine consumption compared with weekdays. The highest cocaine consumption was observed for WWTPs receiving wastewater from large cities, such as Antwerp, Brussels and Charleroi. Results were extrapolated for the total Belgian population and an estimation of a yearly prevalence of cocaine use was made based on various assumptions. An amount of 1.88 tonnes (t) per year [standard error (SE) 0.05 t] cocaine is consumed in Belgium, corresponding to a yearly prevalence of 0.80% (SE 0.02%) for the Belgian population aged 15,64 years. This result is in agreement with an earlier reported estimate of the Belgian prevalence of cocaine use conducted through socio-epidemiological studies (0.9% for people aged 15,64 years). Conclusions Wastewater analysis is a promising tool to evaluate cocaine consumption at both local and national scale. This rapid and direct estimation of the prevalence of cocaine use in Belgium corresponds with socio-epidemiological data. However, the strategy needs to be refined further to allow a more exact calculation of cocaine consumption from concentrations of BE in wastewater. [source] State-space µ analysis for an experimental drive-by-wire vehicleINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 9 2008M. Halton Abstract This paper considers the application of the skewed structured singular value to the robust stability of systems subject to strictly real parametric uncertainty. Three state-space formulations that counteract the discontinuous nature of this problem are detailed. It is shown that the calculation of the supremum of the structured singular value over a frequency range using these formulations transforms into a single skewed structured singular value calculation. Similar to the structured singular value, the exact calculation of the skewed structured singular value is an NP-hard problem. In this work, two efficient algorithms that determine upper and lower bounds on the skewed structured singular value are presented. These algorithms are critically assessed using a series of robustness analysis tests on a safety-critical experimental drive-by-wire vehicle. Copyright © 2008 John Wiley & Sons, Ltd. [source] Novel computer program for fast exact calculation of accessible and molecular surface areas and average surface curvatureJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2002Oleg V. Tsodikov Abstract New computer programs, SurfRace and FastSurf, perform fast calculations of the solvent accessible and molecular (solvent excluded) surface areas of macromolecules. Program SurfRace also calculates the areas of cavities inaccessible from the outside. We introduce the definition of average curvature of molecular surface and calculate average molecular surface curvatures for each atom in a structure. All surface area and curvature calculations are analytic and therefore yield exact values of these quantities. High calculation speed of this software is achieved primarily by avoiding computationally expensive mathematical procedures wherever possible and by efficient handling of surface data structures. The programs are written initially in the language C for PCs running Windows 2000/98/NT, but their code is portable to other platforms with only minor changes in input-output procedures. The algorithm is robust and does not ignore either multiplicity or degeneracy of atomic overlaps. Fast, memory-efficient and robust execution make this software attractive for applications both in computationally expensive energy minimization algorithms, such as docking or molecular dynamics simulations, and in stand-alone surface area and curvature calculations. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 600,609, 2002 [source] Analysis of water solubility data on the basis of HYBOT descriptorsMOLECULAR INFORMATICS, Issue 9-10 2003Part 2. Abstract Solubility data of 787 organic liquids (electrolytes and non-electrolytes) with diverse structures has been quantitatively described by physicochemical property descriptors. Special effects like intra - and intermolecular hydrogen bonds have been shown to be very important for water solubility. It is found that an important part of the solute-solvent interaction is neglected in all correlations of logS with (only) logP, as in this case the solute H-bond donor effect is not considered. As expected intramolecular hydrogen bonds lead to reduced solubility, whereas intermolecular hydrogen bonds (both HB donors and acceptors) of solutes result in higher solubility. An exception to the latter rule are carboxylic acids which due to intermolecular HB-induced dimerization in the pure liquid phase of acids show a three times lower solubility as expected on the basis of their molecular properties. A volume-related term (molecular polarizability ,) was found to have an essential negative contribution to solubility. For the first time the solubility increasing effect of partial ionization of weak acids and bases in saturated aqueous solutions has been quantitatively considered for sets of compounds by exact calculation of the pH determined by the solutes aqueous solubility and pKa value(s). [source] Compatibility factor for the power output of a thermogeneratorPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 6 2007W. Seifert Abstract The compatibility approach introduced by Snyder and Ursell enables the description of both thermoelectric generator (TEG) and Peltier cooler (TEC) within the framework of a unified 1D model. Both TEG's efficiency , and TEC's coefficient of performance (C.O.P.) can be formulated in terms of the reduced current density u, which has been introduced as a new, intensive state variable of a thermoelectric system. For , and C.O.P., integral expressions are formed from additive contributions of all length segments of a thermoelectric ele-ment, enabling exact calculation of these quantities even for arbitrarily graded elements. Maximization of these global performance parameters can thus be deduced to local maximization. Here the maximum power from a TEG with fixed length but variable heat supply is considered, which leads to the new concept of power-related compatibility and to the introduction of a new, different compatibility factor. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dirac particle in a plane wave field and the semi-classical approximationANNALEN DER PHYSIK, Issue 4 2005S. Bourouaine Abstract In this paper we investigate the influence of photon represented by plane wave field on Dirac particle in the context of path integral approach given by Fradkin and Gitman formalism. In our case, although the action relative to Dirac particle in plane wave field seems to be non quadratic, the result obtained by semi-classical approach is the same as that found by an exact calculation. Hence; when we add the plane wave field to any quadratic actions related to Fradkin and Gitman approach, the total action behaves like quadratic. [source] Verformungsvorhersage von vorgespannten und nicht vorgespannten BetonbauteilenBETON- UND STAHLBETONBAU, Issue 6 2009Wolfgang Krüger Prof. Dr.-Ing. habil. Baustoffe; Berechnungs- und Bemessungsverfahren; Spannbeton Abstract Wie vergleichende Untersuchungen zeigen, führt eine Begrenzung der Verformung auf der Grundlage des Schlankheitsnachweises, wie er nach DIN 1045-1 bei Stahlbetonbauteilen möglich ist, nicht immer zu dem gewünschten Erfolg. In diesen Fällen und bei Spannbetonkonstruktionen ist grundsätzlich ein Nachweis der Verformungen erforderlich. Ausgehend von allgemeinen Betrachtungen zum Nachweis der Bauteilverformungen, werden wesentliche materialseitige Einflüsse auf die Verformungsvorhersage diskutiert. Es wird deutlich, dass eine genaue Berechnung der Verformung nur bedingt möglich ist. Im Anschluss wird für die tägliche Berechnungspraxis ein Näherungsansatz zur Vorhersage der Verformung bewehrter Betonbauteile formuliert. Im Rahmen von vergleichenden Betrachtungen wird die Genauigkeit des entwickelten Näherungsansatzes abgeschätzt. Hierbei zeigt sich eine gute baupraktische Übereinstimmung zwischen komplexen Berechnungen und dem vereinfachten Berechnungsansatz. Deformation Forecast of Prestressed and Non-Prestressed Concrete Members Comparative investigations have shown that the limitation of deformation, based on a permitted slenderness ratio as possible according to DIN 1045-1 for reinforced concrete elements, do not always achieve the desired success. An exact calculation of the structure deformation is absolutely necessary for prestressed components and in the case of a non-accomplished slenderness proof for reinforced concrete members. In this paper significant material influences of the deformation forecast will be discussed, proceeding from universal views of the component deformation proof. It will be clear, that an exact deformation calculation is only restricted possible. An approximation procedure for practical use to the forecast of deformations of reinforced and prestressed concrete structures will be formulated, afterwards. The accuracy of this developed approximation procedure will be estimated with the aid of comparative studies. At this, the results of the simplified formulation correlate well with the values of complex, numeric investigations in a range of practical use. [source] Entwurf und überschlägige Berechnung von kreiszylindrischen SchalentragwerkenBETON- UND STAHLBETONBAU, Issue 1 2005Herbert Hotzler Dr.-Ing. Nach einer Definition der Schalen und Faltwerke wird das Tragverhalten kreiszylindrischer Schalentragwerke erläutert. Für eine formtreue Verformung, bei der sich der Querschnitt eines Schalentragwerkes bei lotrechter Belastung nur lotrecht durchbiegt und sich die Normalspannungen ,x über die Querschnittshöhe fast linear wie bei einem Träger verteilen, werden Entwurfshinweise gegeben und einfache Formeln zur Berechnung der Spannungen entwickelt. Hiermit lassen sich PC-Berechnungen nach der FE-Methode einschätzen und überprüfen. Auf die Sonderfälle Temperatur, halbseitige Belastung und Einzellasten wird eingegangen und das Beulen ausführlich erläutert. Die Näherungsberechnung wird an einem Beispiel gezeigt und mit den Ergebnissen einer genauen Berechnung verglichen. Design and Approximate Calculation of Circular Cylindrical Shell Structures At first a definition of shells and folded plates is given. Then the supporting behaviour of circular cylindrical shell-structures is demonstrated. Design advices and simple formulas are given for a so-called unchangeable deformation of the cross-section on which the cross-section deforms only vertically due to vertically loadings and on which the normal stresses ,x are nearly linearely distributed over the high of the cross-section. PC-calculations with FE-methods can be estimated and tested by the given simple formulas. Special cases like temperature, half-side loadings and pointloadings are discussed. The buckling is explained in details. An example of an approximate calculation is demonstrated and the results are compared with an exact calculation. [source] Fisher Information Matrix of the Dirichlet-multinomial DistributionBIOMETRICAL JOURNAL, Issue 2 2005Sudhir R. Paul Abstract In this paper we derive explicit expressions for the elements of the exact Fisher information matrix of the Dirichlet-multinomial distribution. We show that exact calculation is based on the beta-binomial probability function rather than that of the Dirichlet-multinomial and this makes the exact calculation quite easy. The exact results are expected to be useful for the calculation of standard errors of the maximum likelihood estimates of the beta-binomial parameters and those of the Dirichlet-multinomial parameters for data that arise in practice in toxicology and other similar fields. Standard errors of the maximum likelihood estimates of the beta-binomial parameters and those of the Dirichlet-multinomial parameters, based on the exact and the asymptotic Fisher information matrix based on the Dirichlet distribution, are obtained for a set of data from Haseman and Soares (1976), a dataset from Mosimann (1962) and a more recent dataset from Chen, Kodell, Howe and Gaylor (1991). There is substantial difference between the standard errors of the estimates based on the exact Fisher information matrix and those based on the asymptotic Fisher information matrix. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] From linear to non-linear scales: analytical and numerical predictions for weak-lensing convergenceMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Andrew J. Barber ABSTRACT Weak-lensing convergence can be used directly to map and probe the dark-mass distribution in the Universe. Building on earlier studies, we recall how the statistics of the convergence field are related to the statistics of the underlying mass distribution, in particular to the many-body density correlations. We describe two model-independent approximations which provide two simple methods to compute the probability distribution function (pdf) of the convergence. We apply one of these to the case where the density field can be described by a lognormal pdf. Next, we discuss two hierarchical models for the high-order correlations which allow us to perform exact calculations and evaluate the previous approximations in such specific cases. Finally, we apply these methods to a very simple model for the evolution of the density field from linear to highly non-linear scales. Comparisons with the results obtained from numerical simulations, obtained from a number of different realizations, show excellent agreement with our theoretical predictions. We have probed various angular scales in the numerical work and considered sources at 14 different redshifts in each of two different cosmological scenarios, an open cosmology and a flat cosmology with non-zero cosmological constant. Our simulation technique employs computations of the full three-dimensional shear matrices along the line of sight from the source redshift to the observer and is complementary to more popular ray-tracing algorithms. Our results therefore provide a valuable cross-check for such complementary simulation techniques, as well as for our simple analytical model, from the linear to the highly non-linear regime. [source] Spherical quantum dot under an electric fieldPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2004Gerardo J. Vázquez Abstract We investigate the effect of an electric field applied to a spherical quantum dot on the energy groundstate of carriers in the quantum dot using an infinite confining potential well model. We perform a simple variational calculation for low electric fields and we find a quadratic shift of the energy levels with the electric field while for strong fields, the Stark shift of the energy groundstate increases almost linearly with the electric field. There is a transition for quasi-one dimensional to three-dimensional behavior when the dot radius is large. The comparison of our results with previous exact calculations is very good. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||