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Reasonable Description (reasonable + description)
Selected AbstractsEvaluation of drugs in pediatrics using K-PD models: perspectivesFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 6 2008M. Tod Abstract Some pharmacodynamic (PD) models, called K-PD models, have been developed for the description of drug action kinetics in the absence of drug concentration measurements. Because blood samples for drug measurements are not needed, these models may be very useful in pediatric studies, by reducing their invasiveness. In addition, a number of PD measurements are also non-invasive and specific devices exist for measures in children. Therefore, the kinetics of drug action may be characterized with minimal invasiveness. A brief description of the key features of these models is given, and a number of examples of application are presented. K-PD models are expected to be most useful when the drug kinetics is simple (i.e. when the one-compartment model is a reasonable description), or when the response kinetics is slow compared with drug kinetics. K-PD models have already demonstrated their usefulness in animal and adult studies. They are very attractive for pediatric studies and they should facilitate the assessment of drug efficacy and safety. [source] Mean Reversion and the Distribution of United Kingdom Stock Index ReturnsJOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 9-10 2006David Ashton Abstract:, Our purpose here is to develop the Pearson Type IV distribution as a candidate for modelling the evolution of short period stock index returns. Here, early work by Praetz (1972 and 1978) and Blattberg and Gonedes (1974) has shown that the scaled ,t' distribution, which is a particular (symmetric) interpretation of the Pearson Type IV, provides a reasonable description of the way stock index returns evolve over time. Our analysis shows this is certainly not the case for the daily stock index returns on which our empirical analysis is based. There is significant skewness in the data and this cannot be captured by symmetric distributions like the scaled ,t' and normal distributions. However, the Pearson Type IV, which is a skewed generalisation of the scaled ,t', is capable of modelling the skewness inherent in our data and in such a way that it satisfies asymptotically efficient goodness of fit criteria. Furthermore, the Pearson Type IV can be derived from a stochastic differential equation with standard Markov properties. This enables one to integrate the distributional and time series properties of the returns process and thereby, facilitates both the interpretation and understanding of the role played by the distribution's parameters in the generation of the underlying stock index returns. [source] Scaling laws in gravitational clustering for counts-in-cells and mass functionsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000P. Valageas We present an analysis of some of the properties of the density field realized in numerical simulations for power-law initial power spectra in the case of a critical density universe. We study the non-linear regime, which is the most difficult to handle analytically, and we compare our numerical results with the predictions of a specific hierarchical clustering scaling model that have been made recently, focusing specifically on its much wider range of applicability, which is one of its main advantages over the standard Press,Schechter approximation. We first check that the two-point correlation functions, measured from both counts-in-cells and neighbour counts, agree with the known analytically exact scaling requirement (i.e., depend only on ,2), and we also find the stable-clustering hypothesis to hold. Next, we show that the statistics of the counts-in-cells obey the scaling law predicted by the above scaling model. Then we turn to mass functions of overdense and underdense regions, which we obtain numerically from ,spherical overdensity' and ,friends-of-friends' algorithms. We first consider the mass function of ,just-collapsed' objects defined by a density threshold ,=177, and we note, as was found by previous studies, that the usual Press,Schechter prescription agrees reasonably well with the simulations (although there are some discrepancies). On the other hand, the numerical results are also consistent with the predictions of the scaling model. Next, we consider more general mass functions (needed to describe for instance galaxies or Lyman- , absorbers) defined by different density thresholds, which can even be negative. The scaling model is especially suited to account for such cases, which are out of reach of the Press,Schechter approach, and it still shows reasonably good agreement with the numerical results. Finally, we show that mass functions defined by a condition on the radius of the objects also satisfy the theoretical scaling predictions. Thus we find that the scaling model provides a reasonable description of the density field in the highly non-linear regime, for the cosmologies we have considered, for both the counts-in-cells statistics and the mass functions. The advantages of this approach are that it clarifies the links between several statistical tools and it allows one to study many different classes of objects, for any density threshold, provided one is in the fully non-linear regime. [source] Modeling Na clusters in Ar matricesANNALEN DER PHYSIK, Issue 7 2005F. Fehrer Abstract We present a microscopic model for Na clusters embedded in raregas matrices. The valence electrons of the Na cluster are described by time-dependent density-functional theory at the level of the local-density approximation (LDA). Particular attention is paid to the semi-classical picture in terms of Vlasov-LDA. The Na+ ions and Ar atoms are handled as classical particles whereby the Ar atoms carry two degrees of freedom, position and dipole polarization. The interaction between Na+ ions and electrons is mediated through local pseudo-potentials. The coupling to the Ar atoms is described by (long-range) polarization potentials and (short-range) repulsive cores. The ingredients are taken from elsewhere developed standards. A final fine-tuning is performed using the NaAr molecule as benchmark. The model is then applied to embedded systems Na8ArN. By close comparison with quantum-mechanical results, we explore the capability of the Vlasov-LDA to describe such embedded clusters. We show that one can obtain a reasonable description by appropriate adjustments in the fine-tuning phase of the model. [source] | ||||||||||