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Differential Approach (differential + approach)

Distribution by Scientific Domains

Chemistry	42%

Selected Abstracts

Exact Fixed-node Quantum Monte Carlo: Differential Approach

CHINESE JOURNAL OF CHEMISTRY, Issue 11 2005
Hong-Xin Huang
Abstract A differential approach for exact fixed-node quantum Monte Carlo calculation was proposed in this paper. This new algorithm can be used to directly compute the energy differential between two systems in exact fixed-node quantum Monte Carlo process, making the statistical error of calculation reduce to order of 10,2 kJ/mol and recover about more than 90% of the correlation energy. The approach was employed to set up a potential energy surface of a molecule, through a model of rigid move, and Jacobi transformation utilized to make energy calculation for two configurations of a molecule having good positive correlation. So, an accurate energy differential could be obtained, and the potential energy surface with good quality depicted. This novel algorithm was used to study the potential energy curve of the ground state of BH and the potential energy surface of H3, and could be also applied to study other related fields such as molecular spectroscopy and the energy variation of chemical reactions. [source]

The graviton propagator with a non-conserved external generating source

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 11-12 2007
E.B. Manoukian
Abstract A novel general expression is obtained for the graviton propagator from Lagrangian field theory by taking into account the necessary fact that in the functional differential approach of quantum field theory, in order to generate non-linearities in gravitation and interactions with matter, the external source T,,, coupled to the gravitational field, should a priori not be conserved ,,T,,, 0, so variations with respect to its ten components may be varied independently. The resulting propagator is the one which arises in the functional approach and does not coincide with the corresponding time-ordered product of two fields and it includes so-called Schwinger terms. The quantization is carried out in a gauge corresponding to physical states with two polarization states to ensure positivity in quantum applications. [source]

An extension of the differential approach for Bayesian network inference to dynamic Bayesian networks

INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 8 2004
Boris Brandherm
We extend Darwiche's differential approach to inference in Bayesian networks (BNs) to handle specific problems that arise in the context of dynamic Bayesian networks (DBNs). We first summarize Darwiche's approach for BNs, which involves the representation of a BN in terms of a multivariate polynomial. We then show how procedures for the computation of corresponding polynomials for DBNs can be derived. These procedures permit not only an exact roll-up of old time slices but also a constant-space evaluation of DBNs. The method is applicable to both forward and backward propagation, and it does not presuppose that each time slice of the DBN has the same structure. It is compatible with approximative methods for roll-up and evaluation of DBNs. Finally, we discuss further ways of improving efficiency, referring as an example to a mobile system in which the computation is distributed over a normal workstation and a resource-limited mobile device. © 2004 Wiley Periodicals, Inc. Int J Int Syst 19: 727,748, 2004. [source]

On-Line HPLC-UV-mass spectrometry and tandem mass spectrometry for the rapid delineation and characterization of differences in complex mixtures: a case study using toxic oil variants

BIOMEDICAL CHROMATOGRAPHY, Issue 5 2002
Frank W. Crow
An integrated differential approach to the characterization of complex mixtures is presented which includes the targeting of liquid chromatography (LC) peaks for identification using characteristic UV adsorption of the LC peak, subsequent molecular weight and formula determination using accurate mass LC mass spectrometry (MS), and structure characterization using accurate mass LC-tandem mass spectrometry. The use of differential UV adsorption aids in narrowing the scope of the study to only specific peaks of interest. Accurate mass measurement of the molecular ion species provides molecular weight information as well as atomic composition information. The tandem MS (MS/MS) spectra provide fragmentation information which allows for structural characterization of each component. Accurate mass assignment of each of the fragment ions in the MS/MS spectrum provides atomic composition for each of the fragment ions and thus further aids in the structural characterization. These experiments are facilitated through the use of on-line LC-MS and LC-MS/MS with in-line UV detection. A synthetic toxic oil (STO) related to Toxic Oil Syndrome is studied with a focus on possible contaminants resulting from the interaction of aniline, used as a denaturant, with the normal components of the oil. A differential analysis between the STO and a control oil is performed. LC peaks were targeted using UV absorbance to indicate the possible presence of the aniline moiety. Further differential analysis was performed through the determination of the MS signals associated with each component separated on the LC. Finally, the MS/MS data was also used to determine if the fragmentation of the targeted components indicated the presence of aniline. The MS/MS and accurate mass data were used to assign the structures for the targeted components. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Validation of a differential in situ perfusion method with mesenteric blood sampling in rats for intestinal drug interaction profiling

BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 5-6 2010
Joachim Brouwers
Abstract The present study explored the feasibility of a differential setup for the in situ perfusion technique with mesenteric cannulation in rats to assess drug interactions at the level of intestinal absorption. In contrast to the classic, parallel in situ perfusion setup, the differential approach aims to identify intestinal drug interactions in individual animals by exposing the perfused segment to a sequence of multiple conditions. First, the setup was validated by assessing the interaction between the P-glycoprotein (P-gp) inhibitor verapamil and the transport probes atenolol (paracellular transport), propranolol (transcellular) and talinolol (P-gp mediated efflux). While transport of atenolol and propranolol remained constant for the total perfusion time (2,h), a verapamil-induced increase in talinolol transport was observed within individual rats (between 3.2- and 5.2-fold). In comparison with the parallel setup, the differential in situ perfusion approach enhances the power to detect drug interactions with compounds that exhibit strong subject-dependent permeability. This was demonstrated by identifying an interaction between amprenavir and ketoconazole (P-gp and CYP3A inhibitor) in five out of seven rats (permeability increase between 1.9- and 4.2-fold), despite high inter-individual differences in intrinsic permeability for amprenavir. In combination with an increased throughput (up to 300%) and a reduced animal use (up to 50%), the enhanced power of the differential approach improves the utility of the biorelevant in situ perfusion technique with mesenteric blood sampling to elucidate the intestinal interaction profile of drugs and drug candidates. Copyright © 2010 John Wiley & Sons, Ltd. [source]