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Path Method (path + method)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

A critical path method for the estimation of service restoration time in power distribution systems

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 4 2008
C. Lakshminarayana
Abstract Distribution systems (DSs) are invariably subjected to various types of faults, causing power blackouts to occur. Distribution Engineers have the main responsibility to minimizing the duration of these power blackouts. This minimization can be achieved by the detailed study of pre-fault load condition of the DS, isolating the faulted section, and restoring the supply to healthy sections of the DS. Hence the estimation of service restoration time (SRT) is very important in electrical distribution systems (EDS). The estimation of SRT requires detailed knowledge of the commencement time of the emergency diesel generator (EDG) in EDS and also the operating time of the various relays in EDS. This paper introduces a new concept of optimistic time (OT), pessimistic time (PT), and most likely time (MT) of starting of the EDGs in addition to the OT, PT, and MT of the operation of the relays. The proposed concept is tested on 14-bus, 17-bus, and 29-bus distribution networks. The results reveal that it is highly suitable technique for the estimation of SRT under abnormal conditions. Hence this technique can easily be improved in distribution automation/service restoration algorithms. Copyright © 2007 John Wiley & Sons, Ltd. [source]

2-D/3-D multiply transmitted, converted and reflected arrivals in complex layered media with the modified shortest path method

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009
Chao-Ying Bai
SUMMARY Grid-cell based schemes for tracing seismic arrivals, such as the finite difference eikonal equation solver or the shortest path method (SPM), are conventionally confined to locating first arrivals only. However, later arrivals are numerous and sometimes of greater amplitude than the first arrivals, making them valuable information, with the potential to be used for precise earthquake location, high-resolution seismic tomography, real-time automatic onset picking and identification of multiple events on seismic exploration data. The purpose of this study is to introduce a modified SPM (MSPM) for tracking multiple arrivals comprising any kind of combination of transmissions, conversions and reflections in complex 2-D/3-D layered media. A practical approach known as the multistage scheme is incorporated into the MSPM to propagate seismic wave fronts from one interface (or subsurface structure for 3-D application) to the next. By treating each layer that the wave front enters as an independent computational domain, one obtains a transmitted and/or converted branch of later arrivals by reinitializing it in the adjacent layer, and a reflected and/or converted branch of later arrivals by reinitializing it in the incident layer. A simple local grid refinement scheme at the layer interface is used to maintain the same accuracy as in the one-stage MSPM application in tracing first arrivals. Benchmark tests against the multistage fast marching method are undertaken to assess the solution accuracy and the computational efficiency. Several examples are presented that demonstrate the viability of the multistage MSPM in highly complex layered media. Even in the presence of velocity variations, such as the Marmousi model, or interfaces exhibiting a relatively high curvature, later arrivals composed of any combination of the transmitted, converted and reflected events are tracked accurately. This is because the multistage MSPM retains the desirable properties of a single-stage MSPM: high computational efficiency and a high accuracy compared with the multistage FMM scheme. [source]

Exhaustive Structure Generation for Inverse-QSPR/QSAR

MOLECULAR INFORMATICS, Issue 1-2 2010
Tomoyuki Miyao
Abstract Chemical structure generation based on quantitative structure property relationship (QSPR) or quantitative structure activity relationship (QSAR) models is one of the central themes in the field of computer-aided molecular design. The objective of structure generation is to find promising molecules, which according to statistical models, are considered to have desired properties. In this paper, a new method is proposed for the exhaustive generation of chemical structures based on inverse-QSPR/QSAR. In this method, QSPR/QSAR models are constructed by multiple linear regression method, and then the conditional distribution of explanatory variables given the desired properties is estimated by inverse analysis of the models using the framework of a linear Gaussian model. Finally, chemical structures are exhaustively generated by a sophisticated algorithm that is based on a canonical construction path method. The usefulness of the proposed method is demonstrated using a dataset of the boiling points of acyclic hydrocarbons containing up to 12 carbon atoms. The QSPR model was constructed with 600 hydrocarbons and their boiling points. Using the proposed method, chemical structures which had boiling points of 100, 150, or 200,°C were exhaustively generated. [source]

Conformational Structure and Energetics of 2-Methylphenyl(2,-methoxyphenyl)iodonium Chloride: Evidence for Solution Clusters

CHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010
Dr. Yong-Sok Lee
Abstract Diaryliodonium salts allow the efficient incorporation of cyclotron-produced [18F]fluoride ions into electron-rich and electron-deficient arenes to provide potential radiotracers for molecular imaging in vivo with positron emission tomography (PET). This process (ArI+Ar,+18F,,Ar18F+Ar,I) is still not well understood mechanistically. To better understand this and similar reactions, it would be valuable to understand the structures of diaryliodonium salts in organic media, where the reactions are typically conducted. In this endeavor, the X-ray structure of a representative iodonium salt, 2-methylphenyl(2,-methoxyphenyl)iodonium chloride (1), was determined. Our X-ray structure analysis showed 1 to have the conformational M,P dimer as the unit cell with hypervalent iodine as a stereogenic center in each conformer. With the ab initio replica path method we constructed the inversion path between the two enantiomers of 1, thereby revealing two additional pairs of enantiomers that are likely to undergo fast interconversion in solution. Also LC,MS of 1 showed the presence of dimeric and tetrameric anion-bridged clusters in weak organic solution. This observation is consistent with the energetics of 1, both as monomeric and dimeric forms in MeCN, calculated at the B3LYP/DGDZVP level. These evidences of the existence of dimeric and higher order clusters of 1 in solution are relevant to achieve a deeper general understanding of the mechanism and outcome of reactions of diaryliodonium salts in organic media with nucleophiles, such as the [18F]fluoride ion. [source]