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921.
Michael E. Ketzenberg Eve D. Rosenzweig Ann E. Marucheck Richard D. Metters 《European Journal of Operational Research》2007
Technological advances and changes in supply chain management practices have combined to draw attention to the value of information sharing in inventory replenishment. Academic research has produced seemingly conflicting results due to differences in the type of information that is shared, the supply chain structure, and the selection and parameterization of performance goals. This research provides a framework to help explain apparent differences in the extant literature. Our purpose is to understand what determines the value of information. With this specific view, we establish a set of research questions and suggest directions for future research. 相似文献
922.
Marco Michele Sisto Sophie LaRochelle Leslie Ann Rusch Philippe Giaccari 《Photonics Technology Letters, IEEE》2007,19(6):408-410
Modulator bias optimization is a technique used to improve the transmitted radio-frequency power of amplified analog optical links. However, when bias optimization is used, the mean optical power at the modulator output is dependent on the amplitude of the modulation signal. In this letter, we show how fluctuations of the modulation signal power, in conjunction with the dynamic behavior of the erbium optical amplifier, can deteriorate the transmission of data frames compliant to the 802.11 a/g IEEE protocol. Optical and electrical compensating methods, based on mean power clamping at the modulator output, are proposed, and their efficiency in restoring a high-quality transmission is demonstrated 相似文献
923.
This paper considers the situation where users that experience high-mobility transmit data over frequency-selective channels, resulting in a doubly selective channel model (i.e., time- and frequency-selective channels) and this within the framework of Known Symbol Padding (KSP) transmission. KSP is a recently proposed block transmission technique where short sequences of known symbols acting as guard bands are inserted between successive blocks of data symbols. This paper proposes three novel channel estimation methods that allow for an accurate estimation of the time-varying transmission channel solely relying on the knowledge of the redundant symbols introduced by the KSP transmission scheme. The first method is a direct adaptive one while the others rely on a recently proposed model, the Basis Expansion Model (BEM), where the doubly selective channel is approximated with high accuracy using a limited number of complex exponentials. An important characteristic of the proposed methods is that they exploit all the received symbols that contain contributions from the training sequences and blindly filter out the contribution of the unknown surrounding data symbols. Besides these channel identification methods, the classical KSP equalizers are adapted to the context of doubly selective channels, which allows evaluation of the bit-error-rate (BER) performance of a KSP transmission system relying on the proposed channel estimation methods in the context of doubly selective channels. Simulation results show that KSP transmission is indeed a suitable transmission technique toward the delivery of high data rates to users experiencing a high mobility, when adapted KSP equalizers are used in combination with the proposed channel estimation methods. 相似文献
924.
925.
The p-hub center problem is to locate p hubs and to allocate non-hub nodes to hub nodes such that the maximum travel time (or distance) between any origin–destination pair is minimized. We address the p-hub center allocation problem, a subproblem of the location problem, where hub locations are given. We present complexity results and IP formulations for several versions of the problem. We establish that some special cases are polynomially solvable. 相似文献
926.
This paper considers how much margin to allow when designing a large pipe network based on predictions of future gas supply and demand. Thus it deals with forecasting from the engineering aspect of how to cope with variations from the predicted pattern of events.The subject of the paper is the British Gas National Transmission System. The detail of the paper concerns some of the margins used to design the system, in particular their purpose, size and application.The methods used to analyse the margins are: simulation, regression, distribution fitting, convolution and risk analysis.The conclusion of the work is that different parts of the network require different sizes of margin to retain the same level of security, since the impact of localized forecasting errors and predicted plant failures varies significantly across the grid. 相似文献
927.
The energy change in the formation of the intramolecular hydrogen-bonded ring conformers of formic, thiolformic and thionformic acids from the chain conformers has been divided up into distortion and bonding energy components, following the treatment of Smit, Derissen, and van Duijneveldt for the formation of the formic acid dimer. 相似文献
928.
S. Hörbäck Ann -Marie Pendrill Leslie Pendrill M. Pettersson 《Zeitschrift für Physik A Hadrons and Nuclei》1984,318(3):285-290
Doppler-free two-photon laser spectroscopic measurements in the deep red spectral region have been performed on the transition 42 S 1/2→42 D J in the naturally abundant isotopes 39 and 41 of atomic potassium. The 4D level isotope shift, ?81±12 MHz was obtained by combining the current results with data from Rydberg-state spectroscopy. Many-body perturbation theoretical calculations of the specific mass shift in the measured state are also presented. With the use of Brueckner orbitals the value ?70 MHz was obtained in substantial agreement with the experimental result. 相似文献
929.
930.
Tzu‐Ann Wang Ming‐Jen Cheng Shiow‐Ju Lee Cheng‐Wei Yang Hsun‐Shuo Chang Ih‐Sheng Chen 《Helvetica chimica acta》2008,91(6):1036-1044
Investigation of the leaves extract of Litsea lii var. nunkao‐tahangensis led to the isolation of five new butanolides, litsealiicolide A ( 1 ), isolitsealiicolide A ( 2 ), litsealiicolide B ( 3 ), isolitsealiicolide B ( 4 ), and isolitsealiicolide C ( 5 ), along with 17 known compounds. Their structures were determined through in‐depth spectroscopic and mass‐spectrometric analyses. Among the isolates, compounds 1 and 2 were cytotoxic against MCF‐7, NCI‐H460, and SF‐268 cell lines in vitro. Compound 5 and isolinderanolide B ( 6 ) showed marginal cytotoxic activity against these three cell lines in vitro. 相似文献