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This paper analyzes the synchronization process of an assembly-like queueing system in which two distinct types of items/customers arrive at separate buffers, according to independent Poisson processes, so as to be synchronized into pairs at a synchronization node. Once a pair is synchronized it then queues up for service from a single server on a first-in-first-out basis as pairs. It is assumed that the service times of pairs are exponentially distributed and that the system has infinite capacity. Despite their practical significance, such queueing systems have not been adequately treated in the literature due to their transience or null recurrence. We first investigate the transient and asymptotic properties of the synchronization process’ first two moments, both analytically and numerically. Motivated by the observed asymptotic behavior, we then propose an M/M/1 approximation to describe the behavior of such assembly-like queueing systems. Finally, a numerical study of the proposed approximation reveals that it performs sufficiently well for practical applications.  相似文献   
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A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.  相似文献   
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A stabilized finite element method, to carry out the linear stability analysis of a two‐dimensional base flow to three‐dimensional perturbations that are periodic along span, is presented. The resulting equations for the time evolution of the disturbance requires a solution to the generalized eigenvalue problem. The analysis is global in nature and is also applicable to non‐parallel flows. Equal‐order‐interpolation functions for velocity and pressure are utilized. Stabilization terms are added to the Galerkin formulation to admit the use of equal‐order‐interpolation functions and to eliminate node‐to‐node oscillations that might arise in advection‐dominated flows. The proposed formulation is tested on two flow problems. First, the mode transitions in the circular Couette flow are investigated. Two scenarios are considered. In the first one, the outer cylinder is at rest, while the inner one spins. Two linearly unstable modes are identified. The primary mode is real and represents the axisymmetric Taylor vortices. The second mode is complex and consists of spiral vortices. For the counter‐rotating cylinders, the primary transition is via the appearance of spiral vortices. Excellent agreement with results from earlier studies is observed. The formulation is also utilized to investigate the parallel and oblique modes of vortex shedding past a cylinder for the Re = 100 flow. It is found that the flow is associated with a large number of unstable oblique shedding modes. The parallel mode of vortex shedding is a special case of this family of modes and is associated with the largest growth rate. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
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Hybrid organic-inorganic composites were prepared by precipitating silica into hydroxypolybenzoxazole (HPBO) and sulfopolybenzobisthiazole (SPBT) polymers, with interfacial bonding between the phases improved by use of isocyanatopropyltriethoxy silane and N, N-diethylaminopropyltrimethoxy silane, respectively. The materials were transparent, and scanning electron micrographs indicated a uniform distribution of silica particles of domain sizes less than 1 m. Values of the tensile modulus and tensile strength of the HPBO-silica composites were found to increase with the silica content. Values of the modulus of the SPBT-silica composites also increased in this manner, but the improvements in tensile strength were nearly independent of the amount of silica. The composites exhibited thermal decomposition temperatures of approximately 400–500°C, and the thermal stability was significantly increased for both HPBO and SPBT materials with increase in silica content. The water absorption amount for both types of composites decreased significantly compared to that of the pure polymers, suggesting excellent weatherability.  相似文献   
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The interaction of hen egg white lysozyme (HEWL) with Na- and Cs-exchanged saponite was investigated using sorption, structural, and spectroscopic methods as a model system to study clay-protein interactions. HEWL sorption to Na- and Cs-saponite was determined using the bicinchoninic acid (BCA) assay, thermogravimetric analysis, and C and N analysis. For Na-saponite, the TGA and elemental analysis-derived sorption maximum was 600 mg/g corresponding to a surface coverage of 0.85 ng/mm(2) with HEWL occupying 526 m(2)/g based on a cross-sectional area of 13.5 nm(2)/molecule. HEWL sorption on Na-saponite was accompanied by the release of 9.5 Na(+) ions for every molecule of HEWL sorbed consistent with an ion exchange mechanism between the positively charged HEWL (IEP 11) and the negatively charged saponite surface. The d-spacing of the HEWL-Na-saponite complex increased to a value of 4.4 nm consistent with the crystallographic dimensions of HEWL of 3 × 3 × 4.5 nm. In the case of Cs-saponite, there was no evidence of interlayer sorption; however, sorption of HEWL to the "external" surface of Cs-saponite showed a high affinity isotherm. FTIR and Raman analysis of the amide I region of the HEWL-saponite films prepared from water and D(2)O showed little perturbation to the secondary structure of the protein. The overall hydrophilic nature of the HEWL-Na-saponite complex was determined by water vapor sorption measurements. The clay retained its hydrophilic character with a water content of 18% at high humidity corresponding to 240 H(2)O molecules per molecule of HEWL.  相似文献   
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This paper proposes data envelopment analysis (DEA) as a quick-and-easy tool for assessing corporate bankruptcy. DEA is a non-parametric method that measures weight estimates (not parameter estimates) of a classification function for separating default and non-default firms. Using a recent sample of large corporate failures in the United States, we examine the capability of DEA in assessing corporate bankruptcy by comparing it with logistic regression (LR). We find that DEA outperforms LR in evaluating bankruptcy out-of-sample. This feature of DEA is appealing and has practical relevance for investors. Another advantage of DEA over LR is that it does not have assumptions associated with statistical and econometric methods. Furthermore, DEA does not need a large sample size for bankruptcy evaluation, usually required by such statistical and econometric approaches. The need for such a large sample size is a significant disadvantage to practitioners when investment decisions are made using small samples. DEA can bypass such a difficulty related to a sample size. Thus, DEA is a practically appealing method for bankruptcy assessment.  相似文献   
9.
GS Agarwal 《Pramana》1984,22(3-4):303-312
Nonlinear oscillator models are constructed to treat the bistability in situations involving elementary excitations in solids. Such models are shown to be useful not only in describing single photon but also multiphoton bistability. The resulting bistability both with and without cavity is considered. The two-photon excitonic bistability in CuCl is in detail. The effect of local field corrections can also be incorporated, in a simple manner, in such models.  相似文献   
10.
We applied high-temporal-resolution optical imaging utilizing both the fast intrinsic optical signal (fIOS) and voltage-sensitive dyes (VSDs) to observe the spatiotemporal characteristics of rat somatosensory cortex during electrical stimulation. We find that changes in both the fIOS and VSD signals occur rapidly (<30 ms) after the stimulus is applied, suggesting that both membrane depolarization and transmembrane ion movement occur shortly after the stimulus, preceding the more gradual physiological changes in oxygen consumption revealed by the slower component of the intrinsic optical signal. We find that the VSD signal spreads through a much larger area of cortex than the fIOS.  相似文献   
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