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31.
This paper considers polling systems with an autonomous server that remains at a queue for an exponential amount of time before
moving to a next queue incurring a generally distributed switch-over time. The server remains at a queue until the exponential
visit time expires, also when the queue becomes empty. If the queue is not empty when the visit time expires, service is preempted
upon server departure, and repeated when the server returns to the queue. The paper first presents a necessary and sufficient
condition for stability, and subsequently analyzes the joint queue-length distribution via an embedded Markov chain approach.
As the autonomous exponential visit times may seem to result in a system that closely resembles a system of independent queues,
we explicitly investigate the approximation of our system via a system of independent vacation queues. This approximation
is accurate for short visit times only.
相似文献
32.
Ahmad Al Hanbali Roland de Haan Richard J. Boucherie Jan-Kees van Ommeren 《Annals of Operations Research》2012,198(1):57-82
In this paper, we develop a general framework to analyze polling systems with either the autonomous-server or the time-limited service discipline. According to the autonomous-server discipline, the server continues servicing a queue for a certain period of time. According to the time-limited service discipline, the server continues servicing a queue for a certain period of time or until the queue becomes empty, whichever occurs first. We consider Poisson batch arrivals and phase-type service times. It is known that these disciplines do not satisfy the well-known branching property in polling systems. Therefore, hardly any exact results exist in the literature. Our strategy is to apply an iterative scheme that is based on relating in closed-form the joint queue-lengths at the beginning and the end of a server visit to a queue. These kernel relations are derived using the theory of absorbing Markov chains. 相似文献
33.
Laboratory studies are described that suggest reactive uptake of glyoxal on particulate containing HNO(3) could contribute to the formation of secondary organic aerosol (SOA) in the upper troposphere (UT). Using a Knudsen cell flow reactor, glyoxal is observed to react on supercooled H(2)O/HNO(3) surfaces to form condensed-phase glyoxylic acid. This product was verified by derivatization and GC-MS analysis. The reactive uptake coefficient, γ, of glyoxal varies only slightly with the pressure of nitric acid, from γ = 0.5 to 3.0 × 10(-3) for nitric acid pressures between 10(-8) and 10(-6) Torr. The data do not show any dependence on temperature (181-201 K) or pressure of glyoxal (10(-7) to 10(-5) Torr). Using the determined reactive uptake kinetics in a simple model shows that glyoxal uptake to supercooled H(2)O/HNO(3) may account for 4-53% of the total organic mass fraction of aerosol in the UT. 相似文献
34.
Jennifer C. Rea G. Tony Moreno Lisa Vampola Yun Lou Bjorn van Haan Guillaume Tremintin Laura Simmons Adrian Nava Yajun Jennifer Wang Dell Farnan 《Journal of chromatography. A》2012
Size exclusion chromatography (SEC) is widely used in the characterization and quality control of therapeutic proteins to detect aggregates. Aggregation is a carefully monitored quality attribute from the earliest stages of clinical development owing to the possibility of eliciting an immunogenic response in the patient. During early stage molecule assessment for cell culture production, small-scale screening experiments are performed to permit rapid turn-around of results so as to not delay timelines. We report the development of a capillary SEC methodology for preliminary molecule assessment to support the evaluation of therapeutic candidates at an early stage of development. By making several key modifications to a commercially available liquid chromatography system, we demonstrate a platform process to perform capillary SEC with excellent precision, picogram sensitivity and good ruggedness. The limit of quantitation was determined to be approximately 15 pg; picogram sensitivity for SEC analysis of monoclonal antibodies had not been achieved prior to this work. In addition, we have developed a method to capture low levels of antibody (1 μg/mL) from harvested cell culture fluid (HCCF) for capillary SEC analysis. Up to 40% recovery efficiency was achieved using this micro-recovery method on 3 mL HCCF samples. Using early stage cell culture transient transfection samples, which typically have much lower titers than stable cell line samples, we demonstrate a consistent method for analyzing aggregates in low protein concentration HCCF samples for molecule assessment and early stage candidate screening. 相似文献
35.
J.A. Koch N. Izumi L.A. Welser R.C. Mancini S.W. Haan R.W. Lee P.A. Amendt T.W. Barbee Jr. S. Dalhed K. Fujita I.E. Golovkin L. Klein O.L. Landen F.J. Marshall D.D. Meyerhofer H. Nishimura Y. Ochi S. Regan T.C. Sangster V. Smalyuk R. Tommasini 《High Energy Density Physics》2008,4(1-2):1-17
We have measured time-integrated and time-gated electron temperature (Te) and density (Ne) spatial profiles from indirect-drive implosions. In our experiments, we used a multiple-pinhole two-dimensional imaging spectrometer to obtain multispectral X-ray images of the imploded core. Quantitative comparisons between quasi-monochromatic images in different energy bands allowed Te and Ne spatial profiles to be determined using two independent and validated techniques: a multi-objective search and reconstruction analysis, and an analytical analysis. We then compared the results to a simple one-dimensional (1D) mix-free hydrodynamics simulation in order to evaluate the ability of such a model to predict our experiments. Our data show spatial Te profiles that are qualitatively consistent with the predictions of our 1D simulations, but we observe central cores that are 10–25% cooler and emit X-rays as late as 200 ps after peak compression. We infer time-gated spatial Ne profiles that are consistent with our 1D simulations near the times of peak compression, but we find significant disagreement between time-integrated data and 1D simulation predictions at large radii. Careful analysis of the time-gated and time-integrated Te and Ne spatial profiles, together with streaked X-ray emission spectra from core and shell dopants, suggests mixing of shell material into the core is an important process that our 1D hydrodynamics simulations fail to capture, and comparison between image data and a simple analytical model suggests that 2–5 μm of the initial inner shell thickness mixes into the core during the time period of significant X-ray emission. This mix width is consistent with the predictions of a growth-factor analysis that treats instability growth seeded by capsule surface roughness, and points to the need to consider time-dependent mixing effects when interpreting Te and Ne spatial profiles derived from multispectral X-ray image data, particularly at large radii where mixing effects will be most significant. 相似文献
36.
Exact rates are derived for the uniform convergence of the density of intermediate order statistics towards the normal or lognormal density under certain smoothness conditions. Our methods also give the exact rate of convergence in the uniform metric and in the total variation metric. 相似文献
37.
Summary We consider the class of stationary stochastic processes whose margins are jointly min-stable. We show how the scalar elements can be generated by a single realization of a standard homogeneous Poisson process on the upper half-strip [0,1]×R
+ and a group of L
1-isometries. We include a Dobrushin-like result for the realizations in continuous time. 相似文献
38.
A general form for regular variation in IR2 is introduced and applied to domains of attraction of stable distribution in IR2 where the components have different indices. The situation in IRd with d > 2 is more complicated but not essentially different. For simplicity this paper is limited to IR2. 相似文献
39.
M. van Kooten S. de Haan J.C. Lodder A. Lyberatos R.W. Chantrell J.J. Miles 《Journal of magnetism and magnetic materials》1993,120(1-3):145-148
Micromagnetic simulations of the magnetization reversal of clusters of 9 and 25 magnetostatically coupled Co-Cr particles are presented. The magnetostatic interaction between neighbouring particles facilitates reversal. The non-uniform magnetization configuration plays an important role in this effect. 相似文献
40.