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71.
The results of a numerical study are described in which the interactions of a primary shock wave with a secondary diaphragm
in expansion tubes are taken into account. The developing wave pattern in the interacting process of the shock with a secondary
diaphragm are visualized by many kinds of figures (e.g., the time-distance diagrams of the wave phenomena on the axis, the
acoustic impedance contours, and the time histories of the pitot pressure on the axis), and the influences of the shape and
rupture process of the diaphragm on the quality of the test gas are explored. 相似文献
72.
A T Brint 《The Journal of the Operational Research Society》2003,54(11):1177-1188
The annual turnover of online auctions is already in tens of billions of dollars and this amount is predicted to grow substantially over the next few years. Hence, it is important to know how buyers and sellers can influence their chances of success. Therefore, data were collected from eBay auctions for three different categories of collectible items, namely those with a published guide price, those with a rough guide price and those having no easily obtainable guide price. The options available to buyers and sellers of items were then analysed. It was found that it was hard for the seller to influence an item's achieved price significantly, apart from items with no guide price where the starting price could have an effect. Most bidders bid close to the current value and so there were insufficient data to determine the consequences of timing on the placing of high bids. For low bids, delaying a bid was found to improve significantly the chances of winning for one of the data sets. 相似文献
73.
Chin-Tsang Chiang Mei-Cheng Wang 《Annals of the Institute of Statistical Mathematics》2004,56(1):87-100
This paper proposes kernel estimation of the occurrence rate function for recurrent event data with informative censoring.
An informative censoring model is considered with assumptions made on the joint distribution of the recurrent event process
and the censoring time without modeling the censoring distribution. Under the validity of the informative censoring model,
we also show that an estimator based on the assumption of independent censoring becomes inappropriate and is generally asymptotically
biased. To investigate the asymptotic properties of the proposed estimator, the explicit form of its asymptotic mean squared
risk and the asymptotic normality are derived. Meanwhile, the empirical consistent smoothing estimator for the variance function
of the estimator is suggested. The performance of the estimators are also studied through Monte Carlo simulations. An epidemiological
example of intravenous drug user data is used to show the influence of informative censoring in the estimation of the occurrence
rate functions for inpatient cares over time. 相似文献
74.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
75.
Florin Ambro 《manuscripta mathematica》2003,111(1):43-49
We prove a precise inversion of adjunction formula for the log variety (ℂ
d
+1,X), where X is a non-degenerate hypersurface. As a corollary, the minimal log discrepancies of non-degenerate normal hypersurface singularities
are bounded by dimension.
Received: 17 September 2002 / Revised version: 22 November 2002
Published online: 14 February 2003
Current address: DPMMS, CMS, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, England. e-mail: f.ambro@dpmms.cam.ac.uk
Mathematics Subject Classification (2000): Primary 14B05; Secondary 14M25, 52B20 相似文献
76.
In this paper, we use weighted modules ω(?)(f,t)w to study the pointwise approximation on Szasz-type operators, and obtain the direct and converse theorem, as well as characterizations of the pointwise approximation of Jacobi-weighted Szasz-type operators. 相似文献
77.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
78.
79.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
80.
M C Testik J K Cochran G C Runger 《The Journal of the Operational Research Society》2004,55(3):233-239
We study the short-term staffing problem of systems that experience random, non-stationary demand. The typical method to accommodate changes in arrival rate is to use historical data to identify peak periods and associated forecasting for upcoming time windows. In this paper, we develop a method that instead detects change as it happens. Motivated by an automatic call distributor system in a call centre with time-varying arrivals, we propose a change detection algorithm based upon non-homogeneous Poisson processes. The proposed method is general and may be thought of as a feed-forward strategy, in which we detect a change in the arrival process, estimate the new magnitude of the arrival rate, and assign an appropriate number of servers to the tasks. The generalized likelihood ratio statistic is used and a recommendation for its decision limit is developed. Simulation results are used to evaluate the performance of the detector in the context of a telephone call centre. 相似文献