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61.
An experiment on program development 总被引:1,自引:0,他引:1
Peter Naur 《BIT Numerical Mathematics》1972,12(3):347-365
As a contribution to programming methodology, the paper contains a detailed, step-by-step account of the considerations leading to a program for solving the 8-queens problem. The experience is related to the method of stepwise refinement and to general problem solving techniques. 相似文献
62.
The Bootstrap Methodology in Statistics of Extremes—Choice of the Optimal Sample Fraction 总被引:2,自引:0,他引:2
The main objective of statistics of extremes is the prediction of rare events, and its primary problem has been the estimation of the tail index , usually performed on the basis of the largest k order statistics in the sample or on the excesses over a high level u. The question that has been often addressed in practical applications of extreme value theory is the choice of either k or u, and an adaptive estimation of . We shall be here mainly interested in the use of the bootstrap methodology to estimate adaptively, and although the methods provided may be applied, with adequate modifications, to the general domain of attraction of G, , we shall here illustrate the methods for heavy right tails, i.e. for > 0. Special relevance will be given to the use of an auxiliary statistic that is merely the difference of two estimators with the same functional form as the estimator under study, computed at two different levels. We shall also compare, through Monte Carlo simulation, these bootstrap methodologies with other data-driven choices of the optimal sample fraction available in the literature. 相似文献
63.
We consider a production system with finite buffers and arbitrary topology where service time is subject to interruptions in one of three ways, viz. machine breakdown, machine vacations or Npolicy. We develop a unified approximation (analytical) methodology to calculate the throughput of the system using queueing networks together with decomposition, isolation and expansion techniques. The methodology is rigorously tested covering a large experimental region. Orthogonal arrays are used to design the experiments in order to keep the number of experiments manageable. The results obtained using the approximation methodology are compared to the simulation results. The ttests carried out to investigate the differences between the two results show that they are statistically insignificant. Finally, we test the methodology by applying it to several arbitrary topology networks. The results show that the performance of the approximation methodology is consistent, robust and produces excellent results in a variety of experimental conditions. 相似文献
64.
Nishant N. Patel K. B. Joshi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):19-23
Using empirical pseudopotential method Γ-L crossover is found for
the Ga0.74Al0.26Sb. The conduction band minimum is observed to
switch at the (0.87, 0, 0) point for Ga0.51Al0.49Sb which shifts to
the X point for Ga0.21Al0.79Sb and remains at X leading finally to
indirect band gap in AlSb. Band structure calculations for a large number of
alloys are performed and bowing parameters bX and bL are proposed
for the EX and EL respectively. Our findings may serve as
directive to select the materials in a range of composition to examine the
bowing parameters and thereby effective mass experimentally for the
GaxAl1-xSb alloys. 相似文献
66.
Davide Baccherini 《Discrete Mathematics》2008,308(18):4165-4176
We study some combinatorial properties of Tetris-like games by using Schützenberger methodology and probability generating functions. We prove that every Tetris-like game is equivalent to a finite state automaton and propose a straight foward algorithm to transform a Tetris-like game into its corresponding automaton. In this way, we can study the average number of pieces inserted during a game and the average score as a function of the player's ability and the pieces extrusion. 相似文献
67.
Bennis and O’Toole [Bennis, W.G., O’Toole, J., 2005. How business schools lost their way. Harvard Business Review 83, 96–104] have recently argued that decision makers need guidance in ‘making decisions in the absence of clear facts’. As such, decision makers must be able to resourcefully use whatever limited information is available and advantageously portray its implications. Based on recently published theory which directly addresses this requirement, this paper demonstrates, through a practical example, how decision makers can make systemic decisions in situations characterized by extremely limited information and, furthermore, what form such decisions can take. Evidence is provided, therefore, that operational research can effectively address what appears to be a gap in management training. 相似文献
68.
V. P. Godambe 《Annals of the Institute of Statistical Mathematics》1999,51(2):201-215
In non-Bayesian statistics, it is often realistic to replace a full distributional assumption by a much weaker assumption about its first few moments; such as for instance, mean and variance. Along the same lines in Bayesian statistics one may wish to replace a completely specified prior distribution by an assumption about just a few moments of the distribution. To deal with such Bayesian semi-parametric models defined only by a few moments, Hartigan (1969, J. Roy. Statist. Soc. Ser. B, 31, 440-454) put forward linear Bayes methodology. By now it has become a standard tool in Bayesian analysis. In this paper we formulate an alternative methodology based on the theory of optimum estimating functions. This alternative methodology is shown to be more readily applicable and efficient in common problems, than the linear Bayes methodology mentioned above. 相似文献
69.
A. Alsaad A. Ahmad 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):151-156
First-principles calculations are performed to compute the e33
piezoelectric coefficients of GaN, ScN and (ScxGa1-xN) alloys
exhibiting an alternation of hexagonal GaN, with hexagonal ScN along the c-axis. For Sc compositions larger than 50%, each atom has nearly five nearest
neighbors (i.e., the ground state exhibits a phase that is five-fold
coordinated). On the other hand, Sc-deficient (Sc, Ga) N alloys adopt a
ground-state that is four-fold coordinated). The magnitude of e33 in
the Sc-deficient ideally ordered (Sc0.25Ga0.75N) is found to be larger
than the magnitude of the corresponding e33 coefficients resulting from
the compositional weighted average over the hexagonal (h-ScN) and the wurtzite (w-GaN) parent compounds. On the other hand, the e33 coefficients of the Sc-rich
ordered (Sc0.75Ga0.25N) is found to be negligibly small. In addition, e33
piezoelectric coefficients in ordered (Sc0.5Ga0.5N) exhibit quite
large magnitudes, due to the nonpolar to polar transition occurs at Sc composition x = 0.5, and thus can bridge the corresponding coefficients of (Ga, In) N and
ferroelectric alloys. The microscopic origins for this huge enhancement in
the piezoelectric behavior in Sc-low and Sc-intermediate alloys and the role
of each atom are revealed and discussed. 相似文献
70.
Recently, efficient extraction of natural products from traditional Chinese medicines (TCMs) by green solvents is deemed an essential area of green technology and attracts extensive attentions. In this work, a green protocol for simultaneous ultrasonic-extraction of the native compounds with different polarities of TCMs by using a hybrid ionic liquids (HILs)-water system was reported for the first time. As a case study, three superior ILs (1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), and 1-allyl-3-methylimidazolium chloride ([AMIM]Cl)) were chosen as the compositions of the HILs system, and the TCMs Suhuang antitussive capsule (SH) containing different-polarity lignans was selected. Primarily, an ultra-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS) method in the multiple reaction monitoring (MRM) mode was established for qualitative and quantitative analysis of 18 lignans. After majorization by uniform design experiment, the HILs prepared with [AMIM]Cl, [EMIM][BF4], and [EMIM][OAc] at a volume ratio of 1:5:5 could simultaneously extract multi-polarity lignans compared to single IL. Subsequently, the conditions of ultrasonic extraction employing with HILs and traditional organic solvent were optimized by the response surface methodology, respectively. The results indicated that the extract efficiency of the HILs system for target compounds was significantly improved compared with the traditional organic solvent-extraction, i.e. the content of total lignans in ethanol system was up to 47 mg/g, while that in the HILs system was up to 69 mg/g, with an increasing of 47%. Additionally, 1H-NMR and 13C-NMR spectra were used to characterize the hydrogen-bond interactions in the HILs-lignan mixtures. Extraction with the HILs in TCMs is a new application schema of ILs, which not only avoids the use of volatile toxic organic solvents, but also shows the potential to be comprehensively applied for the extraction of bioactive compounds from TCMs. 相似文献