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1.
带参数的一阶脉冲微分方程边值问题   总被引:2,自引:0,他引:2  
利用上下解和单调迭代法。讨论了带参数的一阶脉冲微分方程。获得了单边Lipschitz条件下这类方程边值问题的解的存在性。  相似文献   
2.
In recent years, constructing a virtual backbone by nodes in a connected dominating set (CDS) has been proposed to improve the performance of ad hoc wireless networks. In general, a dominating set satisfies that every vertex in the graph is either in the set or adjacent to a vertex in the set. A CDS is a dominating set that also induces a connected sub‐graph. However, finding the minimum connected dominating set (MCDS) is a well‐known NP‐hard problem in graph theory. Approximation algorithms for MCDS have been proposed in the literature. Most of these algorithms suffer from a poor approximation ratio, and from high time complexity and message complexity. In this paper, we present a new distributed approximation algorithm that constructs a MCDS for wireless ad hoc networks based on a maximal independent set (MIS). Our algorithm, which is fully localized, has a constant approximation ratio, and O(n) time and O(n) message complexity. In this algorithm, each node only requires the knowledge of its one‐hop neighbours and there is only one shortest path connecting two dominators that are at most three hops away. We not only give theoretical performance analysis for our algorithm, but also conduct extensive simulation to compare our algorithm with other algorithms in the literature. Simulation results and theoretical analysis show that our algorithm has better efficiency and performance than others. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
3.
Critical current measurements for three polycrystalline rings of YBCO, three Bi-2223, and one YBCO + Ag were developed from a temperature close to 80 K to the critical temperature using a previously reported contactless inductive device based on the transformer method. These data were used to analyze the ability of this device to characterize, in superconducting rings, the Ginzburg-Landau, Ambegaokar-Baratoff, and De Gennes regimes as well as the crossover temperature between them.  相似文献   
4.
We generalize the notion of cyclic codes by using generator polynomials in (non commutative) skew polynomial rings. Since skew polynomial rings are left and right euclidean, the obtained codes share most properties of cyclic codes. Since there are much more skew-cyclic codes, this new class of codes allows to systematically search for codes with good properties. We give many examples of codes which improve the previously best known linear codes.  相似文献   
5.
Over the last century, IQ scores have been steadily rising, a phenomenon dubbed the Flynn effect. Because of the Flynn effect, IQ tests are periodically renormed, making them harder. Given that eligibility for mental retardation (MR) services relies heavily on IQ scores, renormed tests could have a significant impact on MR placements. In longitudinal IQ records from 9 sites around the country, students in the borderline and mild MR range lost an average of 5.6 points when retested on a renormed test and were more likely to be classified MR compared with peers retested on the same test. The magnitude of the effect is large and affects national policies on education, social security, the death penalty, and the military. This paper reports the perceptions of professionals as they relate to IQ score fluctuations in normal, borderline, and/or MR populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
6.
Computer models of the lubrication of piston-rings in internal combustion engines normally present an estimate of the minimum oil-film thickness between ring and cylinder wall as a function of crank angle. As a consequence, experimental measurements of film thickness play a critical role in the verification of theoretical models of piston-ring lubrication. A review is presented of the wide range of techniques that have been used to measure this important variable. The strengths and weaknesses of particular techniques are identified and a number of ways in which the techniques could be developed further are proposed  相似文献   
7.
激光干涉环圆心位置测定技术及应用   总被引:1,自引:0,他引:1  
本文利用在平面内绕定轴旋转的线阵CCD及微机系统自动测定激光干涉环圆心位置及应用于激光外径千分尺平行度检查仪平行度检查结果的自动数字化输出。  相似文献   
8.
The classical spectral analysis of structural response to a gusty wind is applied to the prediction of fatigue damage as expressed by the rate of accumulation of Miner's quotient, using the rainflow algorithm to establish stress-range cycle counts. A general solution in chart form is given for the effect of the broad-band (quasi-static) part of the response spectrum, together with an algebraic formulation for its combination with the effect of narrow-band (quasi-resonant) response.A procedure for integration of the long-term expectation of Miner's quotient is indicated. It is concluded that quasi-static response alone is unlikely to pose a serious fatigue problem. With generally anticipated levels of dynamic response, fatigue damage is greatly increased, but can be controlled at acceptable levels by care to avoid features especially sensitive to fatigue.  相似文献   
9.
10.
The soil microbial biomass quotient (expressed as a percentage of the total soil organic carbon) and the specific rate of carbon-dioxide production by soil microbes (respiration quotient) are often used as indicators of stress on soil microbial populations. A low biomass quotient or a high respiration quotient is considered to be an indication of stress from, for example, toxicity from metals in sewage sludge applied to soils. These metabolic quotients are affected by a wide variety of other factors such as the biodegradability of soil organic-carbon amendments, plant inputs of organic carbon into soils, natural variations in microbial population sizes with depth, and in the rhizosphere of plants. These variations could be sufficiently large to make interpretation of changes in biomass quotient and respiration quotient, as a response to stress, problematical.  相似文献   
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