首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 109 毫秒
1.
在魔术中有一类扑克牌的魔术,当我们看到魔术师经过眼花缭乱的洗牌、抽牌、翻牌的动作之后,在他的手上出现了所想要的牌,不少人叹为观止.在惊奇之余,人们会想魔术师是怎么做到的?是魔术师的超常记忆力,还是魔术师作弊,蒙骗了众人的眼睛?特别是有些魔术需要观众上台配合以显示魔术  相似文献   

2.
本文主要讨论组合地图列举问题.刘的一部专著中提出了一个判定两个地图是否同构的算法.该算法的时间复杂度为O(m2),其中m为下图的规模.在此基础上,本文给出一个用于地图列举以及进而计算任意连通下图的地图亏格分布的通用算法.本文所得结果比之前文献中所给结果更优.  相似文献   

3.
在新课程理论指导下,我们的课堂教学打破了传统教学中老师主宰一切的局面,形成了可变的师生多向互动的关系,形成了开放的课堂教学.在这个过程中,会促使课堂数学中多向、多种类型信息得到交流,学生的个性得到充分的发展,学生的认知、情感等得到有效的发展.……  相似文献   

4.
拜读了王先进老师的文章《例谈选择题的命制》,不禁有感而发:命制一份合格的试卷,除了知识点的覆盖,题目的坡度、难度以及题目的处置等之外,题目的来源和新颖也是命题者必须考虑的因素.直接搬用现有的题目,在一定的情况下会有损试卷的信用度,公平公正就打折扣.如何组织题目,这就涉及到对题目的技术处理.本文试以案例的形式,浅谈解答题命制的几种方法.  相似文献   

5.
三角板、直尺、量角器是学生们熟悉的文具用品,以它们为"道具",以学生常见、熟悉的几何图形为载体,并辅之以平移、旋转、叠放、拼摆等变换手段的问题,能为学生提供动手实践操作设计的空间,较好地考查了学生观察、操作、想象、猜想、类比、联想、类比、归纳、推断、明理的能力以及运动变化、分类讨论思想等的综合运用能力.这类操作性的题目格调清新,立意新颖,充分体现了课标中提出的"培养学生动手动脑、实践探索的能力"的要求,既注重基础知识,同时又具有很强的综合性,因此受到了各地中考命题专家的眷顾.本文以2010年的中考试题中为例,进行分类评析,供大家参考.  相似文献   

6.
本文提出一种估计与调控飞行员宏观数量的方法.文章给出了当航空兵的兵力规模保持稳定、只考虑飞行员年龄分布的情况下,战斗部队飞行员和航校教员总数量与每年的补充量、淘汰率、服役年限之间的函数关系;给出了当航空兵的兵力规模需要变更时,尽快达到变更目标的数学规划模型,模型考虑了每年的补充量、淘汰率、服役年限以及航校学制、规模和效率之间的关系.  相似文献   

7.
一道以群的定义为背景的高考试题赏析   总被引:2,自引:0,他引:2  
每一年的高考数学试卷中都有一些以高等数学背景立意的好题目,如2006年四川卷理科第16题,是一道以近世代数中群的定义为背景立意的填空题,这样的试题能够有效考查学生的学习能力、思维能力和数学创新意识,这为高校选拔学习潜质好的学生创造了条件.……  相似文献   

8.
“1”的自述     
我是数字1,大家对我似乎很熟悉,其实却不然,为了以后我们能够成为好朋友,也为了同学们能学好数学,下面请听我的自我介绍:一、我是最小的正整数,我的绝对值还是我;我的相反数是-1,-1的绝对值也是我;我的任何次幂都是我1n=1;我的算术根还是我n1=1;一个数与它倒数的积也等于我,怎么样,牛吧?其实这也不算什么,下面还有更牛的呢.  相似文献   

9.
负数的自述     
我是负数,你以前虽然见过我,但我们还不很熟悉.下面就听听我的自述,我们会成为好朋友的.一、我的出现是实际生活的需要.数的扩充都是由于实际的需要而产生的,负数的引入也不例外,它是由于表示具有相反意义的量的需要而产生的.小学学过的自然数和分数只能表示相反意义的量中的一个量,不能满足实际需要,为了更好的记数而引入一种  相似文献   

10.
数学与文学     
龟兔赛跑的故事,是大家很熟悉的.兔子本来跑在前面,但由于骄傲,路上睡了一觉,结果输给了乌龟.作为文学作品来说,当然要大力渲染兔子的骄傲自满,乌龟的坚持不懈.而从数学角度来看,则可抽象为下面的行程图.  相似文献   

11.
12.
彭忠益  王艳 《运筹与管理》2020,29(7):144-155
定量的评判城市老旧居住小区整体交通环境质量并进而科学有效的提出老旧小区交通环境更新与改善措施,对城市老旧居住小区交通环境进行了调查,明确了老旧居住小区存在的突出交通问题,并提出了城市老旧居住小区交通环境评价的指标体系,包括行人跨路出行指数、无人行道路段长度占比、停车泊位供需比、路内非法停车占比、平均停车步行距离、泊位数量户数比、人均步行空间、无障碍通道、盲道设置比例、非机动车泊位供需比、地面停放车辆数小区面积比、外部穿行交通周转量小区面积比等。并给出了具体指标的计算方法与获得办法。以长沙市四个典型老旧居住小区为例,对评价方法进行了论证,并得到城市老旧居住小区存在的一般问题,包括人车混杂、人车交织现象严重,停车泊位短缺、车辆乱停乱放,交通设施、特别是弱势群体交通设施缺乏。给出的评价指标、评价方法与结论可为城市老旧小区改造更新,特别是其中很重要的交通环境更新提供决策依据。  相似文献   

13.
The influence of displacements of tensioned fibers on the impregnation of fibrous layers with a polymer melt and on the final composite structure is studied. Using computer simulation, it is shown that, during impregnation, the structure of tensioned fibrous layers changes considerably depending on the initial arrangement and tensioning of fibers. The consolidated regions formed under the melt front move inside the impregnated layer with the advancing melt front. Displacement of the tensioned fibers as well as the formation of “washouts” favors the impregnation of internal layers, but cause significant inhomogeneity of the polymer structure. The surface (on the side of the melt flow) regions are more saturated with the polymer than the internal ones. A difference in the melt percolation mechanisms at various impregnation regimes is revealed. The effective permeability coefficients of a tensioned fiber layer are not constant but depend on the conditions and regimes of impregnation. Submitted to the 11th Conference on the Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 2, pp. 259–270, March–April, 2000.  相似文献   

14.
How much information does a small number of moments carry about the unknown distribution function? Is it possible to explicitly obtain from these moments some useful information, e.g., about the support, the modality, the general shape, or the tails of a distribution, without going into a detailed numerical solution of the moment problem? In this, previous and subsequent papers, clear and easy to implement answers will be given to some questions of this type. First, the question of how to distinguish between the main-mass interval and the tail regions, in the case we know only a number of moments of the target distribution function, will be addressed. The answer to this question is based on a version of the Chebyshev–Stieltjes–Markov inequality, which provides us with upper and lower, moment-based, bounds for the target distribution. Then, exploiting existing asymptotic results in the main-mass region, an explicit, moment-based approximation of the target probability density function is provided. Although the latter cannot be considered, in general, as a satisfactory solution, it can always serve as an initial approximation in any iterative scheme for the numerical solution of the moment problem. Numerical results illustrating all the theoretical statements are also presented.  相似文献   

15.
A generalization of both the hierarchical product and the Cartesian product of graphs is introduced and some of its properties are studied. We call it the generalized hierarchical product. In fact, the obtained graphs turn out to be subgraphs of the Cartesian product of the corresponding factors. Thus, some well-known properties of this product, such as a good connectivity, reduced mean distance, radius and diameter, simple routing algorithms and some optimal communication protocols, are inherited by the generalized hierarchical product. Besides some of these properties, in this paper we study the spectrum, the existence of Hamiltonian cycles, the chromatic number and index, and the connectivity of the generalized hierarchical product.  相似文献   

16.
We consider a productive asset, called equipment or capital good, and we examine the properties of, as well as the interactions between, the operating policies, which are determined by its optimal utilization and maintenance, and the capital policy of scrapping, which defines the optimal time when the productive asset is retired from its current use. Starting with an abstract model and using the approach of optimal control, initially we characterize the various types of equipment by assigning to them a single total profit index, which indicates how the above policies affect the flow of operating revenues plus capital gains or losses. This index is a function of market-determined prices. So using it we then investigate how the operating and capital policies are influenced by the rate of discount, the price of new equipment, and the rise or fall of the price of new equipment relative to the value of its output. Among other interesting results, we find that the effects of these prices on the nature and interactions of optimal policies depend crucially on whether the equipment is of the usual profit making type, where output is the main source of revenue, or of the antique type, where the main source of revenue is capital gains.  相似文献   

17.
The efficiency of hot-pressed diamond-containing composite materials (DCM) for various tool applications is greatly affected by microdefects, namely, the residual porosity of the metal matrix, damaged diamond grains, and imperfect diamond-matrix interfaces. An instrumental evaluation of these microdefects, predetermining the quality of a tool equipped with DCM, is rather difficult due to the small size, the nonstandard shape, and the strong heterogeneity of specimens. Proposed here is an alternative, nondestructive technique of DCM quality rating, which includes the measurement of electric resistance and thermal conductivity of diamond-containing composites and processing the obtained data by the methods of composite mechanics. It exploits the fact that diamond, being a dielectric, possesses an extremely high thermal conductivity, which allows estimating the residual porosity of a sintered metal matrix from the ratio of specific electric resistances, one being measured and another predicted by a theory. These data, in turn, are utilized to predict the thermal conductivity ofDCMwith an imperfect matrix. Matching with experiments, after solving the inverse problem gives the thermal resistance of diamond-matrix interface, which, within the frame work of the given model, simulates the damage of both the diamond grains and their bonds with the matrix. Thus, the numerical rating of quality is given in terms of two dimensionless parameters. The first one, 0 < K < 1, reflects the quality of the sintered metal matrix, whereas the second one, 0 < R <1, is an aggregate measure of the integrity of diamond grains and the perfection degree of composite interfaces. The quite satisfactory agreement observed between the theory and experiment confirms the efficiency of the technique and the reliability of the data obtained. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 361–374, May–June, 2006.  相似文献   

18.
The dynamics of damage and of the relaxing force in amorpho-crystalline polymers under constant strain are calculated using the formulas for the probability of rupture of a deformed polymer molecule and a model representation of amorphous interlayers. The main parameters of the model are the maximum and minimum possible deformations of molecular chains, the energy of rupture activation, the function of the chain length distribution, the temperature, the macroscopic strain, and the relative dimensions of the amorphous interlayer. The conformity of the theoretical model and the association of the relaxation spectrum with the internal molecular and structural characteristics of the material are established.Zhambyl Technical Institute of Light and Food Industry, Taraz, Kazakhstan. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 499–508, July–August, 1999.  相似文献   

19.
An asymptotic analysis of the dynamic stress-strain state of a thin laminar packet of anisotropic layers is presented. The statement is nonclassical, since in layer materials the ratio of elastic moduli in the longitudinal and transverse directions can generate small parameters comparable to the relative half-thickness of the packet, as, for example, in high-strength unidirectional composites. Alternation of strong load-carrying layers and a relatively soft filler with a similar difference in the elastic moduli between the layers is also allowed. The averaged two-dimensional equations and the total stress tensor in the layers are determined. The results are classified with respect to the types of anisotropy and the indices of differences in the elastic moduli. It is shown that first-approximation models lead to kinematic relations similar to those of the theories of high-order shear strains. Institute of Problems of Mechanics, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 5, pp. 605–614, September–October, 1999.  相似文献   

20.
The tightening of industrial safety standards for structures generates a need for refined computational methods, which, among other things, must be able to describe the yield surface and the deformation behaviour of non-reinforced thermoplastics. To describe the plastic behaviour of materials, a potential formulation is suggested. This formulation contains a number of known potentials as special cases. The parameters of the model, which are obtained from test data, are restricted by the convexity condition for the potential. The new model allows one to take into account effects of the second order, for instance, the unequal behaviour under tension and compression, the plastic compressibility, and the Poynting-Swift effect. For each particular choice of the parameters, the Poisson ratio in tension is computed. If the restrictions imposed on the Poisson ratio do not hold, the application of a non-associated flow rule is necessary. A simple non-associated flow rule with different values of Poisson ratio intension and compression is proposed. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 3, pp. 367–384, May–June, 2007.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号