会长张弘力在中国珠算心算协会第八届会员大会上的讲话

刚才,大家推选我为中国珠算心算协会第八届理事会会长,我感到十分荣幸,感谢财政部党组和各位理事对我的信任。与此同时,也深感责任重大,珠算心算对我而言,是陌生的全新的领域,担任这一领域如此重要的职务,既是莫大的荣誉,也是巨大的挑战,我将珍惜这一荣誉,竭尽全力,与各位理事、各位会员一道,并在你们的支持和帮助下,去迎接挑战。     

会长张弘力在中国珠算心算协会第八届会员大会上的讲话（2014年7月20日）

刚才,大家推选我为中国珠算心算协会第八届理事会会长,我感到十分荣幸,感谢财政部党组和各位理事对我的信任。与此同时,也深感责任重大,珠算心算对我而言,是陌生的全新的领域,担任这一领域如此重要的职务,既是莫大的荣誉,也是巨大的挑战,我将珍惜这一荣誉,竭尽全力,与各位理事、各位会员一道,并在你们的支持和帮助下,去迎接挑战。     

例谈“以退求进”法解题策略

著名数学家华罗庚说过:善于退,足够的退,退到最原始而不失去重要的地方,是学好数学的一个诀窍.这里所谓的退,当然不是逃跑,而是养精蓄锐,蓄势待发,是在为进寻求途径,即以退为进.它的实质是借助转化的数学思想,把复杂的问题简单化,运动的问题静止化,高维问题低维化,变量问题常量化,抽象问题具体化,代数问     

每次进步一点点,奇迹就会发生

香港海洋公园里有一条大鲸鱼,虽然重达8600 kg,却不但能跃出水面6.6m,还能向游客表演各种杂技.面对这条创造奇迹的鲸鱼,有人向训练师请教训练的秘诀.训练师说,在最初开始训练时,我们会先把绳子放在水面之下,使鲸鱼不得不从绳子上方通过,每通过一次,鲸鱼就能得到奖励.渐渐地,我们会把绳子提高,只不过每次提高的幅度都很小,大约只有2 cm,这样鲸鱼不需花费多大的力气就有可能跃过去,并获得奖励.于是,这条常常受到奖励的鲸鱼,便很乐意地接受下一次训练.随着时间的推移,鲸鱼跃过的高度逐渐上升,最后竟然达到了6.6m.     

善待学生的求简精神

在日常教学中,有时会遇到学生对问题解答提出的奇思妙想,一般都是比常规思路更加简捷的方法,但有时学生不能解释为何出现那样的解法,也不知道解法在理论上是否合理,向我们求助时,我们不妨借题发挥,作为探究的好机会,进一步深入思考,善待学生的求简精神,培养学生严谨求实的科学态度.     

浅议初中数学高效课堂教学

现实的数学课堂教学中,我们不难发现,看上去精彩纷呈的一堂课,学生、老师都表现得很积极,课堂气氛也热闹非凡,其实这样的课堂未必高效,而有时看似很普通的常规课,却往往透着高效.有人总认为高效课堂是名师的专利,对于普通老师来说,上好常规课,做到有效就已经是很努力的事情了,高效课堂是遥不可及的海市蜃楼,其实,在教学过程中,只要我们把功夫花在课前,抓住课堂这块教学的主阵地,落实课后反思,高效课堂也能触手可及.     

我与万公称兄弟

古人道"人到七十古来稀",我看万公一点不稀奇.七十的年龄,六十的身体;五十的为人,四十的魄力;三十的激情,二十的志气;叫我如何称呼您:叫万老师太俗气,叫万老又不随意,叫万专家、还是叫万特级……想来想去都不合我意.现代人说:"年龄不是问题",我大胆说:我与万公称兄弟.他,出生无名,家里薄田少地,连名字都是买来的;他,童年时期,内外战争四起,生活中缺吃又少衣;他,身材瘦小,做事缺少力气,但聪明、活泼、淘气、顽皮;他深受父母的励志教育:是男儿汉,有勇气、有志气;敢作敢当、敢为人先,敢争第一!     

浅谈图形语言在解题中的巧用

美国数学家斯蒂恩说:"如果一个特定的问题可以转化为图形,那么,思想就整体地把握了问题,并且能创造性地思索问题的解法."这就表明,解题时若能挖掘问题的几何意义,配以适当的图形,就有利于分析题中数量之间的关系,丰富表象,拓宽思路,化繁为简,化难为易,迅速找出解决问题的方法,提高分析和解决问题的能力,取得以简驭繁的效果.     

空集的自述

我姓空,我的名字叫空集,我是不含任何元素的集合,可谓腹中空空,一无所有,不过你们别小觑我啊,我的本事大着呢!不信,我说出来,别吓你一跳哟!1.特殊的我我是集合大家庭中的一员,不含任何元素的     

双曲线成双 旋转表示来帮忙

在解有关反比例函数问题时,如果可以找到这样一个合适的点,这个点往往在坐标轴上,而且有垂直于(或者平行于)坐标轴的直线过此点.可设这个点的坐标,再根据题目中的等量关系,依次得到其他点的坐标,然后根据题目需要,将坐标转化为线段的长,从而得到线段之间的关系或者某些图形的面积,为问题的解答提供方便.这种先设某点坐标,然后逐一表示其他点的坐标的方法,叫旋转表示法.这种方法在解决两条双曲线问题中的应用十分广泛.本文以2010年中考试题为例,说明这种方法的应用,供同行参考.     

Fundamentals of Quaternionic Kinematics in Euclidean 4-Space

Based on a kinematic mapping for the group SE(4) of displacements of Euclidean 4-space, we show that the mapping of basic elements (points, oriented lines, oriented planes, oriented hyperplanes, instantaneous screws) can be written compactly in terms of 2 × 2 quaternionic matrices. Moreover we discuss the kinematics on the velocity level by investigating instantaneous screws and their geometric parameters.     

Comparison of analytical and numerical solution for optimal vortex diffuser design

The contribution deals with optimization of wing tip devices, so called vortex diffusers. A comparison is given between an analytical approach for obtaining the optimal circulation loading and the results of a numerical investigation using a lifting line method. The purpose of most wing tip devices is to reduce the induced drag of the main wing by converting vortex energy into thrust. In order to achieve an optimal design, a variational formulation originally proposed by Betz and Prandtl for air screws is applied to the circulation distribution of the diffuser blades. In extension to the inviscid formulation, a viscous correction is applied in order to account for frictional forces. In an effort to validate the analytical results, a comparison is given with numerical solutions from a lifting line method. The loading of the diffuser blades is parametrized and optimized with respect to resulting thrust by use of a quasi-Newton gradient method. Comparison shows that, knowing the velocity distribution in the near wake of the wing, considerable decrease of induced drag may be achieved making use of vortex diffusers. Although actual circulation loading may differ between the analytical and numerical estimation, resulting thrust agrees within a few percent. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Extruder flow

A critical equation is derived for determining extruder output in the case of a Newtonian liquid that adheres to the walls. A method designing screws for maximum output is proposed.Moscow Region. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 932–939, September–October, 1968.     

The apollonian octets and an inversive form of Krause's theorem

Suppose we are given three disjoint circles in the Euclidean plane with the property that none of them contains the other two. Then there are eight distinct circles tangent to the given three, and R.M. Krause has shown that a certain alternating sum of the curvatures of these eight circles must vanish. We express this result in an inversively invariant way and determine the extent to which it generalizes to other configurations of three given circles.     

Modeling and Simulation of Damage Processes based on a Gradient-Enhanced Free Energy Function

Taking into account softening effects in connection with conventional inelastic material models can cause ill-posed boundary value problems. These problems can be established by obtaining no unique solution for the resulting algebraic system or by having a strong mesh dependence of the numerical results. This is the consequence of losing ellipticity of the governing field equations. A possible approach to solve these problems is to introduce a non-local field function in the model which includes an internal material length scale. For this purpose a gradient-enhanced free energy function is used for the current continuum damage model from which two variational equations are resulting. Calculations with less effort can be achieved due to the enhancement of the free energy function in comparison to other approaches. The mentioned model is applied to a material with locally varying damage properties (yield limits). Furthermore, the model is able to describe crack propagation in cases of completely damaged material. Therewith, a matrix material including precipitates, such as carbides, is modeled. This allows to investigate ship screws, which usually exhibit the mentioned composition, with regard to the influence of cavitation. Cavitation describes the implosion of risen vapor bubbles, whereby the impact on screws causes heavy damages which can lead to a complete destruction. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Unsteady flow of shear-thinning non-Newtonian incompressible fluid through a twin-screw extruder

The unsteady flow of viscous incompressible shear-thinning non-Newtonian fluid with mixed boundary is investigated. The boundary condition on the outflow is the modified natural boundary condition, it contains the additional nonlinear term, which enables us to control the kinetic energy of the backward flow. The global existence of weak solution is proved. The fictitious domain method which consists in filling the moving rigid screws with the surrounding fluid and taking into account the boundary conditions on these bodies by introducing a well-chosen distribution of boundary forces is used.     

On the Motion of Shear-Thinning Heat-Conducting Incompressible Fluid-Rigid System

The full Navier-Stokes-Fourier system with mixed boundary condition that describes the motion of shear-thinning and incompressible viscous fluid in a rotating multi-screw extruder is investigated. The viscosity is assumed to depend on the shear rate and the temperature. The global existence of suitable weak solutions is established. The fictitious domain method which consists in filling the moving rigid screws with the surrounding fluid and taking into account the boundary conditions on these bodies by introducing a well-chosen distribution of boundary forces is used.     

Study of posterolateral lumbar arthrodesis by means of a finite element model

Posterolateral lumbar arthrodesis consists in the fixation of the lumbar vertebrae pedicles by means of bars and screws. It is indicated in all those cases in which instability exists previous to the surgery, or in those other cases in which the instability has been caused by the need of bone resections that put the articulations structures in danger.The pedicle fixation of the lumbar arthrodesis is a great advance in the lumbar surgery. It contributes to achieve a stable and biologic fusion. The aim of the present research is the analysis of the contact problem that exists between the screw and the bone as one of the key points to control in order to achieve a good future stability of the arthrodesed spine.In order to achieve such aim, a Finite Elements Model (FEM) of the spine was performed. Such a model was obtained using a computer vision technique that creates 3D bodies using computed tomographies of the sacrum and vertebrae L4 and L5. Not only the bone bodies have been modeled, but also the intervertebral discs that act as the joints of the bones. In order to obtain a complete simulation of the lumbar region the titanium screws and bars have been modeled too.The study of the influence of the contact between bone and screw in the biomechanical behavior of the lumbar column has been studied applying several load conditions simulating different kinds of typical movements of the column. Finally, the stresses on the different elements of the lumbar structure and the relative movements between bone and screw as well as the conclusions of this research are also expounded.     

Fitting sampling distribution agreeing in support and moments and tables of critical values of sphericity criterion

Mixtures of two beta or gamma distributions having given first four, three, or two moments are found and applied to tabulate to three decimals critical values of the locally most powerful criterion of sphericity or proportions of moments of order two of a p-variate normal distribution. Expressions are given for the first four moments of the test statistic.