学了统计学可以有什么样的作为?(续)──介绍统计学的特点和用处

Ⅲ、统计学家是做什么的? 为了描述统计学家工作的各个领域,最好的方法是给出大量的事例.限于篇幅,这里叙述六个事例.第一个事例描述统计学家的一个新的且很有希望的出路,就是在私人单位里当顾问.许多统计学家例如大学里的那些统计学家,在个人的部分时间从事于这种顾问工作. 经历1 A.B.先生与几个公司和研究所一起工作.几乎每周一次,每次花两到四小时与他的委托人中的每一个人联系,虽然他极少看见他们中的一些人.他与他们中的许多人每天都要通过电话谈话.他经常研究他们的问题,并且为了进行工作他或者重复写他的指示或者根据研究的结果所进…     

小于十亿的素数有多少个

貝斯特逊(Berstelsen)在1893年曾計算过小于十亿的素数的个数。D.H.列麦(D.H.Lehmer)証实貝斯特逊在計算上有錯誤。π(10~9)(π(n)表示不超过n的素数的个数)的精确值,依D.H.列麦作的計算,結果是50847534。他也計算了π(10~(10))=455052512。 L.罗黑尔-爱伦斯特(L.Locher-Ernst)在知道这个消息后认为,表达式 f(n)=n/(1/3 1/4 1/5 … 1/n)对于n>50等足够好地給出数π(n)的近似值。例如π(10~3)=168,而f(10~3)=167.1.对于n=10~9,商π     

Determination and Temperature Dependence of Plateau Modulus for Polymerization of Propylene to Isotactic Polypropylene with Ultra-high Molecular Weight under Catalysis of Ziegler-Natta Catalyst

The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight (UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means of oscillatory rheometry at 180 and 200 ℃, whose loss modulus(G") plots at 180 and 200 ℃versus the natural logarithm of angular frequency(ω) present a pronounced maximum at 34.35 and 69.21 rad/s, respectively, and do not show a maximum peak at 0. 01-100 rad/s for Ziegler-Natta catalyzing ethylenepropylene random copolymerization (PPR) with a conventional molecular weight and broad MWD. The fact indicates that the high molecular weight is responsible for a maximum peak of G"(ω) vs. lnω curves for UHPPH. This makes it possible to determine the plateau modulus (G0N) of UHPPH from a certain experimental temperature G"(ω) curve directly. For UHPPH, the G0N determined to be 4. 28×105 and 3. 62×105 Pa at 180and 200 ℃, respectively, decreases with the increase of temperature and is independent of the molecular weight, which directly confirms reputation theoretical prediction that the G0N has no relation to the molecular weight.     

Reflection and transmission of plane waves from fluid-piezothermoelastic solid interface

The reflection and transmission of plane waves from a fluid-piezothermoelastic solid interface are studied. The expressions for amplitude ratios and energy ratios corresponding to reflected waves and transmitted waves are derived analytically. The piezo-thermoelastic solid half-space is assumed to have 6mm type symmetry and assumed to be loaded with water. The effects of angle of the incidence, the frequency, the specific heat, the relaxation time, and the thermal conductivity on the reflected and transmitted energy ratios are studied numerically for a particular model of cadmium selenide (CdSe) and water. Some special cases are also studied.     

关于广义分数次积分的合成

Compositions of generalized fractional integral operators involving Gauss hy-pergeometric function with power weights are studied. Composition formulas for such integrals which are the operators of the same type are obtained. In parti-cular, compositions of two identical operators are given.     

引力波天文学——一个观测宇宙的新窗口

引力波是爱因斯坦\     

Fast calculation of wave front amplitude propagation: a tool to analyze the 3D image on a hologram (Invited Paper)

A simple approach to calculate the amplitude component of a wave front propagating in space from a hologram is proposed. It is able to calculate the amplitude distribution on a plane at any distance rapidly using a standard GPU. This is useful for analyzing and reconstructing the 3D image encoded on a hologram.     

Flow Structures Around Micro-bubbles During Subcooled Nucleate Boiling

The flow structures were investigated around micro bubbles on extremely thin wires during subcooled nucleate boiling.Jet flows emanating from the bubbles were observed visually with the fluid field measurement using high-speed photography and a PIV system.The jet flows induced a strong pumping effect around a bubble.The multi-jet structure was further observed experimentally, indicating the evolution of flow structure around micro bubbles.Numerical simulations explore that the jet flows were induced by a strong Marangoni effect due to high temperature gradients near the wire.The bubble interface with multi-jet structure has abnormal temperature distribution such that the coolest parts were observed at two sides of a bubble extending into the subcooled bulk liquid rather than at the top.Evaporation and condensation on the bubble interface play important roles not only in controlling the intensity of the jet flow,but also in bringing out the multi-jet structure.     

地球和空间的激波

今天,“激波”这个字眼,不论从比喻上或者从字面本来意义上都被广泛使用着。我们每天看报,看到有一件惊心动魄的事件发生时,就说“它把激波传遍全世界”。幸好,这种情况瞬时造成的实际损害,比起自然界的激波,如闪电、火山爆发、陨星撞击、地震,以及由化学武器和核武器产生的人造激波所造成的实际损害要小。虽然如此,我们决不能认为激波和爆炸只会引起破坏,因为如果没有激波和爆炸,便不会有宇宙和生命本身的演化。据我们所知,宇宙被认为是由一次空前的最大爆发,即大爆炸所创造出来的。虽然这个科学模型不象《圣经》的《创世纪》中所描绘的那样具有戏剧性和神奇性,但它还是解释了许多重要的科学观察现象。地球上的生命,茫茫宇宙      

金属配合物[MBr{(Ph_2PCH_2CH_2)_2C_6H_3}],[M=Pd(Ⅱ)、Pt(Ⅱ)]的合成及晶体结构

合成了一个新的双膦配位体：2 ,6 - 双（二苯基膦乙基）溴苯,通过Pd0(DBA）2 ,（DBA为PhHC= CHCOCH=CHPh）, Pt0（PPh3）4 和该配位体的氧化加成反应,分别得到了两个新的金属配合物：［MBr{(Ph_2PCH_2CH_2)_2C_6H_3}］,[M＝Pd(Ⅱ)、Pt(Ⅱ)］(2),并进行了31P NMR,1 H NMR表征。通过X．射线晶体结构测定,这两个配合物的晶体学参数分别为：配合物 （1）的晶体属正交晶系,空间群 Pna21, a＝16．806（2）A,b=18．578（2）A,C＝9．643（5）A;配合物（2）的晶体属单斜晶系,空间群p21／a,a＝12．364（3）A,b＝17.676（4）A,C=13．672（7）A,P=94．86（3）“。