EFFICIENCY OF INVOLUTE GEAR DRIVES WITH UNDERCUT PINIONS USED IN WRIST WATCHES

In wrist watches gear drives with undercut pinions are used. Those pinions have got a tooth number as few as 5—7. The efficiency of such gear drives is important because of the limited energy supply. The mean efficiency of gear drives can be expressed as E_m=1/(φ_2-φ_1)(integral from φ_1 to φ_2(E(φ)dφ)) in which ~0_1, ~_2 are the approach angle and the recess angle respectively. In the discussion we assume that the friction coefficient between the two tooth flanks is constant because the sliding speed is relatively low in wrist watches and the main purpose is to find out the relation between gear parameters and its efficiency rather than to calculate the exact value of the efficiency. In normal conditions ~o_1 and ~o_2 can be found from the gear geometry without much difficulty. However when the pinion is an undercut one we have to first find the forming diameter where the involute profile starts. In this paper equations for the computation of the efficiency and the contact ratio of those gear drives are discussed.     

泡沫铝合金的压缩性能,流通能力及声学性能

研究了泡沫Ａｌ－７Ｓｉ－０．４５Ｍｇ合金的压缩性能、呼能率，压缩后试样在空气中的流通能力，测试闻其吸声和隔声性能，讨论了试样原始孔隙率对上述性能的影响，以及它们之间的相互关系。     

Implications and Constraints of Time-Independent Poisson Ratios in Linear Isotropic and Anisotropic Viscoelasticity

It is proven that time-independent viscoelastic Poisson ratios (PR) can only exist under separation of variable solutions which severely limits the class of applicable problems to quasi-static ones with incompressible homogeneous materials and non-moving boundaries under separable stress or displacement boundary conditions without any thermal expansions. Therefore, composites which are inherently anisotropic and sandwich structures which are nonhomogeneous and anisotropic are generally precluded from having time-independent PRs. Equal time variations for material properties in all directions are shown to be another simultaneous requirement instead of the incompressibility condition for achieving time-independent PRs. However, such restricted models lead to physically unrealistic bulk moduli responses when compared to experimentally determined relaxation moduli and are not generally achievable in current real materials. Consequently, viscoelastic materials are best characterized in terms of relaxation or creep functions, moduli or compliances rather than combinations of the latter with Poisson's ratios. Additionally, the assumption of constant PRs in problems involving thermal and chemical expansions, such as curing and manufacture of viscoelastic composites, is shown to be unjustified and insupportable. The distinct viscoelastic PR definitions, as found in the literature, are examined and classified into five categories. It is further shown that each is inherently unrelated to the others and all are always time-dependent, unless the above extremely limiting conditions are imposed. An extensive literature review indicates that experimental results overwhelmingly confirm the time dependent nature of viscoelastic PRs as no constant experimentally observed PRs were reported.     

组合投资β调整与效用最大化的套期比的选择

为了针对市场风险对风险资产的组合投资进行套期保值，一般认为要选择将组合投资多头和期货合同空头结合起来的头寸方差最小化的套期保值比率，也就是要选择使某一特定函数的期望效用最大化的套期保值比率。但是本认为，由于种种原因，人们更倾向于选择对简单风险最小头寸的套期保值比率。     

Sensitivity and significance of disease outcome measures in inflammatory bowel disease

In inflammatory bowel disease (IBD), proxy measures of clinical outcome are often collected into summary indices of qualitative self-rated disease markers, clinical observations, and quantitative biochemical analyses. In Crohn's disease (CD), a frequently used index is the Crohn's disease activity index (DCAI). This index consists of six qualitative variables and two quantitative variables. The aim of this presentation is to illustrate the use of this index to calculate its range, to estimate errors in the index, its sensitivity, and the number of significant steps in the index. The measure of sensitivity of the summary index was analyzed for the signal-to-noise ratio (SNR), the reference change value (RCV) and the confidence interval (CI). If identical errors were assumed in patient self-rated health and clinically judged disease manifestations, such as tumours and fistulas, the majority of the variance of the index was caused by the self-rated experience of health, the number of days over which the individual variable was rated, and the prognostic multiplier of each variable.The range of the index has no upper limit, but can be estimated to 403 units, of which patient self-rating of well-being account for up to one-third of the summary index maximal score range. The median signal noise measure of index sensitivity was 18 SDs. The two disease classification limits of 150 units for moderate disease and 450 for severe disease on average cover an interval of limit ±41.5 units vs. ±60.5 units. In judgments on change in clinical outcome the RCV interval of steps of 121 units are valid. Conclusion: Both variance and range of the CDAI summary score are primarily decided by the self-rated experience of well-being. Variables on disease signs have a minor impact on the index. Rating of the two important outcome parameters: Self-experienced health and medical outcome would favourably be given in two individual scores.Presented at the 10th Conference Quality in the Spotlight, March 2005, Antwerp, Belgium.     

二能级原子与逆场算符耦合系统的J-C模型

利用表象变换方法,对含逆场算符的J-C模型,分别在相互作用表象中和薛定谔表象中求出了系统的演化波函数,并讨论了失谐量为零时的拉比振动.     

不同压缩比下稀释方式对直喷汽油机节油影响

基于一台1.0 L涡轮增压发动机,在9.6及12的压缩比下,研究了化学当量比、稀薄燃烧(稀燃)及低压废气再循环(EGR)工况下的燃烧与油耗特性.结果表明:EGR在压缩比12、大负荷工况下,节油效果优于稀燃,其余工况下稀燃的节油效果均更好.通过改变压缩比并结合稀燃或EGR,小、中、大负荷下燃油消耗率(BSFC)相比于压缩比9.6化学当量比工况降低最多为7.5%、10.4%和9.3%.结合一维仿真,分析并对比了大负荷下稀燃与EGR的节油原因及其差异.结果表明:在压缩比12、大负荷、过量空气系数(λ)小于1.4的情况下稀燃不能抑制爆震,节油效果不明显;相同工况下EGR可以有效抑制爆震,降低燃油消耗率达5.5%;大负荷下稀燃和EGR的节油来源主要为传热损失和排气损失减少,二者对节油的贡献程度之和大于90%.     

基于多目标准则的流域站网优化

对于流域站网空间布局不合理(含有大量冗余站点及监测空白区等)的问题,基于美国伊利洛伊斯河下游流域27个站点4年的日均径流量数据,以站网中联合熵最大、冗余度最小且数据波动最小3个准则,构建了联合熵比、冗余度比和纳什效率系数(NSE) 3个目标函数对站网的信息量进行定量评估。约简流域冗余站点构成初步优化站点组合,并根据出水口得到的潜在站点确定流域需要新增的站点。结果表明:在原站网的基础上选出11个站点构成初步优化站点组合,其联合熵与原站网相等,冗余度减少74. 2%;在初步优化站点组合基础上新增3个站点,联合熵和冗余度分别增加37. 1%和22. 3%;与原站网相比,优化后的站点数量为14个,联合熵增加了37. 1%,冗余度减少了68. 5%。     

倾斜煤层窄长露天矿分区开采分期境界优化

针对倾斜煤层窄长露天矿,经常采用纵采转横采内排的开采程序,基于其剥离物流向流量的变化对经济合理剥采比大小的影响,提出一种分区、分时期的优化开采境界方法。该方法依据首采区位置的不同可分为A模式(即首采区位于矿权一侧)和B模式(即首采区位于矿权中部)两种开采模式。此外,按照露天剥采工程发展过程中剥离物流向流量变化的情况,将其露天矿山开采过程归结为三个时期:全部外排期、部分内排期和全部内排期。通过构建剥、采、排工程位置模型,系统地研究了两种开采模式分时期境界优化的原则和适用条件,并提出境界优化模型。研究成果在准东露天煤矿开采实践中得到应用,结果表明:准东露天矿的经济合理剥采与其开采境界优化前相比,由原来的1.50m~3/t增加至1.62m~3/t,其经济合理开采深度增加了24.7m,顶帮外扩距离增加了45.65m,经济可采储量增加了85.27Mt。实现了露天开采经济效益的最大化。     

再生骨料混凝土抗压强度的试验研究及其机理分析

通过试验研究再生骨料取代率对C20、C30再生骨料混凝土(RAC)流动性和抗压强度的影响,结果表明:再生骨料混凝土坍落度随再生骨料取代率增大而减小;当再生骨料取代率为20%、40%、60%、80%和100%时,再生骨料混凝土抗压强度较普通混凝土均明显降低,最大降幅分别达27.5%、28.4%;取代率为50%时再生骨料混凝土抗压强度较普通混凝土分别高出7.2%、6.1%。SEM图像显示旧浆体区内存在较多微裂纹,而新浆体区结构更致密。再生骨料取代率及界面过渡区微观结构是影响再生骨料混凝土抗压强度的主要因素。提高再生骨料品质、优化再生骨料级配、改善界面过渡区微观结构是提高再生骨料混凝土抗压强度的根本途径。