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Single-point diamond machining of glasses 单点金刚石玻璃加工
K. Puttick, M. Rudman, K. J. Smith, A. Franks, K. Lindsey
A machine tool of very high stiffness has been constructed and used for single-point diamond grooving of blanks of soda-lime glass and optical glassy quartz. Results show that below a critical depth of cut predicted in order of magnitude by a fracture mechanics analysis, material is removed by the action of plastic flow, leaving crack-free surfaces. Subsequent observations by scanning electron microscopy indicate that a crucial part in the detachment of ribbons of swarf is played by the operation of residual stresses after the passage of the tool, particularly in the case of the amorphous ceramic.
研制了一种高刚度机床,用于碱石灰玻璃和光学玻璃石英毛坯的单点金刚石开槽。结果表明,在断裂力学分析预测的一个数量级的临界切割深度以下,材料在塑性流动的作用下被移除,留下无裂纹表面。随后的扫描电镜观察表明,刀具通过后残余应力的作用,特别是在非晶陶瓷的情况下,在切屑带的剥离中起着至关重要的作用。
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引用次数: 147
Thermally driven shallow cavity flows in porous media: the merged-layer régime 多孔介质中热驱动的浅空腔流动:合并层结构
P. Daniels, P. Simpkins, P. Blythe
An analysis is given of convective motions generated in a shallow rectangular cavity by an applied horizontal temperature gradient; the cavity is filled with a fluid-saturated porous medium. For large Rayleigh numbers R, and for large aspect ratios L, a distinguished limit arises when R = O(L2). In this limit the boundary layers on the horizontal walls merge and completely fill the cavity. The régime is characterized by a non-parallel core flow that provides the dominant structure over a surprisingly wide range of the parameter R/L 2. New results for the merged layer core are compared with the parallel flow convection-dominated boundary layer limit R/L2 → ∞, and with the parallel flow diffusion-dominated limit R/L2 → 0. Heat transfer calculations, which define the dependence of the Nusselt number on R/L2, have also been carried out.
分析了施加水平温度梯度的矩形浅腔内对流运动;所述空腔内填充有流体饱和多孔介质。对于大瑞利数R和大宽高比L,当R = 0 (L2)时出现明显的极限。在这个极限下,水平壁上的边界层合并并完全填充空腔。该系统的特点是非平行的核心流,在参数R/L 2的大范围内提供主导结构。将合并层核的新结果与平行流动对流主导的边界层极限R/L2→∞和平行流动扩散主导的极限R/L2→0进行了比较。传热计算,定义了努塞尔数对R/L2的依赖关系,也进行了。
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引用次数: 10
Velocity and particle-flux characteristics of turbulent particle-laden jets 湍流含颗粒射流的速度和颗粒通量特性
Y. Hardalupas, A. M. Taylor, J. Whitelaw
The velocity and flux of spherical glass beads with nominal diameters of 200, 80 and 40 μm have been obtained by phase-Doppler anemometry in a round unconfined air jet over the first 28 diameters. The jet diameter was 15 mm and the exit velocity was 13 ms-1 giving a Reynolds number of 13 000 and a timescale of 1.15 ms, which increased quadratically with axial distance: the bead inertial time constants were 298, 48 and 12 ms. The purposes of the experiments were to quantify the velocity and flux characteristics of the beads and of the gas phase in the presence of the beads as a function of bead diameter and of the mass loading in the jet nozzle. Due to the large inertia of the 200 μm beads, the mean bead velocity downstream of the exit of the jet was constant and independent of mass loading up to 0.37 and the axial root mean square (r.m.s.) bead velocity decayed by about one-fifth : at the exit of the jet, the axial r.m.s. bead velocity was higher than that of the corresponding clean jet. The mean centreline velocity of the 80 μm beads decayed to about one-half of the bead exit velocity by 28 diameters downstream and was independent of mass loading up to 0.86. The decay rate of the mean gas centreline velocity in the presence of the beads reduced as the loading increased because of momentum transfer from the discrete to the gaseous phase. The axial r.m.s. velocity of the beads was comparable to that of the gas phase and both decreased with increasing loading and the rate of spread of the half width of the jet increased with increasing loading. For the 40 μm beads, the decay rate of the mean centreline velocity of the beads decreased with increasing loading and, in contrast to the 80 μm beads, the rate of spread decreased with increasing loading up to 0.80. The axial r.m.s. velocity of the beads became largest at a position downstream of the nozzle exit, which moved downstream with increasing loading and was larger than the axial r.m.s. velocity of the clean jet, although the beads were not expected to be responsive to the frequencies of the energy-containing eddies. The bead axial r.m.s. velocity was more than twice as large as the radial r.m.s. velocity and the correlation coefficient of the cross correlation was larger than that of the clean jet. The large bead turbulence, anisotropy and strong correlation coefficient are explained by the superposition of bead trajectories from regions of different bead mean velocity and are not because of acquisition of axial turbulent motion from the gaseous phase.
用相位多普勒风速法测量了直径分别为200、80和40 μm的球形玻璃微珠在前28个直径范围内的速度和通量。射流直径为15 mm,出口速度为13 ms-1,雷诺数为13 000,时间标度为1.15 ms,随着轴向距离的增加,其惯性时间常数分别为298、48和12 ms。实验的目的是量化小球和气相在小球存在时的速度和通量特性,作为小球直径和喷嘴中质量载荷的函数。由于200 μm弹珠的惯性较大,射流出口下游的平均弹珠速度恒定且与质量载荷无关,最大可达0.37,轴向均方根(r.m.s.)弹珠速度衰减约五分之一,在射流出口,轴向r.m.s.弹珠速度高于相应的干净射流。80 μm微珠的平均中线速度在下游28个直径处衰减为微珠出口速度的一半左右,且与质量加载无关,最高可达0.86。由于动量从离散相转移到气相,随着载荷的增加,珠粒存在时平均气体中心线速度的衰减率降低。小球的轴向均速与气相相当,均随载荷的增加而减小,射流半宽的扩散速率随载荷的增加而增加。对于40 μm珠粒,随着加载量的增加,珠粒平均中线速度的衰减率减小,而与80 μm珠粒相比,扩散率随着加载量的增加而减小,最高可达0.80。在喷嘴出口下游的位置,微球的轴向转矩速度最大,随着载荷的增加而向下游移动,并且比干净射流的轴向转矩速度大,尽管微球对含能涡流的频率没有响应。其轴向转速是径向转速的2倍以上,相关系数大于净射流的相关系数。大的磁珠湍流、各向异性和强相关系数可以用磁珠平均速度不同区域磁珠轨迹的叠加来解释,而不是由于从气相获得轴向磁珠运动。
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引用次数: 190
The transmission of randomly incident sound through an elastic panel 随机入射的声音通过弹性板的传播
F. G. Leppington
A simple method is given to estimate the power, transmitted through a large elastic panel, when averaged over all directions of an incident plane sound wave, in the limit of short waves compared with plate dimensions. Details are given for the simple prototype example of a rectangular isotropic bending plate. The procedure provides a simple estimate of the forced non-resonant contribution to the power flow, in the short wave asymptotic limit, and previous results are recovered. The method is readily amenable to generalizations to deal with more complicated geometries and plate equations. As an illustration, results are presented for the case of a circular isotropic panel.
本文给出了一种简单的方法来估计通过大弹性板的入射平面声波在所有方向上的平均功率,在短波的限制下与板的尺寸相比较。给出了矩形各向同性弯曲板的简单原型实例。该方法提供了在短波渐近极限下对潮流的强迫非谐振贡献的简单估计,并且恢复了以前的结果。该方法易于推广,以处理更复杂的几何形状和板方程。作为一个例子,给出了圆形各向同性面板的结果。
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引用次数: 5
Green’s tensors and associated potentials for electromagnetic waves in inhomogeneous material media 非均匀介质中电磁波的格林张量和相关势
A. Ben-menahem
The explicit form of the Green’s tensor in unbounded inhomogeneous dielectric, magnetic and partly conducting material is obtained. The tensor is given explicitly in terms of two scalar Green’s function potentials, each of which obeys its own wave equation. It is found that the gradients of the constitutive parameters at the source of the radiating currents may have a strong effect on the multipolar field. For example, an electric dipole embedded in a uniaxially inhomogeneous source-zone is found to produce additional fields with the characteristics of electric quadrupole (l = 2, m = ± 1) and a magnetic dipole (l = 1, m = ± 1). I present a mathematical formulation of Huygens’ principle for inhomogeneous media in terms of the Green’s tensor and its associated tensor potentials, thus extending the use of the Green’s tensor to scattering problems in inhomogeneous finite domains.
得到了无界非均匀介质、磁性和部分导电材料中格林张量的显式形式。张量被明确地用两个标量格林函数势给出,每一个都服从自己的波动方程。研究发现,辐射电流源处本构参数的梯度对多极场有很强的影响。例如,发现嵌入在单轴非均匀源区中的电偶极子会产生具有电四极子(l = 2, m =±1)和磁偶极子(l = 1, m =±1)特征的附加场。我提出了基于格林张量及其相关张量势的非均匀介质惠更斯原理的数学公式,从而将格林张量的使用扩展到非均匀有限域中的散射问题。
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引用次数: 1
The identified ΛΛ-hypernuclei and the predicted H-particle 确定的ΛΛ-hypernuclei和预测的h粒子
R. Dalitz, D. Davis, P. Fowler, A. Montwill, J. Pniewski, J. Zakrzewski
The existence of the H particle, the dihyperon predicted by Jaffe, would bring into question the existence of double hypernuclei. We review the two double hypernucleus events published in the literature. We include an independent report, hitherto unpublished, which was made on the ΛΛ10Be event in 1963 and clarifies the salient features of the event; this report reaffirms its published interpretation. We have made a simple calculation of the energy spectrum for Ξ- hyperons produced with K- beams in past emulsion experiments, with a result which accounts adequately for the paucity of reported double hypernucleus events. We outline a hybrid emulsion experiment that would locate Ξ- hyperon interactions efficiently and could thereby greatly improve our knowledge of double hypernuclei.
Jaffe所预测的双超子H粒子的存在,将对双超核的存在提出质疑。我们回顾了在文献中发表的两个双超核事件。我们包括一份迄今未发表的关于1963年ΛΛ10Be事件的独立报告,该报告澄清了该事件的突出特点;这份报告重申了其公布的解释。我们对过去乳化实验中K束产生的Ξ-超子的能谱作了简单的计算,结果充分说明了报道的双超核事件的稀少性。我们概述了一种混合乳液实验,可以有效地定位Ξ-超子相互作用,从而大大提高我们对双超核的认识。
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引用次数: 97
A logic of authentication 身份验证逻辑
M. Burrows, M. Abadi, R. Needham
Questions of belief are essential in analysing protocols for the authentication of principals in distributed computing systems. In this paper we motivate, set out, and exemplify a logic specifically designed for this analysis: we show how various protocols differ subtly with respect to the required initial assumptions of the participants and their final beliefs. Our formalism has enabled us to isolate and express these differences with a precision that was not previously possible. It has drawn attention to features of protocols of which we and their authors were previously unaware, and allowed us to suggest improvements to the protocols. The reasoning about some protocols has been mechanically verified. This paper starts with an informal account of the problem, goes on to explain the formalism to be used, and gives examples of its application to protocols from the literature, both with shared-key cryptography and with public-key cryptography. Some of the examples are chosen because of their practical importance, whereas others serve to illustrate subtle points of the logic and to explain how we use it. We discuss extensions of the logic motivated by actual practice; for example, to account for the use of hash functions in signatures. The final sections contain a formal semantics of the logic and some conclusions.
信任问题是分析分布式计算系统中主体认证协议的基本问题。在本文中,我们激发、列出并举例说明了一个专门为这种分析设计的逻辑:我们展示了不同的协议在参与者的初始假设和最终信念方面是如何微妙地不同的。我们的形式主义使我们能够精确地分离和表达这些差异,这在以前是不可能的。它使人们注意到我们和它们的作者以前不知道的协议的特性,并允许我们对协议提出改进建议。一些协议的推理已经得到了机械验证。本文从对该问题的非正式描述开始,接着解释了将要使用的形式主义,并给出了其在文献中的协议应用示例,包括共享密钥加密和公钥加密。选择一些例子是因为它们的实际重要性,而其他例子则是为了说明逻辑的微妙之处,并解释我们如何使用它。我们讨论了由实际实践驱动的逻辑的扩展;例如,考虑签名中散列函数的使用。最后的部分包含逻辑的形式语义和一些结论。
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引用次数: 2545
The effects of a linearly increasing ambient temperature on an exothermic reaction in a closed system 线性升高的环境温度对封闭系统中放热反应的影响
T. Boddington, P. Gray, S. R. Kay
Thermal analysis in general, and differential scanning calorimetry in particular, offer rapid and automated techniques for studying exothermic decompositions. When reaction is not too complex, values for the exothermicities and Arrhenius parameters may be extracted. The basis of most mathematical treatments is not deep and quite commonly rests on analyses of ‘static’ situations, in which the responses to constant ambient temperatures are the starting point. In this paper we give an economical analysis of the dynamic process of heating a reactive sample continuously. The reduced variables of thermal explosion theory provide a compact representation of the standard case of a single reaction obeying a first-order rate law with an Arrhenius temperature dependence. An asymptotic treatment is used to refine the equations of mass and energy conservation to a practically important form. The natural variables that arise in this way lead to a model of the system in terms of the rate of the chemical reaction, rather than the more usual temperature of the sample. This new treatment leads to a clear and compact description of the behaviour of the reaction for all useful operating conditions. The well-known Kissinger relation normally derived from static treatments is seen to be relevant in this model, but care must be taken in choosing the precise physical quantities to which it relates.
一般来说,热分析,特别是差示扫描量热法,为研究放热分解提供了快速和自动化的技术。当反应不太复杂时,可以提取放热量和阿伦尼乌斯参数的值。大多数数学处理的基础并不深入,而且通常依赖于对“静态”情况的分析,其中对恒定环境温度的响应是起点。本文对反应样品连续加热的动态过程进行了经济分析。热爆炸理论的约化变量提供了一个符合一阶速率定律的单一反应的标准情况的紧凑表示,它与阿累尼乌斯温度有关。采用渐近处理方法将质量守恒方程和能量守恒方程细化为具有实际意义的形式。以这种方式产生的自然变量导致了以化学反应速率而不是更常见的样品温度为依据的系统模型。这种新的处理方法对所有有用的操作条件下的反应行为进行了清晰而紧凑的描述。通常由静态处理得出的著名的基辛格关系被认为与这个模型有关,但必须小心选择与之相关的精确物理量。
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引用次数: 4
Vortex motion in the neighbourhood of a cosmic string 宇宙弦附近的涡旋运动
G. Gibbons
I consider fluid motions in the neighbourhood of a cosmic string by using complex variable techniques. In particular I study the motion of line vortices and show that a single vortex cannot remain at rest but must orbit the cosmic string. I also discuss the motion of vortices in the flow of a wake induced by a moving cosmic string. Some possible connections with string theory are noted.
我用复变技术来考虑宇宙弦附近的流体运动。我特别研究了线涡旋的运动,并表明单个涡旋不能保持静止,而必须绕宇宙弦运行。我还讨论了由运动的宇宙弦引起的尾流中漩涡的运动。注意到与弦理论的一些可能联系。
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引用次数: 2
Analysis of the dispersal and deposition of radionuclides from Chernobyl across Europe 切尔诺贝利放射性核素在整个欧洲的扩散和沉积分析
H. ApSimon, J. J. Wilson, K. Simms
Following the accident at the Chernobyl 4 nuclear power reactor in the Ukraine, U. S. S. R., on 25 April 1986, computer models were used to analyse dispersal of the radioactive material across Europe according to the meteorological situation, and interpret the available radiological measurements. Subsequently, after Soviet scientists presented their accounts of the accident and its causes in Vienna in August 1986, and as further measurements became available from other countries, more detailed assessments were undertaken of the release pattern over the 10-day period after the initial explosions, and the resulting contamination outside the U. S. S. R.
1986年4月25日,苏联乌克兰切尔诺贝利4号核反应堆发生事故后,利用计算机模型根据气象情况分析了放射性物质在整个欧洲的扩散情况,并解释了现有的放射性测量结果。随后,在苏联科学家于1986年8月在维也纳发表了他们对事故及其原因的描述之后,随着其他国家进一步的测量数据的获得,对最初爆炸后10天内的释放模式以及由此导致的苏联以外的污染进行了更详细的评估。
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引用次数: 38
期刊
Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences
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