A tin whisker with two independent superconducting phase diagrams

Whiskers grown by extrusion from tin plate are known to have irregular cross sections; one such whisker could be regarded as a cylinder of approximately 2 µ in diameter, attached to which, with its plane parallel to the cylinder axis, was a thin film of an approximate thickness of 1000 Å. The superconducting transition of this whisker was studied resistively as a function of magnetic field, temperature, and elastic strain, and is interpreted in terms of two independent phase diagrams, one being attributed to the cylinder and one to the thin film; size effects are discussed. It seems that the cylinder and the thin film behaved as two separate systems in parallel, allowing, for example, the coexistence of a stable superconducting state in the film and a metastable normal state in the cylinder.     

1.16 Extremely uniform thin films by vacuum deposition from a ‘tube source’

A vacuum deposition device without moving parts called ‘tube source’ has been developed which is capable of producing from a small area source on plane extended fixed substrates thin films with 10 times less thickness variation than a film would show deposited from the same small area source as the one used with the ‘tube source’ at the same distance but without the tube source arrangement. For example, using the tube source, a film deposited on a flat circular substrate of 10.4 cm diameter shows a thickness variation less than ± 0.4% at a substrate to source distance of 23.2 cm. The tube source consists of a wide cylinder. At one end on the axis of the cylinder there is a small area source, for example, a $\text{1}\text{2}$ in. commercial dimple boat electrically heated and filled with the material to be deposited; from the other end flat substrates were positioned in a plane perpendicular to the cylinder axis at varying distances. A disc with its plane also perpendicular to the axis and its center on it was suspended with three very thin stretched wires inside the tube in such a way that no vapor atoms could hit the substrate directly, in other words the disc forms a shadow for the source on the substrate. Hereby, the arrival of vapor atoms can be made much more random depending on the geometry (distance of substrate from top end plane of cylinder, distance of source from bottom end plane, a.o.). The tube could be heated by nichrome wire wrapped around it to change the reflectivity of the vapor atoms. Optimum thickness distributions on the substrate were determined by Monte Carlo methods using a computer as well as analytically.     

Analysis of a crack in a disclinated cylinder

In this paper, the stress intensity factors and the opening displacement of a crack loaded by a negative wedge disclination in an isotropic cylinder are numerically determined. The disclination axis coincides with the long axis of the cylinder, and one end of the crack coincides with the disclination location. The cylinder may also be subjected to equal and opposite line loads on its surface. An exact formulation leads to a pair of decoupled singular integral equations of the Cauchy type. Numerical solutions show that if the cylinder represents a grain in a polycrystal, (i) unstable submicroscopic cracks 10^-5 to 10^-1 times the grain size and stable microscopic cracks of the order of the grain size, are predicted, (ii) the submicroscopic crack length to grain size ratio decreases, while the microscopic crack length to grain size ratio increases, as the grain size increases, (iii) significant differences exist, even in the case of the submicroscopic cracks, between the predictions of the exact theory and the approximate theory which ignores stress redistribution, and (iv) the opening displacement is independent of the elastic constants and the crack profile is wedge-shaped.     

A comparative study on effect of plain- and wavy-wall confinement on wake characteristics of flow past circular cylinder

A first attempt is made for identifying the wake characteristics of circular cylinder confined by a wavy wall at laminar flow regime. Numerical study of flow characteristics past circular cylinder with wavy-wall confinement perpendicular to cylinder axis has been carried out in the range of Reynolds number 20–100. The finite volume-based CFD solver Ansys Fluent (Version 15.0) is used for computations. The results are presented in the form of streamline plots, mean drag co-efficient, flow separation angle and recirculation length. Wavy-wall confinement leads to highly significant changes in the cylinder wake such as the evolution of strong x-plane vortices, enhanced fluid mixing, wake suppression near the crest region and vortex stretching near the trough region on the downstream of the cylinder has been observed. Flow separation angle varies significantly along the axis of the cylinder. Increased wall shear stress on rear surface of the cylinder has also been observed. The part of vorticity magnitude as compared to strain rate has been distinguished and identified using vortex identification methods such as Q-criterion and Lambda-2 criterion.     

面向壁厚均匀性的拉深成形TRB板形设计及神经网络预测模型

目的 研究连续变截面板拉深成形过程中圆筒件的壁厚均匀性问题。方法 基于正交试验设计和极差分析方法,研究连续变截面板结构参数对圆筒件拉深成形壁厚均匀性的影响,并结合SSA–BP神经网络预测并验证连续变截面板成形的壁厚均匀性。结果 通过正交试验及极差分析,得到连续变截面板各结构参数按对最大壁厚影响由大到小的顺序依次为薄区厚度>厚区厚度>左侧过渡区长度>右侧过渡区长度;按对最小壁厚影响由大到小的顺序依次为薄区厚度>厚区厚度>右侧过渡区长度>左侧过渡区长度;按对最大壁厚差影响由大到小的顺序依次为薄区厚度>左侧过渡区长度>厚区厚度>右侧过渡区长度。综合考虑最大壁厚、最小壁厚及最大壁厚差,得到最优参数组合如下:厚区厚度为1.1 mm,薄区厚度为0.8 mm,左侧过渡区长度为2.5 mm,右侧过渡区长度为29.5 mm。基于正交试验分析结果建立的SSA–BP神经网络模型具有良好的预测能力,正交试验外5组数据的预测值与真实仿真值的最大误差均在11%以下。结论 基于正交试验分析结果建立的SSA–BP神经网络模型能够实现对TRB板圆筒件拉深成形壁厚的准...     

气缸式蓄能器对压裂泵流体脉动的抑制作用

针对压裂泵流量脉动较大带来的问题,在分析压裂泵脉动产生机理及其特点的基础上,设计可用于高压大流量场合中的气缸式蓄能器,建立气缸式蓄能器回路数学模型,得到脉动流量的幅频特性,仿真研究脉动抑制特性的影响因素,并对压裂泵安装气缸式蓄能器前后的脉动流量进行对比分析,结果表明:气缸式蓄能器可用于高压大流量场合中,其脉动抑制特性随气缸预充气压力、气缸直径、蓄能器连接管长度的增加而减弱,随气缸行程、蓄能器连接管直径的增加而增强;气缸式蓄能器能显著抑制压裂泵流量脉动,可将机械式三缸压裂泵的流量脉动由23.07%降至2.42%,将液压驱动式三缸压裂泵的流量脉动由33.33%降至3.22%;研究结果为高压蓄能器的设计和使用提供了一种新的思路和方法。     

Invariance of the Doppler bandwidth with range cell size above a critical beam-to-flow angle

For a sound beam impinging on a blood vessel, with a range cell much smaller than the vessel diameter, it is known that the breadth of the echo Doppler spectrum is proportional to the velocity of the flow through the range cell. As the range cell is lengthened to include a greater range of velocities, the spectrum is expected to widen proportionately. It is shown theoretically, and confirmed experimentally, that if the beam-to-flow angle is greater than a critical value, the Doppler spectrum bandwidth is independent of the length of the range cell, and depends only on the maximum velocity encompassed by it. This happens because for angles greater than the critical, the narrow spectra produced by lower velocity flows near the vessel walls are contained within the broader spectrum produced by the higher speed flow near the vessel axis. The critical angle is the angle at which the flow axis is normal to one of the beam edges.     

旋转叶片在测试陶瓷浆料固化过程流变特性的应用

将旋转叶片应用于应力控制流变仪,测量陶瓷浆料固化过程中的流变特性.在数据处理上,可将添满陶瓷浆料的旋转叶片等效为一个同心圆筒,并按照同心圆筒进行测试参数的设置.我们采用四叶片的旋转叶片测试不同浓度的聚丙烯酰胺溶液的复数模量G*,并与平行板测试数据比较.结果表明旋转叶片存在有效直径.这个有效直径小于叶片直径.确定了在测试陶瓷浆料固化过程流变特性时的有效直径D_eff.并得到陶瓷浆料固化过程的流变曲线.     

Double-grating interferometer for measurement of cylinder diameters

We describe a double-grating interferometer for the measurement of cylinder diameters. The unique characteristic of this interferometer is that one can freely change the period of the interference fringes by turning the grating, which permits the measurement range of the interferometer also to be changed freely according to the cylinder diameter to be measured. A clear image of the cylinder can be obtained because the aperture diaphragm blocks the beams diffracted from the edge of the cylinder. The outside and inside diameters of the M4 x 0.7 mm hand tap are measured with this double-grating interferometer.     

An economical piezoelectric phase modulator for fiber optic sensors

A homemade piezoelectric phase modulator for interfero-metric fiber optic sensors was fabricated using piezoelectric buzzers as strain elements. Six piezoelectric elements were embedded between the two halves of a bakelite cylinder split along its axis and secured tightly together again to form a cylinder. Single-mode optical fiber was then wound around the cylinder to complete the unit. Up to a frequency of 500 Hz, the phase shift produced by the modulator is linearly proportional to the amplitude of the applied voltage. The sensitivity of the phase modulator is about 3.6 rad/V and has a dynamic range of 1,000 rad, which is sufficient for most phase modulation purposes.     

The instability which leads to the splitting of a conducting liquid cylinder by the current flowing through

Magnetocapillary and electrocapillary instabilities of a conducting liquid cylinder are considered, which cause the splitting of the cylinder throughout its length. Linearized magnetohydrodynamic equations describing such instabilities are considered, and their increments are found in the limit of low viscosity and high conductivity. It is demonstrated that splitting instabilities may arise only when the current reaches some critical value dependent only on the surface tension coefficient, electric potential, and conductor diameter.     

钢筋套筒灌浆连接性能试验研究及筒壁应力分析

完成了12个钢制套筒灌浆连接件的拉拔试验,系统研究了其破坏过程与破坏形态、荷载-位移曲线、套筒应变等,重点分析了锚固长度、钢筋直径对筒壁应力的影响。运用厚壁圆筒理论,明确套筒灌浆连接件中钢筋与灌浆料以及套筒之间的传力过程,并基于轴向拉力建立了筒壁纵、横向应力的计算模型。研究表明:套筒灌浆连接件破坏过程分为弹性、屈服、强化、颈缩四个阶段,屈服强度和极限强度与钢筋材性相近。随钢筋锚固长度增加,筒壁应力略有减小,且随着钢筋直径增加,筒壁的应力明显增大。同时,建议筒壁应力计算值与试验值吻合较好,可为钢筋套筒灌浆连接设计与研究提供借鉴。     

活塞式气体流量标准装置活塞缸内径测量及不确定度评估

针对活塞缸自身结构特点对测量器具的限制,提出了三坐标测量机测量活塞缸内径的方法。以名义内径为19mm、45mm、140mm的活塞缸为例,对活塞缸的内径、外径和厚度进行测量,比较不同方法测量得到的活塞缸内径的差异,验证了三坐标测量机测量活塞缸内径的可靠性。此外,分析了活塞缸的形状特征对其内径测量不确定度的影响,得到活塞缸内径测量结果分别为18.999mm、44.983mm、139.975mm,测量相对不确定度分别为0.016%、0.015%、0.010%。     

单根和双分裂导线风噪声的数值模拟研究

针对单根和双分裂导线风噪声采用混合计算方法进行数值模拟。基于导线的绞线结构进行建模,获得单导线风场和声场的分布特征,并与同直径的光滑圆柱结果进行对比,并针对水平和垂直布置双分裂导线风场和声场进行研究。研究表明:导线的阻力系数和总声压级均小于光滑圆柱,而斯特劳哈尔数大于光滑圆柱;在卓越频率段导线和光滑圆柱的风噪声呈现了明显的8字形指向性,而在远离卓越频率段呈现圆形指向,说明导线和圆柱风噪声是一种偶极子声源;导线和光滑圆柱风噪声的总声压级总体呈圆形、略呈8字形分布;垂直布置双分裂圆柱因相互之间无干扰,总声压级为两根单导线风噪声声压级之和;垂直布置的双分裂导线风噪声略小于水平布置双分裂导线风噪声。     

基于精细传递矩阵法的变厚度圆柱壳自由振动分析

结合精细积分和传递矩阵方法,对变厚度圆柱壳的自由振动进行计算分析。该方法基于圆柱壳的基本微分方程,推导得到关于位移内力向量的一阶齐次偏微分方程,采用精细积分求得场传递矩阵,将其进行组装得到总传递方程,根据边界条件求解总传递方程中系数矩阵的行列式,计算得到变厚度圆柱壳的固有频率。将计算结果与有限元结果进行对比,验证方法的准确性及有效性。同时探究了边界条件、厚度变化形式、厚度变化系数及长径比对自由振动的影响规律。     

A piezoelectric motor using two orthogonal bending modes of a hollow cylinder

This paper proposes a compact ultrasonic motor with low manufacturing costs, a simpler driving circuit, and scalability. The stator of the motor presented in this paper consists of a hollow metal cylinder, whose outside surface was flattened on two sides at 90 degrees to each other, on which two rectangular piezoelectric plates were bonded. Because the cylinder has a partially square/partially circular outside surface, the stator has two degenerated bending modes that are orthogonal to each other. A wobbling motion is generated on the cylinder when only one piezoelectric plate is excited at a frequency between the two orthogonal bending modes. A rod through a pair of ferrules was used as the rotor of this motor. The prototype motor, whose stator was 2.4 mm in diameter and 10 mm in length, operated at 69.5 kHz, was experimentally characterized, and a maximum torque of 1.8 mNm was obtained.     

Determining complex permittivity by measuring the scatteredwaveform from a dielectric circular cylinder

The author describes a method of measuring complex permittivity by making use of a two-dimensional scattered wave from a dielectric circular cylinder. The far-field pattern in the plane perpendicular to the cylinder axis is examined when the dielectric is illuminated by a line-source antenna that is parallel to the axis of the cylinder. An automated measurement of the complex permittivity is compared with a computed result based on theory. When the loss factor is high, this method becomes competitive with other techniques. The complex permittivity can be determined by this method over a wide range except for the case where the dielectric loss is very small     

超声波作用下对位芳纶纤维的超微结构

用X射线衍射和扫描电子显微镜（SEM）对超声波处理的对位芳纶纤维的结晶结构和形态结构进行研究,以揭示对位芳纶纤维的超微结构特点。研究表明,对位芳纶纤维具有皮芯层结构和多重原纤结构特征,纤维表层大量原纤沿纤维轴向高度取向,直径约600 nm;纤维内部圆柱状的微原纤平行于纤维轴,直径为30 nm,且微原纤间存在缝隙和孔洞;...     

Separation in a two-dimensional Stokes flow inside an elliptic cylinder

The two-dimensional Stokes flow due to a line rotlet inside a fixed elliptic cylinder is investigated, where it is assumed that the line rotlet intersects the major axis of each elliptical cross-section of the cylinder. For the case in which the line rotlet coincides with the centre-line of the elliptic cylinder, it is shown that the number of eddies in the flow increases in a roughly linear way with the ratio of length to width of a cross-section of the cylinder. Moreover, results obtained by varying the rotlet position for several different fixed boundary shapes suggest that the aforementioned ratio, and not the rotlet position, is the principal determinant of the number of eddies.     

Dynamics of bi-dispersed settling suspension of non-colloidal particles in rotating cylinder

Non-neutrally buoyant suspension of bi-dispersed non-colloidal particles in viscous fluid rotating in a horizontal cylinder displays in-homogeneities in particle distribution with alternate bands of high and low particle concentrations along the symmetric axis of the cylinder. Experiments were carried out to characterize the axial segregation in bi-dispersed suspension at various filling fraction and rotation speed of cylinder. The mixture of same particles in absence of any suspending fluid did not show any segregation. However, in case of particles suspended in water it was observed that the rate of segregation increases with increase in filling fraction. Once the particles get segregated along the full length of the cylinder, these bands start to migrate along the tube axis finally merging to give wider bands. For a given filling fraction the rate of segregation increases with the angular speed of the rotating cylinder. When the tube is partially filled the particle segregation is observed at higher angular speed, whereas in fully filled case the segregation starts at much lower rotation speed for the same concentration of particles. The segregation pattern changes as the rotation speed is increased. At higher speed the centrifugal force dominates over gravitational and viscous drag forces and this result into completely different segregation patterns. We have also analyzed the evolution of concentration profile from the image analysis of the particles.