Effect of the oxygen partial pressure on the microstructure and optical properties of ZnO:Cu films

Cu-doped zinc oxide (ZnO:Cu) films were deposited on Si substrates using radio frequency reactive magnetron sputtering at different oxygen partial pressures. The effect of oxygen partial pressure on the microstructures and optical properties of ZnO:Cu thin films were systematically investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and fluorescence spectrophotometer. The results indicated that the grain orientation of the films was promoted by appropriate oxygen partial pressures. And with increasing oxygen partial pressure, the compressive stress of the films increased first and then decreased. The photoluminescence (PL) of the samples were measured at room temperature. A violet peak, two blue peaks and a green peak were observed from the PL spectra of the four samples. The origin of these emissions was discussed and the mechanism of violet emission of ZnO:Cu thin films were suggested.     

Attenuation of zero sound and the several low-temperature phases of liquid3He

Measurements of the attenuation of 10-MHz compressional waves in liquid³He along the melting curve reveal a sharp peak at the A transition (2.7 mK). In a magnetic field this feature splits into two attenuation peaks, separated by a temperature difference proportional to H. The shapes of these peaks, though changing markedly betweenH=0 and 1 kOe, are all consistent with the A phase being an anisotropic BCS-type superfluid and inconsistent with an isotropic gap model. Field-dependent time variations in the attenuation and various transient effects provide further clues to the nature of this phase. A third sharp attenuation peak—at the B transition (2 mK)—possibly represents scattering from a liquid-liquid interface. It is, in any event, consistent with an isotropic superfluid B phase. Velocity changes have been observed at both A and B transitions, indicating velocities in the B phase significantly less than that of first sound at the same pressure.This work was supported in part by the National Science Foundation through grants GP-29682 and GH-35692 and also under grant #GH-33637 through the Cornell Materials Science Center, Report #2115.     

大跨度平屋盖表面的风压脉冲特性研究

大跨度平屋盖表面的风压脉冲特性是屋盖风压脉动特性的一个重要表现形式,基于大跨度平屋盖结构的风洞试验研究,结合风压脉冲的形成机理及利用过界峰值法研究屋盖表面风压脉冲对风压脉动的贡献及其出现的频率和峰值的大小,并从中找出反映大跨度屋盖结构的风场绕流特性和风压脉动特性的一些规律。     

A time-space decomposition method for calculating the nearfield pressure generated by a pulsed circular piston

A time-space decomposition approach is derived for numerical calculations of the transient nearfield pressure generated by a circular piston. Time-space decomposition analytically separates the temporal and spatial components of a rapidly converging single integral expression, thereby converting transient nearfield pressure calculations into the superposition of a small number of fast-converging spatial integrals that are weighted by time-dependent factors. Results indicate that, for the same peak error value, time-space decomposition is at least one or two orders of magnitude faster than the Rayleigh-Sommerfeld integral, the Schoch integral, the Field II program, and the DREAM program. Time-space decomposition is also faster than methods that directly calculate the impulse response by at least a factor of 3 for a 10% peak error and by a factor of 17 for a 1% peak error. The results show that, for a specified maximum error value, time-space decomposition is significantly faster than the impulse response and other analytical integrals evaluated for computations of transient nearfield pressures generated by circular pistons.     

Vent sizing: analysis of the blowdown of a hybrid non tempered system

The runaway and blowdown of a non tempered hybrid chemical system (30% cumene hydroperoxide) exposed to an external heat input was investigated using a 0.1l scale tool. The maximum temperature and the maximum temperature rise rate were showed to be sensitive to the vent size. An Antoine type correlation between the maximum temperatures and pressures was observed. These resulted from the presence of vapour, mainly generated by the reaction products. Increasing the initial filling ratio resulted in an earlier vent opening but did not have a significant influence on the blow-down. Three types of mass venting behaviour were observed, when changing the vent area to volume ratio (A/V): ? for large A/V, two-phase venting occurred from the vent opening until the end of the second pressure peak; ? for medium A/V, two-phase venting occurred before and after the turnaround. The data seem to indicate that gas only venting occurred at turn-around; ? for low A/V, two-phase venting was observed only after the second pressure peak. Two-phase venting after the second pressure peak probably results from the boiling of the hot reaction products at low pressure.     

装药位置及形状对某坑道中冲击波压力的影响研究

为了弄清装药位置及形状对某坑道中冲击波压力传播规律的影响,基于Hopkinson比例定律,用LS-DYNA动力有限元软件较为系统地研究了不同装药位置及形状情况下,长坑道中冲击波峰值压力的传播规律.计算结果与其他经验方法的预测结果进行了比较.研究表明,整体上看,柱状装药的压力较大;在爆炸近区,装药位置及形状对预测结果的影响显著.随着传播距离的增加,这种影响越来越小.研究方法和数据可供类似工程问题参考.     

高压对Gd掺杂ZnO的电子结构和磁性影响研究

压力可以作用于物质的晶体结构内部,影响并改变物质整体性质.为进一步探究高压对Gd掺杂ZnO试样的电子结构及磁性影响,运用金刚石对顶砧压机和Materials Studio4.4软件包中的CASTEP运算程序,完成高压实验制备工作;利用基于密度泛函理论的第一性原理计算高压作用下Gd掺杂ZnO试样内部分子的变化情况,并对G...     

The charge transport properties of a-Si:H thin films under hydrostatic pressure

Time resolved thermoelectric effects (TTE) were used to simultaneously determine trap levels and trap state density differences in amorphous (a-Si:H) samples. In particular, the trap state density differences are obtained from the decay of the ambipolar charge distribution, i.e. stage 2 of the TTE transients. The trap state difference density is measured under hydrostatic pressures, up to 2.2 kbar. The trap state density difference changes from a negative peak to a positive peak with increasing hydrostatic pressure, suggesting a significant pressure induced shift of the electron and hole trap levels.     

不同连接方式对钢梁钢柱节点抗爆性能的影响

研究爆炸荷载作用下钢梁钢柱节点的动力学性能,对有效预防整体结构的连续性倒塌具有重要意义。先利用有限元分析软件ANASYS/LS-DYNA对爆炸荷载作用下的钢梁进行数值模拟,并与Amr的实验结果进行对比以验证模型和所用材料参数的合理性;然后研究采用不同连接方式(狗骨式连接和端板螺栓式连接)对钢框架梁、柱节点抗爆性能的影响。研究表明:与端板螺栓式连接相比,在相同爆炸荷载作用下,狗骨式连接时节点的最大应力较小,梁跨中节点的最大挠度最大。由于狗骨式连接在梁的上、下翼缘处进行了一定的削弱处理,使得较长的梁段能同时进入塑性阶段,可有效保护节点。在相同爆炸荷载作用下,端板螺栓式连接时,节点的承载能力和抗塑性变形能力要优于狗骨式连接。     

Crack scattering in polycristalline media

The attenuation of plane elastic compressional waves due to scattering by a distribution of thin circular cracks (in Rayleigh approximation) is compared to the attenuation due to grain-scattering in polycristalline media. An estimation of the range of crack distributions we are able to determine in such media by means of attenuation measurements is then proposed. The influence of porosity is also considered.     

玻璃纤维复合材料孔隙率对超声衰减系数及力学性能的影响

在0.1~0.6 MPa热压压力条件下, 制备了不同孔隙率含量的玻璃纤维布/618环氧树脂层压板试件。采用超声C扫描及烧蚀密度法测定了试件的超声衰减系数与平均孔隙率, 并通过金相显微分析对孔隙的分布、 形状及尺寸进行了表征。讨论了孔隙率对层压板拉伸、 弯曲和层间剪切性能及超声衰减系数的影响规律, 获得了使力学性能下降的临界孔隙率及衰减系数值。结果表明, 随着固化压力减小, 孔隙率从0.976%增加到5.268%, 抗拉强度、 弯曲强度和层间剪切强度均下降, 衰减系数由1.460 dB·mm^-1增加到2.150 dB·mm^-1, 使力学性能下降的临界衰减系数约为1.5 dB·mm^-1。     

碎石机的聚焦冲击波研究和测量

一个椭球反射体的第一焦点水下火花放电产生球面波可以聚焦在第二焦点,产生的脉冲压力可达１００×１０６Ｐａ,本文指出了不同反射体的形状、尺寸和材料对聚焦效果、脉冲形状和焦斑的影响。为了定量研究水下聚焦冲击波,我们研制了一种特殊的冲击波压力传感器（探头）,用这种探头已对国内大部分厂家的碎石机进行电声性能的测试,效果很好。     

The role of ricochet impacts on impact vaporization

Vaporization of carbonate targets by hypervelocity impact increases with decreasing impact angle (from the horizontal), in contrast with expectations based only on peak shock pressures. Experiments at the NASA Ames Vertical Gun Range were designed to allow isolating the underlying controlling processes and probing the vapor composition using high-speed spectroscopy. Vaporization associated with the maximum peak pressures (first contact) was separated from vaporization generated only by downrange ricochet impacts through the use of split targets. Four telescopes isolated the vapor with different velocities and revealed that grazing ricochet debris downrange contributed a significant fraction to the overall vaporization process. These results can be understood by the high temperatures and low pressures created by high strain-rate shear.     

两种含铝炸药水中近场冲击波传播规律研究

为揭示 RS211和 GUHL 两种含铝炸药水中爆炸近场冲击波的传播特性,采用高速扫描相机和阴影照相技术记录了近场冲击波沿柱形装药轴向的传播轨迹,结合 Rankine-Hugoniot 关系推算出了近场冲击波传播速度及阵面压力随传播距离的衰减规律,并与 TNT 炸药的结果进行了对比。同时,还结合近场冲击波的初始参数和Goranson 关系式计算出了炸药的爆压值。结果表明,初始冲击波阵面压力由大到小的顺序为 RS211、TNT、GUHL,在压力的衰减过程中,铝粉的反应使得冲击波的压力衰减速率得到降低,且 GUHL 炸药近场冲击波阵面压力的衰减最为平缓。     

Sound velocity in liquid4He under pressure

We have measured the temperature dependence of the sound velocity in liquid ⁴ He at pressures from the vapor pressure to near the solidification pressure. The data were obtained at frequencies from 12 to 105 MHz and covered the temperature range from below 0.1 to nearly 1.0 K. The velocity data at high pressures do not show any anomaly that can be associated with a distinct shoulder found earlier in the sound attenuation. As observed previously at the vapor pressure, the frequency dependence of the velocity data undergoes an inversion at low temperatures; this unexpected behavior is in agreement with recent theoretical treatments.Based on work performed under the auspices of the U.S. Atomic Energy Commission.     

飞片厚度对冲击波压力峰值衰减特性的影响分析

针对现有研究没有考虑飞片厚度对冲击波压力峰值衰减特性影响的问题,采用数值仿真的方法,通过建立不同厚度的飞片撞击无氧铜靶板的仿真模型,比较飞片与靶板撞击面脉冲宽度的仿真值和理论计算值,验证了数值仿真模型和仿真结果的可信度。采用最小二乘法对仿真数据进行处理,建立了飞片厚度与冲击波压力峰值指数衰减模型衰减系数之间的定量数学关系式,结果表明飞片厚度对冲击波压力峰值衰减特性的影响比较明显,飞片厚度与衰减系数近似成线性关系,飞片厚度越小,衰减系数越大,冲击波压力峰值的衰减速率越快,为相关实验设计与分析提供了理论参考。     

高架桥爆破拆除触地冲击动土压力分析

以南京城西水西门高架爆破工程为研究对象,对高架爆破倒塌触地时振动冲击波引起的冲击动土压力峰值、持时、衰减趋势等方面进行分析,得出触地引起的冲击动土压力主频为0¹0Hz,动土压力随深度增加呈指数衰减规律,为校核地铁隧道稳定性、确保高架桥下部隧道工程的安全提供参考。     

Sound attenuation in3He-4He liquid mixtures under pressure

The attenuation of sound was measured in³He-⁴He mixtures with³He concentrations ranging from 2.89 to 8.03% at pressures of 10 and 20 bar. The quasiparticle interaction potentials were then determined at each pressure by analyzing the sound attenuation data. The superfluid transition temperature of³He and other properties in the mixtures were then estimated from the interaction potentials.     

Near-Critical-Point Thermodynamics from Shock Experiments with Porous Ni Samples

Results of experiments on the expansion of shock-compressed nickel samples into helium are presented. An isentrope with an initial pressure of 170 GPa was studied. The radiance temperature of the nickel sample and the velocity of the shock wave, generated in helium, were measured by a fast multichannel optical pyrometer; other parameters, such as the particle velocity, the pressure on the He-Ni interface, and the temperature of He were calculated using He Hugoniot (chemical plasma model). To increase the shock entropy up to a near-critical value and to intensify the process of heat-mass transfer, porous samples were used. Final states with pressures below 1.5 GPa, determined by the initial He pressure, were generated. The isobaric overheat of nickel by hot shocked helium provided an information about the nickel liquid spinodal. The change in slope of an isentrope in the pressure-particle velocity plane allowed an estimate of the point of its entrance in the two-phase region. Estimates of the critical temperature and pressure were made from peculiarities of P-T path, using various models of the nickel liquid spinodal to represent experimental data.     

Measurement Interpretation and Uncertainty Resulting from Nonlinear Ultrasonic Wave Propagation

Nominally identical ceramic-element ultrasonic transducers, of the type used in the aerospace and metals industries for nondestructive evaluation (NDE), often have variability in the peak pressure of the generated ultrasonic pulses. The generated pressures are also high enough for nonlinear propagation to be present in the water medium, often used as coupling in these types of inspections. In this study, a measurement system for monitoring ultrasonic pulse pressure level and nonlinear propagation in water is presented. Several different industrial NDE measurement applications are examined to quantify the impact of variable pressure and nonlinear propagation with respect to test interpretation and measurement uncertainty. In particular, pulse frequency content, velocity measurements, reference block calibrations, and beam-width measurements are examined. In addition, an experimental demonstration of why nonlinear pulse distortion is not normally observed in practice is presented.