10W/80K高频同轴脉冲管制冷机的实验性能

介绍了一款大冷量高频单级同轴脉冲管制冷机的基本结构、数值模拟和实验性能。其线性压缩机采用Redlich动磁式直线电机驱动,压缩活塞对置布置,使用板弹簧支撑和间隙密封技术,80 K温区工作时的电机效率在83%以上。膨胀机的蓄冷器和脉冲管为同轴型布置,这种结构使冷头与器件之间的耦合非常方便。使用数值软件对制冷机整机和调相部件进行数值模拟,并对模拟结果进行实验验证。对制冷机的运行频率和制冷性能进行实验研究,制冷机在210.3 W输入电功时能获得10 W/80 K的制冷性能,比卡诺效率为12.66%,运行频率为62 Hz,整机重量小于5.5 kg。     

Connecting hose’s operating characteristics and its effect on the cooling performance of an 80 K Oxford split-Stirling-cycle cryocooler

In this paper, a mathematical model on the connecting hose of a one-stage Oxford split-Stirling cryocooler has been made to simulate its dynamic performance. A set of governing equations has been discretized by method of characteristics and dissolved by a numerical method. The present paper emphasizes the validation of this model against experimental results of pressure phase lag and amplitude attenuation through connecting hose, and cooler performance vs. connecting hose in different dimensions. The comparison shows acceptable agreement between the simulation and experimental results.     

Deposition of device quality silicon nitride with ultra high deposition rate (> 7 nm/s) using hot-wire CVD

The application of hot-wire (HW) CVD deposited silicon nitride (SiN_x) as passivating anti-reflection coating on multicrystalline silicon (mc-Si) solar cells is investigated. The highest efficiency reached is 15.7% for SiN_x layers with an N/Si ratio of 1.20 and a high mass density of 2.9 g/cm³. These cell efficiencies are comparable to the reference cells with optimized plasma enhanced (PE) CVD SiN_x even though a very high deposition rate of 3 nm/s is used. Layer characterization showed that the N/Si ratio in the layers determines the structure of the deposited films. And since the volume concentration of Si-atoms in the deposited films is found to be independent of the N/Si ratio the structure of the films is determined by the quantity of incorporated nitrogen. It is found that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high 7 nm/s for device quality SiN_x films, much faster than commercial deposition techniques offer [S. von Aichberger, Photon Int. 3 (2004) 40].     

An investigation on the tribological behavior of AZ91 and AZ91 + 3 wt% RE magnesium alloys at elevated temperatures

The wear behavior of AZ91 and AZ91 + 3 wt% RE magnesium alloys was investigated under a normal load of 20 N at the wear testing temperatures of 25–250 °C and sliding speeds of 0.4 and 1 m s⁻¹. As the sliding speed increased from 0.4 to 1 m s⁻¹ at the wear temperature of 25 °C, the wear rates of AZ91 and AZ91 + 3 wt% RE alloys decreased by about 8% and 60%, respectively. With an increase in the wear temperature to 100 °C, the wear rate of AZ91 alloy was reduced by 58% at a sliding speed of 0.4 m s⁻¹, while the wear rate was sharply increased at a sliding speed of 1 m s⁻¹. At higher wear temperatures, the wear of the AZ91 alloy at both sliding speeds soared as a result of the softening of β-Mg₁₇Al₁₂ phase. However, the wear rate of AZ91 + 3 wt% RE alloy showed a minimum at the wear temperatures of 100 and 200 °C at sliding speeds of 1 and 0.4 m s⁻¹, respectively. Superior wear behavior of AZ91 + 3 wt% RE at the elevated temperatures could be attributed to its higher thermal stability and strength. Furthermore, a rise in sliding speed led to a 55% reduction in the wear rate of AZ91 + 3 wt% RE alloy at the wear temperature of 100 °C due to the formation of stable oxide layers on the wear surface.     

High-rate deposition and mechanical properties of SiOx film at low temperature by plasma enhanced chemical vapor deposition with the dual frequencies ultra high frequency and high frequency

A high efficiency, high-rate deposition process was developed for silicon oxide films using plasma enhanced chemical vapor deposition (PECVD) with an additional ultra high frequency (UHF) power with high frequency (HF) bias. The effect of the UHF input power with HF bias on the anti-scratch properties of the silicon oxide films was examined. The hybrid plasma process was also examined by advanced plasma source. Dissociation of the octamethylycyclodisiloxane (OMCTS) precursor was controlled by the plasma processing parameters. SiO_x films were deposited on polycarbonate substrates by PECVD using OMCTS and oxygen carrier gas. The rate of SiO_x film deposition increased with increasing input energy. The plasma was analyzed by optical emission spectroscopy. The deposition rate was characterized using an alpha-step. The mechanical properties of the coatings were examined using a nano-indenter and pencil hardness measurements. The chemical properties of the coatings were examined by Fourier transform infrared spectroscopy. The deposition rate of the SiO_x films was controlled by the dissociation of OMCTS using the appropriate intensity of excited neutrals, ionized atoms and input UHF input power with HF bias at room temperature.     

The effects of item composition,tag inlay design,reader antenna polarization,power and transponder orientation on the dynamic coupling efficiency of backscatter ultra‐high frequency radio frequency identification

The effects of packaged content, packaging material, transponder inlay design, reader antenna polarization, interrogation power and transponder orientation on the detection rate of ultra‐high frequency radio frequency identification (UHF RFID) passive transponders were studied. The influence of individual factors and their interactions were determined using general linear model analysis of variance. Influences originated in order of importance, from sample type, antenna polarization, power and inlay design. Important interactions in decreasing order of significance exist between: power and antenna polarization; sample type and antenna polarization; sample type and inlay design; inlay design and antenna polarization; sample type, power and antenna polarization; sample type and power; inlay design and power; sample type, inlay design and power. It was also observed that random orientation of tags did not cause a statistically significant variation in tag detection rate. It can be concluded that the use of UHF RFID for item level of food requires multi‐parameter assessment before hand. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of stitching and weave architecture on the high strain rate compression response of affordable woven carbon/epoxy composites

In this study, experimental investigations on stitched and unstitched woven carbon/epoxy laminates under high strain rate compression loading are discussed. Stitched/unstitched laminates are fabricated with aerospace grade plain and satin weave fabrics with room temperature curing SC-15 epoxy resin using affordable vacuum assisted resin infusion molding process. The samples are subjected to high strain rate loading using modified compression split Hopkinson’s pressure bar at three different strain rates ranging from 320 to 1149 s⁻¹. Results are discussed in terms of unstitched/stitched configuration, fabric type and loading directions. Dynamic compression properties are compared with those of static loading. Failure mechanisms are characterized through optical and scanning microscopy.     

An experimental and numerical study of the dynamic response of a free–free aluminum beam under high velocity transverse impact

Experiments and numerical simulations on the dynamic behavior of free–free aluminum beams subjected to high velocity transverse impact were performed using single-stage light gas gun and nonlinear finite element program, LS-DYNA. A cylindrical free–free beam with a diameter of 30 mm is impacted symmetrically and asymmetrically by a cylindrical aluminum projectile with a diameter of 10 mm in the present experiment. The lengths of the beam and projectile are 150 mm and 20 mm, respectively. It is shown that the responses of free–free beam include elastic–plastic deformation, structural failure and fragmentation. The number of fragments, the local deformation and the mass dissipation of the free–free beam increase linearly with the increase of the initial impact velocity of the projectile. However, the non-dimensional velocity at the central point of the free–free beam decreases with the increase of the initial impact velocity of the projectile and is independent of the impact location. It is found that the dependence of the kinetic energy of the free–free beam on the impact velocity of the projectile is similar to the dependence of the maximum velocity at the central point of the beam on the impact velocity of the projectile. Energy partitions are further predicted. For example, when impact velocity is 400 m/s, the ratio of kinetic energy of the beam to impact energy is 3.3 J while the ratios due to plastic energy dissipation and fragmentation are 15 J and 54% respectively. The rest remains in projectile. It is found that the energy partitions in high velocity impact case are nearly independent of impact location, which is different from those subjected to low velocity impact.     

Experimental and theoretical elucidation on the inhibition mechanism of 1-methyl-5-mercapto-1,2,3,4-tetrazole self-assembled films on corrosion of iron in 0.5 M H2SO4 Solutions

The self-assembled films of 1-methyl-5-mercapto-1,2,3,4-tetrazole (MMT) were prepared on the iron surface. By means of electrochemical impedance spectroscopy in 0.5 M H₂SO₄ solutions, the inhibition ability of the film was investigated. Results were discussed through changing the concentrations of the inhibitor and the pH values of the self-assembly solutions. Quantum chemical calculation was applied to elucidate the adsorption mechanism of the inhibitor molecule to iron atom. The study shows that MMT is a good inhibitor for iron in 0.5 M H₂SO₄ solutions. The self-assembled films formed in 10⁻² M acidic solutions have the best protection effect and the inhibition efficiency in 0.5 M H₂SO₄ solutions is 98.0%. Density functional theory proves that MMT molecule is adsorbed on the iron surface by the most negatively charged nitrogen atom and the adsorption can occur spontaneously.     

γ射线辐照对高模量碳纤维及碳纤维/氰酸酯复合材料性能的影响

通过模拟空间γ射线辐照环境,采用⁶⁰Co-γ射线对高模量碳纤维及其增强的改性氰酸酯复合材料进行辐照,采用SEM和XRD对辐照前后的碳纤维及碳纤维/氰酸酯复合材料进行了分析和表征,研究了复合材料的质量损失率、拉伸性能及层间剪切强度随γ射线辐照剂量的变化规律。结果表明,γ射线辐照能增加碳纤维表面粗糙度;质量损失率随γ射线辐照剂量增大先增加后趋于平缓,但均小于1%;碳纤维/氰酸酯复合材料拉伸性能与层间剪切强度均随γ射线辐照剂量增大先提高后降低,在吸收剂量为5×10⁵ rad时出现最大值,拉伸强度为1 803 MPa,拉伸模量为243 GPa,层间剪切强度为72 MPa。     

First principles study on the structural properties and electronic structure of X2B (X = Cr, Mn, Fe, Co, Ni, Mo and W) compounds

First principles calculations are performed to study the stability, electronic and structural properties of X₂B (X = Cr, Mn, Fe, Co, Ni, Mo and W). The calculated cohesive energy and formation enthalpy of these compounds both have negative values, which indicate that they are thermodynamically stable structures. The ground states of Cr₂B and Mn₂B are anti-ferromagnetic; Fe₂B and Co₂B are ferromagnetic; Ni₂B, Mo₂B and W₂B are paramagnetic. The calculated local magnetic of Fe₂B is 1.962μ_B/Fe, and for Co₂B is 1.182μ_B/Co. They are comparable to the values of Fe₃B (1.97μ_B/Fe) and Co₃B (1.18μ_B/Co), but smaller than pure Fe and Co. The observed magnetic behaviors of X₂B compounds can be explained by Stoner’s model. Two main peaks are observed in the calculated PDOS (partial density of states) of these compounds (P1 and P2). P1 is caused by strong covalent X–B bonds and P2 is attributed to metallic X–X bonds.