逆布雷顿循环微型低温制冷机

在目前广泛采用的低温制冷循环中,以透平机械为主的逆布雷顿循环制冷机有望能够满足卫星,宇宙飞船等航天器上低冷量,高性能,高效率的特殊要求,成为空间制冷的一种选择,总结了近几年空间用逆布雷顿循环制冷机的研究成果,表明由ＤＣ－ＡＣ转换器,微型离心式压缩机,微型透平膨胀机及高效紧凑式换热器组成的微型逆布雷顿循环制冷机是一种有前途的微低温制冷机。     

Enhanced green emission from Tb-Bi co-doped GdAlO3 nanophosphors

Bi³⁺ and Tb³⁺ ions co-doped GdAlO₃ (GAP) nanophosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GAP phosphor confirms their orthorhombic phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of GAP:Tb³⁺, Bi³⁺ phosphors consist of a broad band in the shorter wavelength region due to the 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with the 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and some sharp peaks in the longer wavelength region due to f → f transitions of Tb³⁺ ions. The present phosphors exhibit green color due to strong ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The emission intensity was enhanced by co-doping with Bi³⁺ ions under 292 nm excitation, which indicate that the efficient energy transfer occurred from Bi³⁺ to Tb³⁺ ions.     

Different shape of GaAs quantum structures under various growth conditions

We report the influences of growth parameters on the characteristics of GaAs quantum rings (QRs) and quantum dots (QDs) formed on AlGaAs/GaAs by the droplet epitaxy (DE) method. After forming Ga droplets on the AlGaAs/GaAs surface, varying amounts of arsenic (As) flux were introduced to fabricate the GaAs quantum structures. By decreasing the As flux from 8 × 10^− 5 to 3 × 10^− 5 Torr, the shape of the GaAs quantum structures was changed from QDs to elongated QRs. With further decreasing As flux, the shape of the elongated QRs became symmetric. The formation characteristics of the GaAs QRs from the QDs with the amount of As flux were discussed in terms of migration behaviors of the gallium (Ga) atoms on the GaAs(001)-c(4 × 4) surface. The effects of the amount of Ga supply and the growth temperature for the deposition of Ga droplets on the formation of the GaAs quantum structures were also considered.     

石膏型渗流制备泡沫铝填充圆管压缩行为研究

采用石膏型渗流制备开孔泡沫铝并填充到薄壁圆管,制成泡沫铝夹心管.通过准静态压缩试验研究了泡沫铝夹心管的压缩行为.结果表明:采用石膏型渗流法制备的泡沫铝孔隙率在85％左右,其压缩变形阶段可分为弹性段、塑性平台段和致密化段;空心圆管的压缩行为与其本身的结构参数有关;泡沫铝夹心管的力学性能与吸能能力比空心圆管和泡沫铝有了一定...     

热电材料研究的最新进展

热电材料是一种能将电能与热能相互转换的功能材料,近年来备受关注.从块体热电材料、低维热电材料、热电器件及其应用等方面综述了热电材料研究的最新进展,并展望了今后的发展方向.     

Integrated liquid crystal optical switch based on double teeth-shaped structure at telecom wavelengths

The characteristics of a double teeth-shaped plasmonic optical switch are analyzed. Based on the metal–insulator–metal waveguide consisting of double rectangular teeth, a nanoscale liquid crystal optical switch is proposed and numerically simulated by using the finite difference time domain method with a perfectly matched layer absorbing boundary condition. It is found that the double teeth-shaped structure filled with liquid crystal can realize the function of a switch. The modulation depth of the double teeth-shaped structure is larger than 50?dB.     

The solution growth of copper nanowires and nanotubes is driven by screw dislocations

Copper (Cu) nanowires (NWs) are inexpensive conducting nanomaterials intensively explored for transparent conducting electrodes and other applications. However, the mechanism for solution growth of Cu NWs remains elusive so far. Here we show that the one-dimensional anisotropic growth of Cu NWs and nanotubes (NTs) in solution is driven by axial screw dislocations. All three types of evidence for dislocation-driven growth have been conclusively observed using transmission electron microscopy (TEM) techniques: rigorous two-beam TEM analysis that conclusively characterizes the dislocations in the NWs to be pure screw dislocations along <110> direction, twist contour analysis that confirms the presence of Eshelby twist associated with the dislocation, and the observation of spontaneously formed hollow NTs. The reduction-oxidation (redox) electrochemical reaction forming the Cu NWs presents new chemistry for controlling supersaturation to promote dislocation-driven NW growth. Using this understanding to intentionally manipulate the supersaturation, we have further improved the NW growth by using a continuous flow reactor to yield longer Cu NWs under much milder chemical conditions. The rational synthesis of Cu NWs with control over size and geometry will facilitate their applications.     

Studied on a novel human keratinocyte membrane delivery system in vitro

The culture of keratinocytes on flexible membranes has been proposed as a means to simplify, accelerate and improve the efficiency with which proliferating cells are delivered to full thickness or non-healing skin defects. The purpose of this article was to study the ability of chitosan-gelatin manbranes to facilitate the growth of human keratinocytes. The membranes with different chitosan contents were studied. The surface properties of chitosan-gelatin membranes were investigate by SEM, and water contact angle test. The mechanical property of the membranes was tested. Data implied that gelatin could make the membranes more flexible and hydrophilic than chitosan membranes, which may regulate the seeded cells behavior. Loading human keratinocytes on chitosan-gelatin membranes, cells attachment, spread, and growth were investigated by light microscopy, SEM, and MTT test. The results suggested that the adhesion and proliferation of keratinocytes seeded on chitosan-gelatin membranes were same as on tissue culture plate, in which gelatin could modify the interaction between keratinocytes and chitosan membranes. Therefore, chitosan-gelatin membrane is a good candidate for keratinocytes delivery system.     

核壳型碳铁纳米粉体的制备及磁性能研究

采用直流碳弧法制备碳包铁纳米粒子,用透射电子显微镜(TEM)、X射线衍射仪(XRD)对产物的形貌和尺寸、物相结构组成进行分析,并在真空和氮气气氛下在200～800℃对制备的碳包铁纳米粒子进行热处理,用振动样品磁强计测量处理前后的碳包铁纳米粒子的剩磁强度、矫顽力和饱和磁化强度.结果表明,碳包铁纳米粒子的磁滞回线显示出较好的超顺磁特性;剩磁强度、矫顽力和饱和磁化强度随着粉体中铁含量的增加而增大.对碳包铁纳米粒子进行热处理,其磁性能随温度的升高首先改善,温度进一步升高又逐步劣化.在450℃退火,粉体磁性能最佳.