Vacuum‐driven fluid manipulation by a piezoelectric diaphragm micropump for microfluidic droplet generation with a rapid system response time

Recently, we developed a convenient microfluidic droplet generation device based on vacuum‐driven fluid manipulation with a piezoelectric diaphragm micropump. In the present study built on our previous work, we investigate the influence of settings applied to the piezoelectric pump, such as peak‐to‐peak drive voltage (V_p‐p) and wave frequency, on droplet generation characteristics. Stepwise adjustments to the drive voltage in ±10‐V_p‐p increments over the range of 200?250 V_p‐p during droplet creation revealed that the droplet generation rate could be reproducibly controlled at a specific drive voltage. The droplet generation rate switched within <0.5 s after the input of a new voltage. Although the droplet generation rate depended on the drive voltage, this setting had almost no influence on droplet size. The frequency over the selected range (50?60 Hz) did not markedly influence the droplet generation rate or droplet size. We show that the current fluid manipulation system can be conveniently used for both droplet generation and for rapid droplet reading, which is required in many microfluidic‐based applications.     

X-ray radiography of aluminum cathodes eroded in high-current vacuum arcs

The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode.     

Zero dissipation limit to rarefaction wave with vacuum for the one-dimensional non-isentropic micropolar equations

The zero dissipation limit of the one-dimensional non-isentropic micropolar equations is studied in this paper. If the given rarefaction wave which connects to vacuum at one side, a sequence of solution to the micropolar equations can be constructed which converge to the above rarefaction wave with vacuum as the viscosity and the heat conduction coefficient tend to zero. Moreover, the uniform convergence rate is obtained. The key point in our analysis is how to control the degeneracies in the vacuum region in the zero dissipation limit process.     

Spray Freeze-drying – The Process of Choice for Low Water Soluble Drugs?

Most of the novel highly potent drugs, developed on the basis of modern molecular medicine, taking into account cell surface recognition techniques, show poor water solubility. A chemical modification of the drug substance enhancing the solubility often decreases the pharmacological activity. Thus, as an alternative an increase of the solubility can be obtained by the reduction of the size of the drug particles. Unfortunately, it is often difficult to obtain micro or nanosized drug particles by classical or more advanced crystallization using supercritical gases or by milling techniques. In addition, nanosized particles are often not physically stable and need to be stabilized in an appropriate matrix. Thus, it may be of interest to manufacture directly nanosized drug particles stabilized in an inert hydrophilic matrix, i.e. nanostructured and nanocomposite systems. Solid solutions and solid dispersions represent nanostructured and nanocomposite systems. In this context, the use of the vacuum-fluidized-bed technique for the spray-drying of a low water soluble drug cosolubilized with a hydrophilic excipient in a polar organic solvent is discussed. In order to avoid the use of organic solvents, a special spray-freeze-drying technique working at atmospheric pressure is presented. This process is very suitable for temperature and otherwise sensitive drugs such as pharmaproteins.     

Development of Vacuum Monitoring System in the HL-2A tokamak

HL-2A is the first divertor tokamak in China. The vacuum system is one of the important parts of the HL-2A tokamak, which has to be work well during the physics campaign in 2004. As the tokamak machine is separated from the operation staff during discharges, to guarantee the safe and reliable operation of the vacuum system, it is necessary to watch the vacuum system outside the machine hall with an automatic monitoring system. The paper describes the design and manufacture of the monitoring system.     

Simulation of Vacuum Microelectronic Triode Made of Single Carbon Nanotube

Vacuum microelectronic triode performance, based upon a unit cell with a nanotube field emitter, gate, and anode, was evaluated via computer simulation. Electron emission was calculated from the modified Fowler-Nordheim equation. The dependence of emitted current, upon geometrical factors, e.g., nanotube radius, nanotube height, and gate's hole radius, is shown. The device design parameters of trans-conductance, and cutoff frequency have been calculated, which show that this structure can be used as a microwave and millimeter wave amplifier. Electron current flux is shown for time-dependent 1–Thz sinusoidal variation frequency input.     

光辅助超高真空CVD系统制备SiGe异质结双极晶体管研究

介绍了采用紫外光化学汽相淀积(UVCVD)、超高真空化学汽相淀积(UHVCVD)和超低压化学汽相淀积(ULPCVD)技术研制的化学汽相淀积(CVD)工艺系统,简称U³CVD系统.应用该系统,在450℃低温和10^-7Pa超高真空环境下研制出了硅锗(SiGe)材料和硅锗异质结双极晶体管(SiGe HBT)材料.实验表明,该系统制备的SiGe HBT材料性能良好.     

基于优化探测窗口的光斑质心探测方法

哈特曼-夏克波前传感器进行波前探测时，用子孔径光斑强度的一阶矩来计算光斑质心位置，子孔径窗口作为探测窗口，但探测时子孔径窗口内噪声对一阶矩有很大的影响，会使质心探测精度产生很大的误差。因此在计算质心位置时探测窗口的选取对探测精度有重要影响，必须选取合适的探测窗口来提高光斑质心探测精度。为此，在传统算法的基础上提出优化探测窗口的方法来提高质心探测精度,仿真和实验结果表明新方法提高了质心探测的精度，未经处理的高噪声恢复波前的波前残差峰谷值是2.851 4λ，均方根值是0.606 3λ，优化探测窗口后波前残差的峰谷值是1.636 2 λ，均方根值是0.367 1 λ，重构误差减小了40％。证明了算法的可行性和稳定性。     

Ultraviolet photoemission spectroscopy of hydrogen complex deactivation on InP:Zn(1 0 0) surfaces

Ultraviolet photoemission spectroscopy is used to study the kinetics of the H-Zn complex deactivation in Zn doped InP(1 0 0). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultra-high vacuum show a dramatic change in the work function of the material with increasing temperature. Spectral features are also shown to be sensitive to sample temperature. To our knowledge, we show the first view of hydrogen retrapping at the surface using photoemission spectroscopy. A simple photoelectron threshold energy analysis shows the state of charge compensation of the material.