基于径向偏振光束的微粒捕获与操控

因为空间变化的偏振分布及独特的聚焦特性,径向偏振光束在粒子捕获及操控方面有独特的应用价值。从理论和实验方面研究了基于径向偏振光束的微粒捕获与操控。首先,介绍了捕获力的计算方法,重点基于光线理论模型计算了径向偏振光束的轴向及横向捕获效率,并与切向偏振光和圆偏振光的捕获效率进行了比较;然后,基于倒置显微镜和空间光调制器搭建了光学捕获与操控系统,采用两种不同的成像物镜实现了对直径为10μm左右的酵母菌细胞及直径为1μm的苯乙烯小球的捕获和操控,根据预定的轨迹实现了粒子的稳定移动,体现了该类型光镊较为宽阔的应用前景;最后,简要分析了影响粒子捕获及操控的若干因素,为系统改进提供了指导意见。     

超声空化预处理对尖晶石LiMn2O4性能的影响

采用超声空化-固相合成法制备尖晶石LiMn2O4,用TG-DTA、XRD、SEM、激光粒度分析和充放电测试等研究了超声空化对材料的组成、晶体结构、表观形貌、粒度分布和电化学性能的影响.结果表明:超声空化产生的机械活化效应降低了材料的合成温度,提高了尖晶石LiMn2O4的结晶度和结构稳定性;超声空化对材料制备过程中的加速成核和控制晶核的生长是有利的,能得到较好的颗粒形貌和粒度分布;经过超声空化预处理的样品的首次放电比容量为125.34 mAh/g,20次循环后的容量仅衰减5.54%.     

An investigation into major factors in shunt capacitor switchingperformances by vacuum circuit breakers with copper-chromium contacts

The performance of vacuum circuit breakers in switching shunt capacitors depends much more on in-rush current than on interrupting current. This is because when contacts that were fused together by pre-arcs during contact closing are forcibly separated, large protrusions are formed on the contact surface, making it easier for microparticles to be detached from the protrusions. Microparticles are also produced on the entire surface of contacts by mechanical impact or cold weld. Current interruption of a certain magnitude, however, has a conditioning effect because moderate arcs can eliminate such microparticles and lower the protrusions. To clarify the relationship between the behavior of microparticles and the dielectric breakdown, a laser scattering technique was employed. The authors found a microparticle-induced breakdown phenomena that could explain the mechanism of long delayed restrikes that is occasionally observed in vacuum circuit breakers     

水轮机转轮叶片的表面性能研究

研究了表面超音速微粒轰击(纳米化)和喷丸强化两种表面处理方法对疲劳性能的影响,并对沿表面一定深度内残余应力的分布状态、表面组织、硬度变化进行了分析,同时还对每种状态下的抗空化性能进行了试验研究。     

Influence of high-energy impact on the physical and technical characteristics of coal fuels

Currently, in the world’s large-scale coal-fired power industry, the combustion of pulverized coal is the most widely spread technology of combusting the coals. In recent years, the micropulverization technology for preparation and combustion of the coal has been developed in this field. As applied to the small-scale power industry, the method of combusting the coal in the form of a coal–water slurry has been explored for years. Fine coal powders are produced and used in the pulverized-coal gasification. Therefore, the coal preparation methods that involve high-dispersion disintegration of coals attract the greatest interest. The article deals with the problems of high-energy impact on the coal during the preparation of pulverized-coal fuels and coal–water slurries, in particular, during the milling of the coal in ball drum mills and the subsequent regrinding in disintegrators or the cavitation treatment of the coal–water slurries. The investigations were conducted using samples of anthracite and lignite from Belovskii open-pit mine (Kuznetsk Basin). It is shown that both the disintegration and the cavitation treatment are efficient methods for controlling the fuel characteristics. Both methods allow increasing the degree of dispersion of the coal. The content of the small-sized particles reground by cavitation considerably exceeds the similar figure obtained using the disintegrator. The specific surface area of the coal is increased by both cavitation and disintegration with the cavitation treatment producing a considerably greater effect. Being subjected to the cavitation treatment, most coal particles assume the form of a split characterized by the thermodynamically nonequilibrium state. Under external action, in particular, of temperature, the morphological structure of such pulverized materials changes faster and, consequently, the combustion of the treated coal should occur more efficiently. The obtained results are explained from the physical point of view.     

Characterizing biostructures and cellular events in 2D/3D [usingwide-field and confocal optical sectioning microscopy]

Cellular structures are made up of a very interesting puzzle of components, whose changes in molecular distribution are believed to underlie a wide range of cellular functions. For example, the cell cycle of mammalian cells is characterised by a series of ordered biochemical events. The availability of several specific probes has led to a renewed interest in optical microscopy as a very powerful tool in cell and molecular biology. This has led to the development of methods for studying the relationship between the 3D structure of specific cellular constituents and the cell function. Within this framework, several methods have been developed and applied. In the authors' study, wide-field optical sectioning microscopy and confocal scanning laser microscopy have been utilised, demonstrating the feasibility of a 3D reconstruction of biostructures imaged by an optical microscope     

Microsecond laser ablation of thrombus and gelatin under clearliquids: Contact versus noncontact

Laser thrombolysis is a procedure for removing blood clots in occluded arteries using pulsed laser energy. The laser light is delivered through an optical fiber to the thrombus. The ablation process is profoundly affected by whether the optical fiber tip is inside a catheter or is in contact with the thrombus. This study measured ablation efficiency of 1-μs laser pulses to remove a porcine clot confined in a silicone tube. The cavitation process was investigated by visualizing laser-induced bubble formation on gelatin targets with flash photography and measuring the acoustic transients with a pressure transducer. The laser spot size did not affect the mass of material removed. The efficiency of the contact ablation was at least three times greater than that of the noncontact ablation. Finally, the mass removed was closely correlated with the measured bubble expansion pressure     

On-Chip Cell Sorting System Using Thermoreversible Gelation Polymer

We have developed a microfabricated fluorescence-activated cell sorter system using laminar flow of thermoreversible gelation polymer (TGP). The glass sorter chip consists of microchannels with two inlets for sample and buffer solutions, and two outlets for collection and waste of the specimen. A biological specimen containing fluorescently labeled cells, is mixed with a solution containing a TGP. The laminar flow of the mixed solution and buffer solution are then introduced into the sorter chip. The fluorescently labeled target cells were detected with sensitive fluorescence microscopy. In the absence of a fluorescence signal, the laminar flow of the specimen is directed into the waste channel. Upon detection of a fluorescence signal from the target cells, the sol-gel transformation was locally induced by site-directed infrared laser irradiation for the flow switching and for allowing the fluorescent cells to be channeled into the collection reservoir. The flow switching time of 100 ms was achieved. Using this system, we have demonstrated the sorting of Escherichia coli cells expressing fluorescent proteins. These cells were found to be viable after extraction from the sorting system, indicating no damage to the cells     

Corneal refractive surgery with femtosecond lasers

We investigated the use of ultrashort pulsed (femtosecond) laser technology in corneal refractive surgery. When compared to longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable all-solid-state femtosecond laser system for all studies to demonstrate practicality in real-world operating conditions. Contiguous tissue effects were achieved by scanning a 5-μm focused laser spot below the corneal surface at pulse energies of approximately 2-4 μJ. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratornileusis). Preliminary in vivo studies of intrastromal vision correction suggest that consistent refractive changes can also be achieved with this method. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques     

Induction charging of granular materials in an electric field

It is well known that particles can be freely levitated in an electric field due to the charge induced on the particles by the external field. The charge depends upon the electric field strength and particle properties. This paper studies some of these factors to investigate the fundamentals of induction charging for granular materials. An experimental apparatus was set up to collect the levitated particles in a filter contained in a Faraday pail and the charge-to-mass (Q/M) ratio was obtained based on the charge and mass measurements for the samples in the filter. Furthermore, the particle size distribution was measured and analyzed by laser diffraction and microscopy and the surface mean diameter (D/sub s/) and volume mean diameter (D/sub v/) were obtained. In these experiments irregular shaped Al/sub 2/O/sub 3/ particles and spherical glass beads with a size range of 42-390 /spl mu/m were used and tested at different electric field strengths. By combining the results of Q/M, D/sub s/ and D/sub v/, the charge per particle was calculated and the results compared with theoretical values. It was confirmed that the particle charge is dependent upon the electric field strength and the particle properties of size, shape, density, resistivity, and adhesive force.     

Photothermal imaging of nanoparticles and cells

This review summarizes the findings of recent applications of time-domain far-field photothermal (PT) technique to the detection and imaging of nanoscale absorbing particles. This two-beam (pump-probe) technique is based on time-resolved PT visualization of laser-induced thermal effects around nanoparticles. Imaging is accomplished, after an adjustable time delay after the pump laser pulse, with a second probe beam that senses the nanotarget. Using a tunable optical parametric oscillator laser (wavelength, 420 to 570 nm; energy, 0.1-300 /spl mu/J; pulse width, 8 ns) as the pump laser and a Raman shifter (639 nm, 10 nJ, 13 ns) as the probe laser, with a tunable delay of 0 to 5 000 ns of the probe pulse relative to the pump pulse, this approach has demonstrated the capability to visualize nanoscale gold particles (2 to 250 nm) alone and in cells, liposomes (30 to 90 nm), neutral red-stained particles (30 to 500 nm), and polystyrene beads. Different applications of the time-resolved PT technique are discussed, including imaging of absorbing cellular nanostructures and optimization of selective killing of cancer cells and bacteria.     

轴流转桨式水轮机空化程度声信号辨识研究

通过空化声信号判断水轮机中的空化程度是水轮机空化检测的方向和难题,为此进行了轴流转桨式水轮机模型转轮空化试验:选择了4个常用桨叶角度,固定桨叶角度和水头,调整尾水位改变空化状态,试验中用频率范围达1MHz的超声传感器测量空化声信号,并对转轮室空化进行录像。通过观察试验闪频录像,把空化严重程度划分为4个典型的级别,以此作为验证声信号辨识算法的判据。在分析试验数据的基础上,提出空化声信号特征矢量分类法,即把采集到的声信号按频段划分,每个频段的方差作为一维,组成空化特征矢量、通过对特征矢量的空间分类来判别轴流转桨式水轮机空化严重程度。用该方法处理所有试验数据,给出与录像观测进行比较的统计结果,表明该方法是可行和有效的。     

Analysis of cavitation dynamics during pulsed laser tissue ablationby optical on-line monitoring

Flashlamp pumped mid-IR laser systems emitting in the 2-3-μm wavelength range are widely used for various medical applications, especially for tissue ablation. Explosive evaporation is inevitably associated with this process due to the short pulse durations of these laser systems and the high absorption of tissue and water in this spectral regime. Tissue displacement and dissection occur in liquid environment as a consequence of the induced cavitation. Depending on the application these processes might enhance the tissue ablation but can also cause adverse tissue effects. The ablation dynamics were investigated by evaluating the change in reflected probe-light intensity re-emitted from the application fiber tip. The ablated cavity and the signal was correlated to fast-flash photographs of the event. Based on this reflection signal a water/tissue discrimination system is introduced which can widely support medical laser applications. In laser sclerostomy ab externo, for example, this approach can be used as a feedback system to automatically control the ablation process. With such a system, adverse effects to adjacent tissue in the anterior chamber of the eye can be minimized     

空蚀磨损翼型流场特性试验研究

在建立了能够模拟水力机械内部流动特征的翼型空蚀磨损试验装置后,针对翼型表面的流场流动特性进行试验研究.试验采用PIV系统对不同空化数下翼型表面不同断面流场进行大量图像采集,对无空化工况各断面计算其涡量流线及速度分布,对空化工况获取不同时刻翼型表面空穴结构.试验结果揭示了翼型表面涡量流线和速度分布以及其随空化数变化的特征,同时给出了翼型表面空穴结构周期性变化规律及原因,为开展翼型空蚀、磨损及两者联合作用提供了理论支持.     

堆焊不锈钢气蚀和气蚀磨损的研究

通过旋转圆盘式气蚀试验台和回转泥沙磨损试验装置,砰定了18—8、0Cr13Ni16Mo和0Cr16Ni5Mo堆焊金属的抗气蚀和抗气蚀磨损性能。讨论了材料的硬度和冲击韧性对气蚀和气蚀磨损的影响,概述了材料呈现的气蚀破环形状。     

轴流式转轮叶片中弧线形状对空化性能的影响

在轴流式水轮机的运行和维修中,空蚀问题尤其突出,情冴严重的会导致经常停机、维修周期延长,影响了电站的正常运行,造成经济损失。因此,提高轴流式转轮的空化性能是水力优化设计的重点工作。本文将叶片中弧线形状作为研究对象,采用CFD计算模拟和模型试验的方法,展示了两种具有不同中弧线形状叶片的转轮的空化性能。研究表明,具有双向挠曲中弧线的叶片的空化性能优于单向挠曲中弧线的叶片,中弧线形状与转轮空化性能关系紧密,可以作为一个单独的几何参数来优化轴流式转轮叶片翼型。     

Characterization and properties of anatase TiO2 film prepared via colloidal sol method under low temperature

Nanocrystalline titanium dioxide particles and films with anatase structures have been prepared via solvothermal method under low temperature. The products were characterized by X-ray diffraction and transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The optical properties were characterized in the ultraviolet-visible region by optical absorption measurement. The relationship between the optical band gaps and the structures was studied.     

Electrical Conductivity of CeO2 Prepared from Nanosized Powders

Nanosized powders of cerium dioxide with controlled physical properties were prepared by the precipitation technique using ammonium hydroxide or oxalic acid as precipitating agent. The calcined precursors were studied by nitrogen adsorption to determine the specific surface area, X-ray diffraction for phase characterization and crystallite size determination, and by laser scattering for particle size distribution. The morphology of powder particles was observed by scanning electron microscopy. It is shown that both precipitating materials may be used for the preparation of nanocrystalline powders (< 10 nm) with high values of specific surface area (> 90 m² g^{– 1}). The observed differences between powders prepared from hydroxides or oxalates rely on the distribution of particle sizes and in the morphology of the agglomerated particles. Impedance spectroscopy experiments were carried out in the 5 Hz–13 MHz frequency range under controlled partial pressure of oxygen from 10 ppm to 1 atm. The analysis of these results allowed for the determination of the charge carriers responsible for the electrical transport in the ceria sintered pellets.     

Conductivity and space charge in LDPE containing nano- and micro-sized ZnO particles

DC conductivity and ac impedance measurements were made in air and in vacuum on samples of low density polyethylene to which nano-sized and micro-sized ZnO particles and a dispersant had been added. The samples were 150-200 mum thick. The temperature range was 30-70degC. The temperature dependence of the vacuum dc conductivity in samples containing the dispersant and 10% w/w nanosized ZnO followed an Arrhenius relationship closely, the conductivity being 1-2 orders of magnitude lower than that of a sample containing dispersant only. The addition of 10% w/w microsized ZnO had very little effect on the dc conductivity. The ac measurements were made in the frequency range 10 mHz-1 MHz. Addition of nanoparticles increased the ac conductivity at higher frequencies but decreased it at lower frequencies, the cross-over frequency increasing with increasing temperature. The real part of the relative permittivity of samples with nanoparticles was increased relative to that of samples containing dispersant only, at all temperatures, but the corresponding values in samples with microparticles were unchanged, within experimental error. Space charge profiles were obtained using the laser-intensity-modulation-method (LIMM). Space charge densities of order 300 Cm^-3 were measured in the bulk near the electrodes, several hours after poling at field strengths around 30 kV/mm.     

通气对空化引起振动的影响

为了研究通气对旋旋涡空化所引起振动的影响,把不同量的气体通入射流放水阀阀针后部的旋涡空化区。分别在通气和不通气条件下,用安装在分流栅区域阀壁上的加速度仪测量了空化所引起的振动,通过快速富立中变换（FFT）分析了振动加速度的频段分布和强度,发现旋涡空化所引起振动主要发生在10KHZ－23KHZ的频段范围内。通气可以有效地抑 生的振动强度,随通气量的增加振动强度逐渐降低,实验表明,随空气化的减小相同通气量条件。对振动的影响逐渐变弱。