A study of the mixture formation process of a diesel spray under phase change

The purpose of this study was to analyze the structure and to clarify the mixture formation process within evaporative diesel spray. Liquid fuel was injected from a single-hole nozzle (l/d=1.0mm/0.2mm) into a constant-volume vessel under high pressure and temperature in order to visualize the spray phenomena. An exciplex fluorescence method was applied to the evaporative fuel spray to measure and investigate both the liquid and the vapor phase of the injected spray. The region of interest in this experiment was downstream towards the end of the spray. For accurate investigation, images of the liquid and vapor phase regions were recorded with a 35mm still camera and CCD camera, respectively. For the case of the evaporative fuel spray, the images showed that within the region of liquid phase very small droplets could be found outside of the spray and larger droplets at the spray’s tip. This can be explained through the droplet classification defined byStokes number (stk) (Chung et al., 1990). From the 2-dimensional analysis results of the heterogeneous distribution of the inner spray, a 3-dimensional analysis was attempted by using the offset incidence of the laser beam from the spray’s center axis. Finally, in order to quantify the mixture’s state change within the vapor phase region of the injected spray, images analysis were carried out based on the entropy of statistical thermodynamics.     

FTIR spectroscopy and nanotribological comparative studies: influence of the adsorbed water layers on the tribological behaviour

Under ambient conditions, a water film is always present on a silica substrate and generates additional capillary forces between the nanotip and the studied surface. In the present paper, we report AFM measurements of pull-off and friction forces as a function of the temperature and a comparative FTIR spectroscopy study. The AFM results show a net decrease of the forces as the temperature increases, while the IR spectroscopy indicates that the liquid film is removed at high temperature. Consequently, we deduce that a liquid neck is created between the tip and the surface and that the forces measured are mostly capillary forces. The present work shows that temperature studies with AFM can be a useful way to probe the influence of the capillary force in turn to characterize surface properties.     

Thermodynamic and aerodynamic meanline analysis of wet compression in a centrifugal compressor

Wet compression means the injection of water droplets into the compressor of gas turbines. This method decreases the compression work and increases the turbine output by decreasing the compressor exit temperature through the evaporation of water droplets inside the compressor. Researches on wet compression, up to now, have been focused on the thermodynamic analysis of wet compression where the decrease in exit flow temperature and compression work is demonstrated. This paper provides thermodynamic and aerodynamic analysis on wet compression in a centrifugal compressor for a microturbine. The meanline dry compression performance analysis of centrifugal compressor is coupled with the thermodynamic equation of wet compression to get the meanline performance of wet compression. The most influencing parameter in the analysis is the evaporative rate of water droplets. It is found that the impeller exit flow temperature and compression work decreases as the evaporative rate increases. And the exit flow angle decreases as the evaporative rate increases.     

Mechanical properties of plasma membrane and nuclear envelope measured by scanning probe microscope

Atomic force microscopy has been used to visualize nano‐scale structures of various cellular components and to characterize mechanical properties of biomolecules. In spite of its ability to measure non‐fixed samples in liquid, the application of AFM for living cell manipulation has been hampered by the lack of knowledge of the mechanical properties of living cells. In this study, we successfully combine AFM imaging and force measurement to characterize the mechanical properties of the plasma membrane and the nuclear envelope of living HeLa cells in a culture medium. We examine cantilevers with different physical properties (spring constant, tip angle and length) to find out the one suitable for living cell imaging and manipulation. Our results of elasticity measurement revealed that both the plasma membrane and the nuclear envelope are soft enough to absorb a large deformation by the AFM probe. The penetrations of the plasma membrane and the nuclear envelope were possible when the probe indents the cell membranes far down close to a hard glass surface. These results provide useful information to the development of single‐cell manipulation techniques.     

INJECTION VOLUME CONTROL BY THERMAL WAY IN TRANSGENIC DNA MICRO-INJECTION SYSTEM

Nowdays there are several manual or half-automatic methods developed to drive the DNA micro-fluid of transgenic micro-injection and they often fail to control precisely the injection volume at picolitres level. Micro-size of the injector tip and viscosity of the DNA liquid also lead to dead area of volume control. An adequate way is presented utilizing temperature gradients to direct liquid flow in the pipette from the warmer to the cooler. Compared with the previous ones, this way is helpful in decreasing the dead area of controlling through decreasing the viscous rate of DNA liquid, which changes as the temperature varies. The DNA liquid is pushed by a sheer stress at the liquid-pipette interface, which emerges when viscous rate of the liquid changes. Preliminary experimenting results show the efficiency and convenience of this way in improving the system's characteristics.     

原位电离小型便携式质谱法现场快速筛查婴幼儿洗护用品中的危害物质

采用原位电离和小型便携式质谱技术建立了婴幼儿洗护用品中危害物质的现场快速筛查方法。将婴幼儿湿巾样品所含液体滴加在三角形色谱纸基上,再滴加萃取喷雾溶剂,采用纸喷雾电离方式进行萃取和电离;牙膏、奶瓶洗涤剂和护臀膏等黏性样品通过金属微电极蘸取样品,插入预先注入萃取喷雾溶剂的毛细管中,采用萃取纳升喷雾电离方式进行萃取和电离。无需繁琐耗时的样品前处理过程,同时结合小型便携式质谱仪,可在1 min内完成样品的现场快速筛查分析,8种目标物质的检出限在10~50 μg/kg之间。该方法简单快速、灵敏高效,适用于婴幼儿洗护用品中危害物质的现场快速筛查。     

界面张力驱动的微粒自组装研究

界面张力驱动的液-液界面／液-固界面微粒自组装是一种新型的自组装方法，其主要原理是通过物理手段，使微粒在界面张力驱动作用下，聚集成二维有序结构。文中首先介绍了微粒自组装的基本原理和发展现状，而后对作者实现的亚毫米量级微粒自组装作了介绍，最后对实验结果进行了初步的理论分析。     

Glass transitions in nanoscale heated volumes of thin polystyrene films

Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic force microscopy incorporating a thermal tip. Three-dimensional spatial nanoconfinements were achieved by controlling size and boundary conditions of small heated volumes of polymer nanostrands drawn from the polymer surface with the thermal tip, using appropriate loads and temperatures at the tip-polymer contact. Finite element analysis was performed to model mechanical contact and thermal transport, including the effects of contact radius, film thickness, and load on temperature and pressure distributions in the confined volume at the contact. The glass transition temperature (T(g)) was measured by observing the softening of polymers with increasing temperature. The measured surface T(g) exhibited a strong size dependence, while the subsurface T(g) increased with decreasing the distance to the substrate. A large increase in the surface T(g) was observed when the radius of contact was reduced below about 10 nm. The increase in the glass transition temperature at the surface was attributed to the presence of surface and line tension at the nanometer contact, while the enhanced T(g) near the substrate was attributed to the pinning effects that reduces the mobility of the polymer molecules in the film over several hundreds of nanometers away from the polymer-substrate interface.     

基于LS-SVM的机械式温度仪表误差预测研究

机械式温度仪表在测量过程中易受到环境温度、毛细管长度以及内部机构影响而出现测量精度不高、非线性的情况,针对这些问题以液体压力式温度仪表作为研究对象,提出了基于最小二乘支持向量机(LS-SVM)的温度误差建模预测的方法。通过分析液体压力式温度仪表的测温结构和误差影响因素,将环境温度及毛细管长度等特征参数作为模型输入,将误差值及误差随毛细管长度的变化率作为输出。根据回归预测的原理,利用网格搜索和交叉验证的方法寻找最优参数组合,建立液体压力式温度仪表的误差预测模型。实验结果表明,该模型可以有效地描述温度误差,并将此建模方法与常用的支持向量机回归建模方法进行比较,基于LS-SVM得到的误差预测模型精度较高、推广能力强,可以对机械式温度仪表进行补偿,为探索机械式温度仪表自适应补偿机构提供理论依据。     

Iterative image-based modeling and control for higher scanning probe microscope performance

In this article, we develop an image-based approach to model and control the dynamics of scanning probe microscopes (SPMs) during high-speed operations. SPMs are key enabling tools in the experimental investigation and manipulation of nano- and subnanoscale phenomena; however, the speed at which the SPM probe can be positioned over the sample surface is limited due to adverse dynamic effects. It is noted that SPM speed can be increased using model-based control techniques. Modeling the SPM dynamics is, however, challenging because currently available sensing methods do not measure the SPM tip directly. Additionally, the resolution of currently available sensing methods is limited by noise at higher bandwidth. Our main contribution is an iterative image-based modeling method which overcomes these modeling difficulties (caused by sensing limitations). The method is applied to model an experimental scanning tunneling microscope (STM) system and to achieve high-speed imaging. Specifically, we model the STM up to a frequency of 2000 Hz (corresponds to approximately 23 of the resonance frequency of our system) and achieve approximately 1.2% error in 1 nm square images at that same frequency.     

一种医用射流雾化器工作原理的仿真与分析

雾化吸入是临床上常用的介入手段,可帮助气管切开患者进行机械通气,也能够以更有效地方式为呼吸道疾病患者给药。研究从雾化的基本原理着手,分析典型雾化器的几何结构,根据作用机理将雾化过程划分为毛细上升,喷口雾化及撞击回流和气溶胶喷出等三个阶段,并结合流体体积法对雾化过程所涉及到的二相流动进行数值分析。稳态分析结果验证了喷口处由于气流压力小于大气压而产生的负压,确认了毛细上升过程中驱动药液运动的核心动力。瞬态分析结果发现药液沿着液膜-液丝-液滴的流程逐渐雾化成液滴。这些分析结果厘清了雾化器的基本工作过程,对后续雾化器的性能表征和结构优化设计具有指导意义。     

基于双流体动力学的微流体分配新技术

根据驱动原理将非接触式微流体分配技术分为间接驱动和直接驱动。现有技术采用间接驱动原理,通过驱动介质与静止流体的动能交换实现流体的运动,完成分配过程。新技术采用直接驱动原理,根据气液两相流理论,将气体和液体射流同时引入混合腔,在一定的气液流速比范围内,气体和液体射流自发在混合腔内形成气液两相断塞流,可获得均匀间隔、流型稳定的液滴和气泡,气液两相均具有体积一致的特点,可实现不同黏度液体的高频率、微体积的精确分配。     

毛细力辅助飞秒激光直写制备各向异性及多级结构

将飞秒激光双光子聚合加工技术和毛细力诱导自组装技术相结合实现了各向异性结构和多级结构的制备。首先,使用飞秒激光双光子加工技术加工出微柱阵列,将微柱置于显影液中显影,然后放置在空气中。在显影液蒸发的过程中,微柱结构单元受到毛细力的作用而弯曲实现自组装。通过控制微柱的高度和直径的不一致性实现了两种各向异性结构制备方法,并成功制备了底层微柱直径分别为2μm和6μm双层结构。由于毛细力的大小和微柱高度无关,且同样端部变形量下较高微柱的弹性回复力小于较低微柱的弹性回复力,更易发生弯曲;直径较大的微柱具有更强的抗弯曲能力,从而引导直径较小的微柱向较大的微柱倾斜,藉此制备了各向异性结构。使用毛细力自组装辅助飞秒激光微纳加工可以实现灵活可控的复杂3D结构的加工,并将在生物医药、化学分析、微流体等领域发挥重要作用。     

Nanometer-scale heat-conductivity measurements on biological samples

With semiconductor structures reaching the nanometer scale, heat conductivity measurements on the mesoscopic range of some tens of nanometers become an increasingly important aspect for the further improvement in digital processing and storage. Also the attempt to use atomic-force microscopy (AFM) technology for high-density data storage by writing information bits as nanometer-sized indentations into a polymer substrate with a heated cantilever tip asks for a careful investigation of the nano-scale heat-conductivity properties of polymers. Furthermore, in many AFM imaging applications, heat conductivity can provide additional information about the material the imaged structures consist of. In this respect, heat conductivity can also become very interesting in studies of usually quite heterogeneous biological samples, if the resolution can attain the nanometer range. In standard scanning thermal microscopy application, the tip forms a thermocouple, which precludes high-resolution imaging, as thermocouples cannot be made sufficiently small. In this paper, which focuses on biological applications, we demonstrate that by using an ultra sharp AFM cantilever with a Joule heating element above the tip structure different molecular components can be distinguished thanks to their different heat-conductivity properties. In this case, the resolution is determined by the actual tip size, and it can reach 10nm.     

High precision self-alignment using liquid surface tension for additively manufactured micro components

Self-assembly of components using liquid surface tension is an attractive alternative to traditional robotic pick-and-place as it offers high assembly accuracy for coarse initial part placement. One of the key requirements of this method is the containment of the liquid within a designated binding site. This paper looks to expand the applications of self-assembly and investigates the use of topographical structures applied to 3D printed micro components for self-assembly using liquid surface tension. An analysis of the effect of edge geometry on liquid contact angle was conducted. A range of binding sites were produced with varying edge geometries, 45–135°, and for a variety of site shapes and sizes, 0.4–1 mm in diameter, and 0.5 mm × 0.5 mm–1 mm × 1 mm square. Liquid water droplets were applied to the structures and contact angles measured. Significant increases in contact angle were observed, up to 158°, compared to 70° for droplets on planar surfaces, demonstrating the ability of these binding sites to successfully pin the triple contact line at the boundary. Three challenging self-assembly cases were examined: (1) linear initial component misplacement >0.5 mm, (2) angular misplacement of components, and (3) misplacement of droplet. Across all three assembly cases the lowest misalignments in final component position, as well as highest repeatability, were observed for structures with actual edge geometries <90° (excluding 45° nominal), where the mean magnitude of misalignment was found to be 31 μm with 14 μm standard deviation.     

The influence of coating structure on micromachine stiction

Stiction and friction in micromachines is commonly inhibited through the use of silane coupling agents such as 1H-, 1H-, 2H-, 2H-perfluorodecyltrichlorosilane (FDTS). FDTS coatings have allowed micromachine parts processed in water to be released without debilitating capillary adhesion occurring. These coatings are frequently considered as densely-packed monolayers, well-bonded to the substrate. In this paper, it is demonstrated that FDTS coatings can exhibit complex nanoscale structures, which control whether micromachine parts release or not. Surface images obtained via atomic force microscopy reveal that FDTS coating solutions can generate micellar aggregates that deposit on substrate surfaces. Interferometric imaging of model beam structures shows that stiction is high when the droplets are present and low when only monolayers are deposited. As the aggregate thickness (tens of nanometers) is insufficient to bridge the 2 m gap under the beams, the aggregates appear to promote beam–substrate adhesion by changing the wetting characteristics of coated surfaces. Contact angle measurements and condensation figure experiments have been performed on surfaces and under coated beams to quantify the changes in interfacial properties that accompany different coating structures. These results may explain the irreproducibility that is often observed with these films.     

Enhancement of pneumatic nebulization efficiency through application of an electric field

A technique is described for reducing the size of aerosol droplets produced by a pneumatic nebulizer of the kind commonly used in flame or plasma spectrometry. The technique involves the application of an electric field to the tip of the nebulizer, resulting in an induced surface charge on the liquid being nebulized. In turn, the surface charge reduces the liquid's surface tension and results in the generation of a finer aerosol. In this study, the effect of the electric field is quantified in terms of the spatial dispersion and size distribution of aerosol droplets formed in the presence and absence of the field. Droplet size distributions, obtained using the MgO impression technique and analyzed using log-normal and upper-limit functions, reveal a 63% decrease in the volume mean droplet diameter in the field's presence. As a result, this system is expected to be useful in both flame and plasma spectrometry, where reduced droplet size can yield improved precision and freedom from interferences.     

电喷雾萃取电离-四极杆飞行时间质谱快速分析一次性注射器中的挥发性有机物残留

一次性医用注射器中残留的有机物会通过注射药物进入人体,对健康构成危害。本研究利用电喷雾萃取电离-四极杆飞行时间质谱仪(EESI-Q TOF MS)快速检测和分析一次性注射器中的挥发性有机物残留。通过优化载气流量和毛细管电压,确定了最佳实验条件。在3种不同品牌的10 mL一次性医用注射器中检测到多种挥发性物质。选取10个信号强度大于5 000的离子,利用碰撞诱导解离进行定性分析。对注射器中残留的环己酮进行半定量分析,检出限为0.13 μg/L。实验还发现,环己酮在不同品牌的10 mL注射器中的含量为0.39~0.64 μg/L,在50 mL注射器中的最大残留浓度达到2.52 μg/L。结果表明,注射器体积越大,有机物残留量越高。该研究可为一次性注射器有机物残留检测和质量控制提供快速有效的技术手段。     

Monte carlo calculations for the mechanical relaxation of a self-assembled monolayer and for the structures of alkane/metal interfaces

Configurational-bias Monte Carlo calculations have been used to study the mechanical relaxation of a monolayer of CH₃(CH₂)₁₅S admolecules on a gold substrate when subjected to indentation by a force-microscope tip. Compression leads to substantial but reversible changes in molecular tilt angle and chain conformations. The same Monte Carlo technique has been used to probe the structural properties of liquid hexadecane films in contact with a flat metal substrate.     

新型可控焦距液体透镜阵列

为了提高成像品质,提出了一种新型液体透镜阵列镜头。先将油滴沉入弹性体底部形成具有可控焦距的单个液体平凸透镜,再通过唯一平台实验液体透镜阵列,制作液体透镜阵列。通过控制滴入硅胶基底的硅油液体体积大小,控制单个微透镜的折射面曲率和透镜焦距。通过位移平台,控制阵列中微透镜的排布和个数。透镜阵列制作方法简单且成本低,透镜抗挤压能力强,焦距可控,阵列规整,在制造过程中,可以控制镜头光圈和初始焦距,因此是一种实用性较高的透镜阵列。