Micromachining a miniaturized capillary electrophoresis-based chemical analysis system on a chip

Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.     

Capillary-tube scanner for mechanized microbiology. A photoelectric scanner measures growth in agar-filled capillaries and gives a new approach to microbiology

Growing microcolonies of bacteria can be detected by their light-scattering property. We have described a system in which growing bacteria in glass capillaries filled with nutrient agar are counted as the capillaries move through a narrow beam of light. Increased counts after incubation indicate the presence of viable organisms in the original sample; the equipment can detect colonies when they grow to a diameter of 8 microm. Aerobic, anaerobic, and facultative organisms can grow in the capillary environment. The sensitivities of several organisms to antibiotics were determined by adding antibiotics to the agar before the capillaries were filled.     

玻璃毛细管色谱柱在氨基甲酸酯农药残留分析上的应用

氨基甲酸酯农药的广泛应用,给农药残留分析提出了新课题。此类化合物稳定性差,在色谱柱上极易分解;如用衍生化法解决此问题,往往使分析过程复杂。T.A.Wehner 与J.N.Seiber 曾用分离性能强的惰性石英毛细管柱分离了呋喃丹等氨基甲酸酯农药。石英     

Conducting carbon wires in ordered, nanometer-sized channels

The encapsulation of graphite-type carbon wires in the regular, 3-nanometer-wide hexagonal channels of the mesoporous host MCM-41 is reported. Acrylonitrile monomers are introduced through vapor or solution transfer and polymerized in the channels with external radical initiators. Pyrolysis of the intrachannel polyacrylonitrile results in filaments whose microwave conductivity is about 10 times that of bulk carbonized polyacrylonitrile. The MCM host plays a key role in ordering the carbon structure, most likely through the parallel alignment of the precursor polymer chains in the channels. The fabrication of stable carbon filaments in ordered, nanometer-sized channels represents an important step toward the development of nanometer electronics.     

Polywater: methods for identifying polywater columns and evidence for ordered growth

The refractive indices of polywater columns in glass capillaries have been rapidly and accurately measured with an interference microscope. Polywater has been detected by this method in both quartz and Vycor glass capillaries. A comparison of refractive index measurements with measurements of optical anisotropy indicates that polywater initially condenses with an ordered structure.     

Synchrotron X-ray Diffraction from a Microscopic Single Crystal Under Pressure

Metallic filaments with submicrometer diametere have been fabricated. Standard diffraction techniques with conventional x-ray sources were unsuccessful in identifying the structure of these materials. However, with the use of synchrotron radiation produced on a wiggler beam line, diffraction data were obtained in measurement periods as short as 10 milliseconds. Two cylindrical single crystals of bismuth were studied, each with a diameter of 0.22 +/- 0.02 micrometer. The volume of sample illuminated for these measurements was 0.38 cubic micrometer, less than 0.5 femtoliter. The crystals are grown in glass capillaries, and, because bismuth expands on solidification, they are under a residual hoop stress. The crystallographic data indicate the presence of a linear compressive strain of about 2 percent, which is assumed to be the result of a residual stress of about 2 gigapascals.     

微滤机净化污(废)水研究

在滤网孔隙可视为平行等长等半径毛细管和孔隙内流态为层流的假定下,推导并讨论了恒水头作用下的两过滤指数公式.给出了计算平席纹和斜席纹孔隙面积、孔隙率的公式及对MK0、MK1、MK2、04、05网的计算结果.建立了用于SS显微计数的"十字"法,并发现"十字"法比标准法要简单12倍而精度却几乎相同。根据微滤机净化污废水的实验,结果,作者阐明了微滤机理以机械筛滤作用为主.     

等径球颗粒群流动特征实验研究

为考察等径球颗粒流动特性以便正确地设计模型试验或简化离散元计算,进行了透明可视的二维(单层紧密排列)平底仓钢珠卸料实验、拟二维矩形料槽玻璃球卸料实验和三维半圆柱平底仓玻璃球卸料实验。结果表明:二维(单层)精确等径球颗粒床具有微晶格效应,因此流动是畸变的;半圆柱仓的三维流动不出现畸变;而第3方向取几个球厚度的拟二维流动也避免了微晶格效应和畸变。透明半圆柱平底仓的玻璃球卸料实验表明用它取代圆柱仓可以较好反映圆柱仓内颗粒流动规律。拟二维和半圆柱仓的简化对诸如球床式核反应堆堆芯内球流一类问题的模型实验和离散元模拟有实用价值。     

Improving the density of jammed disordered packings using ellipsoids

Packing problems, such as how densely objects can fill a volume, are among the most ancient and persistent problems in mathematics and science. For equal spheres, it has only recently been proved that the face-centered cubic lattice has the highest possible packing fraction phi=pi/18 approximately 0.74. It is also well known that certain random (amorphous) jammed packings have phi approximately 0.64. Here, we show experimentally and with a new simulation algorithm that ellipsoids can randomly pack more densely-up to phi= 0.68 to 0.71 for spheroids with an aspect ratio close to that of M&M's Candies-and even approach phi approximately 0.74 for ellipsoids with other aspect ratios. We suggest that the higher density is directly related to the higher number of degrees of freedom per particle and thus the larger number of particle contacts required to mechanically stabilize the packing. We measured the number of contacts per particle Z approximately 10 for our spheroids, as compared to Z approximately 6 for spheres. Our results have implications for a broad range of scientific disciplines, including the properties of granular media and ceramics, glass formation, and discrete geometry.     

External calcium ions are required for potassium channel gating in squid neurons

The effects of calcium removal on the voltage-dependent potassium channels of isolated squid neurons were studied with whole cell patch-clamp techniques. When the calcium ion concentration was lowered from 10 to 0 millimolar (that is, no added calcium), potassium channel activity, identified from its characteristic time course, disappeared within a few seconds and there was a parallel increase in resting membrane conductance and in the holding current. The close temporal correlation of the changes in the three parameters suggests that potassium channels lose their ability to close in the absence of calcium and simultaneously lose their selectivity. If potassium channels were blocked by barium ion before calcium ion was removed, the increases in membrane conductance and holding current were delayed or prevented. Thus calcium is an essential cofactor in the gating of potassium channels in squid neurons.     

基于PLC 的脐橙分拣及装箱自动系统设计

脐橙的大小对其味道有重要影响,但人工分拣的方式存在随意性大、客观性不强等缺陷,为此设计了一种脐橙自动分拣及装箱系统,采用传感器对传送带上的脐橙进行大小判断后进入不同的通道的方法,达到了良好的分拣效果.并通过PLC对整个脐橙的供料、检测分级、纸箱供应、装箱等过程实现了自动控制,通过测试该系统降低了劳动强度、提高了效率,且排除了人工因素,产品质量得到了更好保证,为脐橙产业经济的发展提供了技术支持.     

Nanowire array composites

Long, nanometer-size metallic wires can be synthesized by injection of the conducting melt into nanochannel insulating plates. Large-area arrays of parallel wires 200 nanometers in diameter and 50 micrometers long with a packing density of 5 x 10(8) per square centimeter have been fabricated in this way. When charged, the ends of the wires generate strong, short-range electric fields. The nanowire electric fields have been imaged at high spatial resolution with a scanning force microscope.     

Transfer of biologically derived nanometer-scale patterns to smooth substrates

Atomic force microscopy has been used to measure the surface profile of a periodic array of 10-nanometer (nm)-diameter holes fabricated by fast-atom beam milling of a smooth graphite surface in which a 3.5-nm-thick titanium oxide screen was used as a mask. The nanostructured titanium oxide mask was itself derived from a protein crystal template. Pattern transfer from the biological crystal to the metal oxide film and finally to the graphite substrate was accomplished entirely by parallel processing.     

木材皱缩现象中的力学问题探讨

长期以来,木材皱缩现象一直被认为主要是因为木材中液体毛细张力产生的“负压强”压溃细胞壁造成的,该文对此提出了质疑.作者根据YoungLaplace定律设计了一组毛细负压强直接测量试验,发现凹液面上的毛细张力并不能使液体的压强降低.根据水在玻璃表面形成二维冰新结构这一最新发现,对毛细负压强及产生皱缩的主要动力问题提出了一些新的假设.     

Structure and properties of metallic glasses

Recent experience has shown that certain metal alloys can be put into glass form by rapid melt-quenching or by various condensation processes. Models for the nature and structure of these glasses are surveyed and shown to be quite parallel to those already developed for the more common nonmetallic glasses. The rather unique magnetic, superconducting, and mechanical properties and the technical potential of metallic glasses are also discussed.     

Three-dimensionally ordered array of air bubbles in a polymer film

We report the formation of a three-dimensionally ordered array of air bubbles of monodisperse pore size in a polymer film through a templating mechanism based on thermocapillary convection. Dilute solutions of a simple, coil-like polymer in a volatile solvent are cast on a glass slide in the presence of moist air flowing across the surface. Evaporative cooling and the generation of an ordered array of breath figures leads to the formation of multilayers of hexagonally packed water droplets that are preserved in the final, solid polymer film as spherical air bubbles. The dimensions of these bubbles can be controlled simply by changing the velocity of the airflow across the surface. When these three-dimensionally ordered macroporous materials have pore dimensions comparable to the wavelength of visible light, they are of interest as photonic band gaps and optical stop-bands.     

Parallel and serial neural mechanisms for visual search in macaque area V4

To find a target object in a crowded scene, a face in a crowd for example, the visual system might turn the neural representation of each object on and off in a serial fashion, testing each representation against a template of the target item. Alternatively, it might allow the processing of all objects in parallel but bias activity in favor of those neurons that represent critical features of the target, until the target emerges from the background. To test these possibilities, we recorded neurons in area V4 of monkeys freely scanning a complex array to find a target defined by color, shape, or both. Throughout the period of searching, neurons gave enhanced responses and synchronized their activity in the gamma range whenever a preferred stimulus in their receptive field matched a feature of the target, as predicted by parallel models. Neurons also gave enhanced responses to candidate targets that were selected for saccades, or foveation, reflecting a serial component of visual search. Thus, serial and parallel mechanisms of response enhancement and neural synchrony work together to identify objects in a scene. To find a target object in a crowded scene, a face in a crowd for example, the visual system might turn the neural representation of each object on and off in a serial fashion, testing each representation against a template of the target item. Alternatively, it might allow the processing of all objects in parallel but bias activity in favor of those neurons that represent critical features of the target, until the target emerges from the background. To test these possibilities, we recorded neurons in area V4 of monkeys freely scanning a complex array to find a target defined by color, shape, or both. Throughout the period of searching, neurons gave enhanced responses and synchronized their activity in the gamma range whenever a preferred stimulus in their receptive field matched a feature of the target, as predicted by parallel models. Neurons also gave enhanced responses to candidate targets that were selected for saccades, or foveation, reflecting a serial component of visual search. Thus, serial and parallel mechanisms of response enhancement and neural synchrony work together to identify objects in a scene.     

Unimpeded permeation of water through helium-leak-tight graphene-based membranes

Permeation through nanometer pores is important in the design of materials for filtration and separation techniques and because of unusual fundamental behavior arising at the molecular scale. We found that submicrometer-thick membranes made from graphene oxide can be completely impermeable to liquids, vapors, and gases, including helium, but these membranes allow unimpeded permeation of water (H(2)O permeates through the membranes at least 10(10) times faster than He). We attribute these seemingly incompatible observations to a low-friction flow of a monolayer of water through two-dimensional capillaries formed by closely spaced graphene sheets. Diffusion of other molecules is blocked by reversible narrowing of the capillaries in low humidity and/or by their clogging with water.     

Ultrahigh-density nanowire arrays grown in self-assembled diblock copolymer templates

We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition, we fabricated vertical arrays of nanowires with densities in excess of 1.9 x 10(11) wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current lithographic processes, and amenable to multilayered device fabrication.     

极化敏感均匀圆阵中PARAFAC信号检测算法

分析了极化敏感均匀圆阵接收到的信号，该信号具有三线性模型特征。提出了极化敏感均匀圆阵中平行因子信号检测算法。该算法利用三线性交替最小二乘（TALS）算法估计出信源矩阵，然后对其进行判决。仿真结果表明；该算法误码率性能接近于非盲解相关方法;与非盲解相关方法相比，在较高的SNR情况下误码率相差不到2dB；且在阵列扰动情况下仍具有较好的误码率性能。该算法无需空域信息和极化信息，是一种盲鲁棒方法。