Experimental Study on Electrical Breakdown for Devices with Micrometer Gaps

The understanding of electrical breakdown in atmospheric air across micrometer gaps is critically important for the insulation design of micro ＆ nano electronic devices. In this paper, planar aluminum electrodes with gaps ranging from 2μm to 40 #m were fabricated by microelectromechanical system technology. The influence factors including gap width and surface dielectric states were experimentally investigated using the home-built test and measurement system. Results showed that for SiO2 layers the current sustained at 2-3 nA during most of the pre-breakdown period, and then rose rapidly to 10-30 nA just before breakdown due to field electron emission, followed by the breakdown. The breakdown voltage curves demonstrated three stages： （1） a constantly decreasing region （the gap width d 〈5 μm）, where the field emission effect played an important role just near breakdown, supplying enough initial electrons for the breakdown process; （2） a plateau region with a near constant breakdown potential （5 μm〈 d 〈10 μm）; （3） a region for large gaps that adhered to Paschen＇s curve （d 〉10μm）. And the surface dielectric states including the surface resistivity and secondary electron yield were verified to be related to the propagation of discharge due to the interaction between initial electrons and dielectrics.

全系统动态误差建模理论分析与应用

对测量系统进行动态特性和精度理论研究必须建立测量系统的数学模型。针对传统建模方法的缺陷,研究分析了全系统动态误差建模理论与方法,该建模理论与方法充分考虑了系统内部各组成环节的信息,建立的模型能够反映实际测量系统内部各结构单元的传递特性随时间变化对系统测量精度的影响。该建模理论与方法具有普遍的适用意义,不管是动态测量系统还是静态测量系统,用该建模理论与方法都能够建立其全误差模型。最后利用全系统动态误差建模理论与方法建立了测微系统(百分表)的全误差模型,并进行了实验验证。

Histological Studies of Atrazine Toxicity on the Thyroid Gland in Rats

Little is known about the toxic activity of the atrazine (a herbicide, commonly used in agricultural production) on the thyroid gland. In this study the compound was administered orally in female albino rats at sublethal exposure equivalent to 0.2 LD50 doses for 6 and 12 days. At termination of dosing the anesthetized animals were killed and blood was drawn for the determination of serum triiodothyronine (T3) and thyroxin (T4). A dose-dependent decrease of serum T3 concentration was observed in all the groups (control: 0.57 nmol·L-1; 6 days: 0.35 nmol·L-1; 12 days: 0.21 nmol·L-1). The thyroid gland was examined light-microscopically. Bouin's solution-fixed thyroids were embedded in paraffin and sections cut at 6 μm, stained separately with toluidine blue according to Slinchenko's method. Histologically in experimental groups epithelium featured small cuboidal cells and occasional structures of the follicles confluence within epitheliomers. A dose-dependent changes of the following parameters were observed: (a) increasing of number of follicle-building thyroid cells; (b) increasing of follicular volume, (c) decreasing of nucleus volume. Investigation of the whole population of thyroid mast cells disclosed no change in degranulation intensity. By contrast, degranulation intensity was decreased in perifollicular mast cells from groups treated with atrazine in dose-dependent manner.There are no changes observed in degranulation of stromal mast cells. These results suggesting that differences in response to the atrazine might account for an aspect of the functional heterogeneity within the rat thyroid mast cell population.

MICROSCOPIC CORROSION STUDIES OF DUPLEX STAINLESS STEELS

Electrochemical scanning tunneling microscopy and scanning electrochemical microscopy have been used for in situ monitoring of localized corrosion processes of different Duplex stainless steels (DSS) in acidic chloride solutions. The techniques allow imaging of local dissolution events with micrometer resolution, as opposed to conventional electrochemical techniques, which only give an overall view of the corrosion behavior. In addition, combined scanning Kelvin probe force microscopy and magnetic force microscopy were used for mapping the Volta potential variation over the surface of DSSs. A significant difference in Volta potential between the austenite and ferrite phases suggests galvanic interaction between the phases. A compositional gradient appears within 2 micrometers across the phase boundary, as seen with scanning Auger microscopy (SAM). In all, the studies suggest that higher alloyed DSS exhibit a more homogeneous dissolution behavior than lower alloyed DSS, due to higher and more similar corrosion resistance of the two phases, and enhanced resistance of the ferrite/austenite phase boundary regions.

The Physical and Biological Properties of NanoTiO₂Material

The physical and biological properties of TiO2 materials including nano TiO2, micrometer-TiO2 and nano TiO2 tubes have been studied using scanning electron and infrared spectrometer, X-ray diffraction instrument as well as 3-(4,5- dimethylthiazol 2-yl)-2,5 diphenyltetrazolium bromide (MTT) colorimetric method, respectively. These materials are prepared by chemical deposition and anode oxidation methods, respectively. The sizes of nano TiO2 are 80 nm and 1000 nm, respectively, their infrared properties of absorption are different, the characteristic peaks of the former are 1271,1615, 2957 and 3422 cm-1, the latter are 1645 and 2356 cm-1. The nano TiO2 tubes can be formed by anode oxidation method, its diameters are between 50-100 nm, different nano TiO2 tubes contain different components of oxygen and titanium. In MTT experiment we discover the changes of properties of proliferation of the liver and chick embryo fibroblast cells under influences of nanoTiO2 relative to those of the controlled groups, when small nanoTiO2 suspension is added in these cultivated liquids of cell, but the influence of nano TiO2 on the proliferation of the person’s liver cell is still very small, therefore, the toxicities of nano TiO2 containing 80nm and 1000 nm to these cells are still first score.

岩土工程应变监测中的线法原理及便携式系列仪器(二)

The Concept of linewise observation and portable instruments are introduced in this paper.The instruments can be used in west geotecnique engineering for fleld monitoring.Along the measuring line marks and casings in same interval are flned instcad of Probes in this way one probe can serve many measuring boreholes and projects.Some probes can monitor axial strain,some one measure both axial and lateral strain or displaCement in one ho1e in any directions.The information and accuracy obtained will be much more and higher than that gained by flxed probes base on pointwise observation.Ten cases are introduced briefly in the paper as well.

Molecular Dynamics Simulations of the Interactions Between Tungsten Dust and Beryllium Plasma-Facing Material

In the present research,molecular dynamics simulation is applied to study the interactions between tungsten dusts and a beryllium plasma-facing material surface.Calculation results show that it is quite difficult for nanometer-size dust particles to damage the plasma-facing material surface,which is different from the micrometer-size ones.The reason may be the size difference between dust and crystal grains.The depth of dust penetration into plasma-facing materials is closely related to the incident velocity,and the impacting angle also plays an important role.Dust and material surface damage is also investigated.Results show that both incident velocity and angle can significantly influence the damage.

04083 Serono与Micromet就MT201签署协议

瑞士Serono公司与德国Micromet公司已就后者的完全人单克隆抗体MT201(adecatumumab)(Ⅰ)的开发和商业化签署专有协议。目前(Ⅰ)处于Ⅱ期临床试验阶段，用于治疗前列腺癌和转移性乳腺癌。

3D X-ray microscopy with a CsPbBr3 nanowire scintillator

X-ray microscopy is an essential imaging method in many scientific fields,which can be extended to three-dimensional(3D)using tomography.Recently,metal halide perovskite(MHP)nanomaterials have become a promising candidate for X-ray scintillators,due to their high light yield,high spatial resolution,and easy fabrication.Tomography requires many projections and therefore scintillators with excellent stability.This is challenging for MHPs,which often suffer from fast degradation under X-ray irradiation and ambient conditions.Here,we demonstrate that MHP scintillators of CsPbBr3 nanowires(diameter:60 nm,length:5–9μm)grown in anodized aluminum oxide(CsPbBr3 NW/AAO)have sufficient stability for X-ray micro-tomography.A tomogram was taken with a Cu X-ray source over 41 h(dose 4.2 Gyair).During this period the scintillator brightness fluctuated less than 5%,which enabled a successful reconstruction.A long-term study with 2 weeks of continuous X-ray exposure(37.5 Gyair)showed less than 14%fluctuations in brightness and no long-term degradation,despite variations in the ambient relative humidity from 7.4%RH to 34.2%RH.The resolution was stable at(180±20)lp·mm−1,i.e.,about 2.8 micron.This demonstrates that CsPbBr3 NW/AAO scintillators are promising candidates for high resolution X-ray imaging detectors.

Whole-brain Optical Imaging:A Powerful Tool for Precise Brain Mapping at the Mesoscopic Level

The mammalian brain is a highly complex network that consists of millions to billions of densely-interconnected neurons.Precise dissection of neural circuits at the mesoscopic level can provide important structural information for understanding the brain.Optical approaches can achieve submicron lateral resolution and achieve“optical sectioning”by a variety of means,which has the natural advantage of allowing the observation of neural circuits at the mesoscopic level.Automated whole-brain optical imaging methods based on tissue clearing or histological sectioning surpass the limitation of optical imaging depth in biological tissues and can provide delicate structural information in a large volume of tissues.Combined with various fluorescent labeling techniques,whole-brain optical imaging methods have shown great potential in the brain-wide quantitative profiling of cells,circuits,and blood vessels.In this review,we summarize the principles and implementations of various whole-brain optical imaging methods and provide some concepts regarding their future development.

Size control of monodisperse nonporous silica particles by seed particle growth

Monodisperse nonporous silica particles were prepared by sol-precipitation via seed particle growth method, and the particle size, which varied from 1.0 to 4.7 μm, was strictly controlled in our experiment, The formation of secondary particles, which resulted in a multimodaI distribution of particle size, was suppressed by changing tetraethoxysilane （TEOS） concentration and reaction temperature. Furthermore, the effect of adding small amounts of electrolyte to the hydrolysis mixture was examined.

Dilatometric Analysis of Irreversible Volume Change during Phase Transformation in Pure Iron

One assumption underlying the conventional dilatometric analysis based on the lever rule is that the volume of the specimen changes isotropically during phase transformation,which conflicts with the irreversible length change shown in actual measurements.The contribution of this irreversible effect to the dilation data of pure iron upon heating and cooling was respectively quantified via conversion equations based on lattice parameters.A model considering the elastic strain and creep deformation was established for both the interpretation of the irreversible volume change and the discrepancy between the results measured by a dilatometer and a micrometer.