平面变立交

你一定都遇到过在十字路口发生交通堵塞的情况,滚滚车流交叉在一起,行进速度异常缓慢,有时甚至寸步难行。为解决堵塞问题,大家就想到了立体交通,使来去多个方向的车辆立体交叉行驶,互不干扰,畅通无阻。如果说平面交通是将车流集中在一处,立体交通就是将车流分布在不同的面。那么你是否想过用分布式的计算环境替代集中式的密集型计算系统呢?随着计算机网络化的发展,许多传统大型机客户纷纷向分布式计算环境转移,这无疑增强了工作站的计算能力,同时也降低了成本,但却带来了如何在分布和异构计算机网络中形成协调一致的计算环境问题。Platform     

Influence of the image quality deterioration of a tilted thick specimen on electron tomography

In electron tomography (ET) based on a transmission electron microscope, the effective thickness of a specimen increases with the tilt angle and, therefore, the projection quality may deteriorate because of electron scattering. The information-missing region, however, can be reduced by broadening the specimen tilt range. To clarify the general influence of these effects on ET, the projection quality varying with the tilt angle was quantitatively evaluated for a 5-microm thick specimen observed with a 3 MV ultrahigh-voltage electron microscope. Simulations of three-dimensional reconstruction were then performed for different specimen thicknesses and tilt ranges. As a result, the ET accuracy was shown to decrease as the specimen thickness increased. However, an optimum specimen-tilt range, at which ET could reach its highest accuracy, was found to exist and become small with the increase of the specimen thickness. The presented results are helpful for determining the specimen thickness limitation on the ET resolution and improving the ET fidelity of thick specimens.     

"Conflicting" motion cues to the visual and vestibular self-motion systems around 0.06 Hz evoke simulator sickness

The basic question this research addressed was, how does simulator sickness vary with simulated motion frequency? Participants were 11 women and 19 men, 20 to 63 years of age. A visual self-motion frequency response curve was determined using a Chattecx posture platform with a VR4 head-mounted display (HMD) or a back-projected dome. That curve and one for vestibular self-motion specify a frequency range in which vestibular and visual motion stimuli could produce conflicting self-motion cues. Using a rotating chair and the HMD, a third experiment supported (p < .01) the hypothesis that conflicting cues at the frequency of maximum "crossover" between the curves (about 0.06 Hz) would be more likely to evoke simulator sickness than would conflicting cues at a higher frequency. Actual or potential applications of this work include a preliminary design guidance curve that indicates the frequency range of simulated motion that is likely to evoke simulator or virtual reality sickness; for simulators intended to operate in this frequency range, appropriate simulator sickness interventions should be considered during the design process.     

Electrochemical detection of single-nucleotide mismatches: application of M-DNA

The detection of a single-nucleotide mismatch in unlabeled duplex DNA by electrochemical methods is presented. Impedance spectroscopy is used to characterize a perfect duplex monolayer and three DNA monolayers differing in the position of the mismatch. The monolayers were studied as B-DNA (normal duplex DNA) and after conversion to M-DNA (a metalated duplex). Modeling of the impedance data to an equivalent circuit provides parameters that are useful in discriminating the four monolayer configurations. The resistance to charge transfer, R(CT), was lower for all duplexes after conversion to M-DNA. Contrary to expectations, R(CT) was also found to decrease for duplexes containing a mismatch. However, R(CT) was found to be diagnostic for mismatch detection. In particular, the difference in R(CT) between B- and M-DNA (deltaR(CT)) decreased from 190(22) omega.cm(2) for a perfectly matched duplex to 95(20), 30(20), and 85(20) omega.cm(2) for a mismatch at the top (distal), middle, and bottom (proximal) positions of the monolayer with respect to the gold surface. Further, a method to form loosely packed single-stranded (ss)-DNA monolayers by duplex dehybridization that is able to rehybridize to target strands is presented. Rehybridization efficiencies were in the range of 40-70%. Under incomplete hybridization conditions, the R(CT) was the same for matched and mismatched duplexes under B-DNA conditions. However, deltaR(CT) between B- and M-DNA, under incomplete hybridization, still provided a distinction. The deltaR(CT) for a perfect duplex was 76(12) omega.cm(2), whereas a mismatch in the middle of the sequence yielded a deltaR(CT) value of 30(15) omega.cm(2). The detection limit was measured and the impedance methodology reliably detected single DNA base pair mismatches at concentrations as low as 100 pM.     

Bead-based electrochemical immunoassay for bacteriophage MS2

Viruses are one of four classes of biothreat agents, and bacteriophage MS2 has been used as a simulant for biothreat viruses, such as smallpox. A paramagnetic bead-based electrochemical immunoassay has been developed for detecting bacteriophage MS2. The immunoassay sandwich was made by attaching a biotinylated rabbit anti-MS2 IgG to a streptavidin-coated bead, capturing the virus, and then attaching a rabbit anti-MS2 IgG-beta-galactosidase conjugate to another site on the virus. beta-Galactosidase converts p-aminophenyl galactopyranoside (PAPG) to p-aminophenol (PAP). PAPG is electroinactive at the potential at which PAP is oxidized to p-quinone imine (PQI), so the current resulting from the oxidation of PAP to PQI is directly proportional to the concentration of antigen in the sample. The immunoassay was detected with rotating disk electrode (RDE) amperometry and an interdigitated array (IDA) electrode. With an applied potential of +290 mV vs Ag/AgCl and a rotation rate of 3000 rpm, the detection limit was 200 ng/mL MS2 or 3.2 x 10(10) viral particles/mL with RDE amperometry. A trench IDA electrode was incorporated into a poly(dimethyl siloxane) channel, within which beads were collected, incubated with PAPG, and PAP generation was detected. The two working electrodes were held at +290 and -300 mV vs Ag/AgCl, and electrochemical recycling of the PAP/PQI couple by the IDA electrode lowered the limit of detection to 90 ng/mL MS2, or 1.5 x 10(10) MS2 particles/mL.     

Absorption coefficient imaging by near-field scanning optical microscopy in bacteria

We present a method for obtaining a position-dependent absorption coefficient from near-field scanning optical transmission microscopy. We show that the optical transmission intensity can be combined with the topography, resulting into an absorption coefficient that simplifies the analysis of different materials within a sample. The method is tested with the dye rhodamine 6G, and we show some analysis in biological samples such as bacteria KIebsiella pneumoniae and Pseudomonas aeruginosa. The calculated absorption coefficient images show important details of the bacteria, in particular for P. aeruginosa, in which membrane vesicles are clearly seen.     

Mapping protein expression in mouse pancreatic islets by immunolabeling and electron energy loss spectrum-imaging

A combination of immuno-electron microscopy and electron energy-loss spectrum-imaging was used to map the distributions of endocrine polypeptide hormones and proteins in mouse pancreatic islet of Langerhans. Tissue was analyzed from control animals and from mice that were heterozygous for the Anx7 gene, which defines a Ca2+/GTP-dependent membrane fusion and ion channel protein. The heterozygous Anx7 (+/-) mouse displays defects in IP3 receptor mediated Ca2+ signaling and insulin secretion. Therefore, information was obtained about the distributions of the hormones insulin and glucagon, as well as the proteins ANX7 and the IP3 receptor. Insulin secretion appears to be defective in the mutants. It was found from immunolabeling experiments that expression of the IP3 receptor is reduced in mutant islets compared to control islets. Subcellular distributions of sulfur and nitrogen obtained by electron energy-loss spectrum-imaging showed that the insulin concentrations of beta granules were essentially the same in control and mutant islets. By contrast, immunogold labeling of mutant islets shows more insulin immunoreactivity in the beta granules. It follows that insulin may be packaged differently in mutant islets, making antigenic determinants more available to the labeling antibody. The increased rate of insulin secretion in the hyperplastic mutant islets can be explained by compensatory increases in islet size, rather than by an increased insulin concentration in the beta cells. The results indicate that reduced ANX7 expression leads to defects in the IP3 receptor expression in the endocrine cells of the mutant mouse. Increased size of the islet or of adrenal medulla may be a compensatory mechanism for secretion defect by individual endocrine cells. Defects in IP3 receptor expression, and documented consequences of a Ca2+ signaling defect, lead to other changes in organelles such as the mitochondrial number in islet beta-cells. The effects and consequences of reduced ANX7 expression on mitochondria are evident in ultrastructural observations.     

Water structures in ion-exchange resin particles: solvation dynamics of Nile Blue A

The structures of water, partitioned in cation-exchange resin particles, were studied on the basis of fluorescence dynamics of Nile Blue A (NB). The fluorescence lifetime of NB in the resin was longer than that in water and increased with increasing cross-linking density of the resin (rho). The results demonstrated that the water structures in the resin were significantly different from those in water and dependent on rho. A study on solvation dynamics of NB in the resin, reflecting structured water around the ion-exchange group, revealed the roles of "bound water" molecules in the water structures, since the solvent relaxation time (tauS) in the resin was much longer than that in water and depended on p; tauS increased from 34 to 55 ps with increasing rho from 2 to 8%. The origin of the rho dependence of tauS was discussed in terms of the separation distance between the ion-exchange groups, and the effects of the counterion of the ion-exchange group on the solvation processes were also discussed.     

Genotypic variation among arcobacter isolates from a farrow-to-finish swine facility

Arcobacter spp. were isolated from nursing sows and developing pigs on three farms of a farrow-to-finish swine operation and market-age pigs at slaughter. Isolates were identified by polymerase chain reaction and genotypic fragment patterns were examined by pulsed-field gel electrophoresis (PFGE). Incidences of Arcobacter-positive samples increased progressively as the pigs aged, resulting in all of the pens at the end of the growth cycle in the finishing barn containing Arcobacter-positive feces. However, only 10 of 350 cecal samples from slaughtered pigs were positive. There was little similarity between genotypic patterns for Arcobacter collected from the three farms. The level of genotypic variation revealed by PFGE suggested that pigs in this farrow-to-finish operation were colonized by multiple Arcobacter parent genotypes that may have undergone genomic rearrangement, common to members of Campylobacteraceae, during successive passages through the animals. Additionally, the level of genotypic diversity seen among Arcobacter isolates from farms of a single farrow-to-finish swine operation suggests an important role for genotypic phenotyping as a source identification and monitoring tool during outbreaks.     

振动磨的周期运动稳定性与分岔

由于碰撞的存在,振动磨系统的响应呈现出复杂的周期运动或混沌运动。本文将振动磨的模型进行简化,建立一维、两自由度、受简谐激振力作用的振动磨碰撞振动力学模型。基于Poincare映射原理,根据映射Jacobi矩阵分析振动磨周期运动的稳定性,并通过理论分析和数值仿真,研究振动磨周期运动的稳定性与分岔,以及由倍周期分岔通向混沌的过程。