rfb mutations in Vibrio cholerae do not affect surface production of toxin-coregulated pili but still inhibit intestinal colonization

The toxin-coregulated pilus (TCP) of Vibrio cholerae is essential for colonization. It was recently reported that rfb mutations in V. cholerae 569B cause the translocation arrest of the structural subunit of TCP, raising the possibility that the colonization defects of lipopolysaccharide mutants are due to effects on TCP biogenesis. However, an rfbB gene disruption in either V. cholerae O395 or 569B has no apparent effect on surface TCP production as assessed by immunoelectron microscopy and CTX phage transduction, and an rfbD::Tn5lac mutant of O395 also shows no defect in TCP expression. We conclude that the colonization defect associated with rfb mutations is unrelated to defects in TCP assembly.     

Identification of the defective genes in three mutant groups of influenza virus

Seven complementation-recombination groups of temperature-sensitive (ts) influenza WSN virus mutants have been previously isolated. Recently two of these groups (IV and VI) were shown to possess defects in the neuraminidase and the hemagglutinin gene, respectively, and two groups (I and III) were reported to have defects in the P3 and P1 proteins which are required for complementary RNA synthesis. In this communication we report on the defects in the remaining three mutant groups. Wild-type (ts+) recombinants derived from ts mutants and different non-ts influenza viruses were analyzed on RNA polyacrylamide gels. This technique permitted the identification of the P2 protein, the nucleoprotein, and the M protein as the defective gene products in mutant groups II, V, and VII, respectively. Based on the physiological behavior of mutants in groups II and V, it appears that P2 protein and nucleoprotein are required for virion RNA synthesis during influenza virus replication.     

高 速 钢 中 的 碳 化 物 缺 陷

 大量碳化物的存在是高速钢组织的重要特征,也是影响高速钢质量和性能的关键因素。碳化物颗粒细小、形状规则和分布均匀的钢其质量和性能都好。但是,钢中的碳化物并不都这样理想,往往存在缺陷。根据对W18Cr4V、W6Mo5Cr4V2、W9Mo3Cr4V和W2Mo9Cr4VCo8等钢中碳化物的研究结果,分析了高速钢中常见的几种缺陷：①碳化物分布不均匀;②颗粒尺寸粗大,形状不规则,多为角状等;③碳化物微裂纹;④碳化物粘连等;⑤二次碳化物稀少。另外,还分析了以上碳化物缺陷产生的原因和危害性,并指出了减少缺陷应采取的措施。     

钢铁中多元夹杂物颗粒的三维评估

为了从钢铁中提取各种夹杂物颗粒,考察了采用无水电解质的恒电位和恒电流的提取方法。结果认为,4%的MS［4 % （V/V）甲基水杨酸-1 % （m/V） 水杨酸-1 %（ m/V） 四甲基氯化铵-甲醇）和10%AA（10 %(V/V)乙酰丙酮-1 % （m/V）四甲基氯化铵-甲醇］电解质溶液适用于提取钢铁中夹杂物TiO_{x和TiAl2O5。尽管这些电解提取法可以提取化学性能不稳定的夹杂物颗粒,然而,因为对夹杂物的观察是在萃取完成后于一个滤膜中进行,因此无法确定金属中每种夹杂物的具体位置。为了确定金属中夹杂物的具体位置,将卤-醇的光蚀刻方法用于以Ti和Al除氧的钢样品表面附近出现的夹杂颗粒,使用扫描电子显微技术和俄歇电子能谱（AES）对精细夹杂物颗粒形貌、尺寸和元素的偏析进行评估,不过卤醇却和钢铁中的金属钛和金属铝发生还原反应。对微小夹杂物颗粒的成分的形态、分离进行估测,然后,使用一种低加速能-扫描电子显微技术和俄歇电子能谱（AES）对用聚焦离子束制备微小夹杂物颗粒截面上元素的微观偏析进行评定。在这些研究结果基础上讨论了多元夹杂物颗粒的形成机理。}     

Microstructure and mechanical behavior of Al-Li-Cu-Mg alloy 8090 microalloyed with V and Be

The effects of microadditions of V and Be on age-hardening, microstructure, and mechanical behavior of Al-Li-Cu-Mg alloy 8090 are investigated. Small additions of V and Be significantly increase the peak hardness and mechanical properties of the alloy aged at 190 °C. A transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive spectroscopy (SEM/ EDS), optical, and X-ray diffraction investigation shows a higherS′ (Al₂CuMg) precipitate density for alloys containing V and Be, indicating an enhanced nucleation rate forS’ precipitation. The V and Be additions are more effective than prior-aging deformation for increasing the yield strength of age-hardened 8090 alloy. The V addition increases ductility significantly, which is attributed to the homogeneous distribution of slip lines and extensive cross slip that occurs during deformation of the V-containing alloy.     

Nonbasal plane defects in 18r martensite and the effect of abnormal defects on thermoelastic martensitic transformation

This investigation, using a Cu-26.4 pct Zn-4.8 pct Al (wt pct) alloy, was carried out to provide more detailed and accurate information on the crystal defects in martensite. By comparing direct-quenched and step-quenched specimens, it has been found that some abnormal defects of martensite, such as nonbasal plane (NBP) planar defects and dislocations, often exist in the martensite obtained by direct quenching. Trace analysis showed that the NBP planar de-fects are often located in the -125 plane of the martensite lattice. High-resolution electron microscopy (HREM) has revealed that the NBP planar defects resulted from basal plane stack-ing faults which break off inside the plate of martensite.In situ observations during heating in the transmission electron microscope (TEM) have proved that martensites which have a great amount of abnormal crystal defects are stable even when heated to high temperature, and the existence of abnormal defects may be one of the reasons for the stabilization of martensite.     

Analysis of multistep transformations in single-crystal NiTi

The effects of composition and heat treatment on the thermally induced phase-transformation behavior of single-crystal NiTi with compositions of 50.1, 50.4, 50.8, and 51.5 at. pct Ni are presented in this article. Differential scanning calorimetry (DSC) experiments reveal that a heat-treated 50.1 at. pct Ni alloy exhibits an unprecedented multiple-step transformation (MST) on both heating and cooling, with up to four peaks. This behavior is absent in the higher-Ni-content alloys. In polycrystalline NiTi alloys, MSTs have been attributed to microstructure heterogeneities such as grain boundaries and dislocations, which influence precipitation. In-situ scanning electron microscopy (SEM) results show that the MST in the 50.1 at. pct Ni alloy is associated with single-crystal defects such as dendrites and low-angle boundaries. A heterogeneous precipitate distribution is observed in transmission electron microscopy (TEM) images of the same low-Ni alloy, also associated with the defects, creating conditions that have been shown in other studies to promote the MST in polycrystals. These MSTs are not observed for high-Ni single-crystal alloys containing the same defects. In this article, we describe the origin of the extraordinary forward and reverse MSTs in the low-Ni alloy and the absence of the MST in high-Ni alloys. Transformation sequences are proposed based on the contrasting precipitate microstructures.     

Defects studies of semiconductor materials

The nature and cause of defects in bulk and epitaxial semiconductor material are determined by combining the information obtained from several different techniques. Etch pit count, X-ray diffraction for measurement of precise cell parameter, X-ray topography, scanning electron microscopy (SEM), and electron microprobe analysis (EMA) are used to supplement each other. It is shown that more than one technique is necessary for a complete understanding of the defects. The approach is illustrated by three example: 1) The homogeneity study of GaAs wafers with equivalent doping but prepared under different conditions shows an excellent agreement between the amount of dislocations per sq cm obtained by the etch pit count, X-ray topography, and the degree of inhomogeneity as determined by variation ina ₀ measurements. 2) The defects studies of the GaAsP epitaxial layer by X-ray topography, precise cell parameter measurements, SEM, and EMA indicate that the crystallographic defects are induced by misorientation during the growth process and by surface contamination of the substrate. 3) The examination of the surface defects of an etched silicon wafer by optical microscopy and X-ray topography indicates the presence of precipitates. Upon further studies using SEM and EMA it is shown that the defects are not precipitates but hillocks produced by surface contamination prior to the etching process.     

激光选区熔化Ti6Al4V合金的工艺参数优化

孔洞、未熔粉、裂纹是在激光选区熔化制备试样过程中常见的缺陷,迄今为止,大量研究均集中在减少缺陷上,关于工艺参数对缺陷影响的研究较少。本文系统研究了工艺参数对激光选区熔化Ti6Al4V合金相对密度、表面粗糙度、力学性能的影响。结果表明,低激光功率、高扫描速度和高层厚将会引起不充分的粉末熔化以及球化效应。最佳工艺参数为激光功率200 W,扫描速度500 mm/s,层厚10 μm,扫描间距105 μm。在该参数下,试样的抗拉强度1077 MPa,屈服强度907 MPa。     

6005A铝合金的表面损伤对其耐海水腐蚀性能的影响

以6005A铝合金商品实际产生的表面少缺陷、多缺陷试样,以及作为比较的完全去除商品表面膜的人工磨制的三种不同表面状态试样为研究对象,研究铝合金商品表面的实际损伤对其耐海水腐蚀性能的影响及其腐蚀电化学行为.通过场发射扫描电镜和激光共聚焦扫描显微镜对具有不同表面状态的6005A铝合金表面形貌和粗糙度进行了表征,表明铝合金商品实际产生的表面缺陷主要为划伤,体现在随着表面缺陷的增多,表面粗糙度Ra明显增大,表面粗糙度Ra大小可以定量描述表面损伤的严重程度. 6005A铝合金在NaCl质量分数3.5%的模拟海水溶液中发生全面腐蚀和点蚀,表面缺陷越多,粗糙度越大,耐蚀性越差;电化学测试结果表明,表面缺陷越多,粗糙度越大,腐蚀电位越低,腐蚀电流密度越大,耐蚀性越差. 6005A铝合金表面损伤对其耐海水腐蚀性能产生影响的原因为:表面损伤造成铝合金商品原表面膜被破坏,表面缺陷越多,粗糙度越大,表面膜的破坏和表面塑性变形越严重,铝元素会因为被活化而迅速溶解,有着更高的腐蚀速率,而缺陷较少表面有较为均匀致密的氧化膜,对基体有着较好的保护性.      

The relationship of increased capillary filtration and bone formation

The effect of functional activity on bone formation and interstitial fluid space in a standardized tibial defect was measured in 19 dogs with one hind limb elevated and the other weight bearing and in 15 dogs bearing weight on all four legs. The interstitial fluid space (V(isf)) of the woven bone of the weight-bearing defect was larger than that in the elevated legs at seven and 14 days. By 28 days, this difference disappeared. In a third group of six dogs, medullary canal pressure was measured in the immobilized and weight-bearing tibias. The pressures were higher in the weight-bearing tibiae at two, three, four, and five days. Because the increase in V(isf) in the weight-bearing defects coincided with the onset of woven bone formation in the defects and an increase in medullary canal pressure, an increase in venous pressure could increase capillary pressure and capillary filtration. Such an increase in filtration might cause the larger V(isf) in the weight-bearing defects and better capillary perfusion of precursor cells of the osteoblast. A hypothesis is that increased fluid flow from increased capillary filtration might produce streaming potentials, a possible signal for increased cellular activity.     

Dorsal column inhibition of nociceptive thalamic cells mediated by gamma-aminobutyric acid mechanisms in the cat

Cells derived from mice homozygous for the severe combined immune deficiency (scid) mutation exhibit hypersensitivity to ionizing radiation, and defects in DNA double-strand break repair and V(D)J recombination. Using the technique of microcell-mediated chromosome transfer, we have introduced a number of dominantly marked human chromosomes into scid cells to localize the human homolog of the murine scid gene. Analysis of human-scid hybrid clones revealed that the presence of human chromosome 8 partially restored accurate V(D)J recombination and radioresistance to scid cells. Subsequent loss of the human chromosome 8 from human-scid hybrid clones rendered these cells sensitive to gamma-radiation and impaired their ability to catalyse V(D)J recombination. Introduction of chromosomes 2, 14, 16 and 19 that encode other repair genes did not result in the correction of these two scid defects. These observations demonstrate that the human homolog of the mouse scid gene resides on human chromosome 8.     

Different risks of thrombosis in four coagulation defects associated with inherited thrombophilia: a study of 150 families

Deficiency of the naturally occurring anticoagulant proteins, such as antithrombin, protein C and protein S, and activated protein C resistance due to the factor V Leiden gene mutation is associated with inherited thrombophilia. So far, no direct comparison of the thrombotic risk associated with these genetic defects is available. In this study, we wish to compare the lifetime probability of developing thrombosis, the type of thrombotic symptoms, and the role of circumstantial triggering factors in 723 first- and second-degree relatives of 150 index patients with different thrombophilic defects. We found higher risks for thrombosis for subjects with antithrombin (risk ratio 8.1, 95% confidence interval [CI], 3.4 to 19.6), protein C (7.3, 95% CI, 2.9 to 18.4) or protein S deficiency (8.5, 95% CI, 3. 5 to 20.8), and factor V Leiden (2.2, 95% CI, 1.1 to 4.7) than for individuals with normal coagulation. The risk of thrombosis for subjects with factor V Leiden was lower than that for those with all three other coagulation defects (0.3, 95% CI, 0.1 to 1.6), even when arterial and superficial vein thromboses were excluded and the analysis was restricted to deep vein thrombosis (0.3, 95% CI, 0.2 to 0.5). No association between coagulation defects and arterial thrombosis was found. The most frequent venous thrombotic manifestation was deep vein thrombosis with or without pulmonary embolism (90% in antithrombin, 88% in protein C, 100% in protein S deficiency, and 57% in factor V Leiden), but a relatively mild manifestation such as superficial vein thrombosis was common in factor V Leiden (43%). There was a predisposing factor at the time of venous thromboembolism in approximately 50% of cases for each of the four defects. In conclusion, factor V Leiden is associated with a relatively small risk of thrombosis, lower than that for antithrombin, protein C, or protein S deficiency. In addition, individuals with factor V Leiden develop less severe thrombotic manifestations, such as superficial vein thrombosis.     

Fast growing protrusions from epitaxial semiconductor surfaces

Epitaxially deposited germanium and silicon layers often exhibit large (typically 20 μ high) dome-shaped surface defects. These protrusions greatly hinder subsequent device fabrication procedures—especially that of masking. Observation by optical and scanning electron microscopy shows that these dome-shaped defects may extend to a height of some twenty times the epitaxial layer thickness and are characterized by geodesic faceting. Cross sectioning experiments on germanium wafers show that they appear not to originate within the substrate but probably nucleate at the site of some surface contamination. Impurity concentrations in the defects were too low to allow positive identification of the species using spark source mass spectrometry or the electron microprobe. However, such defects could be artificially promoted by contaminating the surface with any of a number of materials. Copper was particularly effective in this respect. Mechanisms for this enhanced growth are proposed.     

Combination Effect of Si and P on Tertiary Scale Characteristic of Hot Rolled Strip

For high strength interstitial free(IF)steel containing P element,the salt and pepper(SP)defects exist on the strip surface and could not be eliminated effectively by optimizing the hot rolling process,such as temperature and cooling water.The combination effect of Si and P on the characteristic of tertiary scale has been studied comprehensively by scanning electron microscopy(SEM)and electron probe microanalysis(EPMA),and the concept is proposed firstly that Si and P are of combination effect which can be utilized to eliminate the SP defect.The results show that the SP defects were induced by the rolled-in scale during finish rolling.P can be enriched at the interface between substrate and tertiary scale,which is easy to decrease the adhesion of tertiary scale.However,Si enrichment at the interface between substrate and tertiary scale can increase the adhesion.The SP defects can be eliminated completely,which is attributed to the accompanying enrichment of Si and P.     

电池壳表面典型缺陷图谱及其成因浅谈

电池壳表面微小点缺陷特别是疑似＂砂眼＂缺陷已成为制约其产品质量的最重要因素。运用扫描电镜、光学显微镜、聚焦离子束和电解酸蚀法对电池壳表面常见的几类典型点缺陷表面、截面进行宏观和微观形貌观察。结果表明,钢中非金属夹杂（渣）物是造成电池壳表面点缺陷的重要原因,有害夹杂物临界尺寸下限推进至60μm。其爆发的宏观特征形貌规律,可成为加工单元人工挑拣的依据和失效分析的先期预判,成为进一步检验分析的指南。     

Structure and defects of MBE grown NbAl2O3 interfaces

Single crystal niobium films were grown by Molecular Beam Epitaxy (MBE) on (0001)_S sapphire substrates. Cross-sectional and plan-view specimens of the films were prepared so that the NbAl₂O₃ interface could be investigated by conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The atomistic structure of the interface was identified by HREM. Regions of good matching and regions containing structural defects alternate at the interface. The defects can be described as misfit dislocations with no “stand-off” from the interface. The spacing of the defects corresponds to the 1.9% mismatch between the two lattices. In regions of good matching a fixed translational state between both lattices is established, which could be determined. Image simulations constructed with this translational state were in good agreement with experiment. In plan-view, periodic arrays of fringes were observed. These fringes are formed by a superposition of moire´fringes and dislocation contrast. Weak-beam techniques were used to separate these two contributions.     

Microstructural investigation of as cast and PREP atomised Ti–6Al–4V alloy

Abstract

A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V powders from an alloy electrode. The process parameters and their impact on the material properties are described. The effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure are investigated in detail. Optical microscopy and scanning electron microscopy are used for microstructural characterisation. The analysis shows that cast and extruded Ti–6Al–4V alloys have equiaxial α and α+β phase structures, while plasma rotating electrode processed powder from the same alloy compositions has an acicular or martensitic (α) structure. The microstructure scale depends on the particle size. Microhardness measurements are used to assess mechanical property dependence on the microstructure of this alloy. The rapidly cooled alloy particles have much higher hardness than cast or extruded bulk alloy.     

Agonist and antagonist-dependent internalization of the human vasopressin V2 receptor

In this report we demonstrate that in HEK293 cells stably expressing the human V2 vasopressin receptor, ligand-induced internalization of the hormone receptor occurs via the clathrin-dependent pathway. Studies of receptor trafficking either by direct visualization of the V2 receptor by confocal microscopy or binding experiments show a rapid internalization (half-time 6-7 min). Blocking of the clathrin-dependent pathway by hypertonic sucrose increased vasopressin-induced cellular cAMP production and decreased the desensitization of the V2 receptor-adenylyl cyclase system. Thus, internalization appears to be a major regulatory mechanism terminating vasopressin action in HEK293 cells. Two antagonists of the vasopressin V2 receptor exerted different effects on receptor internalization, as determined by confocal fluorescence microscopy. The nonpeptidic antagonist OPC31260 did not induce any visible receptor internalization, whereas the peptidic antagonist d(CH2)5[D-Tyr(Et)2,Val4,Lys8,Tyr-NH29]VP induced a slow but substantial receptor internalization. These results suggest that long-term treatment with peptidic V2 receptor antagonists might lead to desensitization.