木材强度准则的研究进展

木材的强度准则是木结构理论分析和数值模拟的重要基础。根据国内外的研究进展,对木材单轴、双轴以及多轴应力状态下的强度准则进行系统地介绍,包括最大应力准则、最大应变准则、Hill屈服准则、Hill型强度理论、Tsai-Wu准则、van der Put强度理论和木材剪切强度理论。通过与文献中木材强度实测值的比较,验证木材斜纹强度公式的有效性。对比木材强度准则在多轴应力状态下的强度包络线,总结各强度准则间的差异和适用范围,并讨论张量系数对强度包络线的影响。通过综述木材强度准则在木结构数值模拟中的应用,简要分析各强度准则的优缺点。最后提出木材强度准则需要进一步研究的问题。     

高压断路器的操作振动现象

高压断路器操作过程伴随着一系列冲击振动,对应着内部构件的冲击或运动变化,利用这一点可以作内部状态、故障的外部监测诊断。实测了样品支架上的振动,加速度的幅值可达100g,信噪比高。监测时传感器位置与方位的选择要合适。     

Cyclic-3',5'-nucleotide phosphodiesterase isozymes in cell biology and pathophysiology of the kidney

Investigations of recent years revealed that isozymes of cyclic-3', 5'-nucleotide phosphodiesterase (PDE) are a critically important component of the cyclic-3',5'-adenosine monophosphate (cAMP) protein kinase A (PKA) signaling pathway. The superfamily of cyclic-3', 5'-phosphodiesterase (PDE) isozymes consists of at least nine gene families (types): PDE1 to PDE9. Some PDE families are very diverse and consist of several subtypes and numerous PDE isoform-splice variants. PDE isozymes differ in molecular structure, catalytic properties, intracellular regulation and location, and sensitivity to selective inhibitors, as well as differential expression in various cell types. A number of type-specific "second-generation" PDE inhibitors have been developed. Current evidence indicates that PDE isozymes play a role in several pathobiologic processes in kidney cells. In rat mesangial cells, PDE3 and PDE4 compartmentalize cAMP signaling to the PDE3-linked cAMP-PKA pathway that modulates mitogenesis and PDE4-linked cAMP-PKA pathway that modulates generation of reactive oxygen species. Administration of selective PDE isozyme inhibitors in vivo suppresses proteinuria and pathologic changes in experimental anti-Thy-1.1 mesangial proliferative glomerulonephritis in rats. Increased activity of PDE5 (and perhaps also PDE9) in glomeruli and in cells of collecting ducts in sodium-retaining states, such as nephrotic syndrome, accounts for renal resistance to atriopeptin; diminished ability to excrete sodium can be corrected by administration of the selective PDE5 inhibitor zaprinast. Anomalously high PDE4 activity in collecting ducts is a basis of unresponsiveness to vasopressin in mice with hereditary nephrogenic diabetes insipidus. Apparently, PDE isozymes apparently also play an important role in the pathogenesis of acute renal failure of different origins. Administration of PDE isozyme-selective inhibitors suppresses some components of immune responses to allograft transplant and improves preservation and survival of transplanted organ. PDE isozymes are a target for action of numerous novel selective PDE inhibitors, which are key components in the design of novel "signal transduction" pharmacotherapies of kidney diseases.     

Double-helix coil for occlusion of large patent ductus arteriosus: evaluation in a chronic lamb model

Glyceraldehyde-3-phosphate dehydrogenase (G3PDH) is often used as a control gene for mRNA expression, however it has been proposed to be overexpressed in all hepatocellular carcinomas (HCC). Equal amounts of tumor and paired normal (T/N) RNA, based on OD260/280 nm, were compared using ethidium bromide staining, poly-T probing, gene-specific dot blot and Northern blots using control probes G3PDH, actin and histone H4. Using mRNA blots 13/20 surgical HCC pairs did not overexpress G3PDH. Those 7/20 intact samples which did appear to overexpress G3PDH on Northern blot could not be detected by poly-T probing of dot blots. The apparent overexpression was not specific for the control gene G3PDH nor for the malignancy HCC. It may represent partial mRNA degradation, or the presence of as yet unknown substances which interfere with absorption at 260/280 nm. We advise caution in selecting human T/N pairs for differential gene expression studies. For HCC, no clinicopathological variables, including cirrhosis, predicted whether a T/N sample pair was likely to be balanced or not.     

A re-examination of seasonal variation in suicides in Australia and New Zealand

BACKGROUND: To examine the seasonality of suicides in Australia and New Zealand during the period 1981 to 1993. METHODS: A chi-square test and a harmonic analysis were used to detect the seasonality of the suicide data. RESULTS: The reduced amplitude and a smaller proportion of variance accounted for by seasonality suggested the seasonal effect on suicide is greatly diminished. The absence of biseasonal distribution of female suicides was also consistently found in the two countries. The finding was contrary to the reported results in seventies in many Western countries. CONCLUSIONS: The change in living condition, roles of males and females and communication pattern resulted in the reduction of climatic and environment effect in the seasonality of suicides were suggested. LIMITATIONS: The results would be better if a longer series of suicide date were available.     

Cleavage motifs of the yeast 20S proteasome beta subunits deduced from digests of enolase 1

The 436-amino acid protein enolase 1 from yeast was degraded in vitro by purified wild-type and mutant yeast 20S proteasome particles. Analysis of the cleavage products at different times revealed a processive degradation mechanism and a length distribution of fragments ranging from 3 to 25 amino acids with an average length of 7 to 8 amino acids. Surprisingly, the average fragment length was very similar between wild-type and mutant 20S proteasomes with reduced numbers of active sites. This implies that the fragment length is not influenced by the distance between the active sites, as previously postulated. A detailed analysis of the cleavages also allowed the identification of certain amino acid characteristics in positions flanking the cleavage site that guide the selection of the P1 residues by the three active beta subunits. Because yeast and mammalian proteasomes are highly homologous, similar cleavage motifs might be used by mammalian proteasomes. Therefore, our data provide a basis for predicting proteasomal degradation products from which peptides are sampled by major histocompatibility complex class I molecules for presentation to cytotoxic T cells.     

Endothelin A-receptor blockade worsens endotoxin-induced hepatic microcirculatory changes and necrosis

BACKGROUND & AIMS: Endothelin 1 is considered to be an important regulator of sinusoidal blood flow and increases during endotoxemia. The purpose of this study was to investigate the role of endothelin 1 in hepatic microcirculation, oxygen transport, and liver injury during endotoxemia. METHODS: Male Sprague-Dawley rats were continuously infused with 2.5 mL/h of saline, 0.8 mg . kg-1 . h-1 of lipopolysaccharide (LPS), 3 mg . kg-1 . h-1 of BQ-485, an endothelin A-receptor antagonist, or LPS plus BQ-485 for 7 hours. RESULTS: BQ-485 infusion had no significant effect on hepatic microcirculation and liver injury. LPS increased the plasma levels of aspartate aminotransferase (AST) and total bilirubin and decreased the hepatic adenosine triphosphate (ATP) level and bile flow rate. LPS + BQ-485 infusion further increased the plasma levels of AST and total bilirubin and decreased the bile flow rate and the hepatic ATP level. Dual-spot microspectroscopy revealed mild decreases in sinusoidal erythrocyte velocity and oxygen transport in the LPS group and profound decreases in these parameters in the LPS + BQ-485 group. Histological examinations revealed massive necrotic changes in the pericentral regions of the LPS + BQ-485 group. CONCLUSIONS: These results suggest that blockade of endothelin A receptors disturbs hepatic microcirculation and oxygen transport and aggravates the necrotic injury induced by endotoxin.     

丢失文件的恢复方法与步骤

本文详细分析了计算机文件的链式存贮结构,并针对最常见的两类丢失的文件进行了深入的研究,提出了三种既快速又有效的恢复方法。这些方法简便、可靠,具有很好的参考价值。     

Conformation of xanthene dyes in the sulfhydryl 1 binding site of myosin. 2

The fluorescent dyes 5'-(iodoacetamido)tetramethylrhodamine (5'IATR) and 5'-(iodoacetamido)-fluorescein (5'IAF) bind covalently to the reactive sulfhydryl (SH1) of myosin subfragment 1 (S1), the 5'IATR as a dimer and the 5'IAF as a monomer. The conformation of the dimer and the dye-protein complex was investigated by comparison of several spectroscopic signals of the molecules before and after their association into a complex and interpretation of any changes using a coupled dipole oscillator model adapted for this problem [Burghardt & Ajtai (1995) Biophys. Chem. (submitted for publication)]. Absorption and fluorescence spectroscopies were performed on 5'IAF, 5'IATR, and rhodamine 6G (R6G) and rhodamine B (RB) as models of dimer conformation. Absorption, fluorescence, and circular dichroism (CD) spectroscopies were performed on 5'IATR-modified S1 (5'R-S1) and 5'IAF-modified S1 (5'F-S1). Combined spectroscopic and 2-D NMR data from rhodamines in solution determined the conformations of the dimers. Xanthene rings from dimers of identical dyes (homodimers) stacked in two structures having very different spectroscopic signatures. Xanthene rings from the heterodimer of R6G and RB stacked in one conformation. The two homodimer conformations of 5'IATR are equally likely to form in solution. The other rhodamine homodimers have one dominant, but not exclusive, structure. Both conformations of the 5'IATR dimer were coupled to a tryptophan as a model of the dye-protein interaction at SH1. The calculated CD from one dimer conformer (dimer A) coupled to tryptophan is negative for the lowest energy CD absorption band. The other dimer (dimer B) gives positive CD on the two lowest energy CD absorption bands. Both dimer structures of 5'IATR contributed to the early time-dependent CD signal from 5'IATR binding to SH1, but at equilibrium the CD signal indicated only dimer B, suggesting that the SH1 binding pocket converts dimer A into dimer B. The time-dependent CD signal from 5'IAF changes amplitude but not shape during the reaction with SH1. The model calculation accounting for the spectroscopic signals of 5'R-S1 and 5'F-S1 indicates several likely conformations of the 5'IATR dimer-tryptophan and 5'IAF-tryptophan complexes embedded in S1. These structures fit to the alpha-carbon structure of the SH1 binding pocket when the 5'IATR dimer and 5'IAF interact closely with Trp510 [Rayment et al. (1993) Science 261, 50-58].(ABSTRACT TRUNCATED AT 400 WORDS)