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71.
This paper deals with the identification of a single open crack in a straight pipe containing fluid under pressure by frequency measurements. The crack is assumed to be a transverse partial cut of the pipe wall thickness with straight front and it is simulated by an equivalent elastic spring. It is shown that the measurement of the damage-induced shifts in a pair of natural frequencies of the bending vibration can be used to formulate and solve the diagnostic problem. In particular, it is shown that the change in the first two frequencies in a simply supported uniform pipe is sufficient to localize a small crack, except for a symmetrical position, and to determine the damage severity. Closed-form expressions are provided for damage location and severity. An extension of the method to simply supported uniform pipe with two cracks of equal severity is also presented. The analysis is based on an explicit expression of the frequency sensitivity to damage and allows to consider pipes under general set of boundary conditions. Analytical results agree well with the numerical tests.  相似文献   
72.
Carbon supported Pt-Ru catalysts were prepared by multiple cycles of potentiostatic pulses from aqueous diluted chloroplatinic acid and ruthenium chloride solutions in the presence of ethanol or ethylene glycol at pH 2 and 5. SEM images showed that the metallic deposit prepared at pH 2 consisted of large irregular agglomerates, whereas smaller globular particles were obtained at pH 5. In addition, the average particle size was considerably decreased in the presence of the stabilizers. The supported Pt-Ru alloys were tested as catalysts for methanol electro-oxidation in acid media. Electrocatalytic activity measurements indicated that the most active electrode was obtained with ethylene glycol as additive at pH 5.  相似文献   
73.
The dielectric and piezoelectric properties of (1 ? x)[(Pb0.988La0.012)(Zr0.53Ti0.47)0.997O3]?Cx[Pb0.557Ba0.38La0.022Bi0.02Nb2O6] composite system consisting of both perovskite tetragonal (4 mm) and tungsten bronze orthorhombic (m2 m) phases, prepared in situ by mechanical activation method are presented and discussed in relation to x (PBLBiN) variation. The crystal structure and morphology of the composites were examined with X-ray diffraction and scanning and transmission electron microscopes. Scanning electron micrographs showed structural homogeneity. Dielectric and piezoelectric properties were studied as a function of x to characterize electrical properties of composites. The presence of two trivalent ions (La3+ and Bi3+) in x resulted in high dielectric and piezoelectric properties. The possible mechanisms of mechanical activation technique of (1 ? x)PLZT?CxPBLBiN nanoceramic composite system are discussed. The optimum dielectric and piezoelectric properties were found in x = 0.6 in (1 ? x)PLZT?CxPBLBiN nanoceramic composite system which could be ideal for electromechanical and energy harvesting applications.  相似文献   
74.
VAR2 is an integral thylakoid membrane protein and a member of the versatile FtsH class of metalloproteases in prokaryotes and eukaryotes. Recessive mutations in the VAR2 locus give rise to variegated plants (var2) that contain white sectors with abnormal plastids and green sectors with normal-appearing chloroplasts. In a continuing effort to isolate second-site suppressors of var2 variegation,we characterize in this report ems2505,a suppressor strain that has a vi-rescent phenotype due to a missense mutation in At4g28590,the gene for a pioneer protein. We designated this gene SVR4 (for SUPPRESSOR OF VARIEGATI0N4) and the mutant allele in ems2505 as svr4-1. We demonstrate that SVR4 is located in chloroplasts and that svr4-1 single mutants are normal with respect to chloroplast anatomy and thylakoid membrane protein accumulation. However,they are modestly impaired in several aspects of photochemistry and have enhanced non-photochemical quenching (NPQ) capacity. A T-DNA insertion allele of SVR4,svr4-2,is seedling-lethal due to an early blockage of chloroplast development. We conclude that SVR4 is essential for chloroplast biogenesis,and hypothesize that SVR4 mediates some aspect of thylakoid structure or function that controls NPQ. We propose that in the suppressor strain,photoinhibitory pressure caused by a lack of VAR2 is ameliorated early in chloroplast development by enhanced NPQ capacity caused by reduced SVR4 activity. This would result in an increase in the number of chloroplasts that are able to surmount a threshold necessary to avoid photo-damage and thereby develop into functional chloroplasts.  相似文献   
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This work presents the use of carbon nanotube (CNT) skeletons and the resin infusion process as a path towards the production of polymer composites with high and well dispersed nanotube content. A general purpose low viscosity epoxy resin was used as matrix in the reported process assessment. Thin CNT papers, called skeletons, were initially produced to obtain CNT networks. The impregnation was made by infiltrating the non-diluted resin through the carbon nanotube structure. The results show the proposed processing approach as one capable of producing well dispersed nanocomposites with high CNT loading (more than 15 wt% CNT by composite weight), which are important for developing high performance structures based on carbon nanotubes with good thermal and electrical conductivity. The absolute mechanical performance was lower than expected, and discussed in light of manufacturing problems detected by microscopy observations under scanning electron microscopy (SEM).  相似文献   
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Cutaneous melanoma (CM) is the deadliest skin cancer, whose molecular pathways underlying its malignancy remain unclear. Therefore, new information to guide evidence-based clinical decisions is required. Adenosine diphosphate (ADP)-ribosylation factor-like (ARL) proteins are membrane trafficking regulators whose biological relevance in CM is undetermined. Here, we investigated ARL expression and its impact on CM prognosis and immune microenvironment through integrated bioinformatics analysis. Our study found that all 22 ARLs are differentially expressed in CM. Specifically, ARL1 and ARL11 are upregulated and ARL15 is downregulated regardless of mutational frequency or copy number variations. According to TCGA data, ARL1 and ARL15 represent independent prognostic factors in CM as well as ARL11 based on GEPIA and OncoLnc. To investigate the mechanisms by which ARL1 and ARL11 increase patient survival while ARL15 reduces it, we evaluated their correlation with the immune microenvironment. CD4+ T cells and neutrophil infiltrates are significantly increased by ARL1 expression. Furthermore, ARL11 expression was correlated with 17 out of 21 immune infiltrates, including CD8+ T cells and M2 macrophages, described as having anti-tumoral activity. Likewise, ARL11 is interconnected with ZAP70, ADAM17, and P2RX7, which are implicated in immune cell activation. Collectively, this study provides the first evidence that ARL1, ARL11, and ARL15 may influence CM progression, prognosis, and immune microenvironment remodeling.  相似文献   
80.
An efficient electrochemically induced synthesis of chiral cis β‐lactams has been described, via deprotonation of chiral amides containing an acidic methylene group and a bromine atom as leaving group and bearing a chiral auxiliary or amine function. The electrogenerated base – cyanomethyl anion – is easily obtained by galvanostatic reduction of acetonitrile‐tetraethylammonium hexafluorophosphate solutions under very mild conditions. The yields are high and the cis‐diastereoselection complete. The use of starting chiral amides has allowed in many cases the preparation of the most abundant isomer in a pure form.  相似文献   
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