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排序方式: 共有134条查询结果,搜索用时 125 毫秒
71.
Francisco J.Q. Melo Joaquim A.O. Carneiro Cassilda L. Tavares Pedro P. Camanho Paulo T. de Castro 《Mechanics Research Communications》2006,33(2):190-205
The impact test in structural parts for dynamic applications is an essential procedure for their certification in the presence of time dependent loads. In the case of beam elements, either built with one material or as an assembly of different material members joined with recent developed bonding techniques, an impact test is of leading importance, once the dynamic resistance of the joints involved in the beam fabrication is assessed and evaluated. The pseudo-dynamic method is an alternative to dynamic analysis of structures, here offering to the researcher the possibility of examining with detail the specimen in test for the initiation and progress of eventual damage mechanisms arising in the beam element joints whenever included in the design. 相似文献
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We have investigated photon-stimulated ion desorption from deuterated benzene (C6D6) adsorbed on Si(1 0 0) and Si(1 1 1) surfaces following C 1s core excitation. Using time-of-flight mass spectrometry combined with angle-dependent technique, we measured the dependences of mass-spectra of desorption ions on photon energies and on incident angle (θ) of synchrotron beam. We have found the ion yields for adsorbate-derived fragments of CD+ and CD2+ are enhanced in very small angles of incident X-rays. Moreover, molecular orientation effect appeared in excitation energy dependences of D+ ions from the Si(1 0 0) and Si(1 1 1) surfaces; that is, ion yield spectra measured at θ = 10° are different from that at θ = 65°. Furthermore, it was found that desorption ion yields increase greatly with decreasing incident angles. The angular dependences are consistently similar for all ion species, excitation energies, and indexes of substrates. Possible desorption processes are described on the basis of the observations. 相似文献
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鉴于空间光通信系统中分辨率在很大程度上影响着整个通信系统的性能,而PSD(position sensitive detector)作为APT(acquisition, pointing and tracking)子系统常用的探测器件,具有分辨率高,无盲区,响应速度较快的优点,分析了PSD的基本结构和定位原理,研究了使用PSD作为空间光通信APT子系统粗跟踪技术的位置分辨率,并指出了提高PSD分辨率的着手点。用实验方案对PSD的分辨率进行了具体的实验分析。通过对实验数据分析可知,PSD的平均位置分辨率达到12.6μm,该值与理论分辨率吻合得较好。这说明PSD作为APT子系统精跟踪探测器的可行性。 相似文献
77.
León IR Neves-Ferreira AG Valente RH Mota EM Lenzi HL Perales J 《Journal of mass spectrometry : JMS》2007,42(6):781-792
Matrix-assisted laser desorption ionization (MALDI), Peptide Mass Fingerprinting (PMF) and MALDI-MS/MS ion search (using MASCOT) have become the preferred methods for high-throughput identification of proteins. Unfortunately, PMF can be ambiguous, mainly when the genome of the organism under investigation is unknown and the quality of spectra generated is poor and does not allow confident identification. The post-source decay (PSD) fragmentation of singly charged tryptic peptide ions generated by MALDI-TOF/TOF typically results in low fragmentation efficiency and/or complex spectra, including backbone fragmentation ions (series b and y), internal fragmentation etc. Interpreting these data either manually and/or using de novo sequencing software can frequently be a challenge. To overcome this limitation when studying the proteome of adult Angiostrongylus costaricensis, a nematode with unknown genome, we have used chemical N-terminal derivatization of the tryptic peptides with 4-sulfophenyl isothiocyanate (SPITC) prior to MALDI-TOF/TOF MS. This methodology has recently been reported to enhance the quality of MALDI-TOF/TOF-PSD data, allowing the obtainment of complete sequence of most of the peptides and thus facilitating de novo peptide sequencing. Our approach, consisting of SPITC derivatization along with manual spectra interpretation and Blast analysis, was able to positively identify 76% of analyzed samples, whereas MASCOT analysis of derivatized samples, MASCOT analysis of nonderivatized samples and PMF of nonderivatized samples yielded only 35, 41 and 12% positive identifications, respectively. Moreover, de novo sequencing of SPITC modified peptides resulted in protein sequences not available in NCBInr database paving the way to the discovery of new protein molecules. 相似文献
78.
关于功率谱密度与风速谱的注记 总被引:1,自引:1,他引:0
探讨了随机过程中双边功率谱密度负频率引入的原因,实际的频谱函数应将负频率项与相应正频率项成对合并起来而直流分量保持不变,此即单边功率谱所表达的含义.对目前文献中给出的单边功率谱的表达式和单边功率谱与双边功率谱的关系式进行了修正,并对维纳-辛钦公式的变换形式也做了相应的修正,指出其修正前后在不同风速谱实际应用中的区别.算例证明了本文所给公式的正确性. 相似文献
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《Particuology》2023
In the process of coal seam fracturing with liquid nitrogen (LN2), the change of coal pore structure has an important influence on the efficiency of coalbed methane (CBM) extraction. The nano-scale pore size distribution (PSD) in coal particles before and after freezing with LN2 are experimentally studied in this work. Coal samples are collected from four coal mines, where coal and gas outburst accidents have occurred. Small angle X-ray scattering technology (SAXS) and scanning electron microscopy (SEM) are used to study the pore structure changes of coal samples quantitatively and qualitatively. It is found that the scattering intensity of coal samples increases after freezing. The PSD of all samples significantly changes in the range of 0.8–7 nm, showing new pore spaces in 0.8–4 nm and fewer pores in the 4–7 nm range. Both the pore fractal dimension and the radius of gyration of coal samples increase after freezing and are mainly affected by the changes in pores and the anisotropy of the coal matrix. Crack expansion and pore connections are observed in the surface structure of the coal sample using SEM. This study provides a better understanding of the nano-scale mechanism of coal seam fracturing with LN2 for the prevention of coal and gas outbursts. 相似文献