An experimental investigation on acoustic emission characteristics of sandstone rockburst with different moisture contents

Rockburst occurred frequently during deep mining in China. The mechanism of rockburst is very complicated and related to many factors. In order to investigate the influence of moisture contents of rockmass on rockburst, we conducted a series of laboratory rockburst experiments of sandstone under three different moisture contents by the Modified True-Triaxial Apparatus (MTTA), in which the acoustic emission (AE) system was employed to monitor the internal damage of rock mass. A high-speed video camera was utilized to record the detail of rockburst. Based on the experimental results, the AE characteristics, such as AE count, AE energy, and AE frequency, were analyzed. The rockburst process, type, and indensity under different moisture contents were discussed. The research results show that with the increase of moisture contents, rock strength was soften, the elastic and the cumulative damage of the rock were reduced, resulting in a gradual decrease in AE cumulative counts and cumulative energy over the course of rockburst. This study provides an experimental basis and reference for better understanding to the rockburst mechanism and control.     

Almost strictly total positivity of NUAT B-spline basis

Total positivity of spline basis has been well known in the theory of computer aided geometry design, which is highly related with good shape preserving property. Almost strictly total positivity is stronger, which could determine the positive minors while the other is zero. In this paper, a geometrical approach is proposed to prove the collection matrices of NUAT B-spline basis are almost strictly totally positive. In this paper, knot insertion algorithm combined with coefficient variation of NUAT B-spline function, we put forward an intuitive and geometrical method.     

Synthesis and formation mechanism of hematite hollow microspheres by a one-pot templateless surfactant-free hydrothermal process

Hollow microspheres of hematite (α-Fe₂O₃) were prepared by a simple hydrothermal treatment of ferrous ammonium sulphate hexahydrate ((NH₄)₂Fe(SO₄)₂·6H₂O) aqueous solution without any surfactants and additives at 180–200 °C. The products were characterized by XRD, FE-SEM and TEM. The results show that α-Fe₂O₃ hollow microspheres are about 1 μm in diameters and are composed of α-Fe₂O₃ nanoparticles with a diameter range from 50 nm to 150 nm. The effects of reaction parameters such as reaction time, temperature and [(NH₄)₂Fe(SO₄)₂·6H₂O] on the morphology of the final product were investigated. A potential formation mechanism of α-Fe₂O₃ hollow microspheres was also proposed, where the intermediate, urchin-like goethite, served as a sacrificial template for the formation of hollow structure. The reaction parameters-depended morphologies of the final products consisted well with the proposed formation mechanism.     

基于NSGA-III的多成因变压器直流偏磁控制优化算法

随着电力系统变压器直流偏磁事件的增多及其成因的多样化,变压器直流偏磁的治理与控制已经成为电力部门亟需解决的重要问题,为此,提出了基于参考点的非支配带精英策略的遗传算法(NSGA-Ⅲ)、考虑复杂成因、多目标的变压器直流偏磁全局控制与优化算法.首先建立了变压器直流偏磁控制优化方法模型,接着介绍了采用NSGA-Ⅲ算法的关键步骤,最后采用标准算例进行验证,结果表明了优化方法的有效性.     

Preparation and properties of ZnO nano-whiskers

By a novel controlled combustion synthesis method, a large amount of ZnO nano-whiskers with different morphologies like nanotetrapods, long-leg nanotetrapod and multipods, were prepared without any catalysts and additives in open air at high temperature. Their morphologies, structures and optical properties were investigated by using SEM, XRD and PL spectrum. The possible growth mechanisms on the ZnO nano-whiskers were proposed in this paper. Supported by the National Natural Science Foundation of China (Grant Nos. 50572010, 50742007 and 10672020), National Defense Founds of China (Grant Nos. 51420205BQ0154 and A2220061080), “863” Project of China (Grant No. 2007AA03Z103), and the Scientific Research Foundation of Graduate School of BIT (Grant No. AA200802)     

水力机组流固耦合的数学模型

流固耦合具有强烈的非定常、非线性,因此黏性效应不可避免。文中基于有限元法建立水力机组流固耦合振动的控制方程。通过对现有代表模型的讨论和比较可以看出,文中导出的方程模型是目前较为完善的水轮机组部件流固耦合运动的非线性动力模型。最后分析用ANSYS软件进行流固耦合计算的可能性。     

Spontaneous running wheel improves neuroprotection efficacy of ischemic postconditioning in mice following ischemia/reperfusion injury

Ischemic postconditioning (IP) has been shown to provide protection for ischemia/reperfusion (IR) injury, but its efficacy is limited. In this study we hypothesized that spontaneous running wheel (RW) could improve neuroprotection efficacy of IP for IR. We established mouse models of IR and showed that compared to Sham group, IR group had obvious brain infract and neurological dysfunction. In IR+IP group, brain infract and neurological dysfunction improved compared to IR group. However, in IR+IP+RW group brain infract and neurological dysfunction improved much better. TUNEL assay showed that IP but not RW significantly reduced the number of apoptotic cells after IR. However, the number of apoptotic cells was significantly reduced in RW+IP group. In addition, the levels of pro-apoptotic factors increased in IR group but significantly reduced in IR+IP+RW group, while the levels of antiapoptotic factors decreased in IR group but significantly increased in IR+IP+RW group. Moreover, in IR+IP+RW group, MDA level was further decreased and SOD level was further increased compared to IR+IP group. Finally, both PI3K inhibitor and STAT3 inhibitor significantly worsened brain infract and neurological dysfunction and promoted apoptosis in IR mice. In conclusion, RW combined with IP reduces brain infract and neurological dysfunction in mice after IR, and this is associated with enhanced anti-apoptotic and anti-oxidant benefits via the activation of PI3K and STAT3 pathways.     

Thickness evolution of commercial Li-ion pouch cells with silicon-based composite anodes and NCA cathodes

It is significant to monitor the thickness change of commercial Li-ion pouch cells that are assembled from Si-based electrodes and layered cathodes since the volume variation is critically linked with kinetic reaction mechanism and chemomechanical degradation. In this work, the single-point and full-field measurements are conducted on the thickness evolution of Si Ox/Cgraphite/lithium nickel-cobalt-aluminum oxide(Si Ox-G/NCA) batteries. It is found that an abnormal overshoot that has been rarely observed in the previous studies appears at the beginning of discharge, which is believed to be the combined results between the rapid expansion of NCA and the contraction of graphite related to the state of charge(SOC). Compared with the results of single-point measurement, the spatial displacement distribution obtained from three-dimensional(3D) scanning suggests the full-field thickness evolution of the entire cell scale, which is more feasible and efficient to provide full-field information for supporting pouch cell design and pack integration.     

一种多平台互连网络设计

本文给出了TGRC计算机组网设计方案，分析和比较了计算机网络技术中的拓扑结构技术、网络操作系统技术以及异种机互连技术．结合TGRC的网络应用特点和将来的网络业务扩展，论述了该网络设计方案的先进性、高可靠性、易维护性和易扩充性．     

Plasmon-induced transparency in terahertz metamaterials

The quantum phenomena of electromagneticalty induced transparency （EIT） or plasmonic ana- logue of electromagnetically induced transparency （PIT） can be mimicked in the classical resonators, leading to a unique way to explore the coherent coupling mechanism in metamaterial systems. Various metamaterial structures have been proposed to excite and manipulate the PIT effect with flexibility and performance with geometry-controllable, polarizatiomindependent, broadband-transparency and active-modulated characteristics. These in turn promise the fascinating functionalities and applications of the PIT effects, such as slow-light com- ponents, nonlinear devices and high-sensitivity sensors. Here, we present a review on the progress in developing the PIT effect in terahertz metamaterials over the past few years.