The interaction of doubly periodic cracks

In this paper, an extremely accurate and efficient method for computing the interaction of a set of or multiple sets of general doubly periodic cracks has been presented on the basis of superposition principle, pseudo-traction method, and isolating analysis technique. A great number of typical examples are given in this paper. The stress intensity factors (SIF), the minimum strain energy density factors (SED) of crack tip and the critical stress (CRS) of crack growth are calculated with the accuracy of six significant digits for the rectangularly distributed periodic cracks and five significant digits for the general doubly periodic cracks. The relation of the interaction effect of the double periodic cracks with the periods and the ratio of crack length to crack spacing is analyzed. Also in this paper, the key technique problems for this method are discussed.     

工业SO2及碳黑颗粒紫外成像遥感监测技术

为了准确有效监测工业烟囱排放,基于SO2及碳黑颗粒物的光学特性,设计并研制出一套双通道紫外成像遥感监测系统.该成像系统的两个光谱通道的中心波长分别定于310 nm和330 nm,利用两个通道的光学厚度之差反演SO2浓度图像,颗粒物浓度图像由330 nm通道获取,根据浓度图像结合光流法获取烟羽运动速度,进而计算得出SO2和碳黑颗粒物的排放速率.结果表明,该工业烟囱的SO2及碳黑颗粒物排放速率分别为72.48±3.16 kg/h和6.33±1.18 kg/h.实验采用紫外相机同时对工业烟囱排放的SO2及碳黑颗粒物进行监测,实验表明双通道紫外成像遥感监测兼具高时间分辨率与高空间分辨率,测量结果准确直观,在工业废气污染、船舶尾气污染以及火山喷发污染排放遥感监测中具有非常明显的技术优势及巨大的应用前景.     

An experimental study on seepage behavior of sandstone material with different gas pressures

The seepage evolution characteristic of brittle rock materials is very significant for the stability and safety of rock engineering. In this research, a series of conventional triaxial compression and gas seepage tests were carried out on sandstone specimens with a rock mechanics servo-controlled testing system. Based on the experimental results, the relationship between permeability and deformation is firstly analyzed in detail. The results show that the permeability–axial strain curve can be divided into the following five phases: the phase of micro-defects closure, the phase of linear elastic deformation, the phase of nonlinear deformation, the phase of post-peak stress softening and the phase of residual strength. The seepage evolution characteristic is also closely correlated with the volumetric deformation according to the relationship between permeability and volumetric strain. It is found that the gas seepage pressure has a great effect on the permeability evolution, i.e. permeability coefficients increase with increasing gas seepage pressures. Finally, the influence of gas seepage pressures on the failure behavior of brittle sandstone specimens is discussed.     

Highly Efficient Synthesis of Monodisperse Poly(ethylene glycols) and Derivatives through Macrocyclization of Oligo(ethylene glycols)

A macrocyclic sulfate (MCS)‐based approach to monodisperse poly(ethylene glycols) (M‐PEGs) and their monofunctionalized derivatives has been developed. Macrocyclization of oligo(ethylene glycols) (OEGs) provides MCS (up to a 62‐membered macrocycle) as versatile precursors for a range of monofunctionalized M‐PEGs. Through iterative nucleophilic ring‐opening reactions of MCS without performing group protection and activation, a series of M‐PEGs, including the unprecedented 64‐mer (2850 Da), can be readily prepared. Synthetic simplicity coupled with versatility of this new strategy may pave the way for broader applications of M‐PEGs.     

Ragged oscillation death in coupled nonidentical oscillators

In this paper, the effect of spatial frequencies distributions on the oscillation death in a ring of coupled nonidentical oscillators is studied. We find that the rearrangement of the spatial frequencies may deform the domain of oscillation death and give rise to a ragged oscillation death in some parameter spaces. The usual critical curves with shape V in the parameter space of frequency-mismatch vs coupling-strength may become the shape W (or even shape WV). This phenomenon has been not only numerically observed in coupled nonidentical nonlinear systems, but also well supported by our theoretical analysis.     

SHPB冲击作用下层状千枚岩多尺度破坏机理研究

通过分离式霍普金森杆对层状千枚岩施加动态载荷，得到不同层理倾角下层状千枚岩的动态抗压强度与宏观破坏模式。采用三维激光仪获得断裂面细观形貌，引入分形几何定量计算断口面粗糙度；结合SEM观察到的微观尺度下不同层理倾角断口破坏机理，分析了不同层理倾角下层状岩石的动态破坏机制。研究结果表明:动态压缩下层理弱面对岩石的抗压强度影响较大；不同层理倾角千枚岩的断口形貌分形维数随层理倾角增大呈U型变化；从强度与裂纹扩展两方面考虑层理弱面对层状岩石破坏特征的影响，对于层理倾角为0°的试样，强度由岩石基质控制，但层理弱面仍对岩石破坏的裂纹分布与走向产生较大影响；对于层理倾角为22.5°的试样，强度与裂纹走向受岩石基质与层理弱面共同控制；对于层理倾角为45°～67.5°的试样，强度与裂纹走向受层理弱面控制；而对于层理倾角为90°的试样，动态抗压强度受岩石基质的影响较大，在层理弱面较早形成纵向宏观裂纹，导致该层理弱面角度下裂纹受层理弱面的影响较大。     

Monitoring dendrimer conformational transition using 19F and 1H2O NMR

The conformational transition of a fluorinated amphiphilic dendrimer is monitored by the ¹H signal from water, alongside the ¹⁹F signal from the dendrimer. High-field NMR data (chemical shift δ, self-diffusion coefficient D, longitudinal relaxation rate R₁, and transverse relaxation rate R₂) for both dendrimer (¹⁹F) and water (¹H) match each other in detecting the conformational transition. Among all parameters for both nuclei, the water proton transverse-relaxation rate R₂(¹H₂O) displays the highest relative scale of change upon conformational transition of the dendrimer. Hydrogen/deuterium-exchange mass spectrometry reveals that the compact form of the dendrimer has slower proton exchange with water than the extended form. This result suggests that the sensitivity of R₂(¹H₂O) toward dendrimer conformation originates, at least partially, from the difference in proton exchange efficiency between different dendrimer conformations. Finally, we also demonstrated that this conformational transition could be conveniently monitored using a low-field benchtop NMR spectrometer via R₂(¹H₂O). The ¹H₂O signal thus offers a simple way to monitor structural changes of macromolecules using benchtop time-domain NMR.     

Cryptanalysis and Improvement of Ye et al’s Quantum Private Comparison Protocol

Recently, Ye et al. (Int. J. Theor. Phys. 56, 1517–1529, 2017) proposed a quantum private comparison (QPC) protocol based on five-qubit entanglement state. Two parties can verify that their secret information is equal or not with the help of the semi-honest third party (TP). However, in this paper we will point out the Ye et al.’s initial protocol is not safe under a special participant attack. That is a malicious participant can get the other party’s secret input information illegally under the forgery attack. Furthermore, we give two possible improvement protocols, which can perform this protocol secure against this kind of attack.

     

Ground states of two-component attractive Bose–Einstein condensates I: Existence and uniqueness

We study ground states of two-component Bose–Einstein condensates (BEC) with trapping potentials in ${\mathbb{R}}^2$, where the intraspecies interaction $(?a_1,?a_2)$ and the interspecies interaction ?β are both attractive, $i.e$, $a_1$, $a_2$ and β are all positive. The existence and non-existence of ground states are classified completely by investigating equivalently the associated $L^2$-critical constraint variational problem. The uniqueness and symmetry-breaking of ground states are also analyzed under different types of trapping potentials as $\beta \nearrow {\beta }^{?}=a^{?}+\sqrt{(a^{?}?a_1)(a^{?}?a_2)}$, where $0<a_i<a^{?}:={6w6}_2^2$ ($i=1,2$) is fixed and w is the unique positive solution of $\mathrm{\Delta }w?w+w^3=0$ in ${\mathbb{R}}^2$. The semi-trivial limit behavior of ground states is tackled in the companion paper [12].     

单轴拉伸对Nafion 结构及性能的影响

²H NMR 和PFG-NMR 用于研究拉伸过程中Nafion 结构的改变以及对溶剂分子运动性质的影响．²H 谱表明单轴拉伸Nafion 膜在拉伸比率较低情况下（L < 5），通道排列取向程度随着拉伸比率变大而增大，同时扩散实验表明水分子的运动能力也得到增强，表明取向化的通道网络有助于增强材料取向方向质子的导电能力，可以用于提高质子膜材料性能．在取向达到最大值后（L≥5）继续拉伸，膜内水分子的移动能力相比略有降低．溶胀实验表明取向膜的溶胀行为呈各向异性,拉伸作用致使膜内通道沿拉伸方向取向排列，通道的取向效应使得其在垂直拉伸方向（Y）和膜厚度方向（Z）溶胀更为显著．拉伸Nafion 膜对甲醇的吸附能力随着拉伸比率的增加而增强，同时甲醇的扩散数据显示，甲醇的运动能力在该通道网络中也随着拉伸比率的变大而不断增强，甲醇燃料在该类质子膜内的渗透效
应得以增强，不利于其在直接甲醇燃料电池中的应用．