Caustics method in dynamic fracture problem of orthotropic materials

Caustics method is a powerful optical technique in fracture mechanics because of its high sensitivity to stress gradients. In this paper, it is applied to resolve dynamic fracture problems in orthotropic composites. Considering most orthotropic materials are opaque, reflective caustics method is derived here by combining the fundamental principle of caustics method with the mechanical properties of orthotropic materials. Meanwhile, corresponding experiments are carried out for typical glass fiber-reinforced composites, where mode I and mixed-mode fracture states are taken into account. By recording and analyzing shadow spot patterns during the crack propagation process carefully, crack onset time, dynamic fracture toughness and crack growth velocity of orthotropic composite are determined. These results will be useful to evaluate the dynamic fracture properties of composites and further to optimize their designs.     

Steganalysis for GIF images based on colors-gradient co-occurrence matrix

A steganalysis algorithm based on colors-gradient co-occurrence matrix (CGCM) is proposed in this paper. CGCM is constructed with colors matrix and gradient matrix of the GIF image, and 27-dimensional statistical features of CGCM, which are sensitive to the color-correlation between adjacent pixels and the breaking of image texture, are extracted. Support vector machine (SVM) technique takes the 27-dimensional statistical features to detect hidden message in GIF images. Experimental results indicate that the proposed algorithm is more effective than Zhao's algorithm for several existing GIF steganographic algorithms and steganography tools, especially for multibit assignment (MBA) steganography and EzStego. Furthermore, the time efficiency of the proposed algorithm is much higher than Zhao's algorithm.     

Carrier-envelope phase dependence of the duration of generated solitons for few-cycle rectangular laser pulses propagation

We investigate the nonlinear propagation of few-cycle rectangular laser pulses on resonant intersubband transitions in semiconductor quantum wells using an iterative predictor–corrector finite-difference time-domain method. An initial 2π rectangular pulse will split into Sommerfeld–Brillouin precursors and a self-induced transparency soliton during the course of propagation. The duration of generated soliton depends on the carrier-envelope phase of the incident pulse. In our case, not only the near-resonant frequency components but also the low frequency components could contribute to the generation of the soliton pulse when the condition of multi-photon resonance is satisfied. The phase-sensitive property of the solitons results from the phase-dependent distribution of high and low frequency sidebands of few-cycle rectangular pulses.     

一种基于多特征融合的新型光谱相似性测度

光谱相似性测度是高光谱遥感影像定量化分析和精细地物直接识别的基础,光谱特征的选择和刻画方式是光谱相似性测度的关键.研究表明,利用光谱的单一特征无法全面反应地物光谱间的相似性,光谱识别时需要综合考虑光谱的多种特征.本文在几何距离、相关系数和相对熵的基础上提出了一种结合多种光谱特征的新型光谱相似性测度,即光谱泛相似测度(s...     

Polarization-dependent carrier dynamics in a passive InAs/InP quantum dot waveguide

We investigate carrier dynamics in a passive InAs/InP quantum dot (QD) waveguide using 255 fs optical pulses at a central wavelength of 1568 nm. We observe strong anisotropy of absorption saturation for different polarizations. Pump-probe measurements indicate the presence of carrier relaxation dynamics on a timescale in the order of tens of picoseconds due to cascaded relaxation of carriers generated by two-photon absorption (TPA) from the bulk region to the QDs via the wetting layer. These relaxation timescales are much longer than in QD amplifiers. Our observations are supported by a rate-equation model which includes TPA, showing good agreement with the pump-probe measurements.     

A Turn-on and Reversible Fluorescence Sensor for Zinc Ion Based on 4,5-Diazafluorene Schiff Base

A new 4,5-diazafluorene-based fluorescent chemosensor has been synthesized by Schiff base condensation of 9,9-bis(3,5-dimethyl-4-aminophenyl)-4,5-diazafluorene with salicylaldehyde. The interaction of Schiff base with different metal ions has been studied over photofluorescent spectra. The results showed that Schiff base exhibited 194-fold enhancements in fluorescence at 465 nm after Zn²⁺ ions. Such fluorescent responses could be detected by naked eye under UV-lamp. The complex solution (L-Zn²⁺) exhibited reversibility with EDTA.     

High-throughput screening against $$\sim $$6.1 million structurally diverse,lead-like compounds to discover novel ROCK inhibitors for cerebral injury recovery

Rho-associated protein kinase (ROCK) has been recognized as an attractive therapeutic target to promote neurogenesis, neuroregeneration, and neurorecovery after cerebral injury. Here, a high-throughput screening protocol was described to discover novel ROCK inhibitors from a large chemical library containing \(\sim \)6.1 million structurally diverse, lead-like compounds. The protocol employed empirical rules such as ADMET evaluation and chemical similarity analysis to exclude those of drug-unlike candidates, and then molecular docking and binding affinity predictions were performed to suggest few promising candidates with high scores. Consequently, five compounds were successfully identified to have satisfactory activity profile with \(\hbox {IC}_{50}\) values at nanomolar level. In order to elucidate the molecular mechanism of inhibitor binding to target, the complex structures of ROCK kinase domain with the five identified compounds were modeled and examined in detail. A number of polar chemical forces such as hydrogen bonds and cation-\(\pi \) interactions as well as nonpolar contacts such as \(\pi \)–\(\pi \) stacking and hydrophobic forces were revealed at the complex interface, conferring high affinity and strong specificity to inhibitor binding. In addition, several key residues around the kinase active site, including Val90, Lys105, Asn203, and Phe368, were found to play an important role in binding.     

Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system

A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.     

基于VxWorks新型映像的三模冗余启动机制研究

针对VxWorks启动映像依赖于ROM地址,不能适应航天型号中三模存储要求的缺点,利用VxWorks自带的压缩算法,按照航天型号软件任务要求设计了一种基于VxWorks内存型映像的新型压缩映像,实现了软件映像与ROM区地址无关。并且实现了新型压缩映像的三模冗余引导启动,启动时每一个bit数据都从三份映像获取,并进行三取二判断,将最后结果拷贝到内存作为目的映像的bit数据,目的映像启动后能够回写正确数据自动纠正空间环境下可能发生的单粒子翻转错误,为软件的可靠启动建立了基础。