A critical transition state in liquid metals

Temperature dependence of viscosities of liquid Sn, Cu, Pb_38.1Sn_61.9, Pb_44.8Bi_55.2, and Cu_0.7Sn_99.3 has been studied by a torsional oscillation viscometer. During the measurement process, a deviation from the Arrhenius behavior is found when the temperature is lowered to about 60 K higher than the melting point. The abnormal increasing of the viscosity and the activation energy indicates the changes of the elementary melt structure during cooling towards the melting point. The deviation region from Arrhenius viscosity is defined as the transition state. The differential scanning calorimeter experiments also show the existence of the critical transition state in liquid metals near the melting point. The drastic increase of the viscosity in the transition state can be regarded as continuum transition and be presented well by the amended Arrhenius equation which is based on the critical phenomenon.     

Growth and morphology of nanometer LiMn2O4 powder

The growth of Li_1+xMn₂O₄ via detonation reaction was investigated with respect to the presence of an energetic precursor, such as the metallic nitrate and the degree of confinement of the explosive charge. The detonation products were characterized by scanning electron microscopy. Powder X-ray diffraction and transmission electron microscopy were used to characterize the products. Li_1+xMn₂O₄ with 1-2 μm spherical morphology and more uniform secondary particles, but with smaller primary particles of diameters from 20 to 60 nm and a variety of morphologies were found. The oxides produced by this cheap method affirmed the validity of detonation synthesis of nano-size powders.     

Synthesis and two-photon absorption property of new π-conjugated dendritic fluorophores containing styrylpyridyl moieties

Four new multi-branched two-photon absorption chromophores, namely 1-(4-bromobenzal)-3,5-bis(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)benzene (4), tris(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)-benzene (5), 6-chloro-N²,N⁴-bis(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)-1,3,5-triazine-2,4-diamine (6), tris-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine (7), have been synthesized and characterized. One-photon fluorescence, fluorescent quantum yields and two-photon fluorescence have been investigated. The experimental two-photon absorption cross-sections of 4–7 in DMF are 6, 11, 13 GM (pumped by 740 nm laser) and 19 GM (pumped by 800 nm laser), respectively. The calculated two-photon absorption cross-sections of 4–7 are 5.41, 7.67, 9.57 and 76.14 GM, respectively. The two-photon induced fluorescent peak wavelengths of 4–7 in DMF are 421, 425, 474 and 534 nm pumped by 680, 680, 740 and 800 nm laser, respectively. The results show that molecule 7 is a good two-photon absorption fluorophore possessing long two-photon fluorescent lifetime, good fluorescent quantum yield and large two-photon absorption cross-section. The two-photon absorption peak wavelength of molecule 7 is at 800 nm, which is favourable for initiating two-photon photopolymerization.     

Intrusion detection in web applications using text mining

Information security has evolved from just focusing on the network and server layers to also include the web application layer. In fact, security in some types of web applications is often considered a particularly sensitive subject. Achieving a secure web application involves several different issues like encrypting traffic and certain database information, strictly restricting the access control, etc. In this work we focus on detecting attempts of either gaining unauthorised access or misusing a web application. We introduce an intrusion detection software component based on text-mining techniques. By using text categorisation, it is capable of learning the characteristics of both normal and malicious user behaviour from the log entries generated by the web application server. Therefore, the detection of misuse in the web application is achieved without the need of any explicit programming or code writing, hence improving the system maintainability. Because telemedicine systems are usually critical in terms of the confidential information handled and the responsibilities consequently derived, we apply and evaluate our methods on a real web-based telemedicine system called Arnasa.     

PVA-based activated carbon fibers with lotus root-like axially porous structure

A novel method was developed for the fabrication of activated carbon fiber (ACF) with wet spinning polyvinyl alcohol (PVA) fibers as the precursors. Through a combination of preoxidation, dehydration, carbonization and activation under a certain tension, PVA-based ACFs (PVA-ACFs) with high yields and good mechanical properties were obtained. The surface and cross-section morphologies, pore structures, surface geometries, surface functional groups and crystal structures of the PVA-ACFs were characterized using field emission scanning electron microscopy, low temperature nitrogen adsorption, Fourier transformed infrared spectrophotometry, X-ray photoelectron spectroscopy and X-ray power diffraction. All the PVA-ACF samples prepared had lotus root-like axially meso- and macroporous structures with the domination of micropores. Fractal geometries of PVA-ACFs deduced from nitrogen adsorption isotherms indicates that capillary force dominated in the interactions between nitrogen and the PVA-ACFs. The surface functional groups of the PVA-ACFs depend on the activating agents. Graphitoidal crystal structures were observed for the PVA-ACFs. The small crystal size and short range ordering between the crystallites ensured a high specific surface area of the PVA-ACFs.     

小波变换在求解重力测定反问题中的应用

针对重力测定反问题,提出将其离散为线性不适定问题,利用小波变换方法进行数值求解.该方法将小波变换和正则化方法相结合,选取小波函数作为一组基底,将原不适定问题转化为粗子空间上的适定问题,并给出选取粗子空间基的方法.通过数值模拟已有方法和小波变换方法求解结果的比较,表明了小波变换方法的可行性和有效性.     

A Performance Evaluation of Classic Convolutional Neural Networks for 2D and 3D Palmprint and Palm Vein Recognition

Palmprint recognition and palm vein recognition are two emerging biometrics technologies. In the past two decades, many traditional methods have been proposed for palmprint recognition and palm vein recognition, and have achieved impressive results. However, the research on deep learning-based palmprint recognition and palm vein recognition is still very preliminary. In this paper, in order to investigate the problem of deep learning based 2D and 3D palmprint recognition and palm vein recognition in-depth, we conduct performance evaluation of seventeen representative and classic convolutional neural networks (CNNs) on one 3D palmprint database, five 2D palmprint databases and two palm vein databases. A lot of experiments have been carried out in the conditions of different network structures, different learning rates, and different numbers of network layers. We have also conducted experiments on both separate data mode and mixed data mode. Experimental results show that these classic CNNs can achieve promising recognition results, and the recognition performance of recently proposed CNNs is better. Particularly, among classic CNNs, one of the recently proposed classic CNNs, i.e., EfficientNet achieves the best recognition accuracy. However, the recognition performance of classic CNNs is still slightly worse than that of some traditional recognition methods.

     

Finite-time Containment Control of Nonlinear Delayed Fractional Multi-agent Systems

This article deals with finite-time containment control (FTCC) of nonlinear delayed fractional multi-agent systems (FMASs). Addressing fractional Razumikhin approach, properties of fractional calculus and analytical techniques, a quadratic Lyapunov function is constructed to derive sufficient conditions on FTCC by adopting a discontinuous control protocol, the employed method may overcome well the troubles arising from time delays and fractional derivatives. Numerical simulations further clarify the reliability and validity of our theoretical conclusions.

     

大学英语课堂教学中合作学习有效性探讨

合作学习已经越来越多的被大学教师引入到英语教学中。文章探讨了合作学习中遇到的问题,分析合作学习受阻的原因,提出解决问题的对策。