冬泳(游泳)的热学问题

冬泳一般界定为气温0℃、水温14℃以下的游泳运动，是冷环境中颇具代表性的运动项目，其历史悠久，开展广泛（俄、美、日、法、丹麦等国），参与人数逐年增加。几年来我们总结了冬泳者的宝贵经验，通过热学实验（平均皮肤温度测试），在探究冬泳能耗机制与能耗计算方面做了点滴工作，现撰文简介，从物理视角引发读者兴趣。     

Measurements of the cross section for e(+)e(-) --> hadrons at center-of-mass energies from 2 to 5 GeV

We report values of R = sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->mu(+)mu(-)) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.     

氮化铝结构的高温Raman光谱分析

本文测量了氮化铝在不同温度下的Raman光谱 ,并确定了氮化铝的光学声子模E2 1、A1(TO)、E2 2 、E1(TO)、A1(LO)和E1(LO)Raman散射峰的频率 ,它们分别为 2 5 2cm- 1、6 1 4cm- 1、6 5 8cm- 1、6 72cm- 1、894cm- 1和 91 2cm- 1,其中光学声子模A1(TO)、E2 2 的Raman散射峰比较明显。随着温度的升高 ,A1(TO)、E2 2 散射峰的频率向低波数方向变化 ,表明氮化铝粉末压制体中存在的压应力逐渐减小 ;这两个散射峰的半高宽逐渐增大 ,说明随着温度的升高 ,存在氮原子和铝原子的扩散使得氮化铝粉末压制体中晶体结构逐渐发生变化。由于氮化铝粉末本身在空气中易与水蒸气发生反应 ,生成的Al(OH) 3 或AlOOH在加热过程会发生分解 ,干扰样品高温Raman光谱测量。     

The Nucleation Effect of Grafted Carbon Black on Crystallization of Poly(Ethylene Terephthalate)/Grafted Carbon Black Composite

Poly(ethylene terephthalate)/grafted carbon black (PET/GCB) and poly(ethylene terephthalate)/carbon black (PET/CB) composites were prepared by melt blending. The nucleating effect of CB and GCB were investigated using differential scanning calorimetry (DSC) analysis. The morphologies of the spherulites in PET, PET/CB and PET/GCB composites were observed by means of scanning electron microscopy (SEM). All results showed that GCB had higher nucleating activity than CB in PET and PET/GCB composite had higher rate of nucleation and crystallization. The melting behaviors of neat PET, PET/CB and PET/GCB composites after non‐isothermal crystallization were investigated as well. It was evident that the melting behavior of PET is greatly influenced by addition of CB and GCB.     

Reactive Compatibilization of Poly(Butylene Terephthalate)/Acrylonitrile-Styrene-Acrylate Blends by Epoxy Resin: Morphology and Mechanical Properties

The effect on the notched Izod impact strength of poly(butylene terephthalate) (PBT) by blending it with acrylonitrile-styrene-acrylate (ASA) was examined. Epoxy resin (ER) was demonstrated to be an efficient compatibilizer for the partially compatible blends of PBT/ASA. It requires only a very small amount of ER to improve the toughness of the PBT/ASA blends drastically. Furthermore, there exists an optimum proportion of ER added to achieve maximum notched Izod impact strength. Transmission electron microscopy (TEM) observation suggests that the ER in the PBT/ASA/ER blends suppressing the tendency of coalescence of ASA, leading to better dispersion of the ASA particles. Field emission scanning electron microscopy (FESEM) shows that ER enhances the phase dispersion and the interfacial adhesion between the PBT and ASA phases, it improves the compatibility between PBT and ASA. The compositions in the interphase was continuous, which results in multiphase composites with a graded interphase. It is suggested that enhanced interphase adhesion was necessary to obtain improved dispersion, fine phase morphology, and better toughness.     

Cubature Kalman filters: Derivation and extension

This paper focuses on the cubature Kalman filters （CKFs） for the nonlinear dynamic systems with additive process and measurement noise. As is well known, the heart of the CKF is the third-degree spherical–radial cubature rule which makes it possible to compute the integrals encountered in nonlinear filtering problems. However, the rule not only requires computing the integration over an n-dimensional spherical region, but also combines the spherical cubature rule with the radial rule, thereby making it difficult to construct higher-degree CKFs. Moreover, the cubature formula used to construct the CKF has some drawbacks in computation. To address these issues, we present a more general class of the CKFs, which completely abandons the spherical–radial cubature rule. It can be shown that the conventional CKF is a special case of the proposed algorithm. The paper also includes a fifth-degree extension of the CKF. Two target tracking problems are used to verify the proposed algorithm. The results of both experiments demonstrate that the higher-degree CKF outperforms the conventional nonlinear filters in terms of accuracy.     

Microstructure and properties of Nb/Ta multilayer films irradiated by a high current pulse electron beam

Nb/Ta multilayer films deposited on Ti6Al4V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by a high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. The microstructure and the composition of the outmost surface of melted alloyed layers were investigated using a transmission electron microscope (TEM) equipped with an X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was ～ 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface layer.     

A study on surface symmetry and interfacial enhancement of SrTiO3 by second harmonic generation

The symmetry of the surfaces of SrTiO3and slightly Nb-doped SrTiO3crystals was investigated by the optical reflected second harmonic generation technique.The good agreement between experimental and theoretical results of the second harmonic intensity dependence on the azimuth angle indicates that the SrTiO3(001)surface is with 4mm symmetry and the Nb-doped SrTiO3(111)surface with 3m symmetry.The measurements of the polarization dependent second harmonic intensity confirm that conclusion.The enhancement of the surface polarization in the structure of SrTiO3capped La0.9Sr0.1MnO3films compared with that in the La0.9Sr0.1MnO3films has been obtained.