Design of a PXR experiment based on the NCEL

Parametric X-ray Radiation （PXR） can be used as a novel, quasi-monochromatic energy-tunable and high-yield X-ray source. It is produced at the Bragg angle by a relativistic electron beam passing through the periodic structure of crystal materials. This article concerns the PXR experiment using low energy electrons （10 MeV） from NCEL （Novel Compact Electron-Linac）. The difficulty of the experiment is to distinguish the PXR photons form the background. The design of the experiment relies mainly on the yield of PXR, the Bremsstrahlung background of the X-rays and the capability of the detector.     

Magnetic properties of rare earth ion (Sm) added nanocrystalline Mg-Cd ferrites, prepared by oxalate co-precipitation method

Nanocrystalline ferrite powder having the general formula Mg_1−xCd_xFe₂O₄+5% Sm³⁺ (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) was synthesized by chemical oxalate co-precipitation technique. The synthesized powder was characterized by X-ray, IR and SEM techniques. The XRD analysis confirms cubic spinel phase with orthoferrite secondary phase. The lattice constant increases with increase in Cd²⁺ content (x). It is smaller than that for pure Mg-Cd ferrites. The average crystallite size lies in the range 28.69-32.66 nm. Saturation magnetization and magnetic moment increase with cadmium content up to x=0.4 and decrease thereafter. This is attributed to the existence of localized canted spin. The decrease in saturation magnetization and magnetic moment beyond x=0.4 is due to the presence of triangular spin arrangement on B-site. Coercivity and remanent magnetization decrease while Y-K angles increase with Cd²⁺ content. The Sm³⁺ addition improves the magnetic properties.     

经济研究中的物理学

当前的金融危机再次表明,传统经济学作为一门学科缺乏解释力和预测力.造成这个令人失望的状况的根本原因是由于经济学家没有按照科学的范式来发展这个学科.经济学的现状吸引了一群物理学家进入这个学科并形成了一个新的交叉学科——经济物理学,人们期望它在促进经济学科学化的进程中起决定性作用.文章首先简要介绍了经济学的主要内容,说明经济学理论是建立在理性和均衡假定基础之上的;接着论述了为什么经济学还不是一门科学,指出经济学研究不是基于逻辑实证主义原则来开展的;文章还分析了物理学家是如何研究经济问题的,介绍了经济物理学的主要研究内容和研究方法;文章最后提出经济学范式的转变必须从观察和实验出发,经济学理论必须建立在一个合理设计的量纲体系和对实际经济运行过程的正确理解基础之上.     

Angle‐resolved photoemission spectroscopy and imaging with a submicrometre probe at the SPECTROMICROSCOPY‐3.2L beamline of Elettra

The extensive upgrade of the experimental end‐station of the SPECTROMICROSCOPY‐3.2L beamline at Elettra synchrotron light source is reported. After the upgrade, angle‐resolved photoemission spectroscopy from a submicrometre spot and scanning microscopy images monitoring the photoelectron signal inside selected acquisition angle and energy windows can be performed. As a test case, angle‐resolved photoemission spectroscopy from single flakes of highly oriented pyrolitic graphite and imaging of the flakes with image contrast owing to rotation of the band dispersion of different flakes are presented.     

转动传能量子干涉效应:干涉角影响因素的研究

碰撞转动传能中存在量子干涉效应已经在静态池实验中被观测到,并且积分角也能被测量.利用分子束实验可得到转动传能更准确的信息,进而得到影响干涉角的的具体因素.文中利用一阶含时波恩近似和L-J相互作用势,建立了原子—双原子分子碰撞系统转动传能的量子干涉模型,描述了观察和测量微分干涉角的方法,得到了微分干涉角与碰撞半径和碰撞速度间的关系,同时也得到了积分干涉角和实验温度的关系.此理论模型对于理解和进行分子束实验是非常重要的.     

原子-双原子分子体系碰撞诱导中的量子干涉效应（第十五届全国原子与分子物理学术会议会议论文）

碰撞转动传能中存在量子干涉效应已经在静态池实验中被观测到,并且积分角也能被测量。但静态池掩盖了大量的实验信息,利用分子束实验可得到转动传能更准确的信息,进而得到影响干涉角的的具体因素。文中运用含时微扰的一级波恩近似理论和各向异性相互作用势,建立了原子-双原子分子（混合态）体系碰撞诱导转动能量传递中的量子干涉效应的理论模型,描述了观察和测量微分干涉角的方法,得到了微分干涉角与碰撞半径和碰撞速度间的关系,同时也得到了实验温度对微分干涉角的影响。此理论模型对于理解和进行分子束实验是非常重要的.     

An angle-resolved laser incident beam detector based on a pair ofFabry-Perot etalons

An angle-resolved laser detector based on a pair of a non-mechanical scanning Fabry-Perot cavities is described. The differential signal from the two cavities is approximately independent from the polarization of the incident laser beam and it is used to determine the angle of incidence of the beam on the Fabry-Perot cavities. The F-P etalon is made of interferometric filter combination. A laser incident angle sensor experimental platform is built up, and the experiment is carried out with a given laser range finder. When the incident angle is less than 5°, the transmission difference measured by the laser angle sensor is significantly lower than theoretical value, and deviation is more than 10%. When the incident angle is greater than 10°, the deviation is much lower than that of the situation of the incident angle is lower than 10°.     

Facile fabrication of a lotus-effect composite coating via wrapping silica with polyurethane

A lotus-effect coating was fabricated by wrapping micro-silica and nano-silica with polyurethane (PU) and subsequent spraying. The coating shows the similar self-cleaning property as lotus leaves: the contact angle is as large as 168° and the sliding angle is as low as 0.5°. Surface morphology of the coating was studied with scanning electron microscopy and atomic force microscopy. The composite coating shows the similar structure as lotus leaves.     

Surface modification of porous poly(tetrafluoraethylene) film by a simple chemical oxidation treatment

A simple, inexpensive and environmental chemical treatment process, i.e., treating porous poly(tetrafluoroethylene) (PTFE) films by a mixture of potassium permanganate solution and nitric acid, was proposed to improve the hydrophilicity of PTFE. To evaluate the effectiveness of this strong oxidation treatment, contact angle measurement was performed. The effects of treatment time and temperature on the contact angle of PTFE were studied as well. The results showed that the chemical modification decreased contact angle of as-received PTFE film from 133 ± 3° to 30 ± 4° treated at 100 °C for 3 h, effectively converting the hydrophobic PTFE to a hydrophilic PTFE matrix. The changes in chemical structure, surface compositions and crystal structure of PTFE were examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), respectively. It was found that the F/C atomic ratio decreased from untreated 1.65-0.10 treated by the mixture at 100 °C for 3 h. Hydrophilic groups such as carbonyl (CO) and hydroxyl (OH) were introduced on the surface of PTFE after treatment. Furthermore, hydrophilic compounds K_0.27MnO₂·0.54H₂O was absorbed on the surface of porous PTFE film. Both the introduction of hydrophilic groups and absorption of hydrophilic compounds contribute to the significantly decreased contact angle of PTFE.