Advances in the understanding of multiferroics through soft X-ray diffraction

The magneto-electric multiferroic TbMn₂O₅ has a complex magnetic structure in three different magnetically ordered phases. We have determined the nature of the induced magnetic order on the oxygen sites in the commensurate magnetic phase through full linear X-ray polarisation analysis at the oxygen K edge. This has been achieved rotating the linear polarisation of the incident beam at the source, and using multilayers to analyse the polarisation state of the scattered X-ray beam. We have confirmed that the anisotropy of the magnetic scattering at the oxygen edge is consistent with the anisotropy of the manganese magnetic structure.     

Co3O4纳米立方体的可控合成及其CO氧化反应性能

在乙醇和三乙胺的混合溶液中,采用溶剂热法制备了尺寸为10 nm的Co₃O₄立方体. 考察了钴盐前驱体和溶解氧对Co₃O₄纳米立方体结构的影响规律,通过对合成过程中不同阶段产物的结构分析和表征,提出了Co₃O₄纳米立方体的形成机制是溶解再结晶的过程. 将所制备的Co₃O₄纳米立方体在200 ℃焙烧处理后,尺寸和形貌均可保持稳定,但400 ℃焙烧后,变为球形纳米粒子. 这种主要暴露{100}晶面的Co₃O₄纳米立方体催化CO氧化反应的活性低于纳米粒子({111}晶面),验证了四氧化三钴纳米材料在CO氧化反应中的晶面效应.     

Synthesis of the p-keto acids from benzimidazolium iodides and ethyl malonate

The reaction of benzhnidazole methiodide with ethyl malonate in the existence of base was studied,and a new convenient synthetic method of the β-keto acid was provided.     

Controlled nucleation from solution using polymer microgels

Despite its widespread occurrence in nature and broad application in industrial practice, nucleation of crystalline materials remains largely unpredictable and therefore difficult to control. In this work, we demonstrate a new method to control nucleation with polymer microgels by tuning their microstructure to vary systematically the degree of nanoscopic confinement and its effects on nucleation. We find that the polymer microstructure has a significant impact on nucleation kinetics. Moreover, there exists an optimum polymer mesh size at which the rate of nucleation is dramatically enhanced, the degree to which depends on the extent of polymer-solute interactions. With easily tunable microstructure and chemistry, polymer microgels offer a promising approach for the rational design of materials for controlling nucleation from solution.     

Ice internal friction: Standard theoretical perspectives on friction codified,adapted for the unusual rheology of ice,and unified

Sea ice contains flaws including frictional contacts. We aim to describe quantitatively the mechanics of those contacts, providing local physics for geophysical models. With a focus on the internal friction of ice, we review standard micro-mechanical models of friction. The solid's deformation under normal load may be ductile or elastic. The shear failure of the contact may be by ductile flow, brittle fracture, or melting and hydrodynamic lubrication. Combinations of these give a total of six rheological models. When the material under study is ice, several of the rheological parameters in the standard models are not constant, but depend on the temperature of the bulk, on the normal stress under which samples are pressed together, or on the sliding velocity and acceleration. This has the effect of making the shear stress required for sliding dependent on sliding velocity, acceleration, and temperature. In some cases, it also perturbs the exponent in the normal-stress dependence of that shear stress away from the value that applies to most materials.

We unify the models by a principle of maximum displacement for normal deformation, and of minimum stress for shear failure, reducing the controversy over the mechanism of internal friction in ice to the choice of values of four parameters in a single model. The four parameters represent, for a typical asperity contact, the sliding distance required to expel melt-water, the sliding distance required to break contact, the normal strain in the asperity, and the thickness of any ductile shear zone.     

超声背散射法评价松质骨状况的研究

超声背散射法评价松质骨状况及诊断骨质疏松症是近年来医学超声领域内的研究热点之一,现已取得了显著的进展。本文将介绍近年来超声背散射法及其参量评价松质骨状况的研究进展,并分析超声背散射相关参量频谱质心偏移量（SCS）和平均骨小梁间距（TbSp）与骨矿密度（BMD）的相关性。研究结果表明,超声背散射参量与BMD有较高的相关性。最后提出了将来研究中需要努力的方向。     

第4届国际超声大会(ICU)在新加坡召开

2013年5月2日至5日,第4届国际超声大会（ICU）在新加坡召开。本次会议在国际声学委员会的组织下,由新加坡声学学会主办,由澳大利亚声学学会、印度声学学会、香港声学学会和印度无损检测学会联合承办。会议致力于促进超声不同领域,包括基础研究、工程技术以及生物医学应用等方面的国际交流与合作。     

Crystal structure refinement at high pressures using angle-dispersive powder diffraction techniques

Abstract

The development of area detectors such as the imaging plate (IP) allows the use of angle-dispersive techniques for powder diffraction studies at high pressure. Integration of the 2-d pattern greatly improves the powder averaging and signal-to-noise ratio, making it possible to carry out full Rietveld refinements of crystal structures in high-pressure phases. An IP system is being developed at the Synchrotron Radiation Source (SRS), Daresbury, and the current status of this system -hardware and software -is described. Recent results on La₂CuO₄ and lnSb demonstrate the effectiveness and advantages of the techniques.     

锡掺杂二氧化钛相变过程和微结构分析

本文采用溶胶凝胶法制备了锡掺杂纳米二氧化钛,通过高分辨透射电镜法(HRTEM),X-射线衍射法(XRD)等分析手段对样品的相变过程进行了表征.XRD和HRTEM测试表明纯二氧化钛在烧结温度高于500℃时出现金红石相,而25mol; Sn2+掺杂二氧化钛凝胶在300℃烧结2h后少量锐钛矿相析出的同时结晶出金红石相.实验结果表明Sn2掺杂抑制了锐钛矿和金红石相的晶粒长大;Sn2+掺杂明显地促进了锐钛矿向金红石的转变.Sn2氧化后形成Sn4+,Sn4+置换Ti4+而引起二氧化钛晶格膨胀的同时晶格畸变应力增加.     

Aggregation behavior and thermodynamics of binding between poly(ethylene oxide)-block-poly(2-(diethylamino)ethyl methacrylate) and plasmid DNA

The aggregation behavior and the thermodynamics of binding between poly(ethylene oxide)-block-poly(2-(diethylamino)ethyl methacrylate) (PEO-b-PDEAEMA) block copolymers and plasmid DNA were examined. Binding between the polymer and DNA were confirmed by gel electrophoresis. The high affinity between the polymer and DNA was demonstrated through the ethidium bromide (EtBr) displacement assay, and the binding was found to be related to the stoichiometric balance between the amine group of the polymer and the DNA nucleotide molar ratio (N/P molar ratio). The light scattering and TEM results showed that, at low polymer concentration, the hydrodynamic radii (R(h)) of the polymer/DNA complexes was around 90 nm; however, at sufficiently high polymer concentration, the complexes condensed to around 35 nm induced by a structural rearrangement of the amphiphilic nature of the block copolymer. The isothermal titration calorimetric results showed that the binding between the polymer and DNA is driven by a large favorable enthalpy.