Possible observation of Kondo screening cloud in Yb14MnSb11 *

ABSTRACT

Single crystals of the underscreened Kondo ferromagnet Yb₁₄MnSb₁₁ were investigated using polarised neutron diffraction and magnetisation measurements. The magnitude and direction of the magnetisation at each of the 9 distinct crystallographic sites was measured using polarised neutron diffraction. A large moment of close to 4.2?μ_B was found at the unique Mn site. A compensating antiferromagnetic moment of ≈?0.5?μ_B was found to be distributed uniformly among the remaining Yb and Sb sites, which was not expected from a previous theoretical calculation. The compensating magnetisation, however, is consistent both in size and magnitude with the expected Kondo screening cloud.     

Effect of chain architecture on the phase transition of star and cyclic poly(N‐isopropylacrylamide) in water

The heat‐induced phase transition of aqueous solutions of Poly(N‐isopropylacrylamide) (PNIPAM) in water is examined for a four‐arm PNIPAM star (s‐PNIPAM), a cyclic PNIPAM (c‐PNIPAM), and their linear counterparts (l‐PNIPAM) in the case of polymers (1.0 g L^?1) of 12,700 g mol^?1 < M_n < 14,700 g mol^?1. Investigations by turbidity, high‐sensitivity differential scanning calorimetry (HS‐DSC), and light scattering (LS) indicate that the polymer architecture has a strong effect on the cloud point (T_c: decrease for s‐PNIPAM; increase for c‐PNIPAM), the phase transition enthalpy change (ΔH decrease for s‐PNIPAM and c‐PNIPAM), and the hydrodynamic radius of the aggregates formed above T_c (R_H: c‐PNIPAM < s‐PNIPAM < l‐PNIPAM). The properties of s‐PNIPAM are compared with those of previously reported PNIPAM star polymers (3 to 52 arms). The overall observations are described in terms of the arm molecular weight and the local chain density in the vicinity of the core of the star, by analogy with the model developed for PNIPAM brushes on nanoparticles or planar surfaces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2059–2068.     

基于云模型的三维土工网防护边坡侵蚀稳定性综合评价

在分析各项影响因素分级标准的基础上,建立了三维土工网护坡侵蚀稳定性的综合评价体系.针对三维土工网边坡侵蚀稳定性分析中不确定性问题,将云模型理论引入到综合评判中,实现了定性与定量的不确定性转换.通过构建前件云发生器和后件云发生器,利用不确定推理,确定各项评价指标的具体分值.借助层次分析法与敏感度分析确定各项评价指标的权重,进而得出综合评价体系的整体得分.工程实例计算结果证实了模型的实用性和有效性,为三维土工网防护边坡侵蚀稳定性的评价提供了一条新的途径.     

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] thermoresponsive microspheres: An accurate method based on solute exclusion technique to determine the volume phase transition temperature

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] [poly(NIPAAm-co-AAm-co-HEMA)] copolymer was synthesized as a new thermoresponsive material possessing a lower critical solution temperature (LCST) around 37 °C in phosphate buffer, pH 7.4, at a solution concentration of 1%, w/v. The influence of polymer concentration on LCST was determined by cloud point measurements and by microcalorimetric analysis. The copolymer was transformed in hydrogel microspheres by suspension reticulation of OH groups with glutaraldehyde. The volume phase transition temperature (VPTT) of microspheres was determined by a new approach, which involves measurement of the increase in concentration of a blue dextran (BD) solution at different temperatures in the presence of dry microspheres. The minimum BD concentration that gives reliable and reproducible results was determined to be 1 mg/ml. However, the higher is the concentration of BD in solution the smaller is the error. Contrary to solution of the linear polymer which displays a sharp phase transition temperature, the dependence of water regain of the hydrogel with temperature lasts from 4 °C to 50 °C.     

TVD格式在燃料蒸气云爆炸场数值模拟中的应用

本文采用了有限差分方法——TVD格式(Total Variation Diminishing,A.Harten,1983)对燃料蒸气云爆炸产生的二维轴对称爆炸场进行了数值模拟。爆炸波超压和运动轨迹的数值计算值与实验结果吻合得相当好。     

碳谱化学位移计算式中基值的估算

提出一个计算碳谱化学位移计算式中基值的公式:B=-2.3+12.95(ΣP)^1/3sin^0.9θ₁sin^0.5θ₂f/s²+Σα_σ并提出核周电子密度降低和核周电子云的变形是去屏蔽的基本因素的观点.     

Novel reactive thermosensitive polyethers – control of transition point

A new class of thermosensitive polymers based on polyethers is discussed. Using living anionic polymerisation techniques a series of homo- and block copolymers of 2,3-epoxypropanol-1 (the glycidol), ethoxy ethyl glycidol ether, its hydrophobic derivative, and ethylene oxide of different molar masses and topology (linear and comb-like) was obtained. By simple chemical modification of hydroxyl groups in polyglycidol segments hydrophobic elements were introduced into polymer chains, which allowed to control the transition point related to the lower critical solution temperature between 0 to 100°C. The relation between the transition temperature and the structure of obtained polymers is discussed.     

浊点萃取-荧光光度法测定水中的苯酚

基于非离子表面活性剂Triton X-100,以浊点萃取结合荧光光度法测定水中的苯酚,考察影响浊点萃取的各种因素。在pH=3.0的磷酸氢二钠-磷酸二氢钾缓冲溶液中,采用2.0mL Triton X-100(5%)、82℃平衡温度、8min平衡时间的条件下,苯酚被萃取到Triton X-100表面活性剂相与水相分开,用于环境水样中苯酚的测定,结果令人满意。     

2013年“菲特”台风暴雨数值模拟中微物理方案的对比试验

利用TRMM（热带测雨雷达）搭载的TMI（微波成像仪）反演廓线资料,分析“菲特”台风登陆前、后云团内部水凝物的分布种类,依此选择WRF区域中尺度模式下符合条件的6个云微物理过程参数化方案（Lin,WSM6,Godgce,WDM6,Morrison以及Thompson方案）,模拟2013年10月6~8日的台风过程.从降水落区、强度,水凝物及风场垂直分布,台风路径及强度等方面对预报性能进行对比,结果表明,选用的6个云微物理方案都较好地模拟了浙江暴雨的范围和强度.结合Ts评分,降水量级越大,模拟效果对云微物理方案选择越敏感,其中,Lin方案效果最佳,尤其对极端降水的模拟,其次为WSM6、WDM6及Thompson方案,Morrison和Godgce方案相对较差.结合水凝物平均值廓线分布发现,除WDM6方案外,其他方案对暖雨过程的模拟基本一致,而对冰相过程的模拟6个方案差别较大;同时,各方案对风分量的模拟结果较水凝物廓线差别小,说明对于动力因素模拟不敏感.另外,6个方案对于台风强度的模拟整体偏弱,相较之下,Lin方案较好地模拟了强度变化趋势.     

Water-soluble ABC triblock copolymers based on vinyl ethers: Synthesis by living cationic polymerization and solution characterization

Water-soluble ABC triblock copolymers of methyl vinyl ether (MVE), ethyl vinyl ether (EVE), and methyl tri(ethylene glycol) vinyl ether (MTEGVE) of various block sequences and carrying 20 monomer units in each block were synthesized by living cationic polymerization. In addition to the triblocks, one AB diblock, one BA diblock, and one statistical copolymer of MVE and MTEGVE carrying 20 units of each type of monomer were synthesized as controls. Moreover, three homopolymers each carrying 20 units of MVE and end groups of varying hydrophobicity were synthesized using three different initiators. The molecular weights and molecular weight distributions of all the polymers were determined by gel permeation chromatography (GPC) in tetrahydrofuran (THF). The number average degrees of polymerization (DP_ns) and composition of all the polymers were calculated by proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The molecular weights and degrees of polymerization corresponded to the values expected from the monomer/initiator ratios. The calculated polydispersities were reasonably narrow at 1.3. Aqueous GPC studies at room temperature on the triblock copolymers showed that the polymers exist as isolated chains (unimers) in solution but they tend to assemble and form micelles in the presence of a sufficiently high salt concentration apparently due to the insolubility of the EVE units under the latter conditions. Triblocks with a different block sequence exhibited a different susceptibility to salt-induced micellization, as indicated by the retention volume of the micelles and the relative micelle/unimer peak areas. Similarly, the cloud points of the triblock copolymers covered a relatively wide temperature range from 56 to 72°C. These differences in micellization and cloud points suggest a profound effect of the location of the hydrophilic MTEGVE block on copolymer association. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1181–1195, 1997