Effects of sintering temperature and Bi2O3 content on microstructure and magnetic properties of LiZn ferrites

The effects of sintering temperature and Bi₂O₃ content on the microstructure and magnetic properties of lithium–zinc (LiZn) ferrites prepared by a conventional ceramic method were investigated. The results show that the densification behavior and grain growth rate were greatly improved by the addition of Bi₂O₃, because a liquid phase sintering occurred during the sintering process at high temperature due to the low-melting point of Bi₂O₃ (825 °C). X-ray diffraction (XRD) patterns of the slightly doped samples did not reveal the appearance of any phase other than spinel LiZn ferrite. However, the secondary phase of perovskite BiFeO₃ was detected for Bi₂O₃ content of more than 0.25 wt%. The studies further show that Bi oxide was present at grain boundary, and promoted the grain growth as reaction center at lower temperature. A high saturation magnetization, squareness ratio, minimum ferromagnetic resonance linewidth and low coercive force were obtained for the sample with 1.00 wt% Bi₂O additive at lower sintering temperature (1100 °C).     

菱铁矿FeCO3高压相变与性质的第一性原理研究

采用平面波赝势方法对菱铁矿FeCO₃高压下的晶体结构, 电子构型和电子结构进行了第一性原理计算研究. 研究过程中考虑了菱铁矿FeCO₃真实的反铁磁(AFM) 自旋有序态, 模拟静水压环境, 从零压逐步加压到500 GPa. 在40---50 GPa压力范围内, FeCO₃发生了从高自旋(HS) AFM态到低自旋(LS) 非磁性(NM) 态的磁性相变, 伴随着晶胞体积坍塌10.5%. FeCO₃在相变前后均是绝缘体, 但是相变后的LS-NM态的Fe²⁺ 离子的3d电子局域化程度更强, 能隙随着压力的进一步增大而逐步增大, 离化程度更高, 直到500 GPa没有发生金属绝缘体相变.     

The Bethe lattice treatment of sound attenuation for a spin- 3/2 Ising model

The sound attenuation phenomena is investigated for a spin- 3/2 Ising model on the Bethe lattice in terms of the recursion relations by using the Onsager theory of irreversible thermodynamics. The dependencies of sound attenuation on the temperature (T$T$), frequency (w$w$), Onsager coefficient (γ$\gamma$) and external magnetic field (H$H$) near the second-order (_Tc)$\left(T_c\right)$ and first-order (_Tt)$\left(T_t\right)$ phase transition temperatures are examined for given coordination numbers q$q$ on the Bethe lattice. It is assumed that the sound wave couples to the order-parameter fluctuations which decay mainly via the order-parameter relaxation process, thus two relaxation times are obtained and which are used to obtain an expression for the sound attenuation coefficient (α)$\left(\alpha \right)$. Our investigations revealed that only one peak is obtained near _Tt$T_t$ and three peaks are found near _Tc$T_c$ when the Onsager coefficient is varied at a given constant frequency for q=3$q=3$. Fixing the Onsager coefficient and varying the frequency always leads to two peaks for q=3,4$q=3,4$ and 6 near _Tc$T_c$. The sound attenuation peaks are observed near _Tt$T_t$ at lower values of external magnetic field, but as it increases the sound attenuation peaks decrease and eventually disappear.     

掺杂Eu3+离子的钨酸锂的合成及其光电性能研究

采用固相反应法合成了掺杂Eu^3 的Li2WO4材料，并用X射线粉末衍射仪、荧光分光光度计及交流阻抗技术对样品进行了观察和测试。结果表明：适量Eu2O3的掺入可提高基质材料的发光和导电性能。     

植物抗病毒剂的探寻ⅩⅣ--1,5-二丙酸酯-1,3,5-均三嗪-2,4-二酮的合成

通过对氢化－1，3，5－均三嗪－2，4－二酮衍生物抗病毒活性QSAR计算，预测标题化合物具有较好抗病毒活性，由氢化－1，3，5－均三嗪－2，4－二酮、丙烯酸甲酯和乙二醇衍生物经三步反应合成这些化合物，新化合物经^1H NMR，IR，MS确认结构。     

液相体系中工艺条件对纳米碳酸钙晶形及聚集态的影响

对液相中形成纳米碳酸钙所加的分散剂和晶型控制剂，温度、浓度和搅拌速度等对晶形及聚集态的影响作了初步的研究，在反应温度8～15℃，反应物浓度0.1～0.4mol/L，搅拌速度3～20r/s，反应物加料时间4～12min的工艺条件下，可制备出粒径约50nm的高分散纳米碳酸钙，所控条件和相应的产品结果较令人满意。     

Nanoscale retention‐loss dynamics of polycrystalline PbTiO3 nanotubes

We observed the nanoscale retention dynamics of polycrystalline PbTiO₃ nanotubes using piezoresponse force microscopy. We found that the retention loss of the nanodot domains on the nanotubes showed the stretched exponential relaxation behaviors with stretched exponential factor n being less than 1 (0.523 and 0.692), which are similar to the thin films. In addition, the nanodot domains showed a diverse relaxation time constant τ due to different remnant polarization of each dot domains. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Endemic infrared divergences in QED3 at finite temperature

We demonstrate that massless QED in three dimensions contains endemic infrared divergences. It is argued that these divergences do not affect observables; furthermore, it is possible to choose a gauge that renders the theory finite.     

GPU accelerated simulations of 3D deterministic particle transport using discrete ordinates method

Graphics Processing Unit (GPU), originally developed for real-time, high-definition 3D graphics in computer games, now provides great faculty in solving scientific applications. The basis of particle transport simulation is the time-dependent, multi-group, inhomogeneous Boltzmann transport equation. The numerical solution to the Boltzmann equation involves the discrete ordinates (S_n) method and the procedure of source iteration. In this paper, we present a GPU accelerated simulation of one energy group time-independent deterministic discrete ordinates particle transport in 3D Cartesian geometry (Sweep3D). The performance of the GPU simulations are reported with the simulations of vacuum boundary condition. The discussion of the relative advantages and disadvantages of the GPU implementation, the simulation on multi GPUs, the programming effort and code portability are also reported. The results show that the overall performance speedup of one NVIDIA Tesla M2050 GPU ranges from 2.56 compared with one Intel Xeon X5670 chip to 8.14 compared with one Intel Core Q6600 chip for no flux fixup. The simulation with flux fixup on one M2050 is 1.23 times faster than on one X5670.