Ho2(Co,Si)17化合物的结构与磁晶各向异性

用三弧Czochralski法和真空电弧熔炼法制备了Ho2Co17-xSix化合物.通过X射线衍射和磁性测量手段研究了化合物的结构与内禀磁性.重点讨论了磁晶各向异性和自旋重取向转变.实验结果表明,Ho2Co17为Th2Ni17型六角结构,在0.5≤x≤3的化合物均为Th2Zn17型菱方结构,能够获得单相2:17型化合物的最大Si含量是x=3.在x≤2的浓度范围,化合物的易磁化方向垂直于c轴.随Si含量增加,化合物的居里温度和Co原子平均磁矩单调减少.根据Ho2Co17-xSix化合物的居里温度和自旋重取向温度,获得了磁相图.根据热磁曲线,确定了温度补偿点.在Ho2Co17化合物中观察到了在1005 K发生自旋重取向转变.     

广义BBM方程有理Chebyshev谱逼近的大时间性态

本文考虑广义BBM方程的初值问题,建立了方程的有理Chebyshev谱格式,给出了谱格式的误差估计,并证明了原问题和近似问题所生成的算子半群分别具有整体吸引子A和AN,且AN关于A 是上半连续的．     

Time integration of the non-linear Galerkin method

e-mail: bosco{at}mac.cie.uva.es, frutos@mac.cie.uva.es Numerical tests are presented that, for the Kuramoto-Sivashinskyand a reaction-diffusion equation, compare the non-linear Galerkinmethod with standard pseudospectral and pure spectral Galerkindiscretizations. The results show that, for these problems,the non-linear Galerkin method is not competitive with eitherpure spectral Galerkin or pseudospectral discretizations.     

Exponential stability for a contact problem in thermoelasticity

We consider the unilateral problem for the thermoelastic equationand we show that the solution decays exponentially to zero astime goes to infinity; that is, denoting by E(t) the first-orderenergy of the system, we show that positive constants C and exist which satisfy E(t)CE(0)e^–$$$.     

龙爪芦荟和库拉索芦荟中微量锗的测定与红外光谱区别

采用吸光光度法对龙爪芦荟和库拉索芦荟中的微量锗进行了测定,并探讨了两种芦荟的红外光谱的区别。结果表明,龙爪芦荟中含锗量在26.1～28.6μg·g-1,回收率为91.6%～97 5%。库拉索芦荟中含锗量在16.8～20.0μg·g-1,回收率为87.1%～94.5%。两种芦荟的FT IR光谱图在2100cm-1处有明显差异,由此可区别两种芦荟。     

LIGHT PROMOTION OF SEED GERMINATION IN Datura ferox IS MEDIATED BY A HIGHLY STABLE POOL OF PHYTOCHROME

Abstract— The duration of the far-red light-absorbing form of phytochrome (Pfr) of the photoreceptor pool involved in the control of seed germination was investigated for Datura ferox seeds. These seeds require both Pfr and alternating temperatures (20/30°C) to germinate. After 24 h imbibition (25°C), the seeds received pretreatment-light pulses providing different phytochrome photoequilibria (Pfr/P), followed by a 24 h dark incubation (25°C), and test-light pulses providing different Pfr/P immediately prior to transfer to alternating temperatures. Germination increased with increasing Pfr/P provided by the test-light pulses, but was unaffected by the pretreatment-light pulses. This suggests that phytochrome synthesis, phytochrome degradation and phytochrome-mediated changes in response to phytochrome were negligible. In other experiments, red light-pretreatment pulses were followed by dark incubations (25°C) of different duration before transfer to alternating temperatures. The proportion of Pfr remaining after the 25°C incubation period was estimated by comparing germination rates with those of seeds that received test-light pulses of known calculated Pfr/P immediately prior to the start of the cycles of alternating temperatures. More than 80% of the Pfr established by a Pfr/P= 0.87 light pulse was present and active even after 48 h dark incubation at 25°C. Surprisingly, when a pretreatmentlight pulse providing a Pfr/P= 0.70 was given, the reduction in [Pfr] was significantly faster.
Germination of Datura ferox seeds is under the control of a highly stable (type II like) phytochrome pool. Apparently, this pool follows Pfr dark reversion to the red light-absorbing form, the times to reach half the original Pfr pool being > 96 h or <14 h after light pulses providing Pfr/P= 0.87 or 0.70, respectively.     

CaF2：xYb3+, yEr3+纳米颗粒的合成及其上转换发光性质

采用水热合成法制备了CaF₂：xYb³⁺,yEr³⁺（x=0.1~0.8,y=0.01~0.08）纳米颗粒,利用X射线粉末衍射仪、透射电子显微镜和F-4600荧光分光光度计表征了样品的物相和形貌尺寸,并探究了Yb³⁺和Er³⁺掺杂浓度对样品的上转换发光性质的影响。结果表明,所合成的样品为立方相,球形颗粒,平均直径为 12 nm,敏化剂Yb³⁺的最佳掺杂摩尔分数为20%,而激活剂Er³⁺的最佳掺杂摩尔分数为6%。此时,绿光与红光的强度之比最大。     

香菇多糖L-2A的结构表征

从香菇子实体中提取纯化得到香菇多糖级分L-2A,利用紫外光谱、红外光谱、凝胶渗透色谱和气相色谱分析其结构特征.香菇多糖L-2A糖含量为90.14%;重均分子量是2.03×10 5道尔顿;具有D-葡萄吡喃糖构型,单糖组成主要是由吡喃型葡萄糖组成;香菇多糖L-2A多糖含有o-糖苷键,且主要是o-Ser连接方式;具有与刚果红结合的螺旋结构.香菇多糖L-2A为首次从香菇子实体中分离得到.     

Hydrogen storage inside a toroidal carbon nanostructure C120: Density functional theory computer simulation

Ab initio density functional calculations were performed for a toroidal carbon C₁₂₀ nanostructure. Hydrogen molecules, n = 1–15, were added inside the nanotorus and for each one of these systems a geometry optimization was obtained. The cohesive energy shows that these structures are energetically stable. For example, the binding energies are ?34.95 and ?36.19 Hartrees and the interatomic distances H? H are 0.753 and 0.772 Å for 1 and 14 molecules, respectively. Considering only molecular hydrogen, we have always seen so far weak physisorption into the C₁₂₀ nanotorus. There is no chemisorption until the number oh hydrogen molecules are increased to 14. In this case, four hydrogen atoms are chemisorbed. With 15 molecules, there are 10 hydrogen atoms chemisorbed just at the inner nanotorus surface forming 10 H? C bondings with bond length close to that in methane. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2495–2508, 2010