Single‐crystal X‐ray diffraction and resonant X‐ray magnetic scattering at helium‐3 temperatures in high magnetic fields at beamline P09 at PETRA III

The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14 T vertical field split‐pair magnet. A helium‐3 refrigerator is available that can be fitted inside the magnet's variable‐temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He‐3 insert are presented. By measuring the tetragonal‐to‐orthorhombic phase transition occurring at 2.1 K in the Jahn–Teller compound TmVO<sub>4sub>, it is found that the photon flux at P09 must be attenuated down to 1.5 × 10⁹ photons s^?1 for the sample to remain at temperatures below 800 mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X‐ray magnetic scattering signal at the Tm L<sub>IIIsub> absorption edge associated with the spin‐density wave in TmNi<sub>2sub>B<sub>2sub>C below 1.5 K is intense enough to permit a complete study in magnetic field and at sub‐Kelvin temperatures to be carried out.     

被动线谱检测的子带分解和分方位区间融合算法

目标辐射噪声中低频线谱丰富,而且谱级比高、强度稳定,相比调制谱检测具有优越性。基于子带分解处理的现有融合方法适用在信噪比相对较高情况下,而当干扰是相干的或强宽带信号时,对线谱目标有效检测仍没很好解决。本文从子带空间谱统计特性出发,利用线谱谱级高出连续谱10-25dB;线谱频带所在方位区间的输出方位波动小,而其他分区间的输出方位波动大特点,提出了一种在信噪比低,多目标并存情况下更有效的弱线谱提取融合方法。理论仿真和海试实验数据处理结果验证该方法具有创新性、较常规方位稳定算法适用范围更广、检测效果更好,适合工程应用。     

A simple representation of energy matrix elements in terms of symmetry‐invariant bases

When a system under consideration has some symmetry, usually its Hamiltonian space can be parallel partitioned into a set of subspaces, which is invariant under symmetry operations. The bases that span these invariant subspaces are also invariant under the symmetry operations, and they are the symmetry‐invariant bases. A standard methodology is available to construct a series of generator functions (GFs) and corresponding symmetry‐adapted basis (SAB) functions from these symmetry‐invariant bases. Elements of the factorized Hamiltonian and overlap matrix can be expressed in terms of these SAB functions, and their simple representations can be deduced in terms of GFs. The application of this method to the Heisenberg spin Hamiltonian is demonstrated. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Limit theorems for the convex hull of random points in higher dimensions

We give a central limit theorem for the number of vertices of the convex hull of independent and identically distributed random vectors, being sampled from a certain class of spherically symmetric distributions in that includes the normal family. Furthermore, we prove that, among these distributions, the variance of exhibits the same order of magnitude as the expectation as The main tools are Poisson approximation of the point process of vertices of the convex hull and (sub/super)-martingales.

     

Palladium Sub‐Nanoparticle Decorated ‘Bamboo’ Multi‐Walled Carbon Nanotubes Exhibit Electrochemical Metastability: Voltammetric Sensing in Otherwise Inaccessible pH Ranges

A generic approach for the detection of electroactive species in potential ranges that would normally be inhibited due to the stripping of the electrocatalytic material is presented. We demonstrate, via the example of the electrochemical oxidation of hydrazine, that palladium nanoparticle (< 1 nm) decorated bamboo multi‐walled carbon nanotubes exhibit a metastability such that they allow the sensing of hydrazine in the pH range where palladium metal would normally be voltammetrically stripped (oxidized) from the surface of convectional electrodes.     

非晶Fe73.5Cu1Nb3Si13.5B9合金激光纳米化的超精细结构研究

在CO<sub>2sub>激光功率为50—300W、扫描速度为20mm/s、激光散光斑为20mm照射条件下 ，诱导非 晶Fe<sub>735sub>Cu<sub>1sub>Nb<sub>3sub>Si<sub>135sub>B9sub>带中发生结构重组，产生定量纳米α-F e(Si)晶相形成双相组织结构材料. 利用穆斯堡尔谱研究了非晶Fe<sub>735sub>C u<sub>1sub>Nb<sub>3sub>Si<sub>135sub>B<sub>9sub>合金激光纳米化的 超精细结构. 实验结果表明，激光诱导非晶 Fe<sub>735sub>Cu<sub>1sub>Nb<sub>3sub>Si<sub>135sub>B<sub> 9sub>纳米化后，其超精细磁场的分布随 着激光功率变 化由单峰向双峰变化，在高功率辐照时， 出现了双峰分布，并且峰位向高场移动. 高激光 功率辐照非晶Fe<sub>735sub>Cu<sub>1sub>Nb<sub>3sub>Si<sub>135sub>B<sub>9sub>合金纳米晶化相有四种超精细结 构，即2个超精细磁场较小的初晶相和2个超精细磁场较大的纳米晶化相. 其中超精细磁场较 大(17—25MA/m)的α-Fe(Si)相为DO<sub>3sub>结构. 关键词： 激光 纳米晶α-Fe（Si) 735sub>Cu<sub>1sub>Nb< sub>3sub>Ssub>i<sub>135sub>B<sub>9sub>')" href="#">非晶Fe<sub>735sub>Cu<sub>1sub>Nb< sub>3sub>Ssub>i<sub>135sub>B<sub>9sub> 超精细结构 超精细磁场     

A re‐examination of the sub‐Tm exotherm in polyamide 6: The roles of thermal history,water and clay

The sub‐T<sub>msub> exotherms in polyamide 6 (PA6) have been carefully re‐examined by differential scanning calorimetry and X‐ray diffraction, considering the effects of processing and thermal history, addition of water and clay. The results obtained cast doubt on Khanna's proposal that sub‐T<sub>msub> exotherm in PA6 comes from the release of strain energy absorbed during processing, and suggested that the origin of sub‐T<sub>msub> exotherm is the γ?α transformation at the premelting temperature, namely, the less thermodynamically stable γ‐form (γ^ns) transforming into the more thermodynamically stable α‐form (α^s). The presence of water or clay in PA6 samples facilitated the formation of γ^ns at corresponding cooling rates, and enhanced the development of sub‐T<sub>msub> exotherms. During the heating scan of PA6/clay composites, the initial γ^ns can be transformed into more stable (γ^s)^t and α^s at the same time, which can be thought as the origin of their sub‐T<sub>msub> events. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2385–2393, 2009     

基于混沌加密的小波包盲水印算法

利用混沌系统的特点调制了两种不同的混沌序列,分别用于水印加密和子图像的抽取.对子图像进行小波包分解,通过修改小波包的系数来嵌入数字水印.水印的提取不需要原始图像,实现了盲提取.实验结果表明,该算法对于常见的JPEG压缩、高斯噪声,裁剪和缩放等攻击具有较好的鲁棒性.     

Synthesis of Highly Hydrophilic Polyaniline Nanowires and Sub‐Micro/Nanostructured Dendrites on Poly(propylene) Film Surfaces

Summary: Polyaniline (PANI) nanowires and sub‐micro/nanostructured dendrites are synthesized and immobilized on PP‐g‐PAA film surfaces via routine oxidative polymerization of aniline under different conditions, where grafting poly(acrylic acid) (PAA) served as a template and dopant, and SDS as a surfactant. The immobilized PANI enhances the surface hydrophilicity of the poly(propylene) (PP) films, and a superhydrophilic surface is obtained in this way. The mechanism of forming different morphologies of PANI and of correspondingly obtaining a superhydrophilic surface are briefly discussed.

FESEM image shows the PANI sub‐micro/nanostructured dendrites immobilized on the surfaces of PP films. The modified surface is highly hydrophilic with a water contact angle of 3°.     

16O+94Zr和16O+116Sn的弹性散射角分布测量

用北京Q3D磁谱仪及其重离子焦面探测器系统测量了两个体系的14个弹性散射角分布,即¹⁶O+⁹⁴Zr体系在52,57,59,62,72,82和92MeV 7个能量点及¹⁶O+¹¹⁶Sn体系在57,59,62,67,72,82和92MeV 7个能量点的弹性散射角分布.用耦合道理论的ECIS计算程序拟合数据,初步观察到了“阈反常”现象.