Structural and magnetic properties of Ni/Pt multilayers

In this work, the variation of the magnetic moments of the Ni/Pt multilayers are studied using the linearized augmented plane waves (LAPW) method in the framework of the density functional theory (DFT) implemented in the version of WIEN2K program. The systems have been modeled by seven layers slab separated in z direction by a vacuum region of four substrate layers. We present the results of the dependence of the magnetic properties with respect to the thickness variation of the different multilayers. The modeling of these systems finds an important empirical support. Experiment and theory show the same trends for the magnetic moments: hybridization effects between Ni and Pt are mostly localized at the interface.     

Catalytic synthesis of single-crystalline gallium nitride nanobelts

Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed.     

一阶最优性条件研究

本对由Botsko的关于多变量函数取极值的一阶导数检验条件定理^[1]进行了分析研究，给出了更实用而简捷的差别条件。最后，举出若干例子予以说明。     

静脉滴注的临床决策

提出了静脉滴注的动力学一般模型，讨论了模型的性质，在给药剂量确定的条件下，探讨了调整滴注速率使治疗效果达到最佳的临床决策方法。     

Inner derivations and norm equality

We characterize when the norm of the sum of two bounded operators on a Hilbert space is equal to the sum of their norms.

     

Heisenberg群上Laplace算子的离散谱

本文证明了Heisenberg群上Laplace算子的Dirichlet特征值的存在性，给出了特征值的估计     

扩宽OMA-Ⅵ同时谱宽的新方法

OMA－Ⅵ存在同时谱宽窄的缺点，本文用一种新方法大幅度地扩宽了它的同时谱宽，且不降低其系统分辨率，应用效果甚佳。     

Thermal gradient induced sidebranching in directional solidification

The polycrystalline perovskitelike manganese oxides La_1-xA_xMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (T_c) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie temperature. Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998