Effects of steps and defects on O2 dissociation on clean and modified Cu(1 0 0)

Dissociative chemisorption of O₂ on Cu(1 0 0), S/Cu(1 0 0) and Ag/Cu(1 0 0) surface alloy has been investigated by Auger electron spectroscopy (AES). A strong reduction in the initial O₂ chemisorption probability (S₀) from 0.05 to 7.4 × 10⁻³ is observed already at an Ag coverage of 0.02 ML. Further Ag deposition results only in a moderate decrease in S₀. Similar inhibition of O₂ dissociation is observed on S/Cu(1 0 0). It is concluded that at very low Ag coverages, the reduced reactivity of Ag/Cu(1 0 0) towards O₂ dissociation is primarily due to the steric blocking of the surface defects and that any electronic effects are only secondary and present only at higher Ag coverages.     

Shape, facet evolution and photoluminescence of Ge islands capped with Si at different temperatures

We investigate the embedding of Ge islands in a Si matrix by means of atomic force microscopy and photoluminescence (PL) spectroscopy. The Ge islands were grown between 360°C and 840°C and subsequently capped with Si at different temperatures. For the highest Ge growth temperature (840°C), we show that the surface flattens at high Si capping temperatures while new facets can be identified at the island base for intermediate capping temperatures (650–450°C). At low capping temperatures (300–350°C), the island morphology is preserved. In contrast to the observed island shape changes, the decreasing Si capping temperature causes only a small redshift of the island related PL signal for islands grown on high temperatures. This redshift increases for Ge islands grown at lower temperatures due to an increased Ge content in the islands. By applying low-temperature capping (300°C) on the different island types, we show that the emission wavelength can be extended up to 2.06 μm for hut clusters grown at 400°C. Further decreasing of the island growth temperature to 360°C leads to a PL blueshift, which is explained by charge carrier confinement in Ge quantum dots.     

ICP-AES测定Nd-Pr合金中的杂质元素

用ICP－AES同时测定了Nd-Pr合金中的Dy、Gd、La、Sm、Ce等5种稀土杂质元素，并研究了基体元素Nd及主量元素Pr对杂质元素的光谱干扰，选择了合适的分析线，用基体匹配法对存在的背景干扰进行了校正。方法的检出限为0．009－0．044μg/mL；回收率为90％－103％。该方法准确可靠、简便快速。     

反馈型自联想记忆神经网络

自联想记忆神经网络具有类似于大脑的记忆和联想的特性．在Hopfield网络的理论基础上，提出了一种反馈型的自联想记忆神经网络．和Hopfield模型不同的是，这种神经网络增加了一个隐含层来扩大网络的存储容量，并采用局部相连的拓扑结构来代替全相连，从而减少了计算复杂度．在网络的学习过程中，各神经元之间的权值按照学习规则不断地进行调整，使回忆后的输出结果更加接近期望输出、     

The novel YMn2D6 deuteride synthesized under high pressure of gaseous deuterium

The novel intermetallic deuteride YMn₂D₆ was synthesized under high deuterium pressure. In order to identify the structure and characterize the magnetic properties of this deuteride the powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Mn X-ray absorption near edge structure (XANES) and magnetization measurement (SQUID) were carried out. The crystal structure, the chemical state of Mn and the magnetic properties of this novel deuteride were examined and discussed. It should be noted that the structure of YMn₂D₆ (F-43m) differs dramatically from C15 symmetry of the parent material. Such a great rearrangement of the metal lattice due to deuterium absorption is rather exceptional for C15 Laves phase.     

Thermoelectric properties of Bi-Sb semiconducting alloys prepared by quenching and annealing

Bi_100−xSb_x (x=8-17) alloys were prepared by direct melting of constituent elements, which was followed by quenching and annealing. The synthesis of high-homogeneity alloys was confirmed by X-ray diffraction, differential thermal analyses and electron microprobe analysis. The semiconducting and thermoelectric properties of the samples were investigated by measuring Hall coefficient, electrical resistivity and Seebeck coefficient in the temperature range from 20 to 300 K for both the as-quenched and annealing samples. The properties change gradually with the Sb concentration x, which is attributed to the variation of the energy gap. The Hall mobility was enhanced by annealing, which leads to a small electrical resistivity and a large Seebeck coefficient. Consequently, large values of about 8.5 mW/mK² for the power factor were obtained in the annealed alloys of x=8,12, and 14.     

A three-dimensional model describing stress-induced solid phase transformation with permanent inelasticity

The employment of shape memory alloys (SMA) in a large number of applications in the fields of aeronautical, biomedical, and structural engineering has been the motivation for an increasing interest in the direction of a correct and exhaustive modeling of their macroscopic behaviour.     

Shape optimization of an accommodative intra-ocular lens

Cataract surgery consists in replacing the clouded or opacified crystalline lens by an Intra-Ocular Lens (IOL) having the same mean dioptrical power. Clear vision is then achieved at a given distance and glasses are needed in many situations. A new kind of IOL, potentially accommodative, is proposed. Its design is based on the deep understanding of the accommodation mechanism and on the mathematical modeling and the numerical simulation of the IOL's comportment in vivo. A preliminary version of this IOL is now commercialized by the company HumanOptics under the name ‘1CU’. In a second phase, shape optimization techniques equipped with strong mechanical and physiological constraints, are used to enhance the IOL performance and build a new design. To cite this article: F. Jouve, K. Hanna, C. R. Mecanique 333 (2005).     

Percolation picture for long wavelength phonons in zinc blende alloys: application to GaInAs

We propose a ‘one bond→two modes’ model for the long wavelength optical phonons in random zinc-blende A_xB_1−xC ternary alloys, based on the percolation site theory. Our model takes into account the ‘fractal→normal’ object transition, which goes with the ‘dispersion→continuum’ topology transition at the percolation thresholds of the A-C and B-C bonds. We first introduce the basics of our model in the case of Zn_1−xBe_x(Se,Te) mixed crystals, whose parent binaries display a high contrast in the bond stiffness, which enhances the percolation effects. We then focus our study on standard systems, which display a much weaker contrast in the bond stiffness. The multi-phonon behavior of GaInAs alloys is re-examined in the light of the percolation model, with much success.