Optical spectra of CsI,CsBr, ZuGeP2, and SbSI

We report here the study of the normal reflectivity spectra R and the corresponding derivative spectra (1/R) dR/dE of SbSI between 2 and 6 eV. The spectra show very strong anisotropy. We have also tried to use the change of the wavelength modulation spectrum to monitor the change in the band structure of SbSI due to the phase transition at 292 °C (D_2h¹⁶→C_2v⁹). Careful examination of the spectra at various temperatures around T_c shows no observable change. We report also the wavelength-modulated reflectivity spectra of the chalcopyrite crystal ZnGeP₂ at 5 K between 2 and 6 eV, for E∥ C and E⊥ C. The experimental results are compared with the theoretical band structure calculation by de Alvarez and Cohen. We also present measurements on CsBr, CsI in the vacuum uv (between 5 and 8 eV) at 1.8K, showing noticeable difference with previous reflectivity measurements at 77 K.     

Determining correspondence in 3-D MR brain images using attribute vectors as morphological signatures of voxels

Finding point correspondence in anatomical images is a key step in shape analysis and deformable registration. This paper proposes an automatic correspondence detection algorithm for intramodality MR brain images of different subjects using wavelet-based attribute vectors (WAVs) defined on every image voxel. The attribute vector (AV) is extracted from the wavelet subimages and reflects the image structure in a large neighborhood around the respective voxel in a multiscale fashion. It plays the role of a morphological signature for each voxel, and our goal is, therefore, to make it distinctive of the respective voxel. Correspondence is then determined from similarities of AVs. By incorporating the prior knowledge of the spatial relationship among voxels, the ability of the proposed algorithm to find anatomical correspondence is further improved. Experiments with MR images of human brains show that the algorithm performs similarly to experts, even for complex cortical structures.     

Directivity and bandwidth of single-band and double-band yagi arrays

The purpose of the communication is to obtain the optimum design of a Yagi array under constraints on bandwidth, directivity, or the size of the array. It is shown that the array configuration is determined if any two of these constraints are specified. The present study also shows that a properly designed Yagi array can be operated at two frequency bands with the frequency ratio approximately equal to 3.5.     

In vacuo photocurrent measurements of plasma polymerized styrene films

Photoconductivity measurements were carried out on plasma polymerized styrene (PPS) in vacuo, in air, and in subsequently re-evacuated conditions. Samples with two gold electrodes (Au-PPS-Au) and gold-aluminum electrodes (Au-PPS-Al) were used. Positive short circuit photocurrents in the direction of illumination were observed in both types of specimens. In the case of Au-PPS-Au, photocurrent threshold was about 1.6 eV in vacuo for the virgin film, which is attributed to the energy of hole generation in bulk. Residual free radicals were assumed to be the acceptors in this mechanism. In the case of Au-PPS-Al, electron injection from aluminum was thought to be a more likely mechanism, with an estimated barrier height of approximately 2.6 eV.     

Aromatic ring synthesis by N-aminopyrrole diels-alder reaction. Total synthesis of juncusol

A total synthesis of the cytotoxic phytoalexin juncusol ($\text{1}$) is described.     

一种具有Goldbach性质的可换环上的二次同余

[1]—[3] 用模型论与数论方法讨论了整数环的某些扩环的数论性质,说明一些数论命题间的和谐性与相对独立性。[4]进一步研究了一种具有Golabach性质的可换环R,分析了R与整数环I的异同。[4]证明了R上有与I极不相同的二次同余性质。如R上存在8k±3形素元以2为平方剩余,也存在8k±1形素元不以2为平方剩余,等等。一个自然的问题是对任意非平方数a∈I,任意b,c∈I,若(b,c)=1,是否总存在bk+c形素元以a为     

Coupled Yagi arrays

The purpose of this study is to obtain the optimum design of a three-row Yagi array antenna under constraints on bandwidth, directivity, or the length of the array. It is shown that the array configuration is determined if any two of these contraints are specified. It is also shown that a properly designed coupled Yagi array can be operated at certain frequency band with higher directivity and wider frequency bandwidth than those of a single-row Yagi array.     

砷化镓气相掺硫外延和亚微米薄层的制备

本文介绍了Ga-AsCl_3-H_2体系,研究了气相外延时硫的掺杂行为,讨论了硫的掺杂机理和生长了亚微米薄层。制得的亚微米外延层的质量表明,表面形貌良好,缺陷少,重复性好。典型的电学性质为:当厚度≤0.4μm和浓度为1—2×10~(17)/cm~3时,击穿电压V_B=7—10V。在单层和多层外延结构中,界面浓度基本是突变的,过渡区约0.1μm。这些外延片已用于制备变容管和远红外探测器等。