High-temperature sustainability of strong fiber Bragg gratings written into Sb-Ge-codoped photosensitive fiber: decay mechanisms involved during annealing

An antimony--germanium- (Sb--Ge-) codoped fiber specially designed for the fabrication of fiber Bragg gratings (FBGs) with high temperature sustainability has been developed. The photosensitivity and the high-temperature sustainability of FBGs that have been written into this fiber were tested. The results obtained showed that the FBG written into this fiber has a very high temperature sustainability of 900 degrees C. A decay mechanism that involves cation hopping is presented to explain the observed high temperature sustainability of the grating written into this fiber.     

Interplay between anisotropic strain relaxation and uniaxial interface magnetic anisotropy in epitaxial Fe films on (001) GaAs

Grazing incidence x-ray diffraction study of Fe epitaxial ultrathin films (1.5-13 nm) on GaAs (001) reveals an anisotropy of both domain shape and strain, with [110] and [1-10] as the principal directions. It is shown that the observed thickness-dependent strain anisotropy, together with a uniaxial interface term, can provide an unambiguous explanation to the usual in-plane magnetic anisotropy and its thickness dependence observed in this magnetic thin-film system.     

Poled polymer thin-film gratings studied with far-field optical diffraction and second-harmonic near-field microscopy

Electrical poling induces polar ordering of molecules in a grating that has been holographically inscribed on a thin film of polymer with azobenzene side chains. The resulting chi2 grating, seen by second-harmonic-generation (SHG) near-field scanning optical microscopy, can have a periodic structure that is significantly different from the topographical image. The far-field linear and SHG diffration patterns correlate well with the grating structures. Poling of the thin-film grating, which presumably has photodriven nonuniform material properties within each period, leads to the more complex structure of the chi2 grating.     

Superparallel holographic correlator for ultrafast database searches

We describe a superparallel holographic optical correlator that performs two-dimensional spatial and angular multiplexing simultaneously. The key step in this architecture is the use of a holographic multiplexer to split a query image into many copies before it applies them to the holographic database. A holographic demultiplexer, in conjunction with an aperture, is used to identify the location and the angle of the brightest correlation peak. This architecture uses only O(square root of N) detector elements to search through N unsorted images in a single query. We demonstrate the basic features of this architecture, using three spatial locations with eight angle-multiplexed images in each location.     

Electronic stability of magnetic Fe/Co superlattices with monatomic layer alternation

We report a surprising observation that the growth of the [Fe(1 ML)/Co(1 ML)](n) superlattice of L1(0) structure on Cu(100) is stable only up to six atomic layers (n=3), which cannot be rationalized by stress arguments. Instead, first-principles calculations reveal a transition from the L1(0) to the B2 structure due to the effect of dimensionality on the stability of the electronic structure of the superlattice. Whereas the majority-spin electrons are energetically insensitive to the layer thickness, the minority-spin electrons induce the transition at n=3.     

Entropy of Einstein—Maxwell-Dilaton—Axion Black Holes

The entropy of Einstein—Maxwell-dilaton—axion black holes is calculated by using the improved brick-wall model. Taking into account of the statistical physics, we propose not to consider the superradiant modes. The result shows that the nonsuperradiant modes do contribute exactly the area-law entropy for extreme black hole. Moreover, our cut-off which does not require an angular cut-off is independent of angle . As for the extreme black hole, we found that its entropy is zero.     

Si-based nanoscale SiO2 islands and light-emitting source array

A SiO₂ nanoscale island array was fabricated on a Si substrate by using anodic porous alumina as a mask. Transmission electron microscopy observation and the atomic force microscopy pattern show that the arrangement of SiO₂ islands has a quasi-hexagonal symmetry. Ge ions with a dose of 1×10¹⁷ cm^-2 were subsequently implanted into the SiO₂ island array to form Ge-related light-emitting centers. The photoluminescence (PL) spectra of as-implanted and annealed samples show three PL bands at 370, 400 and 415 nm. Their intensities reach maximums in the sample with an annealing temperature of 700 °C. Spectral analysis suggests that the 370 and 415 nm PL bands arise from Ge-Ge and Ge-Si defect centers, while the 400 nm PL is related to GeO color centers in the SiO₂ islands. The existence of these PL bands indicates the formation of a Si-based nanoscale light source array. PACS 78.55.Mb; 42.72.Bj; 68.65.+g     

Photoacoustic characteristics of dynamical adhesion of films on a metallic substrate

In this communication, we report a numerical model that predicts the mechanical deformations associated with the pulsed laser irradiation of a film surface, based on thermal diffusion theory. The model is consequently advanced to produce a method for evaluating film adhesion strength. The epicenter surface displacements within the irradiated fields have been measured using a heterodyne interferometer. The comparison of the experimental data and the displacements calculated by the model shows good agreement. By investigating the propagating acoustic modes under non-destructive and destructive modes, we reveal that, with or without interface delamination, the phase structure of the longitudinal waves will be altered due to the change of reflection mode at the interface. Applying shock dynamics theory, we evaluate the adhesion strength of the TiN/stainless interface. We also indicate the strain rate can be up to 10⁵∼10⁶ s^-1 during film interface delamination. Received: 5 April 2002 / Accepted: 24 June 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +86-511/879-1919, E-mail: mzhou@ujs.edu.cn     

HAD: an automated database tool for analyzing screening hits in drug discovery

Collecting, organizing, and reviewing chemical information associated with screening hits are human time-consuming. The task depends highly on the individual, and human errors may result in missing leads or wasting resources. To overcome these hurdles, we have developed a decision support system, Hits Analysis Database (HAD). HAD is a software tool that automatically generates an ISIS database file containing compound structures, biological activities, calculated properties such as clogP, hazard fragment labels, structure classifications, etc. All data are processed by available software and packed into a single SD file. In addition to search capabilities, HAD provides an overview of structural classes and associated activity statistics. Chemical structures can be organized by maximum common substructure clustering. The ease of use and customized features make HAD a chief tool in lead selection processes.     

Inocalophyllins A,B and their methyl esters from the seeds of Calophyllum inophyllum

Fractionation of the ethanolic extract of the seeds of Calophyllum inophyllum L. has resulted in the isolation of four novel pyranocoumarin derivatives, designated as inocalophyllins A (1), B (2) and their methyl esters (3, 4) in addition to the known calophyllolide. The structures of these compounds have been determined on the basis of spectroscopic analysis including MS, heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and two dimensional incredible natural abundance double quantum transfer experiment (2D-INADEQUATE). Two new methylated products, 5 and 6 were also prepared by methylation of compounds 1 and 2, respectively.