Erbium-doped silicon and porous silicon for optoelectronics

Silicon forms the backbone of the microelectronics industry, and possibly, of the optoelectronics industry, hitherto dominated by III/V materials. One of the remaining goals is to build an optical source in silicon. Erbium exhibits luminescent 1.54 μm intra-4f transitions in both silicon and porous silicon. This paper reviews the work which has been carried out in this field and discusses some possible additional applications of erbium-doped silicon in optoelectronics, such as a novel on-chip temperature sensor.     

Oxygen absorption kinetics in YBa2Cu3Ox

The oxygen absorption process in highly aligned YBa₂Cu₃O_x samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:

(1 − a_t) ln(1 − a_t) + a_t = k_Dt

The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa₂Cu₃O_x crystals are discussed.     

Optimum design for buckling of plain and stiffened composite axisymmetric shell panels/shells

The buckling of plain and discretely stiffened composite axisymmetric shell panels/shells made of repeated sublaminate construction is studied using the finite element method. In repeated sublaminate construction, a full laminate is obtained by repeating a basic sublaminate, which has a smaller number of plies. The optimum design for buckling is obtained by determining the layup sequence of the plies in the sublaminate by ranking, so as to achieve maximum buckling load for a specified thickness. For this purpose, a four-noded 48-dof quadrilateral composite thin shell element, together with fully compatible two-noded 16-dof composite meridional and parallel circle stiffener elements are used.     

LaNi5-xAlxDy的中子衍射研究

分别测量了LaNi4.25Al0.75和LaNi4.75Al0.25两种合金样品在未吸氘及不同含氘量的氘化物样品的中子衍射谱,用Rietveld程序拟合出它们的晶体结构,并观察到了一些过去未曾注意的现象.LaNi4.25-Al0.75在吸氘过程中,氘原子优先占据的原子坐标为(0.17,0.32,0.45).     

Measurements of distribution of self-bias potential on an RF-plane electrode in plasma etching devices

The self-bias potential (V_dc) induced on an RF-powdered electrode (153 mm Ø) in a plasma is measured using electrical probes which are buried in, de-insulated from, and RF-connected to the electrode. The configuration of the probes allows to study the distribution of V_dc discretely on the electrode. The potential is homogeneous in the absence of external magnetic field. In the presence of a homogeneous magnetic field parallel to the electrode, it is reduced and a monotonous gradient takes place in its distribution due to the plasma shift induced by E × B drift. When the magnetic field is rotated along the axis of the RF-electrode at a frequency less than 50 Hz, the distribution, which is almost identical to the one in a static field, rotates with the magnetic field. On the coordinate system rotating with the magnetic field, the probes are regarded to be rotating. The potential distribution is obtained as a continuous function of the azimuthal angle. Thus the rotation of the field provides information for the experimental interpolation.     

Determining elasticity and strength characteristics of powder coating

Methods are described for forming coating specimens and testing them in pure bending. The proposed tester gives adequate accuracy in determining the elastic characteristics and strength for thin specimens (up to 0.1 mm) of brittle materials of powder-coating type.Translated from Problemy Prochnosti, No. 3, pp. 94–97, March, 1993.     

Instron texture profile of buffalo milk cheddar cheese as influenced by composition and ripening changes

Buffalo milk Cheddar cheese samples of different ages were analysed for compositional attributes (CA), ripening indices (RI) and Instron Textural Profile (ITP). All samples were compositionally alike, except for pH and salt-in-moisture (SM) contents. RI showed significant variations. CA and RI showed highly significant correlations within themselves and with each other, except for moisture with pH, SM with moisture, MNFS, Fat and FDM and Fat with MNFS. The ITPs of cheeses showed significant variations and had highly significant intercorrelations indicating their interdependence. CA (except moisture and MNFS) and RI showed a highly significant correlationship with ITPs. Moisture content showed a highly significant correlationship with all ITPs, except cohesiveness and springiness, where it was significant. MNFS content showed significant correlations only with hardness and brittleness. Stepwise regression analysis revealed that MI was the most predominant factor influencing cheese texture, followed by pH, SM, FDM and TVFA. Knowing Ca and RI, the textural properties of cheeses can be forecast through mathematical equations. Similarly the age of cheese can also be predicted if RI and/or textural properties are known.     

Aromatic nitrations by mixed acid. Slow liquid-liquid reaction regime

Aromatic nitrations by mixed acid have been selected as a specific case of a heterogeneous liquid-liquid reaction. An extensive experimental programme has been followed using adiabatic and heat-flow calorimetry and pilot reactor experiments, supported by chemical analysis. A series of nitration experiments has been carried out to study the influences of different initial and operating conditions such as temperature, stirring speed and sulphuric acid concentration. In parallel, a mathematical model to predict the overall conversion rate has been developed. In this paper the mathematical modelling and the implementation and experimental validation for benzene, toluene and chlorobenzene mononitration in the kinetic control regime (slow liquid-liquid reaction) are presented and discussed.     

β－C_2S固溶体稳定的热力学研究

从热力学理论出发，利用Ｘ射线衍射定性和定量的方法，对β－Ｃ＿２Ｓ固溶体的稳定性进行了分析和研究。经热力学理论推导得出β－Ｃ＿２Ｓ稳定的热力学条件，即掺入的微量元素的化学位μ＿ｉ须小于β－Ｃ＿２Ｓ的反应自由焓△Ｇ＿β，μ＿ｉ＜△Ｇ＿β．并定量地计算出一种微量元素稳定β－Ｃ＿２Ｓ的临界掺加量为；多种微量元素对β－Ｃ＿２Ｓ的稳定性判断条件为：     

Separate assessment of porosity and uncombined carbon in cemented carbides

Porosity and uncombined carbon in cemented carbides are traditionally assessed by comparison to standardized microstructure charts, such as those in ISO 4505-1978. To improve the accuracy in the characterization a fully automatic image analysis procedure has been developed. The analysis is performed using light optical microscopy on unetched polished specimens. The implemented algorithm separates uncombined carbon, C-defects, from pores, A- and B-defects. Pores are approximately distributed in a random way in the structure. Uncombined carbon is on the other hand precipitated into clusters of carbon particles. This difference is together with defect size used as a base for the separation. Small defects situated close together are classified as C-defects, small isolated defects as A-pores and large defects as B-pores. Pores are found to be more round than the somewhat elongated C-defects. The difference in shape is significant and can also be used as a separation criterion.

Image analysis is used to quantitatively characterise the ISO 4505-1978 standard charts with respect to volume fraction, number density and size distribution of defects. The results are compared to measured distributions for true microstructures.