A high resolution transmission electron microscope study of early stage precipitation on dislocation lines in Al-Zn-Mg

The weak beam transmission electron microscopy technique was employed to study the early stages of precipitation on dislocation lines in Al-3.87 wt pct Zn-1.79 wt pct Mg. The heterogeneous precipitation sequence was found to follow the homogeneous sequence in this alloy. The interaction between the initial coherent precipitate particles and the strain fields of the catalyzing dislocations produced “gaps” of background intensity at precipitate locations along the otherwise continuous weak beam images of the dislocation lines. A simple model was developed to relate a distribution of measured weak beam gap lengths to a particle size distribution at a given aging treatment. In this manner the growth kinetics of the initial precipitate phase was observed; it was found that the precipitation followed the Cottrell-Bilbyt ^2/3law, suggesting that matrix dislocations may assist the growth of heterogeneous precipitates in a manner analogous to grain boundary “collector plates.” Weak beam microscopy was found to be superior to standard bright field microscopy for the current study. Particles too small to be visible in bright field were revealed in weak beam. Weak beam observations also indicated that the coherent precipitate particles were positioned asymmetrically about the dislocation cores.     

Influence of systemic arterial hypertension on mid-term survival of patients with acute myocardial infarction treated with fibrinolytic agents

BACKGROUND: The purpose of this study to asses the effect of systemic arterial hypertension on mid-term survival of patients with acute myocardial infarction who received thrombolytic treatment. PATIENTS AND METHOD: We studied 202 consecutive patients with acute myocardial infarction, admitted in the Coronary Care Unit of the Hospital Xeral de Galicia who received intravenous thrombolytic therapy within six hours from the onset of symptoms. The thrombolytics used were: urokinase (79.7%), rt-PA (9.9%), streptokinase (4.9%) and APSAC (5.5%). Left heart catheterization with coronary angiography was performed in 162 patients at 2 weeks after infarction. Patency of the infarction-related artery (IRA) was classified according to Thrombolysis in Myocardial Infarction (TIMI) criteria. A patent artery weas defined as having TIMI grades 2 or 3 antegrade flow. RESULTS: Systemic arterial hypertension was found in 34.7% of patients. IRA patency (TIMI 2-3) was demonstrated in the 75.3% of the patients. Early mortality (first month) was 5.4%. Multivariate analysis identified cardiogenic shock as the only variable with independent predictive value for early mortality. Mean follow-up was for 24 +/- 19 months. Late mortality was 5.2% and cardiac death occurred in 4.2% of patients. Reinfarction occurred in 3.1% of patients. Congestive heart failure, arterial hypertension and reinfarction adversely affected prognosis. Actuarial survival at the end of follow-up period was significantly lower in patients with systemic arterial hypertension (70.4% vs 85.9%; p < 0.05). CONCLUSIONS: These data suggest that systemic arterial hypertension adversely affects mid-term prognosis in patients with acute myocardial infarction who received thrombolytic treatment.     

Socio-economic pitfalls of enhancing indigenous capabilities in household fermentation

Traditional fermentation processes are increasingly attracting the attention of scientists and policy makers as a vital part of food security strategies. New opportunities provided by biotechnology are opening up possibilities to improve or upgrade traditional small-scale processes and make better use of agricultural products. A straightforward transfer-of-technology approach, characteristic for mainstream development assistance to developing countries, is inappropriate to upgrade and improve the traditional food processing sector in developing countries. In this paper, the case of soy sauce fermentation in Indonesia is presented to illustrate the dangers of narrowing traditional food processing to a sequence of operations. These processes and their operations reflect the social, political, cultural and ethnical relations in which they emerged and evolved. Successful upgrading requires that these relations are understood and that, based on such an understanding, modern technologies build upon their traditional predecessors. Any technology or project that neglects the coherence between these relations or is unable to meet social, political and cultural requirements in addition to technical ones, is doomed to fail.     

Correlation of microyield behavior with silicon in X-520 and HIP-50 beryllium

Significant differences were observed in the measured values of the microyield strength (MYS) for the X-520 and HIP-50 grades of beryllium. The MYS values for as-received and heat treated HIP-50 samples were in the range of 17 to 27 kpsi (117 to 186 MPa); those for similarly heat treated X-520 samples, however, ranged only from about 8 to 9 kpsi (55 to 62 MPa). Differences were also noted in the value of the strain exponent, which was measured as the slope of the line generated by plotting the stressvs residual plastic strain data on logarithmic coordinates. Strain exponent values of 0.20 to 0.34 were observed for the HIP-50 data compared to the range of 0.38 to 0.48 observed for the X-520 data. Notable differences were also observed between the X-520 and HIP-50 microstructures which appeared to explain the observed differences in microyield behavior. Second phase particles in both the beryllium grades were mainly located at the grain boundaries. However, the average size of the particles in HIP-50 was typically one-half of those in X-520, and their number density was also much higher. The particles were mainly composed of the oxides of Be in HIP-50; however, the X-520 particles almost always contained Si, Fe, and O. X-ray and STEM results showed that the particles in X-520 were predominantly BeO containing possible reacted regions of the Be₂SiO₄ phase. These results indicated that to produce high MYS Be it is important to keep the Si content low. Use should be made of fine impact attritioned powder, and hot isostatic pressing should be used as the densification procedure. The data indicated that Fe content (to the extent present in X-520 Be) was not very significant.     

Supporting executive functions during children's preliteracy learning with the computer

The present study examined how embedded activities to support executive functions helped children to benefit from a computer intervention that targeted preliteracy skills. Three intervention groups were compared on their preliteracy gains in a randomized controlled trial design: an experimental group that worked with software to stimulate early literacy with embedded executive‐functioning support (EL + EF group), an experimental group that worked with the same early literacy software without the explicit EF‐support (EL group) and a control group that played with language discovery games from the same software. These groups were contrasted on their preliteracy progress over time and on their learning behaviours while working with the software. Results showed that children in the two experimental groups progressed more in preliteracy skills on the long‐term, with the EL + EF group showing the highest learning effects. These results were mainly shown for the children with lower levels of EFs. Moreover, children in the EL + EF group showed more independent behaviour and played more games than children in the EL group. These results indicate that young children can show more effective learning over time during computer interventions when their executive functions are kept active.     

The effects of stress, temperature, and spin flips on polarization switching in vertical-cavity surface-emitting lasers

We discuss the effect of uniaxial planar stress on polarization switching in vertical-cavity surface-emitting lasers (VCSELs). The approach is based on an explicit form of a frequency-dependent complex susceptibility of the uniaxially stressed quantum-well semiconductor material. In this mesoscopic framework, we have taken cavity anisotropies, spin carrier dynamics, and thermal shift of the gain curve into account. In this way, we present a model that provides a global overview of the polarization switching phenomenon. The results are compared with experiments on an air-post VCSEL operating at 980 nm.     

基于相似理论对水下复杂壳体的振动和声辐射预报

采用有限元和球函数相结合的方法，建立水下复杂壳体——两端带半球壳的加肋弹性圆柱壳的振动、耦合振动和声辐射方程，运用方程分析法，导出水下复杂壳体的振动、耦合振动和声辐射的相似关系，根据建立的相似关系实现对壳体的振动响应和声辐射的预报。采用大型有限元软件ANSYS对具有相似关系的模型和原型的振动响应和尸场进行分析，算例表明，方法切实可行并且为预报水下大型复杂结构体的振动响应和耦合声场提供了一种简洁、实用的研究方法。     

The II parallel programming system

A parallel random access machine (PRAM)-oriented programming language called II and its implementation on transputer networks are presented. The approach taken is a compromise between efficiency and simplicity. The II language has been conceived as a tool for the study, design, analysis, verification, and teaching of parallel algorithms. One of the main features of this Pascal-like language is the ability to mix parallelism and recursion allowing a simple and elegant formulation of a large number of parallel algorithms. A method for the complexity analysis of II programs, called PRSW, is introduced. The current version of the II compiler guarantees the conservation of the PRSW complexity of the algorithms translated. Furthermore, the computational results show a good behavior of the system for PRAM efficient algorithms     

酒石酸──H_2O_2──Co（Ⅱ）化学发光反应及其应用研究

本文研究了酒石酸在碱性介质和某些过渡金属离子存在时能与过氧化氢产生化学发光反应的体系，并系统考察了Ｃｏ（Ⅱ）参与反应的最佳条件，在选定的条件下进行痕量钴（Ⅱ）的测定，线性范围为５．９×１０－８～３．３×１０－５ｍｏｌ／Ｌ，检测限可低至０．０４ｐｐｂ，除Ｆｅ（Ⅱ）、Ｃｒ（Ⅲ）和Ｍｎ（Ⅱ）等共存离子的允许量小于１０倍钴量外，其它所试验的２０多种阴阳离子均有很高的允许量，而对于Ｆｅ（Ⅱ）、Ｃｒ（Ⅲ）和Ｍｎ（Ⅱ）造成的干扰则可通过加入柠檬酸来掩蔽消除。本法用于某些食品中钴含量测定，结果令人满意。     

甜鲜乳酪的研制

本文以新鲜牛乳、乳粉、白砂糖等为主要原料,经无菌处理,加入人工培养发酵剂——混合型酵母菌,在一定温度条件下发酵、凝乳制成了新鲜乳酪制品。对人工发酵剂的制备方法及培养条件的选择、甜鲜乳酪的生产工艺过程进行了研究、并对产品成份进行了分析。结果表明,采用本法完全可以生产一种营养丰富、风味独特的发酵乳制品。