Aromatic bisphenol A-based elastomers via hydrosilylation chemistry

The preparation of highly aromatic elastomers from a bisphenol A-based divinyl-terminated resin and polymerization with various aromatic silane containing compounds utilizing a room temperature hydrosilylation reaction is demonstrated. The polymers exhibit high thermal and oxidative stability with 5% weight losses around 430 and 350°C and char yields ranging from 35% to 40%. The thermosets maintained their elastomeric properties with good hardness and mechanical properties as measured by elongation measurements. The toughness of the thermosets was not improved with the inclusion of aromatic moieties but the hardness did appear to increase with the addition of more aromatic groups.     

A discrete-time stochastic learning control algorithm

In this paper, the learning gain, for a selected learning algorithm, is derived based on minimizing the trace of the input error covariance matrix for linear time-varying systems. It is shown that, if the product of the input/output coupling matrices is a full-column rank, then the input error covariance matrix converges uniformly to zero in the presence of uncorrelated random disturbances. However, the state error covariance matrix converges uniformly to zero in presence of measurement noise. Moreover, it is shown that, if a certain condition is met, then the knowledge of the state coupling matrix is not needed to apply the proposed stochastic algorithm. The proposed algorithm is shown to suppress a class of nonlinear and repetitive state disturbance. The application of this algorithm to a class of nonlinear systems is also considered. A numerical example is included to illustrate the performance of the algorithm     

EPR characterisation of carbon black in loose and tight contact with Al2O3 and CeO2 catalysts

The intensity of contact between soot and catalyst is one of the major parameters that determine the soot oxidation reactivity. In the present work the EPR study is focused on the mixtures of carbon black with Al₂O₃ and CeO₂ in loose and tight contacts in order to provide the physicochemical characterisation of the contact. For tight contact CB-catalyst mixtures a new paramagnetic species is observed and can be considered as a fingerprint of the contact between the two solids. These new paramagnetic species increase the catalytic reactivity of CB combustion in the presence of cerium oxide.     

Modelling steel frame behaviour under fire conditions

A formulation for the noblinear analysis of two-dimensional steel frames under fire conditions using the finite element method is presented. Deterioration in material strength with increasing temperature is represented by a set of nonlinear stress-strain-temperature relationships using a Ramberg-Osgood equation in which creep effects are implicitly included. Structures subject to increasing loads or temperatures are analysed using an incremental Newton - Raphson iterative procedure. The analysis permits deformation history and either collapse load or critical temperature to be calculated at a specified temperature or load level respectively. It includes the effects of geometric nonlinearity, temperature dependent nonlinear material behaviour and variations in temperature distributions both along and across each member. The effects of thermal strains, residual stresses and thermal bowing are also considered and different material models may be used. Comparisons are made with fire test results on frames and columns that represent a wide range of problem parameters such as slenderness, end conditions, load levels and temperature distributions. In all cases, the agreement is very satisfactory. An example two-bay frame is analysed to illustrate the potential of the analysis and to show the influence of various forms of partial protection on the collapse temperature of sway frames.     

A new DC model of HBT's including self-heating effect suitable forcircuit simulators

This paper presents a new empirical DC model which includes self-heating effects. The expression of the collector current does not explicitly incorporate the junction temperature of the device to aid convergence process and to simplify the equations involved. A comparison of simulated and experimental DC-IV characteristics over the ohmic and active regions demonstrates the accuracy of the model. This model is suitable for optimization purposes and has been implemented in nonlinear circuit simulators, HSPICE and HP-MDS     

An Alternative Setup for a Base-Station Cellular Antenna

This paper proposes the use of an alternative setup of a cellular base-station antenna with the potential of reducing the cochannel interference. The setup uses a different cell antenna placement strategy where there is one base-station antenna per cell located high at its center. Unlike a traditional base-station antenna radiating in the horizontal direction, the antenna under consideration radiates downward. The beamwidth of the antenna is considered to be wide enough to match the cell diameter. In addition, the radiation pattern beyond the associated beamwidth is assumed to possess a large attenuation. This paper studies the use of the proposed antenna setup by examining the cell geometry and grouping and its effect on the antenna radiation pattern. It is shown that for a sufficiently large attenuation pattern beyond the antenna beamwidth, the corresponding signal-to-interference ratio can be made significantly larger than the one resulting from the traditional antenna setup     

覆盖三个十倍频程的锁定同步正弦波发生器

测试、校准、普通系统操作等模拟应用经常需要具有准确的振幅和频率、THDf总谐波失真）很低的正弦波形。一些应用要求此类波形发生器能用外部时序信号使其输出准确同步。简单的正弦波发生器能提供多个性能级别，但保持低THD和恒定振幅是个问题，特别是如果输出和同步信号必须在扩展的频率范围内保持锁定的话。     

Cardiovascular and neurohumoral responses to behavioral challenge as a function of race and sex.

Cardiovascular and hormonal responses to a structured interview, an electronic video game, a cold pressor test, and exercise on a bicycle ergometer were assessed in 83 normotensive Black and White men and women (aged 25–44 yrs). Black Ss showed significantly greater diastolic blood pressure (DBP) responses than White Ss during the cold pressor test, which were not accounted for by an increase in plasma catecholamines. Exercise produced reliably greater systolic blood pressure (SBP) increases in Black women than in Black men or White women. Men showed significantly greater SBP and DBP changes than women during the video game. The pattern of physiological reactivity elicited by challenge may be related to the Ss' race and sex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)