The accumulation channel driven bipolar transistor (ACBT)

A new three-terminal power switch called the Accumulation Channel driven Bipolar Transistor (ACBT) is proposed and experimentally demonstrated. In the on-state, the characteristics of the ACBT have been found to approach those of a P-I-N rectifier with a MOSFET in series for regulating its current, an equivalent circuit considered to be an ideal for MOS/Bipolar power devices. Unlike previous devices, the high off-state voltage is supported by the formation of a potential barrier to the flow of electrons from the N⁺ emitter into the N-drift region within a depletion region. The absence of the P-base region within the ACBT cells eliminates the parasitic four layer PNPN thyristor which had limited the performance of previous MOS/Bipolar transistor structures. Consequently, the ACBT structure has large maximum controllable and surge current densities in addition to low on-state voltage drop and high-voltage current saturation capability     

A Diffusion Model Analysis of the Effects of Aging in the Lexical-Decision Task.

The effects of aging on response time (RT) are examined in 2 lexical-decision experiments with young and older subjects (age 60-75). The results show that the older subjects were slower than the young subjects, but more accurate. R. Ratcliff s (1978) diffusion model provided a good account of RTs, their distributions, and response accuracy. The fits show an 80-100-ms slowing of the nondecision components of RT for older subjects relative to young subjects and more conservative decision criterion settings for older subjects than for young subjects. The rates of accumulation of evidence were not significantly different for older compared with young subjects (less than 2% and 5% higher for older subjects relative to young subjects in the 2 experiments). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging, practice, and perceptual tasks: A diffusion model analysis.

Practice effects were examined in a masked letter discrimination task and a masked brightness discrimination task for college-age and 60- to 75-year-old subjects. The diffusion model (Ratcliff, 1978) was fit to the response time and accuracy data and used to extract estimates of components of processing from the data. Relative to young subjects, the older subjects began the experiments with slower and less accurate performance; however, across sessions their accuracy improved because the quality of the information on which their decisions were based improved, and this, along with reduced decision criteria, led to shorter response times. For the brightness, but not the letter, discrimination task, the older subjects' performance matched that of the younger group by the end of 4 sessions, except that their nondecision components of processing were slightly slower. These analyses illustrate how a well-specified model can provide a unified view of multiple aspects of data that are often interpreted separately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Application of the diffusion model to two-choice tasks for adults 75-90 years old.

The effects of aging on simple 2-choice decision making was investigated with the diffusion model (R. Ratcliff, 1978). Data for 75- to 90-year-olds were collected and compared with previous data from 60- to 75-year-olds and college students for 5 tasks: a signal detection-like task, letter and brightness discrimination with masking, recognition memory, and lexical decision. The model fit the data well and therefore allows components of processing to be examined as a function of age. Compared with decision-making processes in college students, decision criteria and nondecision components of processing increased with participants' age. However, the quality of the evidence on which decisions were based decreased with age only for letter and brightness discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simplified equations for mesh and step voltages in an AC substation

A large number of grounding grids in substations have shapes other than a square or a rectangle, whereas the simplified formulas for mesh and step voltages available in the literature are derived for square or rectangular grids. Improvements in the simplified equations for determining mesh and step voltages are presented. With the modified simple equations, mesh and step voltages at a substation of any practical shape can be estimated with reasonable accuracy. The results obtained with the improved equations have been compared with accurate results obtained via computer. The error in the values obtained with the derived equations is within 16% for mesh voltage and less than 30% for step voltage     

An open-systems approach to video on demand

Open systems will enable video servers and set-tops to provide different services in a variety of environments. Hewlett-Packard is interested in applying the principles of open systems to video on demand (VOD). In particular, the company is developing a technology base that will allow their servers and set-tops to operate in a variety of environments and enable the provision of a variety of services. The impact that the different VOD system elements have on the video server and set-top are examined from a communications standpoint. Opportunities for open or standard interfaces are identified and recommendations are made on what these should be where possible     

Substation ground grids intertied with buried conductors

A fault current at a substation injected into a grounding grid that is intertied with the grounding grid of another station with buried conductors is dissipated to the ground by the grids at both the stations and by the intertie. The authors present a direct, simple, an easy-to-use approximate method to determine the ground resistance of the system as seen from the station where the current is injected and the ground potential rise at both the stations. A comparison of the results obtained with the approximate method and from the accurate method has been made. An expression for the length constant of the intertie as a function of the resistivity of the soil has been derived. The concept is useful for estimating the distance beyond which the two grids intertied with buried conductors will have a negligible effect on each other     

Driving an Ecological Agenda with Project-Led Research

Here Hugh Whitehead, Irene Gallou, Harsh Thapar, Giovanni Betti and Salmaan Craig of the Specialist Modelling Group (SMG) at Foster + Partners directly address the underlying premise behind the issue. They argue the case for the architect as generalist or ‘centralised controller’, coordinating an often specialised and diverse collaborative design team. As an in-house consultancy within Foster + Partners, SMS provides expertise in complex geometry, computer programming, parametric design and rapid prototyping and environmental simulation, aiming to provided directed specialist support whenever required. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimal reactive power control via loss minimization and voltage control

This paper presents a mathematical formulation of optimal reactive power control problem via loss minimization and voltage control. The model minimizes real power losses, deviation from the optimal active power despatch policy, and the difference between percentage sharing of reactive power by controlling the generator terminal voltage magnitudes, transfer tap setting, and reactive power sources. The constraints set include power flow equations and limits on the variables. A method is developed to solve this problem using reduced gradient and Fletcher's update. Several test problems were solved using the developed technique. Correction to the groups of decision variables are applied simultaneously as well as hierarchically, and the results are compared for 6-bus, 30-bus, and 103-bus sample systems.     

Real-Time Application of Trellis Coding to High-Speed Voiceband Data Transmission

We describe the application of multilevel trellis coding to the transmission of high-speed' voiceband data. The implementation aspects of soft-decision Viterbi decoding associated with such coding are discussed, Real-time performance comparison is made of two coded systems at 9600 bits/s with respect to an uncoded system. The performance sensitivity Of the three systems to DDD channel impairments other than additive Gaussian noise are also described. It is shown that the experimental results agree well with those from theory, and that trellis coding provides significant improvement in performance in the presence of impairments other than additive Gaussian noise.