Input-Output linearization using approximate process models

An approach to approximate feedback linearization is presented which utilizes an approximate input-output normal form model for the process. The approach is valid for minimjm phase systems, and yields a dynamic output feedback controller of order 2N − R + 1, where N is the dynamic approximation order and R is the relative degree of the approximation model. Conditions are presented under which local (linear) stability can be guaranteed despite the plant-model mismatch. Two reactor control case studies are presented to show how the approach can be used both when a fundamental process model is available and when only process input-output data are available.     

Revising for meaning: Effects of knowledge and strategy.

Two experiments examined developmental and individual differences in students' revising for meaning. In Experiment 1, the authors investigated effects of knowledge of topic and knowledge of error location on revising done by middle school and college students. Knowledge of topic helped with meaning-level revising but did not seem necessary when surface-level editing was the goal. More interesting, knowledge of error location helped college students with both editing and revising but focused middle school students on editing at the expense of revising. In Experiment 2, the authors used a dyad-discussion design to investigate further differences in reading strategies during revising. The authors listened as pairs of 7th-grade students of different writing abilities (high, middle, and low) collaboratively revised. The results of Experiment 2 were consistent with the outcomes in Experiment 1, that is, knowing error location may focus less sophisticated writers too narrowly and thereby impede meaning-based revision. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decision models for designing and planning private communication networks

We consider the recently developed reconfigurable digital data networks consisting of T1/T3 circuits and Digital Crossconnect Systems (DCSs). A DCS is a device to patch base channels electronically from one T1/T3 circuit to another with a negligible queuing delay at the connecting node. We present new decision models for the design and circuit leasing policies of such digital backbone networks. Our model takes advantage of the special capabilities of the DCS technology and is likely to result in remarkable economic gains for the private network users. The formulation and analyses presented here simultaneously address the following problems: physical link and capacity selection, logical network configuration and channel assignment, and traffic routing on the logical network. The problem formulation results in a large-scale non-linear mixed integer program, and we propose an efficient solution methodology employing Lagrangean relaxation and subgradient optimization. Several numerical results illustrate the utility of our approach for these complex problems. We show that the economies of scale built into the tariff structure of these digital networks can be successfully exploited, and that the inherent flexibility of DCSs leads to logical networks that are dramatically different from their underlying physical topologies.     

Adolescents' perceptions of process and specialty group therapy.

82 emotionally disturbed adolescents (mean age 16.4 yrs) living in a residential treatment center rated their perceptions of process and specialty group therapies. Ongoing process groups were rated as more helpful for relating to staff and peers, and specialty groups were considered more helpful for cognitive, social, and interpersonal skill development. Despite the findings that both types of group therapy were helpful in different ways, all Ss preferred to deal with their problems in individual therapy. These findings challenge the popular notion that adolescents prefer group therapy to individual psychotherapy, suggesting a need to offer both individual and group therapies to optimize treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Patterning of multilayer dielectric optical coatings for multispectral CCDs

The development of optical sensors for spacecraft applications requires that all components be as lightweight as possible. One method to reduce the weight of a multispectral optical system is to eliminate beamsplitting optics and multiple detectors by patterning a filter array directly onto a CCD. However, techniques commonly used in the production of these filter arrays result in decreased image resolutions. This can greatly impact the performance of sensors used for applications such as planetary probes. To address this issue, we have studied the patterning of multilayer dielectric optical coatings in a small scale, two dimensional array, which will allow development of a four color sensor with a resolution one-half that of monochromatic sensors (compared to one-fourth or less for a four color striped array). We have developed ion milling techniques for the preparation of optical filter arrays which are patterned on a scale as small as 7.5 μm, enabling each pixel of a CCD to have its own associated filter. This paper presents details of the fabrication of these multispectral arrays, and discusses problems associated with pixel-sized filters.     

Continuous biotransformation of pyrogallol to purpurogallin using cross‐linked enzyme crystals of laccase as catalyst in a packed‐bed reactor

Cross‐linked enzyme crystals (CLEC) of laccase were prepared by crystallizing laccase with 75% (NH₄)₂SO₄ and cross‐linking using 1.5% glutaraldehyde. The cross‐linked enzyme crystals were further coated with 1 mmol L^?1 β‐cyclodextrin by lyophilization. The lyophilized enzyme crystals were used as such for the biotransformation of pyrogallol to purpurogallin in a packed‐bed reactor. The maximum conversion (76.28%) was obtained with 3 mmol L^?1 pyrogallol at a residence time of 7.1 s. The maximum productivity (269.03 g L^?1 h^?1) of purpurogallin was obtained with 5 mmol L^?1 pyrogallol at a residence time of 3.5 s. The productivity was found to be 261.14 g L^?1 h^?1 and 251.1 g L^?1 h^?1 when concentrations of 3 mmol L^?1 and 7 mmol L^?1 respectively were used. The reaction rate of purpurogallin synthesis was maximum (2241.94 mg purpurogallin mg^?1 CLEC h^?1) at a residence time of 3.5 s, when 5 mmol L^?1 pyrogallol was used as the substrate. The catalyst to product ratio calculated for the present biotransformation was 1:2241. The CLEC laccase had very high stability in reuse and even after 650 h of continuous use, the enzyme did not lose its activity. Copyright © 2006 Society of Chemical Industry     

Power electronics in German railway propulsion

The state of the art of power electronics is reviewed. Because of the different requirements, such as suburban or long distance traffic and DC or AC supply, various systems are in use and some peculiar configurations, as resistor braking, have become important. With AC supply special line-commutated rectifiers causing low displacement factor and small harmonic content are used for DC motor propulsion. With DC supply choppers allow nondissipative motor control, often combined with special circuits for field weakening and for change of driving/breaking. Particularly important is three-phase propulsion with robust squirrel-cage motors, made possible by the development of suitable variable-frequency inverters. Both current source and voltage source inverters are used in suburban cars as well as for locomotive drives. The most universal but also most complicated system served by the voltage source inverter is described in more detail     

An electronic device for triggering a stimulator during membraneresponsiveness determinations in cardiac tissues

A device is described that monitors the repolarization phase of a cardiac action potential and compares the membrane potential to a voltage selected by the investigator. When the voltages are the same, the device triggers a stimulator that injects the stimulus at the desired membrane potential. The device can stimulate tissue at any membrane potential during the repolarization phase of the action potential between 0 and -100 mV without regard to action potential duration. When it is precisely calibrated, its accuracy is within ±1.0 mV