Mechanical and dynamical mechanical properties of chloroprene rubber and cellulose II composites

Vulcanized composites of chloroprene rubber (CR) with cellulose II (Cel II) as a filler were investigated. Cel II, obtained by the coagulation of cellulose xanthate, was incorporated in the rubber by the traditional method. The filler content varied from 0 to 30 phr. For comparison purposes, carbon black (CB)–CR composites were also studied. The CB amount varied from 0 to 45 phr. The mechanical and dynamic mechanical properties were determined, and the CR composite containing 20 phr of Cel II showed the best set of properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2425–2430, 2004     

Off-line optimization and control for real time integration of a three-phase hydrogenation catalytic reactor

In order to develop and test the integration procedure, in this paper a real time process integration involving the optimization and control of the process is presented, in this case, with the two-layer approach. The used optimization algorithms were Levenberg–Marquardt and SQP that solve a non-linear least square problem subject to bounds on the variables. The two-layer approach is a hierarchical control structure where an optimization layer calculates the set points and manipulated variables to the advanced controller, which is based on the dynamic matrix control with constraints (QDMC). The non-isothermal dynamic model of the three-phase slurry catalytic reactor with appropriate solution procedure was utilized in this work (Vasco de Toledo, E. C., Santana, P. L., Maciel, M. R. W., & Maciel Filho, R. (2001). Dynamic modeling of a three-phase catalytic slurry reactor. Chemical Engineering Science, 56, 6055–6061). The model consists on mass and heat balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. The model was used to describe the dynamic behavior of hydrogenation reaction of o-cresol to obtain 2-methil-cyclohexanol, in the presence of a catalyst Ni/SiO₂.     

Possibilities in the reconstruction of bone defects

The importance of the functional unit "bone-soft-tissue" for the treatment of bone defects is discussed. A division is made between non-vascular and vascular bone transport. The individual methods are explained and their clinical significance is illustrated partly using case material. In general, the best way to fill small defects in vital soft tissue is to use cancellous autografts. For bridging longer bone defects callus distraction is the method of first choice, but in individual cases vascularized bone transfer can be taken from the iliac crest or the fibula. Homo- or heterografts should only be used in cases where no autologic bone material is available or when there is not enough.     

Sensorless vector controller for a synchronous reluctance motor

A new high-performance sensorless speed vector controller that implements the maximum torque per ampere control strategy for the inverter-driven synchronous reluctance machine is presented in this paper. It is based on a parameter-dependent technique for online estimation of rotor position and angular velocity at the control rate. The current ripple principle is used to estimate position. The estimates are fed to a conventional closed-loop observer to predict the new position and angular velocity. The very high accuracy of the sensorless control algorithm at both low and high speeds is confirmed by experimental results     

Home use of a functional electrical stimulation system for standing and mobility in adolescents with spinal cord injury

OBJECTIVE: Functional electrical stimulation (FES) is a technology that may allow some patients with spinal cord injury (SCI) to integrate standing and upright mobility with wheelchair mobility. The purpose of this study was to document the patterns of home and community use of a FES system for standing and mobility. DESIGN: A telephone questionnaire was administered every 1 to 4 weeks for a minimum of 1 year. An interview was given at the end of the study to probe the motivators and barriers to home use. SETTING: Training for use of the FES system was performed in an inpatient pediatric rehabilitation setting. Data collection began after the subjects were discharged to home. PARTICIPANTS: Five adolescents with complete, thoracic-level SCI. INTERVENTION: Subjects participated in a program of FES exercise followed by training in basic mobility skills such as standing transfers, maneuvering, level ambulation, one-handed and reaching activities, and stair ascent/descent. MAIN OUTCOME MEASURE: The frequency with which the FES system was used at home and the activities for which it was utilized were documented. Motivators and barriers to FES home use were examined. RESULTS: Subjects donned the FES system on the average once every 3 to 4 days. Between 51% and 84% of the times donned, the system was used for exercise. The remaining times it was used for standing activities, most commonly reaching, one-handed tasks, and standing for exercise. "Motivators" included being able to do things that would otherwise be difficult, perceiving a healthful benefit or a sense of well-being from standing and exercise, and feeling an obligation to stand as a participant in a research study. "Barriers" to FES use included not finding time to use the system, having difficulty seeing opportunities to stand, and being reluctant to wear the FES system all day.     

The digital divide and t-government in the United States: using the technology acceptance model to understand usage

This paper applies the technology acceptance model to explore the digital divide and transformational government (t-government) in the United States. Successful t-government is predicated on citizen adoption and usage of e-government services. The contribution of this research is to enhance our understanding of the factors associated with the usage of e-government services among members of a community on the unfortunate side of the divide. A questionnaire was administered to members, of a techno-disadvantaged public housing community and neighboring households, who partook in training or used the community computer lab. The results indicate that perceived access barriers and perceived ease of use (PEOU) are significantly associated with usage, while perceived usefulness (PU) is not. Among the demographic characteristics, educational level, employment status, and household income all have a significant impact on access barriers and employment is significantly associated with PEOU. Finally, PEOU is significantly related to PU. Overall, the results emphasize that t-government cannot cross the digital divide without accompanying employment programs and programs that enhance citizens’ ease in using such services.     

Characteristics of WWTP sludge after drying in greenhouse for agricultural purposes

The sludge generated by sewage treatment which meets regulatory standards can be used in agriculture. With this understanding, the focus of this study is the evaluation of the agricultural characteristics and inorganic substances in excess activated sludge, which was subjected to drying in a greenhouse. The variables (factor) evaluated during the drying process were: type of sludge (digested or not digested), addition of lime to the sludge, and the physical layout and rotation of sludge in the greenhouse. The parameters monitored for this assessment were moisture, volatile solids and pH. The greenhouse cover and sides were made of translucent plastic to allow the penetration of solar radiation and prevent water from entering. A impermeable floor was used. The sludge was generated in sewage treatment plants located in the metropolitan region of Grande Vitória, Espírito Santo, Brazil. The solar drying of wastewater sludge in a greenhouse presented satisfactory results.     

Fundamental studies on vacuum circuit breaker arc quenching limitswith a synthetic test circuit

The aim of this work is to demonstrate the use of a synthetic test circuit with LC resonant circuits for fundamental experimental work on CB (vacuum circuit breakers). Studies have been performed on a 36 kV-model CB at test currents of 5 and 10 kA r.m.s. aimed at separating the influence of different parameters of the transient recovery voltage such as average rate of rise and peak value on the breaking capability. Furthermore, the effect of the arcing time on the measured arc quenching limit is presented     

Simulation of reignition processes of vacuum circuit breakers inseries

The present theoretical study is based on experimental investigations and shows the transient behavior of vacuum tubes in series, in the case of reignition. Neglecting the real physical arc and replacing it by a programmable switch (time controlled), it can be demonstrated, in a preliminary study, that the theoretical studies do confirm the experimental results     

Foundational Aspects of Student‐Controlled Learning: A Paradigm for Design,Development, and Assessment Appropriate for Web‐Based Instruction

This paper presents a strategy for the design and organization of materials for Web‐based instruction (WBI) founded upon cognitive modeling for the identification and organization of the major concepts in the domain of interest, based upon the Pathfinder paradigm. The original purpose of the Pathfinder paradigm was to model aspects of human semantic (associative) memory. A brief introduction to the Pathfinder paradigm is presented, and the rationale for its use in WBI is discussed. The development of this paradigm for WBI, in the context of eliciting and representing knowledge from domain experts, and its use in a pilot study is described. The domain used for the pilot study was the A* search algorithm, embedded within an introductory course in artificial intelligence. Assessment of the paradigm is also discussed, and preliminary methods are applied to the pilot study.