Voltage Dip Protection with DC Motorstarter Coils

Continuous process plants are being designed today with fewer and larger components arranged in ``single train' configurations. Maintaining operating continuity with fewer components requires high equipment reliability. Motor controls for larger components are using magnetic contactors equipped with automatic undervoltage reclosing. A voltage dip where contactors drop open and reclose can be very serious because of the nature of motors and their driven loads during voltage transients. The reclosing of magnetic starters on motors with a decaying internal voltage is reviewed. A method of riding through voltage dips with dc coil magnetic contactors is described. Application of this method will depend upon the individual characteristics of each electrical system and the process that it serves.     

Performance Measurement of Training in Engineering Organizations

This work introduces a new training program performance assessment methodology for engineering organizations that is based upon needs assessment, types of training, and training effectiveness measures. The methodology checks whether predefined objectives of a company are identified through a needs assessment. Effectiveness is judged on whether the types of training and coursework content are formulated to fulfill the needs assessment objectives, whether the coursework is available to the proper employees, whether the courses are attended and understood by the employees, and whether the coursework content is utilized in the work place to meet the needs assessment objectives of the company. A case study of three training programs conducted within a public sector engineering organization is included to demonstrate the methodology and evaluate both the three programs and the methodology effectiveness. Conclusions suggest improvements to future training programs for the public sector engineering organization, as well as describe potential enhancements to the effectiveness measures of the methodology that can be recognized through further study of existing training programs.     

An iterative linearised solution to the sinusoidal parameter estimation problem

Signal processing applications use sinusoidal modelling for speech synthesis, speech coding, and audio coding. Estimation of the model parameters involves non-linear optimisation methods, which can be very costly for real-time applications. We propose a low-complexity iterative method that starts from initial frequency estimates and converges rapidly. We show that for N sinusoids in a frame of length L, the proposed method has a complexity of O(LN), which is significantly less than the matching pursuits method. Furthermore, the proposed method is shown to be more accurate than the matching pursuits and time-frequency reassignment methods in our experiments.     

Aurothioglucose inhibits murine thioredoxin reductase activity in vivo

Gold (I)-containing compounds, including aurothioglucose (ATG), are potent in vitro inhibitors of several selenocysteine-containing enzymes. Gold compounds have also been shown to potentiate the virulence of several viruses in mice, including coxsackievirus, implicated as a possible infectious agent in Keshan disease. One possible mechanism by which gold compounds may be increasing the virulence of viral infections in mice is by acting as a selenium antagonist in vivo and inducing oxidative stress. To investigate the possible role of gold compounds in inducing oxidative stress in mice, we assessed the ability of ATG administered in vivo to inhibit the activity of the selenocysteine-containing enzymes thioredoxin reductase (TR) and glutathione peroxidase (GPX1). Doses as low as 0. 025 mg ATG/g body weight caused significant and prolonged inhibition of TR activity in all tissues examined. No such inhibition of GPX1 activity was seen, indicating differential in vivo sensitivity of the enzymes to inhibition by ATG. In liver and heart, some recovery of TR activity was observed after a 7-d period, but no recovery was observed in pancreas or kidney. Because TR is involved in several important cellular redox functions, its inhibition most likely will affect multiple cellular processes. These results indicate that in vivo administration of ATG results in significant and long-lasting inhibition of TR activity. Such inhibition of TR could lead to increased levels of oxidative stress in vivo, thereby increasing the virulence of several viruses including the coxsackievirus.     

Quantitative techniques for analyzing high-resolutioncardiac-mapping data

In high-resolution cardiac mapping, signals are simultaneously recorded from hundreds of electrodes in contact with the myocardium and then analyzed to reveal the underlying activation pattern. Activation mapping has a long history in both experimental and clinical cardiac electrophysiology and has also been used to study other organ systems. Much of the current emphasis in mapping technology is on data analysis-ways to extract useful information from the voluminous data stream-rather than on the acquisition of the data. Hence, in this article, the authors review the traditional method for analyzing and interpreting mapping data, isochronal mapping, and then report on additional techniques that have recently emerged. The authors focus on techniques applicable to quantifying the dynamics of complex tachyarrhythmias such as ventricular fibrillation (VF) and atrial fibrillation (AF)     

Freeze-Thaw Treatment of Membrane Concentrates Derived from Kraft Pulp Mill Operations

Freeze thaw was studied as a waste treatment method for concentration and volume reduction of contaminated waste concentrates that are derived from the use of membrane technology in the treatment of high strength Kraft pulp mill effluents. Unidirectional freezing experiments were conducted to simulate seminatural freezing, in which the independent variables—freezing rate, time frozen, storage temperature, concentration, liquid depth, thawing rate and method of thawing—were examined for their relative importance. Method of thawing followed by freezing rate, rate of thawing, storage temperature, and time frozen were identified as the most important independent variables that contribute significantly to treatment performance. Under ideal conditions, freeze thaw was shown to effectively concentrate and separate the constituent matter of alkaline, extraction-stage membrane concentrate to achieve color removals as high as 73% in the top 70% liquid fraction. The results suggest a new field of use for freeze thaw as a waste treatment process for the management of high strength liquid wastes amenable to mechanical coagulation by freezing.     

Fuel use and design analysis of improved woodburning cookstoves in the Guatemalan Highlands

This study examined the fuel use and design of an improved woodburning cookstove (plancha), in comparison to traditional cooking over an open woodfire. These cookstoves had been randomly introduced into population households in the Guatemalan Highlands that had previously used open woodfires. This research consisted of: (1) a 12-household Kitchen Performance Test (KPT) over a 4-day period and (2) single-day participant observation in five households. The KPT monitored fuel consumption and the number, age, and gender of people who were cooked for, while the participant observation was used to form a complete understanding of fuel use patterns and to examine the influence of stove condition and cooking behavior. In spite of fairly low variability in the fuel use data (coefficients of variation of about 0.34) the KPT did not show statistically significant differences in fuel use between the two cooking methods. It is possible that increased study power through a larger sample size may have resulted in a statistically significant difference in favor of the plancha, but it is doubtful that the size of the effect would be of any practical significance. Thus, although other studies have shown that the plancha is extremely effective in reducing indoor air pollution in the study area, the KPT did not indicate that it offered any benefits with respect to fuel use. Practical and experimental recommendations for future cookstove efficiency studies are presented, with directions for continued work in this area.     

Stress-strain response of a cast 319-T6 aluminum under thermomechanical loading

The stress-strain behavior of cast 319-T6 aluminum-copper alloys with three different secondary dendrite arm spacings (SDASs) was studied at high temperatures and under thermomechanical deformation, exposing marked cyclic softening. A two state-variable unified inelastic constitutive model proposed earlier was modified to describe the stress-strain responses of these alloys by considering the variation of hardening and recovery functions of back-stress and drag stress. The SDAS was incorporated in the model as a length-scale parameter, and the material constants were determined systematically from experiments on a cast 319-T6 aluminum with small and large SDASs. The capabilities of the constitutive model were checked by the comparisons of simulations to experiments in the small-strain regime (<0.005). The results show that the model provides successful simulations for material response after thermal exposure at high temperature and cyclic transient stress-strain behavior. The causes of mechanical behaviors at the macro scale are discussed based on microstructural changes during thermal exposure.