A Low-Cost Thyristor Fuse

Thermal fuses are the devices most commonly used for effective equipment protection against fault currents within solid-state power systems. Original equipment cost versus additional expenditures for protective devices warrants elaborate means for safeguarding the investment while maintaining cost effectiveness. This has resulted in a vast variety of individually high-priced specialty fuses. Experience indicates that a large number of thyristor current-limiting fuses must be expended during the design phase of solid-state power conversion equipment so as to properly investigate converter circuit malfunctions due to nonrecurrent circuit transients. Thermal fatigue of fuses during field use necessitates a considerable logistic support in order to sustain the bulk of multifused complex power converters. This large demand cannot be satisfied at all times due to the limited number of prime suppliers, and due to the range of size, bulk, and price of present thermal thyristor fuses. Thermal analysis and extensive testing furnishes strong evidence that the desirable low-cost thyristor fuse link is feasible. This low-cost item is well-suited to protect thyristors against catastrophic failures within the constraints of any thermal fuse. Since the fuse is renewable, it compares favorably with presently used commercial thyristor fuses in terms of bulk and potential cost savings as well as in its flexible simplified rating mechanisms.     

Ocular symptoms in association with antiphospholipid antibodies

OBJECTIVE: To describe the clinical and serologic findings of 50 antiphospholipid antibody (APA)-positive patients within a retrospective study. METHODS: Measurement of visual acuity, slit-lamp biomicroscopy, tonometry, fundus examination and perimetry. Laboratory tests were performed for detection of APA against thromboplastin and cardiolipin. Antinuclear antibodies (ANA), antibodies to dsDNA, antithyroidal and antiparietal antibodies were also tested. RESULTS: A combination of both transient and permanent visual disturbances was noticed in more than half of the patients. Transient visual disturbances included transient blurred vision, partial defects of the visual fields and amaurosis fugax. The most frequent permanent abnormalities were optic atrophy in 20 patients, due to AION in 9 cases, and disturbances of the choroidal circulation in 17 patients. Fourty-six patients had positive levels of thromboplastin APA; cardiolipin APA were found to be increased in 36 patients. CONCLUSIONS: We did not find a clear correlation between APA activity or the immunoglobulin classes in the individual and the severity of the ocular disease. The benefit from a therapy with the antiplatelet agent acetylsalicylic acid was evident in a reduction of the patients' transient visual disturbances and, in most cases, no further progression of permanent visual field defects was observed.     

Power Transfer in DC Chopper Motor Drive

Under the guidance of the Electric Vehicle Demonstration Act, administered by the Department of Energy, Office of Transportation Programs, the energy efficiency of a dc chopper motor drive was investigated [1]. With the aid of a data acquisition system, data points were taken for a parametric load profile at multiple constant speed settings. The data points were used to determine motor performance when energized from a dc source; and to determine motor performance and heat loss when receiving energy from the propulsion battery through the dc controller. Power losses in the dc controller and the propulsion battery were also determined during the latter test run. The constant speed and parametric load torque performance data are converted into constant power/torque variable speed data and presented graphically.     

The Integrated Power Switch

Utilizing a signal from transistor transistor logic (TTL) circuits, the integrated power switch (IPS) can control 40 kW. Protection against overload conditions enables the use of transistors which have ideal switching characteristics. Each half-section of the IPS is electrically isolated from the signal input using optical couplers. Discrete component assemblies, printed-circuit boards, thick-film or medium-scale integrated substrates each have been utilized. The forced-air-cooled heat sink was designed for maximum cooling. Two types of IPS's were initially constructed: 500 V/60 A, and 100 V/200 A, with additional availability of 500 V/100 A devices in small quantity. Its capability to work from continuous operation to 10 kHz makes the IPS universally applicable to most power-conversion applications with-in its current and voltage limitation.     

Germicidal teat dip in a herd with low prevalence of Streptococcus agalactiae and Staphylococcus aureus mastitis

Effectiveness of an iodophor teat dip in reducing new intramammary infection and clinical mastitis was tested in a herd free of Streptococcus agalactiae and with a low prevalence of Staphylococcus aureus infections. In this 6-mo study with an average of 152 lactating cows on trial on sampling dates, right rear and left front teats were dipped after each milking while right front and left rear teats were undipped controls. Teat dipping significantly reduced new infections by Staphylococcus aureus, streptococci (other than Streptococcus agalactiae), coagulase-negative staphylococci, and Corynebacterium bovis and reduced clinical cases caused by infections established during the trial. However, the dip did not reduce new infections or clinical mastitis caused by coliform bacteria. Therefore, use of a germicidal dip is recommended for herds with a low prevalence of Streptococcus agalactiae and Staphylococcus aureus, but the practice should not be expected to control coliform mastitis.     

Management of dry cows to reduce mastitis

The objective of mastitis control during the dry period is to have as few infected quarters as possible at calving. This depends on enhancing elimination of infections present at drying off and on reducing the new infection rate during the dry period; prevention of new infection appears to offer greater long-term benefits. Incidence of new infection is high in the dry period with periods of high susceptibility shortly after dry off and again prepartum. Pathogens of both contagious and environmental origin cause new dry period infections; however, exposure to contagious pathogens probably decreases with cessation of regular milking, whereas exposure to environmental pathogens continues throughout the dry period. Varying susceptibility over the dry period may be affected by bacterial loads on the teat skin, characteristics of the teat canal, and internal protective mechanisms. At present, antibiotic therapy at the end of lactation is the most effective means of eliminating existing infections and preventing new infections. Although there are reasons to prefer selective therapy, present evidence favors a recommendation for treatment of all cows at the time of drying off. A shortcoming of present therapy regimens for the dry period is that they provide little or no protective effect against new infection prepartum. Other mastitis control methods and management practices have not been shown conclusively to reduce new dry period infections. However, it appears that reduction of exposure to environmental pathogens during dry period should be recommended. More effective means to reduce new infections in the prepartum period are needed.     

Platelet and neutrophil distributions in pump oxygenator circuits. III. Influence of nitric oxide gas infusion

The authors used quantitative gamma scintigraphy to evaluate the influence of nitric oxide gas on platelet and neutrophil deposition in Cobe Duo microporous oxygenators during cardiopulmonary bypass (CPB). The effects of nitric oxide gas on circulating platelet and neutrophil counts and platelet function also were assessed. Animals were prepared by standard methods. Cells were harvested, labeled (111 In platelet and 99mTc neutrophil), infused, and recirculated. Nitric oxide gas, a guanylate cyclase pathway promoter, was infused int he Duo gas port at 500 ppm (t = 0-60 min), increased to 1,000 (t = 60-80 min), and stopped (final, 10 min). Images were taken at 10-15 min intervals during CPB. Standard isotope image corrections were made. No differences between nitric oxide gas and control experiments were observed for flow, pressure, hematocrit, or replacement volume. Nitric oxide gas infusion significantly (p < 0.05) reduced both platelet adherence to the oxygenator and in vitro platelet aggregation. Neutrophil adhesion tended to be lower, and circulating platelet and neutrophil counts tended to be higher with nitric oxide gas infusion. Results of in vitro aggregometry studies using rabbit platelets indicate that the class V phosphodiesterase inhibitor zaprinast can strongly enhance the inhibitory effects of nitric oxide. The authors conclude nitric oxide gas is a promising platelet sparing agent in the setting of CPB.     

Color vision tests for early detection of antiepileptic drug toxicity

A previous suggestion that antiepileptic drugs may induce color vision deficiencies prompted us to examine whether color vision deficiencies may occur at lower drug serum concentrations than those associated with symptoms of neurotoxicity. Eighty patients presenting with epilepsy received monotherapies of valproic acid, phenytoin, or carbamazepine; 18 patients did not receive antiepileptic drug therapy. Color vision was tested by the Farnsworth-Munsell 100-hue test, spectral sensitivity, and the newly developed tritan screening plates. Patients treated with phenytoin or carbamazepine developed blue-yellow color vision deficiencies. In contrast, patients exposed to valproic acid or receiving no drug treatment showed normal color vision. There was a significant correlation (p < 0.0001) between signs of neurotoxicity induced by phenytoin or carbamazepine and blue-yellow color vision deficiencies. In contrast, we found no correlation between these signs of neurotoxicity and the drug serum concentrations (p = 0.0637). Color vision testing in epileptic patients treated with phenytoin or carbamazepine appears to be a sensitive method for early detection and monitoring of clinical neurotoxicity.