The Performance of a Single-Phase Current-Fed Inverter with Counter EMF?Inductive Load

Current-fed inverters that have series diodes to trap the charge on a commutating capacitor can supply ac loads of any power factor. A single-phase circuit with counter emf-inductance load, such as a motor, has been analyzed by digital computer simulation, valid for all modes of operation. The magnitude and phase of the ac load current are graphically related to the direct current and thyristor firing angle with respect to the counter emf. The ratio of the operating frequency to the natural ringing frequency of the commutating capacitance and the load inductance is a parameter of the circuit that significantly affects its behavior. Problems associated with high-frequency operation in a drive system are discussed.     

Symptomatic and asymptomatic left-ventricular systolic dysfunction in an urban population

BACKGROUND: In most previous epidemiological studies on the prevalence of chronic heart failure (CHF) the disorder has been defined on clinical criteria. In a cross-sectional survey of 2000 men and women aged 25-74, randomly sampled from one geographical area, we assessed left-ventricular systolic function by echocardiography. METHODS: 1640 (83%) of those invited took part. They completed a questionnaire on current medication, history, and symptoms of breathlessness. Blood pressure was measured and electrocardiography (ECG) and echocardiography were done. Left-ventricular ejection fraction was measurable in 1467 (89.5%) participants by the biplane Simpson's rate method. FINDINGS: The mean left-ventricular ejection fraction was 47.3%. The prevalence of definite left-ventricular systolic dysfunction (defined as a left-ventricular ejection fraction < or = 30%) was 2.9% overall (43 participants); it increased with age and was higher in men than in women (4.0 vs 2.0%). The left-ventricular systolic dysfunction was symptomatic in 1.5% of participants and asymptomatic in 1.4%, 83% of participants with left-ventricular systolic dysfunction had evidence of ischaemic heart disease (IHD) from history or ECG criteria compared with 21% of those without this abnormality (p < 0.001). Hypertension was also more common in those with left-ventricular systolic dysfunction (72 vs 38%, p < 0.001), but there was no difference between those with and without left-ventricular systolic dysfunction in the rate of hypertension without IHD. INTERPRETATION: Left-ventricular systolic dysfunction was at least twice as common as symptomatic heart failure defined by clinical criteria. The main risk factors are IHD and hypertension in the presence of IHD; screening of such high-risk groups for left-ventricular systolic dysfunction should be considered.     

Function of hexameric RNA in packaging of bacteriophage phi 29 DNA in vitro

A methodology based on high-performance gel exclusion chromatography (HPLC-GEC) has been developed to perform permeability studies of vesicles. Encapsulation of two marker isothiocyanate fluorescein (FITC) dextrans of 4400 and 40,500 molecular mass was used as a model system. Combination of two TSK-PW columns, one efficient in vesicle sizing (G6000 PW), the other in that of dextrans (G4000 PW), was required to achieve complete particle separation and to remove entirely the unentrapped dextran after encapsulation into vesicles. Coupling fluorescence and light scattering detection allowed to control the efficiency of the separation, to quantify the vesicle leakage and to follow both the integrity of the vesicles and changes in their size. This methodology can be applied to other fields such as encapsulation of water soluble compounds and drug delivery systems.     

Integration of titrimetric measurement, off-gas analysis and NOx- biosensors to investigate the complexity of denitrification processes.

The denitrification process, namely the reduction of nitrate (NO3-) to nitrogen gas (N2), often cannot be simply modelled as a single step process. For a more complete and comprehensive model the intermediates, particularly nitrite (NO2-) and nitrous oxide (N2O), need to be investigated. This paper demonstrates the integration of titrimetric measurements and off-gas analysis with on-line nitrite plus nitrate (NOx-) biosensors, highlighting the necessity of measuring process intermediates with high time-scale resolution to study and understand the kinetics of denitrification. Investigation of activated sludge from a full-scale treatment plant showed a significant accumulation of NO2-, which appeared to impact on the overall denitrification rate measured as NOx- reduction or N2 production. A different sludge obtained from a lab-scale bioreactor produced N2O instead of N2 as the end product of denitrification. The two examples both illustrate the complexity of denitrification and stress the need for the more versatile and detailed measurement procedures, as presented in this paper.     

Power electronic circuit topology

A generalized concept of `sources' that embraces both power generators and power consumers is presented. This approach simplifies the basic topological aspects of power electronic converter circuits, which are reduced to an array of switches for selectively interconnecting two source systems. Capacitive and inductive filters can modify the nature of the systems, because they act as short-time sources and determine whether the converter sees a voltage source or a current source at its terminals. These differing source qualities require different types of switching devices and have ramifications in the mode of operation of the equipment. Some basic configurations are presented, and their significant properties are described, with emphasis on the most widely used circuits in high-power equipment, particularly AC/DC converters     

Cell-mediated immunity in nutritional deficiency

Dietary deficiencies of specific nutrients profoundly alter cell-mediated immune responses in man and experimental animals. Both moderate and severe deficiencies are associated with significant changes in immunocompetence. Diets with inadequate levels of protein, calories, vitamin A, pyridoxine, biotin and zinc result in loss of thymic cellularity. Secondary to thymic atrophy, the production of thymic hormones critical for the differentiation of T lymphocytes is reduced, especially in protein-calorie malnutrition and zinc deficiency. Confirmation of a T cell maturational defect in nutritional deprivation comes from the observations of decreased total (T3 and rosette-forming) T cells in the peripheral blood of children with kwashiorkor and marasmus, with preferential loss of helper/inducer (T4) T cell subsets. Reduced number and in vitro function of T cells have also been reported in experimental deficiencies of iron, zinc, copper, and vitamins A and E. Loss of cutaneous hypersensitivity to mitogens and antigens is a consistent sequela of dietary deficiencies of protein, vitamins A and C, pyridoxine, iron and zinc. Cell-mediated immunity directed against allogeneic histocompatibility antigens (e.g. mixed leukocyte cultures, graft versus host, skin graft rejection) may actually be enhanced by experimental protein and polyunsaturated fat deficiencies. Alternatively, pyridoxine, ascorbate and biotin deficiencies resulted in delayed rejection of skin allografts. Cytotoxic T lymphocyte (CTL) activity is impaired in zinc-, iron- and copper-deficient mice, as well as in scorbutic guinea pigs. Natural killer (NK) cell function may be either enhanced or depressed, depending upon the nutrient and its effects on interferon production. Several authors have demonstrated normal or enhanced macrophage activity in a variety of experimental deficiencies. The extrapolation of these observations to infectious disease resistance is not straightforward, and depends upon the nature of the microbe, its own nutrient needs, and the relative importance of innate, as opposed to immunologic, defense mechanisms.     

Tungsten thermionic emitter surfaces improved by chemical vapor deposition

Surfaces can be produced with a high degree of preferred crystal orientation. Observation indicates that emission is uniform.     

Food packaging simulant failure mechanisms in next generation steel packaging

Legislative pressures have led to the mature dominant chromium‐coated steel (ECCS) substrate and epoxy phenolic lacquer replacement in Europe. An investigation was carried out to examine the interaction between a steel surface engineered with a novel, developmental substrate coated using Cr (III)‐based electrolytes and the food stuff being canned. Samples of lacquered material were subjected to a typical retort process (121°C for 90 minutes) and examined using a variety of laboratory analytical techniques. The foodstuff being packaged has a significant impact on the substrate/lacquer adhesion with clear differences in failure mechanisms between foodstuffs. There is clear evidence of chemical species transfer through the next generation lacquer, and this can instigate corrosion at the surface where incomplete chromium coverage leads to exposed iron. In general, the novel developmental material exhibits lower adhesive properties and shows a greater sensitivity to the foodstuff, although this is largely attributed to the homogeneity of the coverage. The novel substrate proves to be a promising alternative to ECCS due to REACH legislation, but improvement is required to achieve equivalent performance.