Characteristics of the emitter-switched thyristor

The first experimental demonstration of 600-V emitter-switched thyristors fabricated using an IGBT (insulated-gate bipolar transistor) process sequence is reported. The forward drop is less than that for the IGBT, but larger than that for a thyristor by about 0.5 V due to the thyristor current flowing via the MOSFET channel. A unique characteristic observed for these devices, not exhibited by any previous MOS-gated thyristor structures, is gate-controlled current saturation even after thyristor latch-up. Switching tests were performed up to a current density of 1000 A/cm² on single-unit cells and the measured turn-off times were about 7 μs     

A new MOS-gated power thyristor structure with turn-off achieved bycontrolling the base resistance

A new MOS-gated power thyristor structure, called the base-resistance-controlled thyristor (BRT), is described. In this structure, the turn-off of a thyristor with an N-drift region is achieved by reducing the resistance of the P-base region under MOS-gate control. In contrast with previous devices, a P-channel MOSFET integrated in the N-drift region is used for this purpose. It has been shown, by two-dimensional numerical simulations and experimental measurements on devices fabricated using a seven-mask process, that devices with 600-V forward blocking capabilities can be achieved with a forward drop close to that for a thyristor. The ability to turn off the thyristor current flow has been verified over a broad range of current densities     

Pulsed laser irradiation impact on two marine diatoms Skeletonema costatum and Chaetoceros gracilis

The ability of pulsed laser irradiations to cause damage on the biofouling organisms is recently being investigated. If this technique is employed in industries such as power generation wherein a large quantity of water is being used for the cooling purpose, many organisms other than the targeted would get affected. In this study, we have investigated the damage caused by the pulsed laser irradiations from an Nd:YAG laser (fluence 0.1J/cm(2)) for varying durations such as 2, 5, 10, 30, 60 and 300 s on two marine diatom species namely Skeletonema costatum and Chaetoceros gracilis. Upon exposure to low power laser irradiations, these diatom species showed mortalities between 52.6+/-9.3% to 97.7+/-3.1% in the case of S. costatum and 57.8+/-2.5% to 98.9+/-0.6% in the case of C. gracilis for 2 and 300 s of irradiations, respectively. The mortality increased with the increase in the duration of laser irradiation. The estimation of the chlorophyll a concentration in the irradiated samples showed a considerable reduction varying between 9.8% and 57% in C. gracilis and 3% and 70.3% in S. costatum for 2 and 300 s of irradiations, respectively. The laser-survived cells grew as the non-irradiated (control) samples. C. gracilis frustules were broken by the laser whilst, the cell materials were drained out of the frustules in the case of S. costatum. The study therefore showed that the low power pulsed laser irradiations could cause significant damage on the two species of planktonic diatoms.     

Telemedicine and tele-health services for cancer-care delivery in India

Noncommunicable diseases including cancer are emerging as major public health problems in India. Awareness of cancer and its management are being taken as a high priority at the national level because of the increase in the incidence of the disease in the country. Telemedicine provides expert-based health care to understaffed remote sites and advanced emergency care through modern telecommunication and information technologies. The incidence of cancer can be reduced if the people are aware of cancer and its root causes. Recently, the introduction of telemedicine in oncology plays a vital role. Telemedicine helps in prevention, early detection, a faster cure, palliative care and rehabilitation in the management of cancer. The status of telemedicine services for cancer care in Kerala, India, and how telemedicine can be an effective solution of cancer- care delivery in India are explored.     

Nickel–Alumina Functionally Graded Materials by Electrophoretic Deposition

Electrophoretic deposition has been used to synthesize nickel–alumina, functionally graded materials from NiO and alumina suspensions in ethanol. Suspension stability and the kinetics of deposition were studied to determine optimum conditions. Deposition starts with an alumina suspension into which a stream of NiO suspension is injected at various flow rates to obtain the desired profiles. The latter were controlled by varying the deposition current density and component flow rate. The green bodies obtained were sintered in Ar/H₂ atmosphere to reduce the NiO to nickel. Various gradation profiles were obtained illustrating the facility of EPD to synthesize continuously graded materials. NiO was used as the precursor for nickel to alleviate settling and rough columnar deposit problems.     

Control relevant modeling of planer solid oxide fuel cell system

This paper provides two types of control relevant models of planer solid oxide fuel cell system with different details. Dynamic models of system components which include heat exchanger, reformer and after-burner are also provided along with the necessary formulation of a fuel cell connected in parallel with a capacitor. Steady-state and dynamic simulations of fuel cell system for both types of models are performed. The results indicate that both models are comparable in predicting stack voltage at lower current load. But, the discrepancy in the stack voltage, power and temperature of different components become more prominent at higher current load.     

Electrolytic recovery of zinc from zinc ash using a catalytic anode

The process of galvanisation of steel generates zinc ash as the waste product, thus creating pollution problems. The recovery of zinc metal from zinc ash, with a zinc content of about 76% by leaching and electrowinning has been studied. The presence of chloride has been identified as the major problem area. A catalytic anode based on iridium dioxide (IrO₂) was used as the anode material to overcome this problem. Catalyst loading was kept at an economically acceptable level. The catalyst's stability, energy consumption and efficiency of zinc recovery are discussed. The service life of the IrO₂ active coating has been established by an accelerated polarisation test. The zinc deposit recovered from the zinc ash has been examined by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Copyright © 2004 Society of Chemical Industry     

Flow transition for natural convective heat transfer in a porous medium saturated with water near 4°C

In this paper, the problem of buoyancy-induced convection flow in water-saturated porous media near 4°C is examined using a numerical model. Darcy's law is used to model flow behavior and a single equation convective heat transfer model is used for the energy equation. As the Boussinesq approximation is not valid for this case, a parabolic dependence of density on the temperature is used. Natural convection is generated and sustained by a uniform heat source. Flow behavior is governed by three natural parameters appearing in the model. They are: (i) dynamical parameter, (ii) geometric parameter, γ = b/a; and (iii) wall temperature, in relation to the reference temperature at the density extremum. For certain ranges of θ_w (<0) and Gr, interesting density inversion effects are possible. Transient solutions are obtained for various aspect ratios and modified Grashof number values. For a wide range of Grashof number, steady state solutions could not be obtained. Flow mutations into periodic and chaotic solutions are investigated for a range of Grashof number (100 to 40,000) and aspect ratio values (1 to 10).