Dual ramptime nonlinear current control applied to a single phase five level cascaded inverter

This paper reports on the application of a zero average current error (ZACE) control method in single-phase five level cascaded inverter based systems. The dual ramptime method and its adaptation to the five level cascaded converter are described in detail. Recommendations on the choice of control parameters and how to improve noise immunity are included. Experimental results demonstrate the suitability of the control method, since the lower order harmonics are negligible and the ripple current frequency is kept within a narrow band.     

Theory of te precipitation and related effects in CdTe Crystals

A thermodynamic calculation is presented which explains the origin of often reported large stress fields in and around Te precipitates and associated punching of dislocation loops in star like patterns. The calculation is based on the consideration that the stoichiometric deviation in Te saturated crystals are accommodated by Te interstitials, Cd multivacancy complexes and Te antisites; the Te interstitials are most mobile of them, and dominate the precipitation process; and the precipitates when they appear first are in droplet form. The droplet state is modelled on the basis of the Lennard-Jones 6-12 interaction potential. The droplet growth is envisaged to occur via the following two processes operating in tandem: first, capture of excess Te interstitials to cause droplet overpressurization, and then, punching of interstitial dislocation loops whenever the pressure exceeds a threshold value. The flow of Te interstitials into the droplets is driven by the difference between their formation energies in the lattice and the free energy change of the droplets per Te atom added. It is shown that the achievable droplet pressures far exceed that required for the loop punching and sustaining the growth cycle. The occurrence of varying precipitate morphologies are explained, and the possibility of nucleating high presssure Te phases is examined. Some experimental evidence is also presented which corroborate the theoretical arguments involved.     

Effect of sodium on cellular calcium transport in rat kidney

The influence of extracellular Na (Na0) on cellular Ca transport and distribution was studied in rat kidney slices. Calcium efflux from prelabeled slices was depressed when Na0 was completely replaced by choline or tetraethylammonium (TEA) ions and it was markedly stimulated when Na was reintroduced in a Na-free medium. However, reducing Na0 (with choline or TEA as substituting ions) did not increase the total slice 40Ca, their total exchangeable Ca pool, or the 40Ca or 45Ca of mitochondria isolated from these slices. Kinetic analyses of steady-state 45Ca desaturation curves showed that reducing Na0 depressed the exchange of Ca across the plasma membrane, slightly decreased the cytosolic Ca pool, but did not significantly affect the mitochondrial Ca pool and Ca cycling. Ouabain (10(-3)M) which should reduce the Na gradient across the plasma membrane had no effect on calcium distribution and transport. These results suggest that in kidney cells low Na0 depresses Ca influx as well as Ca efflux; there may be an interaction between Na and Ca at a possible carrier located in the plasma membrane, but there is no Na/Ca exchange as described in several excitable tissues.     

Zero average current error controlled power flow for AC-DC powerconverters

Unity and controlled power factor AC-DC power converters require a current control technique with zero average current error (ZACE) in each switching period. Acting on the current error signal alone, a ZACE controlled converter offers complete real and reactive power flow control with negligible low order current harmonics, a narrow switching frequency band, and relative immunity to DC link or AC line voltage harmonics. Slope-generated hysteresis, a new ZACE current control method is introduced. Simulation and experimental results in a three phase converter are presented     

Precipitation in CdTe crystals studied through mie scattering

Below gap optical losses in as-grown n-type CdTe crystals were analyzed in terms of free carrier absorption and Mie extinction due to Te precipitates. Experimental absorption spectra measured between 2 to 20 μm exhibited the well-known free carrier absorption behavior α_FCA∼λ^x with x=3 due to scattering by polar optical phonons. In shorter wavelength regions below 6 μm, however, additional contributions to the light loss due to absorption and scattering by precipitates were also observed. Assuming a log-normal size distribution, the precipitate extinction spectra were calculated according to Mie theory within the electric and magnetic dipole and electric quadrupole approximation. A comparison with the experimental spectra identifies the precipitates and enables estimation of their sizes and total number density. In this investigation, both undoped and In-doped CdTe crystals grown from stoichiometric melts by vertical asymmetric Bridgman method were used. It was found that In doping, in general, suppresses Te precipitation. At high doping level (melt containing∼10¹⁹ In atoms cm⁻³), the formation of In₂Te₂ is also indicated. It is demonstrated that the Mie extinction analysis offers an, expedient method to rapidly analyze the precipitates in CdTe and in similar other wide gap materials in a nondestructive manner.     

Lossless Inductor Current Sensing Method With Improved Frequency Response

The lossless inductor current sensing method is well-known and is frequently applied in the measurement of output current in DC-DC converters due to its low cost and simplicity. This technique uses a low-pass filter that is matched to the inductance (L) and winding resistance to compensate for induced voltages due to the inductor. However, the waveform fidelity above the corner frequency of the inductor is generally poor due to large production tolerances and thermal drift. In this letter, we propose the use of a coupled sense winding, which increases the corner frequency of the sensing circuit by more than two orders of magnitude. We show, as an example, that for a 3.85 muH inductor the corner frequency of the measurement circuit can be increased from 36 Hz using the conventional approach to 5.8 kHz using the coupled sense winding method. Above the new corner frequency, a low-pass filter is still required but may now be constructed using a smaller capacitor and with improved high-frequency response.     

Dental health amongst 11-15-year-old children in Sevagram, Maharashtra

Although most subdural hematomas are considered to be venous in origin, they may also be of arterial origin. When subdural bleeding is due to the rupture of an intracranial aneurysm, most commonly at the middle cerebral or internal carotid arteries, the amount of subdural blood is usually small and of no clinical importance. We describe two patients with subdural hematomas secondary to rupture of an intracranial aneurysm, who needed prompt surgical treatment. The first patient had a left internal carotid artery aneurysm at the origin of the ophthalmic artery. In the second patient the aneurysm was at the anterior communicating artery and rebled into the subdural space directly through a right intraparenchymatous frontobasal hematoma. The most probable mechanism of subdural bleeding in our two patients was the existence of adhesions between the aneurysm and the arachnoid due to previous minor hemorrhages. The indication of cerebral angiography in a patient with subdural hematoma is based mainly upon the existence of meningeal signs, the presence of blood in more than one intracranial compartment or the rapid progression of bleeding.