Observer-based stator-flux-oriented vector control ofcycloconverter-fed synchronous motor drive

A six-pulse noncirculating-current cycloconverter-fed synchronous motor with stator-flux-oriented vector control for high-power and low-speed applications is discussed here. Vector control is achieved by stator flux estimation through a novel closed-loop reduced-order observer exhibiting stable speed regulation. Variable displacement factor operation is incorporated to keep both the system current continuous and the system utilization optimum. A simple method is used in designing the controller for armature current regulation with good performance. A generalized digital simulation of the drive system is made, and the simulation results are validated by a low-cost laboratory implementation of the drive with a 386DX PC-based system with 80387 floating point support     

An on-line relay coordination algorithm for adaptive protectionusing linear programming technique

An adaptive system for protecting a distribution network should determine and implement relay settings that are most appropriate for the prevailing state of the power system. This paper presents a technique for determining coordinated relay settings. The technique uses the Simplex two-phase method; Phase I determines whether the constraints selected for illustrating the conditionality between primary and back up relays are feasible, and Phase II finds the optimal relay settings. A looped distribution system, protected by directional overcurrent relays, was used for testing the technique. The tests were conducted in a laboratory environment; some results from those tests are reported in the paper     

Initial oxidation of cobalt

The initial oxidation of pure cobalt has been studied by a manometric method in the range 320 to 520° C for 1 to 15 min using purified dry oxygen at 7. 6 cm of mercury. The oxide thickness varies from 400 Å at the lowest to 5000 Å at the highest temperatures. Oxidation follows a direct logarithmic law and is independent of oxygen pressure. A typical Arrhenius plot shows an anomaly at the allotropie change point ( 386° C) of cobalt, although the activation energies of oxidation of both the allotropes are very much the same. The modified model of Uhlig's mechanism on logarithmic oxidation [7] applies in the present case.     

Structure of the four quasiparticle band in 84Sr

We have been experienced a rare case of large supratentorial neuroepithelial tumor with a subdural cyst originated from the left fronto-parietal lobe in a 14-month-old boy. The tumor was characterized by its voluminous size, a leptomeningeal growth pattern with intense desmoplasia and divergent astrocytic and ganglionic differentiation. Schwann cell differentiation and melanocytes were also minutely demonstrated. These histological findings are characteristic of desmoplastic infantile gangliogliomas, reported by VandenBerg et al in 1987. And this tumor tissue architecture strongly suggests the hamartomatous nature, rather than the ordinary neoplastic lesion.     

Studies on the solvation of amino acids in ethanol and water mixtures

In order to look at the effects of different mixed solvents on amino acids, the compressibility values and the solvation numbers of different amino acids (glycine, alanine, proline, valine, histidine and arginine) in different ethanol—water mixtures have been determined using an ultrasonic interferometer. The changes in the compressibility values and solvation numbers of the amino acids with decreasing water concentration indicate some interesting features and can be explained on the basis of a decrease in the number of solvent molecules, structural rearrangement and preferential solvation of Zwitterions.     

The effects of annealing on the switching characteristics of anion-implanted silicon MESFET

The gate-source and gate-drain capacitances and the drain-source resistance are calculated in the region below pinchoff in the postimplanted annealed condition. It is observed that the capacitances decrease and the resistance increases compared to the case where diffusion of impurity ions due to annealing is not considered. P, B, As, Sb, Ga, and Al dopants are used for the calculation. The delay time is found to be mostly unaffected by annealing. The capacitances in the region above pinchoff show an increase as a result of annealing in the enhancement device compared to the case when diffusion is not taken into account. These capacitances are mainly due to the sidewalls of the space-charge region and are dependent on the threshold voltage, which decreases at higher anneal temperatures in the enhancement mode     

Radiation damage effects in CMR manganite materials

Polycrystalline La_0.5Pb_0.5Mn_1−xCr_xO₃ (x = 0.075 and 0.15) samples have been irradiated with 50 MeV Li³⁺ ions with different fluences and the effects on the transport properties have been studied by means of the temperature and magnetic field dependent resistivity measurements. Due to Li³⁺ ion irradiation, the resistivity increases and the metal–insulator transition temperature (T_mi) decreases. At low temperatures (below T_mi), a dominant contribution of the electron–magnon scattering process is observed for all the irradiated and unirradiated samples. The low temperature resistivity behavior as well as the magnetoresistance is modified due to irradiation. The changes in the magnetotransport properties due to irradiation have been compared with the changes caused due to Mn site substitution.