Generalized Mathematical Modeling of N-Phase Power Systems

ABSTRACT

The analysis of the polyphase power systems is normally carried out by assuming a perfectly balanced system. However, power system is generally unbalanced because of various reasons. Therefore, it is desirable to analyse the power system taking imbalances into account. Hence, it is necessary to develop mathematical formulations of various components of the power systems in phasor co-ordinates. In this paper, detailed mathematical models for general n-phase components have been developed. These models will be useful for conducting the steady state as well as the transient analysis of the multiphase systems in phasor co-ordinates. Finally, the paper concludes with the discussion on the findings based upon these models.     

Less common causes of carpal tunnel syndrome

A new DRB3*02 allele (DRB3*0207) was detected in a female Luxembourg Caucasian blood donor by sequence-based typing. The new allele differs from DRB3*0202 by two substitutions in codon 57 resulting in an amino acid change from a charged aspartic acid to a neutral valine. This is the first example of a DRB3 allele pair differing only at codon 57.     

Synthesis,structure and characterization of ceramic Ca4Bi2Ti4Nb6O30

The polycrystalline samples of Ca₄Bi₂Ti₄Nb₆O₃₀ (herein designated CBTN) were synthesized by the conventional ceramic method. Preliminary X-ray structural study of the compound showed the formation of a single phase solid solution having orthorhombic structure in the paraelectric phase. Measurements of the dielectric constant (ε) and dielectric loss (tan δ) as a function of temperature (−180–200°C) at 1 kHz and 10 kHz and also as a function of frequency (10² Hz to 10⁴ Hz) at five different temperatures [−180°C, −40°C, − 10°C 26°C (room temperature) and 75°C] have shown a dielectric anomaly and a phase transition at − 13 ±1°C in CBTN.     

High-Performance Software Protection Using Reconfigurable Architectures

One of the key problems facing the computer industry today is ensuring the integrity of end-user applications and data. Researchers in the relatively new field of software protection investigate the development and evaluation of controls that prevent the unauthorized modification or use of system software. While many previously developed protection schemes have provided a strong level of security, their overall effectiveness has been hindered by a lack of transparency to the user in terms of performance overhead. Other approaches take to the opposite extreme and sacrifice security for the sake of this transparency. In this work we present an architecture for software protection that provides for a high level of both security and user transparency by utilizing field programmable gate array (FPGA) technology as the main protection mechanism. We demonstrate that by relying on FPGA technology, this approach can accelerate the execution of programs in a cryptographic environment, while maintaining the flexibility through reprogramming to carry out any compiler-driven protections that may be application-specific.     

Structural,SEM and dielectric properties of PLZT

Powder of lanthanum-modified lead zirconate titanate (PLZT) with the composition La/Zr/Ti=8/65/35, was synthesized from aqueous nitrate solutions. A single-phase PLZT was obtained at ∼550 °C. The reactivity of the powder during low-temperature heating was determined using X-ray diffraction and various thermal analysis techniques. The dielectric properties of the compound were also studied at 1 and 10 kHz frequency from room temperature to 200 °C. Diffuse phase transition (DPT) in the material was observed around 136 °C at 1 kHz. An increase in peak-permittivity temperature (i.e. the transition temperature) with increasing frequency (a characteristic of relaxor ferroelectrics) was also observed.     

Interpretation of Resistivity of Nd1.85Ce0.15CuO4: Electron–Phonon Mechanism

The temperature-dependent normal state resistivity of single crystal Nd_1.85Ce_0.15CuO_{4 ? δ} is theoretically analyzed within the framework of classical electron–phonon i.e., Bloch-Gruneisen model of resistivity. For the reason of inherent acoustic (low frequency) phonons (ω_ac) as well as high-frequency optical phonons (ω_op), the contributions to the resistivity were first derived. The optical phonons of the oxygen breathing mode yields a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. Estimated contribution to in-plane resistivity by considering both phonons, i.e., ω_ac and ω_op, along with the zero-temperature-limited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range [25 ≤ T ≤ 300]. Quadratic temperature dependence of ρ_diff. = [ρ_exp. ? {ρ₀ + ρ_e–ph (=ρ_ac + ρ_op)}] is understood in terms of 3D electron–electron inelastic scattering. The comparison of single crystal experimental data appears favorable with the present analysis.     

A Practical Implementation of Silicon Microchannel Coolers for High Power Chips

This paper describes a practical implementation of a single-phase Si microchannel cooler designed for cooling very high power chips such as microprocessors. Through the use of multiple heat exchanger zones and optimized cooler fin designs, a unit thermal resistance 10.5 C-mm² /W from the cooler surface to the inlet water was demonstrated with a fluid pressure drop of <35kPa. Further, cooling of a thermal test chip with a microchannel cooler bonded to it packaged in a single chip module was also demonstrated for a chip power density greater than 300W/cm². Coolers of this design should be able to cool chips with average power densities of 400W/cm² or more     

Analysis of Heat Transfer in the Corroding Sidewall of a Furnace

A mathematical formulation is developed to calculate the rate of corrosion of a refractory sidewall of a furnace in the presence of free convection in the melt. The free-convection phenomena considered are caused by the dependence of the melt density on its temperature and composition. The formulation involves the statement of equations for heat conduction in the refractory wall and movement of the solid-melt interface. The governing equations and the boundary conditions are transformed into nondimensional forms, and the dimensionless parameters which characterize corrosion in the presence of free convection are identified. The equations are solved by using coordinate transformation and a finite-difference method. Calculated results are presented on the shape of the solid-melt interface, temperature distribution in the corroding wall, and the amount of cooling at the outside surface of the wall. The results show how free convection in the melt interacts with heat conduction in a refractory wall to determine the rate of corrosion of the wall.     

Antioxidant and anticholinesterase evaluation of selected Turkish Salvia species

Since Salvia species (Lamiaceae) have been recorded to be used against memory loss in European folk medicine, we herein examined in vitro anticholinesterase and antioxidant activities of 56 extracts prepared with petroleum ether, chloroform, ethyl acetate and methanol obtained from 14 Salvia species (Salvia albimaculata Hedge and Hub, Salvia aucheri Bentham var. canescens Boiss and Heldr, Salvia candidissima Vahl. ssp. occidentalis, Salvia ceratophylla L., Salvia cryptantha Montbret and Bentham, Salvia cyanescens Boiss and Bal., Salvia frigida Boiss, Salvia forskahlei L., Salvia halophilaHedge, Salvia migrostegia Boiss and Bal., Salvia multicaulis Vahl., Salvia sclarea L., Salvia syriaca L., Salvia verticillata L. ssp. amasiaca) growing in Turkey. The antioxidant activities were assessed by both chemical and enzymatic methods against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging and xanthine/xanthine oxidase (XO) system generated superoxide anion radical inhibition. Anticholinesterase effect of the extracts was tested against both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at concentrations of 0.2 and 1 mg/ml using a microplate-reader assay based on the Ellman method. Most of the extracts did not show any activity against AChE at 0.2 mg/ml, while the chloroform extracts had noticeable inhibition against BChE between 47.7% and 74.7%. The most active extracts at 1 mg/ml for AChE inhibition were observed to be petroleum ether extract of Salvia albimaculata (89.4%) and chloroform extract of Salvia cyanescens (80.2%), whereas ethyl acetate extracts of Salvia frigida and Salvia migrostegia, chloroform extracts of Salvia candidissima ssp. occidentalis and Salvia ceratophylla, as well as petroleum ether extract of Salvia cyanescens were found to inhibit potently BChE (92.2%, 89.6%, 91.1%, 91.3%, and 91.8%, respectively). Particularly, the ethyl acetate and methanol extracts were observed to be highly active against both DPPH and XO. Our data indicates that nonpolar extracts of Salvia species for anticholinesterase activity and the polar extracts for antioxidant activity are worth further phytochemical evaluation for identifying their active components.