A General Space Vector PWM Algorithm for Multilevel Inverters, Including Operation in Overmodulation Range

This paper proposes a simple space vector pulsewidth modulation algorithm for a multilevel inverter for operation in the overmodulation range. The proposed scheme easily determines the location of the reference vector and calculates on-times. It uses a simple mapping to generate gating signals for the inverter. A five-level cascaded inverter is used to explain the scheme. The scheme can be easily extended to a n-level inverter. It is applicable to neutral point clamped topology as well. Experimental results are provided for five-level and seven-level cascaded inverters     

An Integer-Programming Approach to the Bicriteria Multicasting Problem in Optical Networks

We consider the problem of designing quality-of-service (QoS)-constrained routes for a set of multicast groups in an all-optical network. We present an integer goal programming formulation with the objectives of minimizing the cost of the multicast solution and minimizing the maximum link load of the network. Based on the structural properties of the problem, we develop a variable-fixing heuristic which is easy to implement, requires a modest amount of CPU time, and provides high-quality solutions. An extensive computational study is presented to justify our claims     

Space–Time/Space–Frequency/Space–Time–Frequency Block Coded MIMO-OFDM System with Equalizers in Quasi Static Mobile Radio Channels Using Higher Tap Order

In 4G broadband wireless communications, multiple transmit and receive antennas are used to form multiple input multiple output (MIMO) channels to increase the capacity (by a factor of the minimum number of transmit and receive antennas) and data rate. In this paper, the combination of MIMO technology and orthogonal frequency division multiplexing (OFDM) systems is analyzed for wideband transmission which mitigates the intersymbol interference and hence enhances system capacity. In MIMO-OFDM systems, the coding is done over space, time, and frequency domains to provide reliable and robust transmission in harsh wireless environment. Also, the performance of space time frequency (STF) coded MIMO-OFDM is analyzed with space time and space frequency coding as special cases. The maximum achievable diversity of STF coded MIMO-OFDM is analyzed and bit error rate performance improvement is verified by simulation results. Simulations are carried out in harsh wireless environment, whose effect is mitigated by using higher tap order channels. The complexity is resolved by employing sphere decoder at the receiver.     

An analytical drain current model for graded channel cylindrical/surrounding gate MOSFET

In the present paper, a comprehensive drain current model incorporating various effects such as drain-induced barrier lowering (DIBL), channel length modulation and impact ionization has been developed for graded channel cylindrical/surrounding gate MOSFET (GC CGT/SGT) and the expressions for transconductance and drain conductance have been obtained. It is shown that GC design leads to drain current enhancement, reduced output conductance and improved breakdown voltage. The effectiveness of GC design was examined by comparing uniformly doped (UD) devices with GC devices of various L₁/L₂ ratios and doping concentrations and it was found that GC devices offer superior characteristics as compared to the UD devices. The results so obtained have been compared with those obtained from 3D device simulator ATLAS and are found to be in good agreement.     

Enhanced photoluminescence from CdS nanocrystals encapsulated by PVP and SHMP

The effects of the stabilizing agent on the structural and luminescence properties of cadmium sulfide (CdS) nanocrystals have been investigated. Samples were prepared by chemical precipitation method using sodium hexametaphosphate (SHMP) and polyvinyl pyrrolidone (PVP). The structural and optical properties have been studied by X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. XRD patterns confirm the presence of cubic zinc blend crystal structure with space group F-43m. The results show the variation in crystallite size with change in surfactant. Blue shift in absorption edge as compared to bulk CdS is found. PL results represent broad and very intense red emission with smaller particle size due to modification of surface emitting states with surfactant.     

A method to design blended rolled edges for compact rangereflectors

A method to design blended rolled edges for compact range reflectors with arbitrary rim shape is presented. The reflectors may be center-fed or offset-fed. The method leads to rolled edges with minimal surface discontinuities. It is shown that the reflectors designed using the prescribed method can be defined analytically using simple expressions. A procedure to obtain optimum rolled parameters is also presented. The procedure leads to blended rolled edges that minimize the diffracted field emanating from the junction between the paraboloid and the rolled edge surface while satisfying certain constraints regarding the reflector size and the minimum operating frequency of the system     

Stochastic analysis of a multi-unit cold standby system working in orbit form

This paper considers the analysis of a single server n-similar unit system. Initially k(<n) units form an orbit which functions if one unit functions at a time and the remaining n − k units work as cold standbys. When a unit fails in the orbit it is instantaneously replaced by one of the standbys with the help of a perfect transfer switch. The system is said to fail when n − k + 1 units have failed. The distribution of time to failure and time to repair of a unit are negative exponential. Using the regenerative point technique several reliability characteristics are obtained to carry out the cost-benefit analysis.     

Computer communication networks—A study in the Indian context

Node location, topological optimization, capacity assignments, optimal cost determination using regression analysis, delay cost trade-offs and routing algorithm of a computer communication network in India are discussed.

The min-max criterion is used, which minimizes the time delay on every link. The optimum cost is calculated on the basis of a shortest-path algorithm, as length is found to be the only significant factor in determination of the cost as a result of regression analysis. As the traffic is low for the communication network under study, fixed routing strategy is found to be most appropriate.     

Lead-free solder reinforced with multiwalled carbon nanotubes

In this study, varying weight percentages of multiwalled carbon nanotubes were successfully incorporated into 95.8Sn-3.5Ag-0.7Cu solder to synthesize novel lead-free composite solders. The composite solders were synthesized using a powder metallurgy route consisting of blending, compaction, sintering, and extrusion. The extruded materials were then characterized for their physical, thermal, and mechanical properties. With the addition of increasing weight percentage of carbon nanotubes, the composite solders experienced a corresponding decrease in density values and an improvement in wetting properties. The melting temperatures of the composite solders were found to be unchanged with additions of carbon nanotubes. However, improvements in the mechanical properties, in terms of microhardness and tensile properties, were observed with increasing weight percentages of carbon nanotubes.     

Terahertz Absorption of Nematic Liquid Crystals

We present the first systematic study of cyanobiphenyls (CBs) and the phenylcyclohexanes in the range between 50 cm^-1 (1.5 THz) and 500 cm^-1 (15 THz). The impact of the alkyl chain length and of variations in the core structure on the spectrum is investigated using liquid crystals from the cyanobiphenyl and phenylcyclohexane families. Our measurements are supported by calculations based on density functional theory. This enables us to shine light on the vibrational dynamics of liquid crystal molecules in the terahertz frequency range.