Fast estimation of outage probabilities in MIMO channels

Fast estimation methods for small outage probabilities of signaling in fading multiple-input multiple-output (MIMO) channels are developed. Communication over such channels is of much current interest, and quick and accurate methods for estimating outage capacities are needed. The methods described herein use adaptive importance sampling (IS) techniques as developed in a series of recent publications. Fast algorithms are provided for evaluating "nonergodic" capacities of Rayleigh fading MIMO channels. The methodology can be extended to more general models. Numerical results on outage capacity are provided, and these extend and complement known results in the literature.     

Failure analysis of air pre-heater tubes of a petrochemicals plant

Heat resistant alloy tubes used in the higher temperature range of 1150–1273 K depends on the protective scale integrity for prevention of corrosion induced premature failures in a mixed gas environment with potential corrodents for oxidation, carburization and sulphidation attack. Cast HK40+Nb alloy tubes of an air pre-heater unit of a petrochemical industry failed prematurely after 13,000 h in service. The unit used smoke gas containing gaseous corrodents that could cause oxidation/sulphidation/carburization type of attack. Failed parts showed crack/punctures below the corrosion product filled pits. The crack occurred in the fully carburized zone present at the thinned out centre of the pit. Factors like excessive temperature cycling, overheating, presence of impurities either in the pre-heating gas mixture or that got introduced while in operation were found to be the reasons for breach of protective scale integrity leading to unwarranted corrosion attack resulting in thinning of tube material and internal corrosion penetration which finally led to premature failure.     

Modeling Steel Frame Buildings in Three Dimensions. II: Elastofiber Beam Element and Examples

This is the second of two papers describing a procedure for the three-dimensional nonlinear time-history analysis of steel-framed buildings. An overview of the procedure and the theory for the panel zone element and the plastic hinge beam element are presented in part I. In this paper, the theory for an efficient new element for modeling beams and columns in steel frames called the elastofiber element is presented, along with four illustrative examples. The elastofiber beam element is divided into three segments—two end nonlinear segments and an interior elastic segment. The cross sections of the end segments are subdivided into fibers. Associated with each fiber is a nonlinear hysteretic stress-strain law for axial stress and strain. This accounts for coupling of nonlinear material behavior between bending about the major and minor axes of the cross section and axial deformation. Examples presented include large deflection of an elastic cantilever beam, cyclic loading of a cantilever beam, pushover analysis of a 20-story steel moment-frame building to collapse, and strong ground motion analysis of a two-story unsymmetric steel moment-frame building.     

Effects of curtailment on an admissions model for a graduate management program.

Developed 2 admissions models to predict future academic performance of graduate management students. The 1st model was based on 40 students who were admitted and enrolled in the program and was uncorrected for curtailment. The 2nd model was developed from the total applicant population of 222 students after curtailment correction. The corrected model demonstrated higher predictive validity than the uncorrected model for 2 future classes of students. Furthermore, different predictors entered each model, affecting the beta weights, validities of predictors, and the total amount of variance explained by the models. A factor analysis and an analysis of admissions decisions offer additional support for the curtailment-corrected model in selecting students with high academic potential. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of changes in the atmosphere on solar insolation

A review of the nature of solar radiation and the spectral distribution of its energy is presented. The attenuation of solar radiation by scattering and absorption and the effects of atmospheric pollutants on radiation attenuation with an estimate of the long-term effects of pollutants is discussed.