Tight error bounds for space-time orthogonal block codes under slow Rayleigh flat fading

The performance of space-time orthogonal block (STOB) codes over slow Rayleigh fading channels and maximum-likelihood (ML) decoding is investigated. Two Bonferroni-type bounds (one upper bound and one lower bound) for the symbol error rate (SER) and bit error rate (BER) of the system are obtained. The bounds are expressed in terms of the pairwise error probabilities (PEPs) and the two-dimensional pairwise error probabilities (2-D PEPs) of the transmitted symbols. Furthermore, the bounds can be efficiently evaluated and they hold for arbitrary (nonstandard) signaling schemes and mappings. Numerical results demonstrate that the bounds are very accurate in estimating the performance of STOB codes. In particular, the upper and lower bounds often coincide even at low channel signal-to-noise ratios, large constellation sizes, and large diversity orders.     

New moment-rotation equation for welded steel beam-to-column connections

A three-parameter tangent inverse equation is generically proposed for the non-linear moment-rotation (M-θ) relationship of semi-rigid steel beam-to-column connections. The parameters are the initial stiffness, the plastic stiffness, and a reference moment. Two commonly used welded moment connections are picked up for moment-rotation calculation and comparison between the results of the proposed model and those of a detailed nonlinear finite elements modeling. Semi-analytical equations are proposed for calculating the parameters containing basic factors affecting behavior of the connections. The coefficients of the equations are computed based on a data bank developed in this study using the finite element method. A large number of finite elements models covering the whole range of common dimensions of the above connections are analyzed. Accuracy of the finite element model is verified on the basis of the available test results from previous studies. Tensile tests for determination of material properties of weld to be used in the modeling are conducted. Comparison between the results of the semi-analytical equations and the finite element models shows that the proposed model is able to estimate the moment-rotation curves of the welded beam-to-column connections with very good accuracy.     

Dynamic response of adjacent structures under spatially variable seismic waves

In this paper the dynamic response of a system of two structures placed adjacent to each other is studied. The force on the system consists of earthquake loading applying for its spatial variability over short distances. The spatially variable ground motion is defined and explored by two different approaches. First, the deterministic approach accounting only for effects of wave passage of surface waves and inclined body waves, and second, the stochastic (random) approach considering also degree of coherency between motions at every two points of the ground surface as a factor. Effects of the ground motions identified as above on the response of the system are examined assuming a harmonic excitation and considering type of the wave and angle of incidence of the body waves. It is shown that resonance frequency increases with closeness of structures. Moreover, for some cases depending on the distance between the adjacent structures, the structural response increases. The random approach gives more satisfactory results in this comparison study.     

Experimental Studies on a Combined Damper for Repairable Steel Moment Connections

Steel structures are among the building systems extensively used in most countries. They have been the subject of numerous studies with the aim of optimizing their performance under vertical and lateral loads. One important issue in this regard is reparability of connection areas under severe earthquakes, i.e., developing connections easy to be restored to their initial state. In this paper a passive control system recently developed by the authors is studied further and enhanced in configuration and behavior. The developed system is a repairable part of the connection zone in a steel moment frame absorbing the seismic damage and producing hysteretic damping. This damper is a rubber-steel core added beneath the beam-to-column connection. The steel bolts core provide for the hysteretic damping and the rubber layer contributes the restoring force. Results of several cyclic tests by varying different parameters of the damper are presented and discussed in this paper.     

A method for rapid estimation of dynamic coupling and spectral responses of connected adjacent structures

A simple method is presented for estimation of dynamic coupling and maximum seismic responses of structures connected through links. The purpose is preparing a simple measure for distinguishing the cases where two connected structures interfere in the response of each individual structure and incorporating such cases in spectral analysis. First, each structure is analysed independently, and the natural modes with considerable interference with the other structure are identified. Then the spectral responses corresponding to such modes are modified in modal space. It is shown that the proposed method can estimate the spectral responses of adjacent systems with good accuracy. Copyright © 2015 John Wiley & Sons, Ltd.     

An approximate method for separated spectral analysis of connected buildings with added damping

The problem of determining maximum seismic responses, or spectral analysis, of connected adjacent structures is studied in this research. The goal of the study is twofold. First, determining when the dynamic coupling is important in such a problem and, second, establishing how to analyze each of the two structures separately when coupling is important. For tall buildings in many cases, the connecting link is intentionally accommodated with an added damping to suppress the lateral displacements. Therefore, effect of the localized damping is also accounted for in the analysis. Using essentials of modal analysis, a criterion is developed for estimation of the dynamic coupling of the two adjacent structures. Also, a procedure is developed for separated analysis of each structure incorporating the stiffness and inertial effects of the adjacent structures when coupling is important. The representative examples confirm good accuracy of the presented method.     

An Efficient Algorithmic Lower Bound for the Error Rate of Linear Block Codes

We present an efficient algorithmic lower bound for the block error rate of linear binary block codes under soft maximum-likelihood decoding over binary phase-shift keying modulated additive white Gaussian noise channels. We cast the problem of finding a lower bound on the probability of a union as an optimization problem that seeks to find the subset that maximizes a recent lower bound - due to Kuai, Alajaji, and Takahara - that we will refer to as the KAT bound. The improved bound, which is denoted by LB-s, is asymptotically tight [as the signal-to-noise ratio (SNR) grows to infinity] and depends only on the code's weight enumeration function for its calculation. The use of a subset of the codebook to evaluate the LB-s lower bound not only significantly reduces computational complexity, but also tightens the bound specially at low SNRs. Numerical results for binary block codes indicate that at high SNRs, the LB-s bound is tighter than other recent lower bounds in the literature, which comprise the lower bound due to Seguin, the KAT bound (evaluated on the entire codebook), and the dot-product and norm bounds due to Cohen and Merhav.     

Segmentation of DNA microarray images using an adaptive graph-based method

Microarray is a powerful tool for simultaneous study of the behaviour of thousands of genes through analysis of produced images. The correct segmentation of each `spot` of the microarray image is a critical step in the analysis of the results of an experiment. A graph-based method is proposed which automatically performs the segmentation. The performance of the algorithm is tested both on real and simulated images. The proposed algorithm successfully detected spots of different sizes and shapes under the presence of variable noise levels. The simulation results proved that the suggested approach has high segmentation accuracy.     

Probabilistic seismic demand model and fragility estimates for critical failure modes of un-anchored steel storage tanks in petroleum complexes

Estimation of seismic vulnerability of existing equipment in petroleum complexes, traditionally has been done by using general fragility curves which have been developed for a group of equipment without considering their physical specifications. Although these kinds of fragility are suitable for preparing emergency plans and governmental decision making, for the sake of seismic upgrading of existing facilities, specific equipment fragilities are needed. In this paper un-anchored steel storage tanks, which is among the most vulnerable equipment in petroleum facilities, are selected for a case study. Probabilistic demand models for Elephant Foot Buckling (EFB) and welding failure at the connection between the bottom plate and shell are developed based on FEM analytical data, and a Bayesian updating rule is used to assess the unknown demand model parameters. The approach properly accounts for both aleatory and epistemic uncertainties. Developed probabilistic demand models are used to estimate the fragility of critical failure modes of selected tanks and real world data. The approach can be applied for other failure modes and other equipment, as well.