Communication channel equalization using complex-valued minimalradial basis function neural networks

A complex radial basis function neural network is proposed for equalization of quadrature amplitude modulation (QAM) signals in communication channels. The network utilizes a sequential learning algorithm referred to as complex minimal resource allocation network (CMRAN) and is an extension of the MRAN algorithm originally developed for online learning in real-valued radial basis function (RBF) networks. CMRAN has the ability to grow and prune the (complex) RBF network's hidden neurons to ensure a parsimonious network structure. The performance of the CMRAN equalizer for nonlinear channel equalization problems has been evaluated by comparing it with the functional link artificial neural network (FLANN) equalizer of J.C. Patra et al. (1999) and the Gaussian stochastic gradient (SG) RBF equalizer of I. Cha and S. Kassam (1995). The results clearly show that CMRANs performance is superior in terms of symbol error rates and network complexity.     

Front-to-back ratio of paraboloidal reflectors

An analysis is presented which uses the uniform geometrical theory of diffraction for determining the near fields diffracted by a paraboloid either with or without a conical flange attached to its circular rim when an axially propagated plane wave is incident on the concave or convex portion of the paraboloidal reflector. The field correlation theorem is used to determine the power coupled by a prime focus feed associated with the paraboloid which is being illuminated by a uniform plane wave. Based on this analysis, the front-to-back ratio of unflanged and flanged paraboloids is computed. Computed results show satisfactory agreement with the available measured as well as computed results based on alternative procedures. The variation in the on-axis gain on a prime-focus reflector when the feed is displaced from the focus is studied. Typical computed results are presented and compared with the available measured data. Computed results on the front-to-back ratio of paraboloids (flanged or unflanged) illuminated by a PFF whose radiated field exhibits phase variation over a constant radius are also presented     

An experimental verification of nonlocal fracture criterion

By using a nonlocal field theory, Eringer et al. [6] obtained a finite solution for the stress at the tip of a sharp crack. This solution permitted the development of a nonlocal fracture criterion for crystalline materials that is given in terms of atomic distance and theoretical cohesive strength.

The nonlocal fracture criterion is generalized for application to real materials by the introduction of a characteristic dimension (a measure of the size of the internal structures). Particleboard, a wood-based composite with controllable internal characteristics (particle dimensions and amount of resin), is used to substantiate the nonlocal fracture criterion.     

Schwa-Deletion in Hindi Text-to-Speech Synthesis

We describe the phenomenon of schwa-deletion in Hindi and how it is handled in the pronunciation component of a multilingual concatenative text-to-speech system. Each of the consonants in written Hindi is associated with an inherent schwa vowel which is not represented in the orthography. For instance, the Hindi word pronounced as [namak] (salt) is represented in the orthography using the consonantal characters for [n], [m], and [k]. Two main factors complicate the issue of schwa pronunciation in Hindi. First, not every schwa following a consonant is pronounced within the word. Second, in multimorphemic words, the presence of a morpheme boundary can block schwa deletion where it might otherwise occur. We propose a model for schwa-deletion which combines a general purpose schwa-deletion rule proposed in the linguistics literature (Ohala, 1983), with additional morphological analysis necessitated by the high frequency of compounds in our database. The system is implemented in the framework of finite-state transducer technology.     

Double stripe reconstruction of the Pt(111) surface

We have studied the reconstruction of the Pt(111) surface theoretically, using a 2D generalization of the Frenkel-Kontorova model. The parameters in the model are obtained by performingab initio density functional theory calculations. The Pt(111) surface does not reconstruct under normal conditions but experiments have shown that there are two ways to induce the reconstruction: by increasing the temperature, or by depositing adatoms on the surface. The basic motif of this reconstruction is a ‘double stripers with an increased surface density and alternatinghcp andfcc domains, arranged to form a honeycomb pattern with a very large repeat distance of 100–300 Å. In this paper, we have studied the ‘double stripe’ reconstruction of the Pt(111) surface. In agreement with experiment, we find that it is favourable for the surface to reconstruct in the presence of adatoms, but not otherwise.     

Finite-SNR diversity-multiplexing tradeoffs in fading relay channels

We analyze the diversity-multiplexing tradeoff in a fading relay channel at finite signal-to-noise ratios (SNRs). In this framework, the rate adaptation policy is such that the target system data rate is a multiple of the capacity of an additive white Gaussian noise (AWGN) channel. The proportionality constant determines how aggressively the system scales the data rate and can be interpreted as a finite-SNR multiplexing gain. The diversity gain is given by the negative slope of the outage probability with respect to the SNR. Finite-SNR diversity performance is estimated using a constrained max-flow min-cut upper bound on the relay channel capacity. Moreover, the finite-SNR diversity-multiplexing tradeoff is characterized for three practical decode and forward half-duplex cooperative protocols with different amounts of broadcasting and simultaneous reception. For each configuration, system performance is computed as a function of SNR under a system-wide power constraint on the source and relay transmissions. Our analysis yields the following findings; (i) improved multiplexing performance can be achieved at any SNR by allowing the source to transmit constantly, (ii) both broadcasting and simultaneous reception are desirable in half-duplex relay cooperation for superior diversity-multiplexing performance, and (iii) the diversity-multiplexing tradeoff at finite-SNR is impacted by the power partitioning between the source and the relay terminals. Finally, we verify our analytical results by numerical simulations     

Heat and mass transfer to spheres in high-temperature surroundings

An experimental investigation of the combined natural and forced convective effects was carried out which involved the measurement of the rate of evaporation of water from porous stationary spheres (1/4, 3/8 and 1/2-in. in diameter) under steady conditions in an electrically-heated stainless steel chamber. The spheres were suspended in a stream of super-heated steam at atmospheres ranging from 50 to 1000°K. Both the opposing and aiding flow cases were investigated. The Reynolds number varied from 0 to 1489 and the turbulence intensity was less than 1%. The parameter [(Gr)/(Re²)] was found to be of fundamental importance in correlating the results. The rates of heat transfer in the mixed flow region for the opposing flow case was higher than for aiding flow. The transition between the two mechanisms was found to be gradual but very complex in the case of opposing flow.     

Simulation of polymer systems

The present paper describes an algorithm which can generate, even on a small computer, arbitrarily long polymer chains, making sure that the configurations generated do not suffer from boundary effects. This has been achieved by employing the concept of a window, which is an analogue of virtual memory scheme. The algorithm has been tested for the case of dilute polymer solution.     

Parameter Estimation in Water Distribution Networks

Estimation of pipe roughness coefficients is an important task to be carried out before any water distribution network model is used for online applications such as monitoring and control. In this study, a combined state and parameter estimation model for water distribution networks is presented. Typically, estimation of roughness coefficient for each individual pipe is not possible due to non-availability of sufficient number of measurements. In order to address this problem, a formal procedure based on K-means clustering algorithm is proposed for grouping the pipes which are likely to have the same roughness characteristics. Also, graph-theoretic concepts are used to reduce the dimensionality of the problem and thereby achieve significant computational efficiency. The performance of the proposed model is demonstrated on a realistic urban water distribution network.     

Exploratory analysis of factors influencing performance dynamics oftelecommuters and traditional office workers

Advances in information technology are enabling the formation of new work arrangements, where employees may perform work activities at any location, at any time. This includes remote locations such as an employee's home or a satellite office. When employees work remotely, there are fewer opportunities for face-to-face (FTF) communication, and more communication occurs in non-FTF modes. Communication is a crucial component of the work process and can affect the performance of work activities. Clearly, the resources necessary to provide an effective work environment are different for traditional and remote workers. It is thus critical to identify and study the dynamics of this environment to foster effective job performance. The authors are particularly interested in the use of communication to coordinate work activities and the resulting effect on performance. We investigate the difference in use of formal, informal, and electronic coordination techniques in the remote and traditional work environments. We also investigate the influence of job characteristics and information technology (IT) factors on job performance in both work environments. The study was conducted through a survey of a large number of telecommuters and a control group of nontelecommuters in eight firms in Atlanta (USA). We use inductive learning to identify patterns of behavior present in the data. Results from the study indicate communication needs in this work environment are much more complex than previously recognized. The research indicates that the method of use of communication channels and the communication partner must be considered, in addition to the work environment of the individual to provide an atmosphere conducive to good performance. We also found that job characteristics and IT factors had differing effects on the groups which should be explored further