Supporting the WWW in Wireless Communications Through Mobile Agents

Mobile computing is considered of major importance to the computing industry for the forthcoming years due to the progress in wireless mobile communications. We present a proxy-based architecture that manages to accelerate Web browsing in wireless Customer Premises Networks (CPN). We discuss how such an architecture is implemented using the IBM Aglets framework for mobile agents. The suggested architecture relies heavily on proxy caches – maintained in base stations – which are relocated to follow a roaming user in other control areas (clusters of cells). The cache management scheme involves relocation of full caches to the most-likely-to-be visited control areas, but also fractions of the cache to less-likely-to-be-visited neighbours. A movement prediction algorithm, based on a learning automaton, is used to determine the future location of the terminal. The discussed architecture components have been implemented as Aglets to allow for the efficient introduction of the service in a CPN infrastructure.     

Role of peripheral vision in the directional control of rapid aiming movements.

This study addresses the question of whether peripheral vision is involved in the control of hand trajectory direction during an aiming task performed at high speed. Ten adult subjects were required to aim at targets in various positions by making a punching movement with their hand. The experimental conditions were varied so that different parts of hand trajectory could be seen in the peripheral field. Two movement times were applied:     

Study on transient heat transfer through multilayer thermal insulation: Numerical analysis and experimental investigation

This paper reports on a numerical and experimental study of heat transfer phenomena through two different multilayer fibrous insulations for building applications. The investigated samples were composed of different layers of fibrous materials and aluminium foils, placed between one or two air gaps in the vertical dimension. An experimental apparatus (a guarded hot box) has been used to measure heat transfer through the samples, while a finite volume numerical model combined radiation/conduction heat transfer was developed to predict the temperature distribution and heat transfer in such insulation systems comprised of the materials separated by multiple reflective foils. The model takes into account the coupling between the solid conduction of the fibrous system and the gaseous conduction and radiation. The radiation heat transfer through the insulation system has been modelled via the two flux approximation. The numerical results were compared with the experimental data from the guarded hot box for model validation, as well as to assess the effectiveness of the reflective foils in changing the resistance of the insulations. The comparative verification of the model showed that the numerical results were consistent with the experimental data through the environmental conditions under examination.     

Resistivity index of fractional wettability porous media

The effects of fractional wettability on electrical resistivity index curves of porous media are investigated using pore network models. A bond percolation-and-fractal roughness model is used to simulate the oil/water drainage of the conventional porous plate method in pore networks composed of randomly distributed ‘strongly water-wet' and ‘strongly oil-wet' capillaries. Based on universal scaling laws of percolation quantities, effective medium approximation and fractal geometry, approximate analytic relationships are developed with respect to the dependence of the resistivity index, capillary pressure and saturation exponent on certain microstructural properties of the pore space and surface fractional wettability over the various water saturation regions. The simulated data are fitted to two-exponent power laws, which in turn are evaluated as macroscopic conceptual models of the resistivity index. At high water saturations, the saturation exponent becomes a strongly increasing function of the fraction of oil-wet pores when the value of this parameter exceeds the percolation threshold of the lattice network and oil percolates spontaneously through network joining clusters of oil-wet pores. At intermediate water saturations, the saturation exponent is a moderately increasing function of the fraction of oil-wet pores, whereas the slope of the capillary pressure curve remains almost unaltered to variations of wettability. At low water saturations, as the fraction of oil-wet pores becomes quite large, permanent trapping of water may occur with result that both the saturation exponent and the slope of the capillary pressure curve tend to infinity at the limit of irreducible water saturation. The exponents of the phenomenological models of the resistivity index change significantly with fractional wettability and are consistent with the values of the saturation exponent obtained with the approximate analytic relationships.     

Channel parameter estimation in mobile radio environments using theSAGE algorithm

This study investigates the application potential of the SAGE (space-alternating generalized expectation-maximization) algorithm to jointly estimate the relative delay, incidence azimuth, Doppler frequency, and complex amplitude of impinging waves in mobile radio environments. The performance, i.e., high-resolution ability, accuracy, and convergence rate of the scheme, is assessed in synthetic and real macro- and pico-cellular channels. The results indicate that the scheme overcomes the resolution limitation inherent to classical techniques like the Fourier or beam-forming methods. In particular, it is shown that waves which exhibit an arbitrarily small difference in azimuth can be easily separated as long as their delays or Doppler frequencies differ by a fraction of the intrinsic resolution of the measurement equipment. Two waves are claimed to be separated when the mean-squared estimation errors (MSEEs) of the estimates of their parameters are close to the corresponding Cramer-Rao lower bounds (CRLBs) derived in a scenario where only a single wave is impinging. The adverb easily means that the MSEEs rapidly approach the CLRBs, i.e., within less than 20 iteration cycles. Convergence of the log-likelihood sequence is achieved after approximately ten iteration cycles when the scheme is applied in real channels. In this use, the estimated dominant waves can be related to a scatterer/reflector in the propagation environment. The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling     

Small punch tests on steels for steam power plant(I)

Conventional test methods for measuring fracture toughness require the removal of large material samples from in-service component. However, recent developments of small punch test technique using miniature specimens have proved its usefulness and accuracy to evaluate the mechanical properties of components. Correlations have been obtained between mechanical characteristics determined from small punch test and uniaxial tensile test. Furthermore, the study showed that an appropriate empirical based-approach could be used to evaluate the Charpy-FATT of as-received and ex-service materials from small punch test.     

A stochastic model of the temporal and azimuthal dispersion seen atthe base station in outdoor propagation environments

A simple statistical model of azimuthal and temporal dispersion in mobile radio channels is proposed. The model includes the probability density function (PDF) of the delay and azimuth of the impinging waves as well as their expected power conditioned on the delay and azimuth. The statistical properties are extracted from macrocellular measurements conducted in a variety of urban environments. It is found that in typical urban environments the power azimuth spectrum (PAS) is accurately described by a Laplacian function, while a Gaussian PDF matches the azimuth PDF. Moreover, the power delay spectrum (PDS) and the delay PDF are accurately modeled by an exponential decaying function. In bad urban environments, channel dispersion is better characterized by a multicluster model, where the PAS and PDS are modeled as a sum of Laplacian functions and exponential decaying functions, respectively     

Sampling concerns in scanline algorithms

This paper investigates the problem of providing suitable interpolation for scanline algorithms. These algorithms are of interest, as they are parallelizable. A structure for analyzing the problem is given. The theory in regard to resampling is developed in the context of a scanline algorithm for image rotation. The theory is compared to results arrived at in practice. Alternative interpolation schemes are discussed, including the use of a cubic Hermite interpolator. The paper points to theoretical limitations of scanline algorithms