Space-Variant Approaches to Recovery of Depth from Defocused Images

The recovery of depth from defocused images involves calculating the depth of various points in a scene by modeling the effect that the focal parameters of the camera have on images acquired with a small depth of field. In the approach to depth from defocus (DFD), previous methods assume the depth to be constant over fairly large local regions and estimate the depth through inverse filtering by considering the system to be shift-invariant over those local regions. But a subimage when analyzed in isolation introduces errors in the estimate of the depth. In this paper, we propose two new approaches for estimating the depth from defocused images. The first approach proposed here models the DFD system as a block shift-variant one and incorporates the interaction of blur among neighboring subimages in an attempt to improve the estimate of the depth. The second approach looks at the depth from defocus problem in the space-frequency representation framework. In particular, the complex spectrogram and the Wigner distribution are shown to be likely candidates for recovering the depth from defocused images. The performances of the proposed methods are tested on both synthetic and real images. The proposed methods yield good results and the quality of the estimates obtained using these methods is compared with the existing method.     

An MLP-based texture segmentation method without selecting a feature set

A texture segmentation technique which employs a multilayer perceptron (MLP) and does not consider the selection of features is presented in this paper. Thus, users can avoid selection and computation of the feature set and hence real-time segmentation may be possible. The technique apparently works in a fashion similar to our visual system whereby we do not consciously compute any feature for texture discrimination. A detailed study has been made for the selection of the network size. A newly proposed variant of the back-propagation algorithm has been used for more efficient training of the network. An edge-preserving noise-smoothing approach has been proposed to remove noise from the segmented image.     

Cost optimization of maintenance scheduling for a system withassured reliability

Systems which have to work at or below a maximum acceptable failure rate should be maintained at predetermined points such that the failure rate does not exceed the acceptable level. As the system ages, the post-maintenance failure rate of the system drops to some newer one, unless the system has been replaced, but does not restore the system to the original state. A branching algorithm with effective dominance rules that curtail the number of nodes created is presented; this algorithm determines the number of maintenance interventions before each replacement in order to minimize the total cost over a finite time horizon. The model considers inflationary trends. A numerical example and computational experience are presented. The authors treat the maintenance cost as constant and successive simple-maintenance intervals as decreasing. Though the cost/maintenance is assumed constant, any increasing maintenance cost function could be incorporated. The optimum solutions depend on the constant improvement factor, first simple-maintenance point, rate of increase in acquisition cost, maintenance cost factor, and planning period     

Vibration of clamped moderately thick general cross-ply plates using a generalized Navier approach

A hitherto unavailable analytical solution to the free vibration problem of general cross-ply laminated rigidly clamped rectangular plates, incorporating first-order shear deformation, and rotatory and in-plane inertias into the formulation, is presented. A recently developed boundary continuous displacement-based generalized Navier solution technique is used to solve the five highly coupled linear second-order partial differential equations with constant coefficients, and the associated geometric boundary conditions. The assumed solution functions are in the form of double Fourier series, which satisfy the rigidly clamped boundary conditions a priori in a manner similar to the conventional Navier method. Convergence characteristics of the natural frequencies of both symmetric and antisymmetric cross-ply plates are numerically established. Other numerical results presented herein include (i) comparison with the corresponding available first-order shear deformation theory-based Galerkin and classical lamination theory-based boundary-discontinuous analytical solutions, and (ii) study of the effects of thickness and aspect ratio on the natural frequencies.     

Parkinson's disease in populations of African origin: a review

Several studies have reported a lower prevalence of Parkinson's disease (PD) in populations of African origin than in populations of European origin, raising the possibility that the former are protected against PD. However, the confounding effects of low case ascertainment and high selective mortality on PD prevalence estimates in populations of African origin cannot be ruled out at this time. One hypothesis consistent with available data is that populations of African origin are vulnerable to vascular parkinsonism, which is associated with high mortality.     

Studies on the electrical conductivity and galvanomagnetic characteristics of short carbon fibre filled thermoplastic elastomers

The electrical resistivity of short carbon fibre filled thermoplastic elastomers based on natural rubber-high density polyethylene (NR-HDPE) blend and styrene-isoprene-styrene (S-I-S) block copolymer has been studied by varying the concentration of fibre from the 0 to 40 phr level. A sharp drop in resistivity is observed in both cases after a critical concentration of fibre is reached, with the S-I-S system showing lower values of critical concentration. At higher concentrations, experimental values of the electrical conductivity agreed reasonably well with the calculated values from a theory based on the probability of formation of a conductive network. The effect of temperature on the resistivity of the composites has also been investigated in a temperature range of 27–120 °C and 27–90 °C for the NR-HDPE system and S-I-S system, respectively. The type of carrier in both the composites is found to be n-type, i.e. electrons, and the activation energy of hopping of the electrons for both the systems has been calculated. A Hall effect study has also been carried out to determine the carrier concentration and drift mobility of both the composites.     

Crystallization of glass in fireclay refractories; part III: Detailed study on the mullite crystal size in the ‘synthetic’ glass

Poor-grade fireclay products contain substantial amount of glass. A glass of similar composition was synthesized, nucleated and heat-treated for crystallization of mullite. The size and size-distribution of mullite crystals, the rate of change of size and the aspect ratio of the crystals were investigated in relation to the nucleating agents and temperature.     

GIBC formulation for the resonant frequencies and fielddistribution of a substrate-mounted dielectric resonator

Dielectric resonators (DR's) are widely used in telecommunication systems. A method is proposed here to find the resonant frequency and field distribution in a substrate-mounted DR structure. The field of a dielectric rod has been decomposed into a combination of guided modes with unknown coefficients and an unknown continuous spectrum of radiation field. The unknowns are then obtained by applying two generalized impedance boundary conditions (GIBC's) representing the substrate and air layers at the top and bottom of the DR. This leads to the calculation of the total (guided+radiation) field as well as the resonant frequency of the structure     

An FDTD/ray-tracing analysis method for wave penetration through inhomogeneous walls

A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic.