Nonlinear and postbuckling analyses of curved composite panels subjected to combined temperature change and edge shear

The results of a detailed study of the nonlinear and postbuckling responses of curved unstiffened composite panels with central circular cutouts are presented. The panels are subjected to uniform temperature change and an applied in-plane edge shear loading. The analysis is based on a first-order shear-deformation Sanders-Budiansky type theory with the effects of large displacements, moderate rotations, transverse shear deformation and laminated anisotropic material behavior included. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. Numerical results are presented for cylindrical panels with central circular cutouts and are subjected to uniform temperature change and an applied in-plane edge shear loading. The results show the effects of variations in the panel curvature, hole diameter, laminate stacking sequence and fiber orientation, on the nonlinear and postbuckling panel responses, and their sensitivity to changes in the various panel, layer and micromechanical parameters.     

Ionizing radiation-induced apoptosis and DNA repair in murine erythroleukemia cells

A morphological study of DNA repair and apoptotic patterns in relationship with cell cycle events was performed on murine erythroleukemia cells. The presence and distribution of DNA replicon sites were evaluated through the BrdU-anti BrdU immunofluorescence and immunogold techniques in light and electron microscopy. Different patterns of labelling and percentages of BrdU positive cells were observed depending on irradiation dose (up to 60 Gy) and time in post-irradiation culture (up to 24 hours). An enlargement of the S phase of the cell cycle was evidenced 18 hours post-irradiation as determined by flow cytometry analysis. The high resolution approach showed that, in spite of several morphological alterations, BrdU labelling was present even in cells displaying early and late apoptotic features.     

Dependence of single-crystalline Si TFT characteristics on the channel position inside a location-controlled grain

To obtain high-performance thin-film transistors (TFTs), a comprehensive study of the channel position of TFTs inside a location-controlled grain was carried out. The location of the grain is precisely controlled by the /spl mu/-Czochralski process using an excimer laser. The grain was grown from a thin Si column embedded in SiO/sub 2/ (grain filter). The characteristics of the TFTs drastically improved when the channel region was not centered above the grain filter. With TFTs whose current-flow direction is parallel to the radial direction of the grain filter, an electron mobility and subthreshold swing of /spl sim/600cm/sup 2//V/spl middot/s and 0.21V/dec respectively were obtained.     

Defining equity in physical access to clinical services using geographical information systems as part of malaria planning and monitoring in Kenya

Distance is a crucial feature of health service use and yet its application and utility to health care planning have not been well explored, particularly in the light of large-scale international and national efforts such as Roll Back Malaria. We have developed a high-resolution map of population-to-service access in four districts of Kenya. Theoretical physical access, based upon national targets, developed as part of the Kenyan health sector reform agenda, was compared with actual health service usage data among 1668 paediatric patients attending 81 sampled government health facilities. Actual and theoretical use were highly correlated. Patients in the larger districts of Kwale and Makueni, where access to government health facilities was relatively poor, travelled greater mean distances than those in Greater Kisii and Bondo. More than 60% of the patients in the four districts attended health facilities within a 5-km range. Interpolated physical access surfaces across districts highlighted areas of poor access and large differences between urban and rural settings. Users from rural communities travelled greater distances to health facilities than those in urban communities. The implications of planning and monitoring equitable delivery of clinical services at national and international levels are discussed.     

Electromagnetic and thermal analysis of high-Tc superconductor in application of current limiting devices

Superconducting fault current limiters (SCFCL) offer an attractive way to limit short-circuit currents in power systems. Analysis into electromagnetic and thermal behaviors of superconductor material is crucial in order to develop a novel design concept of a fault current limiter. A new scheme, which can treat electromagnetic field of the type-II superconductor under transient temperature field, is proposed. In this analysis, one of the critical state models, the Bean model was employed to determine the current distribution in the superconductors and effect of magnetic flux flow was also taken into account. Numerical results indicate that the flux flow strongly affects the stability against the quench in Bi-2212 material. High-T_c superconductor material (Bi-2212) was chosen for the current limiting application. In order to investigate characteristics of the current-quenched Bi-2212 bulk, a 2-dimensional heat transfer equation was numerically solved using the finite element simulation. Heat distributions among the superconductor bars were also simulated and by comparing both the experimental and simulated results, it was found that non-uniformities in a current density or a temperature may exist in the quenching of bulk Bi-2212 superconductor.     

Stochastic analysis of a fault tolerant network system

This paper deals with a stochastic model related to a converter-based communication network system. In this model two converters are connected in parallel with a network system. Each converter has two failure modes—transient failure and latent failure. Transient failures occur due to minor faults in converters. Further the converter may enter into the latent failure mode if major hardware problems arise in the transient failure mode. The converter may recover automatically when it is in a transient failure mode and needs repair when it is in a latent failure mode. The system also enters preventive maintenance at random epochs when both converters are normal. System failure occurs when both the converters are in a latent failure mode. Using the regenerative point technique, various reliability measures are obtained.     

Sensitivity analysis for the dynamic response of viscoplastic shells of revolution

A computational procedure is presented for evaluating the sensitivity coefficients of the dynamic axisymmetric response of viscoplastic shells of revolution. The analytical formulation is based on Reissner's large deformation shell theory with the effects of transverse shear deformation, rotatory inertia and moments turning around the normal to the middle surface included. The material model is chosen to be isothermal viscoplasticity, and an associated flow rule is used with a von Mises effective stress. A mixed formulation is used with the fundamental unknowns consisting of six stress resultants, three generalized displacements and three velocity components. Spatial discretization is performed using finite elements, with discontinuous stress resultants across element interfaces. The temporal integration is performed by using an explicit central difference scheme (leap-frog method) with an implicit constitutive update. The sensitivity coefficients are evaluated using a direct differentiation approach. Numerical results are presented for a spherical cap subjected to step loading, and a circular plate subjected to impulsive loading. The sensitivity coefficients are generated by evaluating the derivatives of the response quantities with respect to the thickness, mass density, Young's modulus, and two of the material parameters characterizing the viscoplastic response. Time histories of the response and sensitivity coefficients are presented, along with spatial distributions of these quantities at selected times.     

Hypermatrix scheme for finite element systems on CDC STAR-100 computer

A study is made of the adaptation of the hypermatrix (block matrix) scheme for solving large systems of finite element equations to the CDC STAR-100 computer. Discussion is focused on the organization of the hypermatrix computation using Cholesky decomposition and the mode of storage of the different submatrices to take advantage of the STAR pipeline (streaming) capability. Consideration is also given to the associated data handling problems and the means of balancing the I/O and cpu times in the solution process. Numerical examples are presented showing anticipated gain in cpu speed over the CDC 6600 to be obtained by using the proposed algorithms on the STAR computer.