[en] Multigrid (MG) methods in computational fluid dynamics and their implementation on supercomputers are discussed in reviews and reports of recent investigations. Topics examined include the use of incomplete matrix factorizations as MG smoothers for vector and parallel computers, an algebraic MG theory for symmetric cases, MG calculation of subvortices, a vectorized MG solver for the three-dimensional Poisson equation, and the numerical solution of the nonlinear stochastic Helmholtz equation with an MG preconditioner. Consideration is given to the application of data-flow concepts to an MG Euler solver, parallel computation of Euler and Navier-Stokes flows, and spectral MG methods for time-dependent Navier-Stokes equations

[en] The fast adaptive composite grid method (FAC) is an algorithm that uses various levels of uniform grids to provide adaptive resolution and fast solution of PDEs. An asynchronous version of FAC, called AFAC, that completely eliminates the bottleneck to parallelism is presented. This paper describes the advantage that this algorithm has in adaptive refinement for moving singularities on multiprocessor computers. This work is applicable to the parallel solution of two- and three-dimensional shock tracking problems. 6 refs

[en] The authors have studied the effects of intense X-ray irradiation on the structure of amorphous Si films. The films were obtained by either physical vapor deposition or by implantation of high energy ions into crystalline Si. They were exposed to different total doses of synchrotron X-rays. From the EXAFS and EXELFS measurements they find that an exposure to X-rays increases the Si coordination number. Also in the PVD films a prolonged X-ray exposure enlarges, by about 2%, the Si-Si bond length. Raman spectroscopy shows that Si amorphized with high energy ions contains small residual amounts of crystalline material. Irradiation of such films with X-rays annihilates those crystallites resulting in homogeneously amorphous layer with a close to four-fold coordination of Si atoms. This rearrangement of the local structure has a pronounced effect on the crystallization process of the amorphous films. Thermal annealing of X-ray irradiated ion amorphized films leads to nearly defect free solid phase epitaxy at 500 C. Also they observe a delay in the onset of the crystallization process in X-ray irradiated PVD films. They associate this with a reduced concentration of nucleation centers in the x-ray treated materials

[en] Preserved irradiated homologous costal cartilage implants were placed in six canine lower lids for a period of 7-12 weeks. The three implants placed under a covering of conjunctiva simulating current clinical technique were well tolerated and demonstrated little change. Exposed implants produced obvious clinical inflammation and two of three exposed grafts disappeared during the 4- to 5-week interval. The single exposed implant that was retained demonstrated partial epithelialization but suffered extensive absorption and remodeling

[en] Pulmonary endothelial cell function (ECF) studies have been shown to be a sensitive indicator of chronic lung injury. We attempted to correlate changes in 5-hydroxytryptamine (5HT) uptake with an acute oxygen radical-mediated lung injury in dogs. Beta-d glucose/glucose oxidase was injected intravenously in an experimental group (n = 10), while the control group (n = 5) received saline. 5HT uptake, measured using a multiple indicator dilution technique before and 20 min after injection, was calculated for both the percent total uptake and the peak extraction ratio of 5HT during a single passage through the lung. The mean pulmonary and systemic arterial pressures (PAP, SAP), total pulmonary resistance (TPR), extravascular lung water (EVLW), and wet-to-dry weight ratios were also determined. The experimental group showed an acute rise in PAP and TPR and a fall in SAP after the injection, all returning to normal by 20 min; total 5HT uptake fell from 81 +/- 2.3% to 47 +/- 6.5% (p = 0.0002) as did the peak extraction ratio from 0.87 +/- 0.013 to 0.44 +/- 0.066 (p = 0.0001). No change in 5HT uptake was observed in the control group. EVLW did not change in either group, but wet-to-dry weight ratio was elevated in the experimental group (5.21 +/- 0.12 versus 4.73 +/- 0.06, p less than 0.01). ECF studies of 5HT uptake appear to be a sensitive indicator of acute lung injury in this large-animal, oxygen radical-induced injury model

[en] A baseline health risk assessment (HRA) was prepared to evaluate potential risks to human health and the environment posed by the Perched Water System (PWS) at the Test Reactor Area (TRA). The PWS has been designated Operable Unit 2-12, one of the 13 operable units identified at TRA. During the period from 1962 to 1990, a total of 6770 million gal of water were discharged from the TRA to unlined surface ponds. Wastewater discharged to the surface ponds at TRA percolates downward through the surficial alluvium and the underlying basalt bedrock. A resulting shallow perched water zone has formed at the interface between the surficial sediments and the underlying basalt. Further downward movement of groundwater is again impeded by a low-permeability layer of silt, clay, and sand encountered at a depth of ∼150 ft. The deep perched water zone occurs on top of this low-permeability interbed. An evaluation was made as to whether potential risks for the PWS could justify implementing a remedial action. The risk evaluation consisted of two parts, the human health evaluation and the ecological evaluation

[en] The focus of this paper is on a parallel algorithm for solving the transport equations in a slab geometry using multigrid. The spatial discretization scheme used is a finite element method called the modified linear discontinuous (MLD) scheme. The MLD scheme represents a lumped version of the standard linear discontinuous (LD) scheme. The parallel algorithm was implemented on the Connection Machine 2 (CM2). Convergence rates and timings for this algorithm on the CM2 and Cray-YMP are shown

[en] A multigrid method for solving the one-dimensional slab-geometry S_N equations with isotropic scattering and absorption is presented. Relaxation is based on a two-cell inversion, which is very efficient because it takes advantage of the structure of the two-cell problem. For interpolation the authors use kinked linear elements. The kink is based on the amount of absorption present. The restriction operator is full weighting. Numerical results show this algorithm to be faster than diffusion synthetic acceleration (DSA) in all regimes. This scheme is also well suited for massively parallel computer architectures

[en] Thermal stability of the microstructure of Alloy 718^TM Plus has been investigated using the non-isothermal differential scanning calorimetry (DSC) technique. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques are used for microstructural analysis. Samples are heat treated at different temperatures before performing DSC tests. The DSC curves exhibited endothermic and exothermic peaks reflecting in situ changes in the microstructure. The ratio of endothermic to exothermic peak area increased as the preheating temperature increased.

[en] Previous investigation of the landfill on the Concord Naval Weapons Station, located in a diked wetland, showed that the sediments exhibited elevated levels of inorganic analytes, as compared to national benchmarks, such as the NOAA ER-Ls. The need to identify a reference marsh was recognized because of the likelihood that these levels of inorganics were representative of ambient conditions, rather than associated with releases to the environment. A marsh location was selected that was upgradient of the landfill, and distant from sources of known contamination, such as roadways and railroad tracks. Sediment samples were analyzed for bulk sediment chemistry, toxicity, and benthic community structure. Bulk sediment chemistry results showed elevated concentrations of lead and petroleum-related organic compounds, perhaps associated with a historic pipeline break. Pore water was prepared from sediment collocated with the bulk chemistry samples and tested with the sea urchin development bioassay. Compared to the control, three of four sediment pore water samples were highly inhibitory of normal development. However, the benthic community survey from the same sampling stations showed a health assemblage of organisms, although one station that exhibited visible petroleum contamination also showed reduced abundance. The conflicting results demonstrate the necessity for taking more than one measure in developing the ecological assessment of a site