In filled PDMS based composites, such as M97XX stress cushions, significant mechanical reinforcement of the polymer component is obtained from hydrogen bonding between the silica filler surface hydroxyls and the siloxane polymer backbone. It is expected that these interactions are influenced by the amount and structure of interfacial water. We have chosen to investigate in detail the effect of chemisorbed and physisorbed water on the interfacial structure and dynamics in silica-filled PDMS-based composites. Toward this end, we have combined classical molecular dynamics simulations and experimental studies employing nanoindentation, temperature programmed desorption (TPD), Dynamic Mechanical Analysis (DMA), and Nuclear Magnetic Resonance (NMR) analyses. Our TPD results suggest that moisture desorption and adsorption in M9787 can be approximated by the interaction of its silica constituents (Cab-0-Sil-M-7D and Hi-Sil-233) with moisture. Our experimental data also reveal that, in general, as heat-treated silica particles are exposed to moisture, chemisorbed states, then physisorbed states are gradually filled up in that order. Molecular modeling results suggest that the polymer-silica contact distance and the mobility of interfacial polymer chains significantly decreased as the hydration level at the interface was reduced. The reduced mobility of the PDMS chains in the interfacial domain reduced the bulk motional properties of …

There are many options for the handling and storage of spent nuclear fuel from naval vessels. This paper summarizes the options that are available and explores the issues that are involved. In many cases choices have been made, not on the basis of which is the best engineering solution or the most cost-effective, but based on the political realities involved. For example, currently it seems that the most prevalent solution for spent fuel interim storage is in dual-purpose (transport-storage) casks. These casks are robust and, politically, they offer the visible evidence that the fuel is ''road-ready'' to be moved from the local area where the fuel is being stored in the interim. However, dual-purpose casks are the most expensive of the storage mediums. Drywell storage (storage in below grade or bermed pipes), on the other hand, the least expensive and most flexible storage option, suffers from an image of permanence (not politically acceptable) and from being improperly implemented in the past. Though these issues are easily resolved from a technical perspective, the option is often not seriously considered because of this past history. It wasn't too many years ago that spent fuel pools were the storage medium of choice. The …

A lead-bismuth eutectic (LBE) target design concept has been developed to drive the subcritical multiplier (SCM) of the accelerator-driven test facility (ADTF). This report gives the target design description, the results from the parametric studies, and the design analyses including physics, heat-transfer, hydraulics, structural, radiological, and safety analyses. The design is based on a coaxial geometrical configuration to minimize the target footprint and to maximize the utilization of the spallation neutrons. The target is installed vertically along the SCM axis. LBE is the target material and the target coolant. Ferritic steel (HT-9 alloy) is the selected structural material based on the current database and the design analyses. Austenitic steel (Type 316 stainless steel) is the backup choice. A uniform proton beam is employed to perform the spallation process. The proton beam has 8.33-mA current and 8.14-cm radius resulting in a current density of 40 {micro}A/cm{sup 2}. The beam power is 5 MW and the proton energy is 600 MeV. The beam tube has 10-cm radius to accommodate the halo current. A hemi-spherical geometry is used for the target window, which is connected to the beam tube. A conical target window with a rounded tip is also considered since it has …

This paper describes a study undertaken to explain the risk profile differences in the results of PRAs of two similar WER-1000 nuclear power plants. The risk profile differences are particularly significant in the area of small steam/feedwater line breaks, small-small LOCAs, support system initiators and containment bypass initiators. A top level (limited depth) approach was used in which we studied design differences, major assumptions, data differences, and also compared the two PRA analyses on an element-by-element basis in order to discern the major causative factors for the risk profile differences. We conclude that the major risk profile differences are due to differences in assumptions and engineering judgment (possibly combined with some design and data differences) involved in treatment of uncertain physical phenomena (primarily sump plugging in LOCAs and turbine building steaming effects in secondary system breaks). Additional major differences are attributable to support system characteristics.

We have synthesized a series of Ti-Si-N coatings with 0 to 20 at. % Si by high-density plasma-assisted vapor-phase deposition. Composition, structure, and atomic short-range order were characterized by Rutherford Backscattering Spectrometry (RBS), Transmission Electron Microscopy (TEM), {Theta}-2{Theta} X-ray Diffraction (XRD), and X-ray Absorption Near Edge Structure (XANES) spectroscopy. The mechanical properties of these coatings were characterized by instrumented nanoindentation, and compared to those of B1-TiN. Our experiments show that the present series of Ti-Si-N coatings are nanocomposites, consisting of a nm-scale mixture of crystalline titanium nitride (TiN) and amorphous silicon nitride (a-Si:N). The mechanical response of the present series of Ti-Si-N coatings was found to be essentially independent of the Si composition, and similar to that of B1-TiN.

We offer a case for active technical management of the radiative forcing of the temperatures of the Earth's fluid envelopes, rather than administrative management of atmospheric greenhouse gas inputs, in order to stabilize both the global- and time-averaged climate and its mesoscale features. We suggest that active management of radiative forcing entails negligible--indeed, likely strongly negative--economic costs and environmental impacts, and thus best complies with the pertinent mandate of the UN Framework Convention on Climate Change. We propose that such approaches be swiftly evaluated in sub-scale in the course of an intensive international program.

The interaction of strong shock waves, such as those generated by the explosion of supernovae with interstellar clouds, is a problem of fundamental importance in understanding the evolution and the dynamics of the interstellar medium (ISM) as it is disrupted by shock waves. Here we present the results of a series of Nova laser experiments investigating the evolution of a high density sphere embedded in a low density medium after the passage of a strong shock wave, thereby emulating the supernova shock-cloud interaction. The Nova laser was utilized to generate a strong ({approx}Mach 10) shock wave that traveled along a miniature beryllium shock tube, 750 {micro}m in diameter, filled with a low-density plastic emulating the ISM. Embedded in the plastic was a copper microsphere (100 {micro}m in diameter) emulating the interstellar cloud. The morphology and evolution as well as the shock wave trajectory were diagnosed via side-on X-ray radiography.

We present a surface compression method that stores surfaces as wavelet-compressed signed-distance volumes. Our approach enables the representation of surfaces with complex topology and arbitrary numbers of components within a single multiresolution data structure. This data structure elegantly handles topological modification at high compression rates. Our method does not require the costly and sometimes infeasible base mesh construction step required by subdivision surface approaches. We present several improvements over previous attempts at compressing signed-distance functions, including an 0(n) distance transform, a zero set initialization method for triangle meshes, and a specialized thresholding algorithm. We demonstrate the potential of sampled distance volumes for surface compression and progressive reconstruction for complex high genus surfaces.

I thought it was important to relate how this project began. Jens Mahler, Mechanical Engineering Deputy Associate Director, recalls that during a discussion between him and Wally Decker, Wally suggested that he document the significant events and the organization of the Mechanical Engineering Department since 1952, i.e., write a history of Mechanical Engineering. Jens agreed that Wally should begin this effort. Upon learning of this, Dave Pehrson, Deputy Associate Director for Engineering, suggested that the History be expanded to include Electronics Engineering and that it be called A History of Engineering. Dave asked me to join Wally on this effort and, unfortunately, Wally died shortly after I started. In the first part of this History, I have attempted to capture the important contributions that Engineering has made to the Programs, since Engineering's primary mission is to provide ''support to the Laboratory Programs.'' In the later parts you will find views discussing the development and application of Engineering's technology base. While Engineering's direct programmatic support had first priority, Engineering had other responsibilities as well. Some of these were to hire and train a competent technical and leadership staff, to anticipate and develop engineering technologies for future use by the Programs, to …

This report is an in-depth study of results from environmental sampling conducted in 1998 by the Lawrence Livermore National Laboratory (LLNL) at Big Trees Park in the city of Livermore. The purpose of the sampling was to determine the extent and origin of plutonium found in soil at concentrations above fallout-background levels in the park. This report describes the sampling that was conducted, the chemical and radio-chemical analyses of the samples, the quality control assessments and statistical analyses of the analytical results, and LLNL's interpretations of the results. It includes a number of data analyses not presented in LLNL's previous reports on Big Trees Park.

Grids comprise an infrastructure that enables scientists to use a diverse set of distributed remote services and resources as part of complex scientific problem-solving processes. We analyze some of the challenges involved in deploying software and components transparently in Grids. We report on three practical solutions used by the Globus Project. Lessons learned from this experience lead us to believe that it is necessary to support a variety of software and component deployment strategies. These strategies are based on the hosting environment.

Monthly newsletter discussing news and activities related to the Atmospheric Radiation Measurement Program, articles about weather and atmospheric phenomena, and other related topics.