Simulation of ductile fracture at the atomic scale reveals many aspects of the fracture process including specific mechanisms associated with void nucleation and growth as a precursor to fracture and the plastic deformation of the material surrounding the voids and cracks. Recently we have studied void coalescence in ductile metals using large-scale atomistic and continuum simulations. Here we review that work and present some related investigations. The atomistic simulations involve three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. No pronounced shear flow is found in the coalescence process. We also discuss a technique for optimizing the calculation of fine-scale information …

The author presents some of the most recent BABAR measurements for rare B decays. These include rate asymmetries in the B decays to K{sup (*)}l{sup +}l{sup -} and K{sup +}{pi}{sup -} and branching fractions in the B decays to l{sup +}{nu}{sub l}, K{sub 1}(1270){sup +}{pi}{sup -} and K{sub 1}(1400){sup +}{pi}{sup -}. The author also reports a search for the B{sup +} decay to K{sub S}{sup 0}K{sub S}{sup 0}{pi}{sup +}.

Spatial resolution tests were performed on beamline 1.4.4 at the Advanced Light Source in Berkeley, CA, USA, a third-generation synchrotron light source. This beamline couples the high-brightness synchrotron source to a Thermo-Electron Continumum XL infrared microscope. Two types of resolution tests were performed in both the mid-IR and near-IR. The results are compared with a diffraction-limited spot size theory. At shorter near-IR wavelengths the experimental results begin to deviate from diffraction-limited so a combined diffraction-limit and electron-beam-source-size model is employed. This description shows how the physical electron beam size of the synchrotron source begins to dominate the focused spot size at higher energies. The transition from diffraction-limited to electron-beam-size-limited performance is a function of storage-ring parameters and the optical demagnification within the beamline and microscope optics. The discussion includes how different facilities, beamlines and microscopes will affect the achievable spatial resolution. As synchrotron light sources and other next-generation accelerators such as energy-recovery LINACs and free-electron lasers achieve smaller beam emittances, beta-functions and/or energy spreads, diffraction-limited performance can continue to higher-energy beams, perhaps ultimately into the extreme ultraviolet.

The K East (KE) Basin facilities are located near the north end of the Hanford Site's 100 K area. The facilities were built in 1950 as part of the KE Reactor complex and constructed within 400 meters of the Columbia River, which is the largest river in the Pacific Northwest and by volume the fourth largest river in the United States. The basin, located adjacent to the reactor, was used for the underwater storage of irradiated nuclear fuel discharged from the reactor. The basin was covered by a superstructure comprising steel columns and beams, concrete, and cement asbestos board (CAB) siding. The project's mission was to complete demolition of the structure over the KE Basin within six months of turnover from facility deactivation activities. The demolition project team applied open-air demolition techniques to bring the facility to slab-on-grade. Several innovative techniques were used to control contamination and maintain contamination control within the confines of the demolition exclusion zone. The techniques, which focused on a defense-in-depth approach, included spraying fixatives on interior and exterior surfaces before demolition began; applying fixatives during the demolition; misting using a fine spray of water during demolition; and demolishing the facility systematically. Another innovative approach that …

The electromagnetic particle-in-cell (PIC) code VORPAL is being used to simulate the interaction of microwave radiation through an electron cloud. The results so far showgood agreement with theory for simple cases. The study has been motivated by previous experimental work on this problem at the CERN SPS [1], experiments at the PEP-II Low Energy Ring (LER) at SLAC [4], and proposed experiments at the Fermilab Main Injector (MI). With experimental observation of quantities such as amplitude, phase and spectrum of the output microwave radiation and with support from simulations for different cloud densities and applied magnetic fields, this technique can prove to be a useful probe for assessing the presence as well as the densityof electron clouds.

Long-range as well as head-on beam-beam effects are expected to limit the LHC performance with design parameters. They are also important consideration for the LHC upgrades. To mitigate long-range effects, current carrying wires parallel to the beam were proposed. Two such wires are installed in RHIC where they allow studying the effect of strong long-range beam-beam effects, as well as the compensation of a single long-range interaction. The tests provide benchmark data for simulations and analytical treatments. Electron lenses were proposed for both RHIC and the LHC to reduce the head-on beam-beam effect. We present the experimental long-range beam-beam program at RHIC and report on head-on compensations studies based on simulations.

We report the results of a search for Z(4430){sup -} decay to J/{psi}{pi}{sup -} or {psi}(2S){pi}{sup -} in B{sup -,0} {yields} J/{psi}{pi}{sup -} K{sup 0,+} and B{sup -,0} {yields} {psi}(2S){pi}{sup -}K{sup 0,+} decays. The data were collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e{sup +}e{sup -} collider operating at center of mass energy 10.58 GeV, and the sample corresponds to an integrated luminosity of 413 fb{sup -1}. Each K{pi}{sup -} mass distribution exhibits clear K*(892) and K*{sub 2}(1430) signals, and the efficiency-corrected spectrum is well-described by a superposition of the associated Breit-Wigner intensity distributions, together with an S-wave contribution obtained from the LASS I = 1/2 K{pi}{sup -} scattering amplitude measurements. Each K{pi}{sup -} angular distribution varies significantly in structure with K{pi}{sup -} mass, and is represented in terms of low-order Legendre polynomial moments. We find that each J/{psi}{pi}{sup -} or {psi}(2S){pi}{sup -} mass distribution is well-described by the reflection of the measured K{pi}{sup -} mass and angular distribution structures. We see no significant evidence for a Z(4430){sup -} signal for any of the processes investigated, neither in the total J/{psi}{pi}{sup -} or {psi}(2S){pi}{sup -} mass distribution, nor in the corresponding distributions for the regions of K{pi}{sup …

Argentina is faced with the challenging problem ofdeveloping technology for near-surface disposal and isolation of low- andintermediate-level radioactive waste (LILW). The preferred option fordisposal of LILW (including both relatively short-lived and long-livedradionuclides) is to use disposal facilities that arenear-surface--either above or below ground level [IAEA, 1985; 2001a;2004]. How individual components of a waste disposal system perform(including waste forms, waste containers, engineered barriers and hostenvironment) will determine system safety and the safety of thesurrounding environment [IAEA, 1999]. The lack of appropriate engineeringfor the backfill, and for the selection of sealing and covering materialsfor trenches, vaults, and ditches, could result in the escape ofradionuclides from the disposed wastes [IAEA, 1994a; 2001b]. Therefore,assessment and design of backfill, barriers, and cover materials are veryimportant, both for preventing invasion of water into the disposalsystem, and for retarding radionuclides that could potentially migratefrom the system into the atmosphere or groundwater [IAEA, 1982; 1994b;2001a].

High level radioactive waste (HLW) is stored in underground carbon steel storage tanks at the Savannah River Site. The underground tanks will be closed by removing the bulk of the waste, chemical cleaning, heel removal, stabilizing remaining residuals with tailored grout formulations, and severing/sealing external penetrations. The life of the carbon steel materials of construction in support of the performance assessment has been completed. The estimation considered general and localized corrosion mechanisms of the tank steel exposed to grouted conditions. A stochastic approach was followed to estimate the distributions of failures based upon mechanisms of corrosion accounting for variances in each of the independent variables. The methodology and results used for one-type of tank is presented.

An initial design of the optics required for producing gamma-gamma collisions was produced for the NLC Zeroth Order Design Report (ZDR) submitted to the 1996 Snowmass workshop. The design incorporated only loose constraints from the interaction region requirements. In this paper we report progress on a design of a gamma-gamma interaction region which incorporates all constraints.

Optical propagation modeling of the National Ignition Facility has been utilized extensively from conceptual design several years ago through to early operations today. In practice we routinely (for every shot) model beam propagation starting from the waveform generator through to the target. This includes the regenerative amplifier, the 4-pass rod amplifier, and the large slab amplifiers. Such models have been improved over time to include details such as distances between components, gain profiles in the laser slabs and rods, transient optical distortions due to the flashlamp heating of laser slabs, measured transmitted and reflected wavefronts for all large optics, the adaptive optic feedback loop, and the frequency converter. These calculations allow nearfield and farfield predictions in good agreement with measurements.

The performance of commercial high-performance fibers is examined for application to flywheel power supplies. It is shown that actual delivered performance depends on multiple factors such as inherent fiber strength, strength translation and stress-rupture lifetime. Experimental results for recent stress-rupture studies of carbon fibers will be presented and compared with other candidate reinforcement materials. Based on an evaluation of all of the performance factors, it is concluded that carbon fibers are preferred for highest performance and E-glass fibers for lowest cost. The inferior performance of the low-cost E-glass fibers can be improved to some extent by retarding the stress-corrosion of the material due to moisture and practical approaches to mitigating this corrosion are discussed. Many flywheel designs are limited not by fiber failure, but by matrix-dominated failure modes. Unfortunately, very few experimental results for stress-rupture under transverse tensile loading are available. As a consequence, significant efforts are made in flywheel design to avoid generating any transverse tensile stresses. Recent results for stress-rupture of a carbon fiber/epoxy composite under transverse tensile load reveal that these materials are surprisingly durable under the transverse loading condition and that some radial tensile stress could be tolerated in flywheel applications.

The disparity between microprocessor clock frequencies and memory latency is a primary reason why many demanding applications run well below peak achievable performance. Software controlled scratchpad memories, such as the Cell local store, attempt to ameliorate this discrepancy by enabling precise control over memory movement; however, scratchpad technology confronts the programmer and compiler with an unfamiliar and difficult programming model. In this work, we present the Virtual Vector Architecture (ViVA), which combines the memory semantics of vector computers with a software-controlled scratchpad memory in order to provide a more effective and practical approach to latency hiding. ViVA requires minimal changes to the core design and could thus be easily integrated with conventional processor cores. To validate our approach, we implemented ViVA on the Mambo cycle-accurate full system simulator, which was carefully calibrated to match the performance on our underlying PowerPC Apple G5 architecture. Results show that ViVA is able to deliver significant performance benefits over scalar techniques for a variety of memory access patterns as well as two important memory-bound compact kernels, corner turn and sparse matrix-vector multiplication -- achieving 2x-13x improvement compared the scalar version. Overall, our preliminary ViVA exploration points to a promising approach for improving application performance …

Economic impacts on individual consumers from possible revisions to U.S. residential-type central air conditioner energy-efficiency standards are examined using a life-cycle cost (LCC) analysis. LCC is the consumer's cost of purchasing and installing a central air conditioner and operating it over its lifetime. This approach makes it possible to evaluate the economic impacts on individual consumers from the revised standards. The methodology allows an examination of groups of the population which benefit or lose from suggested efficiency standards. The results show that the economic benefits to consumers due to modest increases in efficiency are significant. For an efficiency increase of 20percent over the existing minimum standard (i.e., 12 SEER), 35percent of households with central air conditioners experience significant LCC savings, with an average savings of $453, while 25percent show significant LCC losses, with an average loss of $158 compared to apre-standard LCC average of $5,170. The remainder of the population (40percent) are largely unaffected.

Solid low-level radioactive wastes at the Savannah River Site (SRS) are disposed in trenches. In order to determine the permissible radioactive inventory limits for such disposal facilities, it is required to assess the behavior of radioactive waste material over long periods of time. The sensitivity of flow and I-129 (and similar radionuclides) transport in groundwater in the vadose zone to the hydraulic conductivities of the vadose zone subregions and the low-level waste is identified and quantified. A trench configuration and simulation model have been developed to analyze the flow and transport of the radionuclide in the vadose zone as it migrates to the groundwater table. The analysis identifies and quantifies the major dependencies of the flow and radionuclide fractional flux on the subregion hydraulic conductivities. Analysis results indicate the importance of the hydraulic conductivity assigned to the materials modeled, thereby providing the modeler and decision makers with valuable insights on the potential impact of the hydraulic conductivity on flow and radionuclide transport.

The angular dependence of dissociative electron attachment (DEA) to polyatomic targets is formulated in the local complex potential model, under the assumption that the axial recoil approximation describes the dissociation dynamics. An additional approximation, which is found to be valid in the case of H2O but not in the case of H2S, makes it possible to describe the angular dependence of DEA solely from an analysis of the fixed-nuclei entrance amplitude, without carrying out nuclear dynamics calculations. For H2S, the final-vibrational-state-specific angular dependence of DEA is obtained by incorporating the variation of the angular dependence of the entrance amplitude with nuclear geometry into the nuclear dynamics. Scattering calculations using the complex Kohn method and, for H2S, full quantum calculations of the nuclear dynamics using the Multi-Configuration Time-Dependent Hartree method, are performed.

When a fixed anode x-ray tube is placed in a magnetic field (B) that is parallel to the anode-cathode axis, the x-ray exposure increases with increasing B. It was hypothesized that the increase was caused by backscattered electrons which were constrained by B and reaccelerated by the electric field onto the x-ray tube target. We performed computer simulations and physical experiments to study the behavior of the backscattered electrons in a magnetic field, and their effects on the radiation output, x-ray spectrum, and off-focal radiation. A Monte Carlo program (EGS4) was used to generate the combined energy and angular distribution of the backscattered electrons. The electron trajectories were traced and their landing locations back on the anode were calculated. Radiation emission from each point was modeled with published data (IPEM Report 78), and thus the exposure rate and x-ray spectrum with the contribution of backscattered electrons could be predicted. The point spread function for a pencil beam of electrons was generated and then convolved with the density map of primary electrons incident on the anode as simulated with a finite element program (Opera-3d, Vector Fields, UK). The total spatial distribution of x-ray emission could then be calculated. Simulations showed that …

We have examined the elbow angles for 365 different Fab fragments, and observe that Fabs with lambda light chains have adopted a wider range of elbow angles than their kappa-chain counterparts, and that the lambda light chain Fabs are frequently found with very large (>195{sup o}) elbow angles. This apparent hyperflexibility of lambda-chain Fabs may be due to an insertion in their switch region, which is one residue longer than in kappa chains, with glycine occurring most frequently at the insertion position. A new, web-based computer program that was used to calculate the Fab elbow angles is also described.

Recent events are again raising some old issues and creating new opportunities regarding the future disposition of the used, or spent, fuel from nuclear power plants. Handling these challenges well will not only help set the stage for a robust nuclear energy future, but will reflect the growing linkages among nuclear power, nuclear waste management, international security, and public and political acceptance. The emerging global nuclear regime may make spent fuel management not only more important, but improve chances of success.

Ecosystem health with its near infinite number of variables is difficult to measure, and there are many opinions as to which variables are most important, most easily measured, and most robust, Bioassessment avoids the controversy of choosing which physical and chemical parameters to measure because it uses responses of a community of organisms that integrate all aspects of the system in question. A variety of bioassessment methods have been successfully applied to aquatic ecosystems using fish and macroinvertebrate communities. Terrestrial biotic index methods are less developed than those for aquatic systems and we are seeking to address this problem here. This study had as its objective to examine the baseline differences in ant communities at different seral stages from clear cut back to mature pine plantation as a precursor to developing a bioassessment protocol. Comparative sampling was conducted at four seral stages; clearcut, 5 year, 15 year and mature pine plantation stands. Soil and vegetation data were collected at each site. All ants collected were preserved in 70% ethyl alcohol and identified to genus. Analysis of the ant data indicates that ants respond strongly to the habitat changes that accompany ecological succession in managed pine forests and that individual genera …

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The development of multichannel time-reversal (T/R) processing techniques continues to progress rapidly especially when the need to communicate in a highly reverberative environment becomes critical. The underlying T/R concept is based on time-reversing the Green's function characterizing the uncertain communications channel investigating the deleterious dispersion and multipath effects. In this paper, attention is focused on two major objectives: (1) wideband communications leading to a time reference modulation technique; and (2) multichannel acoustic communications in a tunnel (or cave or pipe) with many obstructions, multipath returns, severe background noise, disturbances, long propagation paths ({approx}180) with disruptions (bends). For this extremely hostile environment, it is shown that multichannel T/R receivers can easily be extended to the wideband designs while demonstrating their performance in both the ''canonical'' stairwell of our previous work as well as a tunnel-like structure. Acoustic information signals are transmitted with an 8-element host or base station array to two client receivers with a significant loss in signal levels due to the propagation environment. In this paper, the results of the new wideband T/R processor and modulation scheme are discussed to demonstrate the overall performance for both high (24-bit) and low (1-bit) bit level analog-to-digital (A/D) converter designs. These results …

A Type Ia supernova explosion likely begins as a nuclear runaway near the center of a carbon-oxygen white dwarf. The outward propagating flame is unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz instabilities, which serve to accelerate it to a large fraction of the speed of sound. We investigate the Rayleigh-Taylor unstable flame at the transition from the flamelet regime to the distributed-burning regime, around densities of 10e7 gm/cc, through detailed, fully resolved simulations. A low Mach number, adaptive mesh hydrodynamics code is used to achieve the necessary resolution and long time scales. As the density is varied, we see a fundamental change in the character of the burning--at the low end of the density range the Rayleigh-Taylor instability dominates the burning, whereas at the high end the burning suppresses the instability. In all cases, significant acceleration of the flame is observed, limited only by the size of the domain we are able to study. We discuss the implications of these results on the potential for a deflagration to detonation transition.

The pseudorapidity asymmetry and centrality dependence of charged hadron spectra in d+Au collisions at {radical}s{sub NN} = 200 GeV are presented. The charged particle density at mid-rapidity, its pseudorapidity asymmetry and centrality dependence are reasonably reproduced by a Multi-Phase Transport model, by HIJING, and by the latest calculations in a saturation model. Ratios of transverse momentum spectra between backward and forward pseudorapidity are above unity for p{sub T} below 5 GeV/c. The ratio of central to peripheral spectra in d+Au collisions shows enhancement at 2 < p{sub T} < 6 GeV/c, with a larger effect at backward rapidity than forward rapidity. Our measurements are in qualitative agreement with gluon saturation and in contrast to calculations based on incoherent multiple partonic scatterings.