The process of grain boundary migration involves moving interfaces and topological changes of grain boundary geometry. This can not be effectively modeled by Lagrangian, Eulerian, or arbitrary Lagrangian Eulerian finite element formulation when stress effect is considered. A coupled finite element and meshfree approach is proposed for modeling of grain boundary migration under stress. In this formulation, the material grid carries material kinematic and kinetic variables, whereas the grain boundary grid carries grain boundary kinematic variables. The material domain is discretized by a reproducing kernel partition of unity with built-in strain discontinuity across the grain boundaries. The grain boundaries, on the other hand, are discretized by the standard finite elements. This approach allows an arbitrary evolution of grain boundaries without continuous remeshing.

The ability to extract particle beam bunches from a ring accelerator in arbitrary order can greatly extend an accelerator's capabilities and applications. A prototype solid-state kicker pulser capable of generating asynchronous bursts of 50 kV pulses has been designed and tested into a 50{Omega} load. The pulser features fast rise and fall times and is capable of generating an arbitrary pattern of pulses with a maximum burst frequency exceeding 5 MHz If required, the pulse-width of each pulse in the burst is independently adjustable. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy is switched into each section of the adder by a parallel array of MOSFETs. Test data, capabilities, and limitations of the prototype pulser are described.

This paper presents an improved optical design for the LSST, an fll.25 three-mirror telescope covering 3.0 degrees full field angle, with 6.9 m effective aperture diameter. The telescope operates at five wavelength bands spanning 386.5 nm to 1040 nm (B, V, R, I and Z). For all bands, 80% of the polychromatic diffracted energy is collected within 0.20 arc-seconds diameter. The reflective telescope uses an 8.4 m f/1.06 concave primary, a 3.4 m convex secondary and a 5.2 m concave tertiary in a Paul geometry. The system length is 9.2 m. A refractive corrector near the detector uses three fused silica lenses, rather than the two lenses of previous designs. Earlier designs required that one element be a vacuum barrier, but now the detector sits in an inert gas at ambient pressure. The last lens is the gas barrier. Small adjustments lead to optimal correction at each band. The filters have different axial thicknesses. The primary and tertiary mirrors are repositioned for each wavelength band. The new optical design incorporates features to simplify manufacturing. They include a flat detector, a far less aspheric convex secondary (10 {micro}m from best fit sphere) and reduced aspheric departures on the lenses and tertiary …

Free electron lasers operating in the 0.1 to 1.5 nm wavelength have been proposed for the Stanford Linear Accelerator Center and DESY (Germany). The unprecedented brightness and associated fluence predicted for pulses <300 fs pose new challenges for optical components. A criterion for optical component design is required, implying an understanding of x-ray-matter interactions at these extreme conditions. In our experimental effort, the extreme conditions are simulated by currently available sources ranging from optical lasers, through x-ray lasers (at 14.7 nm) down to K-alpha sources ({approx}0.15 nm). In this paper we present an overview of our research program, including (a) Results from the experimental campaign at a short pulse (100 fs-5 ps) power laser at 800 nm, (b) K-a experiments, and (c) Computer modeling and experimental project using a tabletop high brightness ps x-ray laser at the Lawrence Livermore National Laboratory.

As with all electromagnet radiation, polarization of x-rays is a general phenomenon. Such polarization has been known since the classic experiments of Barkla in 1906. The general implementation of polarization to x-ray analysis had to await the fixed geometry of energy-dispersive systems. The means of optimizing these systems is shown in this review paper. Improved detection limits are the result.

Contemporary microprocessors provide a rich set of integrated performance counters that allow application developers and system architects alike the opportunity to gather important information about workload behaviors. These counters can capture instruction, memory, and operating system behaviors. Current techniques for analyzing data produced from these counters use raw counts, ratios, and visualization techniques to help users make decisions about their application source code. While these techniques are appropriate for analyzing data from one process, they do not scale easily to new levels demanded by contemporary computing systems. Indeed, the amount of data generated by these experiments is on the order of tens of thousands of data points. Furthermore, if users execute multiple experiments, then we add yet another dimension to this already knotty picture. This flood of multidimensional data can swamp efforts to harvest important ideas from these valuable counters. Very simply, this paper addresses these concerns by evaluating several multivariate statistical techniques on these datasets. We find that several techniques, such as statistical clustering, can automatically extract important features from this data. These derived results can, in turn, be feed directly back to an application developer, or used as input to a more comprehensive performance analysis environment, such as …

High voltage, solid state, inductive adder, pulse generators have found increasing application as fast kicker pulse modulators for charged particle beams. The solid state, inductive adder, pulse generator is similar in operation to the linear induction accelerator. The main difference is that the solid state, adder couples energy by transformer action from multiple primaries to a voltage summing stalk, instead of an electron beam. Ideally, the inductive adder produces a rectangular voltage pulse at the load. In reality, there is usually some voltage variation at the load due to droop on primary circuit storage capacitors, or, temporal variations in the load impedance. Power MOSFET circuits have been developed to provide analog modulation of the output voltage amplitude of a solid state, inductive adder, pulse generator. The modulation is achieved by including MOSFET based, variable subtraction circuits in the multiple primary stack. The subtraction circuits can be used to compensate for voltage droop, or, to tailor the output pulse amplitude to provide a desired effect in the load. Power MOSFET subtraction circuits have been developed to modulate short, temporal (60-400 ns), voltage and current pulses. MOSFET devices have been tested up to 20 amps and 800 Volts with a band pass …

Parallel computers used to be, for the most part, one-of-a-kind systems which were extremely difficult to program portably. With SMP architectures, the advent of the POSIX thread API and OpenMP gave developers ways to portably exploit on-the-box shared memory parallelism. Since these architectures didn't scale cost-effectively, distributed memory clusters were developed. The associated MPI message passing libraries gave these systems a portable paradigm too. Having programmers effectively use this paradigm is a somewhat different question. Distributed data has to be explicitly transported via the messaging system in order for it to be useful. In high level languages, the MPI library gives access to data distribution routines in C, C++, and FORTRAN. But we need more than that. Many reasonable and common tasks are best done in (or as extensions to) scripting languages. Consider sysadm tools such as password crackers, file purgers, etc ... These are simple to write in a scripting language such as Python (an open source, portable, and freely available interpreter). But these tasks beg to be done in parallel. Consider the a password checker that checks an encrypted password against a 25,000 word dictionary. This can take around 10 seconds in Python (6 seconds in C). It …

Although programming models and languages appear to be converging, the computational workloads and communication patterns for scientific applications vary dramatically, depending, in part, on the nature of the problem the applications are solving. In this paper, we investigate the scalability, architectural requirements, and inherent behavioral characteristics of eight scalable scientific applications. We provide a comparative analysis of these applications and isolate their performance characteristics using empirical measurements. We refine our analysis into precise explanations of the factors that influence performance and scalability for each application; we distill these factors into common traits and overall recommendations. Initially, we examine the overall scalability of each application. Then, based on these results, we iteratively investigate the primary factors that affect scalability and performance using a combination of measurement techniques, such as message tracing and monitoring hardware counters, until we can understand each application's primary performance properties and the root causes of those properties.

Extremely high quality data was acquired using an experimental ultrasound scanner developed at Lawrence Livermore National Laboratory using a 2D ring geometry with up to 720 transmitter/receiver transducer positions. This unique geometry allows reflection and transmission modes and transmission imaging and quantification of a 3D volume using 2D slice data. Standard image reconstruction methods were applied to the data including straight-ray filtered back projection, reflection tomography, and diffraction tomography. Newer approaches were also tested such as full wave, full wave adjoint method, bent-ray filtered back projection, and full-aperture tomography. A variety of data sets were collected including a formalin-fixed human breast tissue sample, a commercial ultrasound complex breast phantom, and cylindrical objects with and without inclusions. The resulting reconstruction quality of the images ranges from poor to excellent. The method and results of this study are described including like-data reconstructions produced by different algorithms with side-by-side image comparisons. Comparisons to medical B-scan and x-ray CT scan images are also shown. Reconstruction methods with respect to image quality using resolution, noise, and quantitative accuracy, and computational efficiency metrics will also be discussed.

Traditional techniques for performance analysis provide a means for extracting and analyzing raw performance information from applications. Users then reason about and compare this raw performance data to their performance expectations for important application constructs. This comparison can be tedious, difficult, and error-prone for the scale and complexity of today's architectures and software systems. To address this situation, we present a methodology and prototype that allows users to assert performance expectations explicitly in their source code using performance assertions. As the application executes, each performance assertion in the application collects data implicitly to verify the assertion. By allowing the user to specify a performance expectation with individual code segments, the runtime system can jettison raw data for measurements that pass their expectation, while reacting to failures with a variety of responses. We present several compelling uses of performance assertions with our operational prototype including raising a performance exception, validating a performance model, and adapting an algorithm to an architecture empirically at runtime.

The Linac Coherent Light Source (LCLS) is a 1.5 to 15 {angstrom} wavelength Free-Electron Laser (PEL), under development at the Stanford Linear Accelerator Center (SLAC). The photon output consists of high brightness, transversely coherent pulses with duration < 300 fs, together with a broad spontaneous spectrum. The output energy density per unit area, pulse duration, repetition rate, and small FEL spot size pose special challenges for optical components and diagnostics downstream of the undulator. Planning for the photon beam transport, manipulation and diagnostics downstream of the undulator has begun.

We provide unambiguous experimental evidence that the upper limit of {approx}110 K commonly observed for the Curie temperature TC of Ga{sub 1-x}Mn{sub x}As is caused by the Fermi-level-induced hole saturation. This conclusion is based on parallel studies of the location of Mn in the lattice, the effectiveness of acceptor center, and ferromagnetism on a series of Ga{sub 1-x-y}Mn{sub x}Be{sub y}As layers, in which the concentration of magnetic moments and of free holes can be independently controlled by the Mn and Be contents. Ion channeling and magnetization measurements show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of T{sub C} with increasing Be concentration. At the same time the free hole concentration remains relatively constant at {approx}5 x 10{sup 20}cm{sup -3}. These results indicate that the concentrations of free holes as well as of ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors. Based on these results, we propose to use heavy n-type counter-doping of Ga{sub 1-x}Mn{sub x}As (by, e.g., Te) to suppress the formation of Mn interstitials at high x, and thus improve the T{sub C} of the alloy system.

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We analyze the Sudbury Neutrino Observatory (SNO) and Super-Kamiokande (SK) data on charged current (CC), neutral current (NC) and neutrino electron elastic scattering (ES) reactions to constrain the leading weak axial two-body current parameterized by L{sub 1A}. This two-body current is the dominant uncertainty of every low energy weak interaction deuteron breakup process, including SNO's CC and NC reactions. Our method shows that the theoretical inputs to SNO's determination of the CC and NC fluxes can be self-calibrated, be calibrated by SK, or be calibrated by reactor data. The only assumption made is that the total flux of active neutrinos has the standard {sup 8}B spectral shape (but distortions in the electron neutrino spectrum are allowed). We show that SNO's conclusion about the inconsistency of the no-flavor-conversion hypothesis does not contain significant theoretical uncertainty, and we determine the magnitude of the active solar neutrino flux.

An ''equivalent rectangular crack'' approach was employed to predict rupture pressures and leak rates through laboratory generated stress corrosion cracks and steam generator tubes removed from the McGuire Nuclear Station. Specimen flaws were sized by post-test fractography in addition to a pre-test advanced eddy current technique. The predicted and observed test data on rupture and leak rate are compared. In general, the test failure pressures and leak rates are closer to those predicted on the basis of fractography than on nondestructive evaluation (NDE). However, the predictions based on NDE results are encouraging, particularly because they have the potential to determine a more detailed geometry of ligamented cracks, from which failure pressure and leak rate can be more accurately predicted. One test specimen displayed a time-dependent increase of leak rate under constant pressure.

The electron cooling project requires a high current electron beam with high reliability to provide the consistent cooling required by Fermilab's physics program. We are using a 5URE-2 Pelletron to provide this beam. The program is developing a high current DC recirculating electron beam with high recovery efficiency. The present layout uses 2 sets of tubes with acceleration, a 180{sup o} bend, and deceleration for a total of about 10 meters of beam line. The project's nominal operating parameters are .5 A at 4.3 MeV with the emission cathode immersed in a 200-600 G magnetic field.

While working with E.O. Lawrence at Berkeley, R.R. Wilson in 1946 noted the potential for using the Bragg-peak of protons (or heavier ions) for radiation therapy. Thus began the long history of contributions from Berkeley to this field. Pioneering work by C.A. Tobias et al at the 184-Inch Synchrocyclotron led ultimately to clinical applications of proton and helium beams, with over 1000 patients treated through 1974 with high-energy plateau radiation; placing the treatment volume (mostly pituitary fields) at the rotational center of a sophisticated patient positioner. In 1974 the SuperHILAC and Bevatron accelerators at the Lawrence Berkeley Laboratory were joined by the construction of a 250-meter transfer line, forming the Bevalac, a facility capable of accelerating ions of any atomic species to relativistic energies. With the advent of these new beams, and better diagnostic tools capable of more precise definition of tumor volume and determination of the stopping point of charged-particle beams, large-field Bragg-peak therapy with ion beams became a real possibility. A dedicated Biomedical experimental area was developed, ultimately consisting of three distinct irradiation stations; two dedicated to therapy and one to radiobiology and biophysics. These facilities included dedicated support areas for patient setup and staging of animal and …

Hydrogen production from water splitting at high temperatures has been studied with novel mixed oxygen ion-electron conducting cermet membranes. Hydrogen production rates were investigated as a function of temperature, water partial pressure, membrane thickness, and oxygen chemical potential gradient across the membranes. The hydrogen production rate increased with both increasing moisture concentration and oxygen chemical potential gradient across the membranes. A maximum hydrogen production rate of 4.4 cm{sup 3}/min-cm{sup 2} (STP) was obtained with a 0.10-mm-thick membrane at 900 C in a gas containing 50 vol.% water vapor in the sweep side. Hydrogen production rate also increased with decreasing membrane thickness, but surface kinetics play an important role as membrane thickness decreases.

We investigate the statistical properties (e.g., shot-to-shot power fluctuations) of the radiation from a high-gain free-electron laser (FEL) operating in the nonlinear regime. We consider the case of an FEL amplifier reaching saturation whose shot-to-shot fluctuations in input radiation power follow a gamma distribution. We analyze the corresponding output power fluctuations at and beyond first saturation, including beam energy spread effects, and find that there are well-characterized values of undulator length for which the fluctuation level reaches a minimum.

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Engineered covers have been placed on top of buried/subsurface wastes to minimize water infiltration and therefore, release of hazardous contaminants. In order for the cover to protect the environment it must remain free of holes and breaches throughout its service life. Covers are subject to subsidence, erosion, animal intrusion, plant root infiltration, etc., all of which will affect the overall performance of the cover. The U.S. Department of Energy Environmental Management (DOE-EM) Program 2006 Accelerated Cleanup Plan is pushing for rapid closure of many of the DOE facilities. This will require a great number of new cover systems. Some of these new covers are expected to maintain their performance for periods of up to 1000 years. Long-term stewardship will require monitoring/verification of cover performance over the course of the designed lifetime. In addition, many existing covers are approaching the end of their design life and will need validation of current performance (if continued use is desired) or replacement (if degraded). The need for a reliable method of verification and long-term monitoring is readily apparent. Currently, failure is detected through monitoring wells downstream of the waste site. This is too late as the contaminants have already left the disposal area. The …

A quantitative and time-resolved radiographic technique has been used to characterize hollow-cone gasoline sprays in the near-nozzle region. The highly penetrative nature of x-rays promises the direct measurements of dense sprays that are difficult to study by visible-light based techniques. Time-resolved x-radiography measurement enables us to map the mass distribution near the spray nozzle, even immediately adjacent to the orifice. The quantitative nature of the measurement also permits the re-construction of spray structure and the progress of the spray development. It is observed that the speed of fuel injected in the later part of the injection is higher than injected earlier and that the initial fuel speed variation caused the spray plume to be compressed in space.

The numerical simulation of the driving beams in a heavy ion fusion power plant is a challenging task, and simulation of the power plant as a whole, or even of the driver, is not yet possible. Despite the rapid progress in computer power, past and anticipated, one must consider the use of the most advanced numerical techniques, if they are to reach the goal expeditiously. One of the difficulties of these simulations resides in the disparity of scales, in time and in space, which must be resolved. When these disparities are in distinctive zones of the simulation region, a method which has proven to be effective in other areas (e.g., fluid dynamics simulations) is the mesh refinement technique. They discuss the challenges posed by the implementation of this technique into plasma simulations (due to the presence of particles and electromagnetic waves). They present the prospects for and projected benefits of its application to heavy ion fusion, in particular to the simulation of the ion source and the final beam propagation in the chamber. A Collaboration project is under way at LBNL between the Applied Numerical Algorithms Group (ANAG) and the HIF group to couple the Adaptive Mesh Refinement (AMR) library …