If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for RF guns the photo-electron distribution leaving the cathode should have a 3D-ellipsoidal shape. The emittance at the end of the injector could be as small as the cathode emittance. We explore how the emittance and the brightness can be optimized for photoinjector based on RF gun depending on the peak current requirements. Techniques available to produce those ideal laser pulse shapes are also discussed.

We study the structure of the energy spectra along with the character of the states participating in optical transitions in colloidal CdS quantum dots (QDs) using the ab initio accuracy charge patching method combined with the folded spectrum calculations of electronic structure of thousand-atom nanostructures. In particular, attention is paid to the nature of the large resonant Stokes shift observed in CdS quantum dots. We find that the top of the valence band state is bright, in contrast with the results of numerous k {center_dot} p calculations, and determine the limits of applicability of the k {center_dot} p approach. The calculated electron-hole exchange splitting suggests the spin-forbidden valence state may explain the nature of the ''dark exciton'' in CdS quantum dots.

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During the past 50 years Transmission Electron Microscopy (TEM) has evolved from an imaging tool to a quantitative method that approaches the ultimate goal of understanding the atomic structure of materials atom by atom in three dimensions both experimentally and theoretically. Today's TEM abilities are tested in the special case of a Ga terminated 30 degree partial dislocation in GaAs:Be where it is shown that a combination of high-resolution phase contrast imaging, Scanning TEM, and local Electron Energy Loss Spectroscopy allows for a complete analysis of dislocation cores and associated stacking faults. We find that it is already possible to locate atom column positions with picometer precision in directly interpretable images of the projected crystal structure and that chemically different elements can already be identified together with their local electronic structure. In terms of theory, the experimental results can be quantitatively compared with ab initio electronic structure total energy calculations. By combining elasticity theory methods with atomic theory an equivalent crystal volume can be addressed. Therefore, it is already feasible to merge experiments and theory on a picometer length scale. While current experiments require the utilization of different, specialized instruments it is foreseeable that the rapid improvement of electron optical …

The Homeland-Defense Operational Planning System (HOPS), is a new operational planning tool leveraging Lawrence Livermore National Laboratory's expertise in weapons systems and in sparse information analysis to support the defense of the U.S. homeland. HOPS provides planners with a basis to make decisions to protect against acts of terrorism, focusing on the defense of facilities critical to U.S. infrastructure. Criticality of facilities, structures, and systems is evaluated on a composite matrix of specific projected casualty, economic, and sociopolitical impact bins. Based on these criteria, significant unidentified vulnerabilities are identified and secured. To provide insight into potential successes by malevolent actors, HOPS analysts strive to base their efforts mainly on unclassified open-source data. However, more cooperation is needed between HOPS analysts and facility representatives to provide an advantage to those whose task is to defend these facilities. Evaluated facilities include: refineries, major ports, nuclear power plants and other nuclear licensees, dams, government installations, convention centers, sports stadiums, tourist venues, and public and freight transportation systems. A generalized summary of analyses of U.S. infrastructure facilities will be presented.

We correlate topography and diffraction measurements to demonstrate that grain orientation profoundly influences polishing rates in polycrystalline diamond synthesized by chemical vapor deposition. Grains oriented with {l_brace}111{r_brace} or {l_brace}100{r_brace} planes perpendicular to the surface normal polish at significantly lower rates compared with grains of all other orientations when the surface is polished in continuously varying in-plane directions. These observations agree with predictions of the periodic bond chain vector model, developed previously for single crystals, and indicate that the polishing rate depends strongly on the number of PBC vectors that are within 10{sup o} of the exposed surface plane.

As a consequence of the unusual nature of plutonium's electronic structure, point- and extended-defects are expected to, and do exhibit extraordinary properties[1]. Low temperature magnetic susceptibility measurements on Pu and fcc-Pu(Ga) show that the magnetic susceptibility increases as a function of time, yet upon annealing the specimen returns to its initial magnetic susceptibility. This excess magnetic susceptibility (EMS) arises from the {alpha}-decay and U recoil damage cascades which produce vacancy and interstitials as point and extended defects. The temperature of the first annealing stage defines a temperature (<35K) below which we are able to characterize the time and temperature evolution of the accumulating damage cascades as being a saturation function. The temperature dependence of the EMS is well described by a time independent, Curie-Weiss curve arising from a volumetric region surrounding each U damage cascade. This saturation picture also leads directly to a determination of the microscopic volume of the specimen that is affected by the frozen-in damage cascade. For our measurements in d-Pu we calculate a diameter of the magnetically affected volume of {approx} 250 {angstrom} per damage cascade. This should be compared with an estimated volume that encloses the damage cascade itself (determined from molecular dynamics) of {approx}100 …

We have performed experiments using Callisto, the Vulcan 100 TW and the Vulcan Petawatt high intensity lasers to understand the characteristics of high energy, K{alpha} x-ray sources and to implement workable radiography solutions at 20-100 keV. Our measurements show that the K{alpha} size from a simple foil target is larger than 60 {micro}m, far larger than the experiment resolution requirement. The total K{alpha} yield is independent of target thicknesses verifying that refluxing plays a major role in photon generation. Smaller radiating volumes emit brighter K{alpha} radiation. 1-D radiography experiments using small-edge-on foils resolved 10 {micro}m features with high contrast. We tested a variety of small volume 2-D point sources such as cones, wires, and embedded wires, measuring photon yields and comparing our measurements with predictions from hybrid-PIC LSP simulations. In addition to high-energy, high-resolution backlighters, future experiments will also need imaging detectors and diagnostic tools that are workable in the 20-100 keV energy range. An initial look at some of these detector issues is also presented.

High Mach number blast waves were created by focusing a laser pulse on a solid pin, surrounded by nitrogen or xenon gas. In xenon, the initial shock is strongly radiative, sending out a supersonic radiative heat wave far ahead of itself. The shock propagates into the heated gas, diminishing in strength as it goes. The radiative heat wave also slows, and when its Mach number drops to 2 with respect to the downstream plasma, the heat wave drives a second shock ahead of itself to satisfy mass and momentum conservation in the heat wave reference frame; the heat wave becomes subsonic behind the second shock. For some time both shocks are observed simultaneously. Eventually the initial shock dimimishes in strength so much that it can longer be observed, but the second shock continues to propagate long after this time. This sequence of events is a new phenomenon that has not previously been discussed in literature. Numerical simulation clarifies the origin of the second shock, and its position is consistent with an analytical estimate.

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Recently, precision laser spectroscopy on {sup 6}He atoms determined accurately the isotope shift between {sup 4}He and {sup 6}He and, consequently, the charge radius of {sup 6}He. A similar experiment for {sup 8}He is under way. We have performed large-scale ab initio calculations for {sup 4,6,8}He isotopes using high-precision nucleon-nucleon (NN) interactions within the no-core shell model (NCSM) approach. With the CD-Bonn 2000 NN potential we found point-proton root-mean-square (rms) radii of {sup 4}He and {sup 6}He 1.45(1) fm and 1.89(4), respectively, in agreement with experiment and predict the {sup 8}He point proton rms radius to be 1.88(6) fm. At the same time, our calculations show that the recently developed nonlocal INOY NN potential gives binding energies closer to experiment, but underestimates the charge radii.

Atmospheric releases of hazardous materials are highly effective means to impact large populations. We propose an atmospheric event reconstruction framework that couples observed data and predictive computer-intensive dispersion models via Bayesian methodology. Due to the complexity of the model framework, a sampling-based approach is taken for posterior inference that combines Markov chain Monte Carlo (MCMC) and sequential Monte Carlo (SMC) strategies.

Using first-principles density-functional theory calculations, we show that the anomalously large anisotropy of {sigma}-plutonium is a consequence of greatly varying bond-strengths between the 12 nearest neighbors. Employing the calculated bond strengths, we expand the tenants of classical crystallography by incorporating anisotropy of chemical bonds, which yields a structure with the monoclinic space group Cm for {delta}-plutonium rather than face-centered cubic Fm{bar 3}m. The reduced space group for {delta}-plutonium enlightens why the ground state of the metal is monoclinic, why distortions of the metal are viable, and has considerable implications for the behavior of the material as it ages. These results illustrate how an expansion of classical crystallography that accounts for anisotropic electronic structure can explain complicated materials in a novel way.

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To improve the understanding of passive film formation on metallic lithium in organic electrolyte, we synthesized and characterized lithium methyl carbonate (LiOCO{sub 2}CH{sub 3}), a prototypical component of the film. The chemical structure of this compound was characterized with Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR), and its thermal stability and decomposition pathway was studied by thermo-gravimetric analysis (TGA). The FTIR spectrum of chemically synthesized compound enabled us to resolve multiple products in the passive film on lithium in dimethyl carbonate (DMC). Lithium methyl carbonate is only one of the components, the others being lithium oxalate and lithium methoxide.

The Gordon Research Conference (GRC) on 2004 Inorganic Chemistry Gordon Research Conference - July 18-23, 2004 was held at Salve Regina College, July 18-23, 2004. The Conference was well-attended with 110 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.

Mutations are genetic alterations that drive biological evolution and cause many, if not all, human diseases. Mutation originates via two distinct mechanisms: ''vertical'' variation is de novo change of one or few bases, whereas ''horizontal'' variation occurs by genetic recombination, which creates new mosaics of pre-existing sequences. The Mutagenesis Conference has traditionally focused on the generation of mutagenic intermediates during normal DNA synthesis or in response to environmental insults, as well as the diverse repair mechanisms that prevent the fixation of such intermediates as permanent mutations. While the 2004 Conference will continue to focus on the molecular mechanisms of mutagenesis, there will be increased emphasis on the biological consequences of mutations, both in terms of evolutionary processes and in terms of human disease. The meeting will open with two historical accounts of mutation research that recapitulate the intellectual framework of this field and thereby place the current research paradigms into perspective. The two introductory keynote lectures will be followed by sessions on: (1) mutagenic systems, (2) hypermutable sequences, (3) mechanisms of mutation, (4) mutation avoidance systems, (5) mutation in human hereditary and infectious diseases, (6) mutation rates in evolution and genotype-phenotype relationships, (7) ecology, mutagenesis and the modeling of evolution …

Ultraviolet Thomson scattering has been fielded at the Omega Laser Facility to achieve accurate measurements of the plasma conditions in laser-produced high-temperature plasmas. Recent applications to hohlraum targets that have been filled with CH gas or SiO{sub 2} foams have demonstrated a new high temperature plasma regime of importance to laser-plasma interaction studies in a strongly damped regime such as those occurring in indirect drive inertial confinement fusion experiments. The Thomson scattering spectra show the collective ion acoustic features that fit the theory for two ion species plasmas and from which we infer the electron and ion temperature. We find that the electron temperature scales from 2-4 keV when increasing the heater beam energy into the hohlraum from 8-17 kJ, respectively. Simultaneous measurements of the stimulated Raman scattering from a green 527 nm interaction beam show that the reflectivity decreases from 20% to 1% indicating that this instability is strongly damped at high temperatures. These findings support green laser beams as possible driver option for laser-driven fusion experiments.

Flow in metallic glasses is associated with stress-induced cooperative rearrangements of small groups of atoms involving the surrounding free volume. Understanding the details of these rearrangements therefore requires knowledge of the amount and distribution of the free volume and how that distribution evolves with deformation. The present study employs positron annihilation spectroscopy to investigate the free volume change in Zr{sub 58.5}Cu{sub 15.6}Ni{sub 12.8}Al{sub 10.3}Nb{sub 2.8} bulk metallic glass after inhomogeneous plastic deformation by cold rolling and structural relaxation by annealing. Results indicate that the size distribution of open volume sites is at least bimodal. The size and concentration of the larger group, identified as flow defects, changes with processing. Following initial plastic deformation the size of the flow defects increases, consistent with the free volume theory for flow. Following more extensive deformation, however, the size distribution of the positron traps shifts, with much larger open volume sites forming at the expense of the flow defects. This suggests that a critical strain is required for flow defects to coalesce and form more stable nanovoids, which have been observed elsewhere by high resolution TEM. Although these results suggest the presence of three distinct open volume size groups, further analysis indicates that all …

Science-based decision making required robust and high-fidelity mechanistic data about the system dynamics and impacts of system changes. Alkaloid cyanotoxins have the characteristics to warrant consideration for their potential threat. Since insufficient information is available to construct a systems model for the alkaloid cyanotoxins, saxitoxins, anatoxins, and anatoxin-a(S), an accurate assessments of these toxins as a potential threat for use for intentional contamination is not possible. Alkaloid cyanotoxin research that contributed to such a model has numerous areas of overlap for natural and intentional health effects issues that generates dual improvements to the state of the science. The use of sensitivity analyses of systems models can identify parameters that, when determined, result in the greatest impact to the overall system and may help to direct the most efficient use of research funding. This type of modeling-assisted experimentation may allow rapid progress for overall system understanding compared to observational or disciplinary research agendas. Assessment and management of risk from intentional contamination can be performed with greater confidence when mechanisms are known and the relationships between different components are validated. This level of understanding allows high-fidelity assessments that do not hamper legitimate possession of these toxins for research purposes, while preventing intentional …

Desulfovibrio vulgaris Hildenborough belongs to a class ofsulfate-reducing bacteria (SRB) and is found ubiquitously in nature.Given the importance of SRB-mediated reduction for bioremediation ofmetal ion contaminants, ongoing research on D. vulgaris has been in thedirection of elucidating regulatory mechanisms for this organism under avariety of stress conditions. This work presents a global view of thisorganism's response to elevated growth temperature using whole-celltranscriptomics and proteomics tools. Transcriptional response (1.7-foldchange or greater; Z>1.5) ranged from 1,135 genes at 15 min to 1,463genes at 120 min for a temperature up-shift of 13oC from a growthtemperature of 37oC for this organism and suggested both direct andindirect modes of heat sensing. Clusters of orthologous group categoriesthat were significantly affected included posttranslationalmodifications; protein turnover and chaperones (up-regulated); energyproduction and conversion (down-regulated), nucleotide transport,metabolism (down-regulated), and translation; ribosomal structure; andbiogenesis (down-regulated). Analysis of the genome sequence revealed thepresence of features of both negative and positive regulation whichincluded the CIRCE element and promoter sequences corresponding to thealternate sigma factors ?32 and ?54. While mechanisms of heat shockcontrol for some genes appeared to coincide with those established forEscherichia coli and Bacillus subtilis, the presence of unique controlschemes for several other genes was also evident. Analysis of proteinexpression levels using …

The Heavy Ion Fusion (HIF) program is progressing through a series of physics and technology demonstrations leading to an inertial fusion power plant. The High Current Experiment (HCX) at Lawrence Berkeley National Laboratory is exploring the physics of intense beams with high line-charge density. Superconducting focusing quadrupoles have been developed for the HCX magnetic transport studies. A baseline design was selected following several pre-series models. Optimization of the baseline design led to the development of a first prototype that achieved a conductor-limited gradient of 132 T/m in a 70 mm bore, without training, with measured field errors at the 0.1% level. Based on these results, the magnet geometry and fabrication procedures were adjusted to improve the field quality. These modifications were implemented in a second prototype. In this paper, the optimized design is presented and comparisons between the design harmonics and magnetic measurements performed on the new prototype are discussed.

In the summer of 1992, the survey and alignment team at the Stanford Linear Accelerator Center acquired a CMS3000 laser tracker manufactured by Chesapeake Laser Systems in Lanham, Maryland. This paper gives a description of the principles of operation and calibration of the tracker. Several applications are explained and the results shared.