The photodissociation dynamics of small I{sup -}(H{sub 2}O){sub n} (n = 2-5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been studied using photofragment coincidence imaging. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel ({approx}90%) is a 2-body process forming neutral I + (H{sub 2}O){sub n} photofragments, and the minor channel is a 3-body process forming I + (H{sub 2}O){sub n-1} + H{sub 2}O fragments. Both process display translational energy (P(E{sub T})) distributions peaking at E{sub T} = 0 with little available energy partitioned into translation. Clusters excited to the detachment continuum rather than to the CTTS state display the same two channels with similar P(E{sub T}) distributions. The observation of similar P(E{sub T}) distributions from the two sets of experiments suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited (I(H{sub 2}O){sub n}{sup -})* cluster, or, less probably, that the presence of the excess electron has little effect on the departing I atom.

In this paper, we present a three-dimensional quasistatic model for high brightness beam dynamics simulation in rf/dc photoinjectors, rf linacs, and similar devices on parallel computers. In this model, electrostatic space-charge forces within a charged particle beam are calculated self-consistently at each time step by solving the three-dimensional Poisson equation in the beam frame and then transforming back to the laboratory frame. When the beam has a large energy spread, it is divided into a number of energy bins or slices so that the space-charge forces are calculated from the contribution of each bin and summed together. Image-charge effects from conducting photocathode are also included efficiently using a shifted-Green function method. For a beam with large aspect ratio, e.g., during emission, an integrated Green function method is used to solve the three-dimensional Poisson equation. Using this model, we studied beam transport in one Linac Coherent Light Sources photoinjector design through the first traveling wave linac with initial misalignment with respect to the accelerating axis within a range of a few KeV to about 10 KeV.

Dynamic retail pricing, especially real-time pricing (RTP), has been widely heralded as a panacea for providing much-needed demand response in electricity markets. However, in designing default service for competitive retail markets, demand response has been an afterthought, and in some cases not given any weight at all. But that may be changing, as states that initiated customer choice in the past 5-7 years reach an important juncture in retail market design. Most states with retail choice established an initial transitional period during which utilities were required to offer a default or standard offer generation service, often at a capped or otherwise administratively-determined rate. Many retail choice states have reached the end of their transitional period, and several have adopted or are actively considering an RTP-type default service for large commercial and industrial (C&I) customers. In most cases, the primary reason for adopting RTP as the default service has been to advance policy objectives related to the development of competitive retail markets. However, if attention is paid in its design and implementation, default RTP service can also provide a solid foundation for developing price responsive demand, creating an important link between wholesale and retail market transactions. This article, which draws from …

It is shown that the Hugoniot and the critical shear stress required to deform a metal plastically in shock compression can be obtained directly from molecular dynamics simulations without recourse to surface velocity profiles, or to details of the dislocation evolution. Specific calculations are shown for aluminum shocked along the [100] direction, and containing an initial distribution of microscopic defects. The presence of such defects has a minor effect on the Hugoniot and on the dynamic strength at high pressures. Computed results agree with experimental data.

Electron tomograph tomography is a well y well-established technique for three-dimensional structure determination of (almost) amorphous specimens in life science applications. With the recent advances in nanotechnology and the semiconductor industry, there is also an increasing need for high-resolution 3D structural information in physical sciences. In this paper, we evaluate the capabilities and limitations of TEM and HAADF-STEM tomography for the 3D structural characterization of partially crystalline to highly crystalline materials. Our analysis of catalysts, a hydrogen storage material, and different semiconductor devices shows that features with a diameter as small as 1-2 nm can be resolved in 3D by electron tomography. For partially crystalline materials with small single crystalline domains, TEM tomography provides reliable 3D structural information. HAADF-STEM tomography is more versatile and can also be used for high-resolution 3D imaging of highly crystalline materials such as semiconductor devices.

We propose a hierarchical Bayesian model for conducting inference on the location of multiple seismic events (earthquakes) given data on the arrival of various seismic phases to sensor locations. The model explicitly accounts for the uncertainty associated with a theoretical seismic-wave travel-time model used along with the uncertainty of the arrival data. Posterior inferences is carried out using Markov chain Monte Carlo (MCMC).

The Linac Coherent Light Source (LCLS) Project will be an x-ray free-electron laser. It is intended to produce pulses of 800-8,000 eV photons. Each pulse, produced with a repetition frequency of up to 120 Hz, will provide >10{sup 12} photons within a duration of less than 200 femtoseconds. The project employs the last kilometer of the SLAC linac to provide a low-emittance electron beam in the energy range 4-14 GeV to a single undulator. Two experiment halls, located 100m and 350m from the undulator exit, will house six experiment stations for research in atomic/molecular physics, pump-probe dynamics of materials and chemical processes, x-ray imaging of clusters and complex molecules, and plasma physics. Engineering design activities began in 2003, and the project is to be completed in March 2009. The project design permits straightforward expansion of the LCLS to multiple undulators.

A high-speed imaging system with shutter speeds as fast as 2 ns and double frame capability has been used to directly image the formation and evolution of the Sustained Spheromak Physics Experiment (SSPX). Reproducible plasma features have been identified with this diagnostic and divided in three groups, according to the stage in the discharge at which they occur: (1) breakdown and ejection, (2) sustainment, and (3) decay. During the first stage, plasma descends into the flux conserver shortly after breakdown and a transient plasma column is formed. The column then rapidly bends and simultaneously becomes too dim to photograph a few microseconds after formation. We conjecture that this rapid bending precedes the transfer of toroidal to poloidal flux. During sustainment, a stable plasma column different from the transient one is observed. It has been possible to measure the column diameter and compare it to CORSICA, an MHD equilibrium reconstruction code which showed good agreement with the measurements. Elongation and velocity measurements were made of cathode patterns also seen during this stage, possibly caused by pressure gradients or E x B drifts. The patterns elongate in a toroidal-only direction which depends on the magnetic field polarity. During the decay stage the …

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Summary of the conference, summarizing both theoretical and experimental presentations and discussions.

FLUKA is a multipurpose Monte Carlo code which can transport a variety of particles over a wide energy range in complex geometries. The code is a joint project of INFN and CERN: part of its development is also supported by the University of Houston and NASA. FLUKA is successfully applied in several fields, including but not only, particle physics, cosmic ray physics, dosimetry, radioprotection, hadron therapy, space radiation, accelerator design and neutronics. The code is the standard tool used at CERN for dosimetry, radioprotection and beam-machine interaction studies. Here we give a glimpse into the code physics models with a particular emphasis to the hadronic and nuclear sector.

Fast Neutron Resonance Radiography (NRR) has recently become a focus of investigation as a supplement to conventional x-ray systems as a non-invasive, non-destructive means of detecting explosive material concealed in checked luggage or cargo containers at airports. Using fast (1-6 MeV) neutrons produced by the D(d,n){sup 3}He reaction, NRR provides both an imaging capability and the ability to determine the chemical composition of materials in baggage or cargo. Elemental discrimination is achieved by exploiting the resonance features of the neutron cross-section for oxygen, nitrogen, carbon, and hydrogen. Simulations have shown the effectiveness of multiple-element NRR through Monte Carlo transport methods; this work is focused on the development of a prototype system that will incorporate an accelerator-based neutron source and a neutron detection and imaging system to demonstrate the realistic capabilities of NRR in distinguishing the elemental components of concealed objects. Preliminary experiments have exposed significant technical difficulties unapparent in simulations, including the presence of image contamination from gamma ray production, the detection of low-fluence fast neutrons in a gamma field, and the mechanical difficulties inherent in the use of thin foil windows for gas cell confinement. To mitigate these concerns, a new gas target has been developed to simultaneously reduce …

A high pressure deuterium gas target has been designed to provide high-flux fast neutrons using the D(d,n){sup 3}He reaction for use as a neutron source. The deuterium gas cell holds 4 atm D{sub 2} gas at 298K and is projected to tolerate a beam current of {approx}50 {micro}A of 3.0 MeV deuterons for 8 hours of continuous use. The high-pressure gas cell is designed to provide a fast neutron flux on the order of 10{sup 5} n/cm{sup 2}-s at one meter. Measurements of gamma ray production from deuterium impingement have shown tungsten to generate the fewest gamma rays; the primary components of the gas target have been constructed out of tungsten to decrease the number of gamma rays. To accommodate the high gas pressure, thin foil tungsten windows have been structurally reinforced with a tungsten support allowing for more than 60% beam transmission while greatly increasing the structural reliability of the thin windows. Extensive simulation and experimental testing have demonstrated the heating tolerances of the gas target thin windows and have shown that the peak temperature of the thin foils does not exceed 600 C, while the edges of the foil do not exceed 100 C, well within the limits …

We compute the masses of all moduli in the unstable deSitter vacua arising in the toy model of cosmological M-theory flux compactifications on the G{sub 2} holonomy manifolds of [1]. The slow-roll parameters in the tachyonic directions are shown to be too large to be useful for conventional models of inflation. However, it appears that we can find fast roll regimes which could, under certain conditions, account for the current dark energy driven accelerated expansion of the universe.

Several accelerators, including the SLC, JLAB, Mainz, Bates/MIT, and Bonn have successfully operated for medium and high energy physics experiments using polarized electron beams generated by dc-biased guns employing GaAs photocathodes. Since these guns have all used a bias on the order of 100 kV, the longitudinal emittance of the extracted bunch is rather poor. Downstream rf bunching systems increase the transverse emittance. An rf gun with a GaAs photocathode would eliminate the need for separate rf bunchers, resulting in a simpler injection system. In addition, the thermal emittance of GaAs-type cathodes is significantly lower than for other photocathode materials. The environmental requirements for operating activated GaAs photocathodes cannot be met by rf guns as currently designed and operated. These requirements, including limits on vacuum and electron back bombardment, are discussed in some detail. Modifications to actual and proposed rf gun designs that would allow these requirements to be met are presented.