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2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008 (open access)

2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008

This conference brings together scientists interested in a range of basic phenomena linked to the ejection and scattering of electrons from atoms, molecules, clusters, liquids and solids by absorption of light. Photoionization, a highly sensitive probe of both structure and dynamics, can range from perturbative single-photon processes to strong-field highly non-perturbative interactions. It is responsible for the formation and destruction of molecules in astrophysical and plasma environments and successfully used in advanced analytical techniques. Positive ions, which can be produced and studied most effectively using photoionization, are the major components of all plasmas, vital constituents of flames and important intermediates in many chemical reactions. Negative ions are significant as transient species and, when photodetached, the corresponding neutral species often undergoes remarkable, otherwise non-observable, dynamics. The scope of the meeting spans from novel observations in atomic and molecular physics, such as Coulomb Crystals, highly excited states and cold Rydberg plasmas, to novel energy resolved or ultrafast time-resolved experiments, photoionization in strong laser fields, theoretical method development for electron scattering, photoionization and photodetachment and more complex phenomena such as charge transfer and DNA and protein conductivity, important for biological and analytical applications.
Date: March 31, 2009
Creator: GRay, Klaus Muller-Dethefs Nancy Ryan
System: The UNT Digital Library
Exact Lattice Supersymmetry (open access)

Exact Lattice Supersymmetry

We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.
Date: March 31, 2009
Creator: Catterall, Simon; Kaplan, David B. & Unsal, Mithat
System: The UNT Digital Library
Relating D0-anti-D0 Mixing and D0 -> l l- with New Physics (open access)

Relating D0-anti-D0 Mixing and D0 -> l l- with New Physics

We point out how, in certain models of New Physics, the same combination of couplings occurs in the amplitudes for both D{sup 0}-{bar D}{sup 0} mixing and the rare decays D{sup 0} {yields} {ell}{sup +}{ell}{sup -}. If the New Physics dominates and is responsible for the observed mixing, then a very simple correlation exists between the magnitudes of each; in fact the rates for the decay D{sup 0} {yields} {ell}{sup +}{ell}{sup -} are completely fixed by the mixing. Observation of D{sup 0} {yields} {ell}{sup +}{ell}{sup -} in excess of the Standard Model prediction could identify New Physics contributions to D{sup 0}-{bar D}{sup 0} mixing.
Date: March 31, 2009
Creator: Golowich, Eugene; Hewett, JoAnne; Pakvasa, Sandip & Petrov, Alexey A.
System: The UNT Digital Library
Progress on laser plasma accelerator development using transverselyand longitudinally shaped plasmas (open access)

Progress on laser plasma accelerator development using transverselyand longitudinally shaped plasmas

A summary of progress at Lawrence Berkeley National Laboratory is given on: (1) experiments on down-ramp injection; (2) experiments on acceleration in capillary discharge plasma channels; and (3) simulations of a staged laser wakefield accelerator (LWFA). Control of trapping in a LWFA using plasma density down-ramps produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV Ic FWHM, respectively) and with central momenta of 0.76 +- 0.02 MeV Ic, stable over a week of operation. Experiments were also carried out using a 40 TW laser interacting with a hydrogen-filled capillary discharge waveguide. For a 15 mm long, 200 mu m diameter capillary, quasi-monoenergetic bunches up to 300 MeV were observed. By detuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. For a 33 mm long, 300 mu m capillary, a parameter regime with high energy bunches, up to 1 Ge V, was found. In this regime, peak electron energy was correlated with the amount of trapped charge. Simulations show that bunches produced on a down-ramn and iniected into a channel-guided LWFA can produce stable beams with 0.2 MeV Ic-class momentum spread at high …
Date: March 31, 2009
Creator: Leemans, Wim P.; Esarey, E.; Geddes, C.G.R.; Toth, Cs.; Schroeder, C.B.; Nakamura, K. et al.
System: The UNT Digital Library
Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation (open access)

Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation

We propose measurements of the deeply virtual Compton amplitude (DVCS) {gamma}* {yields} H{bar H}{gamma} in the timelike t = (p{sub H} + p{sub {bar H}}){sup 2} > 0 kinematic domain which is accessible at electron-positron colliders via the radiative annihilation process e{sup +}e{sup -} {yields} H{bar H}{gamma}. These processes allow the measurement of timelike deeply virtual Compton scattering for a variety of H{bar H} hadron pairs such as {pi}{sup +}{pi}{sup -}, K{sup +}K{sup -}, and D{bar D} as well as p{bar p}. As in the conventional spacelike DVCS, there are interfering coherent amplitudes contributing to the timelike processes involving C = - form factors. The interference between the amplitudes measures the phase of the C = + timelike DVCS amplitude relative to the phase of the timelike form factors and can be isolated by considering the forward-backward e{sup +} {leftrightarrow} e{sup -} asymmetry. The J = 0 fixed pole contribution which arises from the local coupling of the two photons to the quark current plays a special role. As an example we present a simple model.
Date: March 31, 2009
Creator: Afanasev, Andrei; Brodsky, Stanley J.; Carlson, Carl E. & Mukherjee, Asmita
System: The UNT Digital Library
Multiflavor QCD* on R_3 * S_1: Studying Transition From Abelian to Non-Abelian Confinement (open access)

Multiflavor QCD* on R_3 * S_1: Studying Transition From Abelian to Non-Abelian Confinement

The center-stabilized multiflavor QCD* theories formulated on R{sub 3} x S{sub 1} exhibit both Abelian and non-Abelian confinement as a function of the S{sub 1} radius, similar to the Seiberg-Witten theory as a function of the mass deformation parameter. For sufficiently small number of flavors and small r(S{sub 1}), we show occurrence of a mass gap in gauge fluctuations, and linear confinement. This is a regime of confinement without continuous chiral symmetry breaking ({chi}SB). Unlike one-flavor theories where there is no phase transition in r(S{sub 1}), the multiflavor theories possess a single phase transition associated with breaking of the continuous {chi}S. We conjecture that the scale of the {chi}SB is parametrically tied up with the scale of Abelian to non-Abelian confinement transition.
Date: March 31, 2009
Creator: Shifman, M.; /Minnesota U., Theor. Phys. Inst.; Unsal, M. & /SLAC /Stanford U., Phys. Dept.
System: The UNT Digital Library
Thermodynamics of the Complexation of Uranium(VI) by oxalate in aqueous solution at 10-70oC (open access)

Thermodynamics of the Complexation of Uranium(VI) by oxalate in aqueous solution at 10-70oC

The protonation reactions of oxalate (ox) and the complex formation of uranium(VI) with oxalate in 1.05 mol kg{sup -1} NaClO{sub 4} were studied at variable temperatures (10-70 C). Three U(VI)/ox complexes (UO{sub 2}ox{sub j}{sup (2-2j){sup +}} with j = 1, 2, 3) were identified in this temperature range. The formation constants and the molar enthalpies of complexation were determined by spectrophotometry and calorimetry. The complexation of uranium(VI) with oxalate ion is exothermic at lower temperatures (10-40 C) and becomes endothermic at higher temperatures (55-70 C). In spite of this, the free energy of complexation becomes more negative at higher temperatures due to increasingly more positive entropy of complexation that exceeds the increase of the enthalpy of complexation. The thermodynamic parameters at different temperatures, in conjunction with the literature data for other dicarboxylic acids, provide insight into the relative strength of U(VI) complexes with a series of dicarboxylic acids (oxalic, malonic and oxydiacetic) and rationalization for the highest stability of U(VI)/oxalate complexes in the series. The data reported in this study are of importance in predicting the migration of uranium(VI) in geological environments in the case of failure of the engineering barriers which protect waste repositories.
Date: March 31, 2009
Creator: Di Bernardo, Plinio; Zanonato, Pier Luigi; Tian, Guoxin; Tolazzi, Marilena & Rao, Linfeng
System: The UNT Digital Library
Integrated analysis of breast cancer cell lines reveals unique signaling pathways (open access)

Integrated analysis of breast cancer cell lines reveals unique signaling pathways

Cancer is a heterogeneous disease resulting from the accumulation of genetic defects that negatively impact control of cell division, motility, adhesion and apoptosis. Deregulation in signaling along the EGFR-MAPK pathway is common in breast cancer, though the manner in which deregulation occurs varies between both individuals and cancer subtypes. We were interested in identifying subnetworks within the EGFR-MAPK pathway that are similarly deregulated across subsets of breast cancers. To that end, we mapped genomic, transcriptional and proteomic profiles for 30 breast cancer cell lines onto a curated Pathway Logic symbolic systems model of EGFR-MEK signaling. This model was comprised of 539 molecular states and 396 rules governing signaling between active states. We analyzed these models and identified several subtype specific subnetworks, including one that suggested PAK1 is particularly important in regulating the MAPK cascade when it is over-expressed. We hypothesized that PAK1 overexpressing cell lines would have increased sensitivity to MEK inhibitors. We tested this experimentally by measuring quantitative responses of 20 breast cancer cell lines to three MEK inhibitors. We found that PAK1 over-expressing luminal breast cancer cell lines are significantly more sensitive to MEK inhibition as compared to those that express PAK1 at low levels. This indicates that …
Date: March 31, 2009
Creator: Heiser, Laura M.; Wang, Nicholas J.; Talcott, Carolyn L.; Laderoute, Keith R.; Knapp, Merrill; Guan, Yinghui et al.
System: The UNT Digital Library
FLASH Beam-Off RF Measurements and Analyses (open access)

FLASH Beam-Off RF Measurements and Analyses

The FLASH L-band (1.3 GHz) superconducting accelerator facility at DESY has a Low Level RF (LLRF) system that is similar to that envisioned for ILC. This system has extensive monitoring capability and was used to gather performance data relevant to ILC. In particular, waveform data were recorded with beam off for three, 8-cavity cryomodules to evaluate the input rf stability, perturbations to the SC cavity frequencies and the rf overhead required to achieve constant gradient during the 800-s pulses. In this paper, we discuss the measurements and data analysis procedures and present key findings on the pulse-to-pulse input rf and cavity field stability.
Date: March 31, 2009
Creator: Pei, Shilun; Adolphsen, Chris & Carwardine, John
System: The UNT Digital Library