2004 Electron Donor Acceptor Interactions Gordon Conference - August 8-13, 2004 (open access)

2004 Electron Donor Acceptor Interactions Gordon Conference - August 8-13, 2004

The 2004 Gordon Conference on Donor/Acceptor Interactions will take place at Salve Regina University in Newport, Rhode Island on August 8-13, 2004. The conference will be devoted to the consequences of charge interaction and charge motion in molecular and materials systems.
Date: September 14, 2005
Creator: GUILFORD JONES BOSTON UNIVERSITY PHOTONICS CENTER 8 ST. MARY'S ST BOSTON, MA 02215
System: The UNT Digital Library
Comment on Form Factor Shape and Extraction of $|V_{ub}|$ from $B\to\pi l \nu$ (open access)

Comment on Form Factor Shape and Extraction of $|V_{ub}|$ from $B\to\pi l \nu$

We point out that current experimental data for partial B {yields} {pi}l{nu} branching fractions reduce the theoretical input required for a precise extraction of |V{sub ub}| to the form-factor normalization at a single value of the pion energy. Different parameterizations of the form factor shape leading to this conclusion are compared and the role of dispersive bounds on heavy-to-light form factors is clarified.
Date: September 14, 2005
Creator: Becher, Thomas & Hill, Richard J.
System: The UNT Digital Library
Comparative genome analysis of Bacillus cereus group genomes withBacillus subtilis (open access)

Comparative genome analysis of Bacillus cereus group genomes withBacillus subtilis

Genome features of the Bacillus cereus group genomes (representative strains of Bacillus cereus, Bacillus anthracis and Bacillus thuringiensis sub spp israelensis) were analyzed and compared with the Bacillus subtilis genome. A core set of 1,381 protein families among the four Bacillus genomes, with an additional set of 933 families common to the B. cereus group, was identified. Differences in signal transduction pathways, membrane transporters, cell surface structures, cell wall, and S-layer proteins suggesting differences in their phenotype were identified. The B. cereus group has signal transduction systems including a tyrosine kinase related to two-component system histidine kinases from B. subtilis. A model for regulation of the stress responsive sigma factor sigmaB in the B. cereus group different from the well studied regulation in B. subtilis has been proposed. Despite a high degree of chromosomal synteny among these genomes, significant differences in cell wall and spore coat proteins that contribute to the survival and adaptation in specific hosts has been identified.
Date: September 14, 2005
Creator: Anderson, Iain; Sorokin, Alexei; Kapatral, Vinayak; Reznik, Gary; Bhattacharya, Anamitra; Mikhailova, Natalia et al.
System: The UNT Digital Library
Effective Interactions and Operators in Nuclei within the No-Core Shell Model (open access)

Effective Interactions and Operators in Nuclei within the No-Core Shell Model

We review the application of effective operator formalism to the ab initio no core shell model (NCSM). For short-range operators, such as the nucleon-nucleon potential, the unitary-transformation method works extremely well at the two-body cluster approximation and good results are obtained for the binding energies and excitation spectra of light nuclei (A {<=} 16). However, for long-range operators, such as the radius or the quadrupole moment, performing this unitary transformation at the two-body cluster level, does not include the higher-order correlations needed to renormalize these long-range operators adequately. Usually, such correlations can be obtained either by increasing the order of the cluster approximation, or by increasing the model space. We will discuss the difficulties of these approaches as well as alternate possible solutions for including higher-order correlations in small model spaces.
Date: September 14, 2005
Creator: Barrett, B; Navratil, P; Stetcu, I & Vary, J
System: The UNT Digital Library
Equilibrium Beam Invariants of an Electron Storage Ring with Linear x-y Coupling (open access)

Equilibrium Beam Invariants of an Electron Storage Ring with Linear x-y Coupling

In accelerators, it is common that the motion of the horizontal x-plane is coupled to that of the vertical y-plane. Such coupling will induce tune shifts and can cause instabilities. The damping and diffusion rates are also affected, which in turn will lead to a change in the equilibrium invariants. With the perturbative approach which is also used for synchrobetatron coupling [B. Nash, J.Wu, and A. Chao, work in progress], we study the x-y coupled case in this paper. Starting from the one-turn map, we give explicit formulae for the tune shifts, damping and diffusion rates, and the equilibrium invariants. We focus on the cases where the system is near the integer or half integer, and sum or difference resonances where small coupling can cause a large change in the beam distribution.
Date: September 14, 2005
Creator: Wu, Juhao; Nash, B.E. & Chao, A.W.
System: The UNT Digital Library
Improved Electron Yield and Spin-Polarizaton from III-V Photocathodes Via Bias Enhanced Carrier Drift (open access)

Improved Electron Yield and Spin-Polarizaton from III-V Photocathodes Via Bias Enhanced Carrier Drift

Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile. Preliminary measurements have been carried out on bulk and thin film GaAs. As expected, the yield change far from the bandgap is quite large for bulk material. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. The size of the bias to cause an appreciable effect is rather small reflecting the low drift kinetic energy in the zero bias case.
Date: September 14, 2005
Creator: Mulhollan, Gregory A.; Bierman, John; Brachmann, Axel; Clendenin, James E.; Garwin, Edward; Kirby, Robert et al.
System: The UNT Digital Library
Macroscopic Subdivision of Silica Aerogel Collectors for Sample Return Missions (open access)

Macroscopic Subdivision of Silica Aerogel Collectors for Sample Return Missions

Silica aerogel collector tiles have been employed for the collection of particles in low Earth orbit and, more recently, for the capture of cometary particles by NASA's Stardust mission. Reliable, reproducible methods for cutting these and future collector tiles from sample return missions are necessary to maximize the science output from the extremely valuable embedded particles. We present a means of macroscopic subdivision of collector tiles by generating large-scale cuts over several centimeters in silica aerogel with almost no material loss. The cut surfaces are smooth and optically clear allowing visual location of particles for analysis and extraction. This capability is complementary to the smaller-scale cutting capabilities previously described [Westphal (2004), Ishii (2005a, 2005b)] for removing individual impacts and particulate debris in tiny aerogel extractions. Macroscopic cuts enable division and storage or distribution of portions of aerogel tiles for immediate analysis of samples by certain techniques in situ or further extraction of samples suited for other methods of analysis.
Date: September 14, 2005
Creator: Ishii, H A & Bradley, J P
System: The UNT Digital Library
Progress in Development of Kharkov X-Ray Generator Nestor (open access)

Progress in Development of Kharkov X-Ray Generator Nestor

The sources of the X-rays based on Compton scattering of intense Nd:YAG laser beam on electron beam circulating in a storage ring with beam energy 43-225 MeV is under construction in NSC KIPT. In the paper the progress in development and construction of Kharkov X-ray generator NESTOR is presented. The current status of the main facility system design and development are described. New scheme and main parameters of injection system are presented. The status of power supply system and control system is described. The facility is going to be in operation in the middle of 2007 and generated X-rays flux is expected to be of about 10{sup 13} phot/s.
Date: September 14, 2005
Creator: Androsov, V.; Bulyak, V.; Dovbnya, A.; Drebot, I.; Gladkikh, P.; Grevtsev, V. et al.
System: The UNT Digital Library