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2006 Photoions, Photoionization & Photodetachment held on January 29-February 3, 2006 (open access)

2006 Photoions, Photoionization & Photodetachment held on January 29-February 3, 2006

The 4th Gordon Conference on Photoions, Photoionization and Photodetachment will be held January 29-February 3, 2006 at the Santa Ynez Valley Marriott in Buellton, California. This meeting will continue to cover fundamentals and applications of photoionization and photodetachment, including valence and core-level phenomena and applications to reaction dynamics, ultrashort laser pulses and the study of exotic molecules and anions. Further information will be available soon at the Gordon Conference Website, and will be announced.
Date: September 6, 2006
Creator: Gray, Robert Continetti Nancy Ryan
System: The UNT Digital Library
Accelerated Evolution of Conserved Noncoding Sequences in theHuman Genome (open access)

Accelerated Evolution of Conserved Noncoding Sequences in theHuman Genome

Genomic comparisons between human and distant, non-primatemammals are commonly used to identify cis-regulatory elements based onconstrained sequence evolution. However, these methods fail to detect"cryptic" functional elements, which are too weakly conserved amongmammals to distinguish from nonfunctional DNA. To address this problem,we explored the potential of deep intra-primate sequence comparisons. Wesequenced the orthologs of 558 kb of human genomic sequence, coveringmultiple loci involved in cholesterol homeostasis, in 6 nonhumanprimates. Our analysis identified 6 noncoding DNA elements displayingsignificant conservation among primates, but undetectable in more distantcomparisons. In vitro and in vivo tests revealed that at least three ofthese 6 elements have regulatory function. Notably, the mouse orthologsof these three functional human sequences had regulatory activity despitetheir lack of significant sequence conservation, indicating that they arecryptic ancestral cis-regulatory elements. These regulatory elementscould still be detected in a smaller set of three primate speciesincluding human, rhesus and marmoset. Since the human and rhesus genomesequences are already available, and the marmoset genome is activelybeing sequenced, the primate-specific conservation analysis describedhere can be applied in the near future on a whole-genome scale, tocomplement the annotation provided by more distant speciescomparisons.
Date: July 6, 2006
Creator: Prambhakar, Shyam; Noonan, James P.; Paabo, Svante & Rubin, EdwardM.
System: The UNT Digital Library
The Accelerator Markup Language and the Universal Accelerator Parser (open access)

The Accelerator Markup Language and the Universal Accelerator Parser

A major obstacle to collaboration on accelerator projects has been the sharing of lattice description files between modeling codes. To address this problem, a lattice description format called Accelerator Markup Language (AML) has been created. AML is based upon the standard eXtensible Markup Language (XML) format; this provides the flexibility for AML to be easily extended to satisfy changing requirements. In conjunction with AML, a software library, called the Universal Accelerator Parser (UAP), is being developed to speed the integration of AML into any program. The UAP is structured to make it relatively straightforward (by giving appropriate specifications) to read and write lattice files in any format. This will allow programs that use the UAP code to read a variety of different file formats. Additionally, this will greatly simplify conversion of files from one format to another. Currently, besides AML, the UAP supports the MAD lattice format.
Date: October 6, 2006
Creator: Sagan, D.; Forster, M.; /Cornell U., LNS; Bates, D.A.; /LBL, Berkeley; Wolski, A. et al.
System: The UNT Digital Library
The Age of Human Cerebral Cortex Neurons (open access)

The Age of Human Cerebral Cortex Neurons

The traditional static view of the adult mammalian brain has been challenged by the realization of continuous generation of neurons from stem cells. Based mainly on studies in experimental animals, adult neurogenesis may contribute to recovery after brain insults and decreased neurogenesis has been implicated in the pathogenesis of neurological and psychiatric diseases in man. The extent of neurogenesis in the adult human brain has, however, been difficult to establish. We have taken advantage of the integration of {sup 14}C, generated by nuclear bomb tests during the Cold War, in DNA to establish the age of neurons in the major areas of the human cerebral cortex. Together with the analysis of the cortex from patients who received BrdU, which integrates in the DNA of dividing cells, our results demonstrate that whereas non-neuronal cells turn over, neurons in the human cerebral cortex are not generated postnatally at detectable levels, but are as old as the individual.
Date: April 6, 2006
Creator: Bhardwaj, R. D.; Curtis, M. A.; Spalding, K. L.; Buchholz, B. A.; Fink, D.; Bjork-Eriksson, T. et al.
System: The UNT Digital Library
Atomistically-informed Dislocation Dynamics in fcc Crystals (open access)

Atomistically-informed Dislocation Dynamics in fcc Crystals

We develop a nodal dislocation dynamics (DD) model to simulate plastic processes in fcc crystals. The model explicitly accounts for all slip systems and Burgers vectors observed in fcc systems, including stacking faults and partial dislocations. We derive simple conservation rules that describe all partial dislocation interactions rigorously and allow us to model and quantify cross-slip processes, the structure and strength of dislocation junctions and the formation of fcc-specific structures such as stacking fault tetrahedra. The DD framework is built upon isotropic non-singular linear elasticity, and supports itself on information transmitted from the atomistic scale. In this fashion, connection between the meso and micro scales is attained self-consistently with core parameters fitted to atomistic data. We perform a series of targeted simulations to demonstrate the capabilities of the model, including dislocation reactions and dissociations and dislocation junction strength. Additionally we map the four-dimensional stress space relevant for cross-slip and relate our findings to the plastic behavior of monocrystalline fcc metals.
Date: September 6, 2006
Creator: Martinez, E.; Marian, J.; Arsenlis, T.; Victoria, M. & Perlado, J. M.
System: The UNT Digital Library
Beam Energy Scaling of Ion-Induced Electron Yield from K+ Impact on Stainless Steel (open access)

Beam Energy Scaling of Ion-Induced Electron Yield from K+ Impact on Stainless Steel

Electron clouds limit the performance of many major accelerators and storage rings. Significant quantities of electrons result when halo ions are lost to beam tubes, generating gas which can be ionized and ion-induced electrons that can multiply and accumulate, causing degradation or loss of the ion beam. In order to understand the physical mechanisms of ion-induced electron production, experiments studied the impact of 50 to 400 keV K{sup +} ions on stainless steel surfaces near grazing incidence, using the 500 kV Ion Source Test Stand (STS-500) at LLNL. The experimental electron yield scales with the electronic component (dE{sub e}/dx) of the stopping power and its angular dependence does not follow l/cos({theta}). A theoretical model is developed, using TRIM code to evaluate dE{sub e}/dx at several depths in the target, to estimate the electron yield, which is compared with the experimental results. The experiment extends the range of energy from previous works and the model reproduces the angular dependence and magnitude of the electron yield.
Date: March 6, 2006
Creator: Covo, M K; Molvik, A; Friedman, A; Westenskow, G; Barnard, J J; Cohen, R et al.
System: The UNT Digital Library
Biodiesel R&D at NREL (open access)

Biodiesel R&D at NREL

Discusses NREL's biodiesel research priorities and some current research results, including those concerning biodiesel quality and stability.
Date: February 6, 2006
Creator: McCormick, R.; Alleman, T.; Barnitt, R.; Clark, W.; Hayes, B.; Ireland, J. et al.
System: The UNT Digital Library
Black Hole Entropy, Marginal Stability and Mirror Symmetry (open access)

Black Hole Entropy, Marginal Stability and Mirror Symmetry

We consider the superconformal quantum mechanics associated to BPS black holes in type IIB Calabi-Yau compactifications. This quantum mechanics describes the dynamics of D-branes in the near-horizon attractor geometry of the black hole. In many cases, the black hole entropy can be found by counting the number of chiral primaries in this quantum mechanics. Both the attractor mechanism and notions of marginal stability play important roles in generating the large number of microstates required to explain this entropy. We compute the microscopic entropy explicitly in a few different cases, where the theory reduces to quantum mechanics on the moduli space of special Lagrangians. Under certain assumptions, the problem may be solved by implementing mirror symmetry as three T-dualities: this is essentially the mirror of a calculation by Gaiotto, Strominger and Yin. In some simple cases, the calculation may be done in greater generality without resorting to conjectures about mirror symmetry. For example, the K3 x T{sub 2} case may be studied precisely using the Fourier-Mukai transform.
Date: October 6, 2006
Creator: Aspinwall, Paul S.; Maloney, Alexander & Simons, Aaron
System: The UNT Digital Library
A C++ Framework for Conducting High-Speed, Long-Term Particle Tracking Simulations (open access)

A C++ Framework for Conducting High-Speed, Long-Term Particle Tracking Simulations

For the purpose of conducting parallel, long-term tracking studies of storage rings such as the ones described in [3], [4], maximum execution speed is essential. We describe an approach involving metaprogramming techniques in C++ which results in execution speeds rivaling hand-optimized assembler code for a particular tracking lattice while retaining the generality and flexibility of an all-purpose tracking code.
Date: February 6, 2006
Creator: Kabel, A. C.
System: The UNT Digital Library
Charm and Charmonium Spectroscopy at the e+e- B-Factories (open access)

Charm and Charmonium Spectroscopy at the e+e- B-Factories

Over the past few years, there has been a lot of progress in the areas of charm and charmonium spectroscopy, in large part due to the very large data samples being accumulated at the e{sup +}e{sup -} B-Factories. In this presentation I will focus on results in three areas: the X/Y/Z charmonium-candidate states, the D{sub sJ} charmed-strange mesons, and newly-discovered charmed baryons. Note the absence of a section on pentaquarks: all B-Factory searches for pentaquarks, charmed or otherwise, have not yielded any observation of such states.
Date: June 6, 2006
Creator: Marsiske, Helmut
System: The UNT Digital Library
Coiled-Coil Nanomechanics and Uncoiling and Unfolding of the Superhelix and  α-Helices of Myosin (open access)

Coiled-Coil Nanomechanics and Uncoiling and Unfolding of the Superhelix and α-Helices of Myosin

Article on coiled-coil nanomechanics and uncoiling and unfolding of the superhelix and α-helices of myosin.
Date: January 6, 2006
Creator: Root, Douglas D.; Yadavalli, Vamsi K.; Forbes, Jeffrey G. & Wang, Kuan
System: The UNT Digital Library
Computations of Eigenpair Subsets with the MRRR Algorithm (open access)

Computations of Eigenpair Subsets with the MRRR Algorithm

The main advantage of inverse iteration over the QR algorithm and Divide & Conquer for the symmetric tridiagonal eigenproblem is that subsets of eigenpairs can be computed at reduced cost. The MRRR algorithm (MRRR = Multiple Relatively Robust Representations) is a clever variant of inverse iteration without the need for reorthogonalization. STEGR, the current version of MRRR in LAPACK 3.0, does not allow for subset computations. The next release of STEGR is designed to compute a (sub-)set of k eigenpairs with {Omicron}(kn) operations. Because of the special way in which eigenvectors are computed, MRRR subset computations are more complicated than when using inverse iteration. Unlike the latter, MRRR sometimes cannot ignore the unwanted part of the spectrum. We describe the problems with what we call 'false singletons'. These are eigenvalues that appear to be isolated with respect to the wanted eigenvalues but in fact belong to a tight cluster of unwanted eigenvalues. This paper analyzes these complications and ways to deal with them.
Date: June 6, 2006
Creator: Marques, Osni A.; Parlett, Beresford N. & Vomel, Christof
System: The UNT Digital Library
A Conceptual model of coupled biogeochemical and hydrogeologicalprocesses affected by in situ Cr(VI) bioreduction in groundwater atHanford 100H Site (open access)

A Conceptual model of coupled biogeochemical and hydrogeologicalprocesses affected by in situ Cr(VI) bioreduction in groundwater atHanford 100H Site

The overall objective of this presentation is to demonstratea conceptual multiscale, multidomain model of coupling of biogeochemicaland hydrogeological processes during bioremediation of Cr(VI)contaminated groundwater at Hanford 100H site. A slow releasepolylactate, Hydrogen Release Compound (HRCTM), was injected in Hanfordsediments to stimulate immobilization of Cr(VI). The HRC injectioninduced a 2-order-of-magnitude increase in biomass and the onset ofreducing biogeochemical conditions [e.g., redox potential decreased from+240 to -130 mV and dissolved oxygen (DO) was completely removed]. Athree-well system, comprised of an injection well and upgradient anddowngradient monitoring wells, was used for conducting the in situbiostimulation, one regional flow (no-pumping) tracer test, and fivepumping tests along with the Br-tracer injection. Field measurements wereconducted using a Br ion-selective electrode and a multiparameter flowcell to collect hourly data on temperature, pH, redox potential,electrical conductivity, and DO. Groundwater sampling was conducted bypumping through specially designed borehole water samplers.Cross-borehole radar tomography and seismic measurements were carried outto assess the site background lithological heterogeneity and themigration pathways of HRC byproducts through groundwater after the HRCinjection.
Date: September 6, 2006
Creator: Faybishenko, B.; Long, P. E.; Hazen, T. C.; Hubbard, S. S.; Williams, K. H.; Peterson, J. E. et al.
System: The UNT Digital Library
Cost Comparison of Linear and Circular Accelerators. (open access)

Cost Comparison of Linear and Circular Accelerators.

None
Date: August 6, 2006
Creator: Ruggiero, A.
System: The UNT Digital Library
Current and Potential Distribution in a Divertor with Torioidally-Asymmetric Biasing of the Divertor Plate (open access)

Current and Potential Distribution in a Divertor with Torioidally-Asymmetric Biasing of the Divertor Plate

Toroidally-asymmetric biasing of the divertor plate may increase convective cross-field transport in SOL and thereby reduce the divertor heat load. Experiments performed with the MAST spherical tokamak generally agree with a simple theory of non-axisymmetric biasing. However, some of the experimental results have not yet received a theoretical explanation. In particular, existing theory seems to overestimate the asymmetry between the positive and the negative biasing. Also lacking a theoretical explanation is experimentally observed increase of the average floating potential in the main SOL in the presence of biasing. In this paper we attempt to solve these problems by accounting for the closing of the currents (driven by the biasing) in a strong-shear region near the X-point. We come up with the picture which, at least qualitatively, agrees with these experimental results.
Date: June 6, 2006
Creator: Cohen, R. H.; Ryutov, D. D.; Counsell, G. F. & Helander, P.
System: The UNT Digital Library
Decreasing Magmatic Footprints of Individual Volcanos in a Waning Basaltic Field (open access)

Decreasing Magmatic Footprints of Individual Volcanos in a Waning Basaltic Field

The distribution and characteristics of individual basaltic volcanoes in the waning Southwestern Nevada Volcanic Field provide insight into the changing physical nature of magmatism and the controls on volcano location. During Pliocene-Pleistocene times the volumes of individual volcanoes have decreased by more than one order of magnitude, as have fissure lengths and inferred lava effusion rates. Eruptions evolved from Hawaiian-style eruptions with extensive lavas to eruptions characterized by small pulses of lava and Strombolian to violent Strombolian mechanisms. These trends indicate progressively decreasing partial melting and length scales, or magmatic footprints, of mantle source zones for individual volcanoes. The location of each volcano is determined by the location of its magmatic footprint at depth, and only by shallow structural and topographic features that are within that footprint. The locations of future volcanoes in a waning system are less likely to be determined by large-scale topography or structures than were older, larger volume volcanoes.
Date: June 6, 2006
Creator: Valentine, G. A. & Perry, F. V.
System: The UNT Digital Library
Designing PV Incentive Programs to Promote Performance: A Reviewof Current Practice in the U.S. (open access)

Designing PV Incentive Programs to Promote Performance: A Reviewof Current Practice in the U.S.

In the U.S., the increasing financial support for customer-sited photovoltaic (PV) systems provided through publicly-funded incentive programs has heightened concerns about the long-term performance of these systems. Given the barriers that customers face to ensuring that their PV systems perform well, and the responsibility that PV incentive programs bear to ensure that public funds are prudently spent, these programs should, and often do, play a critical role in addressing PV system performance. To provide a point of reference for assessing the current state of the art, and to inform program design efforts going forward, we examine the approaches to encouraging PV system performance used by 32 prominent PV incentive programs in the U.S. We identify eight general strategies or groups of related strategies that these programs have used to address factors that affect performance, and describe key implementation details. Based on this review, we then offer recommendations for how PV incentive programs can be effectively designed to mitigate potential performance issues.
Date: October 6, 2006
Creator: Barbose, Galen; Wiser, Ryan & Bolinger, Mark
System: The UNT Digital Library
Detailed Simulations of Atmospheric Flow and Dispersion in Urban Downtown Areas by Computational Fluid Dynamics (CFD) Models - An Application of Five CFD Models to Manhattan (open access)

Detailed Simulations of Atmospheric Flow and Dispersion in Urban Downtown Areas by Computational Fluid Dynamics (CFD) Models - An Application of Five CFD Models to Manhattan

Computational Fluid Dynamics (CFD) model simulations of urban boundary layers have improved so that they are useful in many types of flow and dispersion analyses. The study described here is intended to assist in planning emergency response activities related to releases of chemical or biological agents into the atmosphere in large cities such as New York City. Five CFD models (CFD-Urban, FLACS, FEM3MP, FEFLO-Urban, and Fluent-Urban) have been applied by five independent groups to the same 3-D building data and geographic domain in Manhattan, using approximately the same wind input conditions. Wind flow observations are available from the Madison Square Garden March 2005 (MSG05) field experiment. It is seen from the many side-by-side comparison plots that the CFD models simulations of near-surface wind fields generally agree with each other and with field observations, within typical atmospheric uncertainties of a factor of two. The qualitative results shown here suggest, for example, that transport of a release at street level in a large city could reach a few blocks in the upwind and crosswind directions. There are still key differences seen among the models for certain parts of the domain. Further quantitative examinations of differences among the models and the observations are …
Date: March 6, 2006
Creator: Hanna, S. R.; Brown, M. J.; Camelli, F. E.; Chan, S. T.; Coirier, W. J.; Hansen, O. R. et al.
System: The UNT Digital Library
Development of Ultra-Fast Silicon Switches for Active X-Band High Power RF Compression Systems (open access)

Development of Ultra-Fast Silicon Switches for Active X-Band High Power RF Compression Systems

We present the recent results of our research on the high power ultra-fast silicon RF switches. This switch is composed of a group of PIN diodes on a high purity silicon wafer. The wafer is inserted into a cylindrical waveguide under TE{sub 01} mode, performing switching by injecting carriers into the bulk silicon. Our current design uses a CMOS compatible process and the device was fabricated at SNF (Stanford Nanofabrication Facility). 300 ns switching time has been observed, while the switching speed can be improved further with 3-D device structure and faster driving circuit. Power handling capacity of the switch is at the level of 10 MW. The switch was designed for active X-band RF pulse compression systems--especially for NLC, but it is also possible to be modified for other applications and other frequencies.
Date: March 6, 2006
Creator: Guo, Ji-Quan & Tantawi, S.
System: The UNT Digital Library
Dose dependent effects of exercise training and detraining ontotal and regional adiposity in 4,663 men and 1,743 (open access)

Dose dependent effects of exercise training and detraining ontotal and regional adiposity in 4,663 men and 1,743

Objective: To determine if exercise reduces body weight andto examine the dose-response relationships between changes in exerciseand changes in total and regional adiposity. Methods and Results:Questionnaires on weekly running distance and adiposity from a largeprospective study of 3,973 men and 1,444 women who quit running(detraining), 270 men and 146 women who started running (training) and420 men and 153 women who remained sedentary during 7.4 years offollow-up. There were significant inverse relationships between change inthe amount of vigorous exercise (km/wk run) and changes in weight and BMIin men (slope+-SE:-0.039+-0.005 kg and -0.012+-0.002 kg/m2 per km/wk,respectively) and older women (-0.060+-0.018 kg and -0.022+-0.007 kg/m2per km/wk) who quit running, and in initially sedentary men(-0.098+-0.017 kg and -0.032+-0.005 kg/m2 per km/wk) and women(-0.062+-0.023 kg and -0.021+-0.008 kg/m2 per km/wk) who started running.Changes in waist circumference were also inversely related to changes inrunning distance in men who quit (-0.026+-0.005 cm per km/wk) or startedrunning (-0.078+-0.017 cm per km/wk). Conclusions. The initiation andcessation of vigorous exercise decrease and increase body weight andintra-abdominal fat, respectively, and these changes are proportional tothe change in exercise dose.
Date: January 6, 2006
Creator: Williams, Paul T. & Thompson, Paul D.
System: The UNT Digital Library
Durability of Advanced Electrocatalysts for PEM Fuel Cells (open access)

Durability of Advanced Electrocatalysts for PEM Fuel Cells

None
Date: December 6, 2006
Creator: Atanassova, Paolina
System: The UNT Digital Library
Durability Testing of Fluidized Bed Steam Reformer (FBSR) Waste Forms (open access)

Durability Testing of Fluidized Bed Steam Reformer (FBSR) Waste Forms

Fluidized Bed Steam Reforming (FBSR) is being considered as a potential technology for the immobilization of a wide variety of high sodium aqueous radioactive wastes. The addition of clay and a catalyst as co-reactants converts high sodium aqueous low activity wastes (LAW) such as those existing at the Hanford and Idaho DOE sites to a granular ''mineralized'' waste form that may be made into a monolith form if necessary. Simulant Hanford and Idaho high sodium wastes were processed in a pilot scale FBSR at Science Applications International Corporation (SAIC) Science and Technology Applications Research (STAR) facility in Idaho Falls, ID. Granular mineral waste forms were made from (1) a basic Hanford Envelope A low-activity waste (LAW) simulant and (2) an acidic INL simulant commonly referred to as sodium-bearing waste (SBW). The FBSR waste forms were characterized and the durability tested via ASTM C1285 (Product Consistency Test), the Environmental Protection Agency (EPA) Toxic Characteristic Leaching Procedure (TCLP), and the Single Pass Flow Through (SPFT) test. The durability of the FBSR waste form products was tested in order to compare the measured durability to previous FBSR waste form testing on Hanford Envelope C waste forms that were made by THOR Treatment Technologies …
Date: January 6, 2006
Creator: Jantzen, Carol M.; Lorier, T. H.; Marra, J. C. & Pareizs, J. M.
System: The UNT Digital Library
Dynamic Program Phase Detection in Distributed Shared-Memory Multiprocessors (open access)

Dynamic Program Phase Detection in Distributed Shared-Memory Multiprocessors

We present a novel hardware mechanism for dynamic program phase detection in distributed shared-memory (DSM) multiprocessors. We show that successful hardware mechanisms for phase detection in uniprocessors do not necessarily work well in DSM systems, since they lack the ability to incorporate the parallel application's global execution information and memory access behavior based on data distribution. We then propose a hardware extension to a well-known uniprocessor mechanism that significantly improves phase detection in the context of DSM multiprocessors. The resulting mechanism is modest in size and complexity, and is transparent to the parallel application.
Date: March 6, 2006
Creator: Ipek, E; Martinez, J F; de Supinski, B R; McKee, S A & Schulz, M
System: The UNT Digital Library
Economic Systems Modeling for Laser IFE and the Potential advantages of Fast Ignition (open access)

Economic Systems Modeling for Laser IFE and the Potential advantages of Fast Ignition

An updated systems code for a laser-driven IFE power plant has been developed as part of the U.S. High Average Power Laser (HAPL) program. The cost of electricity (COE) is calculated using standardized methods for fusion reactor studies. In this paper, we describe the systems code and present results for capital cost and COE as a function of key design variables and parameters. We show how the COE varies as a function of driver energy and pulse repetition rate for different lasers. We examine the dependence of COE on other parameters such as laser cost ($/J), laser efficiency, plant efficiency, and net power output of the plant. Finally we compare results for a plant using direct-drive central ignition targets to results with fast ignition targets and note the potential advantages of fast ignition for various assumptions.
Date: June 6, 2006
Creator: Meier, W. R.
System: The UNT Digital Library