Modified magnetic ground state in NiMn2O4 thin films (open access)

Modified magnetic ground state in NiMn2O4 thin films

We demonstrate the stabilization of a magnetic ground state in epitaxial NiMn2O4 (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral Mn{sup 4+}:Mn{sup 3+} concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low temperature. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn{sup 4+} while the canted moment ferrimagnetic ordering is preserved below 60 K.
Date: August 3, 2010
Creator: Nelson-Cheeseman, B. B.; Chopdekar, R. V.; Toney, M. F.; Arenholz, E.; Suzuki, Y. & Iwata, J.M.
System: The UNT Digital Library
Electronic structure and spectroscopy of nucleic acid bases: Ionization energies, ionization-induced structural changes, and photoelectron spectra (open access)

Electronic structure and spectroscopy of nucleic acid bases: Ionization energies, ionization-induced structural changes, and photoelectron spectra

We report high-level ab initio calculations and single-photon ionization mass spectrometry study of ionization of adenine (A), thymine (T), cytosine (C) and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed using equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the {omega}B97X-D functional. The ionization-induced geometry changes of the bases are consistent with the shapes of the corresponding molecular orbitals. For the lowest-energy tautomers, the magnitude of the structural relaxation decreases in the following series G > C > A > T, the respective relaxation energies being 0.41, 0.32, 0.25 and 0.20 eV. The computed adiabatic ionization energies (8.13, 8.89, 8.51-8.67 and 7.75-7.87 eV for A,T,C and G, respectively) agree well with the onsets of the photoionization efficiency (PIE) curves (8.20 {+-} 0.05, 8.95 {+-} 0.05, 8.60 {+-} 0.05 and 7.75 {+-} 0.05 eV). Vibrational progressions for the S{sub 0}-D{sub 0} vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra.
Date: August 2, 2010
Creator: Bravaya, Ksenia B.; Kostko, Oleg; Dolgikh, Stanislav; Landau, Arie; Ahmed, Musahid & Krylov, Anna I.
System: The UNT Digital Library
Sensor Configuration Selection for Discrete-Event Systems under Unreliable Observations (open access)

Sensor Configuration Selection for Discrete-Event Systems under Unreliable Observations

Algorithms for counting the occurrences of special events in the framework of partially-observed discrete event dynamical systems (DEDS) were developed in previous work. Their performances typically become better as the sensors providing the observations become more costly or increase in number. This paper addresses the problem of finding a sensor configuration that achieves an optimal balance between cost and the performance of the special event counting algorithm, while satisfying given observability requirements and constraints. Since this problem is generally computational hard in the framework considered, a sensor optimization algorithm is developed using two greedy heuristics, one myopic and the other based on projected performances of candidate sensors. The two heuristics are sequentially executed in order to find best sensor configurations. The developed algorithm is then applied to a sensor optimization problem for a multiunit- operation system. Results show that improved sensor configurations can be found that may significantly reduce the sensor configuration cost but still yield acceptable performance for counting the occurrences of special events.
Date: August 1, 2010
Creator: Lin, Wen-Chiao; Yoo, Tae-Sic & Garcia, Humberto E.
System: The UNT Digital Library
Subduction Controls of Hf and Nd Isotopes in Lavas of the Aleutian Island Arc (open access)

Subduction Controls of Hf and Nd Isotopes in Lavas of the Aleutian Island Arc

The Hf and Nd isotopic compositions of 71 Quaternary lavas collected from locations along the full length of the Aleutian island arc are used to constrain the sources of Aleutian magmas and to provide insight into the geochemical behavior of Nd and Hf and related elements in the Aleutian subduction-magmatic system. Isotopic compositions of Aleutian lavas fall approximately at the center of, and form a trend parallel to, the terrestrial Hf-Nd isotopic array with {var_epsilon}{sub Hf} of +12.0 to +15.5 and {var_epsilon}{sub Nd} of +6.5 to +10.5. Basalts, andesites, and dacites within volcanic centers or in nearby volcanoes generally all have similar isotopic compositions, indicating that there is little measurable effect of crustal or other lithospheric assimilation within the volcanic plumbing systems of Aleutian volcanoes. Hafnium isotopic compositions have a clear pattern of along-arc increase that is continuous from the eastern-most locations near Cold Bay to Piip Seamount in the western-most part of the arc. This pattern is interpreted to reflect a westward decrease in the subducted sediment component present in Aleutian lavas, reflecting progressively lower rates of subduction westward as well as decreasing availability of trench sediment. Binary bulk mixing models (sediment + peridotite) demonstrate that 1-2% of the …
Date: August 29, 2010
Creator: Yogodzinski, Gene; Vervoort, Jeffery; Brown, Shaun Tyler & Gerseny, Megan
System: The UNT Digital Library
"Applications and future trends in polymer materials for green energy systems: from energy generation and storage, to CO2 capture and transportaion" (open access)

"Applications and future trends in polymer materials for green energy systems: from energy generation and storage, to CO2 capture and transportaion"

Presentation describes United Technologies Research Center's recent work in green energy systems, including APRA-E project content to create a synthetic analogue of the carbonic anhydrase enzyme and incorporate it into a membrane for CO2 separation from the flue gas of a coal power plant.
Date: August 24, 2010
Creator: Zafiris, George
System: The UNT Digital Library
2010 GRC VIBRATIONAL SPECTROSCOPY AUGUST 1 - AUGUST 6, 2010 (open access)

2010 GRC VIBRATIONAL SPECTROSCOPY AUGUST 1 - AUGUST 6, 2010

The Vibrational Spectroscopy conference focuses on using vibrational spectroscopy to probe structure and dynamics of molecules in gases, liquids, and at interfaces. The conference explores the wide range of state-of-the-art techniques based on vibrational motion. These techniques span the fields of time-domain, high-resolution frequency-domain, spatially-resolved, nonlinear and multidimensional spectroscopies. The conference highlights the application of these techniques in chemistry, materials, biology, and medicine. The theory of molecular vibrational motion and its connection to spectroscopic signatures and chemical reaction dynamics is the third major theme of the meeting. The goal is to bring together a collection of researchers who share common interests and who will gain from discussing work at the forefront of several connected areas. The intent is to emphasize the insights and understanding that studies of vibrations provide about a variety of molecular systems ranging from small polyatomic molecules to large biomolecules and nanomaterials.
Date: August 6, 2010
Creator: Pate, Brooks
System: The UNT Digital Library
Dynamics of microbial community composition and function during in-situ bioremediation of a uranium-contaminated aquifer (open access)

Dynamics of microbial community composition and function during in-situ bioremediation of a uranium-contaminated aquifer

A pilot-scale system was established to examine the feasibility of in situ U(VI) immobilization at a highly contaminated aquifer (U.S. DOE Integrated Field Research Challenge site, Oak Ridge, TN). Ethanol was injected intermittently as an electron donor to stimulate microbial U(VI) reduction, and U(VI) concentrations fell to below the Environmental Protection Agency drinking water standard (0.03 mg liter{sup -1}). Microbial communities from three monitoring wells were examined during active U(VI) reduction and maintenance phases with GeoChip, a high-density, comprehensive functional gene array. The overall microbial community structure exhibited a considerable shift over the remediation phases examined. GeoChip-based analysis revealed that Fe(III)-reducing bacterial (FeRB), nitrate-reducing bacterial (NRB), and sulfate-reducing bacterial (SRB) functional populations reached their highest levels during the active U(VI) reduction phase (days 137 to 370), in which denitrification and Fe(III) and sulfate reduction occurred sequentially. A gradual decrease in these functional populations occurred when reduction reactions stabilized, suggesting that these functional populations could play an important role in both active U(VI) reduction and maintenance of the stability of reduced U(IV). These results suggest that addition of electron donors stimulated the microbial community to create biogeochemical conditions favorable to U(VI) reduction and prevent the reduced U(IV) from reoxidation and that …
Date: August 15, 2010
Creator: Van Nostrand, J. D.; Wu, L.; Wu, W. M.; Huang, A.; Gentry, T. J.; Deng, Y. et al.
System: The UNT Digital Library
Feature Tracking Using Reeb Graphs (open access)

Feature Tracking Using Reeb Graphs

Tracking features and exploring their temporal dynamics can aid scientists in identifying interesting time intervals in a simulation and serve as basis for performing quantitative analyses of temporal phenomena. In this paper, we develop a novel approach for tracking subsets of isosurfaces, such as burning regions in simulated flames, which are defined as areas of high fuel consumption on a temperature isosurface. Tracking such regions as they merge and split over time can provide important insights into the impact of turbulence on the combustion process. However, the convoluted nature of the temperature isosurface and its rapid movement make this analysis particularly challenging. Our approach tracks burning regions by extracting a temperature isovolume from the four-dimensional space-time temperature field. It then obtains isosurfaces for the original simulation time steps and labels individual connected 'burning' regions based on the local fuel consumption value. Based on this information, a boundary surface between burning and non-burning regions is constructed. The Reeb graph of this boundary surface is the tracking graph for burning regions.
Date: August 2, 2010
Creator: Weber, Gunther H.; Bremer, Peer-Timo; Day, Marcus S.; Bell, John B. & Pascucci, Valerio
System: The UNT Digital Library
2010 Water & Aqueous Solutions (open access)

2010 Water & Aqueous Solutions

Water covers more than two thirds of the surface of the Earth and about the same fraction of water forms the total mass of a human body. Since the early days of our civilization water has also been in the focus of technological developments, starting from converting it to wine to more modern achievements. The meeting will focus on recent advances in experimental, theoretical, and computational understanding of the behavior of the most important and fascinating liquid in a variety of situations and applications. The emphasis will be less on water properties per se than on water as a medium in which fundamental dynamic and reactive processes take place. In the following sessions, speakers will discuss the latest breakthroughs in unraveling these processes at the molecular level: Water in Solutions; Water in Motion I and II; Water in Biology I and II; Water in the Environment I and II; Water in Confined Geometries and Water in Discussion (keynote lecture and poster winners presentations).
Date: August 13, 2010
Creator: Ben-Amotz, Dor
System: The UNT Digital Library
Does Mixing Make Residential Ventilation More Effective? (open access)

Does Mixing Make Residential Ventilation More Effective?

Ventilation dilutes or removes indoor contaminants to reduce occupant exposure. In a multi-zone environment such as a house, there will be different dilution rates and different source strengths in every zone. The total ventilation rate is the most important factor in determining the exposure of occupants to given sources, but the zone- specific distribution of exhaust and supply air, and the mixing of ventilation air can have significant roles. Different types of ventilation systems will provide different amounts of mixing depending on several factors such as air leakage through the building envelope, air distribution systems and the location of sources and occupants. This paper reports recent results of investigations to determine the impact that air mixing has on exposures of residential occupants to prototypical contaminants of concern. Evaluations of existing field measurements and simulations reported in the literature are combined with new analyses to provide an integrated overview of the topic. The results show that for extreme cases additional mixing can be a significant factor but for typical homes looking at average exposures mixing is not helpful and can even make exposures worse.
Date: August 16, 2010
Creator: Sherman, Max & Walker, Iain
System: The UNT Digital Library
Low-speckle holographic beam shaping of high-coherence EUV sources (open access)

Low-speckle holographic beam shaping of high-coherence EUV sources

This paper describes a method to arbitrarily shape and homogenize high-coherence extreme ultraviolet sources using time-varying holographic optical elements and a scanning subsystem to mitigate speckle. In systems with integration times longer than 100 ms, a speckle contrast below 1% can be achieved.
Date: August 1, 2010
Creator: Anderson, Christopher N.; Miyakawa, Ryan H. & Naulleau, Patrick
System: The UNT Digital Library
Array of virtual Frisch-grid CZT detectors with common cathode readout and pulse-height correction (open access)

Array of virtual Frisch-grid CZT detectors with common cathode readout and pulse-height correction

We present our new results from testing 15-mm-long virtual Frisch-grid CdZnTe detectors with a common-cathode readout for correcting pulse-height distortions. The array employs parallelepiped-shaped CdZnTe (CZT) detectors of a large geometrical aspect ratio, with two planar contacts on the top and bottom surfaces (anode and cathode) and an additional shielding electrode on the crystal's sides to create the virtual Frisch-grid effect. We optimized the geometry of the device and improved its spectral response. We found that reducing to 5 mm the length of the shielding electrode placed next to the anode had no adverse effects on the device's performance. At the same time, this allowed corrections for electron loss by reading the cathode signals to obtain depth information.
Date: August 1, 2010
Creator: Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Egarievwe, E. U.; Fochuk, P. M.; Fuerstnau, M. et al.
System: The UNT Digital Library
2010 ELECTRODEPOSITION GORDON RESEARCH CONFERENCE, AUGUST 1-6, 2010 (open access)

2010 ELECTRODEPOSITION GORDON RESEARCH CONFERENCE, AUGUST 1-6, 2010

The 2010 Gordon Conference on Electrodeposition will present cutting-edge research on electrodeposition with emphasis on (i) advances in basic science, (ii) developments in next-generation technologies, and (iii) new and emerging areas. The Conference will feature a wide range of topics, from atomic scale processes, nucleation and growth, thin film deposition, and electrocrystallization, to applications of electrodeposition in devices including microelectronics, solar energy, and power sources. The Conference will bring together investigators from a wide range of scientific disciplines, including chemical engineering, materials science and engineering, physics, and chemistry. The Conference will feature invited speakers at the forefront of the field, and a late-breaking news session that will provide the opportunity for graduate students, post-docs, and junior faculty to participate. The collegial atmosphere of this Conference, with scientific talks and poster sessions, as well as opportunities for informal gatherings in the afternoons and evenings, provides an avenue for scientists from different disciplines to discuss current issues and promotes cross-disciplinary collaborations in the various research areas represented. The Conference will be held at Colby-Sawyer College, located in the Mt. Kearsarge-Lake Sunapee Region of New Hampshire. The surrounding mountains, forests, and lakes provide a beautiful setting for this conference. The attendance is limited …
Date: August 6, 2010
Creator: Searson, Peter
System: The UNT Digital Library
ROCK DEFORMATION 2010 GORDON RESEARCH CONFERENCE, AUGUST 8-13, 2010 (open access)

ROCK DEFORMATION 2010 GORDON RESEARCH CONFERENCE, AUGUST 8-13, 2010

Creep in the crust and mantle is commonly considered a steady-state process. This view prevails despite the fact that earthquakes do not represent steady-state and at the base of the seismogenic zone, for example, the stresses that drive creep must vary with the earthquake cycle. The contribution of transient versus steady-state behavior is not easy to determine from naturally-deformed brittle or plastic rocks and our view of steady-state depends on whether we consider geological or shorter time-scales. Perhaps we avoid a non steady-state picture because we lack appropriate descriptive or quantitative tools. The aim of the 2010 Gordon Research Conference (GRC) in rock deformation is to explore what we know about non steady-state deformation and how we might advance our understanding through geological and geophysical field investigations, laboratory experiments and modeling. This will require an appraisal of the applicability of steady-state concepts as well as an exploration of transient behavior, in which processes and physical properties cycle between different states as might be the case during earthquake cycles, and transitions in behavior, where finite strain or changing environmental conditions lead to changes in processes and properties. Conference sessions will cover seven broad and interlinked topics. (1) What is steady state?; …
Date: August 13, 2010
Creator: Prior, David
System: The UNT Digital Library
Evaluating Energy Efficiency Policies with Energy-Economy Models (open access)

Evaluating Energy Efficiency Policies with Energy-Economy Models

The growing complexities of energy systems, environmental problems and technology markets are driving and testing most energy-economy models to their limits. To further advance bottom-up models from a multidisciplinary energy efficiency policy evaluation perspective, we review and critically analyse bottom-up energy-economy models and corresponding evaluation studies on energy efficiency policies to induce technological change. We use the household sector as a case study. Our analysis focuses on decision frameworks for technology choice, type of evaluation being carried out, treatment of market and behavioural failures, evaluated policy instruments, and key determinants used to mimic policy instruments. Although the review confirms criticism related to energy-economy models (e.g. unrealistic representation of decision-making by consumers when choosing technologies), they provide valuable guidance for policy evaluation related to energy efficiency. Different areas to further advance models remain open, particularly related to modelling issues, techno-economic and environmental aspects, behavioural determinants, and policy considerations.
Date: August 1, 2010
Creator: Mundaca, Luis; Neij, Lena; Worrell, Ernst & McNeil, Michael A.
System: The UNT Digital Library
Mechanical Performance of the LARP Nb{sub 3}Sn Quadrupole Magnet LQS01 (open access)

Mechanical Performance of the LARP Nb{sub 3}Sn Quadrupole Magnet LQS01

As part of the effort towards the development of Nb{sub 3}Sn magnets for future LHC luminosity upgrades, the LHC Accelerator Research Program (LARP) has fabricated and tested the quadrupole magnet LQS01. The magnet implements 3.4 m long Nb{sub 3}Sn coils contained in a support structure characterized by an external aluminum shell segmented in four sections. The room temperature pre-load of the structure is obtained by shimming load keys through bladders, pressurized during the loading operations and removed before cool-down. Temperature compensated strain gauges, mounted on structure components and coil poles, monitor the magnet's mechanical behavior during assembly, cool-down and excitation. During the first test, LQS01 reached the target gradient of 200 T/m; the gauge data indicated that the aluminum shell was pre-tensioned to the target value estimated by numerical models, but a lack of pre-load was measured in the coil inner layer during ramping. As a result, the test was interrupted and the magnet disassembled and inspected. A second test (LQS01b) was then carried out following a re-loading of the magnet. The paper reports on the strain gauge results of the first test and the analysis performed to identify corrective actions to improve the coil pre-stress distribution. The mechanical performance …
Date: August 1, 2010
Creator: Ferracin, P.; Ambrosio, G.; Anerella, M.; Bingham, B.; Bossert, R.; Caspi, S. et al.
System: The UNT Digital Library
Detector Performance of Ammonium-Sulfide-Passivated CdZnTe and CdMnTe Materials (open access)

Detector Performance of Ammonium-Sulfide-Passivated CdZnTe and CdMnTe Materials

Dark currents, including those in the surface and bulk, are the leading source of electronic noise in X-ray and gamma detectors, and are responsible for degrading a detector's energy resolution. The detector material itself determines the bulk leakage current; however, the surface leakage current is controllable by depositing appropriate passivation layers. In previous research, we demonstrated the effectiveness of surface passivation in CZT (CdZnTe) and CMT (CdMnTe) materials using ammonium sulfide and ammonium fluoride. In this research, we measured the effect of such passivation on the surface states of these materials, and on the performances of detectors made from them.
Date: August 1, 2010
Creator: Kim, K. H.; Bolotnikov, A. E.; Camarda, G. S.; Marchini, L.; Yang, G.; Hossain, A. et al.
System: The UNT Digital Library
Transmission Nuclear Resonance Fluorescence Measurements of 238U in Thick Targets (open access)

Transmission Nuclear Resonance Fluorescence Measurements of 238U in Thick Targets

Transmission nuclear resonance fluorescence measurements were made on targets consisting of Pb and depleted U with total areal densities near 86 g/cm2. The 238U content n the targets varied from 0 to 8.5percent (atom fraction). The experiment demonstrates the capability of using transmission measurements as a non-destructive technique to identify and quantify the presence of an isotope in samples with thicknesses comparable to he average thickness of a nuclear fuel assembly. The experimental data also appear to demonstrate the process of notch refilling with a predictable intensity. Comparison of measured spectra to previous backscatter 238U measurements indicates general agreement in observed excited states. Two new 238U excited states and possibly a third state have also been observed.
Date: August 31, 2010
Creator: Quiter, Brian J.; Ludewigt, Bernhard A.; Mozin, Vladimir V.; Wilson, Cody & Korbly, Steve
System: The UNT Digital Library
Field Quality of the First LARP Nb{sub 3}Sn 3.7 m-Long Quadrupole Model of LQ Series (open access)

Field Quality of the First LARP Nb{sub 3}Sn 3.7 m-Long Quadrupole Model of LQ Series

The US-LHC accelerator research program (LARP) built and tested the first 3.7-m long Nb{sub 3}Sn quadrupole model of LQ series with a 90 mm bore diameter and a target field gradient of 200 T/m. The LQ series, developed in collaboration among FNAL, LBNL and BNL, is a scale up of the previously tested 1-m long technology quadrupoles of TQ series based on similar coils and two different mechanical structures (shell-based TQS and collar-based TQC), with a primary goal of demonstrating the Nb{sub 3}Sn accelerator magnet technology for the luminosity upgrade of LHC interaction regions. In this paper, we present the field quality measurements in the first 3.7-m long LQS01 model based on the modified TQS mechanical structure. The results are compared to the expectations from the magnet geometry and magnetic properties of coils and iron yoke. Moreover, we present a comparison between this magnet and the short models previously measured.
Date: August 1, 2010
Creator: Velev, G.V.; Ambrosio, G.; Andreev, N.; Anerella, M.; Bossert, R.; Caspi, S. et al.
System: The UNT Digital Library
Introduction of Nonlinear Properties Into Hierachical Models of Nb3Sn Strands (open access)

Introduction of Nonlinear Properties Into Hierachical Models of Nb3Sn Strands

The development of computational models representing Rutherford cable formation and deformation is necessary to investigate the strain state in the superconducting filaments in Nb{sub 3}Sn magnets. The wide variety of length scales within accelerator magnets suggests usage of a hierarchical structure within the model. As part of an ongoing investigation at LBNL, a three-dimensional simplified nonlinear multiscale model is developed as a way to extend previous linear elastic versions. The inclusion of plasticity models into the problem formulation allows an improved representation of strand behavior compared to the linear elastic model. This formulation is applied to a single Nb{sub 3}Sn strand to find its effective properties as well as the strain state in the conductor under loading.
Date: August 1, 2010
Creator: Collins, B.; Krishnan, J.; Arbelaez, D.; Ferracin, P.; Prestemon, S. O.; Godeke, A. et al.
System: The UNT Digital Library
Thermographic analyses of the growth of Cd1-xZnxTe single crystals (open access)

Thermographic analyses of the growth of Cd1-xZnxTe single crystals

Bulk Cd1-xZnxTe (0<x<0.1) single crystals for gamma-ray detectors are grown mainly from near-stoichiometric melts. We discuss the influence of the thermal pre-history of the melts (superheating, thermo-cycling, and cooling rate) on various physical properties based on our thermographic analyses, electrical conductivity and viscosity measurements. Increasing the Zn content causes non-monotonic dependencies in the quality of the crystals structure.
Date: August 1, 2010
Creator: Kopach, O. V.; Bolotnikov, A.; Shcherbak, Larysa P.; Fochuk, Petro M. & James, Ralph B.
System: The UNT Digital Library
Test Results of the first 3.7 m Long Nb3Sn Quadrupole by LARP and Future Plans (open access)

Test Results of the first 3.7 m Long Nb3Sn Quadrupole by LARP and Future Plans

In December 2009 during its first cold test, LQS01, the first long Nb{sub 3}Sn Quadrupole made by LARP (LHC Accelerator Research Program, a collaboration of BNL, FNAL, LBNL and SLAC), reached its target field gradient of 200 T/m. This target was set in 2005 by the US Department fo Energy, CERN and LARP, as a significant milestone toward the development of Nb{sub 3}Sn quadrupoles for possible use in LHC luminosity upgrades. LQS01 is a 90 mm aperture, 3.7 m long quadrupole using Nb{sub 3}Sn coils. The coil layout is equal to the layout used in the LARP Technological Quadrupoles (TQC and TQS models). Pre-stress and support are provided by a segmented aluminum shell pre-loaded using bladders and keys, similarly to the TQS models. After the first test the magnet was disassembled, reassembled with an optimized pre-stress, and reached 222 T/m at 4.5 K. In this paper we present the results of both tests and the next steps of the Long Quadrupole R&D.
Date: August 1, 2010
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bingham, B.; Bocian, D. et al.
System: The UNT Digital Library
Competitive repair by naturally dispersed repetitive DNA during non-allelic homologous recombination (open access)

Competitive repair by naturally dispersed repetitive DNA during non-allelic homologous recombination

Genome rearrangements often result from non-allelic homologous recombination (NAHR) between repetitive DNA elements dispersed throughout the genome. Here we systematically analyze NAHR between Ty retrotransposons using a genome-wide approach that exploits unique features of Saccharomyces cerevisiae purebred and Saccharomyces cerevisiae/Saccharomyces bayanus hybrid diploids. We find that DNA double-strand breaks (DSBs) induce NAHR-dependent rearrangements using Ty elements located 12 to 48 kilobases distal to the break site. This break-distal recombination (BDR) occurs frequently, even when allelic recombination can repair the break using the homolog. Robust BDR-dependent NAHR demonstrates that sequences very distal to DSBs can effectively compete with proximal sequences for repair of the break. In addition, our analysis of NAHR partner choice between Ty repeats shows that intrachromosomal Ty partners are preferred despite the abundance of potential interchromosomal Ty partners that share higher sequence identity. This competitive advantage of intrachromosomal Tys results from the relative efficiencies of different NAHR repair pathways. Finally, NAHR generates deleterious rearrangements more frequently when DSBs occur outside rather than within a Ty repeat. These findings yield insights into mechanisms of repeat-mediated genome rearrangements associated with evolution and cancer.
Date: August 27, 2010
Creator: Hoang, Margaret L.; Tan, Frederick J.; Lai, David C.; Celniker, Sue E.; Hoskins, Roger A.; Dunham, Maitreya J. et al.
System: The UNT Digital Library
Performance of Nb3Sn Quadrupole Under High Stress (open access)

Performance of Nb3Sn Quadrupole Under High Stress

Future upgrades of the Large Hadron Collider (LHC) will require large aperture and high gradient quadrupoles. Nb{sub 3}Sn is the most viable option for this application but is also known for its strain sensitivity. In high field magnets, with magnetic fields above 12 T, the Lorentz forces will generate mechanical stresses that may exceed 200 MPa in the windings. The existing measurements of critical current versus strain of Nb{sub 3}Sn strands or cables are not easily applicable to magnets. In order to investigate the impact of high mechanical stress on the quench performance, a series of tests was carried out within a LBNL/CERN collaboration using the magnet TQS03 (a LHC Accelerator Research Program (LARP) 1-meter long, 90-mm aperture Nb{sub 3}Sn quadrupole). The magnet was tested four times at CERN under various pre-stress conditions. The average mechanical compressive azimuthal pre-stress on the coil at 4.2 K ranged from 120 MPa to 200 MPa. This paper reports on the magnet performance during the four tests focusing on the relation between pre-stress conditions and the training plateau.
Date: August 1, 2010
Creator: Felice, H.; Bajko, M.; Bingham, B.; Bordini, B.; Bottura, L.; Caspi, S. et al.
System: The UNT Digital Library