Band Collapse and the Quantum Hall Effect in Graphene (open access)

Band Collapse and the Quantum Hall Effect in Graphene

The recent Quantum Hall experiments in graphene have confirmed the theoretically well-understood picture of the quantum Hall (QH) conductance in fermion systems with continuum Dirac spectrum. In this paper we take into account the lattice, and perform an exact diagonalization of the Landau problem on the hexagonal lattice. At very large magnetic fields the Dirac argument fails completely and the Hall conductance, given by the number of edge states present in the gaps of the spectrum, is dominated by lattice effects. As the field is lowered, the experimentally observed situation is recovered through a phenomenon which we call band collapse. As a corollary, for low magnetic field, graphene will exhibit two qualitatively different QHE's: at low filling, the QHE will be dominated by the 'relativistic' Dirac spectrum and the Hall conductance will be odd-integer; above a certain filling, the QHE will be dominated by a non-relativistic spectrum, and the Hall conductance will span all integers, even and odd.
Date: March 16, 2010
Creator: Bernevig, B.Andrei; Hughes, Taylor L.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.; Chen, Han-Dong; /Illinois U., Urbana et al.
Object Type: Article
System: The UNT Digital Library

Community Supervision in Texas: Presentation to the House Committee on Corrections

Presentation providing an overview of the roles, responsibilities, and funding for the Texas Department of Criminal Justice - Community Justice Assistance Division.
Date: March 16, 2010
Creator: Texas. Department of Criminal Justice.
Object Type: Presentation
System: The Portal to Texas History
The Congressional Research Service and the American Legislative Process (open access)

The Congressional Research Service and the American Legislative Process

This report details the ways in which the Library of Congress supports and serves the members of Congress
Date: March 16, 2010
Creator: Brudnick, Ida A. & Back, Stanley
Object Type: Report
System: The UNT Digital Library
Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction (open access)

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

The reaction of the ground state methylidyne radical CH (X2Pi) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 90 oC (363 K), at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by Helimination. The Photoionization Efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (dpyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen …
Date: March 16, 2010
Creator: Soorkia, Satchin; Taatjes, Craig A.; Osborn, David L.; Selby, Talitha M.; Trevitt, Adam J.; Wilson, Kevin R. et al.
Object Type: Article
System: The UNT Digital Library
Direction-Preserving and Schur-Monotonic Semi-Separable Approximations of Symmetric Positive Definite Matrices} (open access)

Direction-Preserving and Schur-Monotonic Semi-Separable Approximations of Symmetric Positive Definite Matrices}

For a given symmetric positive definite matrix A {element_of} R{sup N x N}, we develop a fast and backward stable algorithm to approximate A by a symmetric positive-definite semi-separable matrix, accurate to a constant multiple of any prescribed tolerance. In addition, this algorithm preserves the product, AZ, for a given matrix Z {element_of} R{sup N x d}, where d << N. Our algorithm guarantees the positive-definiteness of the semi-separable matrix by embedding an approximation strategy inside a Cholesky factorization procedure to ensure that the Schur complements during the Cholesky factorization all remain positive definite after approximation. It uses a robust direction-preserving approximation scheme to ensure the preservation of AZ. We present numerical experiments and discuss potential implications of our work.
Date: March 16, 2010
Creator: Gu, M.; Li, X. S. & Vassilevski, P. S.
Object Type: Article
System: The UNT Digital Library
Emergency Communications: The Future of 911 (open access)

Emergency Communications: The Future of 911

This report discusses possible paths toward the modernization of the 911 infrastructure. Efforts to splice newer, digital technologies onto the aging infrastructure have created points of failure where a call can be dropped or misdirected, sometimes with tragic consequences.
Date: March 16, 2010
Creator: Moore, Linda K.
Object Type: Report
System: The UNT Digital Library
Federal Register, Volume 75, Number 50, March 16, 2010, Pages 12433-12656 (open access)

Federal Register, Volume 75, Number 50, March 16, 2010, Pages 12433-12656

Daily publication of the U.S. Office of the Federal Register contains rules and regulations, proposed legislation and rule changes, and other notices, including "Presidential proclamations and Executive Orders, Federal agency documents having general applicability and legal effect, documents required to be published by act of Congress, and other Federal agency documents of public interest" (p. ii). Table of Contents starts on page iii.
Date: March 16, 2010
Creator: United States. Office of the Federal Register.
Object Type: Journal/Magazine/Newsletter
System: The UNT Digital Library
Federal Stafford Act Disaster Assistance: Presidential Declarations, Eligible Activities, and Funding (open access)

Federal Stafford Act Disaster Assistance: Presidential Declarations, Eligible Activities, and Funding

This report provides an overview of the Stafford Act and Stafford Act declarations. The report discusses the types of assistance and eligibility, funding caps and cost shares, hazard mitigation assistance, disaster relief funds, and other issues for the 111th Congress.
Date: March 16, 2010
Creator: Bea, Keith
Object Type: Report
System: The UNT Digital Library
Fermi Liquid Instabilities in the Spin Channel (open access)

Fermi Liquid Instabilities in the Spin Channel

We study the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial waves (F{sub l}{sup a} (l > 0)). The ordered phases are classified into two classes, dubbed the {alpha} and {beta}-phases by analogy to the superfluid {sup 3}He-A and B-phases. The Fermi surfaces in the {alpha}-phases exhibit spontaneous anisotropic distortions, while those in the {beta}-phases remain circular or spherical with topologically non-trivial spin configurations in momentum space. In the {alpha}-phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have nearly isotropic underdamped dispersion relation at small propagating wavevectors. Due to the coupling to the Goldstone modes, the spin wave spectrum develops resonance peaks in both the {alpha} and {beta}-phases, which can be detected in inelastic neutron scattering experiments. In the p-wave channel {beta}-phase, a chiral ground state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.
Date: March 16, 2010
Creator: Wu, Congjun; /Santa Barbara, KITP; Sun, Kai; Fradkin, Eduardo; /Illinois U., Urbana; Zhang, Shou-Cheng et al.
Object Type: Article
System: The UNT Digital Library
German Foreign and Security Policy: Trends and Transatlantic Implications (open access)

German Foreign and Security Policy: Trends and Transatlantic Implications

This report provides an introduction to German foreign and security policy. The report discusses the foundations of German foreign policy, Germany in the European Union (EU), evolving security and defense policy, and transatalantic implications.
Date: March 16, 2010
Creator: Belkin, Paul
Object Type: Report
System: The UNT Digital Library
The Haitian Economy and the HOPE Act (open access)

The Haitian Economy and the HOPE Act

This report discusses the HOPE Act as it relates to U.S. trade policy, the Haitian economy, and post-earthquake reconstruction efforts.
Date: March 16, 2010
Creator: Hornbeck, J. F.
Object Type: Report
System: The UNT Digital Library
High Energy Density Physics Experiments With Intense Heavy Ion Beams (open access)

High Energy Density Physics Experiments With Intense Heavy Ion Beams

The US heavy ion fusion science program has developed techniques for heating ion-beam-driven warm dense matter (WDM) targets. The WDM conditions are to be achieved by combined longitudinal and transverse space-charge neutralized drift compression of the ion beam to provide a hot spot on the target with a beam spot size of about 1 mm, and pulse length about 1-2 ns. As a technique for heating volumetric samples of matter to high energy density, intense beams of heavy ions are capable of delivering precise and uniform beam energy deposition dE/dx, in a relatively large sample size, and the ability to heat any solid-phase target material. Initial experiments use a 0.3 MeV K+ beam (below the Bragg peak) from the NDCX-I accelerator. Future plans include target experiments using the NDCX-II accelerator, which is designed to heat targets at the Bragg peak using a 3-6 MeV lithium ion beam. The range of the beams in solid matter targets is about 1 micron, which can be lengthened by using porous targets at reduced density. We have completed the fabrication of a new experimental target chamber facility for WDM experiments, and implemented initial target diagnostics to be used for the first target experiments in …
Date: March 16, 2010
Creator: Henestroza, E.; Leitner, M.; Logan, B. G.; More, R. M.; Roy, P. K.; Ni, P. et al.
Object Type: Report
System: The UNT Digital Library
Homeland Security: Ongoing Challenges Impact the Federal Protective Service's Ability to Protect Federal Facilities (open access)

Homeland Security: Ongoing Challenges Impact the Federal Protective Service's Ability to Protect Federal Facilities

Testimony issued by the Government Accountability Office with an abstract that begins "Recent events including last month's attack on Internal Revenue Service offices in Texas, and the January 2010 shooting in the lobby of the Nevada, federal courthouse demonstrate the continued vulnerability of federal facilities and the safety of the federal employees who occupy them. These events also highlight the continued challenges involved in protecting federal real property and reiterate the importance of protecting the over 1 million government employees, as well as members of the public, who work in and visit the nearly 9,000 federal facilities. This testimony is based on past GAO reports and testimonies and discusses challenges Federal Protective Service (FPS) faces in protecting federal facilities and tenant agencies' perspective of FPS's services. To perform this work, GAO visited a number of federal facilities, surveyed tenant agencies, analyzed documents, and interviewed officials from several federal agencies."
Date: March 16, 2010
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Immigration: Policy Considerations Related to Guest Worker Programs (open access)

Immigration: Policy Considerations Related to Guest Worker Programs

This report discusses guest worker programs. The United States has two main programs for temporarily importing low-skilled workers, or guest workers. Agricultural guest workers enter through the H-2A visa program, and other guest workers enter through the H-2B visa program.
Date: March 16, 2010
Creator: Bruno, Andorra
Object Type: Report
System: The UNT Digital Library
Interim Continuing Resolutions (CRs): Potential Impacts on Agency Operations (open access)

Interim Continuing Resolutions (CRs): Potential Impacts on Agency Operations

This report discusses how an interim continuing resolutions (CRs), provisions and requirements may impact directly upon an agency. Second, the report analyzes Office of Management and Budget (OMB) and agency documents that have provided guidance or requirements for how an agency should navigate through periods of interim CRs. Third, the report analyzes brief mentions of claims of impact contained in Government Accountability Office (GAO) reports from a 20-year span.
Date: March 16, 2010
Creator: Brass, Clinton T.
Object Type: Report
System: The UNT Digital Library
The International Criminal Court (ICC): Jurisdiction, Extradition, and U.S. Policy (open access)

The International Criminal Court (ICC): Jurisdiction, Extradition, and U.S. Policy

This report focuses on the process by which the Office of the Prosecutor investigates allegations of war crimes and second on U.S policy towards the International Criminal Court (ICC) and how the court might assert jurisdiction over U.S. nationals.
Date: March 16, 2010
Creator: Barbour, Emily C. & Weed, Matthew C.
Object Type: Report
System: The UNT Digital Library
Libya: Background and U.S. Relations (open access)

Libya: Background and U.S. Relations

This report discusses the recent revolution in Libya, from its 2011 uprising to the end of the Qadhafi era. It specifically looks at Libya's weapons of mass destruction (WMD) disarmament, political reform and human rights, and energy as it relates to the Libyan economy.
Date: March 16, 2010
Creator: Blanchard, Christopher M.
Object Type: Report
System: The UNT Digital Library
Low Strain Rate Measurements on Explosives Using DIC (open access)

Low Strain Rate Measurements on Explosives Using DIC

None
Date: March 16, 2010
Creator: Cunningham, B J; Gagliardi, F J & Ferranti, L
Object Type: Article
System: The UNT Digital Library
Measurement/Evaluation Techniques and Nuclear Data Associated with Fission of 239Pu by Fission Spectrum Neutrons (open access)

Measurement/Evaluation Techniques and Nuclear Data Associated with Fission of 239Pu by Fission Spectrum Neutrons

This Panel was chartered to review and assess new evaluations of work on fission product data, as well as the evaluation process used by the two U.S. nuclear weapons physics laboratories. The work focuses on fission product yields resulting from fission spectrum neutrons incident on plutonium, and includes data from measurements that had not been previously published as well as new or revised fission product cumulative yield data, and related quantities such as Q values and R values. This report documents the Panel's assessment of the work presented by Los Alamos National Laboratory (LANL) and Lawrence Livermore National Laboratory (LLNL). Based on the work presented we have seven key observations: (1) Experiments conducted in the 1970s at LANL, some of which were performed in association with a larger, NIST-led, program, have recently been documented. A preliminary assessment of this work, which will be referred to in this document as ILRR-LANL, shows it to be technically sound. (2) LLNL has done a thorough, unbiased review and evaluation of the available literature and is in the process of incorporating the previously unavailable LANL data into its evaluation of key fission product yields. The results of the LLNL effort, which includes a preliminary …
Date: March 16, 2010
Creator: Baisden, Patricia; Bauge, Eric; Ferguson, James; Gilliam, David; Granier, Thierry; Jeanloz, Raymond et al.
Object Type: Report
System: The UNT Digital Library
New Isotope 263Hs (open access)

New Isotope 263Hs

A new isotope of Hs was produced in the reaction 208Pb(56Fe, n)263Hs at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory. Six genetically correlated nuclear decay chains have been observed and assigned to the new isotope 263Hs. The measured cross section was 21+13-8.4 pb at 276.4 MeV lab-frame center-of-target beam energy. 263Hs decays with a half-life of 0.74 ms by alpha-decay and the measured alpha-particle energies are 10.57 +- 0.06, 10.72 +- 0.06, and 10.89 +- 0.06 MeV. The experimental cross section is compared to a theoretical prediction based on the Fusion by Diffusion model [W. J. Swiatecki et al., Phys. Rev. C 71, 014602 (2005)].
Date: March 16, 2010
Creator: Dragojevic, I.; Gregorich, K. E.; Dullmann, Ch. E.; Dvorak, J.; Ellison, P. A.; Gates, J. M. et al.
Object Type: Article
System: The UNT Digital Library
Political Status of Puerto Rico: Options for Congress (open access)

Political Status of Puerto Rico: Options for Congress

This report discusses the current U.S.-Puerto Rico relationship, the history of said relationship, and the current political state of Puerto Rico, as well as relevant pieces of U.S. Congressional legislation concerning Puerto Rico.
Date: March 16, 2010
Creator: Bea, Keith & Garrett, R. Sam
Object Type: Report
System: The UNT Digital Library
Precision Measurements of Tau Lepton Decays (open access)

Precision Measurements of Tau Lepton Decays

Using data collected with the BABAR detector at the SLAC PEP-II electron-positron storage ring operating at a center-of-mass energy near 10.58 GeV, the branching fractions {Beta}({tau}{sup -} {yields} {pi}{sup -}{pi}{sup -}{pi}{sup +}{nu}{sub {tau}}) = (8.83 {+-} 0.01 {+-} 0.13)%, {Beta}({tau}{sup -} {yields} K{sup -}{pi}{sup -}{pi}{sup +}{nu}{sub {tau}}) = (0.273 {+-} 0.002 {+-} 0.009)%, {Beta}({tau}{sup -} {yields} K{sup -}{pi}{sup -}K{sup +}{nu}{sub {tau}}) = (0.1346 {+-} 0.0010 {+-} 0.0036)%, and {Beta}({tau}{sup -} {yields} K{sup -}K{sup -}K{sup +}{nu}{sub {tau}}) = (1.58 {+-} 0.13 {+-} 0.12) x 10{sup -5} are measured where the uncertainties are statistical and systematic, respectively. The invariant mass distribution for the {tau}{sup -} {yields} {pi}{sup -}{pi}{sup -}{pi}{sup +}{nu}{sub {tau}} {yields} K{sup -}{pi}{sup -}{pi}{sup +}{nu}{sub {tau}}, {tau}{sup -} {yields} K{sup -}{pi}{sup -}K{sup +}{nu}{sub {tau}} and {tau}{sup -} {yields} K{sup -}K{sup -}K{sup +}{nu}{sub {tau}} decays are unfolded to correct for detector effects. A measurement of {Beta}({tau}{sup -} {yields} {phi}{pi}{sup -}{nu}{sub {tau}}) = (3.42 {+-} 0.55 {+-} 0.25) x 10{sup -5}, a measurement of {Beta}({tau}{sup -} {yields} {phi}K{sup -}{nu}{sub {tau}}) = (3.39 {+-} 0.20 {+-} 0.28) x 10{sup -5} and an upper limit on {Beta}({tau}{sup -} {yields} K{sup -}K{sup -}K{sup +}{nu}{sub {tau}}[ex.{phi}]) {le} 2.5 x 10{sup -6} {at} 905 CL are determined from …
Date: March 16, 2010
Creator: Nugent, Ian M.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Random Number Generation for Petascale Quantum Monte Carlo (open access)

Random Number Generation for Petascale Quantum Monte Carlo

The quality of random number generators can affect the results of Monte Carlo computations, especially when a large number of random numbers are consumed. Furthermore, correlations present between different random number streams in a parallel computation can further affect the results. The SPRNG software, which the author had developed earlier, has pseudo-random number generators (PRNGs) capable of producing large numbers of streams with large periods. However, they had been empirically tested on only thousand streams earlier. In the work summarized here, we tested the SPRNG generators with over a hundred thousand streams, involving over 10^14 random numbers per test, on some tests. We also tested the popular Mersenne Twister. We believe that these are the largest tests of PRNGs, both in terms of the numbers of streams tested and the number of random numbers tested. We observed defects in some of these generators, including the Mersenne Twister, while a few generators appeared to perform well. We also corrected an error in the implementation of one of the SPRNG generators.
Date: March 16, 2010
Creator: Srinivasan, Ashok
Object Type: Report
System: The UNT Digital Library
Spin Hall effects for cold atoms in a light induced gauge potential (open access)

Spin Hall effects for cold atoms in a light induced gauge potential

We propose an experimental scheme to observe spin Hall effects with cold atoms in a light induced gauge potential. Under an appropriate configuration, the cold atoms moving in a spatially varying laser field experience an effective spin-dependent gauge potential. Through numerical simulation, we demonstrate that such a gauge field leads to observable spin Hall currents under realistic conditions. We also discuss the quantum spin Hall state in an optical lattice.
Date: March 16, 2010
Creator: Zhu, Shi-Liang; /Michigan U., MCTP /South China Normal U.; Fu, Hao; /Michigan U., MCTP; Wu, C.-J.; /Santa Barbara, KITP et al.
Object Type: Article
System: The UNT Digital Library