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From Nucleons To Nuclei To Fusion Reactions (open access)

From Nucleons To Nuclei To Fusion Reactions

Nuclei are prototypes of many-body open quantum systems. Complex aggregates of protons and neutrons that interact through forces arising from quantum chromo-dynamics, nuclei exhibit both bound and unbound states, which can be strongly coupled. In this respect, one of the major challenges for computational nuclear physics, is to provide a unified description of structural and reaction properties of nuclei that is based on the fundamental underlying physics: the constituent nucleons and the realistic interactions among them. This requires a combination of innovative theoretical approaches and high-performance computing. In this contribution, we present one of such promising techniques, the ab initio no-core shell model/resonating-group method, and discuss applications to light nuclei scattering and fusion reactions that power stars and Earth-base fusion facilities.
Date: February 15, 2012
Creator: Quaglioni, S; Navratil, P; Roth, R & Horiuchi, W
System: The UNT Digital Library
Real-structure effects: Band gaps of Mg_xZn_{1-x}O, Cd_xZn_{1-x}O, and n-type ZnO from ab-initio calculations (open access)

Real-structure effects: Band gaps of Mg_xZn_{1-x}O, Cd_xZn_{1-x}O, and n-type ZnO from ab-initio calculations

Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical-absorption spectra (including excitonic effects) for several transparent conducting oxides. We discuss HSE+G{sub 0}W{sub 0} results for band structures, fundamental band gaps, and effective electron masses of MgO, ZnO, CdO, SnO{sub 2}, SnO, In{sub 2}O{sub 3}, and SiO{sub 2}. The Bethe-Salpeter equation is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE+G{sub 0}W{sub 0} approach and the solution of the Bethe-Salpeter equation are very well-suited to describe the electronic structure and the optical properties of various transparent conducting oxides in good agreement with experiment.
Date: February 15, 2012
Creator: Schleife, A & Bechstedt, F
System: The UNT Digital Library
Recent T980 Crystal Collimation Studies at the Tevatron Exploiting a Pixel Detector System and a Multi-Strip Crystal Array (open access)

Recent T980 Crystal Collimation Studies at the Tevatron Exploiting a Pixel Detector System and a Multi-Strip Crystal Array

With the shutdown of the Tevatron, the T-980 crystal collimation experiment at Fermilab has been successfully completed. Results of dedicated beam studies in May 2011 are described in this paper. For these studies, two multi-strip crystals were installed in the vertical goniometer and an O-shaped crystal installed in a horizontal goniometer. A two-plane CMS pixel detector was also installed in order to enhance the experiment with the capability to image the profile of crystal channeled or multiple volume reflected beam. The experiment successfully imaged channeled beam from a crystal for 980-GeV protons for the first time. This new enhanced hardware yielded impressive results. The performance and characterization of the crystals studied have been very reproducible over time and consistent with simulations.
Date: May 15, 2012
Creator: Still, D.; Annala, G. E.; Carrigan, R. A.; Drozhdin, A. I.; Johnson, T. R.; Mokhov, N. V. et al.
System: The UNT Digital Library
Coherent electron cooling proof of principle instrumentation design (open access)

Coherent electron cooling proof of principle instrumentation design

The goal of the Coherent Electron Cooling Proof-of-Principle (CeC PoP) experiment being designed at RHIC is to demonstrate longitudinal (energy spread) cooling before the expected CD-2 for eRHIC. The scope of the experiment is to longitudinally cool a single bunch of 40 GeV/u gold ions in RHIC. This paper will describe the instrumentation systems proposed to meet the diagnostics challenges. These include measurements of beam intensity, emittance, energy spread, bunch length, position, orbit stability, and transverse and temporal alignment of electron and ion beams.
Date: April 15, 2012
Creator: M., Gassner D.; Litvinenko, V.; Michnoff, R.; Miller, T.; Minty, M. & Pinayev, I.
System: The UNT Digital Library
Electroweak Baryogenesis and Colored Scalars (open access)

Electroweak Baryogenesis and Colored Scalars

We consider the 2-loop finite temperature effective potential for a Standard Model-like Higgs boson, allowing Higgs boson couplings to additional scalars. If the scalars transform under color, they contribute 2-loop diagrams to the effective potential that include gluons. These 2-loop effects are perhaps stronger than previously appreciated. For a Higgs boson mass of 115 GeV, they can increase the strength of the phase transition by as much as a factor of 3.5. It is this effect that is responsible for the survival of the tenuous electroweak baryogenesis window of the Minimal Supersymmetric Standard Model. We further illuminate the importance of these 2-loop diagrams by contrasting models with colored scalars to models with singlet scalars. We conclude that baryogenesis favors models with light colored scalars. This motivates searches for pair-produced di-jet resonances or jet(s) + = E{sub T}.
Date: February 15, 2012
Creator: Cohen, Timothy; /SLAC /Michigan U., MCTP; Pierce, Aaron & /Michigan U., MCTP
System: The UNT Digital Library
Simplifying Multi-loop Integrands of Gauge Theory and Gravity Amplitudes (open access)

Simplifying Multi-loop Integrands of Gauge Theory and Gravity Amplitudes

We use the duality between color and kinematics to simplify the construction of the complete four-loop four-point amplitude of N = 4 super-Yang-Mills theory, including the nonplanar contributions. The duality completely determines the amplitude's integrand in terms of just two planar graphs. The existence of a manifestly dual gauge-theory amplitude trivializes the construction of the corresponding N = 8 supergravity integrand, whose graph numerators are double copies (squares) of the N = 4 super-Yang-Mills numerators. The success of this procedure provides further nontrivial evidence that the duality and double-copy properties hold at loop level. The new form of the four-loop four-point supergravity amplitude makes manifest the same ultraviolet power counting as the corresponding N = 4 super-Yang-Mills amplitude. We determine the amplitude's ultraviolet pole in the critical dimension of D = 11/2, the same dimension as for N = 4 super-Yang-Mills theory. Strikingly, exactly the same combination of vacuum integrals (after simplification) describes the ultraviolet divergence of N = 8 supergravity as the subleading-in-1/N{sub c}{sup 2} single-trace divergence in N = 4 super-Yang-Mills theory.
Date: February 15, 2012
Creator: Bern, Z.; Carrasco, J.J.M.; Dixon, L.J.; Johansson, H. & Roiban, R.
System: The UNT Digital Library
Extending MC-SURE to Denoise Sensor Data Streams (open access)

Extending MC-SURE to Denoise Sensor Data Streams

None
Date: November 15, 2012
Creator: Ndoye, M. & Kamath, C.
System: The UNT Digital Library
Evaluating Unsupervised Ensembles when applied to Word Sense Induction (open access)

Evaluating Unsupervised Ensembles when applied to Word Sense Induction

None
Date: February 15, 2012
Creator: Stevens, K D
System: The UNT Digital Library
Threshold for Electron Trapping Nonlinearity in Langmuir Waves (open access)

Threshold for Electron Trapping Nonlinearity in Langmuir Waves

None
Date: August 15, 2012
Creator: Strozzi, D. J.; Williams, E. A.; Rose, H. A.; Hinkel, D. E.; Langdon, A. B. & Banks, J. W.
System: The UNT Digital Library
Elementary Processes Underlying Alpha Channeling in Tokamaks (open access)

Elementary Processes Underlying Alpha Channeling in Tokamaks

Alpha channeling in tokamaks is speculative, but also extraordinarily attractive. Waves that can accomplish this effect have been identified. Key aspects of the theory now enjoy experimental confirmation. This paper will review the elementary processes of wave-particle interactions in plasma that underlie the alpha channeling effect
Date: June 15, 2012
Creator: Fisch, NM.J.
System: The UNT Digital Library
Design of a proton-electron beam overlap monitor for the new RHIC electron lens, based on detecting energetic backscattered electrons (open access)

Design of a proton-electron beam overlap monitor for the new RHIC electron lens, based on detecting energetic backscattered electrons

The optimal performance of the two electron lenses that are being implemented for high intensity polarized proton operation of RHIC requires excellent collinearity of the {approx}0.3 mm RMS wide electron beams with the proton bunch trajectories over the {approx}2m interaction lengths. The main beam overlap diagnostic tool will make use of electrons backscattered in close encounters with the relativistic protons. These electrons will spiral along the electron guiding magnetic field and will be detected in a plastic scintillator located close to the electron gun. A fraction of these electrons will have energies high enough to emerge from the vacuum chamber through a thin window thus simplifying the design and operation of the detector. The intensity of the detected electrons provides a measure of the overlap between the e- and the opposing proton beams. Joint electron arrival time and energy discrimination may be used additionally to gain some longitudinal position information with a single detector per lens.
Date: April 15, 2012
Creator: T., Thieberger; Beebe, E.; Fischer, W.; Gassner, D.; Gu, X.; Hamdi, K. et al.
System: The UNT Digital Library
Heavy Quarkonium: Progress, Puzzles, and Opportunities (open access)

Heavy Quarkonium: Progress, Puzzles, and Opportunities

None
Date: June 15, 2012
Creator: Brambilla, N.; Eidelman, S.; Heltsley, B. K.; Vogt, R.; Bodwin, G. T.; Eichten, E. et al.
System: The UNT Digital Library
Summary of Fermilab's Recycler Electron Cooler Operation and Studies (open access)

Summary of Fermilab's Recycler Electron Cooler Operation and Studies

Fermilab's Recycler ring was used as a storage ring for accumulation and subsequent manipulations of 8 GeV antiprotons destined for the Tevatron collider. To satisfy these missions, a unique electron cooling system was designed, developed and successfully implemented. The most important features that distinguish the Recycler cooler from other existing electron coolers are its relativistic energy, 4.3 MV combined with 0.1-0.5 A DC beam current, a weak continuous longitudinal magnetic field in the cooling section, 100 G, and lumped focusing elsewhere. With the termination of the Tevatron collider operation, so did the cooler. In this article, we summarize the experience of running this unique machine.
Date: May 15, 2012
Creator: Prost, L. R. & Shemyakin, A.
System: The UNT Digital Library
Zeroing in on Supersymmetric Radiation Amplitude Zeros (open access)

Zeroing in on Supersymmetric Radiation Amplitude Zeros

Radiation amplitude zeros have long been used to test the Standard Model. Here, we consider the supersymmetric radiation amplitude zero in chargino-neutralino associated production, which can be observed at the luminosity upgraded LHC. Such an amplitude zero only occurs if the neutralino has a large wino fraction and hence this observable can be used to determine the neutralino eigenstate content. We find that this observable can be measured by comparing the p{sub T} spectrum of the softest lepton in the trilepton {tilde {chi}}{sub 1}{sup {+-}} {tilde {chi}}{sub 2}{sup 0} decay channel to that of a control process such as {tilde {chi}}{sub 1}{sup +} {tilde {chi}}{sub 1}{sup -} or {tilde {chi}}{sub 2}{sup 0} {tilde {chi}}{sub 2}{sup 0}. We test this technique on a previously generated model sample of the 19 dimensional parameter space of the phenomenological MSSM, and find that it is effective in determining the wino content of the neutralino.
Date: February 15, 2012
Creator: Hewett, JoAnne L.; Ismail, Ahmed & Rizzo, Thomas G.
System: The UNT Digital Library
Single- and Two-Photon-Induced Processes at the B Factories (open access)

Single- and Two-Photon-Induced Processes at the B Factories

We discuss single- and two-photon-induced processes in e{sup +}e{sup -} annihilations with center-of-mass energy near 10.58 GeV from the BaBar and Belle experiments. In particular, we present experimental results from two-photon physics of {gamma}{gamma} {yields} {pi}{sup 0}{pi}{sup 0} and {gamma}{gamma}* {yields} {pi}{sup 0}. We also review the observation of the Two-Virtual-Photon-Annihilation process (e{sup +}e{sup -} {yields} {rho}{sup 0}{rho}{sup 0} and e{sup +}e{sup -} {yields} {phi}{rho}{sup 0}) and the observation of e{sup +}e{sup -} {yields} {rho}{sup +}{rho}{sup -}, which should be primarily a one virtual photon process, but whose angular distributions may imply potential interference effects.
Date: June 15, 2012
Creator: Li, Selina Z.
System: The UNT Digital Library
Long Term Thermal Stability In Air Of Ionic Liquid Based Alternative Heat Transfer Fluids For Clean Energy Production (open access)

Long Term Thermal Stability In Air Of Ionic Liquid Based Alternative Heat Transfer Fluids For Clean Energy Production

The purpose of this study was to investigate the effect of long-term aging on the thermal stability and chemical structure of seven different ILs so as to explore their suitability for use as a heat transfer fluid. This was accomplished by heating the ILs for 15 weeks at 200�C in an oxidizing environment and performing subsequent analyses on the aged chemicals.
Date: October 15, 2012
Creator: Fox, Elise B; Kendrick, Sarah E.; Visser, Ann E. & Bridges, Nicholas J.
System: The UNT Digital Library
Atomic data for the ITER Core Imaging X-ray Spectrometer (open access)

Atomic data for the ITER Core Imaging X-ray Spectrometer

The parameters of the ITER core plasmas will be measured using the Core Imaging X-ray Spectrometer (CIXS), a high-resolution crystal spectrometer focusing on the L-shell spectra of highly ionized tungsten atoms. In order to correctly infer the plasma properties accurate atomic data are required. Here, some aspects of the underlying physics are discussed using experimental data and theoretical predictions from modeling.
Date: June 15, 2012
Creator: Clementson, J.; Beiersdorfer, P.; Biedermann, C.; Bitter, M.; Delgado-Aparicio, L. F.; Graf, A. et al.
System: The UNT Digital Library
Analytic Result for the Two-loop Six-point NMHV Amplitude in N = 4 Super Yang-Mills Theory (open access)

Analytic Result for the Two-loop Six-point NMHV Amplitude in N = 4 Super Yang-Mills Theory

We provide a simple analytic formula for the two-loop six-point ratio function of planar N = 4 super Yang-Mills theory. This result extends the analytic knowledge of multi-loop six-point amplitudes beyond those with maximal helicity violation. We make a natural ansatz for the symbols of the relevant functions appearing in the two-loop amplitude, and impose various consistency conditions, including symmetry, the absence of spurious poles, the correct collinear behavior, and agreement with the operator product expansion for light-like (super) Wilson loops. This information reduces the ansatz to a small number of relatively simple functions. In order to fix these parameters uniquely, we utilize an explicit representation of the amplitude in terms of loop integrals that can be evaluated analytically in various kinematic limits. The final compact analytic result is expressed in terms of classical polylogarithms, whose arguments are rational functions of the dual conformal cross-ratios, plus precisely two functions that are not of this type. One of the functions, the loop integral {Omega}{sup (2)}, also plays a key role in a new representation of the remainder function R{sub 6}{sup (2)} in the maximally helicity violating sector. Another interesting feature at two loops is the appearance of a new (parity odd) …
Date: February 15, 2012
Creator: Dixon, Lance J.; Drummond, James M. & Henn, Johannes M.
System: The UNT Digital Library
Ultrafast Photovoltaic Response in Ferroelectric Nanolayers (open access)

Ultrafast Photovoltaic Response in Ferroelectric Nanolayers

We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond timescales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.
Date: February 15, 2012
Creator: Daranciang, Dan
System: The UNT Digital Library
Development of Transparent Ceramic Ce-Doped Gadolinium Garnet Gamma Spectrometers (open access)

Development of Transparent Ceramic Ce-Doped Gadolinium Garnet Gamma Spectrometers

None
Date: November 15, 2012
Creator: Cherepy, N J; Seeley, Z M; Payne, S A; Beck, P R; Drury, O B; O'Neal, S P et al.
System: The UNT Digital Library
Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies (open access)

Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies

We examine the ability for the Large Area Telescope (LAT) to constrain Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest Supersymmetric Particles (LSPs) for a set of {approx}71k experimentally valid supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find that none of these models can be excluded at 95% confidence by the current analysis; nevertheless, many lie within the predicted reach of future LAT analyses. With two years of data, we find that the LAT is currently most sensitive to light LSPs (mLSP < 50 GeV) annihilating into {tau}-pairs and heavier LSPs annihilating into b{bar b}. Additionally, we find that future LAT analyses will be able to probe some LSPs that form a sub-dominant component of dark matter. We directly compare the LAT results to direct detection experiments and show the complementarity of these search methods.
Date: March 15, 2012
Creator: Cotta, R. C.; Drlica-Wagner, A.; Murgia, S.; Bloom, E. D.; Hewett, J. L. & Rizzo, T. G.
System: The UNT Digital Library
Don't Mess with the NEST (open access)

Don't Mess with the NEST

NEST stands for Nuclear Emergency Support Team. The NEST Mission Statement as first established: (1) Conduct, direct, coordinate search and recovery operations for nuclear material, weapons or devices; and (2) Assist in identification and deactivation of Improvised Nuclear Devices (INDs) and Radiological Dispersal Devices (RDDs). Then in 1980 a very sophisticated improvised explosive device was found at Harvey's Casino at Lake Tahoe, Nevada. The FBI and Bomb Squads were unprepared and it detonated. As a result the additional phrase 'and Sophisticated Improvised Explosive Devices (SIEDs)' was added to the Mission Statement.
Date: March 15, 2012
Creator: Larson, M
System: The UNT Digital Library
Bounds and self-consistent estimates for elastic constants of polycrystals of hcp solid He{sup 4} (open access)

Bounds and self-consistent estimates for elastic constants of polycrystals of hcp solid He{sup 4}

Recent advances in methods for computing both Hashin-Shtrikman bounds and related selfconsistent (or CPA) estimates of elastic constants for polycrystals composed of randomly oriented crystals can be applied successfully to hexagonal close packed solid He{sup 4}. In particular, since the shear modulus C{sub 44} of hexagonal close-packed solid He is known to undergo large temperature variations when 20 mK {<=}#20; T {<=}#20; 200 mK, bounds and estimates computed with this class of effective medium methods, while using C{sub 44} {r_arrow} 0 as a proxy for melting, are found to be both qualitatively and quantitatively very similar to prior results obtained using Monte Carlo methods. Hashin- Shtrikman bounds provide significantly tighter constraints on the polycrystal behavior than do the traditional Voigt and Reuss bounds.
Date: February 15, 2012
Creator: Berryman, J. G.
System: The UNT Digital Library
Single-cycle Terahertz Pulses with >0.2 V/A Field Amplitudes via Coherent Transition Radiation (open access)

Single-cycle Terahertz Pulses with >0.2 V/A Field Amplitudes via Coherent Transition Radiation

We demonstrate terahertz pulses with field amplitudes exceeding 0.2 V/{angstrom} generated by coherent transition radiation. Femtosecond, relativistic electron bunches generated at the Linac Coherent Light Source are passed through a beryllium foil, and the emitted radiation is characterized as a function of the bunch duration and charge. Broadband pulses centered at a frequency of 10 THz with energies of 140 {mu}J are measured. These far-below-bandgap pulses drive a nonlinear optical response in a silicon photodiode, with which we perform nonlinear autocorrelations that yield information regarding the terahertz temporal profile. Simulations of the spatiotemporal profile agree well with experimental results.
Date: February 15, 2012
Creator: Daranciang, Dan; Goodfellow, John; Fuchs, Matthias; Wen, Haidan; Ghimire, Shambhu; Reis, David A. et al.
System: The UNT Digital Library