Department of Physics

Permanent URI for this community

https://hdl.handle.net/10919/24211

Browse

Now showing 1 - 20 of 1173

1/N expansion for the degenerate Anderson model in the mixed-valence regime
Zhang, F. C.; Lee, T. K. (American Physical Society, 1983-07)
The 1N expansion method for the degenerate Anderson model is formulated. N is the degeneracy factor of one of the f-electron configurations. Various ground-state properties are calculated. Excellent agreement with the result of Bethe ansatz for N=6 is shown. The rate of convergence of the series is analyzed. The merit and inadequacy of the method are discussed. At zero temperature the ratio of the magnetic susceptibility and the specific-heat linear coefficient is shown to lie within a range of 1 and 1+(N-1)-1.
10 kpc Scale Seyfert Galaxy Outflow: HST/COS Observations of IRAS F22456-5125
Borguet, Benoit C. J.; Edmonds, Douglas; Arav, Nahum; Dunn, Jay; Kriss, Gerard A. (IOP Publishing Ltd., 2012-06)
We present analysis of the UV spectrum of the low-z AGN IRAS F22456-5125 obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The spectrum reveals six main kinematic components, spanning a range of velocities of up to 800 km s (1), which for the first time are observed in troughs associated with C II, C IV, N V, Si II, Si III, Si IV, and S IV. We also obtain data on the O VI troughs, which we compare to those available from an earlier Far Ultraviolet Spectroscopic Explorer epoch. Column densities measured from these ions allow us to derive a well-constrained photoionization solution for each outflow component. Two of these kinematic components show troughs associated with transitions from excited states of Si II and C II. The number density inferred from these troughs, in combination with the deduced ionization parameter, allows us to determine the distance to these outflow components from the central source. We find these components to be at a distance of similar to 10 kpc. The distances and the number densities derived are consistent with the outflow being part of a galactic wind.
14-year program monitoring the flux densities of 33 radio sources at low frequencies
Salgado, José Francisco; Altschuler, Daniel R.; Ghosh, Tapasi; Dennison, Brian K.; Mitchell, Kenneth J.; Payne, Harry E. (IOP PUBLISHING LTD, 1999-01)
We present the results of a low-frequency flux density monitoring program of 33 extragalactic radio sources. The light curves at 318 and 430 MHz over a 14 yr period are presented. The measurements were made with the NAIC Arecibo 305 m radio telescope at approximately bimonthly intervals between 1980 January and 1989 February and at less regular intervals between 1989 October and 1993 October, for a total of 64 observing sessions. In addition, we provide a first discussion of the results, pointing out several source properties and interesting objects.
The 2010 Interim Report of the Long-Baseline Neutrino Experiment Collaboration Physics Working Groups
Collaboration, TLBNE; Akiri, T.; Allspach, D.; Andrews, M.; Arisaka, K.; Arrieta-Diaz, E.; Artuso, M.; Bai, X.; Balantekin, A. B.; Baller, B.; Barletta, W. A.; Barr, G.; Bass, M.; Beck, A.; Becker, B.; Bellini, V.; Benhar, Omar; Berger, B. E.; Bergevin, M.; Berman, E.; Berns, H.; Bernstein, A.; Beroz, F.; Bhatnagar, V.; Bhuyan, B.; Bionta, R.; Bishai, M.; Blake, A.; Blaufuss, E.; Bleakley, B.; Blucher, E.; Blusk, S.; Boehnlein, D.; Bolton, T.; Brack, J.; Bradford, R.; Breedon, R.; Bromberg, C.; Brown, R.; Buchanan, N.; Camilleri, Leslie; Campbell, M.; Carr, Rachel E.; Carminati, G.; Chen, A.; Chen, H.; Cherdack, D.; Chi, C.; Childress, S.; Choudhary, B.; Church, E.; Cline, D.; Coleman, S.; Corey, R.; D'Agostino, M. V.; Davies, G. S.; Dazeley, S.; Jong, J. D.; DeMaat, B.; Demuth, D.; Dighe, A.; Djurcic, Zelimir; Dolph, J.; Drake, G.; Drozhdin, A.; Duan, H.; Duyang, H.; Dye, S.; Dykhuis, T.; Edmunds, D.; Elliott, S.; Enomoto, S.; Escobar, C. O.; Felde, J.; Feyzi, F.; Fleming, B.; Fowler, J.; Fox, W.; Friedland, A.; Fujikawa, B. K.; Gallagher, H.; Garilli, G.; Garvey, G. T.; Gehman, V. M.; Geronimo, G. D.; Gill, R.; Goodman, M.; Goon, J.; Gorbunov, D.; Gran, R.; Guarino, V.; Guarnaccia, E.; Guenette, R.; Gupta, P.; Habig, A.; Hackenburg, R. W.; Hahn, A.; Hahn, R.; Haines, T.; Hans, S.; Harton, J.; Hays, S.; Hazen, E.; He, Q.; Heavey, A.; Heeger, K.; Hellauer, R.; Himmel, A.; Horton-Smith, Glenn A.; Howell, J.; Huber, Patrick; Hurh, P.; Huston, J.; Hylen, J.; Insler, J.; Jaffe, D.; James, C.; Johnson, C.; Johnson, M.; Johnson, R.; Johnson, W.; Johnston, W.; Johnstone, J.; Jones, B.; Jostlein, H.; Junk, T.; Junnarkar, S.; Kadel, R.; Kafka, T.; Kaminski, D.; Karagiorgi, Georgia S.; Karle, A.; Kaspar, J.; Katori, T.; Kayser, B.; Kearns, E.; Kettell, S. H.; Khanam, F.; Klein, J.; Kneller, J.; Koizumi, G.; Kopp, J.; Kopp, S.; Kropp, W.; Kudryavtsev, V. A.; Kumar, A.; Kumar, J.; Kutter, T.; Lackowski, T.; Lande, K.; Lane, C.; Lang, K.; Lanni, F.; Lanza, R.; Latorre, T.; Learned, J.; Lee, D.; Lee, K.; Li, Y.; Linden, S.; Ling, J.; Link, Jonathan M.; Littenberg, L.; Loiacono, L.; Liu, T.; Losecco, J.; Louis, W.; Lucas, P.; Lunardini, C.; Lundberg, B.; Lundin, T.; Makowiecki, D.; Malys, S.; Mandal, S.; Mann, A.; Mantsch, P.; Marciano, W. J.; Mariani, Camillo; Maricic, Jelena; Marino, A.; Marshak, M.; Maruyama, R.; Matthews, J.; Matsuno, S.; Mauger, C.; McCluskey, E.; McDonald, K.; McFarland, K. S.; McKeown, R.; McTaggart, R.; Mehdiyev, R.; Melnitchouk, W.; Meng, Y.; Mercurio, B.; Messier, M.; Metcalf, W.; Milincic, R.; Miller, W.; Mills, G.; Mishra, S.; MoedSher, S.; Mohapatra, D.; Mokhov, N.; Moore, C.; Morfin, J.; Morse, W.; Moss, A.; Mufson, S.; Musser, J.; Naples, D.; Napolitano, J.; Newcomer, M.; Norris, B.; Ouedraogo, S.; Page, B.; Pakvasa, S.; Paley, J.; Paolone, V.; Papadimitriou, V.; Parsa, Z.; Partyka, K.; Pavlovic, Z.; Pearson, C.; Perasso, S.; Petti, R.; Plunkett, R.; Polly, C. C.; Pordes, S.; Potenza, R.; Prakash, A.; Prokofiev, O.; Qian, X.; Raaf, J.; Radeka, V.; Raghavan, R.; Rameika, R.; Rebel, B.; Rescia, S.; Reitzner, D.; Richardson, M.; Riesselmann, K.; Robinson, M.; Rosen, M.; Rosenfeld, C.; Rucinski, R.; Russo, T.; Sahijpal, S.; Salon, S.; Samios, N.; Sanchez, Maria Cristina; Schmitt, R.; Schmitz, D.; Schneps, J.; Scholberg, K.; Seibert, S.; Sergiampietri, F.; Shaevitz, Marjorie Hansen; Shanahan, P.; Shaposhnikov, M.; Sharma, R.; Simos, N.; Singh, V.; Sinnis, G.; Sippach, W.; Skwarnicki, T.; Smy, M.; Sobel, H.; Soderberg, M.; Sondericker, J.; Sondheim, W.; Spitz, Joshua; Spooner, N.; Stancari, M.; Stancu, Ion; Stewart, J.; Stoler, P.; Stone, J.; Stone, S.; Strait, J.; Straszheim, T.; Striganov, S.; Sullivan, G.; Svoboda, R.; Szczerbinska, B.; Szelc, A.; Talaga, R.; Tanaka, H.; Tayloe, R.; Taylor, D.; Thomas, J.; Thompson, L.; Thomson, M.; Thorn, C.; Tian, X.; Toki, W.; Tolich, N.; Tripathi, M.; Trovato, M.; Tseung, H.; Tzanov, M.; Urheim, J.; Usman, S.; Vagins, M. R.; Berg, R. V.; Water, R. V. D.; Varner, G.; Vaziri, K.; Velev, G.; Viren, B.; Wachala, T.; Walter, C.; Wang, H.; Wang, Z.; Warner, D.; Webber, D.; Weber, A.; Wendell, R.; Wendt, C.; Wetstein, M.; White, H.; White, S.; Whitehead, L.; Willis, W.; Wilson, R. J.; Winslow, L.; Ye, J.; Yeh, M.; Yu, B.; Zeller, Geralyn P.; Zhang, C.; Zimmerman, E.; Zwaska, R. (2011-10-27)
In early 2010, the Long-Baseline Neutrino Experiment (LBNE) science collaboration initiated a study to investigate the physics potential of the experiment with a broad set of different beam, near- and far-detector configurations. Nine initial topics were identified as scientific areas that motivate construction of a long-baseline neutrino experiment with a very large far detector. We summarize the scientific justification for each topic and the estimated performance for a set of far detector reference configurations. We report also on a study of optimized beam parameters and the physics capability of proposed Near Detector configurations. This document was presented to the collaboration in fall 2010 and updated with minor modifications in early 2011.
2024 Symposium on Soft Matter and Biological Physics
(Virginia Tech, 2024-08)
A program for the symposium held on August 31, 2024, in Hahn Hall North and Auditorium. This event featured two keynote speakers and a showcase of student poster presentations.
The 750 GeV diphoton excess in unified SU(2)(L) x SU(2)(R) x SU(4) models from noncommutative geometry
Aydemir, U.; Minic, Djordje; Sun, C.; Takeuchi, Tatsu (World Scientific, 2016-06-14)
A machine-learning approach for differentiating borderline personality disorder from community participants with brain-wide functional connectivity
Lahnakoski, Juha M.; Nolte, Tobias; Solway, Alec; Vilares, Iris; Hula, Andreas; Feigenbaum, Janet; Lohrenz, Terry; Casas, Brooks; Fonagy, Peter; Montague, P. Read; Schilbach, Leonhard (Elsevier, 2024-05-26)
Background: Functional connectivity has garnered interest as a potential biomarker of psychiatric disorders including borderline personality disorder (BPD). However, small sample sizes and lack of within-study replications have led to divergent findings with no clear spatial foci. Aims: Evaluate discriminative performance and generalizability of functional connectivity markers for BPD. Method: Whole-brain fMRI resting state functional connectivity in matched subsamples of 116 BPD and 72 control individuals defined by three grouping strategies. We predicted BPD status using classifiers with repeated cross-validation based on multiscale functional connectivity within and between regions of interest (ROIs) covering the whole brain—global ROI-based network, seed-based ROI-connectivity, functional consistency, and voxel-to-voxel connectivity—and evaluated the generalizability of the classification in the left-out portion of non-matched data. Results: Full-brain connectivity allowed classification (∼70 %) of BPD patients vs. controls in matched inner cross-validation. The classification remained significant when applied to unmatched out-of-sample data (∼61–70 %). Highest seed-based accuracies were in a similar range to global accuracies (∼70–75 %), but spatially more specific. The most discriminative seed regions included midline, temporal and somatomotor regions. Univariate connectivity values were not predictive of BPD after multiple comparison corrections, but weak local effects coincided with the most discriminative seed-ROIs. Highest accuracies were achieved with a full clinical interview while self-report results remained at chance level. Limitations: The accuracies vary considerably between random sub-samples of the population, global signal and covariates limiting the practical applicability. Conclusions: Spatially distributed functional connectivity patterns are moderately predictive of BPD despite heterogeneity of the patient population.
ACD estimation of the S-parameter revisited
Ignjatovic, S. R.; Takeuchi, Tatsu; Wijewardhana, L. C. R. (Elsevier, 1997-05-29)
Active-to-sterile neutrino dipole portal and the XENON1T excess
Shoemaker, Ian M.; Tsai, Yu-Dai; Wyenberg, Jason (American Physical Society, 2021-12-27)
In this paper, we find that a magnetic transition dipole moment between tau and sterile neutrinos can account for the XENON1T excess events. Unlike the ordinary neutrino dipole moment, the introduction of the new sterile mass scale allows for astrophysical bounds to be suppressed. Interestingly, the best-fit regions that are compatible with the SN1987A imply either boron-8 as the source flux. We find that sterile neutrinos in the similar to(500-800) keV mass range are capable of evading astrophysical constraints while being able to successfully explain the XENON1T event rate. We also set new constraints on the dipole portal based on the Xenon 1T data. The sterile neutrino in the best fit parameter space may have significant effects on big bang nucleosynthesis (BBN). We show the region in which a low reheating temperature of the Universe may allow the BBN constraints to be alleviated.
Adaptive quantum approximate optimization algorithm for solving combinatorial problems on a quantum computer
Zhu, Linghua; Tang, Ho Lun; Barron, George S.; Calderon-Vargas, F. A.; Mayhall, Nicholas J.; Barnes, Edwin Fleming; Economou, Sophia E. (American Physical Society, 2022-07-11)
The quantum approximate optimization algorithm (QAOA) is a hybrid variational quantum-classical algorithm that solves combinatorial optimization problems. While there is evidence suggesting that the fixed form of the standard QAOA Ansatz is not optimal, there is no systematic approach for finding better Ansatze. We address this problem by developing an iterative version of QAOA that is problem tailored, and which can also be adapted to specific hardware constraints. We simulate the algorithm on a class of Max-Cut graph problems and show that it converges much faster than the standard QAOA, while simultaneously reducing the required number of CNOT gates and optimization parameters. We provide evidence that this speedup is connected to the concept of shortcuts to adiabaticity.
An adaptive variational algorithm for exact molecular simulations on a quantum computer
Grimsley, Harper R.; Economou, Sophia E.; Barnes, Edwin Fleming; Mayhall, Nicholas J. (Springer Nature, 2019-07-08)
Quantum simulation of chemical systems is one of the most promising near-term applications of quantum computers. The variational quantum eigensolver, a leading algorithm for molecular simulations on quantum hardware, has a serious limitation in that it typically relies on a pre-selected wavefunction ansatz that results in approximate wavefunctions and energies. Here we present an arbitrarily accurate variational algorithm that, instead of fixing an ansatz upfront, grows it systematically one operator at a time in a way dictated by the molecule being simulated. This generates an ansatz with a small number of parameters, leading to shallow-depth circuits. We present numerical simulations, including for a prototypical strongly correlated molecule, which show that our algorithm performs much better than a unitary coupled cluster approach, in terms of both circuit depth and chemical accuracy. Our results highlight the potential of our adaptive algorithm for exact simulations with present-day and near-term quantum hardware.
Aging in coarsening diluted ferromagnets
Park, H.; Pleimling, Michel J. (American Physical Society, 2010-10)
We comprehensively study nonequilibrium relaxation and aging processes in the two-dimensional randomsite Ising model through numerical simulations. We discuss the dynamical correlation length as well as scaling functions of various two-time quantities as a function of temperature and of the degree of dilution. For already modest values of the dynamical correlation length L deviations from a simple algebraic growth, L(t)similar to t(1/z), are observed. When taking this nonalgebraic growth properly into account, a simple aging behavior of the auto-correlation function is found. This is in stark contrast to earlier studies where, based on the assumption of algebraic growth, a superaging scenario was postulated for the autocorrelation function in disordered ferromagnets. We also study the scaling behavior of the space-time correlation as well as of the time integrated linear response and find again agreement with simple aging. Finally, we briefly discuss the possibility of superuniversality in the scaling properties of space- and time-dependent quantities.
Aging phenomena in the two-dimensional complex Ginzburg-Landau equation
Liu, Weigang; Täuber, Uwe C. (2019-11)
The complex Ginzburg-Landau equation with additive noise is a stochastic partial differential equation that describes a remarkably wide range of physical systems which include coupled non-linear oscillators subject to external noise near a Hopf bifurcation instability and spontaneous structure formation in non-equilibrium systems, e.g., in cyclically competing populations or oscillatory chemical reactions. We employ a finite-difference method to numerically solve the noisy complex Ginzburg-Landau equation on a two-dimensional domain with the goal to investigate its non-equilibrium dynamics when the system is quenched into the "defocusing spiral quadrant". We observe slow coarsening dynamics as oppositely charged topological defects annihilate each other, and characterize the ensuing aging scaling behavior. We conclude that the physical aging features in this system are governed by non-universal aging scaling exponents. We also investigate systems with control parameters residing in the "focusing quadrant", and identify slow aging kinetics in that regime as well. We provide heuristic criteria for the existence of slow coarsening dynamics and physical aging behavior in the complex Ginzburg-Landau equation.
Aging processes in systems with anomalous slow dynamics
Afzal, N.; Pleimling, Michel J. (American Physical Society, 2013-01-14)
Recently, different numerical studies of coarsening in disordered systems have shown the existence of a crossover from an initial, transient, power-law domain growth to a slower, presumably logarithmic, growth. However, due to the very slow dynamics and the long-lasting transient regime, one is usually not able to fully enter the asymptotic regime when investigating the relaxation of these systems toward equilibrium. We here study two simple driven systems-the one-dimensional ABC model and a related domain model with simplified dynamics-that are known to exhibit anomalous slow relaxation where the asymptotic logarithmic growth regime is readily accessible. Studying two-times correlation and response functions, we focus on aging processes and dynamical scaling during logarithmic growth. Using the time-dependent growth length as the scaling variable, a simple aging picture emerges that is expected to also prevail in the asymptotic regime of disordered ferromagnets and spin glasses.
Algebroids, heterotic moduli spaces and the Strominger system
Anderson, Lara B.; Gray, James A.; Sharpe, Eric R. (Springer, 2014-07-08)
In this paper we study compactifications of heterotic string theory on manifolds satisfying the partial derivative(partial derivative) over bar -lemma. We consider the Strominger system description of the low energy supergravity to first order in alpha' and show that the moduli of such compactifications are subspaces of familiar cohomology groups such as H-1 (TX), H-1 (TXV), H-1 (End(0) (V)) and H-1(End(0) (TX)). These groups encode the complex structure, Kahler moduli, bundle moduli and perturbations of the spin connection respectively in the case of a Calabi-Yau compactification. We investigate the fluctuations of only a subset of the conditions of the Strominger system (expected to correspond physically to F-term constraints in the effective theory). The full physical moduli space is, therefore, given by a further restriction on these degrees of freedom which we discuss but do not explicitly provide. This paper is complementary to a previous tree-level worldsheet analysis of such moduli and agrees with that discussion in the limit of vanishing alpha'. The structure we present can be interpreted in terms of recent work in Atiyah and Courant algebroids, and we conjecture links with aspects of Hitchin's generalized geometry to heterotic moduli.
The ALPS project release 2.0: open source software for strongly correlated systems
Bauer, B.; Carr, L. D.; Evertz, H. G.; Feiguin, A.; Freire, J.; Fuchs, S.; Gamper, L.; Gukelberger, J.; Gull, E.; Guertler, S.; Hehn, A.; Igarashi, R.; Isakov, S. V.; Koop, D.; Ma, P. N.; Mates, P.; Matsuo, H.; Parcollet, O.; Pawlowski, G.; Picon, J. D.; Pollet, L.; Santos, Eunice E.; Scarola, Vito W.; Schollwoeck, U.; Silva, C.; Surer, B.; Todo, S.; Trebst, S.; Troyer, M.; Wall, M. L.; Werner, P.; Wessel, S. (IOP, 2011-05-01)
We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. The code development is centered on common XML and HDF5 data formats, libraries to simplify and speed up code development, common evaluation and plotting tools, and simulation programs. The programs enable non-experts to start carrying out serial or parallel numerical simulations by providing basic implementations of the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended ensemble simulations, exact and full diagonalization (ED), the density matrix renormalization group (DMRG) both in a static version and a dynamic time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for dynamical mean field theory (DMFT). The ALPS libraries provide a powerful framework for programers to develop their own applications, which, for instance, greatly simplify the steps of porting a serial code onto a parallel, distributed memory machine. Major changes in release 2.0 include the use of HDF5 for binary data, evaluation tools in Python, support for the Windows operating system, the use of CMake as build system and binary installation packages for Mac OS X and Windows, and integration with the VisTrails work ow provenance tool. The software is available from our web server at http://alps.comp-phys.org/.
Aluminum plasmonic nanostructures for improved absorption in organic photovoltaic devices
Kochergin, V.; Neely, L.; Jao, C. Y.; Robinson, Hans D. (AIP Publishing, 2011-03)
We model the absorption enhancement in organic photovoltaic devices induced by incorporating Al, Ag, and Au nanoparticles in the active layer. We find that Al nanoparticles should yield significantly greater enhancement than Ag or Au. This is because the much higher plasma frequency of Al ensures a better overlap between plasmon resonance and absorption band of organic semiconductors. Our predictions are verified experimentally by demonstrating enhanced absorbance in a poly(3-hexylthiophene-2,5-diyl): [6,6]-phenyl C61 butyric acid methyl ester layer with embedded functionalized Al nanoparticles. (C) 2011 American Institute of Physics. [doi:10.1063/1.3574091]
An analysis of nonoblique corrections to the Zb¯b vertex
Takeuchi, Tatsu; Grant, Aaron K.; Rosner, Jonathan L. (1994)
We present a model–independent analysis of the Zb¯b vertex, with the aim of constraining contributions of new physics to the left- and right–handed couplings of the b. We find that the left–handed coupling of the b is quite narrowly constrained by present data, but that the right–handed coupling is still largely unconstrained.
Analysis of optical response of long period fiber gratings to nm-thick thin-film coatings
Wang, Zhiyong; Heflin, James R.; Stolen, Rogers H.; Ramachandran, Siddharth (Optical Society of America, 2005-04-01)
We have theoretically and experimentally demonstrated that the resonant wavelength of long period fiber gratings (LPG) can be shifted by a large magnitude by coating with only a nm-thickthin-film that has a refractive index higher than that of the glass cladding. The resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. These results demonstrate the sensitivity of LPG-based sensors can be enhanced by using a film of nm-thickness and refractive index greater than silica. This coating schematic offers an efficient platform for achieving high-performance index-modulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thin-film coating. (C) 2005 Optical Society of America.
An analysis of Precision Electroweak Measurements: Summer 98 Update
Grant, Aaron K.; Takeuchi, Tatsu (1998-07)
We update our analysis of precision electroweak measurements using the latest data announced at Moriond, March 1998. Possible oblique corrections from new physics are parametrized using the STU formalism of Ref.[1], and non-oblique corrections to the Zbb vertex are parametrized using the xi_b zeta_b formalism of Ref.[2]. The implications of the analysis on minimal SU(5) grand unification is discussed.

Browse

Browsing Department of Physics by Title

Results Per Page

Sort Options