Physics Commons^™

Scaling Tests Of The Cross Section For Deeply Virtual Compton Scattering, C. Muñpz Camacho, A. Camsonne, M. Mazouz, C. Ferdi, G. Gavalian, E. Kuchina, M. Amaryan, K. A. Aniol, M. Beaumel, H. Benaoum, D. Hayes, C. E. Hyde-Wright, H. Ibrahim, P. E. Ulmer, L. B. Weinstein

Physics Faculty Publications

We present the first measurements of the ep → epγ cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. The Q² dependence (from 1.5 to 2.3 GeV²) of the helicity-dependent cross section indicates the twist-2 dominance of DVCS, proving that generalized parton distributions (GPDs) are accessible to experiment at moderate Q². The helicity-independent cross section is also measured at Q²=2.3 GeV². We present the first model-independent measurement of linear combinations of GPDs and GPD integrals up to the twist-3 approximation.

Why Do Descending Shells Around Cumulus Clouds Exist?, Thijs Heus, Harm J.J. Jonker

Physics Faculty Publications

No abstract provided.

Lifecycle Analysis Of Cumulus Clouds Using A 3d Virtual Reality Environment, Thijs Heus, Harm J.J. Jonker, Eric J. Griffith, Frits H. Post

Physics Faculty Publications

No abstract provided.

The Influence Of The Sub-Cloud Moisture Field On Cloud Size Distributions And The Consequences For Entrainment, Harm J.J. Jonker, Remco A. Verzijlbergh, Thijs Heus, A. Pier Siebesma

Physics Faculty Publications

No abstract provided.

Phase Contrast Imaging Using Photothermally Induced Phase Transitions In Liquid Crystals, Chandra S. Yelleswarapu, Sri-Rajasekhar Kothapalli, Francisco J. Aranda, D.V.G.L.N. Rao, Yvonne Vaillancourt, Brian R. Kimball

Physics Faculty Publications

Phase contrast imaging is performed for live biological species using photothermal induced birefringence in dye doped liquid crystals. Using typical 4-f configuration, when liquid crystal cell is at back focal plane of Fourier lens, low spatial frequencies at center of Fourier spectrum are intense enough to induce local liquid crystal molecules into isotropic phase, whereas high spatial frequencies on the edges are not intense enough and remain in anisotropic phase. This results in π/2 phase difference between high and low spatial frequencies. This simple, inexpensive, all-optical, user-friendly, self-adaptive phase contrast imaging technique using low-power laser offers several distinct advantages.

Magnetopolaron Effect On Shallow Donors In Gan, A. Wysmolek, R. Stepniewski, M. Potemski, B. Chwalisz-Pietka, K. Pakula, J. M. Baranowski, David C. Look, S. S. Park, S. K. Lee

Physics Faculty Publications

Resonant interaction between longitudinal-optic (LO) phonons and electrons bound on shallow donors in GaN is studied using magnetoluminescence of neutral-donor bound excitons (D⁰X). The experiments were performed on high-quality freestanding GaN material and heteroepitaxial GaN layers grown on sapphire. In addition to the principal recombination channel of D⁰X, in which donors are left in their ground states, two-electron satellites (TES) involving different excited donor excitations, as well as replicas of the principal D⁰X transition due to LO phonons, were observed for the oxygen and silicon donors. In order to separate transitions involving ground and …

Partial-Wave Expansions Of Angular Spectra Of Plane Waves, James A. Lock

Physics Faculty Publications

Focused electromagnetic beams are frequently modeled by either an angular spectrum of plane waves or a partial-wave sum of spherical multipole waves. The connection between these two beam models is explored here. The partial-wave expansion of an angular spectrum containing evanescent components is found to possess only odd partial waves. On the other hand, the partial-wave expansion of an alternate angular spectrum constructed so as to be free of evanescent components contains all partial waves but describes a propagating beam with a small amount of standing-wave component mixed in. A procedure is described for minimizing the standing-wave component so as …

Quantifying Fluid Mixing With The Shannon Entropy, Marco Camesasca, Miron Kaufman, Ica Manas Zloczower

Physics Faculty Publications

We introduce a methodology to quantify the quality of mixing in various systems, including polymeric ones, by adapting the Shannon information entropy. For illustrative purposes we use particle advection of two species in a two-dimensional cavity flow. We compute the entropy by using the probability of finding a suitable chosen group/complex of particles of a given species, at a given location. By choosing the size of the group to be in direct proportion to the overall concentration of the components in the mixture we ensure that the entropic measure is maximized for the case of perfect mixing, that is, when …

Morphology Of The Near-Terminator Martian Ionosphere: A Comparison Of Models And Data, Jane L. Fox, Katherine E. Yeager

Physics Faculty Publications

We have constructed low and high solar activity models of the Martian thermosphere/ionosphere for solar zenith angles from 60 to 90° in 5 degree increments. The solar fluxes that we have adopted are those from the Solar 2000 v2.22 models of Tobiska (2004), without enhancements of the soft X-ray fluxes. The background neutral density and temperature profiles are similar to those that we have recently presented (Fox, 2004). We compute the density profiles for 14 ions and nine neutral species. For all the models, we present altitude profiles of the photoionization rates, electron impact ionization rates, total ion production rates, …

Revisiting Anomalous B(E2;4+1→2+1)/B(E2;2+1→0+1) Values In 98Ru And 180Pt, E. Williams, C. Plettner, E. A. Mccutchan, H. Levine, N. V. Zamfir, R. Cakirli, R. F. Casten, H. Ai, C. W. Beausang, G. Gurdal, A. Heinz, J. Qian, D. A. Meyer, N. Pietralla, V. Werner

Physics Faculty Publications

Recently, a set of nine nonmagic nuclei with anomalous values of the B(E2) ratio B_4/2 ≡ B(E2; 4⁺₁ → 2⁺₁)/B(E2; 2⁺₁ → 0⁺₁) were identified. Such values are outside the range allowed by current collective models. In the present work, the B(E2; 4⁺₁ → 2⁺₁) values for two of these nuclei, ⁹⁸Ru and ¹⁸⁰Pt, were re-measured to determine if the current literature values for these nuclei are correct. ^{98 …}

Collectivity And Configuration Mixing In 186,188Pb And 194Po, T. Grahn, A. Dewald, O. Moller, R. Julin, C. W. Beausang, S. Christen, I. G. Darby, S. Eeckhaudt, P. T. Greenlees, A. Gorgen, K. Helariutta, J. Jolie, P. Jones, S. Juutinen, H. Kettunen, T. Kroll, R. Krucken, Y. Le Coz, M. Leino, A. P. Leppanen, P. Maierbeck, D. A. Meyer, B. Melon, P. Nieminen, M. Nyman, R. D. Page, J. Pakarinen, P. Petkov, P. Rahkila, B. Saha, M. Sandzelius, J. Saren, C. Scholey, J. Uusitalo

Physics Faculty Publications

Lifetimes of prolate intruder states in ¹⁸⁶Pb and oblate intruder states in ¹⁹⁴Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in ¹⁸⁸Pb up to the 8⁺state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters lβ₂l = 0.29(5) and lβ₂l = 0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the …

Magnetic Moment Softening And Domain Wall Resistance In Ni Nanowires, J. D. Burton, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal, Oleg N. Mryasov

Physics Faculty Publications

We perform ab initio calculations of the electronic structure and conductance of atomic-size Ni nanowires with domain walls only a few atomic lattice constants wide. We show that the hybridization between noncollinear spin states leads to a reduction of the magnetic moments in the domain wall resulting in the enhancement of the domain wall resistance. Experimental studies of the magnetic moment softening may be feasible with modern techniques such as scanning tunneling spectroscopy.

Radiative Recombination And Ultralong Exciton Photoluminescence Lifetime In Gan Freestanding Film Via Two-Photon Excitation, Yongchun Zhong, Kam Sing Wong, Weili Zhang, David C. Look

Physics Faculty Publications

We have measured the photoluminescence (PL) lifetime of a freestanding GaN film using one-photon and two-photon excitations to demonstrate the dramatic difference in exciton recombination dynamics at the surface and in the bulk. An ultralong exciton PL lifetime of 17.2 ns at 295 K is observed from a GaN freestanding film using two-photon excitation, whereas less than 100 ps lifetime is observed for one-photon excitation, suggesting that nonradiative processes from surface defects account for the short PL lifetime measured. A monotonic increase in two-photon excited PL lifetime with increasing temperature and the linear dependence of the exciton lifetime with emission …

The Features Of Drosophila Core Promoters Revealed By Statistical Analysis, Naum I. Gershenzon, Edward N. Trifonov, Ilya P. Ioshikhes

Physics Faculty Publications

Background: Experimental investigation of transcription is still a very labor- and time-consuming process. Only a few transcription initiation scenarios have been studied in detail. The mechanism of interaction between basal machinery and promoter, in particular core promoter elements, is not known for the majority of identified promoters. In this study, we reveal various transcription initiation mechanisms by statistical analysis of 3393 nonredundant Drosophila promoters.

Results: Using Drosophila-specific position-weight matrices, we identified promoters containing TATA box, Initiator, Downstream Promoter Element (DPE), and Motif Ten Element (MTE), as well as core elements discovered in Human (TFIIB Recognition Element (BRE) and Downstream …

Scattering Of A Tightly Focused Beam By An Optically Trapped Particle, James A. Lock, Susan Y. Wrbanek, Kenneth E. Weiland

Physics Faculty Publications

Near-forward scattering of an optically trapped 5-mu m-radius polystyrene latex sphere by the trapping beam was examined both theoretically and experimentally. Since the trapping beam is tightly focused, the beam fields superpose and interfere with the scattered fields in the forward hemisphere. The observed light intensity consists of a series of concentric bright and dark fringes centered about the forward-scattering direction. Both the number of fringes and their contrast depend on the position of the trapping beam focal waist with respect to the sphere. The fringes are caused by diffraction that is due to the truncation of the tail of …

Group Iv Solid State Proposals For Quantum Computation, Petru S. Fodor, J. Levy

Physics Faculty Publications

The discovery of the quantum factorization algorithm more than a decade ago triggered intense interest in exploring possible physical realizations of quantum computers. Among the many solid state proposals, electron and nuclear spins in Si and group IV related materials have long coherence times and the capability of state preparation, gating and read-out using electric, magnetic and optical fields. Proposals involving silicon seek to take advantage of an existing mature technology and the implicit promise of scalability from solid state materials. Nevertheless, building such quantum systems depends in many cases on the development of fabrication techniques with nearly atomic precision. …

Deducing The 237U(N,F) Cross Section Using The Surrogate Ratio Method, J. T. Burke, L. A. Bernstein, J. Escher, L. Ahle, J. A. Church, F. S. Dietrich, K. Moody, E. B. Norman, L. Phair, P. Fallon, R. M. Clark, M. A. Deleplanque, M. Descovich, M. Cromaz, I. Y. Lee, A. O. Macchiavelli, M. A. Mcmahan, E. Rodriguez-Vieitez, F. S. Stephens, H. Ai, C. Plettner, C. W. Beausang, B. Crider

Physics Faculty Publications

We have deduced the cross section for ²³⁷U(n, f) over an equivalent neutron energy range from 0 to 20 MeV using the surrogate ratio method. A 55 MeV⁴He beam from the 88 inch cyclotron at Lawrence Berkeley National Laboratory was used to induce fission in the following reactions: ²³⁸U(α, α^f) and ²³⁶U(α, α^f). The ²³⁸U reaction was a surrogate for ²³⁷U(n, f), and the ²³⁶U reaction was used as a surrogate for ²³⁵U(n, f). Scattered α particles were detected in a fully depleted segmented silicon telescope array …

Direct Evidence Of Impurity Decoration Of Ga Vacancies In Gan From Positron Annihilation Spectroscopy, S. Hautakangas, I. Makkonen, V. Ranki, J. Puska, K. Saarinen, X. Xu, David C. Look

Physics Faculty Publications

Positron annihilation spectroscopy, supported by ab initio theory, has been applied to verify the decoration of Ga vacancies in GaN by oxygen and hydrogen. Our results indicate that the Doppler broadening measurement of electron momentum distribution is sensitive enough to distinguish even between N and O atoms neighboring the Ga vacancy. We identify isolated V_Ga in electron irradiated GaN and V_Ga-O_N complexes in highly O-doped high-purity GaN. Evidence of H decoration of Ga vacancies is obtained in epitaxial GaN grown by metalorganic chemical-vapor deposition.

Magnetic Ordering In Gd Monopnictides: Indirect Exchange Versus Superexchange Interaction, Chun-Gang Duan, Renat F. Sabirianov, Wai-Ning Mei, Peter Dowben, Sitaram Jaswal, Evgeny Y. Tsymbal

Physics Faculty Publications

The exchange interaction parameters of Gd monopnictides are deduced from fitting the total energies of different magnetic configurations to those computed within the Heisenberg model. The magnetic structures predicted by first-principles calculations as well as the Curie (Néel) temperatures obtained from Monte Carlo simulations are both in good agreement with experiments. A detailed analysis of the exchange parameters suggests that the Ruderman-Kittel-Kasuya-Yosida-type indirect exchange interactions and antiferromagnetic superexchange interactions coexist in these compounds. The magnetic order changes from ferromagnetic in GdN to antiferromagnetic in other Gd pnictides as a result of the increased ionic radius of a pnictide in the …

Fast Ground State Manipulation Of Neutral Atoms In Microscopic Optical Traps, D. D. Yavuz, P. B. Kulatunga, E. Urban, Todd A. Johnson, N. Proite, T. Henage, T. G. Walker, M. Saffman

Physics Faculty Publications

We demonstrate Rabi flopping at MHz rates between ground hyperfine states of neutral ⁸⁷Rb atoms that are trapped in two micron sized optical traps. Using tightly focused laser beams we demonstrate high fidelity, site specific Rabi rotations with cross talk on neighboring sites separated by 8  μm at the level of 10⁻³. Ramsey spectroscopy is used to measure a dephasing time of 870  μs, which is ≈5000  times longer than the time for a π/2 pulse.

First Investigation Of Excited States In The Odd-Proton Nucleus Fr209, D. A. Meyer, C. W. Beausang, J. J. Ressler, H. Ai, H. Amro, M. Babilon, R. F. Casten, C. R. Fitzpatrick, G. Gurdal, A. Heinz, E. A. Mccutchan, C. Plettner, J. Qian, N. J. Thomas, V. Werner, E. Williams, N. V. Zamfir, Jing-Ye Zhang

Physics Faculty Publications

Excited states in ²⁰⁹Fr were produced following the ¹⁷⁶Yb(³⁷Cl, 4n) reaction. An excitation function was measured with data taken at 173, 179, and 185 MeV. Recoiling fusion-evaporation products were separated using the SASSYER gas-filled spectrometer. HPGe clover detectors of the YRAST Ball array at the target position and at the focal plane were used to detect prompt and delayed gamma ray decays, providing the first spectroscopic information about prompt and delayed transitions in ²⁰⁹Fr. The decay from a proposedπ i_13/2 configuration isomer was observed in ²⁰⁹Fr, and its half-life was measured …

Breakdown Of K Selection In 178Hf, A. B. Hayes, D. Cline, C. Wu, J. Ai, H. Amro, C. W. Beausang, R. F. Casten, J. Gerl, A. A. Hecht, A. Heinz, R. O. Hughes, R.V. F. Janssens, C. J. Lister, A. O. Macchiavelli, D. A. Meyer, E. F. Moore, P. Napiorkowski, R. C. Pardo, Ch. Schlegel, D. Seweryniak, M. W. Simon, J. Srebrny, R. Teng, K. Vetter, H. J. Wollersheim

Physics Faculty Publications

Coulomb activation of the four quasiparticle K^π = 16^{+ 178}Hf isomer (t _1/2 = 31 y) has led to the measurement of a set of Eλ matrix elements coupling the isomer band to the ground band. The present data combined with earlier ¹⁷⁸Hf Coulomb excitation data have probed the K components in the wave functions and revealed the onset and saturation of K mixing in low-K bands, whereas the mixing is negligible in the high-K bands. The implications can be applied to other quadrupole-deformed nuclei.

Trap Loss In A Dual-Species Rb-Ar* Magneto-Optical Trap, H. C. Busch, M. K. Shaffer, E. M. Ahmed, C. I. Sukenik

Physics Faculty Publications

We have investigated trap loss in a dual-species magneto-optical trap (MOT) comprised of 85Rb and metastable 40Ar. We measure the trap loss rate coefficients for each species due to the presence of the other as a function of trap light intensity. We clearly identify both Penning ionization of Rb by Ar* and associative ionization to form the molecular ion RbAr+ as two of the trap loss channels. We have also measured the trap loss rate coefficient for the Ar* MOT alone and observe production of Ar+ and Ar2+ ions.

Magnetic And Transport Properties Of Nimnal Thin Films, Andriy Vovk, Minghui Yu, Leszek Malkinski, Charles O'Connor, Zhenjun Wang, Eden Durant, Jinke Tang, Vladimir Golub

Physics Faculty Publications

The magnetic and transport properties of Ni₂MnAl thin films prepared using pulse laser deposition were investigated. It was shown that the films are granular and multiphase. Contrary to the data reported earlier we observe nonmonotonic temperature dependence of resistance with minimum in the vicinity of 100 K for the films deposited on substrates held at 773 K and negative magnetoresistance (MR) values of about 2.5% at 5 K and 1.6% at RT in magnetic field of 50 kOe. These values of MR are the highest reported up to date for Ni₂MnAl films. Large negative MR in …

Aberration-Free Negative-Refractive-Index Lens, Jiajun Chen, Cosmin Radu, Ashok Puri

Physics Faculty Publications

The aberrations of a spherical lens composed of left-handed materials are studied in this letter. Five Seidel aberrations (spherical, coma, astigmatism, field curvature, and distortion) as a function of the refractive index n and shape factor q of the lens are considered. Our numerical calculations show that the negative refractive index gives much larger windows of small values of aberrations than the positive index, which will significantly enhance the flexibility for the design of an optical lens. Two possible regions with optimized aberrations are proposed: n = −1, q = −2.2 and n = −0.81 and q = 0.83

Quantal Density Functional Theory: Wave Function Arbitrariness Of The Noninteracting Fermion Model, Viraht Sahni, Marlina Slamet

Physics Faculty Publications

In quantal density functional theory (Q-DFT), the mapping from either a ground or excited state of the interacting system to one of noninteracting fermions with equivalent density is such that the state of the latter model S system is arbitrary. Thus, in principle, there are an infinite number of local (multiplicative) effective potential energy functions that can reproduce the density of the interacting system. In the present work, we note that there is also an arbitrariness in the wave function of the model fermions when the S system is constructed in an excited state. Different wave functions lead to the …

Measurement Of The High-Field Q Drop In The Tm010 And Te011 Modes In A Niobium Cavity, Gianluigi Ciovati, Peter Kneisel

Physics Faculty Publications

In the last few years superconducting radio-frequency (rf) cavities made of high-purity ( residual resistivity ratio > 200) niobium achieved accelerating gradients close to the theoretical limits. An obstacle towards achieving reproducibly higher fields is represented by "anomalous'' losses causing a sharp degradation of the cavity quality factor when the peak surface magnetic field (B_p) is above about 90 mT, in the absence of field emission. This effect, called "Q drop'' has been measured in many laboratories with single- and multicell cavities mainly in the gigahertz range. In addition, a low-temperature (100 - 140 °C) "in situ'' baking of …

Measurement Of The X- And Q2 -Dependence Of The Asymmetry A1 On The Nucleon, K. V. Dharmawardane, S. E. Kuhn, P. Bosted, Y. Prok, G. Adams, P. Ambrozewicz, M. Anghinolfi, G. Asryan, H. Avakian, H. Bagdasaryan, M. Bektasoglu, S. Bültmann, S. L. Careccia, G. E. Dodge, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. Klein, J. Lachniet, M. R. Niroula, R. A. Niyazov, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Zhang

Physics Faculty Publications

We report results for the virtual photon asymmetry A₁ on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton (¹⁵NH₃) and deuteron (¹⁵ND₃) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present Letter, we concentrate on our results for A₁ ( x , Q² ) and the related ratio g1 / F₁ ( x , Q² ) in the resonance and the deep inelastic …

Diffuse Light Scattering Dynamics Under Conditions Of Electromagnetically Induced Transparency, V. M. Datsyuk, I. M. Sokolov, D. V. Kupriyanov, M. D. Havey

Physics Faculty Publications

We show that under conditions of electromagnetically induced transparency (EIT) in an ultracold atomic sample in a magneto-optical trap, a significant portion of the incident probe pulse is transferred into Rayleigh and Raman scattering channels. The light scattered into the Rayleigh channel emerges from the sample with an EIT time delay. We show that a proper description of the probe light propagation in the sample should include, in the diffusion dynamics, a spin polariton generated by the two-photon EIT process. The results have important implications for studies of weak light localization and for manipulation of single and few photon states …

Measurement Of Deeply Virtual Compton Scattering With A Polarized-Proton Target, S. Chen, M. Amarian, H. Bagdasaryan, M. Bektasoglu, S. Bültmann, S. L. Careccia, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. Klein, S. E. Kuhn, J. Lachniet, M. R. Niroula, R. A. Niyazov, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, J. Zhang, Clas Collaboration

Physics Faculty Publications

The longitudinal target-spin asymmetry A_UL for the exclusive electroproduction of high-energy photons was measured for the first time in e→p→e′pγ. The data have been accumulated at JLab with the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH₃ target. A significant azimuthal angular dependence was observed, resulting from the interference of the deeply virtual Compton scattering and Bethe-Heitler processes. The amplitude of the sinϕ moment is 0.252±0.042^stat±0.020^sys. Theoretical calculations are in good agreement with the magnitude and the kinematic dependence of the target-spin asymmetry, which is sensitive to the generalized parton distributions …