Physical Sciences and Mathematics Commons^™

Isomeric Decay Of 208Ra, J. J. Ressler, C. W. Beausang, H. Ai, H. Amro, M. Babilon, J. A. Caggiano, R. F. Casten, G. Gurdal, A. Heinz, R. O. Hughes, E. A. Mccutchan, D. A. Meyer, C. Plettner, J. Qian, M.J. S. Sciacchitano, N. J. Thomas, E. Williams, N. V. Zamfir

Physics Faculty Publications

Low-energy excited states of 208Ra were investigated using the 182W(30Si, 4n) reaction at the Wright Nuclear Structure Laboratory of Yale University. Fusion evaporation recoils were selected using the gas-filled spectrometer SASSYER. Delayed γ rays, following isomeric decays, were detected at the focal plane of SASSYER with a small array of three clover Ge detectors. Transitions following a proposed J π = 8+ isomer were observed, and the half-life was measured.

Nonlinear Dynamics Of Piezoelectric High Displacement Actuators In Cantilever Mode, Timothy Usher, Alec Sim

Physics Faculty Publications

Experimental results of the nonlinear dynamic response of a piezoelectric high displacement actuator known as thin-layer composite unimorph ferroelectric driver and sensor were compared to a theoretical model, which utilizes the multiple scales method to connect the effective spring constant to higher-order stiffness constants c4 of the piezoelectric layer. This type of actuator has prestress gradients resulting from the manufacturing process that have been reported to play an important role in enhanced actuation. A value of c₄=−4.7x10²⁰ N/m² was obtained for the higher-order lead zirconate titanate (PZT) stiffness coefficient, which is higher than other published results …

Cofe2o4 Nanostructures With High Coercivity, J S. Jung, J H. Lim, K H. Choi, S L. Oh, Y R. Kim, S H. Lee, D A. Smith, K L. Stokes, L Malkinski, C J. O'Connor

Physics Faculty Publications

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4).. We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600 °C for 2 h in Ar gas forming arrays of cobalt ferrite nanowires inside …

Magneto-Optical Spectra Of Closely Spaced Magnetite Nanoparticles, Damon Allen Smith, Yu A. Barnakov, B L. Scott, S A. White, Kevin L. Stokes

Physics Faculty Publications

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe

3O4 smagnetited nanoparticles s8-nm diameterd and polysmethylmethacrylated . Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for sdilute compositesd to 540 nm concentrated . We present a theory based on the discrete-dipole approximation which accounts for

optical coupling between magnetite particles. Qualitative correlations between theoretical calculations …

Large Plasma-Edge Broadened Magneto-Optic-Polar-Kerr-Effect-Based Broadband Incoherent Detection Of Terahertz Spectral Frequencies, A. De, A. Puri

Physics Faculty Publications

A magneto-optic Kerr effect (MOKE)-based spectroscopic technique is proposed in the terahertz regime. This method relies on very large reflection edge splitting effects, which occur when the cyclotron frequency (CF) is of the same order of magnitude or greater than the plasma frequency. In the event of a very large reflection edge split, the Kerr rotation (KR) no longer occurs at the plasma edge, but instead occurs at Re(ε₊ε₋) ≈ 1, within the macroscopic framework of the Drude model. This implies that one can control the spectral occurrence of the MOKE resonance, simply by tuning …

Ion Cyclotron Waves In The Saturnian Magnetosphere Associated With Cassini's Engine Exhaust, C. T. Russell, J. S. Leisner, K. K. Khurana, M. K. Dougherty, X. Blanco-Cano, Jane L. Fox

Physics Faculty Publications

Five hours after the orbit insertion maneuver that placed Cassini into orbit about Saturn, a long (90 minute) burst of ion cyclotron waves were seen, very different than any waves on the inbound leg of the orbit or on succeeding orbits. The ion cyclotron waves were left-hand elliptically polarized and propagating at a moderately large angle to the local magnetic field. The waves had a noticeable compressional component consistent with their off angle propagation. The frequency band of the signals was moderately broad and consistent with the singly ionized components of the engine exhaust gases: CO₂, N_{2 …}

Frequency Scanned Interferometer Demonstration System, Jason A. Deibel, Sven Nyberg, Keith Riles, Haijun Yang

Physics Faculty Publications

No abstract provided.

Thermospheric Distribution Of Fast O(D-1) Atoms, V. Kharchenko, A. Dalgarno, Jane L. Fox

Physics Faculty Publications

Detailed calculations are carried out of the sources of energetic metastable O(¹D) atoms in the atmosphere at altitudes between 80 km and 200 km, and the corresponding energy distribution functions are derived, taking account of energy transfer and quenching in collisions of the metastable atoms with the ambient atmospheric gas constituents. The energy relaxation of metastable oxygen atoms produced by O₂ and O₃ photolysis and O₂ ⁺ dissociative recombination is determined by solving the time-dependent Boltzmann equation. The O(¹D) thermalization and quenching times are obtained as functions of the altitude. The steady state …

High-Energy Effective Action From Scattering Of Qcd Shock Waves, Ian Balitsky

Physics Faculty Publications

At high energies, the relevant degrees of freedom are Wilson lines—infinite gauge links ordered along straight lines collinear to the velocities of colliding particles. The effective action for these Wilson lines is determined by the scattering of QCD shock waves. I develop the symmetric expansion of the effective action in powers of strength of one of the shock waves and calculate the leading term of the series. The corresponding first-order effective action, symmetric with respect to projectile and target, includes both up and down fan diagrams and pomeron loops.

Phase Transition In Single Crystal Cs2nb4o11, Jianjun Liu, E. P. Kharitonova, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy

Physics Faculty Publications

We studied temperature dependence of complex capacitance, impedance, and polarized Raman spectra of single crystal Cs₂Nb₄O₁₁. First, we observed a sharp λ-shaped peak at 165 °C in the complex capacitance, then found drastic changes in the Raman spectra in the same temperature range. Utilizing the pseudosymmetry search of structure space group, we attributed the observed anomalies to a structural change from the room temperature orthorhombic Pnn2 to another orthorhombic Imm2. We also measured room temperature polarized Raman spectra in different symmetries of normal vibrations and assigned high wavenumber Raman bands to the …

Effects Of Dissociative Recombination On The Composition Of Planetary Atmospheres, Jane L. Fox

Physics Faculty Publications

Because dissociative recombination (DR) reactions of molecular ions are often highly exothermic, in the thermospheres of the Earth and planets DR may be a source of translationally and internally excited fragments. DR is important, therefore, for thermospheric neutral heating; if the excited fragments radiate to space, however, DR may be also a source of thermospheric cooling. DR may produce metastable fragments, which may live long enough to participate in reactions that are not available to ground state species. It is rare, however, for DR to be a significant source of minor species in their ground states. An exception appears to …

Computational Technique For Improvement Of The Position-Weight Matrices For The Dna/Protein Binding Sites, Naum I. Gershenzon, Gary D. Stormo, Ilya P. Ioshikhes

Physics Faculty Publications

Position-weight matrices (PWMs) are broadly used to locate transcription factor binding sites in DNA sequences. The majority of existing PWMs provide a low level of both sensitivity and specificity. We present a new computational algorithm, a modification of the Staden–Bucher approach, that improves the PWM. We applied the proposed technique on the PWM of the GC-box, binding site for Sp1. The comparison of old and new PWMs shows that the latter increase both sensitivity and specificity. The statistical parameters of GC-box distribution in promoter regions and in the human genome, as well as in each chromosome, are presented. The majority …

C And C+ In The Venusian Thermosphere/Ionosphere, Jane L. Fox, L. J. Paxton

Physics Faculty Publications

We have constructed standard low and high solar activity models of the Venus thermosphere, which take into account revised rate coefficients for production and loss processes for C and C⁺, high-resolution cross sections for photodissociation of CO, and recent solar fluxes from the Solar 2000 v1.24 and v2.22 models of Tobiska [2004]. Among the most important changes is the inclusion of the branching ratio for the channel of dissociative recombination of CO₂⁺ that produces C + O₂, which has been measured recently by Seiersen et al. [2003]. We find that unlike Mars, where the …

Dielectric Properties And Maxwell-Wagner Relaxation Of Compounds Acu3ti4o12 (A=Ca,Bi2/3,Y2/3,La2/3), Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy

Physics Faculty Publications

We have studied the frequency and temperature dependences of permittivity and impedance of the compounds ACu3Ti4O12 A=Ca, Bi2/3, Y2/3, La2/3 in the ranges of 10−1–106 Hz and −150–200 °C. All compounds investigated display similar dielectric properties. Specifically, they all have a Debye-like relaxation and their dielectric constants are independent of frequency and temperature over a wide range. They all have two electrical responses in impedance formalism, indicating that there are two distinct contributions. We attribute them to grains and grain boundaries in the ceramic samples and explain the dielectric behaviors by Maxwell-Wagner relaxation arising at the interfaces between grains and …

Entropic Analysis Of Color Homogeneity, Kirill Alemaskin, Ica Manas Zloczower, Miron Kaufman

Physics Faculty Publications

We propose an entropic measure to assess color homogeneity as well as deviations from a standard/ideal color. We illustrate the concept by analyzing samples obtained in a single screw extruder by mixing blue and yellow polymer pellets. Alternatively the proposed technique can be employed to assess the efficiency and degree of distributive mixing attained in polymer processing equipment.

320-Channel Dual Phase Lock-In Optical Spectrometer, Petru S. Fodor, S. Rothenberger, J. Levy

Physics Faculty Publications

The development of a multiple-channel lock-in optical spectrometer (LIOS) is presented, which enables parallel phase-sensitive detection at the output of an optical spectrometer. The light intensity from a spectrally broad source is modulated at the reference frequency, and focused into a high-resolution imaging spectrometer. The height at which the light enters the spectrometer is controlled by an acousto-optic deflector, and the height information is preserved at the output focal plane. A two-dimensional InGaAs focal plane array collects light that has been dispersed in wavelength along the horizontal direction, and in time along the vertical direction. The data is demodulated using …

Exclusive Ρ0 Meson Electroproduction From Hydrogen At Clas, C. Hadjidakis, M. Guidal, M. Garçon, J.-M. Laget, E. S. Smith, M. Vanderhaeghen, G. Adams, P. Ambrozewicz, E. Anciant, M. Anghinolfi, H. Bagdasaryan, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, G. Gavalian, M. Guler, C. E. Hyde-Wright, A. Klein, A. V. Klimenko, S. E. Kuhn, R. A. Niyazov, L. M. Qin, F. Sabatie, L. B. Weinstein, J. Yun

Physics Faculty Publications

The longitudinal and transverse components of the cross section for the ep → e′ pρ⁰ reaction were measured in Hall B at Jefferson Laboratory using the CLAS detector. The data were taken with a 4.247 GeV electron beam and were analyzed in a range of ^xB from 0.2 to 0.6 and of Q² from 1.5 to 3.0 GeV2. The data are compared to a Regge model based on effective hadronic degrees of freedom and to a calculation based on Generalized Parton Distributions. It is found that, at our lowest ^xB values, the transverse part of the …

Exclusive Photoproduction Of The Cascade Ξ Hyperons, H. Bagdasaryan, M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, A. V. Klimenko, S. E. Kuhn, L. M. Qin, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

We report on the first measurement of exclusive Ξ^-(1321) hyperon photoproduction in 𝛾p → K⁺K⁺Ξ^- for 3.2 < E𝛾 < 3.9 GeV. The final state is identified by the missing mass in p(𝛾,K⁺K⁺)X measured with the CLAS detector at Jefferson Laboratory. We have detected a significant number of the ground state Ξ^-(1321)1/2⁺ and have estimated the total cross section for its production. We also have strong evidence for the first excited state Ξ^-(1530)3/2⁺. Photoproduction provides a copious source of Ξ's. We discuss the possibilities of a search for the recently proposed Ξ₅^- and Ξ₅^{+ …}

Global Analysis Of Data On The Proton Structure Function G₁ And The Extraction Of Its Moments, M. Osipenko, S. Simula, W. Melnitchouk, P. Bosted, V. Burkert, E. Christy, K. Griffioen, C. Keppel, S. Kuhn, G. Ricco

Physics Faculty Publications

Inspired by recent measurements with the CLAS detector at Jefferson Lab, we perform a self-consistent analysis of world data on the proton structure function g₁ in the range 0.17 < Q² < 30 (GeV/c)². We compute for the first time low-order moments of g, and study their evolution from small to large values of Q². The analysis includes the latest data on both the unpolarized inclusive cross sections and the ratio R = σ _L/σ_T from Jefferson Lab, as well as a new model for the transverse asymmetry A₂ in the resonance region. The contributions of …

Higher Twist Analysis Of The Proton G₁ Structure Function, M. Osipenko, W. Melnitchouk, S. Simula, P. Bosted, V. Burkert, M. E. Christy, K. Griffioen, C. Keppel, S. E. Kuhn

Physics Faculty Publications

We perform a global analysis of all available spin-dependent proton structure function data, covering a large range of Q², 1 ⩽ Q² ⩽ 30 GeV², and calculate the lowest moment of the g₁ structure function as a function of Q². From the Q² dependence of the lowest moment we extract matrix elements of twist-4 operators, and determine the color electric and magnetic polarizabilities of the proton to be X_E= 0.026 ± 0.015(stat) ± ^0.021_0.024 (sys) and X_B= -0.013 ∓ 0.007(stat) ∓ ^0.010 _0.012(sys), respectively.

Beam-Helicity Asymmetries In Double-Charged-Pion Photoproduction On The Proton, H. Bagdasaryan, M. Bektasoglu, S. Bültmann, Gail Dodge, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. Klein, S. E. Kuhn, L. M. Qin, W. Roberts, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, J. Zhang, Et Al., Clas Collaboration

Physics Faculty Publications

Beam-helicity asymmetries for the two-pion-photoproduction reaction 𝛾⃗p → p π⁺π^- have been studied for the first time in the resonance region for center-of-mass energies between 1.35 and 2.30 GeV. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer using circularly polarized tagged photons incident on an unpolarized hydrogen target. Beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics and dynamics of the reaction. The data are compared with the results of various phenomenological model calculations, and show that these models currently do not …

Levitation Using Microwave-Induced Plasmas, R. J. Exton, S. Popovic, G. C. Herring, M. Cooper

Physics Faculty Publications

The levitation of objects above a microwave horn is demonstrated. High-power microwave pulses generate a low-temperature, diffuse plasma on the surface of the horn window. The thermal effect of the surface plasma brings about a localized increase in the pressure and results in a vertical flow of air, thus levitating the object.

Medical Image Processing Using Transient Fourier Holography In Bacteriorhodopsin Films, Sri-Rajasekhar Kothapalli, Pengfei Wu, Chandra S. Yelleswarapu, D.V.G.L.N. Rao

Physics Faculty Publications

Real time image processing is demonstrated by recording and reconstructing the transient photoisomerizative grating formed in the bR film using Fourier holography. Desired spatial frequencies including both high and low band in the object beam are reconstructed by controlling the reference beam intensity. The results are in agreement with a theoretical model based on photoisomerization grating. We exploit this technique to process mammograms in real-time for identification of microcalcifications buried in the soft tissue for early detection of breast cancer. A feature of the technique is the ability to transient display of selected spatial frequencies in the reconstructing process which …

Laboratory Experiments Of Entrainment In Dry Convective Boundary Layers, Harm J.J. Jonker, Thijs Heus, Esther Hagen, Han Van Dop

Physics Faculty Publications

Entrainment in dry convective boundary layers was studied. A saline convection tank set-up was used as a laboratory model for a dry convective atmospheric boundary layer. The entrainment flux was measured using planar laser induced fluorescence (PLIF). It was found that the entrainment flux reveals a much stronger dependence on the inversion strength than large eddy simulations tend to do.

As-Doped P-Type Zno Produced By An Evaporation/Sputtering Process, David C. Look, G. M. Renlund, R. H. Burgener, J. R. Sizelove

Physics Faculty Publications

Strongly p-type ZnO is produced by the following sequence of steps: (1) evaporation of Zn₃As₂ on a fused-quartz substrate at 350 °C; and (2) sputtering of ZnO with substrate held at 450 °C. The electrical characteristics include: resistivity of 0.4 Ω cm, a mobility of 4 cm²∕V s, and a hole concentration of about 4×10¹⁸ cm⁻³. This resistivity is among the best (lowest) ever reported for p-type ZnO. Secondary-ion mass spectroscopic analysis gives an average As concentration about 5×10¹⁹ cm⁻³, and a simple one-band fit of the …

Micro-Auger Electron Spectroscopy Studies Of Chemical And Electronic Effects At Gan-Sapphire Interfaces, X. L. Sun, S. T. Bradley, G. H. Jessen, David C. Look, Richard J. Molnar, L. J. Brillson

Physics Faculty Publications

We have used cross-sectional micro-Auger electron spectroscopy (AES), coupled with micro-cathodoluminescence (CLS) spectroscopy, in a UHV scanning electron microscope to probe the chemical and related electronic features of hydride vapor phase epitaxy GaN/sapphire interfaces on a nanometer scale. AES images reveal dramatic evidence for micron-scale diffusion of O from Al₂O₃ into GaN. Conversely, plateau concentrations of N can extend microns into the sapphire, corresponding spatially to a 3.8 eV defect emission and Auger chemical shifts attributed to Al-N-O complexes. Interface Al Auger signals extending into GaN indicates AlGaN alloy formation, consistent with a blue-shifted CLS local interface …

Theoretical Study Of The Magnetic Ordering In Rare-Earth Compounds With Face-Centered-Cubic Structure, Chun-Gang Duan, Renat F. Sabirianov, Jianjun Liu, Wai-Ning Mei, Peter A. Dowben, John R. Hardy

Physics Faculty Publications

We present a detailed theoretical study of the magnetic ordering in heavy rare-earth compounds with a face-centered-cubic structure. In addition to the exchange interactions which are counted up to the third nearest neighbors, the effect of the dipolar interactions and magnetic anisotropic effect are also included in our model Hamiltonian. The interactions parameters are obtained from first-principles band-structure calculations by fitting the total energies of different magnetic configurations to the Heisenberg Model. Thus from utilizing the Monte Carlo simulations, we explained the formation of different magnetic structures in the rare-earth compounds.

Response Of The Martian Thermosphere/Ionosphere To Enhanced Fluxes Of Solar Soft X Rays, Jane L. Fox

Physics Faculty Publications

We have investigated the response of the thermosphere and ionosphere of Mars to enhanced fluxes of solar soft X rays, such as those that have been detected by the SNOE satellite (e.g., Bailey et al., 2000 ). We have constructed standard models by adopting the SC#21REFW and F79050N solar fluxes from H. E. Hinteregger (private communication) (see also Torr et al., 1979 ) for the low and high solar activity models, respectively. We then constructed enhanced soft X-ray models by multiplying the solar photon fluxes for wavelengths below 200 Å by a factor of 3 at low solar …

Below Band Gap Photoreflectance Transitions In Epitaxial Gan, Phil W. Yu, Jerry D. Clark, David C. Look, C. Q. Chen, Jinwei Yang, Edmundas Koutstis, M. Asif Khan, Denis V. Tsvertkov, Vladimir A. Dmitriev

Physics Faculty Publications

A photoreflectance (PR) and photoluminescence (PL) study has been performed on a Si-doped epitaxial GaN layer that contains impurity or defect related below band gap features in its PR spectrum. In the 300 K PR spectrum, these features appear at energies of 3.26 and 3.33 eV, respectively, but below 180 K they can no longer be seen. The 3.26 eV line evidently corresponds to a donor acceptor pair transition, also seen in PL. The origin of the 3.33 eV line is uncertain, but may correspond to a transition involving the nitrogen vacancy.

Co2+ Dissociative Recombination: A Source Of Thermal And Nonthermal C On Mars, Jane L. Fox

Physics Faculty Publications

CO₂ ⁺ dissociative recombination has been assumed in the past to proceed overwhelmingly by the channel that produces CO + O. Although the channel that leads to the products C + O₂ is energetically possible, the significant rearrangement of bonds that is required has led to the belief that this channel contributes minimally. Seiersen et al. [2003] have recently measured the branching ratio for the latter channel, and they have reported a value of ∼9% of the total. We have constructed both low and high solar activity models of the Martian thermosphere, and we have tested the effect …