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2002

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Full-Text Articles in Physics

Viscoelasticity From A Microscopic Model Of Dislocation Dynamics, M. Christina Marchetti, Karl Saunders Dec 2002

Viscoelasticity From A Microscopic Model Of Dislocation Dynamics, M. Christina Marchetti, Karl Saunders

Physics

It is shown that the dynamics of a viscoelastic medium can be modeled as that of a two-dimensional crystal with a finite concentration of dislocations, as well as vacancy and interstitial defects. At the longest length scales the viscoelasticity is described by the simplest Maxwell model, whose shear and compressional relaxation times are obtained in terms of microscopic quantities, including the density of free dislocations. At short length scales, t bond orientational order effects become important and lead to wave vector dependent corrections to the relaxation times.


Search For Radiative B,-Hadron Decays In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2002

Search For Radiative B,-Hadron Decays In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have performed a search for radiative b-hadron decays using events produced in pp̅ collisions at √s=1.8 TeV and collected by the Collider Detector at Fermilab. The decays we considered were d0K*0(→K-π+) γ, s0→φ(→K+K-) γ, Λb0→ Λ(→pπ-) γ, and their charge conjugates. Two independent methods to identify photons from such decays were employed. In the first method, the photon was detected in the electromagnetic calorimeter. In the second method, the photon was identified by an electron-positron pair produced through the external photon ...


Limits On Extra Dimensions And New Particle Production In The Exclusive Photon, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2002

Limits On Extra Dimensions And New Particle Production In The Exclusive Photon, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

The exclusive γE/T signal has a small standard model cross section and is thus a channel sensitive to new physics. This signature is predicted by models with a superlight gravitino or with large extra spatial dimensions. We search for such signals at the Collider Detector at Fermilab, using 87   pb-1 of data at √s=1.8   TeV, and extract 95% C.L. limits on these processes. A limit of 221 GeV is set on the scale |F|1/2 in supersymmetric models. For 4, 6, and 8 extra dimensions, model-dependent limits on the fundamental mass scale MD ...


Unusual Sequences Of Tilted Smectic Phases In Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, P. Toledano Dec 2002

Unusual Sequences Of Tilted Smectic Phases In Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, P. Toledano

Chemical Physics Publications

The first theoretical description of the experimentally often-observed isotropic-polar smectic phase transitions of symmetric and asymmetric bent-shape molecules is presented. The isotropic-tilted polar smectic phase transition requires a coupling among three types of ordering processes: polar packing, director tilt, and layer ordering. For explaining the unusual triclinic-monoclinic phase transition with the lower symmetry phase at higher temperature, observed in fluoro-containing compounds recently, a mechanism is proposed in which the layer ordering triggers the simultaneous onset of the tilt and polar order.


Perturbative Calculation Of The Triply Differential Cross Section For Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace Dec 2002

Perturbative Calculation Of The Triply Differential Cross Section For Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

Single-photon, two-electron ionization of He is analyzed, taking into account electron correlation using lowest-order perturbation theory and including all individual electron angular momenta in the final two-electron continuum. Perturbative account of electron correlation in the final state, which describes the so-called TS-1 mechanism of double photoionization, combined with a variational account of electron screening, is found to provide results for the triply differential cross section at an excess energy of 20 eV that are in excellent agreement with both absolute experimental data and results of non-perturbative calculations, for all kinematics of the process in which the TS-1 mechanism is expected ...


Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli Dec 2002

Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli

Chemical Physics Publications

The dielectric fluctuations in the uniaxial nematic phase of a bent-core liquid crystal have been studied by dynamic light scattering. Polarization selection of the scattering cross-section reveals one mode due to ordinary director fluctuations and, in the lower part of the nematic phase, a second mode attributable to fluctuations of the biaxial order parameter. The director fluctuations are similar to100 times slower than observed in typical nematics based on straight-core molecules, suggesting that the bent core nematogenic units may be microscopic smectic domains ("cybotactic" clusters).


Search For The Production Of Single Sleptons Through R-Parity Violation In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration Dec 2002

Search For The Production Of Single Sleptons Through R-Parity Violation In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report the first search for supersymmetric particles via s-channel production and decay of smuons or muon sneutrinos at hadronic colliders. The data for the two-muon and two-jets final states were collected by the D0 experiment and correspond to an integrated luminosity of 94 ± 5 pb-1. Assuming that R parity is violated via the single coupling λ′211, the number of candidate events is in agreement with expectation from the standard model. Exclusion contours are given in the (m0; m½) and (mΧ̅,mν planes for λ′211= 0.09, 0.08, and 0.07.


Chaotic Free-Space Laser Communication Over Turbulent Channel, N. F. Rulkov, Mikhail Vorontsov, L. Illing Dec 2002

Chaotic Free-Space Laser Communication Over Turbulent Channel, N. F. Rulkov, Mikhail Vorontsov, L. Illing

Electro-Optics and Photonics Faculty Publications

The dynamics of errors caused by atmospheric turbulence in a self-synchronizing chaos-based communication system that stably transmits information over a ∼5  km free-space laser link is studied experimentally. Binary information is transmitted using a chaotic sequence of short-term pulses as a carrier. The information signal slightly shifts the chaotic time position of each pulse depending on the information bit. We report the results of an experimental analysis of the atmospheric turbulence in the channel and the impact of turbulence on the bit-error-rate performance of this chaos-based communication system.


He Ii Reverberation In Active Galactic Nucleus Spectra, Mark C. Bottorff, Jack A. Baldwin, Gary J. Ferland, Jason W. Ferguson, Kirk T. Korista Dec 2002

He Ii Reverberation In Active Galactic Nucleus Spectra, Mark C. Bottorff, Jack A. Baldwin, Gary J. Ferland, Jason W. Ferguson, Kirk T. Korista

Physics and Astronomy Faculty Publications

This paper compares the observed reverberation response lags and the intensity ratios of the broad-line region (BLR) emission lines He II λ1640, He II λ4686, and C IV λ1549 with predictions. Published observations indicate that the He II λ1640 lag is 3 times shorter than the lags of He II λ4686 or C IV λ1549. Diverse models, however, do not reproduce this observation. Extensive improved numerical simulations of the hydrogenic isoelectronic sequence emission show that the He II spectrum remains especially simple, even in the central regions of a luminous quasar. Line trapping never builds up a significant population of ...


Two-Photon Bremsstrahlung Processes In Atoms: Polarization Effects And Analytic Results For The Coulomb Potential, A. A. Krylovetskiĭ, N. L. Manakov, S. I. Marmo, Anthony F. Starace Dec 2002

Two-Photon Bremsstrahlung Processes In Atoms: Polarization Effects And Analytic Results For The Coulomb Potential, A. A. Krylovetskiĭ, N. L. Manakov, S. I. Marmo, Anthony F. Starace

Anthony F. Starace Publications

The partial wave analysis of two-photon free–free (bremsstrahlung) electron transition cross sections during scattering by a static potential U(r), as well as by an atom with a nonzero angular momentum, is carried out. The dipole interaction with radiation is taken into account in the second order of perturbation theory for the general case of elliptic polarization of photons. The polarization and angular dependences of the twophoton potential scattering amplitude is presented as a combination of the scalar product of electron momenta and photon polarization vectors and five atomic parameters containing Legendre polynomials of the scattering angle as well ...


Search For Minimal Supergravity In Single-Electron Events With Jets And Large Missing Transverse Energy In Pp̅ Collisions At √S =1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration Dec 2002

Search For Minimal Supergravity In Single-Electron Events With Jets And Large Missing Transverse Energy In Pp̅ Collisions At √S =1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We describe a search for evidence of minimal supergravity (MSUGRA) in 92.7 pb-1 of data collected with the DØ detector at the Fermilab Tevatron pp̅ collider at√s =1.8 TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W +jets, misidentified multijet, tt̅, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of MSUGRA model parameters is obtained.


Fabrication Of Electro-Optic Devices Using Liquid Crystals With A Single Glass Substrate, Il Kim, Daeseung Kang, Dena Mae Agra-Kooijman, Satyendra Kumar Dec 2002

Fabrication Of Electro-Optic Devices Using Liquid Crystals With A Single Glass Substrate, Il Kim, Daeseung Kang, Dena Mae Agra-Kooijman, Satyendra Kumar

Physics Publications

A recently developed phase separated composite film method has been employed to fabricate a liquid crystal(LC) based electro-optical device using a single glass substrate. The resultant device is made of adjacent parallel layers of LC and polymer created by phase separation. The LC layer is confined between a film of solidified polymer layer on one side and the glass substrate on the other. Electro-optical properties of these devices demonstrate their technological potential in light weight and hand-held electronic products.


Isotropization In Brane Gas Cosmology, Scott Watson, Robert H. Brandenberger Dec 2002

Isotropization In Brane Gas Cosmology, Scott Watson, Robert H. Brandenberger

Physics

Brane Gas Cosmology (BGC) is an approach to unifying string theory and cosmology in which matter is described by a gas of strings and branes in a dilaton gravity background. The Universe is assumed to start out with all spatial dimensions compact and small. It has previously been shown that in this context, in the approximation of neglecting inhomogeneities and anisotropies, there is a dynamical mechanism which allows only three spatial dimensions to become large. However, previous studies do not lead to any conclusions concerning the isotropy or anisotropy of these three large spatial dimensions. Here, we generalize the equations ...


Rotational And Vibrational Dynamics Of Interstitial Molecular Hydrogen, Taner Yildirim, A. Brooks Harris Dec 2002

Rotational And Vibrational Dynamics Of Interstitial Molecular Hydrogen, Taner Yildirim, A. Brooks Harris

Department of Physics Papers

The calculation of the hindered roton-phonon energy levels of a hydrogen molecule in a confining potential with different symmetries is systematized for the case when the rotational angular momentum J is a good quantum number. One goal of this program is to interpret the energy-resolved neutron time-of-flight spectrum previously obtained for H2C60. This spectrum gives direct information on the energy-level spectrum of H2 molecules confined to the octahedral interstitial sites of solid C60. We treat this problem of coupled translational and orientational degrees of freedom (i) by construction of an effective Hamiltonian to describe the ...


Biaxial Strain-Modified Valence And Conduction Band Offsets Of Zinc-Blende Gan, Gap, Gaas, Inn, Inp, And Inas, And Optical Bowing Of Strained Epitaxial Ingan Alloys, Gus L. W. Hart, P. R. C. Kent, Alex Zunger Dec 2002

Biaxial Strain-Modified Valence And Conduction Band Offsets Of Zinc-Blende Gan, Gap, Gaas, Inn, Inp, And Inas, And Optical Bowing Of Strained Epitaxial Ingan Alloys, Gus L. W. Hart, P. R. C. Kent, Alex Zunger

Faculty Publications

Using density-functional calculations, we obtain the (001) biaxial strain dependence of the valence and conduction band energies of GaN, GaP, GaAs, InN, InP, and InAs. The results are fit to a convenient-to-use polynomial and the fits provided in tabular form. Using the calculated biaxial deformation potentials in large supercell empirical psuedopotential calculations, we demonstrate that epitaxial strain reduces the InGaN alloy bowing coefficient compared to relaxed bulk alloys.


Si Doping Of High-Al-Mole Fraction Alxga1-Xn Alloys With Rf Plasma-Induced Molecular-Beam-Epitaxy, Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, Alexander N. Cartwright Dec 2002

Si Doping Of High-Al-Mole Fraction Alxga1-Xn Alloys With Rf Plasma-Induced Molecular-Beam-Epitaxy, Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, Alexander N. Cartwright

Physics Faculty Publications

Very high levels of n-type doping of AlxGa1−xN alloys were recently achieved by rf plasma-induced molecular-beam epitaxy on sapphire substrates and Si as a dopant. Electron concentrations were obtained up to 1.25×1020 cm−3 when the Al mole fraction was 50%, and 8.5×1019 cm−3 electrons were measured even when the Al mole fraction was 80%. Other material properties were determined by optical absorption, photoluminescence, cathodoluminescence, x-ray diffraction, and atomic force microscopy measurements and high optical and morphological qualities were shown.


Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan, A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, S. S. Park, S. K. Lee Dec 2002

Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan, A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, S. S. Park, S. K. Lee

Physics Faculty Publications

The neutral donor bound exciton recombination processes in freestanding GaN have been studied. The photoluminescence spectrum shows emission lines related to silicon and oxygen donors. Time-resolved luminescence allows us to correlate the principal donor bound exciton lines with their two-electron satellites. The magnetic field splitting of the two-electron lines is well described by the theory of the hydrogen atom in a magnetic field. For the oxygen donor a 1.5 meV chemical shift and a 30.8 meV effective Rydberg have been evaluated. Two-electron satellites involving excitations to the 2p and 2s donor states are separated by an energy of ...


Two-Dimensional Imaging Of Neutral Alkali Atom Samples Using Surface Ionization, Katharina Gillen-Christandl, Gregory P. Lafyatis, Andrei Modoran, Tung-Hsiu Shih Dec 2002

Two-Dimensional Imaging Of Neutral Alkali Atom Samples Using Surface Ionization, Katharina Gillen-Christandl, Gregory P. Lafyatis, Andrei Modoran, Tung-Hsiu Shih

Physics

We describe the design and characterization of a high resolution, high efficiency detector for two-dimensional imaging of neutral atoms. Incident atoms are surface-ionized by a tungsten-coated hot ribbon and the resulting ions are accelerated into a microchannel plate detector with a phosphor screen output. With this design we can detect individual alkali and other low ionization potential atoms and molecules with a spatial resolution of ∼ 20 μm. We find backgrounds on the order of 30 Hz over an active detection region of 20 mm2, a time response of ⩽ 1/30 s, and a detection efficiency of ∼ 50%. This ...


Quiet Time Variability Of The Geosynchronous Magnetic Field And Its Response To The Solar Wind, Jeff Sanny, J. A. Tapia, D. G. Sibeck, M. B. Moldwin Dec 2002

Quiet Time Variability Of The Geosynchronous Magnetic Field And Its Response To The Solar Wind, Jeff Sanny, J. A. Tapia, D. G. Sibeck, M. B. Moldwin

Physics Faculty Works

We present a survey of the variability of the geosynchronous magnetic field strength on the dayside using observations by the GOES satellites over a period exceeding 4 years. Only intervals of reduced geomagnetic activity, as defined by Dst > −20 nT, were considered in this study. The magnetic field strength data were filtered with a passband of 1.7 mHz to 17 mHz (1–10 minutes), a process that eliminates the diurnal variation of the field strength and the effects of most of the higher frequency (>17 mHz) ultralow-frequency (ULF) waves. The geosynchronous field strength appears to exhibit the greatest variability ...


Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison Dec 2002

Slow Convergence Of The Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison

Physics Faculty Research & Creative Works

It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time ...


N Coupled Nonlinear Schrödinger Equations: Special Set And Applications To N=3, Foek T. Hioe Dec 2002

N Coupled Nonlinear Schrödinger Equations: Special Set And Applications To N=3, Foek T. Hioe

Physics Faculty/Staff Publications

Analytic solutions for a special set of N coupled nonlinear Schrödinger equations characterized by 2N interaction types are presented for N = 1–3. They provide an overview of the important role played by nonlinear couplings


The Bend Stiffness Of S-Dna, Philip C. Nelson, Cornelis Storm Dec 2002

The Bend Stiffness Of S-Dna, Philip C. Nelson, Cornelis Storm

Department of Physics Papers

We formulate and solve a two-state model for the elasticity of nicked, double-stranded DNA that borrows features from both the Worm Like Chain and the Bragg-Zimm model. Our model is computationally simple, and gives an excellent fit to recent experimental data through the entire overstretching transition. The fit gives the first value for the bending stiffness of the overstretched state as about 12 nm · kBT, a value quite different from either B-form or single-stranded DNA.


Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben Dec 2002

Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben

Peter Dowben Publications

Using spin-polarized inverse photoemission and X-ray absorption spectroscopy techniques, we show that the electronic structure of La0.65Pb0.35MnO3 thin films depends on the composition at the surface. With a gentle annealing procedure, the surface provides a maximum of 80% spin asymmetry at 0.5 eV above the Fermi level in spite of extensive Pb segregation. A heavily annealed (restructured) surface exhibits a reduced surface "ordering" temperature of 240 K (compared to the approximately 335 K bulk value) as well as a reduced spin asymmetry value of 40% at 0.5 eV above Fermi energy.


Coexistence Of Ferromagnetic And Glassy States In Mechanically Milled Gdal2, C. Stark, P. M. Shand, T. M. Pekarek, D. Williams, R. Brown, Lanping Yue, Diandra Leslie-Pelecky Dec 2002

Coexistence Of Ferromagnetic And Glassy States In Mechanically Milled Gdal2, C. Stark, P. M. Shand, T. M. Pekarek, D. Williams, R. Brown, Lanping Yue, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

Measurements of DC susceptibility, AC susceptibility, and AC susceptibility with an applied DC bias field were performed on mechanically milled GdAl2. A paramagnetic phase exists above a temperature T ≈ 140 K. However, there are significant deviations from the Curie-Weiss Law in this temperature regime, suggesting multiple magnetic components. Fits to the high temperature data show that two Curie-Weiss terms represent the data quite well. Below 140 K one of these magnetic components becomes ferromagnetic as indicated by a shoulder in the AC susceptibility and DC susceptibility data. This ferromagnetic component is suppressed by the application of sufficiently strong DC ...


Effects Of Germanium On The Electronic Transport Mechanism In Co20 (Cu-XGeX)80 Nanogranular Ribbons, J. He, Z. D. Zhang, J. Ping Liu, David J. Sellmyer Dec 2002

Effects Of Germanium On The Electronic Transport Mechanism In Co20 (Cu-XGeX)80 Nanogranular Ribbons, J. He, Z. D. Zhang, J. Ping Liu, David J. Sellmyer

David Sellmyer Publications

The dependency of giant magnetoresistance (GMR) on the nonmagnetic matrix in nanogranular Co20 (Cu1-xGex)80 ribbons was studied. When the matrix Cu is substituted with semiconductor Ge, the magnetoresistance transitioned from negative to positive at low temperatures. The positive GMR effect is closely related to the quantity of Co/Co3Ge2/Co junctionlike configurations. This result provides evidence for the competition between two types of electronic transport mechanisms in the magnetic granular ribbons: (i) electronic spin-dependent scattering, inducing a negative magnetoresistance and (ii) Coulomb blockade of the electronic tunneling, inducing a positive magnetoresistance.


Poiseuille Advection Of Chemical Reaction Fronts: Eikonal Approximation, R. S. Spangler, Boyd F. Edwards, J. Chem Dec 2002

Poiseuille Advection Of Chemical Reaction Fronts: Eikonal Approximation, R. S. Spangler, Boyd F. Edwards, J. Chem

All Physics Faculty Publications

An eikonal equation including fluid advection is derived from the cubic reaction-diffusion-advection equation, and is used to investigate the speeds and shapes of chemical reaction fronts subject to Poiseuille flow between parallel plates. Although the eikonal equation is usually regarded as valid when the front thickness is small compared to the radius of curvature of the front and to the size of the system, it is also found to be valid when the reaction front is thick with respect to the gap width. This new regime of applicability of the eikonal equation is consistent with its derivation, which requires only ...


Cross Section For Forward J/Ψ Production In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Nov 2002

Cross Section For Forward J/Ψ Production In Pp̅ Collisions At √S=1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

The inclusive cross section for J/ψ production times the branching ratio B(J/ψ→μ+μ-) has been measured in the forward pseudorapidity region: B×dσ[+p→J/ψ(pT>10 GeV/c,2.1<|η|<2.6)+X]/dη=192±9(stat)±29(syst) pb. The results are based on 74.1±5.2 pb-1 of data collected by the CDF Collaboration at the Fermilab Tevatron Collider. The measurements extend earlier measurements of the D0 Collaboration to higher pTJ/ψ. In the kinematic range where the experiments partially overlap, these data are in good agreement with previous measurements.


Heterojunction Diode Fabrication From Polyaniline And A Ferroelectric Polymer, B Xu, Y. Ovchenkov, Mengjun Bai, A. N. Caruso, A.V. Sorokin, Stephen Ducharme, Bermard Doudin, Peter A. Dowben Nov 2002

Heterojunction Diode Fabrication From Polyaniline And A Ferroelectric Polymer, B Xu, Y. Ovchenkov, Mengjun Bai, A. N. Caruso, A.V. Sorokin, Stephen Ducharme, Bermard Doudin, Peter A. Dowben

Peter Dowben Publications

We have fabricated a p – n heterojunction diode by vapor depositing a thin film of polyaniline on top of the crystalline copolymer: poly(vinylidene fluoride with trifluoroethylene). The formation of a diode is expected from the band offsets of the two polymers near the Fermi level. The interface between the two components was investigated, and an abrupt interface was found that is very different from the inorganic analog.


Effect Of Cold Collisions On Spin Coherence And Resonance Shifts In A Magnetically Trapped Ultra-Cold Gas, D. M. Harber, H. J. Lewandowski, J. M. Mcguirk, Eric A. Cornell Nov 2002

Effect Of Cold Collisions On Spin Coherence And Resonance Shifts In A Magnetically Trapped Ultra-Cold Gas, D. M. Harber, H. J. Lewandowski, J. M. Mcguirk, Eric A. Cornell

Physics Faculty Contributions

We have performed precision microwave spectroscopy on ultracold 87Rbconfined in a magnetic trap, both above and below the Bose-condensation transition. The cold collision frequency shifts for both normal and condensed clouds were measured, which allowed the intrastate and interstate density correlations (characterized by sometimes controversial “factors of 2”) to be determined. Additionally, temporal coherence of the normal cloud was studied, and the importance of mean-field and velocity-changing collisions in preserving coherence is discussed.


Stripes From (Noncommutative) Stars, Simon Catterall, J. Ambjorn Nov 2002

Stripes From (Noncommutative) Stars, Simon Catterall, J. Ambjorn

Physics

We show that lattice regularization of noncommutative field theories can be used to study non-perturbative vacuum phases. Specifically we provide evidence for the existence of a striped phase in two-dimensional noncommutative scalar field theory