Digital Commons Network^™

The Tubular Phase Of Self-Avoiding Anisotropic Crystalline Membranes, Mark Bowick, Alex Travesset

Physics - All Scholarship

We analyze the tubular phase of self-avoiding anisotropic crystalline membranes. A careful analysis using renormalization group arguments together with symmetry requirements motivates the simplest form of the large-distance free energy describing fluctuations of tubular configurations. The non-self-avoiding limit of the model is shown to be exactly solvable. For the full self-avoiding model we compute the critical exponents using an epsilon-expansion about the upper critical embedding dimension for general internal dimension D and embedding dimension d. We then exhibit various methods for reliably extrapolating to the physical point (D=2,d=3). Our most accurate estimates are nu=0.62 for the Flory exponent and zeta=0.80 …

Spectroscopy Of Charge-Coupled Devices, Lars Mündermann

Dissertations and Theses

A systematic study of persistent, or residual, images occurring in CCD imagers and a systematic study of dark current generation in CCD imagers are presented. These effects are a source of unwanted signal in frames, and should be considered where very exact, low light-level signal processing is necessary. For both studies explanatory models and statistical analysis techniques have been developed which enable the derivation of the densities and the characteristic energies. Furthermore the importance of understanding these phenomena in the context of today's low light-level imaging is discussed.

Impurity sites are found to be responsible for residual images. Photoelectrons are …

Parity Nonconservation In Neutron Resonances In 238u, Bret E. Crawford, J D. Bowman, P P J. Delheij, C M. Frankle, M Iinuma, J N. Knudsen, L Y. Lowie, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, Y-F Yen, V W. Yuan

Physics and Astronomy Faculty Publications

Parity nonconservation (PNC) was studied for 24 p-wave neutron resonances in ²³⁸U from 10 to 300 eV by measuring the helicity dependence of the total neutron cross section with an improved experimental apparatus. Six resonances show statistically significant (greater than 2.9σ) parity violation. An analysis treating the PNC matrix elements as random variables yields a root-mean-square PNC matrix element M=0.67_-0.16^+0.24 meV. The corresponding weak spreading width Γ_w=(1.35_-0.64^+0.97)×10^-7 eV.

Neutron Resonance Spectroscopy Of 106pd, And 108pd From 20–2000 Ev, Bret E. Crawford, J D. Bowman, P P J. Delheij, T Haseyama, J N. Knudsen, L Y. Lowie, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, V W. Yuan

Physics and Astronomy Faculty Publications

Parity nonconserving asymmetries have been measured in p-wave resonances of ¹⁰⁶Pd and ¹⁰⁸Pd. The data analysis requires knowledge of the neutron resonance parameters. Transmission and capture γ-ray yields were measured for E_n=20–2000 eV with the time-of-flight method at the Los Alamos Neutron Science Center (LANSCE). A total of 28 resonances in ¹⁰⁶Pd and 32 resonances in ¹⁰⁸Pd were studied. The resonance parameters for ¹⁰⁶Pd are new for all except one resonance. In ¹⁰⁸Pd six new resonances were observed and the precision improved for many of the resonance parameters. A Bayesian analysis was …

Parity Nonconservation In Neutron Resonances In 232th,, Sharon L. Stephenson, J D. Bowman, Bret E. Crawford, P P J. Delheij, C M. Frankle, M Iinuma, J N. Knudsen, L Y. Lowie, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Y-F Yen, V W. Yuan

Physics and Astronomy Faculty Publications

Parity nonconservation (PNC) was measured for 24 p-wave resonances from 8 to 300 eV in ²³²Th by measuring the helicity dependence of the total neutron cross section for epithermal neutrons with an improved experimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all positive, thus confirming the previously observed sign correlation. The data are fit to the sum of two terms, a constant asymmetry and a fluctuating asymmetry. With this ansatz the root-mean-square PNC matrix element M=1.12 meV, which corresponds to a weak spreading widthΓ_w=4.7×10^-7 eV. For the …

Angle-Resolved Studies Of Inner Shell Excitations For Argon, Krypton And Xenon Using Third Generation Synchrotron Sources, Ahmad H. Farhat

Dissertations

This dissertation, which is in the area of atomic physics, concentrates on the study of the interaction between VUV-soft X-ray radiation and atoms in the gas phase. The main area of interest is the study of Auger decay in atoms utilizing the process known as the resonance Auger effect, where an inner shell electron is excited to an unfilled orbital followed by the ejection of an Auger electron. The measurements in this thesis were performed by using the high resolution Atomic, Molecular and Optical Physics undulator beam line, which utilizes a spherical grating monochromator at the Advanced Light Source at …

Nature Of Resonant Photoemission In Gd, Shubhra R. Mishra, Thomas K. Cummins, George Daniel Waddill, W. J. Gammon, Gerrit V. Van Der Laan, Kyle W. Goodman, James G. Tobin

Physics Faculty Research & Creative Works

The phenomenon of resonant photoemission happens when, in addition to a direct photoemission channel, a second indirect channel opens up as the absorption threshold of a core level is crossed. A massive increase in emission cross section can occur, but the nature of the process remains clouded. Using novel magnetic linear dichroism in photoelectron spectroscopy experiments and theoretical calculations, we can now clearly demonstrate that temporal matching of the processes as well as energy matching is a requirement for true "resonant photoemission.".

Improved Measurement Of The Pseudoscalar Decay Constant FDS, M. Chada, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We present a new determination of f_Ds using 5 million e⁺e^- → cc̅ events obtained with the CLEO II detector. Our value is derived from our new measured ratio Γ(D_s⁺ → μ⁺ν)/Γ(D_s⁺ → φ π ⁺) = 0.173±0.023 ±0.035. Using Ɓ(D_s⁺ → φ π ⁺) = (3.6±0.9)%, we extract f_Ds = (280±19±28±34) MeV. We compare this result with various model calculations.

Electric Potential In The Classical Hall Effect: An Unusual Boundary-Value Problem, Matthew J. Moelter, James Evans, Greg Elliot, Martin Jackson

Physics

The classical Hall effect presents a surprisingly unusual and challenging problem in electrostatics, with boundary conditions that are not of Dirichlet, Neumann, or of mixed Dirichlet and Neumann type. These unusual boundary conditions create several difficulties not normally encountered in standard problems, and ultimately lead to expansion of the electric potential in a nonorthogonal basis set. We derive the boundary conditions for the potential in a rectangular geometry, construct a solution for the potential, and discuss the relation between this problem and problems of the standard mixed type. We also address a commonly encountered misconception about the current distribution.

Self-Calibrating Method For Measuring Local Multiphotonionization Yields As A Function Of Absolute Intensity, Cornelis J. Uiterwaal, B. Witzel, H. Schröder, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

We present a self-calibrating method for measuring local multiphoton-ionization yields as a function of absolute intensity. In contrast to the method recently described by Walker et al. [Phys. Rev. A 57, R701 (1998)], our method does not require any assumption on the intensity distribution inside a laser focus, nor does it use any mathematical procedure such as deconvolution that would be based on such an assumption. In this sense, our method is self-calibrating. The proposed method immediately gives ion yields as a function of absolute intensity. Furthermore, it allows the intensity distribution inside the focal volume to be measured with …

Cold Relativistic Wavebreaking, J.K. Kim, Donald P. Umstadter

Donald Umstadter Publications

The two-dimensional wave-breaking of relativistic plasma waves driven by a ultrashort high-power lasers, is described within a framework of cold 2-D fluid theory. It is shown that the transverse nonlinearity of the plasma wave results in temporally increasing transverse plasma oscillation in the wake of the laser pulse, inevitably inducing wave-breaking below the 1-D threshold. A condition for wavebreaking is obtained and evaluated. A preformed density channel is found to partially cancel the effect and increase the length of wakefield that survives before wavebreaking occurs.

Statistics Of Active Galactic Nuclei In Rich Clusters Revisited, M. Way, R. Flores, H. Quintana

Physics Faculty Works

Using the spectrophotometry of a large sample of galaxies in 19 Abell clusters, we have selected 42 candidate active galactic nuclei (AGNs) using the criteria used by Dressler and coworkers in their analysis of the statistics of 22 AGNs in 14 rich cluster fields, which are based on the equivalent width of [O II] 3727 Å, Hβ, and [O III] 5007 Å emission. We have then discriminated AGNs from H II region-like galaxies (hereafter H II galaxies) in the manner developed by Veilleux & Osterbrock using the additional information provided by Hα and [N II] 6583 Å or Hα and …

Observation Of B+→ΩK+ And Search For Related B Decays Modes, T. Bergfeld, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for two-body charmless decays of B mesons to purely hadronic exclusive final states including ω or φ mesons using data collected with the CLEO II detector. With this sample of 6.6 X 10⁶ B mesons we observe a signal for the ωK⁺ final state, and measure a branching fraction of Ɓ(B⁺→ωK⁺) = (1.5_-0.6^+0.7 ± 0.2) X 10^-5. We also observe some evidence for the φK* final state, and upper limits are given for 22 other decay modes. These results provide the opportunity …

Final-State-Interaction Effects On One- And Two-Photon Detachment Of H- In The Presence Of A Static Electric Field, Min-Qi Bao, Ilya I. Fabrikant, Anthony F. Starace

Anthony F. Starace Publications

We present a detailed theoretical formulation of the problem of an electron moving in a static electric field, a laser field, and an atomic potential. Our formulation treats the electron-atom interaction in the zero-range potential approximation and employs both the quasienergy approach and an analytic expression for the Green’s function describing electron propagation in a combination of static and laser electric fields. Our formulation is applied to one- and two-photon detachment of H^- in a strong static electric field and takes into account all final-state interactions of the detached electron with the static and laser fields and with the …

Experimental Investigations Of Wavelength And Angular Errors In Holographic Gratings With Non-Bragg-Matched Read Beams, Monish Ranjan Chatterjee, Vivek Ray

Electrical and Computer Engineering Faculty Publications

Perfect Bragg matching is generally desirable for accurate optical interconnections with holographic gratings. In reality, however, gratings may be illuminated by READ beams with non-Bragg-matched angles, or wavelengths, or both. In such cases, the scattered beams are generally misdirected, and may suffer loss of efficiency and possibly more serious errors such as crosstalk noise or missed connections. A conventional wave-vector triad method of analyzing the scattered beam errors leads readily to near-Bragg estimates of the output angular misalignment. However, the READ wave-vector triads appear to indicate a possible wavelength shift in the output beam even with a Bragg-matched READ wavelength, …

Vortex Wake And Exhaust Plume Interaction, Including Ground Effect, Ihab Gaber Adam

Mechanical & Aerospace Engineering Theses & Dissertations

Computational modeling and studies of the near-field wake-vortex turbulent flows, far-field turbulent wake-vortex/exhaust-plume interaction for subsonic and High Speed Civil Transport (HSCT) airplane, and wake-vortex/exhaust-plume interaction with the ground are carried out. The three-dimensional, compressible Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The turbulence models of Baldwin and Lomax, one-equation model of Spalart and Allmaras and two-equation shear stress transport model of Menter are implemented with the RANS solver for turbulent-flow modeling.

For the near-field study, computations are carried out on a fine grid for a rectangular wing with a NACA-0012 airfoil section and …

High Pressure Radio-Frequency Microhollow Cathode Discharges, Anja Annett Muller

Electrical & Computer Engineering Theses & Dissertations

A new field of microhollow cathode discharges is represented by the RF microhollow cathode discharge. So far, the behavior and related physical processes of the RF microhollow cathode discharge are not well investigated.

RF microhollow discharges in air at high pressures were investigated under different experimental conditions. The geometry was changed by reducing the cathode hole diameter and the dielectric spacer thickness. By adding a noble gas to air, the influence of additive gases was explored. Additionally, the parallel operation of RF microhollow discharges was investigated.

It was shown that stable RF microhollow cathode discharges could only be sustained up …

An Injection Modelocked Titanium-Sapphire Laser, James C. Hovater

Electrical & Computer Engineering Theses & Dissertations

I have investigated the possibility of using an injection modelocked Ti-sapphire laser as a illumination source for GaAs photocathodes. A commercial Ti-sapphire laser was modified to accept a seed pulse from a gain-switched diode laser. Modelocked operation was obtained through gain modulation within the Ti-sapphire crystal as a result of injection seeding with a modelocked pulse train from a gain-switched diode laser. The Ti-sapphire laser essentially becomes a pulse amplifier for the diode laser. Unlike conventional modelocked lasers, the pulse repetition rate of this laser can be discretely varied by setting the seed laser repetition rate equal to multiples of …

Next-To-Leading Order Qcd Corrections For The B⁰B⁰ Mixing With An Extended Higgs Sector, Jorg Org Urban, Frank Krauss, Ulrich D. Jentschura, Gerhard Soff

Physics Faculty Research & Creative Works

We present a calculation of the B⁰B⁰ mixing including next-to-leading order (NLO) QCD corrections within the Two-Higgs Doublet Model (2HDM). The QCD corrections at NLO are contained in the factor denoted by η₂ which modifies the result obtained at the lowest order of perturbation theory. In the Standard Model case, we confirm the results for η₂ obtained by Buras, Jamin and Weisz [Nucl. Phys, B 347 (1990) 491]. The factor η₂ is gauge and renormalization prescription invariant and it does not depend on the infrared behaviour of the theory, which constitutes an important test …

Coupled Electrodynamic-Monte Carlo Simulations Of Nanoscale Gaas Terahertz Optical Mixers, Jiang Li

Electrical & Computer Engineering Theses & Dissertations

The concept of mixing or heterodyning has traditionally been used for microwaves and for radio frequency communications. However, the concept can easily be extended into the optical frequency regime. By doing so, the photomixing process can serve as a very versatile tool for both the generation of ultrahigh frequency (terahertz) and the detection of weak optical signals.

The aim of this thesis is to perform a theoretical study of the photomixing process inside GaAs devices as the non-linear elements. A coupled approach which combines the Monte Carlo simulation scheme for the carrier transport, with Maxwell's equation for the electrodynamics, has …

Elementary Excitation Spectrum Of A Trapped Weakly Interacting Bose-Einstein Condensate, Mircea Marinescu, Anthony F. Starace

Anthony F. Starace Publications

An analytic expression is presented for the elementary excitation spectrum of the Bose-Einstein condensate of a trapped boson system in the weakly interacting, low-density limit. Explicit analytic formulas for the elementary excitation spectrum are obtained for harmonic-oscillator traps. These formulas provide information about the behavior of the elementary excitation levels as a function of the number of atoms and their interaction strength for a given trap geometry. They also provide a low-density benchmark for results of fully numerical calculations.

Routes To Self-Assembling Stable Photonic Band-Gap Phases In Emulsions Of Chiral Nematics With Isotropic Fluids, Chien-Yueh Huang, Jonathan J. Stott, Rolfe G. Petschek

Faculty Scholarship

Blue phases are stable phases with crystalline packing of interwoven topological defects in chiral nematic liquid crystals. We argue that chiral nematics with appropriate surfactants are likely to form blue phases for a wide range of parameters. We derive the transition curve for stable emulsified blue phases and find that the required low surface tension is within the accessible range of surfactants. These emulsified blue phases provide possible routes to photonic band-gap materials.

Absolute Triply Differential (E, 2e) Cross Sections For He In The Intermediate Energy Region With Comparison To Theory, J. Röder, H. Ehrhardt, Cheng Pan, Anthony F. Starace, Igor Bray, Dmitry V. Fursa

Anthony F. Starace Publications

Absolute triply differential (e, 2e) cross section measurements are presented for He at incident energies E₀ = 32.6, 44.6, 64.6, and 104.6 eV with equal energy sharing and the θ₁₂ = π configuration. Results of distorted partial-wave calculations agree with the measurements; those of convergent close-coupling calculations agree with the relative angular distributions, and with absolute values after rescaling by consideration of the singly differential cross section.

Pion-Pion Scattering In Two Dimensions, Joseph Schechter, D. Delphenich, S. Vaidya

Physics - All Scholarship

Massive two-flavor QED_2 is known to have many similarities to the two-flavor QCD_4. Here we compare the \pi-\pi scattering amplitudes (actually an analog process in QED_2) of the two theories. The QED_2 amplitude is computed from the bosonized version of the model while the QCD_4 amplitude is computed from an effective low energy chiral Lagrangian. A number of interesting features are noted. For example, the contribution of the two-dimensional Wess-Zumino-Witten (WZW) term in QED_2 is structurally identical to the vector meson exchange contribution in QCD_4. Also it is shown that the QED_2 amplitude computed at tree level is a reasonable …

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xiv. Intensive Optical Spectrophotometric Observations Of Ngc 7469, S.J. Collier, Keith Horne, Shai Kaspi, Hagai Netzer, Bradley M. Peterson, I. Wanders, T. Alexander, R. Bertram, A. Comastri, C. Martin Gaskell, Yu. F. Malkov, D. Maoz, M. Mignoli, Richard William Pogge, V.I. Pronik, S.G. Sergeev, Stephanie A. Snedden, G.M. Stirpe, N.G. Bochkarev, A.N. Burenkov, A.I. Shapovalova, R.M. Wagner

C. Martin Gaskell Publications

We present results of an intensive 2 month campaign of ground-based spectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with a temporal resolution [approximately less than]1 day. The broad Hα and Hβ emission lines respond to ~35% ultraviolet continuum variations with an amplitude of ~10% and time delays of 5.6±1.3 days and 5.4±0.8 days, respectively. We interpret this as evidence of variable Balmer line gas ~5-6 light days from the central source in this object, widely believed to be a supermassive black hole. The virial mass of the central source implied by line widths and time delays is ~10 …

Renormalized Effective Hamiltonian Approach To Qcd, David G. Robertson

Physics Faculty Scholarship

Continuing our previous QCD Hamiltonian studies in the gluonic and quark sectors, we describe a new renormalization procedure which generates an effective Hamiltonian. The formulation, which is in the Coulomb gauge, provides an improved framework for investigating hadron structure.

B→Sγ Constraints On The Minimal Supergravity Model With Large Tanβ, Howard Baer, Michal Brhlik, Diego Castano, Xerxes Tata

Chemistry and Physics Faculty Articles

In the minimal supergravity model (MSUGRA), as the parameter tanβ increases, the charged Higgs boson and light bottom squark masses decrease, which can potentially increase contributions from tH±, ̃gbj and Zibj loops in the decay →bsγ. We update a previous QCD improved →bsγ decay calculation to include in addition the effects of gluino and neutralino loops. We find that, in the MSUGRA model, loops involving charginos also increase, and dominate over tW, tH±, ̃g̃q and Zĩq contributions for tanβ≳5−10. We find for large values of tanβ∼35 that most of the parameter space of the MSUGRA model for μ<0 is ruled out due to too large a value of branching ratio B(→bsγ). For μ>0 and …

Translational Diffusion Of Small And Large Mesoscopic Probes In Hydroxypropylcellulose-Water In The Solutionlike Regime, Kiril A. Streletzky, George D.J. Phillies

Physics Faculty Publications

Quasi-elastic light scattering spectroscopy was used to study the translational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypropylcellulose (HPC) at 25 °C. Probe diameters d spanned 14–455 nm; HPC concentrations were 0⩽c⩽7g/L. Light scattering spectroscopy consistently found spectra having the form g(1)(t)=(1−Af)exp(−θtβ)+Af exp(−θftβf). Here θf and βf refer to the “fast” mode; θ and β describe the “slow” mode. We examine the dependence of θ, β, θf, βf, and Af on d, c, scattering vector q, and viscosity η. β=1 for large probes; elsewise, β and βf are ∈(0,1). The slow mode, with short-lived memory function, is diffusive; for …

Magnetic And Structural Properties Of Prco3–XSiX Compounds, T. Matsui, R. D. Stevenson, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

We have systematically investigated the magnetic properties of the rare-earth compounds PrCo₈Si and PrCo_3–xSi_x, the crystal structures of which are hexagonal CeNi₃-type and rhombohedral Be₃Nb-type, respectively. Sharp cusps were observed in the real and imaginary parts of the ac susceptibility at temperatures between 282 (x = .08) and 209 K (x = .23). Also observed were bifurcations of the zero-field-cooled and field-cooled magnetization curves at the same temperatures, showing that the magnetization was irreversible below these temperatures. The effect of Si substitution for Co in this system …

Hydrogen In R2Fe17 Intermetallic Compounds: Structural, Thermodynamic, And Magnetic Properties, S. Wirth, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

The absorption and diffusion behavior of hydrogen in iron-rich rare-earth intermetallics of the type R₂Fe₁₇ (R=Y, Sm, Gd) and the resulting changes of their magnetic properties are investigated. Intermediate hydrogen concentration indicate the solid-solution character of the hydrides. From equilibrium and nonequilibrium absorption experiments net reaction energies, bulk diffusion constants, and surface barrier energies for Sm₂Fe₁₇ are determined and discussed. The low-temperature quantum diffusion is discussed for the hydride and the corresponding nitride. The interstitial modification changes drastically the crystalline electric field in the rare-earth intermetallics. For Sm₂Fe₁₇H₄ the …