Digital Commons Network^™

Selective Cvd Growth Of Diamond Crystals On Tungsten, Charles Randal Cole

Electrical & Computer Engineering Theses & Dissertations

Typical field emitters consist of sharp metal tips which usually have a short life due to erosion and contamination. To improve the performance of regular field emitters, diamond can be placed on the emitter tip. This is done by selectively growing diamond on tungsten tips using chemical vapor deposition (CVD) processing. Diamond exhibits negative electron affinity, so that electrons will be emitted by properly biasing the tip.

To obtain single crystal growth right at the tip, a cantilever controlled nucleation method was developed which worked better than other methods. Surface preparation was also important to the growth process. An oxide …

First Observation Of Τ→3ΠηνΤ And Τ→ F1ΠνΤ Decays, T. Bergfeld, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have observed new channels for τ decays with an η in the final state. We study 3-prong tau decays, using the η →γγ and η → 3π ⁰ decay modes and 1-prong decays with two π ⁰’s using the η →γγ channel. The measured branching fractions are B(τ^- → π^-π^-π⁺ην_τ) = (3. _-0.5^+0.6 ± 0.6) X 10^-4 and B(τ^- → π^-2π ⁰ην_τ) = (1.4 ± 0.6 ± 0.3) X 10^-4. We observe clear evidence for f_{1 …}

Effects Of Self-Avoidance On The Tubular Phase Of Anisotropic Membranes, Mark Bowick, Emmanuel Guitter

Physics - All Scholarship

We study the tubular phase of self-avoiding anisotropic membranes. We discuss the renormalizability of the model Hamiltonian describing this phase and derive from a renormalization group equation some general scaling relations for the exponents of the model. We show how particular choices of renormalization factors reproduce the Gaussian result, the Flory theory and the Gaussian Variational treatment of the problem. We then study the perturbative renormalization to one loop in the self-avoiding parameter using dimensional regularization and an epsilon-expansion about the upper critical dimension, and determine the critical exponents to first order in epsilon.

Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

The narrow emission line spectra of active galactic nuclei are not accurately described by simple photoionization models of single clouds. Recent Hubble Space Telescope images of Seyfert 2 galaxies show that these objects are rich with ionization cones, knots, filaments, and strands of ionized gas. Here we extend to the narrow-line region the ``locally optimally emitting cloud'' (LOC) model, in which the observed spectra are predominantly determined by powerful selection effects. We present a large grid of photoionization models covering a wide range of physical conditions and show the optimal conditions for producing many of the strongest emission lines. We …

Measurement Of The Proton Structure Function F2 And ΣΓ*ΡTot At Low Q2 And Very Low X At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, E. Anselmo, R. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, I. Gialas, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significantly enhanced the acceptance for very low x and low Q2 inelastic neutral current scattering, e+p → e+X, at HERA. A measurement of the proton structure function F2 and the total virtual photon-proton (γ*p) cross-section is presented for 0.11 ≤ Q2 ≤ 0.65 GeV2 and 2 × 10-6 ≤ x ≤ 6 × 10-5, corresponding to a range in the γ*p c.m. energy of 100 ≤ W ≤ 230 GeV. Comparisons with various models are also presented. © 1997 Published by Elsevier Science B.V.

D* Production In Deep Inelastic Scattering At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, F. Anselmo, R. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, I. Gialas, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

This paper presents measurements of D*f± production in deep inelastic scattering from collisions between 27.5GeV positrons and 820GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel D*+ → (D0 → K-π+)π+ (+c.c.) has been used in the study. The e+p cross section for inclusive D*± production with 5 < Q2 < 100GeV2 and y < 0.7 is 5.3±1.0±0.8nb in the kinematic region 1.3 < pT(D*±) < 9.0GeV and |η(D*±) | < 1.5. Differential cross sections as functions of pT(D*±), η(D*±), W and Q2 are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in pT(D*±) and η(D*±), the charm contribution Fcc̄2(x,Q2) to the proton structure function is determined for Bjorken x between 2 · 10-4 and 5 · 10-3. © 1997 Elsevier Science B.V.

High Coercivity Smfealc Thin Films Fabricated By Multilayer Sputtering, M.L. Yan, Z.S. Shan, Yi Liu, David J. Sellmyer

David Sellmyer Publications

Multilayer sputtering of SmFe/C(Al) plus appropriate thermal processing has been used to fabricate SmFeC thin films with A1 substitution for Fe. It was found that the SmFeAlC thin films exhibited exceptionally high Coercivities. A coercivity of 28 kOe was realized for the thin film with structure of Ta(l000 Å)/|SmFe(40Å)/ C(Al)(5Å)]x50/Ta(200Å) with subsequent annealing at 650°C.

“Atomic Processes In High Energy Density Plasmas," Summaries Of Fy 1997 Research In The Chemical Sciences, Donald P. Umstadter

Donald Umstadter Publications

Several important plasma atomic processes are studied in a controlled manner. These studies are enabled by the recent invention of ultrashortpulse- duration lasers, which produce plasmas with independently controllable parameters.

Ion Acceleration And Anomalous Transport In The Near Wake Of A Plasma Limiter, D. P. Sheehan, J. Bowles, R. Mcwilliams

Physics and Biophysics: Faculty Scholarship

Ion acceleration and anomalous transport were studied experimentally in the near wake region of an electrically floating disk limiter immersed in two different types of collisionless, supersonically flowing, magnetized plasmas: the first initially quiescent, the second initially turbulent. Ion densities and velocity distributions were obtained using a nonperturbing laser induced fluorescence diagnostic. Large-amplitude, low-frequency turbulence was observed at the obstacle edge and in the wake. Rapid ion and electron configuration space transport and ion velocity space transport were observed. Configuration space and velocity space transport were similar for both quiescent and turbulent plasma-obstacle systems, suggesting that plasma-obstacle effects outweigh the …

Observation Of The Decay DS+ → Ωπ+, R. Balest, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using e⁺e^- annihilation data collected by the CLEO II detector at CESR, we have observed the decay D_s⁺ → ωπ⁺. This final state may be produced through the annihilation decay of the i>D_s⁺, or through final state interactions. We find a branching ratio of γ(D_s⁺ → ωπ⁺)/γ(D_s⁺ →ηπ⁺) = 0.16±0.04±0.03, where the first error is statistical and the second is systematic.

Search For Neutrinoless Τ Decays Involving Π0 Or Η Mesons, G. Bonvicini, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for lepton flavor violating decays of the τ lepton using final states with an electron or a muon and one or two π⁰ or η mesons but no neutrinos. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.68 fb^-1. No evidence for signals was found, resulting in much improved limits on the branching fractions for the one-meson modes and the first upper limits for the two-meson modes.

Search For The Decays B0 → D (*)+D (*)-, D. M. Asner, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using the CLEO-II data set we have searched for the decays B⁰ → D^(*)+D^(*)-. We observe one candidate signal event for the decay B⁰ → D^*+D^*- with an expected background of 0.022 ± 0.011 events. This yield corresponds to a branching fraction of B(B⁰ → D^*+D^*-) = [5.317_-3.7^+7.1(stat) ± 1.0(syst)] x 10^-4 and an upper limit of B(B⁰ → D^*+D^*-) < 2.2 X 10^-3 at the 90% C.L. We see no significant excess of signal above …

39th Rocky Mountain Conference On Analytical Chemistry

Rocky Mountain Conference on Magnetic Resonance

Preliminary program and registration information for the 39th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, August 3-7, 1997.

Spurious Electrons In Electron Spectrometers And Their Effect On Differential Electron Impact Ionization Cross-Section Measurements, M. Eugene Rudd

M. Eugene Rudd Publications

The effect of the nonideal response characteristics of electrostatic analyzers is described and equations are derived, which allow a calculation of the distortion that this causes in measurements of angular and energy distributions of electrons from atomic collisions, especially in electron impact. Examples are given that show how a contamination as small as 10^-5 from spurious electrons generated inside an analyzer can explain the peak seen at zero angle in some angular distribution measurements and the filling in of the minimum in the energy distributions in others.

Experimental Investigation Of Nonlinear Dynamics In Single Mode Semiconductor Laser Diodes With Phase Conjugate Feedback, Gordon T. Hengst

Theses and Dissertations

The semiconductor laser diode offers a unique system to investigate nonlinear dynamics when optical feedback is applied. Although there is extensive research of laser diodes with optical feedback from normal dielectric mirrors, very little has been done experimentally to analyze the effects of degenerate phase conjugate feedback from a BaTiO₃ crystal. This research experimentally investigated the dynamics of a single-mode laser diode with weak phase conjugate feedback using both the self-pumped and double phase conjugate geometries. The experimental results validated a mathematical model which numerically evaluates the Lang-Kobayahsi coupled differential equations. The model simulated the nonlinear behavior of a …

Investigation Of Drag Reduction On A Two-Dimensional Circular Cylinder By Ejecting Jet From The Rear Stagnation Region, Satoshi Atsuchi

Mechanical & Aerospace Engineering Theses & Dissertations

Extensive work in the field of drag reduction has been done in the past. However, this field of study is highly desirable today because of various high-speed research programs. The present study attempts to investigate the feasibility of drag reduction on a cylinder by flow injection from the rear stagnation region. A two-dimensional circular cylinder at Reynolds number l x10⁵with a jet ejected from its tail is selected as a physical model. To tackle this problem, a numerical simulation as well as an experimental approach were used. Despite the recent development of computational fluid dynamics (CFD), computing a …

Small Angle Neutron Scattering From Nanodroplet Aerosols, Barbara Ellen Wyslouzil, Janice L. Cheung, Gerald Wilemski, Reinhard Strey

Physics Faculty Research & Creative Works

We report the first measurements of small angle neutron scattering from an aerosol. The aerosol was produced by expanding a D₂O-N₂ vapor mixture in a supersonic Laval nozzle. The neutron wavelength (0.5 nm) is less than the typical particle size, and we can therefore derive the average particle size (5-8 nm), number density (~10¹² cm^-3), and polydispersity of the size distribution directly from the experimental data rather than by inferring them from complex models of particle formation and growth. We also predict and observe a Doppler shift-induced anisotropy in the scattering pattern due to …

A Measurement Of The Michel Parameters In Leptonic Decays Of The Tau, R. Ammar, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have measured the spectral shape Michel parameters ρ and η using leptonic decays of the τ, recorded by the CLEO II detector. Assuming e-μ universality in the vectorlike couplings, we find ρ_eμ = 0.735 ± 0.013 ± 0.008 and η_eμ = 20.015 ± 0.061 ± 0.062, where the first error is statistical and the second systematic. We also present measurements for the parameters for e and μ final states separately.

Initial Polar Mfe Observation Of Substorm Signatures In The Polar Magnetosphere, H. Kawano, G. Le, C. T. Russell, G. Rostoker, T. Mukai, Harlan E. Spence

Physics & Astronomy

This paper studies substorm influences in the polar magnetosphere using data from the POLAR magnetic field experiment (MFE). The POLAR spacecraft remains in the high altitude polar magnetosphere for extended periods around apogee. There it can stay at nearly constant altitude through all phases of a substorm, which was not possible on previous missions. We report such an event on March 28, 1996. Ground magnetometers monitored substorm activity, while the POLAR spacecraft, directly over the pole at (−0.8, −0.6, 8.5) R_E in GSM coordinates, observed a corresponding perturbation in the total magnetic field strength. The total magnetic field first …

Debye-Series Analysis Of The First-Order Rainbow Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, James A. Lock, Charles L. Adler

Physics Faculty Publications

We derive the Debye-series expansion of the partial-wave scattering and interior amplitudes for the interaction of a diagonally incident beam of arbitrary profile with an infinitely long homogeneous dielectric circular cylinder. We then discuss the physical interpretation of the various terms of the series. We also consider the one-internal-reflection Debye-series terms for diagonal plane-wave incidence and examine the first-order rainbow extinction transition as a function of the tilt angle of the incident plane wave. We experimentally observe the first-order rainbow extinction transition and compare our observations with the Debye-series predictions. (C) 1997 Optical Society of America.

Numerical Simulations Of Gravity Waves Imaged Over Arecibo During The 10-Day January 1993 Campaign, M. P. Hickey, R. L. Walterscheid, Michael J. Taylor, W. Ward, G. Schubert, Q. Zhou, F. Garcia, M. C. Kelley, G. G. Shepherd

All Physics Faculty Publications

Recently, measurements were made of mesospheric gravity waves in the OI (5577 Å) nightglow observed from Arecibo, Puerto Rico, during January 1993 as part of a special 10-day campaign. Clear, monochromatic gravity waves were observed on several nights. By using a full-wave model that realistically includes the major physical processes in this region, we have simulated the propagation of two waves through the mesopause region and calculated the O(1 S) nightglow response to the waves. Mean winds derived from both UARS wind imaging interferometer (WINDII) and Arecibo incoherent scatter radar observations were employed in the computations as were the climatological …

Kinetics And Spectroscopy Of Brno, Patrick E. Godfrey

Theses and Dissertations

The infrared spectra and photochemistry of nitrosyl bromide, BrNO, are important to characterizing the performance of a recently demonstrated Br(²P_1/2)-NO(v=2 → v=1) transfer laser pumped by photolysis of iodine molecules. This wavelength agile, mid-infrared laser may be a desirable source for remote sensing and infrared countermeasures missions. Nitrosyl bromide also plays a role in the destruction of stratospheric ozone. The kinetics of BrNO formation and destruction were examined using time-resolved photolysis techniques. The equilibrium constant for the dark reaction Br₂ + 2NO (reversible reaction) 2BrNO was determined as K_eq 168 ± 23 /atm and …

Optimization Considerations For Adaptive Optics Digital Imagery Systems, Robert T. Brigantic

Theses and Dissertations

This dissertation had three objectives. The first objective was to develop image quality metrics that characterize Adaptive Optics System (AOS) performance. The second objective was to delineate control settings that maximize AOS performance. The third objective was to identify and characterize trade-offs between fully and partially compensated adaptive. For the first objective, three candidate image quality metrics were considered: the Strehl ratio, a novel metric that modifies the Strehl ratio by integrating the modulus of the average system optical transfer function to a 'noise-effective-cutoff' frequency at which some specified image spectrum signal-to-noise-ratio level is attained, and the noise-effective-cutoff frequency. It …

Differential Cross Sections Of D*± Photoproduction In Ep Collisions At Hera, J. Breitweg, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. Repond, R. Stanek, R. L. Talaga, R. Yoshida, H. Zhang, Margarita C. K. Mattingly, F. Anselmo, R. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, I. Gialas, R. Giusti, G. Iacobucci, G. Laurenti, G. Levi

Faculty Publications

Inclusive photoproduction of D*± in ep collisions at HERA has been measured with the ZEUS detector for photon-proton centre of mass energies in the range 115 < W < 280 GeV and photon virtuality Q2 < 4 GeV2. The cross section σ → D*X integrated over the kinematic region pDz.ast;⊥ > 3 GeV and -1.5 < ηD* < 1.0 is (10.6 ± 1.7(stat.) ± 1.61.3 (syst.)) nb. Differential cross sections as functions of pD*⊥, ηD* and W are given. The data are compared with two next-to-leading order perturbative QCD predictions. For a calculation using a massive charm scheme the predicted cross sections are smaller than the measured ones. A recent calculation using a massless charm scheme is in agreement with the data. © 1997 Published by Elsevier Science B.V.

First Energetic Neutral Atom Images From Polar, M. G. Henderson, G. D. Reeves, Harlan E. Spence, R. B. Sheldon, A. M. Jorgensen, J. B. Blake, J. F. Fennell

Physics & Astronomy

Energetic neutral atoms are created when energetic magnetospheric ions undergo charge exchange with cold neutral atoms in the Earth's tenuous extended atmosphere (the geocorona). Since they are unaffected by the Earth's magnetic field, these energetic neutrals travel away in straight line trajectories from the points of charge exchange. The remote detection of these particles provides a powerful means through which the global distribution and properties of the geocorona and ring current can be inferred. Due to its 2 × 9 RE polar orbit, the Polar spacecraft provides an excellent platform from which to observe ENAs because it spends much of …

Dephasing In Hyper-Rayleigh Scattering From Organic Materials, S. F. Hubbard, Rolfe G. Petschek, Kenneth D. Singer

Faculty Scholarship

The spectral content of hyper-Rayleigh scattering (HRS) was studied with solutions of disperse red-1 (DR1) in acetone at a specific fundamental wavelength. Dephasing can occur when the effective lifetime of the virtual state approaches a two-photon resonance. Experiments were developed that will measure all six observables in HRS by observing the scattering at 45°, continuously varying the phase of the fundamental by rotating a quarter-waveplate, and using another quarter-waveplate with a linear polarizer to analyze the harmonic. These experiments proved the validity of Kleinmann symmetry in near-resonant and far off-resonant regimes.

In Situ Observations Of Air Traffic Emission Signatures In The North Atlantic Flight Corridor, Hans Schlager, Paul Konopka, P. Schulte, U. Schumann, H. Ziereis, F. Arnold, M. Klemm, Donald E. Hagen, Philip D. Whitefield, J. Ovarlez

Physics Faculty Research & Creative Works

Focussed aircraft measurements have been carried out over the eastern North Atlantic to search for signals of air traffic emissions in the flight corridor region. Observations include NO, NO₂, HNO₃, SO₂, O₃, H₂O, total condensation nuclei (CN), and meteorological parameters. A flight pattern with constant-altitude north-south legs across the major North Atlantic air traffic tracks was flown. Signatures of air traffic emissions were clearly detected for NO_x, SO₂, and CN with peak concentrations of 2 ppbv, 0.25 ppbv, and 500 cm^-3, respectively, exceeding background …

Fabrication Of Micron Scale Magnetic Nickel Features By Selective Area Organometallic Chemical Vapor Deposition, D. Welipitiya, C.N. Borca, Peter A. Dowben

Peter Dowben Publications

We demonstrate that it is possible to deposit a wide range of magnetic features, using photo-assisted and electron radiation induced selective area organometallic chemical vapor deposition. Large arrays of identical micron to nano scale Ni features were deposited by these methods. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features.

A Measurement Of Rb Using A Lifetime-Mass Tag, R. Barate, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

ALEPH's published measurement of Rb = Γ(Ζ → bb̄)/Γ(Ζ → hadrons) using a lifetime tag is updated using the full LEP 1 data sample. Considerable effort has been devoted to understanding systematic effects. Charm background is better controlled by combining the lifetime tag with a tag based on the b/c hadron mass difference. Furthermore, the algorithm used to reconstruct the event primary vertex is designed so as to reduce correlations between the two hemispheres of an event. The value of Rb is measured to be 0.2167 ± 0.0011 (stat) ± 0.0013 (syst).

Analyses Of D+→KS0K+ And D+ → KS0Π+, M. Bishai, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

Using data collected with the CLEO II detector at the Cornell Electron Storage Ring, we present new measurements of the branching fractions for D⁺→K_SK⁺and D⁺ → K_Sπ⁺ . These results are combined with other CLEO measurements to extract the ratios of isospin amplitudes and phase shifts for D → KK and D → K π.