Physical Sciences and Mathematics Commons^™

Far-Ultraviolet Stellar Photometry: Fields In Sagittarius And Scorpius, Edward G. Schmidt, George R. Carruthers

Edward Schmidt Publications

Far-ultraviolet photometry for 741 objects in a field in Sagittarius centered near M8 and 54 1 objects in a field centered near ζ Scorpii is presented. These data were extracted from electrographic images obtained with two cameras during a shuttle flight in 1991 April/May. The cameras provided band passes with λ_eff= 1375 Å and λ_eff= 1781 Å. Synthetic colors show that these bands are sensitive to effective temperature for hot stars. Our measurements were placed on a quantitative far-ultraviolet magnitude scale by convolving the spectra of stars observed by IUE with our cameras' spectral response functions. …

Time-Dependent Perturbation And Exact Results For The Periodically Driven Quantum Harmonic Oscillator, Russell Akridge

Faculty Articles

Transition amplitudes and probabilities for the harmonic oscillator with a forcing function proportional to cos(omegat) beginning at time zero are calculated to lowest nonvanishing order using time-dependent perturbation theory. The results are compared with the exact amplitudes and probabilities. When the exact amplitude is expanded in a Taylor series in powers of the coupling constant, the individual terms turn out to be the perturbation amplitudes, showing that the complete series of perturbation amplitudes converges to the exact amplitude.

Performance Characterization Of The Caltech Compact Torus Injector, P. K. Loewenhardt, Michael R. Brown, J. Yee, P. M. Bellan

Physics & Astronomy Faculty Works

A device is described which is designed to refuel tokamaks of major radius [approximately-equal-to]1 m and magnetic field [approximately-equal-to]1 T by the injection of a compact torus. The injector utilizes an acceleration stage which adds kinetic energy to the compact torus so that it can penetrate the tokamak magnetic field. The performance of the device was found to be optimized in an unexpected parameter regime. It is theorized that in this regime the accelerator takes part in the formation of the CT. A performance threshold with respect to accelerator current will be presented and methods of impurity reduction will be …

Observation Of Parity-Unfavored Transitions In The Nonresonant Photoionization Of Argon, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, R. Wehlitz, U. Becker

Environmental Studies Faculty Publications

Single-photon ionization of an atom or molecule can be subdivided into parity-favored and -unfavored transitions, the latter characterized by electron emission, preferentially perpendicular to the electric vector. The nonresonant existence of these transitions is shown experimentally and studied over an extended energy range for a variety of satellite transitions in atomic argon. The spectra exhibit several clearly resolved satellite lines with strongly negative β values close to -1, independent of the photon energy. The results confirm the corresponding predictions of angular-momentum transfer theory.

Convective Chemical-Wave Propagation In The Belousov- Zhabotinsky Reaction, Y. Wu, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

We investigate the onset of convection for chemical-wave propagation in the Belousov-Zhabotinsky reaction based on the two-variable Oregonator model coupled with the fluid dynamic equations. For chemical waves in a vertical slab, two-dimensional convection occurs only for slab widths greater than a critical threshold width. The convective threshold is different for ascending and descending waves. Convectionless waves are flat and propagate with constant speed. Above the onset of convection, the wave velocity increases and the flat wave deforms due to two counterrotating steady rolls. For a horizontal slab, convection is always present and the wave velocity increases with increasing slab …

Coherent Control Of H- Photodetachment In Parallel Static Electric And Magnetic Fields, Qiaoling Wang, Anthony F. Starace

Anthony F. Starace Publications

Theoretical calculations of quantum interference effects occurring in photodetachement of H- with short-pulse lasers in the presence of a uniform static electric field [Q. Wang and A. F. Starace, Phys. Rev. A 48, R1741 (1993)] are examined in more detail and extended to the case of parallel static electric and magnetic fields. We show that modulation factors characterizing near-threshold cross sections resulting from detachment by relatively long laser pulses may be employed to set the parameters that are most effective for control of detachment cross-section magnitudes with short coherent laser pulses. Use of a static magnetic field to control detached …

Design And Performance Of The Advanced-Light-Source Double-Crystal Monochromator, G. Jones, S. Ryce, Dennis W. Lindle, B. A. Karlin, J. C. Woicik, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

A new “Cowan type” double-crystal monochromator, based on the boomerang design used at National Synchrotron Light Source (NSLS) beamline X-24A, has been developed for beamline 9.3.1 at the Advanced Light Source (ALS), a windowless ultrahigh vacuum beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design of the monochromator has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline …

High-Brightness Beamline For X-Ray Spectroscopy At The Advanced Light Source, Rupert C. Perera, G. Jones, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Beamline 9.3.1 at the Advanced Light Source (ALS) is a windowless beamline, covering the 1-6 keV photon-energy range, designed to achieve the goals of high energy resolution, high flux, and high brightness at the sample. When completed later this year, it will be the first ALS monochromatic hard-x-ray beamline, and its brightness will be an order-of-magnitude higher than presently available in this energy range. In addition, it will provide flux and resolution comparable to any other beamline now in operation. To achieve these goals, two technical improvements, relative to existing x-ray beamlines, were incorporated. First, a somewhat novel optical design …

Semiclassical Treatment Of A Half-Cycle Pulse Acting On A One-Dimensional Rydberg Atom, C. D. Schwieters, John B. Delos

Arts & Sciences Articles

The final-state distribution of hydrogen, acted upon by a 1/2-cycle pulse, has been calculated semiclassically for a proposed one-dimensional experiment. This work was motivated by the recent experimental realization of half-cycle pulses by Jones, You, and Bucksbaum [Phys. Rev. Lett. 70, 1236 (1993)] in which preliminary studies of ionization and state redistribution for hydrogenlike atoms were carried out. To simplify the situation theoretically, an experiment is proposed in which an additional weak static electric field is imposed and approximately one-dimensional states are selected. Within this one-dimensional approximation the transition probability to various n states (n is the principal …

Half-Cycle Pulse Acting On A One-Dimensional Rydberg Atom: Semiclassical Transition Amplitudes In Action And Angle Variables, C. D. Schwieters, John B. Delos

Arts & Sciences Articles

In this paper we derive the expression for the transition coefficient used in the preceding paper [C. D. Schwieters and J. B. Delos, Phys. Rev. A 51, 1023 (1995)] for principal-quantum-number transitions in one-dimensional hydrogen caused by half-cycle pulses. We briefly review the methods of Miller [Adv. Chem. Phys. 25, 69 (1974)] and Marcus [Chem. Phys. Lett. 7, 525 (1970); J. Chem. Phys. 54, 3965 (1971)], and then derive the result using the methods of Maslov and Fedoriuk [Semi-Classical Approximation in Quantum Mechanics, (Reidel, Dordrecht, 1981)]. Also, we examine the approximate reduction of hydrogen …

Closed Orbit Bifurcations In Continuum Stark Spectra, Michael Courtney, Hong Jiao, Neal Spellmeyer, Daniel Kleppner, J. Gao, John B. Delos

Arts & Sciences Articles

We report an experimental and theoretical study of the effect of bifurcations of closed classical orbits in continuum Stark spectra. Our findings provide a natural way to understand how the spectrum evolves from a simple sinusoidal modulation at positive energy to a quasidiscrete spectrum below the classical ionization limit. The experiment employs scaled-energy spectroscopy of lithium. The results provide the first experimental confirmation of a formulation of closed-orbit theory that provides a quantitative description of the behavior of the spectrum at a bifurcation.

Microaccelerometer With Mechanically-Latched Memory, Zhenyu Ma

Theses

A new mechanically-latching micromachined accelerometer is designed in this thesis based on the large deflection of a microcantilever beam. This surface micromachined device moves in the plane of the substrate surface. This device is surface micromachined with no backside etching needed. The interaction of the friction tether and the dimensions of the cantilever beam have been modeled and calculated. The design acceleration sensitivity range is from 100G to 1000G. The photomask set has been designed by using the Mentor Graphics system. The dimension of individual accelerometers ranges from 100 to 1000 micrometers in length to tens of micrometers in width. …

A High Temperature Pressure Sensor Based On Magnetic Coupling And Silicon Wafer Bonding, Deguang Zhu

Theses

In this thesis, the design and fabrication of a bulk micromachined and wafer bonded pressure sensor for high temperature applications is described. The device design is based on the magnetic coupling principle as described by the Biot-Savart law. By combining the mechanical properties of single crystal silicon with magnetic coupling, the designed sensor can be operated up to 600°C. The key components within the sensor are two inductive coils, a silicon diaphragm and a hermetic vacuum cavity.

The modeling based on a nine-turn single level coil device and a 300 μm x 300 diaphragm indicates an output rms voltage range …

Silicon Optical Fiber Pressure Sensor, Jian Pan

Theses

A novel optical fiber pressure sensor based on a micromachined thin silicon diaphragm is proposed. Detail descriptions of the sensor structure, modulation principle and fabrication process are given.

The device operates on the following principle: Pressure deflects a silicon diaphragm which moves the output end of a light source fiber. The emitted light intensity is picked up and shared by two receiving fibers placed side by side. The variation of the intensity ratio in the receiving fibers caused by the relative motion of the emitting fiber can be easily converted to a linear signal versus the deflection of the silicon …

Ultra-Thin Silicon Wafer Bonding, Diyu Yan

Theses

In this thesis the history and recent developments on the silicon direct bonding technique are reviewed. The growing applications of this technique in SOI, SOS and MEMS areas, difficulties and disadvantages of various bonding processes are discussed. A direct bonding procedure for attaching ultra-thin wafers less than 200 μm thick to substrate wafers is developed and described in detail. Difficulties in handling, aligning and annealing ultra-thin wafers are reported. Wafers of different doping concentration, thickness, surface roughness and chemical characteristics are tested for bondability. Methods to minimize voids and other failure mechanisms are proposed. A photodetector is designed based on …

Improved Gaussian Beam-Scattering Algorithm, James A. Lock

Physics Faculty Publications

The localized model of the beam-shape coefficients for Gaussian beam-scattering theory by a spherical particle provides a great simplification in the numerical implementation of the theory. We derive an alternative form for the localized coefficients that is more convenient for computer computations and that provides physical insight into the details of the scattering process. We construct a FORTRAN program for Gaussian beam scattering with the localized model and compare its computer run time on a personal computer with that of a traditional Mie scattering program and with three other published methods for computing Gaussian beam scattering. We show that the …

Linear Transport Theory Of Magnetoconductance In Metallic Multilayers: A Real-Space Approach, Horacio E. Camblong

Physics and Astronomy

The linear transport behavior of metallic multilayers is studied by using the real-space Kubo formula, for a model Hamiltonian consisting of zero-range spin-dependent impurity-scattering potentials. The resulting theory allows a direct comparison with the Boltzmann equation approach in the quasiclassical limit, which is expected to be a good approximation for most magnetic multilayers. Furthermore, the regimes for which quantum corrections might be needed are explicitly indicated. It is explicitly shown that: (i) periodicity is not required as a mechanism for giant magnetoresistance, and (ii) the two main geometries, current in the plane of the layers and perpendicular to the plane …

The Origin Of N Iii Λ990 And C Iii Λ977 Emission In Agn Narrow-Line Region Gas, Jason W. Ferguson, Gary J. Ferland, A. K. Pradham

Physics and Astronomy Faculty Publications

We discuss implications of Hopkins Ultraviolet Telescope (HUT) detections of C III λ977 and N III λ990 emission from the narrow-line region of the Seyfert 2 galaxy NGC 1068. In their discovery paper Kriss et al. showed that the unexpectedly great strength of these lines implies that the emitting gas must be shock-heated if the lines are collisionally excited. Here we investigate other processes which excite these lines in photoionization equilibrium. Recombination, mainly dielectronic, and continuum fluorescence are strong contributors to the line. The resulting intensities are sensitive to the velocity field of the emitting gas and require …

State-Selected Ion-Molecule Reactions: Charge Transfer And Atomic Rearrangement Processes In Thermal Energy Collisions Of H2+ (X;V)+N2 And Of N2+ (X,A;V) + H2, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus

C.J.G.J. Uiterwaal Publications

Using the photo-electron-product-ion-coincidence method (PEPICO) we have measured state-selective cross sections for the following processes: (A) N₂⁺ (X,A;v)+ H₂→N₂H⁺ + H, (B) H₂⁺ (X;v) + N₂→N₂H⁺ + H, (C) N₂⁺ (X,A;v)+H₂→H₂⁺ + N₂, and (D) H₂⁺ (X;v)+N₂→N₂⁺ + H₂ . The measurements were performed at thermal velocities (E_c.m. ≈ 40 meV).We have found that the charge transfer processes (C) and (D) …

Theoretical Lithium 2 2s2 2p And 2 2p3 2d Oscillator Strengths, Z. C. Yan, Gordon W. F. Drake

Physics Publications

The oscillator strengths for the lithium 2 2S2 2P and 2 2P3 2D transitions are calculated to high precision using variational wave functions in Hylleraas coordinates. The calculated oscillator strengths for these transitions are 0.746 957 2(10) and 0.638 570 5(30), respectively. The results resolve disagreements among existing theoretical values and provide definitive predictions. A discrepancy of five standard deviations between the theoretical value and the most accurate measurement of Gaupp et al. [Phys. Rev. A 26, 3351 (1982)] for the 2 2S2 2P transition remains. © 1995 The American Physical Society.

Eigenvalues And Expectation Values For The 1s22s 2s, 1s22p 2p, And 1s23d 2d States Of Lithium, Z. C. Yan, Gordon W. F. Drake

Physics Publications

High-precision variational eigenvalues for the 1s22s 2S, 1s22p 2P, and 1s23d 2D states of lithium are calculated using multiple basis sets in Hylleraas coordinates. Convergence to a few parts in 1010-1011 is achieved. The nonrelativistic energies for infinite nuclear mass are -7.478 060 323 10(31) a.u. for the 1s22s 2S state, -7.410 156 521 8(13) a.u. for the 1s22p 2P state, and -7.335 523 541 10(43) a.u. for the 1s23d 2D state. The corresponding specific isotope shifts due to mass polarization are also calculated with similar accuracy. The 1s22s 2S-1s22p 2P and 1s22p 2P-1s23d 2D transition energies for Li7 and …

Asymptotic-Expansion Method For The Evaluation Of Correlated Three-Electron Integrals, Gordon W. F. Drake, Z. C. Yan

Physics Publications

An asymptotic-expansion method is presented for the evaluation of correlated three-electron integrals arising in Hylleraas-type variational calculations for lithium and other many-electron atoms. The method proves to be very efficient in accelerating the rate of convergence of an infinite series representation of the integrals. An analytic expression for the terms in the series is derived. © 1995 The American Physical Society.

Retarded Dipole-Dipole Dispersion Interaction Potential For Helium, M. J. Jamieson, Gordon W. F. Drake, A. Dalgarno

Physics Publications

The retarded dipole-dipole dispersion interaction potential in helium is evaluated from a set of very accurate effective dipole transition frequencies and oscillator strengths already obtained from a variational calculation. The asymptotic form changes from the inverse sixth to the inverse seventh power of the nuclear separation as the atoms move apart. Simple representations of the potential are given for use in scattering and structure calculations. © 1995 The American Physical Society.

Numerical Results For The Ground-State Interface In A Random Medium, Alan Middleton

Physics - All Scholarship

The problem of determining the ground state of a $d$-dimensional interface embedded in a $(d+1)$-dimensional random medium is treated numerically. Using a minimum-cut algorithm, the exact ground states can be found for a number of problems for which other numerical methods are inexact and slow. In particular, results are presented for the roughness exponents and ground-state energy fluctuations in a random bond Ising model. It is found that the roughness exponent $\zeta = 0.41 \pm 0.01, 0.22 \pm 0.01$, with the related energy exponent being $\theta = 0.84 \pm 0.03, 1.45 \pm 0.04$, in $d = 2, 3$, respectively. These …

B_S Mixing Via Ψ K*, Patricia Mcbride, Sheldon Stone

Physics - All Scholarship

The decay mode Bs à ψ K*is suggested as a very good way to measure the Bs mixing parameter xs. These decays can be gathered using a ψ → ℓ+ℓ− trigger. This final state has a well resolved four track decay vertex, useful for good time resolution and background rejection.

Implications Of Fumi’S Theorem For Auxiliary Particle Methods, S. E. Barnes

Physics Articles and Papers

Fumi’s theorem in conjunction with some general theorems associated with auxiliary particle methods dictates the functional form of the on-shell auxiliary particle self-energy Σ for a certain class of impurity scattering problems. An explicit calculation which confirms the result is described and the implications for various approaches to the Kondo effect discussed.

Growth Characteristics Downstream Of A Shallow Bump: Computation And Experiment, Ronald D. Joslin, Chester E. Grosch

CCPO Publications

Measurements of the velocity field created by a shallow bump on a wall revealed that an energy peak in the spanwise spectrum associated with the driver decays and an initially small-amplitude secondary mode rapidly grows with distance downstream of the bump. Linear theories could not provide an explanation for this growing mode. The present Navier-Stokes simulation replicates and confirms the experimental results. Insight into the structure of the flow was obtained from a study of the results of the calculations and is presented.

Demonstrating Hysteresis In Ferroelectric Materials, Deborah Schurr, Timothy Usher

Physics Faculty Publications

No abstract provided.

Diffuse Band Profiles In The Rho Ophiuchi Cloud, C Gregory Seab, Theodore P. Snow

Physics Faculty Publications

High-resolution, high signal-to-noise ratio line profiles are presented for the 5780 and 5797 A diffuse interstellar bands toward six stars in the Rho Oph dark cloud. Target stars were chosen to exhibit a wide range of interstellar grain properties, as measured by grain polarization and far-UV extinction. The extreme case of the heavily reddened star HD 147889 is included; this star has one of the highest known lambda_max values, indicative of unusually large grains. Despite the differences in the grain properties, the line profiles and central wavelengths for the 5780 A band were found to be essentially identical for …

Prediction Of Signal‐To‐Noise Ratio Gain For Passive Higher‐Order Correlation Detection Of Energy Transients, Lisa A. Pflug, George E. Ioup, Juliette W. Ioup, Robert L. Field

Physics Faculty Publications

In general, higher‐order correlation detectors perform well in passive detection for signals of high third‐ and fourth‐order moments. Previous studies by the authors have shown that the normalized third‐ and fourth‐order signal moments are reliable indicators of higher‐order correlation detector performance [Pflug et al. (1992b)]. For a deterministic energy transient of known moments through fourth order, it is possible to predict theoretically the amount of gain over an ordinary cross‐correlation detector for a bicorrelation or tricorrelation detector applied in a noise environment of known variance. In this paper, formulas that predict detector performance for passive detection at the minimum …