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Full-Text Articles in Physical Sciences and Mathematics
Semiclassical Theory Of Weighted Spectra For Regular Systems: Absorption Spectra And Decay Rates, M. W. Beims, V. Kondratovich, John B. Delos
Semiclassical Theory Of Weighted Spectra For Regular Systems: Absorption Spectra And Decay Rates, M. W. Beims, V. Kondratovich, John B. Delos
Arts & Sciences Articles
We derive a simple semiclassical representation to describe the large-scale structure of the spectrum of regular systems weighted by some arbitrary function W. Examples of weighted spectra are the width-weighted spectrum, which represents the decay rate of an unstable system, and the oscillator-strength-weighted spectrum, which represents the photoabsorption rate. Semiclassical representations of such spectra involve stationary-phase contributions, which are periodic or closed orbits, and end-point contributions, which are loops on an extremal torus. The theory provides the link between semiquantal formulas and the closed-orbit theory of atomic photoabsorption. It also allows calculation of an average decay rate without knowledge …
Classically Forbidden Recurrences In The Photoabsorption Spectrum Of Lithium, V. Kondratovich, John B. Delos, Neal Spellmeyer, Daniel Kleppner
Classically Forbidden Recurrences In The Photoabsorption Spectrum Of Lithium, V. Kondratovich, John B. Delos, Neal Spellmeyer, Daniel Kleppner
Arts & Sciences Articles
We present data on the photoabsorption spectrum of lithium atoms in an electric field at energies between the saddle point of the Stark potential and below the field-free ionization threshold. The spectrum displays a sequence of sharp resonances and a sequence of broad ones. We find that the broad resonances arise from the classically forbidden reflection of waves above a dynamical potential barrier. The recurrence spectrum is also observed and it is dramatically affected by above-barrier reflections. We have developed a semiclassical theory that interprets the spectra using quasiclassical trajectories that undergo above-barrier reflection.
Recurrence Spectroscopy In Time-Dependent Fields, M. R. Haggerty, John B. Delos
Recurrence Spectroscopy In Time-Dependent Fields, M. R. Haggerty, John B. Delos
Arts & Sciences Articles
Closed-orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. We derive an alternative version of closed-orbit theory that applies when the external fields are time dependent. We compare the results of this theory with experiments on lithium atoms in a weak oscillating electric field.
Plasma Source Ion Implantation Of High Voltage Electrodes, Thomas Joseph Venhaus
Plasma Source Ion Implantation Of High Voltage Electrodes, Thomas Joseph Venhaus
Dissertations, Theses, and Masters Projects
Field emission and breakdown characteristics of high voltage, large area electrodes determine the performance of many vacuum-based electron sources. A corroborative project with the Thomas Jefferson National Accelerator Facility involves studying the behavior of such electrodes after nitrogen ion implantation. A Plasma Source Ion Implantation (PSII) facility is designed and constructed at William and Mary, and used to treat stainless steel electrodes. PSII is a novel implantation technique developed at the University of Wisconsin-Madison. A workpiece is submerged in a quiescent plasma of the species to be implanted. A series of high, negative voltages (30--100 kV) is applied to the …
The Absorption Spectrum Of The Hydrogen Atom In Crossed Electric And Magnetic Fields, Dongmei Wang
The Absorption Spectrum Of The Hydrogen Atom In Crossed Electric And Magnetic Fields, Dongmei Wang
Dissertations, Theses, and Masters Projects
This dissertation reports the theoretical interpretation of the measured absorption spectrum of hydrogen atoms in crossed electric and magnetic fields. Closed-orbit theory is modified from two-dimensions to three-dimensions to interpret the large scale structure in the absorption spectrum. A new computational method---a Chirped-Fourier-Transform---is developed to extract the closed orbits from an energy spectrum. A quantitative model is provided to calculate the continuum absorption. We prove that the observed continuum absorption is proportional to the flux of electrons along trajectories which escape within a short time. Einstein-Brillouin-Keller (EBK) quantization theory is applied to obtain an approximate energy spectrum. Our results prove …
Precision Measurements Of The Proton And Deuteron Polarized Structure Functions, Paul Mcconihay King Ii
Precision Measurements Of The Proton And Deuteron Polarized Structure Functions, Paul Mcconihay King Ii
Dissertations, Theses, and Masters Projects
Experiment E155 at the Stanford Linear Accelerator Center measured the longitudinal and transverse polarized deep-inelastic scattering asymmetries for the proton and deuteron using longitudinally-polarized electron beams with energies of 48.3 GeV and 38.8 GeV, respectively. The electron beam polarization was measured by Moller polarimetry to be 0.81 +/- 0.02. Dynamically-polarized solid 15N3 and 6Li2H were used as the target materials. The scattered electrons were detected in three independent spectrometers at 2.75??, 5.5??, and 10.5??, covering a kinematic range of 0.014 ≤ x ≤ 0.9 and 1.0(GeV/ c)2 ≤ Q2 ≤ 40(GeV/ c)2. The 10.5?? spectrometer was constructed for this experiment. …
Redistribution Of Rydberg States By Terahertz Radiation, Jonathan David Curley
Redistribution Of Rydberg States By Terahertz Radiation, Jonathan David Curley
Dissertations, Theses, and Masters Projects
We present the technique and results of our study of the redistribution of Rydberg states in barium by a half cycle pulse (HCP). A survey of previous research concerning the interaction of half cycle pulses with Rydberg atoms reveals a lack of experimental data in the area of state redistribution. This is primarily due to an inability to identify the redistributed states accurately using the currently available tool: selective field ionization (SFI). We present the limitations of SFI as a state identification tool. We then present a survey of isolated core excitation as a state identification tool, along with its …
Surface Processing By Rfi Pecvd And Rfi Psii, Lingling Wu
Surface Processing By Rfi Pecvd And Rfi Psii, Lingling Wu
Dissertations, Theses, and Masters Projects
An RFI plasma enhanced chemical vapor deposition (PECVD) system and a large-scale RF plasma source immersion ion implantation (PSII) system were designed and built to study two forms of 3-D surface processing, PECVD and PSII. Using the RFI PECVD system, Ti-6Al-4V substrates were coated with diamond-like carbon films with excellent tribological and optical properties. as an innovation, variable angle spectroscopic ellipsometry (VASE) was successfully applied for non-destructive, 3-D, large-area tribological coatings quality investigation.;Based on the experience with the RFI PECVD system, a large-scale RFICP source was designed and built for the PSIL Langmuir probe and optical emission spectroscopy studies indicated …
Low Damage Processing And Process Characterization, Xianmin Tang
Low Damage Processing And Process Characterization, Xianmin Tang
Dissertations, Theses, and Masters Projects
Two novel plasma sources (one neutral source and one pulsed inductively coupled plasma source) and ashing process characterization were investigated. The primary goal was to characterize these source properties and develop corresponding applications. The study includes process damage assessment with these two sources and another continuous wave (13.56MHz) plasma source. A global average simulation of the pulsed discharges was also included.;The transient plasma density and electron temperature from the double probe analysis were compared with single Langmuir probe results with sheath displacement corrections in pulsed discharges (200Hz--10kHz). The equivalent resistance method can be used effectively to analyze these double probe …
Broadening, Shifting, And Line Asymmetries In The 2←0 Band Of Co And Co–N2: Experimental Results And Theoretical Calculations, Adriana Predoi-Cross, J. P. Bouanich, D. Chris Benner, A. D. May, J. R. Drummond
Broadening, Shifting, And Line Asymmetries In The 2←0 Band Of Co And Co–N2: Experimental Results And Theoretical Calculations, Adriana Predoi-Cross, J. P. Bouanich, D. Chris Benner, A. D. May, J. R. Drummond
Arts & Sciences Articles
We have measured the room temperature, widths, pressure shifts, and line asymmetry coefficients for many transitions of the first overtone band of CO and CO perturbed by N2." role="presentation" style="display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">N2.N2. The broadening coefficients were obtained with an accuracy of about 1%. The pure CO profiles have been fitted by a Voigt profile while the CO–N2" role="presentation" style="display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: …
Theoretical And Experimental Study Of Generation Mechanisms For Laser Ultrasound In Woven Graphite /Epoxy Composites With Translaminar Stitching, Adam D. Friedman
Theoretical And Experimental Study Of Generation Mechanisms For Laser Ultrasound In Woven Graphite /Epoxy Composites With Translaminar Stitching, Adam D. Friedman
Dissertations, Theses, and Masters Projects
The aerospace industry is beginning to use advanced composite materials for primary load bearing structures and their failure mechanisms must be better understood to predict their behavior in service. The Combined Loads Tests (COLTS) facility is being constructed at the NASA Langley Research Center to characterize these failure mechanisms. Laser based ultrasonic NDE can monitor the samples during dynamic loading without interfering with the structural tests. However, the constraints of implementing laser ultrasound in a structures laboratory reduces the efficiency of the technique. The system has to be "eye-safe" because many people will be present during the structural tests. Consequently, …
Structural Instabilities In Strontium Titanate From First-Principles Calculations, Christopher A. Lasota
Structural Instabilities In Strontium Titanate From First-Principles Calculations, Christopher A. Lasota
Dissertations, Theses, and Masters Projects
For some time now, first-principles calculation methods have proven to be an effective tool for investigating the physics of condensed matter systems. The additional use of density functional theory (DFT) and the local density approximation (LDA) has permitted even complex materials to be studied on desktop workstations with remarkable success. The incorporation of linear response theory into these methods has extended their power, allowing investigation of important dynamical properties.;Contained within the following pages are the results of a first-principles study of SrTiO3. This transition metal oxide is often grouped with ferroelectric materials, due to its similar composition and perovskite structure. …
Studies In Hard Pion Photoproduction, Christian Jens Wahlquist
Studies In Hard Pion Photoproduction, Christian Jens Wahlquist
Dissertations, Theses, and Masters Projects
The production of high transverse momenta mesons via polarized photoproduction can be a means of determining the parton structure of the target. at the regions of highest transverse pion momenta, kT, it can be shown that short distance, direct, pion production dominates and is sensitive to the polarized quark distributions. as the produced pions transverse momenta decreases the importance of pions produced through fragmentation following photon-gluon fusion increases. This process give us sensitivity to the form of the polarized gluon distribution. Both processes are calculable with perturbative Quantum Chromodynamics (pQCD) due to the high kT of the pion produced. Numerical …