Digital Commons Network^™

Effect Of Amplification On Conductance Distribution Of A Disordered Waveguide, Alexey Yamilov, Hui Cao

Physics Faculty Research & Creative Works

Introduction of optical gain in a disordered system results in enhanced fluctuations [F(2)=var(g-tilde)/2] of the dimensionless conductance g-tilde, similar to the effect of Anderson localization in a passive medium. Using numerical simulations we demonstrate that, despite such qualitative similarity, the whole distribution of the conductance of amplifying random media is drastically different from that of a passive system with the same value of F(2).

Self-Optimization Of Optical Confinement In An Ultraviolet Photonic Crystal Slab Laser, Alexey Yamilov, X. Wu, X. Liu, Hui Cao, Robert P. H. Chang

Physics Faculty Research & Creative Works

We studied numerically and experimentally the effects of structural disorder on the performance of ultraviolet photonic crystal slab lasers. Optical gain selectively amplifies the high-quality modes of the passive system. For these modes, the in-plane and out-of-plane leakage rates may be automatically balanced in the presence of disorder. The spontaneous optimization of in-plane and out-of-plane confinement of light in a photonic crystal slab may lead to a reduction of the lasing threshold.

Ionization Of Atoms With Spin Polarized Electrons, J. Lower, S. Bellm, R. Panajotovic, E. Weigold, A. Prideaux, Z. Stegen, Don H. Madison, Colm T. Whelan, B. Lohmann

Physics Faculty Research & Creative Works

The most detailed insight into the process of electron impact-induced ionization of atomic species is provided by measurements in which both kinematical and quantum mechanical variables are determined. Here we describe recent (e,2e) experimental and theoretical studies involving the ionization of xenon and argon by spin-polarized electrons in which the fine-structure levels of the ion are energetically resolved. Such investigations shed light on the mechanisms driving the ionization reaction and the role of exchange and relativistic processes.

Spin Excitations In Fluctuating Stripe Phases Of Doped Cuprate Superconductors, Matthias Vojta, Thomas Vojta, Ribhu K. Kaul

Physics Faculty Research & Creative Works

Using a phenomenological lattice model of coupled spin and charge modes, we determine the spin susceptibility in the presence of fluctuating stripe charge order. We assume the charge fluctuations to be slow compared to those of the spins, and combine Monte Carlo simulations for the charge order parameter with exact diagonalization of the spin sector. Our calculations unify the spin dynamics of both static and fluctuating stripe phases and support the notion of a universal spin excitation spectrum in doped cuprate superconductors.

Theoretical Description Of Two- And Three-Particle Interactions In Single Ionization Of Helium By Ion Impact, M. F. Ciappina, W. R. Cravero, Michael Schulz, R. Moshammer, J. D. Ullrich

Physics Faculty Research & Creative Works

In this work we calculate doubly differential cross sections (DDCS) for single ionization of helium by highly charged ion impact. We study the importance of two-particle interactions in these processes by considering the cross sections as a function of all two-particle subsystems momenta. Experimental DDCSs were obtained recently from kinematically complete experiments on single ionization of He by 100 MeV/amu C6+ and 3.6 MeV/amu Au24,53+ impact. Furthermore, we evaluated the importance of three-particle interactions by plotting the squared momenta of all three collision fragments simultaneously in a Dalitz plot. Using the first Born and distorted-wave approximations for fully differential cross …

Studies In Cpt Violation And 331 Models, David L. Anderson

Dissertations, Theses, and Masters Projects

The Standard Model of particles and fields has been around for about 30 years, and has been remarkably successful. However, it is widely believed to be incomplete, and theorists have studied various extensions to the model. These extensions can take many forms. An example of this is the framework Colladay and Kostelecky have proposed for studying Lorentz and CPT violation in a natural extension of the Standard Model. We determined the first bounds on the parameters in the Higgs sector. The bounds on the CPT---even asymmetric coefficients arise from the one-loop contributions to the photon propagator, those from the CPT---even …

Carbon Nanosheets And Carbon Nanotubes By Rf Pecvd, Mingyao Zhu

Dissertations, Theses, and Masters Projects

A planar antenna RF plasma enhanced chemical vapor deposition apparatus was built for carbon nanostructure syntheses. When operated in inductive and capacitive plasma discharging modes, two carbon nanostructures, carbon nanotube (CNT) and carbon nanosheet (CNS), were synthesized, respectively.;A nanosphere lithography method was developed and used to prepare catalyst patterns for CNT growth. Using capacitively coupled C2H2/NH 3 plasma, randomly oriented CNT were synthesized on Ni dot patterned Si substrates. Aligned CNT arrays were grown on SiO2 coated Si substrates, using both C2H2/NH3 and CH 4/H2 capacitive plasmas.;When operated in inductive coupling mode, CNS were successfully deposited on a variety of …

Automated Peak Identification For Time -Of -Flight Mass Spectroscopy, Haijian Chen

Dissertations, Theses, and Masters Projects

The high throughput capabilities of protein mass fingerprints measurements have made mass spectrometry one of the standard tools for proteomic research, such as biomarker discovery. However, the analysis of large raw data sets produced by the time-of-flight (TOF) spectrometers creates a bottleneck in the discovery process. One specific challenge is the preprocessing and identification of mass peaks corresponding to important biological molecules. The accuracy of mass assignment is another limitation when comparing mass fingerprints with databases.;We have developed an automated peak picking algorithm based on a maximum likelihood approach that effectively and efficiently detects peaks in a time-of-flight secondary ion …

Internal Magnetic Field Distribution Of A Type Ii High Tc Superconductor With Non-Conducting Inclusions, Yuxin Dai

Dissertations, Theses, and Masters Projects

The internal magnetic field distributions for a type II superconductor (a single crystal YBa2Cu3O7-delta ) with large normal inclusions (YBa2Cu3O 7-delta) are studied. A model based on the London Equations has been successfully developed and applied to the interpretation of the pSR data on this system. In our model, these inclusions are assumed to be cylindrical in shape and infinite in length. Therefore, this model should be especially appropriate for the prediction of field distributions in single crystal superconductors in which columnar defects have been purposely introduced to enhance pinning.;muSR experiments on a large single-crystal sample of YBa2C u3O7-delta with …

Time-Resolved Magneto-Optical Imaging Of Superconducting Ybco Thin Films In The High-Frequency Ac Current Regime, Alexander Frey

Dissertations, Theses, and Masters Projects

No abstract provided.

Static And Ultrafast Moke Studies Of Exchange -Biased Cobalt Systems, Keoki A. Seu

Dissertations, Theses, and Masters Projects

We have studied the exchange bias interaction in metal bilayers IrMn/Co and FeMn/Co using the static and ultrafast pump-probe Kerr effects. Experiments conducted on wedged Co samples show that the exchange bias interaction is sensitive to the buffer layers grown beneath it when the antiferromagnetic layer is FeMn. The exchange bias strength, as measured by the shift in the magnetic hysteresis loop, follows a 1/tFM dependence as reported in the literature. The time-domain pump-probe experiments reveal coherent magnetization oscillations, whose frequencies are comparable to those measured by frequency-domain FMR measurements, and they fit well to FMR equations for the frequency. …

Development Of A Fourier Transform Far Infrared (Ftfir) Spectrometer To Characterize Broadband Transmission Properties Of Common Materials In The Terahertz Region, William Paul Ford

Browse all Theses and Dissertations

With sub-millimeter wave or terahertz devices becoming more readily available, there is interest in developing sensors in this region of the spectra. To support this interest, we have developed a Fourier Transform Far InfraRed (FTFIR) spectrometer to characterize broadband transmission and reflectance coefficients of materials. The spectrometer utilizes a broadband blackbody source, a Michelson interferometer, and silicon bolometer. The path difference in the Michelson is obtained using a linear stage and data acquisition and stage control were both implemented in a Labview programming environment. The details of the experimental setup and experimental results are presented in this thesis. The instrument …

Electronic Properties Of Silicon-Based Nanostructures, Gian Giacomo Guzman-Verri

Browse all Theses and Dissertations

We have developed a new unifying tight-binding theory that can account for the electronic properties of recently proposed Si-based nanostructures, namely, Si graphene-like sheets and Si nanotubes. We considered the sp²s* and sp³ models up to first- and second-nearest neighbors, respectively. Our results show that the corresponding Si nanotubes follow the so-called Hamada's rule. Comparison to a recent ab initio calculation is made.

Models Of Disordered Media And Predictions Of Associated Hydraulic Conductivity, L. Aaron Blank Jr.

Browse all Theses and Dissertations

In the late 20th century there was a spill of Technetium in eastern Washington State at the US Department of Energy Hanford site. Resulting contamination of water supplies would raise serious health issues for local residents. Therefore, the ability to predict how these contaminants move through the soil is of great interest. The main contribution to contaminant transport arises from being carried along by flowing water. An important control on the movement of the water through the medium is the hydraulic conductivity, K, which defines the ease of water flow for a given pressure difference (analogous to the electrical conductivity). …

The ²H(E, E'P)N Reaction At High Four-Momentum Transfer, Hassan F. Ibrahim

Physics Theses & Dissertations

This dissertation presents the highest four-momentum transfer, Q², quasielastic (x_Bj = 1) results from Experiment E01-020 which systematically explored the 2H(e, e'p)n reaction ("Electro-disintegration" of the deuteron) at three different four-momentum transfers, Q² = 0.8, 2.1, and 3.5 GeV² and missing momenta, p_miss = 0, 100, 200, 300, 400, and 500 GeV including separations of the longitudinal-transverse interference response function, R_LT, and extraction of the longitudinal-transverse asymmetry, A_LT. This systematic approach will help to understand the reaction mechanism and the deuteron structure down to the short …

Femtosecond Laser Ablation With Single And Two-Photon Excitation For Mems, Mohamed Abdelfattah Kottb Ahmad Elbandrawy

Electrical & Computer Engineering Theses & Dissertations

There is an increasing interest in femtosecond laser micromachining of materials because of the femtosecond laser's unique high peak power, ultrashort pulse width, negligible heat conductivity process during the laser pulse, and the minimal heat affected zone, which is in the same order of magnitude of the ablated submicron spot. There are some obstacles in reaching optimal and reliable micromachining parameters. One of these obstacles is the lack of understanding of the nature of the interaction and related physical processes. These processes include amorphization, melting, re-crystallization, nucleated-vaporization, and ablation.

The focus of this Dissertation was to study the laser-matter interaction …

Initial-State Correlation Effects In Low-Energy Proton Impact Ionization, M. Foster, Jerry Peacher, Ahmad Hasan, Michael Schulz, Don H. Madison

Physics Faculty Research & Creative Works

In this paper, we will report on fully differential cross sections (FDCS) for single ionization of helium by 75 keV proton impact for fixed ejected electron energies and different momentum transfers. These measurements show major discrepancies in the absolute magnitude between experiment and the theoretical, 3DW (three-distorted-wave) model. The 3DW model treats the collision as a three-body process (projectile, ion, ejected electron), and for the scattering plane it has accurately predicted the FDCS for higher energy C⁶⁺ impact ionization of helium. The lack of agreement between the 3DW model and experiment for low energy collisions suggests that a three-body …

Percolation Transition And Dissipation In Quantum Ising Magnets, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of dissipation on a randomly diluted transverse-field Ising magnet close to the percolation threshold. For weak transverse fields, a percolation quantum phase transition separates a superparamagnetic cluster phase from an inhomogeneously ordered ferromagnetic phase. The properties of this transition are dominated by large frozen and slowly fluctuating percolation clusters. This leads to a discontinuous magnetization-field curve and exotic hysteresis phenomena as well as highly singular behavior of magnetic susceptibility and specific heat. We compare our results to the smeared transition in generic dissipative random quantum Ising magnets. We also discuss the relation to metallic quantum magnets …

Theoretical Treatment Of Electron-Impact Ionization Of Molecules, Junfang Gao, Jerry Peacher, Don H. Madison

Physics Faculty Research & Creative Works

There is currently no reliable theory for calculating the fully differential cross section (FDCS) for low energy electron-impact ionization of molecules. All of the existing experimental FDCS data represent averages over all molecular orientations and this can be an important theoretical complication for calculations that are computer intensive. We have found that using an averaged molecular orbital is an accurate approximation for ionization of ground states. In this paper, we will describe the approximation, discuss its expected range of validity and show some FDCS results using the approximation for ionization of H2 and N2

Kinematically Complete Experiment On Single Ionization In 75-Kev P+He Collisions, Michael Schulz, Ahmad Hasan, N. V. Maydanyuk, M. Foster, B. Tooke, Don H. Madison

Physics Faculty Research & Creative Works

We have measured and calculated fully differential single-ionization cross sections for the complete three-dimensional space in 75 keV p+He collisions. Several signatures of the projectile-residual-target-ion interaction, some of which are not observable for fast projectiles and for electron impact, are revealed. Some of these features are qualitatively reproduced by our calculations if this interaction is accounted for. However, overall the agreement between theory and experiment is not very good. Thus, our understanding of effects caused by the projectile-residual-target-ion interaction appears to be rather incomplete.

Observations Of Triboelectric Charging Effects On Langmuir-Type Probes In Dusty Plasma, Aroh Barjatya, C. M. Swenson

Publications

Investigation of Earth’s mesosphere using sounding rockets equipped with a myriad of instruments has been a highly active field in the last 2 decades. This paper presents data from three separate instruments: an RF impedance probe, a DC fixed bias Langmuir probe, and an electric field probe, that were flown on a mesospheric sounding rocket flight investigating the presence of charged dust within and/or around a sporadic metal layer. The combined data set indicates a case of payload surface charging, the causes of which are investigated within this paper. A generic circuit model is developed to analyze payload charging and …

Rocket And Radar Investigation Of Background Electrodynamics And Bottom-Type Scattering Layers At The Onset Of Equatorial Spread F, D. L. Hysell, M. F. Larsen, C. M. Swenson, Aroh Barjatya, Et. Al

Publications

Sounding rocket experiments were conducted during the NASA EQUIS II campaign on Kwajalein Atoll designed to elucidate the electrodynamics and layer structure of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on 7 and 15 August 2004, each comprised of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets deployed trails of trimethyl aluminum (TMA) which yielded wind profile measurements. The Altair radar was …

Quantum Dynamics As An Analog Of Conditional Probability, Matthew S. Leifer

Mathematics, Physics, and Computer Science Faculty Articles and Research

Quantum theory can be regarded as a noncommutative generalization of classical probability. From this point of view, one expects quantum dynamics to be analogous to classical conditional probabilities. In this paper, a variant of the well-known isomorphism between completely positive maps and bipartite density operators is derived, which makes this connection much more explicit. This isomorphism is given an operational interpretation in terms of statistical correlations between ensemble preparation procedures and outcomes of measurements. Finally, the isomorphism is applied to elucidate the connection between no-cloning and no-broadcasting theorems and the monogamy of entanglement, and a simplified proof of the no-broadcasting …

Conditional Density Operators And The Subjectivity Of Quantum Operations, Matthew S. Leifer

Mathematics, Physics, and Computer Science Faculty Articles and Research

Assuming that quantum states, including pure states, represent subjective degrees of belief rather than objective properties of systems, the question of what other elements of the quantum formalism must also be taken as subjective is addressed. In particular, we ask this of the dynamical aspects of the formalism, such as Hamiltonians and unitary operators. Whilst some operations, such as the update maps corresponding to a complete projective measurement, must be subjective, the situation is not so clear in other cases. Here, it is argued that all trace preserving completely positive maps, including unitary operators, should be regarded as subjective, in …

Metric Modifications For A Massive Spin 1 Particle, Br Holstein

Barry R Holstein

Previous evaluations of long range one-photon and one-graviton-loop corrections to the energy-momentum tensor and the metric tensor describing spacetime in the vicinity of massive spinless and spin 1/2 systems have been extended to particles with unit spin and speculations are confirmed concerning universal properties of such forms.

Metric Modifications For A Massive Spin 1 Particle, Barry R. Holstein

Barry R Holstein

Previous evaluations of long range one-photon and one-graviton-loop corrections to the energy-momentum tensor and the metric tensor describing spacetime in the vicinity of massive spinless and spin 1/2 systems have been extended to particles with unit spin and speculations are confirmed concerning universal properties of such forms.

Observation Of Multiple Thresholds In The Cavity Qed Microlaser", Christopher Fang-Yen, C C. Yu, S Ha, K An, R R. Dasari, M S. Feld

Christopher Fang-Yen

No abstract provided.

Relation Between Rotational And Translational Dynamic Heterogeneities In Water, M. Mazza, N. Giovambattista, Francis W. Starr, H. E. Stanley

Francis Starr

No abstract provided.

Shape-Persistent V-Shaped Mesogens-Formation Of Nematic Phases With Biaxial Order, Matthias Lehmann, Shin-Woong Kang, Christiane Köhn, Sönke Haseloh, Ute Kolb, Dieter Schollmeyer, Qingbing Wang, Satyendra Kumar

Satyendra Kumar

A homologous series of shape-persistent V-shaped molecules has been designed to form the biaxial nematic phase. Phenyleneethynylene moieties are attached to a bent fluorenone unit to create an apex angle of about 90°, which is determined from the single crystal structure. Two mesogens, one symmetric and another unsymmetric, have been synthesized by attaching a cyano group to one or both of the peripheral phenyl units, respectively. These groups introduce local dipoles essential for the formation of the nematic phases. The tendency to form a crystalline phase is reduced by laterally substituted hexyloxy chains which allow the nematic phase to be …

Quantum Trajectory Studies Of Many-Atom And Finite Transit-Time Effects In A Cavity Qed Microlaser Or Micromaser, Christopher Fang-Yen

Christopher Fang-Yen

No abstract provided.