Physical Sciences and Mathematics Commons^™

Kinematically Complete Experiment On Transfer Excitation In Intermediate-Energy P + He Collisions, Ahmad Hasan, B. Tooke, M. Zapukhlyak, T. Kirchner, Michael Schulz

Physics Faculty Research & Creative Works

We have performed a kinematically complete experiment on transfer excitation in intermediate-energy proton-helium collisions. The differential cross sections were compared to double excitation data and a nonperturbative time-dependent calculation. This comparison reveals the importance of dynamic couplings between the motion of the heavy nuclei and electronic transitions and/or electron-electron correlation effects.

Kinetic Correlation In Photo-Double-Ionization Processes: The He-Isoelectronic Sequence, Sebastian Otranto, C. R. Garibotti

Physics Faculty Research & Creative Works

Analytical models proposed to represent the two-electron continuum are revisited. Main results obtained with these models are summarized. Recent studies of the photo-double-ionization (PDI) of the He-isoelectronic sequence by means of the recently introduced SC3 model are shown and compared with the results predicted by classical and semi-classical Wannier approaches. By fitting the triply differential cross sections (TDCSs) with the usual dipolar Gaussian form we find that the width has a power dependence on excess energy with exponent 0.25 in the near threshold region and departs from this law with increasing energy

Nonequilibrium Phase Transition On A Randomly Diluted Lattice, Thomas Vojta, Man Young Lee

Physics Faculty Research & Creative Works

We show that the interplay between geometric criticality and dynamical fluctuations leads to a novel universality class of the contact process on a randomly diluted lattice. The nonequilibrium phase transition across the percolation threshold of the lattice is characterized by unconventional activated (exponential) dynamical scaling and strong Griffiths effects. We calculate the critical behavior in two and three space dimensions, and we also relate our results to the recently found infinite-randomness fixed point in the disordered one-dimensional contact process.

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 …

Random Lasing In Weakly Scattering Systems, X. Wu, W. Fang, Alexey Yamilov, A. A. Asatryan, L. C. Botten, Andrey A. Chabanov, Hui Cao

Physics Faculty Research & Creative Works

We present detailed experimental and numerical studies of random lasing in weakly scattering systems. The interference of scattered light, which is weak in the passive systems, is greatly enhanced in the presence of high gain, providing coherent and resonant feedback for lasing. The lasing modes are confined in the vicinity of the pumped volume due to absorption of emitted light outside it. In the ballistic regime where the size of the gain volume is less than the scattering mean free path, lasing oscillation occurs along the direction in which the gain volume is most extended, producing directional laser output. The …

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.

Slow Dynamics At The Smeared Phase Transition Of Randomly Layered Magnets, Shellie Huether, Ryan Kinney, Thomas Vojta

Physics Faculty Research & Creative Works

We investigate a model for randomly layered magnets, viz., a three-dimensional Ising model with planar defects. The magnetic phase transition in this system is smeared because static long-range order can develop on isolated rare spatial regions. Here, we report large-scale kinetic Monte Carlo simulations of the dynamical behavior close to the smeared phase transition, which we characterize by the spin (time) autocorrelation function. In the paramagnetic phase, its behavior is dominated by Griffiths effects similar to those in magnets with point defects. In the tail region of the smeared transition the dynamics is even slower: the autocorrelation function decays like …

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

Ultraviolet Lasing In High-Order Bands Of Three-Dimensional Zno Photonic Crystals, Michael Scharrer, Alexey Yamilov, Xiaohua Wu, Hui Cao, Robert P. H. Chang

Physics Faculty Research & Creative Works

UV lasing in three-dimensional ZnO photonic crystals is demonstrated at room temperature. The photonic crystals are inverse opals with high refractive index contrast that simultaneously confine light and provide optical gain. Highly directional lasing with tunable wavelength is obtained by optical pumping. Comparison of the experimental results to the calculated band structure shows that lasing occurs in high-order bands with abnormally low group velocity. This demonstrates that the high-order band structure of three-dimensional photonic crystals can be used to effectively confine light and enhance emission. Our findings may also impact other applications of photonic crystal devices. ©2006 American Institute of …

Adiabatic-Nonadiabatic Transition In The Diffusive Hamiltonian Dynamics Of A Classical Holstein Polaron, Alex A. Silvius, Paul Ernest Parris, Stephan De Bièvre

Physics Faculty Research & Creative Works

We study the Hamiltonian dynamics of a free particle injected onto a chain containing a periodic array of harmonic oscillators in thermal equilibrium. The particle interacts locally with each oscillator, with an interaction that is linear in the oscillator coordinate and independent of the particle's position when it is within a finite interaction range. At long times the particle exhibits diffusive motion, with an ensemble averaged mean-squared displacement that is linear in time. The diffusion constant at high temperatures follows a power law D~T 5/2 for all parameter values studied. At low temperatures particle transport changes to a hopping process …

Experimental And Theoretical (E,2e) Ionization Cross Sections For A Hydrogen Target At 75.3 Ev Incident Energy In A Coplanar Asymmetric Geometry, Junfang Gao, Don H. Madison, Jerry Peacher, Andrew James Murray, Martyn J. Hussey

Physics Faculty Research & Creative Works

Very recently it was shown that the molecular three-body distorted wave (M3DW) approach gives good agreement with the shape of the experimental data for electron-impact ionization of H₂ in a coplanar symmetric geometry, providing the incident electrons have an energy of 35 eV or greater. One of the weaknesses of these studies was that only the shape of the cross section could be compared to experiment, since there was no absolute or relative normalization of the data. Here we report a joint experimental/theoretical study of electron-impact ionization of H₂ in a coplanar asymmetric geometry where the energy of …

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.

Magnetically Mediated Transparent Conductors: In₂O₃ Doped With Mo, Julia E. Medvedeva

Physics Faculty Research & Creative Works

First-principles band structure investigations of the electronic, optical, and magnetic properties of Mo-doped In2O3 reveal the vital role of magnetic interactions in determining both the electrical conductivity and the Burstein-Moss shift which governs optical absorption. We demonstrate the advantages of the transition metal doping which results in smaller effective mass, larger fundamental band gap, and better overall optical transmission in the visible as compared to commercial Sn-doped In2O3. Similar behavior is expected upon doping with other transition metals opening up an avenue for the family of efficient transparent conductors mediated by magnetic interactions.

Quantum Phase Transitions Of The Diluted O(3) Rotor Model, Thomas Vojta, Rastko Sknepnek

Physics Faculty Research & Creative Works

We study the phase diagram and the quantum phase transitions of a site-diluted two-dimensional O(3) quantum rotor model by means of large-scale Monte Carlo simulations. This system has two quantum phase transitions: a generic one for small dilutions and a percolation transition across the lattice percolation threshold. We determine the critical behavior for both transitions and for the multicritical point that separates them. In contrast to the exotic scaling scenarios found in other random quantum systems, all these transitions are characterized by finite-disorder fixed points with power-law scaling. We relate our findings to a recent classification of phase transitions with …

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 …

Unexpected Higher-Order Effects In Charged Particle Impact Ionization At High Energies, M. Foster, Jerry Peacher, Michael Schulz, Don H. Madison, Zhangjin Chen, H. R. J. Walters

Physics Faculty Research & Creative Works

Most of the experimental and theoretical studies of electron-impact ionization of atoms, referred to as (e, 2e), have concentrated on the scattering plane. The assumption has been that all the important physical effects will be observable in the scattering plane. However, very recently it has been shown that, for C6+-helium ionization, experiment and theory are in nice agreement in the scattering plane and in very bad agreement out of the scattering plane. This lack of agreement between experiment and theory has been explained in terms of higher-order scattering effects between the projectile and target ion. We have examined electron-impact ionization …

Differential Ionization Studies For Positron Impact, Robert D. Dubois, O. G. De Lucio, J. Gavin

Physics Faculty Research & Creative Works

Recent studies of differential ionization by positron impact being performed at the University of Missouri-Rolla are described. Recoil ion-scattered positron and recoil ion-scattered positron-ejected electron coincidences are measured to provide doubly and triply differential ionization data (DDCS and TDCS) for e+ - Ar collisions. the DDCS and TDCS studies are for 750 and 200 eV impact respectively. for the TDCS studies the positron scattering angles are between approximately ± 5° and electrons ejected with energies less than 15 eV and angles between 90° ± 50° with respect to the beam direction are detected. Examples of TDCS data for the scattered …

Electronic Data Discovery: Integrating Due Process Into Cyber Forensic Practice, John W. Bagby, John C. Ruhnka

Journal of Digital Forensics, Security and Law

Most organizations and government agencies regularly become engaged in litigation with suppliers, customers, clients, employees, competitors, shareholders, prosecutors or regulatory agencies that nearly assures the need to organize, retain, find and produce business records and correspondence, emails, accounting records or other data relevant to disputed issues. This article discusses some high visibility cases that constrain how metadata and content is routinely made available to opposing parties in civil litigation, to prosecutors in criminal prosecutions and to agency staff in regulatory enforcement litigation. Public policy, as implemented in the rules of evidence and pretrial discovery, restrict electronic data discovery (EDD) as …

Alphaco: A Teaching Case On Information Technology Audit And Security, Hüseyin Tanriverdi, Joshua Bertsch, Jonathan Harrison, Po-Ling Hsiao, Ketan S. Mesuria, David Hendrawirawan

Journal of Digital Forensics, Security and Law

Recent regulations in the United States (U.S.) such as the Sarbanes-Oxley Act of 2002 require top management of a public firm to provide reasonable assurance that they institute internal controls that minimize risks over the firm’s operations and financial reporting. External auditors are required to attest to the management’s assertions over the effectiveness of those internal controls. As firms rely more on information technology (IT) in conducting business, they also become more vulnerable to IT related risks. IT is critical for initiating, recording, processing, summarizing and reporting accurate financial and non-financial data. Thus, understanding IT related risks and instituting internal …

Table Of Contents

Journal of Digital Forensics, Security and Law

No abstract provided.

Development Of A National Repository Of Digital Forensic Intelligence, Mark Weiser, David P. Biros, Greg Mosier

Journal of Digital Forensics, Security and Law

Many people do all of their banking online, we and our children communicate with peers through computer systems, and there are many jobs that require near continuous interaction with computer systems. Criminals, however, are also “connected”, and our online interaction provides them a conduit into our information like never before. Our credit card numbers and other fiscal information are at risk, our children's personal information is exposed to the world, and our professional reputations are on the line.

The discipline of Digital Forensics in law enforcement agencies around the nation and world has grown to match the increased risk and …

Computer Forensics Field Triage Process Model, Marcus K. Rogers, James Goldman, Rick Mislan, Timothy Wedge, Steve Debrota

Journal of Digital Forensics, Security and Law

With the proliferation of digital based evidence, the need for the timely identification, analysis and interpretation of digital evidence is becoming more crucial. In many investigations critical information is required while at the scene or within a short period of time - measured in hours as opposed to days. The traditional cyber forensics approach of seizing a system(s)/media, transporting it to the lab, making a forensic image(s), and then searching the entire system for potential evidence, is no longer appropriate in some circumstances. In cases such as child abductions, pedophiles, missing or exploited persons, time is of the essence. In …

Table Of Contents

Journal of Digital Forensics, Security and Law

No abstract provided.

Development Of An Ontology Based Forensic Search Mechanism: Proof Of Concept, Jill Slay, Fiona Schulz

Journal of Digital Forensics, Security and Law

This paper examines the problems faced by Law Enforcement in searching large quantities of electronic evidence. It examines the use of ontologies as the basis for new forensic software filters and provides a proof of concept tool based on an ontological design. It demonstrates that efficient searching is produced through the use of such a design and points to further work that might be carried out to extend this concept.

Spirobicyclic Diamines 1: Synthesis Of Proline-Derived Spirolactams Via Thermal Intramolecular Ester Aminolysis, Fintan Kelleher, Sinead Kelly

Articles

Proline derived [4.4]-spirolactams have been synthesised in good yields by a reductive-amination reaction followed by thermal cyclisation of the resulting amine onto the proline ester group in refluxing toluene. The synthesis of the corresponding [4.5]-spirolactams by the same method gave much reduced yields.

Spirobicyclic Diamines 2: Synthesis Of Homochiral Diastereoisomeric Proline Derived [4,4]-Spirolactams, Fintan Kelleher, Sinead Kelly

Articles

L-Proline derived diastereoisomeric [4.4]-spirolactams have been prepared by a reductive-amination reaction of (R)- or (S)-alanine methyl ester followed by thermal cyclisation of the resulting amine onto the proline ester group in refluxing toluene. Under similar conditions (R)- or (S)-phenylalanine methyl ester gave no cyclisation products, while R- or S-a-methylbenzylamine required treatment with NaNH₂ in refluxing toluene to induce cyclisation giving diastereoisomeric [4.4]-spirolactams

Unconfined Versus Confined Speleogenetic Settings: Variations Of Solution Porosity, Alexander Klimchouk

International Journal of Speleology

Speleogenesis in confined settings generates cave morphologies that differ much from those formed in unconfined settings. Caves developed in unconfined settings are characterised by broadly dendritic patterns of channels due to highly competing development. In contrast, caves originated under confined conditions tend to form two- or three-dimensional mazes with densely packed conduits. This paper illustrates variations of solution (channel) porosity resulted from speleogenesis in unconfined and confined settings by the analysis of morphometric parameters of typical cave patterns. Two samples of typical cave systems formed in the respective settings are compared. The sample that represents unconfined speleogenesis consists of solely …

Tracer-Test Design For Losing Stream–Aquifer Systems, Malcolm S. Field

International Journal of Speleology

Hydrological tracer testing is an effective way for assessing the significance and extent of leakage through the bed of an influent (losing and sinking) stream. In karstic terranes, leakage from losing and sinking streams typically resurge at downstream springs, but flow may be intercepted by production wells. Although sinking streams that disappear into swallow holes and caves are relatively easy to trace, developing a tracer test design for a losing stream that allows slow percolation through its bed is complicated by the lack of basic knowledge regarding leakage rate, leakage locations along its length, and temporal variability. To overcome these …

A Class Of Nonlinear Stochastic Volatility Models, Jun Yu, Zhenlin Yang

Research Collection School Of Economics

This paper proposes a class of nonlinear stochastic volatility models based on the Box-Cox transformation which offers an alternative to the one introduced in Andersen (1994). The proposed class encompasses many parametric stochastic volatility models that have appeared in the literature, including the well known lognormal stochastic volatility model, and has an advantage in the ease with which different specifications on stochastic volatility can be tested. In addition, the functional form of transformation which induces marginal normality of volatility is obtained as a byproduct of this general way of modeling stochastic volatility. The efficient method of moments approach is used …