Physical Sciences and Mathematics Commons^™

Fully Differential Cross Section For Four Body Charge Transfer Process, Ujjal Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison

Physics Faculty Research & Creative Works

Recently experimental fully differential cross sections (FDCS) have been reported for double capture in proton helium collisions which disagree with existing theoretical calculations by two orders of magnitude. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. The results of this model are in much better agreement with experimental data.

Low Energy (E, 2e) Study From The 1t₂ Orbital Of Ch₄, Shenyue Xu, Hari Chaluvadi, Xueguang Ren, Thomas Pfluger, Arne Senftleben, Chuangang Ning, Shuncheng Yan, Peng Zhang, Jie Yang, Xinwen Ma, Joachim Hermann Ullrich, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Single ionization of the methane (CH₄) 1t₂ orbital by 54 eV electron impact has been studied experimentally and theoretically. The measured triple differential cross sections cover nearly a 4π solid angle for the emission of low energy electrons and a range of projectile scattering angles. Experimental data are compared with theoretical calculations from the distorted wave Born approximation and the molecular three-body distorted wave models. It is found that theory can give a proper description of the main features of experimental cross section only at smaller scattering angles. For larger scattering angles, significant discrepancies between experiment and …

Conditions For Extracting Photoionization Cross Sections From Laser-Induced High-Order-Harmonic Spectra, Guoli Wang, Cheng Jin, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We show that photoionization cross sections of atoms can be accurately extracted from the high-order-harmonic spectra generated by intense infrared lasers only if the degree of ionization in the gas medium is small, implying that for this purpose the high-order-harmonic generation spectra should be taken at low gas pressure and at low laser intensity experimentally.

Experimental And Computational Validation And Verification Of The Stokes-Darcy And Continuum Pipe Flow Models For Karst Aquifers With Dual Porosity Structure, Xiaolong Hu, Xiaoming Wang, Max Gunzburger, Fei Hua, Yanzhao Cao

Mathematics and Statistics Faculty Research & Creative Works

In our previous study, we developed the Stokes-Darcy (SD) model was developed for flow in a karst aquifer with a conduit bedded in matrix, and the Beavers-Joseph (BJ) condition was used to describe the matrix-conduit interface. We also studied the mathematical well-posedness of a coupled continuum pipe flow (CCPF) model as well as convergence rates of its finite element approximation. in this study, to compare the SD model with the CCPF model, we used numerical analyses to validate finite element discretisation methods for the two models. using computational experiments, simulation codes implementing the finite element discretisations are then verified. Further …

Templated Synthesis Of Nylon Nucleic Acids And Characterization By Nuclease Digestion, Yu Liu, Risheng Wang, Liang Ding, Roujie Sha, Nadrian C. Seeman, James W. Canary

Chemistry Faculty Research & Creative Works

Nylon nucleic acids containing oligouridine nucleotides with pendent polyamide linkers and flanked by unmodified heteronucleotide sequences were prepared by DNA templated synthesis. Templation was more efficient than the single-stranded synthesis; coupling step yields were as high as 99.2%, with up to 7 amide linkages formed in the synthesis of a molecule containing 8 modified nucleotides. Controlled digestion by calf spleen phosphodiesterase enabled the mapping of modified nucleotides in the sequences. a combination of complete degradation of nylon nucleic acids by snake venom phosphodiesterase and dephosphorylation of the resulting nucleotide fragments by bacterial alkaline phosphatase, followed by LCMS analysis, clarified the …

All-Sky Search For Gravitational-Wave Bursts In The Second Joint Ligo-Virgo Run, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration ≲ 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts …

Seismic Site Classifications For The St. Louis Urban Area, Jaewon Chung, J. David Rogers

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

Regional National Earthquake Hazards Reduction Program (NEHRP) soil class maps have become important input parameters for seismic site characterization and hazard studies. The broad range of shallow shear-wave velocity (V_S30, the average shear-wave velocity in the upper 30 m) measurements in the St. Louis area results in significant uncertainties between the actual spot values and the averaged values used to assign NEHRP soil classes for regional seismic hazard studies. In the preparation of an NEHRP site classification map of the St. Louis urban area, we analyzed 92 shear-wave velocity (V_S) measurements, supplemented by 1400+ standard penetration …

Triple Compton Effect: A Photon Splitting Into Three Upon Collision With A Free Electron, Erik Loetstedt, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

The process in which a photon splits into three after the collision with a free electron (triple Compton effect) is the most basic process for the generation of a high-energy multiparticle entangled state composed out of elementary quanta. The cross section of the process is evaluated in two experimentally realizable situations, one employing gamma photons and stationary electrons, and the other using keV photons and GeV electrons of an x-ray free electron laser. For the first case, our calculation is in agreement with the only available measurement of the differential cross section for the process under study. Our estimates indicate …

Upper Limits On A Stochastic Gravitational-Wave Background Using Ligo And Virgo Interferometers At 600-1000 Hz, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of Ω_GW(f) = Ω₃(f/900Hz)³, of Ω₃ < 0.32, assuming a value of the Hubble parameter of h₁₀₀ = 0.71. These new limits are a …

Second-Order Convex Splitting Schemes For Gradient Flows With Ehrlich-Schwoebel Type Energy: Application To Thin Film Epitaxy, Jie Shen, Cheng Wang, Xiaoming Wang, Steven M. Wise

Mathematics and Statistics Faculty Research & Creative Works

We construct unconditionally stable, unconditionally uniquely solvable, and second order accurate (in time) schemes for gradient flows with energy of the form {equation presented} dx. the construction of the schemes involves the appropriate combination and extension of two classical ideas: (i) appropriate convex-concave decomposition of the energy functional and (ii) the secant method. as an application, we derive schemes for epitaxial growth models with slope selection (F(y) = 1/4 (|y| 2 - 1) 2) or without slope selection (F(y) = -1/2 ln(1 + |y| 2)). Two types of unconditionally stable uniquely solvable second-order schemes are presented. the first type inherits …

Long Time Stability Of A Classical Efficient Scheme For Two-Dimensional Navier-Stokes Equations, S. Gottlieb, F. Tone, C. Wang, X. Wang, D. Wirosoetisno

Mathematics and Statistics Faculty Research & Creative Works

This paper considers the long-time stability property of a popular semi-implicit scheme for the two-dimensional incompressible Navier-Stokes equations in a periodic box that treats the viscous term implicitly and the nonlinear advection term explicitly. We consider both the semi discrete (discrete in time but continuous in space) and fully discrete schemes with either Fourier Galerkin spectral or Fourier pseudo spectral (collocation) methods. We prove that in all cases, the scheme is long time stable provided that the timestep is sufficiently small. the long-time stability in the L 2 and H 1 norms further leads to the convergence of the global …

Search For Gravitational Waves From Intermediate Mass Binary Black Holes, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450M_⊙ and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 M_⊙, …

First Low-Latency Ligo+Virgo Search For Binary Inspirals And Their Electromagnetic Counterparts, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was …

Disorder Promotes Ferromagnetism: Rounding Of The Quantum Phase Transition In Sr₁₋ₓcaₓruo₃, Laszlo Demko, Sandor Bordacs, Thomas Vojta, David Nozadze, Fawaz Hrahsheh, Christopher Svoboda, Balazs Dora, Hiroyuki Yamada, Masashi Kawasaki, Yoshinori Tokura, Istvan Kezsmarki

Physics Faculty Research & Creative Works

The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr_1-xCa_xRuO₃ is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a magneto-optical technique, we map the magnetic phase diagram in the composition-temperature space. We find …

Dissipation Effects In Random Transverse-Field Ising Chains, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the zero-temperature quantum phase transition in the random transverse-field Ising chain by means of an (asymptotically exact) analytical strong-disorder renormalization-group approach. We find that Ohmic damping destabilizes the infinite-randomness critical point and the associated quantum Griffiths singularities of the dissipationless system. The quantum dynamics of large magnetic clusters freezes completely, which destroys the sharp phase transition by smearing. The effects of sub-Ohmic dissipation are similar and also lead to a smeared transition. In contrast, super-Ohmic damping is an irrelevant perturbation; the critical behavior is thus identical to that of …

Quantum Griffiths Singularities In Ferromagnetic Metals, David Nozadze, Thomas Vojta

Physics Faculty Research & Creative Works

We present a theory of the quantum Griffiths phases associated with the ferromagnetic quantum phase transition in disordered metals. For Ising spin symmetry, we study the dynamics of a single rare region within the variational instanton approach. For Heisenberg symmetry, the dynamics of the rare region is studied using a renormalization group approach. In both cases, the rare region dynamics is even slower than in the usual quantum Griffiths case because the order parameter conservation of an itinerant ferromagnet hampers the relaxation of large magnetic clusters. The resulting quantum Griffiths singularities in ferromagnetic metals are stronger than power laws. For …

Experimental Evaluation Of The Effect Of Queue Management Schemes On The Performance Of High Speed Tcps In 10gbps Network Environment, Lin Xue, Cheng Cui, Suman Kumar, Seung Jong Park

Computer Science Faculty Research & Creative Works

Queue management schemes at the routers and congestion avoidance schemes at the end points cooperate to provide good congestion solutions in computer networks. While queue management schemes are still being developed, research on congestion avoidance has come a long way to serve the bandwidth requirement of the networks (e.g. high-speed networks, data centers, etc.) at the order of 10Gbps. Because of considerable lack on the evaluation research work, there is no consensus on the choice of the queue management algorithms over these networks. To the best of our knowledge, this is the first work that presents experimental evaluation of the …

Unconventional Rf Photoresponse From A Superconducting Spiral Resonator, Alexander P. Zhuravel, Cihan Kurter, Alexey V. Ustinov, Steven M. Anlage

Physics Faculty Research & Creative Works

Superconducting thin film resonators employing strip geometries show great promise in rf/microwave applications due to their low loss and compact nature. However, their functionality is limited by nonlinear effects at elevated rf/microwave powers. Here, we show that by using a planar spiral geometry carrying parallel currents in adjacent turns, this limitation can be minimized. We investigate the rf current distributions in spiral resonators implemented with Nb thin films via laser scanning microscopy. The rf current density profile along the width of the individual turns of the resonators reveals an unconventional trend: maximum current in the middle of the structure and …

Electronic Properties Of Layered Multicomponent Wide-Band-Gap Oxides: A Combinatorial Approach, Altynbek Murat, Julia E. Medvedeva

Physics Faculty Research & Creative Works

The structural, electronic, and optical properties of 12 multicomponent oxides with layered structure RAMO ₄, where R3 ⁺ = In or Sc, A3 ⁺ = Al or Ga, and M2 ⁺ = Ca, Cd, Mg, or Zn, are investigated using first-principles density functional approach. The compositional complexity of RAMO ₄ leads to a wide range of band-gap values varying from 2.45 eV for InGaCdO ₄ to 6.29 eV for ScAlMgO ₄ as obtained from our self-consistent screened-exchange local density approximation calculations. Strikingly, despite the different band gaps in the oxide constituents, namely, 2-4 eV in CdO, In ₂O …

Search For Gravitational Waves From Low Mass Compact Binary Coalescence In Ligo's Sixth Science Run And Virgo's Science Runs 2 And 3, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M_⊙ this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total …

Bound-Free Pair Production In Ultra-Relativistic Ion Collisions At The Lhc Collider: Analytic Approach To The Total And Differential Cross Sections, Anton N. Artemyev, Ulrich D. Jentschura, Valery G. Serbo, Andrey S. Surzhykov

Physics Faculty Research & Creative Works

A theoretical investigation of the bound-free electron-positron pair production in relativistic heavy ion collisions is presented. Special attention is paid to the positrons emitted under large angles with respect to the beam direction. The measurement of these positrons in coincidence with the down-charged ions is in principle feasible by LHC experiments. In order to provide reliable estimates for such measurements, we employ the equivalent photon approximation together with the Sauter approach and derive simple analytic expressions for the differential pair-production cross section, which compare favorably to the results of available numerical calculations. Based on the analytic expressions, detailed calculations are …

Implementation And Testing Of The First Prompt Search For Gravitational Wave Transients With Electromagnetic Counterparts, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations.

Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify …

Switching Nonlinearity In A Superconductor-Enhanced Metamaterial, Cihan Kurter, Philippe Tassin, Alexander P. Zhuravel, Lei Zhang, Thomas Koschny, Alexey V. Ustinov, Costas M. Soukoulis, Steven M. Anlage

Physics Faculty Research & Creative Works

We demonstrate a nonlinear metamaterial that can be switched between low and high transmission by controlling the power level of the incident beam. The origin of this nonlinear response is the superconducting Nb thin film employed in the metamaterial structure. We show that with moderate RF power of about 22 dBm it is possible to quench the superconducting state as a result of extremely strong current densities at the corners of the metamaterial's split-ring resonators. We measure a transmission contrast of 10 dB and a change in group delay of 70 ns between the low and high power states.

Low-Energy Electron-Impact Ionization Of Argon: Three-Dimensional Cross Section, Xueguang Ren, Thomas Pfluger, Joachim Hermann Ullrich, Oleg I. Zatsarinny, Klaus Bartschat, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Low-energy (E ₀ = 70.8 eV) electron-impact single ionization of a 3p electron in argon has been studied experimentally and theoretically. Our measurements are performed using the so-called reaction microscope technique, which can cover nearly a full 4π solid angle for the emission of a secondary electron with energy below 15 eV and projectile scattering angles ranging from -8° to -30°. The measured cross sections are internormalized across all scattering angles and ejected energies. Several theoretical models were employed to predict the triple-differential cross sections (TDCSs). They include a standard distorted-wave Born approximation (DWBA), a modified version to account for …

Low Energy (E,2e) Measurements Of Ch⁴ And Neon In The Perpendicular Plane, Kate L. Nixon, Andrew James Murray, Hari Chaluvadi, Sadek Amami, Don H. Madison, Chuangang Ning

Physics Faculty Research & Creative Works

Low energy experimental and theoretical triple differential cross sections for the highest occupied molecular orbital of methane (1t₂) and for the 2p atomic orbital of neon are presented and compared. These targets are iso-electronic, each containing 10 electrons and the chosen orbital within each target has p-electron character. Observation of the differences and similarities of the cross sections for these two species hence gives insight into the different scattering mechanisms occurring for atomic and molecular targets. The experiments used perpendicular, symmetric kinematics with outgoing electron energies between 1.5 eV and 30 eV for CH₄ and 2.5 eV …

Localizability Of Tachyonic Particles And Neutrinoless Double Beta Decay, Ulrich D. Jentschura, Benedikt J. Wundt

Physics Faculty Research & Creative Works

The quantum field theory of superluminal (tachyonic) particles is plagued by a number of problems, which include the Lorentz non-invariance of the vacuum state, the ambiguous separation of the field operator into creation and annihilation operators under Lorentz transformations, and the necessity of a complex reinterpretation principle for quantum processes. Another unsolved question concerns the treatment of subluminal components of a tachyonic wave packet in the field-theoretical formalism, and the calculation of the time-ordered propagator. After a brief discussion on related problems, we conclude that rather painful choices have to be made in order to incorporate tachyonic spin-1/2 particles into …

Artificially Disordered Birefringent Optical Fibers, Sumudu Herath, N. P. Puente, Elena I. Chaikina, Alexey Yamilov

Physics Faculty Research & Creative Works

We develop and experimentally verify a theory of evolution of polarization in artificially-disordered multi-mode optical fibers. Starting with a microscopic model of photo-induced index change, we obtain the first and second order statistics of the dielectric tensor in a Ge-doped fiber, where a volume disorder is intentionally inscribed via UV radiation transmitted through a diffuser. A hybrid coupled-power & coupled-mode theory is developed to describe the transient process of de-polarization of light launched into such a fiber. After certain characteristic distance, the power is predicted to be equally distributed over all co-propagating modes of the fiber regardless of their polarization. …

Multiscale Perturbative Approach To Su(2)-Higgs Classical Dynamics: Stability Of Nonlinear Plane Waves And Bounds Of The Higgs Field Mass, V. Achilleos, F. K. Diakonos, D. J. Frantzeskakis, Garyfallia C. Katsimiga, X. N. Maintas, C. E. Tsagkarakis, A. Tsapalis

Physics Faculty Research & Creative Works

We study the classical dynamics of SU(2)-Higgs field theory using multiple-scale perturbation theory. In the spontaneously broken phase, assuming small perturbations of the Higgs field around its vacuum expectation value, we derive a nonlinear Schrödinger equation and study the stability of its nonlinear plane wave solutions. The latter turn out to be stable only if the Higgs amplitude is an order of magnitude smaller than that of the gauge field. In this case, the Higgs field mass possesses some bounds which may be relevant to the search for the Higgs particle at ongoing experiments. © 2012 American Physical Society.

Economics And Finance On Time Scales, Julius Severin Heim

Doctoral Dissertations

"This thesis consists of 6 papers that investigate models in economics and finance based on so-called dynamic equations on time scales. The first paper covers multiplier-accelerator models that can be described by linear second-order dynamic equations. The possibility of taxes as well as the possibility of foreign trade is taken into consideration. The second paper discusses cobweb models, which describe cyclical supply and demand in markets, where the supply is determined before the observation of the price. Cobweb models that can be formulated with first-order linear, second-order linear, and nonlinear dynamic equations are being considered. The third and fourth papers …

Model Reduction Of Linear Pde Systems: A Continuous Time Eigensystem Realization Algorithm, John R. Singler

Mathematics and Statistics Faculty Research & Creative Works

The Eigensystem Realization Algorithm (ERA) is a well known system identification and model reduction algorithm for discrete time systems. Recently, Ma, Ahuja, and Rowley (Theoret. Comput. Fluid Dyn. 25(1) : 233-247, 2011) showed that ERA is theoretically equivalent to the balanced POD algorithm for model reduction of discrete time systems. We propose an ERA for model reduction of continuous time linear partial differential equation systems. The algorithm differs from other existing approaches as it is based on a direct approximation of the Hankel integral operator of the system. We show that the algorithm produces accurate balanced reduced order models for …