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2008

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Articles 31 - 60 of 801

Full-Text Articles in Physics

General Validity Of Reciprocity In Quantum Mechanics, P.T. Leung, H. Y. Xie, D. P. Tsai Dec 2008

General Validity Of Reciprocity In Quantum Mechanics, P.T. Leung, H. Y. Xie, D. P. Tsai

Physics Faculty Publications and Presentations

The concept of reciprocity symmetry for matter-wave propagation is established for nonrelativistic quantum mechanics with previous results in the literature extended to include nonlocal interactions. Examples are given for cases with both local and nonlocal potentials, where we show in particular that reciprocity can be violated for the motion of a charged particle in an external electromagnetic field. In addition, this symmetry is applied to interpret a recent analysis [Phys. Rev. A 64, 042716 (2001)] on the symmetry of transmission through one-dimensional complex potentials, with the emphasis that the validity of reciprocity can go beyond that of time-reversal symmetry, such …

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Built-In Electric Field Assisted Spin Injection In Cr And Mn Δ-Layer Doped Aln/Gan(0001) Heterostructures From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman Dec 2008

Built-In Electric Field Assisted Spin Injection In Cr And Mn Δ-Layer Doped Aln/Gan(0001) Heterostructures From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman

Physics Faculty Research & Creative Works

Highly spin-polarized diluted ferromagnetic semiconductors are expected to be widely used as ideal spin injectors. Here, extensive first-principles density-functional theory calculations have been performed to investigate the feasibility of using Cr- and Mn-doped wurtzite polar AlN/GaN(0001) heterostructures, with the aim to realize the appealing half-metallic character and, hence, efficient electrical spin injection. To overcome the formation of detrimental embedded clusters, we propose digital delta-layer doping perpendicular to the growth direction so as to realize enhanced performance at room temperature. The formation energy, electronic and magnetic properties, and the degree of spin polarization for both neutral and charged valence states for …

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The Adaptability Of Langmuir Probes To The Pico-Satellite Regime, Andrew Jay Auman Dec 2008

The Adaptability Of Langmuir Probes To The Pico-Satellite Regime, Andrew Jay Auman

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The purpose of this thesis is to investigate whether it is feasible to use Langmuir probes on pico-satellites flying in low Earth orbit over mid- to low-latitude geographic regions. Following chapters on the expected ionospheric conditions and an overview of Langmuir probe theory, a chapter addressing the difficulties involved with pico-satellite Langmuir probes is presented. Also, the necessary satellite-to-probe surface area requirements in order to achieve confidence in pico-satellite Langmuir probe data, for the orbital regions of interest to this thesis, are stated.

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Modeling The Electrodynamics Of The Low-Latitude Ionosphere, Christian Stephen Wohlwend Dec 2008

Modeling The Electrodynamics Of The Low-Latitude Ionosphere, Christian Stephen Wohlwend

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial plasma depletions in the ionosphere and the associated equatorial spread F, as well as the differences between a two-dimensional flux tube integrated electrodynamics model and a three-dimensional model for the same time period. The gravity wave seeding study was based on a parameterization of a gravity wave perturbation using a background empirical thermosphere and a physics-based ionosphere for the case of 12 UT on 26 September …

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Extending F10.7'S Time Resolution To Capture Solar Flare Phenomena, Ariel O. Acebal Dec 2008

Extending F10.7'S Time Resolution To Capture Solar Flare Phenomena, Ariel O. Acebal

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Solar ultraviolet (UV) radiation ionizes the neutral components in the atmosphere, which is partly responsible for the formation of the ionosphere, and contributes to heating of the atmosphere. Solar flares change the solar spectrum at times by several orders of magnitude. These changes modify the Earth's upper atmosphere, causing problems to communication systems and space operations, such as increased satellite drag. Unfortunately, solar UV measurements are limited since they can only be observed with space-based sensors. In order to work around this limitation, the solar radio emissions at a wavelength of 10.7 cm have been used as a proxy for …

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Anomalies In Electrostatic Calibrations For The Measurement Of The Casimir Force In A Sphere-Plane Geometry, W. J. Kim, M. Brown-Hayes, D. A.R. Dalvit, J. H. Brownell, R. Onofrio Dec 2008

Anomalies In Electrostatic Calibrations For The Measurement Of The Casimir Force In A Sphere-Plane Geometry, W. J. Kim, M. Brown-Hayes, D. A.R. Dalvit, J. H. Brownell, R. Onofrio

Dartmouth Scholarship

We have performed precision electrostatic calibrations in the sphere-plane geometry, and observed anomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was found to be smaller than expected on the basis of the pure Coulombian contribution, and the residual potential found to be distance dependent. We argue that these findings affect the accuracy of the electrostatic calibrations and invite reanalysis of previous determinations of the Casimir force.

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Calculations Of K-Shell Fluorescence Yields And Photoabsorption Cross Sections For Carbon Ions At The K-Edge, Muhammet Fatih Hasoglu Dec 2008

Calculations Of K-Shell Fluorescence Yields And Photoabsorption Cross Sections For Carbon Ions At The K-Edge, Muhammet Fatih Hasoglu

Dissertations

The advent of new space missions providing high-precision observations has engendered the need for reliable and precise K-shell atomic data in order to interpret these X-ray spectra. In response to this need, we focused on the calculation of K-shell fluorescence yields for 2 nd -row ions. A secondary project was undertaken in order to treat theoretically the K-shell X-ray absorption processes in carbon ions. These calculated fluorescence yields of 2nd -row ions and theX-ray photoabsorption cross sections of carbon are astrophysically important in determining (1) charge-changing probabilities, such as Auger vs. radiative decay, and (2) chemical abundances of the interstellar …

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Intergranular Phases In Cyclically Annealed Yba2cu3o7-X And Their Implications For Critical Current Densities, Andrew Peter Clarke Dec 2008

Intergranular Phases In Cyclically Annealed Yba2cu3o7-X And Their Implications For Critical Current Densities, Andrew Peter Clarke

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

We report changes in the intergranular material and grain morphology of YBa2Cu3O7-x during cyclic anneals between 780 and 980 ºC in oxygen at atmospheric pressure. Two endothermic reactions were detected: (a) the eutectic reaction of YBa2Cu3O7-x with CuO and BaCuO2 at 900 ºC (enthalpy ∆Ha) and (b) the peritectic reaction of YBa2Cu3O7-x with CuO at 950 ºC (∆Hb). During the first anneal, only reaction (b) is detected, and although it should only occur if there is an excess of CuO, …

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Calculations Of Diffusion In Fcc Binary Alloys Using On-The-Fly Kinetic Monte Carlo, Erdi Bleda Dec 2008

Calculations Of Diffusion In Fcc Binary Alloys Using On-The-Fly Kinetic Monte Carlo, Erdi Bleda

All Dissertations

With the recent advancements in computer technologies and the improvements in simulation algorithms, along with the theories, has allowed scientists to carry out diffusion calculations more efficiently, especially for the cases where either the diffusion itself takes longer, or there is no available isotope to carry out the diffusion experiments such as tracer diffusion.
In this work, we present a systematic approach to diffusion in intermetallic alloys such as weakly clustered Cu — Ni and weakly ordered Au — Ag. We use Accelerated Molecular Dynamics (AMD) combined with the Embedded Atom Method (EAM) to find the necessary saddlepoint energies. With …

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Search For Anomalous Wtb Couplings In Single Top Quark Production, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Nov 2008

Search For Anomalous Wtb Couplings In Single Top Quark Production, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

In 0.9 fb-1 of pp collisions, the D0 Collaboration presented evidence for single top quark production in events with an isolated lepton, missing transverse momentum, and two to four jets. We examine these data to study the Lorentz structure of the Wtb coupling. The standard model predicts a left-handed vector coupling at the Wtb vertex. The most general lowest dimension, CP-conserving Lagrangian admits right-handed vector and left- or right-handed tensor couplings as well. We find that the data prefer the left-handed vector coupling and set upper limits on the anomalous couplings. These are the first direct constraints on …

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Search For Neutral Higgs Bosons In Multi-B-Jet Events In Pp Collisions At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Nov 2008

Search For Neutral Higgs Bosons In Multi-B-Jet Events In Pp Collisions At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

Data recorded by the D0 experiment at the Fermilab Tevatron Collider are analyzed to search for neutral Higgs bosons produced in association with b quarks. This production mode can be enhanced in the minimal supersymmetric standard model (MSSM). The search is performed in the three b quark channel using multijet triggered events corresponding to an integrated luminosity of 1 fb-1. No statistically significant excess of events with respect to the predicted background is observed and limits are set in the MSSM parameter space.

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Higher Order Corrections To H± Production, Nikolaos Kidonakis Nov 2008

Higher Order Corrections To H± Production, Nikolaos Kidonakis

Faculty Articles

I discuss recent calculations of higher-order corrections to charged Higgs production through various partonic subprocesses. Particular attention is paid to H− production in association with a top quark at the LHC.

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Parameters Of Pseudorandom Quantum Circuits, Yaakov S. Weinstein, Winton G. Brown, Lorenza Viola Nov 2008

Parameters Of Pseudorandom Quantum Circuits, Yaakov S. Weinstein, Winton G. Brown, Lorenza Viola

Dartmouth Scholarship

Pseudorandom circuits generate quantum states and unitary operators which are approximately distributed according to the unitarily invariant Haar measure. We explore how several design parameters affect the efficiency of pseudorandom circuits, with the goal of identifying relevant tradeoffs and optimizing convergence. The parameters we explore include the choice of single- and two-qubit gates, the topology of the underlying physical qubit architecture, the probabilistic application of two-qubit gates, as well as circuit size, initialization, and the effect of control constraints. Building on the equivalence between pseudorandom circuits and approximate t-designs, a Markov matrix approach is employed to analyze asymptotic convergence properties …

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Measurement Of The Electron Charge Asymmetry In Pp → W + X → Eν + X Events At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Nov 2008

Measurement Of The Electron Charge Asymmetry In Pp → W + X → Eν + X Events At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

We present a measurement of the electron charge asymmetry in pp → W + X → eν + X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.

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Molecular Hydrogen Formation On Low Temperature Surfaces In Temperature Programmed Desorption Experiments, Gianfranco Vidali, Ling Li, J. Roser, E. Congiu Nov 2008

Molecular Hydrogen Formation On Low Temperature Surfaces In Temperature Programmed Desorption Experiments, Gianfranco Vidali, Ling Li, J. Roser, E. Congiu

Physics - All Scholarship

The study of the formation of molecular hydrogen on low temperature surfaces is of interest both because it allows to explore elementary steps in the heterogeneous catalysis of a simple molecule and because of the applications in astrochemistry. Here we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations and …

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Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo Nov 2008

Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo

Christian Binek Publications

The temperature dependence of the training effect is studied in an exchange coupled thin-film bilayer composed of a hard ferromagnetic pinning (CoPtCrB) layer in proximity of a soft ferromagnetic pinned (CoCr) layer. Interlayer exchange shifts the hysteresis loops of the soft layer along the magnetic-field axis. This shift is quantified by the bias field in far reaching analogy to the exchange bias field of conventional antiferromagnetic/ferromagnetic heterostructures. A ferromagnetic domain state induced in the hard layer experiences aging very similar to the training behavior of the antiferromagnetic domain state in conventional exchange bias systems. Training originates from changes in the …

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Quantum Nondemolition Measurement Of Discrete Fock States Of A Nanomechanical Resonator, E. Buks, E. Segev, S. Zaitsev, B. Abdo, M. P. Blencowe Nov 2008

Quantum Nondemolition Measurement Of Discrete Fock States Of A Nanomechanical Resonator, E. Buks, E. Segev, S. Zaitsev, B. Abdo, M. P. Blencowe

Dartmouth Scholarship

We study theoretically a radio frequency superconducting interference device integrated with a nanomechanical resonator and an LC resonator. By applying adiabatic and rotating-wave approximations, we obtain an effective Hamiltonian that governs the dynamics of the mechanical and LC resonators. Nonlinear terms in this Hamiltonian can be exploited for performing a quantum nondemolition measurement of Fock states of the nanomechanical resonator. We address the feasibility of experimental implementation and show that the nonlinear coupling can be made sufficiently strong to allow the detection of discrete mechanical Fock states.

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Phase Separation Induced Polar Electrooptical Effect In A Doped Nematic Liquid Crystal Cell, Ji-Hoon Lee, Daeseung Kang, Rolfe G. Petschek, Charles Rosenblatt Nov 2008

Phase Separation Induced Polar Electrooptical Effect In A Doped Nematic Liquid Crystal Cell, Ji-Hoon Lee, Daeseung Kang, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

A cell prepared for vertical alignment was filled with a mixture of the liquid crystal octylcyano biphenyl, doped with a three-legged molecule, in the isotropic phase in the presence of an imposed temperature gradient perpendicular to the substrates. After cooling the cell through the nematic phase and restoring the temperature uniformity, an electrooptic response was observed on applying an electric field across the cell in one direction but not in the other. This unipolar effect was absent for cells prepared in the absence of a temperature gradient. The results are discussed in terms of phase separation and preferential adsorption of …

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Josephson Physics Mediated By The Mott Insulating Phase, Smitha Vishveshwara, Courtney Lannert Nov 2008

Josephson Physics Mediated By The Mott Insulating Phase, Smitha Vishveshwara, Courtney Lannert

Physics: Faculty Publications

We investigate the static and dynamic properties of bosonic lattice systems in which condensed and Mott insulating phases coexist due to the presence of a spatially varying potential. We formulate a description of these inhomogeneous systems and calculate the bulk energy at and near equilibrium. We derive the explicit form of the Josephson coupling between disjoint superfluid regions separated by Mott insulating regions. We obtain detailed estimates for the case of alternating superfluid and Mott insulating spherical shells in a radially symmetric parabolically confined cold atom system.

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Antiphase Ordering And Surface Phases In Lithium Aluminate, Richard R. Vanfleet, J. A. Simmons, D. W. Hill, M. M. C. Chou, B. H. Chai Nov 2008

Antiphase Ordering And Surface Phases In Lithium Aluminate, Richard R. Vanfleet, J. A. Simmons, D. W. Hill, M. M. C. Chou, B. H. Chai

Faculty Publications

Antiphase domains are seen in single crystal gamma lithium aluminate (gamma-LiAlO2) with 16.7 nm periodicity in the <110> direction. Alternate domains have a (1/2) [001] shift. Beta phase lithium aluminate (beta-LiAlO2) is seen to form on the surface of the as-received wafers with an epitaxial strain limited relationship with the bulk gamma phase. The orthorhombic beta phase aligns with the a and b axes (0.528 and 0.630 nm) matching with the tetragonal gamma phase's a and c axes (0.5168 and 0.6268 nm). The gamma and beta phases are seen to have different etch rates. The beta phase converts back to the …

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Modeling Of Spin Metal-Oxide-Semiconductor Field-Effect Transistor: A Nonequilibrium Green’S Function Approach With Spin Relaxation, Tony Low, Mark Lundstrom, Dmitri Nikonov Nov 2008

Modeling Of Spin Metal-Oxide-Semiconductor Field-Effect Transistor: A Nonequilibrium Green’S Function Approach With Spin Relaxation, Tony Low, Mark Lundstrom, Dmitri Nikonov

Birck and NCN Publications

A spin metal-oxide-semiconductor field-effect transistor (spin MOSFET), which combines a Schottky-barrier MOSFET with ferromagnetic source and drain contacts, is a promising device for spintronic logic. Previous simulation studies predict that this device should display a very high magnetoresistance (MR) ratio (between the cases of parallel and antiparallel magnetizations) for the case of half-metal ferromagnets (HMF). We use the nonequilibrium Green’s function formalism to describe tunneling and carrier transport in this device and to incorporate spin relaxation at the HMF-semiconductor interfaces. Spin relaxation at interfaces results in nonideal spin injection. Minority spin currents arise and dominate the leakage current for antiparallel …

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Spectral Time Moment Analysis Of Microgel Deswelling: Effect Of The Heating Rate, Kiril A. Streletzky, John T. Mckenna Nov 2008

Spectral Time Moment Analysis Of Microgel Deswelling: Effect Of The Heating Rate, Kiril A. Streletzky, John T. Mckenna

Physics Faculty Publications

Microgel nanoparticles were synthesized in aqueous solutions of neutral polymer hydroxypropylcellulose (HPC) through the self-association of amphiphilic HPC molecules and the subsequent cross linking at room temperature. Dynamic Light Scattering was used to study the transport properties of HPC microgels below and above the volume phase transition. Highly nonexponential, multimodal microgel spectra were observed and successfully analyzed by spectral time moment analysis. This article expands earlier results and focuses on the effect of the heating rate on microgel deswelling. During the fast heating two identified microgel modes with apparent hydrodynamic radii (RH) of 25–30 nm and 400–650 nm collapse into …

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Phase Diagram Of Su(2) With 2 Flavors Of Dynamical Adjoint Quarks, Simon Catterall, Joel Giedt, Francesco Sannino, Joe Schneible Nov 2008

Phase Diagram Of Su(2) With 2 Flavors Of Dynamical Adjoint Quarks, Simon Catterall, Joel Giedt, Francesco Sannino, Joe Schneible

Physics - All Scholarship

We report on numerical simulations of SU(2) lattice gauge theory with two flavors of light dynamical quarks in the adjoint of the gauge group. The dynamics of this theory is thought to be very different from QCD -- the theory exhibiting conformal or near conformal behavior in the infrared. We make a high resolution survey of the phase diagram of this model in the plane of the bare coupling and quark mass on lattices of size 8^3 \times 16. Our simulations reveal a line of first order phase transitions extending from beta=0 to beta=beta_c \sim 2.0. For beta > beta_c the …

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Measurement Of The Forward-Backward Charge Asymmetry And Extraction Of Sin2ӨWEff In Pp → Z/Γ* +X → E+E- + X Events Produced At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Nov 2008

Measurement Of The Forward-Backward Charge Asymmetry And Extraction Of Sin2ӨWEff In Pp → Z/Γ* +X → E+E- + X Events Produced At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

We present a measurement of the forward-backward charge asymmetry (AFB) in pp → Z/γ* +X → e+e- + X events at a center-of-mass energy of 1.96 TeV using 1.1 fb-1 of data collected with the D0 detector at the Fermilab Tevatron collider. AFB is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the AFB measurement to extract the effective weak mixing angle sin2ӨWeff = 0.2326 ± 0.0018 (stat) ± 0.0006 (syst).

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Magnetic-Field-Induced Optical Anisotropy In Ferrofluids: A Time-Dependent Light-Scattering Investigation, Corneliu Rablau, Prem Vaishnava, Sudakar Chandran, Ronald Tackett, Gavin Lawes, Ratna Naik Nov 2008

Magnetic-Field-Induced Optical Anisotropy In Ferrofluids: A Time-Dependent Light-Scattering Investigation, Corneliu Rablau, Prem Vaishnava, Sudakar Chandran, Ronald Tackett, Gavin Lawes, Ratna Naik

Physics Publications

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (∼6nm) under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced …

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Magnetic-Field-Induced Optical Anisotropy In Ferrofluids: A Time-Dependent Light-Scattering Investigation, Corneliu Rablau, Prem Vaishnava, Chandran Sudakar, Ronald Tackett, Gavin Lawes, Ratna Naik Nov 2008

Magnetic-Field-Induced Optical Anisotropy In Ferrofluids: A Time-Dependent Light-Scattering Investigation, Corneliu Rablau, Prem Vaishnava, Chandran Sudakar, Ronald Tackett, Gavin Lawes, Ratna Naik

Physics Publications

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (∼6nm) under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in …

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Coherent Control Of Nanomagnet Dynamics Via Ultrafast Spin Torque Pulses, Samir Garzon, Longfei Ye, Richard A. Webb, Thomas M. Crawford, Mark Covington, Shehzaad Kaka Nov 2008

Coherent Control Of Nanomagnet Dynamics Via Ultrafast Spin Torque Pulses, Samir Garzon, Longfei Ye, Richard A. Webb, Thomas M. Crawford, Mark Covington, Shehzaad Kaka

Faculty Publications

We demonstrate reliable manipulation of the magnetization dynamics of a precessing nanomagnet by precisely controlling the spin transfer torque on the subnanosecond time scale. Using a simple pulse shaping scheme consisting of two ultrafast spin torque pulses with variable amplitudes and delay, we demonstrate coherent control over the precessional orbits and the ability to tune the switching probability of a nanomagnet at room temperature and 77 K. Our measurements suggest that appropriately shaped spin transfer can be used to efficiently manipulate the orientation of a free layer nanomagnet, thus providing an alternative for spin torque driven spintronic devices.

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The Effect Of Clustering On The Uncertainty Of Differential Reflectivity Measurements, A. R. Jameson, A. B. Kostinski Nov 2008

The Effect Of Clustering On The Uncertainty Of Differential Reflectivity Measurements, A. R. Jameson, A. B. Kostinski

Department of Physics Publications

One of the most important avenues of recent meteorological radar research is the application of polarization techniques to improve radar rainfall estimation. A keystone in many of these methods is the so-called differential reflectivity ZDR, the ratio of the reflectivity factor ZH at horizontal polarization backscattered from a horizontally polarized transmission to that corresponding to a vertically polarized transmission ZV. For such quantitative applications, it is important to understand the statistical accuracy of observations of ZDR. The underlying assumption of all past estimations of meteorological radar uncertainties is that the signals obey Rayleigh …

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State Of Polarization Of A Stochastic Electromagnetic Beam In An Optical Resonator, Olga Korotkova, Min Yao, Yangjian Cai, Halil T. Eyyuboglu, Yahya Baykal Nov 2008

State Of Polarization Of A Stochastic Electromagnetic Beam In An Optical Resonator, Olga Korotkova, Min Yao, Yangjian Cai, Halil T. Eyyuboglu, Yahya Baykal

Physics Articles and Papers

On the basis of the unified theory of coherence and polarization, we investigate the behavior of the state of polarization of a stochastic electromagnetic beam in a Gaussian cavity. Formulations both in terms of Stokes parameters and in terms of polarization ellipse are given. We show that the state of polarization stabilizes, except in the case of a lossless cavity, after several passages between the mirrors, exhibiting monotonic or oscillatory behavior depending on the parameters of the resonator. We also find that an initially (spatially) uniformly polarized beam remains nonuniformly polarized even for a large number of passages between the …

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Regulating Self-Organizing Nanostructures Via External Mechanism, Jiangyu Li, Q. G. Du, Stephen Ducharme Nov 2008

Regulating Self-Organizing Nanostructures Via External Mechanism, Jiangyu Li, Q. G. Du, Stephen Ducharme

Stephen Ducharme Publications

Self-organizing nanostructures are ubiquitous in both natural and synthetic materials. They are not only appealing scientifically, by revealing the intrinsic atomic and molecular interactions that might be difficult to detect otherwise, but may also hold the key for the development of novel functional structures and devices. For their technological potential to be fully realized, the size, morphology, and distribution of the self-organizing nanostructures must be regulated. In this paper, we investigate the principles under which the self-organizing nanostructures can be regulated via external mechanisms. Using nanomesa and nanowell formation in polyvinylidene fluoride trifluoroethylene copolymer film as an example, we demonstrate …

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