Physical Sciences and Mathematics Commons^™

Measurement Of Single- And Double-Spin Asymmetries In Deep Inelastic Pion Electroproduction With A Longitudinally Polarized Target, H. Avakian, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We report the first measurement of the transverse momentum dependence of double-spin asymmetries in semi-inclusive production of pions in deep-inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Jefferson Lab (JLab). Modulations of single spin asymmetries over the azimuthal angle between lepton scattering and hadron production planes φ have been measured over a wide kinematic range in Bjorken x and virtual photon squared four-momentum Q². A significant nonzero sin2φ single spin asymmetry was observed for the first time indicating strong spin-orbit …

Comparative Study Of Field Enhancement Between Isolated And Coupled Metal Nanoparticles: An Analytical Approach, Greg Sun, Jacob B. Khurgin

Physics Faculty Publications

We present an analytical model that takes into account the coupling between the surface plasmon modes in complex metal nanostructures. We apply this model to evaluate the field enhancement in the gap of two coupled Au metal spheres embedded in GaN dielectric and compare the result with that obtained by the single sphere. The results show additional improvement can be obtained in the gap depending on the width of the gap. This approach offers a clear physical insight for the enhancement and a straightforward method for optimization.

Sources Of The Radio Background Considered, Jack Singal, L. Stawarz, A. Lawrence, V. Petrosian

Physics Faculty Publications

We investigate different scenarios for the origin of the extragalactic radio background. The surface brightness of the background, as reported by the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission 2 (ARCADE 2) collaboration, is several times higher than that which would result from currently observed radio sources. We consider contributions to the background from diffuse synchrotron emission from clusters and the intergalactic medium, previously unrecognized flux from low-surface-brightness regions of radio sources and faint point sources below the flux limit of existing surveys. By examining radio source counts available in the literature, we conclude that most of the radio …

Tensor Correlations Measured In 3He(E,E',Pp)N, H. Baghdasaryan, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We have measured the ³He(e, e', pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p_tot. For pair relative momenta between 0.3 and 0:5 GeV / c, the ratio is very small at low p_tot and rises to approximately 0.5 at large p_tot. This …

Synthesis Of Mild–Hard Aao Templates For Studying Magnetic Interactions Between Metal Nanowires, Jin-Hee Lim, Aurelian Rotaru, Seong-Gi Min, Leszek Malkinski, John B. Wiley

Physics Faculty Publications

The sequential application of mild and hard anodization techniques in the fabrication of porous aluminamembranes allows one to decrease the number of continuous pores in anodized aluminium oxide (AAO) templates. Initially, standard mild anodization techniques were used to create porous templates with 100 nm interpore distances and 70 nm pore diameters. Hard anodization treatment on the same membrane then produced interpore distances of about 265 nm with diameters of 110 nm. At the interface between the two anodization steps, many of the mild-side pores were terminated to create a mild–hard membrane (Mi–Ha AAO) where the functional interpore distances were 200–300 …

Defects At Oxygen Plasma Cleaned Zno Polar Surfaces, Y. F. Dong, Z-Q. Fang, David C. Look, Daniel R. Doutt, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson

Physics Faculty Publications

Depth-resolved cathodoluminescence spectroscopy (DRCLS) reveals the evolution of surface and near surface defects at polar surfaces with remote oxygen plasma (ROP) treatment. Furthermore, this evolution exhibits significant differences that depend on surface polarity. ROP decreased the predominant 2.5 eV defect emission related to oxygen vacancies on the O face, while creating a new 2.1 eV defect emission on the Zn face that increases with ROP time. The surface-located 2.1 eV emission correlates with carrier profiles from capacitance-voltage measurements and a shift of the E3 trap to higher binding energy from deep level transient spectroscopy (DLTS). This result suggests that ROP …

Tensor Correlations Measured In 3he(E,E' Pp)N, H. Baghdasaryan, L. B. Weinstein, J. M. Laget, K. P. Adhikarii, M. Aghasyan, M. Amarian, M. Anghinolfi, H. Avakian, J. Ball, M. Battaglieri, R. P. Bennett, S. Bültmann, G. E. Dodge, C. E. Hyde, A. Klein, S. E. Kuhn, M. Mayer, C. Nepali, F. Sabatié, H. Seraydaryan, Z. W. Zhao

Physics Faculty Publications

We have measured the ³He(e,e' pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p_tot. For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low p_tot and rises to approximately 0.5 at large ptot. This shows the dominance of tensor over …

Cosmology With Torsion: An Alternative To Cosmic Inflation, Nikodem Poplawski

Physics Faculty Publications

We propose a simple scenario which explains why our Universe appears spatially flat, homogeneous and isotropic. We use the Einstein–Cartan–Kibble–Sciama (ECKS) theory of gravity which naturally extends general relativity to include the spin of matter. The torsion of spacetime generates gravitational repulsion in the early Universe filled with quarks and leptons, preventing the cosmological singularity: the Universe expands from a state of minimum but finite radius. We show that the dynamics of the closed Universe immediately after this state naturally solves the flatness and horizon problems in cosmology because of an extremely small and negative torsion density parameter,Ω_S≈− …

Cosmic Microwave Background Constraints On Cosmological Models With Large-Scale Isotropy Breaking, Haoxuan Zheng, Emory F. Bunn

Physics Faculty Publications

Several anomalies appear to be present in the large-angle cosmic microwave background anisotropy maps of the Wilkinson Microwave Anisotropy Probe, including the alignment of large-scale multipoles. Models in which isotropy is spontaneously broken (e.g., by a scalar field) have been proposed as explanations for these anomalies, as have models in which a preferred direction is imposed during inflation. We examine models inspired by these, in which isotropy is broken by a multiplicative factor with dipole and/or quadrupole terms. We evaluate the evidence provided by the multipole alignment using a Bayesian framework, finding that the evidence in favor of the model …

Formulation Of The Dutch Atmospheric Large-Eddy Simulation (Dales) And Overview Of Its Applications, Thijs Heus, C. C. Van Heerwaarden, Harmen J.J. Jonker, A. Pier Siebesma, S. Axelsen, K. Van Den Dries, O. Geoffroy, A. F. Moene, D. Pino, S. R. De Roode, J. Vilà-Guerau De Arellano

Physics Faculty Publications

The current version of the Dutch Atmospheric Large-Eddy Simulation (DALES) is presented. DALES is a large-eddy simulation code designed for studies of the physics of the atmospheric boundary layer, including convective and stable boundary layers as well as cloudy boundary layers. In addition, DALES can be used for studies of more specific cases, such as flow over sloping or heterogeneous terrain, and dispersion of inert and chemically active species. This paper contains an extensive description of the physical and numerical formulation of the code, and gives an overview of its applications and accomplishments in recent years.

Deep Traps In Algan/Gan Heterostructures Studied By Deep Level Transient Spectroscopy: Effect Of Carbon Concentration In Gan Buffer Layers, Z-Q. Fang, B. Claflin, David C. Look, D. S. Green, R. Vetury

Physics Faculty Publications

Electrical properties, including leakage currents, threshold voltages, and deep traps, of AlGaN/GaN heterostructure wafers with different concentrations of carbon in the GaN buffer layer, have been investigated by temperature dependent current-voltage and capacitance-voltage measurements and deep level transient spectroscopy (DLTS), using Schottky barrier diodes (SBDs). It is found that (i) SBDs fabricated on the wafers with GaN buffer layers containing a low concentration of carbon (low-[C] SBD) or a high concentration of carbon (high-[C] SBD) have similar low leakage currents even at 500 K; and (ii) the low-[C] SBD exhibits a larger (negative) threshold voltage than the high-[C] SBD. Detailed …

Mechanochemistry Of Hexagonal Boron Nitride: 1. Destruction And Amorphization During Mechanical Treatment, A. N. Streletskii, D. G. Permenov, Kiril A. Streletzky, B. B. Bokhonov, A. V. Leonov

Physics Faculty Publications

The regularities of the mechanical activation of hexagonal boron nitride are analyzed using the X-ray diffraction, IR spectroscopy, transmission electron microscopy, dynamic light scattering, and adsorption methods. At the initial state of mechanical activation, the main process is material destruction. At this stage, the specific surface area increases to 400 m2/g and crystallographically oriented nanosized needles are formed. At the same time, boron nitride crystal structure is disordered with an increase in interplanar distance d(002). The disordering is assumed to be due to a shift along planes (001). At a specific dose of supplied mechanical energy above 6–8 kJ/g, the …

Absorption Of The Ω And Φ Mesons In Nuclei, M. Wood, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

Because of their long lifetimes, the ω and φ mesons are the ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. During the E01-112 experiment at the Thomas Jefferson National Accelerator Facility, the mesons were photoproduced from ²H, C, Ti, Fe, and Pb targets. This Letter reports the first measurement of the ratio of nuclear transparencies for the e⁺e^- channel. The ratios indicate larger in-medium widths compared with what have been reported in other reaction channels. The absorption of the ω meson is stronger than that …

Differential Cross Sections And Recoil Polarizations For The Reaction Γp→K+Σ0, B. Dey, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

High-statistics measurements of differential cross sections and recoil polarizations for the reaction γp → K⁺Σ⁰ have been obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.69 to 2.84 GeV, with an extensive coverage in the K⁺ production angle. Independent measurements were made using the K⁺pπ⁻(γ) and K⁺p(π⁻, γ ) final-state topologies, and were found to exhibit good agreement. Our differential cross sections show good agreement with earlier CLAS, SAPHIR, and LEPS results, while offering better statistical precision and …

Differential Cross Sections And Recoil Polarizations For The Reaction Γp→K+Σ0, B. Dey, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

High-statistics measurements of differential cross sections and recoil polarizations for the reaction γp → K⁺Σ⁰ have been obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass energies ( √s) from 1.69 to 2.84 GeV, with an extensive coverage in the K⁺ production angle. Independent measurements were made using the K⁺pπ⁻(γ) and K⁺p(π⁻, γ) final-state topologies, and were found to exhibit good agreement. Our differential cross sections show good agreement with earlier CLAS, SAPHIR, and LEPS results, while offering better …

The Mechanical Stress–Strain Properties Of Single Electrospun Collagen Type I Nanofibers, Christine C. Helms, Corentin Coulais, Martin Guthold

Physics Faculty Publications

Knowledge of the mechanical properties of electrospun fibers is important for their successful application in tissue engineering, material composites, filtration and drug delivery. In particular, electrospun collagen has great potential for biomedical applications due to its biocompatibility and promotion of cell growth and adhesion. Using a combined atomic force microscopy (AFM)/optical microscopy technique, the single fiber mechanical properties of dry, electrospun collagen type I were determined. The fibers were electrospun from a 80 mg ml⁻¹ collagen solution in 1,1,1,3,3,3-hexafluro-2-propanol and collected on a striated surface suitable for lateral force manipulation by AFM. The small strain modulus, calculated from three-point …

Highly Conductive Zno Grown By Pulsed Laser Deposition In Pure Ar, Robin C. Scott, Kevin D. Leedy, Burhan Bayraktaroglu, David C. Look, Yong-Hang Zhang

Physics Faculty Publications

Ga-doped ZnO was deposited by pulsed laser deposition at 200 °C on SiO₂/Si, Al₂O₃, or quartz in 10 mTorr of pure Ar. The as-grown, bulk resistivity at 300 K is 1.8×10⁻⁴ Ω cm, three-times lower than that of films deposited at 200 °C in 10 mTorr of O₂ followed by an anneal at 400 °C in forming gas. Furthermore, depth uniformity of the electrical properties is much improved. Mobility analysis shows that this excellent resistivity is mostly due to an increase in donor concentration, rather than a decrease in acceptor concentration. Optical …

Particle-Γ Spectroscopy Of The (P,D-Γ)155Gd Reaction: Neutron Single-Quasiparticle States At N=91, J. M. Allmond, C. W. Beausang, J. O. Rasmussen, T. J. Ross, M. S. Basunia, L. A. Bernstein, D. L. Bleuel, W. Brooks, N. Brown, J. T. Burke, B. Darakchieva, K. Dudziak, K. E. Evans, P. Fallon, H. B. Jeppesen, J. Leblanc, S. R. Lesher, M. A. Mcmahan, D. A. Meyer, L. Phair, N. D. Scielzo, S. R. Stroberg, M. Wiedeking

Physics Faculty Publications

A segmented Si telescope and HPGe array is used to study the ¹⁵⁶Gd(p,d-γ)¹⁵⁵Gd direct reaction by d-γ and d-γ-γ coincidence measurements using 25-MeV protons. The present investigation is the first time that this N = 91 nucleus and the N = 90 region—which is known for a rapid change from vibrational to rotational character, several low-lying 0⁺ states in the even-even nuclei, and large Coriolis (ΔΩ = 1) plus ΔN = 2 mixing in the even-odd nuclei—have been studied by particle-γ coincidence following a direct reaction with light ions. Gamma-ray energies and branches, …

Debye Series For Light Scattering By A Coated Nonspherical Particle, Feng Xu, James A. Lock

Physics Faculty Publications

By using the extended boundary condition method, the Debye series is developed for light scattered by a coated nonspherical particle in order to interpret the angular dependence of the scattered intensity in terms of various physical processes. Numerical calculations are performed to study the influence of the coating thickness and the ellipticity of a coated spheroid on the angular position of the alpha and beta primary rainbows, which are produced by partial waves experiencing one internal reflection. The hyperbolic umbilic focal section is demonstrated and is analyzed for both the alpha and the beta rainbows.

Magnetotransport Properties Of High Quality Co:Zno And Mn:Zno Single Crystal Pulsed Laser Deposition Films: Pitfalls Associated With Magnetotransport On High Resistivity Materials, John S. Mccloy, Joseph V. Ryan, Timothy C. Droubay, Tiffany C. Kasper, Scott A. Chambers, David C. Look

Physics Faculty Publications

The electrical resistivity values for a series of pure and doped (Co, Mn, Al) ZnO epitaxial films grown by pulsed laser deposition were measured with equipment designed for determining the direct current resistivity of high resistance samples. Room-temperature resistances ranging from 7 x 10(1) to 4 x 10(8) Omega/sq were measured on vacuum-reduced cobalt-doped ZnO, (Al,Co) co-doped ZnO, pure cobalt-doped ZnO, Mn-doped ZnO, and undoped ZnO. Using a four-point collinear geometry with gold spring-loaded contacts, resistivities were measured from 295 to 5 K for resistances of < approximately 10(12) Omega/sq. In addition, magnetoresistance and Hall effect were measured as a function of temperature for select samples. Throughout the investigation, samples were also measured on commercially available instrumentation with good agreement. The challenges of transport measurements on high resistivity samples are discussed, along with some offered solutions to those challenges.

Surface Roughness Effect On Ultracold Neutron Interaction With A Wall And Implications For Computer Simulations, Albert Steyerl, Surendra S. Malik, A. M. Desai, Charles Kaufman

Physics Faculty Publications

We review the diffuse scattering and the loss coefficient in ultracold neutron reflection from slightly rough surfaces, report a surprising reduction in loss coefficient due to roughness, and discuss the possibility of transition from quantum treatment to ray optics. The results are used in a computer simulation of neutron storage in a recent neutron lifetime experiment that reported a large discrepancy of neutron lifetime with the current particle data value. Our partial reanalysis suggests the possibility of systematic effects that were not included in this publication.

Exotic Smoothness In Four Dimensions And Euclidean Quantum Gravity, Christopher L. Duston

Physics Faculty Publications

In this paper we calculate the effect of the inclusion of exotic smooth structures on typical observables in Euclidean quantum gravity. We do this in the semiclassical regime for several gravitational free-field actions and find that the results are similar, independent of the particular action that is chosen. These are the first results of their kind in dimension four, which we extend to include one-loop contributions as well. We find these topological features can have physically significant results without the need for additional exotic physics.

Carrier Dynamics Of Terahertz Emission Based On Strained Sige/Si Single Quantum Well, K. M. Hung, J.-Y. Kuo, C. C. Hong, Greg Sun, R. A. Soref

Physics Faculty Publications

We report analysis of the carrier distribution during terahertz emission process with carrier–phonon interaction based on p-doped strained SiGe/Si single quantum-well. The results of this analysis show that a considerable number of carriers can penetrate the phonon wall to become “hot” carriers on an approximately picosecond timescale. These hot carriers relax after the removal of the applied voltage, generating a “second” emission in the measurement. This investigation provides an understanding of the carrier dynamics of terahertz emission and has an implication for the design of semiconductor terahertz emitters.

Bandwidth In Bolometric Interferometry, R. Charlassier, Emory F. Bunn, J.-Ch. Hamilton, J. Kaplan, S. Malu

Physics Faculty Publications

Context. Bolometric interferometry is a promising new technology with potential applications to the detection of B-mode polarization fluctuations of the cosmic microwave background (CMB). A bolometric interferometer will have to take advantage of the wide spectral detection band of its bolometers to be competitive with imaging experiments. A crucial concern is that interferometers are assumed to be significantly affected by a spoiling effect known as bandwidth smearing.

Aims. We investigate how the bandwidth modifies the work principle of a bolometric interferometer and affects its sensitivity to the CMB angular power spectra.

Methods. We obtain analytical expressions for …

In Search Of The Elusive Lossless Metal, Jacob B. Khurgin, Greg Sun

Physics Faculty Publications

We show that when one looks beyond the Drude model of metal conductivity, the metals that may be extremely lossy for low frequency electromagnetic waves can become perfectly lossless in the mid-IR region or higher, while retaining the essential metallic characteristic of negative permittivity even at those frequencies. We identify that the transition to the lossless regime occurs when the interatomic distances in the lattice exceed certain values, typically a factor of two larger than those occurring in nature. We believe that advances in nanoassembly may render lossless metals feasible with revolutionary implications for the fields of plasmonics and metamaterials.

Strength And Failure Of Fibrin Fiber Branch Points, Christine C. Helms, E. A. Sparks, C. Der Laughian, Martin Guthold

Physics Faculty Publications

Blood clots form rapidly in the event of vascular injury, to prevent blood loss. They may also form in undesired places, causing heart attacks, strokes, and other diseases. Blood clots can rupture, and fragments of the clotmay lodge in distal blood vessels, causing, for example, ischemic strokes or embolisms. Thus, there has been great interest in understanding the mechanical behavior and failure mechanisms of blood clots and their constituents. To develop a mechanically realistic model of a blood clot, knowledge of the mechanical properties of its constituents is required. The major structural component providing mechanical strength to the clot is …

The Mechanical Properties Of Single Fibrin Fibers, W. Liu, Christine C. Helms, E. A. Sparks, Martin Guthold

Physics Faculty Publications

Background:

Blood clots perform the mechanical task of stemming the flow of blood.

Objectives:

To advance understanding and realistic modeling of blood clot behavior we determined the mechanical properties of the major structural component of blood clots, fibrin fibers.

Methods:

We used a combined atomic force microscopy (AFM)/fluorescence microscopy technique to determine key mechanical properties of single crosslinked and uncrosslinked fibrin fibers.

Results and conclusions:

Overall, full crosslinking renders fibers less extensible, stiffer, and less elastic than their uncrosslinked counterparts. All fibers showed stress relaxation behavior (time-dependent weakening) with a fast and a slow relaxation time, 2 and 52 s. …

Nonlinear Photoacoustics For Measuring The Nonlinear Optical Absorption Coefficient, Chandra S. Yelleswarapu, Sri-Rajasekhar Kothapalli

Physics Faculty Publications

We report a novel photoacoustic Z-scan (PAZ-scan) technique that combines the advantages offered by the conventional Z-scan method and the sensitivity of the photoacoustic detection. The sample is scanned through the focused laser beam and the generated photoacoustic signal is recorded using a 10 MHz focused ultrasound transducer. Since the signal strength is directly proportional to the optical absorption, PAZ-scan displays nonlinear behavior depicting the nonlinear optical absorption of the material. Among many advantages, our experiments on mouse blood show that PAZ-scan can potentially be used as a standard technique to calibrate contrast agents used in theranostics in general and …

Debye Series For Light Scattering By A Spheroid, Feng Xu, James A. Lock, Cameron Tropea

Physics Faculty Publications

The Debye series is developed for electromagnetic scattering by a spheroid in order to decompose the far-zone fields into various physical processes. The geometrical rainbow angle and supernumerary spacing parameter are determined from the Debye intensity by fitting the results to an Airy function and comparing them to their assumed values in ray optics and Airy theory, respectively. Eccentricity-related scattering phenomena including the rainbow's angular shift, the disappearance of the rainbow, and the rainbow-enhanced glory are quantitatively demonstrated and analyzed. (c) 2010 Optical Society of America

Debye Series For Light Scattering By A Nonspherical Particle, Feng Xu, James A. Lock, Gérard Gouesbet

Physics Faculty Publications

The Debye series is developed for scattering of light by a homogeneous nonspherical particle to interpret the angular dependence of the scattered intensity in terms of various physical processes. In contrast to the previously developed Debye series for several regularly shaped particles that mirror the orthogonal curvilinear coordinate system where the variable-separation method can be applied, we develop and verify the Debye series in a coordinate-independent way using the extended boundary condition method. Verification computations are made for an oblate spheroidal water droplet of equivalent-volume sphere radius 10 mu m.