Physical Sciences and Mathematics Commons^™

Measuring Boltzmann's Constant Using Video Microscopy Of Brownian Motion, Paul Nakroshis, Matthew Amoroso, Jason Legere, Christian Smith

USM Physics Program

Boltzmann's constant k was measured by observing the Brownian motion of polystyrene spheres in water. An inexpensive monochrome CCD camera and video card were used to create a video of the spheres' motion. After preprocessing the images, custom routines were used to examine the video and to identify and track the particles from one frame to the next. From the mean squared displacement of the particles versus time, we extracted the value of k from the slope, assuming that the drag force on an individual sphere is well modeled by Stokes' law.

Comparative Study Of Embedding Methods, C. J. Cellucci, Alfonso M. Albano, P. E. Rapp

Physics Faculty Research and Scholarship

Embedding experimental data is a common first step in many forms of dynamical analysis. The choice of appropriate embedding parameters (dimension and lag) is crucial to the success of the subsequent analysis. We argue here that the optimal embedding of a time series cannot be determined by criteria based solely on the time series itself. Therefore we base our analysis on an examination of systems that have explicit analytic representations. A comparison of analytically obtained results with those obtained by an examination of the corresponding time series provides a means of assessing the comparative success of different embedding criteria. The …

Comment On "Performance Of Different Synchronization Measures In Real Data: A Case Study On Electroencephalographic Signals", R. B. Duckrow, Alfonso M. Albano

Physics Faculty Research and Scholarship

Quian Quiroga [Phys. Rev. E 65, 041903 (2002)] reported a similar performance of several linear and nonlinear measures of synchronization when applied to the rat electrocorticogram (ECoG). However, they found that the mutual information measure did not produce robust estimates of synchronization when compared to other measures. We reexamined their data using a histogram method with adaptive partitioning and found the mutual information to be a useful measure of regional ECoG interdependence.

Vertical Nanowire Transistor In Flexible Polymer Foil, Jie Chen, Rolf Könenkamp

Physics Faculty Publications and Presentations

Fabrication and operation of a vertical nanowire field-effect transistor is reported. The device is prepared by growing vertical wires in the cylindrical pores of a polymer foil stack. The nanowirediameter is approximately 100 nm, the packing density up to 10⁸ cm⁻². The polymer foil stack consists of two polymer layers and an intermediate metal layer. Cylindrical holes are prepared in this stack by using fast ion irradiation and subsequent etching. Well-defined cylindrical openings with diameters between 50 and 150 nm are obtained. The semiconductor growth involves electrodeposition of the p-type quaternary compound CuSCN. Electrical measurements on first devices show transistor …

Femtosecond Phase-Coherent Two-Dimensional Spectroscopy, Peifang Tian, Dorine Keusters, Yoshifumi Suzaki, Warren S. Warren

Peifang Tian

Femtosecond phase-coherent two-dimensional (2D) spectroscopy has been experimentally demonstrated as the direct optical analog of 2D nuclear magnetic resonance. An acousto-optic pulse shaper created a collinear three-pulse sequence with well-controlled and variable interpulse delays and phases, which interacted with a model atomic system of rubidium vapor. The desired nonlinear polarization was selected by phase cycling (coadding experimental results obtained with different interpulse phases). This method may enhance our ability to probe the femtosecond structural dynamics of macromolecules.

High Pressure Effects On Electron Transport And Structure Of Colossal Magnetoresistive Materials, Congwu Cui

Dissertations

Pressure effects on the electronic, magnetic properties and structure of several typical colossal magnetoresistive manganites, La_0.60Y_0.07Ca_0.33MnO₃, Pr_1-xCa_xMn0₃ (X = 0.25, 0.30, 0.35), Nd_1-xSr_xMnO₃ (x = 0.45, 0.50), were explored through high pressure resistivity and structure measurements. It was shown that pressure up to ~7 GPa induces more complicated charge, spin and lattice state changes than in the low pressure range explored previously. In La_0.60Y_0.07Ca_0.33MnO₃, pressure induces a local atomic structure transformation at a critical …

Nonlinear Optical Properties Of Novel Nanostructured Ion Implanted Laser Ablated Silicon Using Femtosecond Pulse Excitation, Elaine Nicole Lalanne

Dissertations

The study of the nonlinear optical properties of novel nanostructured ion implanted and laser ablation of Silicon is motivated by the need for materials that exhibit large values of the real part of the third order nonlinear susceptibility (χ⁽³⁾_Re). This property is essential for light controlled phase or refractive index modulation at low power, where the optical properties are used for optical switching devices. Previous nanosecond (ns) measurements indicated values of-2.8 x 10 ^-5; esu ( γ = 532 nm) for χ⁽³⁾_Re.

The characterization of nonlinear optical properties of the samples was studied …

Application Of Adaptive Optics To The Spectroscopic Investigation Of Small-Scale Solar Structures, Klaus Hartkorn

Dissertations

We study bright points, umbral dots and the G-band using a two-dimensional spectrometer and an Adaptive Optics system, which allows us to record high-resolution dopplergrams and residual intensity images. We find evidence that bright points are smaller than 120 km in diameter. Bright points are situated exclusively in regions of enhanced G-band brightness and do not show a change in their shape or a displacement in their position of more than 120 km horizontally over a height range from 0 km to 320 km above photospheric level T = 1. We do not find velocity differences of more than 100 …

Two-Active Electron Approach To Multi-Electron Systems In Intense Ultrashort Laser Pulses: Application To Li–, G. Lagmago Kamta, Anthony F. Starace

Anthony F. Starace Publications

The interaction of Li^– with an ultrashort intense laser pulse is investigated by solving the time-dependent Schrödinger equation (TDSE) in the dipole approximation using a two-active electron approach. We describe the numerical solution of the TDSE and give a more detailed presentation of a technique for obtaining angular distributions for double ionization by intense ultrashort laser pulses. We show how selection rules observed in the angular distributions for double ionization by an intense laser field can be derived from the symmetry properties of the wave function. In an attempt to elucidate the mechanisms for double ionization in the multiphoton …

The Babar Mini, Duncan Brown

Physics - All Scholarship

BaBar has recently deployed a new event data format referred to as the Mini. The Mini uses efficient packing and aggressive noise suppression to represent the average reconstructed BaBar event in under 7 KBytes. The Mini packs detector information into simple transient data objects, which are then aggregated into roughly 10 composite persistent objects per event. The Mini currently uses Objectivity persistence, and it is being ported to use Root persistence. The Mini contains enough information to support detailed detector studies, while remaining small and fast enough to be used directly in physics analysis. Mini output is customizable, allowing users …

Study Of Scalar Mesons And Related Radiative Decays, Joseph Schechter, Deirdre Black, Masayasu Harada

Physics - All Scholarship

After a brief review of the puzzling light scalar meson sector of QCD, a brief summary will be given of a paper concerning radiative decays involving the light scalars. There, a simple vector meson dominance model is constructed in an initial attempt to relate a large number of the radiative decays involving a putative scalar nonet to each other. As an application it is illustrated why a_0(980)-f_0(980) mixing is not expected to greatly alter the f_0/a_0 production ratio for radiative \phi decays.

Unlv Transmutation Research Program Proposal Year Iii: Design And Evaluation Of Processes For Fuel Fabrication, Georg F. Mauer

Fuels Campaign (TRP)

The objective of this project is the design and evaluation of manufacturing processes for transmuter fuel fabrication. The large-scale deployment of remote fabrication and refabrication processes will be required for all transmutation scenarios. Current program emphasis is on a five-year effort to determine the feasibility of transmutation as a technology to limit the need for repository storage of spent commercial fuel. The evaluation of the fabrication processes will create a decision support data base to document design, operations, and costs. Fabrication processes required for different fuel types differ in terms of equipment types, throughput, and cost. Differential cost Implications of …

Spacecraft Charging Research, Eric Crapo

Senior Theses and Projects

No abstract provided.

Highly Oriented Nonepitaxially Grown L10 Fept Films, M.L. Yan, Nathan D. Powers, David J. Sellmyer

David Sellmyer Publications

A method of preparing nonepitaxially grown, highly textured L1₀ FePt thin films is described. A nearly perfect (001) texture was obtained by direct deposition of FePt films on Corning 7059 glass substrates and subsequent rapid thermal annealing. The ordering and orientation of the L1₀-phase FePt grains were controlled by the initial as-deposited film structure, and also by the annealing process. Magnetic measurements reveal large perpendicular anisotropy for these (001) textured films. The substrates and processes used for nonepitaxial growth of L1₀ ordered FePt films are much more compatible with practical applications than those …

Studies Of Magnetic Properties Of The Stabilizing Layer For Synthetic Antiferromagnetically Coupled Media, Z.S. Shan, L. Bitman, S.S. Malhotra, D. Stafford, B. Bian, G. Bertero

David Sellmyer Publications

The effects of the stabilizing layer thickness and its temperature dependence on the magnetic properties were investigated experimentally. These results were used to analyze the magnetic structure of the thin stabilizing layer and its effect on the coupling strength, which is valuable for improving the design of synthetic antiferromagnetically coupled media.

Structure And Magnetic Properties Of Sputtered Hard/Soft Multilayer Magnets, W. Liu, Z.D. Zhang, J. Ping Liu, B.Z. Cui, X.K. Sun, J. Zhou, David J. Sellmyer

David Sellmyer Publications

The films with HM = (Pr,Dy)(Fe,Co,Nb,B) _5.5 and SM=Fe, FeCo were prepared by sputtering and subsequent heat treatment. The coercivity of Ti-buffered (Pr,Dy)(Fe,Co,Nb,B) _5.5 single-layer film with 320 nm thickness is as large as 18.8 kOe at room temperature. X-ray diffraction results reveal that the Pr₂Fe₁₄B-type phase is randomly oriented in almost all the multilayer films. For the multilayers of Ti(30 nm)/[HM(16 nm)Fe(x nm)]×20/Ti(30 nm)/Si(substrate), the remanence increases and the coercivity decreases with the addition of Fe content, in comparison with the results of the single-layer film and the maximum energy product of 14.8 MGOe is …

Exchange Through Nonmagnetic Insulating Matrix, Ralph Skomski, Arti Kashyap, Y. Quiang, David J. Sellmyer

David Sellmyer Publications

Exchange interactions between hard-magnetic particles in a nonmagnetic matrix are investigated by model calculations. A Landau–Ginzburg approach is developed to describe the net exchange interactions between spheres of arbitrary diameters. Introducing cylindrical coordinates and integrating over the surfaces of the adjacent spheres yields an exchange coupling which decreases with a decay length depending on interatomic exchange, intra-atomic exchange, and temperature. Typically, the decay length does not exceed a few interatomic distances. The decay is exponential but also contains a prefactor depending on the surface curvature of the grains. It increases with decreasing curvature, but this dependence is only a small …

Copt Hard Magnetic Nanoparticle Films Synthesized By High Temperature Chemical Reduction, Yucheng Sui, Lanping Yue, Ralph Skomski, Xingzhong Li, J. Zhou, David J. Sellmyer

David Sellmyer Publications

The synthesis of hard-magnetic CoPt nanoparticle films by hydrogen reduction of Co nitride and Pt chloride mixture is reported. Thin porous alumina films are adopted as the carrier of the initial aqueous solution and of the final reducing products of CoPt nanoparticles. It is found that chemical ordering of L₀–CoPt occurs above 400 °C. Partial phase transformation occurs in the alumina substrate when the treatment temperature is higher than 600 °C. The film coercivity increases with increasing annealing temperature and reaches a maximum value of 24.2 kOe when the reduction is carried out at 700 °C for 2 …

Magnetic Hysteresis Of Mechanically Alloyed Sm–Co Nanocrystalline Powders, J. Zhou, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

Mechanically alloyed Sm–Co powders and Sm₁₂ (Co,Cu,Ti) ₈₈ powders are investigated. X-ray diffraction patterns show that after annealing, structures of 2:7, 1:5, and 1:7 phases form. A room-temperature coercivity of 41 kOe was obtained in Sm₂Co₇ powders. Magnetic hysteresis was investigated by the method of δ m curves. Positive value δ m curves were obtained in Sm₂Co₇ and SmCo₅, while negative values were found in SmCo_7.3 and SmCo₈ indicating different magnetization reversal mechanisms. Nanocrystalline powders of Sm₁₂ (Co,Cu,Ti) ₈₈ with a mixture of 1:5 and 2:17 phases form …

Spin Structure At Nanojunctions And Constrictions, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

A micromagnetic Green-function approach is used to investigate the effect of nanojunctions, constraints, and other obstacles on spin-dependent conduction. Depending on geometry, the determination of the spin structure involves several types of Bessel functions. A common feature of the Green functions is the involvement of the domain-wall width of the main phase, which can be interpreted as the decay length of the magnetization perturbation away from the junction. This length is typically on the order of 10 nm and independent of the strength of the perturbation. Only the magnitude of the magnetization perturbation depends on the strength of the inhomogenity. …

Design And Analysis For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides: Quarterly Progress Report 2/16/03- 5/15/03, Yitung Chen, Randy Clarksean, Darrell Pepper

Fuels Campaign (TRP)

Progress continues on the analysis of casting and solidification of the melt into molds. Modeling results for constant pressure casting, which is more realistic, have been obtained and produce physically realistic results for flow that starts, flows, and then eventually stops as it enters the mold. Potential mass transfer modeling features (Lammuir’s law for example) are being studied to enhance the capabilities of a mass transfer in a detailed system model. Different parameters are being varied as part of a parametric study to evaluate factors that impact the flow of the melt into the molds. The ability to include the …

Equivalence Of Sweep-Rate And Magnetic-Viscosity Dynamics, Ralph Skomski, Roger D. Kirby, David J. Sellmyer

Roger Kirby Publications

The irreversible response of magnetic materials to magnetic fields of arbitrary time dependence is investigated by a master-equation approach. The magnetization reversal is expressed in terms of renormalized magnetization modes, and the resulting set of two-level master equations is solved by direct integration. The theory applies not only to linear energy-barrier laws but also to the physically more reasonable case where the activation energy is a nonlinear function of the applied field. Particular emphasis is on the relation between sweep-rate and magnetic-viscosity dynamics. Other regimes, such as oscillating magnetic fields, can be mapped onto sweep-rate dynamics. Magnetic-viscosity and sweep-rate experiments …

Giant Magnetoresistance Properties Of The La1-2xrxaxmno3 (R=Nd, A=Ca) Perovskites, Darshan C. Kundaliya, A. A. Tulapurkar, S. R. Shinde, R. Pinto, William B. Yelon, R. G. Kulkarni, S. K. Malik

Physics Faculty Research & Creative Works

The giant magneto resistive behavior of an antiferromagnetic insulator, LaMnO₃, was investigated by studying the effect of simultaneous substitution of Nd and Ca on the compound. the volume of unit cell decreased with increasing concentration of Nd/Ca. the changes in the temperature dependent resistivity, and ferromagnetic transition were observed with the increase in the compound series. the observing of metal-insulator transition at different temperatures, and magnetoresistance in the 2 T applied field were also recorded.

Finite-Temperature Spin Polarization In Half-Metallic Ferromagnets, Peter A. Dowben, Ralph Skomski

Peter Dowben Publications

The temperature dependence of the spin polarization of half-metallic ferromagnets is investigated. A unitary spinor transformation shows that the corresponding spin mixing goes beyond finite-temperature smearing of the Fermi level, leading to a nonzero density of states in the gap of the insulating spin channel. As a consequence, the resistance ratio of the two spin channels changes from infinity to some finite value and, in a strict sense, half-metallic ferromagnetism is limited to zero temperature. Bloch-type spin waves and crystal imperfections contribute to the density of states in the gap but only partly explain the pronounced changes at about 0.2 …

Magnetic Properties Of L10 Fept And Fept:Ag Nanocluster Films, Yinfan Xu, Zhiguang Sun, Y. Qiang, David J. Sellmyer

David Sellmyer Publications

A sputtering gas-aggregation technique has been used to prepare FePt and FePt:Ag nanocluster films. The cluster size was controlled in a range from 3 to 6 nm. FePt cluster films were directly deposited onto Si substrate; FePt:Ag cluster films were fabricated by depositing a FePt cluster layer between a Ag underlayer and overlayer. Nanostructure and magnetic properties of the samples were characterized by x-ray diffraction, transmission electron microscopy, and magnetometry. The high magnetic anisotropy L1₀ fct phase was realized in the films annealed at a temperature of 550 °C and above. The orientation of clusters is random. The …

Effects Of Rapid Thermal Annealing On Nanostructure, Texture And Magnetic Properties Of Granular Fept:Ag Films For Perpendicular Recording (Invited), Y. Shao, M.L. Yan, David J. Sellmyer

David Sellmyer Publications

We report effects of rapid thermal annealing on nanostructure, texture, and magnetic properties of granular FePt:Ag films. It was found that the orientations of FePt grains were dependent strongly on the as-deposited multilayer structure and the annealing processes. Through the control of the annealing processes, (001) textured L1₀ granular FePt:Ag films were obtained. Magnetic measurements revealed that saturation magnetization M_s, perpendicular coercivity H_c, and remanence ratio M_r/M_s, were also dependent on the annealing temperature, annealing time and Ag content. Perpendicular H_c values increased from 1.5 to 15 kOe …

Spin-Wave Modes In Magnetic Nanowires, Ralph Skomski, M. Chipara, David J. Sellmyer

David Sellmyer Publications

Spin-wave modes in magnetic transition-metal nanowires having diameters of about 10 nm and lengths on the order of 1 µm are investigated by model calculations. There are quasicontinuous modes with k vectors parallel to the wires axis and discrete modes with k vectors perpendicular to the wire axis. Due to the small cross section of the wires, the perpendicular modes can be ignored in many cases and the low-temperature behavior of the wires is quasi one-dimensional. Using an analytic approach and exploiting the analogy between micromagnetism and quantum mechanics it is shown that all spin-wave modes with k vectors parallel …

Recording Characteristics Of Perpendicular Magnetic Media With Cozrnb, Nifenb, And Exchange-Pinned Nifenb Soft Magnetic Underlayers, Min Zheng, Albert Chekanov, Geon Choe, Kenneth E. Johnson, Lan Gao, Sy_Hwang Liou

Sy-Hwang Liou Publications

The recording performance of perpendicular media with amorphous CoZrNb, nanocrystalline NiFeNb, and exchange-pinned FeMn/NiFeNb soft magnetic underlayers (SULs) has been studied. A method has been proposed to quantify the spike noises from the SUL. We found that media with higher permeability NiFeNb SULs showed 4 db higher signal-to-noise ratio than media with lower permeability CoZrNb SULs. The exchange-pinned NiFeNb SUL suppresses spike noise and offers good recording performance. Furthermore, the recording frequency dependence of dynamic coercivity (H_c) was strongly affected by the use of different SULs. The increase in dynamic H_c with linear density is negligibly …

Magnetotransport Properties Of Cro2 Films Down To Single-Grain Sizes, Lu Yuan, Y. Ovchenkov, Andrei Sokolov, C.-S. Yang, Bernard Doudin, Sy_Hwang Liou

Sy-Hwang Liou Publications

The magnetotransport properties of CrO₂ films down to single-grain sizes have been investigated. The magnetoresistance of highly grain oriented CrO₂ (100) films, deposited onto TiO₂ (100) substrates using a high pressure cell, has been measured in the temperature range of 1.5–300 K and in magnetic fields up to 6 T. The difference in the magnetoresistance at the low temperature of these samples is related to the value of the residual resistance ratio (RRR = R_{273 K}/R_{4.2 K}) of the samples. The negative magnetoresistance observed in some of these films is likely due …

Development Of Dose Coefficients For Radionuclides Produced In Spallation Neutron Sources, Phillip W. Patton

Transmutation Sciences Physics (TRP)

A research consortium comprised of representatives from several universities and national laboratories has been established as part of this on-going project to generate internal and external dose conversion coefficients for radionuclides produced in spallation neutron sources. Information obtained from this multi-year study will be used to support the siting and licensing of future accelerator-driven nuclear initiatives within the U.S. Department of Energy complex, including the Spallation Neutron Source (SNS) and the Advanced Fuel Cycle Initiative (AFCI) Projects. Determination of these coefficients will also fill data gaps for several hundred radionuclides that exist in Federal Guide Report No. 11 and in …