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Full-Text Articles in Physics

Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John Geddes Mar 2013

Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John Geddes

John B. Geddes

When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow ...


Incommensurate Spin Fluctuations In High-Transition Temperature Superconductors, Barrett Wells, Young Lee, Marc Kastner, Rebecca Christianson, Robert Birgeneau, Kazuyoshi Yamada, Yasuo Endoh, Gen Shirane Jul 2012

Incommensurate Spin Fluctuations In High-Transition Temperature Superconductors, Barrett Wells, Young Lee, Marc Kastner, Rebecca Christianson, Robert Birgeneau, Kazuyoshi Yamada, Yasuo Endoh, Gen Shirane

Rebecca J. Christianson

Neutron scattering experiments have revealed a fascinating interplay between the hole doping, the spin fluctuations, and the superconductivity of the cuprate superconductors. Recently, electrochemical techniques have been used to produce large single crystals of La2CuO4+ y, which has mobile oxygen dopants. Staging behavior of the excess oxygen has been demonstrated, and the low-energy spin fluctuations in stage 6 La2CuO4+ y have been measured. The spin fluctuations are incommensurate with the lattice and have spatial, energy, and temperature dependencies very much like those in La2− xSrxCuO4, with similar high transition temperature. This establishes the universality of the incommensurate spin fluctuations among ...


Structures And Incommensurate Spin Excitations In Excess Oxygen-Doped La2cuo4+Y, Robert Birgeneau, Rebecca Christianson, Yasuo Endoh, Marc Kastner, Young Lee, Gen Shirane, Barrett Wells, Kazuyoshi Yamada Jul 2012

Structures And Incommensurate Spin Excitations In Excess Oxygen-Doped La2cuo4+Y, Robert Birgeneau, Rebecca Christianson, Yasuo Endoh, Marc Kastner, Young Lee, Gen Shirane, Barrett Wells, Kazuyoshi Yamada

Rebecca J. Christianson

Over the past decade, we have studied in detail the low-energy spin fluctuations in :a2−xSrxCuO4 for xbetween 0 and 0.18. Our experiments, as well as those by others, have revealed a fascinating interplay between the hole doping, the static and dynamic spin fluctuations and superconductivity. Recently, using electrochemical techniques, we have learned how to produce large single crystals of La2CuO4+y which are relatively homogenous. In this latter system, the dopants are characterized by annealed rather than quenched disorder. Furthermore, we have demonstrated staging behavior of the excess oxygen analogous to staging in intercalated graphite. We have now ...


A Reduced Model Of Cavitation Physics For Use In Sonochemistry, Brian Storey, Andrew Szeri Jul 2012

A Reduced Model Of Cavitation Physics For Use In Sonochemistry, Brian Storey, Andrew Szeri

Brian Storey

Sonochemistry involves focusing acoustic energy through cavitation bubbles to increase chemical activity. The violent bubble collapses lead to temperatures of several thousand kelvin, which drive chemical reactions. In previous work, we gave a detailed computational model of a single bubble collapse, taking into account phase change, mass diffusion, heat diffusion and chemical reactions. All of these phenomena are important in determining the conditions at collapse. The present work involves development of a much simpler model that includes all the physics relevant to the determination of the reaction products. Comparisons with the more detailed computations are made; the reduced model is ...


Water Vapour, Sonoluminescence And Sonochemistry, Brian Storey, Andrew Szeri Jul 2012

Water Vapour, Sonoluminescence And Sonochemistry, Brian Storey, Andrew Szeri

Brian Storey

Sonoluminescence is the production of light from acoustically forced bubbles; sonochemistry is a related chemical processing technique. The two phenomena share a sensitive dependence on the liquid phase. The present work is an investigation of the fate and consequences of water vapour in the interior of strongly forced argon micro–bubbles. Due to the extreme nonlinearity of the volume oscillations, excess water vapour is trapped in the bubble during a rapid inertial collapse. Water vapour is prevented from exiting by relatively slow diffusion and non–equilibrium condensation at the bubble wall. By reducing the compression heating of the mixture and ...


Temperature Distribution In An Oscillatory Flow With A Sinusoidal Wall Temperature, Eduardo Ramos, Brian Storey, Fernando Sierra, Raul Zuniga, Andriy Avramenko Jul 2012

Temperature Distribution In An Oscillatory Flow With A Sinusoidal Wall Temperature, Eduardo Ramos, Brian Storey, Fernando Sierra, Raul Zuniga, Andriy Avramenko

Brian Storey

The temperature field generated by an oscillatory boundary layer flow in the presence of a wall with a sinusoidal temperature distribution is analyzed. A linear perturbation method is used to find closed form analytical solutions for the temperature field when the amplitude of the velocity oscillation is small. The analytical solutions only consider long-time behavior when the temperature fields oscillate with the frequency of the flow. The structure of the equation that governs the temperature correction due to convection is similar to that of diffusive waves with the solution consisting of traveling or standing waves. The temperature distribution is also ...


Nonextensive Statistical Mechanics For Rotating Quasi-Two-Dimensional Turbulence, Sunghwan Jung, Brian Storey, Julien Aubert, Harry Swinney Jul 2012

Nonextensive Statistical Mechanics For Rotating Quasi-Two-Dimensional Turbulence, Sunghwan Jung, Brian Storey, Julien Aubert, Harry Swinney

Brian Storey

We have conducted experiments on an asymmetrically forced quasi-two-dimensional turbulent flow in a rapidly rotating annulus. Assuming conservation of potential enstrophy and energy, we maximize a nonextensive entropy function to obtain the azimuthally averaged vorticity as a function of radial position. The predicted vorticity profile is in good accord with the observations. A nonextensive formalism is appropriate because long-range correlations between small-scale vortices give rise to large coherent structures in the turbulence. We also derive probability distribution functions for the vorticity from both extensive and nonextensive entropies, and we find that the prediction from nonextensive theory is in better accord ...


Radiation Dose Distributions In Three Dimensions From Tomographic Optical Density Scanning Of Polymer Gels: Ii. Optical Properties Of The Bang Polymer Gel, Yevgeniya Zastavker, Marek Maryanski, John Gore Jun 2012

Radiation Dose Distributions In Three Dimensions From Tomographic Optical Density Scanning Of Polymer Gels: Ii. Optical Properties Of The Bang Polymer Gel, Yevgeniya Zastavker, Marek Maryanski, John Gore

Yevgeniya V. Zastavker

A newly developed method of radiation dosimetry makes use of the optical properties of polymer gels. The dose-response mechanism relies on the production of light-scattering polymer micro-particles in the gel at each site of radiation absorption. The scattering produces an attenuation of transmitted light intensity that is directly related to the dose and independent of dose rate. For the BANG polymer gel (bis, acrylamide, nitrogen, and gelatin) the shape of the dose-response curve depends on the fraction of the cross-linking monomer in the initial mixture and on the wavelength of light. At 500 nm the attenuation coefficient (μ) increases by ...


Dynamical Signature Of The Mott-Hubbard Transition In Ni(S,Se)(2), Yevgeniya Zastavker, Anke Husmann, Deborah Jin, Thomas Rosenbaum, X Yao, J Honig Jun 2012

Dynamical Signature Of The Mott-Hubbard Transition In Ni(S,Se)(2), Yevgeniya Zastavker, Anke Husmann, Deborah Jin, Thomas Rosenbaum, X Yao, J Honig

Yevgeniya V. Zastavker

The transition metal chalcogenide Ni(S,Se)2 is one of the few highly correlated, Mott-Hubbard systems without a strong first-order structural distortion that normally cuts off the critical behavior at the metal-insulator transition. The zero-temperature (T) transition was tuned with pressure, and significant deviations were found near the quantum critical point from the usual T1/2 behavior of the conductivity characteristic of electron-electron interactions in the presence of disorder. The transport data for pressure and temperature below 1 kelvin could be collapsed onto a universal scaling curve.


Performance Characteristics Of Nanocrystalline Diamond Vacuum Field Emission Transistor Array, S Hsu, W Kang, J Davidson, J Huang, David Kerns May 2012

Performance Characteristics Of Nanocrystalline Diamond Vacuum Field Emission Transistor Array, S Hsu, W Kang, J Davidson, J Huang, David Kerns

David V. Kerns

Nitrogen-incorporated nanocrystalline diamond (ND) vacuum field emission transistor (VFET) with self-aligned gate is fabricated by mold transfer microfabrication technique in conjunction with chemical vapor deposition (CVD) of nanocrystalline diamond on emitter cavity patterned on silicon-on-insulator (SOI) substrate. The fabricated ND-VFET demonstrates gate-controlled emission current with good signal amplification characteristics. The dc characteristics of the ND-VFET show well-defined cutoff, linear, and saturation regions with low gate turn-on voltage, high anode current, negligible gate intercepted current, and large dc voltage gain. The ac performance of the ND-VFET is measured, and the experimental data are analyzed using a modified small signal circuit model ...


Oxygen Line Mapping Of Sn 1006 With Suzaku, Aya Bamba, Hiroya Yamaguchi, Katsuji Koyama, Junko Hiraga, Stephen Holt, John Hughes, Hideaki Katagiri, Jun Kataoka, Satoru Katsuda, Shunji Kitamoto, Motohide Kokubun, Hironori Matsumoto, Emi Miyata, Koji Mori, Hiroshi Nakajima, Masanobu Ozaki, Robert Petre, Akiko Sekiguchi, Tadayuki Takahashi, Takaaki Tanaka, Yukikatsu Terada, Hiroshi Tomida, Yohko Tsuboi, Masahiro Tsujimoto, Hiroshi Tsunemi, Yasunobu Uchiyama, Masaru Ueno, Shin Watanabe May 2012

Oxygen Line Mapping Of Sn 1006 With Suzaku, Aya Bamba, Hiroya Yamaguchi, Katsuji Koyama, Junko Hiraga, Stephen Holt, John Hughes, Hideaki Katagiri, Jun Kataoka, Satoru Katsuda, Shunji Kitamoto, Motohide Kokubun, Hironori Matsumoto, Emi Miyata, Koji Mori, Hiroshi Nakajima, Masanobu Ozaki, Robert Petre, Akiko Sekiguchi, Tadayuki Takahashi, Takaaki Tanaka, Yukikatsu Terada, Hiroshi Tomida, Yohko Tsuboi, Masahiro Tsujimoto, Hiroshi Tsunemi, Yasunobu Uchiyama, Masaru Ueno, Shin Watanabe

Stephen Holt

SN1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region ...


Nanofluid Properties And Their Effects On Convective Heat Transfer In An Electronics Cooling Application, Jessica Townsend, Rebecca Christianson Apr 2012

Nanofluid Properties And Their Effects On Convective Heat Transfer In An Electronics Cooling Application, Jessica Townsend, Rebecca Christianson

Rebecca J. Christianson

In the search for new, more effective coolant fluids, nanoparticle suspensions have shown promise due to their enhanced thermal conductivity. However, there is a concomitant increase in the viscosity, requiring an increase in pumping power to achieve the same flow rate.Studies of flow cooling in simple geometries indicate that there is a benefit to using nanofluids, but it is difficult to justify extending these results to the far more complicated geometries. Moreover, with the variability of property measurements found in literature, it is possible to show conflicting results from the same set of flow-cooling data. In this work we ...


Nanofluid Properties And Their Effects On Convective Heat Transfer In An Electronics Cooling Application, Jessica Townsend, Rebecca Christianson Apr 2012

Nanofluid Properties And Their Effects On Convective Heat Transfer In An Electronics Cooling Application, Jessica Townsend, Rebecca Christianson

Jessica Townsend

In the search for new, more effective coolant fluids, nanoparticle suspensions have shown promise due to their enhanced thermal conductivity. However, there is a concomitant increase in the viscosity, requiring an increase in pumping power to achieve the same flow rate.Studies of flow cooling in simple geometries indicate that there is a benefit to using nanofluids, but it is difficult to justify extending these results to the far more complicated geometries. Moreover, with the variability of property measurements found in literature, it is possible to show conflicting results from the same set of flow-cooling data. In this work we ...


Non-Linear Dynamic Intertwining Of Rods With Self-Contact, Christopher Lee, Sachin Goyal, Noel Perkins Apr 2012

Non-Linear Dynamic Intertwining Of Rods With Self-Contact, Christopher Lee, Sachin Goyal, Noel Perkins

Christopher Lee

Twisted marine cables on the sea floor can form highly contorted three-dimensional loops that resemble tangles. Such tangles or ‘hockles’ are topologically equivalent to the plectomenes that form in supercoiled DNA molecules. The dynamic evolution of these intertwined loops is studied herein using a computationalrod model that explicitly accounts for dynamicself-contact. Numerical solutions are presented for an illustrative example of a long rod subjected to increasing twist at one end. The solutions reveal the dynamicevolution of the rod from an initially straight state, through a buckled state in the approximate form of a helix, through the dynamic collapse of this ...


Bistability In A Simple Fluid Network Due To Viscosity Contrast, John Geddes, Brian Storey, David Gardner, Russell Carr Mar 2012

Bistability In A Simple Fluid Network Due To Viscosity Contrast, John Geddes, Brian Storey, David Gardner, Russell Carr

Brian Storey

We study the existence of multiple equilibrium states in a simple fluid network using Newtonian fluids and laminar flow. We demonstrate theoretically the presence of hysteresis and bistability, and we confirm these predictions in an experiment using two miscible fluids of different viscosity—sucrose solution and water. Possible applications include blood flow, microfluidics, and other network flows governed by similar principles.


The Implications Of A Robust Curriculum In Introductory Mechanics, Chance Hoellwarth, Matthew Moelter Feb 2012

The Implications Of A Robust Curriculum In Introductory Mechanics, Chance Hoellwarth, Matthew Moelter

Chance Hoellwarth

We have developed a curriculum for introductory mechanics that emphasizes interactive engagement and conceptual understanding using the studio format. As previously reported, we have shown in three different quarters that the curriculum much improved the students’ conceptual understanding compared to the traditional course without significantly affecting the scores on a traditional final exam. Here we report the results for the entire three-year period during which the course was taught, 34 sections of the course were taught with 11 different instructors to over 1200 students. In each term, these sections had common exams, syllabus, and schedule. Student experiences were very similar ...


Two-Magnon Excitations Observed By Neutron Scattering In The Two-Dimensional Spin-5/2 Heisenberg Antiferromagnet Rb2mnf4, T. Huberman, R. Coldea, R. A. Cowley, D. A. Tennant, R. L. Leheny, Rebecca Christianson, C. D. Frost Sep 2011

Two-Magnon Excitations Observed By Neutron Scattering In The Two-Dimensional Spin-5/2 Heisenberg Antiferromagnet Rb2mnf4, T. Huberman, R. Coldea, R. A. Cowley, D. A. Tennant, R. L. Leheny, Rebecca Christianson, C. D. Frost

Rebecca J. Christianson

The low-temperature magnetic excitations of the two-dimensional spin- 52 square-lattice Heisenberg antiferromagnetRb2MnF4 have been probed using pulsed inelastic neutron scattering. In addition to dominant sharppeaks identified with one-magnon excitations, a relatively weak continuum scattering is also observed at higherenergies. This is attributed to neutron scattering by pairs of magnons and the observed intensities are consistentwith predictions of spin wave theory.


Space Weather Community Operations Workshop: Planning For The Next Decade, J. Fulgham, Jennifer Meehan, W. Tobiska Sep 2011

Space Weather Community Operations Workshop: Planning For The Next Decade, J. Fulgham, Jennifer Meehan, W. Tobiska

Jennifer (Jinni) Meehan

No abstract provided.


Analysis Of Electroluminescence Spectra Of Silicon And Gallium Arsenide P-N Junctions In Avalanche Breakdown, M Lahbabi, A Ahaitoufa, M. Fliyou, E. Abarkan, J.-P. Charles, A. Bath, A. Hoffmann, Sherra Kerns, David Kerns, Jr. Jun 2011

Analysis Of Electroluminescence Spectra Of Silicon And Gallium Arsenide P-N Junctions In Avalanche Breakdown, M Lahbabi, A Ahaitoufa, M. Fliyou, E. Abarkan, J.-P. Charles, A. Bath, A. Hoffmann, Sherra Kerns, David Kerns, Jr.

David V. Kerns

We present a generalized study of light emission from reverse biased p–n junctions under avalanche breakdown conditions. A model is developed based on direct and indirect interband processes including self-absorption to describe measured electroluminescence spectra. This model was used to analyze experimental data for silicon (Si) and gallium arsenide p–n junctions and can be extended to several types of semiconductors regardless of their band gaps. This model can be used as a noninvasive technique for the determination of the junction depth. It has also been used to explain the observed changes of the Si p–n junction electroluminescence ...


Understanding Space Weather Customers In Gps-Reliant Industries, Jennifer Meehan, G. Fisher, W. Murtagh Dec 2009

Understanding Space Weather Customers In Gps-Reliant Industries, Jennifer Meehan, G. Fisher, W. Murtagh

Jennifer (Jinni) Meehan

No abstract provided.


Hexagons And Squares In A Passive Nonlinear Optical System, John Geddes, R.A. Indik, J.V. Moloney, Willie Firth Dec 1993

Hexagons And Squares In A Passive Nonlinear Optical System, John Geddes, R.A. Indik, J.V. Moloney, Willie Firth

John B. Geddes

Pattern formation is analyzed and simulated in a nonlinear optical system involving all three space dimensions as well as time in an essential way. This system, counterpropagation in a Kerr medium, is shown to lose stability, for sufficient pump intensity, to a nonuniform spatial pattern. We observe hexagonal patterns in a self-focusing medium, and squares in a self-defocusing one, in good agreement with analysis based on symmetry and asymptotic expansions.