Physics Commons^™

Optical Control Of Thermocapillary Effects In Complex Nanofluids, Yuval Lamhot, Assaf Barak, Carmel Rotschild, Mordechai Segev, Meirav Saraf, Efrat Lifshitz, Abraham Marmur, Ramy El-Ganainy, Demetrios N. Christodoulides

Ramy El-Ganainy

We study the strong coupling of light and nanoparticle suspensions and their surface tension effect in capillaries. We show experimentally and theoretically that increasing the intensity of a narrow laser beam passing through a capillary far away from the surface results in a significant decrease in the fluid level. The underlying mechanism relies on light-induced redistribution of nanoparticles in the bulk and the surface of the fluid, facilitating continuous optical control over the surface position. The experiments manifest optical control from afar over properties of fluid surfaces.

Thermocapillary Effects In Driven Dewetting And Self-Assembly Of Pulsed Laser-Irradiated Metallic Films, Mikhail Khenner

Mikhail Khenner

A mathematical model for the evolution of pulsed laser-irradiated, molten metallic films has been developed using the lubrication theory. The heat transfer problem that incorporates the absorbed heat from a single laser beam or the interfering laser beams is solved analytically. Using this temperature field, we derive the 3D long-wave evolution PDE for the film height. To get insights into dynamics of dewetting, we study the 2D version of the evolution equation by means of a linear stability analysis and by numerical simulations. The stabilizing and destabilizing effects of various system parameters, such as the reflectivity, the peak laser beam …

Polarimetry Studies For The Npdgamma Experiment At The Sns, Jonny Dadras

Jonny Dadras

The NPDGamma collaboration aims to measure a parity-violating directional gamma-ray asymmetry from the capture of polarized cold neutrons on protons. The asymmetry, predicted to be on the order of 50 ppb, is a result of the weak interaction between mesons and nucleons during the neutron capture reaction. The experiment is designed to make a statistics limited measurement of the asymmetry at the level of about 20%. The experiment will be carried out at the Fundamental neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS). The neutron beam is polarized by a super-mirror polarizer. A 9.5 G magnetic field guides …

Analysis Of Nonequilibrium Hcp Precipitate Growth In Fcc Matrices: Application To Al–Ag, Daniel Finkenstadt, Duane D. Johnson

Duane D. Johnson

Hexagonal-close-packed (hcp) γ-precipitates with large aspect ratios form rapidly in some face-centered cubic (fcc) solid-solutions. No model explains the observed time-dependent increase in aspect ratio, nor irregular intermediate growth shapes. We propose a nonequilibrium process involving trapezoidal offshoots (controlled only by energetics) that governs the growth behavior (kinetics) and yields nonequilibrium structures in agreement with observation. Then, combining nucleation theory and diffusion-limited growth both of secondary nuclei and ledges, we derive a general growth equation for γ-precipitates due to solute-segregation to precipitate–matrix interfaces that includes our modification of the Jones–Trivedi model for thickening to account for the slow growth of …

Nonlinear Optical Dynamics In Nonideal Gases Of Interacting Colloidal Nanoparticles, Ramy El-Ganainy, Demetrios N. Christodoulides, E. M. Wright, W. M. Lee, K. Dholakia

Ramy El-Ganainy

We show that many-body effects in stabilized nanocolloidal suspensions can have a profound effect on their optical nonlinearity. By considering the screened Coulomb repulsions between nanoparticles, we find that the nonlinear optical behavior of these colloids can range from polynomial to exponential depending on their composition and chemistry. The dynamics and stability properties of optical beams propagating in such nonideal gas environments of interacting colloidal particles are investigated. Our analysis provides a theoretical foundation for understanding the recently observed super-Kerr nonlinear optical response of such systems.

Measurements Of Electron Density, Temperature And Photoionization Cross Sections Of The Excited States Of Neon In A Discharge Plasma, Shaukat Mahmood, Nek Shaikh, M. Kalyar, Naveed Piracha, M. Baig

Naveed K. Piracha

In the present work emission and absorption spectroscopy have been used to determine the plasma parameters of neon in a hollow cathode discharge lamp. The excitation temperature is determined using the intensity ratio method and Boltzmann’s plot method whereas the electron density is determined from the Stark broadening of the spectral lines. The behavior of the optogalvanic signal as a function of laser energy has been studied for three transitions from the 2p53s [1/2]2 metastable state following ΔJ=ΔK=0, ±1 dipole selection rules. The saturation technique has been used to measure the photoionization cross section from three intermediate states 2p53p′ [1/2]1, …

Giant Surface-Plasmon-Induced Drag Effect (Spider) In Metal Nanowires, Maxim Durach, Anastasia Rusina, Mark I. Stockman

Anastasia Rusina

Here, for the first time we predict a giant surface-plasmon-induced drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. In nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ∼10⁵–10⁶  V/cm. The giant SPIDER is an ultrafast effect whose bandwidth for nanometric wires is ∼20  THz. It opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.

Does Stellar Feedback Create H I Holes? A Hubble Space Telescope/Very Large Array Study Of Holmberg Ii, Daniel R. Weisz, Evan Skillman, John Cannon, Andrew E. Dolphin, Robert C. Kennicutt, Janice Lee, Fabian Walter

John Cannon

No abstract provided.

Type-1.5 Superconducting State From An Intrinsic Proximity Effect In Two-Band Superconductors, Egor Babaev, Johan Carlstrom, Martin Speight

Egor Babaev

We show that in multiband superconductors even small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in unusual response to low magnetic fields leading to phase separation into domains of a two-component Meissner states and vortex droplets.

Absolute Nitrogen Atom Density Measurements By Two-Photon Laser-Induced Fluorescence Spectroscopy In Atmospheric Pressure Dielectric Barrier Discharges Of Pure Nitrogen, Et-Touhami Es-Sebbar, Christian Sarra-Bournet, Nicolas Naudé, Françoise Massines, Nicolas Gherardi

Dr. Et-touhami Es-sebbar

In this paper, two-photon absorption laser induced fluorescence spectroscopy is used to follow the nitrogen atom density in flowing dielectric barrier discharges fed with pure nitrogen and operating at atmospheric pressure. Two different dielectric barrier discharge regimes are investigated: the Townsend regime, which is homogeneous although operating at atmospheric pressure, and the more common filamentary regime. In both regimes, densities as high as 3x1014 /cm3 are detected. However, the N atoms kinetic formation depends on the discharge regime. The saturation level is reached more rapidly with a filamentary discharge. For a given discharge regime, the N atom density depends strongly …

Contributions To The Development Of The S.E.T.U.P. (Experimental And Theoretical Simulations Useful For Planetology) Project, E. Arzoumanian, C. Romanzin, M-C. Gazeau, Et. Es-Sebbar, A. Jolly, S. Perrier, Y. Benilan

Dr. Et-touhami Es-sebbar

No abstract provided.

Multiwavelength Studies For Titan's Atmospheric Composition Analysis, Y. Benilan, Et. Es-Sebbar, N. Fray, M-C. Gazeau, A. Jolly, M. Schwell, J. Guillemin

Dr. Et-touhami Es-sebbar

Titan's atmosphere mainly made of nitrogen and methane is rich in organic molecules. Hydrocarbons are formed from the photolytic dissociation of CH4 and nitriles are created by dissociation of N2 followed by reactions with hydrocarbons. In order to understand the physicochemical mechanisms responsible for the evolution of Titan's atmosphere, photochemical models are built. The latter need constrains for vertical profiles of organic compounds from the high thermosphere down to the low stratosphere as well as photodissociation rates. Those profiles over the entire atmosphere can be retrieved from Cassini observations, in particular by limb sounding, coupling infrared and ultraviolet spectroscopy. However, …

Competition Between Multiple Totally Asymmetric Simple Exclusion Processes For A Finite Pool Of Resources, L. Jonathan Cook, R. K. P. Zia, Beate Schmittmann

Beate Schmittmann

Using Monte Carlo simulations and a domain-wall theory, we discuss the effect of coupling several totally asymmetric simple exclusion processes (TASEPs) to a finite reservoir of particles. This simple model mimics directed biological transport processes in the presence of finite resources such as protein synthesis limited by a finite pool of ribosomes. If all TASEPs have equal length, we find behavior which is analogous to a single TASEP coupled to a finite pool. For the more generic case of chains with different lengths, several unanticipated regimes emerge. A generalized domain-wall theory captures our findings in good agreement with simulation results.

Electron Self-Injection And Trapping Into An Evolving Plasma Bubble, Serguei Y. Kalmykov, Sunghwan A. Yi, Vladimir N. Khudik, Gennady Shvets

Serge Youri Kalmykov

The blowout (or bubble) regime of laser wakefield acceleration is promising for generating monochromatic high-energy electron beams out of low-density plasmas. It is shown analytically and by particle-in-cell simulations that self-injection of the background plasma electrons into the quasistatic plasma bubble can be caused by slow temporal expansion of the bubble. Sufficient criteria for the electron trapping and bubble’s expansion rate are derived using a semianalytic nonstationary Hamiltonian theory. It is further shown that the combination of bubble’s expansion and contraction results in monoenergetic electron beams.

Neutrons And Hadronic Parity Violation, Br Holstein

Barry R Holstein

The history and phenomenology of hadronic parity violation are reviewed, and the important role of the neutron in unlocking the physics of this subject is outlined.

Optimal Site-Centered Electronic Structure Basis Set From A Displaced-Center Expansion: Improved Results Via A Priori Estimates Of Saddle Points In The Density, Aftab Alam, Duane D. Johnson

Duane D. Johnson

Site-centered, electronic-structure methods use an expansion inside nonoverlapping “muffin-tin” (MT) spheres plus an interstitial basis set. As the boundary separating the more spherical from nonspherical density between atoms, the “saddle-point” radii (SPR) in the density provide an optimal spherical region for expanding in spherical harmonics, as used in augmented plane wave, muffin-tin orbital, and multiple-scattering [Korringa, Kohn, and Rostoker (KKR)] methods. These MT-SPR guarantee unique, convex Voronoi polyhedra at each site, in distinction to Bader topological cells. We present a numerically fast, two-center expansion to find SPR a priori from overlapping atomic charge densities, valid also for disordered alloys. We …

A Comparison Of New Methods For Generating Energy-Minimizing Configurations Of Patchy Particles, Eric Jankowski, Sharon C. Glotzer

Eric Jankowski

Increasingly complex particles are pushing the limits of traditional simulation techniques used to study self-assembly. In this work, we test the use of a learning-augmented Monte Carlo method for predicting low energy configurations of patchy particles shaped like “Tetris®” pieces. We extend this method to compare it against Monte Carlo simulations with cluster moves and introduce a new algorithm—bottom-up building block assembly—for quickly generating ordered configurations of particles with a hierarchy of interaction energies.

Vuv Photostability Of Prebiotic Species, M. Schwell, Y. Bénilan, M.-C. Gazeau, N. Fray, A. Jolly, Et. Es-Sebbar, N. Champion, S. Leach, H. W Jochims, H. Baumgärtel, E. Rühl

Dr. Et-touhami Es-sebbar

No abstract provided.

S.E.T.U.P. Experimental And Theoretical Simulations Useful For Planetology- Related Studies In The Frame Of A Program Of Titan’S Atmosphere Laboratory Simulations, M.-C. Gazeau, Et. Es-Sebbar, E. Arzoumanian, C. Romanzin, A. Jolly, S. Perrier, Y. Bénilan

Dr. Et-touhami Es-sebbar

No abstract provided.

Flexoelectricity Of A Calamitic Liquid Crystal Elastomer Swollen With A Bent-Core Liquid Crystal, M. Chambers, R. Verduzco, J. T. Gleeson, S. Sprunt, Antal Jakli

Antal Jakli

We have measured the electric current induced by mechanical distortion of a calamitic liquid crystal elastomer (LCE) swollen with a low molecular weight bent-core nematic (BCN) liquid crystal, and have determined, for the first time, the bend flexoelectric coefficient e(3) of such a BCN-LCE composite. In one method, we utilise air-pressure to induce a mechanical bend deformation and flexoelectric polarization in a BCN-LCE film, and then measure the polarization current as a function of time. An alternative technique uses a rotary-motor driven scotch yoke to periodically flex the BCN-LCE; in this case, the magnitude and phase of the induced current …

Light-Driven Molecular Switches With Tetrahedral And Axial Chirality, Lisa Green, Yannian Li, Timothy White, Augustine Urbas, Timothy Bunning, Quan Li

Quan Li

Two light-driven molecular switches with tetrahedral and axial chirality were synthesized, which can induce a helical superstructure in an achiral liquid crystal host and dynamically phototune it to achieve reversible reflection color.

A Switch In Retrograde Signaling From Survival To Stress In Rapid Onset Neurodegeneration, Jennifer Ross, Erika L.F Holzbaur, Robert G. Kalb, Karen E. Wallace, Ram Dixit, Goo-Bo Jeong, Eran Perlson

Jennifer Ross

Retrograde axonal transport of cellular signals driven by dynein is vital for neuronal survival. Mouse models with defects in the retrograde transport machinery, including the Loa mouse (point mutation in dynein) and the Tgdynamitin mouse (overexpression of dynamitin), exhibit mild neurodegenerative disease. Transport defects have also been observed in more rapidly progressive neurodegeneration, such as that observed in the SOD1G93A transgenic mouse model for familial amyotrophic lateral sclerosis (ALS). Here, we test the hypothesis that alterations in retrograde signaling lead to neurodegeneration. In vivo, in vitro, and live-cell imaging motility assays show misregulation of transport and inhibition of retrograde signaling …

Surface Geometry Of C60 On Ag(111), H. I. Li, K. Pussi, K. J. Hanna, Lin-Lin Wang, Duane D. Johnson, H.-P. Cheng, H. Shin, S. Curtarolo, W. Moritz, J. A. Smerdon, R. Mcgrath, R. D. Diehl

Duane D. Johnson

The geometry of adsorbed C60 influences its collective properties. We report the first dynamical low-energy electron diffraction study to determine the geometry of a C60 monolayer, Ag(111)−(23√×23√)30°−C60, and related density functional theory calculations. The stable monolayer has C60 molecules in vacancies that result from the displacement of surface atoms. C60 bonds with hexagons down, with their mirror planes parallel to that of the substrate. The results indicate that vacancy structures are the rule rather than the exception for C60 monolayers on close-packed metal surfaces.

Non-Isotropy Of The Cmb Power Spectrum In Single Field Inflation, John Donoghue, Koushik Dutta, Andreas Ross

John Donoghue

Contaldi et al. [1] have suggested that an initial period of kinetic energy domination in single field inflation may explain the lack of CMB power at large angular scales. We note that in this situation it is natural that there also be a spatial gradient in the initial value of the inflaton field, and that this can provide a spatial asymmetry in the observed CMB power spectrum, manifest at low multipoles. We investigate the nature of this asymmetry and comment on its relation to possible anomalies at low multipoles.

Rheological Properties Of Bent-Core Liquid Crystals, C. Bailey, K. Fodor-Csorba, J. T. Gleeson, Samuel N. Sprunt, Antal Jákli

Antal Jakli

We show that bent-core liquid crystalline materials exhibit non-Newtonian flow in their optically isotropic liquid phase. We conjecture that this behavior is due to the existence of nanostructured, fluctuating clusters composed of a few smectic-like layers. Shear alignment of these clusters explains the shear thinning observed in bent-core liquid crystals having either a nematic phase or non-modulated smectic phase. By contrast, smectogens having a modulated smectic phase do not shear thin at low shear rates, but even show a slight shear thickening which may be due to entanglements of wormlike and/or helical clusters.

Charge Transfer Assisted By Collective H-Bonding Network Dynamics, Omar F. Mohammed, Christina M. Othon, Oh-Hoon Kwon, Ahmed H. Zewail

Christina M Othon

Although there have been numerous studies of solvation, the role of solvent specific and collective interactions, especially for charge-transfer processes, remains difficult to unravel. Here, we report, using femtosecond fluorescence up-conversion and steady-state spectroscopic measurements, studies of well-designed single-sited formylperylene (FPe) in binary solvents. One of the solvents (methanol, MOH) can selectively hydrogen (H) bond to the carbonyl (C=O) site, while the other (acetonitrile, ACN) cannot, but both have similar polarity ( for MOH and for ACN). The results reveal that ultrafast charge transfer from the perylene unit to the carbonyl group of FPe is facilitated by site-specific H-bonding interactions …

Comet C/2004 Q2 (Machholz): Parent Volatiles, A Search For Deuterated Methane, And Constraint On The Ch4 Spin Temperature, Boncho P. Bonev, Michael J. Mumma, Erika L. Gibb, Michael A. Disanti, Geronimo L. Villanueva, Karen Magee-Sauer, Richard S. Ellis

Erika Gibb

Acoustically Driven Oscillations Of Freely Suspended Liquid Crystal Filaments, J. Petzold, A. Nemes, A. Eremin, C. Bailey, N. Diorio, Antal Jakli, R. Stannarius

Antal Jakli

Some liquid crystalline phases of bent-core mesogens are known to form stable freely-suspended filaments with length to diameter ratios of 1000 and larger. These structures can behave like thin liquid chords. We study filament oscillations excited with harmonic sound waves. From amplitudes of the filament motion and phase shifts respective to the harmonic excitation signal we develop a model for the filament dynamics. Like in solid chords, the resonance frequency f(0) is inversely proportional to their length. The dependence of f(0) upon the filament radius allows one to draw conclusions on the nature of the filament tension. For thin filaments, …

Bacterial Growth And Motility In Sub-Micron Constrictions, Jaan Männik, Rosalie Driessen, Peter Galajda, Juan E. Keymer, Cees Dekker

Jaan Männik

In many naturally occurring habitats, bacteria live in micrometer-size confined spaces. Although bacterial growth and motility in such constrictions is of great interest to fields as varied as soil microbiology, water purification, and biomedical research, quantitative studies of the effects of confinement on bacteria have been limited. Here, we establish how Gram-negative Escherichia coli and Gram-positive Bacillus subtilis bacteria can grow, move, and penetrate very narrow constrictions with a size comparable to or even smaller than their diameter. We show that peritrichously flagellated E. coli and B. subtilis are still motile in microfabricated channels where the width of the channel …

Molecular Beam Epitaxy Of High Mobility In0.75Ga0.25As For Electron Spin Transport Applications, Paul J. Simmonds, S. N. Holmes, H. E. Beere, I. Farrer, F. Sfigakis, D. A. Ritchie, M. Pepper

Paul J. Simmonds

The authors describe the molecular beam epitaxy of relaxed, nominally undoped In_0.75Ga_0.25As–In_0.75Al_0.25As quantum well structures grown on InP substrates. The maximum two-dimensional electron density is 2 × 10¹¹cm⁻², with a peak mobility of 2.2 × 10⁵cm² V⁻¹s⁻¹ at 1.5K. In high magnetic field, the electron g-factor was shown to have a magnitude of 9.1 ± 0.1 at Landau-level filling factor of 4. The Rashba coefficient, determined from the analysis of the magnetoresistance at high Landau-level filling factor (>12), …