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Selected Works

2006

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Articles 1 - 30 of 58

Full-Text Articles in Physics

Coefficient Of Bohm Diffusion In Fully Ionized Plasma And Its Theoretical Proof, Ahmad Talaei, Reza Amrollahi Dec 2006

Coefficient Of Bohm Diffusion In Fully Ionized Plasma And Its Theoretical Proof, Ahmad Talaei, Reza Amrollahi

Ahmad Talaei

Unlike classical diffusion that scales inversely as the square of the magnetic field strength, it is quite usual that transport especially in laboratory plasma in not by classical mechanisms, instead it is a rapid diffusion and then loss of plasma particles across magnetic field lines that scales inversely with the magnetic field strength. In this work, by the simple set of single-fluid magnetohydrodynamic (mhd) equations applied for fully ionized plasma in steady state, the empirical bohm diffusion and time are extracted.


Guiding Of Laser Beams In Plasmas By Radiation Cascade Compression, Serguei Y. Kalmykov, Gennady Shvets Nov 2006

Guiding Of Laser Beams In Plasmas By Radiation Cascade Compression, Serguei Y. Kalmykov, Gennady Shvets

Serge Youri Kalmykov

The near-resonant beatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few-fs electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the beat frequency. Consequently, the cascade of sidebands red- and blue-shifted from the fundamental by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion [S. Kalmykov and G. Shvets, Phys. Rev. E 73, 46403 (2006)]. In the ...


Vortex Matter, Effective Magnetic Charges, And Generalizations Of Dipolar Superfluidity Concept In Layered Systems, Egor Babaev Oct 2006

Vortex Matter, Effective Magnetic Charges, And Generalizations Of Dipolar Superfluidity Concept In Layered Systems, Egor Babaev

Egor Babaev

In the first part of this letter we discuss electrodynamics of an excitonic condensate in a bilayer. We show that under certain conditions the system has a dominant energy scale and is described by the effective electrodynamics with "planar magnetic charges". In the second part of the paper we point out that a vortex liquid state in bilayer superconductors also possesses dipolar superfluid modes and establish equivalence mapping between this state and a dipolar excitonic condensate. We point out that a vortex liquid state in an N-layer superconductor possesses multiple topologically coupled dipolar superfluid modes and therefore represents a generalization ...


Injection, Trapping, And Acceleration Of Electrons In A Three-Dimensional Nonlinear Laser Wakefield, Serguei Y. Kalmykov, Leonid M. Gorbunov, Patrick Mora, Gennady Shvets Oct 2006

Injection, Trapping, And Acceleration Of Electrons In A Three-Dimensional Nonlinear Laser Wakefield, Serguei Y. Kalmykov, Leonid M. Gorbunov, Patrick Mora, Gennady Shvets

Serge Youri Kalmykov

It is demonstrated that the accelerating and focusing phases of the nonlinear three-dimensional axisymmetric laser wake can almost entirely overlap starting from a certain distance behind the laser pulse in homogeneous plasma. Such field structure results from the curvature of phase fronts due to the radially inhomogeneous relativistic shift of plasma frequency. Consequently, the number of trapped low-energy electrons can be much greater than that predicted by the linear wake theory. This effect is favorable for quasi-monoenergetic acceleration of a considerable charge (several hundreds of pC) to about 1 GeV per electron in the plasma wakefield driven by an ultrashort ...


Snapshots Of Laser Wakefields, Nicholas H. Matlis, Steven A. Reed, Stepan S. Bulanov, Vladimir Chvykov, Galina Kalintchenko, Takeshi Matsuoka, Pascal Rousseau, Victor Yanovsky, Anatoly Maksimchuk, Serguei Y. Kalmykov, Gennady Shvets, Michael C. Downer Oct 2006

Snapshots Of Laser Wakefields, Nicholas H. Matlis, Steven A. Reed, Stepan S. Bulanov, Vladimir Chvykov, Galina Kalintchenko, Takeshi Matsuoka, Pascal Rousseau, Victor Yanovsky, Anatoly Maksimchuk, Serguei Y. Kalmykov, Gennady Shvets, Michael C. Downer

Serge Youri Kalmykov

Tabletop plasma accelerators can now produce GeV-range electron beams and femtosecond X-ray pulses, providing compact radiation sources for medicine, nuclear engineering, materials science and high-energy physics. In these accelerators, electrons surf on electric fields exceeding 100 GeV m^{−1}, which is more than 1,000 times stronger than achievable in conventional accelerators. These fields are generated within plasma structures (such as Langmuir waves or electron density ‘bubbles’) propagating near light speed behind laser or charged-particle driving pulses. Here, we demonstrate single-shot visualization of laser-wakefield accelerator structures for the first time. Our ‘snapshots’ capture the evolution of multiple wake periods, detect ...


Simulation Of Ultrashort Laser Pulses In Nonlinear Media, Jeremy Gulley Sep 2006

Simulation Of Ultrashort Laser Pulses In Nonlinear Media, Jeremy Gulley

Jeremy R. Gulley

No abstract is currently available.


Real-Time Measurements On Electron Plasma Response In Dielectrics Under Influence Of Ultrafast Laser Radiation, Sebastian Winkler, Jeremy Gulley, Igor Burakov, Razvan Stoian, Nadezhda Bulgakova, Anton Husakou, Alexandre Mermillod-Blondin, Arkadi Rosenfeld, David Ashkenasi, Ingolf Hertel, William Dennis Aug 2006

Real-Time Measurements On Electron Plasma Response In Dielectrics Under Influence Of Ultrafast Laser Radiation, Sebastian Winkler, Jeremy Gulley, Igor Burakov, Razvan Stoian, Nadezhda Bulgakova, Anton Husakou, Alexandre Mermillod-Blondin, Arkadi Rosenfeld, David Ashkenasi, Ingolf Hertel, William Dennis

Jeremy R. Gulley

No abstract is currently available.


Nanostructured Bi2se3 Films And Their Thermoelectric Transport Properties., Xiaofeng Qiu, Leah Austin, Philip Muscarella, Jeffrey Dyck, Clemens Burda Aug 2006

Nanostructured Bi2se3 Films And Their Thermoelectric Transport Properties., Xiaofeng Qiu, Leah Austin, Philip Muscarella, Jeffrey Dyck, Clemens Burda

Jeffrey Dyck

No abstract provided.


The Nuclear Central Force In The Chiral Limit, John Donoghue Aug 2006

The Nuclear Central Force In The Chiral Limit, John Donoghue

John Donoghue

Chiral perturbation theory supplemented by the Omnes function is employed to study the strength of the isoscalar central nuclear interaction, G_S, in the chiral limit vs the physical case. A very large modification is seen, i.e. eta_s = G_S ~ chiral /G_S ~ physical = 1.37 +- 0.10 . This large effect is seen to arise dominantly at low energy from the extra contributions made by massless pions at energies near the physical threshold where the physical spectral function must vanish kinematically. The slope away from the chiral limit, d_S, is also calculated and is correspondingly large. I also explain why this large ...


Precision And Accuracy Of Thermal Calibration Of Atomic Force Microscopy Cantilevers, Nancy Burnham, G Matei, E Thoreson, J Pratt, D Newell Jul 2006

Precision And Accuracy Of Thermal Calibration Of Atomic Force Microscopy Cantilevers, Nancy Burnham, G Matei, E Thoreson, J Pratt, D Newell

Nancy A. Burnham

To have confidence in force measurements made with atomic force microscopes(AFMs), the spring constant of the AFM cantilevers should be known with good precision and accuracy, a topic not yet thoroughly treated in the literature. In this study, we compared the stiffnesses of uncoated tipless uniform rectangular silicon cantilevers among thermal, loading, and geometric calibration methods; loading was done against an artifact from the National Institute of Standards and Technology (NIST). The artifact was calibrated at NIST using forces that were traceable to the International System of units. The precision and accuracy of the thermal method were found to ...


Selective Light-Induced Desorption: The Mechanism Of Photoalignment Of Liquid Crystals At Adsorbing Solid Surfaces, V. G. Nazarenko, O. P. Boiko, A. B. Nych, Yu. A. Nastishin, V. M. Pergamenshchik, Philip J. Bos Jul 2006

Selective Light-Induced Desorption: The Mechanism Of Photoalignment Of Liquid Crystals At Adsorbing Solid Surfaces, V. G. Nazarenko, O. P. Boiko, A. B. Nych, Yu. A. Nastishin, V. M. Pergamenshchik, Philip J. Bos

Philip J. Bos

We demonstrate experimentally that bare solid surfaces with adsorbed organic molecules can orient liquid crystals after UV light irradiation. The detailed structure and behavior of the surface-adsorbed molecules are not important to the effect: just their UV light absorption should depend on their orientation. The only requirement to the solid substrates is their transparency to the UV light. The universal reason for the photoinduced anisotropy in such systems is that photons clean from the surface those molecules that absorb them most intensively. This is a kind of light rubbing resulting in the anisotropic ablation of the adsorbed material.


Undulated Cylinders Of Charged Diblock Copolymers, Gregory M. Grason, Christian Santangelo Jul 2006

Undulated Cylinders Of Charged Diblock Copolymers, Gregory M. Grason, Christian Santangelo

Christian Santangelo

We study the cylinder to sphere morphological transition of diblock copolymers in aqueous solution with a hydrophobic block and a charged block. We find a metastable undulated cylinder configuration for a range of charge and salt concentrations which, nevertheless, occurs above the threshold where spheres are thermodynamically favorable. By modeling the shape of the cylinder ends, we find that the free-energy barrier for the transition from cylinders to spheres is quite large and that this barrier falls significantly in the limit of high polymer charge and low solution salinity. This suggests that observed undulated cylinder phases are kinetically trapped structures.


Substantial Pressure Effect On The Resistivity And Curie Temperature For The Diluted Magnetic Semiconductor Sb2–X Vx Te3., Jeffrey Dyck, K. Ahilan, M. Aronson, C. Uher, P. Lošťák Jun 2006

Substantial Pressure Effect On The Resistivity And Curie Temperature For The Diluted Magnetic Semiconductor Sb2–X Vx Te3., Jeffrey Dyck, K. Ahilan, M. Aronson, C. Uher, P. Lošťák

Jeffrey Dyck

The influence of hydrostatic pressure on the electrical resistivity ρ and ferromagnetic transition temperature T C of bulk, single crystal Sb1–x Vx Te3 with x = 0.03 is presented. Pressure strongly suppresses ρ at all temperatures, with an overall decrease of about 35% at 1.6 GPa. The peak in ρ , a signature of T C, moves to lower temperature with increasing pressure. An overall suppression of T C near 40% at 1.6 GPa is observed. The results are discussed within the context of a carrier-mediated ferromagnetic exchange interaction.


Gauging Nonlinear Supersymmetry, T. Clark, S. Love, Muneto Nitta, Tonnis Ter Veldhuis Jun 2006

Gauging Nonlinear Supersymmetry, T. Clark, S. Love, Muneto Nitta, Tonnis Ter Veldhuis

Tonnis ter Veldhuis

No abstract provided.


Smectic Liquid Crystals: Materials With One-Dimensional, Periodic Order, Randall D. Kamien, Christian Santangelo May 2006

Smectic Liquid Crystals: Materials With One-Dimensional, Periodic Order, Randall D. Kamien, Christian Santangelo

Christian Santangelo

Smectic liquid crystals are materials formed by stacking deformable, fluid layers. Although smectics prefer to have flat, uniformly-spaced layers, boundary conditions can impose curvature on the layers. Since the layer spacing and curvature are intertwined, the problem of finding minimal configurations for the layers becomes nontrivial. We discuss various topological and geometrical aspects of these materials and present recent progress on finding some exact layer configurations. We also exhibit connections to the study of certain embedded minimal surfaces and briefly summarize some important open problems.


Conformation Of A Clathrin Triskelion In Solution, Matthew Ferguson, Kondury Prasad, Dan Sackett, Hacène Boukari, Eileen Lafer, Ralph Nossal May 2006

Conformation Of A Clathrin Triskelion In Solution, Matthew Ferguson, Kondury Prasad, Dan Sackett, Hacène Boukari, Eileen Lafer, Ralph Nossal

Matthew L. Ferguson

A principal component in the protein coats of certain post-golgi and endocytic vesicles is clathrin, which appears as a three-legged heteropolymer (known as a triskelion) that assembles into polyhedral cages principally made up of pentagonal and hexagonal faces. In vitro, this assembly depends upon the pH, with cages forming more readily at low pH and less readily at high pH. We have developed procedures, on the basis of static and dynamic light scattering, to determine the radius of gyration, Rg, and hydrodynamic radius, RH, of isolated triskelia, under conditions where cage assembly occurs. Calculations based on rigid molecular bead models ...


Bistable Linear Electro-Optical Switching In The B-7 ' Phase Of Novel Bent-Core, S. Umadevi, Antal Jakli, B. K. Sadashiva May 2006

Bistable Linear Electro-Optical Switching In The B-7 ' Phase Of Novel Bent-Core, S. Umadevi, Antal Jakli, B. K. Sadashiva

Antal Jakli

Three novel symmetrical bent-core compounds were synthesized where the terminal alkoxy linkages of the original bent-core inesogen forming a B-2 phase was converted to n-alkyl carboxylates. It is found that instead of the B-2 phase, all three compounds exhibit a transition between B-7' and B-2 mesophases. The physical and electro-optical properties have been investigated by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electric field experiments. The higher temperature B-7' phase has been shown to exhibit bistable but analogous linear electro-optical Switching Without,my observable polarization peak. We analyze two theoretical models and find that a local triclinic symmetry ...


Compression Of Laser Radiation In Plasmas Via Electromagnetic Cascading, Serguei Y. Kalmykov, Gennady Shvets Apr 2006

Compression Of Laser Radiation In Plasmas Via Electromagnetic Cascading, Serguei Y. Kalmykov, Gennady Shvets

Serge Youri Kalmykov

A train of few-laser-cycle relativistically intense radiation spikes with a terahertz repetition rate can be organized self-consistently in plasma from two frequency detuned co-propagating laser beams of low intensity. Large frequency bandwidth for the compression of spikes is produced via laser-induced periodic modulation of the plasma refractive index. The beat-wave-driven electron plasma wave downshifted from the plasma frequency creates a moving index grating thus inducing a periodic phase modulation of the driving laser (in spectral terms, electromagnetic cascading). The group velocity dispersion compresses the chirped laser beat notes to a few-cycle duration and relativistic intensity either concurrently in the same ...


Terahertz Photo-Hall Measurements Of Carrier Mobility In Gaas And Inp, James Heyman, D Bell, T Khumalo Apr 2006

Terahertz Photo-Hall Measurements Of Carrier Mobility In Gaas And Inp, James Heyman, D Bell, T Khumalo

James Heyman

No abstract provided.


Post-Outburst Infrared Spectra Of V1647 Ori, The Illuminating Star Of Mcneil's Nebula, Erika Gibb, T W. Rettig, S D. Brittain, D Wasikowski, Theodore Simon, William D. Vacca, Michael C. Cushing Apr 2006

Post-Outburst Infrared Spectra Of V1647 Ori, The Illuminating Star Of Mcneil's Nebula, Erika Gibb, T W. Rettig, S D. Brittain, D Wasikowski, Theodore Simon, William D. Vacca, Michael C. Cushing

Erika Gibb

V1647 Ori is a low-mass star in the L1630 star-forming region that underwent an outburst in late 2003 and early 2004. We present postoutburst infrared spectra obtained with NIRSPEC (Keck II) and SpeX (IRTF) and compare these to spectra taken during the outburst. The results show that the temperature of the hot CO formed in the inner part of the disk has declined by ~800 K, while the water and CO ice and low-J CO gas features remained unchanged, consistent with previous assertions that the latter, low-temperature features arise in the foreground cloud. The P Cygni profiles of the Paschen ...


Velocity Imaging For The Liquid–Gas Interface In The Near Field Of An Atomizing Spray: Proof Of Concept, David L. Sedarsky, Megan E. Paciaroni, Mark A. Linne, James R. Gord, Terrence R. Meyer Mar 2006

Velocity Imaging For The Liquid–Gas Interface In The Near Field Of An Atomizing Spray: Proof Of Concept, David L. Sedarsky, Megan E. Paciaroni, Mark A. Linne, James R. Gord, Terrence R. Meyer

Terrence R Meyer

We describe adaptation of ballistic imaging for the liquid core of an atomizing spray. To describe unambiguously the forces that act to break apart the liquid core in a spray, one must directly measure the force vectors themselves. It would be invaluable, therefore, to obtain velocity and acceleration data at the liquid-gas interface. We employ double-image ballistic imaging to extract velocity information through the application of image analysis algorithms. This method is shown to be effective for liquid phase droplet features within the resolution limit of the imaging system. In light of these results, it is clear that a three- ...


Nonlinear Evolution Of The Plasma Beat Wave: Compressing The Laser Beat Notes Via Electromagnetic Cascading, Serguei Y. Kalmykov, Gennady Shvets Mar 2006

Nonlinear Evolution Of The Plasma Beat Wave: Compressing The Laser Beat Notes Via Electromagnetic Cascading, Serguei Y. Kalmykov, Gennady Shvets

Serge Youri Kalmykov

The near-resonant beat wave excitation of an electron plasma wave (EPW) can be employed for generating the trains of few-femtosecond electromagnetic (EM) pulses in rarefied plasmas. The EPW produces a comoving index grating that induces a laser phase modulation at the difference frequency. As a result, the cascade of sidebands red and blue shifted by integer multiples of the beat frequency is generated in the laser spectrum. The bandwidth of the phase-modulated laser is proportional to the product of the plasma length, laser wavelength, and amplitude of the electron density perturbation. When the beat frequency is lower than the electron ...


Substrate Rigidity Regulates The Formation And Maintenance Of Tissues, Nancy Burnham, Wei-Hui Guo, Margo Frey, Yu-Li Wang Mar 2006

Substrate Rigidity Regulates The Formation And Maintenance Of Tissues, Nancy Burnham, Wei-Hui Guo, Margo Frey, Yu-Li Wang

Nancy A. Burnham

The ability of cells to form tissues represents one of the most fundamental issues in biology. However, it is unclear what triggers cells to adhere to one another in tissues and to migrate once a piece of tissue is planted on culture surfaces. Using substrates of identical chemical composition but different flexibility, we show that this process is controlled by substrate rigidity: on stiff substrates, cells migrate away from one another and spread on surfaces, whereas on soft substrates they merge to form tissue-like structures. Similar behavior was observed not only with fibroblastic and epithelial cell lines but also explants ...


Scalar Mesons In D And B Decays, Stefan Spanier Feb 2006

Scalar Mesons In D And B Decays, Stefan Spanier

stefan spanier

The decays of D and B mesons provide new insights into the natur of light scalar mesons. Several recent measurements are presented.


High Magnetic Field Thermal-Expansion And Magnetostriction Of Uru2si2, Victor Correa, Timothy Murphy, Eric Palm, Stanley Tozer, Peter Sharma, Neil Harrison, Jamie Marcelo, George Schmiedeshoff, John Mydosh Dec 2005

High Magnetic Field Thermal-Expansion And Magnetostriction Of Uru2si2, Victor Correa, Timothy Murphy, Eric Palm, Stanley Tozer, Peter Sharma, Neil Harrison, Jamie Marcelo, George Schmiedeshoff, John Mydosh

George Schmiedeshoff

We present high magnetic field (up to 45 T) thermal-expansion and magnetostriction results on URu2Si2 single crystals. The volume change associated with the transition to the ``hidden'' order phase becomes increasingly discontinous as the magnetic field is raised above 30 T. This confirms recent thermal conductivity and specific heat experiments indicating a strong coupling between the ``hidden'' order parameter and the lattice which suggest some sort of charge ordered state. Several other transitions are observed at higher fields, many of them showing hysteresis, while a change in the sign of the magnetostriction coefficient is observed at the metamagnetic transition (BM ...


Complexity, Challenge And Creation In Curriculum Design, Stephen Mecca, J. Thompson Dec 2005

Complexity, Challenge And Creation In Curriculum Design, Stephen Mecca, J. Thompson

Stephen J. Mecca

Schools today are faced with both the internal and external imposition of standards or benchmarks, which we will term BKs, that are expected to drive curriculum. Benchmarks, such as those of Project 2061 from the American Association for the Advancement of Science, are often structured on multiple levels representing a complex network of standards. Furthermore, schools are expected to demonstrate student accomplishment of benchmarks through effective assessment strategies. The instructional landscape in which curriculum is played out is painted with experienced teachers, who have generally been responsible for working in the context of their own grade and their own classroom ...


Variational Path Integral Simulations Using Discretized Coordinates, Robert Hinde Dec 2005

Variational Path Integral Simulations Using Discretized Coordinates, Robert Hinde

Robert Hinde

We describe a variational path integral simulation algorithm for quantum Monte Carlo studies of many-body systems in which particles are restricted to occupy sites on a regular simple cubic lattice with lattice constant s, and discuss the algorithm’s potential computational benefits. Application of the algorithm to the weakly bound cluster Ne3 shows that accurate coordinate-space observables for this system can be computed using lattice constants as large as s = 0.2 a0.


Dependence Of The H2–H2 Interaction On The Monomer Bond Lengths: Steps Toward An Accurate Ab Initio Estimate, Robert Hinde Dec 2005

Dependence Of The H2–H2 Interaction On The Monomer Bond Lengths: Steps Toward An Accurate Ab Initio Estimate, Robert Hinde

Robert Hinde

We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2–H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster theory and find that a fully iterative treatment of connected triples may be required to estimate the H2–H2 vibrational coupling accurately using coupled cluster theory.


An Undular Bore Solution For The Higher-Order Korteweg-De Vries Equation, Tim Marchant Dec 2005

An Undular Bore Solution For The Higher-Order Korteweg-De Vries Equation, Tim Marchant

Tim Marchant

Undular bores describe the evolution and smoothing out of an initial step in mean height and are frequently observed in both oceanographic and meteorological applications. The undular bore solution for the higher-order Korteweg-de Vries (KdV) equation is derived, using an asymptotic transformation which relates the KdV equation and its higher-order counterpart. The higher-order KdV equation considered includes all possible third-order correction terms (where the KdV equation retains second-order terms). The asymptotic transformation is then applied to the KdV undular bore solution to obtain the higher-order undular bore. Examples of higher-order undular bores, describing both surface and internal waves, are presented ...


Solitary Wave Interaction And Evolution For A Higher-Order Hirota Equation, Tim Marchant Dec 2005

Solitary Wave Interaction And Evolution For A Higher-Order Hirota Equation, Tim Marchant

Tim Marchant

Solitary wave interaction and evolution for a higher-order Hirota equation is examined. The higher-order Hirota equation is asymptotically transformed to a higher-order member of the NLS hierarchy of integrable equations, if the higher-order coefficients satisfy a certain algebraic relationship. The transformation is used to derive higher-order one- and two-soliton solutions. It is shown that the interaction is asymptotically elastic and the higher-order corrections to the coordinate and phase shifts are derived. For the higher-order Hirota equation resonance occurs between the solitary waves and linear radiation, so soliton perturbation theory is used to determine the details of the evolving wave and ...