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Articles 91 - 120 of 633

Full-Text Articles in Physics

X-Ray Radiation From Nonlinear Thomson Scattering Of An Intense Femtosecond Laser On Relativistic Electrons In A Helium Plasma, K. Ta Phuoc, A. Rousse, M. Pittman, J.P. Rousseau, V. Malka, S. Fritzler, Donald Umstadter, D. Hulin Jul 2015

X-Ray Radiation From Nonlinear Thomson Scattering Of An Intense Femtosecond Laser On Relativistic Electrons In A Helium Plasma, K. Ta Phuoc, A. Rousse, M. Pittman, J.P. Rousseau, V. Malka, S. Fritzler, Donald Umstadter, D. Hulin

Donald P. Umstadter

We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a0. This radiative process is dominant for a0 greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma.


Method For Generating A Plasma Wave To Accelerate Electrons, Donald Umstadter, Eric Esarey, Joon K. Kim Jul 2015

Method For Generating A Plasma Wave To Accelerate Electrons, Donald Umstadter, Eric Esarey, Joon K. Kim

Donald P. Umstadter

The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode …


Development Of A Source Of Quasi-Monochromatic Mev Energy Photons, Donald Umstadter, Sudeep Banerjee, Viswanathan Ramanathan, Nathan Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith Jul 2015

Development Of A Source Of Quasi-Monochromatic Mev Energy Photons, Donald Umstadter, Sudeep Banerjee, Viswanathan Ramanathan, Nathan Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith

Donald P. Umstadter

We report current progress on a project to develop an all-optically-driven x-ray photon source. A laser pulse with 40-50 TW of peak power is focused on a supersonic helium nozzle to drive a relativistic plasma wave. Electron beams with energies of 320 MeV (+/- 28 MeV) are accelerated by means of laser wakefield acceleration. Remarkably, the acceleration region is only 3 mm in length. This accelerator is currently being employed to demonstrate the generation of MeV- energy x-ray by means of all-optical Thomson scattering. By this mechanism, a lower power, laser pulse (from the same laser system) is focused onto …


A Cone Of Coherent Light, S.-Y. Chen, A. Maksimchuk, E. Esarey, Donald Umstadter Jul 2015

A Cone Of Coherent Light, S.-Y. Chen, A. Maksimchuk, E. Esarey, Donald Umstadter

Donald P. Umstadter

Lasers come in infrared and visible varieties, but none yet in the x-ray band. A compact and powerful source of coherent x rays is the dream of many physicists, who see applications such as making atomic scale, three-dimensional movies of a melting crystal or an operating photosynthesis protein. In a step toward that goal, a research team has detected high frequency coherent light generated by a new process. As they report in the 12 June PRL, intense laser pulses can stimulate free electrons in a plasma to emit coherent light at triple the input frequency in a narrowly-directed cone. The …


Plasma Density Gratings Induced By Intersecting Laser Pulses In Underdense Plasmas, Z.-M. Sheng, J. Zhang, Donald Umstadter Jul 2015

Plasma Density Gratings Induced By Intersecting Laser Pulses In Underdense Plasmas, Z.-M. Sheng, J. Zhang, Donald Umstadter

Donald P. Umstadter

Electron and ion density gratings induced by two intersecting ultrashort laser pulses at intensities of 1016 W/cm2 or lower are investigated. The ponderomotive force generated by the inhomogeneous intensity distribution in the intersecting region of the interfering pulses produces deep electron and ion density modulations at a wavelength less than a laser wavelength in vacuum. Dependence of the density modulation on the plasma densities, temperatures, and the ion mass, as well as the laser pulse parameters are studied analytically and by particle-in-cell simulations. It is found that the density peaks of such gratings can be a few times that of …


Observation Of Relativistic Cross-Phase Modulation In High-Intensity Laser-Plasma Interactions, Shouyuan Chen, Matthew Rever, P. Zhang, W. Theobald, Donald Umstadter Jul 2015

Observation Of Relativistic Cross-Phase Modulation In High-Intensity Laser-Plasma Interactions, Shouyuan Chen, Matthew Rever, P. Zhang, W. Theobald, Donald Umstadter

Donald P. Umstadter

A nonlinear optical phenomenon, relativistic cross-phase modulation, is reported. A relativistically intense light beam (I=1.3×1018 W cm-2, λ =1.05 μm) is experimentally observed to cause phase modulation of a lower intensity, copropagating light beam in a plasma. The latter beam is generated when the former undergoes the stimulated Raman forward scattering instability. The bandwidth of the Raman satellite is found to be broadened from 3.8–100 nm when the pump laser power is increased from 0.45–2.4 TW. A signature of relativistic cross-phase modulation, namely, asymmetric spectral broadening of the Raman signal, is observed at a pump power of 2.4 TW. The …


A Unidirectional, Pulsed Far-Infrared Ring Laser, W.A. Peebles, Donald Umstadter, D.L. Brower, N.C. Luhmann Jul 2015

A Unidirectional, Pulsed Far-Infrared Ring Laser, W.A. Peebles, Donald Umstadter, D.L. Brower, N.C. Luhmann

Donald P. Umstadter

The first study of a pulsed, far-infrared, ring laser is described. Unidirectional, traveling-wave operation is observed, thereby eliminating the spatial hole burning effects present in linear cavities. Single-mode output powers of 100 kW have been obtained.


Experimental Observation Of Relativistic Nonlinear Thomson Scattering, Szu-Yuan Chen, Anatoly Maksimchuk, Donald Umstadter Jul 2015

Experimental Observation Of Relativistic Nonlinear Thomson Scattering, Szu-Yuan Chen, Anatoly Maksimchuk, Donald Umstadter

Donald P. Umstadter

Classical Thomson scattering—the scattering of low-intensity light by electrons—is a linear process, in that it does not change the frequency of the radiation; moreover, the magnetic-field component of light is not involved. But if the light intensity is extremely high (~1018 Wcm–2), the electrons oscillate during the scattering process with velocities approaching the speed of light. In this relativistic regime, the effect of the magnetic and electric fields on the electron motion should become comparable, and the effective electron mass will increase. Consequently, electrons in such high fields are predicted to quiver nonlinearly, moving in figure-eight patterns rather than in …


International Conference On Phonon Scattering In Condensed Matter (Phonons 2015), Thomas Wilson Jun 2015

International Conference On Phonon Scattering In Condensed Matter (Phonons 2015), Thomas Wilson

Thomas E. Wilson

Dr. Thomas E. Wilson, professor of physics, had an abstract accepted for an oral presentation at the 15th International Conference on Phonon Scattering in Condensed Matter (Phonons 2015), held at the University of Nottingham, United Kingdom July 12-17.


Converting Glx2-1 Into An Active Glyoxalase Ii, Pattraranee Limphong, Nicole Adams, Matthew Rouhier, Ross Mckinney, Melissa Naylor, Brian Bennett, Christopher Makaroff, Michael Crowder Jun 2015

Converting Glx2-1 Into An Active Glyoxalase Ii, Pattraranee Limphong, Nicole Adams, Matthew Rouhier, Ross Mckinney, Melissa Naylor, Brian Bennett, Christopher Makaroff, Michael Crowder

Matthew F Rouhier

Arabidopsis thaliana glyoxalase 2-1 (GLX2-1) exhibits extensive sequence similarity with GLX2 enzymes but is catalytically inactive with SLG, the GLX2 substrate. In an effort to identify residues essential for GLX2 activity, amino acid residues were altered at positions 219, 246, 248, 325, and 328 in GLX2-1 to be the same as those in catalytically active human GLX2. The resulting enzymes were overexpressed, purified, and characterized using metal analyses, fluorescence spectroscopy, and steady-state kinetics to evaluate how these residues affect metal binding, structure, and catalysis. The R246H/N248Y double mutant exhibited low level S-lactoylglutathione hydrolase activity, while the R246H/N248Y/Q325R/R328K mutant exhibited a …


Economics Of Nuclear Power And Climate Change Mitigation Policies, Nico Bauer, Robert Brecha, Gunnar Luderer Jun 2015

Economics Of Nuclear Power And Climate Change Mitigation Policies, Nico Bauer, Robert Brecha, Gunnar Luderer

Robert J. Brecha

The events of March 2011 at the nuclear power complex in Fukushima, Japan, raised questions about the safe operation of nuclear power plants, with early retirement of existing nuclear power plants being debated in the policy arena and considered by regulators. Also, the future of building new nuclear power plants is highly uncertain. Should nuclear power policies become more restrictive, one potential option for climate change mitigation will be less available. However, a systematic analysis of nuclear power policies, including early retirement, has been missing in the climate change mitigation literature. We apply an energy economy model framework to derive …


Accelerating Diffraction-Free Beams In Photonic Lattices, K. Makris, I. Kaminer, Ramy El-Ganainy, N. Efremidis, Zhigang Chen, M. Segev, Demetrios Christodoulides Jun 2015

Accelerating Diffraction-Free Beams In Photonic Lattices, K. Makris, I. Kaminer, Ramy El-Ganainy, N. Efremidis, Zhigang Chen, M. Segev, Demetrios Christodoulides

Ramy El-Ganainy

We study nondiffracting accelerating paraxial optical beams in periodic potentials, in both the linear and the nonlinear domains. In particular, we show that only a unique class of z-dependent lattices can support a true accelerating diffractionless beam. Accelerating lattice solitons, autofocusing beams and accelerating bullets in optical lattices are systematically examined.


Enhancing Optical Isolator Performance In Nonreciprocal Waveguide Arrays, Miguel Levy, Turhan Carroll, Ramy El-Ganainy Jun 2015

Enhancing Optical Isolator Performance In Nonreciprocal Waveguide Arrays, Miguel Levy, Turhan Carroll, Ramy El-Ganainy

Ramy El-Ganainy

We investigate the operation of optical isolators based on magneto-optics waveguide arrays beyond the coupled mode analysis. Semi-vectorial beam propagation simulations demonstrate that evanescent tail coupling and the effects of radiation are responsible for degrading the device’s performance. Our analysis suggests that these effects can be mitigated when the array size is scaled up. In addition, we propose the use of radiation blockers in order to offset some of these effects, and we show that they provide a dramatic improvement in performance. Finally, we also study the robustness of the system with respect to fabrication tolerances using the coupled mode …


Observation Of Accelerating Wannier-Stark Beams In Optically Induced Photonic Lattices, Xinyuan Qi, Konstantinos Makris, Ramy El-Ganainy, Peng Zhang, Jintao Bai, Demetrios Christodoulides, Zhigang Chen Jun 2015

Observation Of Accelerating Wannier-Stark Beams In Optically Induced Photonic Lattices, Xinyuan Qi, Konstantinos Makris, Ramy El-Ganainy, Peng Zhang, Jintao Bai, Demetrios Christodoulides, Zhigang Chen

Ramy El-Ganainy

We generate optical beams analogous to the Wannier–Stark states in semiconductor superlattices and observe that the two main lobes of the WS beams self-bend (accelerate) along two opposite trajectories in a uniform one-dimensional photonic lattice. Such self-accelerating features exist only in the presence of the lattice and are not observed in a homogenous medium. Under the action of nonlinearity, however, the beam structure and acceleration cannot be preserved. Our experimental observations are in qualitative agreement with theoretical predictions.


Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, Suwit Suthirakun, Salai Ammal, Guoliang Xiao, Fanglin Chen, Kevin Huang, Hans Zur Loye, Andreas Heyden May 2015

Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, Suwit Suthirakun, Salai Ammal, Guoliang Xiao, Fanglin Chen, Kevin Huang, Hans Zur Loye, Andreas Heyden

Salai C. Ammal

No abstract provided.


Ab Initio Study Of Formazan And 3-Nitroformazan, G. Buemi, F. Zuccarello, P. Venuvanalingam, M. Ramalingam, Salai Ammal May 2015

Ab Initio Study Of Formazan And 3-Nitroformazan, G. Buemi, F. Zuccarello, P. Venuvanalingam, M. Ramalingam, Salai Ammal

Salai C. Ammal

Formazan and 3-nitroformazan have been investigated at abinitio level (MP2/6-31G** and B3LYP/6-31G**) in all their possible conformations, for studying the various possibilities of intramolecular hydrogen bonding formation. The trans-syn-s-cis (TSSC), known also asyellowform, has been found to be the most stable conformer (at least in the gas phase) in both compounds. This particular structure is strongly stabilized by a N–H···N hydrogen bridge, which gives rise to a hexatomic chelate ring, with the possibility of a proton transfer process.This closely resembles that of malondialdehyde, previously studied, in the evolution of the potential energy shape but with a greater barrier height. Various …


Modeling The Noble Metal/Tio2 (110) Interface With Hybrid Dft Functionals: A Periodic Electrostatic Embedded Cluster Model Study, Salai Ammal, Andreas Heyden May 2015

Modeling The Noble Metal/Tio2 (110) Interface With Hybrid Dft Functionals: A Periodic Electrostatic Embedded Cluster Model Study, Salai Ammal, Andreas Heyden

Salai C. Ammal

The interaction of Aun and Ptn (n=2,3) clusters with the stoichiometric and partially reduced rutile TiO2 (110) surfaces has been investigated using periodic slab and periodic electrostatic embedded cluster models. Compared to Au clusters, Pt clusters interact strongly with both stoichiometric and reduced TiO2 (110) surfaces and are able to enhance the reducibility of the TiO2 (110) surface, i.e., reduce the oxygen vacancy formation energy. The focus of this study is the effect of Hartree–Fock exchange on the description of the strength of chemical bonds at the interface of Au/Pt clusters and the TiO2 (110) surface. Hartree–Fock exchange helps describing …


Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Kevin Huang, Hans-Conrad Zur Loye, Andreas Heyden May 2015

Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Kevin Huang, Hans-Conrad Zur Loye, Andreas Heyden

Salai C. Ammal

No abstract provided.


Computer-Aided Design Of Novel Heterogeneous Catalysts—A Combinatorial Computational Chemistry Approach, K. Yajima, Y. Ueda, H. Tsuruya, T. Kanougi, Y. Oumi, Salai Ammal, S. Takami, M. Kubo, A. Miyamoto May 2015

Computer-Aided Design Of Novel Heterogeneous Catalysts—A Combinatorial Computational Chemistry Approach, K. Yajima, Y. Ueda, H. Tsuruya, T. Kanougi, Y. Oumi, Salai Ammal, S. Takami, M. Kubo, A. Miyamoto

Salai C. Ammal

No abstract provided.


Dynamic Path Bifurcation For The Beckmann Reaction: Observation And Implication, H. Yamataka, M. Sato, H. Hasegawa, Salai Ammal May 2015

Dynamic Path Bifurcation For The Beckmann Reaction: Observation And Implication, H. Yamataka, M. Sato, H. Hasegawa, Salai Ammal

Salai C. Ammal

The reaction of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles instead of amides when the cations have reasonable stability. The reactions of oxime derivatives of 1-substituted-phenyl-2-propanones and 3-substituted-phenyl-2-butanones in aqueous solvents gave both rearrangement and fragmentation products, the ratio of which was dependent on substituents. Transition state (TS) optimizations and intrinsic reaction coordinate (IRC) calculations for the reaction of 1-phenyl-2-propanone oximes showed that there is a single TS for each substituted compound. The IRC path from the TS either led to a rearrangement product or a fragmentation product depending on the …


Density Functional Theory Calculations Of Molecular Nitrogen On A Ruthenium Cluster, K. Shrivastavaa, Salai Ammal, H. Tsuruya, S. Takami, A. Endou, M. Kubo, K. Teraishi, A. Miyamoto, A. Ozaki May 2015

Density Functional Theory Calculations Of Molecular Nitrogen On A Ruthenium Cluster, K. Shrivastavaa, Salai Ammal, H. Tsuruya, S. Takami, A. Endou, M. Kubo, K. Teraishi, A. Miyamoto, A. Ozaki

Salai C. Ammal

No abstract provided.


Ab Initio And Dft Investigations Of Lithium/Hydrogen Bonded Complexes Of Trimethylamine, Dimethyl Ether And Dimethyl Sulfide, Salai Ammal, P. Venuvanalingam May 2015

Ab Initio And Dft Investigations Of Lithium/Hydrogen Bonded Complexes Of Trimethylamine, Dimethyl Ether And Dimethyl Sulfide, Salai Ammal, P. Venuvanalingam

Salai C. Ammal

Ab initio and DFT computations have been carried out on LiF and HF complexes of a set of n-donors viz. trimethylamine, dimethyl ether and dimethyl sulfide with a 6-31++G(d,p) basis set. The effect of correlation has been included with MP2, MP4 and DFT calculations. NBO analyses of the wavefunctions have been performed to examine the intermolecular interaction at the orbital level. Calculations reveal that these donors form strong n→σ* complexes and computed binding energies of the (CH3)2O···HF complex agree very well with the experimental binding energies from IR spectroscopy. LiF forms stronger complexes than HF, …


Π-Systems As Lithium/Hydrogen Bond Acceptors: Some Theoretical Observations, Salai Ammal, P. Venuvanalingam May 2015

Π-Systems As Lithium/Hydrogen Bond Acceptors: Some Theoretical Observations, Salai Ammal, P. Venuvanalingam

Salai C. Ammal

Ab initio calculations at the Hartree–Fock and correlated levels and density functional theory calculations have been performed with 6-31++G(d,p) and 6-311++G(d,p)basis sets on LiF and HF complexes of benzene, ethylene, and acetylene. Complex binding energies have been corrected for basis set superposition error, and zero point energy corrections have been done on Hartree–Fock binding energies. Computed results indicate that the complexes exist in different conformations and among them those with π-lithium and π-hydrogen bonds are the most stable. π-lithium bonds are stronger than π-hydrogen bonds. The computed binding energies and geometry of HF complexes correlate well with the available experimental …


Electron Donor-Acceptor Complexes Of I2 With Diethyl Ether And Diethyl Sulphide. An Ab Initio Mo Study, Salai Ammal, S. Ananthavel, J. Chandrasekhar, P. Venuvanalingam, M. Hegde May 2015

Electron Donor-Acceptor Complexes Of I2 With Diethyl Ether And Diethyl Sulphide. An Ab Initio Mo Study, Salai Ammal, S. Ananthavel, J. Chandrasekhar, P. Venuvanalingam, M. Hegde

Salai C. Ammal

No abstract provided.


Combinatorial Computational Chemistry Approach To The Design Of Metal Oxide Electronics Materials, B. Rodion, Salai Ammal, Y. Inaba, Y. Oumi, S. Takami, M. Kubo, A. Miyamoto, M. Kawasaki, M. Yoshimoto, H. Koinuma May 2015

Combinatorial Computational Chemistry Approach To The Design Of Metal Oxide Electronics Materials, B. Rodion, Salai Ammal, Y. Inaba, Y. Oumi, S. Takami, M. Kubo, A. Miyamoto, M. Kawasaki, M. Yoshimoto, H. Koinuma

Salai C. Ammal

Combinatorial chemistry has been developed as an experimental method where it is possible to synthesize hundreds of samples all at once and examine their properties. Recently, we introduced the concept of combinatorial approach to computational chemistry for material design and proposed a new method called `a combinatorial computational chemistry'. In this approach, the effects of large number of dopants, substrates, and buffer layers on the structures, electronic states, and properties of metal oxide electronics material is estimated systematically using computer simulations techniques, in order to predict the best dopant, substrate, and buffer layer for each metal oxide electronics materials.


Chemical Interaction Of Nf3 With Si (Part Ii): Density Functional Calculation Studies, A. Endou, T. Little, A. Yamada, K. Teraishi, M. Kubo, Salai Ammal, A. Miyamoto, M. Kitajima, F. Ohuchi May 2015

Chemical Interaction Of Nf3 With Si (Part Ii): Density Functional Calculation Studies, A. Endou, T. Little, A. Yamada, K. Teraishi, M. Kubo, Salai Ammal, A. Miyamoto, M. Kitajima, F. Ohuchi

Salai C. Ammal

No abstract provided.


Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden May 2015

Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden

Salai C. Ammal

The electronic conductivity and thermodynamic stability of mixed n-type and p-type doped SrTiO3 have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained ab initio thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO3 at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of n- and p-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20% Nb-doped Sr-deficient SrTiO3 to a non-Sr-deficient phase …


Ultraviolet Photoelectron Spectroscopy Of Complexes Of Bromine With N-Donors In The Vapor Phase, S. Ananthavel, Salai Ammal, P. Venuvanalingam, J. Chandrasekhar, M. Hegde May 2015

Ultraviolet Photoelectron Spectroscopy Of Complexes Of Bromine With N-Donors In The Vapor Phase, S. Ananthavel, Salai Ammal, P. Venuvanalingam, J. Chandrasekhar, M. Hegde

Salai C. Ammal

No abstract provided.


Spatial-Rank Order Selection Filters, Kenneth Barner, Russell Hardie May 2015

Spatial-Rank Order Selection Filters, Kenneth Barner, Russell Hardie

Russell C. Hardie

Chapter 3: "Spatial-Rank Order Selection Filters"
3.1 Introduction
3.2 Selection Filters and Spatial-Rank Ordering
3.3 Spatial-Rank Order Selection Filters
3.4 Optimization
3.5 Applications
3.6 Future Directions


Gradient-Based Edge Detection Using Nonlinear Edge-Enhancing Prefilters, Russell Hardie, Charles Boncelet May 2015

Gradient-Based Edge Detection Using Nonlinear Edge-Enhancing Prefilters, Russell Hardie, Charles Boncelet

Russell C. Hardie

This correspondence examines the use of nonlinear edge enhancers as prefilters for edge detectors. The filters are able to convert smooth edges to step edges and suppress noise simultaneously. Thus, false alarms due to noise are minimized and edge gradient estimates tend to be large and localized. This leads to significantly improved edge maps.