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    ABSTRACT: In a superconductor pair occupancy probabilities are doubly defined with conflicting values when normal and umklapp scattering coexist with the same destination momentum. To resolve this issue a new pairing scheme is introduced to assert normal–umklapp frustration under such circumstances. Superconductivity then arises solely from residual umklapp scattering to destination momenta not reached by normal scattering. Consequent Tc calculations from first principles for niobium, tantalum, lead and aluminum turn out to be accurate within a few percent. A new perspective is revealed to support Matthias׳ rule. New light is also shed relevant to the future study of metallic hydrogen.
    Solid State Communications 08/2014; 192:56–59. DOI:10.1016/j.ssc.2014.04.016
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    ABSTRACT: Recently, a hybrid distribution function [Tribeche et al., Phys. Rev. E 85, 037401 (2012)] was proposed to describe a plasma species with an enhanced superthermal component. This combines a Cairns-type "nonthermal" form with the Tsallis theory for nonextensive thermodynamics. Using this alternative model, the propagation of arbitrary amplitude ion acoustic solitary waves in a two-component plasma is investigated. From a careful study of the distribution function it is found that the model itself is valid only for a very restricted range in the q-nonextensive parameter and the nonthermality parameter, α. Solitary waves, the amplitude and nature of which depend sensitively on both q and α, can exist within a narrow range of allowable Mach numbers. Both positive and negative potential structures are found, and coexistence may occur.
    Physical Review E 08/2013; 88(2):023103. DOI:10.1103/PhysRevE.88.023103
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    ABSTRACT: Beam divergences of high-order extreme ultraviolet harmonics from intense laser interactions with steep plasma density gradients are studied through experiment and Fourier analysis of the harmonic spatial phase. We show that while emission due to the relativistically oscillating mirror mechanism can be explained by ponderomotive surface denting, in agreement with previous results, the divergence of the emission due to the coherent wake emission mechanism requires a combination of the dent phase and an intrinsic emission phase. The temporal dependence of the divergences for both mechanisms is highlighted while it is also shown that the coherent wake emission divergence can be small in circumstances where the phase terms compensate each other.
    Physical Review Letters 04/2013; 110(16):165002. DOI:10.1103/PhysRevLett.110.165002
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    ABSTRACT: Dust-acoustic waves are investigated in a three-component plasma consisting of strongly coupled dust particles and Maxwellian electrons and ions. A fluid model approach is used, with the effects of strong coupling being accounted for by an effective electrostatic "pressure" which is a function of the dust number density and the electrostatic potential. Both linear and weakly nonlinear cases are considered by derivation and analysis of the linear dispersion relation and the Korteweg-de Vries equation, respectively. In contrast to previous studies using this model, this paper presents the results arising from an expansion of the dynamical form of the electrostatic pressure, accounting for the variations in its value in the vicinity of the wave.
    Physical Review E 12/2012; 86(6-2):066404. DOI:10.1103/PhysRevE.86.066404
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    ABSTRACT: We made numerical simulations of the generation of narrowband beams of extreme ultraviolet radiation from intense laser interaction with a blazed grating surface. Strong fifth harmonic emission into its blazed diffraction order was observed as well as heavy suppression of the fundamental frequency with comparison to a typical harmonic spectrum from a flat target. The results demonstrate a new highly efficient method of generating near-monochromatic harmonics from the fundamental with minimal effect on the pulse duration.
    Optics Letters 06/2011; 36(12):2333-5. DOI:10.1364/OL.36.002333
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    ABSTRACT: Results from a joint experimental study of electron attachment to dichlorodifluoromethane (CCl(2)F(2)) molecules in the gas phase are reported. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for formation of the dominant anion Cl(-) was measured over the energy range 0.001-1.8 eV at the gas temperature T(G) = 300 K. It exhibits cusp structure at thresholds for vibrational excitation of the nu(3)(a(1)) mode due to interaction with the attachment channels. With reference to the thermal attachment rate coefficient k(T = 300 K) = 2.2(8) x 10(-9) cm(3) s(-1) (fitted average from several data), a new highly resolved absolute attachment cross section for T(G) = 300 K was determined. Partial cross sections for formation of the anions Cl(-), Cl(2)(-), F(-), ClF(-), and CCl(2)F(-) were measured over the range 0-12 eV, using three different electron beam experiments of medium energy resolution. The dependence of the attachment rate coefficient k(T(e);T(G) = 300 K) on electron temperature T(e) was calculated over the range 50-15 000 K, based on a newly constructed total cross section for anion formation at T(G) = 300 K. R-matrix calculations for Cl(-) production have been carried out for comparison with the experimental data. The R-matrix results are in line with the main experimental observations and predict the dependence of the DEA cross section on the initial vibrational level nu(3)() and on the vibrational temperature. Furthermore, the cross section for vibrational excitation of the nu(3) mode has been computed.
    The Journal of Physical Chemistry A 01/2010; 114(3):1474-84. DOI:10.1021/jp9081992
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    ABSTRACT: The experimental arrangement for the investigation of high-field laser-induced processes using a broadband proton probe beam has been modified to enable the detection of the ultrafast motion of field fronts. It is typical in such experiments for the target to be oriented perpendicularly with respect to the principal axis of the probe beam. It is demonstrated here, however, that the temporal imaging properties of the diagnostic arrangement are altered drastically by placing the axis (or plane) of the target at an oblique angle to the transverse plane of the probe beam. In particular, the detection of the motion of a laser-driven field front along a wire at a velocity of (0.95+/-0.05)c is described.
    The Review of scientific instruments 11/2009; 80(11):113506. DOI:10.1063/1.3262630
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    ABSTRACT: In some recent on board space observations, it has been studied that high streaming ions play a major role on the physical mechanism for nonlinear wave structures. We have investigated here ion-acoustic solitons in a plasma with nonthermal electrons and weakly relativistic ions. Such plasmas occur in plasma sheet boundary layer of earth’s magnetosphere, Van-Allen belts. We have set up and solved KdV equation in a stationary frame to obtain the expression for the peak soliton amplitude and width. These quantities are significantly influenced by the relativistic effect, the nonthermal parameters and ratio of ion to electron temperatures. It is observed that for specific range of nonthermal parameter values, we observe compressive solitons and above which the rarefactive solitons are observed. The nonthermal parameter also affects the double layers.
    Chaos Solitons & Fractals 11/2009; 42(3-42):1638-1645. DOI:10.1016/j.chaos.2009.03.065
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    ABSTRACT: The interaction of a 3x10;{19} W/cm;{2} laser pulse with a metallic wire has been investigated using proton radiography. The pulse is observed to drive the propagation of a highly transient field along the wire at the speed of light. Within a temporal window of 20 ps, the current driven by this field rises to its peak magnitude approximately 10;{4} A before decaying to below measurable levels. Supported by particle-in-cell simulation results and simple theoretical reasoning, the transient field measured is interpreted as a charge-neutralizing disturbance propagated away from the interaction region as a result of the permanent loss of a small fraction of the laser-accelerated hot electron population to vacuum.
    Physical Review Letters 06/2009; 102(19):194801. DOI:10.1103/PHYSREVLETT.102.194801
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    ABSTRACT: Coherent wake emission is a unique source of extreme ultraviolet radiation and has been recently shown to provide the basis for intense attosecond light. Here we present a novel scheme, supported by particle-in-cell simulations, demonstrating that enhancement and spectral control of the coherent wake emission signal can be achieved by modifying the interaction plasma density ramp. Significant tunable enhancement of harmonic emission is verified experimentally, with factors of >50 in relative signal increase achieved in a narrow band of harmonics at the cutoff frequency.
    Physical Review Letters 06/2009; 102(22):225002. DOI:10.1103/PHYSREVLETT.102.225002
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