Effects of positron density and temperature on ion acoustic dressed solitons in an electron–positron–ion plasma

Ion acoustic dressed solitons in a three component plasma consisting of cold ions, hot electrons and positrons are studied. Using reductive perturbation method, Korteweg–de Vries (KdV) equation and a linear inhomogeneous equation, governing respectively the evolution of first and second order potentials are derived for the system. Renormalization procedure of Kodama and Taniuti is used to obtain nonsecular solutions of these coupled equations. It is found that electron–positron–ion plasma system supports only compressive solitons. For a given amplitude of soliton on increasing the positron concentration, velocity of the KdV as well as dressed soliton increases. For any arbitrary values of soliton's amplitude and positron concentration, velocity of the dressed soliton is found to be larger than that of the KdV soliton. For small amplitude of solitons, the width of KdV as well as dressed soliton decreases as positron concentration increases and width of dressed soliton is found to be larger than that of the KdV soliton. However, for a large value of soliton's amplitude as concentration of positrons increases, instead of decreasing width of dressed soliton starts to increase.     

The CΠu state of Na2 revisited: A comprehensive study by polarization labeling spectroscopy technique

This paper contains the analysis of the C(2)¹Π_u state of Na₂ molecule based on a large data set (3030 lines) obtained from a polarization labeling spectroscopy experiment on the transition. The energies of rovibrational levels in the C state, spanning a wide range of v (0 ? v ? 43) and J (12 ? J ? 100) quantum numbers, are fitted to a Dunham polynomial expansion and also to a numerical potential curve constructed by the inverted perturbation approach (IPA) method.     

Speed and shape of solitary waves in relativistic warm plasma

Large-amplitude solitary waves are investigated in a relativistic plasma with finite ion-temperature. The mass of electron is also considered. The Sagdeev’s pseudopotential is determined in terms ofu, the ion speed. It is found that there exists a critical value ofu ₀, the value ofu at which (u′)²=0, beyond which the solitary waves cease to exist. The critical value also depends on the parameters likeν, the soliton velocity;μ, the electronion mass ratio orσ, the temperature ratio of ion to electron. This result reproduces our previous result [Czech. J. Phys., Vol. 54 (2004), No. 4, 489–496] when the ion temperature is neglected.     

Energy confinement and high-k turbulence on HT-7 tokamak

A CO₂ collective scattering system has been developed to measure medium and high-k density fluctuation on HT-7 tokamak. Energy confinement and high-k density fluctuation are studied in ohmic discharges. The saturation of confinement was observed at approximately . For kθ=23 cm⁻¹ turbulence, it is found that fluctuation levels have great increase for , and simultaneously a high frequency turbulence feature appear in the frequency spectra. For kθ=14 cm⁻¹ turbulence, it is observed that fluctuation levels have no changes in uncertainties and the spectra are similar at all discharges in this experiment.     

A novel realization of the Virasoro algebra in number state space

The group of diffeomorphisms is crucial in quantum computing. Representing it by vector fields over a d-manifold, d?2, accounting for both projective action and conformal symmetry at the quantum mechanical level, requires the direct-sum decomposition of tensor product for non-compact algebras, viable only for su(1,1). As a step towards the solution, a realization of the (d=1) Virasoro algebra Vir∼Diff₊(S(1)) in the universal envelope of su(1,1) (and h(1)) is presented, which is simple in the discrete positive series irreducible unitary representation of su(1,1).     

Ion-acoustic dressed solitons in electron-positron-ion plasmas

Expanding the Sagdeev potential to include fourth-order nonlinearities of electric potential and integrating the resulting energy equation, an exact soliton solution is determined for ion-acoustic waves in an electron-positron-ion (e-p-i) plasma system. This exact solution reduces to the dressed soliton solution obtained for the system using renormalization procedure in the reductive perturbation method (RPM), when Mach number (M) is expanded in terms of soliton velocity (λ) and terms up to order of λ² are retained in the analysis. Variation of shape, velocity, width and product (P) of amplitude (A) and square of width (W²) for the KdV soliton, core structure, dressed soliton, and exact soliton are graphically represented for different values of fractional positron concentration (p). It is found that for a given value of the fractional positron concentration (p) and amplitude of soliton, the velocity of the dressed soliton is faster and width is narrower than the KdV or exact soliton, and agrees qualitatively with the experimental observations of Ikezi et al. for small amplitude solitons in the plasma free from positron component. Among all these structures, the product P(AW²) is found to be lowest for the dressed soliton and it decreases as Mach number of soliton or fractional positron concentration in the plasma increases.     

Coherent information storage with photon echoes produced by switching electric fields

We demonstrate modified photon echoes in Eu³⁺:Y₂SiO₅ by controlling the inhomogeneous broadening of the optical transition in Eu³⁺. These modified photon echoes are shown to be capable of storing phase and amplitude modulation.     

The derivative nonlinear Schrödinger equation on the half-line

We analyze the derivative nonlinear Schrödinger equation on the half-line using the Fokas method. Assuming that the solution q(x,t) exists, we show that it can be represented in terms of the solution of a matrix Riemann-Hilbert problem formulated in the plane of the complex spectral parameter ζ. The jump matrix has explicit x,t dependence and is given in terms of the spectral functions a(ζ), b(ζ) (obtained from the initial data q₀(x)=q(x,0)) as well as A(ζ), B(ζ) (obtained from the boundary values g₀(t)=q(0,t) and g₁(t)=q_x(0,t)). The spectral functions are not independent, but related by a compatibility condition, the so-called global relation. Given initial and boundary values {q₀(x),g₀(t),g₁(t)} such that there exist spectral functions satisfying the global relation, we show that the function q(x,t) defined by the above Riemann-Hilbert problem exists globally and solves the derivative nonlinear Schrödinger equation with the prescribed initial and boundary values.     

Quantum ion acoustic solitary waves in electron-ion plasmas: A Sagdeev potential approach

Linear and nonlinear ion acoustic waves are studied in unmagnetized electron-ion quantum plasmas. Sagdeev potential approach is employed to describe the nonlinear quantum ion acoustic waves. It is found that density dips structures are formed in the subsonic region in a electron-ion quantum plasma case. The amplitude of the nonlinear structures remains constant and the width is broadened with the increase in the quantization of the system. However, the nonlinear wave amplitude is reduced with the increase in the wave Mach number. The numerical results are also presented.     

A relativistic wave equation for the Skyrmion

We propose a relativistically invariant wave equation for the Skyrme soliton. It is a differential equation on the space R^1,3×S³ which is invariant under the Lorentz group and isospin. The internal variable valued in SU(2)≡S³ describes the orientation of the soliton. The mass of a particle of spin and isospin both equal to is predicted to be which agrees with the known spectrum for low angular momentum. The iso-scalar magnetic moment is predicted to be , where Σ is the spin.     

Σu and Πu states of the hydrogen molecule: Nonadiabatic couplings and vibrational levels

Nonadiabatic coupling matrix elements are computed for six lowest and four lowest ¹Π_u electronic states of H₂ in a wide range of internuclear distances. These matrix elements are used together with the adiabatic potentials to determine the bound ro-vibrational levels of the 10 electronic states for rotational quantum numbers J ? 10. The computed energies agree quite well with existing experimental term values. However, some of the experimental levels should be assigned differently.     

Effect of electron inertia on the speed and shape of ion-acoustic solitary waves in relativistic plasma

Ion-acoustic solitary waves are investigated in a cold collisionless relativistic plasma. Electron inertia is also considered. The Sagdeevs pseudopotential is determined in terms of u, the ion speed and depends on v, the velocity of the wave. It is found that there exists a critical value of u ₁ ( 0), the value of u at which (u)² = 0, beyond which the solitary waves cease to exist. The critical value also depends on the relativistic parameter u ₀/c when u ₀ is the drift velocity of the ion and c is the speed of light.     

Speed and shape of large-amplitude solitary waves in ion-beam plasma system

Large-amplitude solitary waves are investigated in ion-beam plasma system. The Sagdeev’s pseudopotential is determined in terms of the ion speedu. It is found that there exists a critical value ofu ₀, the value ofu at (u′)² = 0, beyond which the solitary waves cease to exist. The critical value also depends on σ (the ion temperature) or σ_b (the ion beam temperature). One of the author (PC) is grateful to UGC, India for the financial support under SAP(No F.510/8/DRS/2004(SAP-1)).     

Effect of twist inhomogeneity on soliton spin excitations in a helimagnet

The effect of twist inhomogeneity on the soliton spin excitations in a one-dimensional inhomogeneous helimagnet in the semiclassical limit is investigated by solving a generalised perturbed fourth order nonlinear Schrödinger equation in the continuum limit. A multiple scale perturbation analysis shows that the amplitude of the perturbed soliton depends on the nature of the inhomogeneity, but its velocity remains constant.     

Antiresonance of electron tunneling through a four-quantum-dot ring with two side-coupled quantum dots

Making use of the equation of motion method and Keldysh Green function technique, we obtain the current formula for a two-terminal four-quantum-dot-ring with two side-coupled quantum dots under a DC bias voltage. Antiresonance and resonance of electron tunneling is studied by numerical calculations. Only when the quantum dots in the ring has the same single electron energy level with that of the side-coupled quantum dots, i.e. and both side-coupling are turned on at the same time, the antiresonance appear exactly at ε₀.     

Quantum tomograms from intermediate entangled states

We show that for quantum tomography there exist two mutually conjugating intermediate coordinate-momentum entangled states |η₁,η_2〉λ,ν and |?₁,?_2〉σ,τ. The Radon transforms of the Wigner operators are just the pure-state density matrices and , respectively. As a result, the tomogram of quantum states is the module-square of their wave function in these representations. A new convenient formalism of quantum tomogram is thus established.     

Analysis of the effects of plasmas and beam slippage in optical klystron FEL devices

We examine here the effects of plasmas and beam slippage on the gain of an optical klystron (OK) free electron laser (FEL) device under the influence of a weak guiding magnetic field and background plasma. The beam energy spread decreases with background plasma density nop and increases with beam plasma density nob. The maximum gain (Gmax) scales proportional to . The beam slippage phase Δψ scales directly to five power of relativistic factor γ₀ and one half power to nob.