Electrostatic Solitary Waves in Relativistic Degenerate Electron-Positron-Ion Plasma

The linear and nonlinear properties of ion acoustic excitations propagating in warm dense electron-positron-ion plasma are investigated. Electrons and positrons are assumed relativistic and degenerate, following the Fermi-Dirac statistics, whereas the warm ions are described by a set of classical fluid equations. A linear dispersion relation is derived in the linear approximation. Adopting a reductive perturbation method, the Korteweg-de Vries equation is derived, which admits a localized wave solution in the form of a small-amplitude weakly super-acoustic pulse-shaped soliton. The analysis is extended to account for arbitrary amplitude solitary waves, by deriving a pseudoenergy-balance like equation, involving a Sagdeev-type pseudopotential. It is shown that the two approaches agree exactly in the small-amplitude weakly super-acoustic limit. The range of allowed values of the pulse soliton speed (Mach number), wherein solitary waves may exist, is determined. The effects of the key plasma configuration parameters, namely, the electron relativistic degeneracy parameter, the ion (thermal)-to-the electron (Fermi) temperature ratio, and the positron-to-electron density ratio, on the soliton characteristics and existence domain, are studied in detail. Our results aim at elucidating the characteristics of ion acoustic excitations in relativistic degenerate plasmas, e.g., in dense astrophysical objects, where degenerate electrons and positrons may occur.

Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme waves

A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.

Energy levels, radiative rates and lifetimes for transitions in Br-like ions with 38 ≤ Z ≤ 42

Energy levels and radiative rates for transitions in five Br-like ions (Sr IV, Y V, Zr VI, Nb VII and Mo VIII) are calculated with the general-purpose relativistic atomic structure package (GRASP). Extensive configuration interaction has been included and results are presented among the lowest 31 levels of the 4s²4p⁵, 4s²4p⁴4d and 4s4p⁶ configurations. Lifetimes for these levels have also been determined, although unfortunately no measurements are available with which to compare. However, recently theoretical results have been reported by Singh et al (2013 Phys. Scr. 88 035301) using the same GRASP code. But their reported data for radiative rates and lifetimes cannot be reproduced and show discrepancies of up to five orders of magnitude with the present calculations.

Energy levels, radiative rates, and lifetimes for transitions in W LVIII

Energy levels and radiative rates are reported for transitions in Cl-like W LVIII. Configuration interaction (CI) has been included among 44 configurations (generating 4978 levels) over a wide energy range up to 363 Ryd, and the general-purpose relativistic atomic structure package (grasp) adopted for the calculations. Since no other results of comparable complexity are available, calculations have also been performed with the flexible atomic code (fac), which help in assessing the accuracy of our results. Energies are listed for the lowest 400 levels (with energies up to ~98 Ryd), which mainly belong to the 3s²3p⁵, 3s3p⁶, 3s²3p⁴3d, 3s²3p³3d², 3s3p⁴3d², 3s²3p²3d³, and 3p⁶3d configurations, and radiative rates are provided for four types of transitions, i.e.E1, E2, M1, and M2. Our energy levels are assessed to be accurate to better than 0.5%, whereas radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions.

Energy levels, radiative rates, and lifetimes for transitions in W XL

Energy levels and radiative rates are reported for transitions in Br-like tungsten, W XL, calculated with the general-purpose relativistic atomic structure package (grasp). Configuration interaction (CI) has been included among 46 configurations (generating 4215 levels) over a wide energy range up to 213 Ryd. However, for conciseness results are only listed for the lowest 360 levels (with energies up to ~43 Ryd), which mainly belong to the 4s²4p⁵,4s²4p⁴4d,4s²4p⁴4f,4s4p⁶,4p⁶4d,4s4p⁵4d,4s²4p³4d², and 4s²4p³4d4f configurations, and provided for four types of transitions, E1, E2, M1, and M2. Comparisons are made with existing (but limited) results. However, to fully assess the accuracy of our data, analogous calculations have been performed with the flexible atomic code, including an even larger CI than in grasp. Our energy levels are estimated to be accurate to better than 0.02 Ryd, whereas results for radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions.

Generation of overdense and high-energy electron-positron-pair plasmas by irradiation of a thin foil with two ultraintense lasers

A scheme for enhanced quantum electrodynamics (QED) production of electron-positron-pair plasmas is proposed that uses two ultraintense lasers irradiating a thin solid foil from opposite sides. In the scheme, under a proper matching condition, in addition to the skin-depth emission of gamma-ray photons and Breit-Wheeler creation of pairs on each side of the foil, a large number of high-energy electrons and photons from one side can propagate through it and interact with the laser on the other side, leading to much enhanced gamma-ray emission and pair production. More importantly, the created pairs can be collected later and confined to the center by opposite laser radiation pressures when the foil becomes transparent, resulting in the formation of unprecedentedly overdense and high-energy pair plasmas. Two-dimensional QED particle-in-cell simulations show that electron-positron-pair plasmas with overcritical density 10(22) cm(-3) and a high energy of 100s of MeV are obtained with 10 PW lasers at intensities 10(23) W/cm(2), which are of key significance for laboratory astrophysics studies.

Gamma-ray Spectra and Enhancement Factors for Positron Annihilation with Core Electrons

Many-body theory is developed to calculate the γ spectra for positron annihilation in noble-gas atoms. Inclusion of electron-positron correlation effects and core annihilation gives spectra in excellent agreement with experiment [K. Iwata et al., Phys. Rev. Lett. 79, 39 (1997)]. The calculated correlation enhancement factors γnl for individual electron orbitals nl are found to scale with the ionization energy I_nl (in eV), as γnl=1+ √A/Inl+(B/I_nl)β, where A≈40  eV, B≈24  eV, and β≈2.3.

Positron measurements in Mg-doped GaN and development of digital Doppler broadening spectroscopy

In this work parameters of Mg-doped GaN samples were studied using positron annihilation spectroscopy and analyzed. It is shown that gallium vacancies exist in an unintentionally doped sample. Next, the sample with higher concentration of Mg and low growth temperature contains vacancy clusters. In case of low concentration of Mg the growth temperature does not affect the formation of defects. Analog electronics can be replaced by a modern digital device. While promising a high quantity of benefits, the performance of these digitizers requires thorough adjustment. A 14-bit two channel digitizer has been tested in order to achieve better performance than the one of a traditional analog setup, and the adjustment process is described. It has been shown that the digital device is unable to achieve better energy resolution, but it is quite close to the corresponding attribute of the available analog system, which had been used for measurements in Mg-doped GaN.

Generalization of the BTK Theory to the Case of Finite Quasiparticle Lifetimes

A generalization to the BTK theory is developed based on the fact that the quasiparticle lifetime is finite as a result of the damping caused by the interactions. For this purpose, appropriate self-energy expressions and wave functions are inserted into the strong coupling version of the Bogoliubov equations and subsequently, the coherence factors are computed. By applying the suitable boundary conditions to the case of a normal-superconducting interface, the probability current densities for the Andreev reflection, the normal reflection, the transmission without branch crossing and the transmission with branch crossing are determined. Accordingly the electric current and the differential conductance curves are calculated numerically for Nb, Pb, and Pb0.9Bi0.1 alloy. The generalization of the BTK theory by including the phenomenological damping parameter is critically examined. The observed differences between our approach and the phenomenological approach are investigated by the numerical analysis.

Bayesian Analysis of Simple Step-stress Model under Weibull Lifetimes

Department of Statistics, Cochin University of Science & Technology, Part of this work has been supported by grants from DST and CSIR, Government of India. 2Department of Mathematics and Statistics, IIT Kanpur

Atmospheric chemistry of C4F9OC2H5 (HFE-7200), C4F9OCH3 (HFE-7100), C3F7OCH3 (HFE-7000) and C3F7CH2OH: temperature dependence of the kinetics of their reactions with OH radicals, atmospheric lifetimes and global warming potentials

The atmospheric chemistry of several gases used in industrial applications, C4F9OC2H5 (HFE-7200), C4F9OCH3 (HFE-7100), C3F7OCH3 (HFE-7000) and C3F7CH2OH, has been studied. The discharge flow technique coupled with mass-spectrometric detection has been used to study the kinetics of their reactions with OH radicals as a function of temperature. The infrared spectra of the compounds have also been measured. The following Arrhenius expressions for the reactions were determined (in units of cm3 molecule-1 s-1): k(OH + HFE-7200) = (6.9+2.3-1.7) × 10-11 exp(-(2030 ± 190)/T); k(OH + HFE-7100) = (2.8+3.2-1.5) × 10-11 exp(-(2200 ± 490)/T); k(OH + HFE-7000) = (2.0+1.2-0.7) × 10-11 exp(-(2130 ± 290)/T); and k(OH + C3F7CH2OH) = (1.4+0.3-0.2) × 10-11 exp(-(1460 ± 120)/T). From the infrared spectra, radiative forcing efficiencies were determined and compared with earlier estimates in the literature. These were combined with the kinetic data to estimate 100-year time horizon global warming potentials relative to CO2 of 69, 337, 499 and 36 for HFE-7200, HFE-7100, HFE-7000 and CF3CF2CF2CH2OH, respectively.

Solvent influences on metastable polymorph lifetimes: real-time interconversions using energy dispersive X-ray diffractometry

Solvent influences on the crystallization of polymorph and hydrate forms of the nootropic drug piracetam (2-oxo-pyrrolidineacetamide) were investigated from water, methanol, 2-propanol, isobutanol, and nitromethane. Crystal growth profiles of piracetam polymorphs were constructed using time-resolved diffraction snapshots collected for each solvent system. Measurements were performed by in situ energy dispersive X-ray diffraction recorded in Station 16.4 at the synchrotron radiation source (SRS) at Daresbury Laboratory, CCLRC UK. Crystallizations from methanol, 2-propanol, isobutanol, and nitromethane progressed in a similar fashion with the initial formation of form I which then converted relatively quickly to form II with form III being generated upon further cooling. However, considerable differences were observed for the polymorphs lifetime and both the rate and temperature of conversion using the different solvents. The thermodynamically unstable form I was kinetically favored in isobutanol and nitromethane where traces of this polymorph were observed below 10 degrees C. In contrast, the transformation of form II and subsequent growth of form III were inhibited in 2-propanol and nitromethane solutions. Aqueous solutions produced hydrate forms of piracetam which are different from the reported monohydrate; this crystallization evolved through successive generation of transient structures which transformed upon exchange of intramolecular water between the liquid and crystalline phases. (c) 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:1069-1078, 2007.

Statistical analysis of the Doppler broadening coincidence spectrum of electron-positron annihilation radiation in silicon

We report a statistical analysis of Doppler broadening coincidence data of electron-positron annihilation radiation in silicon using a (22)Na source. The Doppler broadening coincidence spectrum was fit using a model function that included positron annihilation at rest with 1s, 2s, 2p, and valence band electrons. In-flight positron annihilation was also fit. The response functions of the detectors accounted for backscattering, combinations of Compton effects, pileup, ballistic deficit, and pulse-shaping problems. The procedure allows the quantitative determination of positron annihilation with core and valence electron intensities as well as their standard deviations directly from the experimental spectrum. The results obtained for the core and valence band electron annihilation intensities were 2.56(9)% and 97.44(9)%, respectively. These intensities are consistent with published experimental data treated by conventional analysis methods. This new procedure has the advantage of allowing one to distinguish additional effects from those associated with the detection system response function. (C) 2009 Elsevier B.V. All rights reserved.

An experimental and theoretical investigation into positron and electron scattering from formaldehyde

We report on measurements of total cross sections (TCSs) for positron scattering from the fundamental organic molecule formaldehyde (CH(2)O). The energy range of these measurements was 0.26-50.3 eV, whereas the energy resolution was similar to 260 meV. To assist us in interpreting these data, Schwinger multichannel level calculations for positron elastic scattering from CH(2)O were also undertaken (0.5-50 eV). These calculations, incorporating an accurate model for the target polarization, are found to be in good qualitative agreement with our measured data. In addition, in order to compare the behaviour of positron and electron scattering from this species, independent atom model-screened additivity rule theoretical electron TCSs, now for energies in the range 1-10 000 eV, are also reported.

(6)Li direct breakup lifetimes

alpha-d coincidence data are studied for the (6)Li + (59)Co reaction at E(lab) = 29.6 MeV. A kinematic analysis is used to identify which process, leading to the same final state, has the major contribution for selected angular regions. The contributions of the (6)Li sequential and direct breakup to the incomplete fusion/transfer process is discussed by considering the corresponding lifetimes obtained by using a semiclassical approach.