Channeling of fast ions through the bent carbon nanotubes:The extended two-fluid hydrodynamic model

We investigate the interactions of charged particles with straight and bent single-walled carbon nanotubes(SWNTs)under channeling conditions in the presence of dynamic polarization of the valence electrons in carbon. This polarization is described by a cylindrical, two-fluid hydrodynamic model with the parameters taken from the recent modelling of several independent experiments on electron energy loss spectroscopy of carbon nano-structures. We use the hydrodynamic model to calculate the image potential for protons moving through four types of SWNTs at a speed of 3 atomic units. The image potential is then combined with the Doyle–Turner atomic potential to obtain the total potential in the bent carbon nanotubes.Using that potential, we also compute the spatial and angular distributions of protons channeled through the bent carbon nanotubes, and compare the results with the distributions obtained without taking into account the image potential.     

The kinetic description of the accelerated-electron flux in solar flares

We propose an accurate quantitative model describing the propagation of flare-accelerated electrons in the solar atmosphere. This model is based on a kinetic equation considering Coulomb collisions of accelerated electrons with thermal electrons and protons in the plasma of the solar corona and chromosphere. Using a self-consistent approach, we find the distribution function of accelerated electrons and the electric field of the reverse current balancing the electric current carried by the accelerated-electron flux. We compare our two-dimensional (in the velocity space) model with the widely used classical one-dimensional model that overlooks the reverse-current effect.     

低能质子束在氢等离子体中的能损研究

实验测量了100 keV的质子束穿过部分电离氢等离子体靶后的能量损失. 等离子体靶由气体放电方式产生, 其自由电子密度在10¹⁶ cm^-3量级, 电子温度约1–2 eV, 维持时间在微秒量级. 研究结果表明: 质子束在等离子体靶中的能量损失与自由电子密度密切相关且明显大于在同密度条件下中性气体靶中的能量损失; 在自由电子密度达到峰值处, 通过实验结果计算得到此时的自由电子库仑对数约为10.8, 与理论计算结果符合较好, 该值比Bethe公式给出的中性气体靶中束缚电子库仑对数高4.3倍,相应的能损增强因子为2.9.     

Two Methods of Amplification of Coherent Extreme Ultraviolet Radiation During Harmonic Generation in Plasmas

Different recently revealed approaches of harmonic enhancement in plasmas are reviewed. The 4-step analytical model of resonant enhancement of high-order harmonic generation is extended to the systems possessing resonant transitions of inner-shell electrons. Role of inelastic scattering is discussed by simulation of excited state’s population dynamics. The enhancement of harmonics in the In plasma using different pumps is analyzed to prove the concept. We also discuss the plasma emission and harmonic generation spectra in the case of resonance enhancement of single harmonic using various laser-produced plasmas. The analysis of these spectra showed that the enhancement of harmonics depended on the oscillator strengths of the nearby ionic transitions rather than the plasma emission transitions. Finally, we review some recent experimental studies of the phase-matching of high-order harmonic generation in multi-jet plasmas.     

Plasma-induced neutrino helicity flip in a supernova core and a constraint on the Dirac neutrino magnetic moment

We investigate the neutrino helicity flip under supernova core conditions, where the left-handed neutrinos being produced can be converted into right-handed neutrinos sterile with respect to weak interactions owing to the interaction of the magnetic moments with plasma electrons and protons. In calculating the probability for the conversion neutrino scattering by plasma components, we take into account the polarization effects attributable to both electrons and protons in the photon propagator. Based on realistic models with radial distributions and time evolution of physical parameters in a supernova core, we have obtained upper limits on the Dirac neutrino magnetic moment averaged over flavors and time from the condition that the influence of the right-handed neutrino emission on the total cooling time scale should be limited.     

Spin-wave contribution to the nuclear spin-lattice relaxation in triplet superconductors

We discuss collective spin-wave excitations in triplet superconductors with an easy axis anisotropy for the order parameter. Using a microscopic model for interacting electrons, we estimate the frequency of such excitations in Bechgaard salts and ruthenate superconductors to be 1 and 20 GHz, respectively. We introduce an effective bosonic model to describe spin-wave excitations and calculate their contribution to the nuclear spin-lattice relaxation rate. We find that, in the experimentally relevant regime of temperatures, this mechanism leads to the power law scaling of 1/T1 with temperature. For two- and three-dimensional systems, the scaling exponents are 3 and 5, respectively. We discuss experimental manifestations of the spin-wave mechanism of the nuclear spin-lattice relaxation.     

Laser-stimulated formation and stabilization of antihydrogen atoms

Laser-stimulated radiative transitions from states close to the ionization threshold to low-lying atomic levels are considered for protons (antiprotons) in a cold electron (positron) plasma and estimates for the resulting formation rate of hydrogen (antihydrogen) atoms in the ground state are given. The estimates apply to both laser-stimulated recombination and induced radiative stabilization of high Rydberg levels. First experiments concerning laser-stimulated recombination in merged beams of electrons and protons are discussed, which have confirmed the rate predictions for this process. In view of antihydrogen formation in a cold trapped positron plasma, the use of two successive stimulated transitions is considered for obtaining a high formation rate of ground-state atoms at relatively low radiation intensity.     

Neutrino absorption by <Emphasis Type="Italic">W</Emphasis> production in the presence of a magnetic field

In this work we calculate the damping rate of the electron type neutrinos into W bosons and electrons in the presence of an external uniform magnetic field. The damping rate is calculated from the imaginary part of the W exchange neutrino self-energy diagram but in the weak field limit, and we compare our result with the existing one.     

Persistent currents in one dimension: the counterpart of Leggett's theorem

We discuss the sign of the persistent current of N electrons in one dimensional rings. Using a topology argument, we establish lower bounds for the free energy in the presence of arbitrary electron-electron interactions and external potentials. Those bounds are the counterparts of upper bounds derived by Leggett. Rings with odd (even) numbers of polarized electrons are always diamagnetic (paramagnetic). We show that unpolarized electrons with N being a multiple of four exhibit either paramagnetic behavior or a superconductorlike current-phase relation.     

Itinerant electron theory of transition metal compounds of mixed valency: La1−xSrxMnO3

We use a simplified model to calculate the electronic band structure of compounds of the type of La_1?xSr_xMnO₃. The model includes two nonequivalent sites for the transition metal ions as well as strong Coulomb and exchange interactions between d electrons. Using the resulting band structure we discuss the correlation between magnetic order and conductivity in these compounds.     

航天器内部孤立导体表面带电面积效应研究

航天器内部孤立导体充放电对航天器的影响更为隐蔽, 造成直接和潜在的伤害更加严重. 综合考虑航天器内部环境中粒子参数及材料二次电子特性等因素, 基于气体动理论, 结合粒子的麦克斯韦速度分布函数, 得出孤立导体球充电电位一般表达式. 利用电位表达式推导得出孤立导体球净电荷量及静电场能量与导体面积关系表达式. 讨论了特殊情况下孤立导体静电场能量与面积及空间环境的关系, 与地面电子元器件电磁脉冲放电损伤值进行了对比, 总结出孤立导体表面带电面积效应规律. 关键词： 孤立导体 表面带电 静电场能量 面积效应     

RPA calculation of the effective charge in a hartree-fock basis

Using a Hartree-Fock basis the diagrams of the Tamm-Dancoff and random-phase approximations have been summed to calculate the effective charge in the (1s0d) shell. The enhancement of the effective charge found by this summation is much less than in an oscillator basis, in fact in most cases the HF RPA result is smaller than the value obtained from the lowest order core polarization diagram in an oscillator basis. The HF neutron effective charges are thus too small. For protons the enhancement of the bare effective charge in a HF basis must also be taken into account, but for cases involving the 0d_5/2 orbital the final result appears rather small.     

Theoretical investigations on propagating and growing modes in a pair plasma having dust grains

Considering a homogenous positron-electron pair plasma, we investigate the propagating and growing modes in the plasma under the presence of heavy dust particles that are negatively charged. Since these dust grains are massive particles, they do not oscillate but contribute to the excitation of the waves by providing restoring force. Normal mode analysis is used to calculate the dispersion relations based on which we analyze the propagating and growing modes in the plasma. Two types of the modes are found to occur whose phase velocities are studied under the effects of temperatures and drift velocities of the electrons and the positrons.     

部分离化激光等离子体的受激喇曼散射不稳定性

由于部分离化激光等离子体中存在束缚电子，它可显著改变其参量不稳定性。本文分析了部分离化激光等离子体的受激喇曼散射的非线性色散关系，计算了钕玻璃倍频和三倍频激光受激喇曼散射的增长率，结果表明，前向受激喇曼散射显著增强，后向受激喇曼散射影响不大。     

Electrostatic instability in magnetically confined inhomogeneous plasma driven by nonlinear force

A theoretical investigation on amplification of electrostatic ion acoustic wave in magnetically confined plasma has been presented in this paper. This investigation considers nonlinear wave–particle interaction process, called plasma maser effect, in presence of drift wave turbulence supported by magnetically confined inhomogeneous plasma. The role of associated nonlinear dissipative force in this effect in a confined plasma has been analyzed. The nonlinear force, which arises as a result of resonant interaction between electrons and modulated fields, is shown to drive the instability. Using the ion fluid equation and the ion equation of continuity, the nonlinear dispersion relation of a test ion acoustic wave has been derived, and the growth rate of ion acoustic wave in presence of low frequency drift wave turbulence has been estimated using Helimak data.     

High-field cross polarization NMR from laser-polarized xenon to surface nuclei

A method for NMR investigations of surface nuclei using cross polarization from optically polarized xenon (OPCP) is described. We find this methodology results in enhancement factors of approximately 10³ upon application to surface protons. The dynamics of¹²⁹Xe transfer to protons is examined in some detail, including the time, temperature, and multiple contact dependences of signal intensities. Furthermore, we discuss the sensitivity of the transfer process to spatial diffusion. Finally, we report on application of the OPCP experiment to a low total surface area sample.     

Parity-violating electron scattering – an experimental overview

We discuss the current status and future plans of world-wide efforts of parity-violating asymmetry measurements in the scattering of longitudinally polarized electrons off unpolarized fixed targets. One thrust is the measurements of nucleon neutral weak form factors at intermediate four-momentum transfer (0.1 < Q ² < 1) (GeV/c)² which provides information about the role of virtual strange quarks on the charge and current distributions inside nucleons. A new topic is the elastic neutral weak amplitude at very low Q ² from scattering off a heavy spinless nucleus, which is sensitive to the presence of a neutron skin. Finally, we discuss the neutral current elastic amplitude at very low Q ² off protons and electrons and in the DIS regime off deuterium, which allows precision measurements of the weak mixing angle at low energy and is thus sensitive to new physics at the TeV scale. The physics implications of recent results, potential measurements from experiments under construction as well as new ideas at future facilities are discussed.     

High electrical conductivity in nonlinear model lattice crystals mediated by thermal excitation of solectrons

The quantum statistics of electrons interacting with nonlinear excitations of a classical heated nonlinear lattice of atoms is studied. By using tight-binding approximation, Wigner momentum distributions and computer simulations we show the existence of quite fast and nearly loss-free motions of charges along crystallographic axes and estimate the range of values of transport coefficients. Using minimization of free energy we estimate the density of mobile bound states between electrons and lattice solitons (so-called solectrons). We calculate the momenta of Wigner velocity distributions and from Kubo relations the diffusivity and the electrical conductivity using the relaxation time approximation. We show that thermally excited solectrons in nonlinear media may lead to a significant transport enhancement. Our estimates and computer simulations demonstrate the existence of a temperature window, where solectrons are relatively stable and contribute strongly to transport. The electrical conductivity may be enhanced up to two orders of magnitude.     

Low-energy electron diffraction and resonances in DNA and other helical macromolecules

We propose a framework to calculate the intermolecular multiple elastic scattering of low-energy electrons from helical macromolecules and indicate how it affects the resonant capture cross section. Using a model of DNA, an appreciable enhancement of the elastic and resonant capture cross sections is predicted at incident energies below 15 eV. These results may qualitatively explain the observed prominence of low-energy resonances in strand breaking of plasmid DNA.