Ground-state energy of pionic hydrogen to one loop

We investigate the ground-state energy of the atom (pionic hydrogen) in the framework of QCD + QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at next-to-leading order in the low-energy expansion in the framework of the relevant effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths - evaluated in pure QCD - at next-to-leading order in isospin-breaking and in the low-energy expansion. We compare our result with available model calculations. Received: 11 June 2002 / Published online: 9 October 2002     

Observation of weak impact of a stochastic magnetic field on fast-ion confinement

Fast ions are observed to be very well confined in the Madison Symmetric Torus reversed field pinch despite the presence of stochastic magnetic field. The fast-ion energy loss is consistent with the classical slowing down rate, and their confinement time is longer than expected by stochastic estimates. Fast-ion confinement is measured from the decay of d-d neutrons following a short pulse of a 20 keV atomic deuterium beam. Ion confinement agrees with computation of particle trajectories in the stochastic magnetic field, and is understood through consideration of ion guiding center islands.     

Optimum conditions for pumping laser transitions of cadmium ions by various processes in a hollow-cathode discharge

The interaction of electrons of various energies with helium and cadmium atoms in a hollow-cathode discharge is analyzed. On the basis of the results of this analysis the conclusion is made that helium is ionized predominantly by electrons moving from the cathode wall to the cavity axis and having energies 70<ε<300 eV, whereas helium and cadmium are ionized predominantly by electrons with energies 9<ε<70 eV which move chaotically. For each of these energy ranges, the kinetic equation is solved and the electron energy distribution function (EDF) is determined, which is used for calculating pumping rates for laser transitions of cadmium ions. The conclusion is made that the rate of population of laser transitions through charge transfer is determined by electrons having a predominant direction of motion and an anisotropic EDF. The population rate associated with electron impact and the Penning ionization is determined by electrons moving chaotically and having an isotropic EDF. The analysis of the EDF made it possible to explain differences in discharge conditions (helium and cadmium pressures) providing optimum lasing for lines pumped by different processes. Radial profiles of pump rates obtained from the analysis made it possible to calculate and explain the dependence of the laser output power on the cathode diameter.     

On the role of strong turbulence in low-pressure rf discharges in a magnetic field

The results of an experimental and theoretical investigation of strong turbulence produced by an external rf field in the plasma of a beam-plasma discharge are presented. The modulation instability of a rf electric field, perpendicular to a constant magnetic field, in the frequency range between the lower-hybrid and ionic Langmuir frequencies, has been investigated. It is shown that the low-frequency fields can be used to control beam relaxation. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 608–612 (10 November 1996)     

Nonequilibrium plasma produced by microwave nanosecond radiation:parameters, kinetics, and practical applications

The results of the investigation of nonequilibrium plasma produced by powerful microwave nanosecond radiation is reviewed. Nanosecond microwave discharge is a new branch of gas discharge physics. At present, this type of discharge is intensively investigated. Interesting properties and peculiarities of such a discharge and various its applications are discussed, first of all for the creation of an artificial ionized layer (AIL) in the earth's atmosphere. The laboratory experiments performed and the new effects which appear in nanosecond microwave discharge are briefly summarized. Different applications of AIL are analyzed on the basis of the experimental modeling     

Structure and phase composition of the intermetallide Ni3Al+0.5 at.% B synthesized under pressure

We have used x-ray structural analysis, together with transmission and scanning electron microscopy, to study the phase composition, structure, and elemental distribution in the intermetallide Ni₃Al+0.5 at.% B, produced by self-propagating high-temperature synthesis under pressure. It is shown that the synthesized material is an ordered alloy of the type L1₂. The phase composition of the alloy Ni₃Al+0.5 at.% B is represented by the phases Ni₃Al (the fundamental phase), grains of a layered NiAl composition, and inclusions of Ni₃B. The latter is found inside the Ni₃Al grains, in the form of surrounded particles, and at dislocations and at grain boundaries in the NiAl phase. Institute for the Physics of Strength and Materials Production. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 59–64, September, 1996.     

Coulomb blockade electrometer with a high-T c island

We report on a successful attempt to fabricate a Coulomb blockade electrometer consisting of an ultrasmall YBa₂Cu₃O_7−δ (YBCO) island coupled to two gold electrodes through a high-resistance native surface tunnel barrier. A third electrode placed near the island was used as an electrostatic gate. Spectra typical for tunneling into the YBCO superconductor were reproducibly measured. At temperatures below 0.5 K the low-bias conductance was suppressed by the Coulomb blockade. The blockade could be periodically varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via the island but without any change in the period of the Coulomb oscillations. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 112–117 (25 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Interband phototransitions involving free electrons: I. Crystals with a direct band gap

Nonlinear absorption of laser radiation with a photon energy exceeding the half-width of the direct band gap of crystal but lower than its width has been considered. It is shown that, in the case of singlephoton resonance at transitions between two conduction bands, even at radiation intensities j ??10⁵?C10⁶ W/cm², there is a range of j values where the optical absorption and concentration of nonequilibrium electron-hole pairs sharply increase with an increase in j. The transition of the material between states with different optical and electric properties occurs for few nanoseconds.     

Estimation of detection limits in electron probe X-ray microanalysis

Different local methods of analysis are estimated with the aim of revealing the possibility for determining the minimum concentrations of chemical elements. Among all examined approaches, electron probe X-ray microanalysis (EPMA) has been chosen as the most accurate and promising technique. The dependences between the elemental detection limit and the analyzer??s technical parameters are investigated. It has been ascertained that the experimentally determined detection limits of light elements are substantially higher than those of heavy elements. The reasons leading to the less efficient EPMA of light elements, as well as possible ways of elimination thereof, are discussed. It is demonstrated that an X-ray mirror can be used to reach the theoretically predicted detection limits of B, O, and C.     

Crystal electric field effects in Pr0.5Sr0.5CoO3

The energy structure and temperature evolution of the magnetic excitation spectra of Pr_0.5Sr_0.5CoO₃ are studied by inelastic neutron scattering. The measurements are performed on a polycrystalline sample of Pr_0.5Sr_0.5CoO₃ and its non-magnetic analogue La_0.5Sr_0.5CoO₃ on the high intensity time-of-flight spectrometer IN4 (ILL, Grenoble) in the temperature range 10 K < T < 300 K. The crystal electric field parameters in Pr_0.5Sr_0.5CoO₃ are calculated and the splitting scheme of the 4f ground multiplet of Pr³⁺ ions is determined based on the experimental data.