bluuebunny/crossref_metadata_2025 huggingface dataset:
Low temperature physics without a cryostat: laser cooling and trapping of atoms
Authors: Bigelow N. P.
Published: July 2002

In recent years, there has been significant interest in the laser manipulation of neutral atoms, and specifically in the use of light fields to manipulate not only the internal but also the external coordinates of an atom. Among the most dramatic results of this work have been the production of dense ultra-cold samples of trapped neutral atoms. These samples have been used to expand the horizons of fundamental physics and have made possible significant advancements in metrology. Furthermore, the ability to manipulate atomic motion with light has helped to create entirely new fields of research such as atom optics where matter wave analogues of light wave systems are investigated and optical where light is used to create a periodic array of atoms similar to crystals.
Mapping of 2D contact perturbations by electrons on a helium film
Authors: Teske E. , Wyder P. , Leiderer P. , Shikin V.
Published: July 2002

A promising way to investigate 2D contact phenomena is proposed. This method is based on the idea of depositing surface state electrons (SSE) on a thin layer of liquid helium covering the surface of a solid sample containing a 2D charge carrier system. The density of SSE adjusts to screen contact-induced perturbations of the electrostatic potential across the sample. As a result, the helium layer thickness varies due to the variation of the electrostatic pressure, thus providing a map. This map may be read off interferometrically by a technique already employed for the investigation of multi-electron dimples on helium. We have realized this mapping for a structured electrode as a test sample to demonstrate the resolution of the method.
Experimental and theoretical studies of levitated quantum fluids
Authors: Schmidt J. , Halley J. W. , Giese C. F.
Published: July 2002

We describe the opportunities for improved scientific understanding and technical manipulation of cryogenic fluids, particularly molecular hydrogen, by the use of carefully designed magnetic field configurations produced with assemblies of permanent magnets. We discuss the levitation of hydrogen in order to perfect technical means for handling this and other cryogenic fluids. The development of the techniques to be explored here provide extraordinary opportunities for improved methods for handling rocket fuels and cryogenic fluids in low gravity environments.
Hall effect studies in YBCO films
Authors: Solovjov A. L.
Published: July 2002

The longitudinal, ρxx(T), transverse, ρxy(T), and Hall, ρH(T) resistivities have been measured for YBa2Cu3Ox (YBCO) films, showing positive resistivity buckling and those with usual linear ρxx(T) dependence. In the former case unexpected peak on ρxy(T) and unusual ρH(T) dependence with double sign change just above transition temperature Tc have been revealed. The data are analyzed using recent theory for the sign of the Hall conductivity in strongly correlated systems.
Bound electron pairs in strongly correlated models of high-temperature superconductivity
Authors: Boyaci H. , Kulik I. O.
Published: July 2002

The ground-state energy of two electrons on a ring is calculated for the one-dimensional Hubbard model with positive and negative on-site interaction and for the contraction model with additive and multiplicative interaction terms. The hc/2e periodicity of the ground-state energy with respect to a flux Φ threading the loop is derived. The periodicity may serve as an indication of superconductivity. The results are shown to be consistent with the Lieb–Wu solution for Φ=0 limit. In addition, the new states that were missing in the Lieb–Wu solution are derived.
Stability of a bounded charged He film on a metal substrate
Authors: Shikin V. B. , Lebedeva E. V.
Published: July 2002

Peculiarities in the problem of surface stability of a charged bounded helium film on a metal substrate are considered. The dependence of critical instability parameters on the in-plane film size is determined. A method is proposed for observing metastable states of a charged liquid film.
Continuous radiation of excimer complexes in argon and neon crystals
Authors: Belov A. G. , Fugol’ I. Ya. , Yurtaeva E. M.
Published: July 2002

This research is devoted to an analysis of continuous luminescence spectra of argon and neon crystals in the ranges 4–7 and 9–17 eV, respectively. The experimental results of this research are compared comprehensively with the data on the gaseous phase and with the luminescence of exciplexes of inert-gas halogenides. It is proposed on the basis of the detailed comparison of different experimental data that the continuum with a peak at 6.2 eV can be identified with radiation decay of the excimer complex Ar2+O−. The formation of a similar exciplex Ne2+O− with charge transfer is observed in the neon matrix doped strongly with oxygen.
On transfer of motion between superfluid liquid and superconducting condensate
Authors: Shevchenko S. I. , Terent’ev S. V.
Published: July 2002

The problem of transfer of motion from a superfluid He4 film to electrons in a superconducting film is considered. The conditions under which atoms of He4 film drag superconducting electrons are determined. An experiment is proposed for detecting the predicted effect.
Effect of electron-magnon coupling on the electronic spectrum of weakly doped high-Tc compounds
Authors: Ivanov M. A. , Loktev V. M. , Pogorelov Yu. G.
Published: July 2002

A theoretic analysis of magnon-induced damping Γ of quasiparticle states in the normal phase of doped copper-oxide high-Tc materials is developed, based on a microscopic model which accounts for the specific 2D structure of their electron and magnon spectra. Among the obtained energy and temperature dependencies of Γ in different regimes, the most peculiar is the anomalously early onset of linear temperature dependence Γ∝T with a doping-independent coefficient.
Quasiperiodic superconducting V/Zr multilayers: critical magnetic fields and crossover
Authors: Fogel N. Ya. , Cherkasova V. G. , Mikhaı̆lov M. Yu. , Bomze Yu. V. , Yuzephovich O. I. , Dmitrenko I. M. , Stetsenko A. N.
Published: July 2002

Critical magnetic fields parallel and perpendicular to the planes of quasiperiodic superconducting Fibonacci multilayers (ML) consisting of vanadium and zirconium are measured. The temperature dependence of the parallel critical field Hc∥ displays two crossovers. The Hc∥(T) dependence is of square-root type in the vicinity of the transition temperature Tc and linear at low temperatures. Between these temperature intervals, the dependence follows a power law: Hc∥∼(1−T/Tc)α, α=0,78±0,02. The complex nature of this dependence can be explained in the framework of the Ginzburg–Landau theory for a quasiperiodic ML, as well as by the scaling theory for fractal multilayers which takes into account the different structure length scales in the case of ML with a complex sequence of layers.
Influence of mechanisms of nonequilibrium quasiparticle scattering on the properties of phase-slip centers
Authors: Churilov G. E. , Agafonov A. B. , Dikin D. A. , Dmitriev V. M.
Published: July 2002

Electrical characteristics of homogeneous superconducting tin films with phase-slip centers (PSC) and with structures of the superconductor–normal metal–superconductor (SNS) type are studied experimentally. It is found that near the superconducting transition temperature, elastic scattering of nonequilibrium quasiparticles can play a significant role in PSC by reducing the effective charge disbalance time, and hence the diffusion length for quasiparticles as compared to similar processes in the SNS structure. The application of an external electromagnetic field of frequency ∼1010 Hz in the vicinity of the superconducting transition temperature reduces the resistance of the SNS structure to zero, indicating a superconducting transition in the N region. An increase in the transport current results in the formation of the first PSC just in this region. Non-Josephson oscillations appear in this region at certain temperatures, currents, and radiation power.
Order parameter fluctuations and superconducting transition temperature in quasi-2D metals with arbitrary carrier density
Authors: Loktev V. M. , Turkowski V. M.
Published: July 2002

It is shown that the order parameter fluctuations result in a power dependence of the superconducting transition temperature in quasi-2D metals on the probability of fermion hopping between layers. The dependence of this temperature on the carrier concentration is determined for a model with indirect attraction between carriers. It is found that the transition takes place at temperatures lower than those expected from the BCS theory.
Instability of a one-dimensional quantum antiferromagnet under magnetic anisotropy
Authors: Apal’kov D. M. , Zvyagin A. A.
Published: July 2002

It is shown by using the exact quantum-mechanical solution that a one-dimensional antiferromagnetic Heisenberg spin chain is unstable to the emergence of an easy-plane magnetic anisotropy in a real three-dimensional crystal. It is shown that the magnetic anisotropy is due to a Jahn–Teller type effect, i.e., a strong spin–lattice coupling. A change in the equilibrium position of ligands induces magnetic anisotropy in the spin chain.
On electron states localized at intercrystallite and twin boundaries
Authors: Feldman E. P. , Yurchenko V. M.
Published: July 2002

It is stated that an electron can be in a state localized at an intercrystallite or twin boundary or stacking fault irrespective of the specific structure of the transition region. It is important that the crystal containing such a boundary must be non-periodic “as a whole.” The one-dimensional model (two abutting Kronig–Penney lattices for which the spectrum of localized states is determined) is considered. The bands containing one or two discrete levels alternate in a complex way in the spectrum.
Anomalously rapid transport of matter during dissolution of solid clusters of He3 in separated He3–4He mixtures
Authors: Gan’shin A. N. , Maidanov V. A. , Omelaenko N. F. , Penzev A. A. , Rudavskii E. Ya. , Rybalko A. S.
Published: July 2002

The kinetics of growth and dissolution of a new phase during phase separation and homogenization of solid He3–4He mixtures is studied experimentally. It is found that both these processes have different kinetics, while homogenization is ensured by an anomalously rapid transport of matter in the crystal. It is shown that the prevailing theories about diffusion processes in a quantum crystal cannot explain the obtained results.
Anomalous transport behavior of La0.825Sr0.175MnO3−δ polycrystalline samples below Curie temperature
Authors: Pogorilyi A. N. , Belous N. A. , Tovstolytkin A. I. , Belous A. G. , Yanchevski O. Z.
Published: July 2002

The temperature (T) dependencies of resistivity (ρ0) and magnetoresistance (MR) in the range of 100–300 K have been investigated in La0.825Sr0.175MnO3−δ polycrystalline samples with different sintering temperatures TS (1300 °C and 1360 °C). Two peaks on the ρ0(T) curve were found in the sample with the lower value of TS. Inhomogeneity of the spin configuration and multiply-connectedness of ferromagnetic phase is believed to give rise to anomalous behavior of resistivity below the Curie temperature.
Magnetic ordering at the stepped ferro/antiferromagnetic interface
Authors: Dudko O. K. , Kovalev A. S.
Published: July 2002

A nonuniform distribution of magnetic disclination type magnetization connected with the atomic size step on the ferro/antiferromagnetic boundary is studied. The obtained results are generalized to the case of periodic stepped ferro/antiferromagnetic interface.
Effect of linearly polarized light on metamagnetic phase transition in Ca3Mn2Ge3O12 garnet
Authors: Bedarev V. A. , Gapon V. I. , Gnatchenko S. L.
Published: July 2002

It has been found that the field Ht of a metamagnetic phase transition in Ca3Mn2Ge3O12 garnet changes as a result of illumination of the crystal with linearly polarized light. The value of Ht decreases under the illumination with the light polarization E‖[110] and increases in the case of the light polarization E‖[11̄0]. The difference in the values of transition field in these two cases amounts to ∼100 Oe at the temperature T=7 K, for which Ht≃31.2 kOe in an unexposed crystal. The change in the value of the metamagnetic phase transition field is attributed to the photoinduced magnetic moment whose magnitude and direction depend on the polarization of the inducing radiation.
Low-temperature lattice instability in SnTe
Authors: Nashchekina O. N. , Rogacheva E. I. , Fedorenko A. I. , Isakina A. P. , Prokhvatilov A. I.
Published: July 2002

The temperature dependences of the unit cell parameter a(T) of tin telluride with different extents of deviation from stoichiometry are obtained during heating from 80 to 290 K. The a(T) dependence for a sample with the stoichiometric composition (50 at.%Te) displays an anomaly in the temperature range 90–100 K, which is attributed to the well-known ferroelectric phase transition (PT). Well-pronounced jumps in the unit cell parameter (Δa/a≈0.015) observed for 50.4 at.%Te in the intervals 135– 150 K and 200-215 K correspond to a negative thermal expansion coefficient. Upon a further increase in the deviation from stoichiometry (50.8 at.%Te) these effects become less pronounced. The instability in the crystal lattice in certain temperature intervals is attributed to phase transitions in the subsystem of intrinsic defects (nonstoichiometric vacancies) associated with their redistribution over the cation sublattice upon a change in the temperature and composition. The role of relaxation phenomena in the rearrangement of crystal defect subsystem is determined.
Static phenomena at the charged surface of liquid hydrogen
Authors: Levchenko A. A. , Kolmakov G. V. , Mezhov-Deglin L. P. , Mikhailov M. G. , Trusov A. B.
Published: July 2002

Evolution of the shape of the equipotentially charged surface of the liquid hydrogen layer covering the lower plate of a horizontally arranged flat diode in increasing external stretching electric fields has been studied experimentally for the first time. Reconstruction of a flat charged surface (formation of a stationary hump) at voltages higher than a certain critical value Uc1 is observed under conditions of total compensation of the electric field in the bulk of the liquid by a surface charge. It is shown that the transition of the flat charged surface to the reconstructed state is a phase transition close to a second-order transition. The height of the hump is found to increase with voltage, the reconstructed surface loses its ability at a voltage Uc2>1.2Uc1, and a streamed discharge is observed. Evolution of the shape of a charged droplet of constant volume suspended from the upper plate of a diode is studied with increasing electric field under the conditions when the forces of gravity and stretching electric field act in the same direction.
Nature of anomalous behavior of the surface resistance of YBa2Cu3O7−δ films in a microwave field
Authors: Prokhorov V. G. , Kaminsky G. G. , Lee Yong Pak
Published: July 2002

The temperature dependence of the surface resistance of overdoped YBCO films is studied experimentally. It is shown that the observed unusual behavior of the surface resistance can be described within the framework of spin-flip scattering of carriers, which leads to pair-breaking and the emergence of the gapless state.
Lower critical fields of texturized high-Tc superconductors. II On the possibility of studying the anisotropy of Hc1
Authors: Finkel’ V. A.
Published: July 2002

The concepts about the possibility of studying the anisotropy of lower critical fields of HTSC are developed by measuring the values of Hc1 in texturized samples for different angles of rotation of the investigated sample relative to the axis perpendicular to the external magnetic field H.
Interaction of nonuniform elastic waves with two-dimensional electrons in AlGaAs–GaAs–AlGaAs heterostructures
Authors: Fil’ D. V.
Published: July 2002

The interaction of a double-layer electron system in a AlGaAs–GaAs–AlGaAs heterostructure with nonuniform elastic modes localized in the GaAs layer is considered. The dependence of the interaction constant on the ratio between the thickness of the GaAs layer and the wavelength is calculated in a system with interfaces parallel to the (001) plane for waves with the wave vector directed along the [110] axis, the polarization vector lying in the (11̄0) plane. It is shown that the interaction constant attains its maximum value for the wavelength of the order of the thickness of the GaAs layer. The renormalization of the velocity of elastic waves is found for the case when the electron system is under the conditions of the fractional quantum Hall effect. It is shown that for some modes, the dependence of the velocity renormalization on the wave vector is modified qualitatively upon a transition of the electron system to a state corresponding to the Halperin wave function.
Thermal disorder of proustite cationic sublattice
Authors: Borovoı̆ N. A. , Gololobov Yu. P. , Salivonov I. N.
Published: July 2002

Temperature dependences of acoustic emission and relative intensity of some structural x-ray peaks for proustite (Ag3AsS3) samples are investigated in the temperature range 100–300 K. Anomalous behavior of the obtained dependences is observed at T∼150 K. The experimental results have been analyzed by using different models of positional disorder of the silver sublattice. The entire body of the obtained data can be explained assuming that an increase in temperature starting from T∼150 K leads to predominant disordering of the part of the cationic sublattice of proustite, that is formed by right spirals (AgS)∞.
“High-temperature” oscillations of bismuth conductivity in the ultra-quantum limit
Authors: Krasovitsky Vit. B. , Khotkevich V. V. , Jansen A. G. M. , Wyder P.
Published: July 2002

The results of joint studies of Shubnikov–de Haas oscillations and “high-temperature” oscillations (HTO) of diagonal and nondiagonal components of the magnetoresistance tensor for pure bismuth in magnetic fields up to 20 T are presented. The oscillations are measured for magnetic field directions close to trigonal and binary crystallographic axes at temperatures 4–43 K. A comparison of the variation of energy spectrum parameters for bismuth in ultra-quantum limit with peculiarities of “high-temperature” oscillations leads to the conclusion confirming the correspondence between HTO periods to the width of the energy band overlapping region. In the case when light electrons in two ellipsoids are in the ultra-quantum limit, a correlation between the exit of the last Landau level of heavy electrons (i.e., complete closure of the third electron ellipsoid) and the vanishing of HTO periods is observed in high magnetic fields. This experimental fact can play a key role in the theoretical description of the nature of HTO.
Effects of alloying and pressure on magnetic properties of itinerant intermetallic compound UFe2
Authors: Panfilov A. S. , Svechkarev I. V. , Diko P. , Mihalik M. , Zentko A.
Published: July 2002

The ferromagnetic state of the itinerant compound UFe2 correlated with a peak in the density of states at the Fermi level is well known to be strongly suppressed by replacing Fe with other 3d elements. To separate the effect of change in filling of the band from that of its deformation under alloying, the magnetic susceptibility of both quasi-binary alloys U(Fe1−xMex)2 (Me=Mn, Co) with a varying number of valence electrons and isoelectronic quasi-ternary alloys U(Fe1−xTx)2, U(Fe0.9−xMn0.1Tx)2 and U(Fe0.9−xCo0.1Tx)2 (T=Mn0.5Co0.5) was studied in the temperature range 4.2 K⩽T⩽300 K. Both effects were found to play important roles in suppression of the ferromagnetic state in UFe2-based alloys. In addition, the magnetic susceptibility of U(Fe1−xMnx)2 and U(Fe1−xTx)2 alloys and UCo2 compound have been studied under pressure up to 4 kbar at T=78 and 293 K. The volume dependence of the exchange enhancement in spin paramagnetism of the UFe2 compound and its alloys has been derived from analysis of the pressure effects in the framework of the Stoner model.
Natural electron oscillations in Te granules deposited on rough surfaces
Authors: Shklyarevsky I. N. , Bondarenko Yu. Yu. , Makarovsky N. A.
Published: July 2002

Granular tellurium films deposited on rough surfaces of NaCl and KCl single crystals heated to 150 °C consist of two layers in each of which a resonance band is excited simultaneously. A band with frequency ω0 of natural electron oscillations is excited in isolated granules of the upper layer. The plasma frequency of bulk tellurium is calculated from the measured values of ω0 and the known permittivities of NaCl and KCl.
Optical surface modes in a system of fine metallic particles
Authors: Blank A. Ya. , Garanina L. V. , Grechko L. G.
Published: July 2002

The interaction of electromagnetic radiation with a low-density disordered system of fine metallic particles located in a dielectric matrix is considered in a quasi-static approach with allowance for dipole-dipole interaction. The electric dipole moment of the system is calculated in a pair approximation. The case of nonidentical particles differing in their sizes or dielectric functions is presented. Allowance for particle nonidentity leads to doubling of the number of their surface modes and to the appearance of band gaps in the spectrum. The spectrum peculiarities are revealed in the fine structure of electromagnetic absorption.
Time correlation functions and generalized transport coefficients of semiquantum helium
Authors: Ignatyuk V. V. , Tokarchuk M. V. , Mryglod I. M.
Published: July 2002

The dynamic properties of semiquantum He4 are analyzed at two temperatures above the point of superfluid phase transition. Investigations are carried out in the framework of the dynamic thermal viscous model for low and intermediate values of the wave vector. The “momentum–momentum” and “enthalpy–enthalpy” time correlation functions are evaluated and the partial contributions of the collective excitations to these functions are separated. The recurrent relations for memory kernels are used to calculate the time–space dispersion of the generalized transport coefficients.
Description of critical behavior of Ising ferromagnet in the ρ6 model approximation taking into account confluent correction. I. Region above the phase transition point
Authors: Pylyuk I. V.
Published: July 2002

The behavior of a 3D Ising system at temperatures above Tc is studied in the approximation of sextic distribution for modes of spin moment density oscillations (ρ6 model). An original method is developed in this higher non-Gaussian approximation for calculating the thermodynamic characteristics of the 3D Ising model near Tc taking into account the first confluent correction. The contributions to the thermodynamic functions of an Ising ferromagnet (free energy, entropy, internal energy, and specific heat) from the short-wave and long-wave modes of spin density oscillations are considered separately. A nonuniversal factor determined by microscopic characteristics of the system is singled out in the expressions for leading critical amplitudes and the amplitudes of the confluent correction. Numerical estimates of the critical region size, phase transition temperature, leading critical amplitudes, and the amplitudes of the correction to scaling of specific heat and susceptibility of the system are given for different values of effective radius of the exponentially decreasing interaction potential.
Critical current density and granularity in crystals of K3C60 fulleride
Authors: Buntar V. A. , Buntar A. G.
Published: July 2002

The temperature dependence of the critical current density Jc(T) in superconducting fulleride K3C60 crystals is investigated on the basis of magnetization measurements in these materials. According to ac susceptibility data, the best crystals do not exhibit granularity for supercurrent flows, and can be regarded as single crystals from this point of view. The obtained results on Jc in K3C60 are compared with those for other crystalline and powder-type compounds AxByC60. Possible granularity of the crystals and its influence on Jc are discussed in detail. The irreversibility line for a K3C60 single crystal is also determined.
Transport critical current in granular high-temperature superconductors
Authors: Bogolyubov N. A.
Published: July 2002

The temperature and size dependences of critical current in three Bi-based ceramic HTSC samples with a circular cross section and in a sample with a right triangular cross section in zero magnetic field are studied by a contactless technique. It is shown that the critical current of ceramic HTSC can be presented as the product of the temperature- and size-dependent factors. The temperature-dependent factor describes individual properties of the Josephson net of each sample, while the size-dependent factor is a homogeneous function whose exponent does not depend on the shape of the sample cross section. An analysis of experimental data is used to find the radial distribution of critical current density in round samples and to determine its dependence on the magnetic induction in granular HTSC.
Sound attenuation in the superconducting amorphous alloy ZrTiCuNiBe
Authors: Bezuglyı̆ E. V. , Gaiduk A. L. , Fil V. D. , Johnson W. L. , Bruls G. , Lüthi B. , Wolf B. , Zherlitsyn S. V.
Published: July 2002

The superconducting energy gap and the parameter η determining the intensity of electron scattering at two-level systems in amorphous ZrTiCuNiBe are determined from the results of measurements of sound attenuation. The mechanism of adiabatic renormalization of the amplitude of coherent tunneling is used for a quantitative description of the peculiarities of sound absorption in the vicinity of Tc.
Motion of vortices in an annular region
Authors: Zueva T. I.
Published: July 2002

The vortex solutions of the nonlinear Schrödinger equation in a bounded region are analyzed. The asymptotic limit in which the dimensions of the vortex cores are much smaller than the distance between vortices is investigated. A system of equations describing the dynamics of vortices in the annular region (ring) between two coaxial cylinders is derived. It is shown that as the inner radius of the ring decreases, the system of equations reduces to the corresponding system on a disk, and as the gap decreases, the motion obtained is analogous to that in a rectilinear channel. An analytical solution of the equation is given for the case when there is only one vortex in the ring, and a numerical simulation of the motion of two vortices with arbitrary signs of the vortex strength is carried out for different initial positions of the vortices.
Crowdion dynamics in a nonuniformly deformed three-dimensional crystal
Authors: Natsik V. D. , Nazarenko E. I.
Published: July 2002

The problem of crowdion motion is formulated and analyzed as a dynamical problem of a three-dimensional crystal lattice formed by atoms of several kinds, which interact with each other by means of short-range pair potentials. It is explained that in order for the the crowdion excitations of the close-packed atomic rows to be distinguishable against the background of small dynamic deformations of the crystal as a whole, the microscopic parameters of the crystal structure must meet certain stated requirements. The equation of motion of a crowdion in an arbitrary elastic strain field of the crystal is derived in the Lagrangian formalism. Expressions are obtained which relate the effective mass and the rest energy of a crowdion with the geometric and force parameters of the crystal lattice.
Low-field electrodynamics of granular high-temperature superconductors
Authors: Ignat’ev V. K. , Neginskiı̆ I. V.
Published: July 2002

Studies of the low-field electrodynamics of YBaCuO ceramic superconductors are described. An analytical treatment and a numerical simulation are carried out in the model of pinning and viscous flow of hypervortices in high-Tc superconductors (HTSCs) to find the dependence of the real and imaginary components of the surface impedance on the modulus of a static magnetic field and on the amplitude and frequency of an alternating field. Experimental results are presented on the magnetic-field dependence of the impedance components. The studies were carried out in the frequency range from 30 Hz to 1 kHz and at amplitudes of the alternating component of the field from 0.1 to 10 Oe. It is shown that the critical-state model is applicable to HTSCs in the region of low frequencies and small amplitudes of the alternating component of the field. The model of viscous flow of hypervortices gives a good description of the low-field electrodynamics of HTSCs over a wide range of frequencies and, in particular, predicts the experimentally observed hysteresis of the magnetic-field dependence of the surface impedance.
Charge ordering in quasi-two-dimensional high-temperature superconductors
Authors: Sergeeva G. G.
Published: July 2002

The hypothesis that the semiconducting trend of the resistivity ρc(T) in quasi-two-dimensional high-Tc superconductors is of a fluctuational nature, due to charge ordering and a superconducting transition, is discussed. At temperatures T>T* (T* is the charge ordering temperature) these are fluctuations that prevent charge ordering. For T⩽Tc0, where Tc0 is the temperature of the two-dimensional superconducting transition in mean-field theory, regions with strong superconducting fluctuations arise in the copper–oxygen plane, leading to a substantial temperature dependence of the probability tc(T) for the tunneling of charge along the ĉ axis in the normal state.
Some properties of dynamic solitons of nonlinear systems that are determined by the linearized equation
Authors: Kosevich A. M.
Published: July 2002

The features of dynamic solitons in nonlinear systems described by differential equations with fourth-order spatial derivatives are discussed for systems of different dimensionalities. The existence conditions for a nonradiative soliton are formulated for the case when the internal frequency of the soliton lies in the continuous spectrum of harmonic oscillations of the system under study. These conditions are determined by the form of the dispersion relation of the linear oscillations. The use of the stated conditions for determining the parameters of two-dimensional solitons is demonstrated.
Vorticity transport and wake structure for bluff bodies at finite Reynolds number
Authors: Leal L. G.
Published: July 2002

This paper is concerned with the structure of recirculating wakes downstream of bluff bodies at finite Reynolds number, and the relationship between these wakes and asymptotic behavior for R→∞. It is shown that recirculating eddies at finite Reynolds number are not necessarily a precursor of the asymptotic phenomenon of separation that is ‘‘predicted’’ via boundary-layer theory. In some cases, such as the flow around deformable gas bubbles, recirculating eddies may appear at intermediate Reynolds numbers, but then disappear with further increase of the Reynolds number. In other cases, recirculating eddies exist downstream of the body at finite Reynolds number that are completely detached from the body. These examples suggest that recirculating eddies at large, but finite Reynolds number do not necessarily imply anything about the solution behavior for R→∞, even for solid bodies where it is usually assumed that wakes for R∼O(10–100) are a manifestation of the same processes that lead to separation of boundary layers for R→∞.
Effects of corrugation parameters on fluid mixing characteristics in corrugated passages
Authors: Gaiser Gerd , Kottke Volker
Published: July 2002

Static mixers are well established in process engineering. Their particular advantages are in-line mixing, no moving parts, low power consumption, and simultaneous homogenization of residence time behavior. Several species of static mixers are well known. An example of their arrangement is based on corrugated passages formed by layers of single plates with opposing orientation. Until now, the corrugation parameters of this species have mainly been designed according to few experimental studies. However, flow phenomena, implied by the geometry of the corrugated structure, are of significant influence on the mixing behavior, the pressure drop, and the residence time characteristics in corrugated passages. In new investigations, the effects of a variety of corrugation parameters on flow phenomena, mixing characteristics/and pressure drop have been systematically determined. The results prove that there are quite different kinds of flow phenomena depending on the geometrical parameters of the structure. Some parameter combinations lead to no mixing at all, others lead to a homogeneous mixing within a small length. Examples are shown of flow behavior in corrugated passages; here the flow has been traced locally making the flow direction evident.

The effects of corrugation parameters on the fundamental flow phenomena will be discussed. In order to describe and predict the flow behavior in these corrugated passages, a model has been set up based on the fundamental flow phenomena. This model allows the simulation of flow behavior in corrugated passages, thereby allowing, also, the simulation of the mixing characteristics and the residence time behavior of the fluid in these structures. Examples of the simulation, where the local addition of a tracer and its mixing across the structure has been simulated, are shown. Further results of flow simulation on mixing characteristics and dynamic aspects will be compared to experiments. Combined with the pressure drop in corrugated passages, the model allows the optimization of motionless mixer design. Several aspects of structure optimization will be discussed.
Fractal interfaces and product generation in the two-dimensional mixing layer
Authors: Jiménez Javier , Martel Carlos
Published: July 2002

The dependence of product generation on Péclet and Reynolds numbers in a numerically simulated, reacting, two-dimensional, temporally growing mixing layer is related theoretically to the fractal dimension of the passive scalar interfaces. This relation is verified using product generation measurements and fractal dimensions derived from the box counting technique. A transition from a low initial dimension to a higher one of approximately (5)/(3) is identified and shown to be associated to the kinematic distortion of the flow field during the first pairing interaction. It is suggested that the structures responsible for this transition are nondeterministic, nonrandom, inhomogeneous fractals. In the range of Schmidt numbers investigated (0.25–4), only the large scales are involved. No further transitions, either in the spectra of the vorticity field or in the mixing behavior, are found for Reynolds numbers up to 90 000.
Fine structure of energy transfer in turbulence
Authors: Kida Shigeo , Ohkitani Koji
Published: July 2002

The energy transfer process in wave-number space is investigated numerically in a forced developed turbulence of Taylor microscale Reynolds number 186 with high symmetry. The energy flow to/from Fourier modes in each wave-number band changes direction repeatedly in time. The inflow and outflow phases align along curves with positive slopes in the (k,t) plane, k being the wave number and t the time. This suggests that the energy is carried step-by-step to larger wave numbers. A blob of modal energy is transferred to larger wave numbers in a way consistent with k∝(t*−t)−3/2 as predicted by Kolmogorov’s dimensional arguments, where t* is a constant.
Shock wave propagation in a magnetic flux tube
Authors: Ferriz-Mas A. , Moreno-Insertis F.
Published: July 2002

The propagation of a shock wave in a magnetic flux tube is studied within the framework of the Brinkley–Kirkwood theory adapted to a radiating gas. Simplified thermodynamic paths along which the compressed plasma returns to its initial state are considered. It is assumed that the undisturbed medium is uniform and that the flux tube is optically thin. The shock waves investigated, which are described with the aid of the thin flux-tube approximation, are essentially slow magnetohydrodynamic shocks modified by the constraint of lateral pressure balance between the flux tube and the surrounding field-free fluid; the confining external pressure must be balanced by the internal gas plus magnetic pressures. Exact analytical solutions giving the evolution of the shock wave are obtained for the case of weak shocks.
Chaotic mixing in a spatially periodic continuous mixer
Authors: Ling F. H.
Published: July 2002

Mixing in a spatially periodic continuous mixer, the partitioned pipe mixer, is studied using bifurcation analysis with the help of geometric construction of periodic orbits and a knowledge of the symmetry of the mixing system. Mixing windows, where motion in the mixer is nearly globally chaotic, are found in the parameter space. Uniform ultimate mixtures are expected in the mixing windows as verified with the Poincaré sections. The present analysis provides a better understanding of the existing experimental results.
On universality of geometrical invariants in turbulence—Experimental results
Authors: Bershadskii A. , Kit E. , Tsinober A.
Published: July 2002

Experimental results on probability distribution functions (pdf’s) of full dissipation ε, enstrophy ω2, and enstrophy generation ωiωjsij in two different turbulent flows: turbulent grid flow (Reλ=74) and turbulent jet center (Reλ=880) demonstrate the possibility of universal behavior of the pdf’s of these quantities.
On the interaction between two nonpropagating hydrodynamic solitons
Authors: Yan J. R. , Yan X. H. , You J. Q. , Zhong J. X.
Published: July 2002

The evolution equation governing the positions of two interacting nonpropagating solitons is found by using the variational principle approach. Furthermore, the potential which characterizes the interaction between solitons is derived, from which some important results are obtained: (1) Two solitons with the same polarity always attract each other, while those with opposite polarity repel. (2) The repulsion is much weaker than the attraction and both attraction and repulsion are of short distance. (3) The period of mutual oscillation caused by interaction between two solitons with the same polarity increases as the drive amplitude rises; especially, the period can spread from zero to infinity as the initial distance between solitons increases. All the above results are well coincident with experiments.
Effects of coherent density fluctuations on the ion–ion hybrid resonance
Authors: Romero H. , Morales G. J.
Published: July 2002

An analytic and numerical study is made of the effects caused by coherent density fluctuations, localized near the ion–ion hybrid resonance, on the propagation and absorption of fast Alfvén waves. The system is represented by a Budden equation that incorporates static fluctuations in the ion density profiles. The unperturbed system contains a resonance at x=0 and a cutoff at x=d; the Alfvén wave number at resonance is kA. Two cases are considered: fluctuations in the ion concentration ratio η and bulk density fluctuations. When the incident wave directly approaches the resonance, the fluctuation in the concentration ratio δη/η0 is less than 20%, and kAd<1, a ‘‘renormalized’’ Budden potential yields analytic expressions in good agreement with numerical results. In this regime, the reflection coefficient exhibits a new contribution arising from the modifications of the resonance layer. For direct approach, kAd>1, and concentration fluctuations 2%<δη/η0<5%, enhanced reflection leads to decreased absorption. For these parameters, the net absorption is reduced by more than 10% for noise wave numbers larger than 10 kA. However, the efficiency of the resonant absorption process remains unaffected. For kAd>2 and fluctuations δη/η0>5%, a regime of multiple resonances is encountered in which substantial absorption results. For indirect approach, a similar process takes place: The reflection coefficient is reduced from its unperturbed ∼1 value to ∼0. For bulk fluctuations, backscattering is the dominant physical process.
Experimental study of a transformer-driven spheromak plasma
Authors: Young P. E. , Wysocki F. J. , Yamada M. , Janos A.
Published: July 2002

An axial transformer was installed in the Proto S-1/C spheromak device [Yamada et al., Phys. Rev. Lett. 46, 188 (1981)] in order to study physics issues pertaining to sustained spheromak operation. An increase in both the toroidal plasma current and the toroidal flux was observed when the transformer current was pulsed. The ratio of these two quantities remained constant (within experimental error) indicating that the equilibrium spheromak magnetic field was maintained through a relaxation mechanism. At transformer currents of 10 kA, the toroidal current increased from 37 to 51 kA and the toroidal flux increased from 3.7×105 to 4.4×105 G cm2.
Short wavelength x-ray laser research at the Lawrence Livermore National Laboratory
Authors: MacGowan B. J. , Da Silva L. B. , Fields D. J. , Keane C. J. , Koch J. A. , London R. A. , Matthews D. L. , Maxon S. , Mrowka S. , Osterheld A. L. , Scofield J. H. , Shimkaveg G. , Trebes J. E. , Walling R. S.
Published: July 2002

Laboratory x-ray lasers are currently being studied by researchers worldwide. This paper reviews some of the recent work carried out at Lawrence Livermore National Laboratory. Laser action has been demonstrated at wavelengths as short as 35.6 Å while saturation of the small signal gain has been observed with longer wavelength schemes. Some of the most successful schemes to date have been collisionally pumped x-ray lasers that use the thermal electron distribution within a laser-produced plasma to excite electrons from closed shells in neon- and nickel-like ions to metastable levels in the next shell. Attempts to quantify and improve the longitudinal and transverse coherence of collisionally pumped x-ray lasers are motivated by the desire to produce sources for specific applications. Toward this goal there is a large effort underway to enhance the power output of the Ni-like Ta x-ray laser at 44.83 Å as a source for x-ray imaging of live cells. Improving the efficiency of x-ray lasers in order to produce saturated output with smaller pump lasers is also a goal of this work.
Magnetic field penetration and electron heating in weakly nonuniform plasmas
Authors: Fruchtman A. , Gomberoff K.
Published: July 2002

The simultaneous magnetic field penetration and electron heating in plasmas of nonuniform density and of azimuthal cylindrical symmetry are studied. The penetration is caused by both the convective skin effect and the pressure gradient. The shock penetration of the current layer into a cold unmagnetized plasma is shown to result in equal magnetic field energy and electron thermal energy. A direct relation is shown between the heating of an electron along its orbit and the deviation from the frozen-in law. General Hugoniot relations are presented for the shock penetration into warm magnetized plasmas. The profiles of the magnetic field and of the electron thermal energy are found in the steady skin layer that is formed in the case of no penetration.
The effect of the radial electric field on the L–H transitions in tokamaks
Authors: Rozhansky V. , Tendler M.
Published: July 2002

It is well known that usual assumptions of neoclassical theory become invalid if very large gradients occur at the plasma edge. Therefore neoclassical theory of plasma rotation in tokamaks is revisited in order to account for anomalous transport driven by a turbulence. It is shown that this model yields both steep and gradual profiles for the poloidal rotation velocity at the edge corresponding to the H and L regimes of confinement, respectively. Results and conclusions are focused on experiments employing the biased electrode technique. Regimes with fast poloidal rotation in excess of poloidal sound speed are considered with the emphasis on relaxation.
Propagation of a narrow plasma beam in an oblique magnetic field
Authors: Heidbrink W. W. , Adams D. , Drum S. , Evans K. , Manson J. , Price T. , Urayama P. , Wessel F. J.
Published: July 2002

The propagation of an intense neutralized ion beam (v∼5×108 cm/sec, n∼1010 cm−3) through a large insulated vacuum chamber is measured as a function of magnetic field strength and direction. When the beam propagates parallel to the applied field, beam divergence is reduced. When the beam propagates perpendicular to the applied field, the downstream beam density decreases with increasing field strength. When the beam velocity vector intersects the magnetic field at an oblique angle, beam propagation is determined primarily by the perpendicular component of the field.
Viscoresistive stabilization of the Z pinch
Authors: Cochran F. L. , Robson A. E.
Published: July 2002

A two-dimensional magnetohydrodynamic code that includes resistivity and viscosity has been used to study the growth of m=0 perturbations of a Z pinch in which the current increases with time. Stability for all wave numbers was found when the product SR was less than about 1000, where S is the Lundquist number and R is the Alfvén–Reynolds number. Since SR depends only on the line density N, the stability criterion translates as N<2×1016 ions cm−1 (deuterium). This is two to three orders of magnitude smaller than the line density of fiber pinch experiments that have shown anomalous stability, and it is concluded that viscoresistive effects are inadequate to account for these observations.
Modified Langmuir turbulence equations with the self-generated magnetic field
Authors: Li L. H.
Published: July 2002

A set of three mutually coupled equations, very similar to the Zakharov equations, are derived from two-time-scale two-fluid hydrodynamic equations of a plasma with the self-generated magnetic field taken into account when an external magnetic field that is not very strong [(Ωe/ωpe)2≤1/3, where Ωe is the electron gyrofrequency, ωpe the electron plasma frequency] is present. They can be used to study the interactions between the self-generated and external magnetic fields.
Formation of a nearly spherical field-reversed configuration
Authors: Nakata Shuhei , Sekiguchi Tadashi , Isaka Masazumi
Published: July 2002

By utilizing a laser-produced plasma technique, the possibility of realizing a field-reversed configuration (FRC) with a nearly spherical plasma cross section is examined experimentally on the basis of a double-cusp bias magnetic field. Plasma measurements by magnetic probes and x-ray pinhole camera confirm the formation of a nearly spherical FRC.
Neoclassical ion transport in rotating axisymmetric plasmas
Authors: Hinton F. L. , Wong S. K.
Published: July 2002

The neoclassical theory of ion transport in rotating axisymmetric plasmas is formulated. The flow speed is allowed to be of the order of the ion thermal speed. It is shown that the ion distribution function becomes Maxwellian, with temperature uniform on a magnetic surface, and the poloidal flow decays, in a few transit or collision times, in general. A drift kinetic equation is derived which is a simple generalization of the drift kinetic equation for nonrotating plasmas. The radial gradient of the toroidal angular velocity appears as a driving term like the temperature gradient. Both gradients drive the transport of toroidal angular momentum and energy, in general; Onsager relations for the two-by-two transport matrix are derived. The off-diagonal transport coefficients are shown to be zero if the magnetic field has up–down symmetry. A simple expression for the enhancement of the ion thermal conductivity in the banana regime, caused by rotation, is derived. The neoclassical viscosity is shown not to be enhanced by rotation in the banana regime, and to be small in the collisionality parameter in the collisional regime, assuming up–down symmetry. In the collisional regime, the thermal conductivity is shown to be suppressed by the effects of rotation.