bluuebunny/crossref_metadata_2025 huggingface dataset:
SUPPRESSION OF SPIN FLUCTUATIONS IN YMn2 BY HYDROSTATIC PRESSURE
Authors: BAUER E. , DUBENKO I.S. , GRATZ E. , HAUSER R. , MARKOSYAN A. , PAYER K.
Published: November 2004

The cubic Laves phase compound YMn2 exhibits a huge spontaneous volume magnetostriction at the Néel temperature (TN=100 K). The magnetic moment per Mn atom is 2.7 μB at 2 K. From polarized neutron diffraction in the paramagnetic state it has been shown that the effective moment persisting above TN is reduced (1.6 μB at 120 K). The anomalously large pressure dependence of TN (dTN/dp=–35 K/kbar) is an evidence for the sensitive role played by the Mn—Mn interatomic distances. In the paramagnetic state, the influence of spin fluctuations dominates the physical properties. We have studied the effect of pressure on the resistivity up to 16 kbar. From dρ/dT we have estimated the spinfluctuation temperature as a function of pressure. The value at ambient pressure is 15 K which is in agreement with that determined in the paramagnetic Y0.9Lu0.1Mn2 compound.
ELECTRONIC PROPERTIES OF UCo4B
Authors: NAKOTTE H. , HAVELA L. , KUANG J.P. , DE BOER F.R. , BUSCHOW K.H.J. , BRABERS J.H.V.J. , KURODA T. , SUGIYAMA K. , DATE M.
Published: November 2004

We present susceptibility, high-field magnetization, specific-heat and electrical-resistivity measurements on UCo4B. The magnetic susceptibility passes a maximum in both its temperature and its field dependence. We attribute these maxima to spin fluctuations, as there is no clear indication for a long-range magnetic order in the observed temperature range. Strong evidence for the occurrence of spin fluctuations is also given by the specific-heat measurements, whereas the electrical resistivity displays a more normal metallic behaviour.
MAGNETISM IN UPtIn
Authors: HAVELA L. , SECHOVSKY V. , NAKOTTE H. , BRÜCK E. , SVOBODA P. , DE BOER F.R.
Published: November 2004

Magnetic and specific heat measurements were performed on polycrystalline samples of UPtIn. The results point to antiferromagnetic ordering below 15 K. Comparison of the magnetization behaviour of oriented powder and a polycrystal suggests a planar type of magnetic anisotropy in contrast to other UTX compounds of Fe2P-structure type, which are uniaxial.
MAGNETIC PROPERTIES OF Mn3−xCoxGaC (x≤0.5)
Authors: KANOMATA T. , KANEKO T.
Published: November 2004

The magnetic properties of Mn3–xCoxGaC(x≤0.5) are studied in order to investigate the nature of the magnetic order-order phase transitions. The magnetic phase diagram for the transition temperatures versus concentration is determined. On the basis of these results, the relation between the effect of alloying and of pressure on the magnetic transitions of Mn3−xCoxGaC system is discussed.
POSSIBILITY OF THERMALLY INDUCED FERROMAGNETISM IN YCo2.9Hy AND THE RELATED HYDRIDES
Authors: KANEMATSU KAZUO
Published: November 2004

An anomalous, sharp peak in the susceptibi1ity near 200 K is observed in PuNi3 type hydrides Y1−xZrxCo2.9Hy (x<0.2, y=3−4). The peak reduces with time and then disappears. The absorbed hydrogen acts to make the cobalt magnetic moment decrease. According to Misawa theory based on Fermi- liquid description, susceptibi1ity maximum, thermally induced ferromagnetism and ferromagnetism occur with increase of a parameter, interaction strength. The inhomogeneous hydrogen distribution in the crystal may form locally areas of various interaction strength, also appropriate for thermally induced ferromagnetism, which is considered to be an origin of the susceptibility peak. The magnetic studies of Y(FexCo1−x)2.9Hy (y=3−4) were performed and the varation from the Pauli paramagnetism of anomalous peak to the ferommagnetism with increasing Fe concentration were interpreted by Misawa theory.
A SPIN POLARIZED RELATIVISTIC VERSION OF THE KKR-CPA— APPLICATION TO FexPt1–x and CoxPt1–x
Authors: EBERT H. , AKAI H.
Published: November 2004

The Coherent Potential Approximation (CPA) approach to deal with disordered alloys has been combined with the spin polarized version of relativistic multiple scattering theory (SPRKKR-CPA). This formalism allows to calculate the electronic structure of magnetic alloys treating all relativistic effects in a rigorous manner. By this way one gets access to a number of interesting spin-orbit induced properties. This is demonstated by results for the orbital contributions to the magnetic moments and the hyperfine fields in the alloy systems FexPt1–x and CoxPt1–x. It is shown that both quantities are closely related to one another. Furthermore it turns out that they are non-negligible compared to the corresponding spin contributions—even for relatively light elements.
ATOMIC MAGNETIC MOMENT AND ELECTRONIC STRUCTURE OF Fe-B AMORPHOUS ALLOYS BASED ON X-RAY PHOTOELECTRON SPECTROSCOPY
Authors: BATIREV I.G. , LEIRO J.A. , HEINONEN M.
Published: November 2004

The electronic structure of amorphous and crystalline Fe100–xBx alloys for 14≤x≤19.5 has been studied by x-ray photoelectron spectroscopy and calculated in terms of the modified coherent potential approximation. Exchange splitting measurements of 3s-spectra were used to estimate the atomic magnetic moment of the Fe atom in Fe-B amorphous and crystalline alloys. These results agree qualitatively with saturation magnetization measurements including the deviation from the Slater-Pauling curve. This deviation according to our calculations is the result of the specific charge transfer of s, p and d electrons at about 15.5 at % B. The calculation in ternary alloy approach shows a stable ferromagnetic state of Fe atoms for the studied alloy concentrations.
FIELD-INDUCED NON-COLLINEAR MAGNETIC STRUCTURES IN AMORPHOUS Co-R-B AND Fe-R-B ALLOYS (R=Gd, Ho and Er)
Authors: RADWAŃSKI R.J. , KRISHNAN R. , FRANSE J.J.M. , LASSRI H. , MARREKCHI O.El.
Published: November 2004

High-field magnetization studies performed at 4.2 K in magnetic fields up to 38 T on amorphous Fe80−xHoxB20 alloys have revealed, for samples with the stoichiometry close to that of a compensated ferrimagnet, a magnetic transition. Such a transition is not trivial in systems with a sperimagnetic structure, due to the random local anisotropy, for which a continuous and gradual approach to saturation is expected. The occurrence of the transition can rather be understood within a model of two magnetic sublattices. Under action of high magnetic fields a non-collinear magnetic structure of the rare-earth and Fe sublattices is realized. A similar behaviour has been observed for Co80−xErxB20 and Fe80−xGdxB20 alloys. From the non-collinear regime, the exchange interactions between the 3d and rare-earth magnetic sublattices have been accurately evaluated and they are found to be close to that observed in crystalline compounds.
MAGNETIC PROPERTIES OF THE DISORDERED Fe-Rh ALLOYS
Authors: JEZIERSKI A.
Published: November 2004

The electronic and magnetic properties of the disordered Fe1−cRhc alloys are studied by the TB LMTO-CPA method. The paramagnetic density of states is computed for the fcc and bcc Fe-Rh systems. The dependence of the magnetic moment on the concentration was estimated using the Stoner model.
CORRELATION OF TRANSPORT AND TOPOLOGICAL/SPIN DISORDER FOR SOME AMORPHOUS METALLIC AND MAGNETIC ALLOYS
Authors: BÄRNER K. , SCHÜNEMANN J.-W. , HEINEMANN K. , GANIN A.A. , BERSENEV Yu.S. , MEDVEDEVA I.V.
Published: November 2004

The resistivity ρ and the permeability μ of amorphous magnetic ribbons (Fe100−xMnx)75P15C10 are determined at ambient pressure and pressures up to 15 kbar and correlated with the topological and magnetic disorder. The characterization includes the Curie temperature Tc, its pressure derivative ∂Tc/∂p and the pressure dependence of the resistivity minimum temperature.
AGING PHENOMENA IN SPIN GLASSES: A PROBE FOR THE STRUCTURE OF THE PHASE SPACE
Authors: LEFLOCH F. , HAMMANN J. , OCIO M. , VINCENT E.
Published: November 2004

We discuss some typical results on the time decay of the low frequency (f=0.1Hz) out-of-phase susceptibility χ” at T<Tg. In zero or in constant non-zero dc fields, any negative temperature step to T-∆T starts a new decay of χ”, but as the temperature is raised back to T, χ” resumes its former relaxation. We have related this behavior to a hierarchical organization of the available states. Positive or negative field variations always induce a renewed time decay of χ”.
ISING SPIN GLASS: RECENT PROGRESS IN THE FIELD THEORY APPROACH
Authors: DOMINICIS C. DE , KONDOR I. , TEMESVARI T.
Published: November 2004

A loop expansion around Parisi's replica symmetry breaking mean field theory is constructed, in zero field. We obtain the equation of state (and associated Parisi's solution) below the upper critical dimension du=6, and, in particular, explicit corrections in εlnt and (εlnt)2 with t=(Tc−T)/Tc and ε=6−d. This allows us to verify that standard scaling is satisfied with β=1+ε/2+0(ε2).

We have also investigated the transverse (replicon) correlation function, particularly at zero overlap. Near du, G00 (p) ~ t/P4 (for p~0) is the most obvious obstacle to a meaningful theory in d=3. If we make the twofold assumption that (i) scaling applies, and (ii) the replicon propagator is dominated by the spectrum of the (small) transverse masses, we obtain the softer behavior G00(p) ~ (1/p2–η). (t/p1/v)β and a prediction for a soft replicon spectrum in tγk2γ/β γ/β instead of tk2 at du. We have checked tγ to one loop and work is in progress to check k2γ/β to the same order. Taking the above divergence in p−(d+2−η)/2 as the leading divergence defines the lower critical dimension d ℓ by d ℓ=2−η (d ℓ). Known values of η (at d=6, from the ε expansion at Tc, or from numerical work at d=4, 3) are compatible with d ℓ ~ 2.5±.3.
ANOMALOUS MAGNETIC BEHAVIORS OF RE-ENTRANT SPIN GLASSES IN AMORPHOUS TRANSITION METALS
Authors: KAKEHASHI YOSHIRO
Published: November 2004

The reentrant spin glasses (RSG) in amorphous transition metals are examined on the basis of the finite-temperature theory of amorphous metallic magnetism. It is shown that a competition between the short-range ferromagnetic couplings and the long-range antiferromagnetic couplings forms the itinerant-electron RSG via the structural disorder characteristic to the amorphous pure metals. Calculated high-field susceptibilities, forced volume magnetostriction, and T-p phase diagram explain well the experimental data of Fe-rich amorphous alloys around 90 at.% Fe. This supports that the RSG around 90 at.% Fe in Fe-rich amorphous alloys are dominated by the structural disorder.
ROLE OF FRUSTRATION IN MAGNETISM AND THERMODYNAMIC PROPERTIES OF YMn2 AND β-Mn
Authors: SHIGA M. , YOSHIMOTO K. , NAKAMURA H. , WADA H.
Published: November 2004

The temperature dependence of the magnetic susceptibility, the specific heat and the electrical resistivity of Y(Sc) (Mn1−xAlx)2 and β-Mn1−xAlx systems has been measured. It is shown that the ground state for x=0 is not a simple Pauli paramagnet but may be regarded as a quantum spin liquid. The substitution of Al for Mn results in the spin glass freezing. The role of frustration is discussed for understanding these phenomena.
AXIAL ESCAPE OF NEMATICS IN BEND-CYLINDRICAL CONFIGURATION
Authors: SPARAVIGNA A. , STRIGAZZI A. , PALFFY-MUHORAY P.
Published: November 2004

We investigated the possibility of axial escape of a nematic liquid crystal confined between two concentric cylinders with surface-imposed pure bend distortion. We found that this effect appears also in the case of strong anchoring. When the twist-anchoring is weak only at one of the surfaces, the critical thickness dc of the structure is affected by the saddle-splay elastic constant K24. Moreover, if the twist-anchoring is weak at the external surface, a transition of the first order was found, dc playing the role of an order parameter. Such a transition, characterized by bistability and hysteresis, may be driven by K24 and by the anchoring strength.
DISSIPATIVE STEADY-STATE SPATIAL ORDERING IN PHOTOEXCITED POLAR SEMICONDUCTORS
Authors: ESPERIDIĀO ANTONIO SERGIO , VASCONCELLOS AUREA R. , LUZZI ROBERTO
Published: November 2004

We consider the question of formation of patterned dissipative structures in condensed matter under high levels of excitation. The case of n-doped direct-gap polar semiconductors under continuous laser illumination is studied. We show that the solution consisting of the homogeneous population of electrons and holes, that develops from the equilibrium state with increasing values of the laser power flux, presents a bifurcation point. A new solution emerges from it corresponding to the formation of a steady-state spatially organized structure in the carrier charge density in the form of a polarization wave. This dissipative structure occurs beyond a critical distance from equilibrium, when a fluctuation drives the carrier system to such self-organized macroscopically ordered state. It is stabilized by the joint action of collective and dissipative effects.
IRREVERSIBILITY AND QUANTUM MACROSCOPIC EFFECTS IN CLASSICALLY CHAOTIC SYSTEMS
Authors: BONCI LUCA , RONCAGLIA ROBERTO , VITALI D. , WEST BRUCE J. , GRIGOLINI PAOLO
Published: November 2004

We show that in classically chaotic systems the quantum uncertainty, in spite of being assumed to be extremely small so as to make the classical approximation possible, increases very quickly thereby making these classical systems strongly quantum. It is argued that these systems also exhibit an irreversible-like behavior, albeit the phase correlations among different regions of the wavefunction make them reversible. From a statistical point of view it is difficult to distinguish the quantum behavior of these systems from the predictions of the classical approximation, unless the resulting transport process does not essentially rest either on tunneling or on localization processes (or on both). The dinstinctively quantum mechanical features of the transport process might be destroyed by the interaction between the system and environment. This possible role of environmental fluctuations, dealt within a fully quantum formalism, is discussed.
HIGH FIELD TRANSPORT IN a-Si:H
Authors: NEBEL C.E. , STREET R.A.
Published: November 2004

Electric field dependent DC-dark and transient photoconductivity data measured over a broad temperature (10 K ≤T≤300 K ) and field regime (102 V/cm ≤F≤6×105 V/cm ) in phosphorus and boron doped and intrinsic amorphous hydrogenated silicon (a-Si:H) are described. The data demonstrate the strong influence of the electric field on carrier propagation. Enhancements over 6 orders of magnitude in conductivity (σ) are achieved for fields greater than 105 V/cm , which changes a-Si:H films from highly insulating to very conductive at low temperatures. The field dependence is described empirically by a power law a~Fy with y in the range 10≤y≤17. The enhancement and y depend on doping level with significant differences between electron and hole currents. These results are confirmed by transient photoconductivity experiments on intrinsic a-Si:H from which the carrier mobility (μ D ) and the μτ-product are deduced. The drift mobility is enhanced by many orders of magnitude up to values of μ D >10−2 cm 2/ Vs and is identified as parameter which dominates high field transport. The increase in mobility is comparable to the increase in conductivity and shows a time- and thickness dependence indicative of dispersive transport. The data is interpreted introducing a field-enhanced nearest neighbor hopping model which is governed by ballistic capture and field induced re-emission.
EQUIVALENCE IN GEOMETRIC SCALING OF TRANSPORT PROPERTIES AND WAVEFUNCTIONS
Authors: BASU CHAITALI , MOOKERJEE ABHIJIT
Published: November 2004

The transport properties and wavefunction behave identically with respect to multifractal scaling. To establish the above statement, we carried out multifractal analysis on normalised transmittance and normalised wavefunction of two types of electron states, namely the resonance state and the localised state of a one-dimensional Anderson model.
THE DUALISATION METHOD REVISITED: DUALISATION OF PRODUCT LAGUERRE COMPLEXES AS A UNIFYING FRAMEWORK
Authors: GÄHLER FRANZ , STAMPFLI PETER
Published: November 2004

A general framework based on the dualisation of Laguerre cell complexes is presented, which allows to construct and understand a large variety of quasiperiodic tilings, both new ones and well known old ones. The general framework is illustrated with many examples, which are all based on cell complexes which are products of 2-dimensional complexes. The simple structure of these examples makes it particularly easy to understand how the general procedure works. Yet the examples are sufficiently versatile to exploit the power and flexibility of the method.
DEFECTIVE VERTEX CONFIGURATIONS IN QUASICRYSTALLINE STRUCTURES
Authors: BEN-ABRAHAM S.I.
Published: November 2004

Defective vertex configurations are important for the whole range of models for quasicrystalline structures from quasiperiodic tilings through random tilings to polyhedral glasses. The combinatorially possible vertex configurations are enumerated for the 1D Fibonacci chain, for the 2D Penrose pattern with its generalizations, as well as for the Beenker pattern and the triangle pattern, and for the 3D simple icosahedral tiling. The methods for quantifying the deviation of vertex configurations from perfection are reviewed. The simple method of partial dual overlap provides a means to estimate the abundancy of vertex configurations within random tilings. More sophisticated is the method of the defectivity functional; it is particularly suitable to deal with nearly perfect tilings. Local configurations are formally classified by characteristic integers: degree, rank and order. Some possible applications are hinted at.
PHASON ELASTICITY IN THE ICOSAHEDRAL MODEL OF THE LIQUID CRYSTALLINE BLUE FOG
Authors: TREBIN HANS-RAINER , FINK WERNER , STARK HOLGER
Published: November 2004

The Blue Fog is a thermodynamically stable phase of chiral nematic liquid crystals with short pitch. Its structure is still unknown. One model description proposed is a quasiperiodic icosahedral quadrupole tensor field. On a mesoscopic scale the system is described by a Landau-Ginzburg-de Gennes energy functional, which we exploit to determine a complete set of phonon and phason elastic constants.
SELF-AVOIDING WALKS ON QUASILATTICES
Authors: BRIGGS KEITH
Published: November 2004

I consider the asymptotic properties of self-avoiding walks on a variety of quasilattices. The critical points and exponents are estimated. Walks on several of the patterns appear to belong to the same universality class as walks on the hexagonal periodic lattice.
GRANULAR MEDIA ON A VIBRATING PLATE: A MOLECULAR DYNAMICS SIMULATION
Authors: GALLAS JASON A.C. , HERRMANN HANS J. , SOKOLOWSKI STEFAN
Published: November 2004

When sand or other granular materials are shaken, poured or sheared many intriguing phenomena can be observed. We will model the granular medium by a packing of elastic spheres and simulate it via Molecular Dynamics. Dissipation of energy and shear friction at collisions are included. The onset of fluidization can be determined and is in good agreement with experiments. On a vibrating plate we observe the formation of convection cells due to walls or amplitude modulations. Density and velocity profiles on conveyor belts are measured and the influence of an obstacle discussed. We mention various types of rheology for flow down an inclined chute or through a pipe and outflowing containers.
DISCRETE PARTICLE SIMULATION OF FLOW PATTERNS IN TWO-DIMENSIONAL GAS FLUIDIZED BEDS
Authors: TANAKA T. , KAWAGUCHI T. , TSUJI Y.
Published: November 2004

The flow patterns in two-dimensional gas fluidized bed were simulated numerically by the Distinct Element Method, Gas is issued through the entire width of the base with uniform velocity. Several flow patterns, such as slugging and bubbling, are observed in the results. As the gas flow rate increases, the flow pattern changes from slugging to bubbling. It is confirmed that particle mixing is promoted by bubbling. The flow pattern of bubbling is irregular in comparison with the case of gas injection through a central nozzle which was simulated in our previous study.
MULTIPHASE FLOWS IN MAGMATISM
Authors: KOYAGUCHI TAKEHIRO
Published: November 2004

Diversity of volcanic activities reflects various styles of magma flows. One of the most important characters of the magma flows is that they are composed of gas, liquid and solid phases (multiphase flow). Macroscopic behaviours of multiphase flows are affected by their internal microstructures including the distribution of each phase and the shape of the boundaries between the two phases. Magma segregation from partially molten rock occurs by porous flow being accompanied with compaction of the matrix rock, the macroscopic behaviours of which are governed by microscopic flows of the melt at grain boundaries and deformation of each crystal. The fluctuation of magma effusion at volcanic eruptions is explained by instability of gas-liquid two-phase flow, which depends on motion of each bubble and the ability of bubbles to coalesce. Complex features of pyroclastic flow result from a wide range of grain-size, and hence, variable settling velocities of volcanic fragments within the flow. Physical processes of these multiphase flows in magmatism are reviewed.
GRAIN NON-SPHERICITY EFFECTS ON THE ANGLE OF REPOSE OF GRANULAR MATERIAL
Authors: GALLAS JASON A.C. , SOKOLOWSKI STEFAN
Published: November 2004

We use a site-site model to describe non-sphericity of particles composing a granular media. Specific effects of grain non-sphericity 011 the angle of repose are investigated. We report evidence indicating the possible existence of a shape-roughness threshold for grains: below it angles of repose are essentially the same as those obtained for spherical grains; above it there are pronounced changes 011 the angle of repose and it is possible to find rather large piles of grains.
MEAN FIELD APPROXIMATION FOR ANYONS IN A MAGNETIC FIELD
Authors: WESTERBERG ERIK
Published: November 2004

The mean field equations for anyons in an external homogeneous magnetic field are studied and two classes of mean field solutions are explicitly constructed. The first class of solutions, corresponding to one filled Landau level in the combined external and smeared out statistical magnetic fields, is compared to the corresponding exact groundstate solutions. The energies are found to agree well at low densities and when the statistical field is not too strong compared to the background field. At high densities the fermi pressure increases the mean field energy indefinitely. The mean field solutions also miss the lower part of the energy spectrum.

To the second class of mean field solutions no corresponding anyon state is known. These solutions represent the anyonic continuation of the fermi state with two filled Landau levels.
SELF-SIMILAR RENORMALIZATION AS EQUATION OF MOTION
Authors: YUKALOV V.I. , YUKALOVA E.P.
Published: November 2004

We consider a general approximating sequence generated by some kind of perturbation theory or iterative technique. An arbitrary sequence of this sort can be made fastly convergent, or at least semiconvergent, by means of a renormalization procedure called the method of self-similar approximations. We show that such a procedure can be treated as an equation of motion describing the evolution of an autonomous dynamical system. Approximating cascades and flows are introduced. The sequence of approximations composes a trajectory whose form is governed by a set of governing functions. The sought limit of the sequence plays the role of an attractor. Different types of attractors are analysed. The method is exemplified by an eigenvalue problem.
A GAUSSIAN, NON-MARKOVIAN APPROACH TO LONG MEMORY WITH APPLICATION TO A STOCHASTIC THEORY OF LINE SHAPE
Authors: VLAD MARCEL OVIDIU
Published: November 2004

A new approach to long memory effects is suggested. The main assumption is that the regression of fluctuations occurs via a clustering mechanism. The regression of a scalar variable takes place through a succession of linear decay processes, resulting in a long time tail of the autocorrelation function. The number of decay events is a random variable obeying a self-similar probability distribution whose fractal exponent determines the long time behavior of fluctuation regression. The overall fluctuation dynamics is described by a stationary Gaussian and non-Markovian random process. The theory is applied to the stochastic theory of line shape. The relaxation function ϕ(t) can be exactly evaluated. We show that the memory effects lead to a narrowing of the relaxation function for large time. As the time t tends to infinity, ϕ(t) may be approximated by a ‘contracted’ exponential ϕ(t) ~ exp(-const. t2−H) where 1≥H>0 is the fractal exponent describing the clustering process.
THE SINGLE-SITE APPROXIMATION TO THE HUBBARD MODEL
Authors: CORRIAS MASSIMO
Published: November 2004

The diagrammatic formulation of the single-site approximation to the Hubbard model immediately yields the exact solution to the Falikov-Kimball model in infinite dimensions. By an extension of the alloy analogy, we then derive a two-fluid model, dividing self-consistently the electron system among itinerating and relatively localized particles. Our theory coincides with the CPA only the at half-filling and u=∞. We start by studying the mean field approximation to our theory and identify a phase boundary in the particle density-interaction strength (n−u) plane at which the Fermi liquid model breaks down. Then the effect of fluctuations in the Fermi liquid regime is considered and, finally, we construct, at half-filling, a model which interpolates between the Fermi liquid and the Mott insulating phases.
LATTICE HEAT CAPACITY OF CRYSTALS: A q-OSCILLATOR DEBYE MODEL
Authors: LEELAMMA K.K. , KURIAKOSE V.C. , JOSEPH K. BABU
Published: November 2004

The Debye model for lattice heat capacity is modified retaining all the basic assumptions except that each mode is here treated as a q-deformed quantum harmonic oscillator. The lattice heat capacity Cv is evaluated in the high and low temperature limits. When T≪θD, Cv∝T3 and when T ≫θD, Cv∝T2. In the case of the alkali elements Rb, Cs and K whose Debye temperatures are relatively low, the calculated values compare remarkably well with experimental results over a wide range of temperatures.
STEADY-SQUEEZING STATES
Authors: BAKASOV A.A.
Published: November 2004

Wave functions have been determined which realize constant squeezing (steady-squeezing states) for a quadrature component of the oscillator with a quadratic self-coupling at an á priori given initial complex amplitude of the oscillator. The set of these wave functions forms a kernel of a special generating operator and is divided into two mutually orthogonal subsets: the subset of superpositions of the states with an even number of quanta of fluctuations around the classical value of the oscillator energy and the subset of analogous states but with odd number of such quanta. The value of the steady squeezing is not a monotonic function of the self-coupling constant and possesses an unexpected minimum. Steady-squeezing states do not minimize the uncertainty product and are not the Gaussian states at the same time.
NUCLEAR MAGNETIC ORDER, USE OF SPIN DEPENDENT AMPLITUDES
Authors: STEINER MICHAEL
Published: November 2004

The use of the spin dependent part of the nuclear scattering length gives access to neutron scattering to the field of nuclear magnetism. This paper presents the theoretical and experimental background for such experiments. The available results on nuclear order will be reviewed and put if possible in the larger frame of many body physics. The possibilities of using nuclear magnetism for new applications or the improvement of scattering techniques will be stressed as well.
IMPACT OF NEUTRON SCATTERING ON THE STUDY OF WATER AND AQUEOUS SOLUTIONS
Authors: SOPER A K , TURNER J
Published: November 2004

Neutron scattering is making a major impact on our physical and chemical understanding of water structure in aqueous solution. In combination with the technique of isotope substitution it can probe, via the partial pair correlation functions of the system, both the structural aspects of the water itself in solution and the correlation of water molecules with individual dissolved ions and molecules. Moreover it can also investigate the way the solute species distribute themselves in solution. The use of the so-called first-order difference method to look at the hydration of inorganic ions in solution has already been widely reported in several previous reviews, so this account concentrates largely on recent advances in the application of the second order hydrogen-deuterium substitution method to the study of water under non-ambient conditions, and to the measurement of water structure in a variety of solutions and heterogeneous media. It is also shown how the same technique can be used to investigate the nature of solute-solute correlations in solution, and the way water organizes itself around organic molecules and ions in solution.
THEORY OF THE AMPLITUDE-PHASE RETRIEVAL IN ANY LINEAR TRANSFORM SYSTEM AND ITS APPLICATIONS
Authors: YANG GUO-ZHEN , GU BEN-YUAN , DONG BI-ZHEN
Published: November 2004

This paper is based on our previous works in the past decade and is a summary of the theory of the amplitude-phase retrieval problem in any linear transform system and its applications. We describe the general statement on the amplitude-phase retrieval problem in an imaging system and derive a set of equations governing the amplitude-phase distributions in terms of the rigorous mathematical derivation. By using these equations and an iterative algorithm, a variety of amplitude-phase problems can be successfully handled. We carry out systematical investigations and comprehensive numerical calculations to demonstrate the utilization of this new algorithm in various transform systems. We also indicated the relationship and distinction between our algorithm and the original Gerchberg-Saxton algorithm. This new algorithm possesses considerable capability to deal with the various phase-retrieval problems in the arbitrary linear transform system and some inverse problems in solid state physics.
A PHASE SPACE FORMULATION OF QUANTUM STATE FUNCTIONS
Authors: SOBOUTI Y. , NASIRI S.
Published: November 2004

Allowing for virtual paths in phase space permits an extension of Hamilton’s principle of least action, of lagrangians and of hamiltonians to phase space. A subsequent canonical quantization, then, provides a framework for quantum statistical mechanics. The classical statistical mechanics and the conventional quantum mechanics emerge as special case of this formalism. Von Neumann’s density matrix may be inferred from it. Wigner’s functions and their evolution equation may also be obtained by a unitary transformation.
THE OPTICAL STARK EFFECT OF THE EXCITON DUE TO DYNAMICAL COUPLING BETWEEN QUANTIZED STATES OF THE ELECTRON AND HOLE IN QUANTUM WELLS
Authors: QUANG NGUYEN HONG
Published: November 2004

Optical Stark effect of the exciton in quantum wells is treated by taking into account not only dynamical coupling by pump field between quantized states of the electron in the conduction band but also the coupling between quantized states of the hole in the valence band. The changes in the calculated one-photon absorption probability by exciton depend essentially on pump field detuning.
DYNAMICAL SYSTEMS FROM QUANTUM INTEGRABILITY
Authors: Bellon M.P. , Maillard J-M. , Viallet C-M.
Published: November 2004

We describe a class of non-linear transformations acting on many variables. These transformations have their origin in the theory of quantum integrability: they appear in the description of the symmetries of the Yang-Baxter equations and their higher dimensional generalizations. They are generated by involutions and act as birational mappings on various projective spaces. We present numerous figures, showing successive iterations of these mappings. The existence of algebraic invariants explains the aspect of these figures. We also study deformations of our transformations.
Quasi-Particles, Conformal Field Theory, and q-Series
Authors: Dasmahapatra S. , Dedem R. , Klassen T.R. , McCoy B.M. , Melzer E.
Published: November 2004

We review recent results concerning the representation of conformal field theory characters in terms of fermionic quasi-particle excitations, and describe in detail their construction in the case of the integrable three-state Potts chain. These fermionic representations are q-series which are generalizations of the sums occurring in the Rogers-Ramanujan identities.
PHOTOINDUCED CHARGE CARRIERS IN INSULATING CUPRATES: FERMI GLASS INSULATOR, METAL-INSULATOR TRANSITION AND SUPERCONDUCTIVITY
Authors: YU GANG , HEEGER ALAN J.
Published: November 2004

The results of photoexcitation experiments in partially doped, insulating cuprates are reviewed, and the physical implications of these “photodoping” experiments are discussed. The existence of a Fermi-glass insulating state at intermediate doping levels is thoroughly explored. The localized electronic states near the Fermi energy (EF) are characterized through transport, steady-state photoconductivity (including spectral response) and time resolved transient photodoping experiments (sub-nanosecond through microsecond). The experimental results indicate an Anderson-type metal-insulator transition in the doped cuprates; i.e., the transition from metal to insulator is dominated by disorder-induced localization. The Fermi energy can be shifted across the mobility edge either by increasing the doping level or by transient photoexcitation at high pump intensities, thereby causing the metal-insulator transition. The high-Tc superconductors, therefore, can be characterized as disordered metals with the Fermi energy relatively close to the mobility edge (Ec). Although the photo-generated carriers are generated homogeneously, the data indicate electronic phase separation into metallic “droplets”. The temperature dependence of the photoinduced conductivity implies that these droplets become superconducting below the intrinsic transition temperature observed in the heavily doped metallic regime.
MOTION OF CHARGED PARTICLES IN DC-AC ELECTRIC FIELDS
Authors: ZHAO XIAN-GENG , ZHANG XIN-WEI , CHEN SHI-GANG , ZHANG WAN-XIANG
Published: November 2004

The motion of charged particles on a one-dimensional lattice under the influence of dc-ac electric fields is investigated. Analytic probability propagators in real space have been obtained, taking into account of the long-range intersite interactions. It is found that the effect of dynamic localization and delocalization arises mainly from the coupling of dc fields and ac fields. Various situations for the occurrence of localization and delocalization have been discussed in detail. The theoretical analyses show that such phenomena of dynamic localization and delocalization should be observable.
THEORETICAL ASPECTS OF FULLERENES
Authors: GONZÁLEZ JOSÉ , GUINEA F, FRANCISCO , VOZMEDIANO MARÍA A.H.
Published: November 2004

This is a review of the geometrical structure and fundamental properties of various fullerene formations including the most common C 60. Their electronic and vibrational modes are studied by means of a unified very simple continuum model derived from graphite that can be applied to all different shapes. The results are discussed and compared with other approaches and with numerical computations.
CURRENT OPERATORS IN THE LOWEST LANDAU LEVEL
Authors: MARTÍNEZ JUAN , STONE MICHAEL
Published: November 2004

We use Noether’s theorem to generate a consistent definition of the current operator for electrons restricted to the lowest Landau level. We exhibit the connection between this current and the Moyal bracket, or W∞, algebra, and use it to derive the edge-charge algebra for the ν=1/(2n+1) FQHE states.
DYNAMICAL MODEL OF TURBULENT EDDIES
Authors: DUBOVIKOV M.S.
Published: November 2004

Dynamical equations for the velocities and temperature fluctuations of turbulent eddies are presented. In the right side of the equation for the velocities are the external force, the turbulent force caused by interactions with larger-scale eddies, and the viscous force caused by interactions with smaller-scale eddies. The structure of the equation for the temperature fluctuations is analogous. The forces are specified on the basis of the well-known Wyld diagram technique of stochastic hydrodynamics so that the theory does not contain free parameters. The basic equations of the theory are approximately equivalent to Navier-Stokes equations and are particularly effective in the limit of very large Reynolds number. Turbulent convection is considered as an example of application of the basic equations.
LINEAR, NONLINEAR, AND TIME-DEPENDENT RESPONSE OF A DISSIPATIVE QUANTUM PARTICLE IN PERIODIC COSINE POTENTIALS
Authors: CHEN YONG-CONG
Published: November 2004

We review some of our recent results on the dynamics of a dissipative quantum particle in periodic cosine potentials. The dissipation is modeled by the Caldeira-Leggett prescription. Exact real-time Wigner distributions for the particle alone can be obtained in powers of V0 (the strength of the cosine potentials), which is suitable for calculations of various time-dependent averages. Special interest is devoted to summing over the whole series. For Ohmic dissipation, we have the following results: (a) The Kubo-Einstein relation for the linear response is shown to hold rigorously to all orders. (b) In the small viscosity limit, nearly exact analytic expressions for the nonlinear mobility and the nonlinear time-dependent response are found. (c) The resummation can also be performed in certain regimes of the dissipative Hafstadter problem in two dimensions. These results we believe can have useful applications in experiments in Josephson junctions and other mesoscopic systems.
CHAOS AND COMPLEXITY IN ABNORMAL OSCILLATIONS OF TWO EXCITABLE NEURONS AND A 2D NETWORK MODEL COUPLED VIA GAP JUNCTIONS
Authors: GE MANLING , GUO HONGYONG , SUN MINGUI , GUSPHYL JUSTIN , DONG GUOYA , ZHAO TONGJUN , YAN WEILI
Published: November 2004

Many electrophysiological experiments have shown that epileptic seizures often originate from the synchronous activities of abnormally excitable neurons. The dynamic process of epilepsy is very complex, and characterized by a seemingly rapid and dramatic birth of new oscillations, essentially leading to a propagation and amplification of the original aberrant activity. It is very difficult to thoroughly understand the mechanism from a theoretical standpoint, however some special work can prove helpful. Here we present a theoretical framework to investigate chaos and complexity in the synchrony of excitable neurons in an effort to study the collective oscillations within a neural network. As endogenous rhythms, oscillations arise because most cellular processes contain feedback. The Chay model of excitable neurons is chosen because the model describes the abnormal process, where spiking can be transformed into bursting via bifurcation.

In our study, the Chay model is regarded as an abnormal oscillator and coupled via a resistor representing the effect of gap junctions (electrical synapses). In this paper, we present some models developed from the original Chay model, for the synchrony of two cells and a 2D neural network. Lyapunov exponent and phase portrait are utilized to evaluate the chaotic dynamics. Finally, approximate entropy is utilized to measure its complexity. Our results show that the synchrony of abnormal oscillations can occur when the coupling strength of the gap junction is sufficiently large. It is also found that the concentration of Ca 2+ ions does not synchronize. In the 2D network, approximate entropies of different oscillations with strong coupling strength are greater than those with weak coupling strength. It is indicated that synchronous neurons have greater ability to produce new oscillations than asynchronous ones. This work shows that nonlinear analytical methods may prove useful in elucidating the mechanisms of pathologic conditions, where new oscillations are born and propagated, such as in epilepsy.
THE HIERARCHY THEORY OF THE FRACTIONAL QUANTUM HALL EFFECT
Authors: YANG J. , SU W. P.
Published: November 2004

A recently developed hierarchy theory of the fractional quantum Hall effect (FQHE) is reviewed in this article. We use a many quasiparticle (QP) wave function to obtain the effective partition function of a FQHE system in the path-integral representation, which has been shown to be formally equivalent to an anyon system confined to the lowest Landau level. However the two systems are different in the dimension of the Hilbert space, which implies that the standard hierarchy theory is invalid beyond second hierarchical states. The only way to overcome the difficulty is to place anyons in higher Landau levels. By making a mean-field approximation to the statistical gauge field, the QPs are converted to bosons and a constraint boson system is derived. We find a new type of condensate of the bosonic QPs, which results in a new type of incompressible states of the electrons. These states which involve only two hierarchies should have higher stability over others. That explains why some sequences of filling fractions occur prominently in experiment. Finally, we show that there is a one-to-one correspondence between the new hierarchy theory and the composite fermion theory proposed by Jain.
SPATIAL SYMMETRIES AND GEOMETRICAL PHASES IN CLASSICAL DISSIPATIVE SYSTEMS
Authors: LANDSBERG A. S.
Published: November 2004

We describe the emergence of geometrical phases in dissipative systems with continuous spatial symmetries. The phase characterizes the spatial shift of a wave pattern that arises as the result of a cyclic adiabatic transport of control parameters of the system. Geometrical phases are calculated for both stationary and propagating wave patterns. Complementary formulations are provided for finite-dimensional and continuum systems. The theory is used to determine the phase shift for a traveling wave front in a standard reaction-diffusion model.
LUTTINGER-LIQUID BEHAVIOUR IN 2D: THE VARIATIONAL APPROACH
Authors: GROS CLAUDIUS , VALENTÍ ROSER
Published: November 2004

We study a variational formulation of the Luttinger-liquid concept in two dimensions. We show that a Luttinger-liquid wavefunction with an algebraic singularity at the Fermiedge is given by a Jastrow-Gutzwiller type wavefunction, which we evaluate by variational Monte Carlo for lattices with up to 38 × 38 = 1444 sites. We therefore find that, from a variational point of view, the concept of a Luttinger liquid is well defined even in 2D. We also find that the Luttinger liquid state is energetically favoured by the projected kinetic energy in the context of the 2D t-J model. We study and find coexistence of d-wave superconductivity and Luttinger-liquid behaviour in two-dimensional projected wavefunctions. We then argue that generally, any two-dimensional d-wave superconductor should be unstable against Luttinger-liquid type correlations along the (quasi-1D) nodes of the d-wave order parameter, at temperatures small compared to the gap.
THE ENERGY GAP IN THE HIGH-Tc COPPER OXIDE SUPERCONDUCTORS
Authors: LI YONGHONG , LIEBER CHARLES M.
Published: November 2004

We briefly review high-resolution electron energy loss spectroscopy (HREELS) studies of the low energy excitations in the high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8. HREELS has been used to determine the magnitude and temperature dependence of the energy gap (2Δ) for Bi 2 Sr 2 CaCu 2 O 8 single crystals. Below the transition temperature low-energy excitations are detected in the energy loss spectra. Because the energy loss spectra are proportional to the real part of the frequency dependent resistivity, ρR(ω), the energy gap can be determined directly from the HREEL data. At low temperature 2Δ = 6kT c and Δ develops sharply for T < T c . The constraints that these new results place on potential mechanisms of superconductivity are discussed.
ON THE KOSTERLITZ–THOULESS TRANSITION ON COMPACT RIEMANN SURFACES
Authors: SPELIOTOPOULOS ACHILLES D. , MORRISON HARRY L.
Published: November 2004

A Lagrangian for the two-dimensional vortex gas is derived from a general microscopic Lagrangian for 4 He atoms on an arbitrary compact Riemann Surface without boundary. In the constant density limit the vortex Hamiltonian obtained from this Lagrangian is found to be the same as the Kosterlitz and Thouless Coulombic interaction Hamiltonian. The partition function for the Kosterlitz–Thouless ensemble on the general compact is formulated and mapped into the sine–Gordon field theory.
AN ULTRASONIC INVESTIGATION OF Sm-Ba-Cu-O HIGH-Tc SUPERCONDUCTOR
Authors: REDDY P. VENUGOPAL , REDDY R. RAVINDER , REDDI B. V.
Published: November 2004

The ultrasonic longitudinal velocity and attenuation in the high-T c superconductor Sm-Ba-Cu-O have been determined by the pulse transmission technique over a temperature range 80–300 K. The longitudinal velocity is found to decrease with decreasing temperature attaining a minimum of 170 K. Similarly, ultrasonic longitudinal attenuation is also found to exhibit an attenuation peak at the same temperature. The observed behavior is explained qualitatively on the basis of a model.
HOPPING CONDUCTION AT VERY LOW TEMPERATURES: SOME NEW RESULTS ON AN OLD PROBLEM
Authors: DAI PEIHUA , ZHANG YOUZHU , SARACHIK M. P.
Published: November 2004

We briefly review the temperature dependence of hopping conduction in doped semiconductors near the metal-insulator transition, with emphasis on recent experimental results in Si:B at very low temperatures. Our main finding is that at sufficiently low temperature the conduction is simply activated in zero magnetic field, indicating the presence of a "hard" gap in the density of states. A magnetic field suppresses this unexpectedly strong temperature dependence, changing it to the variable-range-hopping form expected for a "soft" Coulomb gap. This suggests that the density of states is determined by electron correlations due to exchange as well as charge.
THEORY OF BRILLOUIN SCATTERING FROM A PERIODICALLY CORRUGATED SURFACE OF AN OPAQUE SOLID
Authors: GIOVANNINI L. , NIZZOLI F. , MARVIN A. M.
Published: November 2004

We calculate, in the small corrugation limit, the surface-acoustic phonon normal modes and the Brillouin scattering ripple cross-section for a grating on the Si(001) surface. Both the discrete and continuous spectra of acoustic modes have been studied within the elasticity theory. In the continuum the Rayleigh wave becomes a resonance and hybridizes with the longitudinal pseudo-mode of the flat surface, giving rise to a gap. The theory explains quantitatively recent experimental results.
EFFECT OF MULTIPLE SCATTERING IN A QUANTUM WELL
Authors: SHENG HANYU , CHUA SOO-JIN , SINKKONEN JUHA
Published: November 2004

This paper gives a potentially useful application to quantum well of the theory of scattering in the Born approximation. The simple formulae for multiple scattering in a quantum well of double barrier structure are derived. The multiple scattering parameter is the complex mean free path. We show that the amplitude of the coherent wave will be exponentially attenuated and the phase of the wave will be delayed because of the scattering.
NON-RESONANT MICROWAVE ABSORPTION STUDIES ON BI-V-SR-CA-CU-O SUPERCONDUCTING SYSTEM
Authors: BABU D. SURESH , RAO G. NARSINGA
Published: November 2004

Microwave absorption studies have been carried out on samples Bi 2 Sr 2 Ca 2 Cu 3 O y (sample A) and Bi 1.6 V 0.4 Sr 2 Ca 2 Cu 3 O y (sample B). dc microwave absorption studies of these samples showed that sample A had a small volume of 2223 phase and a large volume of 2212 phase, whereas sample B had a single 2223 phase. Variation of LFMA signal amplitude of sample A with temperature showed definite peaks at 97 K and 70 K which may correspond to the 2223 and 2212 phases. In the case of sample B it showed a single peak at 90 K corresponding to the 2223 phase. The average Josephson loop diameter was estimated for these samples and found to be 1.23 μm to 3.11 μm and 0.7 μm to 1.86 μm for samples A and B respectively.