bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monte Carlo simulation of cluster kinetics in three‐dimensional Ising model
Authors: Behrens M. , Stauffer D. 
Published: May 2007

AbstractSimulations in lattices of size 1003 at the critical point of the three‐dimensional Glauber kinetic Ising model indicate that the 1935 Becker‐Doring equation no longer works there: The growth rates decay in time. These conclusions confirm those in two dimensions.
Anisotropic coherence lengths of YBa2Cu3O7‐δ from specific heat measurements near Tc
Authors: Schnelle W. , Ernst P. , Wohlleben D. 
Published: May 2007

AbstractWe present a detailed analysis of high resolution measurements of the specific heat anomalies at the Tc of three YBa2Cu3O7‐δ‐samples. The anomalies can be described by the sum of a mean field (MF) step and a contribution from gaussian fluctuations of the order parameter. These fluctuations are threedimensional (3D) near Tc and show a crossover to 2D‐behaviour some K away from Tc. By means of a Lawrence‐Doniach type description of the fluctuations we estimate the anisotropic coherence lengths ξ and ξ⊥. The values are consistent with data of the fluctuation contribution to the susceptibility above Tc. We give data for ΔCMF and discuss the relevance of critical fluctuations. The influence of the oxygen content δ on the broadening and splitting of the transition is shown.
Theory of light rectification in scanning tunneling microscopy in the presence of an adsorbed molecule
Authors: Yeyati A. Levy , Flores F. 
Published: May 2007

AbstractWe consider the problem of the rectified current induced by laser radiation in the STM junction when the tip is placed above a small molecule like CO or NO. This is calculated assuming a simple tight‐binding model for the tunneling junction including the adsorbate and using nonequilibrium Green's functions techniques. The coupling between tunneling electrons and the molecule vibrational modes is taken into account by a local electron‐phonon interaction term. In a second step we estimate the excitation rate of the molecule vibrations for a given laser power. This value is then used to obtain the relative change in the rectified current when the laser is in resonance with a molecule vibration. For a moderate laser power of 2 kW/cm2 a relative change of 1 to 3% is predicted.
Isochromat spectroscopy of photons emitted from metal surfaces in an STM
Authors: Berndt Richard , Gimzewski James K. 
Published: May 2007

AbstractThe pronounced variation of the intensity of photons emitted from the tunneling gap of an STM with respect to the applied bias voltage Vt is studied experimentally using simultaneous measurements of tunneling characteristics and photon emission. We show that the structure in isochromat photon spectra are determined by the following: bias‐dependent changes in tunneling characteristics, density of initial and final states, and modifications of tip‐induced plasmon modes. It is demonstrated that isochromat spectra provide a conclusive test for the inelastic tunneling mechanism. Coupling between tunneling electrons and tip‐induced plasmon modes which gives rise to the intense photon emission observed is discussed within this model.
Photovoltaic characterization of WSe2 with the scanning tunneling microscope
Authors: Akari S. , Lux‐Steiner M. Ch. , Glöckler K. , Schill T. , Heitkamp R. , Koslowski B. , Dransfeld K. 
Published: May 2007

AbstractIn the present study we use the Scanning Tunneling Microscope (STM) as an instrument to investigate the photovoltaic properties of semiconducting materials. The surfaces of the layered semiconductor WSe2 were optically illuminated during the tunneling process. The resulting photo‐induced tunneling current (PITC) was measured as a function of the wavelength. Microscopic information on the energy dependent generation and recombination of the photo‐electrons in the vicinity of the tunneling tip was obtained by this method without the necessity of covering the surface with a conducting electrode. The analysis of the wavelength dependence of the PITC points at the existence of excitonic excitations. Compared to the spectral response of conventional photosensitive heterodiodes our PITC spectra exhibit a more structured response and an increase of the signal in the UV region. Finally, PITC studies on differently treated WSe2 surfaces show an improved photoactivity for WSe2 crystals treated with NaI/I2 solutions.
Influence of giant angular resonances on the electromagnetic characteristics of low‐lying states
Authors: Mikhailov I. N. , Usmanov Ph. N. 
Published: May 2007

AbstractThe two‐rotor model0 with the Feshbach projection operator method is applied for investigating the properties of the positive parity low‐lying collective states in the rare earth nuclei. The calculations of the energy spectra, E2‐transition probability and magnetic properties of the states of β‐ and γ‐bands are carried out for the isotopes 164, 166, 168Er. The B(M1) values from 1+ states to the ground band are estimated.
Magnetic and other normal properties of Y‐Ba‐Cu‐O caused by Cu‐O chain fragments
Authors: Uimin G. , Stepanov V. 
Published: May 2007

AbstractWe discuss the questions related to modifications of the orthorhombic phase of YBCO. A general approach of statistical mechanics allows to determine numerically such quantities as the paramagnetic Curie constant, concentration of holes doped into Cu(2) planes from chain fragments, the fractions of copper ions in differently coordinated positions. Where the experimental information is available, we discuss a correspondence between our theoretical results end experimental ones.
Anomalies of the photo‐response and thermal boundary resistance of a YBaCuO/YSZ structure
Authors: Bonch‐Osmolovskii M. M. , Galkina T. I. , Golovashkin A. I. , Dovydenko K. Yu. , Klokov A. Yu. , Krasnosvobodtsev S. I. , Oktyabrskii S. R. , Romanov E. G. 
Published: May 2007

AbstractThe photoresponse of a YBaCuO/ZrO2 bolometric structure was measured under modulated (λ = 630 nm) and pulsed (τ ≈ 7 – 8 ns; λ = 337 nm) laser excitation. The shape of the measured photoresponse was interpreted by a thermal model; nevertheless, the pulse amplitude for vanishing YBaCuO film resistance was 5–6 times greater than predicted; the thermal boundary resistance RBd between YBaCuO and YSZ was evaluated ⋍ 10−2 K × cm2/Watt, which is considerably larger than estimated theoretically for the similar situation of YBaCuO/MgO [5].
Dilatometrische und dielektrische Anomalien bei den Phasenumwandlungen in Ba(Ti1‐xSnx)O3
Authors: Kajtoch Czesław 
Published: May 2007

AbstractThe temperature dependence of the thermal expansion, the dielectric constant, the pyroelectric current and the remanent polarization in polycrystalline samples of Ba(Ti1‐xSnx)O3 was measured. The influence of the external electric field and Sn‐substitution on the character of all phase transitions was investigated.
Classical Becker‐Döring cluster equations: Rigorous results on metastability and long‐time behaviour
Authors: Kreer Markus 
Published: May 2007

AbstractWe consider the classical Becker‐Döring cluster equations with constant monomer concentration c1 = z > 0 and

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as a model which describes the kinetics of a first‐order phase transition. For a large class of positive coefficients al and bl (including the ones commonly used in physics and chemistry) we prove the following:
(i) When the monomer concentration z is slightly greater than zs = liml→∞ bl/al then all initial states ‐ containing only subcritical clusters of size l < l* (where l* denotes the critical size of a nucleus and depends on the supersaturation z‐zs > 0) ‐ converge within a fairly short time towards a metastable state. In this metastable state only subcritical clusters are present. The “metastable equilibrium” has an exponentially long lifetime TM ∼ exp (C(z‐zs)−ω) (where C and ω are some positive constants).(ii) For times greater than the lifetime TM this metastable state breaks down in the following sense: as t→∞ each of the cl(t) converges towards the Becker‐Döring steady‐state solution fl(z) like cl(t)‐fl(z) = O (exp (‐ | λ1 | t)) (where λ1 < 0 is the eigenvalue closest to 0 of a certain infinite transition matrix) and the total mass of supercritical clusters (i.e. clusters of size l > l*) diverges in this limit. For large times the cluster‐number increases linearly in time in the sense that limt→∞ n (t)/t = J(z), where J(z) > 0 is the Becker‐Döring steady‐state current. For the average cluster size l = Σ lcl(t)/Σt=1 c(t), we find for sufficiently large times algebraic growth in time t, that is, μ1t1/(1‐α) < l(t) < μ2 t1(1‐α) (where 0 < α < 1 is the algebraic growth exponent of the al ∼ lα and μ1, μ2 are suitable positive constants). This bound covers previous suggestions due to computer simulations and heuristic calculations.
Frequency shifts in a cesium atomic clock due to Majorana transitions
Authors: Bauch Andreas , Schröder Roland 
Published: May 2007

AbstractThis paper deals with a theoretical model which describes the effect of Majorana transitions on the frequency of a cesium atomic clock. In contrast to the explanations given in the past, the phase correlation between the individual successive excitations in inhomogeneous magnetic fields and the microwave resonator are for the first time taken into account.The π transitions with the selection rule ΔF = 1, Δm = ± 1 are of particular importance. The theory allows experimental results obtained in the past with the CSX apparatus, in particular the large frequency shifts observed, to be interpreted. The effect on the determination of the uncertainty of primary atomic clocks will be discussed.
Theoretical study of the temperature dependence of the width of magnetic domain walls
Authors: Jensen P. J. , Bennemann K. H. 
Published: May 2007

AbstractThe temperature dependence of magnetic domain walls in ferromagnetic systems with strong exchange coupling and weak lattice anisotropy is studied assuming that the thermal influence results mainly from the temperature dependence of the magnetization. We obtain that in lattices with an uniaxial symmetry like Co the wall width increases with temperature, but stays finite up to the Curie temperature Tc. In contrary, for a cubic lattice like Fe the wall width diverges for T → Tc, if only the lattice anisotropy is taken into account. The shape of the domain walls is not conserved, since at Tc the wall is determined only by the lowest order of anisotropy. In addition, the temperature dependence of a domain wall width for a thin magnetic film is determined. Using a special symmetry, we obtain a diverging wall width at a temperature markedly lower than Tc. However, the consideration of additional domain wall modes should modify this result.
Grad theory and extended thermodynamics
Authors: Nettleton R. E. 
Published: May 2007

AbstractGrad‐type approaches introduce an ansatz involving tensor Hermite functions with coefficients expresed in terms of moments of the ansatz. This formalism in usual form yields terms linear in first‐order spatial derivatives in kinetic equations for the moments. Such terms disagree with alternative statistical derivations and phenomenological arguments. This disagreement is removed if different ansatzes are used to calculate entropy and moment equations. These are non‐unique, and so Grad theory, while providing theoretical expressions for transport coefficients, does not serve uniquely to determine the structure of phenomenological equations.
Aging of supersaturated Al‐Cu‐Co decagonal phase
Authors: Grushko B. 
Published: May 2007

AbstractAging of the supersaturated Al68Cu11Co21 decagonal phase was studied by transmission and scanning electron microscopy. Changes in the twofold [12100] electron diffraction patterns are reported. The decagonal phase aged at 700–800°C exhibited a reduction of the intensities of the quasiperiodic odd‐n reflections and the appearance of extra‐reflections along quasiperiodic directions.
Dynamics of radiation induced quasiparticles in superconducting tunnel junction detectors
Authors: Jochum J. , Kraus H. , Gutsche M. , Kemmather B. , v. Feilitzsch F. , Mössbauer R. L. 
Published: May 2007

AbstractIn order to achieve a high resolution in the spectroscopy of low energy X‐rays, detectors based on superconducting tunnel junctions as sensors are presently investigated. The knowledge of the processes affecting the signal generation in such sensors is essential for the interpretation of the detector response. Starting from a diffusion model including decay and tunneling of excess quasiparticles in the metal layers of a superconducting tunnel junction detector, the detector response is determined as a function of absorption position and of rate constants. Model predictions agree very well with experimental data. The advantages of a detector employing quasiparticle trapping are pointed out and the parameters determining the signal gain are deduced. The linearity of the detector signal is much more affected by pair recombination of the quasiparticles during their tunneling rather than during their diffusive propagation into the tunneling region.
Cluster equations for the Glauber kinetic Ising ferromagnet: I. Existence and uniqueness
Authors: Kreer Markus 
Published: May 2007

AbstractThe infinite set of cluster equations, proposed by Binder and Müller‐Krumbhaar for a Glauber kinetic Ising ferromagnet in 1974, generalize the Becker‐Döring equations used in classical nucleation theory. For positive symmetric transition rates satisfying certain growth conditions and a detailed balance condition we prove for sufficiently fast decaying initial cluster distributions the existence of a positive cluster distribution with finite density for all finite times solving the cluster equations. Uniqueness is proven under some further conditions on the transition rates. Our existence and uniqueness results apply e.g. for a Glauber kinetic Ising ferromagnet in two dimensions.
Light scattering and small angle neutron scattering experiments with an aggregating binary liquid mixture of critical composition
Authors: Schmitz J. , Belkoura L. , Woermann D. 
Published: May 2007

AbstractResults of light scattering and small angle neutron scattering experiments with a 2‐butoxyethanol (2‐C4E1)/D2O mixture of critical composition (stoichiometric mole fraction of 2‐C4E1x = 0.0598; critical temperature Tc (visual) = 42.714 °C) are reported. They are carried out with the aim to find out whether the temperature dependence of the correlation length ξ characterizing the extension of concentration fluctuations near Tc is different from that characterizing the size of aggregates of the 2‐C4E1 molecules which appear to exist at temperatures away from Tc. The experiments show that the temperature dependence of ξ near Tc is the same as that away from Tc within the uncertainty of the measurements. – As a by‐product of this study, neutron scattering data were collected corresponding to a wide range of values of the scaling variable x (3 < x < 2100; x = qξ q is the absolute value of the scattering vector). They are analysed in terms of the limiting form of the universal correlation scaling function gξ(x) = C1x−(2‐η) to determine the value of the universal critical exponent η. A value of η = 0.039 ± 0.004 is found. It is considered consistent with the theoretically expected values.
On local and global currents in mesoscopic conductors
Authors: Loosen Roland , Menne Rolf , Hajdu János 
Published: May 2007

AbstractUsing linear response theory we show that, in a quasi‐stationary state, the local multiprobe conductance of a mesoscopic system of non‐interacting electrons with a time reversal invariant Hamiltonian does not depend on the local shape of the driving self‐consistent potential and thus is entirely determined by the asymptotic values of the potential in the leads. In the ballistic limit, the local conductance in the lateral direction exhibits oscillations depending on the occupation of channels. Scattering by a point impurity leads to softening of the quantized global conductance steps. In addition to that for an attractive scattering potential, a dip occurs in each plateau regime the shape of which is calculated for different values of the potential strength. We also investigate the local conductance for both a point scatterer and a finite scattering region.
Metallic solutions of the continuum model for conducting polymers
Authors: Streitwolf H. W. , Puff H. 
Published: May 2007

AbstractIn the continuum approximation of the Su‐Schrieffer‐Heeger model for degenerate and nondegenerate ground state systems, an exhaustive survey of solutions of the standard gap equations is given. With special emphasis on the electronic energy spectrum, the pertinent results of Takahashi [1] are extended to the whole μ, k‐plane. Periodic metallic phases and their grand potentials are discussed.
Cluster radioactivities of odd‐mass nuclei
Authors: Poenaru D. N. , Hourani E. , Greiner W. 
Published: May 2007

AbstractThe partial half‐lives of the hypothetical even‐even equivalent of an odd‐mass nucleus for cluster transitions toward various excited states of the daughter, used as a reference to find the hindrance factor, can be calculated within analytical superasymmetric fission model, by taking into account the angular momentum of the emitted cluster. Detailed tables are presented for 14C radioactivity of 221Fr, 221,223Ra, 225Ac; 24Ne radioactivity of 233U, 231Pa, and 23F decay of 231Pa, showing that, except for 225Ac, the existing experimental evidences, do not exclude (moderate) hindered transitions to the ground states of the daugther nuclei.
Beschleunigungsreaktionen von Neutronen
Authors: Petrov Yuri V. 
Published: May 2007

Acceleration of neutrons by isomeric nuclei.The inelastic neutron acceleration (INNA) by long living isomeric nuclei is studied. The theoretical estimates of the INNA cross‐sections for thermal neutrons for a number of isomers give the values in the range 0.1 ‐ 102b. Inelastic acceleration of thermal neutrons was observed by 152mEu and 180mHf, and confirmed the high value of the INNA cross‐sections. As a result of the high probability of acceleration some isomeric nuclei 113mIn, 115mIn, are not usual moderators but accelerators of neutrons. The use of the INNA reaction for the study of high excited levels and the nature of various nuclear hindrances are discussed.
Peltier‐effect in the mixed state of (Bi, Pb)2Sr2Ca2Cu3Oδ
Authors: Galffy M. , Hohn Ch. , Freimuth A. 
Published: May 2007

AbstractWe present measurements of the Peltier‐effect in the mixed state of Bi1.76Pb0.24Sr2Ca2Cu3Oδ. The Peltier‐coefficient broadens in a magnetic field quite similar to the resistivity and the thermopower. Comparison with the thermopower shows that Onsagers relation holds well. The occurrence of the Peltier‐heat in the mixed state well below Tc implies that the electric current is accompanied by a large heat current. We show that the vortex contribution to the Peltier‐heat is negligibly small. Therefore the heat current has to be attributed to normal quasiparticle excitations. Our results indicate that this quasiparticle contribution to the heat current remains large even at temperatures far below Tc.
Calculated effects of charge fluctuations on the phonon dispersion of YBa2Cu3O6 and YBa2Cu3O7. I. The model
Authors: Klenner M. , Falter C. , Chen Q. 
Published: May 2007

AbstractIn this paper we present a microscopic model that allows us to study the effects of charge fluctuations on the phonon dispersion of the high‐temperature superconductor YBa2Cu3O7 and its insulating counterpart, YBa2Cu3O6. An ab‐initio rigid‐ion model with pair potentials calculated by the Gordon‐Kim method from the free‐ion charge densities is used as a reference system. Starting from this reference system, charge fluctuations at the copper‐ and oxygen ions are introduced into the model. The charge fluctuations are treated as adiabatic degrees of freedom in a non‐phenomenological way. The parameters entering the model are estimated consistently with the reference system from first principles rather than refering to the experimentally determined phonon dispersion. In addition to the metallic behavior (appropriate to YBa2Cu3O7) obtained in this way, insulating behavior (appropriate to YBa2Cu3O6) is simulated by requiring the polarizability function to fulfill a corresponding long. wavelength sum rule. Screened site‐potential changes are defined that (besides the charge fluctuations) constitute a qualitative measure of the electron‐phonon‐interaction potential. Furthermore we investigate the long‐wavelength limiting behavior of the most important quantities occurring in our formalism. We derive formulae that allow us to calculate the contribution of the charge fluctuations to the macroscopic dielectric constant and the transverse effective charges in the insulating phase.
Nonlinear conductance fluctuations in a mesoscopic ring
Authors: Bockhorst H. , Zwerger W. 
Published: May 2007

AbstractWe study the conductance of a single particle on a ring subject to an arbitrary dc electric field, which is generated by a linearly in time increasing magnetic flux. The full quantum mechanical time development is calculated numerically by splitting the dynamics into independent consecutive Zener tunneling transitions and free motion on the ring. The Zener transitions occur near the avoided crossings of the bandstructure which arises from the adiabatic eigenstates as a function of flux in the presence of a static scattering potential. To account for the necessary dissipation the particle is coupled to an appropriate oscillator bath which is adjusted to give a strictly linear current‐voltage characteristic for arbitrary voltage and temperature in the absence of scattering. Taking a single δ‐function scatterer we find that the dissipative coupling eliminates the localization in energy space found previously and leads to a well defined resistive steady state. The scattering introduces reproducible fluctuations around the average Ohmic behavior which are caused by coherent backscattering. Their magnitude depends on the strength of the scattering potential and decays slowly for large voltages. The associated correlation energy is determined by the uncertainty of the eigenstates due to the dissipative bath coupling. Thermal averaging leads to a decrease of the conductance fluctuations proportional to T−1.
A Machian interpretation of the cosmological constant
Authors: Liu Hongya , Mashhoon Bahram 
Published: May 2007

AbstractA 5D Machian generalization of Einstein's theory of gravitation is described in which the cosmological constant appears as the contribution of the rest of the universe to the gravitational field of an “isolated” source. This work amounts to a Machian interpretation of the Kaluza‐Klein theory. The standard cosmological models are derived in this framework, and it is shown that ‐ in conformity with the interpretation presented here ‐ the cosmological constant does not directly contribute to the geometric description of the universe as a whole.
Rapid evaluation of oscillating lattice sums
Authors: Jensen P. J. 
Published: May 2007

AbstractWe have generalized a method for the rapid evaluation of oscillating lattice sums for layered geometries, based on the Ewald's summation technique. Different types of long range interactions as well as different lattice symmetries can be considered, in particular modulated magnetic structures, periodic domain patterns, or periodic lattice distortions. As examples the demagnetizing energies for different thin films systems and magnetic excitations in a single atomic layer are calculated.