bluuebunny/crossref_metadata_2025 huggingface dataset:
Corner transfer matrix study of an inhomogeneous Ising model
Authors: Peschel Ingo , Wunderling Roland
Published: May 2007

We consider a planar Ising model with an extended defect described by couplings of the form K(r) = K·(1 + A/r). We determine the spectrum of the corner transfer matrix numerically and analytically and use it to calculate the local magnetization at the defect and the corresponding, non‐universal critical exponent.
Migdal‐Kadanoff renormalization of a nonlinear supervector model with hyperbolic symmetry
Authors: Drunk W. , Fuchs D. , Zirnbauer M. R.
Published: May 2007

The Migdal‐Kadanoff approximation is applied to a nonlinear σ model with fields taking values in a perfectly graded noncompact superspace G/K of rank one. It is shown how to implement the spherical transform for this model space numerically in a controlled manner. The correlation length exponent ν, and the dimensions of a series of G‐invariant scaling operators at the fixed point, are computed for 2 < d ⩽ 3. No perturbative instability of the type found by Kravtsov et al. and Wegner is observed.
Hyperfine interactions of 111Cd in TiO2 (Rutile) studied by perturbed angular correlations
Authors: Wenzel Th. , Bartos A. , Lieb K. P. , Uhrmacher M. , Wiarda D.
Published: May 2007

The time‐differential perturbed angular correlation for 111Cd nuclei has been measured after 111In implantation into polycrystalline TiO2. The observed perturbation functions are characterized by a well‐defined electric field gradient with the quadrupole coupling constant νQ = 105(1) MHz and the asymmetry parameter η = 0.18(1). We attribute these hyperfine parameters to 111Cd on the (distorted) substitutional cation site in rutile. The PAC results are compared with those in SnO2 rutile as well as with X‐ray diffraction, RBS channeling experiments and point charge model calculations including relaxation of the probe atom surrounding.
A note on Δn ≠ 0 Stark transitions in hydrogenlike atoms
Authors: Kretzschmar Martin , Steinmetz Andreas
Published: May 2007

In a gaseous helium or hydrogen target slow muons or antiprotons are captured into orbits with a high principal quantum number (n = 15 to 50) to form (μ− α)+ ions, (pα)+ ions, or (pp) atoms respectively. In the subsequent deexcitation process Stark mixing of the intermediary states plays an important role. The successful Mainz Cascade Model assumed Δn = 0 for the Stark transitions, although formally no such selection rule exists. This note examines the reasons why Δn ≠ 0 Stark transitions play only a negligible role in the deexcitation cascade.
Spinfluctuations versus phonons: The case of Heavy‐Fermion superconductivity
Authors: Welslau B. , Grewe N.
Published: May 2007

Superconductivity of Heavy‐Fermions, with an emphasis on hexagonal UPt3, is investigated microscopically on the basis of the LNCA‐approximation for strongly correlated electrons in a Kondo lattice and of Eliashberg theory for anisotropic singlet and triplet superconducting order. The effective interaction kernel incorporates exchange of spin fluctuations carried by strongly renormalized particle‐hole excitations as well as exchange of phonons generated by the breathing mechanism. Particular care is taken to include realistic anisotropies in band structure and couplings and to expand interaction kernel and order parameter in appropriate Fermi surface harmonics. Separate interactions and corresponding gap equations are used for pseudo‐spin‐singlet and ‐triplet channel, with a restriction to the case of weak spin‐orbit coupling. Our main results include a detailed study of phonon‐ and spin‐fluctuation mechanisms as a possible source for superconductivity and, in combination, their mutual influence and competition. Furthermore, the questions regarding singlet or triplet order, conventional or unconventional symmetry, order parameter zeros and phase transitions between different superconducting states are addressed. We propose a possible scenario of Heavy‐Fermion superconductivity.
3D‐solitons in a strongly magnetized plasma: Transition from flat to spherical waves of the Zakharov‐Kuznetsov equation
Authors: Murawski K.
Published: May 2007

The Zakharov‐Kuznetsov equation has been used to describe ion‐acoustic wave propagation in a strong magnetic plasma. An initial‐value problem has been solved for this equation on the basis of a numerical method that uses the fast Fourier transform technique for calculating space derivatives and a fourth order Runge‐Kutta method for the time scheme. Numerical simulations have shown that the disturbed flat solitary waves can break up into spherical ones.
Magnetic‐field‐induced damage in a superconducting YBa2Cu3O7−x film
Authors: Brüll P. , Kirchgässner D. , Leiderer P. , Berberich P. , Kinder H.
Published: May 2007

During investigations of the magnetic flux dynamics in thin superconducting YBa2Cu3O7−x films we have observed the spontaneous formation of a damage in the film, apparently induced by the applied magnetic field of 0.1 T. The damage developed within less than 40 ms (the time resolution of the experiment) and showed up in the magnetiooptically recorded image of the flux above the sample as a path for massive flux penetration. A subsequent analysis revealed a 1 μm wide gap in the YBa2Cu3O7−x film which had developed over a major portion of the 1 · 1 cm2 sample. It is suggested that the film locally melted as a result of an instability of the superconductor in the critical state.
Influence of magnetic impurities on the de Haas‐van Alphen oscillations
Authors: Stephan F. , Keiter H.
Published: May 2007

Using a simple extension of Shiba's formula for the de Haas‐van Alphen‐oscillations, the influence of scattering by magnetic impurities is studied. Already for a classical spin model one obtains a minimum in the dHvA amplitudes as function of the magnetic‐field, which is influenced by normal scattering. The change of this behavior for the Anderson model is studied within the Non‐Crossing‐Approximation, and raises questions for a comparison between experiment and theory.
How many spectral lines are statistically significant?
Authors: Freund J.
Published: May 2007

When experimental line spectra are fitted with least squares techniques one frequently does not know whether n or n + 1 lines may be fitted safely. This paper shows how an F‐test can be applied in order to determine the statistical significance of including an extra line into the fitting routine.
Metastable phase formation and structural change characteristics of vapor deposited semiconductor films
Authors: Fuxi Gan , Songsheng Xue , Zhengxiu Fan
Published: May 2007

Reported here are studies about the thermal and laser induced metastable phase formation in amorphous GeSb2Te4 thin films prepared by RF‐magnetron sputtering. The general structural properties of this most promising optical phase change recording material are discussed from the point of view of fast structural phase transformation.
Unbiased estimate of forces from measured correlation functions, including the case of strong multiplicative noise
Authors: Borland Lisa , Haken Hermann
Published: May 2007

Starting from appropriate short‐time correlation function measurements, we propose a dynamical “learning” method to derive the deterministic and stochastic forces underlying an observed process, even if this process contains strong multiplicative noise. To do this we extend the ideas of our previous paper [1] to establish mathematical relationships in this more general case between the joint distribution function of the process and its corresponding Ito‐Langevin equation. A numerical example for a simulated process containing strong multiplicative noise shows good agreement with the theory.
Resistivity, fluctuation‐enhanced conductivity, and irreversibility line of high‐quality Tl2Ba2Ca2Cu3O10 single crystals
Authors: Winzer K. , Kumm G. , Maaß P. , Thomas H. , Schwarzmann E. , Aghaie A. , Ladenberger F.
Published: May 2007

We present measurements of the resistivity tensor components ρa (T) and ρc (T) of high‐quality Tl2Ba2Ca2Cu3O10 single crystals wit Tc = 118 … 121 K. The in‐plane resistivity ρa as well as the out‐of‐plane resistivity ρc show a metal‐like temperature dependence with an anisotropy ratio ρc/ρa of up to 103. The coherence length ξc (0) = 0.15 nm could be determined from an analysis of the fluctuation conductivity above Tc. From measurements of the ac‐susceptibility in magnetic fields up to 10 Tesla the temperature dependence of the depinning line could be obtained. The diffusion coefficient of the flux lines obtained from the frequency dependence of the depinning temperature shows a thermally activated behaviour of the flux motion in the field range 0.1 T ⩽ B ⩽ 10 T.
Some notes on stationary vacuum solutions of the Einstein equations with shearing nongeodesic eigenrays
Authors: Horváth I. , Lukács B.
Published: May 2007

The stationary vacuum solutions of the Einstein equations of General Relativity give the external space‐time around stationary mass distributions, as e.g. final states of stellar evolution. The Kerr solution has shear‐free geodesic eigenrays and describes all black hole configurations with good asymptotic behaviour at infinity. Other solutions of this class are unphysical. Classes with shearing geodesic or shearfree nongeodesic eigenrays do not contain physical solutions at all, so for other physical configurations one must turn to the generic case of shearing nongeodesic eigenrays. For the stationary axisymmetric case Ansätze for solutions can be formulated in form of a specific functional dependence between the parameters of shear and nongeodesicity, unless they both are constants. Here we investigate the second subcase. Our result is that there is no solution of the vacuum Einstein equations in this subclass, except when both parameters vanish.
Second order Hamiltonian formalism and constraints algebra for non‐polynomial supergravities
Authors: Foussats A. , Repetto C. , Zandron O. P. , Zandron O. S.
Published: May 2007

The second order Hamiltonian formalism for a non‐polynomial N = 1D = 10 supergravity coupled to super Yang‐Mills theory is developed. This is done by starting from the first order canoncial covariant formalism on group manifold. The Hamiltonian, generator of time evolution, is found as a functional of the first class constraints of this coupled system. These contraints close the constraint algebra and they are the generators of all the Hamiltonian gauge symmetries.
Lyapunov exponents from quantum dynamics
Authors: Haake Fritz , Wiedemann Harald , Życzkowski Karol
Published: May 2007

We extract classical Lyapunov exponents from the time dependence of quantum mechanical expectation values. Classical chaos is revealed as a quantum transient with a liftetime ∼︁ ln ħ. Our strategy is shown to work for the example of a periodically kicked top.
Scanning tunneling microscopy/spectroscopy, etching and modification of surfaces of YbBa2Cu3O7‐δ single crystals using an STM
Authors: Yang X. , Rosner K. , Winzer K. , von Minnigerode G.
Published: May 2007

The surface of YbBa2Cu3O7‐δ single crystals was investigated using a scanning tunneling microscope at room temperature in air. Growth steps with step heights equal to the lattice parameter c as well as steps with step heights of multiples of 1.35 c were obtained. On smooth surfaces atoms arranged in a 3.8 Å square lattice could be resolved. We observed a tunneling‐induced etching effect leading to an etch pit on the surface. Furthermore, by applying voltage pulses with amplitude > 5.0 V and duration > 100 μs holes with diameters of ∼︁ 150 nm could be produced. Scanning tunneling spectroscopic measurements were performed yielding I‐V and ln I‐s characteristics. The extremely small effective barrier height of ϕ = 0.3 eV inferred from d ln I/ds may be caused by dirt between the surface and the tip.
RPA in wavefunction representation
Authors: Reinhard P.‐G. , Gambhir Y. K.
Published: May 2007

The RPA is formulated in subspaces of coordinate‐like and momentum‐like 1 ph operators. This allows to embed a large class of approximative schemes into a generalized RPA treatment. We give a detailed formulation in terms of wavefunctions in coordinate space which is ideally suited to practical programming. In particular, we work out the reduction to spherical tensors in the case of spherical symmetry which is most often the starting point in finite Fermion systems.
From sum rules to RPA: 1. Nuclei
Authors: Reinhard P.‐G.
Published: May 2007

We take up the flexible formulation of RPA in subspaces of coordinate‐like and momentum‐like 1 ph operators which was developed in the preceeding paper. We draw the connection to many of the known collective approximations to RPA by proper choice of the subspace of operators. We finally apply the newly developed scheme to comparative studies of a hierarchy of approaches for the RPA spectra of doubly magic nuclei described with Skyrme forces.
Pressure effects on 2p5 3p ‐ 2p5 3d transitions in neon
Authors: Trawiński R. S. , Bielski A. , Ciuryło R. , Szudy J.
Published: May 2007

The collisional broadening and shift of four spectral lines of neon (747.2, 748.8, 753.5, 754.4 nm) arising from 2p5 3p ‐ 2p5 3d transitions, emitted from a low‐pressure glow discharge in pure neon and neon‐helium mixtures have been measured using a Fabry‐Perot interferometer. The values of pressure broadening and shift coefficients are determined and analyzed in terms of the impact theory.
The anomaly of the specific heat of La2‐xSrxCuO4+δ near Tc
Authors: Ernst P. , Schnelle W. , Breuer M. , Borowski R.
Published: May 2007

The specific heat of three polycristalline samples of La2‐xSrxCuO4+δ (x = 0.15, 0.15, 0.16) near Tc was measured with a resolution better than 0.1%. The anomaly at Tc is analysed for fluctuations for the first time. It is well described by a superposition of a mean field step and a contribution due to gaussian fluctuations. By a fit of a Lawrence‐Doniach type of model to the specific heat near Tc we estimate ΔCMF and the anisotropic coherence lengths ξ and ξ⊥ of the superconductor.
Surface phonons and elastic surface waves
Authors: Büscher H. , Klein‐Heßling W. , Ludwig W.
Published: May 2007

Theoretical investigations on the dynamics of the (001), (110) and (111) surfaces of some cubic metals (Ag, Cu, Ni) will be reviewed. Both, lattice dynamical and continuum theoretical results are obtained via a Green's function formalism. The main attitude of this paper is the comparison of our results with experiments and with results obtained via slab‐calculations. The calculation of elastic surface waves has been performed using a modified surface‐green‐function‐matching method. We have used two different approaches of calculation the bulk Green's function (a) using the spectral representation and (b) a method, what works on residues. The investigations are carried out using shortrange phenomenological potentials. The atomic force constants in the first surface layers are modified to describe surface phonon anomalies, observed by experiments. In the case of Ag (100) and Ag(110) we conclude that the detection of odd symmetry shear modes by Erskine et al. [1 a, b] was not very accurate.
Stochastic fluctuations of persistent currents in mesoscopic rings
Authors: Eckern Ulrich , Schmid Albert
Published: May 2007

We investigate systematically the effect of the electronic Coulomb interaction on the stochastic fluctuations (from sample to sample) in the persistent currents I(Φ) of mesoscopic rings threaded by a magnetic flux Φ. In contrast to our recent publication [Europhys. Lett. 18 (1992) 457], we avoid separation of impurity and interaction scattering events and we present here a comprehensive view. By this alternative procedure, we are able to confirm our earlier result, namely that 〈I2〉1/2 ∼ evF/L, which is a much larger quantity than the average current 〈I〉 ∼ evFl/L2.
Collective diffusion of Brownian particles with square well and hydrodynamic interaction
Authors: Vogel Jürgen
Published: May 2007

The low wavenumber collective diffusion coefficient of a semi‐dilute suspension of spherical Brownian particles interacting via square well potential and hydrodynamic pair interaction is considered. The first two nonvanishing terms of an expansion in powers of the wavenumber are calculated. Analytical expressions are found for extremely narrow wells and in the limit of large well diameters.
Metastable phases in vapour‐quenched Al78Cu22 film
Authors: Yan Haibo , Gan Fuxi , Wang Lixin
Published: May 2007

The structure and structural changes of an Al78Cu22 (at%) alloy film produced by coevaporation onto a cooled substrate have been investigated with transmission electron microscopy. A series of metastable phase transitions were observed during the crystallization from the as‐deposited amorphous phase to the final equilibrium state. The deposit structure at room temperature consists of a mixture of fine grained α' crystallites (fcc, α = 4.81 Å) with an amorphous phase, and some welldefined crystals with an fcc lattice (a = 7.18 Å, namely α1). The subsequent annealing led to the grown crystals transforming to an ordered α′ phase. It is argued that the development of such a transition is the result of a gradual atomic rearrangement – first topologically then a chemically predominant disorder‐order transition.
The astrophysical S‐factor of the reaction 7Be (p, γ)8B in the direct capture model
Authors: Krauss H. , Grün K. , Rauscher T. , Oberhummer H.
Published: May 2007

The astrophysical S‐factor for the reaction 7Be(p, γ)8B up to an energy of 2 MeV (c.m.) and the capture cross section of 7Li(n,γ)8Li up to 1 MeV (c.m.) are calculated using the Direct Capture model (DC). Both calculations are in good agreement with experimental data.
Specific heat of a BCS superconductor
Authors: Ferrell Richard A.
Published: May 2007

By expressing the free energy as an appropriate temperature integration over the square of the BCS energy gap function and by substituting simple but accurate analytic expressions for the latter, corresponding expressions are obtained for the specific heat in the superconducting state. In the upper portion of the temperature range, the ratio of the specific heats in the superconducting and normal states is 2.43 (1 + 0.936 in t), to better than one per cent accuracy, where t is the reduced temperature. Thus, the semilog plot of temperature versus the ratio of specific heat to temperature is a straight line over a large portion of one decade of specific heat. Corresponding expressions of similar simplicity and accuracy are obtained for the middle and low temperature ranges.
On the composition‐dependent isotope effect of HTSC in the two‐band model
Authors: Konsin P. , Kristoffel N. , Örd T.
Published: May 2007

The oxygen isotope effect in high‐TC superconductors has been investigated on the basis of a two‐band model where superconducting phase transition is induced by interband (mainly Coulombic) interaction. The isotope shift of TC appears due to the dependence of averaged interband electronphonon coupling constant on oxygen mass. This coupling has a repulsive nature and gives a relatively small contribution to the total interaction inducing superconductivity. The calculated isotope effect exponent depending on the carrier concentration has been compared with the experimental one as a function of x for La2‐xSrxCuO4.
Statistical properties of Lyapunov exponents and of quantum conductance of random systems in the regime of hopping transport
Authors: Markoš P. , Kramer B.
Published: May 2007

The statistics of the zero‐temperature conductance and the Lyapunov exponents of one‐, two‐ and three‐dimensional disordered systems in the regime of strong localization is studied numerically. In one dimension, the origin of the universality of the moments of the conductance is explained. The relation between the most probable value of the conductance and its configurational average is discussed. The relative fluctuations of the conductance (and of the resistance) are shown to grow exponentially with the system length. In higher dimensions the conductance is almost entirely determined by the smallest of the Lyapunov exponents. The statistics of the conductance is therefore the same as in the one dimensional case. A model is proposed for the treatment of the fluctuations in hopping transport at finite temperatures. An exponential dependence of the relative fluctuations of the conductance/resistance on the temperature is predicted, log (δg/g) ∞ T−a with α = 1/(d+1). It is concluded that the presently available experimental data on the temperature dependence of the conductance fluctuations in the hopping regime can be understood by replacing the system size in the zerotemperature result for the fluctuations of the conductance by the hopping length.
Linear response, persistent currents and related problems
Authors: Janßen Martin , Gummich Ute , Hajdu János , Viehweger Olaf
Published: May 2007

Based on a general linear response approach we provide a systematic and unified survey of existing theories on persistent currents. The central notions in this context are equilibrium and dynamic persistent currents which are analyzed with respect to their similarities and differences in the canonical and grand canonical ensemble. We present criteria which relate the existence of persistent currents to the equipartition law and ergodicity for current correlators. We find that in additive Fermion systems at low temperatures both kinds of persistent currents coincide in the canonical ensemble whereas they differ in the grand canonical ensemble. Comparing different works on averaged persistent currents in diffusive mesoscopic rings within our framework and discussing several methods of calculating canonical currents with the help of grand canonical ensembles, we clarify some misunderstandings which have arisen in methodologically different approaches to the phenomenon of persistent currents. Finally, we relate the presence of dynamic persistent currents to the Hall conductivity on a finite cylinder and the center coordinate Kubo formula for the Hall conductivity.
Ferromagnetism in the Hubbard model: instability of the Nagaoka state on the square lattice
Authors: Hanisch Th. , Müller‐Hartmann E.
Published: May 2007

The instability of the fully polarized ferromagnetic ground state (Nagaoka state) of the Hubbard model on the square lattice is investigated. We use single spin flip variational wave functions including majority spin correlation effects and calculate spin flip energies in the thermodynamic limit. With very local wave functions and with moderate numbers of variational parameters we reproduce the best known estimate for the critical hole density δcr = 0.29 and we obtain an estimate of Ucr = 63 t for the critical coupling which is considerably better than the best estimate of Ucr = 42 t previously known. The simplicity of our wave functions makes the physical origin of the various aspects of the instability particularly transparent.
Electronic band structure of Cu3Au: An angle‐resolved photoemission study along the [111]‐direction
Authors: Lau Markus , Löbus Stefan , Courths Ralf , Halilov Samed , Gollisch Herbert , Feder Roland
Published: May 2007

High‐resolution normal photoemission (ARPE) spectra have been recorded for Cu3Au(111) with the use of polarized synchrotron and rare‐gas resonance radiation in the photon energy range from 9 to 27 eV. It is for the first time that dispersions of the gold‐like bands have been found experimentally. Using a fully relativistic layer‐KKR photoemission formalism, occupied and unoccupied bands as well as one‐step‐model photoemission spectra have been calculated. The comparison of calculated spectra with experimental ones and the observation of direct‐transition resonances upon photon energy near the Brillouin zone‐center reveal a shift of the unoccupied ground‐state bands by about +2.5 eV (self‐energy shift). The direct‐transition structures in the experimental spectra have been exploited to determine the dispersions of the occupied bands along the [111] direction (A line in k space). In order to determine the wave vector of the experimental direct transitions we used as final state that calculated unoccupied band along [111], which also exists in pure copper and gold up to about 20 eV above the Fermi energy (“unfolded” band structure), shifted by + 2.5 eV. The experimental occupied bands with Cu character are in very good agreement with theory after shifting the latter by about 0.3 eV to lower energy, whereas somewhat bigger discrepancies exist for the gold‐like bands.
Complete determination of the transition amplitudes from a comprehensive data analysis of the fusion reactions D(d,p)3H and D(d,n)3He for Ed<500 keV
Authors: Lemaître S. , Paetz gen. Schieck H.
Published: May 2007

All relevant low‐energy transition amplitudes for the D(d,n)3He and D(d,p)3H reactions were determined from a fit to Legendre expansion coefficients of the available experimental data. A simple barrier penetrability model was used. Quintet S‐wave transitions are found to contribute strongly thus obliterating the idea of neutron‐lean “polarized” fusion energy production. The D+D interaction radius was determined with good accuracy for both reactions individually. The astrophysical S functions show a small S‐wave enhancement and P‐wave suppression of the D(d,p)3H branch.
The superconducting penetration depth from the semiclassical model
Authors: Chandrasekhar B. S. , Einzel D.
Published: May 2007

The semiclassical approach of Onsager and Pippard has been very successful in relating the electronic properties of a normal metal to its band structure and fermi surface. This paper extends the method to a superconductor. A generalized London equation relating the supercurrent density to the vector potential is obtained, in terms of band and fermi surface parameters and an energy gap which may be anisotropic. The results allow an interpretation of measured penetration depths directly in terms of the electronic and gap structures of the superconductor. They lead to easy physical visualization of the origin of anisotropies and other features of measured penetration depths.
Dynamics of a quantum particle in a random potential
Authors: Groß M. , Bosse J. , Gabriel H.
Published: May 2007

The motion of a quantum particle in a random potential with short‐range fluctuations is analyzed using a generalized mode‐coupling approximation. The original theory of Götze was extended by introducing a wave‐vector dependent current relaxation kernel. Here we apply the theory to the special case of exciton dynamics in a binary molecular crystal. We find a localization–delocalization transition in three dimensions with a critical exponent of 1 for the inverse localization length. In the intermediate time regime, our theory predicts a region of anomalous diffusion. This can be interpreted as a precursor to localization. At the transition point it leads to the known asymptotic low‐frequency behaviour D″(ω) α ω1/3.
Formal power series representation for gauge boson stars
Authors: Schunck Franz E.
Published: May 2007

We represent spherically symmetric, static, and non‐singular solutions of the Einstein SU(2)‐Yang‐Mills and the Yang‐Mills‐dilaton system by means of formal power series expansions. Their coefficients are algebraically expressed in terms of new recursion relations. The solutions of Bartnik and McKinnon, found by numerical integration, are contained in our solution manifold.
From sum rules to RPA: 2. 3He droplets
Authors: Weisgerber S. , Reinhard P.‐G.
Published: May 2007

We investigate the excitation spectra of closed‐shell 3He droplets using a flexible formulation of the RPA which has been presented in preceeding papers. The calculations are based on an energy functional which thorougly employs finite‐range interactions. We compare the results for different stages in a hierarchy of approximations to the full RPA. We furthermore discuss the consequences of taking the zero‐range limit of the present energy functional, i.e. of using Skyrme‐type interactions.
Diffusion controlled growth of hydrogen clusters in metals
Authors: Nowakowski B. , Frisch H. L. , Borzi Carlos , Mijovilovich Ana
Published: May 2007

We show that a simple diffusion controlled growth, with subsequent aggregation, mean field theory accounts numerically for the growth of hydrogen clusters in certain metals (e.g. V, Nb, Zr, etc.). We also calculate the percolation threshold for the formation of an “infinite” aggregate both analytically and by a Monte Carlo simulation in a cubic lattice. The results are comparable and seem to correspond to the observed physical behavior.
Complex conductivity in high‐Tc single crystal superconductors
Authors: Ciccarello I. , Fazio C. , Guccione M. , Li Vigni M.
Published: May 2007

The electromagnetic surface impedance of single crystal high‐Tc superconductors has been examined within the framework of the two‐fluid model and the hypothesis that the e m field modulates the partial concentrations of both normal and condensate fluids. A comparison with experimental data is reported.
Electronic transport time through mesoscopic devices with contact barriers
Authors: Altland Alexander
Published: May 2007

Information about the transport time of electrons through a quasi one‐dimensional sample is obtained by calculating the energy auto‐correlation function of the conductance. Depending on the length of the sample and its coupling to the external device (here modelled by perfectly conducting leads), the transport time undergoes a smooth crossover between two different limiting regimes. In the case of long samples and good coupling it coincides with the diffusion time. In the opposite limit of short and weakly coupled systems, however, the transport time is given by the reciprocal of the quantum mechanical decay width into the leads. The transition between both regimes is discussed in terms of a few model independent concepts.
Dirac particle, gravity, and inertial effects
Authors: Huang Justin C.
Published: May 2007

Dirac's equation with gravity for a noninertial observer is derived using local coordinate methods. Calculations for the equation are carried out to second order in the local coordinates. For easy application to interference experiments, the Schrödinger form of the Dirac equation with a well defined Hamiltonian in the local coordinates is presented. The presence of gravitational weighting factors in the scalar product lead to hermitian and antihermitian sectors for the Hamiltonian. The antihermitian part depends directly on the curvature and vanishes for zero curvature. The hermitian part which is important for the determination of phases is studied in detail and the nonrelativistic case is obtained by the application of three successive Foldy‐Wouthuysen transformations. The results also give local currents and interactions which have pure inertial, pure gravity and mixed sectors. The pure inertial terms are the ones obtained by Hehl and Ni. The pure gravity and mixed sectors have contributions which are electric, magnetic and double magnetic in character. The focus is on the curvature contributions. Some are well within reach of the anticipated accuracy of atomic interferometers currently under consideration and other terms may follow if improvements can be made.
Influence of the Ca:Pb ratio on the superconducting properties of Bi‐based ceramics of type 2223
Authors: Rentschler T. , Schulz C. , Zoller P. , Lösch S. , Raff E. , Wischert W. , Kemmler‐Sack S. , Kessler P. , Lichte H. , Nissel T. , Huebener R. P.
Published: May 2007

From a study of the influence of the Ca: Pb ratio on the superconducting properties of Bibased ceramics of 2223 type it follows that as a second parameter the employed gas atmosphere must be taken into consideration. In case of air preparation good intragrain and intergrain properties are obtained for Ca rich samples (e.g. Bi1.8Pb0.2Sr1.9Ca2.1 Cu3Oz); whereas for Pb rich materials (e.g. Bi1.7Pb0.5Sr1.9Ca1.9 Cu3Oz) improved conditions are encountered by employment of an Ar/O2 (8%) atmosphere during synthesis. Independently, the transition temperature is situated near 108 K.
Bound states and superfluidity in strongly coupled Fermion systems
Authors: Röpke G.
Published: May 2007

The crossover from Bardeen‐Cooper‐Schrieffer pairing to Bose‐Einstein condensation is considered with special emphasis to a consistent description of bound pair formation. A nonequilibrium approach is considered, and wave equations for the two‐particle states and the pair amplitude are derived in the stationary state. The critical temperature is calculated for a simple model system.
Noises generated by nonlinear autoregression
Authors: Kumičák J.
Published: May 2007

A nonlinear generalization of autoregressive scheme of first order is suggested as approximate model for 1/fk noises. The iterative generation makes use of reducing function instead of a constant. Computer simulations – carried out over three decades of frequency – have demonstrated that there is such a family of these functions that to any function of the family there exists a unique value of standard deviation of white noise source such that the noise generated by the iterative scheme has the spectral factor k ≈ 1.

Implications of the results for understanding the origin, structural stability and ubiquity of 1/f noise are discussed.
Low frequency acoustic and dielectric measurements on glasses
Authors: Classen J. , Enss C. , Bechinger C. , Weiss G. , Hunklinger S.
Published: May 2007

The acoustic and dielectric properties of different glasses at audio frequencies and temperatures below 1 K have been investigated with the vibrating reed and a capacitance bridge technique. We found the temperature dependence of the absorption of vitreous silica (Suprasil W) to agree with the predictions of the tunneling model which is commonly used to explain the low temperature behaviour of amorphous materials. The variation of the sound velocity and of the dielectric constant, however, shows significant deviations from the expected behaviour which cannot be accounted for by a simple modification of the model. Instead, it seems to be necessary to introduce a temperature dependence of some relevant model parameters. Moreover, at very low temperatures (T < 0.1 K) the sound velocity strongly depends on the excitation levels. The absence of this effect at higher temperatures proves that it can be ascribed to a nonlinear response of tunneling systems. Similar results were found in sound velocity measurements on a cover glass and on a superconducting metallic glass (Pd30Zr70, Tc = 2.6 K), which indicates that these features are a general aspect of the dynamics of tunneling states in glasses. In contrast to the insulating glasses we found that in Pd30Zr70 also the internal friction is strain dependent.
Investigation of positively charged acceptor states in Si and Ge under uniaxial stress by phonon induced conduction
Authors: Groß P. , Laßmann K.
Published: May 2007

We use superconducting Al‐tunnel junctions as tunable phonon generators in the meV‐range to determine ground state splitting at zero stress of positively charged states associated with single acceptors in Si and double acceptors in Ge. From the stress and energy dependence of the conductivity induced by high frequency phonon irradiation of the corresponding two‐ and three‐hole states we find that the splitting is below 0.1 meV for the ground states of Si:B+ and Ge:Be+, and 1 meV and 1.2 meV for Si:Ga+ and Si:Al+, respectively. These level separations are comparable to those found previously for the ground states of the corresponding acceptor bound excitons A0X. For the deeper acceptors Si:In+, Si:Tl+, and Ge:Zn+ the results are qualitatively different.
Coherent tunneling of lithium defect pairs in KCl crystals
Authors: Weis R. , Enss C. , Würger A. , Luty F.
Published: May 2007

The tunneling of two lithium ion impurities on next‐nearest neighbor sites in potassium chloride are investigated both experimentally and theoretically. The strong dipolar interaction leads to coherent tunneling motion of the two defect ions between degenerate off‐center positions. Comparing data of rotary echo experiments for impurity pairs 7Li—7Li, 6Li—6Li, and 7Li—6Li with theory permits a thorough investigation of the isotope effect and of the effect of the interaction on the tunnel states. Our findings confirm the tunneling model with <111> off‐center states to be valid even for strongly interacting impurities. Using degenerate perturbation theory in terms of two‐particle states, we obtain essentially exact expressions for the tunneling spectrum and the dynamical susceptibility which agree well with the measured data.
Effective Hamiltonian for scalar theories in the Gaussian approximation
Authors: Naus H. W. L. , Gasenzer T. , Pirner H.‐J.
Published: May 2007

We use a Gaussian wave functional for the ground state to reorder the Hamiltonian into a free part with a variationally determined mass and the rest. Once spontaneous symmetry breaking is taken into account, the residual Hamiltonian can, in principle, be treated perturbatively. In this scheme we analyze the O(1) and O(2) scalar models. For the O(2)‐theory we first explicitly calculate the massless Goldstone excitation and then show that the one‐loop corrections of the effective Hamiltonian do not generate a mass.
Spin depolarization of spreading and propagating wave packets
Authors: Krenzlin H. M. , Kehr K. W.
Published: May 2007

Spin relaxation of spin‐1/2 quantum particles on linear chains with random Larmor frequencies is studied. Wave packets are prepared with initial spin polarization in the propagation direction and with either zero, or finite group velocity. The discrete Schrödinger‐Pauli equation is solved numerically. Exponential spin relaxation is observed in a restricted time range. The decay constant depends on the width of the distribution of the Larmor frequencies and on the group velocity. No dependence on the initial halfwidth of the wave packet is found.
Magnetic moment of a two‐dimensional degenerate electron gas in mesoscopic samples
Authors: Ovchinnikov Yu. N. , Lehle W. , Schmid A.
Published: May 2007

The orbital magnetism of two‐dimensional electrons in mesoscopic samples is studied in models where the interaction between electrons is neglected. Various geometries are considered as there are disc, plaquette, bracelet with hard wall confinement and also a confinement with a parabolic potential. We calculate the average magnetic moment which means an average with respect to size fluctuations and de Haas‐van Alphen oscillations which arise in the case of a sharp Fermi cutoff. We see three distinct ranges in the magnetic field: (i) small field region where perturbation theory applies; (ii) moderate fields where edge currents play a prominent role; and (iii) the high field range with a Landau type susceptibility. In a quasiclassical picture, the electronic orbits are not qualitatively changed by a magnetic field in (i); skipping orbits are important in (ii); and in (iii), the cyclotron radius is smaller than the sample size. As a rule, we find an enhancement of the magnetic response which increases with kFL, that is, with sample size divided by the Fermi wave length. Also, we have found out that the quasiclassical approximation fails in the calculation of the magnetic properties; on the other hand, we have seen no essential differences between the canonical ensemble (fixed particle number) and the grand canonical ensemble (chemical potential given). In the case of plaquettes, in particular for samples in the form of squares, we have found agreement with experimental results by Lévy, Reich, Pfeiffer and West.
Non‐linear conductivity of charge‐density‐wave systems
Authors: Werner C. R. , Eckern U.
Published: May 2007

We consider the problem of sliding motion of a charge‐density‐wave subject to static disorder within an elastic medium model. Starting with a field‐theoretical formulation, which allows exact disorder averaging, we propose a self‐consistent approximation scheme to obtain results beyond the standard large‐velocity expansion. Explicit calculations are carried out in three spatial dimensions. For the conductivity, we find a strong‐coupling regime at electrical fields just above the pinning threshold. Phase and velocity correlation functions scale differently from the high‐field regime, and static phase correlations converge to the pinned‐phase behaviour. The sliding charge‐density‐wave is accompanied by narrow‐band noise.
Synthesis, larvicidal, QSAR and structural studies of some triorganotin 2,2,3,3‐tetramethylcyclopropanecarboxylates
Authors: Song Xueqing , Zapata Alejandra , Hoerner Jana , de Dios Angel C. , Casabianca Leah , Eng George
Published: May 2007

A series of triorganotin 2,2,3,3‐tetramethylcyclopropanecarboxylates, where R = methyl, ethyl, n‐propyl, n‐butyl, phenyl and cyclohexyl, have been synthesized. Elemental analysis, Mössbauer, infrared and NMR spectroscopies were used to characterize their structures. Based on the spectroscopic results, all the complexes in the solid state with the exception of the tricyclohexyl compound were found to be five‐coordinated, while the tricyclohexyltin derivative was determined to be four‐coordinated. Based on the NMR results, all the complexes in solution have a tetrahedral configuration. Larvicidal activities of the complexes were evaluated against the second instar stage of the Aedes aegypti, Anopheles stephensi and Culex pipiens quinquefasciatus mosquitoes. The toxicity results indicated that this series of triorganotins are effective larvicides against all three species of larvae. In addition, quantitative structure–activity relationships (QSARs) were also developed for each species of larvae. Copyright © 2007 John Wiley & Sons, Ltd.
Organotin compounds containing four‐membered distannoxane [Sn(µ‐OH)]2 units
Authors: Chandrasekhar Vadapalli , Singh Puja , Gopal Kandasamy
Published: May 2007

Compounds containing the distannoxane core [Sn(µ‐OH)]2 are reviewed. Synthesis and structural aspects of these compounds are summarized in this article. Copyright © 2007 John Wiley & Sons, Ltd.
First 1,1‐organoboration reactions of vinyltin compounds—a route to boryl‐substituted stannolanes and organo‐substituted stannol‐3‐enes
Authors: Wrackmeyer Bernd , Tok Oleg L.
Published: May 2007

Dimethyl(divinyl)tin 1 reacts with triethylborane, BEt3 2a, triallylborane, BAll3 2b, tribenzylborane, BBz3 2c, trivinylborane, BVin3 2d, triphenylborane, BPh3 2e, and 1‐boraadamantane 2f by intermolecular 1,1‐organoboration via cleavage of the Snvinyl bond, followed by ring closure via intramolecular 1,1‐organoboration (cleavage of the second Snvinyl bond) to give the boryl‐substituted stannolanes 3a–e, and 7 and 8. The heterocycles 3a–e can undergo dehydroboration, hydroboration, and/or further reactions. If dialkylboranes such as 9‐borabicylo[3.3.1]nonane 11 (9‐BBN) or diethylborane (Et2BH) 12 are used, the first expected step is the hydroboration of one of the vinyl groups in 1, and the second step is the ring closure to boryl‐substituted stannolanes 13 and 6a, respectively, by intramolecular 1,1‐organoboration. The mechanism of the second step, in contrast to the literature, was confirmed by the reaction of dimethyl‐ (9) and diphenyl(di‐2‐propenyl)tin (10) with the boron hydrides 11 and 12. In the resulting stannolanes 14 and 15, the 3,5‐positions of the methyl groups support the mechanism of 1,1‐organoboration. The structures of the new cyclic organotin compounds are assigned on the basis of consistent one‐ and two‐dimensional 1H, 11B, 13C and 119Sn NMR spectroscopic data sets. Copyright © 2007 John Wiley & Sons, Ltd.
Role of GTPases in ribosome assembly
Authors: Karbstein Katrin
Published: May 2007

GTPases are a universally conserved class of regulatory proteins involved in such diverse cellular functions as signal transduction, translation, cytoskeleton formation, and intracellular transport. GTPases are also required for ribosome assembly in eukaryotes and bacteria, where they present themselves as possible regulatory molecules. Strikingly, in bacteria they represent the largest class of essential assembly factors. A review of their common structural, biochemical and genetic interactions is presented and integrated with models for their function in ribosome assembly. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 1–11, 2007

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Size of surgical margin does not influence recurrence rates after curative liver resection for colorectal cancer liver metastases
Authors: Bodingbauer M , Tamandl D , Schmid K , Plank C , Schima W , Gruenberger T
Published: May 2007

Background

The aim of this study was to examine the relationship between surgical margin status and site of recurrence after potentially curative liver resection for colorectal metastases using an ultrasonic dissection technique.

Methods

Between January 2000 and December 2003, 176 patients underwent liver resection with curative intent for colorectal metastases at a single institution. Demographics, operative data, pathological margin status, site of recurrence and long-term survival data were collected prospectively and analysed.

Results

On pathological analysis, resection margins were positive in 43 patients, negative by 1–9 mm in 110, and clear by more than 9 mm in 23 patients. At a median follow-up of 33 months, 133 of 176 patients had developed a recurrence, only five of whom had recurrence at the surgical margin. Recurrence at the surgical margin was not significantly related to the size of the margin. Overall, the median time to recurrence was 12·6 months, which was independent of surgical margin size, although there was a significantly higher proportion of patients with multiple metastases in the group with a positive margin (P = 0·008). Margin status did not correlate significantly with either recurrence-free or overall survival.

Conclusion

The rate of recurrence at the surgical margin was low and a positive margin was not associated with an increased risk of recurrence either at the surgical margin or elsewhere.
Excision biopsy of breast lesions changes the pattern of lymphatic drainage
Authors: Estourgie S H , Valdés Olmos R A , Nieweg O E , Hoefnagel C A , Rutgers E J T , Kroon B B R
Published: May 2007

Background

The aim was to validate the sentinel node biopsy procedure in women who had previous breast excision biopsy by means of determining the reproducibility of lymphoscintigraphy after surgery.

Methods

Twenty-five women scheduled for excision biopsy of a breast lesion were investigated. The day before surgery, 99mTc-labelled nanocolloid was injected into the tumour. Lymphoscintigraphy was repeated a minimum of 2 weeks after surgery.

Results

Preoperative lymphoscintigraphy visualized at least one sentinel node in all 25 women. Discrepancy in the drainage patterns after surgery was noted in 17 of 25 patients. A change in the drainage pattern in the axilla after excision biopsy was seen in 11 women. Drainage to the internal mammary chain was noted before surgery in 13 women, but only three had the same drainage pathways after excision biopsy.

Conclusion

After breast excision biopsy lymphoscintigraphy usually showed a different drainage pattern. This implies that sentinel node biopsy should be performed before excision biopsy to ensure optimal sensitivity.