bluuebunny/crossref_metadata_2025_split huggingface dataset:
Subspaces and Subgroups in Five‐Dimensional Gravity
Authors: Matos T. 
Published: May 2007

AbstractA systematic investigation of the one‐ and two‐dimensional subspaces of the potential space in the projective field theory is made. From the one‐dimensional subspaces some stationary charged solutions can be generated. The two‐dimensional subspaces have an isometry group SU(1,1) which corresponds to the Einstein equations in vacuum, an O(2,1) group which corresponds to stationary charged solutions with constant scalar field, and an Abelian group which has no counterpart in the Einstein‐Maxwell theory.
On the Theory of Gravitational Field in Finsler Spaces ‐ III
Authors: Ikeda Satoshi 
Published: May 2007

AbstractFrom the vector bundle‐like standpoint, the Finslerian gravitational field is regarded as the total space of the vector bundle whose fibre is the internal (y)‐field spanned by vectors {y} (i.e., the so‐called internal space spanned by {y}) and whose base is the external (x)‐field spanned by points {x} (i.e., the Einstein's gravitational field). Along this line, in this paper, different from a previous paper [1], the so‐called mapping process of the (y)‐field on the (x)‐field is not taken into account and following Miron's method [2, 3], the Finslerian field equations will be derived from the Einstein's field equation for the total space. Some physical considerations will be made on those field equations.
A Direct Proof of Slavnov's Identity in Pure Yang‐Mills Theory
Authors: Geyer B. , Mülsch D. 
Published: May 2007

AbstractFor pure Yang‐Mills theories with semi‐simple compact gauge group a direct prove of the Slavnov identity is given without to solve the related cohomology problem explicitly. To achieve this use is made of two related identities which result by differentiating the Slavnov identity with respect to the fields carrying the same Faddeev‐Popov charge as the Slavnov operator itself. The method which is based on the renormalized quantum action principles may be extended to Yang‐Mills theories in interaction with matter fields and/or within external background configurations.
Time‐Dependent Photoconductivity in Semi‐Insulating Gallium‐Arsenide
Authors: Queisser Hans J. 
Published: May 2007

AbstractAn alternative interpretation is offered to explain a photoconductivity, rising exponentially with time under constant illumination, which has been detected in semiinsulating GaAs. Spatial inhomogeneities, caused by nonuniform defect density, present potential barriers to current flow. Illumination neutralizes the space charge, thus reduces these barriers, hence increases current at constant bias. Local electric fields consequently vary in time, which may establish polarization effects and lifetime discontinuities via exciton dissociation.
The Spectrum of Squeezing in Degenerate Four‐Wave Mixing
Authors: Lugiato L. A. , Kaige Wang 
Published: May 2007

AbstractWe analyze a simple model for degenerate four wave mixing, introduced by Savage and Walls. In the resonant case, the system exhibits a phase instability when the pump intensity is increased well beyond the threshold for generation of the signal mode. Still in the resonant configuration, we calculate the amplitude and phase squeezing spectra both for the signal and the pump mode. In the signal (pump) mode, the squeezing becomes especially large when the signal (pump) mode is much more damped than the pump (signal) mode. The signal field can exhibit both phase and amplitude squeezing, in distinct domains of the parameter space. On the other hand, the pump field can show squeezing only in the amplitude quadrature component. In general, the model exhibits sizable squeezing over very extended regions of the parameter space.
A Clear Atomic Example for the Surface Sensitivity of Penning Ionization: He*(23S) + Yb
Authors: Hotop H. , Ruf M.‐W. , Yencha A. J. , Fricke B. 
Published: May 2007

AbstractUsing a crossed‐beam apparatus with a double hemispherical electron spectrometer, we have studied the spectrum of electrons released in thermal energy ionizing collisions of metastable He*(23S) atoms with ground state Yb(4f14 6s2 1S0) atoms, thereby providing the first Penning electron spectrum of an atomic target with 4f‐electrons. In contrast to the Hel (58.4 nm) and NeI (73.6/74.4 nm) photoelectron spectra of Yb, which show mainly 4f‐ and 6s‐electron emission in about a 5:1 ratio, the He*(23S) Penning electron spectrum is dominated by 6s‐ionization, accompanied by some correlation‐induced 6p‐emission (8% Yb+(4f14 6p 2P) formation) and very little 4f‐ionization (≲2.5%). This astounding result is attributed to the electron exchange mechanism for He*(23S) ionization and reflects the poor overlap of the target 4f‐electron wavefunction with the 1s‐hole of He*(23S), as discussed on the basis of Dirac‐Fock wave functions for the Yb orbitals and through calculations of the partial ionization cross sections involving semiempirical complex potentials. The presented case may be regarded as the clearest atomic example for the surface sensitivity of He*(23S) Penning ionization observed so far.
Lattice Location of 12B in Single‐Crystal Ni3Al Studied by β‐Radiation Detected NMR
Authors: Fischer B. , Ittermann B. , Diehl E. , Dippel R. , Ergezinger K. H. , Frank H.‐P. , Jäger E. , Seelinger W. , Sulzer G. , Ackermann H. , Stöckmann H.‐J. , Bohn H. G. 
Published: May 2007

Abstractβ‐radiation detected nuclear magnetic resonance was applied to determine the location of 12B probe nuclei in a Ni3Al single crystal. Combining our results with those of channeling experiments it turned out that more than 90% of the 12B ions occupy the octahedral interstitial site with six Ni ions as nearest neighbours.
Release Studies of Atomic Technetium
Authors: Ames F. , Kluge H.‐J. , Otten E.‐W. , Suri B. M. , Venugopalan A. , Herrmann G. , Rimke H. , Trautmann N. , Kirchner R. , Eichler B. 
Published: May 2007

AbstractApplication of a laser ion source (LIS) is a promising new technique for trace analysis with high efficiency and selectivity. One of the problems which can limit its efficiency attained in practice is the adsorption of sample atoms on the hot walls of the LIS cavity. We have studied the release of atomic technetium from different wall materials at temperatures up to 2500 K. For these investigations resonance ionization of technetium atoms applying a copper vapour pumped dye laser system and γ‐spectrometry of 6‐h 99mTc have been used. Theoretical calculations of the heat of desorption for technetium on different wall materials are presented and compared with experimental data. Though the results reported concern technetium, most of the considerations are quite general for a laser ion source.
Threshold Behaviour of Electron Impact lonisation Cross Sections for Rare Gas Atoms
Authors: Lebius H. , Koslowski H. R. , Wiesemann K. , Huber B. A. 
Published: May 2007

AbstractFor electron energies from direct ionisation threshold up to several eV above cross sections for the production of He+, He2+, Ne+ up to Ne4+, Kr2+, Kr3+ and Xe2+ up to Xe4+ ions by single electron impact on atoms were measured. By a least square fit a power law was fitted to the cross sections. The exponents obtained by this procedure are compared with several models, i.e. a simple phase‐space calculation, the Wannier model considering interelectronic repulsion and a statistical approach similar to Russek's statistical energy deposition model. We find that especially ionisation of many‐electron atoms to high degrees of ionisation can not be described by the Wannier model, however, within the statistical approach.
Separable Approximations to the Helium Trimer
Authors: Loucks Roger , Levinger J. S. 
Published: May 2007

AbstractWe extend Blatt's and Lim's calculations for the energy of the helium trimer (4He)3, for a Herzfeld potential. We use the unitary pole approximation. We constrain the effective range and scattering lenght to values of 7.4 A and infinity, respectively. As the core radius increases from 0 to 2.8 A, the trimer energy increases monotonically from −97 to −59 millikelvin. The Yamaguchi potential gives a trimer energy of −123 mK. Two additional two‐body parameters suffice to fit these, and earlier, calculations of the trimer energy: i.e., the expectation value of the kinetic energy for the dimer, and Sprung's wound integral Io.
Reaction Dynamics of Heavy Ion Collisions Studied by Hard Photon Emission
Authors: Metag V. 
Published: May 2007

AbstractThe role of photons as a probe of heavy ion reaction dynamics is discussed. Experimental data on the systems 16O + W and 92Mo + 92Mo illustrate that hard photons render a time differential information on the evolution of heavy ion collisions ranging from proton — neutron bremsstrahlung in the initial phase to thermal emission from highly excited reaction products in the last stage of the reaction. Measured hard photon multiplicities provide in addition a new approach to determine the impact parameter of heavy ion collisions. A systematics of hard photon emission probabilities reveals the role of the nucleonic Fermi motion in the collision zone. Prospects for future experiments focussing on photon and neutral meson production at relativistic bombarding energies are outlined.
Quantum Pendellösung in Atom Diffraction by a Light Grating
Authors: Meystre P. , Schumacher E. , Wright E. M. 
Published: May 2007

AbstractWe calculate the Bragg scattering of a two‐level atom from a quantized standing‐wave light field. The granular nature of the radiation field is shown to produce collapse and revivals in the atom diffraction and to lead to a quantum version of the Pendellösung.
A Kinetic Equation for Quantum Gases
Authors: Nacher P. J. , Tastevin G. , Laloe F. 
Published: May 2007

AbstractWe apply the formalism of the free Wigner transform to the derivation of a kinetic equation valid for dilute quantum gases; this formalism is compatible with a precise treatment of two‐body correlations and allows the inclusion of second virial corrections. We generalize the results obtained in previous articles where the calculation of the collision integral was limited to zero (“local”) and first order gradient terms; here we use a more general (“non‐local”) form for the interaction term which is an integral of higher dimension (18). The conservation laws are studied in this formalism, which implies non‐linear expressions for the local hydrodynamic quantities in terms of the function appearing in the kinetic equation. The pressure at thermal equilibrium is then evaluated and found to be equal to the value predicted by the Beth‐Uhlenbeck formula, without adjusting any free parameter of the theory.
Corner Transfer Matrices for the Gaussian Model
Authors: Peschel I. , Truong T. T. 
Published: May 2007

AbstractWe study Baxter's corner transfer matrix for a Gaussian model on a strongly anisotropic square lattice of finite size. The problem is equivalent to finding the normal modes of a vibrating chain with position‐dependent masses and springs. The eigenvalues are found analytically, using Carlitz polynomials, and the predictions of conformal invariance are verified for the critical system.
Metal‐Nonmetal Transition and Homogeneous Nucleation of Mercury Vapour
Authors: Uchtmann H. , Rademann K. , Hensel F. 
Published: May 2007

AbstractThe paper presents ionization potentials of mercury clusters obtained by photoelectron spectroscopy which provide evidence that a size‐dependent gradual transition from van der Waals‐type to metallic interaction occurs in Hgx‐clusters for × > 13. In order to probe the role of this nonmetal to metal transition in the homogeneous nucleation process of supersaturated mercury vapour we have determined the supersaturation necessary for homogeneous condensation of mercury vapour in the temperature range 250 to 320 K. The measurements were made using an upward thermal diffusion cloud chamber. The results demonstrate that none of the current theories for homogeneous nucleation satisfactorily predict the observed critical supersaturations. The measured values are about 3 orders of magnitude lower than the values predicted by the conventional Becker‐Döring‐Zeldovitch‐theory.
The Deformations Energy and Barrier Height of Super Heavy Nuclei
Authors: Osman Ahmed , Abdel‐Aziz S. S. 
Published: May 2007

AbstractThe liquid drop energy and barrier height are calculated for the super heavy nuclei 250X and 251X, resulting from heavy ion reactions, at finite temperatures. Our calculations are compared with both the idealized nuclei 250Es and 251 Es (being isobars of 250X and 251X) and that obtained by previous work. The main reason of the descrepancies between the present calculated values of the barrier height and the fissility parameters and those obtained by others are found to be mainly due to the important role of Coulomb energy over the surface energy for heavy nuclei. It has been found that the temperature has the effect lowering the fission barrier and shifting the saddle point to lower values.
State Representations for Renormalized Energy Equations in Quantum Field Theory
Authors: Grimm G. , Hailer B. , Stumpf H. 
Published: May 2007

AbstractQuantum fields with interaction do not allow the application of the Fock representation. Rather the algebraic G.N.S. procedure has to be used which leads to nonorthonormal basis states. This raises the problem of explicit state construction with respect to such states. In the present paper this problem is treated for the case of a sufficiently regularized, selfinteracting spinorfield. By some theorems it is demonstrated that a consequent treatment of its field Hamiltonian which respects the general algebraic requirements leads to Dyson's renormalized energy equation. In addition this approach allows explicit state constructions which so far have not been realized in conventional quantum field theory.
Metal‐insulator transition in Bi‐doped, amorphous Ga:Ar mixtures: Influence of spin‐orbit scattering
Authors: Bögershausen M. , Micklitz H. 
Published: May 2007

AbstractDoping amorphous GaxAr1−x mixtures with the strong spin‐orbit scatterer Bi has a dramatic effect on the metal‐insulator transition (MIT) occurring in this system at a critical metal atomic concentration xc: (i) the MIT is shifted from x′c = 0.36 ± 0.01 (corresponding to a critical metal volume fraction v′c = 0.19 ± 0.01) of the undoped system to a lower value of xc = 0.25 ± 0.01 (vc = 0.14 ± 0.01) for (Ga0.9Bi0.1)xAr1−x and (ii) the critical exponent v and g of the dc conductivity and Hall coefficient, respectively, change from v′ = 0.5 ± 0.1 and g′ = 0 for the undoped samples to v = 1.3 ± 0.3 and g = 0.5 ± 0.1 for (Ga0.9Bi0.1)xAr1−x.
Electron‐phonon matrix elements and deformation potentials in silicon and germanium in the quasi‐ion model
Authors: Klenner M. , Falter C. , Ludwig W. 
Published: May 2007

AbstractWe have calculated electron‐phonon matrix elements relevant for indirect optical absorption, intervalley matrix elements and intravalley deformation potentials as well as splitting parameters for the k = 0 states in silicon and germanium within the rigid quasi‐ion model. In contrast to the “atomic” potentials in conventional rigid‐ion models the quasi‐ion potentials are well‐defined. The agreement with experiment and with other theoretical results is satisfactory in most cases. We have also studied the role of distortion corrections to the rigid quasi‐ion approximation. We find that the influence of distortions is small, indicating that the rigid quasi‐ion model is an adequate description ‐ at least in case of these two materials.
Temperature dependence of band gaps in Si and Ge in the quasi‐ion model
Authors: Klenner M. , Falter C. , Ludwig W. 
Published: May 2007

AbstractWe have calculated the temperature dependence of the direct and indirect band gaps in silicon and germanium. The electron‐phonon potential as well as the phonon frequencies and eigenvectors are calculated consistently within the rigid quasi‐ion model. Comparison is made with experiment and with the theoretical results of Allen and Cardona and Lautenschlager et al.
The soliton of the effective chiral action in a heat‐kernel expansion
Authors: Kämpfer B. , Reinhardt H. 
Published: May 2007

AbstractIt is shown that the heat‐kernel expansion (rather than the gradient expansion) of the effective chiral action of the quark loop yields in next‐to‐leading (i.e., fourth) order an effective low‐energy lagrangian which possesses stable soliton solutions. The baryon number‐one soliton solution of this effective chiral lagrangian is found numerically.
Correlated hyperspherical harmonics
Authors: Zickendraht W. , Levinger J. S. 
Published: May 2007

AbstractThe expansion of the wavefunction for a bound three particle state in the five‐dimensional hyperspace of hyperspherical harmonics in some cases suffers bad convergence, especially for weakly bound states. For this reason correlated hyperspherical harmonics are proposed, of which the ordinary hyperspherical harmonics are one special choice. The “best” suited correlated hyperspherical harmonics are chosen from an infinite set of complete orthogonal systems by a Ritz variational calculation.
Pressure coefficient K0′ of bulk modulus for cubic elements
Authors: Mimkes Jürgen 
Published: May 2007

AbstractThe Grüneisen relation Γ = αp KTV/Cν has been integrated with respect to T at constant volume. This leads to a potential E(V) with the two exponents Γ = m/3 and δ = n/3. The Grüneisen constant Γ is the exponent of the repulsive term. The exponent δ of the attractive term may be determined from heat capacity, thermal expansion and cohesive energy, δ = Cp/αp/ϵc.The pressure coefficient of the bulk modulus of an m‐n potential E(V) is given by K0′ = m/3 + n/3 + 2. According to the calculations above we obtain K0′ from thermophysical data by K0′ = Γ + δ + 2 = αpKTV/Cν + Cp/αp/ϵc + 2, with K0′ = 4‐5 for alkali metals, K0′ = 5.2‐6.2 for transition metals and K0′ = 7‐8 for solid rare gas crystals. This is in good agreement with high pressure data.
Transition between layered and filamentary types of anisotropy in layered superconducting structures
Authors: Kuptsov D. A. 
Published: May 2007

AbstractA model of layered superconducting structure consisting of alternating anisotropic superconducting layers S1 and S2 with different transition temperatures is considered. It is shown that due to competition between two origins of anisotropy ‐ effective‐mass anisotropy of individual layers and proximity‐induced anisotropy the effective anisotropy of the whole system signficiantly varies temperature. The components of the effective‐mass tensor mc (along the anisotropy axis) and ma (perpendicular to the anisotropy axis) strongly depend upon temperature. This may lead to transition between layered (mc > ma) and quasi one‐dimensional (mc < ma) types of anisotropy as well as to biaxial‐type anisotropy which is also temperature dependent. The field distribution in a tilted vortex in a biaxial superconductor is calculated. The change in the properties of the vortex lattice with temperature in such systems is also investigated. The properties of YBa2Cu3Ox/PrBa2Cu3Oy multilayers are discussed in this connection.
Composition and superconductivity in single layer Bi‐2201 phases
Authors: Schlichenmaier M. , Wischert W. , Kemmler‐Sack S. 
Published: May 2007

AbstractSeveral materials with nominal 2201 composition were prepared from various systems Bi2+xSr2‐xCuO6+z, Bi2Sr2‐xCuO6+z, Bi2‐xPbxSr2O6+z, Bi2.1‐xPbxCuO6+z,Bi2Sr2‐yLayCuO6+z, Bi1.9Pb0.1Sr2‐yLayCuO6+z, Bi2‐xPbxSr1.6La0.4CuO6+z and Bi2.1‐xPbxSr1.5La1.4CuO6+z in different gas atmospheres. According to the structural investigations the 2201 phase shows solid solution behaviour. However, irrespectively of the method of preparation the appearance of superconductivity is confined to multiphase material. Furthermore, the superconducting volume fraction is uniformly as low as ≲ 3%. The observed presence of trace superconductivity is easily explainable by small admixtures of superconducting foreign phases and in disagreement with the assumption of intrinsic superconducting properties of the Bi based 2201 phase.
Millimetre‐wave investigation of the soft mode in ferroelectric PbHPO4
Authors: Briskot M. , Happ H. 
Published: May 2007

AbstractThe complex dielectric function along the a axis of PbHPO4 single crystals is determined from reflection measurements at frequencies between 70 and 225 GHz in the paraelectric and the ferroelectric phase near the transition temperature Tc = 310 K. The data are complemented by a remeasurement of the properties of the lowest far‐infrared mode. The mm‐wave data can be described by a simple Debye formula. The relaxation time exhibits critical slowing down, and the corresponding relaxation frequency varies between about 2 and 60 GHz near Tc. Proton tunneling appears to play no essential role in this dielectric mechanism related to proton ordering.
DC Conductivity and Peierls instability in the quasi‐one‐dimensional organic charge density wave conductor (fluoranthene)2X
Authors: Brütting W. , Rieß W. , Schwoerer M. 
Published: May 2007

AbstractDue to the high anisotropy of the dc conductivity (σ|/σ⊥ ≈ 104) the organic conductor (fluoranthene)2X can be regarded as a model system for studying the Peierls instability in quasi‐one‐dimensional systems. The temperature dependence of the dc conductivity σ| (T) along the highly conducting crystal axis exhibits the typical behaviour of a quasi‐one‐dimensional metal with a Peierls transition at about 180 K to a charge density wave (CDW) ground state. As expected for a highly one‐dimensional conductor the exact transition temperature depends on three‐dimensional coupling effects and therefore on the size of the counterion X− = PF, AsF, SbF. Above the Peierls transition σ| (T) can be described quantitatively within a model of CDW fluctuations leading to a pseudo gap in the electronic density of states. Below, the existence of a real energy gap at the Fermi level with a BCS‐like temperature dependence determines the charge transport over more than eight orders of magnitude in the electrical resistance. For the intrinsic energy gaps 2 Δ (0), which characterize the ground state of the Peierls semiconductor, values of 120‐180 meV have been found for different crystals.
The field‐theoretic description of dynamics of interfaces in disordered media
Authors: Stepanow S. 
Published: May 2007

AbstractThe time evolution of an interface in a disordered media is described by using the propagator method. The method enables one to represent the perturbation expansions of different quantities characterizing the interface by means of diagrams which are familiar from the field theory. By the analysis of the divergences in the vicinity of the critical dimension dc = 4 we found that the regularization of the theory demands the renormalization of the mobility and all moments of the disorder correlator excepting the zero one. The renormalization group (RG) calculations of the average velocity of the interface, the roughness, and the functional RG equation of the disorder correlator are presented to order ϵ = 4 ‐ d. The latter coincides with the result obtained by D. S. Fisher in the equilibrium case. The RG equations have a pole at the value of the driving force, which coincides with the value of the threshold below which the interface becomes pinned as predicted by Bruinsma and Aeppli. The behavior of the mobility in the vicinity of the pole is discussed.