bluuebunny/crossref_metadata_2025 huggingface dataset:
Das Axion‐Problem
Authors: Lanius K.
Published: May 2007

Verbunden mit dem Mechanismus der spontanen Symmetriebrechung wird das Auftreten skalarer Teilchen durch die Theorie vorhergesagt. In die QCD wurde ein derartiges Teilchen, das Standard‐Axion, zur Verhinderung der CP‐Verletzung eingeführt. Eine Zusammenfassung der experimentellen Situation bei der Axion‐Suche wird gegeben. Bisher wurden keine Hinweise auf die Existenz der Standard‐Axionen gefunden. Astrophysikalische und kosmologische Randbedingungen zur Bestimmung der Eigenschaften der Axionen werden angegeben, und die Möglichkeit, daß die „unsichtbaren”︁ Axionen zur Dunkelmaterie im Universum beitragen, wird betrachtet.
Sind Festkörperreaktionen ohne Beteiligung von Wasser möglich?
Authors: Kolditz Lothar
Published: May 2007

An Beispielen wird gezeigt, daß die reaktionsbeeinflussende Wirkung des Wassers bei Festkörperreaktionen häufig eintritt und eine absolute Wasserfreiheit in zahlreichen Fällen bisher nicht erreicht werden konnte. Die Rolle des Wassers liegt in der Regel bei Festkörperreaktionen in einer Erniedrigung der Aktivierungsenergie. Festkörperreaktionen bedürfen aber prinzipiell nicht der Anwesenheit des Wassers.
Zum Gefrieren von Wasser in porösen Festkörpern, Glas‐ oder Phasenübergang?
Authors: Pfeifer H. , Oehme W. , Siegel H.
Published: May 2007

In der vorliegenden Arbeit werden poröse Festkörper mit definierten Hohlraumstrukturen und homogener innerer Oberfläche (Sauerstoffatome bei Zeolithen und porösen Gläsern) verwendet, um das Gefrieren von Aggregaten bestehend aus wenigen Wassermolekülen experimentell zu untersuchen. Es zeigt sich, daß Aggregate mit weniger als etwa fünf Wassermolekülen beim Abkühlen ohne Strukturänderung erstarren (Glasübergang), während für etwa zehn bis dreißig Wassermoleküle die Ergebnisse von Molwärme‐ und magnetischen Protonenresonanzmessungen mit einer semiempirischen Theorie durch einen diffusen Phasenübergang 1. Ordnung und mehr oder weniger stark reduzierter integraler Schmelzwärme erklärt werden können.
The Transition Probability for States of *‐Algebras
Authors: Uhlmann A.
Published: May 2007

We explain how to define, in consistence with Quantum Theory, “transition probabilities” for general mixed states. Then some theorems concerning this quantity will be proved. It turns out the possibility to characterize the transition probability by a minimal condition among state functions which depend on two states.
Gemeinsame Aspekte und Probleme in Physik und Geologie
Authors: Watznauer A.
Published: May 2007

Die griechische Naturphilosophie, vor allem Aristoteles, verstand unter „Physik”︁ die Naturwissenschaft in toto. Die Aufspaltung dieser universellen Naturphilosophie in Fachdisziplinen betrifft sowohl den Gegenstand als auch, daraus abgeleitet, die Methodik der Darstellung. Die Physik, deren Gegenstand seit Galilei „die reinen Fälle”︁ sind, ist ahistorisch. Die Geologie, die komplexe Systeme untersucht, ist dagegen eine historische Wissenschaft.
The BPHZ Theorem for Massless Fields
Authors: Maślanka Pawel
Published: May 2007

It is proved that under certain conditions the conventional BPHZ procedure works for the case of massless fields.
The Unified Renormalization Group Description of Dilute and Semi‐dilute Polymer Solutions
Authors: Helmis G. , Stepanow S.
Published: May 2007

Modification of renormalization group analysis of the theory of OHTA and OONO permits to describe dilute and semi‐dilute polymer solutions in a unified way in a wide z region. Osmotic compressibility represented as a function of reduced concentration weakly depends on z in agreement with experimental observations by Wiltzius et al.
Bildung von Metall‐Metall‐Mischkristallen mittels Ionenstrahl‐induzierter Mischung
Authors: Hohmuth K. , Rauschenbach B.
Published: May 2007

Die Ionenstrahl‐induzierte Mischung der Dünnfilm‐Systeme CuAg und CrFe nach Bestrahlung mit energiereichen Xe‐und Ar‐Ionen bei Raumtemperatur wurde untersucht. Die Präparation der Multischicht‐Systeme, die aus dünnen Filmen der beiden Elemente bestehen, erfolgt durch Aufdampfen auf inerte Substrate. Die bestrahlten Systeme wurden mit Hochspannungs‐Elektronenmikroskopie, Feinbereichsbeugung und Rutherford‐Rückstreuung analysiert. Beim System CuAg entstehen über den gesamten Konzentrationsbereich metastabile Mischkristallphasen. Die Ionenstrahl‐induzierte Mischung des CuAu‐Systems führt nach einer thermischen Nachbehandlung zur Bildung von Überstrukturen. Durch Bestrahlung des CrFe‐Systems werden CrFe‐Martensit und eine δ'‐CrFe Hochdruckphase gebildet. Die δ'‐CrFe‐Ausscheidungen sind senrecht zum Ionenstrahl und senkrecht zueinander orientiert.
Zur Ankopplung der Gravitation an das quantisierte elektromagnetische Feld I
Authors: Kreisel Eckhard
Published: May 2007

Zur Ankopplung der Gravitation an die Quantenfeldtheorie wurden ortsabhängige unitäre Transformationen betrachtet und Ableitungen eingeführt, die einen nichtintegrablen Paralleltransport für Hilbert‐Raumzustände implizieren [1]. Zur Vorbereitung der Quantisierung der mit diesen Ableitungen gebildeten Maxwell‐Gleichungen wird zunächst die Quantisierung im Minkowski‐Raum ohne Einführung des elektromagnetischen Potentials, direkt auf den Feldstärken basierend, gegeben.
Zum elektrischen Durchschlag technischer Isolierungen aus Polymeren
Authors: Mosch Wolfgang
Published: May 2007

Die von ROBERT ROMPE bereits vor mehr als 30 Jahren vorgeschlagene Unterteilung des Mechanismus beim elektrischen Durchschlag fester Isolierstoffe – in eine reversible und eine nichtreversible Phase – erweist sich auch für derzeitig relevante Isolierstoffuntersuchungen als eine sehr brauchbare und anschauliche Hypothese.

Mit moderner Meßtechnik, die auch eine empfindliche Registrierung der Vorgänge während der reversiblen Phase erlaubt, konnten wertvolle Erkenntnisse z. B. über den Wirkungsmechanismus von Spannungsstabilisatoren im Polyethylen erhalten werden.
Notizen zur Wissenschaftsentwicklung
Authors: Schmellenmeier Heinz
Published: May 2007

„Wissenschaft”︁ und „Technik”︁ sind eine Einheit. Heute läßt sich eine Grenze zwischen den Bereichen schwer finden. Es wird versucht, zu zeigen, wie moderne sozialistische Formen der Wissenschaftsorganisation den Fortschritt fördern. Unter den heutigen Bedingungen der Klassenauseinandersetzung der beiden Weltsysteme auf dem Gebiet der Wissenschaft kann es eine echte Internationalität der Wissenschaft nicht geben.
Möglichkeiten und Grenzen der Kompression von Femtosekunden‐Lichtimpulsen
Authors: Wilhelmi Bernd
Published: May 2007

Aus der Wellengleichung werden Beziehungen zur Beschreibung des simultanen Einflusses von Dispersion und Nichtlinearität verschiedener Ordnung auf ultrakurze Lichtimpulse in Materialien, deren Eigenfrequenzen weit von der Mittenfrequenz des Lichtes entfernt liegen, hergeleitet. Unter bestimmten Voraussetzungen über Eingangsimpuls und Material nehmen diese Beziehungen die Struktur der nichtlinearen Schrödinger‐Gleichung an, deren Anwendungsbereich dadurch abgesteckt werden kann. Es werden Bedingungen für die Erzeugung von komprimierten, chirp‐freien Impulsen angegeben und Grenzen für die erreichbare Impulsdauer diskutiert.
The Attributes of Nonclassical Light and their Mutual Relationship
Authors: Schubert Max
Published: May 2007

In the present paper the attributes of nonclassical light with respect to the theoretical basis, the experimental verification, and the applications are discussed and compared. If one ore more of the corresponding statistical measures (fluctuation excess, bunching excess, Poisson excess) attain negative values, surprising new properties of photon states occur. The analysis shows that under certain temporal and interaction conditions squeezing, antibunching, and sub‐Poisson behavior can accompany one or more of the other attributes. Also the connection of the attributes with the Glauber‐Sudarshan P‐representation of the corresponding states is studied and yields important assertions.
Investigation of X‐ray Emission from Plasmas Created by NIXE 6‐nsec Nd: Glass Laser System
Authors: Förster E. , Goetz K. , Zimmer D. , Glas P. , Goetsch A. , Koch R. , Naumann M. , Nickles P. V. , Schnürer M. , Will I.
Published: May 2007

This paper reports details on the design of the Nd: glass laser facility NIXE at the Central Institute of Optics and Spectroscopy, including the target chamber and the x‐ray diagnostics, spatial and temporal behaviour of the 1.06 μm radiation generated are given.

Plane, massive targets of aluminium and silicon have been irradiated with 6‐nsec FWHM laser pulses.

Investigations of laser produced Al‐ and Si‐plasmas have been performed with spectral and spatial high resolution diagnostics, consisting of a 3 channel crystal‐spectrometer, 2 crystal‐microscopes, and 2 pinhole cameras and the results are presented. Line spectra have been interpreted within the hypothesis of a steady state coronal equilibrium. He‐like lines of the Al‐plasma indicate temperatures up to 400 eV and densities up to 2 · 1020 cm−3. Total x‐ray photon flux in the He‐like resonance line has been calculated giving 1013 phot/ster.
Kaluza‐Klein Cosmology: Friedmann Models with Phenomenological Matter
Authors: Bleyer U. , Liebscher D.‐E.
Published: May 2007

We reduce the FRIEDMANN models in generalized KALUZA‐KLEIN cosmologies, in which the ordinary space‐time is supplemented by internal factor spaces, to the motion of a tensorial mass particle in a scalar field. Some general properties of these models as well as exact solutions for the case of one internal space are discussed for different mixtures of phenomenological matter components.
Über die Ablenkung des Lichtes im Schwarzschild‐Raum
Authors: Gackstatter Fritz
Published: May 2007

Es wird eine trigonometrische Näherungsformel für die Lichtbahnen im Schwarzschild‐Raum hergeleitet und eine Formel für die Ablenkungswinkel des Lichts längs der Erdbahn. Weiterhin wird ein Experiment beschrieben und durchgerechnet, bei dem Winkeländerungen der Größenordnung 1/2 · 1,75″ auftreten, ohne daß eine Sonnenfinsternis nötig ist.
On a Quantum System with Memory
Authors: Löffelholz J.
Published: May 2007

We consider the integro‐differential equation for the classical trajectory of an oscillator coupled to another one. On the quantum level the elimination of the coordinate A of the “unvisible” oscillator leads to an effective path integral (X, Ξ, μ) for the associated imaginary time stochastic process t ϵ, (‐∞,∞) → x(t). We prove reflection positivity of the measure dμ ≈ F · dξ, where dξ governes the free oscillator x and F is the counterpart of Feynman's influence functional. Finally, realizing the Hamiltonian semigroup exp(‐tH), t ≧ 0, in the physical Hilbert space ℋ︁ = L2(X, Γ, μ), where Γ ⊆ Ξ+, we try to understand what is memory.
On Berry Phases Along Mixtures of States
Authors: Uhlmann A.
Published: May 2007

Concepts connected with Berry's phase can be extended to curves and loops in state spaces defined by von Neumann algebras. This includes the important space of density operators.
On the Theory of Gravitational Field in Finsler Spaces ‐ II
Authors: Ikeda Satoshi
Published: May 2007

Continuing the last paper [1], more detailed considerations are made on the spatial structure of the Finslerian gravitational field: firstly, a unified field between the external (x)‐field and the internal (y)‐field is constructed from a vector bundle‐like standpoint, where the intrinsic behavior (i.e., δy) of the internal vector variable y is taken into account; secondly, the connection structure and the metrical structure are determined by setting the base and dual base properly in the unified field; thirdly, a compactification process of the internal field (i.e., a mapping process of the (y)‐field on the (x)‐field) is considered in order to realize a four‐dimensional Finslerian structure.
Quantum Logics and Relative Lindenbaum Property
Authors: Giuntini R.
Published: May 2007

The relative Lindenbaum property is considered in orthomodular quantum logic and in partial class ical logic. The properties of these models are connected with the possibility of hidden‐variable reconstruction of particular (1/2‐spin particle e.g.) quantum physical systems.
A Study of the Phase Transition in the System [Ag1−x(Na)x]NO3 by Infrared Spectroscopy
Authors: El‐Kabbany F. , Badr Y. , Taha S. , Tosson M.
Published: May 2007

A complete infrared study of the mixed crystal system of AgNO3 and NaNO3 is carried out in the region 400–4000 cm−1. The study includes internal fundamental normal vibrations of the NO−3 ion in the ordered and disordered phases of AgNO3 at different values of the sodium concentration, the I.R. spectra, spectral band shape intensities, and frequencies of the internal modes as functions of the sodium ion concentration. Special attention is paid to bending mode, combination mode, asymmetric stretching mode, and over‐tone. The rotational energy barrier is determined at different concentrations of the sodium ions in the system.
Intercomparison of Different Types of Locally Prepared Concretes and Its Usability for Reactor Neutron Shielding
Authors: El‐Kolaly M. A. , Makarious A. S. , Bashter I. I. , Kansouh W. A.
Published: May 2007

Measurements have been carried out to study the attenuation of neutron from a horizontal channel of the ET‐RR‐1 reactor. The assessments of neutron distribution inside three different types of locally prepared concretes have been evaluated.

Neutron intensities in ilmenite‐limonite concrete shield show an exponential decrease with increasing concrete thickness. Ilmenite concrete is a good attenuator for thermal and intermediate neutrons. However, ordinary and ilmenite‐limonite concretes show efficient shielding for fast neutrons.
Subspaces and Subgroups in Five‐Dimensional Gravity
Authors: Matos T.
Published: May 2007

A 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.
Stability of Scalar Modified Schwarzschild Solution
Authors: Agnese A. G. , La Camera M.
Published: May 2007

It is shown that the Schwarzschild solution in general relativity, reconsidered adding to the vacuum a massless scalar field, is stable to perturbations from radiation fields of spin s = 0, ±1/2, ±1, ±2.
On the Theory of Gravitational Field in Finsler Spaces ‐ III
Authors: Ikeda Satoshi
Published: May 2007

From 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.
Large‐Noise Expansions for the Stationary Solution of Fokker‐Planck Equations
Authors: Bunke U. , Ebeling W.
Published: May 2007

Stationary solutions of the Fokker‐Planck equation are found by Taylor expansions with respect to the reciprocal noise strength. The convergence of this expansion is proven under certain conditions; special cases are studied.
A Direct Proof of Slavnov's Identity in Pure Yang‐Mills Theory
Authors: Geyer B. , Mülsch D.
Published: May 2007

For 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

An 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

We 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

Using 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

β‐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

Application 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.
Information Flow in Synergetic Computers
Authors: Haken H.
Published: May 2007

Synergetic computers are a new class of highly parallel computers which are constructed on the basic principles of synergetics in which the analogy between pattern recognition and pattern formation is exploited. We show that the information flow in such computers can be determined explicitly. In this way the channel capacity, needed in such parallel computers, can be determined.
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

For 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

We 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

The 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

We 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

We 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

We 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

The 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

The 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

Quantum 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.
Bemerkungen zur Relativitätstheorie und zu den Quanten
Authors: Bergmann Peter G.
Published: May 2007

Die theoretischen und experimentellen Grundlagen von Gravitations‐ und Quantenphysik, die Beziehung beider Theorien und die Bedeutung wesentlicher Begriffe, wie Observable, werden diskutiert.
Quantum General Relativity and the Meaning of (R + R2) Theories
Authors: von Borzeszkowski H. H.
Published: May 2007

It is argued that, due to the cut‐off lengths arising in Quantum General Relativity, R2 corrections of Einstein's theory cannot be interpreted as quantum corrections.
Metal‐insulator transition in Bi‐doped, amorphous Ga:Ar mixtures: Influence of spin‐orbit scattering
Authors: Bögershausen M. , Micklitz H.
Published: May 2007

Doping 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

We 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

We 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

It 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

The 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

The 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

A 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.
Integrals of the motion for a nonlinear quantum oscillator
Authors: Man'ko Vladimir I. , Haake Fritz
Published: May 2007

We construct and discusss explicitly time dependent integrals of the motion of non‐autonomous quantum systems. Such integrals may exist even when the classical limit of the dynamics is non‐integrable.
Composition and superconductivity in single layer Bi‐2201 phases
Authors: Schlichenmaier M. , Wischert W. , Kemmler‐Sack S.
Published: May 2007

Several 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

The 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

Due 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

The 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.
The Green's function of confined electrons in an external magnetic field: Analytical formulation
Authors: Klama S. , Rössler U.
Published: May 2007

We derive the analytical form of the Green's function of 2‐dimensional electrons with lateral confinement in a perpendicular magnetic field. The confinement potentials considered are infinite barriers at radius R (quantum dot) and at r and R (quantum ring).
Effect of fluctuating inertial forces on the critical dynamics of a pure fluid
Authors: Ferrel Richard A.
Published: May 2007

A calculation is carried out of the effect of imposed inertial forces on the critical dynamics of a pure fluid near the liquid‐vapor critical point. The mechanism for the relaxation of the critical fluctuations of the order parameter is the Brownian motion in the long wavelength hydrodynamic shear modes. The additional fluctuating inertial forces add noise to these modes, leading to an increase inγq, the order parameter relaxation rate for a fluctuation of wave number q. A general formula is derived for Δ γq/γq, the fractional increase in relaxation rate, in terms of the acceleration power spectral density. The predicted strong dependences on temperature, angle, and q provide crucial tests for the theory.
Thermal motion of one‐dimensional domain walls in monolayers of a polar polymer observed by Video‐STM
Authors: Ludwig Ch. , Eberle G. , Gompf B. , Petersen J. , Eisenmenger W.
Published: May 2007

Scanning tunneling microscopy (STM) has been used to investigate monolayers of the ferroelectric copolymer polyvinylidenefluoride/trifluoroethylene P(VDF/TrFE) showing images of ordered polymer monolayers. By scanning with video frame rate, direct observation of the motion of onedimensional domain walls was also possible for the first time. The images clearly show domain walls normal to the polymer chains. From measurements of the temperature dependence of the domain wall velocities the activation energy for the thermally generated kink motion was estimated. These results are compared with theoretical models describing domain wall motion in ferroelectric PVDF.
Transmission of electrons through ferromagnetic material and applications to detection of electron spin polarization
Authors: Schönhense G. , Siegmann H. C.
Published: May 2007

The salient features of the total low energy inelastic electron scattering cross section in transition metals are described by a constant term σ0 plus a term σd that is proportional to the number of unoccupied d‐orbitals. This simple model predicts that low energy electrons transmitted through a ferromagnetic ultrathin film acquire a transport spin polarization a(χ). Using the ratio σ0/σd as the only adjustable parameter, the model predicts the enhancement of the spin polarization of the low energy cascade electrons as well as a(χ) in reasonable agreement with the existing observations on Fe, Co and Ni. A detector for electron spin polarization P based on the spin dependent transmission of electrons through ferromagnetic material is proposed which should be superior to existing P‐detectors by 1–2 orders of magnitude.
Influence of the electron concentration on the superconducting properties of the spinel system Li1‐yTi2O4
Authors: Rygula M. , Kemmler‐Sack S. , Nissel T. , Hübener R. P.
Published: May 2007

In the spinel system Li1‐y Ti2O4 the Li content was reduced by oxidative extraction by means of a solution of I2 as well as Br2 in CH3CN or by oxygen. The extraction is associated with a transition of Ti3+ to Ti4+: the system is Li1‐y Ti3+1‐yTi4+1+y O4. Consequently, with increasing y the charge carrier concentration decreases from the starting value of 0.5 electrons/Ti ion for LiTi2O4. The extraction proceeds in two steps. At the beginning, the Ti2O4 framework remains intact and the transition to superconductivity increases with decreasing charge carrier concentration to a maximal value of 13.2 K. Separated by a two‐phase region for medium extraction levels for higher y values, a Li depleted material of approximate composition Li0.3Ti2O4 is obtained. The crystal structure of Li0.3Ti2O4 can be deduced from the original spinel lattice by a partial Ti migration from 16d to 16c and 8 a sites (space group Fd3m). Consequently, the Ti2O4 framework of Li0.3Ti2O4 is disconnected and the material is no longer superconducting.
Quark‐gluon plasma formation in heavy‐ion collision
Authors: Wolschin G.
Published: May 2007

To account for the non‐equilibrium character of quark‐gluon plasma formation in relativistic heavy‐ion collisions, it is proposed to use the product of energy density ϵ and interaction time τint (rather than ϵ) as the critical quantity for plasma formation. In a geometrical model, τ is approximated by the transit time, and ϵ by the maximum energy density calculated in the center‐of‐mass frame. For central collisions, an analytical expression for ϵ·τ is given. As an example, the systems 16O + 16O and 208Pb + 208Pb are investigated as functions of c.m. energy, and their respective suitability for plasma formation is discussed.
The statistical mechanics of kinetically‐controlled RNA folding pathways
Authors: Fernández Ariel
Published: May 2007

By systematically assigning weights to kinetically‐controlled folding pathways we introduce a novel scheme of statistical inference. We provide supporting experimental evidence to show that this approach is suitable to explain the expediency and robustness of RNA folding. The statistical scheme is constructed in four stages, the last of which leads to a suitable representation that allows for direct comparison with experiment: a) An appropriate space of folding histories is defined; b) The space is endowed with a measure and in this way an ensemble is defined; c) The ensemble is systematically simplified by coarse‐graining each copy or replica of conformation space. This procedure entails lumping together rapidly‐interconverting conformations; d) A base‐pair probability matrix (BPPM) is introduced by representing all structures contributing to the ensemble at a given instant. Thus, we take a convenient cross‐section of the ensemble by taking a fixed instant in time. The BPPM is contrasted vis‐a‐vis experimental information on biologically‐competent conformations. This last procedure is paramount to verify the theory. Moreover, the essential properties of folding are captured by showing that the statistical weight is concentrated on a very limited domain of closely‐related folding pathways whose biological competence has been established experimentally.
Macroscopic intrinsic stress formation in amorphous CuTi films
Authors: Dina S. , Geyer U. , v. Minnigerode G.
Published: May 2007

During the growth of amorphous CuTi films prepared under UHV conditions onto quartz substrates, macroscopic intrinsic stresses are generated. The intrinsic stresses are measured in situ as a function of the film thickness for a wide range of substrate temperatures and film compositions. Depending on the preparation conditions, compressive stresses during the early growth stages and thickness‐independent tensile stresses at higher thicknesses are observed. Films with Cu‐content above 50 at% deposited at room temperature do not generate any detectable intrinsic stresses. The results are discussed in terms of a model for the growth of amorphous binary alloy films published earlier.
Quantum statistics and discreteness. Differences between the canonical and grand canonical ensembles for a fermionic lattice gas
Authors: Kutner R. , Przeniosło R. , Kwiatkowski M.
Published: May 2007

Studying the electronic properties of small metallic particles Kubo and subsequently Denton, Mühlschlegel and Scalapino recognized the surprising effect that the mean occupation numbers of noninteracting fermions (electrons) are not given within the canonical ensemble by the usual expression of Fermi‐Dirac statistics. The fermions behave as if they are colder and observed deviations are most significant in the vicinity of the Fermi level. The results of our Monte Carlo simulations, as well as our complementary numerical and analytical results are in very good agreement with the predictions of Denton et al. We found that the effect vanishes for very small and very large spacing between the energy levels in comparison to the thermal energy kBT. Associated with this effect are the particle‐hole correlations. Extending the method used by Denton et al. we derive an analytical formula for the particle‐hole correlation functions whose predictions are again in very good agreement with our numerical results. The low‐temperature aspects of the effect are considered by applying a two‐state model. The role of the finite‐size effect is also discussed.
Resonances in the current‐voltage characteristics of a dissipative Josephson junction
Authors: Müllers J. , Schmid A.
Published: May 2007

The I‐V characteristics of a Josephson junction shunted by an Ohmic resistor shows sharp peaks when levels in neighbouring wells are crossing. We consider the shape and size of these peaks using a double‐well model where the wells are given in parabolic approximation. The friction of arbitrary strength is included by the help of a bath of infinitely many degrees of freedom. 74.50.+z.