bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ab initio vel ex eventu. II
Authors: Thiessen P. A. , Treder H.‐J. 
Published: May 2007

AbstractJedes „initium”︁ wird durch „experimenta crucis”︁ zum „eventus”︁. Jedes theoretisch interpretierbare ex‐eventu‐Resultat führt auf ein neues Initium. Gerade dies ist die gemeinsame Aussage von Atomistik, Quantenmechanik und Relativitätstheorie.
Some Remarks on Unsharp Quantum Measurements, Quantum Non‐Demolition, and All That
Authors: Busch Paul , Lahti Pekka J. 
Published: May 2007

AbstractThe theory of unsharp quantum measurements is reviewed as a generalization of the von Neumann‐Lüders measurement theory and applied to measurements of continuous quantities. A generalized notion of repeatability is proposed which is applicable even to intrinsically unsharp continuous observables. As an illustration a precise formulation of a quantum non‐demolition (QND) measurement performed on a harmonic oscillator is given.
Electron Emission from Clean Solid Surfaces by Fast Ions
Authors: Hasselkamp D. , Hippler S. , Scharmann A. , Schmehl T. 
Published: May 2007

AbstractTotal backward electron yields from 27 elemental, non‐crystalline, clean solids were measured during bombardment by H+‐, H‐, H‐, He+‐ and Ar+‐ions in the energy range from 100 keV to 800 keV. The yields were found to exhibit an oscillatory dependence on the atomic number of the target material correlated with the periods of the periodic system. These Z2‐oscillations are relatively insensitive to the type of projectile and the impact energy at the high projectile energies of this experiment. Present theories of electron emission cannot explain the main experimental results. The reasons for this failure are discussed.
Diffusion by Turbulence
Authors: Grossmann Siegfried 
Published: May 2007

AbstractThe turbulent diffusivity K of the atmosphere has first been studied by Richardson 1926 who empirically found that K depends on the scale l, K = Alα, with α = 4/3 and A = 0.6 cm2/3 s−1. This empirical scaling law is derived here from a unified theory (based on the Navier‐Stokes equation) together with an explicit result for the prefactor, A = 2.4 ϵ1/3. The mean atmospheric dissipation rate compatible with this is ϵ = 0.016 cm2 s−3. For windtunnels with typical dissipation rates ϵ ≅ 1 m2 s−3 the turbulent diffusion coefficient should be K/cm2 s−1 = 52 (l/cm)4/3.
Integrabilität, Irreversibilität und Kosmogonie
Authors: Treder Hans‐Jürgen 
Published: May 2007

AbstractIn der berühmten Diskussion über die Begründbarkeit der statistischen Thermodynamik stand hinter Zermelos Angriffen auf Boltzmann Planck selbst. Zermelos Einwände gegen Boltzmanns Atomistik und Boltzmanns Antwort sind heute wieder aktuell. Boltzmann begründete die statistische Thermodynamik letztendlich kosmogonisch.
Strahlteilungs‐ und Interferenzexperimente mit Photonenpaaren
Authors: Brendel J. , Lange R. , Mohler E. , Martienssen W. 
Published: May 2007

AbstractWir führen eine Reihe von elementaren optischen Experimenten mit einem nichtklassischen Lichtfeld durch, das über parametrische Fluoreszenz erzeugt wird und die Besonderheit aufweist, daß die Photonen ausschließlich paarweise auftreten. Beim Auftreffen auf einen verlustfreien, teildurchlässigen Spiegel werden die Photonen eines Paares gemäß einer Binomialverteilung auf das reflektierte und das transmittierte Bündel verteilt. Dieses Ergebnis ist unabhängig vom Kohärenzgrad. Die beobachtete Invarianz der Verteilung kann auf eine Balance zwischen quantenmechanischen Stimulations‐ und Interferenzeffekten in den Ein‐ und Ausgangsarmen des Strahlteilers zurückgeführt werden. Beim zweimaligen Durchlaufen eines Strahlteilers in einem Michelson‐Interferometer treten Interferenzen zwischen den verschiedenen möglichen Zweiphotonenzuständen im Interferometer auf. Das Korrelations‐Interferogramm für Photonenpaare besitzt eine höhere Auflösung als das Intensitäts‐Interferogramm für die Transmission einzelner Photonen. Wir deuten dieses Verhalten als quantenmechanische Interferenz zwischen der größeren Zahl von Möglichkeiten, die ein Photonenpaar im Vergleich zu einzelnen Photonen hat, das Interferometer zu durchlaufen. Die Anwendung dieser Überlegungen auf Lichtfelder mit Paaren von Photonen unterschiedlicher Energie führt zu Korrelations‐Interferogrammen, die deutlich von den mit klassischen Feldern aufgenommenen Interferogrammen abweichen.
Derivation of Composite Particle Dynamics by Weak Mapping of Quantum Fields
Authors: Kerschner R. , Stumpf H. 
Published: May 2007

AbstractAlternatively to path integrals quantum fields can be characterized by functional equations. Weak mappings of quantum fields are defined by mappings between such functional equations. This is exemplified for a regularized nonlinear spinor field theory and a boson theory of bound states. A corresponding weak mapping theorem is derived. In the appendix strong mappings, i.e. operator mappings are critically discussed.
Macroscopic State of Gases in a Light Field
Authors: Nienhuis G. , van Enk S. J. 
Published: May 2007

AbstractWe consider a gas or a gas mixture in a radiation field. The microscopic evolution equations for the distribution functions for the various particle states are separated into a rapid and a slow time scale. This separation defines the relevant quantities that specify the macroscopic state of the system. The evolution equations for the macroscopic variables take the form of a modified diffusion equation in the case of a dilute vapor in a buffer gas, and of generalized Navier‐Stokes equations for a single‐component gas. The equations contain light‐induced fluxes as source terms, and the transport coefficients are modified by the light.
Pion Interferometry in High Energy Hadron and Nuclear Collisions: Radial Expansion and Freeze‐Out
Authors: Stock R. 
Published: May 2007

AbstractIt is shown that the transverse radius, obtained from analysis of two‐pion correlation functions in the mid‐rapidity domain, should reflect the radius of the pion emitting volume. Emission is interpreted as the decoupling from strong interaction, during expansion of the initial interaction volume. Assuming an isotropic expansion without radial flow, and a simultaneous freeze‐out of pions throughout the source volume we show that the transverse radius from interferometry should be proportional to the square root of the hadron rapidity density, dN/dy, observed at mid‐rapidity. Recent data from hadron‐hadron and nucleus‐nucleus collisions at or above √s ≈︁ 20 GeV per nucleon are well interpolated by this result.
Why Are Most Nuclei Axially Symmetric?
Authors: Zickendraht W. 
Published: May 2007

AbstractA previous publication was concerned with the average prolateness of nuclei [1]. With the same methods as there it is shown here that axial symmetry should be predominant in nuclei, which it is indeed. The tools for the proof are special collective and single particle coordinates. The nucleon‐nucleus interaction is approximated by a shell model potential plus Nilsson coupling; strong coupling is used. The minimum of the total energy is found for axial symmetry.
Chiral Soliton Model with Dynamical Restoration of Chiral Symmetry from Quark Flavour Dynamics
Authors: Reinhardt H. , Kämpfer B. 
Published: May 2007

AbstractThe Nambu‐Jona‐Lasinio model as a particular model of quark flavour dynamics is bosonized in the low‐energy regime using a generalized heat kernel expansion with local mass scale. The resulting effective meson Lagrangian defines a chiral soliton model, the solutions of which show a partial restoration of chiral symmetry inside the soliton.
A Connecting Link between Lorentz and Dirac Theories of Electrons
Authors: Thattey Sudhir 
Published: May 2007

AbstractA theory, that is an initial step towards bridging the gap between Lorentz and Dirac theories of electrons, is presented. An electromagnetic Lagrangian density is postulated, such that, the theory can be cast into a form, similar to Dirac theory. Electromagnetic interpretation of conserved currents, and of usual bilinear covariants in the Dirac theory, is obtained. A counterpart of Abraham‐Lorentz equation, with oscillatory solutions is derived. Self‐energy of electrons is expressed in terms of their self‐potentials and self‐currents.
Interference in Phase Space
Authors: Dowling J. P. , Schleich W. P. , Wheeler J. A. 
Published: May 2007

AbstractA central problem in quantum mechanics is the calculation of the overlap, that is, the scalar product between two quantum states. In the semiclassical limit (Bohr's correspondence principle) we visualize this quantity as the area of overlap between two bands in phase space. In the case of more than one overlap the contributing amplitudes have to be combined with a phase difference again determined by an area in phase space. In this sense the familiar double‐slit interference experiment is generalized to an interference in phase space. We derive this concept by the WKB approximation, illustrate it by the example of Franck‐Condon transitions in diatomic molecules, and compare it with and contrast it to Wigner's concept of pseudo‐probabilities in phase space.
Forward‐Backward Coupling in Superfluorescence
Authors: Steudel H. 
Published: May 2007

AbstractIt is shown that — within the framework of an idealized model with taking into account backscattering at density fluctuations — there is a number NK of atoms such that for an atomic number N ≫ NK forward‐backward independence will be found while N ≪ NK leads to synchronized superfluorescence pulses in both directions.
Zur Reflexion und Transmission elektromagnetischer Wellen bei senkrechtem Einfall auf ebene Grenzflächen zwischen unterschiedlich absorbierenden Medien
Authors: Richter G. 
Published: May 2007

AbstractBorn und Ladenburg bemerkten bereits 1911, daß bei der Reflexion und Transmission elektromagnetischer Wellen durch eine Grenzfläche zwischen zwei verschieden stark absorbierenden Medien außer den mit den laufenden Wellen verbundenen Poyntingvektoren noch ein zur Erfüllung der Energiebilanz an der Grenzfläche notwendiger, sog. „gemischter”︁ Poyntingvektor zu beachten ist. Die mit diesem Vektor beschriebene Energieströmung ist stets dorthin gerichtet, wo aus derselben mehr Energie absorbiert wird. Sie entsteht im Zusammenhang mit einer räumlichen Modulation des Energieverbrauchs im partiell stehenden Interferenzfeld der einlaufenden und der reflektierten Welle, wobei die Energieabsorption bei den meisten Substanzen durch das elektrische Feld erfolgt, während das Magnetfeld daran praktisch unbeteiligt ist.Da jedoch die Mitberücksichtigung der magnetischen Effekte zum besseren Verständnis des gemischten Poyntingvektors beitragen kann. wird im folgenden zu ihrer quantitativen Beschreibung in die zweite Maxwellsche Gleichung ein dem Stromglied in der ersten Maxwell‐Gleichung analoger Zusatzterm eingeführt. Die Amplitude des „gemischten”︁ Poyntingvektors erweist sich dann als wesentlich abhängig vom Verhältnis der elektrischen zu den magnetischen Verlusten. Dies wird durch Betrachtung eines Mediums verdeutlicht, in welchem außer den Verlusten durch das elektrische Feld auch hiermit vergleichbare Verluste über das Magnetfeld auftreten, wobei beide Verlustarten zusammen eine an die räumliche Verteilung der Feldenergie besser angepaßte Absorption ergeben. Bei gleichen Energiedichten und Energieverlusten des elektrischen und des magnetischen Feldes verschwindet der „gemischte”︁ Poyntingvektor.
Intracavity Multi‐Photon‐Absorption and the Quantum Noise Spectrum of Light
Authors: Herzog Ulrike 
Published: May 2007

AbstractThe intensity noise spectrum is investigated quantum‐mechanically for incident coherent light passing through a resonator which is filled with a k‐photon‐absorber. For k⩽ 2 the noise of the outgoing light is reduced below the shot noise level the reduction being maximal for frequencies that are small in comparison to the cavity bandwidth. It turns out that the highest possible value of this low‐frequency noise reduction is obtained when the resonator losses due to transmission through the outcoupling mirror are 2k – 1 times as large as the k‐photon absorption losses. In this case the noise at zero frequency is reduced with respect to the shot noise level by a factor of k/(2k – 1).
Crossover from BCS‐superconductivity to Bose‐condensation
Authors: Drechsler M. , Zwerger W. 
Published: May 2007

AbstractStarting from a model of free Fermions in two dimensions with an arbitrary strong effective interaction, we derive a Ginzburg‐Landau theory describing the crossover from BCS‐superconductivity to Bose‐condensation. We find a smooth crossover from the standard BCS‐limit to a Gross‐Pitaevski type equation for the order parameter in a Bose superfluid. The mean field transition temperature exhibits a maximum at a coupling strength, where the behaviour crosses over from BCS to Bose like with corresponding values of 2 Δ0/Tc ≈ 5 which are characteristic for high Tc superconductors.
Strong linear amplification of quantum fields
Authors: Bandilla A. 
Published: May 2007

AbstractGoing ahead with investigations started by ideas of H. Paul it is examined how different quantum properties in the initial field state show up in the strongly amplified output field. As examples of extreme quantum fields the number state and the recently introduced phase optimized state are used. For the linear laser amplifier the inevitable noise is fully taken into account. These results are compared with those for a coherent input field. The characteristic differences in the macroscopic output fields allow unique conclusions onto the initial field. For the calculations the positive definite Glauber's P‐representation after strong amplification is applied.
Investigations on macroscopic intrinsic stress in amorphous binary‐alloy films
Authors: Dina S. , Geyer U. , v. Minnigerode G. 
Published: May 2007

AbstractMacroscopic tensile and compressive mechanical stresses in the film plane are observed during the growth of amorphous binary‐alloy films of ZrCo and TbCo prepared by the condensation of the metal vapours from two electron‐beam evaporators. The mechanical stress is measured by a capacitive cantilever beam technique. Both kinds of stresses are affected by composition and substrate temperature, but the compressive stress additionally depends on the film thickness, evaporation rate and substrate material. The results are discussed in terms of a model for the growth of amorphous films published earlier.
Dynamik einer Anordnung aus zwei Tunnelkontakten ultrakleiner Kapazität mit supraleitenden Elektroden
Authors: Seume F. , Krech W. 
Published: May 2007

Dynamics of an Array of two Tunnel Junctions with Ultrasmall Capacitances and Superconducting ElectrodesThe dynamics of a series array of two voltage‐biased SET junctions with superconducting electrodes is investigated in the frame of a master equation formalism. Explicit expressions for the number of electrons on the central electrode and the electric current are given in the zero temperature case. Situations without current are analyzed in detail and using current‐voltage characteristics, special properties of the system in the stationary regime are discussed.
Response of finite many‐electron systems beyond the time‐dependent local density approximation: Application to small metal clusters
Authors: Pacheco J. M. , Ekardt W. 
Published: May 2007

AbstractA linear response formalism is developed which is based on density functional theory within the local density approximation, but which is now corrected for its spurious self‐interaction errors, in the way originally proposed by Perdew and Zunger for ground state calculations. The original formulation is extended to incorporate self‐interaction corrections in the scrrening terms. The general formalism is then applied to the calculation of the static and dynamic response of the metal clusters {Na8, Na9+}, {Na20, Na} and {Na40 Na} within the jellium model. Comparison with experimental data and with other theoretical calculations indicates that the present formalism accounts for the overall (and most of the fine) features of the photoabsorption spectrum of these systems, providing a systematic improvement with respect to previous approaches. The remaining discrepancies are rationalized in terms of the effects to be expected by correctly accounting for the discrete structure of the ionic cores.
Mean values and fluctuations in the fragmentation of mesoscopic systems using an exactly solvable model with strict particle conservation and quantum symmetry
Authors: Gross D. H. E. , Ecker A. , Deangelis A. R. 
Published: May 2007

AbstractA detailed discussion of self‐similarities in fragment‐size distributions and fluctuations is presented using an exactly solvable model of fragmentation (the “chain model”). The effects of particle‐number conservation and quantum symmetry can rigorously be considered in systems ranging from microscopic to macroscopic. Due to the analyticity of the model the various scalings can be studied free of any statistical noise. Using a tuning parameter we can generate self‐similar distributions with realistic power‐laws and/or fluctuations which show intermittency. Finite‐size effects neither destroy nor cause intermittency. The relation of self‐similarity in both the averages and the fluctuations can be studied analytically. It is found that they are unlinked ‐ there are cases where the size‐distribution is a power‐law with realistic exponents τ between −2 and −3 but no intermittency. Two cases will even be shown which have indistinguishable fragment distributions but very different factorial moments. We also discuss the interpretation of both the size and slope of the factorial moments in terms of multiplicity and bin mixing. We show that while either is sufficient to produce large moments, one must have bin mixing to produce large slopes. The two types of mixing are necessarily linked in constrained systems such as described by our model.
Fragmentation, dissipative expansion, and freeze‐out in medium energy heavy‐ion collisions
Authors: Gross D. H. E. , Li Bao‐An , DeAngelis A. R. 
Published: May 2007

AbstractThe collision dynamics of 96Mo + 96Mo at 55 A MeV is simulated by solving numerically the Boltzmann‐Uehling‐Uhlenbeck (BUU) transport equation for the one‐body phase‐space distribution‐function of nucleons with and without Coulomb interaction. A scatter‐plot of the one‐body density distribution shows an initial compression, subsequent homogeneous expansion, a breaking into “fragments”, a very slow creeping expansion up to a freeze‐out and in the case of included Coulomb‐interaction a Coulomb‐explosion. In the calculation which included Coulomb‐interaction the overall shape of the ensemble of dense fragments is spherical. The fragments are created over the entire volume of the dense part of the source and not at the surface only. In the simulation without Coulomb interaction a doughnut‐like shape may develop.
Observation of sharp resistance anomalies near Tc in granular superconductors
Authors: Rubin S. , Schimpfke T. , Weitzel B. , Voßloh C. , Micklitz H. 
Published: May 2007

AbstractGranular films prepared from well‐defined In clusters embedded in Kr (⋍ 10‐40 at % Kr) show sharp resistance anomalies very close to the superconducting transition temperature. The observed resistance peak(s), which go(es) above the normal state resistance RN and which can be as high as ⋍ 1.5 RN, can be explained by a “mesoscopic” effect: Superconducting percolation aggregates of size ξρ, larger than the superconducting coherence length ξS, but smaller than the quasiparticle relaxation length λQ*, have a superconducting gap, but are not yet able to carry a supercurrent.
Positons of the modified Korteweg de Vries equation
Authors: Stahlhofen A. A. 
Published: May 2007

AbstractThe concept of positons, i.e. certain multiparametric solutions of the Korteweg de Vries equation with new properties, is extended to the modified Korteweg de Vries equation. It is shown that the essential features of positons carry over to this case; the collision of positons, the solitary‐wave‐positon interaction and simple generalizations are discussed in detail. Suggestions for future research and possible applications of the present work are sketched.
Measurement of the impedance of very thin superconducting YBaCuO films at 10 GHz with a cavity perturbation method between 4 and 300 K
Authors: Schaumburg G. , Helberg H. W. , Berberich P. , Kinder H. 
Published: May 2007

AbstractWe have measured the complex film impedance 1/σd (σ conductivity, d film thickness) of three YBaCuO thin films with d = 44, 115, and 168 nm on MgO substrates at 10.2 GHz in the temperature range between 300 and 4 K. Below Tc, the experimental results are discussed in terms of the two‐fluid model and the BCS theory. The residual resistance decreases with the film thickness. The thinnest film has a residual surface resistance of 3 · 10−4 Ω. For this film, the complex microwave conductivity is calculated and compared with the models. Apart from the residual resistance, the measured conductivity is in agreement with the peak caused by the energy gap of the BCS theory. All measurements were performed with a cavity perturbation method which we have to our knowledge applied for the first time to superconducting thin films. The method allows to determine the complex impedance of films with arbitrary thickness. In particular, films with thicknesses small compared to the skin depth δ or the London penetration depth λ can be measured. Therefore, we are able to measure the impedance both in the normal and superconducting state.
Tunnelling in periodically driven systems
Authors: Goetsch P. , Graham R. 
Published: May 2007

AbstractTunnelling in periodically driven bistable symmetric potential wells is investigated in an analytical approximation in a domain where the driving frequency is large compared to the tunnelling frequency and only the four lowest lying levels contribute significantly. The influence of finite level widths is taken into account, and a smooth variation of the amplitude of the driving field is allowed for.
On the clumpy structure of molecular clouds
Authors: Yue Z. Y. , Zhang B. , Winnewisser G. , Stutzki J. 
Published: May 2007

AbstractTwo‐dimensional hydrodynamic calculations for a self‐gravitating, magnetic and compressible medium are carried out. The results based on numerical simulations show that the joint effect of the nonlinearity of the hydrodynamic equations and self‐gravity is the mechanism for generating the observed complex structure of molecular clouds (e.g. clumps and filaments). In addition, parameters such as the evolution time of molecular clouds, the density contrast, fractal dimension, and the velocity probability distribution are derived. Their possible relation to the observed properties of molecular clouds are discussed.
Dynamic nonlinear σ‐model of electron localization
Authors: Horbach M. L. , Schön G. 
Published: May 2007

AbstractWe review the nonlinear σ‐model approach to the localization problem. However, different from usual, we do not make use of replicas or superfields in order to perform the averaging over the realizations of the disorder. Instead, we pursue the derivation of the nonlinear σ‐model as an effective theory for the disordered electron system within the framework of the so‐called time‐path formalism, which is a real‐time finite‐temperature quantum field theory. This formalism is especially suitable for the description of the disordered electron system due to the automatic normalization of real‐time quantities, thereby avoiding the denominator problem. We shall compare this dynamic method with the replica‐ and superfield‐methods as the perturbative level of the calculation of physical quantities.
Effects of geometry on transfer matrices, spin chains and critical behaviour
Authors: Davies Brian , Peschel Ingo 
Published: May 2007

AbstractWe consider two‐dimensional Ising models bounded by general parabolic curves and study their transfer matrices and associated quantum spin chains. We derive their eigenvalue spectra numerically and analytically, both at the critical point and in its vicinity. From this we find how the geometrical form of the system is reflected in the spectrum and how it influences the critical behaviour near the tip.