bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zur Geschichte der Bohr‐Sommerfeldschen Quantentheorie
Authors: Schöpf Hans‐Georg 
Published: May 2007

AbstractIn der vorliegenden Arbeit werden Artikel von N. Bohr, P. Ehrenfest, A. Sommerfeld, P. Epstein und K. Schwarzschild im Hinblick auf die wesentlichen Konzeptiontionen in der Geschichte der älteren Quantentheorie im Zeitraum von 1914 bis 1918 besprochen.
Solar Anisotropy of Muon Component of Cosmic Rays
Authors: Bishara A. A. , Darwish A. A. 
Published: May 2007

AbstractCosmic‐ray underground observations are used together with the difference coupling coefficients to determine, by spectrographic method, features of the differential energy spectrum of solar anisotropy of cosmic rays. The differential energy spectrum is found to have a constant form up to an upper effective rigidity boundary which changes with solar activity.
Monte Carlo simulation of overdamped motion in a double well potential under the influence of coloured noise
Authors: Müller Judith , Schnakenberg Jürgen 
Published: May 2007

AbstractWe present a Monte Carlo simulation algorithm for evaluating the stationary probability and the mean and the variance of first passage times in any dynamical system under the influence of additive coloured Gaussian and Marcovian noise (Ornstein‐Uhlenbeck process). Our algorithm generates the Ornstein‐Uhlenbeck process by a superposition of a finite number of random telegraph processes. We obtain our results from a direct evaluation of the trajectories. We apply our method to the overdamped motion of a particle in a double well potential. We compare our simulation results with various analytic approximations for the stationary probability and the mean first passage times.
Magnetization of disordered ballistic quantum billards
Authors: Braun Daniel , Gefen Yuval , Montambaux Gilles 
Published: May 2007

AbstractWe study the magnetic response of mesoscopic quantum dots in the ballistic regime where the mean free path le is larger that the size L of the sample, yet smaller than L(KFL)d−1. In this regime, disorder plays an important role. Employing a semiclassical picture we calculate the contribution of long tranjectories which are strongly affected by static disorder and which differ sharply from those of clean systems. In the case of a magnetic field, they give rise to a large linear paramagnetic susceptibility (which is disorder independent), whose magnitude is in agreement with recent experimental results. In the case of a Aharonov‐Bohm flux, the susceptibility is disorder dependent and is proportional to the mean free path as in the diffusive regime. We also discuss the corresponding non‐linear susceptibilities.
Towards a theory of the integer quantum Hall transition: From the nonlinear sigma model to superspin chains
Authors: Zirnbauer Martin R. 
Published: May 2007

AbstractA careful study of the supersymmetric version of Pruisken's nonlinear σ model for the integer quantum Hall effect is presented. The lattice regularized model is cast in Hamiltonian form by taking the anisotropic limit and interpreting the topological density as an alternating sum of Wess Zumino terms. It is argued that the relevant large‐scale physics of the model is preserved by projection of the quantum Hamiltonian on its sector of degenerate strong‐coupling ground states. For values of the Hall conductivity close to e2/2h (mod e2/h), where a delocalization transition occurs, this yields the Hamiltonian of a quantum superspin chain which is closely related to an anisotropic version of the Chalker‐Coddington model. The relation implies that the ratio of magnetic length over potential correlation length is an irrelevant parameter at the transition. The superspin chain resembles a 1 d isotropic antiferromagnet with spin 1/2. It has an alternating structure which however permits an invariance under translation by one site. The conductance coefficients of a quantum Hall system with N small contacts translate into N‐superspin correlation functions which are governed by conformal invariance. The superspin formalism provides a framework for studying the crossover from classical to quantum percolation. It does not however encompass the frequency‐dependent correlations of wave amplitudes at criticality.
Dielectric dispersion of ferroelectric ceramics and single crystals at microwave frequencies
Authors: Arlt G. , Böttger U. , Witte S. 
Published: May 2007

AbstractThe dielectric constant of ferroelectric ceramics shows strong Debye‐like relaxation at GHz frequencies. This relaxation is caused by sound generation inside the crystallites. The ferroelastic domain walls which vibrate in the electric ac field are very effective shear wave transducers. The shear wave emission has a maximum when the wavelength of the sound wave is comparable to the width of the domains. Above this frequency the domain walls can no longer vibrate due to inertia and do not contribute to the dielectric constant. The observed dependence of the microwave dispersion on temperature, doping and grain size of the ferroelectric ceramic is in good agreement with the proposed mechanism of the emission of acoustic shear waves.
Relaxation of translational energy in binary mixtures of dense hard sphere systems
Authors: Cukrowski A. S. , Fritzsche S. , Haberlandt R. 
Published: May 2007

AbstractStarting from the Enskog equation we derive an analytical equation for the relaxation time necessary for the equilibration between translational energies of the components in a dense binary mixture of hard spheres. Also we give an expression for the collision number describing the average number of collisions of one particle during the relaxation time. The analytical expressions are verified by molecular dynamics simulations for various values of the packing fraction. The results are shown to be valid even for very dense systems, i.e. for liquids in the ranges of density corresponding to the freezing point.
Acoustic wavefront imaging
Authors: Wolfe J. P. , Hauser M. R. 
Published: May 2007

AbstractWe introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media. Simply stated, we have devised a means of observing the expanding acoustic wavefront from a point disturbance in a solid. The data may be viewed as a movie or a series of snapshots. The observed wavefronts represent the group‐velocity surfaces of acoustic waves, which reflect the basic elastic anisotropy of the solid. The technique has been applied to coherent acoustic waves with frequencies in the megahertz range (at ambient temperatures) and to incoherent heat pulses in the hundred‐gigahertz range (at liquid‐helium temperatures). In this article, we first provide a pedagogical introduction to wave propagation in elastically anisotropic media, reviewing some early methods for visualizing acoustic waves. Next, we describe the “acoustic wavefront imaging” method and give representative results in crystals and composite materials. Finally, we show how this method relates to recent advances in phonon imaging and internal diffraction of ultrasound.
The influence of thin helium films on the phonon spectrum of optically excited silicon
Authors: Türk F. , Ullrich G. , Kinder H. 
Published: May 2007

AbstractWe have studied the phonon spectra resulting from laser pulse excitation of a silicon surface. We used a phonon spectrometer based on pressure tuned boron levels in silicon (Si: B‐spectrometer). A new design allowed us to use the spectrometer in vacuum for the first time. We observed phonon frequencies up to 1 THz. The pulse shapes indicated both, quasidiffusion and a long exciton lifetime. On adding helium films to the surface we have found dramatic changes of the spectrum. Full thermalisation was reached already at a thickness of 1.5 monolayers. This indicates a strong anharmonic interaction in the very first monolayers at these high frequencies and, in addition, a strong confinement of the phonons to the surface by quasidiffusion.
Frequency multiplication of microwave radiation in a semiconductor superlattice by electrons capable to perform Bloch oscillations
Authors: Grenzer J. , Schomburg E. , Ignatov A. A. , Renk K. F. , Pavel'ev D. G. , Koschurinov Yu. , Melzer B. Ja. , Ivanov S. , Schaposchnikov S. , Kop'ev P. S. 
Published: May 2007

AbstractWe report the observation of frequency multiplication of microwave radiation in a GaAs/AlAs semiconductor superlattice at room temperature. We observed, for a fundamental frequency of 9 GHz, second and third harmonic generation. We associate the harmonic generation with a nonlinear current‐voltage characteristic that is determined by Bloch oscillations of electrons propagating along the superlattice axis. Our results suggest for the frequency multiplication an upper limit in the tetrahertz frequency range.
On the waves and instability in self‐gravitating magnetic molecular clouds with ambipolar diffusion Part 1: Planar modal approach
Authors: Yue Z. Y. , Zhang B. , Winnewisser G. , Stutzki J. 
Published: May 2007

AbstractIt is well established that molecular clouds are the main sites of active star formation in our Galaxy. The interaction of the three major physical agents in molecular clouds, i.e. the self‐gravity, magnetic fields, and ambipolar diffusion, in the form of waves and instability, governs the dynamics and evolution of molecular clouds. The present work is a new effort on this subject.This work consists of two parts. In Part 1, we complete the planar modal analysis by removing the restrictions on the direction of the velocity perturbation which were used in previous studies. Thus, the wave number vector k is allowed to take any direction with respect to the mean field B0. The exact general dispersion relation is found to be a seventh‐order equation and can be reduced to a quartic equation as the first approximation about the small parameter xρ = ρi, 0/ρn,0, the density ratio between ions and neutrals. The growth rate contour maps in the k plane are obtained for various values of the basic dimensionless parameters Λ and σ, where Λ = VA,n/Cn is the ratio between the Alfvén speed and the sound speed in the neutrals, and the “coupling factor” σ = vi/ωg,n is the ratio between the average collision frequency of a neutral with ions and the self‐gravitation response frequency. It is shown that, in all directions, magnetic field only reduces the growth rate but does not change the critical wave length for instability. The reduction of the growth rate depends on not only Λ, the dimensionless measure of the field strength, but also the direction of k as well as the coupling factor σ. The frequencies and the dissipation rates of the Alfvén waves and the fast and slow self‐gravitating magnetosonic waves are calculated for all directions of k. The solutions of these waves are also given.Although the planar modal approach is important in understanding the basic mechanism of magnetic waves and instability, it does not take into account the three‐dimensionality and the finite size of the cloud and is therefore only suitable to the local analysis. Thus, in order to discuss the global properties, we will develop a cylindrical modal approach in Part 2. There, we will also discuss certain nonlinear effects and show their importance in leading to a self‐adjusting mechanism which slows down the global collapse at the early stage of cloud evolution and refreshes the outward propagating Alfvén and fast magnetosonic waves caused by star‐forming or core‐forming activities. In this way, a significant portion of the released gravitational energy during the global collapse is turned into the magnetic waves to support the cloud against the global collapse itself.
Mesoscopic systems with fixed number of electrons
Authors: Lehle W. , Schmid A. 
Published: May 2007

AbstractIn this paper, we study the physics of mesoscopic systems with noninteracting electrons of fixed number. From a technical point of view, this means a discussion of the differences between the canonical and the grand canonical ensemble (fixed versus fluctuating number of particles). Such a discussion is not trivial since the grand canonical ensemble is the most convenient basis for the statistics of identical particles and one has to spend labour in order to retrieve the canonical ensemble. Specifically, we are considering ensembles of mesoscopic systems with disorder, either by atomic defects or by fluctuations in their geometric definitions and we discuss various forms of disorder averages.
Transport in a fluctuating potential
Authors: Mielke Andreas 
Published: May 2007

AbstractWe study the overdamped motion of a particle in a fluctuating one‐dimensional periodic potential. The potential has no inversion symmetry, and the fluctuations are correlated in time. At finite temperatures, a stationary current is induced. The amplitude and the direction of the current depend on the details of the noise process that is responsible for the potential fluctuations. We discuss several limiting situations for a general case. Furthermore we calculate the current in the case of a piecewise linear potential for different noise processes and parameters. A detailed discussion of the results is given, including a discussion of the mechanism that is responsible for the current reversal. We compare the present results with results for transport in a ratchet‐like potential due to a fluctuating force. We also discuss the biological relevance of the present models for molecular motors. We present a model for the motion of molecular motors that explains why similar molecular motors can move in different directions.
Regioselective Borylation of Porphyrins by CH Bond Activation under Iridium Catalysis to Afford Useful Building Blocks for Porphyrin Assemblies
Authors: Hata Hiroshi , Yamaguchi Shigeru , Mori Goro , Nakazono Satomi , Katoh Taisuke , Takatsu Keishi , Hiroto Satoru , Shinokubo Hiroshi , Osuka Atsuhiro 
Published: May 2007

AbstractHighly regioselective and efficient borylation of a variety of porphyrins has been achieved by reaction with bis(pinacolato)diboron through CH bond activation under iridium catalysis on the basis of the synthetic protocol developed by Miyaura, Hartwig, and Smith. A boryl group can be selectively introduced at sterically uncongested positions in the peripheral aryl groups of porphyrin substrates whose peripheral β‐positions are sterically hindered. Curiously, β substituents adjacent to the aryl group to be borylated have unexpectedly large effects on the regioselectivity, because the iridium catalyst can discriminate between subtle steric differences. Chemoselective borylation was also achieved for several functionalized porphyrins. This borylation protocol can be applied to various monomeric and oligomeric functional porphyrins, hence offering an efficient route to elaborate multiporphyrin‐based molecular constructs.
A semi‐Markov model of disease recurrence in insured dogs
Authors: Wang Xikui , Pai Jeffrey S. , Shand Kevin J. 
Published: May 2007

AbstractWe use a semi‐Markov model to analyse the stochastic dynamics of disease occurrence of dogs insured in Canada from 1990 to 1999, and the probability pattern of death from illness. After statistically justifying the use of a stochastic model, we demonstrate that a stationary first‐order semi‐Markov process is appropriate for analysing the available data set. The probability transition function is estimated and its stationarity is tested statistically. Homogeneity of the semi‐Markov model with respect to important covariates (such as geographic location, insurance plan, breed and age) is also statistically examined. We conclude with discussions and implications of our results in veterinary contents. Copyright © 2007 John Wiley & Sons, Ltd.
Eine neue Darstellungsweise für 1.3‐Diketone aus Vinylacetat und Säurechloriden
Authors: Sieglitz Adolf , Horn Otto 
Published: May 2007

AbstractEs wird die Umsetzung von Säurechloriden mit Vinylacetat in Gegenwart von Aluminiumchlorid zu symmetrischen 1.3‐Diketonen beschrieben. Als Nebenprodukte entstehen Acylacetone. Die Anwendbarkeit der Reaktion auf verschiedene Säurechloride wurde untersucht.
Darstellung und Wirkungen von Acetyl‐Derivaten des Cysteamins
Authors: Kuhn Richard , Quadbeck Günter 
Published: May 2007

AbstractÄthylenimin reagiert mit Thioessigsäure unter Bildung von N‐Acetyl‐cysteamin, das durch Keten in N.S‐Diacetyl‐cysteamin und durch Essigsäureanhydrid in N.N.S‐Triacetyl‐cysteamin verwandelt werden kann. Die di‐und Triacetyl‐Verbindung bewirken eine langanhaltende Blutdrucksenkung.
Reaktionen mit Lithiumaluminiumhydrid: Reduktion von Heterocyclen mit Lithiumaluminiumhydrid
Authors: Bohlmann Ferdinand 
Published: May 2007

AbstractBei der Einwirkung von Lithiumaluminiumhydrid auf heterocyclische Verbindungen entstehen im allgemeinen die sonst oft nur schwer zugänglichen, sehr empfindlichen Dihydroverbindungen.
Die Spaltung des α‐Oxy‐tryptophans in die optischen Antipoden
Authors: Kotake Munio , Sakan Takeo , Miwa Toshio 
Published: May 2007

Abstract(+)‐α‐Oxy‐tryptophan, das von H. Wieland und B. Witkop als Bestandteil des Phalloidins in Amanita phalloides aufgefunden worden ist, wurde durch Spaltung der d,l‐Verbindung über das Brucin‐Salz der N‐Acetyl‐Verbindung ebenso wie die (−)‐Verbindung erhalten.
Über Abkömmlinge des Pantothenals
Authors: Bergel Franz , Hindley Nathan C. , Morrison Alexander L. , Moss A. Ronald 
Published: May 2007

AbstractDie Diäthylacetale des d,l‐ und d(+)‐Pantothenals wurden hergestellt und einer milden Verseifung und Oxydation unterworfen, wobei in gewissem Maße Salze der entsprechenden Pantothensäuren gebildet wurden. Aus dem d,l‐Pantothenal ‐ diäthylacetal entstand durch Säurebehandlung eine hochschmelzende Verbindung, für die die vorläufige Formel eines „Dipantothenals”︁ (II) vorgeschlagen wird. Im Ratten‐Wachstumsversuch Zeigt diese Substanz eine deutliche Vitaminwirkung.
Über eine neue Synthese des β‐Oxindolyl‐(3)‐alanins (α‐Oxy‐tryptophans); ein Beitrag zum Anwendungsbereich der Sörenschen Aminosäure‐Synthese
Authors: Behringer Hans , Weissauer Hermann 
Published: May 2007

AbstractEs wird bewiesen, daß bei der Kondensation von Malonester mit Thiokresylmethylen‐oxindol (II; R′=H, X=S·C 6H4·CH3) diese in 2‐Stellung des Oxindolrings erfolgt, was auch für die Umsetzung einiger anderer aktiver Methylenverbindungen mit Abkömmlingen des Oxymethylen‐oxindols wahrscheinlich ist. Chlormethylen‐oxindol (II; R′=H, X=Cl) läßt sich dagegen mit Natrium‐formamino‐malonester in den α‐Carbäthoxy‐α‐formamino‐β‐[isatyliden‐(3)]‐ propionsäureester (IV; R′=H, R″=NH·CHO) überführen, der durch Reduktion und Totalhydrolyse β‐Oxindolyl‐(3)‐alanin (I) liefert.Es wird auf die Möglichkeit hingewiesen, aus dem erwähnten Zwischenprodukt IV das Dioxindolyl‐alanin (XII) zu synthetisieren, das als Vorstufe des N′ ‐Formyl‐kynurenins beim biologischen Abbau des Tryptophans in Betracht kommt.
Notiz über eine Reaktion des Pyridin‐aldehyds‐(4)
Authors: Mathes Wilhelm , Sauermilch Walter 
Published: May 2007

AbstractBei dem Versuch zur Darstellung des γ‐Pyridoins wird ein Reaktionsverlauf festgestellt, der unmittelbar zum hydrierten Pyridoin, dem Bis‐[γ‐pyridyl]‐glykol führt, das in 2 isomeren Formen erhalten wird.
Konstitution und Lichtabsorption, VI. Mitteil.: Zur Deutung von Polyacetylen‐Spektren, sowie Darstellung von Bis‐tert.‐butyl‐decapentain‐(1.3.5.7.9)
Authors: Bohlmann Ferdinand 
Published: May 2007

AbstractDurch Darstellung des bisher noch fehlenden Gliedes, einer Pentaacetylen‐Verbindung, wurde die Reihe der Polyine vervollständigt. Die Unterschiede in den Spektren der Polyine gegenüber denen der Polyene werden gedeutet. Die verschiedene Lage der Maxima kommt durch die unterschiedlichen Bindungsabstände und die sich daraus ergebenden Unterschiede in der Länge der π‐Elektronenwolken zustande. Die größere Intensität der Banden bei den Polyinen ergibt sich aus der erhöhten Übergangswahrscheinlichkeit.
Reaktionen an der Carbonamid‐Gruppe
Authors: Heyns Kurt , Woyrsch Oscar‐Felix 
Published: May 2007

AbstractEs werden die Umsetzungen von ϵ‐Caprolactam, 2.5‐Diketo‐piperazin, N‐Methyl‐acetamid und Glycylglycin mit Salpetriger Säure und Reaktionen der erhaltenen Nitroso‐Verbindungen untersucht. Gegenüber Diazomethan verhielt sich die ‐CO·NH‐Gruppe bisher widerstandsfähig.
Synthesen von α‐Aminosäuren, III. Mitteil.: threo‐p‐Nitro‐phenylserin
Authors: Ehrhart Gustav 
Published: May 2007

AbstractEs wird die Kondensation von p‐Nitro‐benzaldehyd mit Glykokoll zu p‐Nitro‐phenylserin beschrieben und seine threo‐Konfiguration auf verschiedenen Wegen bewiesen.
Eine Synthese der Phenol‐β‐d‐glucuronsäure
Authors: Heyns Kurt , Kelch Claus 
Published: May 2007

AbstractEs wird eine Synthese von Phenol‐β‐d‐glucuronid, ausgehend von d‐Glucuron, über den 1‐Brom‐triacetyl‐α‐d‐glucuronsäure‐methylester, beschrieben.
Über die Bildung von 1.3.4.5‐Tetraacetyl‐β‐d‐fructopyranose aus Keto‐ditrityl‐triacetyl‐fructose mittels Acetylbromids bzw. Perchlorsäure in Essigsäureanhydrid (Untersuchungen über Fructose‐acetate, II. Mitteilung
Authors: Hennig Ingeborg 
Published: May 2007

AbstractBei der Umsetzung von Keto‐ditrityl‐triacetyl‐fructose mit Acetylbromid in Essigsäureanhydrid oder Chloroform entsteht in der Kälte 1.3.4.5‐Tetraacetyl‐β‐d‐fructopyranose über Acetobromfructose als Zwischenstufe. In der Wärme findet einfacher Austausch von Trityl gegen Acetyl‐Gruppen zu Keto‐pentaacetyl‐fructose statt. Entsprechend Acetylbromid reagieren Essigsäureanhydrid + Perchlorsäure.
Über α‐ und β‐Sulfonyl‐sulfonium‐Salze
Authors: Böhme Horst , Heller Paul 
Published: May 2007

Abstractα‐Sulfonyl‐sulfonium‐Salze lassen sich durch Oxydation von Alkylmercaptomethyl‐sulfonium‐Salzen mit Peressigsäure gewinnen; sie sind als Reineckate oder Methansulfonate beständig, zerfallen als Chloride hingegen in wäßriger Lösung unter Bildung von α‐Mercaptosulfonen.β‐Sulfonyl‐sulfonium‐Salze entstehen durch Anlagerung von Alkylhalogeniden an β‐Sulfonyl‐sulfide; sie sind in wäßriger Lösung beständig und zerfallen bei Gegenwart von Alkali wie die analogen γ‐Keto‐sulfonium‐Salze in Dialkyl‐sulfide und Alkyl‐ bzw. Aryl‐vinyl‐sulfone.
Über das Dimere des α‐Phenyl‐butadiens. Zur Kenntnis der Dien‐Synthese mit unsymmetrischen Addenden
Authors: Alder Kurt , Haydn Joseph , Vogt Wilhelm 
Published: May 2007

AbstractDie Konstitution und Konfiguration eines trans‐1‐Phenyl‐2‐styryl‐Δ5‐cyclohexens für das Dimerisationsprodukt aus α‐Phenyl‐butadien wurde bewiesen. Die Dimerisation stellt eine “partielle 1.4‐Addition” vor. Die ortho‐Stellung der Substituenten Phenyl und Styryl im Dimeren folgt den allgemeinen Regeln, die für Dien‐Synthesen mit unsymmetrischen Addenden gelten.
Über 1.2.4‐Thiodiazole, II. Mitteil.): N‐Methyl‐Derivate der Amino‐thiodiazole und Imino‐thiodiazoline
Authors: Goerdeler Joachim , Huppertz Andreas , Wember Kurt 
Published: May 2007

AbstractDurch Umsetzung der 5‐Amino‐1.2.4‐thiodiazole mit Methyljodid oder durch Ringschluß‐Synthesen werden die im Kern methylierten Imino‐thiodiazoline erhalten. Die exocyclisch methylierten Amine sind über die 5‐Chlor‐Verbindung zugänglich, gelegentlich auch durch Umlagerung aus dem entsprechenden Thiodiazolin. Beide Klassen, von deren Hauptvertretern eine Anzahl Substitutions‐ und Abbauprodukte hergestellt wurden, unterscheiden sich charakteristisch in ihren Basizitäten, UV‐Spektren und Polarogrammen. Aus den Befunden wird geschlossen, daß die tautomeren 5‐Amino‐thiodiazole als Amine vorliegen.