bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mean‐field dynamo with cubic non‐linearity
Authors: Kleeorin N. I. , Ruzmaikin A. A. 
Published: July 2007

AbstractThe turbulent mean‐field dynamo of αω‐type with a mean helicity quadratically dependent on the magnetic field is investigated. A nonlinear system of ordinary differential equation is derived for the amplitudes of the magnetic field expansion over the eigenvectors of the linear problem.In a one‐mode approximation the non‐linear supercritical solution is stable when dγ/dD> 0, where γ is the growth rate of the linear solution andDis the dynamo number.Non‐linear interation between two modes of dipole and quadrupole symmetry is considered. The conditions are found for the synchronization and beats of these modes under the assumption that the quadrupole mode is weaker than the dipole one.
Some observational results on long‐time variability of stars with magnetic fields
Authors: Scholz G. 
Published: July 2007

AbstractThe intention of this paper is a summary of long‐time phenomena of magnetic stars which we obtained at the Potsdam Observatory. The considered magnetic stars are γ Equ, HD 9996, 53 Cam, 52, Her, and v Cep. Many results have been published already; here, they are compiled and completed by new details.
Accretion with uniform eddy diffusivity I. Polytropic–tube models
Authors: Rüdiger G. , Tschäpe R. 
Published: July 2007

AbstractWe consider accretion onto a two–dimensional polytropic tube. In contrast to the standard papers we apply spatially uniform eddy viscosity (and eddy conductivity in part II resp.). In principle, the resulting rotation law is non–keplerian and proves to be rather flat. Wether the angular velocity increases or decreases inwadly depends on the strength of the torque exerted on the outer surface which is due to the inflow of angular momentum. Large (small) torque cause super–(sub–)rotation. The frictionally originated luminosity varies for various models. It lies one or two orders of magnitude below the total avialable accretion energy. For certain combinations of the Mach numbers the radial inflow profile possesses a sonic point.
General precession computed by numerical integration of ordinary differential equations
Authors: Andersen T. B. 
Published: July 2007

AbstractIt is suggested that the effects of change in the celestial coordinates due to general precession be computed by solving numerically the differential equations for the instataneous rates of change in right ascension and declination. An approximate solution in closed from is given. Similar differential equations may be solved for the complete rotation matrix, requiring only the knowledge of the variations of the two function m and n with time. This suggests the existence of a relation between the classical precessional elements z, ζ0 and Θ, and this relation is derived. Some numerical examples are also presented.
On static spherical symmetric solutions of the Bach‐Einstein gravitational field equations
Authors: Schmidt H.‐J. 
Published: July 2007

AbstractFor field equations of 4th order, follwing from a Lagrangian “Ricci scalar plus Weyl scalar”, it is shown (using methods of non‐standard analysis) that in a neighbourhood of Minkowski space there do not exist regular static spherically symmetric solutions. With that (besides the known local expansions aboutr= o nadr= ∞ resp.) for the first time a global statement on the existence of such solutions is given. Finally, this result will be discussed in connection with Einstein's particle programme.
Messung der Lichtablenkung während der Sonnenfinsternis am 15. Februar 1961
Authors: Schmeidler F. 
Published: July 2007

AbstractDuring the total eclipse, a plate of the stars near the Sun was taken on the Monte Cónero near Ancona in Italy, on which 12 stars were measurable. Comparison with another plate of the same stars taken at night showed strong distortion on the eclipse plate which was very probably due to anomalous refraction. The differences of coordinates between both plates were represented by a general secondorder expression. The value L = I″.98 ± o″.46 was derived for the gravitational deflection on the solar limb.
Zur Interpretation der Messungen der Lichtablenkung am Sonnenrand
Authors: Schmeidler F. 
Published: July 2007

AbstractThe agreement between radiastronomical measurements of the gravitational deflection of light at the solar limb and the theory of relativity is compatible with the exces found by most optical observers. The optical excess is caused by stars so near to the Sun that radioastronomical observations are impossible. Optical and radioastronomical measurements both make it likely that there is an additional term inversely proportional to a power higher than the first of the distance from the Sun. Results found by BOUET indicate that this additional term is of solar origin.
The determination of the gravitational potential of axisymmetric mass distribution in spherical coordinates. II
Authors: Tschaepe R. 
Published: July 2007

AbstractThe numerical computation of gravitational potential of rotational‐symmetric mass distribution in spherical coordinates requires a lot of computing time. We discuss direct methods and present a reduction method which is superior to methods used so far. Results for accuracy which is similar to that of other methods and computing times are given in Fig. 2 and 3.
Measurements of stellar scintillation using photon counting statistics
Authors: Stecklum B. 
Published: July 2007

AbstractMittels photonenzählender Photometrie hoher Zeitauflösung wurden Eigenschaften der Intensitätsszintillation untersucht. Die Abhängigkeit der Szintillationsleistung von der Zenitdistanz erwies sich als schwächer als theoretisch vorhergesagt. Die Wellenlängenabhängigkeit der Szintillationsleistung und die Verteilung der Intensitätsfluktuationen gemäß einer logarithmischen Normalverteilung entsprechen den theoretisch zu erwartenden. Das zeitliche Verhalten der Szintillation wird durch Korrelationszeitskalen von weniger als 10 ms bzw. einige 10 s gekennzeichnet, was als Hinweis auf die innere und äußere Skala der atmosphärischen Turbulenz gedeutet werden kann. Es wurden die Einflüsse anderer Vorgänge, die ebenfalls zu Intensitätsschwankungen führen, auf die Messung der Szintillationsleistung untersucht.
Beobachtungen Kleiner Planeten. IV
Authors: Börngen F. , Kirsch K. 
Published: July 2007

AbstractEs wird eine Übersicht über die im Jahr 1983 auf Tautenburger Schmidtplatten gefundenen Kleinen Planeten gegeben. Es wurden 147 Objekte entdeckt und für sie 272 Positionen gerechnet. Für vierzehn im Berichtszeitraum numerierte Planeten haben Tautenburger Beobachtungen einen Beitrag geleistet. Der in Tautenburg entdeckte Planet 1981 VL 2 erhielt die permanente Bezeichnung (2861). Er bekam zu Ehren von Prof. HERMANN LAMBRECHT († 4. 6. 1983) den Namen Lambrecht.
A magnetic neutral sheet as cause of the flare productivity of a δ sunspot group
Authors: Seehafer N. 
Published: July 2007

AbstractFlare observations in the solar activity complex HR 16862, 16863, 16864 at the end of May 1980 are compared with the structure of force‐free magnetic fields calculated from photospheric magnetograph measurements. A series of homologous flares connected with a δ configuration in HR 16864 was possibly caused by a magnetic neutral sheet. The δ configuration consisted of the large preceding spot of HR 16864 and a small satellite of opposite polarity. All magnetic flux from the satellite is connected to the main spot, and at the outer edge of the satellite, away from the main spot, a magnetic neutral sheet is found. This agrees with the observation that all penumbra was situated between parent spot and satellite, which is typical of such † configurations. It is suggested that the flare productivity of these configurations is generally caused by magnetic neutral sheets at the penumbra‐free outer boundary of the satellites.
On the inhomogeneous structure of the chromosphere‐corona transition region above sunspot umbrae
Authors: Staude J. 
Published: July 2007

AbstractMultiple wavelength observations of sunspot umbrae can only be expalined by an inhomogeneous, two‐component model for the structure of the umbral transition region and lower corona. The ‘Wroclaw‐Ondrejov sunspot model’ was a first step in this direction. This working model has now been improved using analytic expressions for the atmospheric structure in each component and fitting the free parameters to recent sunspot observations, particularly in EUV lines. The main component has a shallow transition region and a deep‐set corona. The second, ‘active’ component has a vast transition region in relatively cool fine structure elements embedded in the coronal main component. The spatial filling factor of this active component amounts to 5–10% in sunspots with bright EUV plumes, but is is more than ten times smaller in sunspot without such plumes. Observations with high spatial and temporal resolutions are necessary to understand in more detail the basic physical processes.
The search for possible time variations in Davis' measurements of the argon production rate in the solar neutrino experiment
Authors: Haubold H. J. , Gerth E. 
Published: July 2007

AbstractWith the gradual accumulation of experimental data in the solar neutrino experiment of DAVIS and collaborators (runs 18–74 for 1970–1982), the question, whether there are time variations of the solar neutrino flux, is of renewed interest. We discuss the mathematical‐numerical methods applied to the statistical analysis of DAVIS' argon‐37 production rate up till now known in the literature. These methods are characterized by the arbitrary arrangement of the DAVIS data in a time series. We perform a certain Fourier transformation for unequally‐spaced time series of the measuring data of the argon‐37 production rate, discuss the discovered periods and give significance criteria with respect to each period. We find that all periods discussed in the literature are contained in our series of periods. Pointing out the more mathematical character of the time series analysis we emphasize the predominant significance of the detected periods.
Photometric and spectroscopic observations of the variable star ET And. II
Authors: Scholz G. , Gerth E. , Panov K. P. 
Published: July 2007

AbstractNew spectroscopic and photometric observations of the variable Ap star ET And carried out 1982 and 1983 confirm once again the existence of short‐time variations. For the radial velocity variations a period of 0.19771 days and for the light variations a period of 0.0989 days was found. Some spectrograms show a velocity progression of the Balmer lines. The gradient is of such a kind that the radial velocity values increase from the line Hγ to H15. Different models for the interpreation of the velocity progression are discussed.
An analytic approach to the connection between stellar structure parameters and the neutrino emission rate in a simple stellar model
Authors: Haubold H. J. , Mathai A. M. 
Published: July 2007

AbstractIn order to obtain the internal structure of a main‐sequence star such as the Sun usually one has to solve the detailed structure equations numerically. This paper is an attempt to construct analytic models for the stellar nuclear energy generation. We give closed‐form analytic results for the stellar luminosity and stellar neutrino emission rate when the radial matter density of the spherical star under consideration is linear. For the numerical estimation of the neutrino flux of a specified stellar nuclear reaction we take into account parameters of the standard solar model. The present paper gives for the first time the connection between stellar structure parameters and neutrino fluxes in an analytic stellar model.
The position of ET And in the Hertzsprung‐Russell diagram
Authors: Scholz G. 
Published: July 2007

AbstractThe interstellar lines of Call (K) and NaI (D) are the main means used to estimate the distance of the Ap star ET And to derive its position in the HRD, because the classical methods for the determination of M are affected by some restrictions. By these means the star lies distinctly above the main sequence. The post‐main sequence evolutionary stage suggests to assume that pulsations are the reason for the observed short‐time spectroscopic and photemetric variations. Possibly, the 1.61‐day period is also caused by pulsations.
Beobachtungen Kleiner Planeten. V
Authors: Börngen F. , Kirsch K. 
Published: July 2007

AbstractEs wird eine übersicht über die im Jahr 1984 auf Tautenburger Schmidtplatten gefundenen Kleinen Planeten gegeben. Es wurden 84 Objekte entdeckt und für sie 205 Positionen gerechnet. Darunter sind 17 numerierte Planeten, 16 bereits früher beobachtete und 51 neue Planeten mit provisorischen Bezeichnungen. Für sieben im Berichtszeitraum numerierte Planeten haben Tautenburger Beobachtungen einen Beitrag geleistetet. Der in Tautenburg entdeckte Planet 1964 EC erheilt die permanente Beziechnung (3181). Er bekam zu Ehren von Dr. PAUL AHNERT (*22. 11. 1897) den Namen Ahnert.
Positions of extragalactic objects in the vicinity of M3 and M31 (5C3 radio field) and in the 5C1 radio field
Authors: Dick W. R. , Lorenz H. , Notni P. , Schilbach E. , Scholz R.‐D. , Richter G. A. 
Published: July 2007

AbstractWe have determined the positions of 65 compact extragalactic objects with magnitudes between 16m and 21m.7. The mean error of one position is about 0″.3 in α cos δ and in δ. Some hitherto unpublished redshifts are also listed.
Eigenschaften singularitätenfreier, statischer, zentralsymmetrischer Lösungen gewisser Gravitationsfeldgleichungen 4. Ordnung
Authors: Schmidt H.‐J. , Fiedler B. , Günther M. 
Published: July 2007

AbstractVon FIEDLER und SCHIMMING (1983) wurde bewiesen, daß die von TREDER vorgeschlagenen Gravitationsfeldgleichungen 4. Ordnung mit einer Linearkombination des Bachtensors und des Einsteintensors auf der linken Seite statische, zentralsymmetrische Lösungen besitzen, welche in einer Umgebung des Symmetriezentrums analytisch und nicht flach sind. Die zunrchst nur in einer kleinen Umgebung von r = o gesicherten Existenz dieser Lösungen (r Radius) läßt sich nun mit Hilfe des abstrakten Satzes über inverse Funktionen auf Intervalle o ≦ r ≦ α mit beliebig groß vorgegebenem α ausdehnen. Ferner wird gezeigt, daß die Schwarzschildmetriken in einem gewissen Sinn die einzigen um r = +∞ analytischen, asymptotisch flachen, statischen, zentralsymmetrischen Lösungen obiger Gleichungen sind.
Extended thermodynamics in the early Universe
Authors: Lukács B. , Martinás K. , Pacher T. 
Published: July 2007

AbstractIt is a general belief that in some early stages of the evolution of the Universe unequilibrium situations played important role. In order to incorporate some deviations from thermal equilibrium into the description of the evolution, here an extension of the thermodynamic formalism is given, where, using the notion of ekaentropy, new terms are introduced into the Gibbs‐Duhem relation for representing the deviation. Two situations are investigated in simplified models: the primordial thermalisation in the symmetric phase of GUT, and the development of a nonthermal distribution for massive neutrinos.
Effective resonant formation of 20Ne in stars
Authors: Md. Khairozzaman A. E. 
Published: July 2007

AbstractThe resonant reaction rates of 16O(α, γ)20Ne have been determined for the 5.64(3‐) MeV 5.8(1‐) MeV excited states of 20Ne under strong screening conditions utilizing the temperature‐density plots of the helium plasma after ITOH et al. (1977). The screened reaction rates were found to be many times greater than the unscreened ones. It has been found that the most effective resonant formation of 20Ne takes place at density 108 g cm‐3. As the density increases beyond 108 g cm‐3 with corresponding rise of temperature the screened reaction rates (i. e. effective reaction rates) decrease. Such a decrease affects the presupernova yields from massive stars drastically The giant and dwarf stage of stellar evolution under pycnonuclear density conditions (108‐‐109 g cm‐3) will be retarded beyond the density of 108 g cm‐3 in stellar interiors.
Deviation of the Cosmic Background Radiation from a black‐body spectrum due to axion‐electromagnetic coupling
Authors: Wolf C. 
Published: July 2007

AbstractThe low energy coupling of the electromagnetic field to the axion leads to two distinct dispersion relations for the electromagneticaxion oscillations. The one frequency being the normal electromagnetic (E. M.) oscillation while the other represents a coupled oscillation. When a non‐zero chemical potential is associated with the axion‐electromagnetic oscillation and the spectrum of the two oscillations are super‐imposed, a formula emerges that suggests how the Cosmic Background Radiation (C.B.R.) might differ from that of a black body if axions do in fact couple to the background radiation.
On the space‐time structure and its relation to quantum mechanics
Authors: Kasper U. 
Published: July 2007

AbstractThe Weyl covariant formulation of Dirac's equation by means of a rest mass the Weyl type of which is — 1, implies the introduction of a Riemann structure in addition to the Weyl structure. The Ehlers‐Pirani‐Schild attempt to specify the space‐time structure and the lowest order of the WKB approximation are compatible with each other. Only the requirement that the connection to which the Dirac field couples minimally is identical to the connection the autoparallels of which are the world lines of structure‐less test particles, leads to a reduction of the Weyl structure to the Riemannian one.
Gauge‐invariant perturbations in generalized inflation
Authors: Matarrese S. 
Published: July 2007

AbstractOne considers the birth and evolution of scalar and tensor gauge‐invariant perturbations in “generalized inflationary models”, that is cosmological models with a suitable early phase of accelerated expansion. In this frame the classical analysis that BARDEEN et al. performed for the standard de Sitter inflation is extended to a more general context.
The conformal potential of the stationary axisymmetric vacuum
Authors: Perjés Z. 
Published: July 2007

AbstractIn a stationary axisymmetric vacuum gravitational field, the conformal structure of the 3‐space is determined by the symmetric, trace free and divergence‐less tensor Yir. Using the Killing vector Ki of the axisymmetry, the conformal potential U can be defined by U,i = εijkKjYkrKr. Conversely, the tensor Yik is given algebraically in terms of the gradient U,i of the conformal potential. An attempt is made here to re‐formulate the field equations Rλμ = 0 in terms of the conformal potential. Introducing the Ernst potential as a complex coordinate, the cylindrical radius can be eliminated from the field equations.
Duality rotations and type D solutions of Einstein‐Born‐Infeld theory
Authors: Salazar H. , Garcia D. A. , Plebanski J. F. 
Published: July 2007

AbstractWithin the non‐linear electrodynamics of Born‐Infeld type, constrained by the condition that admits the freedom of the duality rotations the explicit type D solutions, which generalize the charged Taub‐NUT metric with cosmological constant, are constructed. The obtained type D solution exhausts all solutions within the considered class, assumed that the real eigenvectors of the electromagnetic field are aligned along the geodesic and shear‐free principa null directions.
Cometary dust coma models. II. Computer experiments
Authors: Gottlöber S. , Liebscher D.‐E. , Mücket J. P. , Müller V. 
Published: July 2007

AbstractComputer simulations of a cometary dust coma are presented which take into account different distribution functions of the ejected material as well as anisotropic ejection due to the rotation of the nucleus and single active regions on its surface.
Zur Metallhäufigkeit in offenen Sternhaufen
Authors: Götz W. 
Published: July 2007

AbstractEs wurde die starke Streuung der Einzelwerte in der Metallhäufigkeit offener Sternhaufen untersucht und nachgewiesen, daß bei Sternhaufen mit |z| ≦ 0,3 Kpc neben der Abhängigkeit der Metallhäufigkeit vom galaktozentrischen Abstand (RGC) auch eine Beziehung zur galaktischen Länge der Objekte wirksam ist. In offenen Sternhaufen großer Abstände von der galaktischen Ebene (|z| ≧ 0,3 Kpc) gilt jedoch diese Beziehung nicht. Hier ist die Metallhäufigkeit neben ihrer Kopplung mit dem galaktozentrischen Abstand mit der jeweiligen |z|‐Distanz in Verbindung zu bringen.
Some regularization in the N‐body problem
Authors: Diacu F. N. 
Published: July 2007

AbstractWe consider the simultaneous collision of n bodies in the general N‐body problem, 2 ≤ n ≤ N, in the k‐dimensional Euclidian space and eliminate the singularities which arise from that collision in the equations of motion by suitable coordinates and time transformations. The singularity of that solution is removed by throwing the collision instant to infinity. The new equations of motion are therefore defined in the large and they give a better description of the motion near the collision.
On the detectability of distant clusters of galaxies
Authors: Von Berlepsch R. , Fröhlich H.‐E. , Schmidt K.‐H. 
Published: July 2007

AbstractJ‐magnitude limits (KRON'S J) which have to be reached to detect a cluster of galaxies of given redshift (up to z ≊ 1) and richness class against the background of field galaxies are given.
The forest of QSO absorption lines and cosmological models with unstable dark matter
Authors: Müller V. , Mücket J. P. , Haubold H. J. 
Published: July 2007

AbstractIndications on clustering features in the two‐point correlation function of Ly α line separations in published high‐resolution spectra of quasars are presented. They are in contradiction to the self‐similar hierarchical clustering model, but they could be explained by a first generation of small‐scale pancakes in a model with unstable dark matter. A characteristic scale of velocity dispersion Δv ≈ 150 km/s of absorption clouds within pancakes is described by corresponding coherent regions of positive correlation, while the structure adjacent on the lines of sight are separated by a comoving distance of (18 ± 6) Mpc (H0 = 50 km/s Mpc). The appropriate coherence length of the fluctuation spectrum may result from the free streaming length of (unstable) neutrinos of (100 … 200) eV rest mass.
On the problem of secular variability in the stellar initial mass function
Authors: Meusinger H. 
Published: July 2007

AbstractThe hypothesis of secular variations in the stellar initial mass function (IMF) is studied. It is found that neither the present‐day mass function of the nearby main sequence field stars nor the velocity distribution of these stars are contradictory with this hypothesis. The luminosity functions of unbiased kinematically defined age‐groups of the nearby stars also provide no strong constraints. Simple evolution models with time‐dependent IMF and star formation rate enable to fit the data of blue irregular galaxies. Some problems with an universal IMF are pointed out.
Analysis of light curves produced by surface inhomogeneities on magnetic CP stars
Authors: Hempelmann A. , Schöneich W. 
Published: July 2007

AbstractThe problem of the determination of surface brightness distribution parameters from the observed CP2‐star variability, usually explained with the “oblique rotator model”, is discussed.A simple geometrical model of the surface brightness distribution is derived from the common properties of the observed light curves of these stars. This “spot model” which is supported from the known facts concerning the magnetic field structure and the surface distributions of chemical elements serves as a basis of the special inverse problem: the determination of the number of large scale inhomogeneities, their locations and extents and further parameters, from all the observed light curves of a given star.A suitable technique for solving the special inverse problem is explained. The problem of ambiguity which even arises for the proposed simple model and, in connection with that, the remaining possibilities to win the relevant information on the inhomogeneities of surface brightness are discussed. For the purpose of illustration, the result of the light curve analysis of the CP2 star HD 8441 is given.