104 research outputs found
Highly accurate calculation of rotating neutron stars: Detailed description of the numerical methods
We give a detailed description of the recently developed multi-domain
spectral method for constructing highly accurate general-relativistic models of
rapidly rotating stars. For both "ordinary" and "critical" configurations, it
is exhibited by means of representative examples, how the accuracy improves as
the order of the approximation increases. Apart from homogeneous fluid bodies,
we also discuss models of polytropic and strange stars.Comment: 22 pages, 4 figures, 9 tables, version accepted by A&
Equilibrium Configurations of Homogeneous Fluids in General Relativity
By means of a highly accurate, multi-domain, pseudo-spectral method, we
investigate the solution space of uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies. It turns out that this space can be
divided up into classes of solutions. In this paper, we present two new classes
including relativistic core-ring and two-ring solutions. Combining our
knowledge of the first four classes with post-Newtonian results and the
Newtonian portion of the first ten classes, we present the qualitative
behaviour of the entire relativistic solution space. The Newtonian disc limit
can only be reached by going through infinitely many of the aforementioned
classes. Only once this limiting process has been consummated, can one proceed
again into the relativistic regime and arrive at the analytically known
relativistic disc of dust.Comment: 8 pages, colour figures, v3: minor additions including one reference,
accepted by MNRA
Sulfur is limiting the glucosinolate accumulation in nasturtium in vitro plants (Tropaeolum majus L.)
It is well established that sulfate fertilisation significantly enhances the content of mustard oil glucosides in glucosinolate containing plants. However, with respect to tissue cultures and in vitro-plants, corresponding data are missing. In this study the influence of sulfur on the accumulation of glucosinolates was analyzed in nasturtium in vitro-plants (Tropaeolum majus). The glucotropaeolin content in plants grown on standard media (MS) varied between 10 and 50 ÎĽmol/g DW, corresponding to only about 20 % to 70 % of the glucotropaeolin content in earth grown plants. A fivefold enhancement of the sulfate concentration resulted in a massive increase in the glucotropaeolin content of the in vitro-plants. A decline of sulfate in the medium leads to corresponding diminutions of the glucosinolates accumulated. These data clearly demonstrate the high impact of sulfur availability on glucosinolate biosynthesis and accumulation
Collisions of rigidly rotating disks of dust in General Relativity
We discuss inelastic collisions of two rotating disks by using the
conservation laws for baryonic mass and angular momentum. In particular, we
formulate conditions for the formation of a new disk after the collision and
calculate the total energy loss to obtain upper limits for the emitted
gravitational energy.Comment: 30 pages, 9 figure
Relativistic Dyson Rings and Their Black Hole Limit
In this Letter we investigate uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies with a toroidal shape. The corresponding
field equations are solved by means of a multi-domain spectral method, which
yields highly accurate numerical solutions. For a prescribed, sufficiently
large ratio of inner to outer coordinate radius, the toroids exhibit a
continuous transition to the extreme Kerr black hole. Otherwise, the most
relativistic configuration rotates at the mass-shedding limit. For a given
mass-density, there seems to be no bound to the gravitational mass as one
approaches the black-hole limit and a radius ratio of unity.Comment: 13 pages, 1 table, 5 figures, v2: some discussion and two references
added, accepted for publication in Astrophys. J. Let
Experimental field cultivation of in vitro propagated high-yield varieties of Tropaeolum majus L.
About 10,000 mass propagated clonal progenies of the medicinal plant Tropaeolum majus L. had been cultivated in an experimental field trial to analyze the large scale cultivation of nasturtium-plants for pharmaceutical utilization. The glucotropaeolin contents of the eight Tropaeolum-clones, which had been established and propagated by in vitro-culture techniques, had been monitored and compared with unselected plants from commercial seed mixtures (sm-plants). Whereas the intra-clonal variation of the glucosinolate levels was significantly lower than the variability of the sm-plants, the glucotropaeolin content in the clonal progenies was markedly lower than in both, in the clonal mother plants as well as in the sm-plants. The proposed explanation for this phenomenon is based on the fact that the genetically identical cloned plants reveal only a very narrow phenotypical amplitude, which accordingly resulted in designated glucosinolate levels due to the certain environmental situations. However, under changing conditions, the corresponding glucotropaeolin content might be much lower. In contrast, the sm-plants reveal – due to the strong genetic heterogeneity – a much broader phenotypical amplitude of their physiological characteristics. Consequently, under changing growth conditions various individual plants may accumulate high amounts of glucotropaeolin. These coherences explain both, firstly, the finding that the clonal mother plants revealed very high glucotropaeolin levels under the certain – maybe spatial limited cultivation conditions – whereas their progenies accumulate far less glucosinolates; and secondly, that the average content in the sm-plants is higher than the mean content of the clonal progenies.These data suggest that the much cheaper growing of nasturtium plants from seeds should be favoured over the more sophisticated in vitro-propagation techniques. Anyhow, for industrial farming there is one great advantage for the usage of in vitro generated Tropaeolum plants: the selected, high glucosinolate-nasturtium clones all reveal a compact growth with short tendrils. Therefore, the mechanical harvest of the corresponding clonal progenies, is quite unproblematic in comparison to the difficile harvest of sm-plants, most exhibiting tendrils of several meters
Differentially rotating disks of dust
We present a three-parameter family of solutions to the stationary
axisymmetric Einstein equations that describe differentially rotating disks of
dust. They have been constructed by generalizing the Neugebauer-Meinel solution
of the problem of a rigidly rotating disk of dust. The solutions correspond to
disks with angular velocities depending monotonically on the radial coordinate;
both decreasing and increasing behaviour is exhibited. In general, the
solutions are related mathematically to Jacobi's inversion problem and can be
expressed in terms of Riemann theta functions. A particularly interesting
two-parameter subfamily represents Baecklund transformations to appropriate
seed solutions of the Weyl class.Comment: 14 pages, 3 figures. To appear in "General Relativity and
Gravitation". Second version with minor correction
Phase transitions in open quantum systems
We consider the behaviour of open quantum systems in dependence on the
coupling to one decay channel by introducing the coupling parameter
being proportional to the average degree of overlapping. Under critical
conditions, a reorganization of the spectrum takes place which creates a
bifurcation of the time scales with respect to the lifetimes of the resonance
states. We derive analytically the conditions under which the reorganization
process can be understood as a second-order phase transition and illustrate our
results by numerical investigations. The conditions are fulfilled e.g. for a
picket fence with equal coupling of the states to the continuum. Energy
dependencies within the system are included. We consider also the generic case
of an unfolded Gaussian Orthogonal Ensemble. In all these cases, the
reorganization of the spectrum occurs at the critical value of
the control parameter globally over the whole energy range of the spectrum. All
states act cooperatively.Comment: 28 pages, 22 Postscript figure
Dirichlet Boundary Value Problems of the Ernst Equation
We demonstrate how the solution to an exterior Dirichlet boundary value
problem of the axisymmetric, stationary Einstein equations can be found in
terms of generalized solutions of the Backlund type. The proof that this
generalization procedure is valid is given, which also proves conjectures about
earlier representations of the gravitational field corresponding to rotating
disks of dust in terms of Backlund type solutions.Comment: 22 pages, to appear in Phys. Rev. D, Correction of a misprint in
equation (4
Interfering Doorway States and Giant Resonances. I: Resonance Spectrum and Multipole Strengths
A phenomenological schematic model of multipole giant resonances (GR) is
considered which treats the external interaction via common decay channels on
the same footing as the coherent part of the internal residual interaction. The
damping due to the coupling to the sea of complicated states is neglected. As a
result, the formation of GR is governed by the interplay and competition of two
kinds of collectivity, the internal and the external one. The mixing of the
doorway components of a GR due to the external interaction influences
significantly their multipole strengths, widths and positions in energy. In
particular, a narrow resonance state with an appreciable multipole strength is
formed when the doorway components strongly overlap.Comment: 20 pages, LaTeX, 3 ps-figures, to appear in PRC (July 1997
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