1,344 research outputs found
Rotating Boson Stars and Q-Balls
We consider axially symmetric, rotating boson stars. Their flat space limits
represent spinning Q-balls. We discuss their properties and determine their
domain of existence. Q-balls and boson stars are stationary solutions and exist
only in a limited frequency range. The coupling to gravity gives rise to a
spiral-like frequency dependence of the boson stars. We address the flat space
limit and the limit of strong gravitational coupling. For comparison we also
determine the properties of spherically symmetric Q-balls and boson stars.Comment: 22 pages, 18 figure
On the Existence of Energy-Preserving Symplectic Integrators Based upon Gauss Collocation Formulae
We introduce a new family of symplectic integrators depending on a real
parameter. When the paramer is zero, the corresponding method in the family
becomes the classical Gauss collocation formula of order 2s, where s denotes
the number of the internal stages. For any given non-null value of the
parameter, the corresponding method remains symplectic and has order 2s-2:
hence it may be interpreted as an order 2s-2 (symplectic) perturbation of the
Gauss method. Under suitable assumptions, we show that the free parameter may
be properly tuned, at each step of the integration procedure, so as to
guarantee energy conservation in the numerical solution. The resulting
symplectic, energy conserving method shares the same order 2s as the generating
Gauss formula.Comment: 19 pages, 7 figures; Sections 1, 2, and 6 sliglthly modifie
Black strings in (4+1)-dimensional Einstein-Yang-Mills theory
We study two classes of static uniform black string solutions in a
(4+1)-dimensional SU(2) Einstein-Yang-Mills model. These configurations possess
a regular event horizon and corresponds in a 4-dimensional picture to axially
symmetric black hole solutions in an Einstein-Yang-Mills-Higgs-U(1)-dilaton
theory. In this approach, one set of solutions possesses a nonzero magnetic
charge, while the other solutions represent black holes located in between a
monopole-antimonopole pair. A detailed analysis of the solutions' properties is
presented, the domain of existence of the black strings being determined. New
four dimensional solutions are found by boosting the five dimensional
configurations. We also present an argument for the non-existence of finite
mass hyperspherically symmetric black holes in SU(2) Einstein-Yang-Mills
theory.Comment: 19 Revtex pages, 27 eps-figures; discussion on rotating black holes
modifie
Einstein-Yang-Mills solutions in higher dimensional de Sitter spacetime
We consider particle-like and black holes solutions of the
Einstein-Yang-Mills system with positive cosmological constant in d>4 spacetime
dimensions. These configurations are spherically symmetric and present a
cosmological horizon for a finite value of the radial coordinate, approaching
asymptotically the de Sitter background. In the usual Yang--Mills case we find
that the mass of these solutions, evaluated outside the cosmological horizon at
future/past infinity generically diverges for d>4. Solutions with finite mass
are found by adding to the action higher order gauge field terms belonging to
the Yang--Mills hierarchy. A discussion of the main properties of these
solutions and their differences from those to the usual Yang-Mills model, both
in four and higher dimensions is presented.Comment: 17 pages, 8 figure
Zur Diagnostik des Diabetes insipidus unter besonderer BerĂŒcksichtigung hypophysektomierter Patienten
Verschiedene, am gleichen Patienten durchgefĂŒhrte Stimulationsteste fĂŒr die ADH-Sekretion (17-Std.-Durstversuch, Carter-Robbins-Test, osmotische Diurese) zeigen eine ausgezeichnete Korrelation. Auf Grund dieser Ergebnisse werden Richtlinien zur möglichst einfachen Diagnostik einer Konzentrationsstörung vorgeschlagen. In den meisten FĂ€llen kann allein schon auf Grund eines exakt durchgefĂŒhrten Durstversuchs eine Konzentrationsstörung nachgewiesen (höchste UrinosmolalitĂ€t 750 mOsm/kg) werden. Lediglich bei einer höchsten UrinosmolalitĂ€t im 17-Std.-Durstversuch zwischen 500 und 750 mOsm/kg mĂŒssen aufwendigere und den Patienten mehr belastende Tests (z. B. Carter-Robbins-Test) eingesetzt werden, um das Vorliegen bzw. den Grad einer Konzentrationsstörung endgĂŒltig diagnostizieren zu können. ADH-Injektionen dienen dabei zur Differenzierung zwischen einem ADH-Mangel und einer mangelhaften ADH-Ansprechbarkeit der Niere. Unsere Untersuchungen an hypophysektomierten Patienten (N=29) zeigen auch bei Patienten ohne polyurisch-polydiptisches Syndrom (N=22) eine gegenĂŒber Normalpersonen signifikant eingeschrĂ€nkte Konzentrationsleistung im 17-Std.-Durstversuch.The results of three different stimulation tests for ADH (17 hours thirst period, Carter-Robbins-test, osmotic diuresis) correlate well in the same patient. Because of this we propose a simplified procedure for the detection of failure to produce a concentrated urine. In most cases merely on the basis of a precisely executed thirst period test, one can either recognize an abnormality of concentration (highest urine osmolality less than 500 mOsm/kg), or exlude it (highest urine osmolality greater than 750 mOsm/kg). Only when the highest urine osmolality lies between 500 and 750 mOsm/kg after a 17 hour thirst must more painstaking tests (e.g. Carter-Robbins test) be employed to determine both the presence of and the degree of a failure to produce a concentrated urine. An injection of ADH can be used to differentiate between a deficiency of ADH and a defective response of the kidneys to ADH. Our investigations on hypophysectomized patients (n=29) showed that also in patients without the syndrome of polyuria-polydypsia (n=22), there was a significantly reduced capacity to concentrate urine during a 17 hour thirst period, as compared with normal people
High density QCD on a Lefschetz thimble?
It is sometimes speculated that the sign problem that afflicts many quantum
field theories might be reduced or even eliminated by choosing an alternative
domain of integration within a complexified extension of the path integral (in
the spirit of the stationary phase integration method). In this paper we start
to explore this possibility somewhat systematically. A first inspection reveals
the presence of many difficulties but - quite surprisingly - most of them have
an interesting solution. In particular, it is possible to regularize the
lattice theory on a Lefschetz thimble, where the imaginary part of the action
is constant and disappears from all observables. This regularization can be
justified in terms of symmetries and perturbation theory. Moreover, it is
possible to design a Monte Carlo algorithm that samples the configurations in
the thimble. This is done by simulating, effectively, a five dimensional
system. We describe the algorithm in detail and analyze its expected cost and
stability. Unfortunately, the measure term also produces a phase which is not
constant and it is currently very expensive to compute. This residual sign
problem is expected to be much milder, as the dominant part of the integral is
not affected, but we have still no convincing evidence of this. However, the
main goal of this paper is to introduce a new approach to the sign problem,
that seems to offer much room for improvements. An appealing feature of this
approach is its generality. It is illustrated first in the simple case of a
scalar field theory with chemical potential, and then extended to the more
challenging case of QCD at finite baryonic density.Comment: Misleading footnote 1 corrected: locality deserves better
investigations. Formula (31) corrected (we thank Giovanni Eruzzi for this
observation). Note different title in journal versio
Effect of Cattail (Typha domingensis) Extracts, Leachates, and Selected Phenolic Compounds on Rates of Oxygen Production by Salvinia (Salvinia minima)
Salvinia (Salvinia minima Willd.) is a water fern found in Florida waters, usually associated with Lemna and other small free-floating species. Due to its buoyancy and mat-forming abilities, it is spread by moving waters. In 1994, salvinia was reported to be present in 247 water bodies in the state (out of 451 surveyed public waters, Schardt 1997). It is a small, rapidly growing species that can become a nuisance due to its explosive growth rates and its ability to shade underwater life (Oliver 1993). Any efforts toward management of salvinia populations must consider that, in reasonable amounts, its presence is desirable since it plays an important role in the overall ecosystem balance. New management alternatives need to be explored besides the conventional herbicide treatments; for example, it has been shown that the growth of S. molesta can be inhibited by extracts of the tropical weed parthenium (Parthenium hysterophorus) and its purified toxin parthenin (Pande 1994, 1996).
We believe that cattail, Typha spp. may be a candidate for control of S. minima infestations. Cattail is an aggressive aquatic plant, and has the ability to expand over areas that weren't previously occupied by other species (Gallardo et al. 1998a and references cited there). In South Florida, T. domingensis is a natural component of the Everglades ecosystem, but in many cases it has become the dominant marsh species, outcompeting other native plants. In Florida public waters, this cattail species is the most dominant emergent species of aquatic plants (Schardt 1997). Several factors enable it to accomplish opportunistic expansion, including size, growth habits, adaptability to changes in the surroundings, and the release of compounds that can prevent the growth and development of other species.
We have been concerned in the past with the inhibitory effects of the T. domingensis extracts, and the phenolic compounds mentioned before, towards the growth and propagation of S. minima (Gallardo et al. 1998b). This investigation deals with the impact of cattail materials on the rates of oxygen production of salvinia, as determined through a series of Warburg experiments (Martin et al. 1987, Prindle and Martin 1996)
Precision Mass Measurements of 129-131Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process
Masses adjacent to the classical waiting-point nuclide 130Cd have been
measured by using the Penning- trap spectrometer ISOLTRAP at ISOLDE/CERN. We
find a significant deviation of over 400 keV from earlier values evaluated by
using nuclear beta-decay data. The new measurements show the reduction of the N
= 82 shell gap below the doubly magic 132Sn. The nucleosynthesis associated
with the ejected wind from type-II supernovae as well as from compact object
binary mergers is studied, by using state-of-the-art hydrodynamic simulations.
We find a consistent and direct impact of the newly measured masses on the
calculated abundances in the A = 128 - 132 region and a reduction of the
uncertainties from the precision mass input data
Sharp interface limits of phase-field models
The use of continuum phase-field models to describe the motion of
well-defined interfaces is discussed for a class of phenomena, that includes
order/disorder transitions, spinodal decomposition and Ostwald ripening,
dendritic growth, and the solidification of eutectic alloys. The projection
operator method is used to extract the ``sharp interface limit'' from phase
field models which have interfaces that are diffuse on a length scale . In
particular,phase-field equations are mapped onto sharp interface equations in
the limits and , where and are
respectively the interface curvature and velocity and is the diffusion
constant in the bulk. The calculations provide one general set of sharp
interface equations that incorporate the Gibbs-Thomson condition, the
Allen-Cahn equation and the Kardar-Parisi-Zhang equation.Comment: 17 pages, 9 figure
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