357 research outputs found
On the steady states of the spherically symmetric Einstein-Vlasov system
Using both numerical and analytical tools we study various features of
static, spherically symmetric solutions of the Einstein-Vlasov system. In
particular, we investigate the possible shapes of their mass-energy density and
find that they can be multi-peaked, we give numerical evidence and a partial
proof for the conjecture that the Buchdahl inequality , the quasi-local mass, holds for all such steady states--both
isotropic {\em and} anisotropic--, and we give numerical evidence and a partial
proof for the conjecture that for any given microscopic equation of state--both
isotropic {\em and} anisotropic--the resulting one-parameter family of static
solutions generates a spiral in the radius-mass diagram.Comment: 34 pages, 18 figures, LaTe
Sharp bounds on 2m/r for static spherical objects
Sharp bounds are obtained, under a variety of assumptions on the eigenvalues
of the Einstein tensor, for the ratio of the Hawking mass to the areal radius
in static, spherically symmetric space-times.Comment: We changed a footnote in which an earlier result of H\aa{}kan
Andr\'{e}asson was not described correctl
A numerical investigation of the stability of steady states and critical phenomena for the spherically symmetric Einstein-Vlasov system
The stability features of steady states of the spherically symmetric
Einstein-Vlasov system are investigated numerically. We find support for the
conjecture by Zeldovich and Novikov that the binding energy maximum along a
steady state sequence signals the onset of instability, a conjecture which we
extend to and confirm for non-isotropic states. The sign of the binding energy
of a solution turns out to be relevant for its time evolution in general. We
relate the stability properties to the question of universality in critical
collapse and find that for Vlasov matter universality does not seem to hold.Comment: 29 pages, 10 figure
Global existence for the spherically symmetric Einstein-Vlasov system with outgoing matter
We prove a new global existence result for the asymptotically flat,
spherically symmetric Einstein-Vlasov system which describes in the framework
of general relativity an ensemble of particles which interact by gravity. The
data are such that initially all the particles are moving radially outward and
that this property can be bootstrapped. The resulting non-vacuum spacetime is
future geodesically complete.Comment: 16 page
Sharp bounds on the critical stability radius for relativistic charged spheres
In a recent paper by Giuliani and Rothman \cite{GR}, the problem of finding a
lower bound on the radius of a charged sphere with mass M and charge Q<M is
addressed. Such a bound is referred to as the critical stability radius.
Equivalently, it can be formulated as the problem of finding an upper bound on
M for given radius and charge. This problem has resulted in a number of papers
in recent years but neither a transparent nor a general inequality similar to
the case without charge, i.e., M\leq 4R/9, has been found. In this paper we
derive the surprisingly transparent inequality
The
inequality is shown to hold for any solution which satisfies
where and are the radial- and tangential pressures respectively
and is the energy density. In addition we show that the inequality
is sharp, in particular we show that sharpness is attained by infinitely thin
shell solutions.Comment: 20 pages, 1 figur
On the area of the symmetry orbits in symmetric spacetimes with Vlasov matter
This paper treats the global existence question for a collection of general
relativistic collisionless particles, all having the same mass. The spacetimes
considered are globally hyperbolic, with Cauchy surface a 3-torus. Furthermore,
the spacetimes considered are isometrically invariant under a two-dimensional
group action, the orbits of which are spacelike 2-tori. It is known from
previous work that the area of the group orbits serves as a global time
coordinate. In the present work it is shown that the area takes on all positive
values in the maximal Cauchy development.Comment: 27 pages, version 2 minor changes and correction
Existence of initial data satisfying the constraints for the spherically symmetric Einstein-Vlasov-Maxwell system
Using ODE techniques we prove the existence of large classes of initial data
satisfying the constraints for the spherically symmetric
Einstein-Vlasov-Maxwell system. These include data for which the ratio of total
charge to total mass is arbitrarily large.Comment: 12 page
Optimal consumption, investment and housing with means-tested public pension in retirement
© 2017 Elsevier B.V. In this paper, we develop an expected utility model for retirement behaviour in the decumulation phase of Australian retirees with sequential family status subject to consumption, housing, investment, bequest, and government-provided means-tested Age Pension. We account for mortality risk and risky investment assets, and we introduce a âhealthâ proxy to capture the decreasing level of consumption for older retirees. Then, we find the optimal housing at retirement, the optimal consumption and optimal risky asset allocation depending on age and wealth. The model is solved numerically as a stochastic control problem, and it is calibrated using the maximum likelihood method with empirical data of consumption and housing from the Australian Bureau of Statistics 2009â2010 Survey. The model fits the characteristics of the data well to explain the behaviour of Australian retirees. The key findings are as follows. First, the optimal policy is highly sensitive to means-tested Age Pension early in retirement, but this sensitivity fades with age. Second, the allocation to risky assets shows a complex relationship with the means-tested Age Pension. As a general rule, when wealth decreases, the proportion allocated to risky assets increases, because the Age Pension works as a buffer against investment losses. Third, couples can be more aggressive with risky allocations owing to their longer life expectancy compared with singles
Isolation and properties of PS II membrane fragments depleted of the non heme iron center
AbstractThe functional properties and the content of non heme iron and cytochrome b559 were investigated by measuring flash induced transient changes of the relative fluorescence quantum yield and applying Mössbauer spectroscopy. It was found that untreated PS II membrane fragments contain a heterogeneous population of two types of non heme iron centers and about 2 cytochrome b559 per PS II. Twofold treatment of these samples with a recently described âiron depletionâ procedure (MacMillan, F., Lendzian, F., Renger, G. and Lubitz, W. (1995) Biochemistry 34, 3144â8156) leads to a complete loss (below the detection limit of Mössbauer spectroscopy) of the non heme iron center while more than 50% of the PS II complexes retain the functional integrity for light induced formation of the âstableâ radical pair YZOX P680Pheo QAâ.. This sample type deprived of virtually all non heme iron in PS II provides a most suitable material for magnetic resonance studies that require an elimination of the interaction between Fe2+ and nearby radicals
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