4,752 research outputs found
Old Folks and Spoiled Brats:Why the baby Boomers' Saving Crisis Need Not be that Bad
We study the impact of an anticipated "baby boom" in an overlapping generations economy.The rise of the working population lowers the wage, and the high demand for assets causes a rise in the price of capital which will be reversed when the baby boomers leave the work-force.However, the swings in factor prices are substantially dampened if we allow for more than two generations, endogenous labor supply, and convex capital adjustment costs.This is mainly due to the intertemporal shifts in labor market participation that can be observed if agents work for more than one period.Optimal saving and labor supply decisions of the baby boomers' preceding and subsequent generations partly offset the impact of the unfavorable demographic shock.Accordingly, the impact of a baby boom on the welfare of different generations crucially depends on the elasticity of labor supply
BBO and the Neutron-Star-Binary Subtraction Problem
The Big Bang Observer (BBO) is a proposed space-based gravitational-wave (GW)
mission designed primarily to search for an inflation-generated GW background
in the frequency range 0.1-1 Hz. The major astrophysical foreground in this
range is gravitational radiation from inspiraling compact binaries. This
foreground is expected to be much larger than the inflation-generated
background, so to accomplish its main goal, BBO must be sensitive enough to
identify and subtract out practically all such binaries in the observable
universe. It is somewhat subtle to decide whether BBO's current baseline design
is sufficiently sensitive for this task, since, at least initially, the
dominant noise source impeding identification of any one binary is confusion
noise from all the others. Here we present a self-consistent scheme for
deciding whether BBO's baseline design is indeed adequate for subtracting out
the binary foreground. We conclude that the current baseline should be
sufficient. However if BBO's instrumental sensitivity were degraded by a factor
2-4, it could no longer perform its main mission. It is impossible to perfectly
subtract out each of the binary inspiral waveforms, so an important question is
how to deal with the "residual" errors in the post-subtraction data stream. We
sketch a strategy of "projecting out" these residual errors, at the cost of
some effective bandwidth. We also provide estimates of the sizes of various
post-Newtonian effects in the inspiral waveforms that must be accounted for in
the BBO analysis.Comment: corrects some errors in figure captions that are present in the
published versio
Microfield Dynamics of Black Holes
The microcanonical treatment of black holes as opposed to the canonical
formulation is reviewed and some major differences are displayed. In particular
the decay rates are compared in the two different pictures.Comment: 22 pages, 4 figures, Revtex, Minor change in forma
Curve matching with applications in medical imaging
In the recent years, Riemannian shape analysis of curves and surfaces has found several applications in medical image analysis. In this paper we present a numerical discretization of second order Sobolev metrics on the space of regular curves in Euclidean space. This class of metrics has several desirable mathematical properties. We propose numerical solutions for the initial and boundary value problems of finding geodesics. These two methods are combined in a Riemannian gradient-based optimization scheme to compute the Karcher mean. We apply this to a study of the shape variation in HeLa cell nuclei and cycles of cardiac deformations, by computing means and principal modes of variations
A numerical framework for sobolev metrics on the space of curves
Statistical shape analysis can be done in a Riemannian framework by endowing the set of shapes with a Riemannian metric. Sobolev metrics of order two and higher on shape spaces of parametrized or unparametrized curves have several desirable properties not present in lower order metrics, but their discretization is still largely missing. In this paper, we present algorithms to numerically solve the geodesic initial and boundary value problems for these metrics. The combination of these algorithms enables one to compute Karcher means in a Riemannian gradient-based optimization scheme and perform principal component analysis and clustering. Our framework is sufficiently general to be applicable to a wide class of metrics. We demonstrate the effectiveness of our approach by analyzing a collection of shapes representing HeLa cell nuclei.All authors were partially
supported by the Erwin Schr odinger Institute programme: In nite-Dimensional Riemannian Geometry
with Applications to Image Matching and Shape Analysis. M. Bruveris was supported by the BRIEF
award from Brunel University London. M. Bauer was supported by the FWF project \Geometry of
shape spaces and related in nite dimensional spaces" (P246251
Second order elastic metrics on the shape space of curves
Second order Sobolev metrics on the space of regular unparametrized planar curves have several desirable completeness properties not present in lower order metrics, but numerics are still largely missing. In this paper, we present algorithms to numerically solve the initial and boundary value problems for geodesics. The combination of these algorithms allows to compute Karcher means in a Riemannian gradient-based optimization scheme. Our framework has the advantage that the constants determining the weights of the zero, first, and second order terms of the metric can be chosen freely. Moreover, due to its generality, it could be applied to more general spaces of mapping. We demonstrate the effectiveness of our approach by analyzing a collection of shapes representing physical objects
Theoretical survey of tidal-charged black holes at the LHC
We analyse a family of brane-world black holes which solve the effective
four-dimensional Einstein equations for a wide range of parameters related to
the unknown bulk/brane physics. We first constrain the parameters using known
experimental bounds and, for the allowed cases, perform a numerical analysis of
their time evolution, which includes accretion through the Earth. The study is
aimed at predicting the typical behavior one can expect if such black holes
were produced at the LHC. Most notably, we find that, under no circumstances,
would the black holes reach the (hazardous) regime of Bondi accretion.
Nonetheless, the possibility remains that black holes live long enough to
escape from the accelerator (and even from the Earth's gravitational field) and
result in missing energy from the detectors.Comment: RevTeX4, 12 pages, 4 figures, 5 tables, minor changes to match the
accepted version in JHE
Simulation of underground gravity gradients from stochastic seismic fields
We present results obtained from a finite-element simulation of seismic
displacement fields and of gravity gradients generated by those fields. The
displacement field is constructed by a plane wave model with a 3D isotropic
stochastic field and a 2D fundamental Rayleigh field. The plane wave model
provides an accurate representation of stationary fields from distant sources.
Underground gravity gradients are calculated as acceleration of a free test
mass inside a cavity. The results are discussed in the context of
gravity-gradient noise subtraction in third generation gravitational-wave
detectors. Error analysis with respect to the density of the simulated grid
leads to a derivation of an improved seismometer placement inside a 3D array
which would be used in practice to monitor the seismic field.Comment: 24 pages, 12 figure
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