6,366 research outputs found
A survey of spinning test particle orbits in Kerr spacetime
We investigate the dynamics of the Papapetrou equations in Kerr spacetime.
These equations provide a model for the motion of a relativistic spinning test
particle orbiting a rotating (Kerr) black hole. We perform a thorough parameter
space search for signs of chaotic dynamics by calculating the Lyapunov
exponents for a large variety of initial conditions. We find that the
Papapetrou equations admit many chaotic solutions, with the strongest chaos
occurring in the case of eccentric orbits with pericenters close to the limit
of stability against plunge into a maximally spinning Kerr black hole. Despite
the presence of these chaotic solutions, we show that physically realistic
solutions to the Papapetrou equations are not chaotic; in all cases, the
chaotic solutions either do not correspond to realistic astrophysical systems,
or involve a breakdown of the test-particle approximation leading to the
Papapetrou equations (or both). As a result, the gravitational radiation from
bodies spiraling into much more massive black holes (as detectable, for
example, by LISA, the Laser Interferometer Space Antenna) should not exhibit
any signs of chaos.Comment: Submitted to Phys. Rev. D. Follow-up to gr-qc/0210042. Figures are
low-resolution in order to satisfy archive size constraints; a
high-resolution version is available at http://www.michaelhartl.com/papers
Widely-tunable mid-IR frequency comb source based on difference frequency generation
We report on a mid-infrared frequency comb source of unprecedented tunability
covering the entire 3-10 {\mu}m molecular fingerprint region. The system is
based on difference frequency generation in a GaSe crystal pumped by a 151 MHz
Yb:fiber frequency comb. The process was seeded with Raman shifted solitons
generated in a highly nonlinear suspended-core fiber with the same source.
Average powers up to 1.5 mW were achieved at 4.7 {\mu}m wavelength.Comment: 3 pages, 3 figure
Orbital evolution of a particle around a black hole: II. Comparison of contributions of spin-orbit coupling and the self force
We consider the evolution of the orbit of a spinning compact object in a
quasi-circular, planar orbit around a Schwarzschild black hole in the extreme
mass ratio limit. We compare the contributions to the orbital evolution of both
spin-orbit coupling and the local self force. Making assumptions on the
behavior of the forces, we suggest that the decay of the orbit is dominated by
radiation reaction, and that the conservative effect is typically dominated by
the spin force. We propose that a reasonable approximation for the
gravitational waveform can be obtained by ignoring the local self force, for
adjusted values of the parameters of the system. We argue that this
approximation will only introduce small errors in the astronomical
determination of these parameters.Comment: 11 pages, 7 figure
Error threshold in the evolution of diploid organisms
The effects of error propagation in the reproduction of diploid organisms are
studied within the populational genetics framework of the quasispecies model.
The dependence of the error threshold on the dominance parameter is fully
investigated. In particular, it is shown that dominance can protect the
wild-type alleles from the error catastrophe. The analysis is restricted to a
diploid analogue of the single-peaked landscape.Comment: 9 pages, 4 Postscript figures. Submitted to J. Phy. A: Mat. and Ge
Failure of RQC machinery causes protein aggregation and proteotoxic stress
Translation of messenger RNAs lacking a stop codon results in the addition of a carboxy-terminal poly-lysine tract to the nascent polypeptide, causing ribosome stalling. Non-stop proteins and other stalled nascent chains are recognized by the ribosome quality control (RQC) machinery and targeted for proteasomal degradation. Failure of this process leads to neurodegeneration by unknown mechanisms. Here we show that deletion of the E3 ubiquitin ligase Ltn1p in yeast, a key RQC component, causes stalled proteins to form detergent-resistant aggregates and inclusions. Aggregation is dependent on a C-terminal alanine/threonine tail that is added to stalled polypeptides by the RQC component, Rqc2p. Formation of inclusions additionally requires the poly-lysine tract present in non-stop proteins. The aggregates sequester multiple cytosolic chaperones and thereby interfere with general protein quality control pathways. These findings can explain the proteotoxicity of ribosome-stalled polypeptides and demonstrate the essential role of the RQC in maintaining proteostasis
Temporal and dimensional effects in evolutionary graph theory
The spread in time of a mutation through a population is studied analytically
and computationally in fully-connected networks and on spatial lattices. The
time, t_*, for a favourable mutation to dominate scales with population size N
as N^{(D+1)/D} in D-dimensional hypercubic lattices and as N ln N in
fully-connected graphs. It is shown that the surface of the interface between
mutants and non-mutants is crucial in predicting the dynamics of the system.
Network topology has a significant effect on the equilibrium fitness of a
simple population model incorporating multiple mutations and sexual
reproduction. Includes supplementary information.Comment: 6 pages, 4 figures Replaced after final round of peer revie
On a Conjecture of Rapoport and Zink
In their book Rapoport and Zink constructed rigid analytic period spaces
for Fontaine's filtered isocrystals, and period morphisms from PEL
moduli spaces of -divisible groups to some of these period spaces. They
conjectured the existence of an \'etale bijective morphism of
rigid analytic spaces and of a universal local system of -vector spaces on
. For Hodge-Tate weights and we construct in this article an
intrinsic Berkovich open subspace of and the universal local
system on . We conjecture that the rigid-analytic space associated with
is the maximal possible , and that is connected. We give
evidence for these conjectures and we show that for those period spaces
possessing PEL period morphisms, equals the image of the period morphism.
Then our local system is the rational Tate module of the universal
-divisible group and enjoys additional functoriality properties. We show
that only in exceptional cases equals all of and when the
Shimura group is we determine all these cases.Comment: v2: 48 pages; many new results added, v3: final version that will
appear in Inventiones Mathematica
SMaSH: A Benchmarking Toolkit for Human Genome Variant Calling
Motivation: Computational methods are essential to extract actionable
information from raw sequencing data, and to thus fulfill the promise of
next-generation sequencing technology. Unfortunately, computational tools
developed to call variants from human sequencing data disagree on many of their
predictions, and current methods to evaluate accuracy and computational
performance are ad-hoc and incomplete. Agreement on benchmarking variant
calling methods would stimulate development of genomic processing tools and
facilitate communication among researchers.
Results: We propose SMaSH, a benchmarking methodology for evaluating human
genome variant calling algorithms. We generate synthetic datasets, organize and
interpret a wide range of existing benchmarking data for real genomes, and
propose a set of accuracy and computational performance metrics for evaluating
variant calling methods on this benchmarking data. Moreover, we illustrate the
utility of SMaSH to evaluate the performance of some leading single nucleotide
polymorphism (SNP), indel, and structural variant calling algorithms.
Availability: We provide free and open access online to the SMaSH toolkit,
along with detailed documentation, at smash.cs.berkeley.edu
An aperture masking mode for the MICADO instrument
MICADO is a near-IR camera for the Europea ELT, featuring an extended field
(75" diameter) for imaging, and also spectrographic and high contrast imaging
capabilities. It has been chosen by ESO as one of the two first-light
instruments. Although it is ultimately aimed at being fed by the MCAO module
called MAORY, MICADO will come with an internal SCAO system that will be
complementary to it and will deliver a high performance on axis correction,
suitable for coronagraphic and pupil masking applications. The basis of the
pupil masking approach is to ensure the stability of the optical transfer
function, even in the case of residual errors after AO correction (due to non
common path errors and quasi-static aberrations). Preliminary designs of pupil
masks are presented. Trade-offs and technical choices, especially regarding
redundancy and pupil tracking, are explained.Comment: SPIE 2014 Proceeding -- Montrea
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