47,407 research outputs found
Orbital evolution of a test particle around a black hole: higher-order corrections
We study the orbital evolution of a radiation-damped binary in the extreme
mass ratio limit, and the resulting waveforms, to one order beyond what can be
obtained using the conservation laws approach. The equations of motion are
solved perturbatively in the mass ratio (or the corresponding parameter in the
scalar field toy model), using the self force, for quasi-circular orbits around
a Schwarzschild black hole. This approach is applied for the scalar model.
Higher-order corrections yield a phase shift which, if included, may make
gravitational-wave astronomy potentially highly accurate.Comment: 4 pages, 3 Encapsulated PostScript figure
Implementing fully relativistic hydrodynamics in three dimensions
We report on our numerical implementation of fully relativistic hydrodynamics
coupled to Einstein's field equations in three spatial dimensions. We briefly
review several steps in our code development, including our recasting of
Einstein's equations and several tests which demonstrate its advantages for
numerical integrations. We outline our implementation of relativistic
hydrodynamics, and present numerical results for the evolution of both stable
and unstable Oppenheimer-Volkov equilibrium stars, which represent a very
promising first test of our code.Comment: 5 Pages, 4 Figures, submitted to Proceedings of the 8th Canadian
Conference on General Relativity and Relativistic Astrophysic
Recent integral cross section validation measurements at the ASP facility
This work presents new integral data measured at the ASP 14 MeV neutron
irradiation facility at Aldermaston in the UK, which has recently become
available for fusion-related work through the CCFE materials programme.
Measurements of reaction products from activation experiments using elemental
foils were carried out using gamma spectrometry in a high efficiency,
high-purity germanium (HPGe) detector and associated digital signal processing
hardware. Following irradiation and rapid extraction to the measurement cell,
gamma emissions were acquired with both energy and time bins. Integral cross
section and half-life data have been derived from these measurements. Selected
integral cross section values are presented from the measurement campaigns.Comment: 4 pages, 5 figure
Competing Adiabatic Thouless Pumps in Enlarged Parameter Spaces
The transfer of conserved charges through insulating matter via smooth
deformations of the Hamiltonian is known as quantum adiabatic, or Thouless,
pumping. Central to this phenomenon are Hamiltonians whose insulating gap is
controlled by a multi-dimensional (usually two-dimensional) parameter space in
which paths can be defined for adiabatic changes in the Hamiltonian, i.e.,
without closing the gap. Here, we extend the concept of Thouless pumps of band
insulators by considering a larger, three-dimensional parameter space. We show
that the connectivity of this parameter space is crucial for defining quantum
pumps, demonstrating that, as opposed to the conventional two-dimensional case,
pumped quantities depend not only on the initial and final points of
Hamiltonian evolution but also on the class of the chosen path and preserved
symmetries. As such, we distinguish the scenarios of closed/open paths of
Hamiltonian evolution, finding that different closed cycles can lead to the
pumping of different quantum numbers, and that different open paths may point
to distinct scenarios for surface physics. As explicit examples, we consider
models similar to simple models used to describe topological insulators, but
with doubled degrees of freedom compared to a minimal topological insulator
model. The extra fermionic flavors from doubling allow for extra gapping
terms/adiabatic parameters - besides the usual topological mass which preserves
the topology-protecting discrete symmetries - generating an enlarged adiabatic
parameter-space. We consider cases in one and three \emph{spatial} dimensions,
and our results in three dimensions may be realized in the context of
crystalline topological insulators, as we briefly discuss.Comment: 21 pages, 7 Figure
AGAPEROS: Searching for variable stars in the LMC Bar with the Pixel Method. I. Detection, astrometry and cross-identification
We extend the work developed in previous papers on microlensing with a
selection of variable stars. We use the Pixel Method to select variable stars
on a set of 2.5 x 10**6 pixel light curves in the LMC Bar presented elsewhere.
The previous treatment was done in order to optimise the detection of long
timescale variations (larger than a few days) and we further optimise our
analysis for the selection of Long Timescale and Long Period Variables
(LT&LPV). We choose to perform a selection of variable objects as comprehensive
as possible, independent of periodicity and of their position on the colour
magnitude diagram. We detail the different thresholds successively applied to
the light curves, which allow to produce a catalogue of 632 variable objects.
We present a table with the coordinate of each variable, its EROS magnitudes at
one epoch and an indicator of blending in both colours, together with a finding
chart.
A cross-correlation with various catalogues shows that 90% of those variable
objects were undetected before, thus enlarging the sample of LT&LPV previously
known in this area by a factor of 10. Due to the limitations of both the Pixel
Method and the data set, additional data -- namely a longer baseline and near
infrared photometry -- are required to further characterise these variable
stars, as will be addressed in subsequent papers.Comment: 11 pages with 10 figure
Meteoroid detector
A meteoroid detector is described which uses, a cold cathode discharge tube with a gas-pressurized cell in space for recording a meteoroid puncture of the cell and for determining the size of the puncture
An octonionic formulation of the M-theory algebra
We give an octonionic formulation of the N = 1 supersymmetry algebra in D =
11, including all brane charges. We write this in terms of a novel outer
product, which takes a pair of elements of the division algebra A and returns a
real linear operator on A. More generally, with this product comes the power to
rewrite any linear operation on R^n (n = 1,2,4,8) in terms of multiplication in
the n-dimensional division algebra A. Finally, we consider the reinterpretation
of the D = 11 supersymmetry algebra as an octonionic algebra in D = 4 and the
truncation to division subalgebras
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