31,974 research outputs found
Parameter choices and ranges for continuous gravitational wave searches for steadily spinning neutron stars
We consider the issue of selecting parameters and their associated ranges for
carrying out searches for continuous gravitational waves from steadily rotating
neutron stars. We consider three different cases (i) the "classic" case of a
star spinning about a principal axis; (ii) a biaxial star, not spinning about a
principal axis; (iii) a triaxial star spinning steady, but not about a
principal axis (as described in Jones, MNRAS vol 402, 2503 (2010)). The first
of these emits only at one frequency; the other two at a pair of harmonically
related frequencies. We show that in all three cases, when written in terms of
the original "source parameters", there exist a number of discrete
degeneracies, with different parameter values giving rise to the same
gravitational wave signal. We show how these can be removed by suitably
restricting the source parameter ranges. In the case of the model as written
down by Jones, there is also a continuous degeneracy. We show how to remove
this through a suitable rewriting in terms of "waveform parameters", chosen so
as to make the specialisations to the other stellar models particularly simple.
We briefly consider the (non-trivial) relation between the assignment of prior
probabilities on one set of parameters verses the other. The results of this
paper will be of use when designing strategies for carrying out searches for
such multi-harmonic gravitational wave signals, and when performing parameter
estimation in the event of a detection.Comment: Updated to match version accepted by MNRAS: One new equation
(equation 82)); typo (sign-error) corrected in equation (88); one more
paragraph inserted into Summary and Discussion sectio
Health-aware control of an octorotor UAV system based on actuator reliability
A major goal in modern flight control systems is the
need of improving the reliability. This work presents a reliable
control approach of an octorotor UAV that allows distributing
the control effort among the actuators using health actuator
information. The octorotor is an over-actuated system where
the redundancy of the actuators allows the redistribution of the
control effort among the existing actuators according to a given
control strategy. The priority is given to each actuator according
to the capabilities and reliability of this actuatorPeer ReviewedPostprint (author's final draft
Deterministic Global Attitude Estimation
A deterministic attitude estimation problem for a rigid body in an attitude
dependent potential field with bounded measurement errors is studied. An
attitude estimation scheme that does not use generalized coordinate
representations of the attitude is presented here. Assuming that the initial
attitude, angular velocity and measurement noise lie within given ellipsoidal
bounds, an uncertainty ellipsoid that bounds the attitude and the angular
velocity of the rigid body is obtained. The center of the uncertainty ellipsoid
provides point estimates, and its size gives the accuracy of the estimates. The
point estimates and the uncertainty ellipsoids are propagated using a Lie group
variational integrator and its linearization, respectively. The estimation
scheme is optimal in the sense that the attitude estimation error and the size
of the uncertainty ellipsoid is minimized at each measurement instant, and it
is global since the attitude is represented by a rotation matrix.Comment: IEEE Conference on Decision and Control, 2006. 6 pages, 6 figure
Profinite complexes of curves, their automorphisms and anabelian properties of moduli stacks of curves
Let , for , be the D-M moduli stack of smooth
curves of genus labeled by unordered distinct points. The main result
of the paper is that a finite, connected \'etale cover {\cal M}^\l of , defined over a sub--adic field , is "almost" anabelian in
the sense conjectured by Grothendieck for curves and their moduli spaces.
The precise result is the following. Let \pi_1({\cal M}^\l_{\ol{k}}) be the
geometric algebraic fundamental group of {\cal M}^\l and let
{Out}^*(\pi_1({\cal M}^\l_{\ol{k}})) be the group of its exterior
automorphisms which preserve the conjugacy classes of elements corresponding to
simple loops around the Deligne-Mumford boundary of {\cal M}^\l (this is the
"-condition" motivating the "almost" above). Let us denote by
{Out}^*_{G_k}(\pi_1({\cal M}^\l_{\ol{k}})) the subgroup consisting of
elements which commute with the natural action of the absolute Galois group
of . Let us assume, moreover, that the generic point of the D-M stack
{\cal M}^\l has a trivial automorphisms group. Then, there is a natural
isomorphism: {Aut}_k({\cal M}^\l)\cong{Out}^*_{G_k}(\pi_1({\cal
M}^\l_{\ol{k}})). This partially extends to moduli spaces of curves the
anabelian properties proved by Mochizuki for hyperbolic curves over
sub--adic fields.Comment: This paper has been withdrawn because of a flaw in the paper
"Profinite Teichm\"uller theory" of the first author, on which this paper
built o
Entropy of Classical Histories
We consider a number of proposals for the entropy of sets of classical
coarse-grained histories based on the procedures of Jaynes, and prove a series
of inequalities relating these measures. We then examine these as a function of
the coarse-graining for various classical systems, and show explicitly that the
entropy is minimized by the finest-grained description of a set of histories.
We propose an extension of the second law of thermodynamics to the entropy of
histories. We briefly discuss the implications for decoherent or consistent
history formulations of quantum mechanics.Comment: 35 pages RevTeX 3.0 + 5 figures (postscript). Minor corrections and
typos. To appear in Physical Review
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