38,516 research outputs found
Effects of visual and motion simulation cueing systems on pilot performance during takeoffs with engine failures
Data are presented that show the effects of visual and motion during cueing on pilot performance during takeoffs with engine failures. Four groups of USAF pilots flew a simulated KC-135 using four different cueing systems. The most basic of these systems was of the instrument-only type. Visual scene simulation and/or motion simulation was added to produce the other systems. Learning curves, mean performance, and subjective data are examined. The results show that the addition of visual cueing results in significant improvement in pilot performance, but the combined use of visual and motion cueing results in far better performance
Tensor Generalizations of Affine Symmetry Vectors
A definition is suggested for affine symmetry tensors, which generalize the
notion of affine vectors in the same way that (conformal) Killing tensors
generalize (conformal) Killing vectors. An identity for these tensors is
proved, which gives the second derivative of the tensor in terms of the
curvature tensor, generalizing a well-known identity for affine vectors.
Additionally, the definition leads to a good definition of homothetic tensors.
The inclusion relations between these types of tensors are exhibited. The
relationship between affine symmetry tensors and solutions to the equation of
geodesic deviation is clarified, again extending known results about Killing
tensors.Comment: 11 page
Evolution of Binary Black Hole Spacetimes
We describe early success in the evolution of binary black hole spacetimes
with a numerical code based on a generalization of harmonic coordinates.
Indications are that with sufficient resolution this scheme is capable of
evolving binary systems for enough time to extract information about the orbit,
merger and gravitational waves emitted during the event. As an example we show
results from the evolution of a binary composed of two equal mass, non-spinning
black holes, through a single plunge-orbit, merger and ring down. The resultant
black hole is estimated to be a Kerr black hole with angular momentum parameter
a~0.70. At present, lack of resolution far from the binary prevents an accurate
estimate of the energy emitted, though a rough calculation suggests on the
order of 5% of the initial rest mass of the system is radiated as gravitational
waves during the final orbit and ringdown.Comment: 4 pages, 3 figure
Single Shot Quantum State Estimation via a Continuous Measurement in the Strong Backaction Regime
We study quantum tomography based on a stochastic continuous-time measurement
record obtained from a probe field collectively interacting with an ensemble of
identically prepared systems. In comparison to previous studies, we consider
here the case in which the measurement-induced backaction has a nonnegligible
effect on the dynamical evolution of the ensemble. We formulate a maximum
likelihood estimate for the initial quantum state given only a single instance
of the continuous diffusive measurement record. We apply our estimator to the
simplest problem -- state tomography of a single pure qubit, which, during the
course of the measurement, is also subjected to dynamical control. We identify
a regime where the many-body system is well approximated at all times by a
separable pure spin coherent state, whose Bloch vector undergoes a conditional
stochastic evolution. We simulate the results of our estimator and show that we
can achieve close to the upper bound of fidelity set by the optimal POVM. This
estimate is compared to, and significantly outperforms, an equivalent estimator
that ignores measurement backaction.Comment: 10 pages, 5 epic figure
Optimizing evacuation flow in a two-channel exclusion process
We use a basic setup of two coupled exclusion processes to model a stylised
situation in evacuation dynamics, in which evacuees have to choose between two
escape routes. The coupling between the two processes occurs through one common
point at which particles are injected, the process can be controlled by
directing incoming individuals into either of the two escape routes. Based on a
mean-field approach we determine the phase behaviour of the model, and
analytically compute optimal control strategies, maximising the total current
through the system. Results are confirmed by numerical simulations. We also
show that dynamic intervention, exploiting fluctuations about the mean-field
stationary state, can lead to a further increase in total current.Comment: 16 pages, 6 figure
Structure of human transthyretin complexed with bromophenols: a new mode of binding
The binding of two organohalogen substances, pentabromophenol (PBP) and 2,4,6-tribromophenol (TBP), to human transthyretin (TTR), a thyroid hormone transport protein, has been studied by in vitro competitive binding assays and by X-ray crystallography. Both compounds bind to TTR with high affinity, in competition with the natural ligand thyroxine (
Testing a Simplified Version of Einstein's Equations for Numerical Relativity
Solving dynamical problems in general relativity requires the full machinery
of numerical relativity. Wilson has proposed a simpler but approximate scheme
for systems near equilibrium, like binary neutron stars. We test the scheme on
isolated, rapidly rotating, relativistic stars. Since these objects are in
equilibrium, it is crucial that the approximation work well if we are to
believe its predictions for more complicated systems like binaries. Our results
are very encouraging.Comment: 9 pages (RevTeX 3.0 with 6 uuencoded figures), CRSR-107
Reheating predictions in single field inflation
Reheating is a transition era after the end of inflation, during which the
inflaton is converted into the particles that populate the Universe at later
times. No direct cosmological observables are normally traceable to this period
of reheating. Indirect bounds can however be derived. One possibility is to
consider cosmological evolution for observable CMB scales from the time of
Hubble crossing to the present time. Depending upon the model, the duration and
final temperature after reheating, as well as its equation of state, may be
directly linked to inflationary observables. For single-field inflationary
models, if we approximate reheating by a constant equation of state, one can
derive relations between the reheating duration (or final temperature), its
equation of state parameter, and the scalar power spectrum amplitude and
spectral index. While this is a simple approximation, by restricting the
equation of state to lie within a broad physically allowed range, one can in
turn bracket an allowed range of and for these models. The added
constraints can help break degeneracies between inflation models that otherwise
overlap in their predictions for and .Comment: 32 pages, 15 figures. Revised in response to comments on the original
version, and in preparation for submission for publication. More references
and a new figure were adde
- …