7,414 research outputs found
Multi-camera Realtime 3D Tracking of Multiple Flying Animals
Automated tracking of animal movement allows analyses that would not
otherwise be possible by providing great quantities of data. The additional
capability of tracking in realtime - with minimal latency - opens up the
experimental possibility of manipulating sensory feedback, thus allowing
detailed explorations of the neural basis for control of behavior. Here we
describe a new system capable of tracking the position and body orientation of
animals such as flies and birds. The system operates with less than 40 msec
latency and can track multiple animals simultaneously. To achieve these
results, a multi target tracking algorithm was developed based on the Extended
Kalman Filter and the Nearest Neighbor Standard Filter data association
algorithm. In one implementation, an eleven camera system is capable of
tracking three flies simultaneously at 60 frames per second using a gigabit
network of nine standard Intel Pentium 4 and Core 2 Duo computers. This
manuscript presents the rationale and details of the algorithms employed and
shows three implementations of the system. An experiment was performed using
the tracking system to measure the effect of visual contrast on the flight
speed of Drosophila melanogaster. At low contrasts, speed is more variable and
faster on average than at high contrasts. Thus, the system is already a useful
tool to study the neurobiology and behavior of freely flying animals. If
combined with other techniques, such as `virtual reality'-type computer
graphics or genetic manipulation, the tracking system would offer a powerful
new way to investigate the biology of flying animals.Comment: pdfTeX using libpoppler 3.141592-1.40.3-2.2 (Web2C 7.5.6), 18 pages
with 9 figure
A note on a gauge-gravity relation and functional determinants
We present a refinement of a recently found gauge-gravity relation between
one-loop effective actions: on the gauge side, for a massive charged scalar in
2d dimensions in a constant maximally symmetric electromagnetic field; on the
gravity side, for a massive spinor in d-dimensional (Euclidean) anti-de Sitter
space. The inclusion of the dimensionally regularized volume of AdS leads to
complete mapping within dimensional regularization. In even-dimensional AdS, we
get a small correction to the original proposal; whereas in odd-dimensional
AdS, the mapping is totally new and subtle, with the `holographic trace
anomaly' playing a crucial role.Comment: 6 pages, io
Spectral Action for Robertson-Walker metrics
We use the Euler-Maclaurin formula and the Feynman-Kac formula to extend our
previous method of computation of the spectral action based on the Poisson
summation formula. We show how to compute directly the spectral action for the
general case of Robertson-Walker metrics. We check the terms of the expansion
up to a_6 against the known universal formulas of Gilkey and compute the
expansion up to a_{10} using our direct method
Phase transition in a static granular system
We find that a column of glass beads exhibits a well-defined transition
between two phases that differ in their resistance to shear. Pulses of
fluidization are used to prepare static states with well-defined particle
volume fractions in the range 0.57-0.63. The resistance to shear is
determined by slowly inserting a rod into the column of beads. The transition
occurs at for a range of speeds of the rod.Comment: 4 pages, 4 figures. The paper is significantly extended, including
new dat
Brief of Law Professors as \u3cem\u3eAmici Curiae\u3c/em\u3e in Support of Petitioner
Amici curiae respectfully submit this brief in support of Petitioner, Edward Lane, encouraging the reversal of the judgment of the Eleventh Circuit, because the judgment below is inconsistent with both the Court’s general historical approach to public employee speech and the specific approach to such speech that the Court adopted in Garcetti v. Ceballos, 547 U.S. 410 (2006).
Amici are law professors who teach and write about the constitutional rights of public employees and have published a number of scholarly articles on these topics. Amici have no financial stake in the outcome of this case, and in this brief do not ask the Court to reconsider Garcetti. But we are troubled by the tendency in some courts of appeals to misread this Court’s decision in Garcettito articulate ever-broadening readings of the narrow exemption from First Amendment protection the Court carved out. We file this brief to urge this Court to correct these rulings by clarifying the narrow nature of the exemption it recognized
Further functional determinants
Functional determinants for the scalar Laplacian on spherical caps and
slices, flat balls, shells and generalised cylinders are evaluated in two,
three and four dimensions using conformal techniques. Both Dirichlet and Robin
boundary conditions are allowed for. Some effects of non-smooth boundaries are
discussed; in particular the 3-hemiball and the 3-hemishell are considered. The
edge and vertex contributions to the coefficient are examined.Comment: 25 p,JyTex,5 figs. on request
Prolongations of Geometric Overdetermined Systems
We show that a wide class of geometrically defined overdetermined semilinear
partial differential equations may be explicitly prolonged to obtain closed
systems. As a consequence, in the case of linear equations we extract sharp
bounds on the dimension of the solution space.Comment: 22 pages. In the second version, a comparison with the classical
theory of prolongations was added. In this third version more details were
added concerning our construction and especially the use of Kostant's
computation of Lie algebra cohomolog
Boundary dynamics and multiple reflection expansion for Robin boundary conditions
In the presence of a boundary interaction, Neumann boundary conditions should
be modified to contain a function S of the boundary fields: (\nabla_N +S)\phi
=0. Information on quantum boundary dynamics is then encoded in the
-dependent part of the effective action. In the present paper we extend the
multiple reflection expansion method to the Robin boundary conditions mentioned
above, and calculate the heat kernel and the effective action (i) for constant
S, (ii) to the order S^2 with an arbitrary number of tangential derivatives.
Some applications to symmetry breaking effects, tachyon condensation and brane
world are briefly discussed.Comment: latex, 22 pages, no figure
Canine Sense and Sensibility: Tipping Points and Response Latency Variability as an Optimism Index in a Canine Judgement Bias Assessment
Recent advances in animal welfare science used judgement bias, a type of cognitive bias, as a means to objectively measure an animal\u27s affective state. It is postulated that animals showing heightened expectation of positive outcomes may be categorised optimistic, while those showing heightened expectations of negative outcomes may be considered pessimistic. This study pioneers the use of a portable, automated apparatus to train and test the judgement bias of dogs. Dogs were trained in a discrimination task in which they learned to touch a target after a tone associated with a lactose-free milk reward and abstain from touching the target after a tone associated with water. Their judgement bias was then probed by presenting tones between those learned in the discrimination task and measuring their latency to respond by touching the target. A Cox\u27s Proportional Hazards model was used to analyse censored response latency data. Dog and Cue both had a highly significant effect on latency and risk of touching a target. This indicates that judgement bias both exists in dogs and differs between dogs. Test number also had a significant effect, indicating that dogs were less likely to touch the target over successive tests. Detailed examination of the response latencies revealed tipping points where average latency increased by 100% or more, giving an indication of where dogs began to treat ambiguous cues as predicting more negative outcomes than positive ones. Variability scores were calculated to provide an index of optimism using average latency and standard deviation at cues after the tipping point. The use of a mathematical approach to assessing judgement bias data in animal studies offers a more detailed interpretation than traditional statistical analyses. This study provides proof of concept for the use of an automated apparatus for measuring cognitive bias in dogs
Magnetorotational collapse of very massive stars to black holes in full general relativity
We perform axisymmetric simulations of the magnetorotational collapse of very
massive stars in full general relativity. Our simulations are applicable to the
collapse of supermassive stars (M > 10^3M_sun) and to very massive Pop III
stars. We model our initial configurations by n=3 polytropes. The ratio of
magnetic to rotational kinetic energy in these configurations is chosen to be
small (1% and 10%). We find that such magnetic fields do not affect the initial
collapse significantly. The core collapses to a black hole, after which black
hole excision is employed to continue the evolution long enough for the hole to
reach a quasi-stationary state. We find that the black hole mass is M_h = 0.95M
and its spin parameter is J_h/M_h^2 = 0.7, with the remaining matter forming a
torus around the black hole. We freeze the spacetime metric ("Cowling
approximation") and continue to follow the evolution of the torus after the
black hole has relaxed to quasi-stationary equilibrium. In the absence of
magnetic fields, the torus settles down following ejection of a small amount of
matter due to shock heating. When magnetic fields are present, the field lines
gradually collimate along the hole's rotation axis. MHD shocks and the MRI
generate MHD turbulence in the torus and stochastic accretion onto the central
black hole. When the magnetic field is strong, a wind is generated in the
torus, and the torus undergoes radial oscillations that drive episodic
accretion onto the hole. These oscillations produce long-wavelength
gravitational waves potentially detectable by LISA. The final state of the
magnetorotational collapse always consists of a central black hole surrounded
by a collimated magnetic field and a hot, thick accretion torus. This system is
a viable candidate for the central engine of a long-soft gamma-ray burst.Comment: 17 pages, 13 figures, replaced with the published versio
- …