17,206 research outputs found
An analysis of airline landing flare data based on flight and training simulator measurements
Landings by experienced airline pilots transitioning to the DC-10, performed in flight and on a simulator, were analyzed and compared using a pilot-in-the-loop model of the landing maneuver. By solving for the effective feedback gains and pilot compensation which described landing technique, it was possible to discern fundamental differences in pilot behavior between the actual aircraft and the simulator. These differences were then used to infer simulator fidelity in terms of specific deficiencies and to quantify the effectiveness of training on the simulator as compared to training in flight. While training on the simulator, pilots exhibited larger effective lag in commanding the flare. The inability to compensate adequately for this lag was associated with hard or inconsistent landings. To some degree this deficiency was carried into flight, thus resulting in a slightly different and inferior landing technique than exhibited by pilots trained exclusively on the actual aircraft
Search for Variable Stars in the Globular Cluster M3
We describe here results of a photometric time-sequence survey of the
globular cluster M3 (NGC 5272), in a search for contact and detached eclipsing
binary stars. We have discovered only one likely eclipsing binary and one SX
Phe type star in spite of monitoring 4077 stars with and observing 25
blue stragglers. The newly identified SX Phe star, V237, shows a light curve
with a variable amplitude. Variable V238 shows variability either with a period
of 0.49 d or with a period of 0.25 d. On the cluster colour-magnitude diagram,
the variable occupies a position a few hundredths of magnitude to the blue of
the base of the red giant branch. V238 is a likely descendent of a binary blue
straggler. As a side result we obtained high quality data for 42 of the
previously known RR Lyrae variables, including 33 of Bailey type ab, 7 type c
and 2 double-mode pulsators. We used equations that relate the physical
properties of RRc stars to their pulsation periods and Fourier parameters to
derive masses, luminosities, temperatures and helium parameters for five of the
RRc stars. One of the RRd stars (V79) has switched modes. In previous studies,
it was classified as RRab, but our observations show that it is an RRd star
with the first overtone mode dominating. This indicates blueward evolution on
the horizontal branch.Comment: 21 pages including 14 figures, Latex, requires mn.sty, psfig.sty.
Submitted, MNRA
Adaptive Filters Revisited - RFI Mitigation in pulsar observations
Pulsar detection and timing experiments are applications where adaptive
filters seem eminently suitable tools for radio-frequency-interference (RFI)
mitigation. We describe a novel variant which works well in field trials of
pulsar observations centred on an observing frequency of 675 MHz, a bandwidth
of 64 MHz and with 2-bit sampling. Adaptive filters have generally received bad
press for RFI mitigation in radio astronomical observations with their most
serious drawback being a spectral echo of the RFI embedded in the filtered
signals. Pulsar observations are intrinsically less sensitive to this as they
operate in the (pulsar period) time domain. The field trials have allowed us to
identify those issues which limit the effectiveness of the adaptive filter. We
conclude that adaptive filters can significantly improve pulsar observations in
the presence of RFI.Comment: Accepted for publication in Radio Scienc
Bounds on the force between black holes
We treat the problem of N interacting, axisymmetric black holes and obtain
two relations among physical parameters of the system including the force
between the black holes. The first relation involves the total mass, the
angular momenta, the distances and the forces between the black holes. The
second one relates the angular momentum and area of each black hole with the
forces acting on it.Comment: 13 pages, no figure
The case for increasing the statistical power of eddy covariance ecosystem studies: why, where and how?
ArticleThis is the final version of the article. Available from Wiley via the DOI in this record.Eddy covariance (EC) continues to provide invaluable insights into the dynamics of Earth's surface processes. However, despite its many strengths, spatial replication of EC at the ecosystem scale is rare. High equipment costs are likely to be partially responsible. This contributes to the low sampling, and even lower replication, of ecoregions in Africa, Oceania (excluding Australia) and South America. The level of replication matters as it directly affects statistical power. While the ergodicity of turbulence and temporal replication allow an EC tower to provide statistically robust flux estimates for its footprint, these principles do not extend to larger ecosystem scales. Despite the challenge of spatially replicating EC, it is clearly of interest to be able to use EC to provide statistically robust flux estimates for larger areas. We ask: How much spatial replication of EC is required for statistical confidence in our flux estimates of an ecosystem? We provide the reader with tools to estimate the number of EC towers needed to achieve a given statistical power. We show that for a typical ecosystem, around four EC towers are needed to have 95% statistical confidence that the annual flux of an ecosystem is nonzero. Furthermore, if the true flux is small relative to instrument noise and spatial variability, the number of towers needed can rise dramatically. We discuss approaches for improving statistical power and describe one solution: an inexpensive EC system that could help by making spatial replication more affordable. However, we note that diverting limited resources from other key measurements in order to allow spatial replication may not be optimal, and a balance needs to be struck. While individual EC towers are well suited to providing fluxes from the flux footprint, we emphasize that spatial replication is essential for statistically robust fluxes if a wider ecosystem is being studied.Natural Environment Research Council. Grant Numbers: NE/J015644/1, NE/K002619/
Generalized Massive Gravity and Galilean Conformal Algebra in two dimensions
Galilean conformal algebra (GCA) in two dimensions arises as contraction of
two copies of the centrally extended Virasoro algebra ( with ). The central charges of
GCA can be expressed in term of Virasoro central charges. For finite and
non-zero GCA central charges, the Virasoro central charges must behave as
asymmetric form . We propose that, the bulk
description for 2d GCA with asymmetric central charges is given by general
massive gravity (GMG) in three dimensions. It can be seen that, if the
gravitational Chern-Simons coupling behaves as of order
O() or (), the central charges
of GMG have the above dependence. So, in non-relativistic scaling
limit , we calculated GCA parameters and finite
entropy in term of gravity parameters mass and angular momentum of GMG.Comment: 9 page
Collision damping in the pi 3He -> d'N reaction near the threshold
We present a simple quantum mechanical model exploiting the optical potential
approach for the description of collision damping in the reaction pi 3He -> d'N
near the threshold, which recently has been measured at TRIUMF. The influence
of the open d'N -> NNN channel is taken into account. It leads to a suppression
factor of about ten in the d' survival probability. Applications of the method
to other reactions are outlined.Comment: RevTeX4, 14 pages, 3 Postscript figures, uses epsfig.sty, to appear
in Phys.Rev.
Effects of Uniform and Differential Rotation on Stellar Pulsations
We have investigated the effects of uniform rotation and a specific model for
differential rotation on the pulsation frequencies of 10 \Msun\ stellar models.
Uniform rotation decreases the frequencies for all modes. Differential rotation
does not appear to have a significant effect on the frequencies, except for the
most extreme differentially rotating models. In all cases, the large and small
separations show the effects of rotation at lower velocities than do the
individual frequencies. Unfortunately, to a certain extent, differential
rotation mimics the effects o f more rapid rotation, and only the presence of
some specific observed frequencies with well identified modes will be able to
uniquely constrain the internal rotation of pulsating stars.Comment: 33 pages, 16 figures. Accepted for publication in Ap
Cluster, Classify, Regress: A General Method For Learning Discountinous Functions
This paper presents a method for solving the supervised learning problem in
which the output is highly nonlinear and discontinuous. It is proposed to solve
this problem in three stages: (i) cluster the pairs of input-output data
points, resulting in a label for each point; (ii) classify the data, where the
corresponding label is the output; and finally (iii) perform one separate
regression for each class, where the training data corresponds to the subset of
the original input-output pairs which have that label according to the
classifier. It has not yet been proposed to combine these 3 fundamental
building blocks of machine learning in this simple and powerful fashion. This
can be viewed as a form of deep learning, where any of the intermediate layers
can itself be deep. The utility and robustness of the methodology is
illustrated on some toy problems, including one example problem arising from
simulation of plasma fusion in a tokamak.Comment: 12 files,6 figure
The Reaction 7Li(pi+,pi-)7B and its Implications for 7B
The reaction 7Li(pi+,pi-)7B has been measured at incident pion energies of
30-90 MeV. 7Li constitutes the lightest target nucleus, where the pionic charge
exchange may proceed as a binary reaction to a discrete final state. Like in
the Delta-resonance region the observed cross sections are much smaller than
expected from the systematics found for heavier nuclei. In analogy to the
neutron halo case of 11Li this cross section suppression is interpreted as
evidence for a proton halo in the particle-unstable nucleus 7B.Comment: 4 pages, 4 figure
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