137,314 research outputs found
Bird Migration Through A Mountain Pass Studied With High Resolution Radar, Ceilometers, And Census
Autumnal migration was studied with high-resolution radar, ceilometer, and daily census in the area of Franconia Notch, a major pass in the northern Appalachian Mountains. Under synoptic conditions favorable for migration, broadfront movements of migrants toward the south passed over the mountains, often above a temperature inversion. Birds at lower elevations appeared to be influenced by local topography. Birds moving southwest were concentrated along the face of the mountain range. Birds appeared to deviate their flights to follow local topography through the pass. Specific migratory behavior was not associated with species or species groups. Under synoptic conditions unfavorable for southward migration, multimodal movements probably associated with local flights were as dense as the southward migrations described above. Avian migrants reacting to local terrain may result in concentrations of migrants over ridge summits or other topographic features
Who You Gonna Call? Runaway Ghosts, Higher Derivatives and Time-Dependence in EFTs
We briefly review the formulation of effective field theories (EFTs) in
time-dependent situations, with particular attention paid to their domain of
validity. Our main interest is the extent to which solutions of the EFT capture
the dynamics of the full theory. For a simple model we show by explicit
calculation that the low-energy action obtained from a sensible UV completion
need not take the restrictive form required to obtain only second-order field
equations, and we clarify why runaway solutions are nevertheless typically not
a problem for the EFT. Although our results will not be surprising to many, to
our knowledge they are only mentioned tangentially in the EFT literature, which
(with a few exceptions) largely addresses time-independent situations.Comment: 12 page
Optimal Quantum Circuits for General Two-Qubit Gates
In order to demonstrate non-trivial quantum computations experimentally, such
as the synthesis of arbitrary entangled states, it will be useful to understand
how to decompose a desired quantum computation into the shortest possible
sequence of one-qubit and two-qubit gates. We contribute to this effort by
providing a method to construct an optimal quantum circuit for a general
two-qubit gate that requires at most 3 CNOT gates and 15 elementary one-qubit
gates. Moreover, if the desired two-qubit gate corresponds to a purely real
unitary transformation, we provide a construction that requires at most 2 CNOTs
and 12 one-qubit gates. We then prove that these constructions are optimal with
respect to the family of CNOT, y-rotation, z-rotation, and phase gates.Comment: 6 pages, 8 figures, new title, final journal versio
Accurate determination of ambient temperature at burial depth for high voltage cable ratings
A Very Large Array 3.6cm continuum survey of Galactic Wolf-Rayet stars
We report the results of a survey of radio continuum emission of Galactic
Wolf-Rayet stars north of declination -46 degrees. The observations were
obtained at 8.46 GHz (3.6cm) using the Very Large Array (VLA), with an angular
resolution of about 6 x 9 arcsec and typical rms noise of 0.04 mJy/beam. Our
survey of 34 WR stars resulted in 15 definite and 5 probable detections, 13 of
these for the first time at radio wavelengths. All detections are unresolved.
Time variations in flux are confirmed in the cases of WR98a, WR104, WR105 and
WR125. WR79a and WR89 are also variable in flux and we suspect they are also
non-thermal emitters. Thus, of our sample 20-30% of the detected stars are
non-thermal emiters. Average mass loss rates determinations obtained excluding
definite and suspected non-thermal cases give similar values for WN (all
subtypes) and WC5-7 stars, while a lower value was obtained for WC8-9 stars.
Uncertainties in stellar distances largely contribute to the observed scatter
in mass loss rates. Upper limits to the mass loss rates were obtained in cases
of undetected sources or for sources which probably show additional non-thermal
emission.Comment: 21 pages, Latex, 21 postscript figures, to be published in The
Astronomical Journal, May 200
Self-Tuning at Large (Distances): 4D Description of Runaway Dilaton Capture
We complete here a three-part study (see also arXiv:1506.08095 and
1508.00856) of how codimension-two objects back-react gravitationally with
their environment, with particular interest in situations where the transverse
`bulk' is stabilized by the interplay between gravity and flux-quantization in
a dilaton-Maxwell-Einstein system such as commonly appears in
higher-dimensional supergravity and is used in the Supersymmetric Large Extra
Dimensions (SLED) program. Such systems enjoy a classical flat direction that
can be lifted by interactions with the branes, giving a mass to the would-be
modulus that is smaller than the KK scale. We construct the effective
low-energy 4D description appropriate below the KK scale once the transverse
extra dimensions are integrated out, and show that it reproduces the
predictions of the full UV theory for how the vacuum energy and modulus mass
depend on the properties of the branes and stabilizing fluxes. In particular we
show how this 4D theory learns the news of flux quantization through the
existence of a space-filling four-form potential that descends from the
higher-dimensional Maxwell field. We find a scalar potential consistent with
general constraints, like the runaway dictated by Weinberg's theorem. We show
how scale-breaking brane interactions can give this potential minima for which
the extra-dimensional size, , is exponentially large relative to
underlying physics scales, , with where
can be arranged with a small hierarchy between fundamental
parameters. We identify circumstances where the potential at the minimum can
(but need not) be parametrically suppressed relative to the tensions of the
branes, provide a preliminary discussion of the robustness of these results to
quantum corrections, and discuss the relation between what we find and earlier
papers in the SLED program.Comment: 37 pages + appendice
Simulation of gaseous core nuclear rocket mixing characteristics using cold and arc heated flows
Mixing phenomena of cold and arc heated jets from coaxial flows of helium or nitrogen related to gaseous core nuclear rocket
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