119,102 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
Coping with a changing world: the UK Open University approach to teaching ICT
The rapid pace of change in the ICT field has affected all HE providers, but for the UK Open University (UKOU), used to print-based courses lasting eight years or more, it has been a particular challenge. This paper will present some of the ways the UKOU has been coping with this problem by discussing the design of three courses, the first developed almost a decade ago. All three are distance learning courses that are either core or optional in a variety of bachelors' degrees, including the BSc programmes in: Information and Communication Technology; IT and Computing; and Technology; as well as the BEng (Hons) engineering programme.
The first course, Information and Communication Technology: people and interactions is a level 2 (second year undergraduate) course first presented in 2002. It is predominately a print-based course with an eight year lifetime. The second course Networked Living: exploring information and communication technologies is a level 1 (first year undergraduate) course first presented some three-and-a-half years later in 2005. It is expected to have a course life of five years, and uses a mix of print-based (60%) and computer-based (40%) material. Both these courses use assignments as key tools for annual updating.
The third course, Keeping ahead in ICT is aimed primarily at equipping students with advanced information searching and evaluation skills that will serve them well in professional life, and is presented at level 3 (final year undergraduate). It was first presented in 2007 and has an expected course life of 8 years. It uses much less print than in most OU courses, and has a greater reliance on third-party resources such as newspaper, conference and journal articles, websites, and other electronic resources. Some elements in each block are designed to change from year to year, in order to retain currency.
Finally, the paper will look forward to the development of a new level 2 course with an expected first presentation in 2010, drawing out the lessons learned about course updating, and predicting the approach that the course team may tak
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
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
The color of sea level: importance of spatial variations in spectral shape for assessing the significance of trends
We investigate spatial variations in the shape of the spectrum of sea level variability, based on a homogeneously-sampled 12-year gridded altimeter dataset. We present a method of plotting spectral information as color, focusing on periods between 2 and 24 weeks, which shows that significant spatial variations in the spectral shape exist,
and contain useful dynamical information. Using the Bayesian Information Criterion, we determine that, typically, a 5th order autoregressive model is needed to capture the structure in the spectrum. Using this model, we show that statistical errors in fitted local trends range between less than 1 and more than 5 times what would be calculated assuming “white” noise, and the time needed to detect a 1 mm/yr trend ranges between about 5 years and many decades. For global-mean sea level, the statistical error reduces to 0.1 mm/yr over 12 years, with only 2 years needed to detect a 1 mm/yr trend. We find significant regional differences in trend from the global mean. The
patterns of these regional differences are indicative of a sea level trend dominated by dynamical ocean processes, over this perio
The Gravity of Dark Vortices: Effective Field Theory for Branes and Strings Carrying Localized Flux
A Nielsen-Olesen vortex usually sits in an environment that expels the flux
that is confined to the vortex, so flux is not present both inside and outside.
We construct vortices for which this is not true, where the flux carried by the
vortex also permeates the `bulk' far from the vortex. The idea is to mix the
vortex's internal gauge flux with an external flux using off-diagonal kinetic
mixing. Such `dark' vortices could play a phenomenological role in models with
both cosmic strings and a dark gauge sector. When coupled to gravity they also
provide explicit ultra-violet completions for codimension-two brane-localized
flux, which arises in extra-dimensional models when the same flux that
stabilizes extra-dimensional size is also localized on space-filling branes
situated around the extra dimensions. We derive simple formulae for observables
such as defect angle, tension, localized flux and on-vortex curvature when
coupled to gravity, and show how all of these are insensitive to much of the
microscopic details of the solutions, and are instead largely dictated by
low-energy quantities. We derive the required effective description in terms of
a world-sheet brane action, and derive the matching conditions for its
couplings. We consider the case where the dimensions transverse to the bulk
compactify, and determine how the on- and off-vortex curvatures and other bulk
features depend on the vortex properties. We find that the brane-localized flux
does not gravitate, but just renormalizes the tension in a magnetic-field
independent way. The existence of an explicit UV completion puts the effective
description of these models on a more precise footing, verifying that
brane-localized flux can be consistent with sensible UV physics and resolving
some apparent paradoxes that can arise with a naive (but commonly used)
delta-function treatment of the brane's localization within the bulk.Comment: 36 pages + appendices, 7 figure
EFT for Vortices with Dilaton-dependent Localized Flux
We study how codimension-two objects like vortices back-react gravitationally
with their environment in theories (such as 4D or higher-dimensional
supergravity) where the bulk is described by a dilaton-Maxwell-Einstein system.
We do so both in the full theory, for which the vortex is an explicit classical
`fat brane' solution, and in the effective theory of `point branes' appropriate
when the vortices are much smaller than the scales of interest for their
back-reaction (such as the transverse Kaluza-Klein scale). We extend the
standard Nambu-Goto description to include the physics of flux-localization
wherein the ambient flux of the external Maxwell field becomes partially
localized to the vortex, generalizing the results of a companion paper to
include dilaton-dependence for the tension and localized flux. In the effective
theory, such flux-localization is described by the next-to-leading effective
interaction, and the boundary conditions to which it gives rise are known to
play an important role in how (and whether) the vortex causes supersymmetry to
break in the bulk. We track how both tension and localized flux determine the
curvature of the space-filling dimensions. Our calculations provide the tools
required for computing how scale-breaking vortex interactions can stabilize the
extra-dimensional size by lifting the dilaton's flat direction. For small
vortices we derive a simple relation between the near-vortex boundary
conditions of bulk fields as a function of the tension and localized flux in
the vortex action that provides the most efficient means for calculating how
physical vortices mutually interact without requiring a complete construction
of their internal structure. In passing we show why a common procedure for
doing so using a -function can lead to incorrect results. Our
procedures generalize straightforwardly to general co-dimension objects.Comment: 45 pages + appendix, 6 figure
Monolayers of 3He on the Surface of Bulk Superfluid 4He
We have used quantum evaporation to investigate the two-dimensional fermion
system that forms at the free surface of (initially isotopically pure) 4He when
small quantities of 3He are added to it. By measuring the first-arrival times
of the evaporated atoms, we have determined that the 3He-3He potential in this
system is V_3S/k_B=(0.23+/-0.02) K nm^2 (repulsive) and estimated a value of
m_3S=(1.53+/-0.02)m_3 for the zero-coverage effective mass. We have also
observed the predicted second layer-state which becomes occupied once the first
layer-state density exceeds about 0.6 monolayers.Comment: 2 pages, 3 figures. Submitted to Proc. LT-22 (1999) to appear in
Physica
SCRAM: Software configuration and management for the LHC Computing Grid project
Recently SCRAM (Software Configuration And Management) has been adopted by
the applications area of the LHC computing grid project as baseline
configuration management and build support infrastructure tool.
SCRAM is a software engineering tool, that supports the configuration
management and management processes for software development. It resolves the
issues of configuration definition, assembly break-down, build, project
organization, run-time environment, installation, distribution, deployment, and
source code distribution. It was designed with a focus on supporting a
distributed, multi-project development work-model.
We will describe the underlying technology, and the solutions SCRAM offers to
the above software engineering processes, while taking a users view of the
system under configuration management.Comment: Computing in High Energy and Nuclear Physics, La Jolla, California,
March 24-28, 2003 1 tar fil
- …