820 research outputs found
Examination of the Impact of Various Training Approaches on Different UAS Operator Populations
In recent years, the UAS industry has extended beyond military and recreational use and is now positioned to become a major portion of the aviation industry. As we move toward UAS integration into the national airspace system, UAS operators need effective training to ensure safe operation. Training UAS operators in an engaging way is important to ensure the best performance and transfer of training. Training methods that elicit high levels of learner engagement have been shown to improve knowledge gains, performance, and therefore such training techniques provide an opportunity for improving UAS training effectiveness and transfer. The growth of the UAS industry across various domains such as first responders and industrial inspectors has resulted in a broad demographic of end users. Given this, training may need to be tailored based on the population to ensure an engaging experience. To examine this topic, a study was conducted in which UAS pilots from the student population and first responder population participated in UAS training to test the effect of different training approaches on learner engagement of different end user populations. Participants engaged in instructional videos, simulation challenges, and live obstacle courses and were measured on their engagement levels and performance. This presentation will describe the methods and findings associated with the study along with implications for the aviation industry
Supernovae as a probe of particle physics and cosmology
It has very recently been demonstrated by Csaki, Kaloper and Terning (CKT)
that the faintness of supernovae at high redshift can be accommodated by mixing
of a light axion with the photon in the presence of an intergalactic magnetic
field, as opposed to the usual explanation of an accelerating universe by a
dark energy component. In this paper we analyze further aspects of the CKT
mechanism and its generalizations. The CKT mechanism also passes various
cosmological constraints from the fluctuations of the CMB and the formation of
structure at large scales, without requiring an accelerating phase in the
expansion of the Universe. We investigate the statistical significance of
current supernova data for pinning down the different components of the
cosmological energy-momentum tensor and for probing physics beyond the standard
models.Comment: 17 pages, LaTeX, 4 figures; v2: typos corrected, minor changes,
references added; v3: updated figures, details regarding fits include
The Effect of Negative-Energy Shells on the Schwarzschild Black Hole
We construct Penrose diagrams for Schwarzschild spacetimes joined by massless
shells of matter, in the process correcting minor flaws in the similar diagrams
drawn by Dray and 't Hooft, and confirming their result that such shells
generate a horizon shift. We then consider shells with negative energy density,
showing that the horizon shift in this case allows for travel between the
heretofore causally separated exterior regions of the Schwarzschild geometry.
These drawing techniques are then used to investigate the properties of
successive shells, joining multiple Schwarzschild regions. Again, the presence
of negative-energy shells leads to a causal connection between the exterior
regions, even in (some) cases with two successive shells of equal but opposite
total energy.Comment: 12 pages, 10 figure
Cosmological models with linearly varying deceleration parameter
We propose a new law for the deceleration parameter that varies linearly with
time and covers Berman's law where it is constant. Our law not only allows one
to generalize many exact solutions that were obtained assuming constant
deceleration parameter, but also gives a better fit with data (from SNIa, BAO
and CMB), particularly concerning the late time behavior of the universe.
According to our law only the spatially closed and flat universes are allowed;
in both cases the cosmological fluid we obtain exhibits quintom like behavior
and the universe ends with a big-rip. This is a result consistent with recent
cosmological observations.Comment: 12 pages, 7 figures; some typo corrections; to appear in
International Journal of Theoretical Physic
Radiative processes as a condensation phenomenon and the physical meaning of deformed canonical structures
Working with well known models in we discuss the physics behind the
deformation of the canonical structure of these theories. A new deformation is
constructed linking the massless scalar field theory with the self-dual theory.
This is the exact dual of the known deformation connecting the Maxwell theory
with the Maxwell-Chern-Simons theory. Duality is used to establish a web of
relations between the mentioned theories and a physical picture of the
deformation procedure is suggested.Comment: revtex4 file, 16 page
Model for a Universe described by a non-minimally coupled scalar field and interacting dark matter
In this work it is investigated the evolution of a Universe where a scalar
field, non-minimally coupled to space-time curvature, plays the role of
quintessence and drives the Universe to a present accelerated expansion. A
non-relativistic dark matter constituent that interacts directly with dark
energy is also considered, where the dark matter particle mass is assumed to be
proportional to the value of the scalar field. Two models for dark matter
pressure are considered: the usual one, pressureless, and another that comes
from a thermodynamic theory and relates the pressure with the coupling between
the scalar field and the curvature scalar. Although the model has a strong
dependence on the initial conditions, it is shown that the mixture consisted of
dark components plus baryonic matter and radiation can reproduce the expected
red-shift behavior of the deceleration parameter, density parameters and
luminosity distance.Comment: 11 pages and 6 figures. To appear in GR
Cosmological Magnetic Fields from Primordial Helicity
Primordial magnetic fields may account for all or part of the fields observed
in galaxies. We consider the evolution of the magnetic fields created by
pseudoscalar effects in the early universe. Such processes can create
force-free fields of maximal helicity; we show that for such a field magnetic
energy inverse cascades to larger scales than it would have solely by flux
freezing and cosmic expansion. For fields generated at the electroweak phase
transition, we find that the predicted wavelength today can in principle be as
large as 10 kpc, and the field strength can be as large as 10^{-10} G.Comment: 13 page
Finite-temperature scalar fields and the cosmological constant in an Einstein universe
We study the back reaction effect of massless minimally coupled scalar field
at finite temperatures in the background of Einstein universe. Substituting for
the vacuum expectation value of the components of the energy-momentum tensor on
the RHS of the Einstein equation, we deduce a relationship between the radius
of the universe and its temperature. This relationship exhibit a maximum
temperature, below the Planck scale, at which the system changes its behaviour
drastically. The results are compared with the case of a conformally coupled
field. An investigation into the values of the cosmological constant exhibit a
remarkable difference between the conformally coupled case and the minimally
coupled one.Comment: 7 pages, 2 figure
Boundary Term in Metric f(R) Gravity: Field Equations in the Metric Formalism
The main goal of this paper is to get in a straightforward form the field
equations in metric f(R) gravity, using elementary variational principles and
adding a boundary term in the action, instead of the usual treatment in an
equivalent scalar-tensor approach. We start with a brief review of the
Einstein-Hilbert action, together with the Gibbons-York-Hawking boundary term,
which is mentioned in some literature, but is generally missing. Next we
present in detail the field equations in metric f(R) gravity, including the
discussion about boundaries, and we compare with the Gibbons-York-Hawking term
in General Relativity. We notice that this boundary term is necessary in order
to have a well defined extremal action principle under metric variation.Comment: 12 pages, title changes by referee recommendation. Accepted for
publication in General Relativity and Gravitation. Matches with the accepted
versio
Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter
The Bianchi type III dark energy models with constant deceleration parameter
are investigated. The equation of state parameter is found to be time
dependent and its existing range for this model is consistent with the recent
observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy
clustering statistics. The physical aspect of the dark energy models are
discussed.Comment: 12 pages, 2 figures, Accepted version of IJT
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