11,061 research outputs found
The CHASE laboratory search for chameleon dark energy
A scalar field is a favorite candidate for the particle responsible for dark
energy. However, few theoretical means exist that can simultaneously explain
the observed acceleration of the Universe and evade tests of gravity. The
chameleon mechanism, whereby the properties of a particle depend upon the local
environment, is one possible avenue. We present the results of the Chameleon
Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark
energy. CHASE marks a significant improvement other searches for chameleons
both in terms of its sensitivity to the photon/chameleon coupling as well as
its sensitivity to the classes of chameleon dark energy models and standard
power-law models. Since chameleon dark energy is virtually indistinguishable
from a cosmological constant, CHASE tests dark energy models in a manner not
accessible to astronomical surveys.Comment: Version 2 is the submission to IDM 2010 conference proceedings,
Montpellier, France (slightly longer and two more figures), Version 1 is the
submission to ICHEP 2010 conference proceedings, Paris, France (6 pages, four
figures
Optimal boarding method for airline passengers
Using a Markov Chain Monte Carlo optimization algorithm and a computer
simulation, I find the passenger ordering which minimizes the time required to
board the passengers onto an airplane. The model that I employ assumes that the
time that a passenger requires to load his or her luggage is the dominant
contribution to the time needed to completely fill the aircraft. The optimal
boarding strategy may reduce the time required to board and airplane by over a
factor of four and possibly more depending upon the dimensions of the aircraft.
In addition, knowledge of the optimal boarding procedure can inform decisions
regarding changes to methods that are employed by a particular carrier. I
explore some of the salient features of the optimal boarding method and discuss
practical modifications to the optimal. Finally, I mention some of the benefits
that could come from implementing an improved passenger boarding scheme.Comment: Accepted for publication in the Journal of Air Transport Management.
This study was motivated by an experience that occurred while traveling to a
conference. Version 1: 15 pages, 7 figures--likely to be of more technical
interest. Version 2: 14 pages, 6 figures--more complete bibliography and some
additional commentar
Detecting New Planets in Transiting Systems
I present an initial investigation into a new planet detection technique that
uses the transit timing of a known, transiting planet. The transits of a
solitary planet orbiting a star occur at equally spaced intervals in time. If a
second planet is present, dynamical interactions within the system will cause
the time interval between transits to vary. These transit time variations can
be used to infer the orbital elements of the unseen, perturbing planet. I show
analytic expressions for the amplitude of the transit time variations in
several limiting cases. Under certain conditions the transit time variations
can be comparable to the period of the transiting planet. I also present the
application of this planet detection technique to existing transit observations
of the TrES-1 and HD209458 systems. While no convincing evidence for a second
planet in either system was found from those data, I constrain the mass that a
perturbing planet could have as a function of the semi-major axis ratio of the
two planets and the eccentricity of the perturbing planet. Near low-order,
mean-motion resonances (within about 1% fractional deviation), I find that a
secondary planet must generally have a mass comparable to or less than the mass
of the Earth--showing that these data are the first to have sensitivity to sub
Earth-mass planets orbiting main sequence stars. These results show that TTV
will be an important tool in the detection and characterization of extrasolar
planetary systems.Comment: Ph.D. dissertation (2006). 108 page
Kepler's Missing Planets
We investigate the distributions of the orbital period ratios of adjacent
planets in high multiplicity \kepler\ systems (four or more planets) and low
multiplicity systems (two planets). Modeling the low multiplicity sample as
essentially equivalent to the high multiplicity sample, but with unobserved
intermediate planets, we find some evidence for an excess of planet pairs
between the 2:1 and 3:1 Mean Motion Resonances in the low multiplicity sample.
This possible excess may be the result of strong dynamical interactions near
these or other resonances or it may be a byproduct of other evolutionary events
or processes such as planetary collisions. Three planet systems show a
significant excess of planets near the 2:1 Mean Motion Resonance that is not as
prominent in either of the other samples. This observation may imply a
correlation between strong dynamical interactions and observed planet
number---perhaps a relationship between resonance pairs and the inclinations or
orbital periods of additional planets. The period ratio distributions can also
be used to identify targets to search for missing planets in the each of the
samples, the presence or absence of which would have strong implications for
planet formation and dynamical evolution models.Comment: Accepted to MNRA
Experimental test of airplane boarding methods
We report the results of an experimental comparison of different airplane
boarding methods. This test was conducted in a mock 757 fuselage, located on a
Southern California soundstage, with 12 rows of six seats and a single aisle.
Five methods were tested using 72 passengers of various ages. We found a
significant reduction in the boarding times of optimized methods over
traditional methods. These improved methods, if properly implemented, could
result in a significant savings to airline companies.Comment: 8 pages, submitted to the Journal of Air Transport Managemen
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