1,137 research outputs found
Dirichlet boundary value problem for Chern-Simons modified gravity
Chern-Simons modified gravity comprises the Einstein-Hilbert action and a
higher-derivative interaction containing the Chern-Pontryagin density. We
derive the analog of the Gibbons-Hawking-York boundary term required to render
the Dirichlet boundary value problem well-defined. It turns out to be a
boundary Chern-Simons action for the extrinsic curvature. We address
applications to black hole thermodynamics.Comment: 4 pages, revtex4, v2: added Refs., made one statement stronger, added
footnote and added paragraph on single field inflatio
A Perpetual Harvest Greenhouse System: Integrating Barn, Biofilter, and Greenhouse
A prototype was built to evaluate the performance of an integrated barn-biofilter-greenhouse system. The greenhouse floor in the integrated system consisted of a bed of gravel to store maximum solar energy. A vertical airflow biofilter (3.34 x 3.34 m) was constructed inside a solar energy greenhouse (floor area of 15 x 6.7 m); exhaust air from a barn was passed through the biofilter for odour treatment before being released into the greenhouse. A booster fan was used to provide a steady airflow rate of 1.4 m3/s to the biofilter. Data were collected from October 19 to December 6, 2007. The maximum temperature drop along the 15.5 m long, and insulated (R-20) duct carrying the exhaust air from the hog barn to the biofilter was 7°C. The lowest temperature recorded on top of the biofilter surface was 1.3°C when the biofilter booster fan was not working, while the lowest floor temperature was -3°C. On the coldest day in December, when the biofilter booster fan was not in service, the daily average temperature inside the greenhouse was 4.3°C, whereas the outdoor daily average temperature was -25°C. In order to keep the minimum greenhouse temperature at 10°C, the maximum required volumetric flow rate of barn exhaust air at 15°C was 1.60m3/s. Maximum hydrogen sulfide (H2S) removal efficiency was 55%. The weekly average concentration of carbon dioxide (CO2) inside the greenhouse varied from 841 to 1536 ppm. The system has shown promise at creating an environment suitable for plant growth inside the greenhouse using a waste gas stream from a hog barn to provide both auxiliary heat and enhanced CO2 levels
Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
The extended Kepler mission, K2, is now providing photometry of new fields
every three months in a search for transiting planets. In a recent study,
Foreman-Mackey and collaborators presented a list of 36 planet candidates
orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar
and planetary properties for all systems. We combine ground-based
seeing-limited survey data and adaptive optics imaging with an automated
transit analysis scheme to validate 21 candidates as planets, 17 for the first
time, and identify 6 candidates as likely false positives. Of particular
interest is K2-18 (EPIC 201912552), a bright (K=8.9) M2.8 dwarf hosting a 2.23
\pm 0.25 R_Earth planet with T_eq = 272 \pm 15 K and an orbital period of 33
days. We also present two new open-source software packages which enable this
analysis. The first, isochrones, is a flexible tool for fitting theoretical
stellar models to observational data to determine stellar properties using a
nested sampling scheme to capture the multimodal nature of the posterior
distributions of the physical parameters of stars that may plausibly be
evolved. The second is vespa, a new general-purpose procedure to calculate
false positive probabilities and statistically validate transiting exoplanets.Comment: 17 pages, 5 figures, 5 tables, accepted for publication in the
Astrophysical Journal. Updated to closely reflect published version in ApJ
(2015, 809, 25
Decoherence-induced geometric phase in a multilevel atomic system
We consider the STIRAP process in a three-level atom. Viewed as a closed
system, no geometric phase is acquired. But in the presence of spontaneous
emission and/or collisional relaxation we show numerically that a
non-vanishing, purely real, geometric phase is acquired during STIRAP, whose
magnitude grows with the decay rates. Rather than viewing this
decoherence-induced geometric phase as a nuisance, it can be considered an
example of "beneficial decoherence": the environment provides a mechanism for
the generation of geometric phases which would otherwise require an extra
experimental control knob.Comment: 9 pages, 12 figure
Extended de Sitter Theory of Two Dimensional Gravitational Forces
We present a simple unifying gauge theoretical formulation of gravitational
theories in two dimensional spacetime. This formulation includes the effects of
a novel matter-gravity coupling which leads to an extended de Sitter symmetry
algebra on which the gauge theory is based. Contractions of this theory
encompass previously studied cases.Comment: 19pp, no figs., CTP 2228, UCONN-93-
Thermodynamics of Black Holes in Two (and Higher) Dimensions
A comprehensive treatment of black hole thermodynamics in two-dimensional
dilaton gravity is presented. We derive an improved action for these theories
and construct the Euclidean path integral. An essentially unique boundary
counterterm renders the improved action finite on-shell, and its variational
properties guarantee that the path integral has a well-defined semi-classical
limit. We give a detailed discussion of the canonical ensemble described by the
Euclidean partition function, and examine various issues related to stability.
Numerous examples are provided, including black hole backgrounds that appear in
two dimensional solutions of string theory. We show that the Exact String Black
Hole is one of the rare cases that admits a consistent thermodynamics without
the need for an external thermal reservoir. Our approach can also be applied to
certain higher-dimensional black holes, such as Schwarzschild-AdS,
Reissner-Nordstrom, and BTZ.Comment: 63 pages, 3 pdf figures, v2: added reference
Baryon Structure and the Chiral Symmetry of QCD
Beyond the spontaneous chiral symmetry breaking scale light and strange
baryons should be considered as systems of three constituent quarks with an
effective confining interaction and a chiral interaction that is mediated by
the octet of Goldstone bosons (pseudoscalar mesons) between the constituent
quarks.Comment: Lecture given at the 35. Universit\"atswochen f\"ur Kern- und
Teilchenphysik, Schladming, Austria, March 1996 (Perturbative and
Nonperturbative Aspects of Quantum Field Theory, ed. by H. Latal and W.
Schweiger, Springer 1996). Paper (23 pages) with 2 figures and the required
macro lamuphy
Centerscope
Centerscope, formerly Scope, was published by the Boston University Medical Center "to communicate the concern of the Medical Center for the development and maintenance of improved health care in contemporary society.
Graviton 1-loop partition function for 3-dimensional massive gravity
The graviton 1-loop partition function in Euclidean topologically massive
gravity (TMG) is calculated using heat kernel techniques. The partition
function does not factorize holomorphically, and at the chiral point it has the
structure expected from a logarithmic conformal field theory. This gives strong
evidence for the proposal that the dual conformal field theory to TMG at the
chiral point is indeed logarithmic. We also generalize our results to new
massive gravity.Comment: 19 pages, v2: major revision, considerably stronger conclusions,
added comparison with LCFT partition function, confirmation of LCFT
conjecture, added autho
Restoration of rotational invariance of bound states on the light front
We study bound states in a model with scalar nucleons interacting via an
exchanged scalar meson using the Hamiltonian formalism on the light front. In
this approach manifest rotational invariance is broken when the Fock space is
truncated. By considering an effective Hamiltonian that takes into account two
meson exchanges, we find that this breaking of rotational invariance is
decreased from that which occurs when only one meson exchange is included. The
best improvement occurs when the states are weakly bound.Comment: 20 pages, 6 figures, uses feynMF; changed typos, clarified use of
angular momentu
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