14,333 research outputs found
Using a cognitive prosthesis to assist foodservice managerial decision-making
The artificial intelligence community has been notably unsuccessful in producing intelligent agents that think for themselves. However, there is an obvious need for increased information processing power in real life situations. An example of this can be witnessed in the training of a foodservice manager, who is expected to solve a wide variety of complex problems on a daily basis. This article explores the possibility of creating an intelligence aid, rather than an intelligence agent, to assist novice foodservice managers in making decisions that are congruent with a subject matter expert\u27s decision schema
Constraining the dark fluid
Cosmological observations are normally fit under the assumption that the dark
sector can be decomposed into dark matter and dark energy components. However,
as long as the probes remain purely gravitational, there is no unique
decomposition and observations can only constrain a single dark fluid; this is
known as the dark degeneracy. We use observations to directly constrain this
dark fluid in a model-independent way, demonstrating in particular that the
data cannot be fit by a dark fluid with a single constant equation of state.
Parameterizing the dark fluid equation of state by a variety of polynomials in
the scale factor , we use current kinematical data to constrain the
parameters. While the simplest interpretation of the dark fluid remains that it
is comprised of separate dark matter and cosmological constant contributions,
our results cover other model types including unified dark energy/matter
scenarios.Comment: 5 pages, 5 figures incorporated. Updated to new observational data
including SHOES determination of H0; new citations adde
Unified dark energy and dark matter from a scalar field different from quintessence
We explore unification of dark matter and dark energy in a theory containing
a scalar field of non-Lagrangian type, obtained by direct insertion of a
kinetic term into the energy-momentum tensor. This scalar is different from
quintessence, having an equation of state between -1 and 0 and a zero sound
speed in its rest frame. We solve the equations of motion for an exponential
potential via a rewriting as an autonomous system, and demonstrate the
observational viability of the scenario, for sufficiently small exponential
potential parameter \lambda, by comparison to a compilation of kinematical
cosmological data.Comment: 10 pages RevTeX4 with 5 figures incorporate
Reconstructing thawing quintessence with multiple datasets
In this work we model the quintessence potential in a Taylor series
expansion, up to second order, around the present-day value of the scalar
field. The field is evolved in a thawing regime assuming zero initial velocity.
We use the latest data from the Planck satellite, baryonic acoustic
oscillations observations from the Sloan Digital Sky Survey, and Supernovae
luminosity distance information from Union2.1 to constrain our models
parameters, and also include perturbation growth data from the WiggleZ, BOSS
and the 6dF surveys. The supernova data provide the strongest individual
constraint on the potential parameters. We show that the growth data
performance is competitive with the other datasets in constraining the dark
energy parameters we introduce. We also conclude that the combined constraints
we obtain for our model parameters, when compared to previous works of nearly a
decade ago, have shown only modest improvement, even with new growth of
structure data added to previously-existent types of data.Comment: 9 pages, 4 figures and 1 table. Version 2 with minor changes to match
Physical Review D accepted versio
Cold dark matter models with high baryon content
Recent results have suggested that the density of baryons in the Universe,
OmegaB, is much more uncertain than previously thought, and may be
significantly higher. We demonstrate that a higher OmegaB increases the
viability of critical-density cold dark matter (CDM) models. High baryon
fraction offers the twin benefits of boosting the first peak in the microwave
anisotropy power spectrum and of suppressing short-scale power in the matter
power spectrum. These enable viable CDM models to have a larger Hubble constant
than otherwise possible. We carry out a general exploration of high OmegaB CDM
models, varying the Hubble constant h and the spectral index n. We confront a
variety of observational constraints and discuss specific predictions. Although
some observational evidence may favour baryon fractions as high as 20 per cent,
we find that values around 10 to 15 per cent provide a reasonable fit to a wide
range of data. We suggest that models with OmegaB in this range, with h about
0.5 and n about 0.8, are currently the best critical-density CDM models.Comment: 14 pages, LaTeX, with 9 included figures, to appear in MNRAS. Revised
version includes updated references, some changes to section 4. Conclusions
unchange
A dark energy view of inflation
Traditionally, inflationary models are analyzed in terms of parameters such
as the scalar spectral index ns and the tensor to scalar ratio r, while dark
energy models are studied in terms of the equation of state parameter w.
Motivated by the fact that both deal with periods of accelerated expansion, we
study the evolution of w during inflation, in order to derive observational
constraints on its value during an earlier epoch likely dominated by a dynamic
form of dark energy. We find that the cosmic microwave background and
large-scale structure data is consistent with w_inflation=-1 and provides an
upper limit of 1+w <~ 0.02. Nonetheless, an exact de Sitter expansion with a
constant w=-1 is disfavored since this would result in ns=1.Comment: 5 pages, 4 figures; v2: minor modifications to match published
versio
Mixed mode oscillations in a conceptual climate model
Much work has been done on relaxation oscillations and other simple
oscillators in conceptual climate models. However, the oscillatory patterns in
climate data are often more complicated than what can be described by such
mechanisms. This paper examines complex oscillatory behavior in climate data
through the lens of mixed-mode oscillations. As a case study, a conceptual
climate model with governing equations for global mean temperature, atmospheric
carbon, and oceanic carbon is analyzed. The nondimensionalized model is a
fast/slow system with one fast variable (corresponding to ice volume) and two
slow variables (corresponding to the two carbon stores). Geometric singular
perturbation theory is used to demonstrate the existence of a folded node
singularity. A parameter regime is found in which (singular) trajectories that
pass through the folded node are returned to the singular funnel in the
limiting case where . In this parameter regime, the model has a
stable periodic orbit of type for some . To our knowledge, it is the
first conceptual climate model demonstrated to have the capability to produce
an MMO pattern.Comment: 28 pages, 11 figure
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