208 research outputs found
Coral disease hotspots in the Caribbean
Recent outbreaks of coral diseases in the Caribbean have been linked to increasingly stressful seaâsurface temperatures (SSTs). Yet, ocean warming is spatially heterogeneous and therefore has the potential to lead to hotspots of disease activity. Here, we take an epidemiological approach to examine spatial differences in the risk of whiteâband disease on Acropora spp. and yellowâband disease on Orbicella spp. in the Caribbean. Our analysis involved examining the spatial patterns of disease prevalence, and creating a Bayesianârisk model that tested for regional differences in disease risk. The spatial examination of disease prevalence showed several clusters of whiteâband disease, including high prevalence in the Turks and Caicos, Jamaica, Puerto Rico, the Virgin Islands, and Belize, whereas yellowâband disease seemed most prevalent along the Yucatan Peninsula. The Bayesianârisk model showed regional clusters of whiteâband disease near the southern Dominican Republic, Puerto Rico, the Virgin Islands, and the Lesser Antilles, whereas the risk of yellowâband disease was highest in the southern Caribbean. The relative risk of both diseases increased with warmer SSTs. The Bayesianârisk model allowed us to predict where we should expect future outbreaks of coral diseases at a regional scale, and suggests regions where the implementation of disease mitigation plans may be most urgent
Some coral diseases track climate oscillations in the Caribbean
Disease outbreaks continue to reduce coral populations worldwide. Understanding coral diseases and their relationships with environmental drivers is necessary to forecast disease outbreaks, and to predict future changes in coral populations. Yet, the temporal dynamics of coral diseases are rarely reported. Here we evaluate trends and periodicities in the records of three common coral diseases (white-band disease, yellow-band disease, and dark-spot syndrome) that were surveyed between 1997 and 2014 at 2082 sites throughout the Caribbean. The relationship between the periodicities of disease prevalence and El Niño Southern Oscillation (ENSO) cycles was examined using cross-wavelet analyses and convergent cross mapping (CCM). The prevalence of the diseases peaked every two to four years, and matched periodicities in ENSO conditions. CCM models suggested that environmental conditions associated with recent ENSO cycles may have influenced the patterns in disease prevalence. We also found no increasing trends in disease prevalence through time. Instead, our work suggests that the prevalence of coral diseases is dynamic and complex. The gradual increase in sea-surface temperature, a consequence of increasing greenhouse gas emissions, progressively raises the modal temperature threshold of each ENSO cycle. These dynamic cycles and the increasing modal temperatures appear to influence the dynamics of coral diseases
Scales of the Extra Dimensions and their Gravitational Wave Backgrounds
Circumstances are described in which symmetry breaking during the formation
of our three-dimensional brane within a higher-dimensional space in the early
universe excites mesoscopic classical radion or brane-displacement degrees of
freedom and produces a detectable stochastic background of gravitational
radiation. The spectrum of the background is related to the unification energy
scale and the the sizes and numbers of large extra dimensions. It is shown that
properties of the background observable by gravitational-wave observatories at
frequencies Hz to Hz contain information about
unification on energy scales from 1 to TeV, gravity propagating
through extra-dimension sizes from 1 mm to mm, and the dynamical
history and stabilization of from one to seven extra dimensions.Comment: 6 pages, Latex, 1 figure, submitted to Phys. Re
Numerical wave propagation for the triangular - finite element pair
Inertia-gravity mode and Rossby mode dispersion properties are examined for
discretisations of the linearized rotating shallow-water equations using the
- finite element pair on arbitrary triangulations in planar
geometry. A discrete Helmholtz decomposition of the functions in the velocity
space based on potentials taken from the pressure space is used to provide a
complete description of the numerical wave propagation for the discretised
equations. In the -plane case, this decomposition is used to obtain
decoupled equations for the geostrophic modes, the inertia-gravity modes, and
the inertial oscillations. As has been noticed previously, the geostrophic
modes are steady. The Helmholtz decomposition is used to show that the
resulting inertia-gravity wave equation is third-order accurate in space. In
general the \pdgp finite element pair is second-order accurate, so this leads
to very accurate wave propagation. It is further shown that the only spurious
modes supported by this discretisation are spurious inertial oscillations which
have frequency , and which do not propagate. The Helmholtz decomposition
also allows a simple derivation of the quasi-geostrophic limit of the
discretised - equations in the -plane case, resulting in a
Rossby wave equation which is also third-order accurate.Comment: Revised version prior to final journal submissio
Gauge/string duality and scalar glueball mass ratios
It has been shown by Polchinski and Strassler that the scaling of high energy
QCD scattering amplitudes can be obtained from string theory. They considered
an AdS slice as an approximation for the dual space of a confining gauge
theory. Here we use this approximation to estimate in a very simple way the
ratios of scalar glueball masses imposing Dirichlet boundary conditions on the
string dilaton field. These ratios are in good agreement with the results in
the literature. We also find that they do not depend on the size of the slice.Comment: 5 pages, no figures. References updated. Version published in JHE
Age Constraints on Brane Models of Dark Energy
Inspired by recent developments in particle physics, the so-called brane
world cosmology seems to provide an alternative explanation for the present
dark energy problem. In this paper, we use the estimated age of high-
objects to constrain the value of the cosmological parameters in some
particular scenarios based on this large scale modification of gravity. We show
that such models are compatible with these observations for values of the
crossover distance between the 4 and 5 dimensions of the order of .Comment: 4 pages, 2 figures, 1 table, to appear in Phys. Rev.
Lend Me a Hand: Auxiliary Image Data Helps Interaction Detection
In social settings, people interact in close proximity. When analyzing such encounters from video, we are typically interested in distinguishing between a large number of different interactions. Here, we address training deformable part models (DPMs) for the detection of such interactions from video, in both space and time. When we consider a large number of interaction classes, we face two challenges. First, we need to distinguish between interactions that are visually more similar. Second, it becomes more difficult to obtain sufficient specific training examples for each interaction class. In this paper, we address both challenges and focus on the latter. Specifically, we introduce a method to train body part detectors from nonspecific images with pose information. Such resources are widely available. We introduce a training scheme and an adapted DPM formulation to allow for the inclusion of this auxiliary data. We perform cross-dataset experiments to evaluate the generalization performance of our method. We demonstrate that our method can still achieve decent performance, from as few as five training examples
The Deformable Universe
The concept of smooth deformations of a Riemannian manifolds, recently
evidenced by the solution of the Poincar\'e conjecture, is applied to
Einstein's gravitational theory and in particular to the standard FLRW
cosmology. We present a brief review of the deformation of Riemannian geometry,
showing how such deformations can be derived from the Einstein-Hilbert
dynamical principle. We show that such deformations of space-times of general
relativity produce observable effects that can be measured by four-dimensional
observers. In the case of the FLRW cosmology, one such observable effect is
shown to be consistent with the accelerated expansion of the universe.Comment: 20 pages, LaTeX, 3 figure
Brane World Cosmologies and Statistical Properties of Gravitational Lenses
Brane world cosmologies seem to provide an alternative explanation for the
present accelerated stage of the Universe with no need to invoke either a
cosmological constant or an exotic \emph{quintessence} component. In this paper
we investigate statistical properties of gravitational lenses for some
particular scenarios based on this large scale modification of gravity. We show
that a large class of such models are compatible with the current lensing data
for values of the matter density parameter
(). If one fixes to be , as suggested by
most of the dynamical estimates of the quantity of matter in the Universe, the
predicted number of lensed quasars requires a slightly open universe with a
crossover distance between the 4 and 5-dimensional gravities of the order of
.Comment: 6 pages, 3 figures, revte
Non-linear bigravity and cosmic acceleration
We explore the cosmological solutions of classes of non-linear bigravity
theories. These theories are defined by effective four-dimensional Lagrangians
describing the coupled dynamics of two metric tensors, and containing, in the
linearized limit, both a massless graviton and an ultralight one. We focus on
two paradigmatic cases: the case where the coupling between the two metrics is
given by a Pauli-Fierz-type mass potential, and the case where this coupling
derives from five-dimensional brane constructions. We find that cosmological
evolutions in bigravity theories can be described in terms of the dynamics of
two ``relativistic particles'', moving in a curved Lorenzian space, and
connected by some type of nonlinear ``spring''. Classes of bigravity
cosmological evolutions exhibit a ``locking'' mechanism under which the two
metrics ultimately stabilize in a bi-de-Sitter configuration, with relative
(constant) expansion rates. In the absence of matter, we find that a generic
feature of bigravity cosmologies is to exhibit a period of cosmic acceleration.
This leads us to propose bigravity as a source of a new type of dark energy
(``tensor quintessence''), exhibiting specific anisotropic features. Bigravity
could also have been the source of primordial inflation.Comment: 55 pages, 4 figures, references and comments added, final version
published in Phys. Rev.
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