1,289 research outputs found
Landscape of fear visible from space
By linking ecological theory with freely-available Google Earth satellite imagery, landscape-scale footprints of behavioural interactions between predators and prey can be observed remotely. A Google Earth image survey of the lagoon habitat at Heron Island within Australia's Great Barrier Reef revealed distinct halo patterns within algal beds surrounding patch reefs. Ground truth surveys confirmed that, as predicted, algal canopy height increases with distance from reef edges. A grazing assay subsequently demonstrated that herbivore grazing was responsible for this pattern. In conjunction with recent behavioural ecology studies, these findings demonstrate that herbivores' collective antipredator behavioural patterns can shape vegetation distributions on a scale clearly visible from space. By using sequential Google Earth images of specific locations over time, this technique could potentially allow rapid, inexpensive remote monitoring of cascading, indirect effects of predator removals (e.g., fishing; hunting) and/or recovery and reintroductions (e.g., marine or terrestrial reserves) nearly anywhere on earth
Problems with Time-Varying Extra Dimensions or "Cardassian Expansion" as Alternatives to Dark Energy
It has recently been proposed that the Universe might be accelerating as a
consequence of extra dimensions with time varying size. We show that although
these scenarios can lead to acceleration, they run into serious difficulty when
taking into account limits on the time variation of the four dimensional
Newton's constant. On the other hand, models of ``Cardassian'' expansion based
on extra dimensions which have been constructed so far violate the weak energy
condition for the bulk stress energy, for parameters that give an accelerating
universe.Comment: 8 pages, minor changes. To appear in Physical Review
Creative reminiscence as an early intervention for depression: results of a pilot project.
Reminiscence may help in resolving conflicts from the past and making up the balance of one’s life. Life-review may be further enhanced by the creative expression of memories in stories, poems or drawings. In this way people are encouraged to create and discover metaphors, images and stories that symbolically represent the subjective and inner meaning of their lives. In this article, a new intervention, which combines reminiscence and creative expression aimed at early treatment of depression, is described. A pilot project showed that the intervention Searching for the meaning in life may generate small-sized effects in reducing depression. Additionally, it appears to generate effects of medium size in enhancing mastery. Several possible ways to improve the effectiveness of the intervention are described
A composite axion from a supersymmetric product group
A global symmetry is protected from gravitational effects in
the s-confining product group theory with
matter. If the family symmetry is gauged and an appropriate tree-level
superpotential is added, then the dynamically generated superpotential
spontaneously breaks and
produces a QCD axion. Small values of the -violating parameter are
then possible without any fine-tuning, as long as the product group is suitably
large. By introducing a second copy of the s-confining product group
also coupled to the gauged , we find that values as small as are
consistent with , even under the pessimistic assumption
that the dominant contribution to the axion quality is at tree level.Comment: 16 pages, 3 figures, 4 tables, 2 appendice
Stealth Supersymmetry
We present a broad class of supersymmetric models that preserve R-parity but
lack missing energy signatures. These models have new light particles with
weak-scale supersymmetric masses that feel SUSY breaking only through couplings
to the MSSM. This small SUSY breaking leads to nearly degenerate fermion/boson
pairs, with small mass splittings and hence small phase space for decays
carrying away invisible energy. The simplest scenario has low-scale SUSY
breaking, with missing energy only from soft gravitinos. This scenario is
natural, lacks artificial tunings to produce a squeezed spectrum, and is
consistent with gauge coupling unification. The resulting collider signals will
be jet-rich events containing false resonances that could resemble signatures
of R-parity violation. We discuss several concrete examples of the general
idea, and emphasize gamma + jet + jet resonances, displaced vertices, and very
large numbers of b-jets as three possible discovery modes.Comment: 12 pages, 4 figure
Mangroves enhance the biomass of coral reef fish communities in the Caribbean
Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs
A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus
The Trojan population consists of two swarms of asteroids following the same
orbit as Jupiter and located at the L4 and L5 Lagrange points of the
Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid
617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit
of this double system was hitherto unknown. Here we report that the components,
separated by 680 km, move around the system centre of mass, describing roughly
a circular orbit. Using the orbital parameters, combined with thermal
measurements to estimate the size of the components, we derive a very low
density of 0.8 g/cc. The components of Patroclus are therefore very porous or
composed mostly of water ice, suggesting that they could have been formed in
the outer part of the solar system.Comment: 10 pages, 3 figures, 1 tabl
Sparticle Spectrum of Large Volume Compactification
We examine the large volume compactification of Type IIB string theory or its
F theory limit and the associated supersymmetry breakdown and soft terms. It is
crucial to incorporate the loop-induced moduli mixing, originating from
radiative corrections to the Kahler potential. We show that in the presence of
moduli mixing, soft scalar masses generically receive a D-term contribution of
the order of the gravitino mass m_{3/2} when the visible sector cycle is
stabilized by the D-term potential of an anomalous U(1) gauge symmetry, while
the moduli-mediated gaugino masses and A-parameters tend to be of the order of
m_{3/2}/8pi^2. It is noticed also that a too large moduli mixing can
destabilize the large volume solution by making it a saddle point.Comment: 29 page
TeV scale mirage mediation in NMSSM
We study the next-to-minimal supersymmetric standard model. We consider soft
supersymmetry breaking parameters, which are induced by the mirage mediation
mechanism of supersymmetry breaking. We concentrate on the mirage mediation,
where the so-called mirage scale is the TeV scale. In this scenario, we can
realize the up-type Higgs soft mass of O(200) GeV, while other masses such as
gaugino masses and stop masses are heavy such as 1 TeV or more. Cancellation
between the effective \mu-term and the down-type Higgs soft mass ameliorates
the fine-tuning in the electroweak symmetry breaking even for \mu=O(500) GeV.
The mixing between the doublet and singlet Higgs bosons is suppressed by
(\lambda/\kappa)/tan\beta. Then the lightest doublet Higgs mass naturally
reaches 125 GeV lifted by the new quartic coupling. The higgsino and singlino
are light and their linear combination is the lightest superparticle.Comment: 24 pages, 24 figures, Numerical analysis is replaced with the version
calculated by NMSSMTools. Comments and references are added on the suppressed
doublet-singlet mixing and cases in which the 125 GeV boson is the 2nd
lightest CP-even scalar. The version accepted by JHE
- …