696 research outputs found
Coastal fish indicators response to natural and anthropogenic drivers–variability at temporal and different spatial scales
AbstractEcological indicators are increasingly used in marine and freshwater management but only few are developed towards full operationalization with known patterns of variability and documented responses to natural and anthropogenic environmental drivers. Here, we evaluate potential sources of indicator variability at two different spatial scales in three coastal fish-based indicators of environmental status in the Baltic Sea; abundance of cyprinids, abundance of perch and the proportion of larger perch. The study was performed on a data set covering 41 monitoring areas subject to different levels of anthropogenic impact, at a latitudinal range of 56–66°N and a salinity range of 2–8. Interannual variation was clearly minor relative to spatial variation. Small-scale spatial variation was related to water depth, wave exposure and water temperature. The remaining variation was assessed in relation to differences in natural and anthropogenic drivers between monitoring areas. Cyprinids showed a clear inverse relationship to water transparency, which was used as a proxy for eutrophication, indicating increased abundances in nutrient enriched areas. None of the indicators showed an expected negative relationship to the level of coastal commercial fisheries catches. Rather, a positive relationship for Perch suggested that the coastal fisheries were concentrated to areas with strong perch populations in the studied areas. The effect of salinity and climate (temperature during the growth season) among monitoring areas were small. The results emphasize the importance of assigning area-specific boundary levels to define good environmental status in the coastal fish indicators, in order to account for natural sources of variability. Further, although long-term monitoring in reference areas is crucial for obtaining a historical baseline, our results suggest that the status assessment of coastal fish would generally gain precision by increasingly including spatially based assessments. We propose that similar analytical approaches could be applied to other ecosystem components, especially in naturally heterogenic environments, in order to separate indicator variability attributed to potential anthropogenic impact
Gamma-rays from dark matter annihilations strongly constrain the substructure in halos
Recently, it has been shown that electrons and positrons from dark matter
(DM) annihilations provide an excellent fit to the Fermi, PAMELA, and HESS
data. Using this DM model, which requires an enhancement of the annihilation
cross section over its standard value to match the observations, we show that
it immediately implies an observable level of gamma-ray emission for the Fermi
telescope from nearby galaxy clusters such as Virgo and Fornax. We show that
this DM model implies a peculiar feature from final state radiation that is a
distinctive signature of DM. Using the EGRET upper limit on the gamma-ray
emission from Virgo, we constrain the minimum mass of substructures within DM
halos to be > 5x10^-3 M_sun -- about four orders of magnitudes larger than the
expectation for cold dark matter. This limits the cutoff scale in the linear
matter power spectrum to k < 35/kpc which can be explained by e.g., warm dark
matter. Very near future Fermi observations will strongly constrain the minimum
mass to be > 10^3 M_sun: if the true substructure cutoff is much smaller than
this, the DM interpretation of the Fermi/PAMELA/HESS data must be wrong. To
address the problem of astrophysical foregrounds, we performed high-resolution,
cosmological simulations of galaxy clusters that include realistic cosmic ray
(CR) physics. We compute the dominating gamma-ray emission signal resulting
from hadronic CR interactions and find that it follows a universal spectrum and
spatial distribution. If we neglect the anomalous enhancement factor and assume
standard values for the cross section and minimum subhalo mass, the same model
of DM predicts comparable levels of the gamma-ray emission from DM
annihilations and CR interactions. This suggests that spectral subtraction
techniques could be applied to detect the annihilation signal.Comment: 5 pages, 2 figures (published version; minor corrections to figures
and result, equation added
Identification of Vascularised Carotid Plaques Using a Standardised and Reproducible Technique to Measure Ultrasound Contrast Uptake
ObjectivesContrast-enhanced ultrasonography (CEUS) has been used to assess the vascularisation of carotid plaques. Our aim was to develop and validate a standardised semi-automated method for CEUS examination of plaques, and test if the technique could be used to identify vulnerable plaques.MethodsStudy participants were a mixed population of symptomatic and asymptomatic subjects, selected if they had a plaque with height >2.5 mm and <10% acoustic shadowing. Participants received a bolus of ultrasound contrast agent and a 90-s cine-loop was captured. A Contrast Quantification Program (CQP) was developed and trained to identify extent of contrast uptake after motion correction and application of a noise reduction algorithm. The technique was validated by comparing CQP values with visual assessment of contrast uptake. CQP values were also compared with plaque echogenicity and history of clinical events.ResultsCQP values correlated with a visual, 5-scale classification of contrast uptake by two blinded, experienced sonographers. Repeated contrast injections showed high reproducibility. Participants with a history of ipsilateral stroke/TIA had significantly higher CQP values than asymptomatic participants.ConclusionWe present a reproducible, semi-automatic method to identify vascularisation of carotid plaques, which could be used in prospective studies to determine the clinical value of plaque vascularisation
Transplanckian energy production and slow roll inflation
In this paper we investigate how the energy density due to a non-standard
choice of initial vacuum affects the expansion of the universe during
inflation. To do this we introduce source terms in the Friedmann equations
making sure that we respect the relation between gravity and thermodynamics. We
find that the energy production automatically implies a slow rolling
cosmological constant. Hence we also conclude that there is no well defined
value for the cosmological constant in the presence of sources. We speculate
that a non-standard vacuum can provide slow roll inflation on its own.Comment: 16 pages, 2 figures, version 2: minor corrections to section 4 and
references adde
The cosmic ray positron excess and neutralino dark matter
Using a new instrument, the HEAT collaboration has confirmed the excess of
cosmic ray positrons that they first detected in 1994. We explore the
possibility that this excess is due to the annihilation of neutralino dark
matter in the galactic halo. We confirm that neutralino annihilation can
produce enough positrons to make up the measured excess only if there is an
additional enhancement to the signal. We quantify the `boost factor' that is
required in the signal for various models in the Minimal Supersymmetric
Standard Model parameter space, and study the dependence on various parameters.
We find models with a boost factor greater than 30. Such an enhancement in the
signal could arise if we live in a clumpy halo. We discuss what part of
supersymmetric parameter space is favored (in that it gives the largest
positron signal), and the consequences for other direct and indirect searches
of supersymmetric dark matter.Comment: 11 pages, 6 figures, matches published version (PRD
Non-Baryonic Dark Matter - Observational Evidence and Detection Methods
The evidence for the existence of dark matter in the universe is reviewed. A
general picture emerges, where both baryonic and non-baryonic dark matter is
needed to explain current observations. In particular, a wealth of
observational information points to the existence of a non-baryonic component,
contributing between around 20 and 40 percent of the critical mass density
needed to make the universe geometrically flat on large scales. In addition, an
even larger contribution from vacuum energy (or cosmological constant) is
indicated by recent observations. To the theoretically favoured particle
candidates for non-baryonic dark matter belong axions, supersymmetric
particles, and of less importance, massive neutrinos. The theoretical
foundation and experimental situation for each of these is reviewed. Direct and
indirect methods for detection of supersymmetric dark matter are described in
some detail. Present experiments are just reaching the required sensitivity to
discover or rule out some of these candidates, and major improvements are
planned over the coming years.Comment: Submitted to Reports on Progress in Physics, 59 pages, LaTeX, iopart
macro, 14 embedded postscript figure
Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification
We examine indirect signals produced by neutralino self-annihilations, in the
galactic halo or inside celestial bodies, in the frame of an effective MSSM
model without gaugino-mass unification at a grand unification scale. We compare
our theoretical predictions with current experimental data of gamma-rays and
antiprotons in space and of upgoing muons at neutrino telescopes. Results are
presented for a wide range of the neutralino mass, though our discussions are
focused on light neutralinos. We find that only the antiproton signal is
potentially able to set constraints on very low-mass neutralinos, below 20 GeV.
The gamma-ray signal, both from the galactic center and from high galactic
latitudes, requires significantly steep profiles or substantial clumpiness in
order to reach detectable levels. The up-going muon signal is largely below
experimental sensitivities for the neutrino flux coming from the Sun; for the
flux from the Earth an improvement of about one order of magnitude in
experimental sensitivities (with a low energy threshold) can make accessible
neutralino masses close to O, Si and Mg nuclei masses, for which resonant
capture is operative.Comment: 17 pages, 1 tables and 5 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/indirect04.ps.gz or
through http://www.astroparticle.to.infn.it/. Limit from BR(Bs--> mu+ mu-)
adde
Particle Dark Matter Constraints from the Draco Dwarf Galaxy
It is widely thought that neutralinos, the lightest supersymmetric particles,
could comprise most of the dark matter. If so, then dark halos will emit radio
and gamma ray signals initiated by neutralino annihilation. A particularly
promising place to look for these indicators is at the center of the local
group dwarf spheroidal galaxy Draco, and recent measurements of the motion of
its stars have revealed it to be an even better target for dark matter
detection than previously thought. We compute limits on WIMP properties for
various models of Draco's dark matter halo. We find that if the halo is nearly
isothermal, as the new measurements indicate, then current gamma ray flux
limits prohibit much of the neutralino parameter space. If Draco has a moderate
magnetic field, then current radio limits can rule out more of it. These
results are appreciably stronger than other current constraints, and so
acquiring more detailed data on Draco's density profile becomes one of the most
promising avenues for identifying dark matter.Comment: 13 pages, 6 figure
Inflation as a probe of new physics
In this paper we consider inflation as a probe of new physics near the string
or Planck scale. We discuss how new physics can be captured by the choice of
vacuum, and how this leads to modifications of the primordial spectrum as well
as the way in which the universe expands during inflation. Provided there is a
large number of fields contributing to the vacuum energy -- as typically is
expected in string theory -- we will argue that both types of effects can be
present simultaneously and be of observational relevance. Our conclusion is
that the ambiguity in choice of vacuum is an interesting new parameter in
serious model building.Comment: 14 page
- …