9,049 research outputs found
Casting Light on Dark Matter
The prospects for detecting a candidate supersymmetric dark matter particle
at the LHC are reviewed, and compared with the prospects for direct and
indirect searches for astrophysical dark matter. The discussion is based on a
frequentist analysis of the preferred regions of the Minimal supersymmetric
extension of the Standard Model with universal soft supersymmetry breaking (the
CMSSM). LHC searches may have good chances to observe supersymmetry in the near
future - and so may direct searches for astrophysical dark matter particles,
whereas indirect searches may require greater sensitivity, at least within the
CMSSM.Comment: 16 pages, 13 figures, contribution to the proceedings of the LEAP
2011 Conferenc
Global Optimization-Based Calibration Algorithm for a 2D Distributed Hydrologic-Hydrodynamic and Water Quality Model
Hydrodynamic models with rain-on-the-grid capabilities are usually
computationally expensive. This makes the use of automatic calibration
algorithms hard to apply due to the large number of model runs. However, with
the recent advances in parallel processing, computational resources, and
increasing high-resolution climatologic and GIS data, high-resolution
hydrodynamic models can be used for optimization-based calibration. This paper
presents a global optimization-based algorithm to calibrate a fully distributed
hydrologic-hydrodynamic and water quality model (HydroPol2D) using observed
data (i.e., discharge, or pollutant concentration) as input. The algorithm can
find a near-optimal set of parameters to explain observed gauged data. The
modeling framework presented here, although applied in a poorly-gauged
catchment, can be adapted for catchments with more detailed observations. We
applied the algorithm in different cases of the V-Tilted Catchment, the
Wooden-Board catchment, and in an existing urban catchment with heterogeneous
data. The results of automatic calibration indicate for
the V-Tilted catchment, for salt
concentration pollutographs (i.e., 8.3% of the event mean concentration), and
for the urban catchment case study. This paper also
explores the issue of equifinality in modeling calibration (EqMC). Equifinality
is defined as the set of different parameter combinations that can provide
equally good or accepted results, within the physical parameter ranges. EqMC
decreases with the number of events and increases with the choice of partially
or nonproducing runoff ones. Furthermore, results indicate that providing more
accurate parameter ranges based on a priori knowledge of the catchment is
fundamental to reduce the chances of finding a set of parameters with
equifinality.Comment: Preprint submitted to Journal of Hydrolog
Current profiles and AC losses of a superconducting strip with elliptic cross-section in perpendicular magnetic field
The case of a hard type II superconductor in the form of strip with elliptic
cross-section when placed in transverse magnetic field is studied. We approach
the problem in two steps, both based on the critical-state model. First we
calculate numerically the penetrated current profiles that ensure complete
shielding in the interior, without assuming an a priori form for the profiles.
In the second step we introduce an analytical approximation that asumes that
the current profiles are ellipses. Expressions linking the sample magnetization
to the applied field are derived covering the whole range of applied fields.
The theoretical predictions are tested by the comparison with experimental data
for the imaginary part of AC susceptibility.Comment: 12 pages; 3 figure
Quantum Measurement and the Aharonov-Bohm Effect with Superposed Magnetic Fluxes
We consider the magnetic flux in a quantum mechanical superposition of two
values and find that the Aharonov-Bohm effect interference pattern contains
information about the nature of the superposition, allowing information about
the state of the flux to be extracted without disturbance. The information is
obtained without transfer of energy or momentum and by accumulated nonlocal
interactions of the vector potential with many charged particles
forming the interference pattern, rather than with a single particle. We
suggest an experimental test using already experimentally realized superposed
currents in a superconducting ring and discuss broader implications.Comment: 6 pages, 4 figures; Changes from version 3: corrected typo (not
present in versions 1 and 2) in Eq. 8; Changes from version 2: shortened
abstract; added refs and material in Section IV. The final publication is
available at: http://link.springer.com/article/10.1007/s11128-013-0652-
Aerosol size distribution and radiative forcing response to anthropogenically driven historical changes in biogenic secondary organic aerosol formation
Emissions of biogenic volatile organic compounds (BVOCs) have changed in the past millennium due to changes in land use, temperature, and CO2 concentrations. Recent reconstructions of BVOC emissions have predicted that global isoprene emissions have decreased, while monoterpene and sesquiterpene emissions have increased; however, all three show regional variability due to competition between the various influencing factors. In this work, we use two modeled estimates of BVOC emissions from the years 1000 to 2000 to test the effect of anthropogenic changes to BVOC emissions on secondary organic aerosol (SOA) formation, global aerosol size distributions, and radiative effects using the GEOS-Chem-TOMAS (Goddard Earth Observing System; TwO-Moment Aerosol Sectional) global aerosol microphysics model. With anthropogenic emissions (e.g., SO2, NOx, primary aerosols) turned off and BVOC emissions changed from year 1000 to year 2000 values, decreases in the number concentration of particles of size Dp > 80 nm (N80) of > 25% in year 2000 relative to year 1000 were predicted in regions with extensive land-use changes since year 1000 which led to regional increases in the combined aerosol radiative effect (direct and indirect) of > 0.5 W mâ2 in these regions. We test the sensitivity of our results to BVOC emissions inventory, SOA yields, and the presence of anthropogenic emissions; however, the qualitative response of the model to historic BVOC changes remains the same in all cases. Accounting for these uncertainties, we estimate millennial changes in BVOC emissions cause a global mean direct effect of between +0.022 and +0.163 W mâ2 and the global mean cloud-albedo aerosol indirect effect of between â0.008 and â0.056 W mâ2. This change in aerosols, and the associated radiative forcing, could be a largely overlooked and important anthropogenic aerosol effect on regional climates
The Clapper Rail as an Indicator Species of Estuarine Marsh Health
Clapper Rails (Rallus longirostris) can potentially serve as an indicator species of estuarinemarsh health because of their strong site ïŹ delity and predictable diet consisting predominantly of benthic organisms. These feeding habits increase the likelihood of individuals accumulating signiïŹ - cant amounts of contaminants associated with coastal sediments. Moreover, since Clapper Rails are threatened in most of their western range, additional study of the effects of potential toxins on these birds is essential to conservation programs for this species. Here we present techniques (DNA strand breakage, eggshell structure, and human-consumption risk) that can be used to quantify detrimental effects to Clapper Rails exposed to multiple contaminants in disturbed ecosystems as well as humans who may eat them. Adult birds collected near a site contaminated with polychlorinated biphenyls (PCBs) and metals in Brunswick, Georgia had a high degree of strand breakage, while those collected from a nearby reference area had no strand breakage. Although, results showed that eggshell integrity was compromised in eggs from the contaminated sites, these results were more diffuse, reemphasizing that multiple endpoints should be used in ecological assessments. This study also shows that techniques such as eggshell integrity on hatched eggs and DNA strand breakage in adults can be used as non-lethal mechanisms to monitor the population health of more threatened populations such as those in the western US. We also present results from human-based risk assessment for PCBs as a third toxicological endpoint, since these species are hunted and consumed by the public in the southeastern US. Using standard human-risk thresholds, we show a potential risk to hunters who consume Clapper Rails shot near the contaminated site from PCBs because of the additional lifetime cancer risk associated with that consumption
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