180 research outputs found
Effectiveness of Frog Skin Secretions Against UV-B Radiation
As an increasing number of their species face possible extinction, amphibian populations have been steadily declining over the past decades (IUCN). While various factors have been suggested or proven to be partially responsible for this reduction, increased ultraviolet B radiation (UVBR) appears to be one of the more prominent explanations, especially when considering the continual thinning of the Earth’s ozone layer due to anthropogenic climate change. However, it has also been discovered that skin secretions, which are reported to function as a component of amphibians’ innate immune systems, may have an effect on UVBR (Cramp and Franklin). With this in mind, we wondered if the skin secretions of two local frog species, California tree frogs (Pseudacris cadaverina) and Pacific tree frogs (Pseudacris regilla), might be indicative of this. We hypothesized that a small glass slide consisting of an individual frog’s secretory layer would have a lower ultraviolet radiation reading than that of an unaltered glass slide, suggesting that a frog’s secretions protect it from a quantifiable amount of harmful UVBR. Using a consistently positioned UV meter, six frogs of each species were collected and tested independently at the streambank in Arroyo Sequit Park. Wavelengths of an individual’s secretions were recorded five separate times, with control measurements being taken before and after each trial. While nearly all secretions from both sampled species saw a slight decrease in UVBR levels when compared to the control readings, our findings were not significant enough to support our hypothesis, suggesting that amphibians’ skin secretions act as only a minimal deterrent to ultraviolet radiation
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Ultraviolet Radiation Influences Perch Selection by a Neotropical Poison-Dart Frog
Ambient ultraviolet-B radiation can harm amphibian eggs, larvae and adults. However, some amphibians avoid UV-B radiation when given the opportunity. The strawberry poison dart frog, Oophaga pumilio, is diurnal and males vocalize throughout the day in light gaps under forest canopies that expose them to solar radiation. Previous studies have demonstrated that males calling from high perches are more successful at mating than those at lower perches. We investigated whether frogs at higher perches receive more ultraviolet-B than those calling from lower perches. We also investigated whether frogs on perches receiving relatively low ultraviolet-B levels maintained their positions for longer compared to individuals calling from perches receiving higher levels of ultraviolet-B. Finally, since it has been hypothesized that some animals utilize levels of UV-A as a visual cue to avoid UV-B damage, we artificially elevated ultraviolet-A levels to examine whether males exposed to artificially elevated ultraviolet-A abandoned their perches sooner compared to males exposed to visible light. We found that frogs called from perches receiving low ultraviolet-B regardless of perch height, and that frogs maintain their positions longer on perches receiving low ultraviolet-B compared to perches receiving even slightly higher ultraviolet-B levels. Exposing the frogs to artificially elevated levels of ultraviolet-A radiation caused males to move off of their perches faster than when they were exposed to a control light source. These experiments suggest that ultraviolet radiation plays an important role in frog behavior related to perch selection, even in rainforests where much of the solar radiation is shielded by the forest canopy
The rainbow trout is affecting the occupancy of native amphibians in Patagonia
In this work, we assessed the occupancy of two native amphibian species of the Valcheta stream in the Somuncura Plateau, northern Patagonia: the Valcheta frog, Pleurodema somuncurense and the Argentine common toad, Rhinella arenarum. We hypothesized that the occupancy of both amphibian species will be shaped by the presence of trout; we also expected a decline in occupancy assuming that the new predator in the system will affect native amphibian populations. Between December 2014 and March 2015, we conducted surveys in 148 sites along the headwaters of Valcheta stream. We modelled the occupancy by including the presence of trout, the temperature of water and the coverage of rocks and vegetation as site-habitat covariates. Models including trout were among the best ranked for both amphibian species. The presence of trout reduced the occupancy of both species and the magnitude of this reduction was much higher in the Valcheta frog than in the Argentine common toad. Overall, our results are of great relevance for land managers considering that the Valcheta frog is among the only three IUCN Critically Endangered amphibians in Argentina.Facultad de Ciencias Naturales y Muse
Hitting sbottom in natural SUSY
We compare the experimental prospects of direct stop and sbottom pair
production searches at the LHC. Such searches for stops are of great interest
as they directly probe for states that are motivated by the SUSY solution to
the hierarchy problem of the Higgs mass parameter - leading to a "Natural" SUSY
spectrum. Noting that sbottom searches are less experimentally challenging and
scale up in reach directly with the improvement on b-tagging algorithms, we
discuss the interplay of small TeV scale custodial symmetry violation with
sbottom direct pair production searches as a path to obtaining strong sub-TeV
constraints on stops in a natural SUSY scenario. We argue that if a weak scale
natural SUSY spectrum does not exist within the reach of LHC, then hopes for
such a spectrum for large regions of parameter space should sbottom out.
Conversely, the same arguments make clear that a discovery of such a spectrum
is likely to proceed in a sbottom up manner.Comment: 18 pages, 8 figures,v2 refs added, JHEP versio
New Particles Working Group Report of the Snowmass 2013 Community Summer Study
This report summarizes the work of the Energy Frontier New Physics working
group of the 2013 Community Summer Study (Snowmass)
Strongly Correlated Quantum Fluids: Ultracold Quantum Gases, Quantum Chromodynamic Plasmas, and Holographic Duality
Strongly correlated quantum fluids are phases of matter that are
intrinsically quantum mechanical, and that do not have a simple description in
terms of weakly interacting quasi-particles. Two systems that have recently
attracted a great deal of interest are the quark-gluon plasma, a plasma of
strongly interacting quarks and gluons produced in relativistic heavy ion
collisions, and ultracold atomic Fermi gases, very dilute clouds of atomic
gases confined in optical or magnetic traps. These systems differ by more than
20 orders of magnitude in temperature, but they were shown to exhibit very
similar hydrodynamic flow. In particular, both fluids exhibit a robustly low
shear viscosity to entropy density ratio which is characteristic of quantum
fluids described by holographic duality, a mapping from strongly correlated
quantum field theories to weakly curved higher dimensional classical gravity.
This review explores the connection between these fields, and it also serves as
an introduction to the Focus Issue of New Journal of Physics on Strongly
Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas. The
presentation is made accessible to the general physics reader and includes
discussions of the latest research developments in all three areas.Comment: 138 pages, 25 figures, review associated with New Journal of Physics
special issue "Focus on Strongly Correlated Quantum Fluids: from Ultracold
Quantum Gases to QCD Plasmas"
(http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Strongly%20Correlated%20Quantum%20Fluids%20-%20from%20Ultracold%20Quantum%20Gases%20to%20QCD%20Plasmas
Excess Higgs Production in Neutralino Decays
The ATLAS and CMS experiments have recently claimed discovery of a Higgs
boson-like particle at ~5 sigma confidence and are beginning to test the
Standard Model predictions for its production and decay. In a variety of
supersymmetric models, a neutralino NLSP can decay dominantly to the Higgs and
the LSP. In natural SUSY models, a light third generation squark decaying
through this chain can lead to large excess Higgs production while evading
existing BSM searches. Such models can be observed at the 8 TeV LHC in channels
exploiting the rare diphoton decays of the Higgs produced in the cascade decay.
Identifying a diphoton resonance in association with missing energy, a lepton,
or b-tagged jets is a promising search strategy for discovery of these models,
and would immediately signal new physics involving production of a Higgs boson.
We also discuss the possibility that excess Higgs production in these SUSY
decays can be responsible for enhancements of up to 50% over the SM prediction
for the observed rate in the existing inclusive diphoton searches, a scenario
which would likely by the end of the 8 TeV run be accompanied by excesses in
the diphoton + lepton/MET and SUSY multi-lepton/b searches and a potential
discovery in a diphoton + 2b search.Comment: 42 pages, 19 figure
Cost-effectiveness of a structured progressive task-oriented circuit class training programme to enhance walking competency after stroke: The protocol of the FIT-Stroke trial
<p>Abstract</p> <p>Background</p> <p>Most patients who suffer a stroke experience reduced walking competency and health-related quality of life (HRQoL). A key factor in effective stroke rehabilitation is intensive, task-specific training. Recent studies suggest that intensive, patient-tailored training can be organized as a circuit with a series of task-oriented workstations.</p> <p>Primary aim of the FIT-Stroke trial is to evaluate the effects and cost-effectiveness of a structured, progressive task-oriented circuit class training (CCT) programme, compared to usual physiotherapeutic care during outpatient rehabilitation in a rehabilitation centre. The task-oriented CCT will be applied in groups of 4 to 6 patients. Outcome will be defined in terms of gait and gait-related ADLs after stroke. The trial will also investigate the generalizability of treatment effects of task-oriented CCT in terms of perceived fatigue, anxiety, depression and perceived HRQoL.</p> <p>Methods/design</p> <p>The multicentre single-blinded randomized trial will include 220 stroke patients discharged to the community from inpatient rehabilitation, who are able to communicate and walk at least 10 m without physical, hands-on assistance. After discharge from inpatient rehabilitation, patients in the experimental group will receive task-oriented CCT two times a week for 12 weeks at the physiotherapy department of the rehabilitation centre. Control group patients will receive usual individual, face-to-face, physiotherapy. Costs will be evaluated by having each patient keep a cost diary for the first 24 weeks after randomisation. Primary outcomes are the mobility part of the Stroke Impact Scale (SIS-3.0) and the EuroQol. Secondary outcomes are the other domains of SIS-3.0, lower limb muscle strength, walking endurance, gait speed, balance, confidence not to fall, instrumental ADL, fatigue, anxiety, depression and HRQoL.</p> <p>Discussion</p> <p>Based on assumptions about the effect of intensity of practice and specificity of treatment effects, FIT-Stroke will address two key aims. The first aim is to investigate the effects of task-oriented CCT on walking competency and HRQoL compared to usual face-to-face physiotherapy. The second aim is to reveal the cost-effectiveness of task-oriented CCT in the first 6 months post stroke. Both aims were recently recommended as priorities by the American Hearth Association and Stroke Council.</p> <p>Trial registration</p> <p>This study is registered in the Dutch Trial Register as NTR1534.</p
New Physics from the Top at the LHC
The top quark may hold the key to new physics associated with the electroweak
symmetry-breaking sector, given its large mass and enhanced coupling to the
Higgs sector. We systematically categorize generic interactions of a new
particle that couples to the top quark and a neutral particle, which is assumed
to be heavy and stable, thus serving as a candidate for cold dark matter. The
experimental signatures for new physics involving top quarks and its partners
at the Large Hadron Collider (LHC) may be distinctive, yet challenging to
disentangle. We optimize the search strategy at the LHC for the decay of the
new particle to a top quark plus missing energy and propose the study of its
properties, such as its spin and couplings. We find that, at 14 TeV with an
integrated luminosity of 100 fb^-1, a spin-zero top partner can be observed at
the 5-sigma level for a mass of 675 GeV. A spin-zero particle can be
differentiated from spin-1/2 and spin-1 particles at the 5-sigma level with a
luminosity of 10 fb^-1.Comment: 19 pages, 7 figures; v2: journal versio
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