290 research outputs found
Polar bears are inefficient predators of seabird eggs
Climate-mediated sea-ice loss is disrupting the foraging ecology of polar bears (Ursus maritimus) across much of their range. As a result, there have been increased reports of polar bears foraging on seabird eggs across parts of their range. Given that polar bears have evolved to hunt seals on ice, they may not be efficient predators of seabird eggs. We investigated polar bears\u27 foraging performance on common eider (Somateria mollissima) eggs on Mitivik Island, Nunavut, Canada to test whether bear decision-making heuristics are consistent with expectations of optimal foraging theory. Using aerial-drones, we recorded multiple foraging bouts over 11 days, and found that as clutches were depleted to completion, bears did not exhibit foraging behaviours matched to resource density. As the season progressed, bears visited fewer nests overall, but marginally increased their visitation to nests that were already empty. Bears did not display different movement modes related to nest density, but became less selective in their choice of clutches to consume. Lastly, bears that capitalized on visual cues of flushing eider hens significantly increased the number of clutches they consumed; however, they did not use this strategy consistently or universally. The foraging behaviours exhibited by polar bears in this study suggest they are inefficient predators of seabird eggs, particularly in the context of matching behaviours to resource density
A comparative study of the in vitro activity of iodopropynyl butylcarbamate and amphotericin B against Prototheca spp. isolates from European dairy herds.
ABSTRACT The objective of this study was to assess the in vitro effect of iodopropynyl butylcarbamate (IPBC) and amphotericin B (AMB) on Prototheca zopfii genotype 2 and Prototheca blaschkeae isolates recovered from dairy herds of Belgium, France, Italy, Germany, and Poland. The combination of IPBC with AMB on Prototheca isolates and toxicity of IPBC to the bovine mammary epithelial cells were also evaluated. The in vitro activity of IPBC and AMB against 96 isolates of P. zopfii genotype 2 and 42 isolates of P. blaschkeae was performed. Minimum inhibitory concentrations (MIC) and minimum algicidal concentrations (MAC) of IPBC and AMB were determined. To determine any synergistic, additive, or antagonistic effect of the combination of IPBC and AMB, 2-dimensional checkerboard combination tests were also performed to calculate fractional inhibitory concentrations. Cytotoxicity analysis of IPBC to the bovine mammary epithelial cell line was performed using a 3-(4,5-dimethyl-2-thiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The MIC for 50 and 90% of isolates (MIC 50 and MIC 90 , respectively) for IPBC were 4 and 8 mg/L versus 0.5 and 1 mg/L for AMB, respectively. The MIC profiles differed between P. zopfii genotype 2 and P. blaschkeae , with the latter species being more susceptible to both compounds. The MIC 50 and MIC 90 of IPBC were 4 and 8 mg/L for P. zopfii genotype 2 and 1 and 2 mg/L for P. blaschkeae , respectively. The MIC 50 and MIC 90 of AMB were both 1 mg/L for P. zopfii genotype 2 and 0.25 and 1 mg/L for P. blaschkeae , respectively. Both IPBC and AMB exhibited the ability to kill Prototheca spp. The MAC for 90% of isolates of IPBC was twice the MIC 90 , whereas an 8-fold increase of the MIC 90 was algicidal in the case of AMB. Overall, the combined use of IPBC and AMB exhibited an increased algicidal effect, albeit the fractional inhibitory concentration index showed synergistic activity only against 3 P. zopfii genotype 2 isolates. For all the remaining isolates (87.5%), this combination produced only an additive effect. The MTT assay results showed both IPBC and AMB, at the concentrations employed in the study, to be nontoxic to the epithelial mammary gland cells (cell viability >90%). Notably, only IPBC at the highest concentration (i.e., 8 mg/L) exerted a slight cytotoxic effect on the cell line tested (mean cell viability: 88.54 ± 3.88 and 90.66 ± 3.0, after 2 and 4 h of MTT treatment, respectively). The anti- Prototheca activity of IPBC was here demonstrated for the first time. In addition, the combined use of IPBC with AMB enhanced each other's effect, creating an additive rather than synergistic interaction. Both agents, used at concentrations corresponding to MIC values against Prototheca spp., showed no toxic effect for the mammary epithelial cells. In conclusion, IPBC, used either alone or in combination with AMB, can be considered a promising option in the treatment armamentarium for protothecal mastitis in dairy cows
Efficient Blue Electroluminescence Using Quantum-Confined Two-Dimensional Perovskites
Solution-processed
hybrid organic–inorganic lead halide
perovskites are emerging as one of the most promising candidates for
low-cost light-emitting diodes (LEDs). However, due to a small exciton
binding energy, it is not yet possible to achieve an efficient electroluminescence
within the blue wavelength region at room temperature, as is necessary
for full-spectrum light sources. Here, we demonstrate efficient blue
LEDs based on the colloidal, quantum-confined 2D perovskites, with
precisely controlled stacking down to one-unit-cell thickness (<i>n</i> = 1). A variety of low-<i>k</i> organic host
compounds are used to disperse the 2D perovskites, effectively creating
a matrix of the dielectric quantum wells, which significantly boosts
the exciton binding energy by the dielectric confinement effect. Through
the Förster resonance energy transfer, the excitons down-convert
and recombine radiatively in the 2D perovskites. We report room-temperature
pure green (<i>n</i> = 7–10), sky blue (<i>n</i> = 5), pure blue (<i>n</i> = 3), and deep blue (<i>n</i> = 1) electroluminescence, with record-high external quantum
efficiencies in the green-to-blue wavelength region
Search for non-relativistic Magnetic Monopoles with IceCube
The IceCube Neutrino Observatory is a large Cherenkov detector instrumenting
of Antarctic ice. The detector can be used to search for
signatures of particle physics beyond the Standard Model. Here, we describe the
search for non-relativistic, magnetic monopoles as remnants of the GUT (Grand
Unified Theory) era shortly after the Big Bang. These monopoles may catalyze
the decay of nucleons via the Rubakov-Callan effect with a cross section
suggested to be in the range of to
. In IceCube, the Cherenkov light from nucleon decays
along the monopole trajectory would produce a characteristic hit pattern. This
paper presents the results of an analysis of first data taken from May 2011
until May 2012 with a dedicated slow-particle trigger for DeepCore, a
subdetector of IceCube. A second analysis provides better sensitivity for the
brightest non-relativistic monopoles using data taken from May 2009 until May
2010. In both analyses no monopole signal was observed. For catalysis cross
sections of the flux of non-relativistic
GUT monopoles is constrained up to a level of at a 90% confidence level,
which is three orders of magnitude below the Parker bound. The limits assume a
dominant decay of the proton into a positron and a neutral pion. These results
improve the current best experimental limits by one to two orders of magnitude,
for a wide range of assumed speeds and catalysis cross sections.Comment: 20 pages, 20 figure
The IceCube Neutrino Observatory Part VI: Ice Properties, Reconstruction and Future Developments
Papers on ice properties, reconstruction and future developments submitted to
the 33nd International Cosmic Ray Conference (Rio de Janeiro 2013) by the
IceCube Collaboration.Comment: 28 pages, 38 figures; Papers submitted to the 33nd International
Cosmic Ray Conference, Rio de Janeiro 2013; version 2 corrects errors in the
author lis
Determining neutrino oscillation parameters from atmospheric muon neutrino disappearance with three years of IceCube DeepCore data
We present a measurement of neutrino oscillations via atmospheric muon
neutrino disappearance with three years of data of the completed IceCube
neutrino detector. DeepCore, a region of denser instrumentation, enables the
detection and reconstruction of atmospheric muon neutrinos between 10 GeV and
100 GeV, where a strong disappearance signal is expected. The detector volume
surrounding DeepCore is used as a veto region to suppress the atmospheric muon
background. Neutrino events are selected where the detected Cherenkov photons
of the secondary particles minimally scatter, and the neutrino energy and
arrival direction are reconstructed. Both variables are used to obtain the
neutrino oscillation parameters from the data, with the best fit given by
and
(normal mass hierarchy assumed). The
results are compatible and comparable in precision to those of dedicated
oscillation experiments.Comment: 10 pages, 7 figure
Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data
A search for high-energy neutrinos interacting within the IceCube detector
between 2010 and 2012 provided the first evidence for a high-energy neutrino
flux of extraterrestrial origin. Results from an analysis using the same
methods with a third year (2012-2013) of data from the complete IceCube
detector are consistent with the previously reported astrophysical flux in the
100 TeV - PeV range at the level of per flavor and reject a
purely atmospheric explanation for the combined 3-year data at .
The data are consistent with expectations for equal fluxes of all three
neutrino flavors and with isotropic arrival directions, suggesting either
numerous or spatially extended sources. The three-year dataset, with a livetime
of 988 days, contains a total of 37 neutrino candidate events with deposited
energies ranging from 30 to 2000 TeV. The 2000 TeV event is the highest-energy
neutrino interaction ever observed.Comment: 8 pages, 5 figures. Accepted by PRL. The event catalog, event
displays, and other data tables are included after the final page of the
article. Changed from the initial submission to reflect referee comments,
expanding the section on atmospheric backgrounds, and fixes offsets of up to
0.9 seconds in reported event times. Address correspondence to: J. Feintzeig,
C. Kopper, N. Whitehor
Searches for Extended and Point-like Neutrino Sources with Four Years of IceCube Data
We present results on searches for point-like sources of neutrinos using four
years of IceCube data, including the first year of data from the completed
86-string detector. The total livetime of the combined dataset is 1,373 days.
For an E spectrum the median sensitivity at 90\% C.L. is
TeVcms for energies between 1 TeV1 PeV in the northern
sky and TeVcms for energies between 100
TeV 100 PeV in the southern sky. The sensitivity has improved from both the
additional year of data and the introduction of improved reconstructions
compared to previous publications. In addition, we present the first results
from an all-sky search for extended sources of neutrinos. We update results of
searches for neutrino emission from stacked catalogs of sources, and test five
new catalogs; two of Galactic supernova remnants and three of active galactic
nuclei. In all cases, the data are compatible with the background-only
hypothesis, and upper limits on the flux of muon neutrinos are reported for the
sources considered.Comment: 36 pages, 15 figures. Submitted to the Astrophysical Journa
Determining neutrino oscillation parameters from atmospheric muon neutrino disappearance with three years of IceCube DeepCore data
We present a measurement of neutrino oscillations via atmospheric muon
neutrino disappearance with three years of data of the completed IceCube
neutrino detector. DeepCore, a region of denser instrumentation, enables the
detection and reconstruction of atmospheric muon neutrinos between 10 GeV and
100 GeV, where a strong disappearance signal is expected. The detector volume
surrounding DeepCore is used as a veto region to suppress the atmospheric muon
background. Neutrino events are selected where the detected Cherenkov photons
of the secondary particles minimally scatter, and the neutrino energy and
arrival direction are reconstructed. Both variables are used to obtain the
neutrino oscillation parameters from the data, with the best fit given by
and
(normal mass hierarchy assumed). The
results are compatible and comparable in precision to those of dedicated
oscillation experiments.Comment: 10 pages, 7 figure
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