3,420 research outputs found
Kepler Exoplanet Candidate Host Stars are Preferentially Metal Rich
We find that Kepler exoplanet candidate (EC) host stars are preferentially
metal-rich, including the low-mass stellar hosts of small-radius ECs. The last
observation confirms a tentative hint that there is a correlation between the
metallicity of low-mass stars and the presence of low-mass and small-radius
exoplanets. In particular, we compare the J-H--g-r color-color distribution of
Kepler EC host stars with a control sample of dwarf stars selected from the
~150,000 stars observed during Q1 and Q2 of the Kepler mission but with no
detected planets. We find that at J-H = 0.30 characteristic of solar-type
stars, the average g-r color of stars that host giant ECs is 4-sigma redder
than the average color of the stars in the control sample. At the same time,
the average g-r color of solar-type stars that host small-radius ECs is
indistinguishable from the average color of the stars in the control sample. In
addition, we find that at J-H = 0.62 indicative of late K dwarfs, the average
g-r color of stars that host small-radius ECs is 4-sigma redder than the
average color of the stars in the control sample. These offsets are unlikely to
be caused by differential reddening, age differences between the two
populations, or the presence of giant stars in the control sample. Stellar
models suggest that the first color offset is due to a 0.2 dex enhancement in
[Fe/H] of the giant EC host population at M_star = 1 M_Sun, while Sloan
photometry of M 67 and NGC 6791 suggests that the second color offset is due to
a similar [Fe/H] enhancement of the small-radius EC host population at M_star =
0.7 M_Sun. These correlations are a natural consequence of the core-accretion
model of planet formation.Comment: 15 pages, 8 figures, and 1 table in emulateapj format; accepted for
publication in Ap
Breaking the Waves: Modelling the Potential Impact of Public Health Measures to Defer the Epidemic Peak of Novel Influenza A/H1N1
BACKGROUND: On June 11, 2009, the World Health Organization declared phase 6 of the novel influenza A/H1N1 pandemic. Although by the end of September 2009, the novel virus had been reported from all continents, the impact in most countries of the northern hemisphere has been limited. The return of the virus in a second wave would encounter populations that are still nonimmune and not vaccinated yet. We modelled the effect of control strategies to reduce the spread with the goal to defer the epidemic wave in a country where it is detected in a very early stage. METHODOLOGY/PRINCIPAL FINDINGS: We constructed a deterministic SEIR model using the age distribution and size of the population of Germany based on the observed number of imported cases and the early findings for the epidemiologic characteristics described by Fraser (Science, 2009). We propose a two-step control strategy with an initial effort to trace, quarantine, and selectively give prophylactic treatment to contacts of the first 100 to 500 cases. In the second step, the same measures are focused on the households of the next 5,000 to 10,000 cases. As a result, the peak of the epidemic could be delayed up to 7.6 weeks if up to 30% of cases are detected. However, the cumulative attack rates would not change. Necessary doses of antivirals would be less than the number of treatment courses for 0.1% of the population. In a sensitivity analysis, both case detection rate and the variation of R0 have major effects on the resulting delay. CONCLUSIONS/SIGNIFICANCE: Control strategies that reduce the spread of the disease during the early phase of a pandemic wave may lead to a substantial delay of the epidemic. Since prophylactic treatment is only offered to the contacts of the first 10,000 cases, the amount of antivirals needed is still very limited
The complex superstructure in Mg1-xAlxB2 at x~0.5
Electron diffraction and high resolution microscopy have been performed on
Mg1-xAlxB2 with x~0.5. This composition displays a superstructure with a repeat
period of exactly 2c along the c axis and about 10 nm in the a-b plane. The
superstructure results in ring-shaped superreflections in the diffraction
pattern. Irradiation by a strong electron beam results in a loss of the
superstructure and a decrease of about 1% in the c lattice parameter. In-situ
heating and cooling on the other hand showed that the superstructure is stable
from 100 K to 700 K. Possible origins for the superstructure are proposed
SARS-CoV-2 Omicron variants BA.1 and BA.2 both show similarly reduced disease severity of COVID-19 compared to Delta, Germany, 2021 to 2022
German national surveillance data analysis shows that hospitalisation odds associated with Omicron lineage BA.1 or BA.2 infections are up to 80% lower than with Delta infection, primarily in ≥ 35-year-olds. Hospitalised vaccinated Omicron cases’ proportions (2.3% for both lineages) seemed lower than those of the unvaccinated (4.4% for both lineages). Independent of vaccination status, the hospitalisation frequency among cases with Delta seemed nearly threefold higher (8.3%) than with Omicron (3.0% for both lineages), suggesting that Omicron inherently causes less severe disease.Peer Reviewe
Evaluation of Arctic Sea Ice Thickness Simulated by AOMIP Models
We compare results from six AOMIP model simulations with estimates of sea ice thickness obtained from ICESat, moored and submarine-based upward looking sensors, airborne electromagnetic measurements and drill holes. Our goal is to find patterns of model performance to guide model improvement. The satellite data is pan-arctic from 2004-2008, ice-draft data is from moored instruments in Fram Strait, the Greenland Sea and the Beaufort Sea from 1992-2008 and from submarines from 1975-2000. The drill hole data are from the Laptev and East Siberian marginal seas from 1982-1986 and from coastal stations from 1998-2009. While there are important caveats when comparing modeled results with measurements from different platforms and time periods such as these, the models agree well with moored ULS data. In general, the AOMIP models underestimate the thickness of measured ice thicker than about 2 m and overestimate thickness of ice thinner than 2 m. The simulated results are poor over the fast ice and marginal seas of the Siberian shelves. Averaging over all observational data sets, the better correlations and smaller differences from observed thickness are from the ECCO2 and UW models
The Nylon Scintillator Containment Vessels for the Borexino Solar Neutrino Experiment
Borexino is a solar neutrino experiment designed to observe the 0.86 MeV Be-7
neutrinos emitted in the pp cycle of the sun. Neutrinos will be detected by
their elastic scattering on electrons in 100 tons of liquid scintillator. The
neutrino event rate in the scintillator is expected to be low (~0.35 events per
day per ton), and the signals will be at energies below 1.5 MeV, where
background from natural radioactivity is prominent. Scintillation light
produced by the recoil electrons is observed by an array of 2240
photomultiplier tubes. Because of the intrinsic radioactive contaminants in
these PMTs, the liquid scintillator is shielded from them by a thick barrier of
buffer fluid. A spherical vessel made of thin nylon film contains the
scintillator, separating it from the surrounding buffer. The buffer region
itself is divided into two concentric shells by a second nylon vessel in order
to prevent inward diffusion of radon atoms. The radioactive background
requirements for Borexino are challenging to meet, especially for the
scintillator and these nylon vessels. Besides meeting requirements for low
radioactivity, the nylon vessels must also satisfy requirements for mechanical,
optical, and chemical properties. The present paper describes the research and
development, construction, and installation of the nylon vessels for the
Borexino experiment
Unusual effects of anisotropy on the specific heat of ceramic and single crystal MgB2
The two-gap structure in the superconducting state of MgB_2 gives rise to
unusual thermodynamic properties which depart markedly from the isotropic
single-band BCS model, both in their temperature- and field dependence. We
report and discuss measurements of the specific heat up to 16 T on ceramic, and
up to 14 T on single crystal samples, which demonstrate these effects in the
bulk. The behavior in zero field is described in terms of two characteristic
temperatures, a crossover temperature Tc_pi ~ 13 K, and a critical temperature
Tc = Tc_sigma ~ 38 K, whereas the mixed-state specific heat requires three
characteristic fields, an isotropic crossover field Hc2_pi ~ 0.35 T, and an
anisotropic upper critical field with extreme values Hc2_sigma_c ~ 3.5 T and
Hc2_sigma_ab ~ 19 T, where the indexes \pi and \sigma refer to the 3D and 2D
sheets of the Fermi surface. Irradiation-induced interband scattering tends to
move the gaps toward a common value, and increases the upper critical field up
to ~ 28 T when Tc = 30 K.Comment: 31 pages, 9 figures. Accepted in the Physica C special issue on MgB
Far-infrared transmission studies of c-axis oriented superconducting MgB2 thin film
We reported far-infrared transmission measurements on a c-axis oriented
superconducting MgB thin film in the frequency range of 30 250
cm. We found that these measurements were sensitive to values of
scattering rate and superconducting gap . By fitting the
experimental transmission spectra at 40 K and below, we obtained
(700 1000) cm and 42 cm. These two
quantities suggested that MgB belong to the dirty limit.Comment: submitted at May
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