26,649 research outputs found
Orally Administered 6:2 Chlorinated Polyfluorinated Ether Sulfonate (F-53B) Causes Thyroid Dysfunction in Rats
The compound 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), a replacement for perfluorooctanesulfonate (PFOS) in the electroplating industry, has been widely detected in numerous environmental matrices, human sera, and organisms. Due to regulations that limit PFOS use, F-53B use is expected to increase. Therefore, in this study, we performed a subchronic oral toxicity study of F-53B in Sprague Dawley (SD) rats. F-53B was administered orally once daily to male and female rats for 28 days at doses of 5, 20, and 100 mg/kg/day. There were no toxicologically significant changes in F-53B-treated rats, except in the thyroid gland. However, F-53B slightly reduced the serum concentrations of thyroid hormones, including triiodothyronine and thyroxine, compared with their concentrations in the vehicle group. F-53B also induced follicular hyperplasia and was associated with increased thyroid hormone biosynthesis-associated protein expression. These results demonstrate that F-53B is a strong regulator of thyroid hormones in SD rats as it disrupts thyroid function. Thus, caution should be exercised in the industrial application of F-53B as an alternative for PFOS.ope
A diagnostic study of temperature controls on global terrestrial carbon exchange
The observed interannual variability of atmospheric CO2 reflects short-term variability in sources and sinks of CO2 . Analyses using 13CO2 and O2 suggest that much of the observed interannual variability is due to changes in terrestrial CO2 exchange. First principles, empirical correlations and process models suggest a link between climate variation and net ecosystem exchange, but the scaling of ecological process studies to the globe is notoriously difficult. We sought to identify a component of global CO2 exchange that varied coherently with land temperature anomalies using an inverse modeling approach. We developed a family of simplified spatially aggregated ecosystem models (designated K-model versions) consisting of five compartments: atmospheric CO2 , live vegetation, litter, and two soil pools that differ in turnover times. The pools represent cumulative differences from mean C storage due to temperature variability and can thus have positive or negative values. Uptake and respiration of CO2 are assumed to be linearly dependent on temperature. One model version includes a simple representation of the nitrogen cycle in which changes in the litter and soil carbon pools result in stoichiometric release of plant-available nitrogen, the other omits the nitrogen feedback. The model parameters were estimated by inversion of the model against global temperature and CO2 anomaly data using the variational method. We found that the temperature sensitivity of carbon uptake (NPP) was less than that of respiration in all model versions. Analyses of model and data also showed that temperature anomalies trigger ecosystem changes on multiple, lagged time-scales. Other recent studies have suggested a more active land biosphere at Northern latitudes in response to warming and longer growing seasons. Our results indicate that warming should increase NPP, consistent with this theory, but that respiration should increase more than NPP, leading to decreased or negative NEP. A warming trend could, therefore increase NEP if the indirect feedbacks through nutrients were larger than the direct effects of temperature on NPP and respiration, a conjecture which can be tested experimentally. The fraction of the growth rate not predicted by the K-model represents model and data errors, and variability in anthropogenic release, ocean uptake, and other processes not explicitly represented in the model. These large positive and negative residuals from the K-model may be associated with the Southern Oscillation Index
HAT-P-50b, HAT-P-51b, HAT-P-52b, and HAT-P-53b: Three Transiting Hot Jupiters and a Transiting Hot Saturn From the HATNet Survey
We report the discovery and characterization of four transiting exoplanets by
the HATNet survey. The planet HAT-P-50b has a mass of 1.35 M_J and a radius of
1.29 R_J, and orbits a bright (V = 11.8 mag) M = 1.27 M_sun, R = 1.70 R_sun
star every P = 3.1220 days. The planet HAT-P-51b has a mass of 0.31 M_J and a
radius of 1.29 R_J, and orbits a V = 13.4 mag, M = 0.98 M_sun, R = 1.04 R_sun
star with a period of P = 4.2180 days. The planet HAT-P-52b has a mass of 0.82
M_J and a radius of 1.01 R_J, and orbits a V = 14.1 mag, M = 0.89 M_sun, R =
0.89 R_sun star with a period of P = 2.7536 days. The planet HAT-P-53b has a
mass of 1.48 M_J and a radius of 1.32 R_J, and orbits a V = 13.7 mag, M = 1.09
M_sun, R = 1.21 R_sun star with a period of P = 1.9616 days. All four planets
are consistent with having circular orbits and have masses and radii measured
to better than 10% precision. The low stellar jitter and favorable R_P/R_star
ratio for HAT-P-51 make it a promising target for measuring the
Rossiter-McLaughlin effect for a Saturn-mass planet.Comment: Submitted to AJ. 20 pages, 9 figures, 5 tables. Data available at
http://hatnet.org
Angular Power Spectrum of the Microwave Background Anisotropy seen by the COBE Differential Microwave Radiometer
The angular power spectrum estimator developed by Peebles (1973) and Hauser &
Peebles (1973) has been modified and applied to the 2 year maps produced by the
COBE DMR. The power spectrum of the real sky has been compared to the power
spectra of a large number of simulated random skies produced with noise equal
to the observed noise and primordial density fluctuation power spectra of power
law form, with . Within the limited range of spatial scales
covered by the COBE DMR, corresponding to spherical harmonic indices 3 \leq
\ell \lsim 30, the best fitting value of the spectral index is with the Harrison-Zeldovich value approximately
0.5 below the best fit. For 3 \leq \ell \lsim 19, the best fit is . Comparing the COBE DMR at small to
the at from degree scale anisotropy experiments
gives a smaller range of acceptable spectral indices which includes .Comment: 22 pages of LaTex using aaspp.sty and epsf.sty with appended
Postscript figures, COBE Preprint 94-0
Searching for Candidates of Orbital Decays among Transit Exoplanets
Transit observations have become an important technique to probe exoplanets.
Therefore, there are many projects carrying on organized observations of
transit events, which make a huge amount of light-curve and transit timing data
available. We consider this as an excellent opportunity to search for possible
orbital decays of exoplanets from this big number of mid-transit times through
data-model fitting with both fixed-orbit and orbit-decay models. In order to
perform this task, we collect mid-transit-time data from several sources and
construct the most complete database up to date. Among 144 hot Jupiters in our
study, HAT-P-51b, HAT-P-53b, TrES-5b, WASP-12b are classified as the
orbit-decay cases. Thus, in addition to reconfirming WASP-12b as an orbit-decay
planet, our results indicate that HAT-P-51b, HAT-P-53b, TrES-5b are potential
orbit-decay candidates.Comment: 12 pages, 5 figures, 5 tables, accepted by New Astronom
Measurement of the Inclusive Jet Cross Section in pp Collisions at √s = 7 TeV
The inclusive jet cross section is measured in pp collisions with a center-of-mass energy of 7 TeV at the Large Hadron Collider using the CMS experiment. The data sample corresponds to an integrated luminosity of 34 pb^(-1). The measurement is made for jet transverse momenta in the range 18–1100 GeV and for absolute values of rapidity less than 3. The measured cross section extends to the highest values of jet p_T ever observed and, within the experimental and theoretical uncertainties, is generally in agreement with next-to-leading-order perturbative QCD prediction
Measurement of the B^+ Production Cross Section in pp Collisions at √s=7 TeV
Measurements of the total and differential cross sections dσ/dp_T^B and dσ/dy^B for B^+ mesons produced in pp collisions at √s=7 TeV are presented. The data correspond to an integrated luminosity of 5.8 pb^(-1) collected by the CMS experiment operating at the LHC. The exclusive decay B^+→J/ψK^+, with J/ψ→μ^+μ^-, is used to detect B^+ mesons and to measure the production cross section as a function of p_T^B and y^B. The total cross section for p_T^B>5 GeV and |y^B|<2.4 is measured to be 28.1±2.4±2.0±3.1 μb, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement
Measurement of the B^0 Production Cross Section in pp Collisions at √s=7 TeV
Measurements of the differential production cross sections dσ/dp_T^B and dσ/dy^B for B^0 mesons produced in pp collisions at √s=7 TeV are presented. The data set used was collected by the CMS experiment at the LHC and corresponds to an integrated luminosity of 40 pb^(-1). The production cross section is measured from B^0 meson decays reconstructed in the exclusive final state J/ψK_S^0, with the subsequent decays J/ψ→μ^+μ^- and K_S^0→π^+π^-. The total cross section for p_T^B>5 GeV and |y^B|<2.2 is measured to be 33.2±2.5±3.5 μb, where the first uncertainty is statistical and the second is systematic
Differential equations of electrodiffusion: constant field solutions, uniqueness, and new formulas of Goldman-Hodgkin-Katz type
The equations governing one-dimensional, steady-state electrodiffusion are
considered when there are arbitrarily many mobile ionic species present, in any
number of valence classes, possibly also with a uniform distribution of fixed
charges. Exact constant field solutions and new formulas of
Goldman-Hodgkin-Katz type are found. All of these formulas are exact, unlike
the usual approximate ones. Corresponding boundary conditions on the ionic
concentrations are identified. The question of uniqueness of constant field
solutions with such boundary conditions is considered, and is re-posed in terms
of an autonomous ordinary differential equation of order for the electric
field, where is the number of valence classes. When there are no fixed
charges, the equation can be integrated once to give the non-autonomous
equation of order considered previously in the literature including, in the
case , the form of Painlev\'e's second equation considered first in the
context of electrodiffusion by one of us. When , the new equation is a
form of Li\'enard's equation. Uniqueness of the constant field solution is
established in this case.Comment: 29 pages, 5 figure
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