680 research outputs found
{BOAO Photometric Survey of Galactic Open Clusters. II. Physical Parameters of 12 Open Clusters
We have initiated a long-term project, the BOAO photometric survey of open
clusters, to enlarge our understanding of galactic structure using UBVI CCD
photometry of open clusters which have been little studied before. This is the
second paper of the project in which we present the photometry of 12 open
clusters. We have determined the cluster parameters by fitting the Padova
isochrones to the color-magnitude diagrams of the clusters. All the clusters
except for Be 0 and NGC 1348 are found to be intermediate-age to old (0.2 - 4.0
Gyrs) open clusters with a mean metallicity of [Fe/H] = 0.0.Comment: 11 page
Variations of tropical upper tropospheric clouds with sea surface temperature and implications for radiative effects
The variations of tropical upper tropospheric (UT) clouds with sea surface temperature (SST) are analyzed using effective cloud fraction from the Atmospheric Infrared Sounder (AIRS) on Aqua and ice water content (IWC) from the Microwave Limb Sounder (MLS) on Aura. The analyses are limited to UT clouds above 300 hPa. Our analyses do not suggest a negative correlation of tropical-mean UT cloud fraction with the cloud-weighted SST (CWT). Instead, both tropical-mean UT cloud fraction and IWC are found to increase with CWT, although their correlations with CWT are rather weak. The rate of increase of UT cloud fraction with CWT is comparable to that of precipitation, while the UT IWC and ice water path (IWP) increase more strongly with CWT. The radiative effect of UT clouds is investigated, and they are shown to provide a net warming at the top of the atmosphere. An increase of IWP with SST yields an increase of net warming that corresponds to a positive feedback, until the UT IWP exceeds a value about 50% greater than presently observed by MLS. Further increases of the UT IWP would favor the shortwave cooling effect, causing a negative feedback. Sensitivities of UT cloud forcing to the uncertainties in UT CFR and IWC measurements are discussed
Magnetorotational collapse of very massive stars to black holes in full general relativity
We perform axisymmetric simulations of the magnetorotational collapse of very
massive stars in full general relativity. Our simulations are applicable to the
collapse of supermassive stars (M > 10^3M_sun) and to very massive Pop III
stars. We model our initial configurations by n=3 polytropes. The ratio of
magnetic to rotational kinetic energy in these configurations is chosen to be
small (1% and 10%). We find that such magnetic fields do not affect the initial
collapse significantly. The core collapses to a black hole, after which black
hole excision is employed to continue the evolution long enough for the hole to
reach a quasi-stationary state. We find that the black hole mass is M_h = 0.95M
and its spin parameter is J_h/M_h^2 = 0.7, with the remaining matter forming a
torus around the black hole. We freeze the spacetime metric ("Cowling
approximation") and continue to follow the evolution of the torus after the
black hole has relaxed to quasi-stationary equilibrium. In the absence of
magnetic fields, the torus settles down following ejection of a small amount of
matter due to shock heating. When magnetic fields are present, the field lines
gradually collimate along the hole's rotation axis. MHD shocks and the MRI
generate MHD turbulence in the torus and stochastic accretion onto the central
black hole. When the magnetic field is strong, a wind is generated in the
torus, and the torus undergoes radial oscillations that drive episodic
accretion onto the hole. These oscillations produce long-wavelength
gravitational waves potentially detectable by LISA. The final state of the
magnetorotational collapse always consists of a central black hole surrounded
by a collimated magnetic field and a hot, thick accretion torus. This system is
a viable candidate for the central engine of a long-soft gamma-ray burst.Comment: 17 pages, 13 figures, replaced with the published versio
The SPEAR Instrument and On-Orbit Performance
The SPEAR (or 'FIMS') instrumentation has been used to conduct the first
large-scale spectral mapping of diffuse cosmic far ultraviolet (FUV, 900-1750
AA) emission, including important diagnostics of interstellar hot (10^4 K -
10^6 K) and photoionized plasmas, H_2, and dust scattered starlight. The
instrumentation's performance has allowed for the unprecedented detection of
astrophysical diffuse far UV emission lines. A spectral resolution of 550 and
an imaging resolution of 5' is achieved on-orbit in the Short (900 - 1175 AA)
and Long (1335 - 1750 AA) bandpass channels within their respective 7.4 deg x
4.3' and 4.0 deg x 4.6' fields of view. We describe the SPEAR imaging
spectrographs, their performance, and the nature and handling of their data
Testing gravitational-wave searches with numerical relativity waveforms: Results from the first Numerical INJection Analysis (NINJA) project
The Numerical INJection Analysis (NINJA) project is a collaborative effort
between members of the numerical relativity and gravitational-wave data
analysis communities. The purpose of NINJA is to study the sensitivity of
existing gravitational-wave search algorithms using numerically generated
waveforms and to foster closer collaboration between the numerical relativity
and data analysis communities. We describe the results of the first NINJA
analysis which focused on gravitational waveforms from binary black hole
coalescence. Ten numerical relativity groups contributed numerical data which
were used to generate a set of gravitational-wave signals. These signals were
injected into a simulated data set, designed to mimic the response of the
Initial LIGO and Virgo gravitational-wave detectors. Nine groups analysed this
data using search and parameter-estimation pipelines. Matched filter
algorithms, un-modelled-burst searches and Bayesian parameter-estimation and
model-selection algorithms were applied to the data. We report the efficiency
of these search methods in detecting the numerical waveforms and measuring
their parameters. We describe preliminary comparisons between the different
search methods and suggest improvements for future NINJA analyses.Comment: 56 pages, 25 figures; various clarifications; accepted to CQ
The impact of measurement errors in the identification of regulatory networks
<p>Abstract</p> <p>Background</p> <p>There are several studies in the literature depicting measurement error in gene expression data and also, several others about regulatory network models. However, only a little fraction describes a combination of measurement error in mathematical regulatory networks and shows how to identify these networks under different rates of noise.</p> <p>Results</p> <p>This article investigates the effects of measurement error on the estimation of the parameters in regulatory networks. Simulation studies indicate that, in both time series (dependent) and non-time series (independent) data, the measurement error strongly affects the estimated parameters of the regulatory network models, biasing them as predicted by the theory. Moreover, when testing the parameters of the regulatory network models, p-values computed by ignoring the measurement error are not reliable, since the rate of false positives are not controlled under the null hypothesis. In order to overcome these problems, we present an improved version of the Ordinary Least Square estimator in independent (regression models) and dependent (autoregressive models) data when the variables are subject to noises. Moreover, measurement error estimation procedures for microarrays are also described. Simulation results also show that both corrected methods perform better than the standard ones (i.e., ignoring measurement error). The proposed methodologies are illustrated using microarray data from lung cancer patients and mouse liver time series data.</p> <p>Conclusions</p> <p>Measurement error dangerously affects the identification of regulatory network models, thus, they must be reduced or taken into account in order to avoid erroneous conclusions. This could be one of the reasons for high biological false positive rates identified in actual regulatory network models.</p
LHC Signatures of a Minimal Supersymmetric Hidden Valley
We investigate the LHC signals of a minimal supersymmetric hidden valley. Our
theory consists of the supersymmetric Standard Model along with a light hidden
U(1)_x gauge multiplet and a pair of hidden chiral superfields that
spontaneously break the new Abelian gauge symmetry near a GeV. The visible and
hidden sectors interact exclusively through supersymmetric gauge kinetic
mixing. We perform a thorough examination of the hidden decay cascades
initiated by the lightest Standard Model superpartner and we study the range of
LHC signals they can produce. In particular, we find parameter regions that
give rise to missing energy, single and multiple lepton jets, and displaced
vertices. Given the simplicity of the underlying theory and the broad range of
collider signals it can produce, we propose that this model is a useful
benchmark for LHC studies of (supersymmetric) hidden valleys.Comment: 45 pages, 15 figures; typos corrected but conclusions unchange
Cyclic Nucleotide-Gated Channels Contribute to Thromboxane A2-Induced Contraction of Rat Small Mesenteric Arteries
Background: Thromboxane A 2 (TxA 2)-induced smooth muscle contraction has been implicated in cardiovascular, renal and respiratory diseases. This contraction can be partly attributed to TxA2-induced Ca 2+ influx, which resulted in vascular contraction via Ca 2+-calmodulin-MLCK pathway. This study aims to identify the channels that mediate TxA2-induced Ca 2+ influx in vascular smooth muscle cells. Methodology/Principal Findings: Application of U-46619, a thromboxane A2 mimic, resulted in a constriction in endothelium-denuded small mesenteric artery segments. The constriction relies on the presence of extracellular Ca 2+, because removal of extracellular Ca 2+ abolished the constriction. This constriction was partially inhibited by an L-type Ca 2+ channel inhibitor nifedipine (0.5–1 mM). The remaining component was inhibited by L-cis-diltiazem, a selective inhibitor for CNG channels, in a dose-dependent manner. Another CNG channel blocker LY83583 [6-(phenylamino)-5,8-quinolinedione] had similar effect. In the primary cultured smooth muscle cells derived from rat aorta, application of U46619 (100 nM) induced a rise in cytosolic Ca 2+ ([Ca 2+]i), which was inhibited by L-cis-diltiazem. Immunoblot experiments confirmed the presence of CNGA2 protein in vascular smooth muscle cells. Conclusions/Significance: These data suggest a functional role of CNG channels in U-46619-induced Ca 2+ influx and contraction of smooth muscle cells
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