21,232 research outputs found
Encoding the infrared excess (IRX) in the NUVrK color diagram for star-forming galaxies
We present an empirical method of assessing the star formation rate (SFR) of
star-forming galaxies based on their locations in the rest-frame color-color
diagram (NUV-r) vs (r-K). By using the Spitzer 24 micron sample in the COSMOS
field (~16400 galaxies with 0.2 < z < 1.3) and a local GALEX-SDSS-SWIRE sample
(~700 galaxies with z = <
L_IR / L_UV > can be described by a single vector, NRK, that combines the two
colors. The calibration between and NRK allows us to recover the IR
luminosity, L_IR, with an accuracy of ~0.21 dex for the COSMOS sample and ~0.27
dex for the local one. The SFRs derived with this method agree with the ones
based on the observed (UV+IR) luminosities and on the spectral energy
distribution fitting for the vast majority (~85 %) of the star-forming
population. Thanks to a library of model galaxy SEDs with realistic
prescriptions for the star formation history, we show that we need to include a
two-component dust model (i.e., birth clouds and diffuse ISM) and a full
distribution of galaxy inclinations in order to reproduce the behavior of the
stripes in the NUVrK diagram. In conclusion, the NRK method, based only
on rest-frame UV and optical colors available in most of the extragalactic
fields, offers a simple alternative of assessing the SFR of star-forming
galaxies in the absence of far-IR or spectral diagnostic observations.Comment: 21 pages, 22 figures, in publication in Astronomy & Astrophysic
Primordial Lepton Family Asymmtries in Seesaw Model
In leptogenesis scenario, the decays of heavy Majorana neutrinos generate
lepton family asymmetries, and . They are sensitive to
CP violating phases in seesaw models. The time evolution of the lepton family
asymmetries are derived by solving Boltzmann equations. By taking a minimal
seesaw model, we show how each family asymmetry varies with a CP violating
phase. For instance, we find the case that the lepton asymmetry is dominated by
or depending on the choice of the CP violating phase. We
also find the case that the signs of lepton family asymmetries and
are opposite each other. Their absolute values can be larger than
the total lepton asymmetry and the baryon asymmetry may result from the
cancellation of the lepton family asymmetries.Comment: 26 pages, 8 figures, ptp.styl
Modulation-mode assignment for SVD-assisted and iteratively detected downlink multiuser MIMO transmission schemes
In this contribution we jointly optimize the number of multiple-input multiple-output (MIMO) layers and the number of bits per symbol within an iteratively-detected multiuser MIMO downlink (DL) transmission scheme under the constraint of a given fixed data throughput and integrity. Instead of treating all the users jointly as in zero-forcing (ZF) multiuser transmission techniques, the investigated singular value decomposition (SVD) assisted DL multiuser MIMO system takes the individual user's channel characteristics into account. In analogy to bit-interleaved coded irregular modulation, we introduce a MIMO-BICM scheme, where different user-specific signal constellations and mapping arrangement were used within a single codeword. Extrinsic information transfer (EXIT) charts are used for analyzing and optimizing the convergence behaviour of the iterative demapping and decoding. Our results show that in order to achieve the best bit-error rate, not necessarily all user-specific MIMO layers have to be activate
A Turnover in the Galaxy Main Sequence of Star Formation at for Redshifts
The relationship between galaxy star formation rates (SFR) and stellar masses
() is re-examined using a mass-selected sample of 62,000
star-forming galaxies at in the COSMOS 2-deg field. Using new
far-infrared photometry from -PACS and SPIRE and -MIPS 24
m, along with derived infrared luminosities from the NRK method based on
galaxies' locations in the restframe color-color diagram vs. , we are able to more accurately determine total SFRs for our complete
sample. At all redshifts, the relationship between median and
follows a power-law at low stellar masses, and flattens to nearly constant SFR
at high stellar masses. We describe a new parameterization that provides the
best fit to the main sequence and characterizes the low mass power-law slope,
turnover mass, and overall scaling. The turnover in the main sequence occurs at
a characteristic mass of about at all redshifts.
The low mass power-law slope ranges from 0.9-1.3 and the overall scaling rises
in SFR as a function of . A broken power-law fit below
and above the turnover mass gives relationships of below the turnover mass and above
the turnover mass. Galaxies more massive than have on average, a much lower specific star formation rate (sSFR) than
would be expected by simply extrapolating the traditional linear fit to the
main sequence found for less massive galaxies.Comment: 16 pages, 7 figures. Accepted for publication in Ap
Improved Bounds for Drawing Trees on Fixed Points with L-shaped Edges
Let be an -node tree of maximum degree 4, and let be a set of
points in the plane with no two points on the same horizontal or vertical line.
It is an open question whether always has a planar drawing on such that
each edge is drawn as an orthogonal path with one bend (an "L-shaped" edge). By
giving new methods for drawing trees, we improve the bounds on the size of the
point set for which such drawings are possible to: for
maximum degree 4 trees; for maximum degree 3 (binary) trees; and
for perfect binary trees.
Drawing ordered trees with L-shaped edges is harder---we give an example that
cannot be done and a bound of points for L-shaped drawings of
ordered caterpillars, which contrasts with the known linear bound for unordered
caterpillars.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
The Second Transmembrane Domain of P2X7 Contributes to Dilated Pore Formation
Activation of the purinergic receptor P2X7 leads to the cellular permeability of low molecular weight cations. To determine which domains of P2X7 are necessary for this permeability, we exchanged either the C-terminus or portions of the second transmembrane domain (TM2) with those in P2X1 or P2X4. Replacement of the C-terminus of P2X7 with either P2X1 or P2X4 prevented surface expression of the chimeric receptor. Similarly, chimeric P2X7 containing TM2 from P2X1 or P2X4 had reduced surface expression and no permeability to cationic dyes. Exchanging the N-terminal 10 residues or C-terminal 14 residues of the P2X7 TM2 with the corresponding region of P2X1 TM2 partially restored surface expression and limited pore permeability. To further probe TM2 structure, we replaced single residues in P2X7 TM2 with those in P2X1 or P2X4. We identified multiple substitutions that drastically changed pore permeability without altering surface expression. Three substitutions (Q332P, Y336T, and Y343L) individually reduced pore formation as indicated by decreased dye uptake and also reduced membrane blebbing in response to ATP exposure. Three others substitutions, V335T, S342G, and S342A each enhanced dye uptake, membrane blebbing and cell death. Our results demonstrate a critical role for the TM2 domain of P2X7 in receptor function, and provide a structural basis for differences between purinergic receptors. © 2013 Sun et al
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