2,668 research outputs found
Observational Constraints on Exponential Gravity
We study the observational constraints on the exponential gravity model of
f(R)=-beta*Rs(1-e^(-R/Rs)). We use the latest observational data including
Supernova Cosmology Project (SCP) Union2 compilation, Two-Degree Field Galaxy
Redshift Survey (2dFGRS), Sloan Digital Sky Survey Data Release 7 (SDSS DR7)
and Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP7) in our analysis.
From these observations, we obtain a lower bound on the model parameter beta at
1.27 (95% CL) but no appreciable upper bound. The constraint on the present
matter density parameter is 0.245< Omega_m^0<0.311 (95% CL). We also find out
the best-fit value of model parameters on several cases.Comment: 14pages, 3 figures, accepted by PR
Anodization of nanoporous alumina on impurity-induced hemisphere curved surface of aluminum at room temperature
Nanoporous alumina which was produced by a conventional direct current anodization [DCA] process at low temperatures has received much attention in various applications such as nanomaterial synthesis, sensors, and photonics. In this article, we employed a newly developed hybrid pulse anodization [HPA] method to fabricate the nanoporous alumina on a flat and curved surface of an aluminum [Al] foil at room temperature [RT]. We fabricate the nanopores to grow on a hemisphere curved surface and characterize their behavior along the normal vectors of the hemisphere curve. In a conventional DCA approach, the structures of branched nanopores were grown on a photolithography-and-etched low-curvature curved surface with large interpore distances. However, a high-curvature hemisphere curved surface can be obtained by the HPA technique. Such a curved surface by HPA is intrinsically induced by the high-resistivity impurities in the aluminum foil and leads to branching and bending of nanopore growth via the electric field mechanism rather than the interpore distance in conventional approaches. It is noted that by the HPA technique, the Joule heat during the RT process has been significantly suppressed globally on the material, and nanopores have been grown along the normal vectors of a hemisphere curve. The curvature is much larger than that in other literatures due to different fabrication methods. In theory, the number of nanopores on the hemisphere surface is two times of the conventional flat plane, which is potentially useful for photocatalyst or other applications
OGLE-2018-BLG-0532Lb: Cold Neptune With Possible Jovian Sibling
We report the discovery of the planet OGLE-2018-BLG-0532Lb, with very obvious
signatures in the light curve that lead to an estimate of the planet-host mass
ratio . Although there are
no obvious systematic residuals to this double-lens/single-source (2L1S) fit,
we find that can be significantly improved by adding either a third
lens (3L1S, ) or second source (2L2S, ) to
the lens-source geometry. After thorough investigation, we conclude that we
cannot decisively distinguish between these two scenarios and therefore focus
on the robustly-detected planet. However, given the possible presence of a
second planet, we investigate to what degree and with what probability such
additional planets may affect seemingly single-planet light curves. Our best
estimates for the properties of the lens star and the secure planet are: a host
mass , system distance kpc and planet mass
with projected separation au.
However, there is a relatively bright (and also relatively blue) star
projected within mas of the lens, and if future high-resolution images
show that this is coincident with the lens, then it is possible that it is the
lens, in which case, the lens would be both more massive and more distant than
the best-estimated values above.Comment: 48 pages, 9 figures, 7 table
Observational Constraints on Teleparallel Dark Energy
We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations
(BAO), and Cosmic Microwave Background (CMB) observations to constrain the
recently proposed teleparallel dark energy scenario based on the teleparallel
equivalent of General Relativity, in which one adds a canonical scalar field,
allowing also for a nonminimal coupling with gravity. Using the power-law, the
exponential and the inverse hyperbolic cosine potential ansatzes, we show that
the scenario is compatible with observations. In particular, the data favor a
nonminimal coupling, and although the scalar field is canonical the model can
describe both the quintessence and phantom regimes.Comment: 19 pages, 6 figures, version accepted by JCA
Generation of ROR gamma t(+) Antigen-Specific T Regulatory 17 Cells from Foxp3(+) Precursors in Autoimmunity
Th17 cells are potent mediators in autoimmune diseases, and RORgt is required for their development. Recent studies have shown that ROR gamma t(+) Treg cells in the gut regulate intestinal inflammation by inhibiting effector T cell function. In the current study, we report that ROR gamma t(+) Treg cells were also found in lymph nodes following immunization. Not only distinct from intestinal ROR gamma t(+) Treg cells in their transcriptomes, peripheral ROR gamma t(+) Treg cells were derived from Foxp3(+) thymic Treg cells in an antigen-specific manner. Development of these ROR gamma t(+) Treg cells, coined T regulatory 17 (Tr17) cells, depended on IL-6/Stat3 signaling. Tr17 cells showed suppressive activity against antigen-specific effector T cells in vitro. In addition, Tr17 cells efficiently inhibited myelin-specific Th17-cell-mediated CNS auto-inflammation in a passive EAE model. Collectively, our study demonstrates that Tr17 cells are effector Treg cells that potentially restrict autoimmunity.</p
Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M-dwarf
We report the discovery of a microlensing planet
OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio . The planetary signal, which is characterized by a short "bump" on the rising side of the lensing light curve, was densely
covered by ground-based surveys. We find that the signal can be explained by a
bright source that fully envelops the planetary caustic, i.e., a "Hollywood"
geometry. Combined with the source proper motion measured from , the
satellite parallax measurement makes it possible to precisely
constrain the lens physical parameters. The preferred solution, in which the
planet perturbs the minor image due to lensing by the host, yields a
Uranus-mass planet with a mass of orbiting
a mid M-dwarf with a mass of . There is also
a second possible solution that is substantially disfavored but cannot be ruled
out, for which the planet perturbs the major image. The latter solution yields
and . By
combining the microlensing and data together with a Galactic model, we
find in either case that the lens lies on the near side of the Galactic bulge
at a distance . Future adaptive optics
observations may decisively resolve the major image/minor image degeneracy.Comment: 34 pages, 8 figures, Submitted to AAS journa
Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition
The strong interest in graphene has motivated the scalable production of high
quality graphene and graphene devices. Since large-scale graphene films
synthesized to date are typically polycrystalline, it is important to
characterize and control grain boundaries, generally believed to degrade
graphene quality. Here we study single-crystal graphene grains synthesized by
ambient CVD on polycrystalline Cu, and show how individual boundaries between
coalescing grains affect graphene's electronic properties. The graphene grains
show no definite epitaxial relationship with the Cu substrate, and can cross Cu
grain boundaries. The edges of these grains are found to be predominantly
parallel to zigzag directions. We show that grain boundaries give a significant
Raman "D" peak, impede electrical transport, and induce prominent weak
localization indicative of intervalley scattering in graphene. Finally, we
demonstrate an approach using pre-patterned growth seeds to control graphene
nucleation, opening a route towards scalable fabrication of single-crystal
graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material
An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb
We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio q2 = 0:9- 1:2 Ă 10-5 = 3-4 qâ at 1Ï, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries (4. q=qâ. 6), it fills out the previous empty sector at the bottom of the triangular (log s; log q) diagram, where s is the planet-host separation in units of the angular Einstein radius ΞE. Hence, these discoveries call into question the existence, or at least the strength, of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-q planets. Due to the extreme magnification of the event, Amax ⌠1450 for the underlying single-lens event, its light curve revealed a second companion with q3 ⌠0:05 and j log s3j ⌠1, i.e., a factor ⌠10 closer to or farther from the host in projection. The measurements of the microlens parallax âŒE and the angular Einstein radius âŒE allow estimates of the host, planet and second companion masses, (M1;M2;M3) ⌠(0:3Mâ; 1:0Mâ; 17MJ ), the planet and second companion projected separations, (aâ„;2; aâ„;3) ⌠(1:5; 0:15 or 15) au, and system distance DL ⌠1 kpc. The lens could account for most or all of the blended light (I ⌠19:3) and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system. The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events. The detection of this planet, despite the considerable difficulties imposed by COVID-19 (two KMT sites and OGLE were shut down), illustrates the potential utility of this program
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