3,222 research outputs found
First detection of GeV emission from an ultraluminous infrared galaxy: Arp 220 as seen with the Fermi Large Area Telescope
Cosmic rays (CRs) in starburst galaxies produce high energy gamma-rays by
colliding with the dense interstellar medium (ISM). Arp 220 is the nearest
ultra luminous infrared galaxy (ULIRG) that has star-formation at extreme
levels, so it has long been predicted to emit high-energy gamma-rays. However,
no evidence of gamma-ray emission was found despite intense efforts of search.
Here we report the discovery of high-energy gamma-ray emission above 200 MeV
from Arp 220 at a confidence level of using 7.5 years of
\textsl {Fermi} Large Area Telescope observations. The gamma-ray emission shows
no significant variability over the observation period and it is consistent
with the quasi-linear scaling relation between the gamma-ray luminosity and
total infrared luminosity for star-forming galaxies, suggesting that these
gamma-rays arise from CR interactions. As the high density medium of Arp 220
makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to
measure the efficiency of powering CRs by supernova (SN) remnants given a known
supernova rate in Arp 220. We find that this efficiency is about
for CRs above 1 GeV.Comment: Accepted by ApJL, 6 pages, 3 figure
Primordial Gravitational Waves Measurements and Anisotropies of CMB Polarization Rotation
Searching for the signal of primordial gravitational waves in the B-modes
(BB) power spectrum is one of the key scientific aims of the cosmic microwave
background (CMB) polarization experiments. However, this could be easily
contaminated by several foreground issues, such as the thermal dust emission.
In this paper we study another mechanism, the cosmic birefringence, which can
be introduced by a CPT-violating interaction between CMB photons and an
external scalar field. Such kind of interaction could give rise to the rotation
of the linear polarization state of CMB photons, and consequently induce the
CMB BB power spectrum, which could mimic the signal of primordial gravitational
waves at large scales. With the recent polarization data of BICEP2 and the
joint analysis data of BICEP2/Keck Array and Planck, we perform a global
fitting analysis on constraining the tensor-to-scalar ratio by considering
the polarization rotation angle which can be separated into a background
isotropic part and a small anisotropic part. Since the data of BICEP2 and Keck
Array experiments have already been corrected by using the "self-calibration"
method, here we mainly focus on the effects from the anisotropies of CMB
polarization rotation angle. We find that including the anisotropies in the
analysis could slightly weaken the constraints on , when using current CMB
polarization measurements. We also simulate the mock CMB data with the
BICEP3-like sensitivity. Very interestingly, we find that if the effects of the
anisotropic polarization rotation angle can not be taken into account properly
in the analysis, the constraints on will be dramatically biased. This
implies that we need to break the degeneracy between the anisotropies of the
CMB polarization rotation angle and the CMB primordial tensor perturbations, in
order to measure the signal of primordial gravitational waves accurately.Comment: 7 pages, 5 figure
The leptonic decay using the principle of maximum conformality
In the paper, we study the leptonic decay width
by using the principle of maximum
conformality (PMC) scale-setting approach. The PMC adopts the renormalization
group equation to set the correct momentum flow of the process, whose value is
independent to the choice of the renormalization scale and its prediction thus
avoids the conventional renormalization scale ambiguities. Using the known
next-to-next-to-next-to-leading order perturbative series together with the PMC
single scale-setting approach, we do obtain a renormalization scale independent
decay width, keV,
where the error is squared average of those from
, GeV and the choices of
factorization scales within of their central values. To compare with
the result under conventional scale-setting approach, this decay width agrees
with the experimental value within errors, indicating the importance of a
proper scale-setting approach.Comment: 6 pages, 4 figure
Remote information concentration and multipartite entanglement in multilevel systems
Remote information concentration (RIC) in -level systems (qudits) is
studied. It is shown that the quantum information initially distributed in
three spatially separated qudits can be remotely and deterministically
concentrated to a single qudit via an entangled channel without performing any
global operations. The entangled channel can be different types of genuine
multipartite pure entangled states which are inequivalent under local
operations and classical communication. The entangled channel can also be a
mixed entangled state, even a bound entangled state which has a similar form to
the Smolin state, but has different features from the Smolin state. A common
feature of all these pure and mixed entangled states is found, i.e., they have
common commuting stabilizers. The differences of qudit-RIC and qubit-RIC
() are also analyzed.Comment: 10 pages, 3 figure
Electrolysis-based on-chip dispensing system for ESI-MS
We report here an integrated on-chip sample dispensing system for Electrospray Ionization-Mass Spectrometry (ESI-MS) applications. The stand-alone chip includes an electrolysis-based micropump, a passive micro mixer and an ESI nozzle. Operation of the chip doesn't require any external fluidic coupling because the chip is designed to have samples filled, sealed and stored in reservoirs inside the chip before testing. Demonstrated here is a chip with two sample reservoirs and dispensing of the samples is electrically controlled individually. Experimentally, on-chip co-dispensing of two different samples is successfully achieved with a dispensing flow rate about 50 nl/min and a continuous spray for 2 minutes
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