4,472 research outputs found
Atomic Entanglement vs Photonic Visibility for Quantum Criticality of Hybrid System
To characterize the novel quantum phase transition for a hybrid system
consisting of an array of coupled cavities and two-level atoms doped in each
cavity, we study the atomic entanglement and photonic visibility in comparison
with the quantum fluctuation of total excitations. Analytical and numerical
simulation results show the happen of quantum critical phenomenon similar to
the Mott insulator to superfluid transition. Here, the contour lines
respectively representing the atomic entanglement, photonic visibility and
excitation variance in the phase diagram are consistent in the vicinity of the
non-analytic locus of atomic concurrences.Comment: 4 pages, 2 figure
HST and LAMOST discover a dual active galactic nucleus in J0038+4128
We report the discovery of a kiloparsec-scale dual active galactic nucleus
(AGN) in J0038+4128. From the Hubble Space Telescope (HST) Wide Field Planetary
Camera (WFPC2) images, we find two optical nuclei with a projection separation
of 4.7 kpc (3.44 arcsec). The southern component (J0038+4128S) is
spectroscopically observed with the HST Goddard High Resolution Spectrograph in
the UV range and is found to be a Seyfert 1 galaxy with a broad Ly alpha
emission line. The northern component (J0038+4128N) is spectroscopically
observed during the Large Sky Area Multi-Object Fibre Spectroscopic Telescope
(also named the Guoshoujing Telescope) pilot survey in the optical range. The
observed line ratios as well as the consistency of redshift of the nucleus
emission lines and the host galaxy's absorption lines indicate that J0038+4128N
is a Seyfert 2 galaxy with narrow lines only. These results thus confirm that
J0038+4128 is a Seyfert 1-Seyfert 2 AGN pair. The HST WFPC2 F336W/U-band image
of J0038+4128 also reveals for the first time for a dual AGN system two pairs
of bi-symmetric arms, as are expected from the numerical simulations of such
system. Being one of a few confirmed kiloparsec-scale dual AGNs exhibiting a
clear morphological structure of the host galaxies, J0038+4128 provides an
unique opportunity to study the co-evolution of the host galaxies and their
central supermassive black holes undergoing a merging process.Comment: 6 pages, 4 figures, 2 tables, Accepted for publication in MNRAS
Letter
A cosmic ray super high multicore family event. 1: Experiment and general features
Information on the fragmentation region in super high energy hadronic interactions can be obtained through the observations of gamma-ray families produced by cosmic rays. Gamma-ray families with the sum of E sub gamma or 1000 TeV are receiving increasing interests in emulsion chamber experiments. There exist some complications caused by the superposition of nuclear and electromagnetic cascades and the uncertainty in the nature of the primary particles. These complications usually make the conclusions drawn from various interesting phenomena observed in family events not so definite. An interesting family event KO E19, which is likely to have suffered only very slight disturbances is described. It was found in the Mt. Kambala emulsion chamber experiment. The production height of the event is determined to be H=(70 + or - 30)m and some conclusions are given
Intensities of high-energy cosmic rays at Mount Kanbala
The energy spectra of atmospheric cosmic rays at Mt. Kanbala (520 g/sq cm.) are measured with emulsion chambers. The power indexes of the spectra are values of about 2.0 for both gamma-rays and hadrons. Those fluxes are consistent with the ones expected from the model of primary cosmic rays with heavy nuclei of high content in the energy around 10 to the 15th power eV
Ages and Masses of 0.64 million Red Giant Branch stars from the LAMOST Galactic Spectroscopic Survey
We present a catalog of stellar age and mass estimates for a sample of
640\,986 red giant branch (RGB) stars of the Galactic disk from the LAMOST
Galactic Spectroscopic Survey (DR4). The RGB stars are distinguished from the
red clump stars utilizing period spacing derived from the spectra with a
machine learning method based on kernel principal component analysis (KPCA).
Cross-validation suggests our method is capable of distinguishing RC from RGB
stars with only 2 per cent contamination rate for stars with signal-to-noise
ratio (SNR) higher than 50. The age and mass of these RGB stars are determined
from their LAMOST spectra with KPCA method by taking the LAMOST -
giant stars having asteroseismic parameters and the LAMOST-TGAS sub-giant stars
based on isochrones as training sets. Examinations suggest that the age and
mass estimates of our RGB sample stars with SNR 30 have a median error of
30 per cent and 10 per cent, respectively. Stellar ages are found to exhibit
positive vertical and negative radial gradients across the disk, and the age
structure of the disk is strongly flared across the whole disk of
\,kpc. The data set demonstrates good correlations among stellar age,
[Fe/H] and [/Fe]. There are two separate sequences in the [Fe/H] --
[/Fe] plane: a high-- sequence with stars older than
\,8\,Gyr and a low-- sequence composed of stars with ages
covering the whole range of possible ages of stars. We also examine relations
between age and kinematic parameters derived from the Gaia DR2 parallax and
proper motions. Both the median value and dispersion of the orbital
eccentricity are found to increase with age. The vertical angular momentum is
found to fairly smoothly decrease with age from 2 to 12\,Gyr, with a rate of
about 50\,kpc\,km\,s\,Gyr. A full table of the catalog is
public available online.Comment: 16 pages, 22 figures,accepted by MNRA
Robust nonparametric detection of objects in noisy images
We propose a novel statistical hypothesis testing method for detection of
objects in noisy images. The method uses results from percolation theory and
random graph theory. We present an algorithm that allows to detect objects of
unknown shapes in the presence of nonparametric noise of unknown level and of
unknown distribution. No boundary shape constraints are imposed on the object,
only a weak bulk condition for the object's interior is required. The algorithm
has linear complexity and exponential accuracy and is appropriate for real-time
systems. In this paper, we develop further the mathematical formalism of our
method and explore important connections to the mathematical theory of
percolation and statistical physics. We prove results on consistency and
algorithmic complexity of our testing procedure. In addition, we address not
only an asymptotic behavior of the method, but also a finite sample performance
of our test.Comment: This paper initially appeared in 2010 as EURANDOM Report 2010-049.
Link to the abstract at EURANDOM repository:
http://www.eurandom.tue.nl/reports/2010/049-abstract.pdf Link to the paper at
EURANDOM repository: http://www.eurandom.tue.nl/reports/2010/049-report.pd
Peierls distorted chain as a quantum data bus for quantum state transfer
We systematically study the transfer of quantum state of electron spin as the
flying qubit along a half-filled Peierls distorted tight-binding chain
described by the Su-Schrieffer-Heeger (SSH) model, which behaves as a quantum
data bus. This enables a novel physical mechanism for quantum communication
with always-on interaction: the effective hopping of the spin carrier between
sites and connected to two sites in this SSH chain can be induced by
the quasi-excitations of the SSH model. As we prove, it is the Peierls energy
gap of the SSH quasi-excitations that plays a crucial role to protect the
robustness of the quantum state transfer process. Moreover, our observation
also indicates that such a scheme can also be employed to explore the intrinsic
property of the quantum system.Comment: 10 pages, 6 figure
Nonoptimal component placement of the human connectome supports variable brain dynamics
Neural systems are shaped by multiple constraints, balancing region communication with the cost of establishing and maintaining physical connections. It has been suggested that the lengths of neural projections be minimized, reducing their spatial and metabolic impact on the organism. However, long-range connections are prevalent in the connectomes across various species, and thus, rather than rewiring connections to reduce length, an alternative theory proposes that the brain minimizes total wiring length through a suitable positioning of regions, termed component placement optimization. Previous studies in nonhuman primates have refuted this idea by identifying a nonoptimal component placement, where a spatial rearrangement of brain regions in silico leads to a reduced total wiring length. Here, for the first time in humans, we test for component placement optimization. We show a nonoptimal component placement for all subjects in our sample from the Human Connectome Project (N = 280; aged 22–30 years; 138 females), suggesting the presence of constraints—such as the reduction of processing steps between regions—that compete with the elevated spatial and metabolic costs. Additionally, by simulating communication between brain regions, we argue that this suboptimal component placement supports dynamics that benefit cognition
The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?
We use 297 042 main sequence turn-off stars selected from the LSS-GAC to
determine the radial and vertical gradients of stellar metallicity of the
Galactic disk in the anti-center direction. We determine ages of those turn-off
stars by isochrone fitting and measure the temporal variations of metallicity
gradients. Our results show that the gradients, both in the radial and vertical
directions, exhibit significant spatial and temporal variations. The radial
gradients yielded by stars of oldest ages (>11 Gyr) are essentially zero at all
heights from the disk midplane, while those given by younger stars are always
negative. The vertical gradients deduced from stars of oldest ages (>11Gyr) are
negative and show only very weak variations with the Galactocentric distance in
the disk plane, , while those yielded by younger stars show strong
variations with . After being essentially flat at the earliest epochs of
disk formation, the radial gradients steepen as age decreases, reaching a
maxima (steepest) at age 7-8 Gyr, and then they flatten again. Similar temporal
trends are also found for the vertical gradients. We infer that the assemblage
of the Milky Way disk may have experienced at least two distinct phases. The
earlier phase is probably related to a slow, pressure-supported collapse of
gas, when the gas settles down to the disk mainly in the vertical direction. In
the later phase, there are significant radial flows of gas in the disk, and the
rate of gas inflow near the solar neighborhood reaches a maximum around a
lookback time of 7-8 Gyr. The transition of the two phases occurs around a
lookback time between 8 and 11 Gyr. The two phases may be responsible for the
formation of the Milky Way thick and thin disks, respectively. And, as a
consequence, we recommend that stellar age is a natural, physical criterion to
distinguish thin and thick disk stars. ... (abridged)Comment: 31 pages, 17 figures, Accepted for publication in a special issue of
Research in Astronomy and Astrophysics on LAMOST science
Weak Field Phase Diagram for an Integer Quantum Hall Liquid
We study the localization properties in the transition from a two-dimensional
electron gas at zero magnetic field into an integer quantum Hall (QH) liquid.
By carrying out a direct calculation of the localization length for a finite
size sample using a transfer matrix technique, we systematically investigate
the field and disorder dependences of the metal-insulator transition in the
weak field QH regime. We obtain a different phase diagram from the one
conjectured in previous theoretical studies. In particular, we find that: (1)
the extended state energy for each Landau level (LL) is {\it always}
linear in magnetic field; (2) for a given Landau level and disorder
configuration there exists a critical magnetic field below which the
extended state disappears; (3) the lower LLs are more robust to the
metal-insulator transition with smaller . We attribute the above results
to strong LL coupling effect. Experimental implications of our work are
discussed.Comment: 4 pages, ReVTeX 3.0, 4 figures (available upon request
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