5,234 research outputs found
Spin Squeezing under Non-Markovian Channels by Hierarchy Equation Method
We study spin squeezing under non-Markovian channels, and consider an
ensemble of independent spin-1/2 particles with exchange symmetry. Each
spin interacts with its own bath, and the baths are independent and identical.
For this kind of open system, the spin squeezing under decoherence can be
investigated from the dynamics of the local expectations, and the multi-qubit
dynamics can be reduced into the two-qubit one. The reduced dynamics is
obtained by the hierarchy equation method, which is a exact without
rotating-wave and Born-Markov approximation. The numerical results show that
the spin squeezing displays multiple sudden vanishing and revival with lower
bath temperature, and it can also vanish asymptotically.Comment: 7 pages, 4 figure
A systematic TMRT observational study of Galactic C/C ratios from Formaldehyde
We present observations of the C-band (4.8 GHz) and Ku-band
(14.5 GHz) K-doublet lines of HCO and the C-band
(4.6 GHz) line of HCO toward a large sample of
Galactic molecular clouds, through the Shanghai Tianma 65-m radio telescope
(TMRT). Our sample with 112 sources includes strong HCO sources from the
TMRT molecular line survey at C-band and other known HCO sources. All three
lines are detected toward 38 objects (43 radial velocity components) yielding a
detection rate of 34\%. Complementary observations of their continuum emission
at both C- and Ku-bands were performed. Combining spectral line parameters and
continuum data, we calculate the column densities, the optical depths and the
isotope ratio HCO/HCO for each source. To evaluate photon
trapping caused by sometimes significant opacities in the main isotopologue's
rotational mm-wave lines connecting our measured K-doublets, and to obtain
C/C abundance ratios, we used the RADEX non-LTE model accounting
for radiative transfer effects. This implied the use of the new collision rates
from \citet{Wiesenfeld2013}. Also implementing distance values from
trigonometric parallax measurements for our sources, we obtain a linear fit of
C/C = (5.081.10)D + (11.866.60), with a
correlation coefficient of 0.58. D refers to Galactocentric distances.
Our C/C ratios agree very well with the ones deduced from CN and
CO but are lower than those previously reported on the basis of HCO,
tending to suggest that the bulk of the HCO in our sources was formed on
dust grain mantles and not in the gas phase.Comment: 27 pages, 8 figures, 7 tables. Accepted for publication in The
Astrophysical Journa
Instrumentation of YSZ oxygen sensor calibration in liquid lead-bismuth eutectic
Liquid lead-bismuth eutectic (LBE), a good candidate for the coolant in the subcritical transmutation blanket, is known to be very corrosive to the stainless steel that transports it. Such a corrosion problem can be prevented by producing and maintaining a protective oxide layer on the exposed surface of the stainless steel. Proper formation of the oxide layer critically depends on the accurate measurement and control of the oxygen concentration in liquid LBE. An oxygen sensor calibration/measurement apparatus has been designed and built to deliberately calibrate an yttria stabilized zirconia (YSZ) oxygen sensor. A detailed description of this system with its main components and their functions is presented. Calibration curves of voltage vs. temperature, ranging from 350°C to 550°C, under various oxygen concentrations in liquid LBE have been obtained for the YSZ oxygen sensors, and are presented and analyzed. The characteristics of this YSZ oxygen sensor are analysed and discussed
Electronic Structure of KFeSe from First Principles Calculations
Electronic structure and magnetic properties for iron-selenide KFeSe
are studied by first-principles calculations. The ground state is stripe-like
antiferromagnetic with calculated 2.26 magnetic moment on Fe atoms; and
the , coupling strengths are calculated to be 0.038 eV and 0.029 eV.
The states around are dominated by the Fe-3d orbitals which hybridize
noticeably to the Se-4p orbitals. While the band structure of KFeSe is
similar to a heavily electron-doped BaFeAs or FeSe system, the Fermi
surface of KFeSe is much closer to \fs11 system since the electron
sheets around is symmetric with respect to - exchange. These
features, as well as the absence of Fermi surface nesting, suggest that the
parental KFeSe could be regarded as an electron over-doped 11 system
with possible local moment magnetism.Comment: accepted by Chinese Physics Letter, to appear as Chinese Physics
Letter, Vol 28, page 057402 (2011
Effects of Mo content on corrosion and tribocorrosion behaviours of Ti-Mo orthopaedic alloys fabricated by powder metallurgy
Effects of Mo content on corrosion and tribocorrosion of Ti-(8-20)Mo alloys fabricated by powder metallurgy (PM) were investigated. With a higher Mo content, the Ti-Mo alloys showed an increased corrosion resistance, and correspondingly their tribocorrosion resistance presented an initial increase but a subsequent decrease. Ti-16Mo alloy possessed the lowest wear rate of 1.0 × 10-3 mm3/m•N under tribocorrosion condition, which was about 30% of that of as-cast pure Ti (3.3 × 10-3 mm3/m•N) and 91% of that of Ti-6Al-4 V alloy (1.1 × 10-3 mm3/m•N), respectively. The highest tribocorrosion resistance and adequate corrosion resistance make the Ti-16Mo alloy a promising candidate for orthopaedic applications
Effect of gauge boson mass on the phase structure of QED
Dynamical chiral symmetry breaking (DCSB) in QED with finite gauge
boson mass is
studied in the framework of the rainbow approximation of Dyson-Schwinger
equations.
By adopting a simple gauge boson propagator ansatz at finite temperature, we
first numerically solve the
Dyson-Schwinger equation for the fermion self-energy to
determine the chiral phase diagram of QED with finite gauge boson mass
at finite chemical potential and finite temperature, then we study the
effect of the finite gauge mass on the phase diagram of QED. It is found
that the gauge boson mass suppresses the occurrence of
DCSB. The area of the region in the chiral phase diagram corresponding to
DCSB phase decreases as
the gauge boson mass increases. In
particular, chiral symmetry gets restored when is above a
certain critical value. In this paper, we use DCSB to describe the
antiferromagnetic order and use the gauge boson mass to describe the
superconducting order. Our results give qualitatively a physical
picture on the competition and coexistence between antiferromagnetic
order and superconducting orders in high temperature cuprate superconductors.Comment: 10 pages, 2 figure
A genuine maximally seven-qubit entangled state
Contrary to A.Borras et al.'s [1] conjecture, a genuine maximally seven-qubit
entangled state is presented. We find a seven-qubit state whose marginal
density matrices for subsystems of 1,2- qubits are all completely mixed and for
subsystems of 3-qubits is almost completely mixed
Cross-Correlation Detection of Point Sources in WMAP First Year Data
We apply a Cross-correlation (CC) method developed previously for detecting
gamma-ray point sources to the WMAP first year data by using the Point-Spread
Function of WMAP and obtain a full sky CC coefficient map. Analyzing this map,
we find that the CC method is a powerful tool to examine the WMAP foreground
residuals which can be further cleaned accordingly. Evident foreground signals
are found in WMAP foreground cleaned maps and Tegmark cleaned map. In this
process 101 point-sources are detected, and 26 of them are new sources besides
the originally listed WMAP 208 sources. We estimate the flux of these new
sources and verify them by another method. As a result, a revised mask file
based on the WMAP first year data is produced by including these new sources.Comment: 14 pages, 10 figures; accepted for publication by ChJA
Oxygen-vacancy effect on structural, magnetic, and ferroelectric properties in multiferroic YMnO3 single crystals
We have investigated the structural, magnetic, and ferroelectric properties of magnetically frustrated multiferroic YMnO3 single crystals. The ferroelectric domain structures of YMnO3 samples were studied by piezoresponse force microscopy. Instead of domain vortex structure in stoichiometric crystals, YMnO3-delta exhibits a random domain configuration with straight domain walls. In magnetic measurements, the YMnO3-delta crystal shows typical antiferromagnetic behavior with higher Neel temperature and lower magnetization compared to the stoichiometric sample. The ordered oxygen vacancies dominate multiferroicity through tailoring the domain wall structure. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676000
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