7,175 research outputs found
CFHTLenS: the Canada–France–Hawaii Telescope Lensing Survey – imaging data and catalogue products
We present data products from the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg^2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u*g′r′i′z′. The scientific aims of the CFHTLenS team are weak gravitational lensing studies supported by photometric redshift estimates for the galaxies. This paper presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60 and 70 mas with respect to Sloan Digital Sky Survey (SDSS) data, and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion of the order of 0.01–0.03 mag for g′r′i′z′ and about 0.04 mag for u* with respect to SDSS sources down to i_(SDSS) ≤ 21. We demonstrate in accompanying papers that our data meet necessary requirements to fully exploit the survey for weak gravitational lensing analyses in connection with photometric redshift studies. In the spirit of the CFHTLS, all our data products are released to the astronomical community via the Canadian Astronomy Data Centre at http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/community/CFHTLens/query.html. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies
Weak Gravitational Flexion
Flexion is the significant third-order weak gravitational lensing effect
responsible for the weakly skewed and arc-like appearance of lensed galaxies.
Here we demonstrate how flexion measurements can be used to measure galaxy halo
density profiles and large-scale structure on non-linear scales, via
galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation
functions. We describe the origin of gravitational flexion, and discuss its
four components, two of which are first described here. We also introduce an
efficient complex formalism for all orders of lensing distortion. We proceed to
examine the flexion predictions for galaxy-galaxy lensing, examining isothermal
sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric
and elliptical cases. We show that in combination with shear we can precisely
measure galaxy masses and NFW halo concentrations. We also show how flexion
measurements can be used to reconstruct mass maps in 2-D projection on the sky,
and in 3-D in combination with redshift data. Finally, we examine the
predictions for cosmic flexion, including convergence-flexion
cross-correlations, and find that the signal is an effective probe of structure
on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA
Quantum communication between trapped ions through a dissipative environment
We study two trapped ions coupled to the axial phonon modes of a
one-dimensional Coulomb crystal. This system is formally equivalent to the "two
spin-boson" model. We propose a scheme to dynamically generate a maximally
entangled state of two ions within a decoherence-free subspace. Here the
phononic environment of the trapped ions, whatever its temperature and number
of modes, serves as the entangling bus. The efficient production of the pure
singlet state can be exploited to perform short-ranged quantum communication
which is essential in building up a large-scale quantum computer.Comment: 4 pages, 2 figure
Richardson-Gaudin integrability in the contraction limit of the quasispin
Background: The reduced, level-independent, Bardeen-Cooper-Schrieffer
Hamiltonian is exactly diagonalizable by means of a Bethe Ansatz wavefunction,
provided the free variables in the Ansatz are the solutions of the set of
Richardson-Gaudin equations. On the one side, the Bethe Ansatz is a simple
product state of generalised pair operators. On the other hand, the
Richardson-Gaudin equations are strongly coupled in a non-linear way, making
them prone to singularities. Unfortunately, it is non-trivial to give a clear
physical interpretation to the Richardson-Gaudin variables because no physical
operator is directly related to the individual variables. Purpose: The purpose
of this paper is to shed more light on the critical behavior of the
Richardson-Gaudin equations, and how this is related to the product wave
structure of the Bethe Ansatz. Method: A pseudo-deformation of the quasi-spin
algebra is introduced, leading towards a Heisenberg-Weyl algebra in the
contraction limit of the deformation parameter. This enables an adiabatic
connection of the exact Bethe Ansatz eigenstates with pure bosonic multiphonon
states. The physical interpretation of this approach is an adiabatic
suppression of the Pauli exclusion principle. Results: The method is applied to
a so-called "picket-fence" model for the BCS Hamiltonian, displaying a typical
critical behavior in the Richardson-Gaudin variables. It was observed that the
associated bosonic multiphonon states change collective nature at the critical
interaction strengths of the Richardson-Gaudin equations. Conclusions: The
Pauli exclusion principle is the main responsible for the critical behavior of
the Richardson-Gaudin equations, which can be suppressed by means of a pseudo
deformation of the quasispin algebra.Comment: PACS 02.30.Ik, 21.10.Re, 21.60.Ce, 74.20.F
On Calculation of Thermal Conductivity from Einstein Relation in Equilibrium MD
In equilibrium molecular dynamics, Einstein relation can be used to calculate
the thermal conductivity. This method is equivalent to Green-Kubo relation and
it does not require a derivation of an analytical form for the heat current.
However, it is not commonly used as Green-Kubo relationship. Its wide use is
hindered by the lack of a proper definition for integrated heat current (energy
moment) under periodic boundary conditions. In this paper, we developed an
appropriate definition for integrated heat current to calculate thermal
conductivity of solids under periodic conditions. We applied this method to
solid argon and silicon based systems; compared and contrasted with the
Green-Kubo approach.Comment: We updated this manuscript from second version by changing the title
and abstract. This paper is submitted to J. Chem. Phy
The unrestricted Skyrme-tensor time-dependent Hartree-Fock and its application to the nuclear response from spherical to triaxial nuclei
The nuclear time-dependent Hartree-Fock model formulated in the
three-dimensional space,based on the full Skyrme energy density functional and
complemented with the tensor force,is presented for the first time. Full
self-consistency is achieved by the model. The application to the isovector
giant dipole resonance is discussed in the linear limit, ranging from spherical
nuclei (16O, 120Sn) to systems displaying axial or triaxial deformation (24Mg,
28Si, 178Os, 190W, 238U).
Particular attention is paid to the spin-dependent terms from the central
sector of the functional, recently included together with the tensor. They turn
out to be capable of producing a qualitative change on the strength
distribution in this channel. The effect on the deformation properties is also
discussed. The quantitative effects on the linear response are small and,
overall, the giant dipole energy remains unaffected.
Calculations are compared to predictions from the (quasi)-particle random
phase approximation and experimental data where available, finding good
agreement
Vero cytotoxin-producing Escherichia coli O157 outbreaks in England and Wales, 1995: phenotypic methods and genotypic subtyping.
Vero cytotoxin-producing Escherichia coli O157 belonging to four phage types (PTs) caused 11 outbreaks of infection in England and Wales in 1995. Outbreak strains of different PTs were distinguishable by DNA-based methods. Pulsed-field gel electrophoresis best discriminated among strains belonging to the same PT, distinguishing six of the seven PT2 outbreak strains and both PT49 outbreak strains
Scalability of quantum computation with addressable optical lattices
We make a detailed analysis of error mechanisms, gate fidelity, and
scalability of proposals for quantum computation with neutral atoms in
addressable (large lattice constant) optical lattices. We have identified
possible limits to the size of quantum computations, arising in 3D optical
lattices from current limitations on the ability to perform single qubit gates
in parallel and in 2D lattices from constraints on laser power. Our results
suggest that 3D arrays as large as 100 x 100 x 100 sites (i.e.,
qubits) may be achievable, provided two-qubit gates can be performed with
sufficiently high precision and degree of parallelizability. Parallelizability
of long range interaction-based two-qubit gates is qualitatively compared to
that of collisional gates. Different methods of performing single qubit gates
are compared, and a lower bound of is determined on the
error rate for the error mechanisms affecting Cs in a blue-detuned
lattice with Raman transition-based single qubit gates, given reasonable limits
on experimental parameters.Comment: 17 pages, 5 figures. Accepted for publication in Physical Review
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