8,093 research outputs found
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
Microscopic Study of the Isoscalar Giant Monopole Resonance in Cd, Sn and Pb Isotopes
The isoscalar giant monopole resonance (ISGMR) in Cd, Sn and Pb isotopes has
been studied within the self-consistent Skyrme Hartree-Fock+BCS and
quasi-particle random phase approximation (QRPA). Three Skyrme parameter sets
are used in the calculations, i.e., SLy5, SkM* and SkP, since they are
characterized by different values of the compression modulus in symmetric
nuclear matter, namely K=230, 217, and 202 MeV, respectively. We also
investigate the effect of different types of pairing forces on the ISGMR in Cd,
Sn and Pb isotopes. The calculated peak energies and the strength distributions
of ISGMR are compared with available experimental data. We find that SkP fails
completely to describe the ISGMR strength distribution for all isotopes due to
its low value of the nuclear matter incompressibility, namely K=202 MeV. On the
other hand, the SLy5 parameter set, supplemented by an appropriate pairing
interaction, gives a reasonable description of the ISGMR in Cd and Pb isotopes.
A better description of ISGMR in Sn isotopes is achieved by the SkM*
interaction, that has a somewhat softer value of the nuclear incompressibility.Comment: Submitted to Phys. Rev.
An exactly solvable model of a superconducting to rotational phase transition
We consider a many-fermion model which exhibits a transition from a
superconducting to a rotational phase with variation of a parameter in its
Hamiltonian. The model has analytical solutions in its two limits due to the
presence of dynamical symmetries. However, the symmetries are basically
incompatible with one another; no simple solution exists in intermediate
situations. Exact (numerical) solutions are possible and enable one to study
the behavior of competing but incompatible symmetries and the phase transitions
that result in a semirealistic situation. The results are remarkably simple and
shed light on the nature of phase transitions.Comment: 11 pages including 1 figur
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Testing a phantom eye under various signal-to-noise ratio conditions using eleven different OCT devices
We compared eleven OCT devices in their ability to quantify retinal layer thicknesses under different signal-strength conditions, using a commercially available phantom eye. We analyzed a medium-intensity 50 µm layer in an identical manner for all devices, using the provided log-scale images and a reconstructed linear-scale tissue reflectivity metric. Thickness measurements were highly comparable when the data were analyzed in an identical manner. With optimal signal strength, the thickness of the 50 µm layer was overestimated by a mean of 4.3 µm in the log-scale images and of 2.7 µm in the linear-scale images
Classical mappings of the symplectic model and their application to the theory of large-amplitude collective motion
We study the algebra Sp(n,R) of the symplectic model, in particular for the
cases n=1,2,3, in a new way. Starting from the Poisson-bracket realization we
derive a set of partial differential equations for the generators as functions
of classical canonical variables. We obtain a solution to these equations that
represents the classical limit of a boson mapping of the algebra. The
relationship to the collective dynamics is formulated as a theorem that
associates the mapping with an exact solution of the time-dependent Hartree
approximation. This solution determines a decoupled classical symplectic
manifold, thus satisfying the criteria that define an exactly solvable model in
the theory of large amplitude collective motion. The models thus obtained also
provide a test of methods for constructing an approximately decoupled manifold
in fully realistic cases. We show that an algorithm developed in one of our
earlier works reproduces the main results of the theorem.Comment: 23 pages, LaTeX using REVTeX 3.
Dual-moods and creativity in organisation: A bidirectional mood regulation perspective
The mixed impacts of mood states on creativity call for reconciliation. Contrary to the prevailing notion that positive moods foster creativity, an emerging body of research suggests that negative moods can also boost creativity, and even that positive moods may impair creativity. More recent research suggests that the dual-moods, instead of singular positive or negative moods, can jointly foster creativity, opening a new avenue for mood-creativity research. Nevertheless, the current research which focuses on static mood states is still inadequate to explain the dynamic impacts of moods on creativity over time. To answer this question, we propose that a bidirectional moodregulatory process can reconcile the mixed impacts of dual-moods on creativity with respect to mood changes, and discuss possible research approaches
Hermitian boson mapping and finite truncation
Starting from a general, microscopic fermion-to-boson mapping that preserves
Hermitian conjugation, we discuss truncations of the boson Fock space basis. We
give conditions under which the exact boson images of finite fermion operators
are also finite (e.g., a 1+2-body fermion Hamiltonian is mapped to a 1+2-body
boson Hamiltonian) in the truncated basis. For the most general case, where the
image is not necessarily exactly finite, we discuss how to make practical and
controlled approximations.Comment: 12 pages in RevTex with no figures, Los Alamos preprint #
LA-UR-94-146
Six-dimensional Davidson potential as a dynamical symmetry of the symplectic Interacting Vector Boson Model
A six-dimensional Davidson potential, introduced within the framework of the
Interacting Vector Boson Model (IVBM), is used to describe nuclei that exhibit
transitional spectra between the purely rotational and vibrational limits of
the theory. The results are shown to relate to a new dynamical symmetry that
starts with the reduction. Exact
solutions for the eigenstates of the model Hamiltonian in the basis defined by
a convenient subgroup chain of SO(6) are obtained. A comparison of the
theoretical results with experimental data for heavy nuclei with transitional
spectra illustrates the applicability of the theory.Comment: 9 pages, 4 figure
Spin dependent photoelectron tunnelling from GaAs into magnetic Cobalt
The spin dependence of the photoelectron tunnel current from free standing
GaAs films into out-of- plane magnetized Cobalt films is demonstrated. The
measured spin asymmetry (A) resulting from a change in light helicity, reaches
+/- 6% around zero applied tunnel bias and drops to +/- 2% at a bias of -1.6 V
applied to the GaAs. This decrease is a result of the drop in the photoelectron
spin polarization that results from a reduction in the GaAs surface
recombination velocity. The sign of A changes with that of the Cobalt
magnetization direction. In contrast, on a (nonmagnetic) Gold film A ~ 0%
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