62,320 research outputs found
Breakdown of the classical double copy for the effective action of dilaton-gravity at NNLO
We demonstrate that a recently proposed classical double copy procedure to construct the effective action of two massive particles in dilaton-gravity from the analogous problem of two color charged particles in Yang-Mills gauge theory fails at next-to-next-to-leading orders in the post-Minkowskian (3PM) or post-Newtonian (2PN) expansions
Topological Phenomena in Classical Optical Networks
We propose a scheme to realize a topological insulator with optical-passive
elements, and analyze the effects of Kerr-nonlinearities in its topological
behavior. In the linear regime, our design gives rise to an optical spectrum
with topological features and where the bandwidths and bandgaps are
dramatically broadened. The resulting edge modes cover a very wide frequency
range. We relate this behavior to the fact that the effective Hamiltonian
describing the system's amplitudes is long-range. We also develop a method to
analyze the scheme in the presence of a Kerr medium. We assess robustness and
stability of the topological features, and predict the presence of chiral
squeezed fluctuations at the edges in some parameter regimes.Comment: 18 pages, 9 figure
Rotational properties of nuclei around No investigated using a spectroscopic-quality Skyrme energy density functional
Nuclei in the mass region represent the heaviest systems where
detailed spectroscopic information is experimentally available. Although
microscopic-macroscopic and self-consistent models have achieved great success
in describing the data in this mass region, a fully satisfying precise
theoretical description is still missing.
By using fine-tuned parametrizations of the energy density functionals, the
present work aims at an improved description of the single-particle properties
and rotational bands in the nobelium region. Such locally optimized
parameterizations may have better properties when extrapolating towards the
superheavy region.
Skyrme-Hartree-Fock-Bogolyubov and Lipkin-Nogami methods were used to
calculate the quasiparticle energies and rotational bands of nuclei in the
nobelium region. Starting from the most recent Skyrme parametrization, UNEDF1,
the spin-orbit coupling constants and pairing strengths have been tuned, so as
to achieve a better agreement with the excitation spectra and odd-even mass
differences in Cf and Bk.
The quasiparticle properties of Cf and Bk were very well
reproduced. At the same time, crucial deformed neutron and proton shell gaps
open up at and , respectively. Rotational bands in Fm, No, and
Rf isotopes, where experimental data are available, were also fairly well
described. To help future improvements towards a more precise description,
small deficiencies of the approach were carefully identified.
In the mass region, larger spin-orbit strengths than those from
global adjustments lead to improved agreement with data. Puzzling effects of
particle-number restoration on the calculated moment of inertia, at odds with
the experimental behaviour, require further scrutiny.Comment: 9 pages, 10 figures; to be published in Physical Review
Two-photon transport through a waveguide coupling to a whispering gallery resonator containing an atom and photon-blockade effect
We investigate the two-photon transport through a waveguide side-coupling to
a whispering-gallery-atom system. Using the Lehmann-Symanzik-Zimmermann (LSZ)
reduction approach, we present the general formula for the two-photon processes
including the two-photon scattering matrices, the wavefunctions and the second
order correlation functions of the out-going photons. Based on the exact
results of the second order correlation functions, we analyze the quantum
statistics behaviors of the out-going photons for two different cases: (a) the
ideal case without the inter-modal coupling in the whispering gallery
resonator; (b) the case in the presence of the inter-modal coupling which leads
to more complex nonlinear behavior. In the ideal case, we show that the system
consists of two independent scattering pathways, a free pathway by a cavity
mode without atomic excitation, and a "Jaynes-Cummings" pathway described by
the Jaynes-Cummings Hamiltonian of a single-mode cavity coupling to an atom.
The free pathway does not contribution to correlated two-photon processes. In
the presence of intermodal mixing, the system no longer exhibit a free resonant
pathway. Instead, both the single-photon and the two photon transport
properties depend on the position of the atom. Thus, in the presence of
intermodal mixing one can in fact tune the photon correlation properties by
changing the position of the atom. Our formalism can be used to treat resonator
and cavity dissipation as well.Comment: 9 pages, 7 figure
Deformations and quasiparticle spectra of nuclei in the nobelium region
We have performed self-consistent Skyrme Hartree-Fock-Bogolyubov calculations
for nuclei close to No. Self-consistent deformations, including
as functions of the rotational frequency, were determined for
even-even nuclei Fm, No, and Rf. The
quasiparticle spectra for N=151 isotones and Z=99 isotopes were calculated and
compared with experimental data and the results of Woods-Saxon calculations. We
found that our calculations give high-order deformations similar to those
obtained for the Woods-Saxon potential, and that the experimental quasiparticle
energies are reasonably well reproduced.Comment: 6 pages, 2 figures; ICFN5 conference proceeding
Structure and superconductivity in the binary ReMo alloys
The binary ReMo alloys, known to cover the full range of solid
solutions, were successfully synthesized and their crystal structures and
physical properties investigated via powder x-ray diffraction, electrical
resistivity, magnetic susceptibility, and heat capacity. By varying the Re/Mo
ratio we explore the full ReMo binary phase diagram, in all its
four different solid phases: hcp-Mg (), -Mn
(), -CrFe (), and bcc-W (),
of which the second is non-centrosymmetric with the rest being centrosymmetric.
All ReMo alloys are superconductors, whose critical temperatures
exhibit a peculiar phase diagram, characterized by three different
superconducting regions. In most alloys the is almost an order of
magnitude higher than in pure Re and Mo. Low-temperature electronic
specific-heat data evidence a fully-gapped superconducting state, whose
enhanced gap magnitude and specific-heat discontinuity suggest a moderately
strong electron-phonon coupling across the series. Considering that several
-Mn-type Re alloys ( = transition metal) show time-reversal
symmetry breaking (TRSB) in the superconducting state, while TRS is preserved
in the isostructural MgIrB or NbOs, the
ReMo alloys represent another suitable system for studying the
interplay of space-inversion, gauge, and time-reversal symmetries in future
experiments expected to probe TRSB in the Re family.Comment: 8 pages, 7 figures, accepted for publication on Physical Review
Material
A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars
A comprehensive model atom for Fe with more than 3000 energy levels is
presented. As a test and first application of this model atom, Fe abundances
are determined for the Sun and five stars with well determined stellar
parameters and high-quality observed spectra. Non-LTE leads to systematically
depleted total absorption in the Fe I lines and to positive abundance
corrections in agreement with the previous studies, however, the magnitude of
non-LTE effect is smaller compared to the earlier results. Non-LTE corrections
do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient
stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars
HD 84937 and HD 122563, respectively, depending on the assumed efficiency of
collisions with hydrogen atoms. Based on the analysis of the Fe I/Fe II
ionization equilibrium in these two stars, we recommend to apply the Drawin
formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe II
lines, non-LTE corrections do not exceed 0.01 dex in absolute value. The solar
non-LTE abundance obtained from 54 Fe I lines is 7.56+-0.09 and the abundance
from 18 Fe II lines varies between 7.41+-0.11 and 7.56+-0.05 depending on the
source of the gf-values. Thus, gf-values available for the iron lines are not
accurate enough to pursue high-accuracy absolute abundance determinations.
Lines of Fe I give, on average, a 0.1 dex lower abundance compared to those of
Fe II lines for HD 61421 and HD 102870, even when applying a differential
analysis relative to the Sun. A disparity between Fe I and Fe II points to
problems of stellar atmosphere modelling or/and effective temperature
determination.Comment: 19 pages, 8 figures, online material, accepted by A&
Microbubble Cavitation Imaging
Ultrasound cavitation of microbubble contrast agents has a potential for therapeutic applications such as sonothrombolysis (STL) in acute ischemic stroke. For safety, efficacy, and reproducibility of treatment, it is critical to evaluate the cavitation state (moderate oscillations, stable cavitation, and inertial cavitation) and activity level in and around a treatment area. Acoustic passive cavitation detectors (PCDs) have been used to this end but do not provide spatial information. This paper presents a prototype of a 2-D cavitation imager capable of producing images of the dominant cavitation state and activity level in a region of interest. Similar to PCDs, the cavitation imaging described here is based on the spectral analysis of the acoustic signal radiated by the cavitating microbubbles: ultraharmonics of the excitation frequency indicate stable cavitation, whereas elevated noise bands indicate inertial cavitation; the absence of both indicates moderate oscillations. The prototype system is a modified commercially available ultrasound scanner with a sector imaging probe. The lateral resolution of the system is 1.5 mm at a focal depth of 3 cm, and the axial resolution is 3 cm for a therapy pulse length of 20 mu s. The maximum frame rate of the prototype is 2 Hz. The system has been used for assessing and mapping the relative importance of the different cavitation states of a microbubble contrast agent. In vitro (tissue-mimicking flow phantom) and in vivo (heart, liver, and brain of two swine) results for cavitation states and their changes as a function of acoustic amplitude are presented
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