281 research outputs found
Equivalence of two optical quality metrics to predict the visual acuity of multifocal pseudophakic patients
This article studies the relationship between two metrics, the area under the modulation transfer function (MTFa) and the energy efficiency (EE), and their ability to predict the visual quality of patients implanted with multifocal intraocular lenses (IOLs). The optical quality of IOLs is assessed in vitro using two metrics, the MTFa and EE. We measured them for three different multifocal IOLs with parabolic phase profile using image formation, through-focus (TF) scanning, three R, G, B wavelengths, and two pupils. We analyzed the correlation between MTFa and EE. In parallel, clinical defocus curves of visual acuity (VA) were measured and averaged from sets of patients implanted with the same IOLs. An excellent linear correlation was found between the MTFa and EE for the considered IOLs, wavelengths and pupils (R2 > 0.9). We computed the polychromatic TF-MTFa, TF-EE, and derived mathematical relationships between each metrics and clinical average VA. MTFa and EE proved to be equivalent metrics to characterize the optical quality of the studied multifocal IOLs and also in terms of clinical VA predictability
Disturbance Driven Colony Fragmentation as a Driver of a Coral Disease Outbreak
In September of 2010, Brewerâs Bay reef, located in St. Thomas (U.S. Virgin Islands), was simultaneously affected by
abnormally high temperatures and the passage of a hurricane that resulted in the mass bleaching and fragmentation of its
coral community. An outbreak of a rapid tissue loss disease among coral colonies was associated with these two
disturbances. Gross lesion signs and lesion progression rates indicated that the disease was most similar to the Caribbean
coral disease white plague type 1. Experiments indicated that the disease was transmissible through direct contact between
colonies, and five-meter radial transects showed a clustered spatial distribution of disease, with diseased colonies being
concentrated within the first meter of other diseased colonies. Disease prevalence and the extent to which colonies were
bleached were both significantly higher on unattached colony fragments than on attached colonies, and disease occurred
primarily on fragments found in direct contact with sediment. In contrast to other recent studies, disease presence was not
related to the extent of bleaching on colonies. The results of this study suggest that colony fragmentation and contact with
sediment played primary roles in the initial appearance of disease, but that the disease was capable of spreading among
colonies, which suggests secondary transmission is possible through some other, unidentified mechanism
Visual acuity of pseudophakic patients predicted from in-vitro measurements of intraocular lenses with different design
The optical quality of a set of IOLs (modeling set: one monofocal and two bifocals) was assessed through focus by the area under the modulation transfer function (MTFa) metric and related to the visual acuity (VA) defocus curves of pseudophakic patients implanted with said IOLs. A non-linear relationship between the MTFa and clinical VA was obtained with an asymptotic limit found to be the best VA achievable by the patients. Two mathematical fitting functions between clinical VA and MTFa were derived with high correlation coefficients (R-2 >= 0.85). They were applied to the MTFa obtained from a different set of IOLs with advanced designs (trial set: one extended range of vision -ERV-, one trifocal ERV and one trifocal apodized) to predict VA versus defocus of patients implanted with these IOLs. Differences between the calculated VA and the clinical VA for both fitting models were within the standard deviation of the clinical measurements in the range of -3.00 D to 0.00 D defocus. thus proving the suitability of the MTFa metric to predict clinical VA performance of new IOL designs. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
A cluster theory for a Janus fluid
Recent Monte Carlo simulations on the Kern and Frenkel model of a Janus fluid
have revealed that in the vapour phase there is the formation of preferred
clusters made up of a well-defined number of particles: the micelles and the
vesicles. A cluster theory is developed to approximate the exact clustering
properties stemming from the simulations. It is shown that the theory is able
to reproduce the micellisation phenomenon.Comment: 27 pages, 8 figures, 6 table
Viral outbreak in corals associated with an in situ bleaching event: atypical herpes-like viruses and a new megavirus infecting Symbiodinium
Previous studies of coral viruses have employed either microscopy or metagenomics, but few have attempted to comprehensively link the presence of a virus-like particle (VLP) to a genomic sequence. We conducted transmission electron microscopy imaging and virome analysis in tandem to characterize the most conspicuous viral types found within the dominant Pacific reef-building coral genus Acropora. Collections for this study inadvertently captured what we interpret as a natural outbreak of viral infection driven by aerial exposure of the reef flat coincident with heavy rainfall and concomitant mass bleaching. All experimental corals in this study had high titers of viral particles. Three of the dominant VLPs identified were observed in all tissue layers and budding out from the epidermis, including viruses that were âŒ70, âŒ120, and âŒ150 nm in diameter; these VLPs all contained electron dense cores. These morphological traits are reminiscent of retroviruses, herpesviruses, and nucleocytoplasmic large DNA viruses (NCLDVs), respectively. Some 300â500 nm megavirus-like VLPs also were observed within and associated with dinoflagellate algal endosymbiont (Symbiodinium) cells. Abundant sequence similarities to a gammaretrovirus, herpesviruses, and members of the NCLDVs, based on a virome generated from five Acropora aspera colonies, corroborated these morphology-based identifications. Additionally sequence similarities to two diagnostic genes, a MutS and (based on re-annotation of sequences from another study) a DNA polymerase B gene, most closely resembled Pyramimonas orientalis virus, demonstrating the association of a cosmopolitan megavirus with Symbiodinium. We also identified several other virus-like particles in host tissues, along with sequences phylogenetically similar to circoviruses, phages, and filamentous viruses. This study suggests that viral outbreaks may be a common but previously undocumented component of natural bleaching events, particularly following repeated episodes of multiple environmental stressors
Comparison of visual and optical quality of monofocal versus multifocal intraocular lenses
Objective: To compare visual quality in patients implanted with Tecnis Âź monofocal (ZCB00) and multifocal (ZMB00) intraocular lenses taking into account their optical quality measured in vitro with an eye model.
Methods: In total, 122 patients participated in this study: 44 implanted with monofocal and 78 with multifocal intraocular lenses. Measurements of visual acuity and contrast sensitivity were performed. The optical quality of the intraocular lenses was evaluated in three image planes (distance, intermediate and near) using an eye model on a test bench. The metric considered was the area under the curve of the modulation transfer function.
Results: Optical quality at the far focus of the monofocal intraocular lens (area under the curve of the modulation transfer function = 66.97) was considerably better than that with the multifocal lens (area under the curve of the modulation transfer function = 32.54). However, no significant differences were observed between groups at the distance-corrected visual acuity. Distance-corrected near vision was better in the multifocal (0.15 ± 0.20 logMAR) than that in the monofocal group (0.43 ± 0.21 logMAR, p < 0.001), which correlated with the better optical quality at near reached by the multifocal intraocular lens (area under the curve of the modulation transfer function = 29.11) in comparison with the monofocal intraocular lens (area under the curve of the modulation transfer function = 5.0). In intermediate vision, visual acuity was 0.28 ± 0.16 logMAR (multifocal) and 0.36 ± 0.14 logMAR (monofocal) with p = 0.014, also in good agreement with the values measured in the optical quality (area under the curve of the modulation transfer function = 10.69 (multifocal) and 8.86 (monofocal)). The contrast sensitivity was similar in almost all frequencies. PelliâRobson was slightly better in the monofocal (1.73) than in the multifocal group (1.64; p = 0.023).
Conclusion: Patients implanted with multifocal ZMB00 achieved a distance visual acuity similar to those implanted with monofocal ZCB00, but showed significantly better intermediate and near visual acuity. A correlation was found between intraocular lensesâ optical quality and patientsâ visual acuity. Contrast sensitivity was very similar between the multifocal and monofocal groups
Tracing the evolution of nearby early-type galaxies in low density environments. The Ultraviolet view from GALEX
We detected recent star formation in nearby early-type galaxies located in
low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of
star formation may be present in the nucleus and in outer rings/arm like
structures. Our study suggests that such star formation may be induced by
different triggering mechanisms, such as the inner secular evolution driven by
bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV)
color vs. Mg2 correlation, and suggest that it relates to "downsizing" in
galaxy formation.Comment: Conference "UV Universe 2010" S. Petersburg 31 May - 3 June, 2010
Accepted for publication in Astrophysics & Space Science . The final
publication is available at http://www.springerlink.co
Large scale magnetogenesis from a non-equilibrium phase transition in the radiation dominated era
We study the generation of large scale primordial magnetic fields by a
cosmological phase transition during the radiation dominated era. The setting
is a theory of N charged scalar fields coupled to an abelian gauge field, that
undergoes a phase transition at a critical temperature much larger than the
electroweak scale. The dynamics after the transition features two distinct
stages: a spinodal regime dominated by linear long-wavelength instabilities,
and a scaling stage in which the non-linearities and backreaction of the scalar
fields are dominant. This second stage describes the growth of horizon sized
domains. We implement a recently introduced formulation to obtain the spectrum
of magnetic fields that includes the dissipative effects of the plasma. We find
that large scale magnetogenesis is very efficient during the scaling regime.
The ratio between the energy density on scales larger than L and that in the
background radiation r(L,T) = rho_B(L,T)/rho_{cmb}(T) is r(L,T) \sim 10^{-34}
at the Electroweak scale and r(L,T) \sim 10^{-14} at the QCD scale for L \sim 1
Mpc. The resulting spectrum is insensitive to the magnetic diffusion length. We
conjecture that a similar mechanism could be operative after the QCD chiral
phase transition.Comment: LaTex, 25 pages, no figures, to appear in Phys. Rev.
Magnetic field generation from non-equilibrium phase transitions
We study the generation of magnetic fields during the stage of particle
production resulting from spinodal instabilities during phase transitions out
of equilibrium. The main premise is that long-wavelength instabilities that
drive the phase transition lead to strong non-equilibrium charge and current
fluctuations which generate electromagnetic fields. We present a formulation
based on the non-equilibrium Schwinger-Dyson equations that leads to an exact
expression for the spectrum of electromagnetic fields valid for general
theories and cosmological backgrounds and whose main ingredient is the
transverse photon polarization out of equilibrium. This formulation includes
the dissipative effects of the conductivity in the medium. As a prelude to
cosmology we study magnetogenesis in Minkowski space-time in a theory of N
charged scalar fields to lowest order in the gauge coupling and to leading
order in the large N within two scenarios of cosmological relevance. The
long-wavelength power spectrum for electric and magnetic fields at the end of
the phase transition is obtained explicitly.
It follows that equipartition between electric and magnetic fields does not
hold out of equilibrium. In the case of a transition from a high temperature
phase, the conductivity of the medium severely hinders the generation of
magnetic fields, however the magnetic fields generated are correlated on scales
of the order of the domain size, which is much larger than the magnetic
diffusion length. Implications of the results to cosmological phase transitions
driven by spinodal unstabilities are discussed.Comment: Preprint no. LPTHE 02-55, 30 pages, latex, 2 eps figures. Added one
reference. To appear in Phys. Rev.
Dynamical renormalization group approach to transport in ultrarelativistic plasmas: the electrical conductivity in high temperature QED
The DC electrical conductivity of an ultrarelativistic QED plasma is studied
in real time by implementing the dynamical renormalization group. The
conductivity is obtained from the realtime dependence of a dissipative kernel
related to the retarded photon polarization. Pinch singularities in the
imaginary part of the polarization are manifest as growing secular terms that
in the perturbative expansion of this kernel. The leading secular terms are
studied explicitly and it is shown that they are insensitive to the anomalous
damping of hard fermions as a result of a cancellation between self-energy and
vertex corrections. The resummation of the secular terms via the dynamical
renormalization group leads directly to a renormalization group equation in
real time, which is the Boltzmann equation for the (gauge invariant) fermion
distribution function. A direct correspondence between the perturbative
expansion and the linearized Boltzmann equation is established, allowing a
direct identification of the self energy and vertex contributions to the
collision term.We obtain a Fokker-Planck equation in momentum space that
describes the dynamics of the departure from equilibrium to leading logarithmic
order in the coupling.This determines that the transport time scale is given by
t_{tr}=(24 pi)/[e^4 T \ln(1/e)}]. The solution of the Fokker-Planck equation
approaches asymptotically the steady- state solution as sim e^{-t/(4.038
t_{tr})}.The steady-state solution leads to the conductivity sigma = 15.698
T/[e^2 ln(1/e)] to leading logarithmic order. We discuss the contributions
beyond leading logarithms as well as beyond the Boltzmann equation. The
dynamical renormalization group provides a link between linear response in
quantum field theory and kinetic theory.Comment: LaTex, 48 pages, 14 .ps figures, final version to appear in Phys.
Rev.
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