287 research outputs found
B-mode ultrasound assessment of pupillary function: feasibility, reliability and normal values
PURPOSE: To evaluate B-mode ultrasound as a novel method for the examination of pupillary function and to provide normal values for the pupillary reflex as assessed by B-mode ultrasound. METHODS: 100 subjects (49 female, 51 male, mean [range] age 51 [18-80 years]) with no history of ophthalmologic disease, no clinically detectable pupillary defects, and corrected visual acuity >= 0.8 were included in this prospective observational study. B-mode ultrasound was performed with the subjects eyes closed using an Esaote-Mylab25 system according to current guidelines for orbital insonation. A standardized light stimulus was applied. RESULTS: The mean +/- standard deviation left and right pupillary diameters (PD) at rest were 4.7 +/- 0.8 and 4.5 +/- 0.8 mm. Following an ipsilateral light stimulus (Lstim), left and right constricted PD were 2.8 +/- 0.6 and 2.7 +/- 0.6 mm. Following a contralateral Lstim, left and right constricted PD were 2.7 +/- 0.6 and 2.6 +/- 0.5 mm. Left and right pupillary constriction time (PCT) following ipsilateral Lstim were 970 +/- 261.6 and 967 +/- 220 ms. Left and right PCT following a contralateral Lstim were 993.8 +/- 192.6 and 963 +/- 189.4 ms. Patient age was inversely correlated with PD at rest and with PD after ipsilateral and contralateral Lstim (all p<0.001), but not with PCT. CONCLUSIONS: B-mode ultrasound is a simple, rapid and objective method for the quantitative assessment of pupillary function, which may prove useful in a variety of settings where eyelid retraction is impeded or an infrared pupillometry device is unavailable
No evidence for retinal damage evolving from reduced retinal blood flow in carotid artery disease
Introduction. Carotid artery disease (CAD) comprising high-grade internal carotid artery stenosis (CAS) or carotid artery occlusion (CAO) may lead to ipsilateral impaired cerebral blood flow and reduced retinal blood supply. Objective. To examine the influence of chronic CAD on retinal blood flow, retinal morphology, and visual function. Methods. Patients with unilateral CAS ≥ 50% (ECST criteria) or CAO were grouped according to the grade of the stenosis and to the flow direction of the ophthalmic artery (OA). Retinal perfusion was measured by transorbital duplex ultrasound, assessing central retinal artery (CRA) blood flow velocities. In addition, optic nerve and optic nerve sheath diameter were measured. Optical coherence tomography (OCT) was performed to study retinal morphology. Visual function was assessed using high- and low-contrast visual paradigms. Results. Twenty-seven patients were enrolled. Eyes with CAS ≥ 80%/CAO and retrograde OA blood flow showed a significant reduction in CRA peak systolic velocity (no-CAD side: 0.130 ± 0.035 m/s, CAS/CAO side: 0.098 ± 0.028; p = 0.005; n = 12). OCT, optic nerve thicknesses, and visual functional parameters did not show a significant difference. Conclusion. Despite assessable hemodynamic effects, chronic high-grade CAD does not lead to gaugeable morphological or functional changes of the retina
Confinement and scaling in deep inelastic scattering
We show that parton confinement in the final state generates large
corrections to Bjorken scaling, thus leaving less room for the logarithmic
corrections. In particular, the -scaling violations at large are
entirely described in terms of power corrections. For treatment of these
non-perturbative effects, we derive a new expansion in powers of for
the structure function that is free of infra-red singularities and which
reduces corrections to the leading term. The leading term represents scattering
from an off-mass-shell parton, which keeps the same virtual mass in the final
state. It is found that this quasi-free term is a function of a new variable
, which coincides with the Bjorken variable for . The
two variables are very different, however, at finite . In particular, the
variable depends on the invariant mass of the spectator particles.
Analysis of the data at large shows excellent scaling in the variable , and determines the value of the diquark mass to be close to zero. -scaling allows us to extract the structure function near the elastic
threshold. It is found to behave as . Predictions for the
structure functions based on -scaling are made.Comment: Discussion of target mass corrections is added. Accepted for
publication in Phys. Rev.
The theory of canonical perturbations applied to attitude dynamics and to the Earth rotation. Osculating and nonosculating Andoyer variables
The Hamiltonian theory of Earth rotation, known as the Kinoshita-Souchay
theory, operates with nonosculating Andoyer elements. This situation parallels
a similar phenomenon that often happens (but seldom gets noticed) in orbital
dynamics, when the standard Lagrange-type or Delaunay-type planetary equations
unexpectedly render nonosculating orbital elements. In orbital mechanics,
osculation loss happens when a velocity-dependent perturbation is plugged into
the standard planetary equations. In attitude mechanics, osculation is lost
when an angular-velocity-dependent disturbance is plugged in the standard
dynamical equations for the Andoyer elements. We encounter exactly this
situation in the theory of Earth rotation, because this theory contains an
angular-velocity-dependent perturbation (the switch from an inertial frame to
that associated with the precessing ecliptic of date).
While the osculation loss does not influence the predictions for the figure
axis of the planet, it considerably alters the predictions for the
instantaneous spin-axis' orientation. We explore this issue in great detail
Non-perturbative structure of the polarized nucleon sea
We investigate the flavour and quark-antiquark structure of the polarized
nucleon by calculating the parton distribution functions of the nucleon sea
using the meson cloud model. We find that the SU(2) flavor symmetry in the
light antiquark sea and quark-antiquark symmetry in the strange quark sea are
broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar.
The polarization of the strange sea is found to be positive, which is in
contradiction to previous analyses. We predict a much larger quark-antiquark
asymmetry in the polarized strange quark sea than that in the unpolarized
strange quark sea. Our results for both polarized light quark sea and polarized
strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure
Chaos in free electron laser oscillators
The chaotic nature of a storage-ring Free Electron Laser (FEL) is
investigated. The derivation of a low embedding dimension for the dynamics
allows the low-dimensionality of this complex system to be observed, whereas
its unpredictability is demonstrated, in some ranges of parameters, by a
positive Lyapounov exponent. The route to chaos is then explored by tuning a
single control parameter, and a period-doubling cascade is evidenced, as well
as intermittence.Comment: Accepted in EPJ
Multiple functional self-association interfaces in plant TIR domains
The self-association of Toll/interleukin-1 receptor/resistance protein (TIR) domains has been implicated in signaling in plant and animal immunity receptors. Structure-based studies identified different TIR-domain dimerization interfaces required for signaling of the plant nucleotide-binding oligomerization domain-like receptors (NLRs) L6 from flax and disease resistance protein RPS4 from Arabidopsis. Here we show that the crystal structure of the TIR domain from the Arabidopsis NLR suppressor of npr1-1, constitutive 1 (SNC1) contains both an L6-like interface involving helices alpha D and alpha E (DE interface) and an RPS4-like interface involving helices alpha A and alpha E (AE interface). Mutations in either the AE- or DE-interface region disrupt cell-death signaling activity of SNC1, L6, and RPS4 TIR domains and full-length L6 and RPS4. Self-association of L6 and RPS4 TIR domains is affected by mutations in either region, whereas only AE-interface mutations affect SNC1 TIR-domain self-association. We further show two similar interfaces in the crystal structure of the TIR domain from the Arabidopsis NLR recognition of Peronospora parasitica 1 (RPP1). These data demonstrate that both the AE and DE self-association interfaces are simultaneously required for self-association and cell-death signaling in diverse plant NLRs.11139Ysciescopu
Regularization-independent study of renormalized non-perturbative quenched QED
A recently proposed regularization-independent method is used for the first
time to solve the renormalized fermion Schwinger-Dyson equation numerically in
quenched QED. The Curtis-Pennington vertex is used to illustrate the
technique and to facilitate comparison with previous calculations which used
the alternative regularization schemes of modified ultraviolet cut-off and
dimensional regularization. Our new results are in excellent numerical
agreement with these, and so we can now conclude with confidence that there is
no residual regularization dependence in these results. Moreover, from a
computational point of view the regularization independent method has enormous
advantages, since all integrals are absolutely convergent by construction, and
so do not mix small and arbitrarily large momentum scales. We analytically
predict power law behaviour in the asymptotic region, which is confirmed
numerically with high precision. The successful demonstration of this efficient
new technique opens the way for studies of unquenched QED to be undertaken in
the near future.Comment: 20 pages,5 figure
BioJS: An open source standard for biological visualisation - its status in 2014
BioJS is a community-based standard and repository of functional components to represent biological information on the web. The development of BioJS has been prompted by the growing need for bioinformatics visualisation tools to be easily shared, reused and discovered. Its modular architecture makes it easy for users to find a specific functionality without needing to know how it has been built, while components can be extended or created for implementing new functionality. The BioJS community of developers currently provides a range of functionality that is open access and freely available. A registry has been set up that categorises and provides installation instructions and testing facilities at http://www.ebi.ac.uk/tools/biojs/. The source code for all components is available for ready use at https://github.com/biojs/biojs
Quark Imaging in the Proton Via Quantum Phase-Space Distributions
We develop the concept of quantum phase-space (Wigner) distributions for
quarks and gluons in the proton. To appreciate their physical content, we
analyze the contraints from special relativity on the interpretation of elastic
form factors, and examine the physics of the Feynman parton distributions in
the proton's rest frame. We relate the quark Wigner functions to the
transverse-momentum dependent parton distributions and generalized parton
distributions, emphasizing the physical role of the skewness parameter. We show
that the Wigner functions allow to visualize quantum quarks and gluons using
the language of the classical phase space. We present two examples of the quark
Wigner distributions and point out some model-independent features.Comment: 20 pages with 3 fiture
- …