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Search Results: 1 - 10 of 2074 matches for " Ioannis Margetis "
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A clinical study of annular cyclitis
Marilita Michael Moschos, Yan Guex-Crosier, Ioannis Margetis, Leonidas Zografos
Clinical Ophthalmology , 2009, DOI: http://dx.doi.org/10.2147/OPTH.S4915
Abstract: clinical study of annular cyclitis Original Research (4510) Total Article Views Authors: Marilita Michael Moschos, Yan Guex-Crosier, Ioannis Margetis, Leonidas Zografos Published Date February 2009 Volume 2009:3 Pages 215 - 217 DOI: http://dx.doi.org/10.2147/OPTH.S4915 Marilita Michael Moschos1, Yan Guex-Crosier2, Ioannis Margetis1, Leonidas Zografos2 1Department of Ophthalmology, University of Athens, Greece; 2Jules Gonin Eye Hospital, University of Lausanne, Switzerland Purpose: To investigate six cases of annular cyclitis. Methods: All patients with impairment of visual acuity underwent complete ophthalmologic examination, color fundus photography, laboratory tests and fluorescein angiography. Indocyanine green (ICG) angiography and B-scan ultrasonography were also performed in three cases in order to diagnose the disease. Results: All patients presented a unilateral or bilateral granulomatous uveitis, associated with inflammatory annular cyclitis. They had a shallow anterior chamber, a mildly elevated intraocular pressure (under 25 mm Hg) and an annular serous retinal detachment. A resolution was observed after specific therapy associated with systemic prednisolone therapy and antiglaucomatous drops. Conclusion: This is the first description of an observational study of six patients with inflammatory annular cyclitis.
A clinical study of annular cyclitis
Marilita Michael Moschos,Yan Guex-Crosier,Ioannis Margetis,Leonidas Zografos
Clinical Ophthalmology , 2009,
Abstract: Marilita Michael Moschos1, Yan Guex-Crosier2, Ioannis Margetis1, Leonidas Zografos21Department of Ophthalmology, University of Athens, Greece; 2Jules Gonin Eye Hospital, University of Lausanne, SwitzerlandPurpose: To investigate six cases of annular cyclitis.Methods: All patients with impairment of visual acuity underwent complete ophthalmologic examination, color fundus photography, laboratory tests and fluorescein angiography. Indocyanine green (ICG) angiography and B-scan ultrasonography were also performed in three cases in order to diagnose the disease.Results: All patients presented a unilateral or bilateral granulomatous uveitis, associated with inflammatory annular cyclitis. They had a shallow anterior chamber, a mildly elevated intraocular pressure (under 25 mm Hg) and an annular serous retinal detachment. A resolution was observed after specific therapy associated with systemic prednisolone therapy and antiglaucomatous drops.Conclusion: This is the first description of an observational study of six patients with inflammatory annular cyclitis.Keywords: cyclitis, uveitis, malignant glaucoma
Unified continuum approach to crystal surface morphological relaxation
Dionisios Margetis
Physics , 2007, DOI: 10.1103/PhysRevB.76.193403
Abstract: A continuum theory is used to predict scaling laws for the morphological relaxation of crystal surfaces in two independent space dimensions. The goal is to unify previously disconnected experimental observations of decaying surface profiles. The continuum description is derived from the motion of interacting atomic steps. For isotropic diffusion of adatoms across each terrace, induced adatom fluxes transverse and parallel to step edges obey different laws, yielding a tensor mobility for the continuum surface flux. The partial differential equation (PDE) for the height profile expresses an interplay of step energetics and kinetics, and aspect ratio of surface topography that plausibly unifies observations of decaying bidirectional surface corrugations. The PDE reduces to known evolution equations for axisymmetric mounds and one-dimensional periodic corrugations.
Solvable model for pair excitation in trapped Boson gas at zero temperature
Dionisios Margetis
Physics , 2007, DOI: 10.1088/1751-8113/41/38/385002
Abstract: In Bose-Einstein condensation, a macroscopically large number of particles occupy the same single-particle quantum state. Our goal is to study time-dependent aspects of particle excitations to states other than the single-particle macroscopic state in trapped dilute atomic gases. We adopt the view that atoms are excited in pairs so that their scattering from the single-particle state to vector positions x and y at time t is described by the pair-excitation function, K0(x,y,t). We solve a nonlocal equation for K0 under a slowly varying external potential by assuming that the wave function of the macroscopic state satisfies a time-independent nonlinear Schroedinger equation. For zero initial excitation (K0=0 at t=0) and sufficiently large t, we evaluate asymptotically K0 in terms of the one-variable Lommel function for any distance |x-y|.
Bose-Einstein condensation at finite temperatures: Mean field laws with periodic microstructure
Dionisios Margetis
Physics , 2015,
Abstract: At finite temperatures below the phase transition point, the Bose-Einstein condensation, the macroscopic occupation of a single quantum state by particles of integer spin, is not complete. In the language of superfluid helium, this means that the superfluid coexists with the normal fluid. Our goal is to describe this coexistence in trapped, dilute atomic gases with repulsive interactions via mean field laws that account for a {\em spatially varying} particle interaction strength. By starting with the $N$-body Hamiltonian, $N\gg 1$, we formally derive a system of coupled, nonlinear evolution equations in $3+1$ dimensions for the following quantities: (i) the wave function of the macroscopically occupied state; and (ii) the single-particle wave functions of thermally excited states. For stationary (bound) states and a scattering length with {\em periodic microstructure} of subscale $\epsilon$, we heuristically extract effective equations of motion via periodic homogenization up to second order in $\epsilon$.
Anisotropic diffusion in continuum relaxation of stepped crystal surfaces
John Quah,Dionisios Margetis
Physics , 2007, DOI: 10.1088/1751-8113/41/23/235004
Abstract: We study the continuum limit in 2+1 dimensions of nanoscale anisotropic diffusion processes on crystal surfaces relaxing to become flat below roughening. Our main result is a continuum law for the surface flux in terms of a new continuum-scale tensor mobility. The starting point is the Burton, Cabrera and Frank (BCF) theory, which offers a discrete scheme for atomic steps whose motion drives surface evolution. Our derivation is based on the separation of local space variables into fast and slow. The model includes: (i) anisotropic diffusion of adsorbed atoms (adatoms) on terraces separating steps; (ii) diffusion of atoms along step edges; and (iii) attachment-detachment of atoms at step edges. We derive a parabolic fourth-order, fully nonlinear partial differential equation (PDE) for the continuum surface height profile. An ingredient of this PDE is the surface mobility for the adatom flux, which is a nontrivial extension of the tensor mobility for isotropic terrace diffusion derived previously by Margetis and Kohn. Approximate, separable solutions of the PDE are discussed.
On solutions of Maxwell's equations with dipole sources over a thin conducting film
Dionisios Margetis,Mitchell Luskin
Physics , 2015,
Abstract: We derive and interpret solutions of time-harmonic Maxwell's equations with a vertical and a horizontal electric dipole near a planar, thin conducting film, e.g. graphene sheet, lying between two unbounded isotropic and non-magnetic media. Exact expressions for all field components are extracted in terms of rapidly convergent series of known transcendental functions when the ambient media have equal permittivities and both the dipole and observation point lie on the plane of the film. These solutions are simplified for all distances from the source when the film surface resistivity is large in magnitude compared to the intrinsic impedance of the ambient space. The formulas reveal the analytical structure of two types of waves that can possibly be excited by the dipoles and propagate on the film. One of these waves is intimately related to the surface plasmon-polariton of transverse-magnetic (TM) polarization of plane waves.
Anisotropic step stiffness from a kinetic model of epitaxial growth
Dionisios Margetis,Russel E. Caflisch
Physics , 2007,
Abstract: Starting from a detailed model for the kinetics of a step edge or island boundary, we derive a Gibbs-Thomson type formula and the associated step stiffness as a function of the step edge orientation angle, $theta$. Basic ingredients of the model are: (i) the diffusion of point defects (``adatoms'') on terraces and along step edges; (ii) the convection of kinks along step edges; and (iii) constitutive laws that relate adatom fluxes, sources for kinks, and the kink velocity with densities via a mean-field approach. This model has a kinetic (nonequilibrium) steady-state solution that corresponds to epitaxial growth through step flow. The step stiffness, $\tbe(\theta)$, is determined via perturbations of the kinetic steady state for small edge Peclet number, P, which is the ratio of the deposition to the diffusive flux along a step edge. In particular, $\tbe$ is found to satisfy $\tbe =O(\theta^{-1})$ for $O(P^{1/3}) <\theta \ll 1$, which is in agreement with independent, equilibrium-based calculations.
Impurity and quaternions in nonrelativistic scattering from a quantum memory
Dionisios Margetis,Manoussos G. Grillakis
Physics , 2007, DOI: 10.1088/1751-8113/41/6/065307
Abstract: Models of quantum computing rely on transformations of the states of a quantum memory. We study mathematical aspects of a model proposed by Wu in which the memory state is changed via the scattering of incoming particles. This operation causes the memory content to deviate from a pure state, i.e. induces impurity. For nonrelativistic particles scattered from a two-state memory and sufficiently general interaction potentials in 1+1 dimensions, we express impurity in terms of quaternionic commutators. In this context, pure memory states correspond to null hyperbolic quaternions. In the case with point interactions, the scattering process amounts to appropriate rotations of quaternions in the frequency domain. Our work complements a previous analysis by Margetis and Myers (2006 J. Phys. A 39 11567--11581).
Apriori Estimates for Many-Body Hamiltonian Evolution of Interacting Boson System
Manoussos G. Grillakis,Dionisios Margetis
Mathematics , 2008,
Abstract: We study the evolution of a many-particle system whose wave function obeys the N-body Schroedinger equation under Bose symmetry. The system Hamiltonian describes pairwise particle interactions in the absence of an external potential. We derive apriori dispersive estimates that express the overall repulsive nature of the particle interactions. These estimates hold for a wide class of two-body interaction potentials which are independent of the particle number, N. We discuss applications of these estimates to the BBGKY hierarchy for reduced density matrices analyzed by Elgart, Erdos, Schlein and Yau.
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