311 research outputs found
Symmetry characterization of eigenstates in opal-based photonic crystals
The complete symmetry characterization of eigenstates in bare opal systems is
obtained by means of group theory. This symmetry assignment has allowed us to
identify several bands that cannot couple with an incident external plane wave.
Our prediction is supported by layer-KKR calculations, which are also
performed: the coupling coefficients between bulk modes and externally excited
field tend to zero when symmetry properties mismatch.Comment: 7 pages, 5 figures, submitted to Physical Review
Systematic design of single-mode coupled-resonator optical waveguides in photonic crystals
By establishing a direct relation between the dispersion and the field profile of a coupled-resonator optical waveguide (CROW) and those of its constituent cavities, we present a systematic method for the design of a single-mode CROW and for control of its dispersion. The procedure includes the design of a single-mode cavity and control of its frequency by engineering its structure. Then, by chaining these cavities in the proper direction and at an appropriate distance, we achieve the desired dispersion for the CROW
Poles and zeros of the scattering matrix associated to defect modes
We analyze electromagnetic waves propagation in one-dimensional periodic
media with single or periodic defects. The study is made both from the point of
view of the modes and of the diffraction problem. We provide an explicit
dispersion equation for the numerical calculation of the modes, and we
establish a connection between modes and poles and zeros of the scattering
matrix.Comment: 6 pages (Revtex), no figure
DMEK Surgery at a Tertiary Hospital in Sweden. Results and Complication Risks
Kinga Dabrowska-Kloda,1 Eydis Olafsdottir,1 Anastasia Stefanou,1 Sven Crafoord1,2 1Department of Ophthalmology, Örebro University Hospital, Örebro, Sweden; 2Department of Ophthalmology, Faculty of Medicine and Health, Örebro University, Örebro, SwedenCorrespondence: Kinga Dabrowska-Kloda, Department of Ophthalmology, Örebro University Hospital, PO Box 1613, Örebro, SE 70116, Sweden, Tel +46 19 6021000, Fax +46 19 6021052, Email [email protected]: This study reports clinical outcomes up to 6 years after Descemet’s membrane endothelial keratoplasty (DMEK) performed at the Department of Ophthalmology, Örebro University Hospital, Örebro, Sweden.Methods: The study has a cross-sectional and case series design. Inclusion criteria were all DMEK-operated eyes during 2013– 2018 until repeat keratoplasty.Results: Altogether 162 eyes from 120 patients were enrolled. Among eyes without preoperative comorbidities, examined 1– 6 years after DMEK, 85.8% achieved visual acuity of 0.1 logMAR or better. The median endothelial cell density (ECD) loss was 27% in a cohort of eyes examined 1– 2 years post-DMEK, 31% at 2– 3 years, 42% at 3– 4 years, and > 60% at 4– 6 years post–DMEK. ECD at the examination timepoint was correlated with donor ECD (as expected) and time since surgery.Conclusion: The results from DMEK surgeries in Örebro, Sweden, are promising. Further studies with even longer follow–up are needed to evaluate graft sustainability.Keywords: DMEK, Descemet’s membrane endothelial keratoplasty, endothelial cell density, endothelial cell loss, corneal surgery in Sweden, corneal surgery in Scandinavi
Towards New Half-Metallic Systems: Zinc-Blende Compounds of Transition Elements with N, P, As, Sb, S, Se, and Te
We report systematic first-principles calculations for ordered zinc-blende
compounds of the transition metal elements V, Cr, Mn with the sp elements N, P,
As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb,
and MnAs. They show ferromagnetic half-metallic behavior for a wide range of
lattice constants. We discuss the origin and trends of half-metallicity,
present the calculated equilibrium lattice constants, and examine the
half-metallic behavior of their transition element terminated (001) surfaces.Comment: 2nd Version: lattice constants calculations added, text revise
Nonlocal electrodynamics of two-dimensional wire mesh photonic crystals
We calculate analytically the spectra of plasma waves and electromagnetic
waves (EMW) in metallic photonic crystal consisting of the parallel thin
infinite metallic cylinders embedded in the dielectric media. The axes of
metallic cylinders form a regular square lattice in a plane perpendicular to
them. The metal inside the cylinders is assumed to be in the high frequency
regime , where is the relaxation time. The proposed
analytical theory is based upon small parameters , where is the
volume fraction of the metal, and , where is the wave vector and
is the radius of the cylinder. It is shown that there are five different
branches of the EMW that cover all frequency range under consideration except
one very small omnidirectional gap in the vicinity of the frequency of the
surface plasmon. However, at some directions of propagation and polarizations
the gap may be much larger. The reflection and refraction of the EMW is also
considered. The general theory of refraction is proposed which is complicated
by the spatial dispersion of the dielectric constant, and one particular
geometry of the incident EMW is considered.Comment: 14 pages, 8 figure
Scattering of elastic waves by periodic arrays of spherical bodies
We develop a formalism for the calculation of the frequency band structure of
a phononic crystal consisting of non-overlapping elastic spheres, characterized
by Lam\'e coefficients which may be complex and frequency dependent, arranged
periodically in a host medium with different mass density and Lam\'e
coefficients. We view the crystal as a sequence of planes of spheres, parallel
to and having the two dimensional periodicity of a given crystallographic
plane, and obtain the complex band structure of the infinite crystal associated
with this plane. The method allows one to calculate, also, the transmission,
reflection, and absorption coefficients for an elastic wave (longitudinal or
transverse) incident, at any angle, on a slab of the crystal of finite
thickness. We demonstrate the efficiency of the method by applying it to a
specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press
Electron energy loss and induced photon emission in photonic crystals
The interaction of a fast electron with a photonic crystal is investigated by
solving the Maxwell equations exactly for the external field provided by the
electron in the presence of the crystal. The energy loss is obtained from the
retarding force exerted on the electron by the induced electric field. The
features of the energy loss spectra are shown to be related to the photonic
band structure of the crystal. Two different regimes are discussed: for small
lattice constants relative to the wavelength of the associated electron
excitations , an effective medium theory can be used to describe the
material; however, for the photonic band structure plays an
important role. Special attention is paid to the frequency gap regions in the
latter case.Comment: 12 pages, 7 figure
Patient-specific computational modeling of subendothelial LDL accumulation in a stenosed right coronary artery: effect of hemodynamic and biological factors
Patient-specific computational modeling of subendothelial LDL accumulation in a stenosed right coronary artery: effect of hemodynamic and biological factors. Am J Physiol Heart Circ Physiol 304: H1455-H1470, 2013. First published March 15, 2013; doi:10.1152/ajpheart.00539.2012.-Atherosclerosis is a systemic disease with local manifestations. Low-density lipoprotein (LDL) accumulation in the subendothelial layer is one of the hallmarks of atherosclerosis onset and ignites plaque development and progression. Blood flow-induced endothelial shear stress (ESS) is causally related to the heterogenic distribution of atherosclerotic lesions and critically affects LDL deposition in the vessel wall. In this work we modeled blood flow and LDL transport in the coronary arterial wall and investigated the influence of several hemodynamic and biological factors that may regulate LDL accumulation. We used a three-dimensional model of a stenosed right coronary artery reconstructed from angiographic and intravascular ultrasound patient data. We also reconstructed a second model after restoring the patency of the stenosed lumen to its nondiseased state to assess the effect of the stenosis on LDL accumulation
Multiscale - Patient-Specific Artery and Atherogenesis Models
In this work, we present a platform for the development of multiscale patient-specific artery and atherogenesis models. The platform, called ARTool, integrates technologies of 3-D image reconstruction from various image modalities, blood flow and biological models of mass transfer, plaque characterization, and plaque growth. Patient images are acquired for the development of the 3-D model of the patient specific arteries. Then, blood flow ismodeled within the arterial models for the calculation of the wall shear stress distribution (WSS). WSS is combined with other patient-specific parameters for the development of the plaque progression models. Real-time simulation can be performed for same cases in grid environment. The platform is evaluated using both animal and human data
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