Characteristics of patients with multiple arterial aneurysms.

Background: The aim of this retrospective cross-sectional observational study was to determine differences of patients with multiple arterial aneurysms to patients with single arterial aneurysms. Patients and methods: Patients with the diagnosis of an arterial aneurysm from January 2006 to January 2016 in the department of vascular surgery Heidelberg were investigated. Excluded were patients with hereditary disorders of connective tissue or systemic inflammatory disease, as well as other arterial pathologies than true aneurysms. Patients with multiple aneurysms (defined by at least four aneurysms) were compared to patients with single aneurysms concerning age at initial diagnosis, sex and affected arterial site. To verify the findings, a replication of the study was performed at a comparable institution. Results: Of 3107 patients with arterial aneurysms, 918 were excluded. Of the resulting 2189 patients, 1238 (56.6%) patients had a single, 808 (36.9%) two or three, and 143 (6.5%) at least four aneurysms (group mult-AA). Nine hundred seventy-two patients (44.4%) had a single abdominal aortic aneurysm (group sing-AAA). Age at initial diagnosis differed between mult-AA (66.7±9.5 y) and sing-AAA (69.1±8.6 y) (p=0.0338). Within mult-AA, 138 patients (96.5%) were male, compared with 865 patients (89.0%) in sing-AAA (p=0.0041). The most frequent aneurysm localization shifted from the abdominal aorta and its branches in patients with a single aneurysm (n=1029; 83.1%) to pelvic and leg arteries in patients with at least four aneurysms (n=318; 63.2%). The replication of the study at the department of vascular surgery Frankfurt confirmed the younger age at initial diagnosis in mult-AA (67.3±12.5 y) compared to sing-AAA (70.9±9.6 y) (p=0.0259) and the distribution shift toward the arteries below the aortic bifurcation in mult-AA. Conclusions: Patients with multiple aneurysms are younger at initial diagnosis and differ concerning aneurysm localization compared to patients with a single aneurysm.

Two-dimensional Green's tensor for gyrotropic clusters composed of circular cylinders.

The construction of Green's tensor for two-dimensional gyrotropic photonic clusters composed of cylinders with circular cross sections using the semi-analytic multipole method is presented. The high efficiency and accuracy of the method is demonstrated. The developed method is applied to gyrotropic clusters that support topological chiral Hall edge states. The remarkable tolerance of chiral Hall edge modes toward substantial cluster separation is revealed. The transformation of chiral Hall edge states as the cluster separation increases is also presented. The excitation of chiral Hall edge modes for different source orientations is considered. Both gyroelectric and gyromagnetic (ferrite) clusters are treated.

Mode-based analysis of silicon nanohole arrays for photovoltaic applications.

We investigate the optical properties of silicon nanohole arrays for application in photovoltaic cells in terms of the modes within the structure. We highlight three types of modes: fundamental modes, important at long wavelengths; guided resonance modes, which enhance absorption for wavelengths where the intrinsic absorption of silicon is low; and channeling modes, which suppress front-surface reflection. We use this understanding to explain why the parameters of optimized nanohole arrays occur in specific ranges even as the thickness is varied.

Absorption enhancing proximity effects in aperiodic nanowire arrays.

Aperiodic Nanowire (NW) arrays have higher absorption than equivalent periodic arrays, making them of interest for photovoltaic applications. An inevitable property of aperiodic arrays is the clustering of some NWs into closer proximity than in the equivalent periodic array. We focus on the modes of such clusters and show that the reduced symmetry associated with cluster formation allows external coupling into modes which are dark in periodic arrays, thus increasing absorption. To exploit such modes fully, arrays must include tightly clustered NWs that are unlikely to arise from fabrication variations but must be created intentionally.

Modal formulation for diffraction by absorbing photonic crystal slabs.

A finite element-based modal formulation of diffraction of a plane wave by an absorbing photonic crystal slab of arbitrary geometry is developed for photovoltaic applications. The semianalytic approach allows efficient and accurate calculation of the absorption of an array with a complex unit cell. This approach gives direct physical insight into the absorption mechanism in such structures, which can be used to enhance the absorption. The verification and validation of this approach is applied to a silicon nanowire array, and the efficiency and accuracy of the method is demonstrated. The method is ideally suited to studying the manner in which spectral properties (e.g., absorption) vary with the thickness of the array, and we demonstrate this with efficient calculations that can identify an optimal geometry.

Modal analysis of enhanced absorption in silicon nanowire arrays.

We analyze the absorption of solar radiation by silicon nanowire arrays, which are being considered for photovoltaic applications. These structures have been shown to have enhanced absorption compared with thin films, however the mechanism responsible for this is not understood. Using a new, semi-analytic model, we show that the enhanced absorption can be attributed to a few modes of the array, which couple well to incident light, overlap well with the nanowires, and exhibit strong Fabry-Pérot resonances. For some wavelengths the absorption is further enhanced by slow light effects. We study the evolution of these modes with wavelength to explain the various features of the absorption spectra, focusing first on a dilute array at normal incidence, before generalizing to a dense array and off-normal angles of incidence. The understanding developed will allow for optimization of simple SiNW arrays, as well as the development of more advanced designs.

Local observation of modes from three-dimensional woodpile photonic crystals with near-field microspectroscopy under supercontinuum illumination.

A near-field microscope coupled with a near-infrared (NIR) supercontinuum source is developed and applied to characterize optical modes in a three-dimensional (3D) woodpile photonic crystal (PC) possessing a NIR partial bandgap. Spatially resolved near-field intensity distributions under different illumination wavelengths demonstrate that the electric fields preferentially dwell in the polymer rods or in the gaps between rods, respectively, for frequencies below or above the stop gap, as predicted by the 3D finite-difference time-domain modeling. Near-field microspectroscopy further reveals that the position-dependent band-edge effect plays an important role in PC-based all-optical integrated devices.

Suppression of Anderson localization in disordered metamaterials.

We study wave propagation in mixed, 1D disordered stacks of alternating right- and left-handed layers and reveal that the introduction of metamaterials substantially suppresses Anderson localization. At long wavelengths, the localization length in mixed stacks is orders of magnitude larger than for normal structures, proportional to the sixth power of the wavelength, in contrast to the usual quadratic wavelength dependence of normal systems. Suppression of localization is also exemplified in long-wavelength resonances which largely disappear when left-handed materials are introduced.

Transverse coupling to the core of a photonic crystal fiber: the photo-inscription of gratings.

The effect of the microstructure on transversely coupled laser light into the core of a photonic crystal fiber is investigated. Computational two-dimensional modeling and direct experimental measurements indicate that there exist angles and positions of the fiber microstructure, relative to a transversely launched laser beam, that preferentially couple laser light into the fiber core. The implications of these observations on long period and fiber-Bragg grating fabrication in photonic crystal fibers are discussed.