On the heliolatitudinal variation of the galactic cosmic-ray intensity. Comparison with Ulysses measurements

International audienceWe study the dependence of cosmic rays with heliolatitude using a simple method and compare the results with the actual data from Ulysses and IMP spacecraft. We reproduce the galactic cosmic-ray heliographic latitudinal intensity variations, applying a semi-empirical, 2-D diffusion-convection model for the cosmic-ray transport in the interplanetary space. This model is a modification of our previous 1-D model (Exarhos and Moussas, 2001) and includes not only the radial diffusion of the cosmic-ray particles but also the latitudinal diffusion. Dividing the interplanetary region into "spherical magnetic sectors" (a small heliolatitudinal extension of a spherical magnetized solar wind plasma shell) that travel into the interplanetary space at the solar wind velocity, we calculate the cosmic-ray intensity for different heliographic latitudes as a series of successive intensity drops that all these "spherical magnetic sectors" between the Sun and the heliospheric termination shock cause the unmodulated galactic cosmic-ray intensity. Our results are compared with the Ulysses cosmic-ray measurements obtained during the first pole-to-pole passage from mid-1994 to mid-1995

Optimization in Differentiable Manifolds in Order to Determine the Method of Construction of Prehistoric Wall-Paintings

In this paper a general methodology is introduced for the determination of potential prototype curves used for the drawing of prehistoric wall-paintings. The approach includes a) preprocessing of the wall-paintings contours to properly partition them, according to their curvature, b) choice of prototype curves families, c) analysis and optimization in 4-manifold for a first estimation of the form of these prototypes, d) clustering of the contour parts and the prototypes, to determine a minimal number of potential guides, e) further optimization in 4-manifold, applied to each cluster separately, in order to determine the exact functional form of the potential guides, together with the corresponding drawn contour parts. The introduced methodology simultaneously deals with two problems: a) the arbitrariness in data-points orientation and b) the determination of one proper form for a prototype curve that optimally fits the corresponding contour data. Arbitrariness in orientation has been dealt with a novel curvature based error, while the proper forms of curve prototypes have been exhaustively determined by embedding curvature deformations of the prototypes into 4-manifolds. Application of this methodology to celebrated wall-paintings excavated at Tyrins, Greece and the Greek island of Thera, manifests it is highly probable that these wall-paintings had been drawn by means of geometric guides that correspond to linear spirals and hyperbolae. These geometric forms fit the drawings' lines with an exceptionally low average error, less than 0.39mm. Hence, the approach suggests the existence of accurate realizations of complicated geometric entities, more than 1000 years before their axiomatic formulation in Classical Ages

Optical Signatures of Quantum Emitters in Suspended Hexagonal Boron Nitride

Hexagonal boron nitride (h-BN) is a tantalizing material for solid-state quantum engineering. Analogously to three-dimensional wide-bandgap semiconductors like diamond, h-BN hosts isolated defects exhibiting visible fluorescence, and the ability to position such quantum emitters within a two-dimensional material promises breakthrough advances in quantum sensing, photonics, and other quantum technologies. Critical to such applications, however, is an understanding of the physics underlying h-BN's quantum emission. We report the creation and characterization of visible single-photon sources in suspended, single-crystal, h-BN films. The emitters are bright and stable over timescales of several months in ambient conditions. With substrate interactions eliminated, we study the spectral, temporal, and spatial characteristics of the defects' optical emission, which offer several clues about their electronic and chemical structure. Analysis of the defects' spectra reveals similarities in vibronic coupling despite widely-varying fluorescence wavelengths, and a statistical analysis of their polarized emission patterns indicates a correlation between the optical dipole orientations of some defects and the primitive crystallographic axes of the single-crystal h-BN film. These measurements constrain possible defect models, and, moreover, suggest that several classes of emitters can exist simultaneously in free-standing h-BN, whether they be different defects, different charge states of the same defect, or the result of strong local perturbations

APCVD of dual layer transparent conductive oxides for photovoltaic applications

We report the atmospheric pressure chemical vapour deposition (APCVD) of a dual layer transparent conductive oxide (TCO). This combines a fluorine doped tin oxide (FTO) base layer with a fluorine doped zinc oxide (FZO) top layer, where we seek to utilise the respective advantages of each material and the differences in their associated industrial deposition process technologies. Deposition of a 250 nm thick FZO layer on FTO was enough to develop features seen with FZO only layers. The crystallographic orientation determined by the FZO dopant concentration. Changes to the deposition parameters of the underlying FTO layer effected stack roughness and carrier concentration, and hence optical scattering and absorption. Photovoltaic cells have been fabricated using this TCO structure showing promising performance, with efficiencies as high as 10.21% compared to reference FTO only values of 9.02%. The bulk of the coating was FTO, providing the majority of conductivity and the large surface features associated with this material, whilst keeping the overall cost low by utilising the very fast growth rates achievable. The FTO was capped with a thinner FZO layer to provide a top surface suitable for wet chemical or plasma etching, allowing the surface morphology to be tuned for specific applications

Induced crystallization in CW laser-irradiated sol-gel deposited titania films

Isothermal annealing of amorphous TiO{sub 2} films deposited from acidic sol-gel precursor solutions results in film densification and concomitant increase in refractive index. Subsequent heating above 300C leads to irreversible transformation to an anatase crystalline phase. Similar phenomena occur when such amorphous films are subjected to focused cw laser irradiation. Controlled variations in laser fluence are used to densify or crystallize selected regions of the film. Low fluence conditioning leads to the evolution of a subtle nanograin-size morphology, evident in AFM images, which appears to retard subsequent film crystallization when such regions are subjected to higher laser fluence. Time-resolved Raman spectroscopy has been used to characterize irradiated regions in order to follow the crystallization kinetics, assess phase homogeneity, and evaluate accompanying changes in residual film stress

Simultaneously performed off-pump coronary artery bypass grafting and colectomy: a case report

This is written so as to report the case of a 71-year-old male with a diagnosis of sigmoid adenocarcinoma accompanied by severe coronary artery disease and unstable angina, which was subject to simultaneous surgical treatment. The patient initially underwent an off-pump coronary artery revascularization in order to avoid the complications of cardiopulmonary bypass, providing the opportunity of a colectomy at the same time with the use of safe surgical means. Our case suggests that performing an off-pump bypass procedure prior to cancer surgery can be an appropriate course of action in carefully selected cases