Linke turbidity factors for several sites in Africa

International audienceThe Linke turbidity factor (TL) has been estimated at sixteen locations in Africa (9 stations in Egypt, 2 in Mozambique and Zimbabwe, 1 in Algeria, Tunisia and Zambia). An appropriate processing of time-series of measurements of daily sums of solar global radiation spanning several years provides mean values of TL for each month with a sufficient accuracy. Though limited to the Mediterranean area, Egypt and sub-tropical Southeastern part, this work greatly extends the knowledge on the clearness of the atmosphere in Africa, an area not much addressed in the literature. The relationship between TL and the climate is evidenced. TL is almost constant throughout the year close to the Mediterranean basin with values around 3.5. Stations located in the sub- tropical Southeastern part exhibit large variations of TL

Chain of algorithms to calculate advanced radiation parameters

International audienceAlgorithms linked to form focused chains of algorithms are needed to fill gaps between often measured or available data resources and the parameters requested by many solar applications. This paper describes the formulation of a chain of algorithms for shortwave radiation. The basic inputs into the chain are monthly mean values of the Linke turbidity factor and global radiation. The outputs of the chain are hourly values of global shortwave radiation on inclined planes. This is achieved via stochastic generation of daily and hourly values of global radiation, splitting the global into beam and diffuse radiation and finally calculating the radiation on inclined planes. The cloudless sky chain is based on an improved version of the clear sky model of Rigollier et al. (2000). The stochastic generation process is based on Aguiar et al. (1988, 1992) but important improvements have been made by cross-linking to the clear sky model. The Perez models (1986, 1990) are used for splitting the radiation into its components and for estimating radiation on tilted planes. Datasets produced with the described chains can be accessed via the prototype of the SoDa project at www.soda-is.org

Class 4 sections at elevated temperature

The steel cross-sections behave stable or unstable. The behavior of slender cross sections of steel beams is influenced by local buckling. The buckling can be observed on beam web and/or flange and reduce the load bearing capacity of the beam. Design models adopted for daily design procedures are based on the so-called effective width approach. The design at fire situation is simplified which means that the same effective cross section as for cold design is used neglecting the changes of stiffness of steel. The research is focused on getting the knowledge of behaving of steel beams with welded Class 4 cross-sections exposed to high temperatures. This article describes the progress of the experiments

The Bousso entropy bound in selfgravitating gas of massless particles

The Bousso entropy bound is investigated in a static spherically symmetric spacetime filled with an ideal gas of massless bosons or fermions. Especially lightsheets generated by spheres are considered. Statistical description of the gas is given. Conditions under which the Bousso bound can be violated are discussed and it is shown that a possible violating region cannot be arbitrarily large and it is contained inside a sphere of unit Planck radius if number of independent polarization states $g_s$ is small enough. It is also shown that central temperature must exceed the Planck temperature to get a violation of the Bousso bound for $g_s$ not too large.Comment: 14 pages, 4 figures, a paragraph added, version published in Gen. Rel. Gra

Study of effective distances for interpolation schemes in meteorology

International audienceThis work explores the possibility of integrating the geographical elements such as orography and presence of water bodies as well as the latitudinal effects into an effective distance when interpolating meteorological fields. This effective distance may then be used in any interpolation methods instead of the standard geodetic distance. Several hundreds of sites are used in Europe to assess the benefits of several effective distances. The meteorological parameters under concern are ten-years averages of monthly means of daily sum of horizontal global irradiation, daily sum of sunshine duration, daily extremes of air temperature, atmospheric pressure and water vapor pressure, and of monthly sums of precipitation. This work demonstrates that taking into account the latitudinal effects in the distance increases the accuracy in interpolation. Such effects have been seldom mentioned in previous publications. The orographic effects may be partly corrected by adding the weighted difference in elevation to the geodetic distance. The proposed effective distance between the point P and each of the measuring sites Xi for all parameters, is found to give better results than the others

Metastable gravity on classical defects

We discuss the realization of metastable gravity on classical defects in infinite-volume extra dimensions. In dilatonic Einstein gravity, it is found that the existence of metastable gravity on the defect core requires violation of the Dominant Energy Condition for codimension Nc = 2 defects. This is illustrated with a detailed analysis of a six-dimensional hyperstring minimally coupled to dilaton gravity. We present the general conditions under which a codimension Nc > 2 defect admits metastable modes, and find that they differ from lower codimensional models in that, under certain conditions, they do not require violation of energy conditions to support quasi-localized gravity.Comment: 10 pages, 3 figures, uses RevTeX, typos corrected, matches published versio

Worldwide Linke turbidity information

International audienceThis paper describes the algorithms and data used to construct a worldwide Linke turbidity factor (TL, for an air mass equal to 2)database. Two main steps had to be performed to obtain the information: 1. Assembling estimates of TL and 2. fusing different background layers for the construction of the TL maps. The estimates of TL have two forms: either they stand for specific geographical locations and have a high accuracy, or they are available as gridded data averaged over large areas. Point information was gathered from measured time series of hourly beam and daily global radiation, which were transformed to TL. From publications and networks like AERONET other turbidity quantities were obtained and transformed to TL. The basic gridded data are the maps of daily global irradiation supplied by the NASA-Langley Research Center. The included monthly clear sky irradiations were converted to TL with the same method as for the ground sites. Further gridded information was taken from NOAA pathfinder aerosol data and NASA NVAP. An algorithm was devised to fuse these two types of data and to produce gridded maps in a canonical projection and 5' arc angle cells. These final maps should reproduce the values observed at specific locations. The root mean square error of the interpolation is 0.73 TL units

Fusing ground measurements and satellite-derived products for the construction of climatological maps in atmosphere optics

International audienceClimatological maps (gridded data) of optical parameters of the atmosphere often result from application of numerical models or processing of satellite images. Such maps usually exhibit very large cell sizes, of the order of 1 of arc angle. There is a need to increase their spatial resolution to obtain a cell size closer to the spatial representation obtained by standard meteorological instruments at ground level, i.e. 5' of arc angle. It then permits to fuse ground measurements and gridded data, especially to correct for bias ob- served in gridded data. Taking advantage of the availability of other data sets of relevance to the parameter under concern, though different, a method is proposed for the synthesis of the initial gridded data at a higher resolution by the means of a fusion process. This paper describes the method with an application for the con- struction of worldwide maps of the Linke turbidity factor with cells of 5' in size. This factor characterises the atmospheric optical turbidity under clear skies and is a very important parameter in solar radiation studies

Retinometer predicts visual outcome in Descemet membrane endothelial keratoplasty.

PURPOSE To analyze the preoperative predictive value of retinometer visual acuity (VA) in eyes following Descemet membrane endothelial keratoplasty (DMEK). METHODS Patients undergoing DMEK between August 2011 and July 2020 were included. Preoperative interference visual acuity was assessed using Heine Lambda 100 Retinometer. Depending on the presence or absence of concomitant ocular disease, the Retinometer was evaluated for its ability to preoperatively predict best-corrected visual acuity (BCVA) six months after surgery using correlation, simple and multiple linear regression, contingency analyses, and receiver operating characteristic (ROC) analysis. Preoperative corneal backscatter was correlated with Retinometer prediction accuracy. RESULTS A total of 198 eyes were included in the analysis. There was a significant correlation between Retinometer VA and postoperative BCVA (r = 0.647, P < 0.001). Regardless of the presence or absence of concomitant ocular disease and the surgery procedure (DMEK & triple DMEK), Retinometer VA was the most significant predictor of postoperative BCVA (P < 0.001). ROC analysis revealed reliable diagnostic performance of the Retinometer (AUC = 0.829, P < 0.001). A Retinometer VA ≥ 0.5 accurately predicted a postoperative BCVA ≥ 0.5 in 91% of cases. No association was found between corneal backscatter and prediction accuracy (P = 0.566). CONCLUSIONS Retinometer VA can be used for preoperative prediction of postoperative BCVA in DMEK and triple DMEK patients, independent of increased backscatter values and the presence or absence of concomitant ocular disease. By using this simple but effective tool, indication for DMEK can be facilitated and postoperative outcomes can be realistically predicted preoperatively

First Steps in the Cross-Comparison of Solar Resource Spatial Products in Europe

International audienceYearly sum of global irradiation is compared from six spatial (map) databases: ESRA, PVGIS, Meteonorm, Satel-Light, HelioClim-2, and NASA SSE. This study does not identify the best database, but in a relative cross-comparison it points out to the areas of higher variability of outputs. Two maps are calculated to show an average of the yearly irradiation for horizontal surface together with the standard deviation that illustrates the combined effect of differences between the databases at the regional level. Differences at the local level are analysed on a set of 37 randomly selected points: global irradiation is calculated from subset of databases for southwards inclined (at 34°) and 2-axis tracking surfaces. Differences at the regional level indicate that within 90% of the study area the uncertainty of yearly global irradiation estimates (expressed by standard deviation) does not exceed 7% for horizontal surface, 8.3% for surface inclined at 34°, and 10% for 2-axis tracking surface. Higher differences in the outputs from the studied databases are found in complex climate conditions of mountains, along some coastal zones and in areas where solar radiation modelling cannot rely on sufficient density and quality of input dat