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Molecular dynamics simulations have been used for decades to investigate continuum mechanics failure to give the correct distribution of stress near discontinuities, such as holes and crack tips. In this paper, stress distribution around elliptical holes in a sheet material has been examined in an atomistic and a continuum model. Atomistic interactions are described by the Tersoff potential tuned for carbon. Calculations were conducted for the problem of stress distribution around the elliptic hole in a 2D graphene sheet subjected to the gradually increasing uniaxial tension load. The atomistic stress is calculated as spatial average utilizing Hardy’s formulation. The results have been compared with the Kirsch solution for stress concentration at the edge of the circular hole. A quantitative measure for switching from atomistic to continuum model and vice versa has been proposed. Routes toward the effective data- driven coupling of macro- and micromechanical models where continuum mechanics approach fails are pointed out.

We develop a statistical framework to test the hypothesis of the existence of an ionospheric cooling trend related to the global warming hypothesis; both are attributed to the same driver, namely the increased concentration of greenhouse gases. However, the study of a temporal trend in the ionosphere is easier because there are fewer covariates to be taken into account. The hypothesis that a cooling trend in the ionosphere exists has been an important focus of space physics research for over two decades. A central difficulty in reaching broadly agreed—on conclusions has been the absence of data with sufficiently long temporal and sufficiently broad spatial coverage. Complete time series of data that cover several decades exist only in a few separated (industrialized) regions. The space physics community has struggled to combine the information contained in these data, and often contradictory conclusions have been reported based on the analyses relying on one or a few locations. We present a statistical analysis that uses all data, even those with incomplete temporal coverage. It is based on a new functional regression approach that can handle spatially indexed curves whose temporal domain depends on location and may contain gaps. The test statistic combines spatial and temporal dependence in the data and is approximately normally distributed. We conclude that a statistically significant cooling trend exists in the Northern Hemisphere. This confirms the hypothesis put forward in the space physics community over two decades ago.

International audience; In this work, we investigate the use of artificial neural networks (ANNs) as a post-processing technique in order to improve mesoscale WRF solar radiation outputs.More precisely, one day ahead (with a 1 h temporal resolution) global horizontal irradiance (GHI) forecasts calculated by the WRF model are bias-corrected through the use of an ANN.ANNs are data driven approaches capable of recognizing patterns in data. Training data obtained from a ground station are used to construct the ANN model in order to reduce the bias of the WRF forecasts. A bias error analysis allows the determination of the relevant ANN's inputs necessary to this bias correction. Among others, one can cite the solar zenith angle and the clear sky index.This specific model output statistics (MOS) technique is applied in the frame of a solar PV forecasting project that takes place in La Reunion Island, a French oversea territory located in the Indian Ocean. This insular feature makes solar forecasting very challenging, hence the need for advanced solar forecasting methods.

Spatial Averaging Filters (SAF) are extensively used in image processing for image smoothing and denoising. Their latest implementations have already achieved constant time computational complexity regardless of kernel size. However, all the existing O(1) algorithms require additional memory for temporary data storage. In order to minimize memory usage in embedded systems, we introduce a new two-dimensional recursive SAF. It uses previous resultant pixel values along both rows and columns to calculate the current one. It can achieve constant time computational complexity without using any additional memory usage. Experimental comparisons with previous SAF implementations shows that the proposed 2D-Recursive SAF does not require any additional memory while offering a computational time similar to the most efficient existing SAF algorithm. These features make it especially suitable for embedded systems with limited memory capacity., SPIE Photonics Europe, Sunday 3 April 2016, Brussels, Belgium, Series: Proceedings of SPIE; no. 9897

This paper examines the properties of the homentropic Euler equations when the characteristics of the equations have been spatially averaged. The new equations are referred to as the characteristically averaged homentropic Euler (CAHE) equations. An existence and uniqueness proof for the modified equations is given. The speed of shocks for the CAHE equations are determined. The Riemann problem is examined and a general form of the solutions is presented. Finally, numerically simulations on the homentropic Euler and CAHE equations are conducted and the behaviors of the two sets of equations are compared.

Two large-aperture infrared scintillometers were positioned at heights (z) of 10 and 1.5 m with beams propagated horizontally over pasture for distances of 3.1 km and 141 m, respectively. From each scintillometer a half-hourly average value of the path-averaged, temperature-structure parameter (CT2) was obtained in unstable atmospheric conditions. The result suggested CT2 to scale with height as z-2/3. Using the CT2-profile method a path-averaged measure of the Obukhov length (L0) was calculated for each half-hour period, whence L0 was used to determine the friction velocity, u* and the surface-layer temperature scaling parameter, T*. The scintillometer-based sensible heat flux density Hsc was then calculated from Hsc = ρ Cpu*T*. A time series of half-hourly averaged Hsc compared to Hec obtained by the eddy covariance method agreed to within 10%, with R2 = 0.67, for a range of unstable conditions (- 0.2 ≤ z/L0 ≤ - 0.01).

12th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 5-9 March 2012, Villa Mondragone, A study of the latitudinal trend of the retrieved salinity performances along a Southwards transect has been performed, analyzing the trade-off between geophysical effects in cold seawater and the concomitant temporal oversampling under various processing configurations. Quantitative sensitivity with respect to sea surface temperature gradient has been evaluated

International audience; Classical upscaling methods like spatial averaging or periodic homogenization allow for a description of various transport processes in heterogeneous media from one scale to another. Moreover, the effective parameters appearing in the scaled equations are related to the microgeometry by the associated closure problems, which are generally completed by periodic boundary conditions. This is why these methods are mostly applied to either simple periodic structures (array of spheres for example) or computer-generated media with enforced structural periodicity, for the purpose of obtaining closure relations that can be applied to general media. With the development of imaging techniques like X-rays tomography, it is now possible to access the 3D microstructure of heterogeneous media. In some cases, the traditional periodic closure problem may be used to give an acceptable estimate of the effective properties, but the periodicity conditions may result in dramatic errors in the case of low-porosity materials (like cementious materials for example). We propose here to study another set of boundary conditions, which could allow for a good prediction of the effective diffusivity of a saturated, low-porosity medium. In order to do that, the question of the importance of the periodic boundary conditions appearing in the classical closure problem is investigated. Both analytical and numerical studies on 2D and 3D media show that these periodic conditions could, advantageously, be replaced by homogeneous Dirichlet conditions and that the condition of scale separation seems to be sufficient to achieve a good determination of the effective properties. A simple method is also proposed to dramatically improve the convergence of the non-periodic solution toward reference solution. As an application, the effective diffusivity tensor is computed on 3D image of computer-generated cement paste with very low porosity, showing very good agreement with available experimental data.

A multiscale formulation is derived for the mechanics of a dilute fiber network microstructure, as occurs in in vitro reconstituted collagen gels, to accommodate the deterministic solution of a uniform-stress condition in the fiber network. The macroscale two-phase equations are derived based on the integral volume-averaging approach of the spatial averaging theorem, modified for the averaging volume to deform materially in the solid phase and thereby ensuring consistent network mass conservation. For low-Reynolds-number fiber-fluid interaction with no hydrodynamic interaction between fibers, the macroscale Darcy law arises naturally as a function of average fiber orientation and volume fraction, with no additional empirical specification. The macroscale equations are solved using finite element analysis with the averaging volumes centered at Gauss points of integration. The macroscale solid stress and fluid velocity are obtained by microscale deterministic solution of network and Stokesian mechanics within the averaging volume at each Gauss point, whereas the macroscale displacements and fluid pressure are solved as interpolated finite element field variables. The theory when applied to describe confined compression of collagen gels reproduced the strain-rate dependent behavior observed in poroelastic materials. The deformation of the averaging region and the reorientation of the collagen network in response to strain are also discussed. © 2008 Society for Industrial and applied Mathematics. 7 22 43 22-43

In a given hurricane season, several tropical disturbances propagate across environments favorable for development; however, only a few disturbances actually strengthen into tropical cyclones. The lack of a consolidated theory on tropical cyclogenesis makes it difficult for forecasters to predict a storm’s development. Previous studies have approached this problem by comparing large-scale influences on storms that developed into tropical cyclones and on those that did not. This study used a similar approach to characterize the environmental influences on cyclogenesis in the 2005 Eastern Pacific Hurricane season. Data for each storm were taken from the NCEP/NCAR Final Analysis model and analyzed over a 48-hour period during the development stage. The non-developing storms were selected based on certain atmospheric parameters to resemble the developing storms prior to cyclogenesis. Composites and spatial averaging were used to compare 12 developing storms and 11 non-developing storms during this season. The results showed that the environments of the developing storms had large regions of increased moisture above the boundary layer and greater temperatures in the upper troposphere. Regions of increased potential vorticity penetrated deeper into the troposphere for the developing storms. Lastly, the storms that developed were in environments with relatively strong wind shear to the south of the vortex. The results suggest that the moisture, temperature, and wind shear fields preceded development, while the vorticity fields were more of an indicator of development. Identifying these large-scale characteristics as possible determining influences can lead to a better understanding of tropical cyclogenesis.

Title and contents Introduction 3 Chapter 1. Fundamentals 6 Chapter 2. Airborne remote sensing measurements 12 Chapter 3. Artificial cloud generation 24 Chapter 4. Three-dimensional radiative transfer simulations 31 Chapter 5. Cloud radiative smoothing 40 Chapter 6. Effect of horizontal and vertical averaging and layering on retrieval schemes of cloud properties 57 Summary 72 Acknowledgements 76 List of figures and tables 77 Bibliography 83, The central subject of this work is to improve the understanding of multiple scattering and absorption in the presence of 3d cloud fields. A systematic investigation of the effect of 3d cloud structure on the atmospheric radiation field is carried out. The investigations are based on (3d) radiative transfer simulations and observations taken during a measurement campaign. After the introduction of basic theory and methods, the utilised intruments and the measurement campaign are presented. In this context, a spatial high-resolution cloudmask was developed. The cloudmask is needed for data preprocessing. The radiative transfer is computed with a Monte Carlo model. First, a method to reduce the signal-to-noise ratio is introduced, and second, the validation of the model against other radiative transport models was successfully carried out. To provide the radiative transport model with input fields, a cloud generator based on Fourier transformations was developed. The so generated input fields are used to characterise the noise behaviour of the model. Two other cloud generators are introduced: so called iterative amplitude adapted Fourier transform surrogates and large eddy simulation models. These models either produce the cloud geometry or the liquid water content. Therefore, microphysical properties are discussed in the following, and a special mixing scheme is developed. The discussion of the effect of 3d cloud structure on solar radiative transport focuses on cloud radiative smoothing and the analysis of spatial averaging. The effect of gas absorption, surface albedo, and two layer clouds on cloud radiative smoothing is investigated by applying the power spectrum analysis to observed and simulated nadir radiances. In this work the terms large and small scale cloud radiative smoothing are introduced, which marks an extension of the usually used term and emphasises the scale dependence of the effects. Even in completely overcasted cases large surface albedos result in significant large scale cloud radiative smoothing. The spectral behaviour of two layer clouds causes comparable findings and is analysed for the first time. Absorption influences large and small scale radiative smoothing. In particular, it reduces horizontal photon transport and the scale break (transition between large and small scale effects). The results from the observations and the computations are in excellent agreement. The effect of spatial averaging on the nadir radiance and the retrieval of cloud properties is also based on observations and simulations. The analysis of the effect of spatial averaging showed, that in case of different resolutions a simple adjustment through averaging should be accompanied by an exact allocation of both measurements. The investigation of the effect of vertical layering on the nadir radiance is followed by a paramerterisation of the mean photon path length with optical thickness and effective radius. The former reveals that the intensity of the absorption and the volume extinction at cloud top are the dominant dependencies. The second analysis demonstrates that the dependence of the mean photon path length on the effective radius is significant. The parameterisation offers a way to improve retrieval schemes and computation of gas absorption in GCMs., Die vorliegende Arbeit hat unter anderem zum Ziel, das Verständnis von Mehrfachstreuung und Absorption in der bewölkten Atmosphäre zu verbessern. Zu diesem Zweck wird eine umfangreiche Diskussion des Einflusses der dreidimensionalen (3d) Struktur von Wolken auf die solare Strahlung präsentiert. Die Untersuchungen basieren auf 3d Strahlungstransportrechnungen und auf Daten, die während einer Messkampagne gewonnen wurden. Nachdem eine Einführung in gundlegende Theorien und Methoden gegeben wurde, werden die eingesetzten Messgeräte und die Messkampagne vorgestellt. Eine räumlich hochaufgelöste Wolkenmaske wurde in diesem Zusammenhang entwickelt. Diese wird für eine spätere Vorprozessierung der Daten benötigt. Die Strahlungstransportrechnungen werden mit einem Monte Carlo Modell durchgeführt. Zunächst wird eine spezielle Methode vorgestellt, um das Verhältnis von Signal und Rauschen zu verbessern. Anschliessend wird das Strahlungstransportmodell durch Vergleich mit anderen Modellen validiert. Um das Strahlungstransportmodell mit Eingabefeldern zu versorgen, wurde ein Wolkengenerator auf Basis von Fouriertransformationen entwickelt. Die so bereitgestellten Felder werden zur Charakterisierung des Rauschverhaltens des Modells herangezogen. Zwei weitere Methoden zur Wolkengenerierung werden vorgestellt: sogenannte "iterative amplitude adapted Fourier transform" Surrogaten und ein "large eddy simulation" Modell. Da die bisher genannten Modelle vornehmlich die geometrische Struktur bzw. den Flüssigwassergehalt liefern, werden im weiteren mikrophysikalische Eigenschaften diskutiert und ein spezielles Mischungsschema eingeführt. Zwei grundlegende Aspekte des Einflusses von 3d Wolkenstrukturen auf solaren Strahlungstransport werden untersucht: Strahlungsglättung und Effekte durch räumliches Mitteln. Die Strahlungsglättung wird untersucht, indem die sogenannte "power spectrum" Analyse auf Messungen und Simulationen angewandt wird. Die Analyse konzentriert sich auf den Einfluss von Gasabsorption, Bodenalbeden und Zweischichtwolken. In dieser Arbeit werden die Ausdrücke groß- und kleinskalige Strahlungsglättung eingeführt, welches eine Erweiterung des sonst üblichen Begriffes darstellt und die Skalenabhängigkeit der Einflüsse betont. Große Bodenalbeden führen selbst bei völlständiger Bedeckung zu signifikanter, großskaliger Strahlungsglättung. Das spektrale Verhalten von Zweischichtwolken resultierte in vergleichbaren Ergebnissen und ist im Rahmen dieser Arbeit erstmalig untersucht worden. Absorption beeinflusst groß- und kleinskalige Strahlungsglättung. Insbesondere verringert sie den horizontalen Photonentransport und damit den Skalenbruch (Übergang von groß- zu kleinskaligen Effekten). Die anhand von Messungen gewonnenen Ergebnisse werden anschliessend mittels der Simulationsergebnisse erfolgreich verifiziert. Der Einfluss von räumlichem Mitteln auf die Nadirstrahldichte und Wolkenableitungsverfahren wird ebenfalls auf Basis von hochaufgelösten Messungen und Simulationen untersucht. Die Analysen zum Einfluss von horizontalem Mitteln zeigen, dass bei unterschiedlichen Auflösungen das Angleichen durch Mitteln unbedingt durch eine exakte Übereinstimmung der Position begleitet sein muss. Der Untersuchung des Einflusses von vertikaler Schichtung auf die Nadirstrahldichte folgt eine Parameterisierung der mittleren Photonenweglänge mit der optischen Dicke und dem Effektivradius. Ersteres zeigt, dass die Intensität der Absorption und die Volumenextinktion an der Wolkenoberseite die beherrschenden Parameter sind. Die zweite Analyse offenbart, dass die Abhängigkeit der mittleren Photonenweglänge vom Effektivradius signifikant ist. Die erweiterte Parameterisierung öffnet Möglickeiten zur Verbesserung von Ableitungsverfahren und der Einbindung von Gasabsorption in globalen Zirkulationsmodellen.

A reliability approach to a slope stability analysis, considering spatially correlated soil properties, is used to systematically evaluate the various sources of uncertainty that arise in these types of problems. Measurement errors and bias that often occur during soil investigations are now incorporated into the probabilistic model of soil properties in addition to the spatial variability and the effects of spatial averaging. The results of the analysis show that the unconditional approach, which considers spatial variability, but does not account for measurement-related uncertainties, can yield unconservative results because of an unrealistically large variance reduction. In contrast, the results obtained from the unconditional approach, which does consider spatial variability and measurement-related uncertainties, as well as those from the conditional approach, lead to significantly lower probabilities of failure that are much less sensitive to the scales of fluctuation.