Absolute calibration of VEGETATION derived from an interband method based on the Sun glint over ocean

Absolute radiometric calibration is one of the main elements that contribute to the quality of measurements obtained with optical remote sensing instruments, but maintaining a good calibration accuracy during the whole life of an instrument is a difficult task. Since the sensitivity of an instrument generally changes after launch and degrades with time, many sensors have been equipped with onboard calibration devices. But these devices being not perfectly reliable, independent calibration methods based on natural targets are necessary to validate the results. The Sun glint calibration method is an interband calibration method that uses the specular reflection of the Sun on the ocean surface to transfer the absolute calibration of one reference spectral band to other spectral bands, from visible to short wave infrared wavelengths. Despite the drawback of relying on the absolute calibration of a reference spectral band, this method is one of the rare methods that can provide accurate calibration results for near-infrared spectral bands up to 1650 nm, without requiring costly in situ measurements simultaneously to the satellite overpass. This paper details the Sun glint calibration method and its error budget, and gives the results obtained with the VEGETATION instrument that was recently launched onboard the Systeme Pour l'Observation de la Terre 5 (SPOT-5) satellite. These results compare very well with the results of other calibration methods.     

Simulation of fresh concrete flow using Discrete Element Method (DEM): theory and applications

This article provides an overview of the development and the contemporary state of research in the field of simulating fresh concrete flow using the Discrete Element Method (DEM). First, this work originating from TC 222-SCF simulation of fresh concrete flow, covers the mathematical methodology, the identification of the model parameters and the link between the rheological properties of fresh concrete and the parameters of DEM-based models. Various examples of the estimation of model parameters and calibration of the model were demonstrated, followed by verifications by comparing the numerical results and the corresponding predictions by analytical formula and laboratory experiments. Furthermore, software used in concrete engineering and existing industrial applications of the developed particle models were described, showing the potential of DEM.     

Optimal configurations for perfectly matched layers in FDTD simulations

To be effective a perfectly matched layer (PML) must be reflectionless to all impinging waves over a broad band of frequencies whilst not overly increasing the computational burden. This can be difficult to achieve as one must find a balance between the discretization error, the number of PML layers and the reflection coefficient. This work presents an optimized solution for simulating PMLs for the finite-difference time-domain (FDTD) technique using both the mono-objective genetic algorithm (GA) and multiobjective genetic algorithm (MGA). The main goal is to implement a tool capable of finding the best choice of parameters for the conductivity profile to achieve a minimum for both the reflection and computation time.     

Natural carbonation of aged alkali-activated slag concretes

Alkali-activated slag concretes stored for 7 years under atmospheric conditions are assessed, and the structural characteristics of naturally carbonated regions are determined. Concretes formulated with a 400 kg/m³ and water/binder (w/b) ratio between 0.42 and 0.48 present similar natural carbonation depths, although these concretes report different permeabilities after 28 days of curing. The inclusion of increased contents of binder leads to a substantial reduction of the CO₂ penetration in these concretes, so that negligible carbonation depth values (2 mm) are identified in concretes formulated with 500 kg/m³ of binder. Calcite, vaterite, and natron are identified as the main carbonation products formed in these concretes. These observations differ from the trends which would be expected in comparable ordinary Portland cement-based concretes, which is attributable to the physical (permeability) and chemical properties of alkali-activated slag concretes promoting high long-term stability and acceptably slow carbonation progress under natural atmospheric conditions.     

Discrete adjoint gradient evaluations for linear stress and vibration analysis

This paper presents methods used to perform discrete adjoint gradient evaluations for linear stress and vibration analysis. The methods are implemented within the framework of a discrete adjoint structural solver being developed for multidisciplinary adjoint optimizations of turbomachinery components. The code is differentiated using the algorithmic differentiation tool CoDiPack in tandem with manual treatment of the iterative solvers. Stress analysis leads to a linear system of equations that is typically solved by an iterative solver (e.g. GMRES). To ensure accuracy, the adjoint problem is formulated as a new linear system of equations to be solved. Vibration analysis results in a generalized eigenvalue problem that is also typically solved by an interative solver. The adjoint problem takes out the generalized eigenvalue solve and replaces it by one outer product per eigenfrequency, leading to significantly cheap eigenfrequency gradients for vibration analysis.