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1 VenSAR on EnVision: Taking earth observation radar to Venus 2017-10-21             

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Publication date: February 2018
Source:International Journal of Applied Earth Observation and Geoinformation, Volume 64

Author(s): Richard C. Ghail, David Hall, Philippa J. Mason, Robert R. Herrick, Lynn M. Carter, Ed Williams

Venus should be the most Earth-like of all our planetary neighbours: its size, bulk composition and distance from the Sun are very similar to those of Earth. How and why did it all go wrong for Venus? What lessons can be learned about the life story of terrestrial planets in general, in this era of discovery of Earth-like exoplanets? Were the radically different evolutionary paths of Earth and Venus driven solely by distance from the Sun, or do internal dynamics, geological activity, volcanic outgassing and weathering also play an important part? EnVision is a proposed ESA Medium class mission designed to take Earth Observation technology to Venus to measure its current rate of geological activity, determine its geological history, and the origin and maintenance of its hostile atmosphere, to understand how Venus and Earth could have evolved so differently. EnVision will carry three instruments: the Venus Emission Mapper (VEM); the Subsurface Radar Sounder (SRS); and VenSAR, a world-leading European phased array synthetic aperture radar that is the subject of this article. VenSAR will obtain images at a range of spatial resolutions from 30m regional coverage to 1m images of selected areas; an improvement of two orders of magnitude on Magellan images; measure topography at 15m resolution vertical and 60m spatially from stereo and InSAR data; detect cm-scale change through differential InSAR, to characterise volcanic and tectonic activity, and estimate rates of weathering and surface alteration; and characterise of surface mechanical properties and weathering through multi-polar radar data. These data will be directly comparable with Earth Observation radar data, giving geoscientists unique access to an Earth-sized planet that has evolved on a radically different path to our own, offering new insights on the Earth-sized exoplanets across the galaxy.





2 New insights into the formation of submicron silica particles using CO2 as anti-solvent 2017-10-21             

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Publication date: March 2018
Source:The Journal of Supercritical Fluids, Volume 133, Part 1

Author(s): A. Montes, D. Williamson, F. Hanke, I. Garcia-Casas, C. Pereya, E. Martínez de la Ossa, U. Teipel

A supercritical anti-solvent (SAS) process was carried out to obtain micron and submicron particles (0.35–1.78μm) of silica from a solution with a silica precursor. The effects of different parameters such as pressure (120 and 150bar), temperature (323 and 333K), CO2 flow rate (20 and 35g/min), liquid solution flow rate (4 and 8mL/min) and nozzle diameter (0.1 and 0.2μm) on the outcome of the SAS process were analyzed. The TEOS: water molar ratio (1:4–1:17) was also evaluated and seems to play a major role in the precipitation of particles, especially in terms of agglomeration and morphology in that a higher amount of water leads to lower agglomeration of particles. Higher CO2 and lower liquid solution flow rates are recommended to obtain a smaller particle size with narrow particle size distribution (0.35±0.17μm). Lower temperatures are recommended to reduce the particle size. The rest of the assayed variables did not have a significant influence on particle size and size distribution. As far as the textural properties are concerned, silica particles with low porosity (1.41–10.22m2/g) and certain hydrophilic character were generally produced.

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3 Model order reduction and low-dimensional representations for random linear dynamical systems 2017-10-21             

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Publication date: February 2018
Source:Mathematics and Computers in Simulation, Volume 144

Author(s): Roland Pulch

We consider linear dynamical systems of ordinary differential equations or differential algebraic equations. Physical parameters are substituted by random variables for an uncertainty quantification. We expand the state variables as well as a quantity of interest into an orthogonal system of basis functions, which depend on the random variables. For example, polynomial chaos expansions are applicable. The stochastic Galerkin method yields a larger linear dynamical system, whose solution approximates the unknown coefficients in the expansions. The Hardy norms of the transfer function provide information about the input–output behaviour of the Galerkin system. We investigate two approaches to construct a low-dimensional representation of the quantity of interest, which can also be interpreted as a sparse representation. Firstly, a standard basis is reduced by the omission of basis functions, whose accompanying Hardy norms are relatively small. Secondly, a projection-based model order reduction is applied to the Galerkin system and allows for the definition of new basis functions within a low-dimensional representation. In both cases, we prove error bounds on the low-dimensional approximation with respect to Hardy norms. Numerical experiments are demonstrated for two test examples.





4 A multiscale separated representation to compute the mechanical behavior of composites with periodic microstructure 2017-10-21             

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Publication date: February 2018
Source:Mathematics and Computers in Simulation, Volume 144

Author(s): S. Metoui, E. Pruliere, A. Ammar, F. Dau, I. Iordanoff

The requirements for advanced numerical computations are very high when studying the multiscale behavior of heterogeneous structures such as composites. For the description of local phenomena taking place on the microscopic scale, the computation must involve a fine discretization of the structure. This condition leads to problems with a high number of degrees of freedom that lead to prohibitive computational costs when using classical numerical methods such as the finite element method (FEM). To overcome these problems, this paper presents a new domain decomposition method based on the proper generalized decomposition (PGD) to predict the behavior of periodic composite structures. Several numerical tests are presented. The PGD results are compared with those obtained using the classical finite element method. A very good agreement is observed.





5 N-dimensional error control multiresolution algorithms for the cell average discretization 2017-10-21             

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Publication date: February 2018
Source:Mathematics and Computers in Simulation, Volume 144

Author(s): J. Ruiz, J.C. Trillo

We present N -dimensional multiresolution algorithms with error control strategies in the cell average setting as a generalization to N dimensions of the work done in this direction. We present results proving the stability and giving explicit error bounds. We also explain how to carry out the programming and we include two numerical experiments to exemplify the utility of these algorithms.





6 Delay-controlled primary and stochastic resonances of the SD oscillator with stiffness nonlinearities 2017-10-20             

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Publication date: 15 March 2018
Source:Mechanical Systems and Signal Processing, Volume 103

Author(s): Tao Yang, Qingjie Cao

This work presents analytical studies of the stiffness nonlinearities SD (smooth and discontinuous) oscillator under displacement and velocity feedback control with a time delay. The SD oscillator can capture the qualitative characteristics of quasi-zero-stiffness and negative-stiffness. We focus mainly on the primary resonance of the quasi-zero-stiffness SD oscillator and the stochastic resonance (SR) of the negative-stiffness SD oscillator. Using the averaging method, we have been analyzed the amplitude response of the quasi-zero-stiffness SD oscillator. In this regard, the optimum time delay for changing the control intensity according to the optimization standard proposed can be obtained. For the optimum time delay, increasing the displacement feedback intensity is advantageous to suppress the vibrations in resonant regime where vibration isolation is needed, however, increasing the velocity feedback intensity is advantageous to strengthen the vibrations. Moreover, the effects of time-delayed feedback on the SR of the negative-stiffness SD oscillator are investigated under harmonic forcing and Gaussian white noise, based on the Langevin and Fokker-Planck approaches. The time-delayed feedback can enhance the SR phenomenon where vibrational energy harvesting is needed. This paper established the relationship between the parameters and vibration properties of a stiffness nonlinearities SD which provides the guidance for optimizing time-delayed control for vibration isolation and vibrational energy harvesting of the nonlinear systems.





7 Thermo-visco-elasticity for Norton–Hoff-type models with homogeneous thermal expansion 2017-10-20             

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Publication date: April 2018
Source:Nonlinear Analysis: Real World Applications, Volume 40

Author(s): Piotr Gwiazda, Filip Z. Klawe, Sebastian Owczarek

In this work we study a quasi-static evolution of thermo-visco-elastic model with homogeneous thermal expansion. We assume that material is subject to two kinds of mechanical deformations: elastic and inelastic. Inelastic deformation is related to a hardening rule of Norton–Hoff-type. Appearance of inelastic deformation causes transformation of mechanical energy into thermal one, hence we also take into the consideration changes of material’s temperature. The novelty of this paper is to take into account the thermal expansion of material. We are proposing linearization of the model for homogeneous thermal expansion, which preserves symmetry of system and therefore total energy is conserved. Linearization of material’s thermal expansion is performed in definition of Cauchy stress tensor and in heat equation. In previous studies, it was done in different way. Consideration of such linearization leads to system where the coupling between temperature and displacement occurs in two places, i.e. in the constitutive function for the evolution of visco-elastic strain and in the additional term in the heat equation, in comparison to models without thermal expansion. The second coupling was not considered previously. For such system of equations we prove the existence of solutions. Moreover, we obtain existence of displacement’s time derivative, which has not been done previously.





8 Application of high pressure processing for prevention of greenish-gray yolks and improvement of safety and shelf-life of hard-cooked peeled eggs 2017-10-20             

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Publication date: February 2018
Source:Innovative Food Science & Emerging Technologies, Volume 45

Author(s): Hafiz Muhammad Shahbaz, Bora Jeong, Jeong Un Kim, Namho Ha, Hyunah Lee, Sang-Do Ha, Jiyong Park

Hard-cooked peeled eggs (HCEs) are value-added ready-to-use egg products susceptible to microbial re-contamination during post-processing stages. A post-processing terminal step using high hydrostatic pressure (HHP 500, 550, 600MPa for 5min at 25°C) was applied to ensure maximum safety of HCEs and the effects of processing were evaluated and compared with a commercial thermal post-processing intervention using steam heating. A significant discoloration in the form of greenish-gray yolks was observed in HCEs after steam heat post-processing due to overcooking. Color values of the HCE yolk (L*, a*, b*) after HHP post-processing were not significantly different (P>0.05) from non-post-processed HCEs. Non-thermal and thermal post-processing interventions each kept the growth of microbial contaminants at <104 CFU/g throughout 45days of refrigerated storage. Microbial counts in non-post-processed HCEs exceeded this safety limit within 3d. Sensory analysis showed significantly higher preference scores for the quality attributes of HCEs post-processed with HHP than with steam heating. Inactivation curves of Salmonella Enteritidis inoculated onto HCE surfaces after all HHP levels were well-fitted to the biphasic mathematical model. HHP post-package pasteurization at 550MPa for 5min showed potential as a terminal non-thermal kill step for commercial production of HCEs. Industrial relevance A non-thermal post-processing intervention using HHP can be considered as a terminal kill step during commercial production of HCEs to ensure maximum microbiological safety and to extend the shelf life of HCEs without formation of unappetizing greenish-gray yolks. The biphasic mathematical model can be used to predict growth and survival of Salmonella Enteritidis in HCEs and to conduct a risk analysis of this type of food products.





9 Medical image encryption using high-speed scrambling and pixel adaptive diffusion 2017-10-20             

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Publication date: March 2018
Source:Signal Processing, Volume 144

Author(s): Zhongyun Hua, Shuang Yi, Yicong Zhou

This paper presents a new encryption scheme of protecting medical images. It has high efficiency and shows robustness of defending some impulse noise and data loss. First, some random data are inserted into surroundings of the image. Then, two rounds of high-speed scrambling and pixel adaptive diffusion are performed to randomly shuffle neighboring pixels and spread these inserted random data over the entire image. The proposed encryption scheme can be directly applied to medical images with any representation format. We provide two kinds of operations to implement the pixel adaptive diffusion: bitwise XOR and modulo arithmetic. The former has high efficiency in hardware platforms while the latter can achieve fast speed in software platforms. Simulations and evaluations show that both encryption schemes using bitwise XOR and modulo arithmetic have high security levels, can achieve much faster speeds, and can better adapt to impulse noise and data loss interference than several typical and state-of-the-art encryption schemes.





10 Effect of different types of surfactants on the microstructure of methyltrimethoxysilane-derived silica aerogels: A combined experimental and computational approach 2017-10-19             

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Publication date: 15 February 2018
Source:Journal of Colloid and Interface Science, Volume 512

Author(s): João P. Vareda, Pedro Maximiano, Luís P. Cunha, André F. Ferreira, Pedro N. Simões, Luísa Durães

Hypothesis Surfactants interfere with sol-gel particle/pore growth, influencing the structure and properties of silica aerogels. Their ability to induce microscopic changes in the aerogel’s structure may be useful to improve/control the thermal insulation performance of aerogels. Experiments The influence of different types of surfactants (anionic, cationic and non-ionic) on the microstructural arrangement and macroscopic properties of methyltrimethoxysilane (MTMS)-based aerogels was evaluated for the first time, using an experimental and computational comparative approach. Molecular dynamics simulations were performed based on two representative silica molecular structures derived from MTMS, while the experimentally-obtained silica aerogels were characterized in terms of chemical/structural/mechanical/thermal insulation properties. Findings The use of both hexadecyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) led to a decrease in bulk density, thermal conductivity and average pore size of the aerogels, with notorious increase of their flexibility. The observed changes were due to microstructural arrangements, as evidenced by scanning electron microscopy (SEM). However, the non-ionic surfactant, Pluronic F-127, did not have a positive impact on the desired properties. Globally, the simulation results support the experimental findings, suggesting differentiated microstructural changes induced by the use of cationic or anionic surfactants. The addition of CTAB and SDS generally resulted in smaller or larger silica aggregates, respectively.

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