Modelling the Microstructure and the Viscoelastic Behaviour of Carbon Black Filled Rubber Materials from 3D Simulations

Volume fraction and spatial repartition of fillers impact the physical properties of rubber. Extended percolating networks of nano-sized fillers significantly modify the macroscopic mechanical properties of rubbers. Random models that describe the multiscale microstructure of rubber and efficient Fourier-based numerical algorithms are combined to predict the material’s mechanical properties. From TEM image analysis, various types of multiscale models were proposed and validated, accounting for the non-homogeneous distribution of fillers: in the present work, aggregates are located outside of an exclusion polymer simulated by two families of random models. The first model generates the exclusion polymer by a Boolean model of spheres. In the second model, the exclusion polymer is a mosaic model built from a Johnson-Mehl tessellation. Here the exclusion polymer and the polymer containing the filler show a similar morphology, contrary to the Boolean model. Aggregates are then described as the intersection of a Boolean model of spheres and of the complementary of the exclusion polymer. Carbon black particles are simulated by a Cox model of spheres in the aggregates. The models rely on a limited number of parameters fitted from experimental covariance and cumulative granulometry. The influence of the model parameters on percolation properties of the models is studied numerically from 3D simulations. Finally, a novel Fourier-based algorithm is proposed to estimate the viscoelastic properties of linear heterogeneous media, in the harmonic regime. The method is compared to analytical results and to a different, time-discretized FFT scheme. As shown in this work, the proposed numerical method is efficient for computing the viscoelastic response of microstructures containing rubbers and fillers

References for organic farming systems: proposal for an innovative analytical frame

The RefAB project, associating about twenty people from research, training and development produced methodological framework of production of references at the level of the agricultural systems, built for organic farming but relevant to any type of agriculture. It is thus proposed to analyze the agricultural systems (in their economic, social and environmental performances) via five fundamental principles and properties in organic farming: resilience, autonomy, diversity, equity and ecology (referring to IFOAM principles). Various criteria, evaluated by indicators, make it possible to characterize the organic agricultural systems. If certain indicators are classically used in production of references, others are more innovative. The potential of the approach relies in the global approach that is proposed at the level of the farm

Co-Designing an organic framework: the ”REF’AB” Project in France

To help the development of Organic Food and Farming (OFF) systems, there is the need to consolidate conversions to OF, to support entry into organic farming, and to develop existing organic farms. Therefore a group of extensionists, researchers and educators has being working 2 years long to co-design a framework for OFF, taking into account the need to (i) embrace all forms of OFF, and at the same time to (ii) address the specificities of OFF. This project, called REF’AB (REFerentiel de l’Agriculture Biologique, 2010-2012) aims at designing the organization of set of references produced on shared methodological bases. The approach consisted in identifying key-issues of OFF systems, defining indicators, identifying relevant databases and references to feed the framework, and providing recommendations for governance to optimise the establishment and circulation of references. The outcomes of this project is that first it was not necessarily clear what a framework for OFF should be, and therefore a conference of consensus was used as a methodological tool to share views by multi-stakeholders. Second, we used sustainability assessment as an integrative process of the three levels (technical-economic, environmental, and social) and third, to manage to share a more transversal approach, we proposed a framework with 3 levels of key-proprieties: 1) security and efficiency, 2) durability through the protection of resources, and 3) autonomy and resilience

Infinite-contrast periodic composites with strongly nonlinear behavior: Effective-medium theory versus full-field simulations

This paper presents a combined numerical-theoretical study of the macroscopic behavior and local field distributions in a special class of two-dimensional periodic composites with viscoplastic phases. The emphasis is on strongly nonlinear materials containing pores or rigid inclusions. Full-field numerical simulations are carried out using a Fast-Fourier Transform algorithm [H. Moulinec, P. Suquet, C. R. Acad. Sci. Paris II 318, 1417 (1994)] Moulinec, P. Suquet, C. R. Acad. Sci. Paris II 318, 1417 (1994), while the theoretical results are obtained by means of the `second-order' nonlinear homogenization method [P. Ponte Castaneda, J. Mech. Phys. Solids 50, 737 (2002)]. The effect of nonlinearity and inclusion concentration is investigated in the context of power-law (with strain-rate sensitivity m) behavior for the matrix phase under in-plane shear loadings. Overall, the `second-order' estimates are found to be in good agreement with the numerical simulations, with the best agreement for the rigidly reinforced materials. For the porous systems, as the nonlinearity increases (m decreases), the strain field is found to localize along shear bands passing through the voids (the strain fluctuations becoming unbounded) and the effective stress exhibits a singular behavior in the dilute limit. More specifically, for small porosities and fixed nonlinearity m>0, the effective stress decreases linearly with increasing porosity. However, for ideally plastic behavior (m = 0), the dependence on porosity becomes non-analytic. On the other hand, for rigidly-reinforced composites, the strain field adopts a tile pattern with bounded strain fluctuations, and no singular behavior is observed (to leading order) in the dilute limit.Comment: 28 pages, 28 B&W figures, 2 tables of color maps, to be published in International Journal of Solids and Structures (in press

Limits on the high redshift growth of massive black holes

We place firm upper limits on the global accretion history of massive black holes at z>5 from the recently measured unresolved fraction of the cosmic X-ray background. The maximum allowed unresolved intensity observed at 1.5 keV implies a maximum accreted-mass density onto massive black holes of rho_acc < 1.4E4 M_sun Mpc^{-3} for z>5. Considering the contribution of lower-z AGNs, the value reduces to rho_acc < 0.66E4 M_sun Mpc^{-3}. The tension between the need for the efficient and rapid accretion required by the observation of massive black holes already in place at z>7 and the strict upper limit on the accreted mass derived from the X-ray background may indicate that black holes are rare in high redshift galaxies, or that accretion is efficient only for black holes hosted by rare galaxies.Comment: 5 pages, 1 figure, published in A&A Letter

Formate Oxidase (FOx) from Aspergillus oryzae: One Catalyst Enables Diverse H 2 O 2 -Dependent Biocatalytic Oxidation Reactions

An increasing number of biocatalytic oxidation reactions rely on H2O2 as a clean oxidant. The poor robustness of most enzymes towards H2O2, however, necessitates more efficient systems for in situ H2O2 generation. In analogy to the well‐known formate dehydrogenase to promote NADH‐dependent reactions, we here propose employing formate oxidase (FOx) to promote H2O2‐dependent enzymatic oxidation reactions. Even under non‐optimised conditions, high turnover numbers for coupled FOx/peroxygenase catalysis were achieved.The authors gratefully acknowledge funding by the European Research Commission (ERC consolidator grant, No. 648026), the European Union (H2020‐BBI‐PPP‐2015‐2‐1‐720297), the Netherlands Organisation for Scientific Research (VICI grant No. 724.014.003), the National Science Foundation (NSF) of the United States (grant IIP‐1540017) and the Comunidad de Madrid Synergy CAM ProjectOrganisation for Scientific Research

The estimation of black-hole masses in distant radio galaxies

We have estimated the masses of the central supermassive black holes of 2442 radio galaxies froma catalog compiled using data from the NED, SDSS, and CATS databases. Mass estimates based on optical photometry and radio data are compared. Relationships between the mass of the central black hole $M_p^{bh}$ and the redshift $z_p$ are constructed for both wavelength ranges. The distribution of the galaxies in these diagrams and systematic effects influencing estimation of the black-hole parameters are discussed. Upperenvelope cubic regression fits are obtained using the maximum estimates of the black-hole masses. The optical and radio upper envelopes show similar behavior, and have very similar peaks in position, $z_p \simeq 1.9$, and amplitude, $\log M_p^{bh}$ = 9.4. This is consistent with a model in which the growth of the supermassive black holes is self-regulating, with this redshift corresponding to the epoch when the accretion-flow phase begins to end and the nuclear activity falls off.Comment: 8 pages, 6 figure

Diagnostic yield of next-generation sequencing in very early-onset inflammatory bowel diseases: a multicenter study (vol 12, pg 1104, 2021)

Transplantation and immunomodulatio