Le développement de l'embryon zygotique chez Vitis vinifera L.

The development of the zygotic embryo of Vitis vinifera L.The embryonic development of Vitis vinifera from the zygote to the mature embryo has been studied. The planes of early cell divisions are irregular, thus leading to formation of a large globular proembryo comprising about 1500 undifferentiated cells above a bulky suspensor. Organogenesis of the embryo sta rts with initiation of the cotyledons and constitution of the radicular meristem. The intercotyledonary zone, future shoot apex, is formed by about 300 cells. In this zone, cells remain undifferentiated throughout embryogenesis; its organization begins to be completed only after germination. The radicular meristem, on the other hand, is functioning from the embryonic stage. The meristem of the embryonic radicle and the meristem of the adventitious root are identical in their ('open' type) organization

Ad-blocking Games: Monetizing Online Content Under the Threat of Ad Avoidance

Much of the Internet economy relies on online advertising for monetizing digital content: Users are expected to accept the presence of online advertisements in exchange for content being free. However, online advertisements have become a serious problem for many Internet users: while some are merely annoyed by the incessant display of distracting ads cluttering Web pages, others are highly concerned about the privacy implications - as ad providers typically track users' behavior for ad targeting purposes. Similarly, security problems related to technologies and practices employed for online advertisement have frustrated many users. Consequently, a number of software solutions have emerged that block online ads from being downloaded and displayed on users' screens as they browse the Web. We focus on these advertisement avoidance technologies for online content and their economic ramifications for the monetization of websites. More specifically, our work addresses the interplay between users' attempts to avoid commercial messages and content providers' design of countermeasures. Our investigation is substantiated by the development of a game-theoretic model that serves as a framework usable by content providers to ponder their options to mitigate the consequences of ad avoidance techniques. We complement our analytical approach with simulation results, addressing different assumptions about user heterogeneity. Our findings show that publishers who treat each user individually, and strategically deploy fee-financed or ad-financed monetization strategy, obtain higher revenues, compared to deploying one monetization strategy across all users. In addition, our analysis shows that understanding the distribution of users' aversion to ads and valuation of the content is essential for publishers to make a well-informed decision

A niche remedy for the dynamical problems of neutral theory

We demonstrate how niche theory and Hubbell's original formulation of neutral theory can be blended together into a general framework modeling the combined effects of selection, drift, speciation, and dispersal on community dynamics. This framework connects many seemingly unrelated ecological population models, and allows for quantitative predictions to be made about the impact of niche stabilizing and destabilizing forces on population extinction times and abundance distributions. In particular, the existence of niche stabilizing forces in our blended framework can simultaneously resolve two major problems with the dynamics of neutral theory, namely predictions of species lifetimes that are too short and species ages that are too long.Comment: 47 pages, 4 figures, Accepted to Theoretical Ecolog

Stochastic Spatial Models in Ecology: A Statistical Physics Approach

Ecosystems display a complex spatial organization. Ecologists have long tried to characterize them by looking at how different measures of biodiversity change across spatial scales. Ecological neutral theory has provided simple predictions accounting for general empirical patterns in communities of competing species. However, while neutral theory in well-mixed ecosystems is mathematically well understood, spatial models still present several open problems, limiting the quantitative understanding of spatial biodiversity. In this review, we discuss the state of the art in spatial neutral theory. We emphasize the connection between spatial ecological models and the physics of non-equilibrium phase transitions and how concepts developed in statistical physics translate in population dynamics, and vice versa. We focus on non-trivial scaling laws arising at the critical dimension of spatial neutral models, and their relevance for biological populations inhabiting two-dimensional environments. We conclude by discussing models incorporating non-neutral effects in the form of spatial and temporal disorder, and analyze how their predictions deviate from those of purely neutral theories.MAM is grateful to the Spanish-MINECO for financial support (under Grant FIS2013-43201-P; FEDER funds

Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data

Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/ or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles

Transition rugueuse et localisation pour une singularité linéaire dans un espace à deux ou trois dimensions

The continuous Gaussian approximation is used to describe the thermodynamical properties of an interfacial line in the two-dimensional Ising model ; the exact results concerning the roughening transition of the Abraham model are recovered for TR ⪡ Tc. Furthermore the correlation function for the displacements of the interfacial points is calculated and the influence of a uniform applied field is also studied. The same model is extended to the case of a linear singularity in the three-dimensional space : it is shown that one can get a roughening transition and the free energy exhibits an essential singularity - exp - (A/TR-T).Le modèle gaussien continu est utilisé pour décrire les propriétés thermodynamiques de la ligne d'interface dans le modèle d'Ising à deux dimensions ; on retrouve les résultats exacts concernant la transition rugueuse du modèle d'Abraham pour TR ⪡ Tc On calcule en outre la fonction de corrélation de position des points de l'interface et on étudie l'influence d'un champ extérieur uniforme. Le même modèle est étendu au cas d'une singularité linéaire dans l'espace d = 3 : on montre qu'on peut avoir une transition rugueuse avec une énergie libre possédant une singularité en exp- (A/TR-T)

Critical behaviour of compressible Ising models at marginal dimensionalities

Renormalization group methods are applied to study the critical behaviour of a compressible n-component Ising model with short range interactions at d = 4 and a one component Ising model with dipolar interactions at d = 3. The recursion equations are exactly solved in the case of an elastic system of spherical symmetry (d = 4) or cylindrical symmetry (d = 3); new types of logarithmic corrections, corresponding to a Fisher renormalization at marginal dimensions, are found. It is shown that the system exhibits a first-order transition for constant pressure external conditions or when anisotropy is taken into account. The relevance of the calculations to the critical behaviour of uniaxial ferroelectrics is discussed.Les méthodes du groupe de renormalisation sont appliquées à l'étude du comportement critique du modèle d'Ising compressible à n composantes avec interaction à courte distance à d = 4 et du modèle d'Ising à une composante avec interactions dipolaires à d = 3. Les équations de récurrence sont résolues exactement dans le cas d'un système élastique de symétrie sphérique (d = 4) ou de symétrie cylindrique (d = 3); de nouveaux types de corrections logarithmiques sont obtenus, correspondant à une renormalisation de Fisher pour la dimension marginale. On montre que le système présente une transition du premier ordre dans des conditions de pression extérieure constante ou quand l'anisotropie est prise en compte. On discute l'intérêt des présents calculs pour l'étude du comportement critique des ferro-électriques uniaxiaux