A note on the rate of convergence for a sequence of random polarizations

It was shown by Burchard and Fortier that the expected $L^1$ distance between $f^*$ and $n$ random polarizations of an essentially bounded function $f$ with support in a ball of radius $L$ is bounded by $2dm(B_{2L})||f||_{\infty}n^{-1}$. The purpose of this note is to expand on that result. It is shown that the same expected $L^1$ distance is bounded by $c_nn^{-1}$ with $\limsup_{n\rightarrow \infty}c_n \leq 2^{d+1}||\nabla f||_1$ for every $f \in W_{1,1}(B_L) \cap L^{\infty}(B_L)$. Furthermore, the aforementioned expected $L^1$ distance is $O(n^{-1/q})$ for $f \in L^p(B_L)$ with $p>1$ and $\frac{1}{p} + \frac{1}{q} = 1$. An exponential lower bound is provided for the expected measure of the symmetric difference between the random polarizations of measurable sets and their Schwarz symmetrization. Finally, the rate $n^{-1}$ is shown to be, in a sense, best possible for the random polarizations of measurable sets: the expected symmetric difference between the random polarization of a ball and its corresponding Schwarz symmetrization decays at the rate $n^{-1}$.Comment: 13 pages. Improved the presentation, added rate of convergence estimates for unbounded functions, and made major changes to the section on the random polarization of ball

AndroSSL : Développement d'une plateforme automatisée pour la validation des connexions sécurisées des applications Android

Affiche présentée dans le cadre du Colloque de l'ARC, «La relève scientifique et la recherche collégiale : pratiques inspirantes au regard des chercheuses et chercheurs, et enjeux spécifiques à la formation des étudiantes et étudiants», dans le cadre du 84e Congrès de l'Acfas, Université du Québec à Montréal, Montréal, le 10 mai 2016.Le premier prix a été décerné à Marc-Antoine Ferland et Marc-Antoine Fortier au concours des Prix étudiants 2015-2016 de l'ARC.Le monde de la technologie mobile est en pleine croissance et des centaines de millions d’utilisateurs à travers le monde font confiance aux différentes applications qui leur sont proposées. Mais est-ce que ces applications sont dignes de confiance quant à la protection des données des utilisateurs? Malheureusement, le monde du développement Android est dénué de normes de gestion des échanges sécurisés sur le Web et plusieurs développeurs laissent, sans nécessairement le savoir, plusieurs failles de sécurité dans leurs applications. Actuellement, aucune plateforme ne permet de valider facilement et automatiquement la fiabilité et la sécurité d’une application lors de ses connexions réseau avec son serveur. Notre objectif était de développer une méthodologie novatrice qui certifie la sécurité des applications mobiles de manière efficace et automatique. Nous avons ainsi donné naissance à AndroSSL, une plateforme presque entièrement automatisée qui confirme la sécurité des applications Android touchant des échanges de données par le protocole SSL. À notre connaissance, il s’agit du premier outil de ce genre dans le domaine. Il rend possible la validation d'une quantité impressionnante d’applications avec un effort minime, lequel se résume à exécuter une seule fois les étapes de connexion d’un utilisateur. Notre outil a généré des résultats inquiétants, qui dressent un nouveau portrait de l’état de la sécurité sous Android

A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures

The 18F(p,alpha) reaction was recognized as one of the most important for gamma ray astronomy in novae as it governs the early 511 keV emission. However, its rate remains largely uncertain at nova temperatures. A direct measurement of the cross section over the full range of nova energies is impossible because of its vanishing value at low energy and of the short 18F lifetime. Therefore, in order to better constrain this reaction rate, we have performed an indirect experiment taking advantage of the availability of a high purity and intense radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges, Spain, 20-24 May 2002, 5 pages, 3 figure

(Not) being at home: Hsu Ming Teo's Behind the Moon (2005) and Michelle de Kretser's Questions of Travel (2012)

This article examines some interventions of Asian Australian writing into the debate over multiculturalism, and the shift from negative stereotyping of Asian migrants, to reification of racial divisions and propagation of a masked racism, to the creation of new alignments and the revival of pre-existing affiliations by migrant and second generation subjects. It compares the practices of not-at-homeness by Asian migrants and their descendants and white Australians in Hsu Ming Teo’s Behind the Moon with those of a Sri Lankan refugee and a white Australian traveller in Michelle de Kretser’s Questions of Travel. The changing concepts of belonging in the novels show a realignment of core and periphery relations within the nation state under the pressures of multiculturalism and globalization: where home is and how it is configured are questions as important for white Australians whose sense of territory is challenged as they are for Asian migrants who seek to establish a new belonging

High methylmercury in Arctic and subarctic ponds is related to nutrient levels in the warming eastern Canadian Arctic

Permafrost thaw ponds are ubiquitous in the eastern Canadian Arctic, yet little information exists on their potential as sources of methylmercury (MeHg) to freshwaters. They are microbially active and conducive to methylation of inorganic mercury, and are also affected by Arctic warming. This multiyear study investigated thaw ponds in a discontinuous permafrost region in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a continuous permafrost region in the Arctic tundra (Bylot Island, NU). MeHg concentrations in thaw ponds were well above levels measured in most freshwater ecosystems in the Canadian Arctic (>0.1 ng L−1). On Bylot, ice-wedge trough ponds showed significantly higher MeHg (0.3−2.2 ng L−1) than polygonal ponds (0.1−0.3 ng L−1) or lakes (<0.1 ng L−1). High MeHg was measured in the bottom waters of Subarctic thaw ponds near Kuujjuarapik (0.1−3.1 ng L−1). High water MeHg concentrations in thaw ponds were strongly correlated with variables associated with high inputs of organic matter (DOC, a320, Fe), nutrients (TP, TN), and microbial activity (dissolved CO2 and CH4). Thawing permafrost due to Arctic warming will continue to release nutrients and organic carbon into these systems and increase ponding in some regions, likely stimulating higher water concentrations of MeHg. Greater hydrological connectivity from permafrost thawing may potentially increase transport of MeHg from thaw ponds to neighboring aquatic ecosystems

Passive Mineral Carbonation of Mg-rich Mine Wastes by Atmospheric CO2

Mg-rich process tailings and waste rocks from mining operations can react spontaneously with atmospheric CO2 to form stable carbonate minerals by exothermic reactions. Over the last decade, we have conducted a number of laboratory and field experiments and surveys on both mine waste rocks and different types of mine tailings from Ni-Cu, chrysotile, and diamond mines. The experiments and surveys cover a wide range of time (103 to 108 s) and mass (1-108 g) scales. Mine waste rich in brucite or chrysotile enhances the mineral carbonation reactions. Water saturation, but more importantly, watering frequency, are highly important to optimize carbonation. Adjusting the chemical composition of the interstitial water to favour Mg dissolution and to prevent passivation of the reaction surfaces is crucial to ensure the progress of the carbonation reactions. Preservation of the permeability structure is also critical to facilitate water and CO2 migration in the rock wastes and tailings. In field experiments, CO2 supply controled by diffusion in the mining waste is slower than the reaction rate which limits the capture of atmospheric CO2. Industrial implementation of passive mineral carbonation of mine waste by atmospheric CO2 can be optimized using the above parameters

Life in the fast lane: Revisiting the fast growth—High survival paradigm during the early life stages of fishes

Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth-Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow-growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two-thirds of field studies, leaving a non-negligible fraction of cases showing either an absence of or inverse growth-selective survival, suggesting the growth-survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth-selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population-specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre-recruited life. -- Keywords : critical period ; growth-mortality ; individual characteristics ; larval physiology ; predation ; recruitment endpoint

Convergence Results for Rearrangements: Old and New.

The purpose of this thesis is twofold. On the one hand, it aims to give a thorough review and exposition of current best results regarding approximating the symmetric decreasing rearrangement by polarizations and Steiner symmetrizations. These results include those of Van Schaftingen on explicit universal approximation to the symmetric decreasing rearrangement by sequences of polarizations as well as his results on almost sure convergence of rearrangements to the symmetric decreasing rearrangement. They also include those of Klartag and Milman which yield rates of convergence for Steiner symmetrizations of convex bodies. On the other hand, new results are proven. We extend Van Schaftingen's results on almost sure convergence of polarizations and Steiner symmetrizations by showing that the conditions on the random variables can be weakened without affecting almost sure convergence to the symmetric decreasing rearrangement. Lastly, we derive rates of convergence for polarizations and Steiner symmetrizations of Hölder continuous functions.MAS

Le Caniche Français et Le Carlin Anglais

One figure, the "French Poodle", detail, legs; Cast by Atelier du Bronze foundry, this is a two-piece "diptych" sculpture of two over-life-size figures of a masked man, holding a pug and a masked woman holding a miniature French poodle, symbolizing the British and French heritage in Canada with both realism and a sense of social satire. The Pug and the French Poodle are looking at each other across the plaza while the owners are looking in opposite directions. Fortier was born in Montreal. Source: M.A.J. Fortier [artist website]; http://majfortier.com (accessed 6/18/2014