The InSight lander will deliver geophysical instruments to Mars in 2018, including seismometers installed directly on the surface (Seismic Experiment for Interior Structure, SEIS). Routine operations ...will be split into two services, the Mars Structure Service (MSS) and Marsquake Service (MQS), which will be responsible, respectively, for defining the structure models and seismicity catalogs from the mission. The MSS will deliver a series of products before the landing, during the operations, and finally to the Planetary Data System (PDS) archive. Prior to the mission, we assembled a suite of
a priori
models of Mars, based on estimates of bulk composition and thermal profiles. Initial models during the mission will rely on modeling surface waves and impact-generated body waves independent of prior knowledge of structure. Later modeling will include simultaneous inversion of seismic observations for source and structural parameters. We use Bayesian inversion techniques to obtain robust probability distribution functions of interior structure parameters. Shallow structure will be characterized using the hammering of the heatflow probe mole, as well as measurements of surface wave ellipticity. Crustal scale structure will be constrained by measurements of receiver function and broadband Rayleigh wave ellipticity measurements. Core interacting body wave phases should be observable above modeled martian noise levels, allowing us to constrain deep structure. Normal modes of Mars should also be observable and can be used to estimate the globally averaged 1D structure, while combination with results from the InSight radio science mission and orbital observations will allow for constraint of deeper structure.
We present the results of a combined theoretical and experimental study of the stability of a uniformly stratified fluid bounded by a sidewall moving vertically with constant velocity. This ...arrangement is perhaps the simplest in which boundary effects can drive instability and, potentially, layering in a stratified fluid. Our investigations reveal that for a given stratification and diffusivity of the stratifying agent, the sidewall boundary-layer flow becomes linearly unstable when the wall velocity exceeds a critical value. The onset of instability is clearly observed in the experiments, and there is good quantitative agreement with some predictions of the linear stability analysis.
L'art populaire est le reflet d'une société, de la perspective de ses créateurs, dont les approches sont tantôt traditionnelles et rationnelles, tantôt indisciplinées et débridées. D'hier ou ...d'aujourd'hui, l'art populaire révèle toute son expressivité, met en valeur les objets anciens et contemporains. Du coq à l'âme. L'art populaire au Québec est le résultat de plusieurs années de recherche et de rencontres avec des créateurs, des collectionneurs et des chercheurs, tous passionnés de cette forme de créativité originale et authentique. L'anthropologue Jean-François Blanchette jette un regard historique et photographique sur les collections d'art populaire québécois du Musée canadien de l'histoire, dont la très prestigieuse collection de Nettie Covey Sharpe, acquise en 2002. Par sa vision identitaire, la présente publication vise à mieux faire connaître l'histoire culturelle et sociale et à présenter la créativité d'artistes québécois souvent peu reconnus. Vous y découvrirez l'histoire de l'art populaire, les artistes et leurs œuvres. Du coq à l'âme. L'art populaire au Québec vient circonscrire l'art populaire et présenter son développement dans le temps, depuis sa forme traditionnelle, fort ancienne, jusqu'à sa forme indisciplinée, plus récente, du graffiti.
Inflammation and neurodegeneration characterize the pathogenesis of multiple sclerosis (MS). Slow axonal degeneration, rather than acute inflammation, is considered the cause of chronic disability in ...MS. The signs of acute axonal damage and loss have been shown to occur early in the lesion development of patients with chronic MS and often correlate with demyelination and inflammation. While immune activity in the central nervous system has traditionally been considered to be a detrimental event in MS, recent studies have found that autoimmune T cells may play an important role in protecting neurons from the ongoing spreading damage. Neuroprotection in MS is a new and evolving concept, and many questions remain with regard to potential targets for therapeutic intervention. Preliminary studies, both in animals and in humans, have suggested that glatiramer acetate (GA) may confer neuroprotective activity in addition to bystander suppression. Additional research is needed to determine if these promising neuroprotective effects correlated with the long-term effect of GA in MS.
Modern information systems not only capture a seemingly endless amount of transactional data, but also tend to retain it for indefinite periods of time. We argue that privacy policies must address ...not only collection and access to transactional information, but also its timely disposal. One unintended side effect of data retention is the disappearance of social forgetfulness, which allows individuals a second chance, the opportunity for a fresh start in life. We examine three domains in which social policy has explicitly recognized the importance of such a principle: bankruptcy law, juvenile crime records, and credit reports. In each case, we frame the issue in terms of the social benefits of forgetfulness, rather than in terms of individual privacy protection. We examine how different policy approaches to privacy might handle the retention of data and propose a comprehensive policy that includes a variety of strategies. The broad conclusion of the article is that data retention and disposal should be addressed as a part of a broader and comprehensive policy approach, rather than in a piecemeal fashion or as an afterthought.
Marine lakes are emerging ecological and evolutionary natural experimental systems, with genetically isolated resident populations that exhibit extreme population dynamics and rapid phenotypic ...change. Marine lakes are posited to be marine islands, however, unlike terrestrial islands for which rich models have been developed over the past half-century, we know little of the mechanisms driving changes in marine lakes. This is a critical knowledge gap in efforts to reconcile theory on, or distinguish differences among, island and island-like systems. To reduce this critical knowledge gap, we present a mathematical model describing marine lakes based on a case study of Jellyfish Lake (Ongeim’l Tketau, Mecherchar: OTM), Palau. Empirical data show that marine lakes exhibit delayed and reduced tidal motions, suggesting exchange of a limited amount of water with the neighboring (‘mainland’) ocean. Our model tracks changes in lake level, allowing determination of an exchange rate that is a physical null model for biological colonization and a proxy for colonization distance in island biogeography theory. In addition, we track horizontally averaged in-lake quantities such as salinity and temperature (i.e., marine weather, climate) and stratification (i.e., habitat) — that are known to influence resident species’ distributions and population dynamics — by solving an advection-diffusion equation. We find that weather, ocean conditions, groundwater, and exchanges through tunnels determine the abiotic environment in OTM. By comparing simulations and data, we estimate the difficult-to-measure properties of the surrounding groundwater — the ‘matrix’ in the vernacular of habitat islands — and give a range of realistic values for the effective diffusion coefficient. This coefficient is found to increase in a tropical storm, suggesting that other drivers can be important during perturbations.
We present a theoretical and numerical investigation of streamlines and mixing within drops flowing in capillaries. We first study theoretically the limit case of purely viscous flow around a drop of ...negligible radius, and find that, owing to geometrical constraints, recirculating regions are always present at the front and back of such drops. Using two-dimensional simulations, we visualize streamlines for larger drops, showing that the extent of these recirculating torii increases with drop size and decreases with Reynolds number. We study the mixing within drops as they are subjected to time-dependent shear, thus modeling a sinusoidal channel, and find that while cross-stream mixing is efficient, streamwise mixing is hindered by the front and back recirculating regions.
PDF
