Effects of population density on the sediment mixing induced by the gallery-diffusor Hediste (Nereis) diversicolor O.F. Müller, 1776

The aim of this work was to quantify the intensity of sediment mixing induced by the gallery-diffusor (functional bioturbation group) Hediste diversicolor as a function of density, using particles tracers (luminophores). In order to assess the impact of density on sediment reworking, a 1-D model was used to obtain sediment reworking coefficients such as Db (biodiffusion-like) and r (biotransport). Densities used in this experiment corresponded to population densities observed in the sampling area (Saint-Antoine Canal, Gulf of Fos, France): 144, 288, 577, 1153 indiv/m2. At first, results showed that neither luminophore maximum burying depth nor the more marked tracer accumulation areas were influenced by density. Thus density did not seem to have any influence on size of galleries or complexity of structure. Then, density-dependent relations with Db (biodiffusion-like mixing) and r (biotransport) were highlighted with an observed process intensity rate twice as high at highest worm density. On the other hand, Db and r per capita coefficients were negatively influenced by density. Db and r per capita at highest density were equal to ∼20% of individual Db and r obtained at the lowest density. Finally, this study showed the importance of density which appears to be a key parameter in the functioning of the sedimentary ecosystem

Imperfect Construction of Microclusters

Microclusters are the basic building blocks used to construct cluster states capable of supporting fault-tolerant quantum computation. In this paper, we explore the consequences of errors on microcluster construction using two error models. To quantify the effect of the errors we calculate the fidelity of the constructed microclusters and the fidelity with which two such microclusters can be fused together. Such simulations are vital for gauging the capability of an experimental system to achieve fault tolerance.Comment: 5 pages 2 figure

Computing tie strength

Relationships make social media social. But, not all relationships are created equal. We have colleagues with whom we correspond intensely, but not deeply; we have childhood friends we consider close, even if we fell out of touch. Social media, however, treats everybody the same: someone is either a completely trusted friend or a total stranger, with little or nothing in between. In reality, relationships fall everywhere along this spectrum, a topic social science has investigated for decades under the name tie strength, a term for the strength of a relationship between two people. Despite many compelling findings along this line of research, social media does not incorporate tie strength or its lessons. Neither does most research on large-scale social phenomena. In social network analyses, a link either exists or not. Relationships have few properties of their own. Simply put, we do not understand a basic property of relationships expressed online. This dissertation addresses this problem, merging the theories behind tie strength with the data from social media. I show how to reconstruct tie strength from digital traces in online social media, and how to apply it as a tool in design and analysis. Specifically, this dissertation makes three contributions. First, it offers a rich, high-accuracy and general way to reconstruct tie strength from digital traces, traces like recency and a message???s emotional content. For example, the model can split users into strong and weak ties with nearly 89% accuracy. I argue that it also offers us a chance to rethink many of social media???s most fundamental design elements. Next, I showcase an example of how we can redesign social media using tie strength: a Twitter application open to anyone on the internet which puts tie strength at the heart of its design. Through this application, called We Meddle, I show that the tie strength model generalizes to a new online community, and that it can solve real people???s practical problems with social media. Finally, I demonstrate that modeling tie strength is an important new tool for analyzing large-scale social phenomena. Specifically, I show that real-life diffusion in online networks depends on tie strength (i.e., it depends on social relationships). As a body of work, diffusion studies make a big simplifying assumption: simple stochastic rules govern person-to-person transmission. How does a disease spread? With constant probability. How does a chain letter diffuse? As a branching process. I present a case where this simplifying assumption does not hold. The results challenge the macroscopic diffusion properties in today???s literature, and they hint at a nest of complexity below a placid stochastic surface. It may be fair to see this dissertation as linking the online to the offline; that is, it connects the traces we leave in social media to how we feel about relationships in real life

Efficacy of a Novel Through-Thickness Perfusion Bioreactor to Create Scaffold-Free Tissue Engineered Cartilage

Articular cartilage is an avascular, aneural tissue that covers the ends of diarthroidal joints. Once damaged by disease or injury, cartilage lacks the ability to self-repair. Generating tissue engineered cartilage is an exciting field that may provide a possible solution to this problem. The purpose of this study is to determine the efficacy of a through-thickness perfusion bioreactor to generate scaffoldree tissue engineered cartilage. The results of the study show that allowing long-term static culture to cell constructs before perfusion increases the efficacy of the bioreactor. Immediate perfusion of cell constructs in the bioreactor is shown to decrease the efficacy to produce scaffoldree constructs with desirable biomechanical and biochemical properties. The results of the study also show possible options in future works that could increase the efficacy of the bioreactor

Benthic macrofauna and sediment reworking quantification in contrasted environments in the Thau Lagoon

As part of the Microbent-PNEC Program: ‘‘Biogeochemical processes at the wateresediment interface in eutrophicated environment’’, the aim of this work was to specifically investigate and quantify the relationships between macrobenthos and sediment reworking in the Thau Lagoon in order to provide information on the potential contaminant distribution and movements at the wateresediment interface. In order to achieve this, three cores were sampled at two stations (in the central part of the Thau Lagoon and near the shellfish farming zone) in the Thau Lagoon, in December 2001, April 2002, August 2002, January 2003 and May 2003. On the basis of quantification of macrobenthos and sediment reworking, evidence is provided of: (1) similar sediment mixing intensities for different species composition at the two stations; (2) the major role of functional bioturbation groups (e.g., biodiffusors and gallery-diffusors) modulated by seasonal variability on sediment mixing; (3) an increase of intensity in summer suggesting potentially different patterns of redistribution, bioaccumulation and chemical fate (e.g., speciation) of deposited contaminants

THE EVOLUTION OF MORPHOLOGICAL DIVERSITY AND SEXUAL DIMORPHISM IN STICK AND LEAF INSECTS

How has the diversity of life forms come to be? This question is at the core of evolutionary biology and can be addressed at different scales: by studying the processes that drive modifications within populations of organisms generation after generation (microevolution), or by investigating patterns of changes on the tree of life over long periods of time (macroevolution). Understanding the ultimate drivers of morphological diversity eventually entails connecting microevolutionary processes with macroevolutionary patterns. My dissertation investigates the diversification of body and egg form and its drivers in a relatively small but particularly diverse insect order: the stick and leaf insects (Phasmatodea). As masters of camouflage, the 3,400 described species of phasmids are an ideal system to study morphological evolution as they vary tremendously in body morphology, going from long slender branch mimics to wide, flat animals that look exactly like leaves. This remarkable diversity of forms enables phasmids to avoid detection by visually-hunting predators. Even their remarkably diverse hardshelled eggs resemble a wide variety of plant seeds. In addition, males and females of the same species often look very different from each other, with females in extreme cases more than ten times the size of the males. In chapters one, two and three, I investigate the patterns of variation of female body morphology, sexual dimorphism and egg morphology respectively, and potential ecological, life history and biomechanical correlates in a phylogenetic context. I describe repeated convergence towards multiple body forms associated with habitat transitions but find substantial variation in the strength of convergence and underlying evolutionary paths. Then, I show that variation in the extent of sexual dimorphism is best explained by variation in selective pressures acting on males, namely locomotor (flight) performance and male competition (sexual selection). Finally, I show that variation in egg size and shape is driven by variation in life history strategies, mechanical constraints and oviposition strategy. In chapters four, five and six, I investigate the microevolutionary processes behind the primary macroevolutionary forces driving variation in sexual dimorphism. In chapter four, I show in leaf insects (Phyllium philippinicum) that larger males are poor flyers, suggesting that selection for flight performance favors smaller male body sizes in this species, and reinforcing the broader taxonomic findings of chapter two. In chapters five and six, I describe how a change in the mating system of thorny devil stick insects (Eurycantha calcarata) switched the direction of sexual selection and led to the evolution of exceptionally large male body sizes and exaggerated hindleg weapons, confirming the pervasive role of sexual selection in driving variation in male size and sexual dimorphism. Collectively, my research contributes to our understanding of the forces that shape the evolution of morphology in animals and their eggs

Spin-orbit torque induced dipole skyrmion motion at room temperature

We demonstrate deterministic control of dipole-field-stabilized skyrmions by means of spin-orbit torques arising from heavy transition-metal seed layers. Experiments are performed on amorphous Fe/Gd multilayers that are patterned into wires and exhibit stripe domains and dipole skyrmions at room temperature. We show that while the domain walls and skyrmions are achiral on average due to lack of Dzyaloshinskii-Moriya interactions, the N\'eel-like closure domain walls at each surface are chiral and can couple to spin-orbit torques. The current-induced domain evolutions are reported for different magnetic phases, including disordered stripe domains, coexisting stripes and dipole skyrmions and a closed packed dipole skyrmion lattice. The magnetic textures exhibit motion under current excitations with a current density ~10^8 A/m2. By comparing the motion resulting from magnetic spin textures in Fe/Gd films with different heavy transition-metal interfaces, we confirm spin currents can be used to manipulate achiral dipole skyrmions via spin-orbit torques.Comment: 23 pages, 8 figure

Early intestinal infection kinetics and immune responses to Toxoplasma gondii in pigs

Toxoplasma gondii is an obligate intracellular parasite, able to infect all homeothermic animals mostly through ingestion of food or drinks contaminated with tissue cysts or oocysts. Recently, we showed a T. gondii strain-specific clearance from tissues upon infection in pigs. While the swine-adapted LR strain persisted in muscle tissues, the human-adapted Gangji strain was cleared from these tissues. We hypothesized that intestinal immune responses short after infection might play a role in this strain-specific clearance. To assess this possibility, the parasite load in duodenal, jejunal and ileal lymph node cells and blood immune cells (PBMCs) as well as the IFNγ secretion by these cells were evaluated at 2, 4, 8, 14 and 28 days post oral inoculation of pigs with both strains. Interestingly, at day 4 post inoculation with the LR strain the parasite was only detected by qPCR in the duodenal lymph node cells, while in the jejunal and ileal lymph node cells and PBMCs the parasite was detected from day 8 post inoculation onwards. Although we observed a similar profile upon inoculation with the Gangji strain, the parasite load in the examined cells was much lower. This was reflected in a significantly higher T. gondii-specific serum IgG response in LR than Gangji infected pigs at day 28 post inoculation. Unexpectedly, this was not reflected in the IFNγ secretion upon re-stimulation of the cells. However, the recall test most likely does not pick up the IFNγ production by innate immune cells, which might have been more important for clearance. In conclusion, our results show that T. gondii first enters the host at the duodenum and then probably disseminates from this site to the other host tissues

Rapid coastal deoxygenation due to ocean circulation shift in the NW Atlantic.

Global observations show that the ocean lost approximately 2% of its oxygen inventory over the last five decades 1-3, with important implications for marine ecosystems 4, 5. The rate of change varies with northwest Atlantic coastal waters showing a long-term drop 6, 7 that vastly outpaces the global and North Atlantic basin mean deoxygenation rates 5, 8. However, past work has been unable to resolve mechanisms of large-scale climate forcing from local processes. Here, we use hydrographic evidence to show a Labrador Current retreat is playing a key role in the deoxygenation on the northwest Atlantic shelf. A high-resolution global coupled climate-biogeochemistry model 9 reproduces the observed decline of saturation oxygen concentrations in the region, driven by a retreat of the equatorward-flowing Labrador Current and an associated shift toward more oxygen-poor subtropical waters on the shelf. The dynamical changes underlying the shift in shelf water properties are correlated with a slowdown in the simulated Atlantic Meridional Overturning Circulation 10. Our results provide strong evidence that a major, centennial-scale change of the Labrador Current is underway, and highlight the potential for ocean dynamics to impact coastal deoxygenation over the coming century