Weak truth table degrees of structures

We study the weak truth table (wtt) degree spectra of first-order relational structures. We prove a dichotomy among the possible wtt degree spectra along the lines of Knight's upward-closure theorem for Turing degree spectra. We prove new results contrasting the wtt degree spectra of finite-and infinite-signature structures. We show that, as a method of defining classes of reals, the wtt degree spectrum is, except for some trivial cases, strictly more expressive than the Turing degree spectrum

Reverse mathematics of first-order theories with finitely many models

We examine the reverse-mathematical strength of several theorems in classical and effective model theory concerning first-order theories and their number of models. We prove that, among these, most are equivalent to one of the familiar systems RCA(0), WKL0, or ACA(0). We are led to a purely model-theoretic statement that implies WKL0 but refutes ACA(0) over RCA(0)

Doping dependence of chiral superconductivity in near 45∘45^\circ twisted bilayer cuprates

We study a one-band Hubbard model for a twisted cuprate bilayer with a twist angle of 43.6$^\circ$ and a moire cell containing 58 sites. We use the variational cluster approximation (VCA), which treats short-range correlations exactly and leads, in single layers, to a dome of $d$-wave superconductivity away from half-filling from strong on-site repulsion alone. We find a time-reversal-symmetry (TRS) breaking phase in a small doping interval in the overdoped region when interlayer tunneling is strong enough. Contrary to expectations, being closer to the $45^{\circ}$ twist angle does not expand this TRS region compared to a previous study [Phys. Rev. B 105, 245127 (2022)] on a $53^{\circ}$ twist angle. This is attributed to the fact that the two superconducting states in competition have almost identical nodal structures.Comment: 6 page

On the jumps of degrees below an recursively enumerable degree

We consider the set of jumps below a Turing degree, given by JB(a) = {x(1) : x <= a}, with a focus on the problem: Which recursively enumerable (r.e.) degrees a are uniquely determined by JB(a)? Initially, this is motivated as a strategy to solve the rigidity problem for the partial order R of r.e. degrees. Namely, we show that if every high(2) r.e. degree a is determined by JB(a), then R cannot have a nontrivial automorphism. We then defeat the strategy-at least in the form presented-by constructing pairs a(0), a(1) of distinct r.e. degrees such that JB(a(0)) = JB(a(1)) within any possible jump class {x : x' = c}. We give some extensions of the construction and suggest ways to salvage the attack on rigidity

Cerebral tissue pO2 response to stimulation is preserved with age in awake mice

Published in final edited form as: Neurosci Lett. 2019 April 23; 699: 160–166. doi:10.1016/j.neulet.2019.02.007.Compromised oxygen supply to cerebral tissue could be an important mechanism contributing to age-related cognition decline. We recently showed in awake mice that resting cerebral tissue pO2 decreases with age, a phenomenon that manifests mainly after middle-age. To extend these findings, here we aimed to study how tissue pO2 response to neuronal stimulation is affected by aging. We used two-photon phosphorescence lifetime microscopy to directly measure the brain tissue pO2 response to whisker stimulation in healthy awake young, middle-aged and old mice. We show that despite a decrease in baseline tissue pO2, the amplitude of the tissue pO2 response to stimulation is well preserved with age. However, the response dynamics are altered towards a slower response with reduced post-stimulus undershoot in older ages, possibly due to stiffer vessel wall among other factors. An estimation of the net oxygen consumption rate using a modified Krogh model suggests that the O2 overshoot during stimulation may be necessary to secure a higher capillary O2 delivery to the tissue proportional to increased CMRO2 to maintain the capillary tissue pO2. It was observed that the coupling between the CMRO2 and capillary O2 delivery is preserved with age.Accepted manuscrip

Growth controls of rhodoliths (Lithothamnion glaciale) and relationships between structural complexity and macrofaunal diversity in subarctic rhodolith beds

Coastal benthic ecosystems are major contributors to oceans global productivity and biodiversity. Research has historically focused on charismatic ecosystems such as coral reefs, kelp beds and seagrass meadows. This paradigm may overshadow the biogeochemical functions and ecological importance to coastal oceans of other less studied communities. Rhodoliths are benthic, unattached, slow-growing coralline red algae. Rhodoliths may aggregate into extensive and diverse communities called rhodolith beds, which occur within the photic zone in all oceans, from the tropics to the poles. This thesis used long-term laboratory and field experiments as well as seasonal surveys to characterize controls of growth in Lithothamnion glaciale rhodoliths and to investigate the relationship between structural complexity and the diversity of rhodolith-associated macrofauna in a subarctic rhodolith bed from southeastern Newfoundland. Results showed that rhodolith growth is negatively affected by elevated nutrient (N and P) concentrations and biofouling. Rhodolith growth was mainly controlled by irradiance and was unaffected by temperatures between ~1 and 17°C, but appeared to be inhibited by temperatures ≤ 0.5°C. Rhodolith bed structure showed little annual spatial and temporal variations. Macrofaunal density scaled positively with total rhodolith volume per surface area, whereas biomass did not. Results also suggest that rhodolith morphology exerts a control on the diversity of macrofauna associated to rhodoliths. Macrofaunal assemblages varied spatially and temporally in most taxonomic groups with few, uncommon taxa being generally responsible for dissimilarity between sites and among seasons. These findings provide novel insights into the ecology and vulnerability of rhodoliths to anthropogenic threats and climate change while elevating the importance of subarctic L. glaciale beds as a key ecosystem in the Northwest Atlantic

Utilisation de la faune macrobenthique comme bioindicateur de la qualité de l’environnement marin côtier

Les écosystèmes marins côtiers sont des milieux de plus en plus affectés par l’activité humaine. L’industrialisation et le développement des villes et des sociétés humaines en zone côtière sont les principales causes de l’augmentation de la pression écologique exercée sur ces milieux. Afin de parvenir à contrer la dégradation des milieux naturels marins il est essentiel de développer des outils d’évaluation et de suivi de la qualité de l’environnement. La science de la bioindication, c’est-à-dire de l’utilisation d’organismes vivants dans le but d’évaluer les conditions environnementales d’un milieu donné, a développé de nombreux outils (bioindicateurs, biomoniteurs, bioaccumulateurs, biomarqueurs, etc.) permettant la gestion et le maintien des écosystèmes marins côtiers. Ceux-ci sont principalement aux prises avec des problèmes de contamination impliquant les métaux lourds, les biocides, les BPC, les hydrocarbures et les rejets d’eaux usées près des côtes. Parmi les différents bioindicateurs pouvant être utilisés afin d’évaluer la qualité du milieu marin, ceux issus de la macrofaune benthique présentent de nombreux avantages et ont été abondamment utilisés par les chercheurs jusqu’à présents. Les porifères, les échinodermes, les coraux, les vers marins et les mollusques représentent les groupes d’organismes les plus utilisés en raison de certaines caractéristiques qui leurs sont propres comme l’abondance, la taille, le mode de vie sédentaire et les régimes alimentaires spécifiques. L’emploi de ces bioindicateurs macrobenthiques est de plus en plus répandu au sein des organismes internationaux oeuvrant dans les domaines de la conservation et du développement durable et ils comptent parmi les meilleurs outils mis à la disposition de l’homme pour faire face aux différents défis environnementaux présents et futurs auxquels doivent faire face les écosystèmes marins côtiers. Le grand défi des générations à venir consiste à mettre sur pied des méthodes d’évaluation environnementale accessibles à tous les pays et à développer des systèmes d’échange d’informations permettant le suivi et la conservation des milieux marins côtiers à l’échelle internationale