Propriétés optiques hors-équilibre des nanotubes de carbone nus ou fonctionnalisés

This thesis is devoted to the experimental study by femtosecond pump-probe spectroscopy of micellar solutions of carbon nanotubes. The properties of carbon nanotubes are greatly affected by their 1D geometry. Quantum confinement of electrons in 1D leads to enhanced coulomb interactions giving rise to strongly bound excitons. Many-body effects between excitons is investigated by the moment method analysis of the transient absorption spectra. The relaxation of excitons is controlled by diffusion-limited collisions between excitons. The presence of excitons in the lowest subband results in a broadening and an uniform blue-shift of the excitonic energy spectrum. Intra and intersubband interactions turn out to be of the same magnitude, in agreement with a simple mean field theory of excitonic interactions.Moreover, the one-layer structure of nanotubes results in strong interaction with the environment. We take advantage of the environmental sensitivity of nanotubes in hybrid compounds where the non-covalent functionalization with dyes opens a new extrinsic monochromatic excitation channel of the nanotubes through an efficient and ultrafast energy transfer between dyes and nanotubes. Once the exciton transferred to the nanotube, its relaxation is similar to the one observed in bare nanotubes.Cette thèse est consacrée à l'étude expérimentale par spectroscopie pompe-sonde femtoseconde des propriétés optiques hors-équilibre de solutions micellaires de nanotubes de carbone. Les propriétés des nanotubes de carbone sont profondément affectées par leur géométrie unidimensionnelle. Les interactions coulombiennes exaltées du fait du confinement quantique des électrons à une dimension donnent naissance à des excitons fortement liés. L'analyse des spectres d'absorption transitoire par la méthode des moments permet une étude des interactions entre excitons. La relaxation des excitons s'avère gouvernée par les collisions entre excitons, limitées par la diffusion à 1D dans le nanotube. La présence d'excitons dans une sousbande conduit à un décalage uniforme vers le bleu de l'ensemble des transitions excitoniques et à un élargissement de même ampleur. Ainsi, les interactions croisées entre excitons de sousbandes différentes sont de même amplitude qu'entre excitons de même sousbande, en accord avec une modélisation simple.Par ailleurs, les nanotubes sont constitués uniquement d'atomes de surface, ce qui leur confère une forte sensibilité à l'environnement. Cette sensibilité est mise à profit dans des composés hybrides où la fonctionnalisation non-covalente par des colorants ouvre une nouvelle voie d'excitation des nanotubes. Notre étude montre que le transfert d'énergie entre les colorants et les nanotubes permet une excitation monochromatique efficace et uniforme de l'ensemble des espèces de nanotubes. Une fois l'exciton transféré au nanotube, sa relaxation s'avère ensuite identique à celle observée dans les nanotubes nus

Retrospective case control study of pet ferrets with cystine urolithiasis in Quebec, Canada : epidemiological and clinical features

Objective: To describe epidemiological and clinical features of cystine urolithiasis in pet ferrets. Methods: Retrospective case control study on medical records from four private clinics and one teaching hospital for pet ferrets diagnosed with cystine urolithiasis confirmed by spectrophotometry presented between July 2014 and July 2019 in Quebec, Canada; these cases were then compared to a reference population of 210 ferrets (controls) presented at the same facilities over the same timeframe. Results: Among the 36 identified cases, most affected ferrets were neutered males (32/36, 89%) and the mean age at presentation was 1.8 (± 1.0 standard deviation) year. Grain-free diets of six different brands were offered for at least three weeks prior to the presentation to 34/36 (94%) of the included cases. The ferrets that developed cystine urolithiasis were 57.9 times (Odds ratio [OR], 95% Confidence interval [95% CI]: 11.0, 304.8) more likely to receive a grain-free diet compared to the reference population. No significant difference in the values for the energy, protein, cysteine, and methionine contents were detected between the grainfree and the cereal-based diets offered to these pet ferrets. Among ferrets with uroliths, those with urethral calculi were 4.7 times (OR, 95% CI: 2.1, 10.4) more likely to develop an acute urinary tract obstruction. Conclusion: Although a definitive causation could not be drawn solely from these clinical cases, this case control study highlights a possible nutritional aetiology in the complex pathogenesis of cystine urolithiasis in ferrets

Twin gradients in APOBEC3 edited HIV-1 DNA reflect the dynamics of lentiviral replication

The human immunodeficiency virus (HIV) Vif protein blocks incorporation of two host cell cytidine deaminases, APOBEC3F and 3G, into the budding virion. Not surprisingly, on a vif background nascent minus strand DNA can be extensively edited leaving multiple uracil residues. Editing occurs preferentially in the context of TC (GA on the plus strand) and CC (GG) depending on the enzyme. To explore the distribution of APOBEC3F and –3G editing across the genome, a product/substrate ratio (AA + AG)/(GA + GG) was computed for a series of 30 edited genomes present in the data bases. Two highly polarized gradients were noted each with maxima just 5′ to the central polypurine tract (cPPT) and LTR proximal polypurine tract (3′PPT). The gradients are in remarkable agreement with the time the minus strand DNA remains single stranded. In vitro analyses of APOBEC3G deamination of nascent cDNA spanning the two PPTs showed no pronounced dependence on the PPT RNA:DNA heteroduplex ruling out the competing hypothesis of a PPT orientation effect. The degree of hypermutation varied smoothly among genomes indicating that the number of APOBEC3 molecules packaged varied considerably

Maternal Occupational Exposure to Polycyclic Aromatic Hydrocarbons: Effects on Gastroschisis among Offspring in the National Birth Defects Prevention Study

Background: Exposure to polycyclic aromatic hydrocarbons (PAHs) occurs in many occupational settings. There is evidence in animal models that maternal exposure to PAHs during pregnancy is associated with gastroschisis in offspring; however, to our knowledge, no human studies examining this association have been conducted

Ernst Freund as Precursor of the Rational Study of Corporate Law

Gindis, David, Ernst Freund as Precursor of the Rational Study of Corporate Law (October 27, 2017). Journal of Institutional Economics, Forthcoming. Available at SSRN: https://ssrn.com/abstract=2905547, doi: https://dx.doi.org/10.2139/ssrn.2905547The rise of large business corporations in the late 19th century compelled many American observers to admit that the nature of the corporation had yet to be understood. Published in this context, Ernst Freund's little-known The Legal Nature of Corporations (1897) was an original attempt to come to terms with a new legal and economic reality. But it can also be described, to paraphrase Oliver Wendell Holmes, as the earliest example of the rational study of corporate law. The paper shows that Freund had the intuitions of an institutional economist, and engaged in what today would be called comparative institutional analysis. Remarkably, his argument that the corporate form secures property against insider defection and against outsiders anticipated recent work on entity shielding and capital lock-in, and can be read as an early contribution to what today would be called the theory of the firm.Peer reviewe

The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR

[abridged] We analyzed mid-infrared high-contrast coronagraphic images of the beta Pictoris system, taking advantage of the NEAR experiment using the VLT/VISIR instrument. The goal of our analysis is to investigate both the detection of the planet beta Pictoris b and of the disk features at mid-IR wavelengths. In addition, by combining several epochs of observation, we expect to constrain the position of the known clumps and improve our knowledge on the dynamics of the disk. To evaluate the planet b flux contribution, we extracted the photometry and compared it to the flux published in the literature. In addition, we used previous data from T-ReCS and VISIR, to study the evolution of the position of the southwest clump that was initially observed in the planetary disk back in 2003. While we did not detect the planet b, we were able to put constraints on the presence of circumplanetary material, ruling out the equivalent of a Saturn-like planetary ring around the planet. The disk presents several noticeable structures, including the known southwest clump. Using a 16-year baseline, sampled with five epochs of observations, we were able to examine the evolution of the clump: the clump orbits in a Keplerian motion with an sma of 56.1+-0.4 au. In addition to the known clump, the images clearly show the presence of a second clump on the northeast side of the disk and fainter and closer structures that are yet to be confirmed. We found correlations between the CO clumps detected with ALMA and the mid-IR images. If the circumplanetary material were located at the Roche radius, the maximum amount of dust determined from the flux upper limit around beta Pictoris b would correspond to the mass of an asteroid of 5 km in diameter. Finally, the Keplerian motion of the southwestern clump is possibly indicative of a yet-to-be-detected planet or signals the presence of a vortex.Comment: Accepted in Astronomy and Astrophysic

Sex differences in children’s toy preferences: A systematic review, meta-regression and meta-analysis

From an early age, most children choose to play with toys typed to their own gender. In order to identify variables that predict toy preference, we conducted a meta-analysis of observational studies of the free selection of toys by boys and girls aged between 1 and 8 years. From an initial pool of 1788 papers, 16 studies (787 boys and 813 girls) met our inclusion criteria. We found that boys played with male-typed toys more than girls did (Cohen's d = 1.03, p < .0001) and girls played with female-typed toys more than boys did (Cohen's d = −0.91, p < .0001). Meta-regression showed no significant effect of presence of an adult, study context, geographical location of the study, publication date, child's age, or the inclusion of gender-neutral toys. However, further analysis of data for boys and girls separately revealed that older boys played more with male-typed toys relative to female-typed toys than did younger boys (β = .68, p < .0001). Additionally, an effect of the length of time since study publication was found: girls played more with female-typed toys in earlier studies than in later studies (β = .70, p < .0001), whereas boys played more with male-typed toys (β = .46, p < .05) in earlier studies than in more recent studies. Boys also played with male-typed toys less when observed in the home than in a laboratory (β = −.46, p < .05). Findings are discussed in terms of possible contributions of environmental influences and age-related changes in boys' and girls' toy preference

Flow of foam through a convergent channel

International audienceWe study experimentally the flow of a foam confined as a bubble monolayer between two plates through a convergent channel. We quantify the velocity, the distribution and orientation of plastic events, and the elastic stress, using image analysis. We use two different soap solutions: a sodium dodecyl sulfate (SDS) solution, with a negligible wall friction between the bubbles and the confining plates, and a mixture containing a fatty acid, giving a large wall friction. We show that for SDS solutions, the velocity profile obeys a self-similar form which results from the superposition of plastic events, and the elastic deformation is uniform. For the other solution, the velocity field differs and the elastic deformation increases towards the exit of the channel. We discuss and quantify the role of wall friction on the velocity profile, the elastic deformation, and the rate of plastic events