Etude expérimentale de nanocristaux comme sources de photons uniques

Wet-chemically synthesized colloidal nanocrystals are promising single photon emitters at room temperature, due to the strong quantum confinement induced by the small dimensions. However, their applications have been so far limited by two main drawbacks: the blinking of their photo-luminescence and a non-polarized emission. This manuscript is consecrated to the study of the optical properties of a particular type of colloidal nanocrystals, called dot-in-rod (DR), in which a spherical CdSe core is surrounded by a rod-like CdS shell. We demonstrate for the first time a suppression of the blinking in thick shell DRs. In contrast to spherical nanocrystals, we show that it can be obtained while keeping a good quality of the single photon emission and a high degree of linear polarization. A complete room-temperature characterization of the optical, and especially quantum optical, properties of DRs is provided for several geometrical parameters. In particular, an original approach, based on an ensemble photoluminescence measurement, is developed to assess the quality of a sample of nanocrystals as single photon sources. By studying single DRs in a confocal microscope, we analyze the influence of the core size and of the shell thickness and length on the photon anti-bunching, radiative lifetime and polarization of the emission. This systematic study brings a contribution to the understanding of the interaction processes of the confined carriers in semiconductor nanocrystals. The interplay of radiative and non-radiative recombinations and, in particular, the role of the Auger effect in the photo-luminescence blinking and in the emission of non-classical light are deeply investigatedLes nanocristaux colloïdaux synthétisés par voie chimique sont des émetteurs de photons uniques très prometteurs à température ambiante, grâce au fort confinement quantique induit par leur petite taille. Toutefois, leurs applications ont été jusqu'ici limitées par deux problèms: le scintillement de leur photo-luminescence et l émission non polarisée. Ce manuscrit est consacré à l'étude des propriétés optiques d'un nouveau type de nanocristaux colloïdaux, appelés dots-in-rod (DR), dans lequels un cœur sphérique de CdSe est entouré par une coquille de CdS en forme de cylindre. Nous démontrons pour la première fois une suppression du scintillement dans des DRs à la coquille épaisse. Contrairement aux nanocristaux sphériques, nous montrons que cette suppression peut être obtenue tout en conservant une bonne qualité de l'émission de photons uniques et un degré de polarisation linéaire très elévé. Une caractérisation complète des propriétés optiques et optique quantique des DRs est réalisée à température ambiante pour différents paramètres géométriques.En particulier, nous avons développé une technique originale pour évaluer la qualité d'un échantillon de nanocristaux comme sources de photons uniques, baséé sur une mesure de photo-luminescence d'ensemble. Grâce à une étude en microscopie confocale des DRs á l'echelle individuelle, nous avons analysé l'influence de la taille du cœur et de l'épaisseur de la coquille et de sa longueur sur les propriétés de dégroupement des photons, de durée de vie radiative et de polarisation de l'émission. Cette étude systématique apporte une contribution à la compréhension des processus d'interaction entre les porteurs confinés dans les nanocristaux semi-conducteurs. L'interaction entre les recombinaisons radiative et non radiative et, en particulier, le rôle de l'effet Auger dans le scintillement de la photo-luminescence et dans l'émission de lumière non-classique sont étudiés en détail.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Multiple Types of Legionella pneumophila Serogroup 6 in a Hospital Heated-Water System Associated with Sporadic Infections

Five sporadic cases of nosocomial Legionnaires’ disease were documented from 1989 to 1997 in a hospital in northern Italy. Two of them, which occurred in a 75-year-old man suffering from ischemic cardiopathy and in an 8-year-old girl suffering from acute leukemia, had fatal outcomes. Legionella pneumophila serogroup 6 was isolated from both patients and from hot-water samples taken at different sites in the hospital. These facts led us to consider the possibility that a single clone of L. pneumophila serogroup 6 had persisted in the hospital environment for 8 years and had caused sporadic infections. Comparison of clinical and environmental strains by monoclonal subtyping, macrorestriction analysis (MRA), and arbitrarily primed PCR (AP-PCR) showed that the strains were clustered into three different epidemiological types, of which only two types caused infection. An excellent correspondence between the MRA and AP-PCR results was observed, with both techniques having high discriminatory powers. However, it was not possible to differentiate the isolates by means of ribotyping and analysis of rrn operon polymorphism. Environmental strains that antigenically and chromosomally matched the infecting organism were present at the time of infection in hot-water samples taken from the ward where the patients had stayed. Interpretation of the temporal sequence of events on the basis of the typing results for clinical and environmental isolates enabled the identification of the ward where the patients became infected and the modes of transmission of Legionella infection. The long-term persistence in the hot-water system of different clones of L. pneumophila serogroup 6 indicates that repeated heat-based control measures were ineffective in eradicating the organism

A clinical assessment of the Mucus Shaver

International audienceObjective: We evaluated a new device designed to clean the endotracheal tube in mechanically ventilated patients, the Mucus Shaver. Design: Prospective, randomized trial. Setting: University hospital intensive care unit. Patients: We enrolled 24 patients expected to remain ventilated for >72 hrs. Interventions: The Mucus Shaver is a concentric inflatable catheter for the removal of mucus and secretions from the interior surface of the endotracheal tube. The Mucus Shaver is advanced to the distal endotracheal tube tip, inflated, and subsequently withdrawn over a period of 3–5 secs. Patients were prospectively randomized within 2 hrs of intubation to receive standard endotracheal tube suctioning treatment or standard suctioning plus Mucus Shaver use until extubation. Measurements and Main Results: During the study period, demographic data, recent medical history, adverse events, and staff evaluation of the Mucus Shaver were recorded. At extubation, each endotracheal tube was removed, cultured, and analyzed by scanning electron microscopy. Twelve patients were assigned to the study group and 12 were assigned to the control group. No adverse events related to the use of the Mucus Shaver were observed. At extubation, only one endotracheal tube from the Mucus Shaver group was colonized, whereas in the control group ten endotracheal tubes were colonized (8% vs. 83%; p < .001). Scanning electron microscopy showed little secretions on the endotracheal tubes from the study group, whereas thick bacterial deposits were present on all the endotracheal tubes from the control group (p < .001 by Fisher exact test, using a maximum biofilm thickness of 30 μm as cut-off). The nursing staff was satisfied by the overall safety, feasibility, and efficacy of the Mucus Shaver. Conclusions: The Mucus Shaver is a safe, feasible, and efficient device for endotracheal tube cleaning in the clinical setting. The Mucus Shaver is helpful in preventing endotracheal tube colonization by potentially harmful microorganisms

ENUBET: A monitored neutrino beam for high precision cross section measurements

International audienceThe main source of systematic uncertainty on neutrino cross section measurements at the GeV scale is represented by the poor knowledge of the initial flux. The goal of cutting down this uncertainty to 1% can be achieved through the monitoring of charged leptons produced in association with neutrinos, by properly instrumenting the decay region of a conventional narrow-band neutrino beam. Large angle muons and positrons from kaons are measured by a sampling calorimeter on the decay tunnel walls (tagger), while muon stations after the hadron dump can be used to monitor the neutrino component from pion decays. This instrumentation can provide a full control on both the muon and electron neutrino fluxes at all energies. Furthermore, the narrow momentum width (<10%) of the beam provides a O(10%) measurement of the neutrino energy on an event by event basis, thanks to its correlation with the radial position of the interaction at the neutrino detector. The ENUBET project has been funded by the ERC in 2016 to prove the feasibility of such a monitored neutrino beam and is cast in the framework of the CERN neutrino platform (NP06) and the Physics Beyond Colliders initiative. In our contribution, we summarize the ENUBET design, physics performance and opportunities for its implementation in a timescale comparable with next long baseline neutrino experiments