19 research outputs found
Insertion of CdSe quantumdots in ZnSe nanowires : MBE growth and microstructure analysis
ZnSe nanowire growth has been successfully achieved on ZnSe (100) and (111)B
buffer layers deposited on GaAs substrates. Cubic [100] oriented ZnSe nanowires
or [0001] oriented hexagonal NWs are obtained on (100) substrates while [111]
oriented cubic mixed with [0001] oriented hexagonal regions are obtained on
(111)B substrates. Most of the NWs are perpendicular to the surface in the last
case. CdSe quantum dots were successfully incorporated in the ZnSe NWs as
demonstrated by transmission electron microscopy, energy filtered TEM and high
angle annular dark field scanning TEM measurements
Curvature-bias corrections using a pseudomass method
Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √(s)=13 TeV during 2016, 2017 and 2018. The biases are determined using Z→μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10-4 GeV-1 level, improves the Z→μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass
Helium identification with LHCb
The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √(s) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb-1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to O(10^12). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei
Mise en forme analytique de courbes et de surfaces fermées
Les représentations de courbes ou de surfaces gauches par ensembles de coordonnées obtenues expérimentalement mobilisent un nombre élevé de données numériques. On propose une procédure basée sur la méthode des moindres carrés et minimisant le nombre final de données utiles. On donne des exemples simples et on suggère quelques autres applications possibles ainsi que des voies de développement de la méthode
Mise en forme analytique de courbes et de surfaces fermées
Representation of plane curves or tridimensionnal surfaces by coordinates sets needs a high amount of numerical data. We propose a procedure based upon the least mean square method which minimizes the final number of useful data. We give some elementary examples and we suggest some other applications and ways of method developing.Les représentations de courbes ou de surfaces gauches par ensembles de coordonnées obtenues expérimentalement mobilisent un nombre élevé de données numériques. On propose une procédure basée sur la méthode des moindres carrés et minimisant le nombre final de données utiles. On donne des exemples simples et on suggère quelques autres applications possibles ainsi que des voies de développement de la méthode
Polluants émergents : des campagnes prospectives à la surveillance réglementaire, les actions du laboratoire national de référence AQUAREF
National audienceLes polluants dits « émergents » sont pour la plupart mal connus et les méthodes permettant leur surveillance sont souvent peu robustes. Le processus d’identification de ces polluants par de vastes campagnes prospectives puis leur mise en surveillance réglementaire se heurtent donc parfois à des problématiques techniques liées à l’échantillonnage ou à l’analyse. AQUAREF, le laboratoire national de référence pour la surveillance des milieux aquatiques, a contribué à l’ensemble de ce processus, depuis les campagnes prospectives jusqu’à la déclinaison opérationnelle dans la réglementation nationale. Les campagnes nationales récentes ont montré le besoin de prendre en compte de façon précoce les questions de fiabilité des données. Concernant l’échantillonnage par exemple, la maitrise des contaminations ainsi que la connaissance de la stabilité des substances sont apparues comme des points clés pour la fiabilité des données. Suite aux campagnes prospectives, il est nécessaire de permettre une mise en surveillance régulière fiable de ces substances par des recommandations techniques réalistes et adaptées aux besoins des gestionnaires. Enfin AQUAREF joue également un rôle dans le processus de transfert de méthodes vers les laboratoires prestataires. Tous ces éléments ne sont pas spécifiques des polluants émergents mais il semble indispensable qu’ils soient pris en compte très tôt dans le processus d’identification et de surveillance de ce type de polluants
Use of catalase and superoxide dismutase to assess the roles of hydrogen peroxide and superoxide in the TiO2 or ZnO photocatalytic destruction of 1,2-dimethoxybenzene in water
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The LHCb Upgrade I
The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software