Mirror development for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a planned observatory for very-high energy gamma-ray astronomy. It will consist of several tens of telescopes of different sizes, with a total mirror area of up to 10,000 square meters. Most mirrors of current installations are either polished glass mirrors or diamond-turned aluminium mirrors, both labour intensive technologies. For CTA, several new technologies for a fast and cost-efficient production of light-weight and reliable mirror substrates have been developed and industrial pre-production has started for most of them. In addition, new or improved aluminium-based and dielectric surface coatings have been developed to increase the reflectance over the lifetime of the mirrors compared to those of current Cherenkov telescope instruments.Fil: Forster, A.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Armstrong, T.. Durham University; Reino UnidoFil: Baba, H.. Ibaraki University; JapónFil: Bähr, J.. No especifíca;Fil: Bonardi, A.. Universitat Tübingen; AlemaniaFil: Bonnoli, G.. Osservatorio Astronomico di Brera; ItaliaFil: Brun, P.. No especifíca;Fil: Canestrari, R.. Osservatorio Astronomico di Brera; ItaliaFil: Chadwick, P.. Durham University; Reino UnidoFil: Chikawa, M.. University of Tokyo; JapónFil: Carton, P.-H.. Centre de Saclay; FranciaFil: De Souza, V.. Universidade de Sao Paulo; BrasilFil: Dipold, J.. Universidade de Sao Paulo; BrasilFil: Doro, M.. Università di Padova; ItaliaFil: Durand, D.. No especifíca;Fil: Dyrda, M.. Polish Academy of Sciences; ArgentinaFil: Giro, E.. Osservatorio Astronomico di Padova; ItaliaFil: Glicenstein, J.-F.. No especifíca;Fil: Hanabata, Y.. Kinki University; JapónFil: Hayashida, M.. University of Tokyo; JapónFil: Hrabovski, M.. No especifíca;Fil: Jeanney, C.. Centre de Saclay; FranciaFil: Kagaya, M.. Ibaraki University; JapónFil: Katagiri, H.. Ibaraki University; JapónFil: Lessio, L.. Osservatorio Astronomico di Padova; ItaliaFil: Mandat, D.. Institute of Physics of the Academy of Sciences of the Czech Republic; República ChecaFil: Mariotti, M.. Università di Padova; ItaliaFil: Medina, Maria Clementina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Yoshida, T.. Ibaraki University; Japón33rd International Cosmic Ray ConferenceRío de JaneiroBrasilBrazilian Physical Societ

Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

International audienceThis paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r. Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge

CMS physics technical design report : Addendum on high density QCD with heavy ions

Peer reviewe

Effect of the gas flow rate on the spatiotemporal distribution of Ar(1s(5)) absolute densities in a ns pulsed plasma jet impinging on a glass surface

This work presents spatial (axial-z and transversal-y) and temporal distributions of Ar(1s(5)) metastable absolute densities in an atmospheric pressure argon micro-plasma jet impinging on an ungrounded glass surface. Guided streamers are generated with a DBD device driven by pulsed positive high voltages of 6 kV in amplitude, 224 +/- 3 ns in FWHM and 20 kHz in frequency. The argon flow rate is varied between 200 and 600 sccm. The glass plate is placed at 5 mm away from the reactor's nozzle and perpendicular to the streamers propagation. At these conditions, a diffuse stable discharge is established after the passage of the streamers allowing the quantification of the Ar(1s(5)) absolute density by means of a conventional TDLAS technique coupled with emission spectroscopy and ICCD imaging. The good reproducibility of the absorption signals is demonstrated. The experiments show the strong dependence of the maximum density (0.5-4 x 10(13) cm(-3)) on the gas flow rate and the axial and transversal position. At 200 sccm, high maximum densities (>2.4 x 10(13) cm(-3)) are obtained in a small area close to the plasma source, while with increasing flow rate this area expands towards the glass plate. In the transversal direction, density maxima are obtained in a small zone around the propagation axis of the streamers. Finally, a noticeable increase is measured on the Ar(1s(5)) effective lifetime close to the glass surface by varying the flow rate from 200 to 600 sccm. In overall, the effective lifetime varies between similar to 25 and similar to 550 ns, depending on the gas flow rate and the values of z and y coordinates. The results obtained suggest that the present system can be implemented in various applications and particularly in what concerns the detection of weakly volatile organic compounds present in trace amounts on different surfaces

A Highly Efficient, Angle-Insensitive Solar Quantum Concentrator Based on Microstructured Plastic Optical Fiber

International audienceA new device made of very specific microstructured fluorescent plastic optical fibers, capable of concentrating solar radiation towards photovoltaic solar cells is studied in the QUYOS project. This device transforms a multidirectionnal and polychromatic flux of solar light to a monochromatic and monodirectionnal intense flux of light with a high conversion efficiency. The very specific behaviour of these fibers is due to the convergence of several quantum phenomena. Mainly the coincidence of the fluorescent band of the dye with the forbidden band of the photonic crystal from the microstructured fiber restricts the phase space of desexcitation only along the axis of the fiber. Moreover, a coupling of the fluorescence with the allowed modes of the central waveguide of the fiber does enhance the radiative desexcitation thanks to the Purcell effect

Burst pacemaker activity of the sinoatrial node in sodium–calcium exchanger knockout mice

In sinoatrial node (SAN) cells, electrogenic sodium–calcium exchange (NCX) is the dominant calcium (Ca) efflux mechanism. However, the role of NCX in the generation of SAN automaticity is controversial. To investigate the contribution of NCX to pacemaking in the SAN, we performed optical voltage mapping and high-speed 2D laser scanning confocal microscopy (LSCM) of Ca dynamics in an ex vivo intact SAN/atrial tissue preparation from atrial-specific NCX knockout (KO) mice. These mice lack P waves on electrocardiograms, and isolated NCX KO SAN cells are quiescent. Voltage mapping revealed disorganized and arrhythmic depolarizations within the NCX KO SAN that failed to propagate into the atria. LSCM revealed intermittent bursts of Ca transients. Bursts were accompanied by rising diastolic Ca, culminating in long pauses dominated by Ca waves. The L-type Ca channel agonist BayK8644 reduced the rate of Ca transients and inhibited burst generation in the NCX KO SAN whereas the Ca buffer 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (acetoxymethyl ester) (BAPTA AM) did the opposite. These results suggest that cellular Ca accumulation hinders spontaneous depolarization in the NCX KO SAN, possibly by inhibiting L-type Ca currents. The funny current (I(f)) blocker ivabradine also suppressed NCX KO SAN automaticity. We conclude that pacemaker activity is present in the NCX KO SAN, generated by a mechanism that depends upon I(f). However, the absence of NCX-mediated depolarization in combination with impaired Ca efflux results in intermittent bursts of pacemaker activity, reminiscent of human sinus node dysfunction and “tachy-brady” syndrome