•A process for manufacturing self-supporting parabolic solar modules was developed.•A 0.818m2 sector part of a full 5m dish with 2.5m focal was characterized.•The reflected power is concentrated in a ...spot of 58mm in diameter at the focus.•Power losses are estimated to be lower than 7.6% of the incident power.•By calorimetry we esteem an overall optical efficiency of 80±4%.
A process to build modular solar reflectors by using plane mirrors and a sandwich structure has been developed. We applied this process to manufacture parabolic modules that can be assembled in a parabolic dish of 5m in diameter with the focus at 2.5m. This paper discusses the evaluation of the light collection performances of a single parabolic module. The reflectance of the mirror material was characterized by means of a UV–Vis spectrophotometer, in the 250–1200nm wavelength range, and of a pyrheliometer, with respect to a direct solar spectrum. The illumination profile of a module mounted on a sun-tracking system was tested by power density measurements in and out of the focal plane, and spots were compared with a theoretical one. In order to evaluate the high-flux solar energy arriving at the focus of a module, a flat-plate calorimeter was built. The study was carried out by measuring the energy absorbed by the water flow and the external losses due to convection. Based on an energy balance, the intercept factor and the overall optical efficiency of the collector were estimated.
Poly (lactic acid) nanocomposites containing lauryl-functionalized cellulose nanoparticles were prepared by solution-casting method and structurally characterized. The gas transport process was ...studied in ~ 50 μm thick nanocomposite films with filler contents up to 12 vol% using He, 2H2, N2 and CO2 as test gases. The gas permeability and diffusivity was evaluated by studying the permeation process using a specific mass spectroscopy technique in the temperature range from 298 K to 340 K in transient and stationary transport conditions. We present original diffusivity and permeability data as a function of the temperature together with the obtained values for the activation energy. Gas transport data were correlated with information on the nanocomposite free volume structure obtained by positron annihilation lifetime spectroscopy. The results indicate that the decrease of the gas barrier performances observed in nanocomposites with filler contents larger than ~ 5 vol% is due to an increased gas solubility caused by the formation of rigid cavities at the interface between the polymer matrix and micrometer-sized filler aggregations.
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•Bio-nanocomposites gas barrier film of PLA with functionalized nanocellulose fibrils.•Nanocavities at internal PLA-NC interfaces detected by PALS.•Interface nanocavities degrade the gas barrier performances of bio-nanocomposites.•Nanocavities act as additional solution sites hosting gas molecules.•Gas transport data and activation energy values for neat and PLA nanocomposites.
Advanced spectroscopy experiments and new physics experiments with positronium atoms in vacuum will benefit from positronium production in an environment free of magnetic and electrostatic fields. ...Here, we present a novel scheme for generating a bunched positron beam. The positron bunches are prebunched before extraction from a buffer-gas trap, nonadiabatically extracted from a 700 G magnetic field, energy elevated up to 20 kV, and bunched on a target in a free field. According to simulations of the system, 60% of cooled positrons in the buffer-gas trap are extracted and focused on the target in a time spread of 2.5 ns full width tenth maximum (FWTM) and a spot of about 4 mm FWTM for positron implantation energy higher than 3 keV. These performance numbers are achieved in the same apparatus through a combination of several innovative beam manipulations.
The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high ...interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics--the moiré deflectometer--for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter.
A novel method for the measurement of the number of positrons contained in intense positron bunches is presented. The technique is based on the Poisson distribution of the number of gamma rays ...emitted by many simultaneous positron–electron annihilations in a small solid angle. The results have been found in good agreement with those achieved with a calibrated CsI(Tl) detector coupled to a photodiode. The small dimension of the required equipment and the reduced constraints of the technique open the possibility of monitoring, in complex positrons systems, the number of positrons at different positions that are too difficult to reach with other devices.
We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3 and 2.4 mu m. These include data taken on the Subaru 8.3 m telescope, the KPNO and CTIO 4 m ...telescopes, and the CFHT 3.6 m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard-star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.
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