A discrimination technique for extensive air showers based on multiscale, lacunarity and neural network analysis

We present a new method for the identification of extensive air showers initiated by different primaries. The method uses the multiscale concept and is based on the analysis of multifractal behaviour and lacunarity of secondary particle distributions together with a properly designed and trained artificial neural network. In the present work the method is discussed and applied to a set of fully simulated vertical showers, in the experimental framework of ARGO-YBJ, to obtain hadron to gamma primary separation. We show that the presented approach gives very good results, leading, in the 1–10 TeV energy range, to a clear improvement of the discrimination power with respect to the existing figures for extended shower detectors

An experimental investigation on the poor hydrogen sorption properties of nano-structured LaNi5 prepared by ball-milling

Nano-structured LaNi5 hydrogen storage materials prepared by ball-milling is analysed using differential scanning calorimetry (DSC) and x-ray photoelectron spectroscopy (XPS). DSC results indicate a partial elimination of defects at 500 °C in a more efficient way for the short-time ball-milled powders compared to the long-time ball-milled ones. XPS results show almost no change in the core-level electronic structure for La and Ni of LaNi5 in the bulk and the nano-structured forms, but gives an indication that the self-restoring mechanism of the active surface observed in the bulk sample (Siegmann et al. Phys. Rev. Lett. 40, 972) may not be occurring in the nano-powders. Results from the X-ray diffraction and the local structural studies together with the above observations suggest that the reduced unit-cell volume and the enhanced atomic disorder in the nano-structured LaNi5 cause a larger energy barrier for the hydrogen sorption reactions of the long-time ball-milled samples

Observation of the cosmic ray moon shadowing effect with the ARGO-YBJ experiment

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the observation of the cosmic ray Moon shadowing effect carried out by the ARGO-YBJ experiment in the multi-TeV energy region with high statistical significance (55 standard deviations). By means of an accurate Monte Carlo simulation of the cosmic rays propagation in the Earth-Moon system, we have studied separately the effect of the geomagnetic field and of the detector point spread function on the observed shadow. The angular resolution as a function of the particle multiplicity and the pointing accuracy have been obtained. The primary energy of detected showers has been estimated by measuring the westward displacement as a function of the particle multiplicity, thus calibrating the relation between shower size and cosmic ray energy. The stability of the detector on a monthly basis has been checked by monitoring the position and the deficit of the Moon shadow. Finally, we have studied with high statistical accuracy the shadowing effect in the ''day/night’’ time looking for possible effect induced by the solar wind

Highlights from the ARGO-YBJ experiment

The ARGO-YBJ experiment at YangBaJing in Tibet (4300 m a.s.l.) has been taking data with its full layout since October 2007. Here we present a few significant results obtained in gamma-ray astronomy and cosmic-ray physics. Emphasis is placed on the analysis of gamma-ray emission from point-like sources (Crab Nebula, MRK 421), on the preliminary limit on the antiproton/proton flux ratio, on the large-scale cosmic-ray anisotropy and on the proton–air cross-section. The performance of the detector is also discussed, and the perspectives of the experiment are outlined

The ARGO-YBJ experiment in Tibet

The setting up of the ARGO detector at the YangBaJing Cosmic Ray Laboratory (4300ma.s.l., Tibet, P.R. China) has been completed during the last spring (2007). It consists of a central carpet made of 130 identical sub-units of 12 RPCs each (a ‘‘cluster’’), covering a surface of about 5800m2 with 93% active area, and a guard ring of 24 further clusters of the same type surrounding the centralcarpet with a lower sampling density. Signals are picked up by external electrodes of small size, thus allowing the sampling of EAS with high space-time granularity. Shower events are detected at a trigger rate of about 4 kHz. Events with a few particles detected by a single cluster are counted in scaler mode on a time base of 500 ms. The intrinsic modularity of the ARGO detector allowed us to collect data even during the setting-up period, using only the central carpet (or even part of it). Some preliminary results from the analysis of events collected in a few months of data taking are presented

Integrated production of fresh water, sea salt and magnesium from sea water

Seawater desalination is becoming an important source of fresh water in several countries all around the world. One of the main drawbacks of desalination processes, however, is related to the disposal of large quantities of concentrated brine, which is an always-present by-product of the process. An integrated production of fresh water and salts may be achieved using the discharge brine from a desalination plant as a feed for conventional salt ponds, with the advantages of using brine more concentrated than sea water and, in the case of thermal desalination plants, warmer than sea water. By doing so, the process is faster as a consequence of the enhancement of evaporation rate on the surface of ponds. The above concept has been proposed already several years ago, but only rare examples exist of real applications. A pilot test has been performed in the last 4 years in Trapani (Italy), where a 36,000-m3/d multiple effects desalination with thermal vapour compression plant is operating very close to a traditional salt pond normally fed with sea water. Furthermore, the use of fractionated crystallisation process, typically adopted in conventional salt ponds, allows for the easy separation of salts like calcium carbonates and sulphates, sodium chloride and a final saturated brine which is extremely rich in magnesium as a sole bivalent cation. Thus, the possibility of a further exploitation of such saturated brine has been experimentally analysed by laboratory tests in order to produce high-purity magnesium to be commercialised in the pharmaceutical, food and metal industries. Results have shown a very promising enhancement of the salt pond production capacity, keeping at the same time the very high quality standards required for the production of food-grade salt from sea water. On the other side, laboratory experiments indicated the actual possibility of producing high-purity magnesium salts, thus encouraging towards further investigation for the development of a pilot process development and installation. © 2012 Desalination Publications. All rights reserved