1,721,125 research outputs found
Entropy and Efficiency of the ETF Market
Full text linkWe investigate the relative information efficiency of financial markets by measuring the entropy of the time series of high frequency data. Our tool to measure efficiency is the Shannon entropy, applied to 2-symbol and 3-symbol discretisations of the data. Analysing 1-min and 5-min price time series of 55 Exchange Traded Funds traded at the New York Stock Exchange, we develop a methodology to isolate residual inefficiencies from other sources of regularities, such as the intraday pattern, the volatility clustering and the microstructure effects. The first two are modelled as multiplicative factors, while the microstructure is modelled as an ARMA noise process. Following an analytical and empirical combined approach, we find a strong relationship between low entropy and high relative tick size and that volatility is responsible for the largest amount of regularity, averaging 62% of the total regularity against 18% of the intraday pattern regularity and 20% of the microstructure
The potential of radiocarbon analysis for the detection of art forgeries
Full text linkArt objects form an essential part of cultural heritage and are appreciated for their artistic values. However, the observed investment in art and capacity for high monetary returns encourages counterfeiting of art objects. The art market's lack of transparency and traditional confidential protocols amplifies the problem. Radiocarbon analysis provides a tool to detect anachronistic materials. Measurement of bomb peak radiocarbon, which was observed in the atmosphere during the last 70 years, can provide clear evidence of post-1950 material. Here we briefly introduce the method and discuss its application in detecting forgeries. Three accelerator mass spectrometry AMS laboratories performed a 14C dating inter-comparison study on the material used in art. Results obtained on modern cotton paper, two antique sheets of paper, one parchment, and one textile demonstrate the radiocarbon dating capacity to date the material accurately. The excellent agreement between laboratories is crucial for the broader application of this scientific tool in forensic studies and court cases
Characterisation of lead carbonate white pigments submitted to AMS radiocarbon dating
No full textThe possibility of dating by radiocarbon lead carbonate, widely used as white pigment since ancient times, has been recently demonstrated. In this paper we tested two different samples processing procedures for the extraction of the carbon fraction from lead carbonate to be submitted to Accelerator Mass Spectrometry 14C dating. Samples with different origins were selected for this study: geological cerussite, modern sample produced by following ancient recipe and lead white used for restoration purposes. All the samples were characterised by using different techniques: X-Ray diffraction, X-Ray Fluorescence and Raman spectroscopy in order to highlight the chemical composition and identify the mineral phases. The 14C content was then measured by AMS in the carbon fraction extracted by acid hydrolysis or via thermal decomposition at different temperatures. Indeed, the selection of a proper temperature (500 °C) resulted in the possibility to get rid of the possible contamination from calcium carbonate. We also present the results obtained in the analysis of samples intentionally contaminated with 14C-free calcium carbonate and processed with the two different procedures
Radiocarbon age anomalies in pre- and post-bomb land snails from the coastal Mediterranean Basin
No full textThe shell carbonate of pre- and post-bomb samples of 2 species of terrestrial gastropods (Theba pisana and Cernuella virgata) sampled along the coast of Apulia, southern Italy, were dated using accelerator mass spectrometry and carbon stable isotopes were analyzed. The analyses show, for both species, significant anomalies in the radiocarbon age due to the possible presence of a 14C-depleted source of carbon in the formation of the shell aragonite. The magnitude of the age anomaly was quantified in the studied area to ~1000 14C yr. © 2007 by the Arizona Board of Regents on behalf of the University of Arizona
The synergistic role of pH and calcination temperature in sol–gel titanium dioxide powders
No full textTitanium dioxide (TiO2) nanoparticles were prepared by the sol–gel method starting from a volume of 1.5 mL of titanium tetraisopropoxide (TTIP) dissolved in 10 mL of ultrapure water milliQ grade (pH 5). The pH of the solution was adjusted by adding HNO3 and NaOH to reach an acidic and basic character of the sol, respectively. A wide pH range from 1 to 10 was explored. The prepared TiO2 nanopowders were annealed at three different calcination temperatures, 100, 450 and 800 °C for 3 h. The synergic effect of pH and calcination temperature on the structural and morphological properties of TiO2 nanoparticles was investigated by XRD and Raman analyses. At the lowest (100 °C) and highest (800 °C) calcination temperatures, we observed the dominance of anatase and rutile phases, respectively. A mixture of these phases was observed for the titania powders calcinated at 450 °C. In particular, the nanoparticles produced in strong acidic medium showed a coexistence of anatase and rutile with a dominance of rutile, whereas the anatase was the crystalline phase favored in alkaline medium environment
Plasma enhanced-chemical vapour deposi-tion of scuff-resistant hydrogenated amorphous carbon coatings on C100 steel
No full textHydrogenated amorphous carbon coatings, deposited by low pressure plasma to minimize the wear of C100 steel components, were optimized and characterized. In order to ensure good adhesion of the films to the steel surface, a thin Ti interlayer was deposited, by magnetron sputtering, before the plasma deposition.
The chemical characterization of the deposits was performed by means of RAMAN, XPS, RBS and ERDA analysis, while nanoindentation, nanoscratch and nanowear tests allowed to estimate the tribomechanical properties of the deposits, with the aim of evaluating their scuff-resistance.
It was found that the optimized plasma deposited hydrogenated amorphous carbon coatings were well adherent to C100 steel and increased more than 70 % its surface hardness
A RADIOCARBON CHRONOLOGY FOR "GROTTE DI PERTOSA" IN CAMPANIA, SOUTHERN ITALY
No full textThe Pertosa Caves, today also known as the Pertosa-Auletta Caves, constitute an important karst system in the Campania region (southern Italy). Crossed by the waters of a river that re-emerges on the surface, they have an overall development of about 3 km. Thanks to the width of the entrance, the excellent location along a natural communication route through the mountains and the natural availability of water directly on the site, the initial part of the cavity was frequented by humans, without interruption, from prehistoric times to the Middle Ages. During the protohistory, in particular, the moment of most marked human presence is recorded in the cave. In this phase an extensive pile dwelling system was built on the waters of the underground river. The system was probably created to make the location, subject to frequent flooding, suitable for human settlement. This structure today constitutes an archaeological unicum not only in Italy but throughout Europe. We briefly analyze its general characteristics providing the results of a radiocarbon dating campaign which allowed to assess the occupation phases of the different contexts and the life span of the wooden artifacts, which came to us in a very good state of preservation. Radiocarbon data allowed to assess the chronological range of the human frequentation of the caves and to date the exceptionally well preserved underground pile dwelling system
Proton beams of laser-hydrogenated metal targets
No full textIn this paper, we report a study on proton beams produced via laser interaction from hydrogenated solid targets useful for the development of new sources devoted to medical applications, such as hadron therapy and isotope production. The hydrogenation of the targets was made before the laser-matter interaction. In this study, we used as solid targets, pure samples of Ti, Ta and Al which in a first phase were treated by laser cleaning (via KrF excimer laser at the irradiance I = 3×107 W/cm2) and then they were exposed to laser irradiation (1500 pulses, I = 3×107 W/cm2}) under a constant flow of H2 (HiQ Hydrogen 6.0, highly pure). After that, the targets were maintained under H2 flow for 5 minutes, in order to promote a further hydrogen adsorption. We report laser ablation measurements performed at fluences of 1.3, 2.5 and 5.0 J/cm2. The results on hydrogenated targets showed an increase of proton yield of 25% (Ti), 64% (Al) and 550% (Ta), with respect to the corresponding untreated ones
Carbon stable isotope analysis of 14C-AMS dated vegetal remains: a possible paleoclimatological signal at the III millenium BC Ebla site (Syria)
No full textGeometric and electromagnetic characterization of electron beams produced by nanodiamond photocathodes
No full textIn this work, the geometric and electromagnetic characteristics of electron beams generated by three photocathodes (PCs), two based on nanodiamond (ND) layers and one based on Cu (generally used as reference) were investigated. Specifically, the active layers of the ND-based PCs consisted of untreated and hydrogenated (H-ND) nanoparticles (250 nm in size) deposited by pulsed spray technique on p-doped silicon substrates as uniform coating. Photoemission measurements carried out by a KrF nanosecond excimer laser (λ = 248 nm) in a vacuum chamber at 10-6 mbar and the emittance evaluation, performed by the pepper pot method, are reported and discussed. For the last, radio-chromic films (HD-810 Gafchromic) were used as sensible screen for electrons. The study of the emittance was performed by varying the laser spot onto the PC surface and the accelerating voltage (5, 10 and 15 kV) . From emittance values, the normalized brightness was also estimated for all the cathodes. The obtained results showed quantum efficiency values of the ND-based photocathodes higher than that of the reference Cu one, but, at the same time, higher emittances and therefore worse performancers as the result of the enlarged beam divergence. Despite this, H-ND resulted to be the best PC between those investigated for the highest normalized beam brightness, thanks to its high electron current and low normalized emittance
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