Theory of plastic mechanism control for MRF–CBF dual systems and its validation

In this paper the theory of plastic mechanism control is presented for moment resisting frame–concentrically braced frames dual systems, i.e. for structural systems combined by moment resisting frames and concentrically braced frames. It is aimed at the design of structures failing in global mode, i.e. whose collapse mechanism is characterised by the yielding of all the tensile diagonals and the occurrence of buckling in the compressed ones, and by plastic hinge formation at all the beam ends and at the base of first storey columns. The proposed methodology is based on the application of the kinematic theorem of plastic collapse, by imposing that the global mechanism equilibrium curve has to lie below all the other equilibrium curves corresponding to undesired mechanisms. The practical application of the design methodology is illustrated by means of a worked example. In addition, the results of a non-linear static pushover and dynamic analyses of the designed structure are also discussed in order to demonstrate the effectiveness of the proposed design procedure.     

Chemical characterization of fine particulate matter during peak PM10 episodes in Apulia (South Italy)

Some peak PM10 episodes, occurred during PM monitoring campaigns performed on October 2005 and February and June 2006 in Bari town, have been characterized. Moreover back trajectories of air masses and Principal Component Analyses were applied. Three of the peak PM10 episodes investigated were related to local emissions of primary pollutants during poor atmospheric dispersion conditions. The other two peak PM10 episodes considered are related with long range transport air masses toward Apulia region: in one case the chemical characterization and the back trajectories analysis indicate that high PM10 value detected is due to the Saharan dust advection in the Apulia region; in the other case air masses with different origin give rise to high PM10 value.Moreover PM10 daily mean concentrations, presented in this paper collected from January 2005 to August 2007 and obtained by automatic device in six stations of air quality monitoring networks in Bari territory, do not show a seasonal trend for PM10 concentrations, contrary to the PM10 trend shown in the towns of North Italy. This can be explained mostly considering that our region presents generally meteo-climatic conditions that favour pollutants dispersion.     

Space Weathering of Small Solar System Bodies

Micrometeorite bombardment and irradiation by solar wind and cosmic ions cause variations in the optical properties of the small Solar System bodies surface materials. These space weathering processes are reasonably well understood for the Moon and S-type asteroids. The research is based on laboratory experiments performed by several groups on meteorites and minor bodies surface analogues, whose results have been applied to the spectral modeling and interpretation of observations from large surveys and space missions. Recent results from young asteroidal families, and the relation between spectral slopes and dynamical properties, have stressed the role of the solar wind exposure timescale. Space weathering processes remain poorly investigated in the case of other types of asteroids, and they are still unclear in the case of outer Solar System bodies, due to a strong dependence of the weathering process on the original composition.     

First observations of the Na exosphere of Mercury with the high-resolution spectrograph of the 3.5M Telescopio Nazionale Galileo

Analysis of three spectra of the exosphere of Mercury in the Na-D lines are presented. Spectra were secured with the high-resolution spectrograph (SARG) of the 3.5 M Telescopio Nazionale Galileo (TNG, located on the Roque de los Muchachos, Canaries) on the evenings of August 23 and 24, 2002. Spectra have resolution ; the slit length was 26.7”. The Na column abundances range from 4.3 to with the highest abundances being close to the illuminated limb. Our observations at true anomaly angles (TAA) from 171°to 174°show the traces of the emission lines to be strongly peaked at the illuminated limb, supportive of recent modeling that shows thermal desorption to be a strong factor in determining the distribution of Na about the planet.     

Optical and X-Ray Observations of the Symbiotic System Ag Draconis During Quiescence and Outburst

We review the main characteristics of the symbiotic system AG Draconis, with special emphasis on its optical and X-ray variations. We also discuss the X-ray to visual energy distribution during quiescence and outburst and describe our spectroscopic and X-ray observations during the 2003 outburst. Based on X-ray observations collected with the XMM–Newton Observatory, on INES data from the IUE satellite, and on optical spectra collected with the Asiago–Cima Ekar, Bologna–Loiano and La Palma–Galileo Italian telescopes.     

Elastic collisions in ion irradiation experiments: A mechanism for space weathering of silicates

Ion irradiation experiments have been performed on silicates (bulk samples) rich of olivine, pyroxene, and serpentine to simulate the effects of space weathering induced on asteroids by solar wind ions. We have used different ions (H⁺, He⁺, Ar⁺, Ar²⁺) having different energies (from 60 to 400 keV) to weather the samples, probed by Raman spectroscopy and UV-vis-NIR reflectance spectroscopy. All the irradiated materials have shown reddening and darkening of reflectance spectra in the 0.25-2.7 μm spectral range. We have found that the increase of the spectral slope of the continuum across the 1-μm band is strongly related with the number of displacements caused by colliding ions because of elastic collisions with the target nuclei. The spectral slopes have been compared, at increasing ion fluence, with those from irradiated Epinal meteorite. We show that formation of nuclear displacements by solar wind ion irradiation is a physical mechanism that reddens the asteroidal surfaces on a time-scale lower than 10⁶ years.     

Statistical assessment of seismicity patterns in Italy: Are they precursors of subsequent events?

The variations of seismicity rate in Central Apenninesprior to the sequence started in September, 1997 (at00:33 UTC, M _L5.6) has been analysedby statistical methods, with the purpose of pointingup eventual periods of quiescence. The analysis wascarried out on the instrumental catalogue of theIstituto Nazionale di Geofisica (ING), covering theperiod from January 1975 to March 1998. In apreliminary phase, the catalogue was declustered usingthe Reasenberg algorithm. After that, eventualmagnitude shifts due to variations in the modalitiesof observation have been individuated and corrected.The subsequent analysis, carried out making use of theZmap software package, has put in evidence thatthe sequence of September 1997 was preceded bya 2.5 year period characterised by absence of eventsof magnitude larger than 3.2, in an area approximately20 × 40 km wide, including the epicentre of themain shock. The statistical methodology shows thatonly 1/10³ of the space-time volumes analysed inthis study, exhibited quiescence of the same level.The study of seismicity rate change correlated toprevious main shocks in a larger area of CentralApennines shows that none of them were preceded by aseismic quiescence, specially close to the epicentreof the main shock, and lasting until the time ofoccurrence of the main shock as in the 1997 case.Actually, we found other patterns of precursoryquiescence with different time or space distribution.We conclude that precursory quiescence is a realfeature of Central Apennines seismicity, but it isdifficult to define a simple hypothesis, which appliesto the generality of cases and can be tested beforeimplementation in a system of earthquake riskmitigation.     

Hydrochemistry of high altitude alpine lakes

The chemical characteristics of 320 Italian alpine lakes are presented and discussed: 38% of them have low ionic concentrations and conductivities below 20 μS/cm; 56% show a conductivity range of 20.1 to 200 μS/cm, and 6% are characterized by higher solute concentrations, up to 34.5 meq/l, with a corresponding maximum conductivity of 1,265 μS/cm.     

Multi-year drought frequency analysis at multiple sites by operational hydrology - A comparison of methods

This paper compares two generators of yearly water availabilities from sources located at multiple sites with regard to their ability to reproduce the characteristics of historical critical periods and to provide reliable results in terms of the return period of critical sequences of different length. The two models are a novel multi-site Markov mixture model explicitly accounting for drought occurrences and a multivariate ARMA. In the case of the multisite Markov mixture model parameter estimation is limited to a search in the parameter space guided by the value of parameter λ to show the sensitivity of the model to this parameter. Application to two of the longest time series of streamflows available in Sicily (Italy) shows that the models can provide quite different results in terms of estimated return periods of historic droughts, although they seem to perform more uniformly when it comes to simulate drought-related statistics such as drought length, severity and intensity. The role of parameter selection for the multisite Markov mixture model and of the marginal probability of generated flows in providing results consistent with the characteristics of the observed series is discussed. Both models are applied to the system of sources supplying the city of Palermo (Sicily) and its environs showing the applicability of the newly developed multisite Markov mixture model to medium-to-large scale water resources systems.