On the oxygen abundance in our Galaxy

The compilation of published spectra of Galactic HII regions with available diagnostic [OIII]4363 line has been carried out. Our list contains 71 individual measurements of 13 HII regions in the range of galactocentric distances from 6.6 to 14.8 kpc. The oxygen abundances in all the HII regions were recomputed in the same way, using the classic Te - method. The oxygen abundance at the solar galactocentric distance traced by those HII regions is in agreement with the oxygen abundance in the interstellar medium in the solar vicinity derived with high precision from the interstellar absorption lines towards stars. The derived radial oxygen abundance distribution was compared with that for HII regions from the Shaver et al. (1983) sample which is the basis of many models for the chemical evolution of our Galaxy. It was found that the original Shaver et al.'s oxygen abundances are overestimated by 0.2-0.3 dex. Oxygen abundances in HII regions from the Shaver et al. sample have been redetermined with the recently suggested P - method. The radial distribution of oxygen abundances from the Shaver et al. sample redetermined with the P - method is in agreement with our radial distribution of (O/H)_Te abundances

Multi-frequency data analysis in AFM by wavelet transform

Interacting cantilevers in Atomic Force Microscopy (AFM) experiments generate non-stationary, multi-frequency signals consisting of numerous excited flexural and torsional modes and their harmonics. The analysis of such signals is challenging, requiring special methodological approaches and a powerful mathematical apparatus. The most common approach to the signal analysis is to apply the Fourier transform (FT) analysis, which decomposes the signal into constituent frequencies displayed in the spectrum as resonance peaks. FT analysis gives accurate spectra for stationary signals. For signals changing their spectral content over time, FT provides only an averaged spectrum. Hence, for non-stationary and rapidly varying signals, such as those from interacting AFM cantilevers, a method that shows the spectral evolution in time is needed. One of the most powerful techniques, allowing detailed time-frequency representation of signals, is the wavelet transform (WT). WT is a method of analysis that allows representation of energy associated to the signal at a particular frequency and time, providing correlation between the spectral and temporal features of the signal, unlike FT [1, 2]. This is particularly important in AFM because signals nonlinearities contains valuable information about tip-sample interactions and consequently surfaces properties [3-5]. The present work is aimed to show the advantages of WT in comparison with FT using as an example the force curve analysis in dynamic force spectroscopy

An integrated overview of physiological and biochemical responses of Celtis australis to drought stress

Trees in Mediterranean areas frequently face severe drought stress events, due to sudden decreases in soil water availability associated to intense heat waves. The knowledge of strategies adopted by plants to cope with the environmental pressures associated to Mediterranean climate is crucial for reforestation strategies and planning future urban greening. Here we investigated the physiological and biochemical adjustments activated by Celtis australis in response to drought stress during summer. Despite widely used for reforestation in Southern Mediterranean, how C. australis responds to the severe challenges imposed by Mediterranean climate has not investigated yet. In our study, we performed analyses of water relations, gas exchange and PSII performance, the concentration of photosynthetic pigments, the activity and the concentration of primary antioxidants in plants exposed to drought stress of increasing severity. Data of our study reveal that C. australis displays both conservative water use and isohydric behavior in response to drought, and diffusive resistance mostly limits photosynthesis even at severe drought. Our study also reveals an effective down-regulation rather than permanent impairment of PSII photochemistry in response to drought stress of increasing severity, since excess electron transport due to declines in photosynthesis (-61% at severe stress, compared to control) was matched by an increase in nonphotochemical quenching (+71% at severe stress, compared to control). However, our study highlights that under severe drought, zeaxanthin (and neoxanthin) increased by 75% (and 25%), likely served an important function as chloroplast antioxidant, other than sustaining nonphotochemical quenching. Antioxidant enzymes and ascorbate also increased (+132% on average for superoxide dismutase, ascorbate peroxidase, and catalase) and contributed in countering oxidative stress in severely droughted plants. Large adjustments in the suite of physiological and biochemical traits may effectively enable C. australis to gain carbon at appreciable rates while avoiding irreversible damage to the photosynthetic apparatus even when challenged by severe drought stress, thereby making this species an excellent candidate for forest and urban plantings in sites experiencing extended periods of drought stress

AN INTERDISCIPLINARY APPROACH FOR THE SEISMIC VULNERABILITY ASSESSMENT OF HISTORICAL CENTRES IN MASONRY BUILDING AGGREGATES: APPLICATION TO THE CITY OF SCARPERIA, ITALY

Abstract. The seismic vulnerability of masonry building aggregates is very difficult to determine, since it is affected by many uncertainties. The most uncertain quantities concern the historical periodization of structural aggregates. Moreover, the studies made at the urban scale can hardly be thorough, and usually the knowledge achieved on the single units is not fully satisfactory, so that the structural designer has to deal with uncompleted architectonical surveys and partial data; one of the most important problems concerns the lack of knowledge about the boundary conditions between adjacent structures. In order to perform mechanical analyses, an extensive knowledge of materials and techniques adopted is required. In this paper, an integrated methodology for the seismic assessment of building aggregate is presented. It concerns a multidisciplinary knowledge-based approach calibrated over the historical centres and the urban aggregates; the procedure joins different aspects, such as the use of modern technologies for an integrated knowledge, plans reconstructions through archival documents, laser scanner digital survey of urban fronts, non-destructive investigations of the materials. GIS and BIM platforms have been used to implement and collect data in order to perform detailed analyses. The information allowed to assess the seismic vulnerability of the building aggregates and the expected damage scenarios through empirical methodologies. The city of Scarperia, founded a few kilometres from Florence during the Medieval Age and characterized by a medium seismicity, has been chosen as a case study for the presented procedure

Cms gem detector material study for the hl-lhc

A study on the Gaseous Electron Multiplier (GEM) foil material is performed to determine the moisture diffusion rate, moisture saturation level and the effects on its mechanical properties. The study is focused on the foil contact with ambient air and moisture to determine the value of the diffusion coefficient of water in the foil material. The presence of water inside the detector foil can determine the changes in its mechanical and electrical properties. A simulated model is developed with COMSOL Multiphysics v. 4.3 [1] by taking into account the real GEM foil (hole dimensions, shapes and material), which describes the adsorption of water. This work describes the model, its experimental verification, the water diffusion within the entire sheet geometry of the GEM foil, thus gaining concentration profiles and the time required to saturate the system and the effects on the mechanical properties

Confidence limits of evolutionary synthesis models III. On time-integrated quantities

Evolutionary synthesis models are a fundamental tool to interpret the properties of observed stellar systems. In order to achieve a meaningful comparison between models and real data, it is necessary to calibrate the models themselves, i.e. to evaluate the dispersion due to the discreteness of star formation as well as the possible model errors. In this paper we show that linear interpolations in the log M - log t_k plane, that are customary in the evaluation of isochrones in evolutionary synthesis codes, produce unphysical results. We also show that some of the methods used in the calculation of time-integrated quantities (kinetic energy, and total ejected masses of different elements) may produce unrealistic results. We propose alternative solutions to solve both problems. Moreover, we have quantified the expected dispersion of these quantities due to stochastic effects in stellar populations. As a particular result, we show that the dispersion in the 14N/12C ratio increases with time.Comment: 11 pages, 8 figures, accepted by A&

Abundances of Cu and Zn in metal-poor stars: clues for Galaxy evolution

We present new observations of copper and zinc abundances in 90 metal-poor stars, belonging to the metallicity range -3< [Fe/H] < -0.5. The present study is based on high resolution spectroscopic measurements collected at the Haute Provence Observatoire (R= 42000, S/N > 100). The trend of Cu and Zn abundances as a function of the metallicity [Fe/H] is discussed and compared to that of other heavy elements beyond iron. We also estimate spatial velocities and galactic orbital parameters for our target stars in order to disentangle the population of disk stars from that of halo stars using kinematic criteria. In the absence of a firm a priori knowledge of the nucleosynthesis mechanisms controlling Cu and Zn production, and of the relative stellar sites, we derive constraints on these last from the trend of the observed ratios [Cu/Fe] and [Zn/Fe] throughout the history of the Galaxy, as well as from a few well established properties of basic nucleosynthesis processes in stars. We thus confirm that the production of Cu and Zn requires a number of different sources (neutron captures in massive stars, s-processing in low and intermediate mass stars, explosive nucleosynthesis in various supernova types). We also attempt a ranking of the relative roles played by different production mechanisms, and verify these hints through a simple estimate of the galactic enrichment in Cu and Zn. In agreement with suggestions presented earlier, we find evidence that Type Ia Supernovae must play a relevant role, especially for the production of Cu.Comment: Accepted for A&A, 27 pages, 14 figure

Thermo-mechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near infrared pump-probe diffraction experiments

The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nano-disks has been studied by near infrared pump-probe diffraction measurements, over a temporal range spanning from 100 fs to several nanoseconds. The experiments demonstrate that, in these systems, a two-dimensional surface acoustic wave (2DSAW), with a wavevector given by the reciprocal periodicity of the array, can be excited by ~120 fs Ti:sapphire laser pulses. In order to clarify the interaction between the nanodisks and the substrate, numerical calculations of the elastic eigenmodes and simulations of the thermodynamics of the system are developed through finite-element analysis. At this light, we unambiguously show that the observed 2DSAW velocity shift originates from the mechanical interaction between the 2DSAWs and the nano-disks, while the correlated 2DSAW damping is due to the energy radiation into the substrate.Comment: 13 pages, 10 figure

Navigational infrastructure at the East Pacific Rise 9°50′N area following the 2005–2006 eruption : seafloor benchmarks and near-bottom multibeam surveys

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008):Q11T04, doi:10.1029/2008GC002070.Four seafloor benchmarks were deployed with ROV Jason2 at frequently visited areas along the northern East Pacific Rise (NEPR) ridge crest near 9°50′N, within the Ridge2000 EPR integrated study site (ISS) bull's eye. When used in concert with established deep-ocean acoustic positioning techniques, these benchmarks provide navigational infrastructure to facilitate the integration of near-bottom data at this site by allowing efficient and quantitative coregistration of data and observations collected on multiple dives and over multiple cruises. High-resolution, near-bottom multibeam bathymetric surveys also were conducted along and across the ridge crest to provide a morphological and geological context for the benchmark areas. We describe the navigation and data processing techniques used to constrain the benchmark positions and outline operational details to effectively use benchmarks at this and other deep-ocean sites where multidisciplinary time series studies are conducted. The well-constrained positions of the benchmarks provide a consistent geospatial framework that can be used to limit navigational uncertainties during seafloor sampling and mapping programs and enable accurate spatial coregistration and integration of observations. These data are important to test a range of multidisciplinary hypotheses that seek to link geological, chemical, and biological processes associated with crustal accretion and energy transfer from the mantle to the hydrosphere at mid-ocean ridges