1,721,140 research outputs found
Il ritmo della vita. L’etica immanente di Carlo Sini
No full textL’articolo indaga il concetto di «vita» nelle opere più recenti di Carlo Sini. Ciò che si intende mostrare è che attraverso questo concetto Sini rinnova la portata etica del suo pensiero dandole una connotazione più immanente
Fenomenologia ed ermeneutica - Parole chiave
No full textLe parole chiave della fenomenologia e dell'ermeneutic
Service life of reinforced concrete structures made with blended cements and exposed in urban environment
Full text linkCarbonation-induced corrosion is one of the main causes of degradation of reinforced concrete (RC) structures exposed outdoor in urban environment. To prevent steel corrosion, a durability design, that considers both the initiation and the propagation time, is of fundamental importance. At this aim, the resistance to carbonation of concrete and the steel corrosion rate in the exposure environment need to be known. This paper reports the carbonation coefficient and the corrosion rate of 7-day cured RC specimens made with different binders and exposed outdoor in Milan in unsheltered conditions. Corrosion rates in laboratory conditions with different temperatures and relative humidities are also reported. Experimental data were used to evaluate the service life in unsheltered condition. RC specimens made with Portland cement exhibited the lowest carbonation coefficient and corrosion rate, while specimens with 30% limestone and with 70% ground granulated blast furnace slag the highest
Carbonation of blended cement concretes after 12 years of natural exposure
Full text linkIn urban environments, the durability of reinforced concrete structures is limited by carbonation-induced corrosion. To prevent steel corrosion, the selection of a proper concrete in terms of type of binder, water/binder ratio and curing time, is of fundamental importance. At this aim the knowledge of the resistance to carbonation in the exposure environment is required. Usually carbonation is evaluated from accelerated tests, however natural exposure tests are needed to validate short-term tests and make reliable predictions of the behaviour in a real environment. This paper reports the carbonation of concretes with different binders, water/binder ratios and curing, exposed for more than twelve years outdoor in Milan in sheltered conditions. Concretes with Portland cement exhibited a higher carbonation in comparison with concretes with limestone and pozzolanic cements. Curing seemed to be less effective than the type of binder and the water/binder ratio
Corrosion rate of carbon steel in carbonated concrete made with different supplementary cementitious materials
No full textCarbonation-induced corrosion limits the durability of reinforced concrete structures exposed in urban environments. In these exposure conditions, the propagation phase of corrosion can be an important part of the service life and, hence the knowledge of the corrosion rate is essential for the design. However, data regarding the corrosion rate in carbonated concrete are scarce and mainly refer to Portland cement concrete. This paper reports the corrosion rate and corrosion potential of steel bars embedded in concretes with different binders and water/binder ratios, exposed both outdoor in unsheltered conditions and in laboratory conditions characterised by different temperatures and relative humidities. Concrete resistivity at different depths is also reported and correlations among these parameters are discussed. Corrosion potential, corrosion rate and concrete resistivity were strongly influenced by the relative humidity, while temperature played an important role only at high relative humidity. Steel in Portland cement concrete showed the lowest corrosion rate
Long-term corrosion behavior of carbon steel in carbonated concrete made with different binders|Corrosione a lungo termine di armature di acciaio in calcestruzzi carbonatati con diverse composizioni
No full textTo properly predict the service life of a reinforced concrete structure subjected to carbonation-induced corrosion, a correct estimation of the propagation period is needed. The propagation period is related to the rate at which the corrosive attack propagates, and mainly depends on the exposure conditions and the concrete quality. This paper reports the preliminary results of a research aimed at investigating the corrosion conditions of steel in carbonated concrete, made with different compositions and exposed for more than 15 years to an unsheltered outdoor environment. Preliminary results showed the fundamental role of concrete composition in determining the corrosion behavior of steel bars, leading to significant different damage conditions, from the absence of cracking to the complete concrete cover detachment. Moreover, the correlations between the corrosion rate and concrete resistivity as well as corrosion potential were investigated
First ALMA Maps of Cosmic-Ray Ionization Rate in High-mass Star-forming Regions
Full text linkLow-energy cosmic rays (<1 TeV) are a pivotal source of ionization of the interstellar medium, where they play a central role in determining the gas chemical composition and drastically influence the formation of stars and planets. Over the past few decades, H3 + absorption line observations in diffuse clouds have provided reliable estimates of the cosmic-ray ionization rate relative to H2 ( ζionH2
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). However, in denser clouds, where stars and planets form, this method is often inefficient due to the lack of H3 + rotational transitions. The ζionH2
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estimates are, therefore, still provisional in this context and represent one of the least understood components when it comes to defining general models of star and planet formation. In this Letter, we present the first high-resolution maps of the ζionH2
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in two high-mass clumps obtained with a new analytical approach recently proposed to estimate the ζionH2
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in the densest regions of molecular clouds. We obtain ⟨ζionH2⟩
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that span from 3 × 10-17 to 10-16 s-1, depending on the different distribution of the main ion carriers, in excellent agreement with the most recent cosmic-ray propagation models. The cores belonging to the same parental clump show comparable ζionH2
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, suggesting that the ionization properties of prestellar regions are determined by global rather than local effects. These results provide important information for the chemical and physical modeling of star-forming regions
First sample of N2H+nitrogen isotopic ratio measurements in low-mass protostars
Full text linkContext The nitrogen isotopic ratio is considered an important diagnostic tool of the star formation process, and N2H+ is particularly important because it is directly linked to molecular nitrogen N2. However, theoretical models still do not provide an exhaustive explanation for the observed 14N/15N values. Aims. Recent theoretical works suggest that the 14N/15N behaviour is dominated by two competing reactions that destroy N2H+: dissociative recombination and reaction with CO. When CO is depleted from the gas phase, if the N2H+ recombination rate is lower with respect to that for N15NH+, the rarer isotopologue is destroyed more quickly. In prestellar cores, due to a combination of low temperatures and high densities, most CO is frozen in ices onto the dust grains, leading to high levels of depletion. On the contrary, in protostellar cores, where temperature are higher, CO ices evaporate back to the gas phase. This implies that the N2H+ isotopic ratio in protostellar cores should be lower than that in prestellar cores, and consistent with the elemental value of ≈440. We aim to test this hypothesis, producing the first sample of N2H+â N15NH+ measurements in low-mass protostars. Methods. We observe the N2H+ and N15NH+ lowest rotational transition towards six young stellar objects in the Perseus and Taurus molecular clouds. We model the spectra with a custom python code using a constant Tex approach to fit the observations. We discuss in the Appendix the validity of this hypothesis. The derived column densities are used to compute the nitrogen isotopic ratios. Results. Our analysis yields an average of 14N/15N|pro = 420 ± 15 in the protostellar sample. This is consistent with the protosolar value of 440, and significantly lower than the average value previously obtained in a sample of prestellar objects. Conclusions. Our results are in agreement with the hypothesis that, when CO is depleted from the gas-phase, dissociative recombinations with free electrons destroy N15NH+ faster than N2H+, leading to high isotopic ratios in prestellar cores where carbon monoxide is frozen onto dust grains
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