Analysis of thermal field within an urban canyon with variable thermophysical characteristics of the building's walls.

In a typical urban configuration, a microclimatic analysis has been carried out. Using a CFD method, a N-S oriented urban street canyon, with a given H/W ratio, has been examined. The standard k–ε turbulence model has been used to simulate a three-dimensional flow field and to calculate the thermo-fluid dynamics parameters that characterize the street canyon. In this study has been analyzed the thermal flow field when the walls of the building change the properties of solar radiation absorption, in particular for α=0.2 and α=0.8. Solar radiation considered is that of 21/07 in Milan in two different hours: at 11:00 a.m. and at 02:00 p.m. The study shows the importance of the thermophysical properties of a wall, in the development of the thermal field and flow field. This is a very important topic, in terms of improvement of well-being and the quality of the air within the cities, through the choice of materials and colors of the facades of buildings.

Living within a One Planet reality: the contribution of personal Footprint calculators

During the last 50 years, humanity's Ecological Footprint has increased by nearly 190% indicating a growing unbalance in the human-environment relationship, coupled with major environmental and social changes. Our ability to live within the planet's biological limits requires not only a major re-think in how we produce and distribute 'things', but also a shift in consumption activities. Footprint calculators can provide a framing that communicates the extent to which an individual's daily activities are compatible with our One Planet context. This paper presents the findings from the first international study to assess the value of personal Footprint calculators in guiding individuals towards sustainable consumption choices. It focuses specifically on Global Footprint Network's personal Footprint calculator, and aims to understand the profile of calculator users and assess the contribution of calculators to increasing individual awareness and encouraging sustainable choices. Our survey of 4245 respondents show that 75% of users resided in 10 countries, 54% were aged 18–34 years and had largely used the calculator within an educational context (62%). The calculator was considered a valuable tool for knowledge generation by 91% of users, and 78% found it useful to motivate action. However, only 23% indicated the calculator provided them with the necessary information to make actual changes to their life and reduce their personal Footprint. The paper discusses how and why this personal Footprint calculator has been effective in enhancing individuals' understanding of the environmental impact of their actions, framing the scale of the problem and empowering users to understand the impacts of different lifestyle choices. Those individual-level and system-level changes needed to generate global sustainability outcomes are also discussed. Similar to other calculators, a gap is also identified in terms of this calculator facilitating individuals to convert new knowledge into action

Condensed phase of Bose-Fermi mixtures with a pairing interaction

We study the condensed phase of a Bose-Fermi mixture with a tunable pairing interaction between bosons and fermions with many-body diagrammatic methods and fixed-node diffusion Quantum Monte Carlo simulations. A universal behavior of the condensate fraction and bosonic momentum distribution with respect to the boson concentration is found to hold in an extended range of boson-fermion couplings and concentrations. For vanishing boson density, we prove that the bosonic condensate fraction reduces to the quasiparticle weight Z of the Fermi polaron studied in the context of polarized Fermi gases, unifying in this way two apparently unrelated quantities.Comment: 5 pages, 4 figures; final version as publishe

Production of atomic hydrogen by cosmic rays in dark clouds

The presence of small amounts of atomic hydrogen, detected as absorption dips in the 21 cm line spectrum, is a well-known characteristic of dark clouds. The abundance of hydrogen atoms measured in the densest regions of molecular clouds can be only explained by the dissociation of H$_2$ due to cosmic rays. We want to assess the role of Galactic cosmic rays in the formation of atomic hydrogen, by using recent developments in the characterisation of the low-energy spectra of cosmic rays and advances in the modelling of their propagation in molecular clouds. We model the attenuation of the interstellar cosmic rays entering a cloud and compute the dissociation rate of molecular hydrogen due to collisions with cosmic-ray protons and electrons as well as fast hydrogen atoms. We compare our results with the available observations. The cosmic-ray dissociation rate is entirely determined by secondary electrons produced in primary ionisation collisions. These secondary particles constitute the only source of atomic hydrogen at column densities above $\sim10^{21}$ cm$^{-2}$. We also find that the dissociation rate decreases with column density, while the ratio between the dissociation and ionisation rates varies between about 0.6 and 0.7. From comparison with observations we conclude that a relatively flat spectrum of interstellar cosmic-ray protons, as the one suggested by the most recent Voyager 1 data, can only provide a lower bound for the observed atomic hydrogen fraction. An enhanced spectrum of low-energy protons is needed to explain most of the observations. Our findings show that a careful description of molecular hydrogen dissociation by cosmic rays can explain the abundance of atomic hydrogen in dark clouds. An accurate characterisation of this process at high densities is crucial for understanding the chemical evolution of star-forming regions.Comment: 7 pages, 7 figures, accepted by Astronomy and Astrophysic

Massive black hole factories: Supermassive and quasi-star formation in primordial halos

Supermassive stars and quasi-stars (massive stars with a central black hole) are both considered as potential progenitors for the formation of supermassive black holes. They are expected to form from rapidly accreting protostars in massive primordial halos. We explore how long rapidly accreting protostars remain on the Hayashi track, implying large protostellar radii and weak accretion luminosity feedback. We assess the potential role of energy production in the nuclear core, and determine what regulates the evolution of such protostars into quasi-stars or supermassive stars. We follow the contraction of characteristic mass scales in rapidly accreting protostars, and infer the timescales for them to reach nuclear densities. We compare the characteristic timescales for nuclear burning with those for which the extended protostellar envelope can be maintained. We find that the extended envelope can be maintained up to protostellar masses of 3.6x10^8 \dot{m}^3 solar, where \dot{m} denotes the accretion rate in solar masses per year. We expect the nuclear core to exhaust its hydrogen content in 7x10^6 yrs. If accretion rates \dot{m}>>0.14 can still be maintained at this point, a black hole may form within the accreting envelope, leading to a quasi-star. Alternatively, the accreting object will gravitationally contract to become a main-sequence supermassive star. Due to the limited gas reservoir in dark matter halos with 10^7 solar masses, the accretion rate onto the central object may drop at late times, implying the formation of supermassive stars as the typical outcome of direct collapse. However, if high accretion rates are maintained, a quasi-star with an interior black hole may form.Comment: 9 pages, 4 figures, submitted to A&A. Comments are welcom

A demonstrator for bolometric interferometry

Bolometric Interferometry (BI) is one of the most promising techniques for precise measurements of the Cosmic Microwave Background polarization. In this paper, we present the results of DIBO (Demonstrateur d'Interferometrie Bolometrique), a single-baseline demonstrator operating at 90 GHz, built to proof the validity of the BI concept applied to a millimeter-wave interferometer. This instrument has been characterized in the laboratory with a detector at room temperature and with a 4 K bolometer. This allowed us to measure interference patterns in a clean way, both (1) rotating the source and (2) varying with time the phase shift among the two interferometer's arms. Detailed modelisation has also been performed and validated with measurements.Comment: 15 pages, 14 figure

Structural geology and petrography of the Naret region (northern Valle Maggia, N.Ticino, Switzerland)

The Naret region has a complex geological history of Alpine polyphase folding and metamorphism that affected pre-Alpine rocks of the Maggia nappe, including the Matorello group (interpreted in this study as late-Variscan intrusives), the Lebendun nappe and Mesozoic rocks of the Bedretto zone. From field observations, four main ductile deformation phases (D1 to D4) can be distinguished and, in combination with thermodynamic modelling, the tectono-metamorphic evolution for the Naret region can be reconstructed. D1 formed the initial nappe stack. During this phase, the Maggia nappe was thrust over the Lebendun nappe, at T ≤ 570°C and P ≤ 10 kbar. D2 caused isoclinal refolding of the nappe pile, at around 610-640°C and 8.5-10 kbar, and produced both the main regional foliation (S2) and a penetrative stretching lineation which is generally parallel to F2 fold axes. D2 is largely responsible for the current complicated geometry of the Lebendun nappe boundary. The main phase of porphyroblastesis occurred between D2 and D3, corresponding to a metamorphic temperature peak of ca. 640-650°C at pressures of ca. 8-9 kbar. D3 produced open folds oblique to the general Alpine trend ("crossfolding”) and locally a crenulation cleavage with a well developed crenulation lineation, at estimated temperatures of 550-610°C. The last important phase, D4, caused open backfolding of all pre-existing structures and is responsible for steepening of the main S2 foliation, to produce the Northern Steep Zone, and for a regional rotation of S3 and L3. D4 developed at T ≥ 550°C and P ≥ 3 kbar. The Lebendun nappe is a complicated structure developed as the result of non-coaxial fold interference related to D1 and D2. From tectono-stratigraphic evidence, the rocks of the Lebendun nappe are interpreted as pre-Triassic in ag

Novel approach for health monitoring of earthen embankments

This paper introduces a novel modular approach for the monitoring of desiccation-induced deterioration in earthen embankments (levees), which are typically used as flood-defense structures. The approach is based on the use of a combination of geotechnical and noninvasive geophysical probes for the continuous monitoring of the water content in the ground. The level of accuracy of the monitoring is adaptable to the available financial resources. The proposed methodology was used and validated on a recently built, 2-km-long river embankment in Galston (Scotland, United Kingdom). A suite of geotechnical probes was installed to monitor the seasonal variation of water content over a 2-year period. Most devices were calibrated in situ. A novel procedure to extrapolate the value of water content from the geotechnical and geophysical probes at any point of the embankment is shown. Desiccation fissuring degrades the resistance of embankments against several failure mechanisms. An index of susceptibility is proposed here. The index is a useful tool to assess the health state of the structure and prioritize remedial interventions

One-flavour QCD at finite temperature

We present results, for heavy to moderate quark masses, of a study of thermodynamic properties of 1-flavour QCD, using the multiboson algorithm. Finite-size scaling behaviour is studied on lattices of size $8^3\times 4$, $12^3\times 4$ and $16^3\times 4$. It is shown that, for heavy quarks, the peak of the Polyakov loop susceptibility grows linearly with the spatial volume, indicating a first order phase transition. The deconfinement ratio and the distribution of the norm of the Polyakov loop corroborate this result. For moderately heavy quarks the first-order transition weakens and becomes a crossover. We estimate the end point of the first-order phase transition to occur at a quark mass of about 1.6 GeV.Comment: 3 pages, 3 PostScript figures; Talk presented at LAT9