3,155 research outputs found
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
Experimental Characterization and Numerical Investigation on the Azzone Visconti Bridge in Lecco (Italy)
AbstractThe paper presents the results of a numerical investigation on the Azzone Visconti Bridge in Lecco (Italy). Starting from the historical data and from an extensive mechanical characterization of both the soil constituting the riverbed and of the masonry constituting the piers, the aim of the analyses is to predict the behaviour of the structure under the testing loading scheme prescribed by the current Italian Code. A finite element structural model has been conceived, and three different models describing the mechanical behaviour of the foundation have been implemented. Limited differences are observed in terms of absolute vertical settlement of the bridge, but important effects are highlighted in terms of stress redistribution within the piers
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 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 cm. 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
Mito-Nuclear Communication in Hepatocellular Carcinoma Metabolic Rewiring
As the main metabolic and detoxification organ, the liver constantly adapts its activity to fulfill the energy requirements of the whole body. Despite the remarkable adaptive capacity of the liver, prolonged exposure to noxious stimuli such as alcohol, viruses and metabolic disorders results in the development of chronic liver disease that can progress to hepatocellular carcinoma (HCC), which is currently the second leading cause of cancer-related death worldwide. Metabolic rewiring is a common feature of cancers, including HCC. Altered mito-nuclear communication is emerging as a driving force in the metabolic reprogramming of cancer cells, affecting all aspects of cancer biology from neoplastic transformation to acquired drug resistance. Here, we explore relevant aspects (and discuss recent findings) of mito-nuclear crosstalk in the metabolic reprogramming of hepatocellular carcinoma
PPARs and Mitochondrial Metabolism: From NAFLD to HCC
Metabolic related diseases, such as type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease (NAFLD), are widespread threats which bring about a significant burden of deaths worldwide, mainly due to cardiovascular events and cancer. The pathogenesis of these diseases is extremely complex, multifactorial, and only partially understood. As the main metabolic organ, the liver is central to maintain whole body energetic homeostasis. At the cellular level, mitochondria are the metabolic hub connecting and integrating all the main biochemical, hormonal, and inflammatory signaling pathways to fulfill the energetic and biosynthetic demand of the cell. In the liver, mitochondria metabolism needs to cope with the energetic regulation of the whole body. The nuclear receptors PPARs orchestrate lipid and glucose metabolism and are involved in a variety of diseases, from metabolic disorders to cancer. In this review, focus is placed on the roles of PPARs in the regulation of liver mitochondrial metabolism in physiology and pathology, from NAFLD to HCC
PPARγ and Oxidative Stress: Con(β) Catenating NRF2 and FOXO
Peroxisome-proliferator activator receptor γ (PPARγ) is a nuclear receptor of central importance in energy homeostasis and inflammation. Recent experimental pieces of evidence demonstrate that PPARγ is implicated in the oxidative stress response, an imbalance between antithetic prooxidation and antioxidation forces that may lead the cell to apoptotic or necrotic death. In this delicate and intricate game of equilibrium, PPARγ stands out as a central player devoted to the quenching and containment of the damage and to foster cell survival. However, PPARγ does not act alone: indeed the nuclear receptor is at the point of interconnection of various pathways, such as the nuclear factor erythroid 2-related factor 2 (NRF2), Wnt/β-catenin, and forkhead box proteins O (FOXO) pathways. Here we reviewed the role of PPARγ in response to oxidative stress and its interaction with other signaling pathways implicated in this process, an interaction that emerged as a potential new therapeutic target for several oxidative-related diseases
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