1,721,156 research outputs found
Effect of balconies on air quality in deep street canyons
No full textThis study discusses the effect of balconies on the dispersion of vehicular pollutants inside a deep street
canyon and on the mass transfer rate between the canyon and the above atmosphere. 3D computational
fluid dynamics (CFD) simulations were performed considering the presence of balconies of different
dimensions in a deep street canyon with aspect ratio H/W 1⁄4 3. The effect of two geometrical parameters
has been investigated: the balcony depth and the horizontal distance between two balconies, the other
geometrical parameters remaining constant. CFD simulations have been carried out adopting the scale
adaptive simulation (SAS) model. Results show that the presence of balconies can determine a significant
modification in the flow field inside the street canyon with a less homogeneous dispersion of pollutants
emitted by vehicles circulating in the street and a less effective mass exchange with the above atmosphere.
At the present models developed to assess pollutant concentration levels in street canyons do not
consider the presence of balconies. As consequence, an underestimation of real concentration levels
could occur. Therefore, results obtained can give a contribution in the development of more feasible air
pollution models in urban areas at local scale, and useful information for design of building facades that
minimize the entrapping of vehicular pollutants at pedestrian level in street canyon
Ultrahigh energy neutrinos scattering off relic light neutrinos to explain UHECR above GZK cut off and thin blazars
No full textUHE neutrinos may transfer highest cosmic-rays energies overcoming BBR and radio-waves opacities (the GZK cut off) from most distant AGN sources at the age of the Universe. These UHE might scatter onto those (light and cosmological) relic neutrinos clustered around our galactic halo or nearby neutrino hot dark halo clustered around the AGN blazar and its jets. The branched chain reactions from a primordial nucleon (via photo production of pions and decay to UHE neutrinos) toward the consequent beam dump scattering on galactic relic neutrinos is at least three order of magnitude more efficient than any known neutrino interactions with Earth atmosphere or direct nucleon propagation. Therefore the rarest cosmic rays (as the 320 EeV event) might be originated at far distances (as Seyfert galaxy MCG 8-11-11); its corresponding UHE radiation power is in agreement with the observed one in MeV gamma energies. The final chain products observed on Earth by the Fly's Eye and AGASA detectors might be mainly neutron and anti-neutrons and delayed, protons and anti-protons at symmetric off-axis angles. These hadronic products are most probably secondaries of or pair productions and might be consistent with the last AGASA discoveries of doublets and one triplet even
Scattering of Ultrahigh Energy (UHE) Extragalactic Neutrinos onto Light Relic Neutrinos in Galactic HDM Halo Overcoming the GZK Cut off
No full textThe rarest cosmic rays above the GZK cut'off are probably born at cosmic distances ( tens Mpc) by AGNs (QSRs, BLac, Blazars...). Their puzzling survival over BBR radio waves opacities (the ``GZK cut off'') might find a natural explanation if the traveling primordial cosmic rays were UHE neutrinos (born by UHE photopion decay) which are transparent to or BBR. These UHE might scatter onto those (light and cosmological) relic neutrinos clustered around our galactic halo.
The branched chain reactions from a primordial nucleon (via photoproduction of pions and decay to UHE neutrinos) toward the consequent beam dump scattering on galactic relic neutrinos is at least three order of magnitude more efficient than any known neutrino interactions with Earth atmosphere or direct nucleon propagation. Therefore the rarest cosmic rays (as the 320 EeV event) might be originated at far distances (as Seyfert galaxy MCG 8-11-11). The needed UHE radiation power is in rough agreement with the NCG 8-11-11 observed in MeV gamma energy total output power. The final chain products observed on Earth by the Fly's Eye detector might be mainly neutron and antineutrons as well as, at later stages, protons and antiprotons. These hadronic products are most probably secondaries of or pair productions and might be consistent with the last AGASA discoveries of 6 doublet and one triplet event
Combining marine ecology and economy to roadmap the integrated coastal management: A systematic literature review
Full text linkIntegrated coastal management (ICM) relies on the inclusion of economic issues within marine ecology. To assess the progress of this integration, we applied topic modelling and network analysis to explore the pertinent literature (583 Isi-WoS, and 5459 Scopus papers). We classified the topics of interest (i.e., concepts, approaches, and sectors) that combined ecological and economic issues within marine science, we aggregated these topics in fields pertinent to ICM, and tracked the knowledge-exchange between these fields by using an information-flow network. Main findings were: (i) the high trans-disciplinary fashion of studies about marine protection and of those about commercial fisheries, (ii) the weak interaction between studies focusing on potential biohazards and those about environmental management, (iii) the isolation, in the overall information-flow, of studies about ecotourism and aquaculture. We included in a roadmap all the integration routes we detected within ICM, based on the combination of ecological and economic issues. We conclude that, to improve integration, ICM should: (i) Exploit marine protection as a bridge between ecological and economic concepts and approaches, and between maritime economy sectors, (ii) employ systems ecology to pursue trans-disciplinary investigations, (iii) complement systems ecology with citizen science by means of inclusive economic initiatives, such as ecotourism
A CFD Model to Assess the Impact of Cruise Ship Emissions in the Port of Naples
No full textThe port of Naples is one the most important in the Mediterranean Sea for passengers’ traffic. Due to the proximity of the port to the urban area, ship emissions can have an important impact on air pollution in Naples. The presence of buildings very near to the docks can modify significantly the wind field and, as a consequence, the transport of pollutants emitted when ships are at berth. Models (Calpuff, SPRAY) normally adopted to assess the impact of ship emissions do not take in account this effect. For this reason, a CFD model was developed to assess the impact of cruise ship emissions during the hoteling phase in the port of Naples. A calculation domain of about 7 km2 × 1 km height with 10 million cells has been created. Unsteady CFD simulations have been carried out adopting the Scale Adaptive Simulation (SAS) hybrid model that allows a satisfactory accuracy in the calculation of the turbulence. In particular, the impact of SO2 emissions on seafront building facades and inside the port area are evaluated. Some differences between the results of the CFD model and those obtained by CALPUFF are observed. The CFD model, taking in count the presence of buildings, gives more reliable results about the dispersion of pollutant
Bounds on charged-lepton flavor violations via resonant scattering
Full text linkWe explore the possibility of probing flavor violations in the charged-lepton sector by means of high-luminosity lepton-photon and electron-muon collisions, by inverting initial and final states in a variety of decay channels presently used to bound such violations. In particular, we analyze the resonant lepton, γl→l′, and neutral-meson, e−μ+→φ,η,π0, scattering channels, whose cross sections are critically dependent on the colliding-beams energy spread, being particularly demanding in the case of leptonic processes. For these processes, we compute upper bounds to the cross-section corresponding to present limits on the inverse decay channel rates. In order to circumvent the beam energy spread limitations we extend the analysis to processes in which a photon accompanies the resonance in the final state, compensating the off-shellness effects by radiative return. These processes might be studied at future facilities with moderate energies, in case lepton-photon and electron-muon collisions with sufficiently high luminosity will be available
Using a CFD model to assess the impact of cruise ship emissions on the façades of waterfront buildings in Naples, Italy
No full textThe port of Naples, with about 1 million of cruise passengers corresponding to about 400 calls and 5000
hours at berth per year, is one the most important in the Mediterranean Sea for cruise ships traffic.
Therefore, cruise ship emissions can have an important impact on air pollution in Naples. Moreover,
cruise ships terminal is very near to the center of the town, with some residential and commercial
buildings at only about 200 m from cruise ships docks. The height of these buildings is very close to
that of cruise ship funnels. Therefore, the impact of cruise ship emissions on the façades of these
buildings may be very high, with negative consequences for indoor air quality and health of people
living or working in these buildings. For this reason, a CFD model has been developed with the aim to
assess the impact of atmospheric pollutants emitted by cruise ships at hoteling on the façades of the
nearest buildings. A calculation domain of about 7 km2 and 1 km height with 10 million cells has been
created. Unsteady CFD simulations have been carried out adopting the Scale Adaptive Simulation
(SAS) hybrid model that allows a satisfactory accuracy in the calculation of the turbulence. Most critical
emissive scenarios have been identified based on cruise ships traffic assuming wind flowing from cruise
ships at berth toward the buildings. Emission rates of each pollutant and each cruise ship, during the
hoteling phase, have been evaluated. These data were used as input for CFD simulations. As a result,
contour maps of SO2 on the ground and on the buildings’ façade were obtained. Results of CFD model
are compared with results of simulations with CALPUFF
Ultrahigh energy neutrino scattering onto relic light neutrinos in galactic halo as a possible source of highest energy extragalactic cosmic rays
No full textDiffuse relic neutrinos with light mass are transparent to ultra-high-energy (UHE) neutrinos at thousands of EeV, which are born through the photoproduction of pions by UHE protons on relic 2.73 K blackbody radiation (BBR), and originate in active galactic nuclei (AGNs) at cosmic distances. However, these UHE ν's may interact with others (mainly the heaviest: νμr, ντr, and respective antineutrinos) that are clustered into hot dark matter (HDM) galactic halos. UHE photons or protons, secondaries of ν-νr scattering, might be the final observed signatures of such high-energy chain reactions, and may be responsible for the highest energy extragalactic cosmic-ray (CR) events. Here we consider the conversion efficiency, ramifications, and energetics of these chain reactions for the 1991 October CR event at 320 EeV observed by the Fly's Eye detector in Utah. These quantities seem to be compatible with the distance, direction, and power (observed at MeV gamma energies) of the Seyfert galaxy MCG 8-11-11. The ν-νr interaction probability is favored by at least 3 orders of magnitude over a direct ν scattering onto Earth's atmosphere. Therefore, it may better explain the extragalactic origin of the puzzling 320 EeV event, while offering indirect evidence of a hot dark Galactic halo of light neutrinos (i.e., mν~tens of eV), probably of τ flavor
Conjugate heat transfer from a discrete-source heated plate by offset jet impingement
No full textConvection/conduction simulations have been performed to determine flow and heat transfer phenomena in steady-state, for a plate carrying few embedded discrete heaters, exposed to by a turbulent offset cooling jet. This configuration is relevant, for example, in thermal design of vehicle body segments in aerodynamics conditions: when realized in certain alloys, their configuration will be determined based their discrete structural state prompted by supplied electrical heating. In order to approach an appropriate thermal design of the plate and obtain their precise state, the space of geometric and operating variables needs to be explored by a thorough parametric study based on the governing momentum and energy equations.
In this paper, the interaction between the impinging boundary layer and the conductive effects produced by such discrete heaters is explored, giving rise to a conjugate heat transfer situation. With a flexible notation for discretized heating and temperature-dependent conduction, dimensionless heat transfer is discussed spanning the entire range of design parameters. Results report considerable variation in heat transfer: as an example, air jet over polypropylene plates brings about peak Nusselt numbers between 2000 and 4000 for an inclined configuration at Re ≈ 1 × 106 based on nozzle width, with related strong temperature gradients that must be addressed during design, depending on discrete heaters’ configuration and properties; whereas for alumina plates the peak Nusselt numbers fall down between 600 and 750, featuring much smoother temperature variations and consequent more stable structural states
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