1,454 research outputs found
ANALYSIS OF THE TRADITIONAL PASSIVE SYSTEMS PERFORMANCE THROUGH THE APPLICATION OF CFD SOFTWARE
The need to reduce energy consumption is pushing the building design research to the evaluation of passive conditioning systems, since urban buildings are one of the major energy dissipater resulting in emission of CO2. This approach is not modern, but it is historically rooted in the architectural culture of the Mediterranean area and in the Middle East. The passive systems have ancient origins: they were developed to mitigate the summer heat and the winter cold. To understand the reasons that led to the development of passive systems, it should be remembered that about One-Fifth of the emerged planet surface and One-Third of the world's population live in conditions of warm-dry or hot-humid. In addition, most continental areas, even above high values of latitude (50\ub0), are characterized by climatic conditions with summer temperatures over the limit levels of comfort. Nowadays the scientific knowledge and the modern technologies allow to understand the working of passive systems in order to apply them on buildings to improve indoor comfort. This can be obtained through a new approach that involves the elaboration of design strategies based on the development of techniques and on computational and control tools. This work will show the results of a research that aims to verify the working of natural passive cooling systems employed in existing ancient buildings throughout CFD (Computational Fluid Dynamic) software application. Particularly we will define, through computational tools, models and study cases to compare and to set proposals able to actualize the original passive systems conceived and developed in an empirical way
New stability results for Einstein scalar gravity
We consider asymptotically anti de Sitter gravity coupled to a scalar field
with mass slightly above the Breitenlohner-Freedman bound. This theory admits a
large class of consistent boundary conditions characterized by an arbitrary
function . An important open question is to determine which admit stable
ground states. It has previously been shown that the total energy is bounded
from below if is bounded from below and the bulk scalar potential
admits a suitable superpotential. We extend this result and show that the
energy remains bounded even in some cases where can become arbitrarily
negative. As one application, this leads to the possibility that in
gauge/gravity duality, one can add a double trace operator with negative
coefficient to the dual field theory and still have a stable vacuum
Scalar-mediated forward-backward asymmetry
A large forward-backward asymmetry in production, for large
invariant mass of the system, has been recently observed by the CDF
collaboration. Among the scalar mediated mechanisms that can explain such a
large asymmetry, only the t-channel exchange of a color-singlet weak-doublet
scalar is consistent with both differential and integrated cross
section measurements. Constraints from flavor changing processes dictate a very
specific structure for the Yukawa couplings of such a new scalar. No sizable
deviation in the differential or integrated production cross section
is expected at the LHC.Comment: 22 pages, 1 figure and 2 tables. v2: Corrected Eqs.(50,51,74),
adapted Fig.1, Tab.1 and relevant discussions. Extended discussion of top
decay and single to
Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj
We present U(1) flavor models for leptophobic Z' with flavor dependent
couplings to the right-handed up-type quarks in the Standard Model, which can
accommodate the recent data on the top forward-backward (FB) asymmetry and the
dijet resonance associated with a W boson reported by CDF Collaboration. Such
flavor-dependent leptophobic charge assignments generally require extra chiral
fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor
symmetry calls for new U(1)'-charged Higgs doublets in order for the SM
fermions to have realistic renormalizable Yukawa couplings. The stringent
constraints from the top FB asymmetry at the Tevatron and the same sign top
pair production at the LHC can be evaded due to contributions of the extra
Higgs doublets. We also show that the extension could realize cold dark matter
candidates.Comment: 40 pages, 10 figures, added 1 figure and extended discussion,
accepted for publication in JHE
Temporal Structures in Positron Spectra and Charge-Sign Effects in Galactic Cosmic Rays
We present the precision measurements of 11 years of daily cosmic positron fluxes in the rigidity range from 1.00 to 41.9 GV based on 3.4 Ă106 positrons collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The positron fluxes show distinctly different time variations from the electron fluxes at short and long timescales. A hysteresis between the electron fluxes and the positron fluxes is observed with a significance greater than 5 Ï at rigidities below 8.5 GV. On the contrary, the positron fluxes and the proton fluxes show similar time variation. Remarkably, we found that positron fluxes are modulated more than proton fluxes with a significance greater than 5 Ï for rigidities below 7 GV. These continuous daily positron fluxes, together with AMS daily electron, proton, and helium fluxes over an 11-year solar cycle, provide unique input to the understanding of both the charge-sign and mass dependencies of cosmic rays in the heliosphere
Periodicities in the Daily Proton Fluxes from 2011 to 2019 Measured by the Alpha Magnetic Spectrometer on the International Space Station from 1 to 100 GV
We present the precision measurement of the daily proton fluxes in cosmic rays from May 20, 2011 to October 29, 2019 (a total of 2824 days or 114 Bartels rotations) in the rigidity interval from 1 to 100 GV based on 5.5 Ă109 protons collected with the Alpha Magnetic Spectrometer aboard the International Space Station. The proton fluxes exhibit variations on multiple timescales. From 2014 to 2018, we observed recurrent flux variations with a period of 27 days. Shorter periods of 9 days and 13.5 days are observed in 2016. The strength of all three periodicities changes with time and rigidity. The rigidity dependence of the 27-day periodicity is different from the rigidity dependences of 9-day and 13.5-day periods. Unexpectedly, the strength of 9-day and 13.5-day periodicities increases with increasing rigidities up to âŒ10 GV and âŒ20 GV , respectively. Then the strength of the periodicities decreases with increasing rigidity up to 100 GV
Enhanced warming over the global subtropical western boundary currents
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Climate Change 2 (2012): 161-166, doi:10.1038/nclimate1353.Subtropical western boundary currents are warm, fast flowing currents that
form on the western side of ocean basins. They carry warm tropical water to the
mid-latitudes and vent large amounts of heat and moisture to the atmosphere
along their paths, affecting atmospheric jet streams and mid-latitude storms, as
well as ocean carbon uptake. The possibility that these highly energetic and
nonlinear currents might change under greenhouse gas forcing has raised
significant concerns, but detecting such changes is challenging owing to limited
observations. Here, using reconstructed sea surface temperature datasets and
newly developed century-long ocean and atmosphere reanalysis products, we
find that the post-1900 surface ocean warming rate over the path of these
currents is two to three times faster than the global mean surface ocean warming
rate. The accelerated warming is associated with a synchronous poleward shift
and/or intensification of global subtropical western boundary currents in
conjunction with a systematic change in winds over both hemispheres. This enhanced warming may reduce ocean's ability to absorb anthropogenic carbon
dioxide over these regions. However, uncertainties in detection and attribution of
these warming trends remain, pointing to a need for a long-term monitoring
network of the global western boundary currents and their extensions.This work is supported by China National Key Basic Research Project
(2007CB411800) and National Natural Science Foundation Projects (40788002,
40921004). WC is supported by the Australian Climate Change Science program and
the Southeast Australia Climate Initiative. HN is supported in part by the Japanese
Ministry of Education, Culture, Sports, Science and Technology through Grant-in-Aid
for Scientific Research on Innovative Areas #2205 and by the Japanese Ministry of
Environment through Global Environment Research Fund (S-5). MJM is supported by
NOAAâs Climate Program Office.2012-07-2
Measurement of the muon decay spectrum with the ICARUS liquid Argon TPC
Examples are given which prove the ICARUS detector quality through relevant
physics measurements. We study the muon decay energy spectrum from a sample of
stopping muon events acquired during the test run of the ICARUS T600 detector.
This detector allows the spatial reconstruction of the events with fine
granularity, hence, the precise measurement of the range and dE/dx of the muon
with high sampling rate. This information is used to compute the calibration
factors needed for the full calorimetric reconstruction of the events. The
Michel rho parameter is then measured by comparison of the experimental and
Monte Carlo simulated muon decay spectra, obtaining rho = 0.72 +/- 0.06(stat.)
+/- 0.08(syst.). The energy resolution for electrons below ~50 MeV is finally
extracted from the simulated sample, obtaining (Emeas-Emc)/Emc =
11%/sqrt(E[MeV]) + 2%.Comment: 16 pages, 8 figures, LaTex, A4. Some text and 1 figure added. Final
version as accepted for publication in The European Physical Journal
Status and Recent Results of the Acoustic Neutrino Detection Test System AMADEUS
The AMADEUS system is an integral part of the ANTARES neutrino telescope in
the Mediterranean Sea. The project aims at the investigation of techniques for
acoustic neutrino detection in the deep sea. Installed at a depth of more than
2000m, the acoustic sensors of AMADEUS are based on piezo-ceramics elements for
the broad-band recording of signals with frequencies ranging up to 125kHz.
AMADEUS was completed in May 2008 and comprises six "acoustic clusters", each
one holding six acoustic sensors that are arranged at distances of roughly 1m
from each other. The clusters are installed with inter-spacings ranging from
15m to 340m. Acoustic data are continuously acquired and processed at a
computer cluster where online filter algorithms are applied to select a
high-purity sample of neutrino-like signals. 1.6 TB of data were recorded in
2008 and 3.2 TB in 2009. In order to assess the background of neutrino-like
signals in the deep sea, the characteristics of ambient noise and transient
signals have been investigated. In this article, the AMADEUS system will be
described and recent results will be presented.Comment: 7 pages, 8 figures. Proceedings of ARENA 2010, the 4th International
Workshop on Acoustic and Radio EeV Neutrino Detection Activitie
Recommended from our members
Equator-to-pole temperature differences and the extra-tropical storm track responses of the CMIP5 climate models
This paper aims to understand the physical processes causing the large spread in the storm track projections of the CMIP5 climate models. In particular, the relationship between the climate change responses of the storm tracks, as measured by the 2â6 day mean sea level pressure variance, and the equator-to-pole temperature differences at upper- and lower-tropospheric levels is investigated. In the southern hemisphere the responses of the upper- and lower-tropospheric temperature differences are correlated across the models and as a result they share similar associations with the storm track responses. There are large regions in which the storm track responses are correlated with the temperature difference responses, and a simple linear regression model based on the temperature differences at either level captures the spatial pattern of the mean storm track response as well explaining between 30 and 60 % of the inter-model variance of the storm track responses. In the northern hemisphere the responses of the two temperature differences are not significantly correlated and their associations with the storm track responses are more complicated. In summer, the responses of the lower-tropospheric temperature differences dominate the inter-model spread of the storm track responses. In winter, the responses of the upper- and lower-temperature differences both play a role. The results suggest that there is potential to reduce the spread in storm track responses by constraining the relative magnitudes of the warming in the tropical and polar regions
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