897 research outputs found
Modified Gravitational Waves Across Galaxies from Macroscopic Gravity
We analyze the propagation of gravitational waves in a medium containing
bounded subsystems ("molecules"), able to induce significant Macroscopic
Gravity effects. We establish a precise constitutive relation between the
average quadrupole and the amplitudes of a vacuum gravitational wave, via the
geodesic deviation equation. Then we determine the modified equation for the
wave inside the medium and the associated dispersion relation. A
phenomenological analysis shows that anomalous polarizations of the wave emerge
with an appreciable experimental detectability if the medium is identified with
a typical galaxy. Both the modified dispersion relation (wave velocity less
than the speed of light) and anomalous oscillations modes could be detectable
by the incoming LISA or pulsar timing arrays experiments, having the
appropriate size to see the concerned wavelengths (larger than the molecular
size) and the appropriate sensitivity to detect the expected deviation from
vacuum General Relativity.Comment: 10 pages, comments are welcom
Optimally chosen small portfolios are better than large ones
One of the fundamental principles in portfolio selection models is minimization of risk through diversification of the investment. However, this principle does not necessarily translate into a request for investing in all the assets of the investment universe. Indeed, following a line of research started by Evans and Archer almost fifty years ago, we provide here further evidence that small portfolios are sufficient to achieve almost optimal in-sample risk reduction with respect to variance and to some other popular risk measures, and very good out-of-sample performances. While leading to similar results, our approach is significantly different from the classical one pioneered by Evans and Archer. Indeed, we describe models for choosing the portfolio of a prescribed size with the smallest possible risk, as opposed to the random portfolio choice investigated in most of the previous works. We find that the smallest risk portfolios generally require no more than 15 assets. Furthermore, it is almost always possible to find portfolios that are just 1% more risky than the smallest risk portfolios and contain no more than 10 assets. Furthermore, the optimal small portfolios generally show a better performance than the optimal large ones. Our empirical analysis is based on some new and on some publicly available benchmark data sets often used in the literature
Low Complexity WMMSE Power Allocation In NOMA-FD Systems
In this paper we study the problem of power and channel allocation with the
objective of maximizing the system sum-rate for multicarrier non-orthogonal
multiple access (NOMA) full duplex (FD) systems. Such an allocation problem is
non-convex and, thus, with the goal of designing a low complexity solution, we
propose a scheme based on the minimization of the weighted mean square error,
which achieves performance reasonably close to the optimum and allows to
clearly outperforms a conventional orthogonal multiple access approach.
Numerical results assess the effectiveness of our algorithm.Comment: 5 pages conference paper, 3 figures. Submitted on ICASSP 202
Higgs Boson Production in Association with a Photon in Vector Boson Fusion at the LHC
Higgs boson production in association with two forward jets and a central
photon at the CERN Large Hadron Collider is analyzed, for the Higgs boson
decaying into a b bbar pair in the m_H <= 140 GeV mass region. We study both
irreducible and main reducible backgrounds at parton level. Compared to the
Higgs production via vector-boson fusion, the request of a further photon at
moderate rapidities dramatically enhances the signal/background ratio.
Inclusive cross sections for p_T^\gamma >= 20 GeV can reach a few tens of fb's.
After a suitable choice of kinematical cuts, the cross-section ratio for signal
and irreducible-background can be enhanced up to >= ~1/10, with a signal cross
section of the order of a few fb's, for m_H ~ 120 GeV. The request of a central
photon radiation also enhances the relative signal sensitivity to the WWH
coupling with respect to the ZZH coupling. Hence, a determination of the cross
section for the associated production of a Higgs boson decaying into a b bbar
pair plus a central photon in vector-boson fusion could help in constraining
the b bbar H coupling, and the WWH coupling as well. A preliminary study of QCD
showering effects points to a further significant improvement of the signal
detectability over the background.Comment: 30 pages, 8 figures, 8 tables; minor corrections to the text; version
appeared in Nuclear Physics
Mapping interactions between geology, subsurface resource exploitation and urban development in transforming cities using InSAR Persistent Scatterers: two decades of change in Florence, Italy
Urban expansion and city transformation are increasing reality across the world. Now more than ever it is essential to understand and map at the appropriate scale the processes happening along the verticality and horizontality of cities, to gather robust evidence underpinning strategies for sustainable management of the built environment. This paper explores how established techniques of Persistent Scatterer Interferometry (PSI) can be shaped into a novel dedicated procedure to detect vertical and horizontal urban dynamics including: use and re-use of urban space (new building construction, intentional demolition, renovation projects); exploitation of groundwater resources (induced land subsidence); interactions between new foundations, superficial deposits and bedrock geology (settlement of recent buildings); ground and slope instability affecting settled buildings; susceptibility of heritage assets to structural damages; baseline characterisation prior to planned major infrastructure construction (tunnelling and transportation networks). Florence, central Italy, is used as a demonstration site. This city includes UNESCO World Heritage List historic centre, 20th-century residential, industrial and peri-urban quarters, and is currently in transition to metropolitan area of over 1 million of inhabitants. Velocity decomposition maps were generated based on millimetre-precise estimates of surface displacements retrieved from PSI processing of the full archives of satellite C-band radar images, including 79 ERS-1/2 descending (1992–2000), 70 ENVISAT ASAR ascending and descending (2003–2010) and 101 RADARSAT-1 ascending and descending (2003–2007). 12 macropatterns and 84 micropatterns in the final map of alert areas highlight a dualism which reflects the physical and urban geography of Florence. North-western and south-western quarters show hot spots of new building construction and regeneration projects for residential, business and tertiary service purposes, alongside issues due to groundwater exploitation and induced land subsidence up to 30–40 mm/yr. Local interactions with underlying geology and natural slope instability processes predominate in the southern and north-eastern sectors. At local scale, stable condition was found for the heritage assets and buildings located along the tracks of the planned subway railway and tramway, with motion rates averagely within ±1.5 mm/yr and localised deformation only up to −3.5 mm/yr. Structural assessment based on future PSI monitoring campaign will benefit of this baseline characterisation
A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment
A detailed characterization of the particle induced background is fundamental
for many of the scientific objectives of the Athena X-ray telescope, thus an
adequate knowledge of the background that will be encountered by Athena is
desirable. Current X-ray telescopes have shown that the intensity of the
particle induced background can be highly variable. Different regions of the
magnetosphere can have very different environmental conditions, which can, in
principle, differently affect the particle induced background detected by the
instruments. We present results concerning the influence of the magnetospheric
environment on the background detected by EPIC instrument onboard XMM-Newton
through the estimate of the variation of the in-Field-of-View background excess
along the XMM-Newton orbit. An important contribution to the XMM background,
which may affect the Athena background as well, comes from soft proton flares.
Along with the flaring component a low-intensity component is also present. We
find that both show modest variations in the different magnetozones and that
the soft proton component shows a strong trend with the distance from Earth.Comment: To appear in Experimental Astronomy. Presented at AHEAD Background
Workshop, 28-30 November 2016. Rome, Ital
Smartphone e tablet: il ruolo delle nuove tecnologie per il GIS nel piano di ricostruzione del Comune di Arsita (TE)
Le nuove tecnologie digitali stanno cambiando il nostro modo di pensare e agire e il loro uso sta rivoluzionando interi settori. Se fino ad oggi il personal computer è stato l’attore principale della rivoluzione digitale, ora i nuovi smartphone, tablet e smartwatch sono e saranno i motori di una profonda trasformazione della nostra vita. Questi nuovi strumenti, semplici e leggeri sono straordinari nel lavoro quotidiano. Trovarsi nel luogo di studio direttamente con un tablet e/o uno smartphone con software sviluppati ad hoc, seguendo un preciso metodo di lavoro messo a punto in precedenza ha permesso di ottimizzare i tempi e ridurre in maniera rilevante gli errori fornendo risposte molto più accurate e veloci
A Systematic Analysis of the XMM-Newton Background: I. Dataset and Extraction Procedures
XMM-Newton is the direct precursor of the future ESA ATHENA mission. A study
of its particle-induced background provides therefore significant insight for
the ATHENA mission design. We make use of about 12 years of data, products from
the third XMM-Newton catalog as well as FP7 EXTraS project to avoid celestial
sources contamination and to disentangle the different components of the
XMM-Newton particle-induced background. Within the ESA R&D AREMBES
collaboration, we built new analysis pipelines to study the different
components of this background: this covers time behavior as well as spectral
and spatial characteristics.Comment: To appear in Experimental Astronomy, presented at AHEAD Background
Workshop, 28-30 November 2016, Rome, Italy. 12 pages, 6 figure
Modifiable risk factors associated with bronchiolitis
Background: We sought to clarify possibly modifiable risk factors related to pollution responsible for acute bronchiolitis in hospitalized infants. Methods: For this observational study, we recruited 213 consecutive infants with bronchiolitis (cases: median age: 2 months; age range: 0.5-12 months; boys: 55.4%) and 213 children aged <3 years (controls: median age: 12 months; age range: 0.5-36 months; boys: 54.5%) with a negative medical history for lower respiratory tract diseases hospitalized at 'Sapienza' University Rome and IRCCS Bambino Gesù Hospital. Infants' parents completed a standardized 53-item questionnaire seeking information on social-demographic and clinical characteristics, indoor pollution, eating habits and outdoor air pollution. Multivariate logistic regression analyses were run to assess the independent effect of risk factors, accounting for confounders and effect modifiers. Results: In the 213 hospitalized infants the questionnaire identified the following risk factors for acute bronchiolitis: breastfeeding 3/43 months (OR: 2.1, 95% confidence interval [CI]: 1.2-3.6), presence of older siblings (OR: 2.8, 95% CI: 1.7-4.7), 3/44 cohabitants (OR: 1.5, 95% CI: 1.1-2.1), and using seed oil for cooking (OR: 1.7, 95% CI: 1.2-2.6). Having renovated their home in the past 12 months and concurrently being exposed daily to smoking, involving more than 11 cigarettes and two or more smoking cohabitants, were more frequent factors in cases than in controls (p = 0.021 and 0.05), whereas self-estimated proximity to road and traffic was similar in the two groups. Conclusions: We identified several risk factors for acute bronchiolitis related to indoor and outdoor pollution, including inhaling cooking oil fumes. Having this information would help public health authorities draw up effective preventive measures - for example, teach mothers to avoid handling their child when they have a cold and eliminate exposure to second-hand tobacco smoke
Cyclopentenyl ethylamines active on CNS
Two new cyclopentenylethylamines were prepared and were submitted to a pharmacological screening together with some others previously described and now reprepared. All compounds exhibited different degrees of depressive activity on CNS and good analgesic activity. Compound 5, bearing a phenyl group on the carbon atom to which the amino group is connected, appears rather interesting being the most active as analgesic and the least toxic. Compounds 2 and 3 are able to antagonize in a certain degree lethal doses of physostigmine and also, respectively, of pentylenetetrazole and strychnine
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