5,530 research outputs found
The compound Poisson limit ruling periodic extreme behaviour of non-uniformly hyperbolic dynamics
We prove that the distributional limit of the normalised number of returns to
small neighbourhoods of periodic points of non-uniformly hyperbolic dynamical
systems is compound Poisson. The returns to small balls around a fixed point in
the phase space correspond to the occurrence of rare events, or exceedances of
high thresholds, so that there is a connection between the laws of Return Times
Statistics and Extreme Value Laws. The fact that the fixed point in the phase
space is a repelling periodic point implies that there is a tendency for the
exceedances to appear in clusters whose average sizes is given by the Extremal
Index, which depends on the expansion of the system at the periodic point.
We recall that for generic points, the exceedances, in the limit, are
singular and occur at Poisson times. However, around periodic points, the
picture is different: the respective point processes of exceedances converge to
a compound Poisson process, so instead of single exceedances, we have entire
clusters of exceedances occurring at Poisson times with a geometric
distribution ruling its multiplicity.
The systems to which our results apply include: general piecewise expanding
maps of the interval (Rychlik maps), maps with indifferent fixed points
(Manneville-Pomeau maps) and Benedicks-Carleson quadratic maps.Comment: To appear in Communications in Mathematical Physic
Aspectos fitossociológicos e manejo de plantas espontâneas utilizando espécies de cobertura em cafeeiro Conilon orgânico.
Nitrogen oxides measurements in an Amazon site and enhancements associated with a cold front
International audienceAn intensive atmospheric chemistry study was carried out in a pristine Amazonian forest site (Balbina), Amazonas state, Brazil during the 2001 wet season, as part of the LBA/CLAIRE 2001 (The Large Scale Biosphere Atmosphere Experiment in Amazonia/Cooperative LBA Airborne Regional Experiment) field campaign. Measurements of nitrogen oxide (NO), nitrogen dioxide (NO2) and ozone (O3) were performed simultaneously with aerosol particles and black carbon concentrations and meteorological parameters observations. Very low trace gases and aerosol concentrations are typically observed at this pristine tropical site. During the measurement period, there was a three-day episode of enhancement of NO2 and black carbon concentration. NO2 concentration reached a maximum value of 4 ppbv, which corresponds to three times the background concentration observed for this site. Black carbon concentration increased from the approximated 100 ng/m3 average value to a 200 ng/m3 maximum during the same period. Biomass burning spots were detected southward, between latitudes 15 to 10° S, 5?6 days before this episode from GOES-8 WF_ABBA (Wildfire Automated Biomass Burning Algorithm). An atmospheric numerical simulation of the whole measurement period was carried out using the RAMS model coupled to a biomass burning emission and transport model. The simulation results pictured a smoke transport event from Central Brazil associated to an approach of a mid-latitude cold front, reinforcing the hypothesis of biomass burning products being long-range transported from the South by the cold front and crossing the Equator. This transport event shows how the pristine atmosphere pattern in Amazonia is impacted by biomass burning emissions from sites very far away
Development of weft-knitted and braided polypropylene stents for arterial implant
Textile biomedical materials have been used for various applications contributing considerably in improving quality
of life. The current study aims at improving polypropylene fibre stents which may replace metallic ones. In order to
produce the stents, weft-knitting and braiding technologies were used. In the braiding technique, by varying the takeup
ratio (using gears with the appropriate number of teeth in the braiding machine), it was possible to manufacture
regular braids with angles of 65
°
, 70
°
and 75
°
in order to obtain different covers. In the knitting technique, a circular
machine was used and the tightness of the structure was adjusted by varying the loop length and thus the fabric loop
density, resulting in variations of the sample diameter. The knitting machine had negative feed, and so loop length
variations were achieved by varying the yarn input tension, the stitch cam settings and the fabric take-down tension.
The samples were heat set. Yarns were contracted by setting at 130
°
C and 140
°
C, and this led to increasing the loop
density and the flexural rigidity of the samples. A high cover of the samples resulted in a greater stiffness of the
structures. The stents were evaluated by undertaking the tests required for arterial support: rigidity to radial
compression, resistance to tensile forces and bending rigidity. The best results were obtained with braided structures.
Future work may concentrate in improving the stent design and using new biocompatible fibres.The authors wish to thank the European Commission for awarding research funds under the EU Asia-link programme and the University of Minho (Portugal) and Donghua University (People's Republic of China) for providing research facilities
Deep learnig analysis of the inverse seesaw in a 3-3-1 model at the LHC
Inverse seesaw is a genuine TeV scale seesaw mechanism. In it active
neutrinos with masses at eV scale requires lepton number be explicitly violated
at keV scale and the existence of new physics, in the form of heavy neutrinos,
at TeV scale. Therefore it is a phenomenologically viable seesaw mechanism
since its signature may be probed at the LHC. Moreover it is successfully
embedded into gauge extensions of the standard model as the 3-3-1 model with
the right-handed neutrinos. In this work we revisit the implementation of this
mechanism into the 3-3-1 model and employ deep learning analysis to probe such
setting at the LHC and, as main result, we have that if its signature is not
detected in the next LHC running with energy of 14 TeVs, then, the vector boson
of the 3-3-1 model must be heavier than 4 TeVs
Uncovered diversity of a predominantly Andean butterfly clade in the Brazilian Atlantic Forest : a revision of the genus Praepedaliodes Forster (Lepidoptera : Nymphalidae, Satyrinae, Satyrini)
- …