6,570 research outputs found
Strong evidences for a nonextensive behavior of the rotation period in Open Clusters
Time-dependent nonextensivity in a stellar astrophysical scenario combines
nonextensive entropic indices derived from the modified Kawaler's
parametrization, and , obtained from rotational velocity distribution. These
's are related through a heuristic single relation given by , where is the cluster age. In a nonextensive
scenario, these indices are quantities that measure the degree of
nonextensivity present in the system. Recent studies reveal that the index
is correlated to the formation rate of high-energy tails present in the
distribution of rotation velocity. On the other hand, the index is
determined by the stellar rotation-age relationship. This depends on the
magnetic field configuration through the expression , where
and denote the saturation level of the star magnetic field and its
topology, respectively. In the present study, we show that the connection
is also consistent with 548 rotation period data for single
main-sequence stars in 11 Open Clusters aged less than 1 Gyr. The value of
2.5 from our unsaturated model shows that the mean magnetic field
topology of these stars is slightly more complex than a purely radial field.
Our results also suggest that stellar rotational braking behavior affects the
degree of anti-correlation between and cluster age . Finally, we suggest
that stellar magnetic braking can be scaled by the entropic index .Comment: 6 pages and 2 figures, accepted to EPL on October 17, 201
A nonextensive insight to the stellar initial mass function
the present paper, we propose that the stellar initial mass distributions as
known as IMF are best fitted by -Weibulls that emerge within nonextensive
statistical mechanics. As a result, we show that the Salpeter's slope of
2.35 is replaced when a -Weibull distribution is used. Our results
point out that the nonextensive entropic index represents a new approach
for understanding the process of the star-forming and evolution of massive
stars.Comment: 5 pages, 2 figures, Accepted to EP
Transesterification Reactions With Mg-0/i-2 For The Synthesis Of Sitophilate, (2r*, 3s*) 1-ethylpropyl-2-methyl-3-hydroxypentanoate, An Aggregation Pheromone For Sitophilus Granarius Linnaeus, 1785 (coleoptera: Curculionidae)
The concern to minimize the environmental impacts caused by the use of pesticides in agriculture has led researchers to develop new pest control methods. Thus, the technology based on the use of pheromones has been noted for being highly specific substances, that is act only on individuals of the same species. In this context, we describe the synthesis of sitophilate, aggregation pheromone of Sitophilus granarius, a important pest of stored cereal grains. The sitophilate was obtained by transesterification of methyl-2-methyl-3-oxopentanoate with 3-pentanol mediated by Mg-0/I-2, with subsequent reduction of the ketone group of 1-ethylpropyl-2-methyl-3-oxopentanoate using NaBH4 in the presence of a Lewis acid (ZnCl2, MgCl2, CaCl2 and MnCl2). The experimental results showed that the MnCl2 is the most effective for the formation of syn diastereoisomers, since these are the compounds that exert biological activity on the insect.32413014
Post-partum anoestrus in Anglo-Nubian and Saanen goats raised in semi-arid of North-eastern Brazil.
The aim of this study was to verify the length of post-partum anoestrus (PPA) in Anglo-Nubian and Saanen goats raised in North-eastern Brazi
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
“Read That Article”: Exploring synergies between gaze and speech interaction
Gaze information has the potential to benefit Human-Computer Interaction (HCI) tasks, particularly when combined with speech. Gaze can improve our understanding of the user intention, as a secondary input modality, or it can be used as the main input modality by users with some level of permanent or temporary impairments. In this paper we describe a multimodal HCI system prototype which supports speech, gaze and the combination of both. The system has been developed for Active Assisted Living scenarios.info:eu-repo/semantics/acceptedVersio
Copper and lead removal by peanut hulls: equilibrium and kinetic studies
This research work aims to study the use of peanut hulls, an agricultural and food industry waste, for copper
and lead removal through equilibrium and kinetic parameters evaluation. Equilibrium batch studies were performed
in a batch adsorber. The influence of initial pH was evaluated (3–5) and it was selected between 4.0
and 4.5. The maximum sorption capacities obtained for the Langmuir model were 0.21 ± 0.03 and 0.18 ± 0.02
mmol/g, respectively for copper and lead. In bi-component systems, competitive sorption of copper and lead
was verified, the total amount adsorbed being around 0.21 mmol of metal per gram of material in both mono
and bi-component systems. In the kinetic studies equilibrium was reached after 200 min contact time using a
400 rpm stirring rate, achieving 78% and 58% removal, in mono-component system, for copper and lead respectively.
Their removal follows a pseudo-second-order kinetics. These studies show that most of the metals removal
occurred in the first 20 min of contact, which shows a good uptake rate in all systems
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