12,541 research outputs found
Recent astrophysical observations reproduced by a short-range correlated van der Waals-type model?
We perform an improvement in a van der Waals-type model by including it
effects of short-range correlations (SRC). Attractive and repulsive parts of
the nucleon-nucleon interaction are assumed to be density-dependent functions,
more specifically, we adopt the Carnahan-Starling (CS) method for the latter,
and a suitable expression for the former in order to reproduce the structure of
the Clausius (C) real gas model. The parametrizations of the resulting model,
named as CCS-SRC model, are shown to be capable of reproducing the flow
constraint at the high-density regime of symmetric nuclear matter for
incompressibility values inside the range of MeV. In the
context of stellar matter, our findings point out a good agreement of the
CCS-SRC model with recent astrophysical observational data, namely, mass-radius
contours and dimensionless tidal deformability regions and values, coming from
gravitational waves data related to the GW170817 and GW190425 events, and from
the NASA's Neutron star Interior Composition Explorer (NICER) mission.
Furthermore, the values for the symmetry energy slope of the model () are
in agreement with a recent range found for this quantity, claimed to be
consistent with results reported by the updated lead radius experiment (PREX-2)
collaboration. In this case, higher values of are favored, while the
opposite scenario does not allow simultaneous compatibility between the model
and the astrophysical data.Comment: 9 pages, 11 figure
Generalization of Dirac Non-Linear Electrodynamics, and Spinning Charged Particles
In this note we generalized the Dirac non-linear electrodynamics, by
introducing two potentials (namely, the vector potential A and the
pseudo-vector potential gamma^5 B of the electromagnetic theory with charges
and magnetic monopoles) and by imposing the pseudoscalar part of the product
omega.omega* to be zero, with omega = A + gamma^5 B. We show that the field
equations of such a theory possess a soliton-like solution which can represent
a priori a "charged particle", since it is endowed with a Coulomb field plus
the field of a magnetic dipole. The rest energy of the soliton is finite, and
the angular momentum stored in its electromagnetic field can be identified
--for suitable choices of the parameters-- with the spin of the charged
particle. Thus this approach seems to yield a classical model for the charged
(spinning) particle, which does not meet the problems met by earlier attempts
in the same direction.Comment: standard LaTeX file; 16 pages; it is a corrected version of a paper
appeared in Found. Phys. (issue in honour of A.O.Barut) 23 (1993) 46
A systematic comparison of supervised classifiers
Pattern recognition techniques have been employed in a myriad of industrial,
medical, commercial and academic applications. To tackle such a diversity of
data, many techniques have been devised. However, despite the long tradition of
pattern recognition research, there is no technique that yields the best
classification in all scenarios. Therefore, the consideration of as many as
possible techniques presents itself as an fundamental practice in applications
aiming at high accuracy. Typical works comparing methods either emphasize the
performance of a given algorithm in validation tests or systematically compare
various algorithms, assuming that the practical use of these methods is done by
experts. In many occasions, however, researchers have to deal with their
practical classification tasks without an in-depth knowledge about the
underlying mechanisms behind parameters. Actually, the adequate choice of
classifiers and parameters alike in such practical circumstances constitutes a
long-standing problem and is the subject of the current paper. We carried out a
study on the performance of nine well-known classifiers implemented by the Weka
framework and compared the dependence of the accuracy with their configuration
parameter configurations. The analysis of performance with default parameters
revealed that the k-nearest neighbors method exceeds by a large margin the
other methods when high dimensional datasets are considered. When other
configuration of parameters were allowed, we found that it is possible to
improve the quality of SVM in more than 20% even if parameters are set
randomly. Taken together, the investigation conducted in this paper suggests
that, apart from the SVM implementation, Weka's default configuration of
parameters provides an performance close the one achieved with the optimal
configuration
Consequências fisiológicas da secagem sobre a viabilidade em sementes de muruci.
A porcentagem de germinação das sementes de muruci é normalmente baixa, e a emergência das plântulas é lenta e desuniforme. Este trabalho teve como objetivo verificar as conseqüências fisiológicas da secagem dos pirênios sobre a viabilidade de sementes de muruci. Foram utilizados frutos de muruci do clone Igarapé Açu. Antes da secagem foi retirado amostra para as determinações de teor de água e para os testes de germinação. Os demais pirênios foram submetidos à secagem lenta, durante 24, 48 e 240 horas. Antes e após cada período de secagem foi determinado o teor de água dos pirênios e feito o teste de germinação. Ao final do teste foi considerada a porcentagem de plântulas normais e o tempo médio de germinação. Após o término do teste de germinação foi realizado o teste do tetrazólio com embrião exposto, para identificar as estruturas das sementes. Foi utilizado o delineamento inteiramente casualizado, com quatro tratamentos e três repetições de 50 sementes cada. Verificou-se que os pirênios não submetidos à secagem apresentaram 40% de sementes dormentes. A secagem parcial dos pirênios propiciou redução no número de sementes dormentes. Após a secagem por 240 horas, foi possível obter 94% de emergência. A secagem parcial dos pirênios tem efeito positivo sobre a viabilidade de sementes de muruci, resultando no aumento da emergência de plântulas e redução no tempo médio de germinação.PIBIC-2011
Impacto de espécies de inverno no rendimento de grãos de culturas de verão e de trigo no inverno subseqüente.
bitstream/CNPT-2010/40292/1/p-bp19.pd
Utilização do leite mamitico na alimentação de bezerras leiteiras.
Avaliar a viabilidade da utilização do leite produzido por tetas com mamite subclinica, tratadas com antibiótico na alimentação de bezerras leiteiras
- …