2,523 research outputs found
Exact Solution of an Evolutionary Model without Ageing
We introduce an age-structured asexual population model containing all the
relevant features of evolutionary ageing theories. Beneficial as well as
deleterious mutations, heredity and arbitrary fecundity are present and managed
by natural selection. An exact solution without ageing is found. We show that
fertility is associated with generalized forms of the Fibonacci sequence, while
mutations and natural selection are merged into an integral equation which is
solved by Fourier series. Average survival probabilities and Malthusian growth
exponents are calculated indicating that the system may exhibit mutational
meltdown. The relevance of the model in the context of fissile reproduction
groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.
Molecular genetic evaluation of the Stylosanthes capitata Vog. and Stylosanthes macrocephala Ferr. et Costa germoplasms.
Effective Widths and Effective Number of Phonons of Multiphonon Giant Resonances
We discuss the origin of the difference between the harmonic value of the
width of the multiphonon giant resonances and the smaller observed value.
Analytical expressions are derived for both the effective width and the average
cross-section. The contribution of the Brink-Axel mechanism in resolving the
discrepancy is pointed out.Comment: 9 pages, 4 figure
Fermion Pairing Dynamics in the Relativistic Scalar Plasma
Using many-body techniques we obtain the time-dependent Gaussian
approximation for interacting fermion-scalar field models. This method is
applied to an uniform system of relativistic spin-1/2 fermion field coupled,
through a Yukawa term, to a scalar field in 3+1 dimensions, the so-called
quantum scalar plasma model. The renormalization for the resulting Gaussian
mean-field equations, both static and dynamical, are examined and initial
conditions discussed. We also investigate solutions for the gap equation and
show that the energy density has a single minimum.Comment: 21 pages, latex, 4 postscript figures, new sections, some literary
changes, notation corrections, accepted for publication in Phys. Rev
Breeding specialty soybean cultivars for processing and value-added utilization at Embrapa in Brazil.
Through traditional genetic breeding, specialty characters are introduced into soybean, to make it more suitable for differents uses. To attend this special market, Embrapa Soybean released for commercial cultivation the cultivars BRS 213, BRS 257, BRS 216, BRS 267 and BRSMG 790A for production in organic or in conventional systems. The cultivars BRS 213 and BRS 257 are null lipoxygenases enzymes, and can prevent the development of the beany flavor observed in soybean products. These cultivars make available excellent raw materials for soyfood processing. The cultivar BRS 216 has high protein content and small seed size (10g/100 seeds), what makes it suitable for ?natto? (Japanese fermented food), and for production of soybean sprouts, as ?moyashi?. The cultivar BRS 258, is a conventional cultivar, highly productive that has mild flavor and seeds with yellow hilum. Cultivars BRS 267 and BRSMG 790A presents large seed size (>25g/100seeds), and superior flavor. These cultivars are suitable for ?tofu?, flours and soymilk. BRS 267 and BRSMG 790A can also be consumed as green vegetable soybean (edamame), when harvested at R6 stage (developed grains, but immature). Among Brazilian soybean cultivars there are differences for isoflavone content, and to increase concentration of isoflavones it is suggested sowing them in locations where average temperatures are cooler during the seed filling period
Nonlinear Enhancement of the Multiphonon Coulomb Excitation in Relativistic Heavy Ion Collisions
We propose a soluble model to incorporate the nonlinear effects in the
transition probabilities of the multiphonon Giant Dipole Resonances based on
the SU(1,1) algebra. Analytical expressions for the multi-phonon transition
probabilities are derived. Enhancement of the Double Giant Resonance excitation
probabilities in relativistic ion collisions scales as for
the degree of nonlinearity and is able to reach values
compatible with experimental data. The enhancement factor is found to decrease
with increasing bombarding energy. [KEYWORDS: Relativistic Heavy Ion
Collisions,Double Giant Resonance]Comment: 12 pages, 2 figure
Noether Symmetry Approach in "Cosmic Triad" Vector Field Scenario
To realize the accelerations in the early and late periods of our universe,
we need to specify potentials for the dominant fields. In this paper, by using
the Noether symmetry approach, we try to find suitable potentials in the
"cosmic triad" vector field scenario. Because the equation of state parameter
of dark energy has been constrained in the range of by observations, we derive the Noether conditions for the vector field
in quintessence, phantom and quintom models, respectively. In the first two
cases, constant potential solutions have been obtained. What is more, a fast
decaying point-like solution with power-law potential is also found for the
vector field in quintessence model. For the quintom case, we find an
interesting constraint on the field potentials,
where and are constants related to the Noether symmetry.Comment: 15 pages, no figures, accepted by Classical and Quantum Gravity
Theory of Multiphonon Excitation in Heavy-Ion Collisions
We study the effects of channel coupling in the excitation dynamics of giant
resonances in relativistic heavy ions collisions. For this purpose, we use a
semiclassical approximation to the Coupled-Channels problem and separate the
Coulomb and the nuclear parts of the coupling into their main multipole
components. In order to assess the importance of multi-step processes, we
neglect the resonance widths and solve the set of coupled equations exactly.
Finite widths are then considered. In this case, we handle the coupling of the
ground state with the dominant Giant Dipole Resonance exactly and study the
excitation of the remaining resonances within the Coupled-Channels Born
Approximation. A comparison with recent experimental data is made.Comment: 29 pages, 7 Postscript figures available upon reques
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