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51.
P. M.C. de Oliveira S. Moss de Oliveira D. Stauffer S. Cebrat A. Pękalski 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):245-254
We discovered a dynamic phase transition induced by sexual
reproduction. The dynamics is a pure Darwinian rule applied to diploid
bit-strings with both fundamental ingredients to drive Darwin's
evolution: (1) random mutations and crossings which act in the sense of
increasing the entropy (or diversity); and (2) selection which acts in
the opposite sense by limiting the entropy explosion. Selection wins
this competition if mutations performed at birth are few enough, and
thus the wild genotype dominates the steady-state population. By slowly
increasing the average number m of mutations, however, the
population suddenly undergoes a mutational degradation precisely at a
transition point mc. Above this point, the “bad”
alleles (represented by 1-bits) spread over the genetic pool of the
population, overcoming the selection pressure. Individuals become
selectively alike, and evolution stops. Only below this point, m < mc, evolutionary life is possible.
The finite-size-scaling behaviour of this transition is
exhibited for large enough “chromosome” lengths L, through
lengthy computer simulations. One important and surprising observation
is the L-independence of the transition curves, for large L.
They are also independent on the population size. Another is that mc is near unity, i.e. life cannot be stable with much more
than one mutation per diploid genome, independent of the chromosome
length, in agreement with reality. One possible consequence is that an
eventual evolutionary jump towards larger L enabling the storage
of more genetic information would demand an improved DNA copying
machinery in order to keep the same total number of mutations per
offspring. 相似文献
52.
Labiche M Orr NA Marqués FM Angélique JC Axelsson L Benoit B Bergmann UC Borge MJ Catford WN Chappell SP Clarke NM Costa G Curtis N D'Arrigo A de Góes Brennand E Dorvaux O Fazio G Freer M Fulton BR Giardina G Grévy S Guillemaud-Mueller D Hanappe F Heusch B Jones KL Jonson B Le Brun C Leenhardt S Lewitowicz M Lopez MJ Markenroth K Mueller AC Nilsson T Ninane A Nyman G de Oliveira F Piqueras I Riisager K Saint Laurent MG Sarazin F Singer SM Sorlin O Stuttgé L 《Physical review letters》2001,86(4):600-603
The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation. 相似文献
53.
Marcolan M Martins PA Pedrosa VA Rodrigues MR de Oliveira HP Codognoto L 《Journal of fluorescence》2011,21(2):733-738
A simple, rapid and effective analytical method based on fluorescence spectroscopy for the determination of coumarin in pharmaceutical
formulations without pre-treatment or pre-concentration step was development. Coumarin had maximum excitation and emission
at 310 nm and 390 nm, respectively. Optimum conditions for the detection of coumarin were investigated. Under optimized conditions,
we observed a linear behavior for the sign of coumarin in the concentration range of 2.5 × 10−6 to 1.0 × 10−4 mol L−1, with linearity of 0.998 and sensitivity of 2.9 × 1010 u.a/mol L−1. The proposed method was validated in terms of accuracy, precision and specificity of coumarin using the standard addition
and external calibration. It was noted that the results support (P < 0.05), indicating that the matrices were not an interference in the determination of coumarin by fluorescence spectroscopy.
The results were favorable compared with those obtained by reference chromatographic methods. 相似文献
54.
We investigated some physicochemical properties of an amorphous Se(90)P(10) alloy produced by mechanical alloying through x-ray diffraction, Raman spectroscopy, optical absorption spectroscopy and EXAFS techniques. The total structure factor obtained from x-ray diffraction and the EXAFS χ(k) oscillations on the Se K edge were used in reverse Monte Carlo simulations to obtain structural information such as average coordination numbers and interatomic distances and the distribution of structural units present in the alloy. In addition, we also determined the vibrational modes and the optical band gap energy of the alloy. 相似文献
55.
Some dynamical properties for a problem concerning the acceleration of particles in a wave packet are studied. The model is described in terms of a two-dimensional nonlinear map obtained from a Hamiltonian which describes the motion of a relativistic standard map. The phase space is mixed in the sense that there are regular and chaotic regions coexisting. When dissipation is introduced, the property of area preservation is broken and attractors emerge. We have shown that a tiny increase of the dissipation causes a change in the phase space. A chaotic attractor as well as its basin of attraction are destroyed thereby leading the system to experience a boundary crisis. We have characterized such a boundary crisis via a collision of the chaotic attractor with the stable manifold of a saddle fixed point. Once the chaotic attractor is destroyed, a chaotic transient described by a power law with exponent −1 is observed. 相似文献
56.
França EJ Andrade CG Furlaneto-Maia L Serpa R Oliveira MT Quesada RM Furlaneto MC 《Micron (Oxford, England : 1993)》2011,42(7):726-732
Candida tropicalis has been identified as one of the most prevalent pathogenic yeast species of the Candida-non-albicans (CNA) group. Study of switching in C. tropicalis has not been the subject of extensive research. Therefore, we investigated switching event and characterized the ultrastructural architecture of different phenotypes and biofilm produced in a C. tropicalis clinical strain. Cells switched heritably, reversibly, and at a high frequency between four phenotypes readily distinguishable by the shape of colonies formed on agar at 25°C. SEM analysis was used to verify the architecture of whole Candida colonies at ultrastructural level. The smooth phenotype (parental phenotype) colony showed a hemispherical shape character, while the semi-smooth was characterized by the presence of shallow marginal depressions. The ring and rough phenotypes exhibited more complex architecture and were characterized by the presence of deep central and peripheral depressions areas. The biofilm-forming ability varied among the switch phenotypes. After 12h incubation, the smooth phenotype formed less biofilm compared to the other phenotypes (P<0.05). The electron microscopy analysis revealed that filamentation (pseudohyphae) was associated with ring and rough colonies. The ultrastructural analysis allowed the observation of the arrangement of individual cells within the colonies. At the deep central and peripheral depressions areas of the ring and rough colonies extracellular material was seen in different arrangements. The data presented here open new avenues to study a possible role for extracellular material in the formation and maintenance of the architecture of switch phenotypes in C. tropicalis. It is therefore essential that more strains be investigated to determine the biological significance of extracellular material in C. tropicalis phenotypic switching phenomenon. 相似文献
57.
Some dynamical properties for a dissipative kicked rotator are studied. Our results show that when dissipation is taken into account a drastic change happens in the structure of the phase space in the sense that the mixed structure is modified and attracting fixed points and chaotic attractors are observed. A detailed numerical investigation in a two-dimensional parameter space based on the behavior of the Lyapunov exponent is considered. Our results show the existence of infinite self-similar shrimp-shaped structures corresponding to periodic attractors, embedded in a large region corresponding to the chaotic regime. 相似文献
58.
A. F.R. Rodriguez J. G. Santos L. B. Silveira A. C. Oliveira P. C. Morais O. A.C. Nunes 《The European physical journal. Special topics》2008,153(1):543-546
Photoacoustic spectroscopy (PAS) was used to investigate
samples produced from Baru (Dipteryx alata Vog.), a typical fruit from the Brazilian
Cerrado, which is considered as a good source of nutrients. The
photoacoustic (PA) spectra of samples prepared from Baru seeds present three
different absorption bands in the wavelength range 0.3–1.0 μm, named
Band-C, Band-S, and Band-L. We found that PAS can be useful for monitoring
the strong absorption of visible light by Baru's seeds constituents mainly
in the shorter wavelength measured range. This study is important from both
agricultural and commercial point of view once it introduces PAS as a
potential characterization technique allowing better control of fruit and
seed selection, storage and transportation. 相似文献
59.
Z. Barticevic M. Pacheco C. A. Duque L. E. Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(4):303-309
A theoretical study, within the effective-mass approximation, of the
effects of applied magnetic fields on excitons in disk-shaped
GaAs-Ga1-xAlxAs quantum dots is presented. Magnetic fields
are applied in the growth direction of the semiconductor
heterostructure. The parity of the excitonic envelope function
related to the simultaneous exchange of ze→-ze and
zh→-zh is a good quantum number and the wave
function, both the odd and even parity, can be expanded as
combination of products of the quantum well electron and hole
function that preserves the parity with appropriate Gaussian
functions. We have simultaneously obtained the energies of the
excitonic ground and excited states and discuss the behavior of
these energies as a function of the magnetic field. 相似文献
60.
We study the statistical properties of hourly wind speed time series detected at four weather stations in the state of Pernambuco, Brazil, in the period 2008-2009. We find that the average and maximum hourly wind speeds deviate from a mutual linear relationship, and that they may be well explained individually by a Weibull distribution, however, with different shape parameter values. On the other hand, the long-term correlations of both of these observables obey the same power-law behavior, with two distinct scaling regimes. Our results agree with previous studies on wind speed series correlations in other regions of the world, which is suggestive of universal behavior. 相似文献