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121.
E.?BrigattiEmail author J.?S.?Sá Martins I.?Roditi 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,42(3):431-434
We investigate the scaling properties of the Penna model, which has become a popular tool for the study of population dynamics and evolutionary problems in recent years. We find that the model generates a normalised age distribution for which a simple scaling rule is proposed, that is able to reproduce qualitative features for all genome sizes.Received: 9 October 2004, Published online: 23 December 2004PACS:
87.23.Cc Population dynamics and ecological pattern formation - 89.75.Da Systems obeying scaling laws - 05.10.Ln Monte Carlo methods 相似文献
122.
The quantum resonances occurring with delta-kicked particles are studied with the help of a fictitious classical limit, establishing a direct correspondence between the nearly resonant quantum motion and the classical resonances of a related system. A scaling law which characterizes the structure of the resonant peaks is derived and numerically demonstrated. 相似文献
123.
Villoresi P Bonora S Pascolini M Poletto L Tondello G Vozzi C Nisoli M Sansone G Stagira S De Silvestri S 《Optics letters》2004,29(2):207-209
We present a method for the optimization of high-order harmonic generation based on wave-front correction of the driving laser beam. The technique exploits wave-front adaptive control by means of a deformable mirror, governed by an optimization procedure. 相似文献
124.
Ergodic dynamics in a natural threshold system 总被引:1,自引:0,他引:1
Numerical simulations suggest that certain driven, dissipative mean-field threshold systems, including earthquake models, can be characterized by statistical properties often associated with ergodic dynamics, in the same sense as stochastic Brownian motion. We applied a fluctuation metric proposed by Thirumalai and Mountain [Phys. Rev. E 47, 479 (1993)]] for statistically stationary systems and find that the natural earthquake fault system in California demonstrates similar ergodic dynamics. 相似文献
125.
Duarte MF Martins F Fernandez MT Langley GJ Rodrigues P Barros MT Costa ML 《Rapid communications in mass spectrometry : RCM》2003,17(9):957-962
A series of derivatives of 2-azidoacetic acid and 2-azidoacetone were synthesized and their behaviour under electron ionization conditions was investigated. This paper reports the electron ionization fragmentation mechanisms for five aliphatic alpha-carbonyl azides, which were clarified by accurate mass measurements and B/E linked scans. The substituent influences the abundance and the nature of the ions resulting from the molecular ion fragmentation. 相似文献
126.
The reaction of aryl iodides and bromides with acrolein diethyl acetal in the presence of Pd(OAc)(2), (n)()Bu(4)NOAc, K(2)CO(3), KCl, and DMF, at 90 degrees C until the disappearance of the acetal followed by the addition of 2 N HCl to the crude reaction mixture, affords cinnamaldehydes in good to high yields. A variety of functional groups are tolerated in the aryl halides, including ether, aldehyde, ketone, ester, dialkylamino, nitrile, and nitro groups. The presence of substituents close to the oxidative addition site does not hamper the reaction. 相似文献
127.
Rundle PB Rundle JB Tiampo KF Martins JS McGinnis S Klein W 《Physical review letters》2001,87(14):148501
Earthquake faults occur in interacting networks having emergent space-time modes of behavior not displayed by isolated faults. Using simulations of the major faults in southern California, we find that the physics depends on the elastic interactions among the faults defined by network topology, as well as on the nonlinear physics of stress dissipation arising from friction on the faults. Our results have broad applications to other leaky threshold systems such as integrate-and-fire neural networks. 相似文献
128.
We establish exact results for coupled spin-1/2 chains for special values of the four-spin interaction V and dimerization parameter delta. The first exact result is at delta = 1/2 and V = -2. Because we find a very small but finite gap in this dimerized chain, this can serve as a very strong test case for numerical and approximate analytical techniques. The second result is for the homogeneous chain with V = -4 and gives evidence that the system has a spontaneously dimerized ground state. Numerical diagonalization and bosonization techniques indicate that the interplay between dimerization and interaction could result in gapless phases in the regime 0=V<-2. 相似文献
129.
M. Peres A. Cruz S. Pereira M.R. Correia M.J. Soares A. Neves M.C. Carmo T. Monteiro A.S. Pereira M.A. Martins T. Trindade E. Alves S.S. Nobre R.A. Sá Ferreira 《Applied Physics A: Materials Science & Processing》2007,88(1):129-133
Synthetic ZnO nanocrystals have been intentionally doped with Eu3+ ions. Structural analysis performed on the nanocrystals showed wurtzite-ZnO as the only phase present in the samples. Photoluminescence
in emission and excitation modes allows the assignment of the intra-4f6 transitions for the Eu3+ ions. From the analysis of the optical data we are able to demonstrate that multiple Eu-related optical centres are present
in the studied samples. Oxygen vacancies are likely candidates to be responsible for the ion accommodation in the ZnO lattice
and from the photoluminescence excitation data we tentatively assign a trap level at ∼200 meV below the conduction band to
this intrinsic defect.
PACS 78.66.Hf; 78.67.-n; 82.80.Yc 相似文献
130.
Ferromagnetic Resonance (FMR) measurements at room temperature and X-band microwave frequency were performed on polycrystalline FePt thin films with face-centered cubic structure. With the external field perpendicular to the film plane, the absorption fields Hn of the odd and even spin-wave resonance modes n detected for the Fe0.44Pt0.56(45 nm)/Si(1 0 0) and Fe0.51Pt0.49(105 nm)/Pt(55 nm)/MgO(1 0 0) films, were found to obey the well-known Hn×n2 ratio, giving for these films the exchange stiffness constant values of 3.9×10−8 and 4.4×10–7 erg/cm, respectively. The study of the out-of-plane angular dependence of the absorption field of the uniform FMR mode allowed the measurement of the effective magnetic anisotropy constants of 5.3×106 , 6.4×106 , and 6.7×106 erg/cm3, related, respectively, to the [1 1 1], [1 0 0], and [1 1 0] textures present in the films. 相似文献