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91.
The study of ecological systems has generated deep interest in exploring the complexity of chaotic food chains. The role of chaos in ecosystems is not entirely understood. One approach to have a better comprehension of ecological chaos is by analyzing it in mathematical models of basic food chains. In this article it is considered a classical chaotic food chain model from the literature. We use the theory of symbolic dynamics to study the topological entropy and the parameter space ordering of kneading sequences associated with one-dimensional maps that reproduce significant aspects of the model dynamics. The topological entropy allows us to distinguish different chaotic states in some realistic system parameter region. Another numerical invariant is introduced in order to characterize isentropic dynamics. Studying a set of maps with the same topological entropy, we exhibit numerical results about the relation between the second topological invariant and each of the control parameters in consideration. This work provides an illustration of how our understanding of ecological models can be enhanced by the theory of symbolic dynamics. 相似文献
92.
D. PortesJr. H. Rodrigues S. B. Duarte B. Baseia 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):145-149
We study the exchange of states in coupled fields along their time
evolution. The coupling is described by a quadratic form in terms of
annihilation and creation operator in the field Hamiltonian. An analytical
approach is employed to describe the time evolution of the field state in
Fock's space and the conditions for an arbitrary initial states to be
transferred with 100% fidelity is determined. We show that only for initial
states C0|0>+CN|N>, this situation can occurs. The important
|1〉↔|0〉 qubits transfer is a particular
case of this transference of number state. The relation between the coupling
constant and characteristic field frequencies for complete state
transference is also determined. 相似文献
93.
Roly J. Armstrong Wasim M. Akhtar Tom A. Young Fernanda Duarte Timothy J. Donohoe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(36):12688-12692
Hydrogen borrowing catalysis serves as a powerful alternative to enolate alkylation, enabling the direct coupling of ketones with unactivated alcohols. However, to date, methods that enable control over the absolute stereochemical outcome of such a process have remained elusive. Here we report a catalytic asymmetric method for the synthesis of enantioenriched cyclohexanes from 1,5‐diols via hydrogen borrowing catalysis. This reaction is mediated by the addition of a chiral iridium(I) complex, which is able to impart high levels of enantioselectivity upon the process. A series of enantioenriched cyclohexanes have been prepared and the mode of enantioinduction has been probed by a combination of experimental and DFT studies. 相似文献
94.
The definition and simulation of fractional Brownian motion are considered from the point of view of a set of coherent fractional derivative definitions. To do it, two sets of fractional derivatives are considered: (a) the forward and backward and (b) the central derivatives, together with two representations: generalised difference and integral. It is shown that for these derivatives the corresponding autocorrelation functions have the same representations. The obtained results are used to define a fractional noise and, from it, the fractional Brownian motion. This is studied. The simulation problem is also considered. 相似文献
95.
F.J. Duarte 《Applied physics. B, Lasers and optics》2008,90(1):101-108
Recent experimental results demonstrating coherent emission from an electrically-excited pulsed dye-doped organic semiconductor
interferometric emitter, are discussed from a coherence and a laser perspective. Examination of available results indicates
that there is sufficient evidence to classify the reported emission as being equivalent to broadband dye laser radiation.
From a practical perspective, however, this is an interferometric organic semiconductor emitter that yields a spatially coherent
beam (Δθ≈ 2.53 mrad or 1.1 times the diffraction limit) and an emission linewidth comparable with broadband dye lasers (Δλ≈ 11 nm
at half width). Geometrical dimensions, and electrical excitation parameters, for a significantly smaller interferometric
organic emitter are suggested.
PACS 42.25.Hz; 42.25.Kb; 42.55.Mv; 42.60.Da; 42.60.Jf 相似文献
96.
Miguel Simões J Duarte IS Fonseca PJ Turner GF Clara Amorim M 《The Journal of the Acoustical Society of America》2008,124(2):1332-1338
Courtship and agonistic interactions in an African cichlid species present a richer diversity of acoustic stimuli than previously reported. Male cichlids, including those from the genus Pseudotropheus (P.), produce low frequency short pulsed sounds during courtship. Sounds emitted by P. zebra males in the early stages of courtship (during quiver) were found to be significantly longer and with a higher number of pulses than sounds produced in later stages. During agonistic intrasexual quiver displays, males produced significantly longer sounds with more pulses than females. Also, male sounds had a shorter duration and pulse period in courtship than in male-male interactions. Taken together, these results show that the acoustic repertoire of this species is larger than what was previously known and emphasize the importance of further research exploiting the role of acoustic stimuli in intra- and interspecific communication in African cichlids. 相似文献
97.
98.
Pauline L. Nasatto Frédéric Pignon Joana L. M. Silveira Maria Eugênia R. Duarte Miguel D. Noseda Marguerite Rinaudo 《International Journal of Polymer Analysis and Characterization》2015,20(2):110-118
In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration. 相似文献
99.
De Abreu HA Aparecida Dos S Lago I Souza GP Piló-Veloso D Duarte HA de C Alcântara AF 《Organic & biomolecular chemistry》2008,6(15):2713-2718
(+)-Bergenin (1) was isolated from Sacoglottis uchi, a species of vegetable found in the Amazon region and popularly used for the treatment of several hepatic problems. The structure of 1 was fully characterized using IR, GC-MS and NMR (1D and 2D) analyses. This phytoconstituent has been used as an oriental folk medicine for the treatment of many diseases and shows antihepatotoxic properties. Tests with beta-carotene, DPPH and a heterogeneous Fenton system were carried out, confirming the antioxidant activity of 1. Theoretical calculations were performed to investigate the formation of the radical derivatives of 1 using *H, *OH, *CH(3), and *CCl(3) as initiator radicals. DFT thermodynamic calculations showed that the methoxyl group (O-6-CH(3)) is the most favorable site for radical attack. Frontier molecular orbital analysis showed that nucleophilic radical attack is favored on the aromatic ring of 1 where the LUMO is localized, with antibonding character with respect to the O-6-CH(3) bond. The possibilities of attack at other sites on 1 were investigated in detail in order to understand the regiospecificity of this reaction. 相似文献
100.
Costa EV Pinheiro ML de Souza AD Dos Santos AG Campos FR Ferreira AG Barison A 《Magnetic resonance in chemistry : MRC》2008,46(1):69-74
Using modern NMR techniques, including 1H--13C and 1H--15N heteronuclear correlation experiments, the complete and unambiguous 1H, 13C, and 15N NMR chemical shift assignments of annomontine, methoxyannomontine, and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids were performed. All 1H--1H scalar coupling constants and signal multiplicities were determined, and all nOe observations were also included. 相似文献