RESUMEN
A balanced ecosystem with coexisting constituent species is often perturbed by different natural events that persist only for a finite duration of time. What becomes important is whether, in the aftermath, the ecosystem recovers its balance or not. Here we study the fate of an ecosystem by monitoring the dynamics of a particular species that encounters a sudden increase in death rate. For exploration of the fate of the species, we use Monte-Carlo simulation on a three-species cyclic rock-paper-scissor model. The density of the affected (by perturbation) species is found to drop exponentially immediately after the pulse is applied. In spite of showing this exponential decay as a short-time behavior, there exists a region in parameter space where this species surprisingly remains as a single survivor, wiping out the other two which had not been directly affected by the perturbation. Numerical simulations using stochastic differential equations of the species give consistency to our results.
Asunto(s)
Modelos Biológicos , Simulación por Computador , Método de Montecarlo , Dinámica PoblacionalRESUMEN
Multiple species in the ecosystem are believed to compete cyclically for maintaining balance in nature. The evolutionary dynamics of cyclic interaction crucially depends on different interactions representing different natural habits. Based on a rock-paper-scissors model of cyclic competition, we explore the role of mortality of individual organisms in the collective survival of a species. For this purpose a parameter called "natural death" is introduced. It is meant for bringing about the decease of an individual irrespective of any intra- and interspecific interaction. We perform a Monte Carlo simulation followed by a stability analysis of different fixed points of defined rate equations and observe that the natural death rate is surprisingly one of the most significant factors in deciding whether an ecosystem would come up with a coexistence or a single-species survival.
Asunto(s)
Evolución Biológica , Teoría del Juego , Mortalidad , Modelos TeóricosRESUMEN
Molecular structure and conformational properties of Isobutyl Cyanide (IBCN) have been studied by quantum chemical methods. The quantum chemical methods predict the existence of both the Trans-Gauche (TG) and Gauche-Gauche (GG) rotameric forms of the IBCN molecule. Fresh vibrational assignments corresponding to each of the 39 normal modes are proposed for both the TG and GG rotameric forms of the molecule. The origin of the internal rotational barrier of the TG form of the molecule has been studied by the relaxation effects and with the aid of nuclear virial and natural bond orbital (NBO) analyses technique. For the barrier to internal rotation of the methyl CH(3) (I)/CH(3) (II) groups of the TG form of the IBCN molecule; the combined relaxations of the C(2)-C(3)/C(2)-C(4) bond lengths and H(10)-C(3)-H(11)/C(2)-C(4)-H(13) angles together play a significant role.
Asunto(s)
Cianuros/química , Conformación Molecular , Nitrilos/química , Rotación , Vibración , Modelos Moleculares , Espectrometría Raman , Termodinámica , Torsión MecánicaRESUMEN
The adsorption of 2-amino-4-methylbenzothiazole (2-AMBT) on colloidal silver particles has been investigated by a surface enhanced Raman scattering (SERS) study. The SERS spectra of the 2-AMBT molecule at varied adsorbate concentrations recorded in different time domains are compared with its Fourier transform infrared (FTIR) spectrum and normal Raman spectrum (NRS) in the bulk and in solution. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using ab initio restricted Hatree-Fock (RHF) and density functional theory (DFT) calculations. The most favorable adsorptive sites of the 2-AMBT molecule have been estimated by natural population analysis (NPA) using the above-mentioned high level of theories. The enhancement of the in-plane modes together with the appearance of Ag-N stretching frequency at 215 cm(-1) indicates that the 2-AMBT molecule is adsorbed on the silver surface through the lone pair electrons of both nitrogen atoms with the molecular plane nearly vertical to the surface.
RESUMEN
Surface-enhanced Raman scattering (SERS) spectra of the biologically important 2-aminobenzothiazole (2-ABT) molecule adsorbed on silver hydrosols are compared with its FTIR spectrum and normal Raman spectroscopy (NRS) spectrum in the bulk and in solution. The optimized structural parameters and the computed vibrational wavenumbers of the compound have been estimated from ab initio (Hatree-Fock) and density functional calculations. Some vibrational modes of the molecule have been reassigned. Concentration-dependent SERS spectra of the molecule reveal the existence of two types of vertically adsorbed species on colloidal silver particles, whose relative population varies with the adsorbate concentrations. The adsorption geometry and structural parameters of one type of adsorbed species are related to the NRS spectrum of the chemically prepared and theoretically modeled 2-ABT-Ag(I) coordination compound.