Hopf periodic orbits for a ratio-dependent predator-prey model with stage structure

Agraïments: The second author is partially supported by Dirección de Investigación DIUBB 1204084/R.A ratio-dependent predator-prey model with stage structure for prey was investigated in [8]. There the authors mentioned that they were unable to show if such a model admits limit cycles when the unique equilibrium point E ∗ at the positive octant is unstable. Here we characterize the existence of Hopf bifurcations for the systems. In particular we provide a positive answer to the above question showing for such models the existence of small-amplitude Hopf limit cycles being the equilibrium point E ∗ unstable

Periodic solutions of a periodic FitzHugh-Nagumo differential system

Agraïments: The second author is partially supported by Dirección de Investigación DIUBB 1204084/R.Recently some interest has appeared for the periodic FitzHugh-Nagumo differential systems. Here, we provide sufficient conditions for the existence of periodic solutions in such differential systems

Hopf periodic orbits for a ratio-dependent predator-prey model with stage structure

Agraïments: The second author is partially supported by Dirección de Investigación DIUBB 1204084/R.A ratio-dependent predator-prey model with stage structure for prey was investigated in [8]. There the authors mentioned that they were unable to show if such a model admits limit cycles when the unique equilibrium point E ∗ at the positive octant is unstable. Here we characterize the existence of Hopf bifurcations for the systems. In particular we provide a positive answer to the above question showing for such models the existence of small-amplitude Hopf limit cycles being the equilibrium point E ∗ unstable

Global dynamics of the Buckingham's two-body problem

The equations of motion of the Buckingham system are the ones of a two-body problem defined by the Hamiltonian H=12(px2+py2)+Ae−Bx2+y2−M(x2+y2)3, where A, B and M are positive constants. The angular momentum p: = xp− yp and this Hamiltonian are two independent first integrals in involution. We denote by I (respectively, I) the set of points of the phase space where H (respectively, p) takes the value h (respectively, c). Due to the fact that H and p are first integrals, the sets I and I = I∩ I are invariant under the flow of the Buckingham systems. We describe the global dynamics of the Buckingham system describing the foliation of its phase space by the invariant sets I, the foliation of the invariant set I by its invariant subsets I , and the foliation of invariant set I by the orbits of the system

Growth, thermal desorption and low dose ion bombardment damage of C60 films deposited on Cu(111)

Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Reflection Electron Energy Loss Spectrometry (REELS) were used to characterize the growth and thermal stability of C60 films deposited on Cu(111). By means of LEED we found that while C60 grows in an ordered fashion up to the first monolayer (ML) at room temperature (RT), it turns amorphous beyond that point. On the other hand, when the substrate temperature is kept at 450K films up to two ML with crystalline structure are obtained. For substrate temperatures beyond 570K thick films (more than 1 ML) do not grow at all. By using AES, we found that a thick C60 film starts to desorb at a temperature around 470K but the first monolayer remains stable up to temperatures as high as 900K. A monolayer with a better crystalline order is obtained after desorption than that growth with the substrate at RT or higher temperatures. When the substrate is heated at 970K, the first monolayer is not fully removed but the C60 molecular structure is altered or molecules break up into smaller pieces. The ion induced damage on C60 on Cu(111) films was studied for typical ions, incoming energies and irradiation doses used in Low Energy Ion Scattering (LEIS) experiments. The D-value of C(KLL) Auger spectra and the -plasmon of REELS, were monitored to characterize the damage caused to the film. We found that, at low doses ( 1014 ions/cm2), damage is only detectable for massive ions like Ar, but not for H and He in the 2-8 keV range.Fil: Bonetto, Fernando Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Materiales; ArgentinaFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; ArgentinaFil: Quintero Riascos, Vanessa Alexandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Bonin, Claudio Julio. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Materiales; Argentin

Limit cycles of a perturbation of a polynomial Hamiltonian systems of degree 4 symmetric with respect to the origin

We study the number of limit cycles bifurcating from the origin of a Hamiltonian system of degree 4. We prove, using the averaging theory of order 7, that there are quartic polynomial systems close these Hamiltonian systems having 3 limit cycles

Las orquídeas de la Reserva de la Biosfera Torres del Paine: La necesidad de implementar monitoreo de especies y planificación ecoturística para la conservación de la biodiversidad

The orchid flora of Torres del Paine Biosphere Reserve (TPBR) is described based on botanical surveys, photographicalrecords and herbarium collections carried out by the authors. This list comprises 3 genera and 9 species: Chloraea chica,Chloraea leptopetala, Chloraea magellanica, Codonorchis lessonii, Gavilea araucana, Gavilea gladysiae, Gavilealittoralis, Gavilea lutea and Gavilea supralabellata. G. gladysiae is a new record for this protected area and the firstalbino aberrant phenotype for flowers of Chl. magellanica is reported. A description of the species including key fordetermination, morphology, habitats, local abundances, flowering phenology and photographs is provided. The speciesrichness here reported represents ca. 35% of orchids occurring in the Chilean temperate-austral floristic regions and 75%of the species described for the Magallanes Region, putting the Torres del Paine Biosphere Reserve as one of the mostrepresentative protected areas for this taxonomical group in the region. Based on our results we addressed the need ofestablishing monitoring programs for orchids and promote them as flagship species in ecotourism planning in order toenhance species valuation and encourage biodiversity conservation.  Se describen las orquídeas de la Reserva de la Biosfera Torres del Paine sobre la base de exploraciones botánicas, registrosfotográficos y colecciones de herbario llevadas a cabo por los autores. Esta lista comprende 3 géneros y 9 especies: Chloraeachica, Chloraea leptopetala, Chloraea magellanica, Codonorchis lessonii, Gavilea araucana, Gavilea gladysiae, Gavilealittoralis, Gavilea lutea y Gavilea supralabellata. G. gladysiae es un registro nuevo para esta área protegida y se reporta elprimer fenotipo aberrante de flores albinas de Chl. magellanica. Se provee de una descripción de las especies que incluyemorfología, habitats, abundancias locales, fenología de floración y fotografías. La riqueza de especies aquí reportadarepresenta cerca del 35% de las orquídeas que se distribuyen en las regiones florísticas Templada-Austral y el 75% de lasespecies descritas para la Región de Magallanes, colocando a la Reserva de la Biosfera Torres del Paine como una de lasáreas protegidas más representativas para este grupo taxonómico en Chile. Basados en nuestros resultados recalcamosla necesidad de establecer programas de monitoreo para las orquídeas y promoverlas como especies emblemáticas enplanificación ecoturística para así incrementar la valoración de las especies y reforzar la conservación de la biodiversidad