4,257 research outputs found
Diffusive transport and self-consistent dynamics in coupled maps
The study of diffusion in Hamiltonian systems has been a problem of interest
for a number of years.
In this paper we explore the influence of self-consistency on the diffusion
properties of systems described by coupled symplectic maps. Self-consistency,
i.e. the back-influence of the transported quantity on the velocity field of
the driving flow, despite of its critical importance, is usually overlooked in
the description of realistic systems, for example in plasma physics. We propose
a class of self-consistent models consisting of an ensemble of maps globally
coupled through a mean field. Depending on the kind of coupling, two different
general types of self-consistent maps are considered: maps coupled to the field
only through the phase, and fully coupled maps, i.e. through the phase and the
amplitude of the external field. The analogies and differences of the diffusion
properties of these two kinds of maps are discussed in detail.Comment: 13 pages, 14 figure
Radular ultrastructure of South American Ampullariidae (Gastropoda: Prosobranchia)
The radula of five species of South American Ampullariidae was analysed by Scanning Electron Microscope (SEM) with the purpose of enlarging new studies on the systematic of this family. The studied species were Pomacea canaliculata (Lamarck, 1822), Pomacea scalaris (d'Orbigny, 1835), Pomella (P.) megastoma (Gray, 1847), Asolene A.) platae (Maton, 1809) and Felipponea neritiniformis (Dall, 1919). The central tooth shows different attributes which provide the means for generic determination; the analysis of the central tooth, the lateral and marginal ones by SEM adds further information for species differentiation
The influence of fractional diffusion in Fisher-KPP equations
We study the Fisher-KPP equation where the Laplacian is replaced by the
generator of a Feller semigroup with power decaying kernel, an important
example being the fractional Laplacian. In contrast with the case of the stan-
dard Laplacian where the stable state invades the unstable one at constant
speed, we prove that with fractional diffusion, generated for instance by a
stable L\'evy process, the front position is exponential in time. Our results
provide a mathe- matically rigorous justification of numerous heuristics about
this model
First record of Helobdella hyalina (Hirudinea; Glossiphoniidae) in the mantle cavity of Planorbidae from lentic environments in a Buenos Aires province, Argentina
Biomphalaria peregrina (D’Orbigny, 1835) and Drepanotrema kermatoides (D’Orbigny, 1835) were first reported as hosts of Helobdella hyalina Ringuelet, 1942. Both are important species from the Río de La Plata river basin in Argentina. They are associated with macrophytes of lentic or semilentic environments. They are more frequently observed in semipermanent low-depth environments with vegetation and abundant organic matter (Bonetto et al., 1990).\n(Párrafo extraído del texto a modo de resumen)</i
Relaxation times of unstable states in systems with long range interactions
We consider several models with long-range interactions evolving via
Hamiltonian dynamics. The microcanonical dynamics of the basic Hamiltonian Mean
Field (HMF) model and perturbed HMF models with either global anisotropy or an
on-site potential are studied both analytically and numerically. We find that
in the magnetic phase, the initial zero magnetization state remains stable
above a critical energy and is unstable below it. In the dynamically stable
state, these models exhibit relaxation time scales that increase algebraically
with the number of particles, indicating the robustness of the
quasistationary state seen in previous studies. In the unstable state, the
corresponding time scale increases logarithmically in .Comment: Minor change
Symbionts and diseases associated with invasive apple snails
This contribution summarizes knowledge of organisms associated with apple snails, mainly Pomacea spp., either in a facultative or obligate manner, paying special attention to diseases transmitted via these snails to humans. A wide spectrum of epibionts on the shell and operculum of snails are discussed. Among them algae, ciliates, rotifers, nematodes, flatworms, oligochaetes, dipterans, bryozoans and leeches are facultative, benefitting from the provision of substrate, transport, access to food and protection. Among obligate symbionts, five turbellarian species of the genus Temnocephala are known from the branchial cavity, with T. iheringi the most common and abundant. The leech Helobdella ampullariae also spends its entire life cycle inside the branchial cavity; two copepod species and one mite are found in different sites inside the snails. Details of the nature of the relationships of these specific obligate symbionts are poorly known. Also, extensive studies of an intracellular endosymbiosis are summarized. Apple snails are the first or second hosts of several digenean species, including some bird parasites. A number of human diseases are transmitted by apple snails, angiostrongyliasis being the most important because of the potential seriousness of the disease.Facultad de Ciencias Naturales y Muse
Symbionts and diseases associated with invasive apple snails
This contribution summarizes knowledge of organisms associated with apple snails, mainly Pomacea spp., either in a facultative or obligate manner, paying special attention to diseases transmitted via these snails to humans. A wide spectrum of epibionts on the shell and operculum of snails are discussed. Among them algae, ciliates, rotifers, nematodes, flatworms, oligochaetes, dipterans, bryozoans and leeches are facultative, benefitting from the provision of substrate, transport, access to food and protection. Among obligate symbionts, five turbellarian species of the genus Temnocephala are known from the branchial cavity, with T. iheringi the most common and abundant. The leech Helobdella ampullariae also spends its entire life cycle inside the branchial cavity; two copepod species and one mite are found in different sites inside the snails. Details of the nature of the relationships of these specific obligate symbionts are poorly known. Also, extensive studies of an intracellular endosymbiosis are summarized. Apple snails are the first or second hosts of several digenean species, including some bird parasites. A number of human diseases are transmitted by apple snails, angiostrongyliasis being the most important because of the potential seriousness of the disease.Facultad de Ciencias Naturales y Muse
Long-time discrete particle effects versus kinetic theory in the self-consistent single-wave model
The influence of the finite number N of particles coupled to a monochromatic
wave in a collisionless plasma is investigated. For growth as well as damping
of the wave, discrete particle numerical simulations show an N-dependent long
time behavior resulting from the dynamics of individual particles. This
behavior differs from the one due to the numerical errors incurred by Vlasov
approaches. Trapping oscillations are crucial to long time dynamics, as the
wave oscillations are controlled by the particle distribution inhomogeneities
and the pulsating separatrix crossings drive the relaxation towards thermal
equilibrium.Comment: 11 pages incl. 13 figs. Phys. Rev. E, in pres
In vivo testing of novel vaccine prototypes against Actinobacillus pleuropneumoniae
Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is a Gram-negative bacterium that represents the main cause of porcine pleuropneumonia in pigs, causing significant economic losses to the livestock industry worldwide. A. pleuropneumoniae, as the majority of Gram-negative bacteria, excrete vesicles from its outer membrane (OM), accordingly defined as outer membrane vesicles (OMVs). Thanks to their antigenic similarity to the OM, OMVs have emerged as a promising tool in vaccinology. In this study we describe the in vivo testing of several vaccine prototypes for the prevention of infection by all known A. pleuropneumoniae serotypes. Previously identified vaccine candidates, the recombinant proteins ApfA and VacJ, administered individually or in various combinations with the OMVs, were employed as vaccination strategies. Our data show that the addition of the OMVs in the vaccine formulations significantly increased the specific IgG titer against both ApfA and VacJ in the immunized animals, confirming the previously postulated potential of the OMVs as adjuvant. Unfortunately, the antibody response raised did not translate into an effective protection against A. pleuropneumoniae infection, as none of the immunized groups following challenge showed a significantly lower degree of lesions than the controls. Interestingly, quite the opposite was true, as the animals with the highest IgG titers were also the ones bearing the most extensive lesions in their lungs. These results shed new light on A. pleuropneumoniae pathogenicity, suggesting that antibody-mediated cytotoxicity from the host immune response may play a central role in the development of the lesions typically associated with A. pleuropneumoniae infections
Fractional reaction-diffusion equations
In a series of papers, Saxena, Mathai, and Haubold (2002, 2004a, 2004b)
derived solutions of a number of fractional kinetic equations in terms of
generalized Mittag-Leffler functions which provide the extension of the work of
Haubold and Mathai (1995, 2000). The subject of the present paper is to
investigate the solution of a fractional reaction-diffusion equation. The
results derived are of general nature and include the results reported earlier
by many authors, notably by Jespersen, Metzler, and Fogedby (1999) for
anomalous diffusion and del-Castillo-Negrete, Carreras, and Lynch (2003) for
reaction-diffusion systems with L\'evy flights. The solution has been developed
in terms of the H-function in a compact form with the help of Laplace and
Fourier transforms. Most of the results obtained are in a form suitable for
numerical computation.Comment: LaTeX, 17 pages, corrected typo
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