563 research outputs found
Quantum Mechanical Hysteresis and the Electron Transfer Problem
We study a simple quantum mechanical symmetric donor-acceptor model for
electron transfer (ET) with coupling to internal deformations. The model
contains several basic properties found in biological ET in enzymes and
photosynthetic centers; it produces tunnelling with hysteresis thus providing a
simple explanation for the slowness of the reversed rate and the near 100%
efficiency of ET in many biological systems. The model also provides a
conceptual framework for the development of molecular electronics memory
elements based on electrostatic architectures.Comment: Accepted Physica
Stunting of the penis in Heleobia parchappii (Mollusca: Cochliopidae) and its relationship with parasitism
Penis anatomy is used to discriminate species of gastropods belonging to the family Cochliopidae; however, this characteristic may be affected by the presence of parasites. To evaluate the possible effect of parasites on penis length and number of papillae in Heleobia parchappii, 195 males were collected from the Nahuel Rucá Lagoon, Argentina. Male snails were only infected by trematode digeneans (total prevalence 45.13%). Three out of 9 species of digeneans registered showed prevalence values higher than 10%: Microphallus szidati, M. simillimus, and Notocotylidae sp. 1. The penis length of non-parasitized males and those parasitized by M. szidati and M. similimus increased with increased snail length; however, this increase was lower in infected snails. In the case of snails infected with Notocotylidae sp. 1, no relationship between shell length and penis length was apparent. Differences in the life cycles of these 3 digeneans could explain the null or lower penis growth rate in relation to host body growth. In contrast, no change was observed in the number of penial papillae of H. parchappii when these snails were infected by larval digeneans compared to those that were not infected. This indicates that penial papillae may be a more stable characteristic than penis length to discriminate between species within the Cochliopidae. The study of penial papillae should be central in the taxonomy and identification of new species within the Cochliopidae, as well as in previously described species.Fil: Merlo, Matias Javier. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de BiologĂa. Laboratorio de ParasitologĂa; ArgentinaFil: Parietti, Manuela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de BiologĂa. Laboratorio de ParasitologĂa; ArgentinaFil: Etchegoin, Jorge Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de BiologĂa. Laboratorio de ParasitologĂa; Argentin
Can the studies at a spatial scale of 100s meters detect the spatiotemporal fluctuations of a parasite assemblage?
The importance of small-scale heterogeneity in local factors which overrides that of larger-scales factors, suggest that local factors play a major role in determining the richness and prevalence of larval digeneans in intertidal gastropods. The restricted distribution of the snail Heleobia australis along a 500 m transect in Cangrejo creek (Mar Chiquita, Argentina) provides a good opportunity to test the assumption that a study at spatial scale of 100s meters can detect spatiotemporal fluctuations of a larval digenean assemblage. To analyze that, 3600 specimens of H. australis were collected seasonally during the year 2011. A quantitative variation and a space-time interaction between sampling points and seasons of the year for the total prevalence of larval digeneans and snail’s densities were found, as well as a positive correlation with abiotic factors. These results revealed that the fluctuations in the community of larval digeneans of the snail H. australis can be detected at small spatial scale, using its natural distribution of 500 m. This study also highlights the importance of seasonality as a factor that must be considered in studies focused on the search for patterns structuring the communities of larval digeneans, at medium and large scales.Fil: Parietti, Manuela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Merlo, Matias Javier. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Etchegoin, Jorge Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin
On the Experimental Estimation of Surface Enhanced Raman Scattering (SERS) Cross Sections by Vibrational Pumping
We present an in-depth analysis of the experimental estimation of cross
sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping.
The paper highlights the advantages and disadvantages of the technique,
pinpoints the main aspects and limitations, and provides the underlying
physical concepts to interpret the experimental results. Examples for several
commonly used SERS probes are given, and a discussion on future possible
developments is also presented.Comment: To be submitted to J. Phys. Chem.
Enhancement factor distribution around a single SERS Hot-spot and its relation to Single Molecule detection
We provide the theoretical framework to understand the phenomenology and
statistics of single-molecule (SM) signals arising in Surface-Enhanced Raman
Scattering (SERS) under the presence of so-called electromagnetic hot-spots
(HS's). We show that most characteristics of the SM-SERS phenomenon can be
tracked down to the presence of tail-like (power law) distribution of
enhancements and we propose a specific model for it. We analyze, in the light
of this, the phenomenology of SM-SERS and show how the different experimental
manifestations of the effect reported in the literature can be analyzed and
understood under a unified ``universal'' framework with a minimum set of
parameters.Comment: 13 pages, 4 figures, submitted to J. Chem. Phy
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