2,464 research outputs found
Fractional exclusion statistics and shot noise in ballistic conductors
We study the noise properties of ballistic conductors with carriers
satisfying fractional exclusion statistics. To test directly the nature of
exclusion statistics we found that systems under weakly degenerate conditions
should be considered. Typical of these systems is that the chemical potential,
is in the thermal range . In these conditions the noise
properties under current saturation are found to depend upon the statistical
parameter , displaying suppressed shot noise for , and
enhanced shot noise for , according to the attractive or repulsive
nature of the carrier exclusion statistics.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev.
Opsin vs opsin: new materials for biotechnological applications
The need of new diagnostic methods satisfying, as an early detection, a low
invasive procedure and a cost-efficient value, is orienting the technological
research toward the use of bio-integrated devices, in particular bio-sensors.
The set of know-why necessary to achieve this goal is wide, from biochemistry
to electronics and is summarized in an emerging branch of electronics, called
\textit{proteotronics}. Proteotronics is here here applied to state a
comparative analysis of the electrical responses coming from type-1 and type-2
opsins. In particular, the procedure is used as an early investigation of a
recently discovered family of opsins, the proteorhodopsins activated by blue
light, BPRs. The results reveal some interesting and unexpected similarities
between proteins of the two families, suggesting the global electrical response
are not strictly linked to the class identity.Comment: 10 pages, 8 figures revised version with more figure
Size effects on generation recombination noise
We carry out an analytical theory of generation-recombination noise for a two
level resistor model which goes beyond those presently available by including
the effects of both space charge fluctuations and diffusion current. Finite
size effects are found responsible for the saturation of the low frequency
current spectral density at high enough applied voltages. The saturation
behaviour is controlled essentially by the correlations coming from the long
range Coulomb interaction. It is suggested that the saturation of the current
fluctuations for high voltage bias constitutes a general feature of
generation-recombination noise.Comment: 3 pages, 1 figure. To appear in Applied Physics Letters (2 December
2002 issue
Noise and diffusion of particles obeying asymmetric exclusion processes
The relation between noise and Fick's diffusion coefficient in barrier
limited transport associated with hopping or tunneling mechanisms of particles
obeying the asymmetric simple exclusion processes (ASEP) is physically assessed
by Monte Carlo simulations. For a closed ring consisting of a large number of
barriers the diffusion coefficient is related explicitly to the current noise
thus revealing the existence of a generalized Nyquist-Einstein relation. Both
diffusion and noise are confirmed to decrease as the square root of the number
of barriers as a consequence of the correlation induced by ASEP. By contrast,
for an open linear chain of barriers the diffusion coefficient is found to be
no longer related to current noise. Here diffusion depends on particle
concentration but is independent of the number of barriers
Hierarchy and assortativity as new tools for affinity investigation: the case of the TBA aptamer-ligand complex
Aptamers are single stranded DNA, RNA or peptide sequences having the ability
to bind a variety of specific targets (proteins, molecules as well as ions).
Therefore, aptamer production and selection for therapeutic and diagnostic
applications is very challenging. Usually they are in vitro generated, but,
recently, computational approaches have been developed for the in silico
selection, with a higher affinity for the specific target. Anyway, the
mechanism of aptamer-ligand formation is not completely clear, and not obvious
to predict. This paper aims to develop a computational model able to describe
aptamer-ligand affinity performance by using the topological structure of the
corresponding graphs, assessed by means of numerical tools such as the
conventional degree distribution, but also the rank-degree distribution
(hierarchy) and the node assortativity. Calculations are applied to the
thrombin binding aptamer (TBA), and the TBA-thrombin complex, produced in the
presence of Na+ or K+. The topological analysis reveals different affinity
performances between the macromolecules in the presence of the two cations, as
expected by previous investigations in literature. These results nominate the
graph topological analysis as a novel theoretical tool for testing affinity.
Otherwise, starting from the graphs, an electrical network can be obtained by
using the specific electrical properties of amino acids and nucleobases.
Therefore, a further analysis concerns with the electrical response, which
reveals that the resistance sensitively depends on the presence of sodium or
potassium thus posing resistance as a crucial physical parameter for testing
affinity.Comment: 12 pages, 5 figure
Investigations on the electrical current-voltage response in protein light receptors
We report a theoretical/computational approach for modeling the
current-voltage characteristics of sensing proteins. The modeling is applied to
a couple of transmembrane proteins, bacteriorhodopsin and proteorhodopsin,
sensitive to visible light and promising biomaterials for the development of a
new generation of photo-transducers. The agreement between theory and
experiments sheds new light on the microscopic interpretation of charge
transfer in proteins and biological materials in general.Comment: 4 pages, 3 figures To be published in J Phys. C: Conf Ser. Proceeding
of the Conference IC-MCSQUARE, PRAGUE 201
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