80 research outputs found
Large expansion of Wilson loops in the Gross-Witten-Wadia matrix model
We study the large expansion of winding Wilson loops in the off-critical
regime of the Gross-Witten-Wadia (GWW) unitary matrix model. These have been
recently considered in arXiv:1705.06542 and computed by numerical methods. We
present various analytical algorithms for the precise computation of both the
perturbative and instanton corrections to the Wilson loops. In the gapped phase
of the GWW model we present the genus five expansion of the one-cut resolvent
that captures all winding loops. Then, as a complementary tool, we apply the
Periwal-Shevitz orthogonal polynomial recursion to the GWW model coupled to
suitable sources and show how it generates all higher genus corrections to any
specific loop with given winding. The method is extended to the treatment of
instanton effects including higher order corrections. Several explicit
examples are fully worked out and a general formula for the next-to-leading
correction at general winding is provided. For the simplest cases, our
calculation checks exact results from the Schwinger-Dyson equations, but the
presented tools have a wider range of applicability.Comment: 28 pages, 3 pdf figures. v2: minor additions, extended reference
Distribution of Return Periods of Rare Events in Correlated Time Series
We study the effect on the distribution of return periods of rare events of
the presence in a time series of finite-term correlations with non-exponential
decay. Precisely, we analyze the auto-correlation function and the statistics
of the return intervals of extreme values of the resistance fluctuations
displayed by a resistor with granular structure in a nonequilibrium stationary
state. The resistance fluctuations, , are calculated by Monte Carlo
simulations using the SBRN model introduced some years ago by Pennetta,
Tref\'an and Reggiani and based on a resistor network approach. A rare event
occurs when overcomes a threshold value significantly higher
than the average value of the resistance. We have found that for highly
disordered networks, when the auto-correlation function displays a
non-exponential decay but yet the resistance fluctuations are characterized by
a finite correlation time, the distribution of return intervals of the extreme
values is well described by a stretched exponential, with exponent largely
independent of the threshold . We discuss this result and some of the main
open questions related to it, also in connection with very recent findings by
other authors concerning the observation of stretched exponential distributions
of return intervals of extreme events in long-term correlated time series.Comment: 10 pages, 8 figures, Procs. of 4th. Int. Conf. on Unsolved Problems
on Noise and Fluctuations in Physics, Biology and High Technology (UPoN05),
6-10 June 2005, Gallipoli (Italy), AIP Conf. Procs. (in print
Charge transport in bacteriorhodopsin monolayers: The contribution of conformational change to current-voltage characteristics
When moving from native to light activated bacteriorhodopsin, modification of
charge transport consisting of an increase of conductance is correlated to the
protein conformational change. A theoretical model based on a map of the
protein tertiary structure into a resistor network is implemented to account
for a sequential tunneling mechanism of charge transfer through neighbouring
amino acids. The model is validated by comparison with current-voltage
experiments. The predictability of the model is further tested on bovine
rhodopsin, a G-protein coupled receptor (GPCR) also sensitive to light. In this
case, results show an opposite behaviour with a decrease of conductance in the
presence of light.Comment: 6 pages, 4 figure
Time-reversal violation as loop-antiloop symmetry breaking: the Bessel equation, group contraction and dissipation
We show that the Bessel equation can be cast, by means of suitable
transformations, into a system of two damped/amplified parametric oscillator
equations. The relation with the group contraction mechanism is analyzed and
the breakdown of loop-antiloop symmetry due to group contraction manifests
itself as violation of time-reversal symmetry. A preliminary discussion of the
relation between some infinite dimensional loop-algebras, such as the
Virasoro-like algebra, and the Euclidean algebras e(2) and e(3) is also
presented.Comment: 15 pages, Late
TBA for Sensing Toxic Cations: A Critical Analysis of Structural and Electrical Properties
Food and drinks can be contaminated with pollutants such as lead and strontium, which poses a serious danger to human health. For this reason, a number of effective sensors have been developed for the rapid and highly selective detection of such contaminants. TBA, a well-known aptamer developed to selectively target and thereby inhibit the protein of clinical interest α-thrombin, is receiving increasing attention for sensing applications, particularly for the sensing of different cations. Indeed, TBA, in the presence of these cations, folds into the stable G-quadruplex structure.
Furthermore, different cations produce small but significant changes in this structure that result in changes in the electrical responses that TBA can produce. In this article, we give an overview of the expected data regarding the use of TBA in the detection of lead and strontium, calculating the
expected electrical response using different measurement techniques. Finally, we conclude that TBA should be able to detect strontium with a sensitivity approximately double that achievable for lead
Duality and reciprocity of fluctuation-dissipation relations in conductors
By analogy with linear-response we formulate the duality and reciprocity
properties of current and voltage fluctuations expressed by Nyquist relations
including the intrinsic bandwidths of the respective fluctuations. For this
purpose we individuate total-number and drift-velocity fluctuations of carriers
inside a conductor as the microscopic sources of noise. The spectral densities
at low frequency of the current and voltage fluctuations and the respective
conductance and resistance are related in a mutual exclusive way to the
corresponding noise-source. The macroscopic variance of current and voltage
fluctuations are found to display a dual property via a plasma conductance that
admits a reciprocal plasma resistance. Analogously, the microscopic
noise-sources are found to obey a dual property and a reciprocity relation. The
formulation is carried out in the frame of the grand canonical (for current
noise) and canonical (for voltage noise) ensembles and results are derived
which are valid for classical as well as for degenerate statistics including
fractional exclusion statistics. The unifying theory so developed sheds new
light on the microscopic interpretation of dissipation and fluctuation
phenomena in conductors. In particular it is proven that, as a consequence of
the Pauli principle, for Fermions non-vanishing single-carrier velocity
fluctuations at zero temperature are responsible for diffusion but not for
current noise, which vanishes in this limit.Comment: 5 pages, 1 figur
Charge transport in purple membrane monolayers: A sequential tunneling approach
Current voltage (I-V) characteristics in proteins can be sensitive to
conformational change induced by an external stimulus (photon, odour, etc.).
This sensitivity can be used in medical and industrial applications besides
shedding new light in the microscopic structure of biological materials. Here,
we show that a sequential tunneling model of carrier transfer between
neighbouring amino-acids in a single protein can be the basic mechanism
responsible of the electrical properties measured in a wide range of applied
potentials. We also show that such a strict correlation between the protein
structure and the electrical response can lead to a new generation of
nanobiosensors that mimic the sensorial activity of living species. To
demonstrate the potential usefulness of protein electrical properties, we
provide a microscopic interpretation of recent I-V experiments carried out in
bacteriorhodopsin at a nanoscale length.Comment: 4 pages, 4 figure
Reactive immunization on complex networks
Epidemic spreading on complex networks depends on the topological structure
as well as on the dynamical properties of the infection itself. Generally
speaking, highly connected individuals play the role of hubs and are crucial to
channel information across the network. On the other hand, static topological
quantities measuring the connectivity structure are independent on the
dynamical mechanisms of the infection. A natural question is therefore how to
improve the topological analysis by some kind of dynamical information that may
be extracted from the ongoing infection itself. In this spirit, we propose a
novel vaccination scheme that exploits information from the details of the
infection pattern at the moment when the vaccination strategy is applied.
Numerical simulations of the infection process show that the proposed
immunization strategy is effective and robust on a wide class of complex
networks
Generalized Gumbel distribution of current fluctuations in purple membrane monolayers
We investigate the nature of a class of probability density functions, say
G(a), with a the shape parameter, which generalizes the Gumbel distribution.
These functions appear in a model of charge transport, when applied to a
metal-insulator-metal structure, where the insulator is constituted by a
monolayer of bacteriorhodopsin. Current shows a sharp increase above about 3 V,
interpreted as the cross-over between direct and injection sequential-tunneling
regimes.
In particular, we show that, changing the bias value, the probability density
function changes its look from bimodal to unimodal. Actually, the bimodal
distributions can be resolved in at least a couple of functions with
different values of the shape parameter.Comment: 5 pages, 6 figure
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