134 research outputs found
Thermodynamics of conformal fields in topologically non-trivial space-time backgrounds
We analyze the finite temperature behaviour of massless conformally coupled
scalar fields in homogeneous lens spaces . High and low
temperature expansions are explicitly computed and the behavior of
thermodynamic quantities under thermal duality is scrutinized. The analysis of
the entropy of the different lens spaces in the high-temperature limit points
out the appearance of a topological nonextensive entropy, besides the standard
Stefan-Boltzmann extensive term. The remaining terms are exponentially
suppressed by the temperature. The topological entropy appears as a subleading
correction to the free energy that can be obtained from the determinant of the
lens space conformal Laplacian operator. In the low-temperature limit the
leading term in the free energy is the Casimir energy and there is no trace of
any power correction in any lens space. In fact, the remaining corrections are
always exponentially suppressed by the inverse of the temperature. The duality
between the results of both expansions is further analyzed in the paper.Comment: 21 pages, 2 figure
Charge density and conductivity of disordered Berry-Mondragon graphene nanoribbons
We consider gated graphene nanoribbons subject to Berry-Mondragon boundary
conditions in the presence of weak impurities. Using field--theoretical
methods, we calculate the density of charge carriers (and, thus, the quantum
capacitance) as well as the optical and DC conductivities at zero temperature.
We discuss in detail their dependence on the gate (chemical) potential, and
reveal a non-linear behaviour induced by the quantization of the transversal
momentum.Comment: 17 pages, version accepted for publication in EPJ
The quantum Hall effect in graphene samples and the relativistic Dirac effective action
We study the Euclidean effective action per unit area and the charge density
for a Dirac field in a two--dimensional spatial region, in the presence of a
uniform magnetic field perpendicular to the 2D--plane, at finite temperature
and density. In the limit of zero temperature we reproduce, after performing an
adequate Lorentz boost, the Hall conductivity measured for different kinds of
graphene samples, depending upon the phase choice in the fermionic determinant.Comment: Conclusions extended. References added. 9 pages. 1 figur
Planar QED at finite temperature and density: Hall conductivity, Berry's phases and minimal conductivity of graphene
We study 1-loop effects for massless Dirac fields in two spatial dimensions,
coupled to homogeneous electromagnetic backgrounds, both at zero and at finite
temperature and density. In the case of a purely magnetic field, we analyze the
relationship between the invariance of the theory under large gauge
transformations, the appearance of Chern-Simons terms and of different Berry's
phases. In the case of a purely electric background field, we show that the
effective Lagrangian is independent of the chemical potential and of the
temperature. More interesting: we show that the minimal conductivity, as
predicted by the quantum field theory, is the right multiple of the
conductivity quantum and is, thus, consistent with the value measured for
graphene, with no extra factor of pi in the denominator.Comment: 27 pages, no figures. Minor misprints corrected. Final version, to
appear in J. Phys. A: Math. Ge
Uncertainty in data integration systems: automatic generation of probabilistic relationships
This paper proposes a method for the automatic discovery of probabilistic relationships in the environment of data integration systems. Dynamic data integration systems extend the architecture of current data integration systems by modeling uncertainty at their core. Our method is based on probabilistic word sense disambiguation (PWSD), which allows to automatically lexically annotate (i.e. to perform annotation w.r.t. a thesaurus/lexical resource) the schemata of a given set of data sources to be integrated. From the annotated schemata and the relathionships defined in the thesaurus, we derived the probabilistic lexical relationships among schema elements. Lexical relationships are collected in the Probabilistic Common Thesaurus (PCT), as well as structural relationships
Analytic continuation of the Hurwitz Zeta Function with physical application
A new formula relating the analytic continuation of the Hurwitz zeta function
to the Euler gamma function and a polylogarithmic function is presented. In
particular, the values of the first derivative of the real part of the analytic
continuation of the Hurwitz zeta function for even negative integers and the
imaginary one for odd negative integers are explicitly given. The result can be
of interest both on mathematical and physical side, because we are able to
apply our new formulas in the context of the Spectral Zeta Function
regularization, computing the exact pair production rate per space-time unit of
massive Dirac particles interacting with a purely electric background field.Comment: Replaced version, minor changes. 9 pages, to be published in J. Math.
Phy
LigAdvisor: A versatile and user-friendly web-platform for drug design
Although several tools facilitating in silico drug design are available, their results are usually difficult to integrate with publicly available information or require further processing to be fully exploited. The rational design of multi-target ligands (polypharmacology) and the repositioning of known drugs towards unmet therapeutic needs (drug repurposing) have raised increasing attention in drug discovery, although they usually require careful planning of tailored drug design strategies. Computational tools and data-driven approaches can help to reveal novel valuable opportunities in these contexts, as they enable to efficiently mine publicly available chemical, biological, clinical, and disease-related data. Based on these premises, we developed LigAdvisor, a data-driven webserver which integrates information reported in DrugBank, Protein Data Bank, UniProt, Clinical Trials and Therapeutic Target Database into an intuitive platform, to facilitate drug discovery tasks as drug repurposing, polypharmacology, target fishing and profiling. As designed, LigAdvisor enables easy integration of similarity estimation results with clinical data, thereby allowing a more efficient exploitation of information in different drug discovery contexts. Users can also develop customizable drug design tasks on their own molecules, by means of ligand- and target-based search modes, and download their results. LigAdvisor is publicly available at https://ligadvisor.unimore.it/
Topological entropy and renormalization group flow in 3-dimensional spherical spaces
We analyze the renormalization group (RG) flow of the temperature independent term of the entropy in the high temperature limit ß/a « 1 of a massive field theory in 3-dimensional spherical spaces, M 3, with constant curvature 6/a 2. For masses lower than 2p/ß , this term can be identified with the free energy of the same theory on M 3 considered as a 3-dimensional Euclidean space-time. The non-extensive part of this free energy, S hol, is generated by the holonomy of the spatial metric connection. We show that for homogeneous spherical spaces the holonomy entropy S hol decreases monotonically when the RG scale flows to the infrared. At the conformal fixed points the values of the holonomy entropy do coincide with the genuine topological entropies recently introduced. The monotonic behavior of the RG flow leads to an inequality between the topological entropies of the conformal field theories connected by such flow, i.e. S top UV¿>¿S top IR . From a 3-dimensional viewpoint the same term arises in the 3-dimensional Euclidean effective action and has the same monotonic behavior under the RG group flow. We conjecture that such monotonic behavior is generic, which would give rise to a 3-dimensional generalization of the c-theorem, along the lines of the 2-dimensional c-theorem and the 4-dimensional a-theorem. The conjecture is related to recent formulations of the F-theorem. In particular, the holonomy entropy on lens spaces is directly related to the topological Rényi entanglement entropy on disks of 2-dimensional flat spaces
Heat kernel coefficients for chiral bag boundary conditions
We study the asymptotic expansion of the smeared L2-trace of fexp(-tP^2)
where P is an operator of Dirac type, f is an auxiliary smooth smearing
function which is used to localize the problem, and chiral bag boundary
conditions are imposed. Special case calculations, functorial methods and the
theory of zeta and eta invariants are used to obtain the boundary part of the
heat-kernel coefficients a1 and a2.Comment: Published in J. Phys. A38, 2259-2276 (2005). Record without file
already exists on the SLAC recor
Strong ellipticity and spectral properties of chiral bag boundary conditions
We prove strong ellipticity of chiral bag boundary conditions on even
dimensional manifolds. From a knowledge of the heat kernel in an infinite
cylinder, some basic properties of the zeta function are analyzed on
cylindrical product manifolds of arbitrary even dimension.Comment: 16 pages, LaTeX, References adde
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