1,545 research outputs found
Self-Consistent Screening Approximation for Flexible Membranes: Application to Graphene
Crystalline membranes at finite temperatures have an anomalous behavior of
the bending rigidity that makes them more rigid in the long wavelength limit.
This issue is particularly relevant for applications of graphene in nano- and
micro-electromechanical systems. We calculate numerically the height-height
correlation function of crystalline two-dimensional membranes,
determining the renormalized bending rigidity, in the range of wavevectors
from \AA till 10 \AA in the self-consistent screening
approximation (SCSA). For parameters appropriate to graphene, the calculated
correlation function agrees reasonably with the results of atomistic Monte
Carlo simulations for this material within the range of from
\AA till 1 \AA. In the limit our data for the
exponent of the renormalized bending rigidity is compatible with the previously known analytical results for the
SCSA . However, this limit appears to be reached only for
\AA whereas at intermediate the behavior of
cannot be described by a single exponent.Comment: 5 pages, 4 figure
Thermodynamics of quantum crystalline membranes
We investigate the thermodynamic properties and the lattice stability of
two-dimensional crystalline membranes, such as graphene and related compounds,
in the low temperature quantum regime . A key role is played by
the anharmonic coupling between in-plane and out-of plane lattice modes that,
in the quantum limit, has very different consequences than in the classical
regime. The role of retardation, namely of the frequency dependence, in the
effective anharmonic interactions turns out to be crucial in the quantum
regime. We identify a crossover temperature, , between classical and
quantum regimes, which is K for graphene. Below , the
heat capacity and thermal expansion coefficient decrease as power laws with
decreasing temperature, tending to zero for as required by the
third law of thermodynamics.Comment: 13 pages, 1 figur
Reply to 'Comment on "Thermodynamics of quantum crystalline membranes"'
In this note, we reply to the comment made by E.I.Kats and V.V.Lebedev
[arXiv:1407.4298] on our recent work "Thermodynamics of quantum crystalline
membranes" [Phys. Rev. B 89, 224307 (2014)]. Kats and Lebedev question the
validity of the calculation presented in our work, in particular on the use of
a Debye momentum as a ultra-violet regulator for the theory. We address and
counter argue the criticisms made by Kats and Lebedev to our work.Comment: 5 pages, 4 figure
Entropy production and Kullback-Leibler divergence between stationary trajectories of discrete systems
The irreversibility of a stationary time series can be quantified using the
Kullback-Leibler divergence (KLD) between the probability to observe the series
and the probability to observe the time-reversed series. Moreover, this KLD is
a tool to estimate entropy production from stationary trajectories since it
gives a lower bound to the entropy production of the physical process
generating the series. In this paper we introduce analytical and numerical
techniques to estimate the KLD between time series generated by several
stochastic dynamics with a finite number of states. We examine the accuracy of
our estimators for a specific example, a discrete flashing ratchet, and
investigate how close is the KLD to the entropy production depending on the
number of degrees of freedom of the system that are sampled in the
trajectories.Comment: 14 pages, 7 figure
On some fixed point theorems under (α,ψ,ϕ) -contractivity conditions in metric spaces endowed with transitive binary relations
After the appearance of Nieto and Rodríguez-López’s theorem, the branch of fixed point theory devoted to the setting of partially ordered metric spaces have attracted much attention in the last years, especially when coupled, tripled, quadrupled and, in general, multidimensional fixed points are studied. Almost all papers in this direction have been forced to present two results assuming two different hypotheses: the involved mapping should be continuous or the metric framework should be regular. Both conditions seem to be different in nature because one of them refers to the mapping and the other one is assumed on the ambient space. In this paper, we unify such different conditions in a unique one. By introducing the notion of continuity of a mapping from a metric space into itself depending on a function α, which is the case that covers the partially ordered setting, we extend some very recent theorems involving control functions that only must be lower/upper semi-continuous from the right. Finally, we use metric spaces endowed with transitive binary relations rather than partial orders.This article was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah. N Shahzad acknowledges with thanks DSR for financial support. A-F Roldán-López-de-Hierro is grateful to the Department of Quantitative Methods for Economics and Business of the University of Granada. The same author has been partially supported by Junta de Andalucía by project FQM-268 of the Andalusian CICYE
Diagnóstico radiológico de la fractura de la apófisis coronoides medial del cúbito en el perro
En este trabajo se describen los signos radiológicos de la fractura de la apófisis coronoides medial del cúbito (FAC)en 22 perros de diferentes razas cuyas edades estaban comprendidas entre los 5 meses y los 8 años. En todos los casos se realizaron radiografías de ambos codos en las proyecciones craneolateral- caudomedial, mediolateral, mediolateral flexionada y craneocaudal. Las proyecciones craneolateral-caudomedial, y mediolateral resultaron las más valiosas desde un punto de vista diagnóstico mientras que las dos restantes aportaron una información complementaria.The radiological signs of fragmented medial corono id process (FCP) were described in 22 dogs of different breeds with an age ranged from 5 months to 8 years oId. A study of both elbows was performed in all dogs by means of craneolateral-caudomedial, mediolateral, flexed mediolateral and craneocaudal views. The craneolateral-caudomedial and mediolateral views resulted more diagnostic than the remaining ones which only showed ancillary information to the disease
Síntesis y caracterización del nitruro ternario de titanio y vanadio (TixV1-xN)
En el presente trabajo se aborda la síntesis del nitruro ternario de titanio y vanadio por reducción carbotérmica de una
mezcla de óxidos o bien por nitruración directa de la mezcla de metales, en todo el rango de composiciones empleando
el método de análisis térmico a velocidad controlada (ATVC). La caracterización de los productos obtenidos se ha llevado
a cabo mediante difracción de rayos-X y microscopia electrónica. El empleo de la técnica EELS ha mostrado su capacidad
para la cuantificación de este tipo de materiales, así como la utilización de la técnica espectroscópica XAS nos ha servido
para corroborar los datos obtenidos a partir de los diagramas de difracción de rayos-X sobre distancias de enlace, número
de coordinación y grado de desorden, esto último no detectado por las otras técnicas usadas en la caracterización de los
productos. Los valores de microdureza registrados para las muestras sintetizadas se encuentran dentro del rango de valores
reportados para este tipo de materiales.Peer reviewe
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