1,027 research outputs found
Renormalization group approach to anisotropic superconductivity
The superconducting instability of the Fermi liquid state is investigated by
considering anisotropic electron-boson couplings. Both electron-electron
interactions and anisotropic electron-boson couplings are treated with a
renormalization-group method that takes into account retardation effects.
Considering a non-interacting circular Fermi surface, we find analytical
solutions for the flow equations and derive a set of generalized Eliashberg
equations. Electron-boson couplings with different momentum dependences are
studied, and we find superconducting instabilities of the metallic state with
competition between order parameters of different symmetries. Numerical
solutions for some couplings are given to illustrate the frequency dependence
of the vertices at different coupling regimes.Comment: 9 pages, 7 figures. Final version as published in Phys. Rev.
Brownian Carnot engine
The Carnot cycle imposes a fundamental upper limit to the efficiency of a
macroscopic motor operating between two thermal baths. However, this bound
needs to be reinterpreted at microscopic scales, where molecular bio-motors and
some artificial micro-engines operate. As described by stochastic
thermodynamics, energy transfers in microscopic systems are random and thermal
fluctuations induce transient decreases of entropy, allowing for possible
violations of the Carnot limit. Despite its potential relevance for the
development of a thermodynamics of small systems, an experimental study of
microscopic Carnot engines is still lacking. Here we report on an experimental
realization of a Carnot engine with a single optically trapped Brownian
particle as working substance. We present an exhaustive study of the energetics
of the engine and analyze the fluctuations of the finite-time efficiency,
showing that the Carnot bound can be surpassed for a small number of
non-equilibrium cycles. As its macroscopic counterpart, the energetics of our
Carnot device exhibits basic properties that one would expect to observe in any
microscopic energy transducer operating with baths at different temperatures.
Our results characterize the sources of irreversibility in the engine and the
statistical properties of the efficiency -an insight that could inspire novel
strategies in the design of efficient nano-motors.Comment: 7 pages, 7 figure
Use of rotary kilns for solar thermal applications: Review of developed studies and analysis of their potential
Rotary kilns have a long history of use in classical industries. They are able to achieve high temperatures with higher thermal efficiencies than other reactor types. Their performance has been widely studied and classified according to different parameters. Since it is a well-known technology, rotary kilns have been selected for high temperature solar processes. This article initially presents a brief review of the rotary kiln technology and it focuses on the employment of these devices for thermal and thermochemical processes conducted by concentrating solar energy. Among the solar devices, a novel rotary kiln prototype for thermochemical processes is presented and compared with a static solar reactor. Finally, some practical conclusions on the design and operation of solar rotary kilns are remarked and an analysis of their main limitations is presented.The authors acknowledge the financial support provided by the
FONDECYT project number 3150026 of CONICYT (Chile), the Education Ministry of Chile Grant PMI ANT 1201, as well as CONICYT/FONDAP/ 15110019 ‘‘Solar Energy Research Center” SERC-Chile.
Also, the second author wish to thank to the Plataforma Solar de
Almería and the University of Almería for the collaboration and
assistance devoted to the development of his Ph.D research
Quadrature and polarization squeezing in a dispersive optical bistability model
We theoretically study quadrature and polarization squeezing in dispersive
optical bistability through a vectorial Kerr cavity model describing a
nonlinear cavity filled with an isotropic chi(3) medium in which self-phase and
cross-phase modulation, as well as four--wave mixing, occur. We derive
expressions for the quantum fluctuations of the output field quadratures as a
function of which we express the spectrum of fluctuations of the output field
Stokes parameters. We pay particular attention to study how the bifurcations
affecting the non-null linearly polarized output mode squeezes the orthogonally
polarized vacuum mode, and show how this produces polarization squeezing.Comment: 10 text pages + 12 figure
Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons
We present a method for the study of quantum fluctuations of dissipative
structures forming in nonlinear optical cavities, which we illustrate in the
case of a degenerate, type I optical parametric oscillator. The method consists
in (i) taking into account explicitly, through a collective variable
description, the drift of the dissipative structure caused by the quantum
noise, and (ii) expanding the remaining -internal- fluctuations in the
biorthonormal basis associated to the linear operator governing the evolution
of fluctuations in the linearized Langevin equations. We obtain general
expressions for the squeezing and intensity fluctuations spectra. Then we
theoretically study the squeezing properties of a special dissipative
structure, namely, the bright cavity soliton. After reviewing our previous
result that in the linear approximation there is a perfectly squeezed mode
irrespectively of the values of the system parameters, we consider squeezing at
the bifurcation points, and the squeezing detection with a plane--wave local
oscillator field, taking also into account the effect of the detector size on
the level of detectable squeezing.Comment: 10 figure
Quantum walk with a time-dependent coin
We introduce quantum walks with a time-dependent coin, and show how they include, as a particular case, the generalized quantum walk recently studied by Wojcik [Phys. Rev. Lett. 93, 180601 (2004)] which exhibits interesting dynamical localization and quasiperiodic dynamics. Our proposal allows for a much easier implementation of this particularly rich dynamics than the original one. Moreover, it allows for an additional control on the walk, which can be used to compensate for phases appearing due to external interactions. To illustrate its feasibility, we discuss an example using an optical cavity. We also derive an approximated solution in the continuous limit (long-wavelength approximation) which provides physical insight about the process
Leadership, management, quality, and innovation in organ donation: 2019 Kunming recommendations for One Belt & One Road countries
The findings and recommendations of the 2019 consensus conference in organ donation, held in Kunming, China, are here reported. The main objective of the conference was to gather relevant information from experts involved in the field. The data and opinions provided allowed to propose a series of recommendations for “One Belt & One Road Countries” on how to achieve self-sufficiency in organ donation. Leadership in organ donation should be results-oriented and goal-driven based on the principles of excellence, empowerment, and engagement, providing the means, resources, and strategies necessary to reach the goal in earnest. Management includes good governance and transparency of a national registry of patients in the waiting list, donors, transplants, transplant teams, quality, and safety programs with continuous educational training of health care professionals. Mandatory monitoring, auditing and evaluation of quality must be incorporated into donation practices as relevant points in innovation, as well as the adoption of already established and novel processes and technologies. Achievement of self-sufficiency in organ donation is a crucial step to fight against transplant tourism and to prevent organ trafficking. Based on recommendations arising from the conference, each country could review and develop individualized action plans adjusted to its own circumstances and reality
Improvement of reduced activation 9%Cr steels by ausforming
Forimprovedperformanceofthecomponentsinafusionreactor,anincreasedapplicationtemperatureforstructuralmaterialssuchas9%Crreducedactivationsteelsiscrucial.Theimprovementofthecurrentgenerationof9%Crsteels(i.e.EUROFER)isoneoftheaimsofthecurrentEUROfusionprogrammeforadvancedsteels.Thegoalofthisworkistodeterminethemosteffectivethermo-mechanicaltreatmentofreducedactivationferriticmartensiticsteelswithrespecttohigh-temperaturestrength.Compatibilityofthesetreatmentswithindustrialproductionprocessesisessential.Inthepresentstudy,twodifferentbatchesofEUROFER-2werepreparedwithathermo-mechanicaltreatment.Thematerialsweresolutionannealedat1250°Candthenslowlycooledtotherollingtem-perature,whichwasvariedbetween600and900°C.Hot-rollingwasperformedintheausteniteregimewithasubsequentrapidcoolingtoformtheferritic-martensiticstructure.Thecharacterizationofthematerialswasdoneinas-rolledstateandafterasubsequenttemperingat750°C.ThematerialscharacterizationwasperformedbytensileandCharpyimpacttestsusingminiaturizedspecimens.Themicrostructurewascharacterizedbyscanningelectronmicroscopy(SEM)backscatterim-agesandelectronbackscatterdiffraction(EBSD)maps.Alltheresultswerecomparedtothoseofconven-tionallyprocessedEUROFER-2alloys.Thefirstresultsshowagainintensilestrengthofapproximately50MPaattemperaturesabove600°CcomparedtoconventionallytreatedEUROFERalloys.Microstructuralinvestigationsrevealafineandhomogeneousdistributionofthemartensiticlaths,whiletheprioraustenitegrainsareaboutoneorderofmagnitudelarger.Thiscanbeexplainedbytheexceptionallyhighaustenitizationtemperaturecomparedtotheas-receivedstate
Time series irreversibility: a visibility graph approach
We propose a method to measure real-valued time series irreversibility which
combines two differ- ent tools: the horizontal visibility algorithm and the
Kullback-Leibler divergence. This method maps a time series to a directed
network according to a geometric criterion. The degree of irreversibility of
the series is then estimated by the Kullback-Leibler divergence (i.e. the
distinguishability) between the in and out degree distributions of the
associated graph. The method is computationally effi- cient, does not require
any ad hoc symbolization process, and naturally takes into account multiple
scales. We find that the method correctly distinguishes between reversible and
irreversible station- ary time series, including analytical and numerical
studies of its performance for: (i) reversible stochastic processes
(uncorrelated and Gaussian linearly correlated), (ii) irreversible stochastic
pro- cesses (a discrete flashing ratchet in an asymmetric potential), (iii)
reversible (conservative) and irreversible (dissipative) chaotic maps, and (iv)
dissipative chaotic maps in the presence of noise. Two alternative graph
functionals, the degree and the degree-degree distributions, can be used as the
Kullback-Leibler divergence argument. The former is simpler and more intuitive
and can be used as a benchmark, but in the case of an irreversible process with
null net current, the degree-degree distribution has to be considered to
identifiy the irreversible nature of the series.Comment: submitted for publicatio
- …