Articles de revista
http://hdl.handle.net/2117/3984
2015-07-28T10:49:35ZQuantifying sudden changes in dynamical systems using symbolic networks
http://hdl.handle.net/2117/76333
Quantifying sudden changes in dynamical systems using symbolic networks
Masoller Alonso, Cristina; Hong, Yanhua; Ayad, Sarah; Gustave, Francois; Barland, Stéphane; Pons Rivero, Antonio Javier; Gómez, Sergio; Arenas, Alex
We characterize the evolution of a dynamical system by combining two well-known complex systems' tools, namely, symbolic ordinal analysis and networks. From the ordinal representation of a time series we construct a network in which every node weight represents the probability of an ordinal pattern (OP) to appear in the symbolic sequence and each edge's weight represents the probability of transitions between two consecutive OPs. Several network-based diagnostics are then proposed to characterize the dynamics of different systems: logistic, tent, and circle maps. We show that these diagnostics are able to capture changes produced in the dynamics as a control parameter is varied. We also apply our new measures to empirical data from semiconductor lasers and show that they are able to anticipate the polarization switchings, thus providing early warning signals of abrupt transitions.
2015-02-24T00:00:00ZUltrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal
http://hdl.handle.net/2117/28568
Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal
Trull Silvestre, José Francisco; Sola, Ïñigo; Wang, Bingxia; Parra, Albert; Krolikowski, W.; Sheng, Y.; Vilaseca Alavedra, Ramon; Cojocaru, Crina
Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.
2015-06-01T00:00:00ZSolvation dynamics in liquid water: 1: ultrafast energy fluxes
http://hdl.handle.net/2117/28563
Solvation dynamics in liquid water: 1: ultrafast energy fluxes
Rey Oriol, Rosendo; Hynes, James T.
Solvation dynamics in liquid water is addressed via nonequilibrium energy-transfer pathways activated after a neutral atomic solute acquires a unit charge, either positive or negative. It is shown that the well-known nonequilibrium frequency shift relaxation function can be expressed in a novel fashion in terms of energy fluxes, providing a clear-cut and quantitative account of the processes involved. Roughly half of the initial excess energy is transferred into hindered rotations of first hydration shell water molecules, i.e., librational motions, specifically those rotations around the lowest moment of inertia principal axis. After integration over all water solvent molecules, rotations account for roughly 80% of the energy transferred, while translations have a secondary role; transfer to intramolecular water stretch and bend vibrations is negligible. This picture is similar to that for relaxation of a single vibrationally or rotationally excited water molecule in neat liquid water, although solvation relaxation is more nonlocal. In addition, we find a remarkable independence of the main relaxation channels on the newly created charge’s sign. Although the methodology is applied here to the simplest solute case, the approach is rather general, and it should be at least equally useful in more realistic and complex scenarios.
2015-01-30T00:00:00ZThe limit of mechanical stability in quantum crystals: a diffusion Monte Carlo study of solid He-4
http://hdl.handle.net/2117/28560
The limit of mechanical stability in quantum crystals: a diffusion Monte Carlo study of solid He-4
Cazorla Silva, Claudio; Boronat Medico, Jordi
We present a first-principles study of the energy and elastic properties of solid helium at pressures below the range in which it is energetically stable. We find that the limit of mechanical stability in hcp He is bar, which lies significantly below the spinodal pressure found in the liquid phase (i.e., bar). Furthermore, we show that the pressure variation of the transverse and longitudinal sound velocities close to does not follow a power law of the form , in contrast to what is observed in the fluid.
2015-07-01T00:00:00ZHigh-accuracy determination of the 238U/ 235U fission cross section ratio up to ˜ 1 GeV at n_TOF at CERN
http://hdl.handle.net/2117/28483
High-accuracy determination of the 238U/ 235U fission cross section ratio up to ˜ 1 GeV at n_TOF at CERN
Paradela, C.; Calviani, Marco; Tarrío, D.; Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Gómez Hornillos, María Belén; Pretel Sánchez, Carme; Riego Pérez, Albert
The U238 to U235 fission cross section ratio has been determined at n_TOF up to ˜1 GeV, with two different detection systems, in different geometrical configurations. A total of four datasets has been collected and compared. They are all consistent to each other within the relative systematic uncertainty of 3–4%. The data collected at n_TOF have been suitably combined to yield a unique fission cross section ratio as a function of neutron energy. The result confirms current evaluations up to 200 MeV. Good agreement is also observed with theoretical calculations based on the INCL++/Gemini++ combination up to the highest measured energy. The n_TOF results may help solve a long-standing discrepancy between the two most important experimental datasets available so far above 20 MeV, while extending the neutron energy range for the first time up to ˜1 GeV.
2015-02-09T00:00:00ZAnalysis of extreme rainfall in the Ebre Observatory (Spain)
http://hdl.handle.net/2117/28325
Analysis of extreme rainfall in the Ebre Observatory (Spain)
Pérez Zanón, Núria; Casas Castillo, M. del Carmen; Rodríguez Solá, Raúl; Peña, Juan Carlos; Rius, Anna; Solé, J. Germán; Redaño Xipell, Angel
Relationship between maximum rainfall rates for time intervals between 5 minutes and 24 hours has been studied from almost a century (1905-2003) of rainfall data registered in the Ebre Observatory (Tarragona, Spain). Intensity-duration-frequency (IDF) curves and its master equation for every return period in the location have been obtained, as well as the probable maximum precipitation (PMP) for all the considered durations. In particular, the value of the 1-day PMP has resulted 415 mm, very similar to previous estimations of this variable for the same location. Extreme rainfall events recorded in this period have been analyzed and classified according to their temporal scale. Besides the three main classes of cases corresponding to the main meteorological scales, local, mesoscale and synoptic, a fourth group constituted by complex events with high intense rates for a large range of durations has been identified also, indicating the contribution of different scale meteorological processes acting together in the origin of the rainfall. A weighted intensity index taking into account the maximum rainfall rate in representative durations of every meteorological scale has been calculated for every extreme rainfall event in order to reflect their complexity.
The final publication is available at Springer via http://dx.doi.org/10.1007/s00704-015-1476-0
2015-04-25T00:00:00ZGeneralized equipartition theorem and confining walls
http://hdl.handle.net/2117/28219
Generalized equipartition theorem and confining walls
Rey Oriol, Rosendo
It is shown that the generalized equipartition theorem as applied to the momentum may fail, even though the usual conditions of validity are met. This failure is linked to the nature of the confining walls, with ideal walls constituting a singular case. The corresponding analysis illustrates the use of proper sets of canonical coordinates, and the utility of canonical transformations other than point transformations.
2015-06-01T00:00:00ZA Chandrasekhar mass progenitor for the type Ia supernova remnant 3C 397 from the enhanced abundances of nickel and manganese
http://hdl.handle.net/2117/28214
A Chandrasekhar mass progenitor for the type Ia supernova remnant 3C 397 from the enhanced abundances of nickel and manganese
Yamaguchi, H; Badenes, Carles; Foster, Adam; Bravo Guil, Eduardo; Williams, Brian; Maeda, Keichi; Nobukawa, Masayoshi; Eriksen, Kristoffer; Brickhouse, Nancy; Petre, Robert; Koyama, Katsuyi
Despite decades of intense efforts, many fundamental aspects of Type Ia supernovae (SNe Ia) remain elusive. One of the major open questions is whether the mass of an exploding white dwarf (WD) is close to the Chandrasekhar limit. Here, we report the detection of strong K-shell emission from stable Fe-peak elements in the Suzaku X-ray spectrum of the Type Ia supernova remnant (SNR) 3C 397. The high Ni/Fe and Mn/Fe mass ratios (0.11–0.24 and 0.018–0.033, respectively) in the hot plasma component that dominates the K-shell emission lines indicate a degree of neutronization in the supernova ejecta that can only be achieved by electron capture in the dense cores of exploding WDs with a near-Chandrasekhar mass. This suggests a single-degenerate origin for 3C 397, since Chandrasekhar mass progenitors are expected naturally if the WD accretes mass slowly from a companion. Together with other results supporting the double-degenerate scenario, our work adds to the mounting evidence that both progenitor channels make a significant contribution to the SN Ia rate in star-forming galaxies.
2015-03-12T00:00:00ZLifespan method as a tool to study criticality in absorbing-state phase transitions
http://hdl.handle.net/2117/28182
Lifespan method as a tool to study criticality in absorbing-state phase transitions
de Souza Mata, Angelica; Boguñá, Marian; Castellano, Claudio; Pastor Satorras, Romualdo
In a recent work, a new numerical method (the lifespan method) has been introduced to study the critical properties of epidemic processes on complex networks [M. Boguna, C. Castellano, and R. Pastor-Satorras, Phys. Rev. Lett. 111, 068701 (2013)]. Here, we present a detailed analysis of the viability of this method for the study of the critical properties of generic absorbing-state phase transitions in lattices. Focusing on the well-understood case of the contact process, we develop a finite-size scaling theory to measure the critical point and its associated critical exponents. We show the validity of the method by studying numerically the contact process on a one-dimensional lattice and comparing the findings of the lifespan method with the standard quasistationary method. We find that the lifespan method gives results that are perfectly compatible with those of quasistationary simulations and with analytical results. Our observations confirm that the lifespan method is a fully legitimate tool for the study of the critical properties of absorbing phase transitions in regular lattices.
2015-05-12T00:00:00ZAcoustically penetrable sonic crystals based on fluid-like scatterers
http://hdl.handle.net/2117/28088
Acoustically penetrable sonic crystals based on fluid-like scatterers
Cebrecos, A.; Romero García, Vicenç; Pico Vila, Rubén; Sánchez Morcillo, Victor José; Botey Cumella, Muriel; Herrero Simon, Ramon; Cheng, Yu Chieh; Staliunas, Kestutis
We propose a periodic structure that behaves as a fluid-fluid composite for sound waves, where the building blocks are clusters of rigid scatterers. Such building-blocks are penetrable for acoustic waves, and their properties can be tuned by selecting the filling fraction. The equivalence with a fluid-fluid system of such a doubly periodic composite is tested analytical and experimentally. Because of the fluid-like character of the scatterers, sound structure interaction is negligible, and the propagation can be described by scalar models, analogous to those used in electromagnetics. As an example, the case of focusing of evanescent waves and the guided propagation of acoustic waves along an array of penetrable elements is discussed in detail. The proposed structure may be a real alternative to design a low contrast and acoustically penetrable medium where new properties as those shown in this work could be experimentally realized.
2015-01-21T00:00:00Z