Articles de revista
http://hdl.handle.net/2117/3984
2016-09-30T16:56:04ZLangevin equation approach for slow dynamics in magnetic systems
http://hdl.handle.net/2117/79563
Langevin equation approach for slow dynamics in magnetic systems
Sancho, Jose Maria; Lacasta Palacio, Ana María; Torrent Serra, Maria del Carmen; García Ojalvo, Jordi; Tejeda Gómez, José Arturo
We present a magnetic model based on a Langevin equation which exhibits slow relaxation dynamics of ln(t) type. The system is composed of magnetic particles which are under the influence of a local potential and interact through a mean field. Recent experimental data are interpreted within this model.
2015-11-23T12:56:01ZSancho, Jose MariaLacasta Palacio, Ana MaríaTorrent Serra, Maria del CarmenGarcía Ojalvo, JordiTejeda Gómez, José ArturoWe present a magnetic model based on a Langevin equation which exhibits slow relaxation dynamics of ln(t) type. The system is composed of magnetic particles which are under the influence of a local potential and interact through a mean field. Recent experimental data are interpreted within this model.Fractal structure and predictive strategy of the daily extreme temperature residuals at Fabra Observatory (NE Spain, years 1917-2005)
http://hdl.handle.net/2117/78472
Fractal structure and predictive strategy of the daily extreme temperature residuals at Fabra Observatory (NE Spain, years 1917-2005)
Lana Pons, Francisco Javier; Burgueño, August; Serra de Larrocha, Carina; Martínez Santafé, Maria Dolors
A compilation of daily extreme temperatures recorded at the Fabra Observatory (Catalonia, NE Spain) since 1917 up to 2005 has permitted an exhaustive analysis of the fractal behaviour of the daily extreme temperature residuals, DTR, defined as the difference between the observed daily extreme temperature and the daily average value. The lacunarity characterises the lag distribution on the residual series for several thresholds. Hurst, H, and Hausdorff, Ha, exponents, together with the exponent beta of the decaying power law, describing the evolution of power spectral density with frequency, permit to characterise the persistence, antipersistence or randomness of the residual series. The self-affine character of DTR series is verified, and additionally, they are simulated by means of fractional Gaussian noise, fGn. The reconstruction theorem leads to the quantification of the complexity (correlation dimension, mu*, and Kolmogorov entropy, kappa.) and predictive instability (Lyapunov exponents, lambda, and Kaplan-Yorke dimension, D-KY) of the residual series. All fractal parameters are computed for consecutive and independent segments of 5-year lengths. This strategy permits to obtain a high enough number of fractal parameter samples to estimate time trends, including their statistical significance. Comparisons are made between results of predictive algorithms based on fGn models and an autoregressive autoregressive integrated moving average (ARIMA) process, with the latter leading to slightly better results than the former. Several dynamic atmospheric mechanisms and local effects, such as local topography and vicinity to the Mediterranean coast, are proposed to explain the complex and instable predictability of DTR series. The memory of the physical system (Kolmogorov entropy) would be attributed to the interaction with the Mediterranean Sea.
2015-10-29T10:50:38ZLana Pons, Francisco JavierBurgueño, AugustSerra de Larrocha, CarinaMartínez Santafé, Maria DolorsA compilation of daily extreme temperatures recorded at the Fabra Observatory (Catalonia, NE Spain) since 1917 up to 2005 has permitted an exhaustive analysis of the fractal behaviour of the daily extreme temperature residuals, DTR, defined as the difference between the observed daily extreme temperature and the daily average value. The lacunarity characterises the lag distribution on the residual series for several thresholds. Hurst, H, and Hausdorff, Ha, exponents, together with the exponent beta of the decaying power law, describing the evolution of power spectral density with frequency, permit to characterise the persistence, antipersistence or randomness of the residual series. The self-affine character of DTR series is verified, and additionally, they are simulated by means of fractional Gaussian noise, fGn. The reconstruction theorem leads to the quantification of the complexity (correlation dimension, mu*, and Kolmogorov entropy, kappa.) and predictive instability (Lyapunov exponents, lambda, and Kaplan-Yorke dimension, D-KY) of the residual series. All fractal parameters are computed for consecutive and independent segments of 5-year lengths. This strategy permits to obtain a high enough number of fractal parameter samples to estimate time trends, including their statistical significance. Comparisons are made between results of predictive algorithms based on fGn models and an autoregressive autoregressive integrated moving average (ARIMA) process, with the latter leading to slightly better results than the former. Several dynamic atmospheric mechanisms and local effects, such as local topography and vicinity to the Mediterranean coast, are proposed to explain the complex and instable predictability of DTR series. The memory of the physical system (Kolmogorov entropy) would be attributed to the interaction with the Mediterranean Sea.Aftershock sequences of three seismic crises at southern California, USA, simulated by a cellular automata model based on self-organized criticality
http://hdl.handle.net/2117/78319
Aftershock sequences of three seismic crises at southern California, USA, simulated by a cellular automata model based on self-organized criticality
Monterrubio Velasco, Marisol; Lana Pons, Francisco Javier; Martínez Santafé, Maria Dolors
Several properties of aftershock series related to the main shocks of Landers, Northridge and Hector Mine (southern California, USA) are reproduced by the Dynamic Fiber Bundle Model, DFBM. Optimum values for the three parameters governing DFBM are determined by searching for the best agreement of real aftershock series properties and those of synthetic sequences generated by this model. The analysis of the model parameter values provides details on the underlying physical mechanism of the aftershock sequence generation. First, the ratio of seismic energy radiated as seismic waves and transferred as stress-strain to adjacent faults; second, the degree of stress heterogeneity reproducing the complex behavior of real aftershock series. Additionally, the results of simulations support the coexistence of two types of relaxation processes. One of them is associated with the well-known modified Omori's (MO) law, which involves elapsed times between consecutive aftershocks monotonically increasing; the other is manifested by episodes of sudden stress release, with inter-event times much shorter than those predicted by MO law. These episodes are assumed to be a consequence of the complex distribution of tectonic stresses and fault geometry. The first process is associated to events designed as leading aftershocks, LA. The second process generates series of events which are designed as cascades, CA. It is worth of mention that several properties concerning CAs can be reasonably related to critical changes on stress field along the simulation process.
2015-10-27T11:12:24ZMonterrubio Velasco, MarisolLana Pons, Francisco JavierMartínez Santafé, Maria DolorsSeveral properties of aftershock series related to the main shocks of Landers, Northridge and Hector Mine (southern California, USA) are reproduced by the Dynamic Fiber Bundle Model, DFBM. Optimum values for the three parameters governing DFBM are determined by searching for the best agreement of real aftershock series properties and those of synthetic sequences generated by this model. The analysis of the model parameter values provides details on the underlying physical mechanism of the aftershock sequence generation. First, the ratio of seismic energy radiated as seismic waves and transferred as stress-strain to adjacent faults; second, the degree of stress heterogeneity reproducing the complex behavior of real aftershock series. Additionally, the results of simulations support the coexistence of two types of relaxation processes. One of them is associated with the well-known modified Omori's (MO) law, which involves elapsed times between consecutive aftershocks monotonically increasing; the other is manifested by episodes of sudden stress release, with inter-event times much shorter than those predicted by MO law. These episodes are assumed to be a consequence of the complex distribution of tectonic stresses and fault geometry. The first process is associated to events designed as leading aftershocks, LA. The second process generates series of events which are designed as cascades, CA. It is worth of mention that several properties concerning CAs can be reasonably related to critical changes on stress field along the simulation process.Criticality in the slowed-down boiling crisis at zero gravity
http://hdl.handle.net/2117/78228
Criticality in the slowed-down boiling crisis at zero gravity
Charignon, Thomas; Lloveras Muntané, Pol Marcel; Chatain, Denis; Truskinovsky, Lev; Vives, Eduard; Beysens, Daniel; Nikolayev, Vadim
Boiling crisis is a transition between nucleate and film boiling. It occurs at a threshold value of the heat flux from the heater called CHF (critical heat flux). Usually, boiling crisis studies are hindered by the high CHF and short transition duration (below 1 ms). Here we report on experiments in hydrogen near its liquid-vapor critical point, in which the CHF is low and the dynamics slow enough to be resolved. As under such conditions the surface tension is very small, the experiments are carried out in the reduced gravity to preserve the conventional bubble geometry. Weightlessness is created artificially in two-phase hydrogen by compensating gravity with magnetic forces. We were able to reveal the fractal structure of the contour of the percolating cluster of the dry areas at the heater that precedes the boiling crisis. We provide a direct statistical analysis of dry spot areas that confirms the boiling crisis at zero gravity as a scale-free phenomenon. It was observed that, in agreement with theoretical predictions, saturated boiling CHF tends to zero (within the precision of our thermal control system) in zero gravity, which suggests that the boiling crisis may be observed at any heat flux provided the experiment lasts long enough.
2015-10-26T12:12:09ZCharignon, ThomasLloveras Muntané, Pol MarcelChatain, DenisTruskinovsky, LevVives, EduardBeysens, DanielNikolayev, VadimBoiling crisis is a transition between nucleate and film boiling. It occurs at a threshold value of the heat flux from the heater called CHF (critical heat flux). Usually, boiling crisis studies are hindered by the high CHF and short transition duration (below 1 ms). Here we report on experiments in hydrogen near its liquid-vapor critical point, in which the CHF is low and the dynamics slow enough to be resolved. As under such conditions the surface tension is very small, the experiments are carried out in the reduced gravity to preserve the conventional bubble geometry. Weightlessness is created artificially in two-phase hydrogen by compensating gravity with magnetic forces. We were able to reveal the fractal structure of the contour of the percolating cluster of the dry areas at the heater that precedes the boiling crisis. We provide a direct statistical analysis of dry spot areas that confirms the boiling crisis at zero gravity as a scale-free phenomenon. It was observed that, in agreement with theoretical predictions, saturated boiling CHF tends to zero (within the precision of our thermal control system) in zero gravity, which suggests that the boiling crisis may be observed at any heat flux provided the experiment lasts long enough.Slow relaxation dynamics and aging in random walks on activity driven temporal networks
http://hdl.handle.net/2117/77865
Slow relaxation dynamics and aging in random walks on activity driven temporal networks
Sousa da Mata, Angelica; Pastor Satorras, Romualdo
We investigate the dynamic relaxation of random walks on temporal networks by focusing in the recently proposed activity driven model [N. Perra, B. Gon, calves, R. Pastor-Satorras, A. Vespignani, Sci. Rep. 2, 469 (2012)]. For realistic activity distributions with a power-law form, we observe the presence of a very slow relaxation dynamics compatible with aging effects. A theoretical description of this processes in achieved by means of a mapping to Bouchaud's trap model. The mapping highlights the profound difference in the dynamics of the random walks according to the value of the exponent gamma in the activity distribution.
2015-10-19T09:20:07ZSousa da Mata, AngelicaPastor Satorras, RomualdoWe investigate the dynamic relaxation of random walks on temporal networks by focusing in the recently proposed activity driven model [N. Perra, B. Gon, calves, R. Pastor-Satorras, A. Vespignani, Sci. Rep. 2, 469 (2012)]. For realistic activity distributions with a power-law form, we observe the presence of a very slow relaxation dynamics compatible with aging effects. A theoretical description of this processes in achieved by means of a mapping to Bouchaud's trap model. The mapping highlights the profound difference in the dynamics of the random walks according to the value of the exponent gamma in the activity distribution.Insights into Q2Qbar2 states from an effective perspective
http://hdl.handle.net/2117/77626
Insights into Q2Qbar2 states from an effective perspective
Ametller Congost, Lluís; Talavera Sánchez, Pedro
We discuss the two-photon coupling of the lightest scalar meson on the basis of an extension of χPT. Using low-energy data on the pion form factor and the γγ→π+π−(π0π0) cross sections as inputs, we find Γ(σ→γγ)≅0.126 keV. The smallness of the result and the relative weight between its components, Γγγ→S1Γγγ→ππ→S1≤1, suggests that the scalar 0++ meson is mainly a Q2Q¯2 state.
2015-10-13T12:55:24ZAmetller Congost, LluísTalavera Sánchez, PedroWe discuss the two-photon coupling of the lightest scalar meson on the basis of an extension of χPT. Using low-energy data on the pion form factor and the γγ→π+π−(π0π0) cross sections as inputs, we find Γ(σ→γγ)≅0.126 keV. The smallness of the result and the relative weight between its components, Γγγ→S1Γγγ→ππ→S1≤1, suggests that the scalar 0++ meson is mainly a Q2Q¯2 state.Is long range transport of pollen in the NW Mediterranean basin influenced by Northern Hemisphere teleconnection patterns?
http://hdl.handle.net/2117/77398
Is long range transport of pollen in the NW Mediterranean basin influenced by Northern Hemisphere teleconnection patterns?
Izquierdo Miguel, Rebeca; Alarcón Jordán, Marta; Periago Oliver, M. Cristina; Belmonte Soler, Jordina
Climatic oscillations triggered by the atmospheric modes of the Northern Hemisphere teleconnection patterns have an important influence on the atmospheric circulation at synoptic scale in Western Mediterranean Basin. Simultaneously, this climate variability could affect a variety of ecological processes. This work provides a first assessment of the effect of North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Western Mediterranean Oscillation (WeMO) on the atmospheric long-range pollen transport episodes in the North-Eastern Iberian Peninsula for the period 1994–2011. Alnus, Ambrosia, Betula, Corylus and Fagus have been selected as allergenic pollen taxa with potential long-range transport associated to the Northern Hemisphere teleconnection patterns in the Western Mediterranean Basin. The results showed an increase of long range pollen transport episodes of: (1) Alnus, Corylus and Fagus from Western and Central Europe during the negative phase of annual NAO and AO; (2) Ambrosia, Betula and Fagus from Europe during the negative phase of winter WeMO; (3) Corylus and Fagus from Mediterranean area during the positive phase of the annual AO; and (4) Ambrosia from France and Northern Europe during the positive phase of winter WeMO. Conversely, the positive phase of annual NAO and AO are linked with the regional transport of Alnus, Betula and Corylus from Western Iberian Peninsula. The positive phase of annual WeMO was also positively correlated with regional transport of Corylus from this area.
2015-10-06T17:20:17ZIzquierdo Miguel, RebecaAlarcón Jordán, MartaPeriago Oliver, M. CristinaBelmonte Soler, JordinaClimatic oscillations triggered by the atmospheric modes of the Northern Hemisphere teleconnection patterns have an important influence on the atmospheric circulation at synoptic scale in Western Mediterranean Basin. Simultaneously, this climate variability could affect a variety of ecological processes. This work provides a first assessment of the effect of North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Western Mediterranean Oscillation (WeMO) on the atmospheric long-range pollen transport episodes in the North-Eastern Iberian Peninsula for the period 1994–2011. Alnus, Ambrosia, Betula, Corylus and Fagus have been selected as allergenic pollen taxa with potential long-range transport associated to the Northern Hemisphere teleconnection patterns in the Western Mediterranean Basin. The results showed an increase of long range pollen transport episodes of: (1) Alnus, Corylus and Fagus from Western and Central Europe during the negative phase of annual NAO and AO; (2) Ambrosia, Betula and Fagus from Europe during the negative phase of winter WeMO; (3) Corylus and Fagus from Mediterranean area during the positive phase of the annual AO; and (4) Ambrosia from France and Northern Europe during the positive phase of winter WeMO. Conversely, the positive phase of annual NAO and AO are linked with the regional transport of Alnus, Betula and Corylus from Western Iberian Peninsula. The positive phase of annual WeMO was also positively correlated with regional transport of Corylus from this area.Phase transition in hydrogen-bonded 1-adamantane-methanol
http://hdl.handle.net/2117/77015
Phase transition in hydrogen-bonded 1-adamantane-methanol
Ben Hassine, Bacem; Negrier, Philippe; Barrio Casado, María del; Mondieig, Denise; Massip, Stephane; Tamarit Mur, José Luis
The polymorphism of 1-adarnantane-methanol C11H18O has been investigated by differential thermal analysis and single-crystal and powder X-ray diffraction. Below the melting temperature (389.5 +/- 0.4 K), this compound exhibits an orthorhombic phase (phase I, Pnnm, Z = 12, Z' = 1.5). The melting enthalpy was determined to be 20.5 +/- 0.4 kJ mol(-1), i.e., with an entropy change of (6.34 +/- 0.13)R, which is much higher than the quoted value from Timmermans for the melting orientationally disordered phases (2.5R), thus supporting the orientationally ordered character of phase I. This orthorhombic phase I exhibits a statistical disorder of the hydrogen atom related to the oxygen atom, due to the position of one independent molecule on the mirror. At ca. 272 K, phase I transforms continuously through an order disorder transition to a low-temperature monoclinic phase II (P2(1)/n, Z = 12, Z' = 3). The monoclinic and orthorhombic phases are related by a group subgroup relationship, which perfectly agrees with the continuous character of the II to I transition. Moreover, by a convenient choice of an order parameter related to the continuous tilt of the c-axis, the critical exponent for this transition is found to be close to the theoretical prediction of the three-dimensional Ising model (with a critical exponent of ca. 0.27).
2015-09-22T11:46:59ZBen Hassine, BacemNegrier, PhilippeBarrio Casado, María delMondieig, DeniseMassip, StephaneTamarit Mur, José LuisThe polymorphism of 1-adarnantane-methanol C11H18O has been investigated by differential thermal analysis and single-crystal and powder X-ray diffraction. Below the melting temperature (389.5 +/- 0.4 K), this compound exhibits an orthorhombic phase (phase I, Pnnm, Z = 12, Z' = 1.5). The melting enthalpy was determined to be 20.5 +/- 0.4 kJ mol(-1), i.e., with an entropy change of (6.34 +/- 0.13)R, which is much higher than the quoted value from Timmermans for the melting orientationally disordered phases (2.5R), thus supporting the orientationally ordered character of phase I. This orthorhombic phase I exhibits a statistical disorder of the hydrogen atom related to the oxygen atom, due to the position of one independent molecule on the mirror. At ca. 272 K, phase I transforms continuously through an order disorder transition to a low-temperature monoclinic phase II (P2(1)/n, Z = 12, Z' = 3). The monoclinic and orthorhombic phases are related by a group subgroup relationship, which perfectly agrees with the continuous character of the II to I transition. Moreover, by a convenient choice of an order parameter related to the continuous tilt of the c-axis, the critical exponent for this transition is found to be close to the theoretical prediction of the three-dimensional Ising model (with a critical exponent of ca. 0.27).Epidemic processes in complex networks
http://hdl.handle.net/2117/77005
Epidemic processes in complex networks
Pastor Satorras, Romualdo; Castellano, Claudio; Van Mieghem, Piet; Vespignani, Alessandro
In recent years the research community has accumulated overwhelming evidence for the emergence of complex and heterogeneous connectivity patterns in a wide range of biological and sociotechnical systems. The complex properties of real-world networks have a profound impact on the behavior of equilibrium and nonequilibrium phenomena occurring in various systems, and the study of epidemic spreading is central to our understanding of the unfolding of dynamical processes in complex networks. The theoretical analysis of epidemic spreading in heterogeneous networks requires the development of novel analytical frameworks, and it has produced results of conceptual and practical relevance. A coherent and comprehensive review of the vast research activity concerning epidemic processes is presented, detailing the successful theoretical approaches as well as making their limits and assumptions clear. Physicists, mathematicians, epidemiologists, computer, and social scientists share a common interest in studying epidemic spreading and rely on similar models for the description of the diffusion of pathogens, knowledge, and innovation. For this reason, while focusing on the main results and the paradigmatic models in infectious disease modeling, the major results concerning generalized social contagion processes are also presented. Finally, the research activity at the forefront in the study of epidemic spreading in coevolving, coupled, and time-varying networks is reported.
2015-09-22T08:32:01ZPastor Satorras, RomualdoCastellano, ClaudioVan Mieghem, PietVespignani, AlessandroIn recent years the research community has accumulated overwhelming evidence for the emergence of complex and heterogeneous connectivity patterns in a wide range of biological and sociotechnical systems. The complex properties of real-world networks have a profound impact on the behavior of equilibrium and nonequilibrium phenomena occurring in various systems, and the study of epidemic spreading is central to our understanding of the unfolding of dynamical processes in complex networks. The theoretical analysis of epidemic spreading in heterogeneous networks requires the development of novel analytical frameworks, and it has produced results of conceptual and practical relevance. A coherent and comprehensive review of the vast research activity concerning epidemic processes is presented, detailing the successful theoretical approaches as well as making their limits and assumptions clear. Physicists, mathematicians, epidemiologists, computer, and social scientists share a common interest in studying epidemic spreading and rely on similar models for the description of the diffusion of pathogens, knowledge, and innovation. For this reason, while focusing on the main results and the paradigmatic models in infectious disease modeling, the major results concerning generalized social contagion processes are also presented. Finally, the research activity at the forefront in the study of epidemic spreading in coevolving, coupled, and time-varying networks is reported.Triethylenetetramine dihydrochloride: interactions and conformations in two anhydrous structures and a hydrate
http://hdl.handle.net/2117/76847
Triethylenetetramine dihydrochloride: interactions and conformations in two anhydrous structures and a hydrate
Henriet, Theo; Nicolai, Beatrice; Ghaddar, Carine; Barrio Casado, María del; Do, Bernard; Yagoubi, Najet; Tamarit Mur, José Luis; Rietveld, Ivo B.
Triethylenetetramine is a polyamine type chelating ligand for copper(II), which is currently used, mainly in its dihydrochloride form, as an alternative to d-penicillamine against Wilsons disease. Because knowledge about the solid-state behavior of pharmaceuticals is a prerequisite for the development of an effective dosage form, the crystal structures of two triethylenetetramine dihydrochloride polymorphs have been determined, and the infrared spectra and thermal expansion have been studied. No suitable crystals could be obtained of the two anhydrous forms, for which the structures have been solved from X-ray powder diffraction. Form I is monoclinic P2(1)/n with the cell parameters a = 11.0475(4) angstrom, b = 4.87475(16) angstrom, c = 11.1178(4) angstrom, and beta = 106.9826(13)degrees leading to V = 572.63(3) angstrom(3) with Z = 2. Form II is also monoclinic P2(1)/c with cell parameters a = 10.6734(6) angstrom, b = 12.3613(6) angstrom, c = 9.8479(7) angstrom, and beta = 115.985(3)degrees leading to a unit-cell volume of V = 1167.95(12) angstrom(3) with Z = 4. A recurring structural element is a ionic interaction between two chloride ions and two ammonium groups each organized in a diamond pattern present in the dihydrate (the salt is hygroscopic) and anhydrous form I. The molecular conformations are different in both anhydrous forms and in the dihydrate. Comparison of the thermal expansions demonstrates that form I has the smallest thermal expansion and thus possesses the strongest intermolecular interactions.
2015-09-16T11:05:24ZHenriet, TheoNicolai, BeatriceGhaddar, CarineBarrio Casado, María delDo, BernardYagoubi, NajetTamarit Mur, José LuisRietveld, Ivo B.Triethylenetetramine is a polyamine type chelating ligand for copper(II), which is currently used, mainly in its dihydrochloride form, as an alternative to d-penicillamine against Wilsons disease. Because knowledge about the solid-state behavior of pharmaceuticals is a prerequisite for the development of an effective dosage form, the crystal structures of two triethylenetetramine dihydrochloride polymorphs have been determined, and the infrared spectra and thermal expansion have been studied. No suitable crystals could be obtained of the two anhydrous forms, for which the structures have been solved from X-ray powder diffraction. Form I is monoclinic P2(1)/n with the cell parameters a = 11.0475(4) angstrom, b = 4.87475(16) angstrom, c = 11.1178(4) angstrom, and beta = 106.9826(13)degrees leading to V = 572.63(3) angstrom(3) with Z = 2. Form II is also monoclinic P2(1)/c with cell parameters a = 10.6734(6) angstrom, b = 12.3613(6) angstrom, c = 9.8479(7) angstrom, and beta = 115.985(3)degrees leading to a unit-cell volume of V = 1167.95(12) angstrom(3) with Z = 4. A recurring structural element is a ionic interaction between two chloride ions and two ammonium groups each organized in a diamond pattern present in the dihydrate (the salt is hygroscopic) and anhydrous form I. The molecular conformations are different in both anhydrous forms and in the dihydrate. Comparison of the thermal expansions demonstrates that form I has the smallest thermal expansion and thus possesses the strongest intermolecular interactions.