Articles de revista
http://hdl.handle.net/2117/1087
Sat, 13 Feb 2016 09:07:04 GMT2016-02-13T09:07:04ZOscillatory convection in rotating spherical shells: low Prandtl number and non-slip boundary conditions
http://hdl.handle.net/2117/82104
Oscillatory convection in rotating spherical shells: low Prandtl number and non-slip boundary conditions
García González, Fernando; Sánchez Umbría, Juan; Dormy, Emmanuel; Net Marcé, Marta
A five-degree model, which reproduces faithfully the sequence of bifurcations and the type of solutions found through numerical simulations of the three-dimensional Boussinesq thermal convection
equations in rotating spherical shells with fixed azimuthal symmetry, is derived. A low Prandtl number fluid of s=0. 1 subject to radial gravity, filling a shell of radius ratio ¿=0.35, differentially heated, and with non-slip boundary conditions, is considered. Periodic, quasi-periodic, and temporal chaotic flows are obtained for a moderately small Ekman number, E=10-4,andatsupercritical Rayleigh numbers of order
Ra~O(2Rac). The solutions are classified by means of
frequency analysis and Poincaré sections. Resonant phase locking on the quasi-periodic branches,as well as a sequence of period doubling bifurcations, are also detected.
Wed, 27 Jan 2016 09:57:30 GMThttp://hdl.handle.net/2117/821042016-01-27T09:57:30ZGarcía González, FernandoSánchez Umbría, JuanDormy, EmmanuelNet Marcé, MartaA five-degree model, which reproduces faithfully the sequence of bifurcations and the type of solutions found through numerical simulations of the three-dimensional Boussinesq thermal convection
equations in rotating spherical shells with fixed azimuthal symmetry, is derived. A low Prandtl number fluid of s=0. 1 subject to radial gravity, filling a shell of radius ratio ¿=0.35, differentially heated, and with non-slip boundary conditions, is considered. Periodic, quasi-periodic, and temporal chaotic flows are obtained for a moderately small Ekman number, E=10-4,andatsupercritical Rayleigh numbers of order
Ra~O(2Rac). The solutions are classified by means of
frequency analysis and Poincaré sections. Resonant phase locking on the quasi-periodic branches,as well as a sequence of period doubling bifurcations, are also detected.Corrigendum: particle production from marginally trapped surfaces of general spacetimes
http://hdl.handle.net/2117/81212
Corrigendum: particle production from marginally trapped surfaces of general spacetimes
Senovilla, José MM; Torres Herrera, Ramon
We correct some computations presented in section 4.2 of the article (Class. Quantum Grav. {\bf 32} (2015) 085004), concerning the Kerr-Vaidya space-time. The correct, new results, do support the claims in the paper.
This is an author created, un copyedited version of an article accepted for publication in Classical and quantum gravity. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.
The Version of Record is available online at http://dx.doi.org/10.1088/0264-9381/32/18/189501.
Mon, 11 Jan 2016 13:53:21 GMThttp://hdl.handle.net/2117/812122016-01-11T13:53:21ZSenovilla, José MMTorres Herrera, RamonWe correct some computations presented in section 4.2 of the article (Class. Quantum Grav. {\bf 32} (2015) 085004), concerning the Kerr-Vaidya space-time. The correct, new results, do support the claims in the paper.Mathematical modeling of different molecule removal on on-line haemodiafiltration. Influence of dialysis duration and infusion flow
http://hdl.handle.net/2117/80981
Mathematical modeling of different molecule removal on on-line haemodiafiltration. Influence of dialysis duration and infusion flow
Maduell, Francesc; Sánchez Umbría, Juan; Net Marcé, Marta; Gómez, Miquel; González, Josep Maria; Arias, Marta; Rodriguez, Nestor; Rico, N.; Campistol, Josep
Background: In a previous study on a nocturnal, every-other-day online haemodiafiltration scheme, different removal patterns were observed for urea, creatinine, ß2-¿microglobulin, myoglobin and prolactin. The aim of this study was to evaluate the influence of dialysis duration and infusion flow (Qi) on the removal of different molecular weight (MW) solutes, and to quantify the effect of the different treatments on the kinetics of the solutes by using a classical two-compartment model. Methods: This prospective, in-center study was carried out in 10 patients on a nocturnal, every-other-day online post-dilution haemodiafiltration program. Each patient received four dialysis sessions with different conditions, two 4-h sessions (with infusion flows of 50 or 100 ml/min) and two 8-h sessions (with infusion flows of 50 or 100 ml/min). To analyze the solute kinetics, blood samples were obtained hourly during the dialysis treatments and in the first 3 h post-dialysis. Results: Removal patterns differed in the molecules studied, which were quantified by means of the two-compartment mathematical model. The main results show the impact of dialysis duration on the removal of low molecular weight molecules (urea and creatinine), while the impact of Qi is clearly shown for high molecular weight molecules (myoglobin and prolactin). For middle molecular weight solutes, such as ß2-microglobulin, both factors (duration and Qi) enhance the removal efficiency of the dialyzer. Conclusions: Our study evaluates experimentally and mathematically how treatment time and infusion flow affect the filtration of solutes of different MW during post-dilution haemodiafiltration. The results provided by the present study should help physicians to select and individualise the most appropriate schedules to deliver an optimum diffusive and convective dialysis dose for each patient.
Tue, 22 Dec 2015 10:38:52 GMThttp://hdl.handle.net/2117/809812015-12-22T10:38:52ZMaduell, FrancescSánchez Umbría, JuanNet Marcé, MartaGómez, MiquelGonzález, Josep MariaArias, MartaRodriguez, NestorRico, N.Campistol, JosepBackground: In a previous study on a nocturnal, every-other-day online haemodiafiltration scheme, different removal patterns were observed for urea, creatinine, ß2-¿microglobulin, myoglobin and prolactin. The aim of this study was to evaluate the influence of dialysis duration and infusion flow (Qi) on the removal of different molecular weight (MW) solutes, and to quantify the effect of the different treatments on the kinetics of the solutes by using a classical two-compartment model. Methods: This prospective, in-center study was carried out in 10 patients on a nocturnal, every-other-day online post-dilution haemodiafiltration program. Each patient received four dialysis sessions with different conditions, two 4-h sessions (with infusion flows of 50 or 100 ml/min) and two 8-h sessions (with infusion flows of 50 or 100 ml/min). To analyze the solute kinetics, blood samples were obtained hourly during the dialysis treatments and in the first 3 h post-dialysis. Results: Removal patterns differed in the molecules studied, which were quantified by means of the two-compartment mathematical model. The main results show the impact of dialysis duration on the removal of low molecular weight molecules (urea and creatinine), while the impact of Qi is clearly shown for high molecular weight molecules (myoglobin and prolactin). For middle molecular weight solutes, such as ß2-microglobulin, both factors (duration and Qi) enhance the removal efficiency of the dialyzer. Conclusions: Our study evaluates experimentally and mathematically how treatment time and infusion flow affect the filtration of solutes of different MW during post-dilution haemodiafiltration. The results provided by the present study should help physicians to select and individualise the most appropriate schedules to deliver an optimum diffusive and convective dialysis dose for each patient.Understanding coastal morphodynamic patterns from depth-averaged sediment concentration
http://hdl.handle.net/2117/79295
Understanding coastal morphodynamic patterns from depth-averaged sediment concentration
Ribas Prats, Francesca; Falqués Serra, Albert; de Swart, Huib E.; Dodd, Nicholas; Garnier, Roland Charles; Calvete Manrique, Daniel
This review highlights the important role of the depth-averaged sediment concentration
(DASC) to understand the formation of a number of coastal morphodynamic features that have an
alongshore rhythmic pattern: beach cusps, surf zone transverse and crescentic bars, and
shoreface-connected sand ridges. We present a formulation and methodology, based on the knowledge
of the DASC (which equals the sediment load divided by the water depth), that has been successfully used
to understand the characteristics of these features. These sand bodies, relevant for coastal engineering and
other disciplines, are located in different parts of the coastal zone and are characterized by different spatial
and temporal scales, but the same technique can be used to understand them. Since the sand bodies occur
in the presence of depth-averaged currents, the sediment transport approximately equals a sediment load
times the current. Moreover, it is assumed that waves essentially mobilize the sediment, and the current
increases this mobilization and advects the sediment. In such conditions, knowing the spatial distribution
of the DASC and the depth-averaged currents induced by the forcing (waves, wind, and pressure gradients)
over the patterns allows inferring the convergence/divergence of sediment transport. Deposition (erosion)
occurs where the current flows from areas of high to low (low to high) values of DASC. The formulation and
methodology are especially useful to understand the positive feedback mechanisms between flow and
morphology leading to the formation of those morphological features, but the physical mechanisms for
their migration, their finite-amplitude behavior and their decay can also be explored.
Mon, 16 Nov 2015 11:32:24 GMThttp://hdl.handle.net/2117/792952015-11-16T11:32:24ZRibas Prats, FrancescaFalqués Serra, Albertde Swart, Huib E.Dodd, NicholasGarnier, Roland CharlesCalvete Manrique, DanielThis review highlights the important role of the depth-averaged sediment concentration
(DASC) to understand the formation of a number of coastal morphodynamic features that have an
alongshore rhythmic pattern: beach cusps, surf zone transverse and crescentic bars, and
shoreface-connected sand ridges. We present a formulation and methodology, based on the knowledge
of the DASC (which equals the sediment load divided by the water depth), that has been successfully used
to understand the characteristics of these features. These sand bodies, relevant for coastal engineering and
other disciplines, are located in different parts of the coastal zone and are characterized by different spatial
and temporal scales, but the same technique can be used to understand them. Since the sand bodies occur
in the presence of depth-averaged currents, the sediment transport approximately equals a sediment load
times the current. Moreover, it is assumed that waves essentially mobilize the sediment, and the current
increases this mobilization and advects the sediment. In such conditions, knowing the spatial distribution
of the DASC and the depth-averaged currents induced by the forcing (waves, wind, and pressure gradients)
over the patterns allows inferring the convergence/divergence of sediment transport. Deposition (erosion)
occurs where the current flows from areas of high to low (low to high) values of DASC. The formulation and
methodology are especially useful to understand the positive feedback mechanisms between flow and
morphology leading to the formation of those morphological features, but the physical mechanisms for
their migration, their finite-amplitude behavior and their decay can also be explored.On the quantum corrected gravitational collapse
http://hdl.handle.net/2117/78988
On the quantum corrected gravitational collapse
Torres Herrera, Ramon; Fayos Vallés, Francisco
Based on a previously found general class of quantum improved exact solutions composed of non-interacting (dust) particles, we model the gravitational collapse of stars. As the modeled star collapses a closed apparent 3-horizon is generated due to the consideration of quantum effects. The effect of the subsequent emission of Hawking radiation related to this horizon is taken into consideration. Our computations lead us to argue that a total evaporation could be reached. The inferred global picture of the spacetime corresponding to gravitational collapse is devoid of both event horizons and shell-focusing singularities. As a consequence, there is no information paradox and no need of firewalls.
Tue, 10 Nov 2015 18:30:14 GMThttp://hdl.handle.net/2117/789882015-11-10T18:30:14ZTorres Herrera, RamonFayos Vallés, FranciscoBased on a previously found general class of quantum improved exact solutions composed of non-interacting (dust) particles, we model the gravitational collapse of stars. As the modeled star collapses a closed apparent 3-horizon is generated due to the consideration of quantum effects. The effect of the subsequent emission of Hawking radiation related to this horizon is taken into consideration. Our computations lead us to argue that a total evaporation could be reached. The inferred global picture of the spacetime corresponding to gravitational collapse is devoid of both event horizons and shell-focusing singularities. As a consequence, there is no information paradox and no need of firewalls.Lifted temperature minimum during the atmospheric evening transition
http://hdl.handle.net/2117/77669
Lifted temperature minimum during the atmospheric evening transition
Blay-Carreras, Estel; Pardyjak, Eric; Pino González, David; Hoch, Sebastian; Cuxart Rodamillans, Joan; Martínez, Daniel; Reuder, Joachim
Observations of lifted temperature minimum (LTM) profiles in the nocturnal boundary layer were first reported in 1932. It was defined by the existence of a temperature minimum some centimetres above the ground. During the following decades, several research studies analysed this phenomenon verifying its existence and postulating different hypotheses about its origin.
The aim of this work is to study the existence and characteristics of LTM during the evening transition by using observations obtained during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) campaign. Data obtained from two masts instrumented with thermocouples and wind sensors at different heights close to the ground and a mast with radiometers are used to study the role of mechanical turbulence and radiation in LTM development.
The study shows that LTM can be detected under calm conditions during the day–night transition, several hours earlier than reported in previous work. These conditions are fulfilled under weak synoptic forcing when the local flow shifts associated with a mountain–plain circulation in relatively complex orography. Under these special conditions, turbulence becomes a crucial parameter in determining the ideal conditions for observing LTM. Additionally, LTM observed profiles are also related to a change in the atmospheric radiative characteristics under calm conditions.
Wed, 14 Oct 2015 09:52:48 GMThttp://hdl.handle.net/2117/776692015-10-14T09:52:48ZBlay-Carreras, EstelPardyjak, EricPino González, DavidHoch, SebastianCuxart Rodamillans, JoanMartínez, DanielReuder, JoachimObservations of lifted temperature minimum (LTM) profiles in the nocturnal boundary layer were first reported in 1932. It was defined by the existence of a temperature minimum some centimetres above the ground. During the following decades, several research studies analysed this phenomenon verifying its existence and postulating different hypotheses about its origin.
The aim of this work is to study the existence and characteristics of LTM during the evening transition by using observations obtained during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) campaign. Data obtained from two masts instrumented with thermocouples and wind sensors at different heights close to the ground and a mast with radiometers are used to study the role of mechanical turbulence and radiation in LTM development.
The study shows that LTM can be detected under calm conditions during the day–night transition, several hours earlier than reported in previous work. These conditions are fulfilled under weak synoptic forcing when the local flow shifts associated with a mountain–plain circulation in relatively complex orography. Under these special conditions, turbulence becomes a crucial parameter in determining the ideal conditions for observing LTM. Additionally, LTM observed profiles are also related to a change in the atmospheric radiative characteristics under calm conditions.Turbulence vertical structure of the boundary layer during the afternoon transition
http://hdl.handle.net/2117/77577
Turbulence vertical structure of the boundary layer during the afternoon transition
Darbieu, Clara; Lohou, Fabienne; Lothon, Marie; Vilà Guerau de Arellano, Jordi; Couvreux, Fleur; Durand, Pierre; Pino González, David; Patton, Edward; Nilsson, Erik; Blay-Carreras, Estel; Gioli, Beniamino
We investigate the decay of planetary boundary
layer (PBL) turbulence in the afternoon, from the time the
surface buoyancy flux starts to decrease until sunset. Dense
observations of mean and turbulent parameters were acquired
during the Boundary Layer Late Afternoon and Sunset Tur-
bulence (BLLAST) field experiment by several meteorolog-
ical surface stations, sounding balloons, radars, lidars and
two aircraft during the afternoon transition. We analysed a
case study based on some of these observations and large-
eddy simulation (LES) data focusing on the turbulent vertical
structure throughout the afternoon transition.
The decay of turbulence is quantified through the temporal
and vertical evolution of (1) the turbulence kinetic energy
(TKE), (2) the characteristic length scales of turbulence and
(3) the shape of the turbulence spectra. A spectral analysis of
LES data, airborne and surface measurements is performed
in order to characterize the variation in the turbulent decay
with height and study the distribution of turbulence over eddy
size.
This study highlights the LES ability to reproduce the tur-
bulence evolution throughout the afternoon. LESs and obser-
vations agree that the afternoon transition can be divided in
two phases: (1) a first phase during which the TKE decays
at a low rate, with no significant change in turbulence char-
acteristics, and (2) a second phase characterized by a larger
TKE decay rate and a change in spectral shape, implying an
evolution of eddy size distribution and energy cascade from
low to high wave number.
The changes observed either in TKE decay (during the first
phase) or in the vertical wind spectra shape (during the sec-
ond phase of the afternoon transition) occur first in the upper
region of the PBL. The higher within the PBL, the stronger
the spectra shape changes
Tue, 13 Oct 2015 09:13:50 GMThttp://hdl.handle.net/2117/775772015-10-13T09:13:50ZDarbieu, ClaraLohou, FabienneLothon, MarieVilà Guerau de Arellano, JordiCouvreux, FleurDurand, PierrePino González, DavidPatton, EdwardNilsson, ErikBlay-Carreras, EstelGioli, BeniaminoWe investigate the decay of planetary boundary
layer (PBL) turbulence in the afternoon, from the time the
surface buoyancy flux starts to decrease until sunset. Dense
observations of mean and turbulent parameters were acquired
during the Boundary Layer Late Afternoon and Sunset Tur-
bulence (BLLAST) field experiment by several meteorolog-
ical surface stations, sounding balloons, radars, lidars and
two aircraft during the afternoon transition. We analysed a
case study based on some of these observations and large-
eddy simulation (LES) data focusing on the turbulent vertical
structure throughout the afternoon transition.
The decay of turbulence is quantified through the temporal
and vertical evolution of (1) the turbulence kinetic energy
(TKE), (2) the characteristic length scales of turbulence and
(3) the shape of the turbulence spectra. A spectral analysis of
LES data, airborne and surface measurements is performed
in order to characterize the variation in the turbulent decay
with height and study the distribution of turbulence over eddy
size.
This study highlights the LES ability to reproduce the tur-
bulence evolution throughout the afternoon. LESs and obser-
vations agree that the afternoon transition can be divided in
two phases: (1) a first phase during which the TKE decays
at a low rate, with no significant change in turbulence char-
acteristics, and (2) a second phase characterized by a larger
TKE decay rate and a change in spectral shape, implying an
evolution of eddy size distribution and energy cascade from
low to high wave number.
The changes observed either in TKE decay (during the first
phase) or in the vertical wind spectra shape (during the sec-
ond phase of the afternoon transition) occur first in the upper
region of the PBL. The higher within the PBL, the stronger
the spectra shape changesContinuation of bifurcations of periodic orbits for large-scale systems
http://hdl.handle.net/2117/76843
Continuation of bifurcations of periodic orbits for large-scale systems
Net Marcé, Marta; Sánchez Umbría, Juan
A methodology to track bifurcations of periodic orbits in large-scale dissipative systems depending on two parameters is presented. It is based on the application of iterative Newton-Krylov techniques to extended systems. To evaluate the action of the Jacobian it is necessary to integrate variational equations up to second order. It is shown that this is possible by integrating systems of dimension at most four times that of the original equations. In order to check the robustness of the method, the thermal convection of a mixture of two fluids in a rectangular domain has been used as a test problem. Several curves of codimension-one bifurcations, and the boundaries of an Arnold's tongue of rotation number 1/8, have been computed.
Wed, 16 Sep 2015 09:56:41 GMThttp://hdl.handle.net/2117/768432015-09-16T09:56:41ZNet Marcé, MartaSánchez Umbría, JuanA methodology to track bifurcations of periodic orbits in large-scale dissipative systems depending on two parameters is presented. It is based on the application of iterative Newton-Krylov techniques to extended systems. To evaluate the action of the Jacobian it is necessary to integrate variational equations up to second order. It is shown that this is possible by integrating systems of dimension at most four times that of the original equations. In order to check the robustness of the method, the thermal convection of a mixture of two fluids in a rectangular domain has been used as a test problem. Several curves of codimension-one bifurcations, and the boundaries of an Arnold's tongue of rotation number 1/8, have been computed.Numerical continuation in classical mechanics and thermodynamics
http://hdl.handle.net/2117/76204
Numerical continuation in classical mechanics and thermodynamics
Gimenez, Aleix; chausse, victor; Meseguer Serrano, Álvaro
In this paper, modern numerical continuation methodologies are presented as a way of understanding and computing multiplicity of solutions in undergraduate physics problems. Mechanical and thermodynamical problems are used as a storyline to introduce the mathematical formalism required to clarify the distinction between the uniqueness and multiplicity of equilibrium solutions and the critical states of a nonlinear physical problem, as well as to illustrate how these novel numerical continuation techniques are implemented in practice. The paper provides simple numerical MATLAB codes that are easily adaptable to other problems, as well as updated software and literature resources.
Mon, 20 Jul 2015 06:58:13 GMThttp://hdl.handle.net/2117/762042015-07-20T06:58:13ZGimenez, Aleixchausse, victorMeseguer Serrano, ÁlvaroIn this paper, modern numerical continuation methodologies are presented as a way of understanding and computing multiplicity of solutions in undergraduate physics problems. Mechanical and thermodynamical problems are used as a storyline to introduce the mathematical formalism required to clarify the distinction between the uniqueness and multiplicity of equilibrium solutions and the critical states of a nonlinear physical problem, as well as to illustrate how these novel numerical continuation techniques are implemented in practice. The paper provides simple numerical MATLAB codes that are easily adaptable to other problems, as well as updated software and literature resources.Onshore sandbar migration in the surf zone: new insights into the wave-induced sediment transport mechanisms
http://hdl.handle.net/2117/28552
Onshore sandbar migration in the surf zone: new insights into the wave-induced sediment transport mechanisms
Fernández Mora, María de los Ángeles; Calvete Manrique, Daniel; Falqués Serra, Albert; de Swart, Huib E.
We present a novel process-based morphodynamic model, which includes transport processes due to both velocity and acceleration skewness and a new formulation for intrawave motions, that successfully simulates observations of onshore sandbar migration. Results confirm findings of previous studies, in which each process was considered separately and in which sediment transport was computed from the observed water motion. However, our results indicate that accounting for the joint action of both velocity and acceleration skewnesses causes major improvement of the modeled onshore bar migration and is essential to accurately model the evolution of the entire cross-shore bottom profile, when compared with observations. We also demonstrate that the morphodynamics in the shoaling zone are dominated by velocity skewness (bed shear stresses), while sediment transport induced by acceleration skewness (pressure gradients) controls the morphodynamics in the inner surf zone.
Thu, 09 Jul 2015 12:04:39 GMThttp://hdl.handle.net/2117/285522015-07-09T12:04:39ZFernández Mora, María de los ÁngelesCalvete Manrique, DanielFalqués Serra, Albertde Swart, Huib E.We present a novel process-based morphodynamic model, which includes transport processes due to both velocity and acceleration skewness and a new formulation for intrawave motions, that successfully simulates observations of onshore sandbar migration. Results confirm findings of previous studies, in which each process was considered separately and in which sediment transport was computed from the observed water motion. However, our results indicate that accounting for the joint action of both velocity and acceleration skewnesses causes major improvement of the modeled onshore bar migration and is essential to accurately model the evolution of the entire cross-shore bottom profile, when compared with observations. We also demonstrate that the morphodynamics in the shoaling zone are dominated by velocity skewness (bed shear stresses), while sediment transport induced by acceleration skewness (pressure gradients) controls the morphodynamics in the inner surf zone.