Articles de revista
http://hdl.handle.net/2117/1087
Fri, 06 May 2016 23:14:08 GMT2016-05-06T23:14:08ZEl canvi climàtic a través dels informes de l'IPCC (1990-2014)
http://hdl.handle.net/2117/86567
El canvi climàtic a través dels informes de l'IPCC (1990-2014)
Mazón Bueso, Jordi
Des de que l’any 1990 es va publicar el primer informe del Panell Intergovernamental
del Canvi Climàtic (en anglès IPCC) quatre
més
han aparegut (els anys 1995, 2001, 2007
i 2014), els quals ens donen una visió de l’evolució en l’estat del coneixement sobre el
canvi climàtic en les diferents etapes d’aquest període 1990-2014. A partir del contingut
científic i de les conclusions més destacables recollides en aquests cinc informes, s’ha
analitzat l’evolució del coneixement sobre el canvi climàtic, les polítiques i mesures
proposades per a combatre’l. En poc més de 20 anys s’ha passat d’una exhaustiva
descripció de les bases científiques de l’efecte hivernacle i del canvi climàtic en què
es basava l’informe del 1990, amb moltes incerteses i en el què era científicament
difícil atribuir a l’ésser humà com a unic responsable d’aquest canvi de clima, al darrer
informe del 2014, el qual qualifica d’extremament probable amb un 95% de certesa de
que l’escalfaent del planeta és d’origen antròpic, el qual pot esdevenir irreversible si no
s’actua de forma urgent en la reducció de les emissions.
Wed, 04 May 2016 12:40:40 GMThttp://hdl.handle.net/2117/865672016-05-04T12:40:40ZMazón Bueso, JordiDes de que l’any 1990 es va publicar el primer informe del Panell Intergovernamental
del Canvi Climàtic (en anglès IPCC) quatre
més
han aparegut (els anys 1995, 2001, 2007
i 2014), els quals ens donen una visió de l’evolució en l’estat del coneixement sobre el
canvi climàtic en les diferents etapes d’aquest període 1990-2014. A partir del contingut
científic i de les conclusions més destacables recollides en aquests cinc informes, s’ha
analitzat l’evolució del coneixement sobre el canvi climàtic, les polítiques i mesures
proposades per a combatre’l. En poc més de 20 anys s’ha passat d’una exhaustiva
descripció de les bases científiques de l’efecte hivernacle i del canvi climàtic en què
es basava l’informe del 1990, amb moltes incerteses i en el què era científicament
difícil atribuir a l’ésser humà com a unic responsable d’aquest canvi de clima, al darrer
informe del 2014, el qual qualifica d’extremament probable amb un 95% de certesa de
que l’escalfaent del planeta és d’origen antròpic, el qual pot esdevenir irreversible si no
s’actua de forma urgent en la reducció de les emissions.Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders
http://hdl.handle.net/2117/86416
Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders
López, José M.; Marqués Truyol, Francisco; Avila Cañellas, Marc
The flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction. In these cases heat transfer in the laminar regime occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. The influence of the geometric parameters is comprehensively studied by varying the radius ratio (0.1 <= eta <= 0.99) and the length-to-gap aspect ratio (5 <= Gamma <= 80). Similarly, a wide range of Prandtl, Rayleigh, and Reynolds numbers is explored (0.01 <= sigma <= 100, Ra <= 30,000, and Re <= 1000, respectively). We obtain a simple criterion, Ra which determines whether the infinite-cylinder assumption can be employed. The coefficient a is well approximated by a cubic fit over the whole n-range. Noteworthy the criterion is independent of the Prandtl number and appears robust with respect to Reynolds number even beyond the laminar regime. (C) 2015 Elsevier Ltd. All rights reserved.
Fri, 29 Apr 2016 10:13:31 GMThttp://hdl.handle.net/2117/864162016-04-29T10:13:31ZLópez, José M.Marqués Truyol, FranciscoAvila Cañellas, MarcThe flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction. In these cases heat transfer in the laminar regime occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. The influence of the geometric parameters is comprehensively studied by varying the radius ratio (0.1 <= eta <= 0.99) and the length-to-gap aspect ratio (5 <= Gamma <= 80). Similarly, a wide range of Prandtl, Rayleigh, and Reynolds numbers is explored (0.01 <= sigma <= 100, Ra <= 30,000, and Re <= 1000, respectively). We obtain a simple criterion, Ra which determines whether the infinite-cylinder assumption can be employed. The coefficient a is well approximated by a cubic fit over the whole n-range. Noteworthy the criterion is independent of the Prandtl number and appears robust with respect to Reynolds number even beyond the laminar regime. (C) 2015 Elsevier Ltd. All rights reserved.Testing otter board hydrodynamic performances in wind tunnel facilities
http://hdl.handle.net/2117/85362
Testing otter board hydrodynamic performances in wind tunnel facilities
Mellibovsky Elstein, Fernando; Prat Farran, Joana d'Arc; Notti, Emilio; Sala, Antonello
The feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design.
Thu, 07 Apr 2016 14:06:46 GMThttp://hdl.handle.net/2117/853622016-04-07T14:06:46ZMellibovsky Elstein, FernandoPrat Farran, Joana d'ArcNotti, EmilioSala, AntonelloThe feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design.On the determination of diffusion coefficients in two-component alloys and doped semiconductors: several implications concerning the International Space Station
http://hdl.handle.net/2117/83083
On the determination of diffusion coefficients in two-component alloys and doped semiconductors: several implications concerning the International Space Station
Sánchez Meneses, O.; Ruiz Martí, Xavier; Pujalte, Mónica; Mercader Calvo, María Isabel; Batiste Boleda, Oriol; Gavaldà, Josefina
The accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances - dockings, undockings and Extra Vehicular Activities, EVAs - is considerably lower.
Wed, 17 Feb 2016 18:18:32 GMThttp://hdl.handle.net/2117/830832016-02-17T18:18:32ZSánchez Meneses, O.Ruiz Martí, XavierPujalte, MónicaMercader Calvo, María IsabelBatiste Boleda, OriolGavaldà, JosefinaThe accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances - dockings, undockings and Extra Vehicular Activities, EVAs - is considerably lower.Radial collocation methods for the onset of convection in rotating spheres
http://hdl.handle.net/2117/83082
Radial collocation methods for the onset of convection in rotating spheres
Sánchez Umbría, Juan; García González, Fernando; Net Marcé, Marta
The viability of using collocation methods in radius and spherical harmonics in the angular variables to calculate convective flows in full spherical geometry is examined. As a test problem the stability of the conductive state of a self-gravitating fluid sphere subject to rotation and internal heating is considered. A study of the behavior of different radial meshes previously used by several authors in polar coordinates, including or not the origin, is first performed. The presence of spurious modes due to the treatment of the singularity at the origin, to the spherical harmonics truncation, and to the initialization of the eigenvalue solver is shown, and ways to eliminate them are presented. Finally, to show the usefulness of the method, the neutral stability curves at very high Taylor and moderate and small Prandtl numbers are calculated and shown.
Wed, 17 Feb 2016 17:19:45 GMThttp://hdl.handle.net/2117/830822016-02-17T17:19:45ZSánchez Umbría, JuanGarcía González, FernandoNet Marcé, MartaThe viability of using collocation methods in radius and spherical harmonics in the angular variables to calculate convective flows in full spherical geometry is examined. As a test problem the stability of the conductive state of a self-gravitating fluid sphere subject to rotation and internal heating is considered. A study of the behavior of different radial meshes previously used by several authors in polar coordinates, including or not the origin, is first performed. The presence of spurious modes due to the treatment of the singularity at the origin, to the spherical harmonics truncation, and to the initialization of the eigenvalue solver is shown, and ways to eliminate them are presented. Finally, to show the usefulness of the method, the neutral stability curves at very high Taylor and moderate and small Prandtl numbers are calculated and shown.A mechanism for streamwise localisation of nonlinear waves in shear flows
http://hdl.handle.net/2117/83078
A mechanism for streamwise localisation of nonlinear waves in shear flows
Mellibovsky Elstein, Fernando; Meseguer Serrano, Álvaro
We present the complete unfolding of streamwise localisation in a paradigm of extended shear flows, namely two-dimensional plane Poiseuille flow. Exact solutions of the Navier-Stokes equations are computed numerically and tracked in the streamwise wavenumber-Reynolds number parameter space to identify and describe the fundamental mechanism behind streamwise localisation, a ubiquitous feature of shear flow turbulence. Unlike shear flow spanwise localisation, streamwise localisation does not follow the snaking mechanism demonstrated for plane Couette flow.
Wed, 17 Feb 2016 15:18:45 GMThttp://hdl.handle.net/2117/830782016-02-17T15:18:45ZMellibovsky Elstein, FernandoMeseguer Serrano, ÁlvaroWe present the complete unfolding of streamwise localisation in a paradigm of extended shear flows, namely two-dimensional plane Poiseuille flow. Exact solutions of the Navier-Stokes equations are computed numerically and tracked in the streamwise wavenumber-Reynolds number parameter space to identify and describe the fundamental mechanism behind streamwise localisation, a ubiquitous feature of shear flow turbulence. Unlike shear flow spanwise localisation, streamwise localisation does not follow the snaking mechanism demonstrated for plane Couette flow.Oscillatory 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.