Articles de revista
http://hdl.handle.net/2117/1087
2017-07-27T07:03:49ZNonsingular black holes, the cosmological constant and asymptotic safety
http://hdl.handle.net/2117/105850
Nonsingular black holes, the cosmological constant and asymptotic safety
Torres Herrera, Ramon
Quantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.
2017-06-26T08:31:46ZTorres Herrera, RamonQuantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.Non-singular quantum improved rotating black holes and their maximal extension
http://hdl.handle.net/2117/105845
Non-singular quantum improved rotating black holes and their maximal extension
Torres Herrera, Ramon
We add a prescription to the Newman–Janis algorithm in order to use it as a means of finding new extended rotating black hole spacetimes from static spherically symmetric ones. Then, we apply the procedure to a quantum improved black hole spacetime coming from Quantum Einstein Gravity in order to get the maximally extended spacetime corresponding to a non-singular rotating black hole. We rigourously check for the existence of scalar curvature singularities in the quantum improved rotating spacetime and we show that it is devoid of them. We also analyze the horizons and causal structure of the rotating black hole and provide Penrose diagrams for the maximally extended spacetime.
The final publication is available at Springer via 10.1007/s10714-017-2236-5
2017-06-26T08:04:46ZTorres Herrera, RamonWe add a prescription to the Newman–Janis algorithm in order to use it as a means of finding new extended rotating black hole spacetimes from static spherically symmetric ones. Then, we apply the procedure to a quantum improved black hole spacetime coming from Quantum Einstein Gravity in order to get the maximally extended spacetime corresponding to a non-singular rotating black hole. We rigourously check for the existence of scalar curvature singularities in the quantum improved rotating spacetime and we show that it is devoid of them. We also analyze the horizons and causal structure of the rotating black hole and provide Penrose diagrams for the maximally extended spacetime.Formation mechanisms for self-organized kilometer-scale shoreline sand waves
http://hdl.handle.net/2117/105391
Formation mechanisms for self-organized kilometer-scale shoreline sand waves
Falqués Serra, Albert; Ribas Prats, Francesca; Idier, Déborah; Arriaga García, Jaime Alonso
The feedbacks between morphology and waves through sediment transport are investigated as a source of kilometer-scale shoreline sand waves. In particular, the observed sand waves along Srd. Holmslands Tange, Denmark, are examined. We use a linear stability model based on the one-line approximation, linking the bathymetry to the perturbed shoreline. Previous models that consider the link by shifting the equilibrium profile and neglecting the curvature of the depth contours predict a positive feedback only if the offshore wave incidence angle (¿c) is above a threshold, ¿c¿42°. Considering curvilinear depth contours and using a linearly decaying perturbation in bed level, we find that ¿c can vary over the range 0–90° depending on the background bathymetric profile and the depth of closure, Dc. Associated to the perturbed wave refraction, there are two sources of instability: the alongshore gradients in wave angle, wave angle mechanism, and the alongshore gradients in wave energy induced by wave crest stretching, wave energy mechanism. The latter are usually destabilizing, but the former are destabilizing only for large enough Dc, steep foreshores, and gently sloping shorefaces. The critical angle comes out from the competition between both mechanisms, but when both are destabilizing, ¿c=0. In contrast with earlier studies, the model predicts instability for the Holmslands Tange coast so that the observed sand waves could have emerged from such instability. The key point is considering a larger Dc that is reasonably supported by both observations and wave climate, which brings the wave angle mechanism near the destabilizing threshold.
2017-06-13T16:56:47ZFalqués Serra, AlbertRibas Prats, FrancescaIdier, DéborahArriaga García, Jaime AlonsoThe feedbacks between morphology and waves through sediment transport are investigated as a source of kilometer-scale shoreline sand waves. In particular, the observed sand waves along Srd. Holmslands Tange, Denmark, are examined. We use a linear stability model based on the one-line approximation, linking the bathymetry to the perturbed shoreline. Previous models that consider the link by shifting the equilibrium profile and neglecting the curvature of the depth contours predict a positive feedback only if the offshore wave incidence angle (¿c) is above a threshold, ¿c¿42°. Considering curvilinear depth contours and using a linearly decaying perturbation in bed level, we find that ¿c can vary over the range 0–90° depending on the background bathymetric profile and the depth of closure, Dc. Associated to the perturbed wave refraction, there are two sources of instability: the alongshore gradients in wave angle, wave angle mechanism, and the alongshore gradients in wave energy induced by wave crest stretching, wave energy mechanism. The latter are usually destabilizing, but the former are destabilizing only for large enough Dc, steep foreshores, and gently sloping shorefaces. The critical angle comes out from the competition between both mechanisms, but when both are destabilizing, ¿c=0. In contrast with earlier studies, the model predicts instability for the Holmslands Tange coast so that the observed sand waves could have emerged from such instability. The key point is considering a larger Dc that is reasonably supported by both observations and wave climate, which brings the wave angle mechanism near the destabilizing threshold.Cold outbreaks at the mesoscale in the Western Mediterranean basin: from Raincells to rainbands
http://hdl.handle.net/2117/104892
Cold outbreaks at the mesoscale in the Western Mediterranean basin: from Raincells to rainbands
Mazón Bueso, Jordi; Pino González, David
This paper investigates cold outbreaks that form offshore density currents within the whole mesoscale over the Western
Mediterranean basin. Reflectivity radar and satellite images are used to detect clouds and precipitation that are associated with these
density currents in the meso-
훼
,meso-
훽
, and meso-
훾
over the Western Mediterranean basin (WMB). Version 3.3 of the WRF-ARW
model is used to describe the formation and evolution of these density currents and to estimate their lifetime as well as horizontal
and vertical scales. Based on the observations and simulations, this paper suggests that a new perspective could effectively be
adopted regarding the WMB region delineated by the Balearic Islands, the northeastern Iberian Peninsula, and the Gulf of Lion,
where inland cold outbreaks develop into density currents that move offshore and can produce precipitation ranging from raincells
to rainbands at the whole mesoscale.
2017-05-26T08:49:52ZMazón Bueso, JordiPino González, DavidThis paper investigates cold outbreaks that form offshore density currents within the whole mesoscale over the Western
Mediterranean basin. Reflectivity radar and satellite images are used to detect clouds and precipitation that are associated with these
density currents in the meso-
훼
,meso-
훽
, and meso-
훾
over the Western Mediterranean basin (WMB). Version 3.3 of the WRF-ARW
model is used to describe the formation and evolution of these density currents and to estimate their lifetime as well as horizontal
and vertical scales. Based on the observations and simulations, this paper suggests that a new perspective could effectively be
adopted regarding the WMB region delineated by the Balearic Islands, the northeastern Iberian Peninsula, and the Gulf of Lion,
where inland cold outbreaks develop into density currents that move offshore and can produce precipitation ranging from raincells
to rainbands at the whole mesoscale.The influence of an increase of the Mediterranean Sea Surface Temperature on two nocturnal offshore rainbands: a numerical experiment
http://hdl.handle.net/2117/104218
The influence of an increase of the Mediterranean Sea Surface Temperature on two nocturnal offshore rainbands: a numerical experiment
Mazón Bueso, Jordi; Pino González, David
Using the Weather Research and Forecasting (WRF) – Advanced Research WRF (ARW)
mesoscale model (WRF–ARW), we investigate how two nocturnal offshore rainbands occurring in
the Mediterranean basin are modified in a warmer sea surface temperature (SST). After sunset, the
thermal difference between land and sea air increases. Driven by drainage winds or land breeze, the
inland cold air interacts with the relatively warmer and moister air over the sea. Vertical movement
of sea air over the boundary between the two air masses may induce cloud and rain bands offshore.
When an increase of SST is prescribed in the WRF simulations, a change in the precipitation pattern is
simulated. The numerical experiments show an increase both in the extension and location of the
rainbands and in the precipitation rate. These changes, induced by the modified SST, are analyzed by
estimating and comparing several parameters such as the location of level of free convection (LFC),
Convective Available Potential Energy (CAPE), or the triggering, deceleration and blockage terms of
simplified conceptual models.
2017-05-09T08:02:07ZMazón Bueso, JordiPino González, DavidUsing the Weather Research and Forecasting (WRF) – Advanced Research WRF (ARW)
mesoscale model (WRF–ARW), we investigate how two nocturnal offshore rainbands occurring in
the Mediterranean basin are modified in a warmer sea surface temperature (SST). After sunset, the
thermal difference between land and sea air increases. Driven by drainage winds or land breeze, the
inland cold air interacts with the relatively warmer and moister air over the sea. Vertical movement
of sea air over the boundary between the two air masses may induce cloud and rain bands offshore.
When an increase of SST is prescribed in the WRF simulations, a change in the precipitation pattern is
simulated. The numerical experiments show an increase both in the extension and location of the
rainbands and in the precipitation rate. These changes, induced by the modified SST, are analyzed by
estimating and comparing several parameters such as the location of level of free convection (LFC),
Convective Available Potential Energy (CAPE), or the triggering, deceleration and blockage terms of
simplified conceptual models.Emergence of spatio-temporal dynamics from exact coherent solutions in pipe flow
http://hdl.handle.net/2117/104197
Emergence of spatio-temporal dynamics from exact coherent solutions in pipe flow
Ritter, Paul; Mellibovsky Elstein, Fernando; Avila Cañellas, Marc
Turbulent-laminar patterns are ubiquitous near transition in wall-bounded shear flows. Despite recent progress in describing their dynamics in analogy to non-equilibrium phase transitions, there is no theory explaining their emergence. Dynamical-system approaches suggest that invariant solutions to the Navier–Stokes equations, such as traveling waves and relative periodic orbits in pipe flow, act as building blocks of the disordered dynamics. While recent studies have shown how transient chaos arises from such solutions, the ensuing dynamics lacks the strong fluctuations in size, shape and speed of the turbulent spots observed in experiments. We here show that chaotic spots with distinct dynamical and kinematic properties merge in phase space and give rise to the enhanced spatio-temporal patterns observed in pipe flow. This paves the way for a dynamical-system foundation to the phenomenology of turbulent-laminar patterns in wall-bounded extended shear flows.
2017-05-08T12:21:38ZRitter, PaulMellibovsky Elstein, FernandoAvila Cañellas, MarcTurbulent-laminar patterns are ubiquitous near transition in wall-bounded shear flows. Despite recent progress in describing their dynamics in analogy to non-equilibrium phase transitions, there is no theory explaining their emergence. Dynamical-system approaches suggest that invariant solutions to the Navier–Stokes equations, such as traveling waves and relative periodic orbits in pipe flow, act as building blocks of the disordered dynamics. While recent studies have shown how transient chaos arises from such solutions, the ensuing dynamics lacks the strong fluctuations in size, shape and speed of the turbulent spots observed in experiments. We here show that chaotic spots with distinct dynamical and kinematic properties merge in phase space and give rise to the enhanced spatio-temporal patterns observed in pipe flow. This paves the way for a dynamical-system foundation to the phenomenology of turbulent-laminar patterns in wall-bounded extended shear flows.On regular rotating black holes
http://hdl.handle.net/2117/103448
On regular rotating black holes
Torres Herrera, Ramon; Fayos Vallés, Francisco
Different proposals for regular rotating black hole spacetimes have appeared recently in the literature. However, a rigorous analysis and proof of the regularity of this kind of spacetimes is still lacking. In this note we analyze rotating Kerr-like black hole spacetimes and find the necessary and sufficient conditions for the regularity of all their second order scalar invariants polynomial in the Riemann tensor. We also show that the regularity is linked to a violation of the weak energy conditions around the core of the rotating black hole.
The final publication is available at Springer via 10.1007/s10714-016-2166-7
2017-04-07T11:29:58ZTorres Herrera, RamonFayos Vallés, FranciscoDifferent proposals for regular rotating black hole spacetimes have appeared recently in the literature. However, a rigorous analysis and proof of the regularity of this kind of spacetimes is still lacking. In this note we analyze rotating Kerr-like black hole spacetimes and find the necessary and sufficient conditions for the regularity of all their second order scalar invariants polynomial in the Riemann tensor. We also show that the regularity is linked to a violation of the weak energy conditions around the core of the rotating black hole.Using archives of past floods to estimate future flood hazards
http://hdl.handle.net/2117/103084
Using archives of past floods to estimate future flood hazards
Swierczynski, Tina; Ionita, Monica; Pino González, David
Worldwide, floods cause greater economic damage and loss of human life than any other type of natural disaster. We urgently need better assessments of flood hazards to reduce the societal impact of extreme floods caused by Earth’s rapidly changing climate, among other factors.
One way of assessing flood hazards is to examine past floods using the records provided by hydrological instruments. We can extend this knowledge back through the Holocene period or beyond using historical documents and natural archives (including alluvial, marine, and lake sediments; tree rings; and cave formations). These extended records can provide valuable information about long-term flood trends.
2017-03-30T09:09:23ZSwierczynski, TinaIonita, MonicaPino González, DavidWorldwide, floods cause greater economic damage and loss of human life than any other type of natural disaster. We urgently need better assessments of flood hazards to reduce the societal impact of extreme floods caused by Earth’s rapidly changing climate, among other factors.
One way of assessing flood hazards is to examine past floods using the records provided by hydrological instruments. We can extend this knowledge back through the Holocene period or beyond using historical documents and natural archives (including alluvial, marine, and lake sediments; tree rings; and cave formations). These extended records can provide valuable information about long-term flood trends.Inertial waves in rapidly rotating flows: a dynamical systems perspective
http://hdl.handle.net/2117/102980
Inertial waves in rapidly rotating flows: a dynamical systems perspective
López Moscat, Juan Manuel; Marqués Truyol, Francisco
An overview of recent developments in a wide variety of enclosed rapidly rotating flows is presented. Highlighted is the interplay between inertial waves, which have been predicted from linear inviscid considerations, and the viscous boundary layer dynamics which result from instabilities as the nonlinearities in the systems are increased. Further, even in the absence of boundary layer instabilities, nonlinearity in the system often leads to complicated interior flows due to subcritical instabilities, Eckhaus bands and heteroclinic dynamics. The ensuing spatio-temporally complex dynamics is analysed in terms of equivariant dynamical systems, providing a general perspective for the wide range of dynamics involved.
2017-03-28T14:51:51ZLópez Moscat, Juan ManuelMarqués Truyol, FranciscoAn overview of recent developments in a wide variety of enclosed rapidly rotating flows is presented. Highlighted is the interplay between inertial waves, which have been predicted from linear inviscid considerations, and the viscous boundary layer dynamics which result from instabilities as the nonlinearities in the systems are increased. Further, even in the absence of boundary layer instabilities, nonlinearity in the system often leads to complicated interior flows due to subcritical instabilities, Eckhaus bands and heteroclinic dynamics. The ensuing spatio-temporally complex dynamics is analysed in terms of equivariant dynamical systems, providing a general perspective for the wide range of dynamics involved.Flexible rod design for educational wind balance
http://hdl.handle.net/2117/102821
Flexible rod design for educational wind balance
Raush Alviach, Gustavo Adolfo; Castilla López, Roberto; Gámez Montero, Pedro Javier; Wojciechowski, Jakub; Codina Macià, Esteban
This article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direction without hindering perpendicular movement. The flexural element described here is simple and easily manufactured, and can also be used with other types of wind balance. The flexure described in this article has similar functionality to those mentioned in the reference section, but has a more compact element. The project's effectiveness was demonstrated in a series of experimental comparisons of forces and moments measured on a wing using the N.A.C.A. Clark-Y airfoil profile.
This is a copy of the author 's preprint version of an article published in the journal Experimental techniques. The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0017-9
2017-03-23T11:45:22ZRaush Alviach, Gustavo AdolfoCastilla López, RobertoGámez Montero, Pedro JavierWojciechowski, JakubCodina Macià, EstebanThis article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direction without hindering perpendicular movement. The flexural element described here is simple and easily manufactured, and can also be used with other types of wind balance. The flexure described in this article has similar functionality to those mentioned in the reference section, but has a more compact element. The project's effectiveness was demonstrated in a series of experimental comparisons of forces and moments measured on a wing using the N.A.C.A. Clark-Y airfoil profile.