DSpace Community:
http://hdl.handle.net/2117/3965
Mon, 27 Apr 2015 18:36:56 GMT2015-04-27T18:36:56Zwebmaster.bupc@upc.eduUniversitat Politècnica de Catalunya. Servei de Biblioteques i DocumentaciónoNumerical bifurcation methods and their application to fluid dynamics: analysis beyond simulation
http://hdl.handle.net/2117/21331
Title: Numerical bifurcation methods and their application to fluid dynamics: analysis beyond simulation
Authors: Dijkstra, Hendrik; Wubs, Fred W.; Cliffe, Andrew K.; Doedel, Eusebius J.; Dragomirescu, Ioana Florica; Eckhardt, Bruno; Gelfgat, Alexander Yu; Hazel, Andrew L.; Lucarini, Valerio; Salinger, Andrew G.; Phipps, Erik T.; Sánchez Umbría, Juan; Schuttelaars, Henk M.; Tuckerman, Laurette S.; Thiele, Uwe
Abstract: We provide an overview of current techniques and typical applications of numerical bifurcation analysis in fluid dynamical problems. Many of these problems are characterized by high-dimensional dynamical systems which undergo transitions as parameters are changed. The computation of the critical conditions associated with these transitions, popularly referred to as 'tipping points', is important for understanding the transition mechanisms. We describe the two basic classes of methods of numerical bifurcation analysis, which differ in the explicit or implicit use of the Jacobian matrix of the dynamical system. The numerical challenges involved in both methods are mentioned and possible solutions to current bottlenecks are given. To demonstrate that numerical bifurcation techniques are not restricted to relatively low-dimensional dynamical systems, we provide several examples of the application of the modern techniques to a diverse set of fluid mechanical problems.http://hdl.handle.net/2117/21331Dijkstra, Hendrik; Wubs, Fred W.; Cliffe, Andrew K.; Doedel, Eusebius J.; Dragomirescu, Ioana Florica; Eckhardt, Bruno; Gelfgat, Alexander Yu; Hazel, Andrew L.; Lucarini, Valerio; Salinger, Andrew G.; Phipps, Erik T.; Sánchez Umbría, Juan; Schuttelaars, Henk M.; Tuckerman, Laurette S.; Thiele, UwenoHigh-dimensional dynamical systems, Numerical bifurcation analysis, Transitions in fluid flowsWe provide an overview of current techniques and typical applications of numerical bifurcation analysis in fluid dynamical problems. Many of these problems are characterized by high-dimensional dynamical systems which undergo transitions as parameters are changed. The computation of the critical conditions associated with these transitions, popularly referred to as 'tipping points', is important for understanding the transition mechanisms. We describe the two basic classes of methods of numerical bifurcation analysis, which differ in the explicit or implicit use of the Jacobian matrix of the dynamical system. The numerical challenges involved in both methods are mentioned and possible solutions to current bottlenecks are given. To demonstrate that numerical bifurcation techniques are not restricted to relatively low-dimensional dynamical systems, we provide several examples of the application of the modern techniques to a diverse set of fluid mechanical problems.Evolution of the turbulence during the afternoon transition of the convective boundary layer: a spectral analysis
http://hdl.handle.net/2117/27591
Title: Evolution of the turbulence during the afternoon transition of the convective boundary layer: a spectral analysis
Authors: Darbieu, Clara; Lohou, Fabienne; Lothon, Marie; Couvreux, Fleur; Pino González, David; Durand, Pierre; Blay Carreras, Estel; Vilà Guerau de Arellano, Jordi
Abstract: The transition from a well-mixed convective boundary layer to a residual layer overlying a stabilized nocturnal layer raises several issues, which remain difficult to address from both modeling and observational perspectives. The well mixed convective boundary layer is mainly forced by buoyancy, with fully developed turbulence. The daily decrease of the surface buoyancy flux leads to the decay of the turbulence kinetic energy, and a possible change of the structure of the turbulence before it reaches the stable regime, with more anisotropy and intermittency. It is important to better understand these processes, as it can impact on the dispersion of tracers in the atmosphere, and on the development of the nocturnal and daytime boundary layers of the following days.
The turbulence decay has been studied with laboratory experiments (Monin and Yaglom, 1975, Cole and Fernando 1998), numerical studies (Nieuwstadt and Brost 1986, Sorbjan 1997) and observations (Fitzarrald et al 2004, Grant 1997). The decay is related to the decrease of the surface buoyancy flux, but with complexity gained with shear-driven boundary layers (Pino et al 2006, Goulart et al 2003), which slow the decay. The evolution of the structure of turbulence during its decay remains unclear, with results on the evolution of characteristic scales that vary with the considered approaches and conditions.
An observational and numerical study is proposed to address this related issue, based on the BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) dataset. BLLAST aims at better understanding the turbulent processes of the late afternoon transition, and leans on a field experiment that took place in summer 2011 in South-West France. A well-documented cloud-free weak wind day is considered here to analyze in details the evolution of the turbulence along the day, from midday to sunset. In particular, the decay is studied as a function of height, and the evolution of the turbulence kinetic energy is described with a thorough analysis of the turbulence spectra.
The case study combines observations of the mean structure by radiosondes and remote sensing, and observations of the turbulence with surface stations, tethered balloon and aircraft. It is the base of a complementary idealized numerical study with a large eddy simulation. From both observations and numerical simulations, the turbulence is described with the characteristics of the spectral energy density, especially the typical turbulence lengthscales and the sharpness of the transition from energy-containing eddies to the inertial subrange. An analytical model proposed by Kristensen and Lenschow (1988) for homogeneous non-isotropic turbulence is used to approximate the observed and LES-modeled spectra and estimate their characteristics.
Our analysis enables us to (1) test the capability of the large eddy simulation to represent the turbulence structure of the afternoon decay, (2) evaluate the evolution of integral scales, turbulent kinetic energy, shape of the spectra in both observations and numerical simulation, and as a function of height, (3) further understand the potential decoupling with height that occurs when the surface fluxes get too weak to maintain fully developed turbulence within the entire depth of the convective boundary layer, (4) put into evidence the limitations of the spectral approach for this critical period of the planetary boundary layer diurnal cycle.Mon, 27 Apr 2015 11:20:43 GMThttp://hdl.handle.net/2117/275912015-04-27T11:20:43ZDarbieu, Clara; Lohou, Fabienne; Lothon, Marie; Couvreux, Fleur; Pino González, David; Durand, Pierre; Blay Carreras, Estel; Vilà Guerau de Arellano, JordinoThe transition from a well-mixed convective boundary layer to a residual layer overlying a stabilized nocturnal layer raises several issues, which remain difficult to address from both modeling and observational perspectives. The well mixed convective boundary layer is mainly forced by buoyancy, with fully developed turbulence. The daily decrease of the surface buoyancy flux leads to the decay of the turbulence kinetic energy, and a possible change of the structure of the turbulence before it reaches the stable regime, with more anisotropy and intermittency. It is important to better understand these processes, as it can impact on the dispersion of tracers in the atmosphere, and on the development of the nocturnal and daytime boundary layers of the following days.
The turbulence decay has been studied with laboratory experiments (Monin and Yaglom, 1975, Cole and Fernando 1998), numerical studies (Nieuwstadt and Brost 1986, Sorbjan 1997) and observations (Fitzarrald et al 2004, Grant 1997). The decay is related to the decrease of the surface buoyancy flux, but with complexity gained with shear-driven boundary layers (Pino et al 2006, Goulart et al 2003), which slow the decay. The evolution of the structure of turbulence during its decay remains unclear, with results on the evolution of characteristic scales that vary with the considered approaches and conditions.
An observational and numerical study is proposed to address this related issue, based on the BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) dataset. BLLAST aims at better understanding the turbulent processes of the late afternoon transition, and leans on a field experiment that took place in summer 2011 in South-West France. A well-documented cloud-free weak wind day is considered here to analyze in details the evolution of the turbulence along the day, from midday to sunset. In particular, the decay is studied as a function of height, and the evolution of the turbulence kinetic energy is described with a thorough analysis of the turbulence spectra.
The case study combines observations of the mean structure by radiosondes and remote sensing, and observations of the turbulence with surface stations, tethered balloon and aircraft. It is the base of a complementary idealized numerical study with a large eddy simulation. From both observations and numerical simulations, the turbulence is described with the characteristics of the spectral energy density, especially the typical turbulence lengthscales and the sharpness of the transition from energy-containing eddies to the inertial subrange. An analytical model proposed by Kristensen and Lenschow (1988) for homogeneous non-isotropic turbulence is used to approximate the observed and LES-modeled spectra and estimate their characteristics.
Our analysis enables us to (1) test the capability of the large eddy simulation to represent the turbulence structure of the afternoon decay, (2) evaluate the evolution of integral scales, turbulent kinetic energy, shape of the spectra in both observations and numerical simulation, and as a function of height, (3) further understand the potential decoupling with height that occurs when the surface fluxes get too weak to maintain fully developed turbulence within the entire depth of the convective boundary layer, (4) put into evidence the limitations of the spectral approach for this critical period of the planetary boundary layer diurnal cycle.Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings
http://hdl.handle.net/2117/27590
Title: Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings
Authors: Pietersen, Henk; Vilà Guerau de Arellano, Jordi; Augustin, P; van de Boer, Anneke; de Coster, Olivier; Delbarre, Hervé; Durand, Pierre; Fourmentin, M; Gioli, Beniamino; Hartogensis, Oskar; Lohou, Fabienne; Lothon, Marie; Ouwersloot, Huug; Pino González, David; Reuder, Joachim
Abstract: We study the influence of the large-scale at-
mospheric contribution to the dynamics of the convective
boundary layer (CBL) in a situation observed during the
Boundary Layer Late Afternoon and Sunset Turbulence
(BLLAST) field campaign. We employ two modeling ap-
proaches, the mixed-layer theory and large-eddy simulation
(LES), with a complete data set of surface and upper-air at-
mospheric observations, to quantify the contributions of the
advection of heat and moisture, and subsidence. We find
that by only taking surface and entrainment fluxes into ac-
count, the boundary-layer height is overestimated by 70 %.
Constrained by surface and upper-air observations, we infer
the large-scale vertical motions and horizontal advection of
heat and moisture. Our findings show that subsidence has a
clear diurnal pattern. Supported by the presence of a nearby
mountain range, this pattern suggests that not only synoptic
scales exert their influence on the boundary layer, but also
mesoscale circulations. LES results show a satisfactory cor-
respondence of the vertical structure of turbulent variables
with observations. We also find that when large-scale ad-
vection and subsidence are included in the simulation, the
values for turbulent kinetic energy are lower than without
these large-scale forcings. We conclude that the prototypical
CBL is a valid representation of the boundary-layer dynam-
ics near regions characterized by complex topography and
small-scale surface heterogeneity, provided that surface- and
large-scale forcings are representative for the local boundary layer.Mon, 27 Apr 2015 10:53:52 GMThttp://hdl.handle.net/2117/275902015-04-27T10:53:52ZPietersen, Henk; Vilà Guerau de Arellano, Jordi; Augustin, P; van de Boer, Anneke; de Coster, Olivier; Delbarre, Hervé; Durand, Pierre; Fourmentin, M; Gioli, Beniamino; Hartogensis, Oskar; Lohou, Fabienne; Lothon, Marie; Ouwersloot, Huug; Pino González, David; Reuder, JoachimnoWe study the influence of the large-scale at-
mospheric contribution to the dynamics of the convective
boundary layer (CBL) in a situation observed during the
Boundary Layer Late Afternoon and Sunset Turbulence
(BLLAST) field campaign. We employ two modeling ap-
proaches, the mixed-layer theory and large-eddy simulation
(LES), with a complete data set of surface and upper-air at-
mospheric observations, to quantify the contributions of the
advection of heat and moisture, and subsidence. We find
that by only taking surface and entrainment fluxes into ac-
count, the boundary-layer height is overestimated by 70 %.
Constrained by surface and upper-air observations, we infer
the large-scale vertical motions and horizontal advection of
heat and moisture. Our findings show that subsidence has a
clear diurnal pattern. Supported by the presence of a nearby
mountain range, this pattern suggests that not only synoptic
scales exert their influence on the boundary layer, but also
mesoscale circulations. LES results show a satisfactory cor-
respondence of the vertical structure of turbulent variables
with observations. We also find that when large-scale ad-
vection and subsidence are included in the simulation, the
values for turbulent kinetic energy are lower than without
these large-scale forcings. We conclude that the prototypical
CBL is a valid representation of the boundary-layer dynam-
ics near regions characterized by complex topography and
small-scale surface heterogeneity, provided that surface- and
large-scale forcings are representative for the local boundary layer.Super and massive AGB stars - III. nucleosynthesis in metal-poor and very metal-poor stars - Z = 0.001 and 0.0001
http://hdl.handle.net/2117/27588
Title: Super and massive AGB stars - III. nucleosynthesis in metal-poor and very metal-poor stars - Z = 0.001 and 0.0001
Authors: Doherty, Carolyn L.; Gil Pons, Pilar; Lau, Herbert B.; Lattanzio, John C.; Siess, Lionel; Campbell, Simon W
Abstract: We present a new grid of stellar models and nucleosynthetic yields for super-AGB stars with metallicities Z = 0.001 and 0.0001, applicable for use within galactic chemical evolution models. Contrary to more metal-rich stars where hot bottom burning is the main driver of the surface composition, in these lower metallicity models the effect of third dredge-up and corrosive second dredge-up also have a strong impact on the yields. These metal-poor and very metal-poor super-AGB stars create large amounts of 4He, 13C, 14N and 27Al as well as the heavy magnesium isotopes 25Mg and 26Mg. There is a transition in yield trends at metallicity Z ˜ 0.001, below which we find positive yields of 12C, 16O, 15N and 28Si, which is not the case for higher metallicities. We explore the large uncertainties derived from wind prescriptions in super-AGB stars, finding ˜2 orders of magnitude difference in yields of 22Ne, 23Na, 24, 25, 26Mg, 27Al and our s-process proxy isotope g. We find inclusion of variable composition low-temperature molecular opacities is only critical for super-AGB stars of metallicities below Z ˜ 0.001. We analyse our results, and those in the literature, to address the question: Are super-AGB stars the polluters responsible for extreme population in the globular cluster NGC 2808? Our results, as well as those from previous studies, seem unable to satisfactorily match the extreme population in this globular clusterMon, 27 Apr 2015 10:45:51 GMThttp://hdl.handle.net/2117/275882015-04-27T10:45:51ZDoherty, Carolyn L.; Gil Pons, Pilar; Lau, Herbert B.; Lattanzio, John C.; Siess, Lionel; Campbell, Simon WnoGlobular clusters: individual: NGC 2808, ISM: abundances, Nuclear reactions, nucleosynthesis, abundances, Stars: AGB and post-AGBWe present a new grid of stellar models and nucleosynthetic yields for super-AGB stars with metallicities Z = 0.001 and 0.0001, applicable for use within galactic chemical evolution models. Contrary to more metal-rich stars where hot bottom burning is the main driver of the surface composition, in these lower metallicity models the effect of third dredge-up and corrosive second dredge-up also have a strong impact on the yields. These metal-poor and very metal-poor super-AGB stars create large amounts of 4He, 13C, 14N and 27Al as well as the heavy magnesium isotopes 25Mg and 26Mg. There is a transition in yield trends at metallicity Z ˜ 0.001, below which we find positive yields of 12C, 16O, 15N and 28Si, which is not the case for higher metallicities. We explore the large uncertainties derived from wind prescriptions in super-AGB stars, finding ˜2 orders of magnitude difference in yields of 22Ne, 23Na, 24, 25, 26Mg, 27Al and our s-process proxy isotope g. We find inclusion of variable composition low-temperature molecular opacities is only critical for super-AGB stars of metallicities below Z ˜ 0.001. We analyse our results, and those in the literature, to address the question: Are super-AGB stars the polluters responsible for extreme population in the globular cluster NGC 2808? Our results, as well as those from previous studies, seem unable to satisfactorily match the extreme population in this globular clusterParticle production from marginally trapped surfaces of general spacetimes
http://hdl.handle.net/2117/27538
Title: Particle production from marginally trapped surfaces of general spacetimes
Authors: Senovilla, José MM; Torres Herrera, Ramon
Abstract: We provide a general formalism that allows to analyze the phenomenon of tunneling in arbitrary spacetimes. We show that a flux of particles produced by tunneling through general marginally trapped surfaces may be perceived by some privileged observers. We discuss how this particle perception can be related to Hawking/Unruh radiation in specific cases. Our approach naturally leads to an expression for the effective surface gravity of marginally trapped surfaces. The procedure is applicable to general astrophysical and cosmological dynamical situations. Some practical examples for known and new cases are provided.Thu, 23 Apr 2015 08:50:35 GMThttp://hdl.handle.net/2117/275382015-04-23T08:50:35ZSenovilla, José MM; Torres Herrera, RamonnoTunneling, Black holes, Dynamical horizons, Hawking/Unruh radiationWe provide a general formalism that allows to analyze the phenomenon of tunneling in arbitrary spacetimes. We show that a flux of particles produced by tunneling through general marginally trapped surfaces may be perceived by some privileged observers. We discuss how this particle perception can be related to Hawking/Unruh radiation in specific cases. Our approach naturally leads to an expression for the effective surface gravity of marginally trapped surfaces. The procedure is applicable to general astrophysical and cosmological dynamical situations. Some practical examples for known and new cases are provided.Spontaneous generation of a swirling plume in a stratified ambient
http://hdl.handle.net/2117/27537
Title: Spontaneous generation of a swirling plume in a stratified ambient
Authors: Marqués Truyol, Francisco; López Moscat, Juan Manuel
Abstract: The transition from laminar to complex spatio-temporal dynamics of plumes due to a localized buoyancy source is studied numerically. Several experiments have reported that this transition is sensitive to external perturbations. Therefore, a well-controlled set-up has been chosen for our numerical study, consisting of a localized heat source at the bottom of an enclosed cylinder whose sidewall is maintained at a fixed temperature which varies linearly up the wall. Restricting the dynamics to the axisymmetric subspace, the first instability is to a puffing state. However, for smaller Grashof numbers, the plume becomes unstable to three-dimensional perturbations and a swirling plume spontaneously appears. The next bifurcation, viewed in the rotating frame where the plume is stationary, also exhibits puffing and suggests a connection between the unstable axisymmetric puffing solution and the swirling plume. Further bifurcations result in quasi-periodic states with a very low-frequency modulation, and these eventually become spatio-temporally complex.Wed, 22 Apr 2015 18:26:43 GMThttp://hdl.handle.net/2117/275372015-04-22T18:26:43ZMarqués Truyol, Francisco; López Moscat, Juan Manuelnononlinear instability, plumes/thermals, stratified flows, Number termal-convection, Taylor-Couette flow, Natural-convection, Nonlinear dynamics, Gluing bifurcation, Columnar vortices, Symmetry-breaking, Dust devils, Instability, EnclosuresThe transition from laminar to complex spatio-temporal dynamics of plumes due to a localized buoyancy source is studied numerically. Several experiments have reported that this transition is sensitive to external perturbations. Therefore, a well-controlled set-up has been chosen for our numerical study, consisting of a localized heat source at the bottom of an enclosed cylinder whose sidewall is maintained at a fixed temperature which varies linearly up the wall. Restricting the dynamics to the axisymmetric subspace, the first instability is to a puffing state. However, for smaller Grashof numbers, the plume becomes unstable to three-dimensional perturbations and a swirling plume spontaneously appears. The next bifurcation, viewed in the rotating frame where the plume is stationary, also exhibits puffing and suggests a connection between the unstable axisymmetric puffing solution and the swirling plume. Further bifurcations result in quasi-periodic states with a very low-frequency modulation, and these eventually become spatio-temporally complex.A real-time world-wide ionospheric model for single and multi-frequency precise navigation
http://hdl.handle.net/2117/27516
Title: A real-time world-wide ionospheric model for single and multi-frequency precise navigation
Authors: Rovira Garcia, Adrià; Juan Zornoza, José Miguel; Sanz Subirana, Jaume
Abstract: The ionosphere plays an important role in satellite-based navigation, either in standard navigation, with single frequency mass-market receivers, or in precise navigation, with dual frequency receivers.
In this work, the requirements of a real-time ionospheric model suitable for GNSS applications are explored, in terms of accuracy and confidence bounds. Key factors for an ionospheric determination better than 1 Total Electron Content Unit (TECU) (16 centimeters in L1) are shown to be whether the model has been derived using an ambiguity-fixing strategy and the number of layers used to reproduce the ionospheric delay. Different models are assessed both in mid-latitudes and equatorial regions, near the Solar Cycle maximum.
It will be shown how dual-frequency users take benefit from a precise modelling of the ionosphere. If accurate enough, the convergence of the navigation filter is reduced to achieve high accuracy positioning quickly, (i.e., the Fast Precise Point Positioning technique). Satellite orbits and clocks computed for Fast-PPP will be shown to be accurate to few centimeters and few tenths of nanoseconds, respectively.
Single-frequency users correct its measurements with the predictions provided by any ionospheric model. Thence, the accuracy of the Fast-PPP ionospheric corrections is directly translated to the measurements modelling and, consequently, to the user solution.
Horizontal and vertical 95% accuracies are shown to be better than 36 and 63 centimeters for single-frequency users and 11 and 15 centimeters for dual-frequency users. The assessment is done for several locations, including the equatorial region, for a month of data close to the last Solar Maximum. The trade-off between the formal and actual positioning errors has been carefully studied by means of the Stanford plots to set realistic confidence bounds to the corrections.Wed, 22 Apr 2015 12:46:58 GMThttp://hdl.handle.net/2117/275162015-04-22T12:46:58ZRovira Garcia, Adrià; Juan Zornoza, José Miguel; Sanz Subirana, JaumenoThe ionosphere plays an important role in satellite-based navigation, either in standard navigation, with single frequency mass-market receivers, or in precise navigation, with dual frequency receivers.
In this work, the requirements of a real-time ionospheric model suitable for GNSS applications are explored, in terms of accuracy and confidence bounds. Key factors for an ionospheric determination better than 1 Total Electron Content Unit (TECU) (16 centimeters in L1) are shown to be whether the model has been derived using an ambiguity-fixing strategy and the number of layers used to reproduce the ionospheric delay. Different models are assessed both in mid-latitudes and equatorial regions, near the Solar Cycle maximum.
It will be shown how dual-frequency users take benefit from a precise modelling of the ionosphere. If accurate enough, the convergence of the navigation filter is reduced to achieve high accuracy positioning quickly, (i.e., the Fast Precise Point Positioning technique). Satellite orbits and clocks computed for Fast-PPP will be shown to be accurate to few centimeters and few tenths of nanoseconds, respectively.
Single-frequency users correct its measurements with the predictions provided by any ionospheric model. Thence, the accuracy of the Fast-PPP ionospheric corrections is directly translated to the measurements modelling and, consequently, to the user solution.
Horizontal and vertical 95% accuracies are shown to be better than 36 and 63 centimeters for single-frequency users and 11 and 15 centimeters for dual-frequency users. The assessment is done for several locations, including the equatorial region, for a month of data close to the last Solar Maximum. The trade-off between the formal and actual positioning errors has been carefully studied by means of the Stanford plots to set realistic confidence bounds to the corrections.Molecular Na-channel excitability from statistical physics
http://hdl.handle.net/2117/27423
Title: Molecular Na-channel excitability from statistical physics
Authors: Ramírez de la Piscina Millán, Laureano; Sancho Herrero, José María
Abstract: The excitable properties of the neural cell membrane is the driving mechanism of the neural pulses. Coordinated ionic fluxes across Na and K channels are the devices responsible of this function. Here we present a simple microscopic physical scenario which accounts for this phenomenology. The main elements are ions and channel doors that obey the standard formulation of statistical physics (overdamped Langevin equations) with appropriate nonlinear interacting potentials. From these equations we obtain the ionic flux and the dynamics of the membrane potential. We show that the excitable properties of the membrane are present in a single and simple Na channel. From this framework, additional microscopic information can be obtained, such as statistics of single-channels dynamics or the energetics of action potential events.Fri, 17 Apr 2015 10:52:20 GMThttp://hdl.handle.net/2117/274232015-04-17T10:52:20ZRamírez de la Piscina Millán, Laureano; Sancho Herrero, José MaríanoMolecular channels
Action potential
Langevin equationsThe excitable properties of the neural cell membrane is the driving mechanism of the neural pulses. Coordinated ionic fluxes across Na and K channels are the devices responsible of this function. Here we present a simple microscopic physical scenario which accounts for this phenomenology. The main elements are ions and channel doors that obey the standard formulation of statistical physics (overdamped Langevin equations) with appropriate nonlinear interacting potentials. From these equations we obtain the ionic flux and the dynamics of the membrane potential. We show that the excitable properties of the membrane are present in a single and simple Na channel. From this framework, additional microscopic information can be obtained, such as statistics of single-channels dynamics or the energetics of action potential events.Spin glass behavior in an antiferromagnetic non-frustrated lattice: Sr2FeNbO6 perovskite
http://hdl.handle.net/2117/27352
Title: Spin glass behavior in an antiferromagnetic non-frustrated lattice: Sr2FeNbO6 perovskite
Authors: Rodríguez Solá, Raúl; Fernandez, Alberto; Isalgue Buxeda, Antonio; Rodriguez, Juan; Labarta, Amilcar; Tejada, Javier; Obradors, Xavier
Abstract: From magnetic susceptibility and hysteresis loop measurements on the cubic perovskite Sr2FeNbO6, it is shown that a spin glass transition does exist in this compound which has a non-frustrated lattice, and only antiferromagnetic interactions. This experimental result allows us to conclude that lattice frustration is not an essential feature for the spin glass transition in antiferromagnetic insulators. Moreover, it is argued that short-range atomic correlations, which modify the magnetic phase diagrams of the diluted compounds, make this spin glass transition possibleWed, 15 Apr 2015 11:22:30 GMThttp://hdl.handle.net/2117/273522015-04-15T11:22:30ZRodríguez Solá, Raúl; Fernandez, Alberto; Isalgue Buxeda, Antonio; Rodriguez, Juan; Labarta, Amilcar; Tejada, Javier; Obradors, XaviernoFrom magnetic susceptibility and hysteresis loop measurements on the cubic perovskite Sr2FeNbO6, it is shown that a spin glass transition does exist in this compound which has a non-frustrated lattice, and only antiferromagnetic interactions. This experimental result allows us to conclude that lattice frustration is not an essential feature for the spin glass transition in antiferromagnetic insulators. Moreover, it is argued that short-range atomic correlations, which modify the magnetic phase diagrams of the diluted compounds, make this spin glass transition possibleCriterios para prácticas de evaluación de calidad. Una propuesta de GRAPA-RIMA
http://hdl.handle.net/2117/27350
Title: Criterios para prácticas de evaluación de calidad. Una propuesta de GRAPA-RIMA
Authors: Cadenato Matia, Ana María; Martinez, Maria; Amante García, Beatriz; Gallego Fernández, María Isabel; Jordana Barnils, José; Sánchez Robert, Francesc Josep; Farrerons Vidal, Óscar; Isalgue Buxeda, Antonio; Fabregat Fillet, Jaume
Abstract: El grupo de innovación GRAPA (GRupo de la Evaluación de la Práctica Académica) del
proyecto RIMA de la Universitat Politècnica de Catalunya ha elaborado una serie de criterios, en
forma de rúbrica, como buenas prácticas de evaluación, coherentes con la integración y
evaluación de competencias, exigencia en la implantación de los nuevos grados que se imparten
en los estudios superiores en las universidades españolas.
En la presente comunicación se podrá comprobar que además cualquier actividad de evaluación
que cumpla estos criterios en el máximo nivel de exigencia representa una actividad de calidad,
demostrando que se pueden tener asignaturas de calidad, objetivo común tanto de instituciones
como del profesorado y alumnado. Además en la presente comunicación se mostrarán algunos
ejemplos de estos criterios.Wed, 15 Apr 2015 11:12:05 GMThttp://hdl.handle.net/2117/273502015-04-15T11:12:05ZCadenato Matia, Ana María; Martinez, Maria; Amante García, Beatriz; Gallego Fernández, María Isabel; Jordana Barnils, José; Sánchez Robert, Francesc Josep; Farrerons Vidal, Óscar; Isalgue Buxeda, Antonio; Fabregat Fillet, JaumenoCriterios de evaluación, Rúbricas, CalidadEl grupo de innovación GRAPA (GRupo de la Evaluación de la Práctica Académica) del
proyecto RIMA de la Universitat Politècnica de Catalunya ha elaborado una serie de criterios, en
forma de rúbrica, como buenas prácticas de evaluación, coherentes con la integración y
evaluación de competencias, exigencia en la implantación de los nuevos grados que se imparten
en los estudios superiores en las universidades españolas.
En la presente comunicación se podrá comprobar que además cualquier actividad de evaluación
que cumpla estos criterios en el máximo nivel de exigencia representa una actividad de calidad,
demostrando que se pueden tener asignaturas de calidad, objetivo común tanto de instituciones
como del profesorado y alumnado. Además en la presente comunicación se mostrarán algunos
ejemplos de estos criterios.Numerical-simulation research on building-facade geometry and its effect on fire propagation in wooden facades
http://hdl.handle.net/2117/27263
Title: Numerical-simulation research on building-facade geometry and its effect on fire propagation in wooden facades
Authors: Lacasta Palacio, Ana María; Giraldo, Pilar; Avellaneda Diaz-Grande, Jaime; Burgos Leiva, Camila
Abstract: Fire protection is a very important requirement in the facade of a building. When there is a fire in a building, the facade can be one of the quickest spreading pathways, regardless of the material of which it is constructed. Therefore, in terms of safety, the study of mechanisms controlling the spread of fire through the facade is an issue that needs to be addressed, especially when it involves combustible material claddings such as wood. In several European countries the building regulations restrict the use of combustible materials in facade claddings. The application of passive protection measures to control the spread of fire would help minimize such restrictions.
In this research it was used computer-simulation techniques to study the behaviour of flames ejected through the windows on wooden facades. We studied five wooden facade systems which combine different configurations of windows, eaves and non-combustible elements which act as fire barriers.
The results showed the strong influence of geometrical configuration of the facade elements in controlling fire spreading. They also show that it is possible to establish an acceptable standard of fire protection through non-combustible elements that does not alter the aesthetics of wooden facades.
The study was performed using field models of computational fluid-dynamics. Particularly through the software: Fire Dynamics Simulator (FDS) to solve numerically the mathematical integration models, PyroSim for the graphical interface, and Smokeview for viewing the results.Mon, 13 Apr 2015 09:00:34 GMThttp://hdl.handle.net/2117/272632015-04-13T09:00:34ZLacasta Palacio, Ana María; Giraldo, Pilar; Avellaneda Diaz-Grande, Jaime; Burgos Leiva, CamilanoCombustible cladding, fire dynamics simulator, fire performance on facade, flame spreading control, wooden facades, configuration of the facades.Fire protection is a very important requirement in the facade of a building. When there is a fire in a building, the facade can be one of the quickest spreading pathways, regardless of the material of which it is constructed. Therefore, in terms of safety, the study of mechanisms controlling the spread of fire through the facade is an issue that needs to be addressed, especially when it involves combustible material claddings such as wood. In several European countries the building regulations restrict the use of combustible materials in facade claddings. The application of passive protection measures to control the spread of fire would help minimize such restrictions.
In this research it was used computer-simulation techniques to study the behaviour of flames ejected through the windows on wooden facades. We studied five wooden facade systems which combine different configurations of windows, eaves and non-combustible elements which act as fire barriers.
The results showed the strong influence of geometrical configuration of the facade elements in controlling fire spreading. They also show that it is possible to establish an acceptable standard of fire protection through non-combustible elements that does not alter the aesthetics of wooden facades.
The study was performed using field models of computational fluid-dynamics. Particularly through the software: Fire Dynamics Simulator (FDS) to solve numerically the mathematical integration models, PyroSim for the graphical interface, and Smokeview for viewing the results.Synergistic approach to elucidate the incorporation of magnesium ions into hydroxyapatite
http://hdl.handle.net/2117/27195
Title: Synergistic approach to elucidate the incorporation of magnesium ions into hydroxyapatite
Authors: Bertran Cànovas, Òscar; Valle Mendoza, Luis Javier del; Revilla López, Guillermo; Rivas Cañas, Manuel; Chaves Barboza, Gustavo Adolfo; Casas Becerra, María Teresa; Casanovas Salas, Jordi; Turon Dols, Pau; Puiggalí Bellalta, Jordi; Alemán Llansó, Carlos
Abstract: Although the content of Mg2+ in hard tissues is very low (typically 1.5wt%), its incorporation into synthetic hydroxyapatite (HAp) particles and its role in the mineral's properties are still subject of intensive debate. A combined experimental-computational approach is used to answer many of the open questions. Mg2+-enriched HAp particles are prepared using different synthetic approaches and considering different concentrations of Mg2+ in the reaction medium. The composition, morphology and structure of the resulting particles are investigated using X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning and transmission electron microscopies, FTIR, and wide-angle X-ray diffraction. After this scrutiny, the role of the Mg2+ in the first nucleation stages, before HAp formation, is investigated using atomistic molecular dynamics simulations. Saturated solutions are simulated with and without the presence of DNA, which has been recently used as a soft template in the biomineralization process. This synergistic investigation provides a complete picture of how Mg2+ ions affect the mineralization from the first stages onwardsThu, 09 Apr 2015 08:04:09 GMThttp://hdl.handle.net/2117/271952015-04-09T08:04:09ZBertran Cànovas, Òscar; Valle Mendoza, Luis Javier del; Revilla López, Guillermo; Rivas Cañas, Manuel; Chaves Barboza, Gustavo Adolfo; Casas Becerra, María Teresa; Casanovas Salas, Jordi; Turon Dols, Pau; Puiggalí Bellalta, Jordi; Alemán Llansó, CarlosnoDNA, hydroxyapatite, magnesium, mineral nucleation, molecular dynamics, SUBSTITUTED HYDROXYAPATITE, MOLECULAR-DYNAMICS, CALCIUM-PHOSPHATE, FORCE-FIELD, B-DNA, X-RAY, NANOPARTICLES, CRYSTALLIZATION, CARBONATE, MINERALIZATIONAlthough the content of Mg2+ in hard tissues is very low (typically 1.5wt%), its incorporation into synthetic hydroxyapatite (HAp) particles and its role in the mineral's properties are still subject of intensive debate. A combined experimental-computational approach is used to answer many of the open questions. Mg2+-enriched HAp particles are prepared using different synthetic approaches and considering different concentrations of Mg2+ in the reaction medium. The composition, morphology and structure of the resulting particles are investigated using X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning and transmission electron microscopies, FTIR, and wide-angle X-ray diffraction. After this scrutiny, the role of the Mg2+ in the first nucleation stages, before HAp formation, is investigated using atomistic molecular dynamics simulations. Saturated solutions are simulated with and without the presence of DNA, which has been recently used as a soft template in the biomineralization process. This synergistic investigation provides a complete picture of how Mg2+ ions affect the mineralization from the first stages onwardsInternal organization of macromonomers and dendronized polymers based on thiophene dendrons
http://hdl.handle.net/2117/27194
Title: Internal organization of macromonomers and dendronized polymers based on thiophene dendrons
Authors: Cordova Mateo, Esther; Bertran Cànovas, Òscar; Alemán Llansó, Carlos; Schlüter, A. Dieter; Kroeger, Matin
Abstract: The internal organization of macromonomers (MGs) consisting of all-thiophene dendrons of generation g = 2 and 3 attached to a phenyl core, as well as of the dendronized polymers resulting from polymerization of these macromonomers (PG2 and PG3, respectively), has been investigated using theoretical methods. The conformational preferences of the MGs, determined using density functional theory calculations, are characterized by the relative orientation between dendrons and core. We find that the strain of the MGs increases with the generation number and is alleviated by small conformational re-arrangements of the peripheral thiophene rings. The conformations obtained for the MGs have subsequently been used to construct models for the dendronized polymers. Classical molecular dynamics simulations have evidenced that the interpenetration of dendrons belonging to different repeat units is very small for PG2. In contrast, the degree of interpenetration is found to be very high for PG3, which also shows a significant degree of backfolding (i.e. occurrence of peripheral methyl groups approaching the backbone). Consequently, PG2 behaves as a conventional linear flexible polymer bearing bulk pendant groups, whereas PG3 is better characterized as a semirigid homogeneous cylinder. The two polymers are stabilized by pi-pi stacking interactions, even though these are significantly more abundant for PG3 than for PG2; the average numbers of interactions per repeat unit are 3.0 and 8.8 for PG2 and PG3, respectively. While in these interactions the thiophene rings can adopt either parallel (sandwich) or perpendicular (T-shaped) dispositions, the former scenario turns out to be the most abundantThu, 09 Apr 2015 07:49:34 GMThttp://hdl.handle.net/2117/271942015-04-09T07:49:34ZCordova Mateo, Esther; Bertran Cànovas, Òscar; Alemán Llansó, Carlos; Schlüter, A. Dieter; Kroeger, MatinnoDENSITY-FUNCTIONAL THEORY, LIGHT-EMITTING-DIODES, GAUSSIAN-BASIS SETS, MOLECULAR-DYNAMICS, OLIGOTHIOPHENE DENDRIMERS, COMPUTER-SIMULATION, INTRINSIC-VISCOSITY, HOMOLOGOUS SERIES, EXACT EXCHANGE, FORCE-FIELDThe internal organization of macromonomers (MGs) consisting of all-thiophene dendrons of generation g = 2 and 3 attached to a phenyl core, as well as of the dendronized polymers resulting from polymerization of these macromonomers (PG2 and PG3, respectively), has been investigated using theoretical methods. The conformational preferences of the MGs, determined using density functional theory calculations, are characterized by the relative orientation between dendrons and core. We find that the strain of the MGs increases with the generation number and is alleviated by small conformational re-arrangements of the peripheral thiophene rings. The conformations obtained for the MGs have subsequently been used to construct models for the dendronized polymers. Classical molecular dynamics simulations have evidenced that the interpenetration of dendrons belonging to different repeat units is very small for PG2. In contrast, the degree of interpenetration is found to be very high for PG3, which also shows a significant degree of backfolding (i.e. occurrence of peripheral methyl groups approaching the backbone). Consequently, PG2 behaves as a conventional linear flexible polymer bearing bulk pendant groups, whereas PG3 is better characterized as a semirigid homogeneous cylinder. The two polymers are stabilized by pi-pi stacking interactions, even though these are significantly more abundant for PG3 than for PG2; the average numbers of interactions per repeat unit are 3.0 and 8.8 for PG2 and PG3, respectively. While in these interactions the thiophene rings can adopt either parallel (sandwich) or perpendicular (T-shaped) dispositions, the former scenario turns out to be the most abundantTwo computational approaches for the simulation of fluid problems in rotating spherical shells
http://hdl.handle.net/2117/27104
Title: Two computational approaches for the simulation of fluid problems in rotating spherical shells
Authors: García González, Fernando; Dormy, Emmanuel; Sánchez Umbría, Juan; Net Marcé, Marta
Abstract: Many geophysical and astrophysical phenomena such as magnetic fields generation, or the differential rotation observed in the atmospheres of the major planets are studied by means of numerical simulations of the Navier-Stokes equations in rotating spherical shells. Two different computational codes, spatially discretized using spherical harmonics in the angular variables, are presented. The first code, PARODY, solves the magneto-hydrodynamic anelastic convective equations with finite a difference discretization in the radial direction. This allows the parallelization on distributed memory computers to run massive numerical simulations of second order in time. It is mainly designed to perform direct numerical simulations. The second code, SPHO, solves the fully spectral Boussinesq convective equations, and its variationals, parallelized on shared memory architectures and it uses optimized linear algebra libraries. High-order time integration methods are implemented to allow the use of dynamical systems tools for the study of complex dynamics.Fri, 27 Mar 2015 17:27:29 GMThttp://hdl.handle.net/2117/271042015-03-27T17:27:29ZGarcía González, Fernando; Dormy, Emmanuel; Sánchez Umbría, Juan; Net Marcé, MartanoHydrodynamics, Spherical shells, Parallelism, Direct numerical simulation, Dynamical systemsMany geophysical and astrophysical phenomena such as magnetic fields generation, or the differential rotation observed in the atmospheres of the major planets are studied by means of numerical simulations of the Navier-Stokes equations in rotating spherical shells. Two different computational codes, spatially discretized using spherical harmonics in the angular variables, are presented. The first code, PARODY, solves the magneto-hydrodynamic anelastic convective equations with finite a difference discretization in the radial direction. This allows the parallelization on distributed memory computers to run massive numerical simulations of second order in time. It is mainly designed to perform direct numerical simulations. The second code, SPHO, solves the fully spectral Boussinesq convective equations, and its variationals, parallelized on shared memory architectures and it uses optimized linear algebra libraries. High-order time integration methods are implemented to allow the use of dynamical systems tools for the study of complex dynamics.Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved xray photon correlation spectroscopy
http://hdl.handle.net/2117/27080
Title: Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved xray photon correlation spectroscopy
Authors: Ruta, Beatrice; Giordano, Valentina; Erra, Loredana; Liu, Chaoren; Pineda Soler, Eloi
Abstract: We present a temperature investigation of the structural and dynamical evolution of rapidly quenched metallic glasses of Mg65Cu25Y10 at the atomic length scale by means of in situ high energy x-ray diffraction and time resolved x-ray photon correlation spectroscopy. We find a flattening of the temperature evolution of the position of the first sharp diffraction peak on approaching the glass transition temperature from the glassy state, which reflects into a surprising slowing down of the relaxation ynamics
of even one order of magnitude with increasing temperature. The comparison between structural and dynamical properties strengthens the idea of a stress-induced, rather than pure diffusive, atomic motion in metallic glassesThu, 26 Mar 2015 17:14:00 GMThttp://hdl.handle.net/2117/270802015-03-26T17:14:00ZRuta, Beatrice; Giordano, Valentina; Erra, Loredana; Liu, Chaoren; Pineda Soler, EloinoWe present a temperature investigation of the structural and dynamical evolution of rapidly quenched metallic glasses of Mg65Cu25Y10 at the atomic length scale by means of in situ high energy x-ray diffraction and time resolved x-ray photon correlation spectroscopy. We find a flattening of the temperature evolution of the position of the first sharp diffraction peak on approaching the glass transition temperature from the glassy state, which reflects into a surprising slowing down of the relaxation ynamics
of even one order of magnitude with increasing temperature. The comparison between structural and dynamical properties strengthens the idea of a stress-induced, rather than pure diffusive, atomic motion in metallic glasses