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UPCommons - E-prints UPC Universitat Politècnica de Catalunya (81,070 recursos)
E-prints UPC cobreix dues finalitats: per una banda, és el dipòsit institucional de la UPC que recull els articles de revista, les comunicacions de congrés i els reports de recerca generats en les activitats de recerca del personal docent i investigador de la universitat; per l'altra, és una eina que permet accelerar la producció científica, allotjant versions de documents prèvies a la publicació en una revista o a les actes d’un congrés.

Articles de revista

Mostrando recursos 1 - 20 de 156

1. Super and massive AGB stars - III. nucleosynthesis in metal-poor and very metal-poor stars - Z = 0.001 and 0.0001 - Doherty, Carolyn L.; Gil Pons, Pilar; Lau, Herbert B.; Lattanzio, John C.; Siess, Lionel; Campbell, Simon W
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...

2. Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings - 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
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....

3. Spontaneous generation of a swirling plume in a stratified ambient - Marqués Truyol, Francisco; López Moscat, Juan Manuel
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...

4. Mesoscale numerical simulations of heavy nocturnal rainbands associated with coastal fronts in the Mediterranean Basin - Mazón Bueso, Jordi; Pino González, David
Three offshore rainbands associated with nocturnal coastal fronts formed near the Israeli coastline, the Gulf of Genoa and on the northeastern coast of the Iberian Peninsula, are simulated using version 3.3 of the WRF-ARW mesoscale model in order to study the dynamics of the atmosphere in each case.; The simulations show coastal fronts producing relatively high (in comparison with some other similar rainbands) 1 and 10 h accumulated precipitations that formed in the Mediterranean Basin. According to these simulations, the coastal fronts that formed near the Israeli coastline and over the Gulf of Genoa are quasi-stationary, while the one that...

5. Modeling large scale shoreline sand waves under oblique wave incidence - Van den Berg, Niels; Falqués Serra, Albert; Ribas Prats, Francesca
Postprint (published version)

6. On the mechanism of wavelength selection of self-organized shoreline sand waves - Van den Berg, Niels; Falqués Serra, Albert; Ribas Prats, Francesca; Caballería Suriñach, Miquel
Sandy shorelines exposed to very oblique wave incidence can be unstable and develop self-organized shoreline sand waves. Different types of models predict the formation of these sand waves with an initially dominant alongshore wavelength in the range 1–10 km, which is quite common in nature

7. Modeling shoreline sand waves on the coasts of Namibia and Angola - Ribas Prats, Francesca; Falqués Serra, Albert; Van den Berg, Niels; Caballería Suriñach, Miquel
The southwestern (SW) coast of Africa (Namibia and Angola) features long sandy beaches and a wave climate dominated by energetic swells from the Southsouthwest (SSW), therefore approaching the coast with a very high obliquity. Satellite images reveal that along that coast there are many shoreline sand waves with wavelengths ranging from 2 to 8 km. A more detailed study, including a Fourier analysis of the shoreline position, yields the wavelengths (among this range) with the highest spectral density concentration. Also, it becomes apparent that at least some of the sand waves are dynamically active rather than being controlled by the...

8. Dynamics of single-barred embayed beaches - Ojeda Casillas, Elena; Guillén Aranda, Jorge; Ribas Prats, Francesca
The dynamics of single submerged sandbars of two artificial embayed beaches (La Barceloneta and Bogatell, Barcelona, NW Mediterranean) has been studied with a video-recorded data set of 4.3 years. The alongshore-averaged cross-shore migration, the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions, alongshore sediment transport and shoreline variability.

9. Characteristics and dynamics of surfzone transverse finger bars - Ribas Prats, Francesca; Kroon, A.
Patches of transverse finger bars have been identified in the surf zone of Noordwijk beach (Netherlands). They consisted of three to nine elongated accumulations of sand attached to the low-tide shoreline. The bars extended up to 50 m into the inner surf zone, had an oblique orientation with respect to the shore-normal, and were quasiregularly spaced in the alongshore direction.

10. The "Prediflood" database of historical floods in Catalonia (NE Iberian Peninsula) AD 1035–2013, and its potential applications in flood analysis - Barriendos Valve, Mariano; Ruiz Bellet, Josep Lluís; Tuset Mestre, Jordi; Mazón Bueso, Jordi; Balasch Solanes, Josep Carles; Pino González, David; Ayala, Jose Luis
“Prediflood” is a database of historical floods that occurred in Catalonia (NE Iberian Peninsula), between the 11th century and the 21st century. More than 2700 flood cases are catalogued, and more than 1100 flood events. This database contains information acquired under modern historiographical criteria and it is, therefore, suitable for use in multidisciplinary flood analysis techniques, such as meteorological or hydraulic reconstructions.

11. Development of a Low-Cost Weather Station to Measure in Situ Essential Climate Variables - Rojas Gregorio, José Ignacio; Diaz Gilete, Silvia; Mazón Bueso, Jordi
A weather station is proposed especially designed for developing countries, and to meet the standards of the international scientific community making research on the earth system. The station would measure in situ several ECV (essential climate variables). These data may enable an agricultural breakthrough in countries lacking meteorological infrastructure, help in climate change monitoring, and facilitate diffusion of wind energy. A pre-feasibility analysis is presented. It appears interesting that the station is supplied by a social enterprise. A research to establish the best shelter design using computational fluid dynamics is also reported. The criterion is the accuracy with which the...

12. The BLLAST field experiment: boundary-layer late afternoon and sunset turbulence - Lothon, Marie; Lohou, Fabienne; Pino González, David
Due to the major role of the sun in heating the earth’s surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The after-noon transition, the period of the day that connects the day-time dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state

13. Countergradient heat flux observations during the evening transition period - Blay Carreras, Estel; Pardyjak, Eric; Pino González, David; Alexander, Daniel; Lohou, Fabienne; Lothon, Marie
Gradient-based turbulence models generally assume that the buoyancy flux ceases to introduce heat into the surface layer of the atmospheric boundary layer in temporal consonance with the gradient of the local virtual potential temperature. Here, we hypothesize that during the evening transition a delay exists between the instant when the buoyancy flux goes to zero and the time when the local gradient of the virtual potential temperature indicates a sign change. This phenomenon is studied using a range of data collected over several intensive observational periods (IOPs) during the Boundary Layer Late Afternoon and Sunset Turbulence field campaign conducted in...

14. Land surface spinup for episodic modeling - Angevine, Wayne M.; Bazille, Eric; Legain, Dominique; Pino González, David
Soil moisture strongly controls the surface fluxes in mesoscale numerical models, and thereby influences the boundary layer structure. Proper initialization of soil moisture is therefore critical for faithful simulations. In many applications, such as air quality or process studies, the model is run for short, discrete periods (a day to a month). This paper describes one method for soil initialization in these cases - self-spinup. In self-spinup, the model is initialized with a coarse-resolution operational model or reanalysis output, and run for a month, cycling its own soil variables. This allows the soil variables to develop appropriate spatial variability, and...

15. On the predictability of mid-term cross-shore profile evolution - Fernández Mora, María de los Ángeles; Calvete Manrique, Daniel; Falqués Serra, Albert; Ribas Prats, Francesca; Idier, Déborah
The aim of the present study is to analyse the mid-term beach profile evolution, considering the hypothesis that the alongshore processes can be neglected for the prediction of the mean profile evolution. To this end, a process-based model for the evolution of the cross-shore profile has been used. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, accounting for the effects of wave skewness and asymmetry on sediment transport. Offshore waves and tides conditions and bathymetric profiles measured at the FRF-USACE Duck are used to simulate a mid-term (72 days) onshore sandbar migration event. The model results...

16. Modeling and analyzing observed transverse sand bars in the surf zone - Ribas Prats, Francesca; Swart, Huib E. de; Calvete Manrique, Daniel; Falqués Serra, Albert
A morphodynamic model has been applied to explain the characteristics of transverse sandbars observed in the inner surf zone of open beaches. The model describes the feedback between waves, rollers, depth-averaged currents and bed evolution, so that self-organized processes can develop.

17. Modeling waves, currents and sandbars on natural beaches: The effect of surface rollers - Ribas Prats, Francesca; Swart, Huib E. de; Calvete Manrique, Daniel; Falqués Serra, Albert
A morphodynamic model has been extended to gain more fundamental knowledge about the formation of nearshore sand bars. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, so that self-organized processes can develop. Offshore wave, wind and tide conditions and the bathymetry measured at Egmond site (the Netherlands) are firstly applied to compute the longshore current and wave height profiles.

18. Assessing the suitability of video imaging for studying the Dynamics of nearshore sandbars in tideless beaches - Ribas Prats, Francesca; Ojeda Casillas, Elena; Price, Timothy D.; Guillén Aranda, Jorge
Nearshore sandbars, an important natural defense mechanism of the beaches, can be monitored using shore-based video systems. Before studying bar dynamics with video images, we must establish the relationship between the real bar positions and the videoed bar positions (detected by the preferential wave breaking on the shallows)

19. Observations and modeling of surf zone transverse finger bars at the Gold Coast, Australia - Ribas Prats, Francesca; ten Doeschate, Anneke; de Swart, Huib E.; Ruessink, Gerben; Calvete Manrique, Daniel
The occurrence and characteristics of transverse finger bars at Surfers Paradise (Gold Coast, Australia) have been quantified with 4 years of time-exposure video images. These bars are attached to the inner terrace and have an oblique orientation with respect to the coastline. They are observed during 24 % of the study period, in patches up to 15 bars, with an average lifetime of 5 days and a mean wavelength of 32 m. The bars are observed during obliquely incident waves of intermediate heights. Bar crests typically point toward the incoming wave direction, i.e., they are up-current oriented. The most frequent...

20. Nearshore oblique sand bars - Ribas Prats, Francesca; Falqués Serra, Albert; Montoto Gayete, Amadeo
The coupling between hydrodynamics and the evolving topography in the surf zone has been theoretically examined for oblique wave incidence. It is shown that positive feedback can lead to the initial growth of several types of rhythmic systems of sand bars. The bars can be down-current oriented or up-current oriented, which means that the offshore end of the bar is shifted down-current or up-current with respect to the shore attachment. In the limit of strong current compared to wave orbital motion, very oblique down-current oriented bars are obtained with a spacing of several times the surf zone width. When wave orbital...

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