Cosmological zoo -- accelerating models with dark energy

ecent observations of type Ia supernovae indicate that the Universe is in an accelerating phase of expansion. The fundamental quest in theoretical cosmology is to identify the origin of this phenomenon. In principle there are two possibilities: 1) the presence of matter which violates the strong energy condition (a substantial form of dark energy), 2) modified Friedmann equations (Cardassian models -- a non-substantial form of dark matter). We classify all these models in terms of 2-dimensional dynamical systems of the Newtonian type. We search for generic properties of the models. It is achieved with the help of Peixoto's theorem for dynamical system on the Poincar{\'e} sphere. We find that the notion of structural stability can be useful to distinguish the generic cases of evolutional paths with acceleration. We find that, while the $\Lambda$CDM models and phantom models are typical accelerating models, the cosmological models with bouncing phase are non-generic in the space of all planar dynamical systems. We derive the universal shape of potential function which gives rise to presently accelerating models. Our results show explicitly the advantages of using a potential function (instead of the equation of state) to probe the origin of the present acceleration. We argue that simplicity and genericity are the best guide in understanding our Universe and its acceleration.Comment: RevTeX4, 23 pages, 10 figure

Particle creation, renormalizability conditions and the mass-energy spectrum in gravity theories of quadratic Lagrangians

Massive scalar particle production, due to the anisotropic evolution of a five-dimensional spacetime, is considered in the context of a quadratic Lagrangian theory of gravity. Those particles, corresponding to field modes with non-vanishing momentum component along the fifth dimension, are created mostly in the neighbourhood of a singular epoch where only their high-frequency behaviour is of considerable importance. At the 1-loop approximation level, general renormalizability conditions on the physical quantities relevant to particle production are derived and discussed. Exact solutions of the resulting Klein-Gordon field equation are obtained and the mass-energy spectrum attributed to the scalar field due to the cosmological evolution is being investigated further. Finally, analytic expressions regarding the number and the energy density of the created particles at late times, are also derived and discussed.Comment: LaTeX file, 23 page

Robust estimations of current velocities with four-beam broadband ADCPs

13 páginas, 5 figuras, 2 tablasAn extended explanation of the hypothesis and equations traditionally used to transform between four-beam ADCP radial beam velocities and current velocity components is presented. This explanation includes a dissertation about the meaning of the RD Instrument error velocity and a description of the standard beam-to-current components transformation as a least squares solution. Afterward, the variance–covariance matrix associated with the least squares solution is found. Then, a robust solution for transforming radial beam velocities into current components is derived under the formality of a weighted least squares approach. The associated variance–covariance matrix is also formulated and theoretically proves that the modulus of its elements will be generally lower than the corresponding modulus of the variance–covariance matrix associated with the standard least squares solution. Finally, a comparison between the results obtained using the standard least squares solution and the results of the weighted least squares method, using a high-resolution ADCP dataset, is presented. The results show that, in this case, the weighted least squares solution provides variance estimations that are 4% lower over the entire record period (8 days) and 7% lower during a shorter, more energetic period (12 h)Support for this work came from the Spanish Science and Technology Ministry (grant MAR1999-1039-W2-01, DYBAGA project), Xunta de Galicia (grant 08MMA014402PR, DIPLOMACIA project) and also the Australian Aquafin CRC: Risk and Response Project.Peer reviewe

Flujos residuales de intercambio entre la Ría de Vigo y la plataforma continental

[ES] En este trabajo se realiza la primera descripción cuantitativa de la circulación residual de la Ría de Vigo basada en datos de corrientes. El estudio se centra en el intercambio que se produjo entre la ría y la plataforma a través de las dos bocas de la ría durante un fondeo simultáneo de 10 días de duración, cuya primera mitad se desarrolló en condiciones de intenso hundimiento para pasar después a condiciones de fuerte afloramiento. El objetivo es describir el movimiento residual de la columna de agua frente a los cambios meteorológicos y analizar las diferentes respuestas de la misma en las dos bocas. Durante el periodo de muestreo los perfiles de velocidad residual en la boca norte mostraron una gran homogeneidad vertical. En la boca sur, en cambio, evidenciaron la existencia de dos capas que se movían en sentidos contrarios. Los flujos residuales presentaron una fuerte relación lineal con la componente meridional del viento, Wy, capaz de explicar >90% de la variabilidad de mismos. Bajo régimen de vientos de componente sur (hundimiento) se produjo una salida de agua por toda la boca norte. En la boca sur y durante el mismo periodo, el agua penetró en la ría por la capa superior mientras que por la inferior salía. En la segunda mitad del fondeo, caracterizada por vientos del norte (afloramiento), el sentido de los flujos fue el inverso. El comportamiento de la columna de agua en la boca norte se interpreta como consecuencia del arrastre directo del viento y de la comunicación con la Ría de Pontevedra, situada al norte. Por su parte, la respuesta en la boca sur está relacionada con el transporte de Ekman.[EN] Current, wind and sea level data were taken in the Ría de Vigo so as to make the first quantitative description of its residual circulation based on direct observations. The study is focused on the exchange of water between the Ría de Vigo and the coastal shelf through the ría two main entrances, the northern mouth and the southern mouth, which took place during a 10-day period. In this period, a strong shift between downwelling and upwelling conditions was recorded. Our aim was to analyse the effect of the meteorological context on the vertical velocity profile and on the fluxes of water which entered/ exited the ría. Winds were found to drag water out (downwelling) or in (upwelling) the ría through its northern mouth, which featured a very homogeneous vertical velocity profile. In contrast, a two-layered pattern prevailed in the southern mouth. During downwelling, the Ekman transport to the right of the wind entered water to the ría through the southern mouth as a surface layer, partially compensated by the exit of the deep one. During upwelling the situation reversed, the surface layer exiting the ría and being compensated by the uplifting and entrance of deep waters. Residual fluxes showed a strong linear relationship with the meridional component of the wind, Wy, which explained >90% of the fluxes variability.B. M Míguez es beneficiaria de una beca predoctoral FPU del Ministerio de Educación, Cultura y Deporte.Peer reviewe

Estimaciones robustas de corrientes con ADCPs de cuatro transductores

Poster.-- XIII Congreso Latinoamericano de Ciencias del Mar (COLACMAR), VIII Congreso de Ciencias del Mar de Cuba (MarCuba) y 4º Taller Internacional PESCA, La Habana, 26-30 de Octubre de 2009Los perfiladores de corrientes por efecto Doppler, comúnmente conocidos por ADCPs (Acoustic Doppler Current Profilers), se utilizan para medir las tres componentes de la velocidad de la corriente a distintas profundidades. Para ello disponen de al menos tres transductores, usualmente cuatro, dispuestos en distintas orientaciones. La velocidad que en realidad perciben los ADCPs son velocidades radiales, perpendiculares a sus transductores (velocidad de acercamiento o alejamiento a los transductores), y es necesario transformarla para poder estimar las tres componentes de la velocidad en un sistema de coordenadas oceanográfico (componente Este, componente Norte y componente vertical). Primeramente, antes de calcular las velocidades en coordenadas oceanográficas, las velocidades radiales se transportan a un sistema de cartesiano interno (referido a la geometría del ADCP) normalmente denominado sistema del “instrumento” o “XYZ” (Figura 1). Aquí nos circunscribiremos a los ADCPs de cuatro transductores y a la mejora del algoritmo para transportar velocidades radiales a velocidades en XYZ. Una vez obtenidas las velocidades XYZ su paso a velocidades oceanográficas se consigue girando oportunamente los ejes XYZ en función de la orientación de los mismos con el Norte geográfico y el plano horizontalN

How currents in one real partially mixed stuary are

2 pages, 7 figures.-- 2ª Asamblea hispano-portuguesa de geodesia y geofisica = 2ª Assembleia luso-espanhola de geodesia e geofisica, Lagos (Algarve, Portugal), 8-12 febrero de 2000Since the works of von Richthofen, "ria" is a geographical standard term referring to estuaries with a particular geological configuration. At the origin of the term lie the estuaries on the northern lberian coast, one of which is the Ría de Vigo. Can observed circulation patterns serve also as a paradigm.for a certain type of estuary? In order to explore this possibility, circulation data for spring, summer and autumn seasons in the Ría de Vigo are analysed. Currents are studied quantitatively and separately at different frequency regimes. Tidal current patterns are determined: vertical structure, variability in various time-scales, geographical effects on inflow and outflow regimes are dealt with. The importance of low frequency currents in terms of intensity persistency and energy is assessed. Simultaneous deployrnents in both entrances to the Ría shed light on the different characteristics of the flux of water through them. Some conclusions on the characterisation of the Ría de Vigo as a partially mixed estuary are drawnN

Dynamcis in the Ría de Vigo

Poster.-- Euroconference Water and Life-Oceanography, Meteorology and Marine Resources, Vigo, Mayo 2000Projects CICYT AM395-1084-C03 and the Xunta de Galicia (FEDER funds)N

Baroclinic prognostic modelling of a partially mixed estuary: a model study of the Ría de Vigo

2 pages, 3 figures.-- 2ª Asamblea hispano-portuguesa de geodesia y geofisica = 2ª Assembleia luso-espanhola de geodesia e geofisica, Lagos (Algarve, Portugal), 8-12 febrero de 2000Results of a full baroclinic prognostic model for the Rfa de Vigo are presented. The algorithm is an adapted version of the HAMSOM model, which is a three dimensional multi-level (z co-ordinate) finite difference baroclinic model. Its resolution, stability and speed allow inquiring into the properties of an idealised version of the system. and its response to different external actions. The separate and combined effects of both barotropic and baroclinic forcing are studied and quantitatively evaluated. Tidal dyna,nics, wind driven currents, residual circulation and thermohaline structure are modelled, and results compared to observationsN

Plankton response to weakening of the Iberian coastal upwelling

10 páginas, 4 figurasCoastal upwelling regions, which are affected by equatorward-wind variability, are among the most productive areas of the oceans. It has been suggested that global warming will lead to a general strengthening of coastal upwelling, with important ecological implications and an impact on fisheries. However, in the case of the Iberian upwelling, the long-term analysis of climatological variables described here reveals a weakening in coastal upwelling. This is linked to a decrease of zonal sea level pressure gradient, and correlated with an observed increase of sea surface temperature and North Atlantic Oscillation. Weakening of coastal upwelling has led to quantifiable modifications of the ecosystem. In outer shelf waters a drop in new production over the last 40 years is likely related to the reduction of sardine landings at local harbors. On the other hand, in inner shelf and Ria waters, the observed weakening of upwelling has slowed down the residual circulation that introduces nutrients to the euphotic layer, and has increased the stability of the water column. The drop in nutrient levels has been compensated by an increase of organic matter remineralization. The phytoplankton community has responded to those environmental trends with an increase in the percentage of dinoflagellates and Pseudonitzschia spp. and a reduction in total diatoms. The former favors the proliferation of harmful algal blooms and reduces the permitted harvesting period for the mussel aquaculture industry. The demise of the sardine fishery and the potential threat to the mussel culture could have serious socio-economic consequences for the region.This study was partially funded by the European Commission (EU FP6 CARBOOCEAN Integrated Project, Contract no. 511176) and Xunta de Galiza (PGIDIT05PXIC40203PM, PGIDIT08MMA014402PR, PGIDIT07PXIB402153PR and PGIDIT05- MA40201PR).Peer reviewe