Evaluación ecosistémica del golfo de Cádiz: análisis integral y descripción de procesos

Los modelos y análisis de ecosistemas son herramientas importantes que pueden ayudar a las partes interesadas a comprender sistemas complejos y evaluar cómo estos sistemas responden a los posibles cambios del ecosistema. En la presente tesis doctoral, ha sido investigado el estado del ecosistema del golfo de Cádiz (GoC) y la evolución temporal de sus recursos marinos utilizando un enfoque multidisciplinar, que ha combinado modelación y análisis de integración de datos. Los resultados resaltaron una serie de puntos relevantes para los ecosistemas costero y marino: el ecosistema del GoC en los últimos 20 años ha pasado por muchos cambios, desde la forma como le vemos, su explotación, así como las medidas de protección. En este sentido ese estudio aporta información inédita a través del desarrollo de un análisis integral del ecosistema del GoC, describiendo la evolución temporal del ecosistema de forma holística y conjunta, analizando los efectos naturales y antropogénicos en su principal zona de cría, el estuario del Río Guadalquivir, y, por último, caracterizando la distribución espacio-temporal de la comunidad zooplanctónica. Finalmente, el presente estudio ha identificado futuras líneas de investigación que podrán ayudar en el desarrollo ambiental y socioeconómico, y buscar maneras más eficaces para maximizar la equidad y la sostenibilidad de los recursos marinos

Seasonal variation of zooplankton and environmental conditions along a transect in the Gulf of Cádiz

This study presents seasonal variation in the zooplankton composition of the Gulf of Cádiz was studied between 2001 and 2012. Samples were collected three times per year, in the spring, summer and autumn at three stations situated along a transect perpendicular to the coast. The total zooplankton abundance during the summer was higher than in the spring and autumn. Zooplankton community is characterized by a seasonal cycle mirroring similar cycles in the physical environment. Differences in community composition were also found along the transect, particularly between the coastal station, under the influence of the Guadalquivir River, and the outer station, characterized by oceanic conditions. This study is the first description of the seasonal and spatial variation of this marine component of the Gulf of Cádi

Theory of Disordered Itinerant Ferromagnets I: Metallic Phase

A comprehensive theory for electronic transport in itinerant ferromagnets is developed. We first show that the Q-field theory used previously to describe a disordered Fermi liquid also has a saddle-point solution that describes a ferromagnet in a disordered Stoner approximation. We calculate transport coefficients and thermodynamic susceptibilities by expanding about the saddle point to Gaussian order. At this level, the theory generalizes previous RPA-type theories by including quenched disorder. We then study soft-mode effects in the ferromagnetic state in a one-loop approximation. In three-dimensions, we find that the spin waves induce a square-root frequency dependence of the conductivity, but not of the density of states, that is qualitatively the same as the usual weak-localization effect induced by the diffusive soft modes. In contrast to the weak-localization anomaly, this effect persists also at nonzero temperatures. In two-dimensions, however, the spin waves do not lead to a logarithmic frequency dependence. This explains experimental observations in thin ferromagnetic films, and it provides a basis for the construction of a simple effective field theory for the transition from a ferromagnetic metal to a ferromagnetic insulator.Comment: 15pp., REVTeX, 2 eps figs, final version as publishe

International politics must be considered together with climate and fisheries regulation as a driver of marine ecosystems

Seafood is an essential source of protein globally. As its demand continues to rise, balancing food security and the health of marine ecosystems has become a pressing challenge. Ecosystem-based fisheries management (EBFM) has been adopted by the European Union (EU) Common Fisheries Policy (CFP) to meet this challenge by ac- counting for the multiple interacting natural and socio-economic drivers. The CFP includes both the imple- mentation of regulatory measures to EU stocks and the establishment of bilateral fisheries agreements with neighbouring countries, known as sustainable fisheries partnership agreements (SFPAs). While the effects of fisheries management regulations are well acknowledged, the consequences of the SFPAs on EU ecosystems have been commonly overlooked. Here we investigate the development of the Gulf of Cadiz marine ecosystem over the last two decades and found evidence of the impact of both policy interventions. Our findings reveal the effec- tiveness of regulatory measures in reverting a progressively degrading ecosystem, characterised by high fishing pressure and dominance of opportunistic species, to a more stable configuration, characterised by higher biomass of small pelagics and top predators after 2005. Knock-on effects of the EU-Morocco SFPA and climate effects were detected before 2005, resulting in increased purse seine fishing effort, lower biomass of pelagic species and warmer temperatures. This southern EU marine ecosystem has been one of the latest to introduce regulations and is very exposed to fishery agreements with neighbouring Morocco. Our study highlights the importance of taking into consideration, not only the effects of in situ fisheries regulations but also the indirect implications of political agreements in the framework of EBFM.Marie Curie (re)Integration Grant (M.Ll., FP7-PEOPLE, ref: PERG05-GA-2009-247528), OCAL-DILEMA project (ref: CTM2014-59244-C3-2-R), CAPES Foundation and the Science without Borders fellowship program (ref: 99999.013763/2013- 00), EASME/ EMFF/2018/1.3.2.4/Lot2/SI2.818388-SC03En prensa6,86

Current-Density Functional Theory of the Response of Solids

The response of an extended periodic system to a homogeneous field (of wave-vector $q=0$) cannot be obtained from a $q=0$ time-dependent density functional theory (TDDFT) calculation, because the Runge-Gross theorem does not apply. Time-dependent {\em current}-density functional theory is needed and demonstrates that one key ingredient missing from TDDFT is the macroscopic current. In the low-frequency limit, in certain cases, density polarization functional theory is recovered and a formally exact expression for the polarization functional is given.Comment: 5 pages, accepted in PR

Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions

The results from ten statistical multifragmentation models have been compared with each other using selected experimental observables. Even though details in any single observable may differ, the general trends among models are similar. Thus these models and similar ones are very good in providing important physics insights especially for general properties of the primary fragments and the multifragmentation process. Mean values and ratios of observables are also less sensitive to individual differences in the models. In addition to multifragmentation models, we have compared results from five commonly used evaporation codes. The fluctuations in isotope yield ratios are found to be a good indicator to evaluate the sequential decay implementation in the code. The systems and the observables studied here can be used as benchmarks for the development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume "Dynamics and Thermodynamics with Nuclear Degrees of Freedo

Non-Thermal Behavior in Multifragment Decay

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Assessing the Evolutionary Nature of Multifragment Decay

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

A review of the stable istotope bio-geochemistry of the global silicon cycle and its associated trace elements

Silicon (Si) is the second most abundant element in the Earth's crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc.) have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, δ13C, δ15N, δ18O, δ30Si) of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes) and the potential technical and conceptual limitations that need to be considered for future studies