Functional analysis of secondary tropical dry forests in a region of the Colombia, Caribbean

Secondary tropical forests are increasingly recognized for their role conserving biodiversity in agricultural landscapes and this role is especially important for seasonally dry tropical forests (SDTF), one of the most threatened tropical forested ecosystems. The conservation value of secondary forest is increased by its capacity to maintain ecosystem properties and provide services to humans; which has been hypothesized to have positive links to the species and functional diversity of ecosystems. However very little information is available on the occurrence of this relationship in secondary forests. This dissertation makes an important contribution to the ecological knowledge of secondary SDTF and describes changes in plant species and functional diversity by using a stratified design considering different successional stages along an environmental gradient in a region of the Caribbean coast of Colombia and a multi-trait approach to study functional diversity at three scales: species, communities and landscape. The analysis of the variation in functional traits of SDTF trees at the species level allowed me to support the hypothesis of coordination between leaves and stem traits. Three dimensions of correlated variation were identified: the first related to leaf and stem economy, the second to leaf thickness and organization and the third to the trade-offs between leaf size, stem density and bark thickness. Secondary forests showed high species turnover during succession and increasing diversity from early to late forests. Species composition similarity was higher among late successional forest than early and intermediate stage forests, showing that environmental characteristics are influencing successional trajectories. Frequency distributions of species in the three successional stages showed evidence of functional trait similarity among species and underlined the importance of changes in species abundances determining functional composition during succession. A shift in abundance from individuals with traits that favour survival after disturbance to individuals with denser stems and a more conservative resource use profile was observed from early to late stages of succession. Functional composition was also strongly influenced by environmental variables, especially leaf traits, and a shift of traits from acquisitive to conservative type species was observed with increasing nutrient content and flooding, proxies of water availability. Assessment of ecosystem services was conducted using two independent approaches: semistructured interviews and field data. A high richness of useful woody plants was recorded and the provision of services was related to a high variability in functional traits among species. The provision of the ecosystem services determined by the presence and abundance of useful species showed significant differences between stages. The relationships observed between ecosystem sevices and functional and species diversity indices were not consistent. In contrast species richess showed significant negative relationships at the plot level with most of the ecosystem services assessed, showing a trade-off among the conservation of species richness and the maintenance of service provision. Overall, this research provides novel insights into the dynamic relationships between biodiversity, ecosystem function and ecosystem services in this globally important, but under-researched forest type

Youth Producing Voice: A Video-cued Ethnography of a Media Education Classroom

From mini screens on our cell phones to large flat screens hanging in institutional hallways, visual digital media are part of our everyday lives. This is especially true for youth, who in their leisure time increasingly spend time watching and making video content. Yet there are few opportunities for youth in either their community or school settings to access formal instruction in digital media literacy, including video production. In this dissertation, I examine the possibilities and challenges for doing youth media inside schools. What do youth allow themselves to say when doing media production in school and how do they voice their social and cultural concerns around pressing issues in society? There is little research on youth media inside schools, even as video making and video use continues to grow. Drawing from existing research on youth media, the new literacies and critical media literacy, this study examines how student voice gets shaped in a high school classroom and what role it plays for the students and the school. I carry out a video-cued classroom ethnography to examine the class\u27s norms, discourses and structures. I analyze the students\u27 video-cued focus group interview data, through the lens of heteroglossia, drawing on Bakhtinian ideas of language and identity as heterogenous. Video-cued ethnography provides the research with a multivocal dimension, as the same video clips are shown to various participants who each comment on it, thereby producing a dialogue across positionalities, space, and time. This study shows how student voice is constituted of multiple stances and ideas, at times conflicting ones. Students took on a variety of discursive strategies to produce their videos and to address an audience beyond the media production classroom through the school-wide student news program. The students use their creative agency to mobilize their peers on topics they believed were valuable to students and that point to a shared world within their school. Additionally, the research demonstrates that youth media practices inside school may serve as social and public acts that go beyond the classroom and that approach civic engagement

Ultra--cold gases and the detection of the Earth's rotation: Bogoliubov space and gravitomagnetism

The present work analyzes the consequences of the gravitomagnetic effect of the Earth upon a bosonic gas in which the corresponding atoms have a non--vanishing orbital angular momentum. Concerning the ground state of the Bogoliubov space of this system we deduce the consequences, on the pressure and on the speed of sound, of the gravitomagnetic effect. We prove that the effect on a single atom is very small, but we also show that for some thermodynamical properties the consequences scale as a non--trivial function of the number of particles.Comment: 4 page

Finite Size Effects in Separable Recurrent Neural Networks

We perform a systematic analytical study of finite size effects in separable recurrent neural network models with sequential dynamics, away from saturation. We find two types of finite size effects: thermal fluctuations, and disorder-induced `frozen' corrections to the mean-field laws. The finite size effects are described by equations that correspond to a time-dependent Ornstein-Uhlenbeck process. We show how the theory can be used to understand and quantify various finite size phenomena in recurrent neural networks, with and without detailed balance.Comment: 24 pages LaTex, with 4 postscript figures include

Understanding the cephalopod immune system based on functional and molecular evidence

11 páginas, 6 figurasCephalopods have the most advanced circulatory and nervous system among the mollusks. Recently, they have been included in the European directive which state that suffering and pain should be minimized in cephalopods used in experimentation. The knowledge about cephalopod welfare is still limited and several gaps are yet to be filled, especially in reference to pathogens, pathologies and immune response of these mollusks. In light of the requirements of the normative, in addition to the ecologic and economic importance of cephalopods, in this review we update the work published to date concerning cephalopod immune system. Significant advances have been reached in relation to the characterization of haemocytes and defensive mechanisms comprising cellular and humoral factors mainly, but not limited, in species of high economic value like Sepia officinalis and Octopus vulgaris. Moreover, the improvement of molecular approaches has helped to discover several immune-related genes/proteins. These immune genes/proteins include antimicrobial peptides, phenoloxidases, antioxidant enzymes, serine protease inhibitor, lipopolysaccharide-induced TNF-α factor, Toll-like receptors, lectins, even clusters of differentiation among others. Most of them have been found in haemocytes but also in gills and digestive gland, and the characterization as well as their precise role in the immune response of cephalopods is still pending to be elucidated. The assessment of immune parameters in cephalopods exposed to contaminants is just starting, but the negative impact of some pollutants on the immune response of the common octopus has been reported. This review summarizes the current status of our knowledge about the cephalopod immune system that seems to be far from simply. On the contrary, the advances gained to date point out a complex innate immunity in cephalopodsPeer reviewe

Ideal-Modified Bosonic Gas Trapped in an Arbitrary Three Dimensional Power-Law Potential

We analyze the effects caused by an anomalous single-particle dispersion relation suggested in several quantum-gravity models, upon the thermodynamics of a Bose-Einstein condensate trapped in a generic 3-dimensional power-law potential. We prove that the shift in the condensation temperature, caused by a deformed dispersion relation, described as a non-trivial function of the number of particles and the shape associated to the corresponding trap, could provide bounds for the parameters associated to such deformation. Additionally, we calculate the fluctuations in the number of particles as a criterium of thermodynamic stability for these systems. We show that the apparent instability caused by the anomalous fluctuations in the thermodynamic limit can be suppressed considering the lowest energy associated to the system in question.Comment: 10 pages. arXiv admin note: text overlap with arXiv:1202.380

Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors

We report the fabrication and the characterization of carbon fibre tips for their use in combined scanning tunnelling and force microscopy based on piezoelectric quartz tuning fork force sensors. We find that the use of carbon fibre tips results in a minimum impact on the dynamics of quartz tuning fork force sensors yielding a high quality factor and consequently a high force gradient sensitivity. This high force sensitivity in combination with high electrical conductivity and oxidation resistance of carbon fibre tips make them very convenient for combined and simultaneous scanning tunnelling microscopy and atomic force microscopy measurements. Interestingly, these tips are quite robust against occasionally occurring tip crashes. An electrochemical fabrication procedure to etch the tips is presented that produces a sub-100 nm apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure