Role of Rab5 in synaptic vesicle recycling

During synaptic transmission, NT-filled synaptic vesicles are released by Ca2+-triggered exocytosis at the active zone. Following exocytosis, SV membrane is immediately re-internalized and synaptic vesicles (SVs) are regenerated by a local recycling mechanism within the presynaptic terminal. It is debated whether an endosomal compartment is involved in this recycling process. In contrast, it is well known from cultured mammalian cells, that endocytic vesicles fuse to the early sorting endosome. The early endosome is a major sorting station of the cell where cargo is send into the degradative pathway to late endosome and lysosome or towards recycling. Each trafficking step is mediated by a certain protein of the Rab family. Rab proteins are small GTPases belonging to the Ras superfamily. They accumulate at their target compartments and have thereby been used as markers for the different endocytic organelles in cultured mammalian cells. Rab5 controls trafficking from the PM to the early endosome and has thereby been used as marker for this compartment. A second marker is based on the specific binding of the FYVE zinc finger protein domain to the lipid PI(3)P that is specifically generated at the early endosomal membrane. This study used the Drosophila NMJ as a model system to investigate the SV recycling process. In particular, three questions were addressed: First, is an endosomal compartment present at the synapse? Second, do SVs recycle through an endosome? Third, is Rab5 involved in SV recycling? We used GFP fusions of Rab5 and 2xFYVE to visualize endosomal compartments at the presynaptic terminal of Drosophila third instar larval NMJs. Furthermore, the endosomes are located within the pool of recycling SVs, labeled with the styryl-dye FM5-95. Using the temperature-sensitive mutation in Dynamin, shibirets, we showed that SV recycling involves trafficking through an intermediate endosomal compartment. In cultured mammalian cells, interfering with Rab5 function by expressing the dominant negative version, Rab5SN causes the fragmentation of the endosome and the accumulation of endocytic vesicles. In contrast, when Rab5 is overexpressed enlarged endosomal compartments were observed. In Drosophila, the endosomal compartment was disrupted when loss of function and dominant negative mutants of Rab5 were expressed. In addition, at the ultrastructural we observed an accumulation of endocytic vesicles in Rab5S43N expressing terminals and enlarged endosomes when Rab5 was overexpressed. Furthermore, interfering with Rab5 function using the dominant negative Rab5S43N caused a decrease in the SV recycling kinetics as shown by FM1-43 experiments. In contrast, overexpression of Rab5 or GFP-Rab5 caused an increase in the FM1-43 internalization rate. Finally, standard electrophysiological techniques were used to measure synaptic function. We found that the Rab5-mediated endosomal SV recycling pathway generates vesicles with a higher fusion efficacy during Ca2+-triggered release, compared to SVs recycled when Rab5 function was impaired. We therefore suggest a model in which the endosome serves as organelle to control the SV fusion efficacy and thereby the synaptic strength. Since changes in the synaptic strength are occuring during learning and memory processes, controlling endosomal SV recycling might be a new molecular mechanism involved in learning and memory.

Molekulare Studien zur Evolution der Myrmekophytie in der Gattung Macaranga (Euphorbiaceae)

Im Rahmen der vorliegenden Arbeit wurde eine detaillierte phylogenetische Analyse der Ameisenpflanzen aus der Gattung Macaranga (Euphorbiaceae) und ihres verwandtschaftlichen Umfelds mit Hilfe von AFLP-Fingerprinting („amplified fragment length polymorphisms“) sowie vergleichender Analyse von mehreren nichtkodierenden Chloroplasten-DNA-Loci vorgenommen. Anhand dieser Untersuchungen sollten im Wesentlichen die folgenden Fragen geklärt werden: (1) Wie stellen sich die Verwandtschaftsverhältnisse zwischen den myrmekophytischen Macaranga-Sektionen Pachystemon, Winklerianae und Pruinosae dar? (2) Wie sind die einzelnen Arten dieser Sektionen miteinander verwandt? (3) Wie oft ist die Lebensweise ”Myrmekophytie” unabhängig voneinander entstanden? Gibt es Hinweise auf Reversionen? (4) Wo liegt genealogisch und auch geographisch der Ursprung der Symbiose zwischen den myrmekophytischen Macaranga-Arten und ihren Partnerameisen? (5) Welche Bedeutung spielen koevolutive Entwicklungen für das Macaranga-Crematogaster-Symbiosesystem? Ist Myrmekophytie im Sinne einer Schlüsselinnovation (Givnish, 1997) als Stimulus für eine adaptive Radiation zu betrachten? (1) Für die AFLP-Analyse wurden 108 Proben aus 43 Macaranga-Arten und 5 unbeschriebenen Morphospezies in die phylogenetische Untersuchung einbezogen. Auf der Basis von 426 Merkmalen wurden Phänogramme sowie Kladogramme rekonstruiert. Zur statistischen Absicherung wurden Bootstrap-Analysen durchgeführt und im Falle der Kladogramme darüber hinaus der „consistency“-Index bestimmt. Die AFLP-Datensätze wurden zusätzlich einer Hauptkomponentenanalyse unterzogen. Mit Hilfe der verschiedenen Untersuchungsmethoden konnten weitgehend übereinstimmende Gruppierungen bzw. evolutive Linien identifiziert werden. Die Sektionen Pachystemon und Pruinosae bilden eine jeweils gut gestützte monophyletische Gruppe. Beide sind vermutlich Schwestergruppen und damit gleich alt. Für die Monophylie der nur aus zwei Arten bestehenden Sektion Winklerianae ergab sich keine Unterstützung. Die Arten der Sektion Pruinosae sind im AFLP-Baum gut aufgelöst. Die nicht myrmekophytische M. gigantea sitzt dabei an der Basis und ist Schwestergruppe zu den myrmekophytischen Arten. Innerhalb der Sektion Pachystemon wurden mit Hilfe der AFLP-Analyse vier gut gestützte Gruppen identifiziert. Für die puncticulata-Gruppe konnte hier erstmals auf molekularer Ebene eine Zugehörigkeit zur Sekt. Pachystemon nachgewiesen werden. Der von Davies (2001) vorgenommene Ausschluss von M. recurvata aus der Sekt. Pachystemon konnte bestätigt werden. Die Verwandtschaftsbeziehungen einzelner Arten zueinander sind in den AFLP-Bäumen nicht aufgelöst. (2) Für die vergleichende Chloroplasten-Sequenzierung wurden nach Maßgabe der Sequenzvariabilität in Testsequenzierungen die Bereiche atpB-rbcL und psbI-trnS für die phylogenetische Untersuchung ausgewählt. Für die Chloroplasten-Phylogenie wurden für jeden Locus mehr als 100 Sequenzen analysiert. Neben 29 Pachystemon-Arten inkl. vier unbekannter Morphospezies, acht Pruinosae-Arten inkl. eines möglichen Hybriden und den beiden Arten der Sekt. Winklerianae wurden 22 weitere Macaranga- und 10 Mallotus-Arten in die Untersuchung einbezogen. Zwischen den südostasiatischen Arten bestanden nur geringe Sequenzunterschiede. Maximum-Parsimonie-Kladogramme wurden rekonstruiert und die Sequenzen der beiden Loci wurden sowohl einzeln, als auch kombiniert ausgewertet. Indels wurden kodiert und als separate Merkmalsmatrix an die Sequenzdaten angehangen. Innerhalb von Macaranga konnten nur wenige abgesicherte Gruppen identifiziert werden. Deutlich war die Zusammengehörigkeit der afrikanischen Arten und ihr Entstehung aus den südostasiatischen Arten. Die von Davies (2001) der Sektion Pruinosae zugeordnete M. siamensis steht deutlich außerhalb dieser Sektion. Die Arten der Sektionen Pruinosae, Pachystemon und Winklerianae bilden keine statistisch gesicherten monophyletischen Gruppen. Während der Pilotstudien stellte sich heraus, dass die Chloroplastensequenzen nahe verwandter Arten der Sektion Pachystemon weniger nach den Artgrenzen, sondern vielmehr nach geographischen Kriterien gruppierten. (3) Es wurde daher zusätzlich eine phylogeographische Analyse der Chloroplasten-Sequenzen auf der Basis eines Parsimonie-Netzwerks durchgeführt. Neben dem atpB-rbcL-Spacer und einer Teilsequenze des psbI-trnS-Locus (ccmp2) wurde dafür zusätzlich der ccmp6-Locus (ein Abschnitt des ycf3-Introns) sequenziert. Die phylogeographische Untersuchung wurde mit 144 Proben aus 41 Macaranga-Arten durchgeführt. Darin enthalten waren 29 Arten (inkl. vier Morphospezies) mit 112 Proben der Sektion Pachystemon, sieben 7 Arten (inkl. eines potentiellen Hybriden) mit 22 Proben der Sekt. Pruinosae und zwei Arten mit 5 Proben der Sekt. Winklerianae. Das voll aufgelöste statistische Parsimonie-Netzwerk umfasste 88 Haplotypen. Die Sektionen Pachystemon und Pruinosae bilden jeweils eine monophyletische Gruppe. Das geographische Arrangement der Haplotypen unabhängig von der Artzugehörigkeit könnte durch Introgression und/oder „lineage sorting“ bedingt sein. Mit Hilfe der im Rahmen dieser Arbeit gewonnenen Ergebnisse kann man davon ausgehen, dass eine enge Ameisen-Pflanzen-Symbiose innerhalb der Gattung Macaranga mindestens drei-, möglicherweise viermal unabhängig voneinander entstanden ist Eine Reversion hat mindestens einmal, möglicherweise häufiger in der bancana-Gruppe stattgefunden. Ob sich die Symbiose dabei in Westmalaysia oder in Borneo entwickelt hat, kann man nicht sicher sagen; Ob und inwieweit die große Artenzahl in der bancana-Gruppe als eine Folge der Myrmekophytie anzusehen ist, bleibt zunächst offen. Wesentliche Teile der vorliegenden Arbeit liegen bereits in publizierter Form vor (AFLP-Analyse: Bänfer et al. 2004; Chloroplasten-Analyse: Vogel et al. 2003; Bänfer et al. 2006).

Management approaches in organic potato and tomato production

The presented thesis considered three different system approach topics to ensure yield and plant health in organically grown potatoes and tomatoes. The first topic describes interactions between late blight (Phytophthora infestans) incidence and soil nitrogen supply on yield in organic potato farming focussing in detail on the yield loss relationship of late blight based on results of several field trials. The interactive effects of soil N-supply, climatic conditions and late blight on the yield were studied in the presence and absence of copper fungicides from 2002-2004 for the potato cultivar Nicola. Under conditions of central Germany the use of copper significantly reduced late blight in almost all cases (15-30 %). However, the reductions in disease through copper application did not result in statistically significant yield increases (+0 – +10 %). Subsequently, only 30 % of the variation in yield could be attributed to disease reductions. A multiple regression model (R²Max), however, including disease reduction, growth duration and temperature sum from planting until 60 % disease severity was reached and soil mineral N contents 10 days after emergence could explain 75 % of the observed variations in yield. The second topic describes the effect of some selected organic fertilisers and biostimulant products on nitrogen-mineralization and efficiency, yield and diseases in organic potato and tomato trials. The organic fertilisers Biofeed Basis (BFB, plant derived, AgroBioProducts, Wageningen, Netherlands) and BioIlsa 12,5 Export (physically hydrolysed leather shavings, hair and skin of animals; ILSA, Arizignano, Italy) and two biostimulant products BioFeed Quality (BFQ, multi-compound seaweed extract, AgroBioProducts) and AUSMA (aqueous pine and spruce needle extract, A/S BIOLAT, Latvia), were tested. Both fertilisers supplied considerable amounts of nitrogen during the main uptake phases of the crops and reached yields as high or higher as compared to the control with horn meal fertilisation. The N-efficiency of the tested fertilisers in potatoes ranged from 90 to 159 kg yield*kg-1 N – input. Most effective with tomatoes were the combined treatments of fertiliser BFB and the biostimulants AUSMA and BFQ. Both biostimulants significantly increased the share of healthy fruit and/or the number of fruits. BFQ significantly increased potato yields (+6 %) in one out of two years and reduced R. solani-infestation in the potatoes. This suggests that the biostimulants had effects on plant metabolism and resistance properties. However, no effects of biostimulants on potato late blight could be observed in the fields. The third topic focused on the effect of suppressive composts and seed tuber health on the saprophytic pathogen Rhizoctonia solani in organic potato systems. In the present study 5t ha-1 DM of a yard and bio-waste (60/40) compost produced in a 5 month composting process and a 15 month old 100 % yard waste compost were used to assess the effects on potato infection with R. solani when applying composts within the limits allowed. Across the differences in initial seed tuber infestation and 12 cultivars 5t DM ha-1 of high quality composts, applied in the seed tuber area, reduced the infestation of harvested potatoes with black scurf, tuber malformations and dry core tubers by 20 to 84 %, 20 to 49 % and 38 to 54 %, respectively, while marketable yields were increased by 5 to 25 % due to lower rates of wastes after sorting (marketable yield is gross yield minus malformed tubers, tubers with dry core, tubers with black scurf > 15% infested skin). The rate of initial black scurf infection of the seed tubers also affected tuber number, health and quality significantly. Compared to healthy seed tubers initial black scurf sclerotia infestation of 2-5 and >10 % of tuber surface led in untreated plots to a decrease in marketable yields by 14-19 and 44-66 %, a increase of black scurf severity by 8-40 and 34-86 % and also increased the amount of malformed and dry core tubers by 32-57 and 109-214 %.

Folien zur Vorlesung Sortierverfahren

Die hier frei verfügbare Foliensammlung stammt aus der gleichnamigen Master-Veranstaltung im Sommersemester 2014. Das zugehörige Skript (in Englisch) kann als PDF heruntergeladen werden von der Universität Turku (Lutz M. Wegner, Sorting – The Turku Lectures, Lecture Notes in Computing 2014, Univ. of Turku, Finland, http://tucs.fi/publications/attachment.php?fname=bWegner_LutzMx14a.full.pdf). Das überarbeitete Material geht auf eine dort im Jahre 1987 gehaltene Gastvorlesung zurück. Betrachtet werden Varianten von Quicksort und Heapsort, speziell bei Quicksort solche für Multimengen und Vorsortierung, sowohl für verkettete Listen als auch für Datenstrukturen mit Direktzugriff. Neben dem Standardheapsort werden die Floydverbesserung und Dijkstras Smoothsort vorgestellt. Eine Netzwerkvariante und zwei Externspeicherverfahren auf Basis von Quicksort und Heapsort werden untersucht. Der Stand der Technik bei den stabilen, in-situ Verfahren wird skizziert. Der Stoff eignet sich für eine Vorlesung mit angegliederten Projektübungen, in denen Studierende selbstständig Algorithmen, die als Pseudo-Code vorgegeben sind, in effizienten, lauffähigen Java-Code umsetzen und in einer Laufzeitbibliothek mit vorgegebenen Testdaten messen.

Building Grounded Abstractions for Artificial Intelligence Programming

Most Artificial Intelligence (AI) work can be characterized as either ``high-level'' (e.g., logical, symbolic) or ``low-level'' (e.g., connectionist networks, behavior-based robotics). Each approach suffers from particular drawbacks. High-level AI uses abstractions that often have no relation to the way real, biological brains work. Low-level AI, on the other hand, tends to lack the powerful abstractions that are needed to express complex structures and relationships. I have tried to combine the best features of both approaches, by building a set of programming abstractions defined in terms of simple, biologically plausible components. At the ``ground level'', I define a primitive, perceptron-like computational unit. I then show how more abstract computational units may be implemented in terms of the primitive units, and show the utility of the abstract units in sample networks. The new units make it possible to build networks using concepts such as long-term memories, short-term memories, and frames. As a demonstration of these abstractions, I have implemented a simulator for ``creatures'' controlled by a network of abstract units. The creatures exist in a simple 2D world, and exhibit behaviors such as catching mobile prey and sorting colored blocks into matching boxes. This program demonstrates that it is possible to build systems that can interact effectively with a dynamic physical environment, yet use symbolic representations to control aspects of their behavior.

Review of bio-particle manipulation using dielectrophoresis

During the last decade, large and costly instruments are being replaced by system based on microfluidic devices. Microfluidic devices hold the promise of combining a small analytical laboratory onto a chip-sized substrate to identify, immobilize, separate, and purify cells, bio-molecules, toxins, and other chemical and biological materials. Compared to conventional instruments, microfluidic devices would perform these tasks faster with higher sensitivity and efficiency, and greater affordability. Dielectrophoresis is one of the enabling technologies for these devices. It exploits the differences in particle dielectric properties to allow manipulation and characterization of particles suspended in a fluidic medium. Particles can be trapped or moved between regions of high or low electric fields due to the polarization effects in non-uniform electric fields. By varying the applied electric field frequency, the magnitude and direction of the dielectrophoretic force on the particle can be controlled. Dielectrophoresis has been successfully demonstrated in the separation, transportation, trapping, and sorting of various biological particles.

Inverse Metabolic Engineering of Synechocystis PCC 6803 for Improved Growth Rate and Poly-3-hydroxybutyrate Production

Synechocystis PCC 6803 is a photosynthetic bacterium that has the potential to make bioproducts from carbon dioxide and light. Biochemical production from photosynthetic organisms is attractive because it replaces the typical bioprocessing steps of crop growth, milling, and fermentation, with a one-step photosynthetic process. However, low yields and slow growth rates limit the economic potential of such endeavors. Rational metabolic engineering methods are hindered by limited cellular knowledge and inadequate models of Synechocystis. Instead, inverse metabolic engineering, a scheme based on combinatorial gene searches which does not require detailed cellular models, but can exploit sequence data and existing molecular biological techniques, was used to find genes that (1) improve the production of the biopolymer poly-3-hydroxybutyrate (PHB) and (2) increase the growth rate. A fluorescence activated cell sorting assay was developed to screen for high PHB producing clones. Separately, serial sub-culturing was used to select clones that improve growth rate. Novel gene knock-outs were identified that increase PHB production and others that increase the specific growth rate. These improvements make this system more attractive for industrial use and demonstrate the power of inverse metabolic engineering to identify novel phenotype-associated genes in poorly understood systems.

A Log-linear model of grain size influence on the geochemistry of sediments

Sediment composition is mainly controlled by the nature of the source rock(s), and chemical (weathering) and physical processes (mechanical crushing, abrasion, hydrodynamic sorting) during alteration and transport. Although the factors controlling these processes are conceptually well understood, detailed quantification of compositional changes induced by a single process are rare, as are examples where the effects of several processes can be distinguished. The present study was designed to characterize the role of mechanical crushing and sorting in the absence of chemical weathering. Twenty sediment samples were taken from Alpine glaciers that erode almost pure granitoid lithologies. For each sample, 11 grain-size fractions from granules to clay (ø grades <-1 to >9) were separated, and each fraction was analysed for its chemical composition. The presence of clear steps in the box-plots of all parts (in adequate ilr and clr scales) against ø is assumed to be explained by typical crystal size ranges for the relevant mineral phases. These scatter plots and the biplot suggest a splitting of the full grain size range into three groups: coarser than ø=4 (comparatively rich in SiO2, Na2O, K2O, Al2O3, and dominated by “felsic” minerals like quartz and feldspar), finer than ø=8 (comparatively rich in TiO2, MnO, MgO, Fe2O3, mostly related to “mafic” sheet silicates like biotite and chlorite), and intermediate grains sizes (4≤ø <8; comparatively rich in P2O5 and CaO, related to apatite, some feldspar). To further test the absence of chemical weathering, the observed compositions were regressed against three explanatory variables: a trend on grain size in ø scale, a step function for ø≥4, and another for ø≥8. The original hypothesis was that the trend could be identified with weathering effects, whereas each step function would highlight those minerals with biggest characteristic size at its lower end. Results suggest that this assumption is reasonable for the step function, but that besides weathering some other factors (different mechanical behavior of minerals) have also an important contribution to the trend. Key words: sediment, geochemistry, grain size, regression, step function

Simple Analysis of Network Datasets

Linux commands that are generally useful for analyzing data; it is very easy to reduce phenomena such as links, nodes, URLs or downloads, to multiply repeating identifiers and then sorting and counting appearances.

Factores psicosociales y bienestar del trabajador en investigaciones realizadas en Colombia y España, durante el período 2002-2012 .

Introducción. En el presente trabajo se pretende identificar los factores psicosociales laborales asociados con el bienestar del trabajador en investigaciones realizadas en Colombia y España, durante el periodo 2002 – 2012. Objetivo. Este trabajo tiene como fin, precisar sobre el desarrollo investigativo en lo referente a los factores psicosociales y su relación con el bienestar, de los trabajadores en Colombia y España durante el período 2002-2012, por medio de los estudios encontrados sobre factores psicosociales y su impacto benéfico en el bienestar del trabajador, marco legal de ambos países, así como también, la revisión documental, consolidación y posterior análisis de la literatura, en torno al estado del arte del presente estudio en relación a los factores psicosociales laborales. Método. Se trata de un estudio documental, realizado por medio, de una revisión de literatura en las bases de datos y posterior selección, clasificación, consolidación, sistematización y análisis de los estudios de investigación encontrados, los cuales, analizaban aspectos relacionados con los factores psicosociales y su relación con el bienestar del trabajador en Colombia y España, durante el período 2002-2012. Resultados. En la revisión documental se evidenció que los estudios referentes a los factores psicosociales y su relación con el bienestar del trabajador, representa un importante y permanente reto para las organizaciones. De la misma manera, se destacan los avances que sobre dicha relación presenta España, pues, en Colombia, aun los estudios siguen direccionados hacia los factores de riesgo o perjudiciales, más que hacia factores protectores o de bienestar, generadores de un efecto benéfico en los trabajadores y por ende en la organización.

Aproximación al manejo de la seguridad ambiental canadiense y estadounidense frente a la degradación del sistema de la los Grandes Lagos. Periodo 1995-2000

El propósito de la presente monografía es determinar la relación entre la degradación y navegación en los Grandes Lagos en la noción de seguridad ambiental de Estados Unidos y Canadá en un entorno de interdependencia entre 1995 - 2000. En ese sentido, se busca determinar como los recursos de poder de Canadá y Estados Unidos en la relación degradación-navegación transforma la noción de seguridad ambiental. De este modo, se analiza el concepto de seguridad ambiental desde la navegación, elemento esencial para entender la relación bilateral dentro del sistema de los Grandes Lagos. Esta investigación de tipo cualitativo que responde a las variables de la seguridad ambiental planteadas por Barry Buzan, Thomas Homer-Nixon, y Stephan Libiszewski, y a la teoría de la Interdependencia Compleja por Robert Keohane y Joseph Nye, pretende avanzar hacia la complejización de la dimensión ambiental lejos de la tradicional definición antropocéntrica.

Análisis del gen adra2a receptor alfa 2a adrenergico en pacientes con trastorno de hiperactividad y déficit de atención

El trastorno de hiperactividad y déficit de atención (THDA), es definido clínicamente como una alteración en el comportamiento, caracterizada por inatención, hiperactividad e impulsividad. Estos aspectos son clasificados en tres subtipos, que son: Inatento, hiperactivo impulsivo y mixto. Clínicamente se describe un espectro amplio que incluye desordenes académicos, trastornos de aprendizaje, déficit cognitivo, trastornos de conducta, personalidad antisocial, pobres relaciones interpersonales y aumento de la ansiedad, que pueden continuar hasta la adultez. A nivel global se ha estimado una prevalencia entre el 1% y el 22%, con amplias variaciones, dadas por la edad, procedencia y características sociales. En Colombia, se han realizado estudios en Bogotá y Antioquia, que han permitido establecer una prevalencia del 5% y 15%, respectivamente. La causa específica no ha sido totalmente esclarecida, sin embargo se ha calculado una heredabilidad cercana al 80% en algunas poblaciones, demostrando el papel fundamental de la genética en la etiología de la enfermedad. Los factores genéticos involucrados se relacionan con cambios neuroquímicos de los sistemas dopaminérgicos, serotoninérgicos y noradrenérgicos, particularmente en los sistemas frontales subcorticales, corteza cerebral prefrontal, en las regiones ventral, medial, dorsolateral y la porción anterior del cíngulo. Basados en los datos de estudios previos que sugieren una herencia poligénica multifactorial, se han realizado esfuerzos continuos en la búsqueda de genes candidatos, a través de diferentes estrategias. Particularmente los receptores Alfa 2 adrenérgicos, se encuentran en la corteza cerebral, cumpliendo funciones de asociación, memoria y es el sitio de acción de fármacos utilizados comúnmente en el tratamiento de este trastorno, siendo esta la principal evidencia de la asociación de este receptor con el desarrollo del THDA. Hasta la fecha se han descrito más de 80 polimorfismos en el gen (ADRA2A), algunos de los cuales se han asociado con la entidad. Sin embargo, los resultados son controversiales y varían según la metodología diagnóstica empleada y la población estudiada, antecedentes y comorbilidades. Este trabajo pretende establecer si las variaciones en la secuencia codificante del gen ADRA2A, podrían relacionarse con el fenotipo del Trastorno de Hiperactividad y el Déficit de Atención.

Los intereses estratégicos de EEUU, Rusia, China y Japón como determinantes de la estrategia de mantenimiento de la Estructura en la Península Coreana. 2003-2013.

El propósito principal de esta monografía es ofrecer una perspectiva crítica sobre el conflicto latente en la Península Coreana, haciendo un acercamiento al mismo desde un marco teórico asentado en el realismo estructural de Kenneth Waltz. De este modo, se busca responder a cuestiones sobre los intereses estatales como fundamento básico de las estrategias de mantenimiento de la Estructura en regiones geopolíticamente sensibles. Al final, se llega a la conclusión afirmando que la Estructura ejerce una serie de funciones para garantizar su preservación mediante una acción de convergencia en la conducta de los Estados. Esta realidad ha mantenido a la Península Coreana sin un conflicto bélico en los últimos 50 años, muy a pesar de estar al borde del mismo en varias ocasiones, ya que de llegarse a presentar se rompería la estabilidad de la región, y por ende el Equilibrio de Poderes estaría en grave riesgo.

Unamuno sobre el hombre : naturaleza y cultura, vida trágica, en la educación.

Resumen del autor. Resumen en castellano y en inglés

Enhanced convolution approach for CAC in ATM networks, an analytical study and implementation

The characteristics of service independence and flexibility of ATM networks make the control problems of such networks very critical. One of the main challenges in ATM networks is to design traffic control mechanisms that enable both economically efficient use of the network resources and desired quality of service to higher layer applications. Window flow control mechanisms of traditional packet switched networks are not well suited to real time services, at the speeds envisaged for the future networks. In this work, the utilisation of the Probability of Congestion (PC) as a bandwidth decision parameter is presented. The validity of PC utilisation is compared with QOS parameters in buffer-less environments when only the cell loss ratio (CLR) parameter is relevant. The convolution algorithm is a good solution for CAC in ATM networks with small buffers. If the source characteristics are known, the actual CLR can be very well estimated. Furthermore, this estimation is always conservative, allowing the retention of the network performance guarantees. Several experiments have been carried out and investigated to explain the deviation between the proposed method and the simulation. Time parameters for burst length and different buffer sizes have been considered. Experiments to confine the limits of the burst length with respect to the buffer size conclude that a minimum buffer size is necessary to achieve adequate cell contention. Note that propagation delay is a no dismiss limit for long distance and interactive communications, then small buffer must be used in order to minimise delay. Under previous premises, the convolution approach is the most accurate method used in bandwidth allocation. This method gives enough accuracy in both homogeneous and heterogeneous networks. But, the convolution approach has a considerable computation cost and a high number of accumulated calculations. To overcome this drawbacks, a new method of evaluation is analysed: the Enhanced Convolution Approach (ECA). In ECA, traffic is grouped in classes of identical parameters. By using the multinomial distribution function instead of the formula-based convolution, a partial state corresponding to each class of traffic is obtained. Finally, the global state probabilities are evaluated by multi-convolution of the partial results. This method avoids accumulated calculations and saves storage requirements, specially in complex scenarios. Sorting is the dominant factor for the formula-based convolution, whereas cost evaluation is the dominant factor for the enhanced convolution. A set of cut-off mechanisms are introduced to reduce the complexity of the ECA evaluation. The ECA also computes the CLR for each j-class of traffic (CLRj), an expression for the CLRj evaluation is also presented. We can conclude that by combining the ECA method with cut-off mechanisms, utilisation of ECA in real-time CAC environments as a single level scheme is always possible.