Astrocyte dynamics revisited

A vast amount of experimental evidence hints that astrocytes could be active players in information processing of the brain. It remains unclear nevertheless how these cells could encode synaptic stimuli through variations of their intracellular Ca2+ levels as well as how they could influence the timing of neuronal activity. In this study, we adopt a dynamical system approach and use tools of bifurcation theory and statistics in order to address both these issues. We consider a Li-Rinzel description of astrocyte Ca2+ signalling and we show that thanks to specific choices of biophysical parameters, synaptic activity could be encoded by modulations of Ca2+ oscillations in amplitude (AM), in frequency (FM), or in both (AFM). Interestingly, AM- and FM-encoding pertain to different classes of Ca2+ excitability that are reminiscent of the analogous neuronal ones. In addition, any transition from AM to FM and viceversa is accomplished through a characteristic “Bautin-cusp" bifurcation sequence which could hint the conditions for the coexistence of both these encoding modes. Such a possibility is throughout investigated and eventually formalized in the “CPB rule", a heuristic criterion valid for any system of the Li-Rinzel type that allow us to determine several biophysical conditions under which AFM Ca2+ dynamics could occur in astrocytes. Successively, we demonstrate that different encoding modes could be accomplished not only on the basis of inherent heterogeneities of cellular properties but also thanks to the existence of different (opposite) Ca2+ feedbacks on IP3 production. In this regard we modify the Li-Rinzel system in order to include a third equation for IP3 metabolism which also considers Ca2+ activation of PLC (positive feedback) and Ca2+ activation of IP3 3-kinase (negative feedback). In agreement with experimental data and recent theoretical studies, our analysis hints that Ca2+-dependent activation of PLC could account for a much richer variety of oscillatory regimes and encoding modes with respect to the case of negative feedback. An inspection of the parameter space reveals that this is possible because positive Ca2+ feedback on IP3 production modifies the structure of the system towards the appearance of multistationarity which could also account for Ca2+ dynamics of bursting type. Moreover, we show that the lifetime of IP3 could be a critical limiting factor for the effects of both feedbacks. Meaningfully, IP3 turnover could influence the integrative properties of astrocytic Ca2+ signalling by affecting both the frequency band of Ca2+ oscillations and the threshold stimulus for their onset. In addition, IP3 turnover could regulate the expression of mGlu receptors on the astrocyte plasma membrane. In this regard, we show that the density of mGlu receptors could be proportional to the rate of IP3 turnover and accordingly we provide an estimation of this parameter which otherwise would remain experimentally unknown. In particular, on the basis of our bifurcation data, we estimate that AM-encoding astrocytes could express an average mGluR density between 1-50 receptors/um^2 that is of the same order of AMPA receptor density measured on Bergmann glia somas. We show however that FM-encoding astrocytes could be consistent with an overexpression of mGluRs by a factor of 8 or 10 with respect to AM-encoding cells. In the last part of our study, we finally consider the characterization of the possible integrative properties of astrocyte Ca2+ signalling and the effects of astrocytic Ca2+-dependent glutamate exocytosis on neuronal activity. For this purpose we develop a mathematical description of neuron-glial interactions at the level of a single astrocytic microdomain in which our modified Li-Rinzel model of astrocyte Ca2+/IP3 dynamics is coupled with an ensemble of Tsodyks-Uziel-Markram synapses on the soma a regular spiking Izhikevich neuron. We show that astrocytes of different classes of excitability could respond differently to stimuli of equal intensities and identical interspike-interval (ISI) statistics. On the other hand, stimuli at the same frequency but with different ISI statistics could trigger distinct Ca2+ responses in cells of the same type. All these possibilities are also dependent on the nature of the stimulatory pathway. Astrocyte Ca2+ signalling could therefore result from a complex integration of spatiotemporal features of synaptic stimuli which could represent a form of processing of neuronal activity. Perhaps even more intriguingly, Ca2+ signals could encode information on the past history of synaptic activity which in turn would be transferred back to neuron through Ca2+-dependent glutamate exocytosis with deep consequences on the informational content of postsynaptic neuronal activity. Computation of Fano Factors on simulated time series of postsynaptic action potentials reveal in fact that neuron-astrocyte interactions could substantially affect the rate of neuronal firing by adding long-range correlations to the timing of neuronal spikes. These results are consistent with the possibility that neuron-astrocyte bidirectional signalling could influence information processing of the brain by increasing the information-coding dimension of the neural code

Utilizing a Decision Support System to Optimize Reservoir Operations to Restore the Natural Flow Distribution in the Connecticut River Watershed

Reservoir development on the Connecticut River Basin has altered the natural hydrograph and detrimentally affected the region\u27s aquatic ecosystems that thrive on natural variability. This thesis examines ways in which flows in the river and its triburaries can be returned to a more natural regime withouy negatively impacting other users. The analysis offers alternative operations to meet the various objectives as well as evaluates the impacts of climate change on the basin. This paper focuses on the upper third of the basin as a proof of concept to demonstrate the decision support system and to generate initial results for the large effort. The upper third of the basin contains 11 sub-watersheds, six major reservoirs, and three ecological points of interest. The analysis employs simulation, optimization, and hydrology models that work in symphony. The process starts with a simulation model of the system that reflects the current reservoir operations; this assures the modeling efforts accurately portray the current conditions. The linear program optimization model is used to determine optimal operating policies and the trade-offs between reservoir objectives for three operational schemes: operating for ecological targets, hydropower, and flood control. The output from the optimization model suggests how to alter the operating polices to achieve the given objective. Downscaled climate change meteorological data (temperature and precipitation) from five General Circulation Models and two emissions scenarios are used as input into the hydrology model to produce climate impacted streamflow to examine reservoir operations under climate change. The analysis does not suggest a single operating policy, but rather a range of options to be discussed among stakeholders to best address all objectives

Comparison of the response of different configurations of aircraft repair patches under static and dynamic loading

In the modern era of transportation, air travel has gained a huge pace and still kept increasing. The global demand for air transport is increasing at a rate of 6%, because of population growth and ticket price reductions. Airlines aim at minimizing their operational costs and maximizing aircraft use factor (i.e., make the maximum possible trips with the least turn-around time). Operational costs can be reduced by, for instance, improving the fuel efficiency, reducing the drag acting on aircraft and lowering the maintenance cost. As Aviation structural engineer, better understanding of repair technologies plays an important role in minimizing the operational costs. Namely, a major time consuming process is the maintenance of the aircraft in between flights, to detect early formation of cracks, monitoring crack growth, and fixing the corresponding parts with joints, when necessary. This project is focused on repair technologies of the structural parts in aircraft to regain their strength. In the modern aviation more than 50% of the structure is made of Composites. Composites have many advantages over conventional Aluminium alloys, which have been extensively used since the 1950s. Composites have very high specific strength compared to aluminium alloys, but when they are riveted about 60% of the material strength is lost (the plies of composite are damaged due to the holes made in the structure for riveting, which may fail without any early detection before the scheduled maintenance checks). Riveting of Composite parts is still practiced in the aviation as a quick and temporary fix. To overcome this far-from-optimum, it is necessary to study the methods of repair technologies and compare their behavior under various failure modes especially fatigue. Majority of structural parts fail due to fatigue, which is well known phenomenon in engineering. In this PhD thesis, we present the static and fatigue behavior of repair joints and their response to in-service loading conditions. Static and Fatigue experiments were conducted on metal-metal, metal-composite, composite-composite and composite-metal joint configurations under riveted, adhesive bonded and hybrid joining. Aluminum rivets and araldite adhesive was used in the preparation of specimens. Static and fatigue tests were conducted using a universal testing machine. Later, numerical analysis is performed on the experimentally studied joints using finite element tool ABAQUS. Experimental and numerical results agreed with a maximum margin of 5%. Open source software such as FRANC 2D and FRANC3D were used for fatigue lite prediction and analysis of riveted and adhesive bonded joints. Finally, Autodesk Helius composites tool was used to analyze ply-load distribution, first ply failure with progressive failure analysis and failure envelopes of composite substrate in longitudinal, lateral and through-thickness directions.En la reciente era del transporte, el transporte aéreo ha ido creciendo a un gran ritmo, y lo seguirá haciendo. La demanda global de transporte aéreo está aumentando a una tasa del 6%, como resultado del crecimiento de la población y la reducción de los precios de los pasajes. Las aerolíneas intentan minimizar sus costos operativos y maximizar el factor de uso de sus aeronaves (es decir, tener en vuelo las aeronaves el máximo tiempo posible, con el mínimo tiempo posible en tierra). Los costos operativos pueden reducirse, por ejemplo, mejorando la eficiencia del combustible, reduciendo la resistencia aerodinámica que actúa sobre la aeronave, y reduciendo el costo de mantenimiento. Como ingeniero estructural de aviación, una mejor comprensión de las tecnologías de reparación es esencial para minimizar los costos operativos. Por ejemplo, el mantenimiento de las aeronaves entre vuelos es un proceso que consume mucho tiempo, para poder detectar la formación temprana de grietas, monitorear el crecimiento de grietas, y reparar las partes correspondientes con parches de reparación, si es necesario. Este proyecto se centra en tecnologías de reparación de componentes estructurales de aviones para que recuperen su resistencia. En la industria del transporte aéreo actual, más del 50% de la estructura de los aviones está hecha de materiales compuestos. Los materiales compuestos tienen muchas ventajas si los comparamos con las aleaciones de aluminio convencionales, que se han utilizado ampliamente desde la década de 1950. Los materiales compuestos tienen una resistencia específica muy alta en comparación con las aleaciones de aluminio, pero, cuando se remachan, se pierde aproximadamente el 60% de la resistencia del material (las capas de material compuesto se dañan debido a los agujeros hechos en la estructura para los remaches, y pueden fallar sin dar tiempo a una detección temprana durante las verificaciones de mantenimiento programadas). El remachado de piezas de material compuesto todavía se practica en la industria del transporte aéreo actual como una solución rápida y temporal. Para superar esta práctica que está lejos de ser óptima, es necesario estudiar los diversos métodos incluidos dentro de las tecnologías de reparación, y comparar su comportamiento bajo ciertos modos de carga y fractura, especialmente a fatiga. La mayoría de las piezas estructurales fallan debido a fatiga, un fenómeno bien conocido en ingeniería. En esta tesis doctoral, presentamos el comportamiento estático y a fatiga de parches de reparación y su respuesta a las condiciones de carga en servicio. Se realizaron experimentos con cargas estáticas y de fatiga en parches de reparación con las siguientes configuraciones: metal-metal, metal-composite, composite-composite, y composite-metal, con unión mediante remaches, mediante adhesivo, y unión híbrida (remaches y adhesivo). Para preparar las muestras, se utilizaron remaches de aleación de aluminio y adhesivo Araldite. Los ensayos estáticos y de fatiga se realizaron con una máquina de ensayos universal. Tras ello, se realizó un análisis numérico de las uniones estudiadas utilizando la herramienta de elementos finitos ABAQUS. Los resultados experimentales y numéricos coincidieron con un margen de diferencia máximo del 5%. Además, se utilizó software de código abierto como FRANC2D y FRANC3D para el análisis y predicción de la vida a fatiga de los parches de reparación con uniones remachadas y adhesivas. Finalmente, la herramienta de simulación de composites Autodesk Helius se usó para analizar, en el sustrato de composite, la distribución de la carga en sus diferentes capas, la fractura de la primera capa con análisis de fractura progresiva, y las envolventes de fallo del sustrato en las direcciones longitudinal, lateral, y a través del espesor

Objects, actions, and images: a perspective on early number development

It is the purpose of this article to present a review of research evidence that indicates the existence of qualitatively different thinking in elementary number development. In doing so, the article summarizes empirical evidence obtained over a period of 10 years. This evidence first signaled qualitative differences in numerical processing, and was seminal in the development of the notion of procept. More recently, it examines the role of imagery in elementary number processing. Its conclusions indicate that in the abstraction of numerical concepts from numerical processes qualitatively different outcomes may arise because children concentrate on different objects or different aspects of the objects, which are components of numerical processing

Gallo Worldwide: sustainability of competitive position in Brazil

Case StudyThis project presents a case study of the competitive situation of Gallo Worldwide in Brazil. The Brazilian market for olive oil is experiencing an exponential growth. The awareness of olive oil has been growing among consumers. Gallo Worldwide has already taken advantage of these opportunities and developed a solid competitive position in the Brazilian market. In fact, Gallo Worldwide is currently the leading player in the olive oil Brazilian market. However, the market and the structure of the industry may change and in the future affect Gallo’s competitive situation. Thus, what should Gallo do to sustain its competitive advantage? In this work project the value creating potential of Gallo in Brazil and the sustainability of its competitive situation will be analyzed. These issues are addressed by first presenting a case study and then a case analysis. Since the intention is to examine the real situation of a company, it is believed that a case study would be the most appropriate research method. The case study focuses not only on the attractiveness of the Brazilian market but also on the evaluation of the competitive advantage or disadvantage of Gallo. The case discussion introduces the relevant conceptual frameworks and applies them to the analysis of the case. Our analysis confirms that Gallo has a competitive advantage in Brazil. Furthermore, this advantage may be sustainable or not depending on Gallo’s ability to deal with eventual industry structural changes, which may flip Gallo’s resources and hence its competitive advantage

Psychometric Functioning of The MMPI-A Restructured Form VRIN-R, TRIN-R, CRIN, and Cannot Say Scales with Varying Degrees of Randomness, Acquiescence, Counter-Acquiescence, and Omitted Items

The MMPI-A-RF (Archer, Handel, Ben-Porath & Tellegen, 2016) is a new measure of adolescent personality and psychopathology derived from the MMPI-A (Butcher, Williams, Graham, Archer, Tellegen, Ben-Porath & Kaemmer, 1992) item pool. Similar to the MMPI-A, the MMPI-A-RF includes indexes designed to assess non-content-based responding and omitted items. Building on Handel, Ben-Porath, Tellegen & Archer’s study (2010) on adults, the current study utilized computer simulation of random, acquiescent, counteracquiescent, and omitted responses to examine how adolescent validity scale and RC scale scores are affected by increasing degrees of non-content-based responding. Further, RC scale validity coefficients were examined to see how increasing degrees of non-content-based responding attenuates these relationships. Lastly, this study examines the moderating effects of VRIN-r and TRIN-r on the relationship between RC scale and extra-test variables. Results showed that MMPI-A-RF content non-responsiveness does have a predictable impact on validity scale scores, RC scale scores, and clinical scale relationships through changes in mean T-scores, degradation of validity coefficients, and significant moderating effects. Limitations and implications of the current study are addressed

Agro-Ecological Zoning for Tall Wheatgrass (Thinopyrum Ponticum) as a Potential Energy and Forage Crop in Salt-Affected and Dry Lands of Argentina

Thinopyrum ponticum, is the most disseminated halophyte speciescultivated for forage on hydro-halomorphic soils in the world. Theobjective of the present work was to identify the geographicareas fordevelopment of tall wheatgrass on halomorphic soils in Argentina, for forageand as feedstock for bioenergy. To define the agroclimate in Argentina, we considered the thermal and hydric limits of the species in its place of originand in locations where it is successfully cultivated around the world. The maps corresponding to the bioclimatic indices were drawn using a GIS, andthe map obtained by overlaying them defined the agroclimatic suitability. Thiszoning was finally superimposed on the drylands saline and alkaline soils inthecountry, thus defining the agro-ecological suitability of Argentina forthis species under different moisture regimes: moist-subhumid,dry-subhumid, semiarid to arid climate. The the agro-ecological zoning showsthe potential growing areas for tall wheatgrass in Argentina on soils withhalomorphism processes under dry climates.Fil: Falasca, Silvia Liliana. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Clima y Agua; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Miranda del Fresno, Ma. Carolina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Humanas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pitta-alvarez, Sandra Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Micología y Botánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Micología y Botánica; Argentin