182,270 research outputs found

    Identification of Hindbrain Neural Substrates for Motor Initiation in the hatchling Xenopus laevis Tadpole

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    Animal survival profoundly depends on the ability to detect stimuli in the environment, process them and respond accordingly. In this respect, motor responses to a sensory stimulation evolved into a variety of coordinated movements, which involve the control of brain centres over spinal locomotor circuits. The hatchling Xenopus tadpole, even in its embryonic stage, is able to detect external sensory information and to swim away if the stimulus is considered noxious. To do so, the tadpole relies on well-known ascending sensory pathway, which carries the sensory information to the brain. When the stimulus is strong enough, descending interneurons are activated, leading to the excitation of spinal CPG neurons, which causes the undulatory movement of swimming. However, the activation of descending interneurons that marks the initiation of motor response appears after a long delay from the sensory stimulation. Furthermore, the long-latency response is variable in time, as observed in the slow-summating excitation measured in descending interneurons. These two features, i.e. long-latency and variability, cannot be explained by the firing time and pattern of the ascending sensory pathway of the Xenopus tadpole. Therefore, a novel neuronal population has been proposed to lie in the hindbrain of the tadpole, and being able to 'hold' the sensory information, thus accounting for the long and variable delay of swim initiation. In this work, the role of the hindbrain in the maintenance of the long and variable response to trunk skin stimulation is investigated in the Xenopustadpole at developmental stage 37/38. A multifaceted approach has been used to unravel the neuronal mechanisms underlying the delayed motor response, including behavioural experiments, electrophysiology analysis of fictive swimming, hindbrain extracellular recordings and imaging experiments. Two novel neuronal populations have been identified in the tadpole's hindbrain, which exhibit activation patterns compatible with the role of delaying the excitation of the spinal locomotor circuit. Future work on cellular properties and synaptic connections of these newly discovered populations might shed light on the mechanism of descending control active at embryonic stage. Identifying supraspinal neuronal populations in an embryonic organism could aid in understanding mechanisms of descending motor control in more complex vertebrates

    Rainfall Prediction: A Comparative Analysis of Modern Machine Learning Algorithms for Time-Series Forecasting

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    Rainfall forecasting has gained utmost research relevance in recent times due to its complexities and persistent applications such as flood forecasting and monitoring of pollutant concentration levels, among others. Existing models use complex statistical models that are often too costly, both computationally and budgetary, or are not applied to downstream applications. Therefore, approaches that use Machine Learning algorithms in conjunction with time-series data are being explored as an alternative to overcome these drawbacks. To this end, this study presents a comparative analysis using simplified rainfall estimation models based on conventional Machine Learning algorithms and Deep Learning architectures that are efficient for these downstream applications. Models based on LSTM, Stacked-LSTM, Bidirectional-LSTM Networks, XGBoost, and an ensemble of Gradient Boosting Regressor, Linear Support Vector Regression, and an Extra-trees Regressor were compared in the task of forecasting hourly rainfall volumes using time-series data. Climate data from 2000 to 2020 from five major cities in the United Kingdom were used. The evaluation metrics of Loss, Root Mean Squared Error, Mean Absolute Error, and Root Mean Squared Logarithmic Error were used to evaluate the models' performance. Results show that a Bidirectional-LSTM Network can be used as a rainfall forecast model with comparable performance to Stacked-LSTM Networks. Among all the models tested, the Stacked-LSTM Network with two hidden layers and the Bidirectional-LSTM Network performed best. This suggests that models based on LSTM-Networks with fewer hidden layers perform better for this approach; denoting its ability to be applied as an approach for budget-wise rainfall forecast applications

    Ionic Liquids on Oxide Surfaces

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    Ionic liquids supported on oxide surfaces are being investigated for numerous applications including catalysis, batteries, capacitors, transistors, lubricants, solar cells, corrosion inhibitors, nanoparticle synthesis and biomedical applications. The study of ionic liquids with oxide surfaces presents challenges both experimentally and computationally. The interaction between ionic liquids and oxide surfaces can be rather complex, with defects in the oxide surface playing a key role in the adsorption behaviour and resulting electronic properties. The choice of the cation/anion pair is also important and can influence molecular ordering and electronic properties at the interface. These controllable interfacial behaviours make ionic liquid/oxide systems desirable for a number of different technological applications as well as being utilised for nanoparticle synthesis. This topical review aims to bring together recent experimental and theoretical work on the interaction of ionic liquids with oxide surfaces, including TiO2, ZnO, Al2O3, SnO2 and transition metal oxides. It focusses on the behaviour of ionic liquids at model single crystal surfaces, the interaction between ionic liquids and nanoparticulate oxides, and their performance in prototype devices

    Elasticidad de membrana plasmática de levaduras mediante estudios de retracción de Nanotubo

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    27 h. figuras; tabls.; ilus. Abstract en espa√Īol e ingl√©s. Contiene Referencia Bibliogr√°fica.Las membranas biol√≥gicas constituyen la estructura celular m√°s com√ļn en la materia viva, pudiendo ser consideradas como un ejemplo de alta tecnolog√≠a natural de microencapsulaci√≥n. Las membranas se comportan como barreras mec√°nicas semipermeables, regulando el tr√°nsito y la se√Īalizaci√≥n de los compartimentos celulares con el exterior. A su vez, son extremadamente din√°micas tanto de manera global como a peque√Īa escala espacial. Las interacciones de los l√≠pidos entre s√≠ y con otras mol√©culas presentes en las membranas (principalmente prote√≠nas) son determinantes para muchas funciones, como la se√Īalizaci√≥n, los procesos de fusi√≥n y fisi√≥n o la adhesi√≥n celular. La forma f√≠sica de una estructura membranosa est√° determinada b√°sicamente por su grado de curvatura intr√≠nseca. De igual manera, esta propiedad evidencia la tendencia que tienen los l√≠pidos a formar fases no lamelares. La disposici√≥n de los l√≠pidos en la bicapa est√° directamente relacionada con su forma intr√≠nseca o geom√©trica, que tambi√©n condiciona el modo en que estas mol√©culas se empaquetan e interaccionan entre s√≠. En este trabajo de tesina se puso foco en la capacidad que tiene la membrana plasm√°tica de cambiar localmente su curvatura. Para realizar estos estudios, deformamos la membrana plasm√°tica localmente, generando tubos de membrana de di√°metro nanom√©trico mediante el empleo de pinzas √≥pticas. El trabajo se realiz√≥ sobre membranas de levaduras Saccharomyces cerevisiae de la cepa BY4741. Estudios previos han demostrado que cuando una bicapa lip√≠dica es sometida a un cambio local de curvatura presenta un comportamiento el√°stico, mientras que las membranas celulares de mam√≠feros son marcadamente viscoel√°sticas. Por otro lado, no se han reportado estudios de deformaciones locales de curvatura en membranas de organismos de otros reinos, que no contienen colesterol sino otros esteroles u hopanoides. Mediante estos experimentos se pretendi√≥ poner a punto la metodolog√≠a a fin de estudiar c√≥mo es la energ√©tica de deformaci√≥n fuera del plano de membrana plasm√°tica de levaduras S. cerevisiae cepa BY4741, la cual contiene un alto porcentaje del esterol ergosterol, en comparaci√≥n con el comportamiento ya conocido de membrana plasm√°tica de c√©lulas de mam√≠fero. En este trabajo se encontr√≥ que la relajaci√≥n de nanotubos de membranas plasm√°ticas de levaduras S. cerevisiae cepa BY4741 ocurre con tiempos caracter√≠sticos en el intervalo 0,02-0,5 s, y si promediamos todos los valores encontrados, obtenemos un valor promedio de 0,2 s ¬Ī 0,1 s. Este valor es similar a lo informado para eritrocitos, as√≠ como para c√©lulas tumorales cerebrales en humanos y c√©lulas de ovario de h√°mster chino. Hasta donde sabemos, no hay estudios de este tipo reportados en microorganismos eucariotas.Fil: Bischof, Andrea Alejandra. Universidad Nacional de C√≥rdoba. Facultad de Ciencias Exactas, F√≠sicas y Naturales; Argentina.Fil: Bischof, Andrea Alejandra. Universidad Nacional de C√≥rdoba. Facultad de Ciencias Qu√≠micas. Departamento de Qu√≠mica Biol√≥gica; Argentina.Fil: Bischof, Andrea Alejandra. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro de Investigaciones en Qu√≠mica Biol√≥gica de C√≥rdoba; Argentina

    Speciation of organoarsenicals in aqueous solutions by Raman spectrometry and quantum chemical calculations

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    .Knowledge about the existence and stability of different species of organoarsenicals in solution is of the most significant interest for fields so different as chemical, environmental, biological, toxicological and forensic. This work provides a comparative evaluation of the Raman spectra of four organoarsenicals (o-arsanilic acid, p-arsanilic acid, roxarsone and cacodylic acid) in aqueous solutions under acidic, neutral and alkaline conditions. Speciation of some of these organoarsenicals is possible by Raman spectrometry at different selected pHs. Further, we examine the proficiency of computational chemistry to obtain the theoretical Raman spectra of the four organoarsenicals compounds. To this end, we employ a computational protocol that includes explicit water molecules and conformational sampling, finding that the calculated organoarsenicals spectra agree reasonably well with those experimentally obtained in an aqueous solution in the whole pH range covered. Finally, we highlight the effectiveness of quantum chemical calculations to identify organoarsenicals in an aqueous solution.S

    Lecture Notes on Quantum Field Theory I

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    El documento ha sido corregido por el Servicio de Política Linguística de la Universidad de Valencia.Material docente preparado para la asignatura Teoría Cuántica de Campos en el Master de Física Avanzada.These lectures notes are based on the material covered in the course on Quantum Field Theory I in the Master in Advanced Physics at the University of Valencia, delivered in the years 2017-2021

    New models involving quantum chemical parameters for assessing the chromatographic retention process

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    .Knowledge about the theoretical relationship between the analyte properties and the critical chromatographic parameters is mandatory for a better interpretation of the separation mechanism and a more leisurely development of quantitative studies. In a preliminary stage of this work, we introduce the Gumbel distribution, the extreme value distribution type-I widely used in other fields, as a novel tool for modelling the chromatographic peak shape. Further, we develop mathematical models to evaluate the effect of the experimental variables and various quantum parameters on the chromatographic indices, such as the retention time, capacity factor, asymmetry factor, tailing factor and number of theoretical plates. Finally, we propose a mechanistic behaviour for the chromatographic separation process based on the structure-retention relationship of fifteen selected drugs involving several molecular quantum parametersS

    The emerging quantum technology industry: capital cities, entrepreneurship, and policy

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    This paper provides an empirical account of the evolution of the key emerging technology, quantum technology. It presents a survey of academic and industry sources to explore the current position of Washington DC and London UK as concentrations of relevant innovation activity. It explores the conditions under which certain parts of the innovation process are located in these two capital cities. Elements of the innovation process include the presence of start-up businesses and the emergence of quantum industry clusters in these two places. Also of note is the gender dimension in the commercialisation process, specifically the underrepresentation of female entrepreneurs and senior decision-makers
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