A hybrid model for the computationally-efficient simulation of the cerebellar granular layer

The aim of the present paper is to efficiently describe the membrane potential dynamics of neural populations formed by species having a high density difference in specific brain areas. We propose a hybrid model whose main ingredients are a conductance-based model (ODE system) and its continuous counterpart (PDE system) obtained through a limit process in which the number of neurons confined in a bounded region of the brain tissue is sent to infinity. Specifically, in the discrete model, each cell is described by a set of time-dependent variables, whereas in the continuum model, cells are grouped into populations that are described by a set of continuous variables.Communications between populations, which translate into interactions among the discrete and the continuous models, are the essence of the hybrid model we present here. The cerebellum and cerebellum-like structures show in their granular layer a large difference in the relative density of neuronal species making them a natural testing ground for our hybrid model. By reconstructing the ensemble activity of the cerebellar granular layer network and by comparing our results to a more realistic computational network, we demonstrate that our description of the network activity, even though it is not biophysically detailed, is still capable of reproducing salient features of neural network dynamics. Our modeling approach yields a significant computational cost reduction by increasing the simulation speed at least $270$ times. The hybrid model reproduces interesting dynamics such as local microcircuit synchronization, traveling waves, center-surround and time-windowing

Realizzazione di un prototipo da laboratorio per lo studio della produzione di biogas da fermentazioni di biomasse

L’elaborato vuole evidenziare le potenzialità che il processo di fermentazione anaerobica ha sia nella produzione di energia da fonte rinnovabile, sia come soluzione valida per lo smaltimento di sottoprodotti e reflui di filiere agricole e agroindustriali. Dopo una prima panoramica sullo stato dell’arte di tale settore, a livello nazionale e comunitario, nella quale vengono riportati dati come la produzione annua di biogas, il suo valore energetico equivalente in rapporto al petrolio, il numero degli impianti presenti ad oggi e le potenzialità produttive nazionali, si sottolinea come, in sintonia con gli ultimi studi eseguiti sulla produzione e diffusione delle energie, i quali propendono verso una tipologia di mini e micro-generazione diffusa sul territorio, si potrebbe favorire lo sviluppo di una serie di piccoli impianti basati sull’anaerobiosi anche là dove non sono presenti grandi accorpamenti di allevamenti o agroindustrie. Per la nascita di questi piccoli impianti semplificati, anche ad uso esclusivamente aziendale o di piccole realtà artigianali della trasformazione dei prodotti agroalimentari , occorrono studi che aprano loro la strada. Studi necessari a determinare di volta in volta, in base alla tipologia del sottoprodotto disponibile, la fattibilità e le potenzialità della produzione di biogas da utilizzare anche in autoconsumo interno all’azienda, e che eventualmente stabiliscano una razione ad hoc utilizzando i sottoprodotti comunemente disponibili in loco o nelle vicinanze, senza dover ricorrere all’inserimento nel piano produttivo di colture dedicate, mantenendo così un forte legame con l’idea di fonte rinnovabile e di recupero di materiale di scarto, in modo tale da poter potenzialmente chiudere anche il ciclo produttivo. I vantaggi sono molteplici: la possibilità di auto prodursi un quantitativo variabile di energia elettrica, termica, o mista, per i propri consumi, trovando allo stesso tempo una via alternativa allo smaltimento dei sottoprodotti, spesso macchinosa e costosa. Da qui la necessità di creare un piccolo sistema da laboratorio che simuli la digestione anaerobica di piccole quantità di substrati, per iniziare a indagare su tale tematica e stimarne le capacità. Nell’elaborato vengono riportate le fasi che si sono dovute seguire per la realizzazione tecnica e fisica del prototipo. Alla fine sono stati eseguiti dei test preliminari per verificare la ripetibilità del suo funzionamento e si è provveduto alla stesura di un protocollo per il suo utilizzo, in modo da ovviare ad inconvenienti procedurali. I dati raccolti sono stati poi verificati statisticamente per attestarne la bontà. Nell’ultima parte dell’elaborato vengono tratte le conclusioni sul lavoro svolto fino ad oggi e le possibili strade da seguire per portare avanti tale studio

Optical activity of a dilute dielectric medium: Pasteur and the molecular symmetries

Em 1848 Pasteur conjeturou que a rotação do plano de polarização da luz em um meio diluído é gerada pelas propriedades de simetria das moléculas do meio no qual a luz se propaga. O objetivo do nosso artigo é de mostrar que Pasteur estava correto usando conhecimentos de eletromagnetismo e mecânica quântica de um curso de graduação em física. Faremos um breve retrospecto das ideias básicas da teoria eletromagnética necessárias para o estudo da atividade óptica. A seguir, usando a teoria de perturbações em mecânica quântica e levando em conta as simetrias das moléculas calcularemos a atividade óptica do meio. Mostraremos que as previsões teóricas, que estão plenamente de acordo com os resultados experimentais, comprovam a hipótese de Pasteur.Pasteur proposed in 1848 that the rotation of the polarization plane of the light in a dilute medium is generated by the symmetry properties of the molecules of the medium where the light propagates. Our objective is to show that Pasteur hypothesis was correct using the basic knowledge of electromagnetism and quantum mechanics of the undergraduate physics course. We present a brief review of the fundamental concepts of the electromagnetic theory necessary to understand the optical activity. Next, using the quantum mechanical perturbation theory and taking into account the molecular symmetries we calculate the optical activity of the medium. It will be shown that the theoretical predictions, which are in good agreement with the experimental results, give support to the Pasteur conjecture

Superfluid 4He: brief notes on collective energy excitations and specific heat.

These brief notes about some amazing properties of the helium superfluid have been written to graduate and postgraduate students of physics. We have estimated some collective energy excitations (linear vortices, energy spectrum of the quasiparticles and solitons) and calculated the specific heat of the superfluid helium assuming that the transition superfluid liquid → liquid is an order-disorder transition

Solitrons Hidrodinâmicos de Korteweg-de Vries.

Esse artigo foi escrito para alunos de graduação e pós- graduação em Física e para alunos de Engenharia. Primeiramente mostramos como construir a equação diferencial não-linear de Korteweg e de Vries a partir das equações básicas da hidrodinâmica. Em seguida mostramos como resolvê-la obtendo as ondas denominadas de solitons

História da propagação das citações originais do artigo do Journal of Quantitative Spectroscopy & Radiative Transfer 102/441/2006.

Neste artigo procuraremos descrever a história cronológica das citações originais (aquelas que os nomes dos autores aparecem apenas uma vez, portanto, excluídas as autocitações) da publicação do artigo: M. Cattani and J. M. F. Bassalo, Racemization, Chiral Stability and Weak Interactions, Journal of Quantitative Spectroscopy & Radiative Transfer 102, pp. 441-449, 2006 (CB: JQS&RT 102/441/2006). Para realizar essa história, usamos a WEB OF SCIENCE (acessado: 08/02/2013) disponibilizado pela CAPES/UFPA

A Three Year Study on 14 VOCs at One Site in Rome: Levels, Seasonal Variations, Indoor/Outdoor Ratio and Temporal Trends

Fourteen volatile organic compounds (VOCs)—twelve hydrocarbons and two organochlorine compounds—were monitored both outdoors and indoors for three years at one site in Rome. Results showed that 118 out of 168 indoor seasonal mean values were higher than the corresponding outdoor concentrations. The most relevant source of outdoor hydrocarbons was automotive exhaust emissions. Due to the enforcement of various measures to protect health and the environment, outdoor levels of monoaromatic hydrocarbons decreased about ten fold over 15 years, and aliphatic hydrocarbons also decreased. With the decrease in these outdoor concentrations, indoor air sources are likely to be more relevant for indoor air exposures. Winter outdoor values for monoaromatic hydrocarbons were generally markedly higher than the summer ones. The gradual replacement of the current fleet of circulating cars with new cars complying with EURO 5 standards, further reducing hydrocarbon emissions, may possibly lead to an increase in the observed indoor/outdoor ratios. It is indeed more difficult to remove indoor sources, some of which are still unknown

Giant reed (Arundo donax L.) for biogas production: land use saving and nitrogen utilisation efficiency compared with arable crops

Aiming to improve the sustainability of biogas supply chains, the research for alternative feedstocks is a key issue and giant reed (Arundo donax L.) is a promising no-food crop to be used in anaerobic digestion. In fact, giant reed is a perennial species characterised by low nutrient requirements and is able to provide promising biogas yields. Its suitability for anaerobic digestion is influenced by harvest time, since plant characteristics vary noticeably along the season. Moreover, ensiling is a storage technique that can assure a good preservation of the biomass over time, but also influence the methane yields. Therefore, the aim of this study was to assess the suitability for biogas production of giant reed silage, according to different cutting regimes, and to evaluate the efficiency in saving land and nitrogen for fuelling biogas plants, in comparison with maize and two sorghum varieties. Methane yields per hectare (Nm3 CH4 ha–1) were determined by multiplying the biochemical methane potential of each substrate by the aboveground biomass of the corresponding crop. The land use coefficient (LU), namely the land needed to fuel one kW power (ha kWe–1), was calculated from the estimated methane yields per hectare. Finally, nitrogen utilisation efficiency (NUtE), which is the ratio between the estimated methane yield and the nitrogen uptake per hectare (Nm3 CH4 kgN–1), was determined for each crop species and according to the harvest time and frequency of giant reed. Overall, a good suitability for ensiling was observed in giant reed. When harvested in September, the crop yielded about 9900 Nm3 CH4 ha–1, while in double harvest systems biomethane was about 12,000 Nm3 CH4 ha–1, +35% and +70% than maize and sorghum respectively. Moreover, giant reed under double harvest management was the most land-conservative option, as LU was about 0.22 ha kWe–1, while in annual crops it was about 0.35 ha kWe–1. The higher NUtE was observed in single harvests (up to 64 Nm3 CH4 kgN–1), while double harvests showed remarkably lower values, averaging 48 Nm3 CH4 kgN–1. Annual crops were less efficient, since NUtE ranged from 28 Nm3 CH4 kgN–1 (maize) to 40 Nm3 CH4 kgN–1 (fibre sorghum). In conclusion, giant reed can be an alternative for biogas making, potentially providing land and nitrogen savings compared with conventional annual crops