1,720,971 research outputs found
Studio degli aspetti energetici connessi all'utilizzo di sistemi ad eiezione nella refrigerazione domestica
No full textIl frigorifero è una apparecchiatura che contribuisce in modo significativo sui consumi elettrici residenziali (circa il 10-25%) e per questo sempre più attenzione viene dedicata all'efficienza energetica di tali dispositivi, anche per via del sistema di etichettatura energetica istituito dalla direttiva europea 92/75/CE. Esistono diversi modi per migliorare le prestazioni di un ciclo frigorifero a compressione di vapore. Una possibile via per raggiungere il risparmio energetico in questo tipo di cicli consiste nella sostituzione della valvola di laminazione, o meglio del tubo capillare, con un eiettore che funga da dispositivo di espansione. L'eiettore consente di recuperare l'energia cinetica dall'ugello per aumentare la pressione del flusso del refrigerante che esce dall'evaporatore, in modo da ridurre il lavoro di compressione.
Questa tesi presenta l'evoluzione dell’eiettore nei sistemi di refrigerazione, focalizzando poi l'attenzione nella loro applicazione ai frigoriferi domestici. La parte principale dello studio è incentrata sull’analisi di un ciclo a compressione di vapore utilizzato in un reale frigorifero domestico prodotto da Indesit S.p.A., e mira a valutare l'effetto prodotto dall'introduzione di un eiettore come dispositivo di espansione nel sistema. Differenti configurazioni sono analizzate e confrontate per valutare la più performante in termini energetici, in particolare viene mostrata l'analisi del ciclo con eiettore, considerando sia un eiettore a pressione costante sia uno ad area costante, modificando anche i parametri di sistema e le prestazioni del singolo componente. Le simulazioni dimostrano che il miglior ciclo a livello di prestazione è quello con l’eiettore a pressione costante senza scambiatore di calore in aspirazione. L'ultima parte del lavoro presenta la realizzazione di un prototipo virtuale 3D dell'eiettore sulla base delle simulazioni effettuate e sulla letteratura presente sull'argomento.The household refrigerator-freezer is an electric appliance which contributes significantly in domestic electric consumption (about 10-25%) and always more and more attention is paid to the energy efficiency of such devices due to the energy labelling scheme introduced by the European Directive 92/75/EC. There are several ways of improving the performance of a vapour compression refrigeration cycle. A possible mean for achieving energy saving in this kind of cycle consists in replacing the throttling valve with an ejector as expansion device. The ejector allows to recover the kinetic energy from the nozzle to increase the pressure of the refrigerant stream coming out of the evaporator, so that the work of compression can be reduced.
This work presents the evolution of ejector in the refrigeration systems and focus the attention in household refrigerator. The main part of the work starts by analysing an existing refrigeration cycle for a real household refrigerator produced by Indesit Company and aims at assessing the effect of introducing an ejector as expansion device in the system. Different configurations are analysed and compared in order to evaluate the most performing, in particular the analysis of the ejector cycle, considering both a constant area and a constant pressure device, is presented by varying the schematic of the system and performance parameters. The simulation shows that the best performing cycle is a constant pressure ejector cycle without any suction liquid heat exchanger. The last part of the work presents the realization of a 3D virtual prototype of the ejector on the basis of simulations carried out and on the literature. This prototype will be useful for a possible later experimentation
CO-ESPRESSIONE DI VGLUT1 E VGAT NEL CERVELLO DEL RATTO E DEL TOPO
Full text linkIl glutammato e l’acido γ-amminobutirrico (GABA) sono i neurotrasmettitori della maggior parte delle sinapsi chimiche del sistema nervoso centrale (SNC) dei mammiferi e i principali mediatori della conduzione veloce dei segnali eccitatori ed inibitori. Gli studi sui sistemi di trasmissione eccitatoria glutammatergica e inibitoria GABAergica rivestono un ruolo chiave nella comprensione della funzionalità cerebrale. L’osservazione della co-liberazione di glutammato e GABA da alcuni terminali sinaptici e della co-espressione del trasportatore vescicolare del GABA (VGAT) e dei trasportatori vescicolari del glutammato (VGLUTs) in alcune vescicole sinaptiche ha dato origine ad una nuova concezione della fisiologia della neurotrasmissione amminoacidergica.
Questo studio ha avuto lo scopo di analizzare i terminali glutammatergici e GABAergici nel SNC del ratto e del topo, utilizzando come marcatori i due maggiori trasportatori vescicolari del glutammato (VGLUT1) e del GABA (VGAT) e ha fornito un’estensione delle conoscenze del fenomeno della co-espressione di VGLUT1 e VGAT ai terminali sinaptici glutammatergici e GABAergici delle principali strutture anatomo-funzionali della corteccia cerebrale, dello striato, dell’ippocampo, del talamo e del cervelletto. L’utilizzo della microscopia confocale per l’analisi del grado di co-localizzazione ha permesso di analizzare un grande numero di terminali marcati per ogni area cerebrale studiata.
I dati ottenuti rivelano che, sia in ratto che in topo, in tutti i distretti anatomo-funzionali studiati, ci sono terminali sinaptici glutammatergici e GABAergici che co-esprimono VGLUT1 e VGAT; lo studio restituisce, per entrambe le specie, una mappatura cerebrale dettagliata della percentuale di terminali sinaptici nei quali VGLUT1 e VGAT sono colocalizzati.
La presenza diffusa nel cervello di terminali sinaptici co-esprimenti VGLUT1 e VGAT suggerisce che il fenomeno possa svolgere un ruolo importante nella regolazione della trasmissione sinaptica e nel preservare la fisiologica funzionalità cerebrale da squilibri tra la trasmissione eccitatoria ed inibitoria che concorrono all’insorgenza di gravi patologie come l’autismo, la schizofrenia, l’ansia, l’epilessia e l’Alzheimer.Glutamate and γ-aminobutyric acid (GABA) are the neurotrasmitters of the majority of chemical synapses in the Central Nervous System (CNS) and mediate fast excitatory and inhibitory signalling. Studies on excitatory glutamatergic and inhibitory GABAergic transmission are pivotal to understand brain functionality.
Evidence of glutamate and GABA co-release and of VGLUTs (vesicular glutamate transporters) and VGAT (vescicular GABA transporter) synaptic co-expression has given rise to a new understanding of the physiology of aminoacidergic neurotransmission.
This study aimed to analyse glutamatergic and GABAergic synaptic terminals of rat and mouse CNS marked for the two major vesicular glutamate (VGLUT1) and GABA (VGAT) transporters. A large number of synaptic terminals was investigated for each, selected cerebral area (i.e. cerebral cortex, striatum, hippocampus, thalamus and cerebellum) by the use of confocal microscopy.
This work shed new light to the phenomenon of VGLUT1 and VGAT co-expression at glutamatergic and GABAergic synaptic terminals. The data obtained showed that in all anatomical and functional districts studied there are glutamatergic and GABAergic synaptic terminals co-expressing VGLUT1 and VGAT; a detailed map of the percentage of co-localized VGLUT1 and VGAT was designed.
The widespread co-expression of VGLUT1 and VGAT suggests that these transporters may play an important role in the regulation of synaptic transmission and may contribute to the prevention of excitatory and inhibitory transmission imbalance, which are involved in the pathogenesis of autism, schizophrenia, anxiety, epilepsy and Alzheimer's diseases
The impact of renewable energy systems on local sustainability
No full textThe purpose of the paper is to discuss and assess the impact of renewable energy, RE, generation on sustainable communities, with a specific focus on employment impact. In recent years, local authorities have been involved in the energy planning process due to the site-specific nature of renewable production and thanks to their nearer connection to citizens. Four small and medium-size sustainable communities belonging to Marche region, in central Italy, have been analysed. The work forecasts the employment generated by the RE capacity defined by two different energy scenarios: 1) the 'business as usual' scenario with a 20% CO2 emission reduction target by 2020, where all the energy policies suggested by Sustainable Energy Action Plans have been considered; 2) the 'potential' scenario with a 50% CO2 emission reduction target by 2050. Results show that the spreading of renewable energy, as expected, can increase local jobs, although the high investments required and problems connected to the impact on the grid have to be considered in the analysis of the global economic effect
Optimal management of renewable and fossil fuel energy systems in a smart community
No full textThe present paper focuses on the energy aspects related to sustainable communities aimed at becoming smart. In particular, the paper discusses optimal strategies for the management of renewable energy systems (RES) and fossil fuel energy systems. Marche Region, one of the 21 Italian administrative divisions, has been taken as a reference case in order to compare different strategies. The area is characterized by a high percentage of electricity imported from the grid, suggesting the importance of increasing the local production to become sustainable. The year 2020 has been taken as the target year. An energy model of the area has been built considering RES potential and energy saving initiatives defined in the Regional Energy Master Plan. The model has been developed with EnergyPLAN, an optimization tool developed by Aalborg University and used to assess energy systems Three different solutions for the integration of RES and the minimization of fossil fuel consumption have been considered: i) a Demand Side Management technique related to the introduction of heat pumps seeking to use the excess of electricity derived from renewable production; ii) the use of micro-CHP systems in buildings to compensate for the variability of RES production; iii) the introduction of EVs with dump and smart charge. The best results come from HPs and EVs with smart charge, which are able to reduce the electricity in excess and minimize the primary energy consumption, in particular when a high share of intermittent renewable is introduced
Assessing the impact of micro-generation technologies on local sustainability
No full textThe work addresses the role of local energy planning for the introduction of low carbon policies to
achieve challenging climate targets. Taking as reference case an urban area that aims to become Sustainable
Community, several initiatives have been assessed. Two target years, 2020 and 2050, have been analysed
with the aid of EnergyPlan, an integrated energy system model based on the hourly energy demand
and supply able to consider constraints deriving from grid stability. The effects of climate change, defined
by a regional climate model, have been analysed in the long-term scenario. The work focuses on the
impact of a high share of micro-generation technologies for satisfying the energy demand of the building
sector, following an original comprehensive approach that helps a better understanding of the implication
of such low carbon policy. Both solar devices and micro-combined heat and power systems have
been taken into account, the latter covering different technologies (i.e. internal combustion engines, Stirling
engines, microturbines and fuel cells). Results show that the use of a high share of micro-generation
technologies can help to reduce CO2 emissions and enable an increase in large-scale intermittent renewable
production, only if a coordinated local energy plan combined with an optimal operation strategy is
pursued. Moreover the work outlines the importance of developing an integrated energy system for
introducing such technologies that can help to: (i) decarbonise the building sector, (ii) increase energy
security and iii) postpone the investments in new network capacit
Evaluation of municipal energy planning contribution for the fulfilment of regional energy planning strategies
No full textDubrovnik, HR, September 2011 - Paper #095
Heterogeneity of astrocytic and neuronal GLT-1 at cortical excitatory synapses, as revealed by its colocalization with Na+/K+-ATPase α isoforms
Full text linkGLT-1, the major glutamate transporter, is expressed at perisynaptic astrocytic processes (PAP) and axon terminals (AxT). GLT-1 is coupled to Na+/K+-ATPase (NKA) α1–3 isoforms, whose subcellular distribution and spatial organization in relationship to GLT-1 are largely unknown. Using several microscopy techniques, we showed that at excitatory synapses α1 and α3 are exclusively neuronal (mainly in dendrites and in some AxT), while α2 is predominantly astrocytic. GLT-1 displayed a differential colocalization with α1–3. GLT-1/α2 and GLT-1/α3 colocalization was higher in GLT-1 positive puncta partially (for GLT-1/α2) or almost totally (for GLT-1/α3) overlapping with VGLUT1 positive terminals than in nonoverlapping ones. GLT-1 colocalized with α2 at PAP, and with α1 and α3 at AxT. GLT-1 and α2 gold particles were ~1.5–2 times closer than GLT-1/α1 and GLT-1/α3 particles. GLT-1/α2 complexes (edge to edge interdistance of gold particles ≤50 nm) concentrated at the perisynaptic region of PAP membranes, whereas neuronal GLT-1/α1 and GLT-1/α3 complexes were fewer and more uniformly distributed in AxT. These data unveil different composition of GLT-1 and α subunits complexes in the glial and neuronal domains of excitatory synapses. The spatial organization of GLT-1/α1–3 complexes suggests that GLT-1/NKA interaction is more efficient in astrocytes than in neurons, further supporting the dominant role of astrocytic GLT-1 in glutamate homeostasis
Few, Activity-Dependent, and Ubiquitous VGLUT1/VGAT Terminals in Rat and Mouse Brain
Full text linkIn the neocortex of adult rats VGLUT1 and VGAT co-localize in axon terminals which form both symmetric and asymmetric synapses. They are expressed in the same synaptic vesicles which participate in the exo-endocytotic cycle. Virtually nothing, however, is known on whether VGLUT1/VGAT co-localization occurs in other brain regions. We therefore mapped the distribution of terminals co-expressing VGLUT1/VGAT in the striatum, hippocampus, thalamus, and cerebellar and cerebral cortices of rats and mice. Confocal microscopy analysis revealed that, in both rat and mouse brain, VGLUT1/VGAT+ terminals were present in all brain regions studied, and that their percentage was low and comparable in both species. These results provide the first demonstration that co-expression of VGLUT1 and VGAT is a widespread phenomenon. Since VGLUT1/VGAT+ axon terminals are regulated in an activity-dependent manner and co-release glutamate and GABA, we hypothesize that, though not numerous, they can contribute to regulating excitation/inhibition balance in physiological conditions, thereby playing a role in several neurological and psychiatric diseases
Analysis of an ejector vapour compression cycle for household refrigerator
No full textThere are several ways of improving the performance of a vapour compression refrigeration cycle and using an ejector as expansion device is one of the possibilities. As a matter of fact, the ejector can reduce throttling losses in refrigeration systems. In this paper a comparison between a real vapour compression cycle for a household refrigerator and ejector vapour compression cycles is performed by simulation in order to evaluate the performance enhancement that can be obtained. The analysis of the ejector cycle, considering both a constant area and a constant pressure device, is presented by varying the schematic of the system and performance parameters. The best performing cycle is a constant pressure ejector cycle without any suction liquid heat exchanger: it can allow improvements over the standard reference cycle whenever the primary nozzle efficiency is above 50% and diffuser efficiency above 60%. When all the nozzles efficiency are set to 85%, the COP improvement achievable is about 9%
Heat pumps and Demand Side Management for renewable energy integration in sustainable communities
No full textThe introduction of renewable energy is a key policy for sustainable communities. Some of them are variable energy resources (VERs) since their production varies over the time and are not easily and perfectly predictable. An increasing share of VERs can, indeed, badly impact on the electricity grid. The paper focuses on assessing the effect of introducing a high share of VERs production, taking as reference case a small-size sustainable community, located in Central Italy, which aims to reach, at least, a 30% CO2 emission reduction by 2025. Different energy scenarios have been considered on the basis of local energy policies defined by the Municipal Energy Plan, MEP. Demand Side Management (DSM) strategies related to the introduction of heat pumps (HP) systems powered by the excess derived from VERs, have been studied to reduce the impact into the power grid. In particular the performed analysis is aimed at finding the optimal configurations necessary to achieve thermal comfort in buildings where HP systems are introduced when Demand Side Management strategies are in action
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