1,721,205 research outputs found
External Dissipative Rocking System
Full text linkQuesta tesi ha l'obiettivo di indagare il comportamento dinamico e sismico di edifici esistenti protetti con un sistema esterno di dissipazione basato sul rocking; esso è costituito da una struttura reticolare in acciaio, incernierata a livello di fondazione, il cui movimento oscillante attiva la dissipazione di energia, per mezzo di smorzatori viscosi situati alla base. Nell'ipotesi di comportamento elastico lineare sia del telaio, che della struttura dissipativa, vengono presentate l'equazione del moto del sistema accoppiato ed una generalizzazione del sistema ad un grado di libertà. Per risolvere il problema dinamico è possibile condurre analisi sia nel dominio del tempo, che in quello delle frequenze.
La soluzione nel dominio del tempo si basa su una formulazione alle variabili di stato che, tramite analisi modale complessa del sistema telaio da proteggere-struttura esterna di protezione passiva, permette di valutare l'influenza, sia sul comportamento dinamico che in termini di risposta sismica, dello smorzamento e della linearizzazione degli spostamenti forniti dalla struttura dissipativa. In particolare, la formulazione proposta, consente di valutare separatamente il contributo di ciascuno dei modi di vibrazione complessi del sistema sulla risposta sismica globale. Le analisi armoniche nel dominio delle frequenze, invece, sono particolarmente utili in quanto consentono di lavorare con un sistema algebrico piuttosto che differenziale. Inoltre, scegliendo di rappresentare l'input sismico come un processo stocastico stazionario, è possibile stabilire una relazione tra la densità spettrale di potenza (PSD) dell'input esterno e quella dei parametri di risposta di interesse, tramite analisi armonica del sistema.
Le prestazioni di due casi di studio sono valutate mediante analisi parametriche, riguardanti diversi livelli di smorzamento e rigidezza del sistema di protezione, sia con analisi nel tempo che in frequenza. Infine vengono presentati alcuni aspetti che necessitano di ulteriore approfondimento. Tra di essi la valutazione ed il confronto della performance sismica di smorzatori viscosi a comportamento lineare e non, dimensionati attraverso il criterio di uguaglianza dell'energia dissipata. Le prestazioni del sistema di protezione passiva indagato, vengono confrontate con un'altra configurazione esterna, che prevede l'accoppiamento del telaio con una struttura rigida di contrasto, nota in letteratura come sistema di smorzamento proporzionale alle masse. Infine viene condotta una prima analisi degli effetti dell'interazione terreno-struttura (SSI), mediante l'approccio alle sottostrutture.In this thesis the seismic performance of existing buildings frames coupled with an external dissipative rocking system is investigated; the arrangement consists of a steel truss, hinged at the foundation level, whose rocking motion promotes the dissipation of energy via viscous dampers located at the base. Under the assumption of linear elastic behaviour of both the frame and the dissipative structure, the equation of motion of the system are presented, together with a generalized Single Degree of Freedom (S-DOF) approximation of the system. This way, analysis through time-domain and frequency-domain are allowed for the investigation of the system dynamic behaviour.
Time-domain analysis, based on a state space approach, leads to the complex modal analysis of the coupled system, which allows the evaluation of the influence of the added damping and of the displacements linearization, promoted by the external dissipative rocking system, on both the dynamic behaviour and the seismic response. In particular, the proposed formulation permits to evaluate separately the contribution of each of the complex vibration modes of the system to the global seismic response. On the other hand frequency-domain analysis is particularly useful for the problem under investigation because it allows to work with an algebraic system rather than a differential one. Furthermore by representing the seismic input in terms of a stationary stochastic process, a relation can be established between the Power Spectral Density (PSD) of the input and that of the response parameters of interest via harmonic analysis of the system.
The performance of two case studies is evaluated by means of parametric analysis, involving added damping and stiffness, either through time- and frequency-domain. Finally, some aspects which need a deeper investigation are presented. Among them the evaluation and comparison between linear and non-linear fluid viscous dampers, dimensioned through dissipated energy criterion. The performance of the analyzed dissipative system, is compared with an alternative retrofitting configuration, consisting in the coupling with external stiff contrasting structure, known in literature as mass proportional damping system. At the end a first insight on the effects of Soil-Structure-Interaction (SSI), through the substructure approach, is provided
Competenza e rappresentanza. Alessandro Pizzorno, Pier Luigi Crosta, Bernardo Secchi
No full textIn Italia e in buona parte dell’Europa, la città ha caratteri profondamente diversi rispetto al passato. Il cambiamento è sotto gli occhi di tutti. Il problema non è affermarlo, ma capire come attrezzarsi a coglierlo: dove situare la propria lettura. Questo libro assume il mutamento della città come condizione ambigua, stratificata e altamente contraddittoria sulla quale si delineano nuove relazioni tra competenze e decisioni. Dove per competenze si intendono prioritariamente, ma non esclusivamente, quelle di architetti e urbanisti. Non si tratta oggi di immaginare la buona città, o di esercitarsi in sforzi utopici, ma di capire che ne è di una cultura urbana costruita nel corso del Novecento sulle nozioni di prossimità e continuità a fronte delle nuove dimensioni concettuali (prima ancora che fisiche, sociali ed economiche), della città.
Entro un rinnovato dialogo tra urbanistica e sociologia gli scritti contenuti in questo libro affrontano alcuni aspetti del modo in cui le competenze entrano nella grande trasformazione che muta la città contemporanea. Lo fanno attraverso due mosse. La prima è la delimitazione del campo della riflessione alla città europea. La seconda è l’assunzione di un punto di vista per così dire esterno, a partire dal rapporto che la competenza ha con la rappresentanza, le diversità, la giustizia spaziale
Afterword. Preparedness supporting the transition
No full textTo understand the COVID-19 outbreak and its socio-spatial nature, this book stemmed from the hypothesis that the concept of preparedness is an insightful one, worth to be (re)discussed within the urban and regional studies and, particularly the urban planning and policy field. This hypothesis did represent an open question rather than a consolidated view. This conclusive chapter recaps the main points made in the volume and outlines the definition of preparedness emerging from the chapters. Finally, it argues that preparedness shall not only be intended as an emergency technique to address unforeseeable changes but more broadly as a technology supporting a sustainable spatial and economic transition
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ionic liquids for polymer based supercapacitors
No full textThe interest in supercapacitors has increased enormously in recent years mainly for applications in electric vehicle in which the supercapacitors operating in parallel with batteries and fuel cells are expected to provide power peaks during acceleration, especially with fuel cells which have lower performance power than batteries. Given such application, the focus of interest is on supercapacitors with relatively high specific energy.
We have recently developed an hybrid supercapacitor of high specific energy and power based on activated carbon (AC) as negative electrode and poly(3-methylthiophene) (pMeT) as positive, operating between 3 V and 1.5 V in organic liquid electrolyte (propylene carbonate, PC – Et4NBF4), which outperforms even on a preindustrial scale the double layer activated carbon supercapacitors on the market [1].
To further improve the energy performance of such hybrid supercapacitor, we are pursuing the strategy of increasing its maximum operating voltage and, with this aim, we are evaluating the viability of ionic liquids as electrolytes. Indeed ionic liquids are known for their wide electrochemical stability window and chemical stability at high temperature.
Ionic liquids display chemical-physical properties which depend on the cation and anion chemistry. The imidazolium cation dislays a high cathodic stability and several imidazolium based ionic liquids, generally with ethyl and methyl in 1 and 3 position, with different anions (such as BF4_, PF6_, (CF3SO2)2N_, CF3SO3_, ...) which in turn differently affect the limit of the anodic window, the melting point and hence the conductivity of the ionic liquids, have been prepared and characterized [2]. A few studies have also been devoted to their application in AC double-layer supercapacitors [3] and in polymer-based supercapacitors [4, 5], but the results of the last configuration are related to polymer electrodes too thin to be of practical interest.
Here we report and discuss the results of the study on the 1-buthyl-3-methyl-1-H-imidazolium (BMIM+) X_ (X= BF4_, PF6_) ionic liquids carried out in view of their application in AC//pMeT hybrid supercapacitor. Given that a high electrolyte conductivity is important for high performance supercapacitors, conductivity data from room temperature up to high temperatures of interest for electric vehicle applications, especially for those involving fuel cells, are presented. Also the results of a voltammetric study on the AC and pMeT electrodes sized for a practical supercapacitor, with data of electrochemical stability window of BMIMBF4 and BMIMPF6, and of capacity and capacitance of AC and pMeT electrodes are reported and discussed. All these data are also compared with those obtained with the conventional PC-Et4NBF4 electrolyte
The use of ionic liquids as solvent-free green electrolytes for hybrid supercapacitors
No full textThe aim of this paper is to demonstrate that the use of ionic liquids (ILs) in activated carbon (AC)//poly(3-methylthiophene) (pMeT) hybrid supercapacitors is a very promising strategy to develop high voltage supercapacitors operating above room temperature with solvent-free green electrolytes. The Ils used were 1-butyl-3-methyl-imidazolium tetrafluoroborate, 1-butyl-3-methyl-imidazolium hexafluorophosphate, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide. We report and discuss the performance of AC and pMeT electrodes in such ILs compared to that in propylene carbonate-based electrolytes, in order to give indications for further research effort in IL-based hybrid supercapacitors
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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