1,721,340 research outputs found
La cultura contemporanea per lo sviluppo del territorio urbano. Prospettive socio-economiche e giuridiche
No full textA seguito della dematerializzazione affermatasi con la fase produttiva postmoderna, le città – centri
focali del futuro sviluppo socioeconomico a livello mondiale – hanno dovuto far fronte all’avvento
di nuovi elementi strutturanti il percorso di autorealizzazione degli individui. Elementi che
afferiscono alla dimensione immateriale delle merci o che hanno una vera e propria consistenza
“immateriale”, attinenti a ciò che è stato definito “capitale culturale”.
La cultura, nell’epoca contemporanea, ha assunto una dimensione ben lontana da quelle tradizionali
che si rifanno alla sfera antropologica o a quella di specializzazione dell’attività umana.
Attualmente, non solo si è certificata un’idea del fenomeno culturale intimamente collegata alla
sfera dei significati, ma se ne è anche delineata una specificità che ha a che fare con la funzione
immaginaria dei beni e delle esperienze.
La tesi “La cultura contemporanea per lo sviluppo del territorio urbano. Prospettive socioeconomiche
e giuridiche” si pone l’obiettivo di indagare come questi elementi possano incidere in
contesti territoriali contraddistinti da una sempre più evidente scarsità di risorse economiche.
Vengono presi in considerazione tre scenari urbani: Berlino, Manchester e l’East Village di New
York City, che hanno agito strategicamente in direzione di una trasformazione urbana culture led, e
vengono individuate le caratteristiche essenziali dei territori esaminati riguardo gli elementi
qualificanti il progresso urbano, secondo i parametri della competitività economica e della coesione
sociale.
In ultimo, viene avanzata l’analisi degli strumenti a disposizione degli amministratori territoriali al
fine della conformazione territoriale nel paese a più alta dotazione culturale del mondo, l’Italia.
Le impostazioni teoriche emerse nei primi due capitoli e le evidenze dei casi di studio del terzo e
delle difficoltà operative del quarto, confermano e rafforzano l’idea di una proposta metodologica
che poggi sulla dimensione culturale al fine del raggiungimento di un soddisfacente progresso
sociale ed economico per quei territori che intendano far fronte, in un’ottica (pro)positiva, alle crisi
cicliche che li colpiscono sempre più duramente
Probabilistic seismic response and fragility assessment of steel-concrete composite bridges with dual load path
No full textProbabilistic seismic demand analysis of buildings equipped with nonlinear Viscous dampers
No full textViscous dampers are energy dissipation devices widely employed for the seismic control of new and existing building frames. To date, the performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches neglecting the response dispersion due to the site seismic hazard condition and the record-to-record variability effects. This paper analyzes the probabilistic seismic performance of building frames equipped with viscous dampers by highlighting the influence of damper properties. In particular, a probabilistic methodology based on response hazard curves is employed to evaluate the effect of the damper nonlinearity, measured by the damper exponent, on the performance of structural and non-structural components of building frames, as described by the response hazard curves of the relevant engineering demand parameters. A case study consisting of a steel frame equipped with nonlinear viscous dampers is considered and the performance variations due to changes in the damper nonlinearity level are evaluated by considering design scenarios corresponding to dampers having different exponents designed to provide the same deterministic performance. Both response statistics at different seismic intensity levels and demand hazard curves for the monitored engineering parameters are employed as performance measures. It is shown that the damper nonlinearity strongly affects the seismic performance and different trends are observed for the various demand parameters of interest. A comparison with code provisions shows that further investigation is necessary to provide more reliable design formulas for the dampers accounting for their nonlinearity level
A design method for seismically isolated bridges with abutment restraint
No full textSeismic isolation is a commonly used technique for protecting new and existing bridges. It usually consists of introducing isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake action. This paper deals with partially restrained seismically isolated continuous bridges, which are a particular class of isolated bridges whose transverse motion is restrained at the abutments.
In this study a method is proposed for the preliminary design of these systems, which can be applied to both new and existing bridges. The dynamic problem is described in a variational form in order to obtain a simplified solution based on a pre-fixed transverse deformed shape of the deck. The objective of the design procedure is to control the internal actions on the piers by means of an appropriate configuration of the isolation bearings. Simple formulas for estimating the forces transmitted to the abutments and the superstructure transverse curvature demand are also derived, which account for the contribution of higher modes of vibration.
Validation studies are undertaken for different bridge configurations, in order to assess the ability of the simplified method to control the force demand at the piers
Influence of ground motion characteristics on the optimal single concave sliding bearing properties for base-isolated structures
Full text linkThis study examines the influence of ground motion characteristics on the optimal friction properties of single concave sliding bearings employed for the seismic isolation of structural systems. The evaluation of the optimal properties is carried out by considering a non-dimensional formulation which employs the peak ground acceleration (PGA) and the peak ground acceleration-to-velocity (PGA/PGV) ratio as ground motion parameters. A two-degree-of-freedom (2dof) model is employed to describe the isolated system and two different families of records representative respectively of near fault and far field seismic inputs are considered. Following the nondimensionalization of the equation of motion for the proposed ground motion parameters, it is shown that the non-dimensional responses obtained for the two types of seismic inputs are similar. This result confirms that PGA/PGV is a good indicator of the frequency content and of other characteristics of ground motion records, helping to reduce the scatter in the response. Regression expressions are also obtained for the optimal values of the friction coefficient that minimizes the superstructure displacements relative to the base as a function of the abovementioned ground motion parameter and of the dimensionless system parameters. These expressions can be used for the preliminary estimation of the optimal properties of isolation bearings with a single concave sliding surface or double concave sliding surfaces with equal friction coefficient
OLFACTION IN ACTION
Full text linkRecent evidence has contributed to change the view according to which action representation chiefly depends on visual information. In particular, research on hand grasping actions has emphasized that a multimodal interplay across vision, audition, the sense of touch, and proprioception occurs when performing and understanding an action (e.g., Castiello, 1996; Patchay, Castiello, & Haggard, 2003; Gazzola, Aziz-Zadeh, & Keysers, 2006; Zahariev & MacKenzie, 2007).
The experimental work included in the present thesis aimed at extending the multisensory aspects of action representation to the olfactory domain. I first addressed this issue from the perspective of action execution by asking participants to reach and grasp a target-object under different circumstances of visual and olfactory stimulation. The angular excursion at the level of individual digits, digits’ angular distance, and arm movement duration were recorded. Next, I focused on action understanding by asking participants to observe others’ grasping actions under different visual and olfactory conditions. Here, cerebral activity of the neural system responsible for action understanding, i.e., the Action Observation System (AOS) was recorded.
An overview of this experimentation is outlined in the following section.
OVERVIEW OF THE PRESENT RESEARCH
In the first two experiments (Thesis Chapters 3 and 4) participants were requested to reach towards and grasp either a small or a large visual target calling for different types of grasp, precision grip (PG) and whole hand grasp (WHG), respectively. This task was performed in the absence or in the presence of an odour associated with objects that, if grasped, would require a PG or a WHG. The aim of these experiments was twofold. First, to understand whether the central nervous system (CNS) can use olfactory information to select and execute a ‘grasp’ motor plan. Second, to shed light on how detailed the motor commands embedded within the ‘grasp’ plans elicited by an object’s olfactory representation are. The results showed that merely smelling the odour associated with a small and a large object activates the kinematic parameterization of the action appropriate for grasp that object, i.e., PG and WHG, respectively. Therefore, the CNS is able to convert the geometric features of an olfactory-encoded object (e.g., size) into the motor prototype for interacting with that object. In other words, the visuomotor mechanism underlying the control of action (e.g., Castiello, 1996) appears to be sensitive to olfactory information.
From a perceptual perspective, the representation evoked by the odour seems to contain highly detailed information regarding the object (i.e., volumetric features). This is because the effect of odour ‘size’ was played out on the hand posture at the level of individual digits’ motion. If olfaction had provided a blurred and holistic object’s representation (i.e., a low spatial-resolution of the object’s image), then the odour would have not affected would have not affected the hand in its entirety. From a motor perspective, the olfactory representation seems to be mapped into the action vocabulary with a certain degree of reliability. The elicited motor plan is not an incomplete primal sketch which only provides a preliminary descriptive in the terms of motor execution but it embodies specific and selective commands for handling the ‘smelled’ object.
In the experiments described above the odour associated with the object was always delivered before movement initiation and before the target became visually available. For the motor control system this entailed to prioritize the ‘olfactory’ non-target object with respect to the visual target. Specifically, planning and execution of action was first based on the sense of smell. In this respect, previous research on grasping actions revealed that visual nontarget-objects do not activate the corresponding ‘grasp’ plans when prior knowledge regarding the visual target is given to participants (e.g., Castiello, 1996). In order to investigate whether this caveat also applies for nontarget-objects signalled via olfaction, I performed an experiment (Thesis Chapters 5) similar to those reported above, but participants were given sufficient time to code for the visual target before movement initiation. The results showed that in such circumstances the odour ‘size’ did modulate the temporal organization of the arm movement. Therefore, even when olfactory information plays a secondary role with respect to visual information for action guidance, the olfactory-encoded object is represented within the motor system. And, traces of the ‘grasp’ motor plan associated with the olfactory object remain evident at the level of the arm movement.
Having demonstrated the influence that olfactory stimuli might have for the control of action I reasoned that such phenomenon might be relevant for investigating possible gender differences in the use of olfactory information within the action domain (e.g., Ecuyer-Dab & Robert, 2004). Therefore by using an experimental paradigm similar to that reported in Thesis Chapter 4, I investigated whether gender differences were evident when odours of objects had to be mapped into the corresponding ‘grasp’ motor plans (Thesis Chapter 6). The results showed that for men arm-movement duration increased when the ‘size’ of the odour did not match the size of the visual target. Whereas, for women such effect was not revealed. Remember that a lengthening in movement duration was taken as evidence for an odour-induced activation of the ‘grasp’ motor plans associated with the ‘smelled-objects’ (Thesis Chapter 4). Therefore, it appears that male sense of smell is action-oriented, i.e., tailored to elicit specific and selective motor commands for act upon olfactory-encoded objects. Whereas, in line with previous evidences stemming from research on human olfaction, the female sense of smell would be perception-oriented, i.e., optimised to detect, discriminate, identify, recognise, and categorise odours (e.g., Brand & Millot, 2001).
Once documented that the sense of smell provides useful information for planning and execute an action I investigated whether olfactory cues may also contribute to the understanding of others’ actions. The fMRI experiment reported in Thesis Chapter 7 was conceived to specifically address this issue. The results showed that the neural system devoted to action understanding (i.e., the ASO) represented both a hand grasping an ‘olfactory’ object and a mimed hand grasp. Importantly, evidence that the AOS was also able to differentiate between these two type of actions was also found. The discrimination process might solely be ascribed to the olfactory information which signalled the target-object. Therefore, the role played by olfactory information in action understanding was demonstrated.
With this in mind the central advance of the present work is twofold. First, I demonstrated that processes of selection for the control of actions may be based on olfactory information. This was done by linking current advances in the methodology for recording hand kinematics and paradigms considering the presence of nontarget-object. Second, I provided evidence for the contribution of olfactory information to the understanding of other’s actions. This was achieved by combining the fMRI technique with an action observation paradigm.
REFERENCES
Brand, G., & Millot, J. L. (2001). Sex differences in human olfaction: between evidence and enigma. Quarterly Journal of Experimental Psychology, 54, 259-270.
Castiello, U. (1996). Grasping a fruit: selection for action. Journal of Experimental Psychology: Human Perception and Performance, 22, 582-603.
Ecuyer-Dab, I., & Robert, M. (2004). Have sex differences in spatial ability evolved from male competition for mating and female concern for survival? Cognition, 91, 221-257.
Gazzola, V., Aziz-Zadeh, L., & Keysers, C. (2006). Empathy and the somatotopic auditory mirror system in humans. Current Biology, 16, 1824-1829.
Patchay, S., Castiello, U., & Haggard, P. (2003). A crossmodal interference effect in grasping objects. Psychological Bulletin Reviews, 10, 924-931.
Zahariev M. A., & MacKenzie, C. L. (2007) Grasping at thin air: multimodal contact cues for reaching and grasping. Experimental Brain Research, 180, 69-84.Evidenze ottenute da studi recenti hanno cambiato la concezione secondo cui la rappresentazione dell’azione si basa principalmente sulle informazioni di natura visiva. In particolare, la ricerca sulle azioni di prensione ha dimostrato che si verifica un’interazione tra la visione, l’udito, il tatto e la propriocezione sia quando una persona esegue un’azione sia quando cerca di capire l’azione di un altro individuo (Castiello, 1996; Patchay, Castiello, & Haggard, 2003; Gazzola, Aziz-Zadeh, & Keysers, 2006; Zahariev & MacKenzie, 2007).
Il lavoro sperimentale riportato nella presente tesi ha lo scopo di estendere gli aspetti multisensoriali della rappresentazione dell’azione al dominio olfattivo. Per prima cosa ho trattato questa questione dalla prospettiva dell’esecuzione dell’azione chiedendo ai partecipanti di raggiungere ed afferrare un oggetto target in diverse condizioni di stimolazione visiva ed olfattiva. Ho registrato l’escursione angolare a livello delle singole giunture delle dita della mano e delle distanze tra le dita. Inoltre ho misurato la durata del movimento del braccio. Poi mi sono concentrato sulla comprensione dell’azione chiedendo ai partecipanti di osservare le azioni di prensione compiute da altri individui in diverse condizioni di stimolazione visiva ed olfattiva. Qui, usando la risonanza magnetica funzionale (fMRI), ho registrato l’attività cerebrale dell’Action Observation System (AOS), la rete di aree responsabile della comprensione dell’azione.
Nella seguente sezione fornisco un riassunto di questa sperimentazione.
RIASSUNTO DELLA RICERCA
Nei primi due esperimenti (Capitoli 3 e 4 della Tesi) i partecipanti raggiungevano ed afferravano degli oggetti target grandi oppure piccoli che richiedevano rispettivamente un precision grip (PG) e un whole hand grasp (WHG). Questo compito era svolto in assenza o in presenza di un odore associato con un oggetto che, se afferrato, avrebbe richiesto un PG o un WHG. L’obiettivo di questi esperimenti era duplice. Innanzitutto volevo capire se il sistema nervoso centrale (SNC) può usare l’informazione olfattiva per selezionare ed eseguire un piano motorio di prensione. Poi volevo valutare quanto sono dettagliati i comandi motori inclusi nel piano di prensione eventualmente attivato dall’odore. I risultati mostrano che semplicemente annusare l’odore associato con un oggetto grande oppure piccolo attiva la parametrizzazione cinematica dell’azione di prensione appropriata per agire su quell’oggetto, i.e., rispettivamente un PG e un WHG. Quindi, il SNC è in grado di convertire le caratteristiche geometriche di un oggetto codificato attraverso l’olfatto nel piano motorio per interagire con quell’oggetto. In altre parole il meccanismo visuomotorio sottostante il controllo dell’azione (Castiello, 1996) è sensibile all’informazione olfattiva.
Da una prospettiva percettiva, la rappresentazione evocata dall’odore contiene informazioni altamente dettagliate circa l’oggetto (i.e., caratteristiche volumetriche). Questo perché l’effetto di ‘dimensione’ dell’odore è evidente a livello del movimento delle singole giunture delle singole dita della mano. Se l’olfatto avesse fornito una rappresentazione olistica e non dettagliata dell’oggetto (i.e., un’immagine dell’oggetto a bassa risoluzione spaziale), l’odore non avrebbe modulato la mano nella sua interezza. Da una prospettiva motoria, la rappresentazione olfattiva è mappata nel vocabolario delle azioni con un buon grado di affidabilità. Il piano motorio attivato dall’odore non è una bozza incompleta e primitiva che fornisce solo una descrizione preliminare in termini di esecuzione motoria ma incorpora comandi specifici e selettivi per manipolare l’oggetto ‘annusato’.
Negli esperimenti appena descritti l’odore associato con l’oggetto era sempre somministrato prima dell’inizio del movimento e prima che l’oggetto target diventasse visibile. Per il sistema di controllo motorio questo implica una priorità dell’oggetto ‘olfattivo’ nontareget rispetto al target visivo. Nello specifico, la pianificazione e l’esecuzione dell’azione è basata sull’informazione olfattiva. A tal proposito, la ricerca sulle azioni di prensione ha mostrato che gli oggetti visivi nontarget non attivano i corrispondenti piani motori di prensione quando i partecipanti conoscono in anticipo il target (Castiello, 1996). Al fine di investigare se ciò vale anche per gli oggetti ‘olfattivi’ nontarget, ho condotto un esperimento simile a quelli riportati sopra, tuttavia, qui i partecipanti avevano tempo di codificare il target visivo prima dell’inizio del movimento (Capitolo 5 della Tesi). I risultati mostrano che la ‘dimensione’ dell’odore modula l’organizzazione temporale del movimento del braccio. Quindi, anche quando l’informazione olfattiva gioca un ruolo secondario rispetto all’informazione visiva per la guida dell’azione, l’oggetto ‘olfattivo’ è rappresentato nel sistema motorio.
Dopo aver dimostrato l’influenza degli stimoli olfattivi sul controllo dell’azione, ho pensato che tale fenomeno poteva essere rilevante per investigare possibili differenze di genere nell’uso dell’informazione olfattiva entro il dominio dell’azione (Ecuyer-Dab & Robert, 2004). Quindi, usando un paradigma sperimentale simile a quello riportato nel Capitolo 4 della Tesi, ho valutato se la capacità di trasformare gli odori degli oggetti nei corrispondenti piani motori varia a seconda del genere (Capitolo 6 della Tesi). I risultati mostrano che per i maschi la durata del movimento del braccio aumenta quando la ‘dimensione’ dell’odore non corrisponde alla dimensione del target visivo. D’altra parte, per le femmine questo effetto non è evidente. Si ricordi che l’aumento della durata del movimento del braccio indica l’attivazione del piano motorio di prensione associato con l’oggetto ‘annusato’ (Capitolo 4 della Tesi). Quindi, sembra che l’olfatto dei maschi sia orientato all’azione, i.e., predisposto ad innescare comandi motori specifici e selettivi per agire sugli oggetti codificati a livello olfattivo. Invece, in linea con precedenti evidenze (Brand & Millot, 2001), l’olfatto femminile sarebbe orientato alla percezione, i.e., ottimizzato per rilevare, discriminare, identificare, riconoscere e categorizzare odori.
Una volta dimostrato che l’olfatto fornisce informazioni utili per la pianificazione e l’esecuzione dell’azione, ho indagato se gli indizi olfattivi possono contribuire anche alla comprensione dell’azione altrui. L’esperimento fMRI riportato nel Capitolo 7 della Tesi è stato disegnato per trattare questa questione. I risultati mostrano che l’AOS rappresenta sia una mano che afferra un oggetto di cui si sente l’odore che una prensione mimata. Inoltre l’AOS è in grado di differenziare tra questi due tipi di azione. Questo processo di discriminazione è imputabile solamente all’informazione olfattiva che segnala l’oggetto afferrato da un altro individuo. Quindi il ruolo giocato dall’informazione olfattiva nella comprensione dell’azione risulta dimostrato.
In conclusione le evidenze riportate nella mia tesi forniscono due contributi fondamentali all’idea di rappresentazione dell’azione multimodale. Primo, il processo di selezione dei piani motori per il controllo delle azioni può basarsi sull’informazione olfattiva. Questa nozione poggia sui dati ottenuti combinando le recenti tecniche di registrazione delle cinematiche della mano con i paradigmi che considerano la presenza di oggetti nontarget. Secondo, l’olfatto contribuisce alla comprensione dell’azione degli altri. Ciò è stato dimostrato usando il paradigma di osservazione dell’azione e l’fMRI.
RIFERIMENTI BIBLIOGRAFICI
Brand, G., & Millot, J. L. (2001). Sex differences in human olfaction: between evidence and enigma. Quarterly Journal of Experimental Psychology, 54, 259-270.
Castiello, U. (1996). Grasping a fruit: selection for action. Journal of Experimental Psychology: Human Perception and Performance, 22, 582-603.
Ecuyer-Dab, I., & Robert, M. (2004). Have sex differences in spatial ability evolved from male competition for mating and female concern for survival? Cognition, 91, 221-257.
Gazzola, V., Aziz-Zadeh, L., & Keysers, C. (2006). Empathy and the somatotopic auditory mirror system in humans. Current Biology, 16, 1824-1829.
Patchay, S., Castiello, U., & Haggard, P. (2003). A crossmodal interference effect in grasping objects. Psychological Bulletin Reviews, 10, 924-931.
Zahariev M. A., & MacKenzie, C. L. (2007) Grasping at thin air: multimodal contact cues for reaching and grasping. Experimental Brain Research, 180, 69-84
Simplified transverse behaviour of partially isolated bridges
No full textSeismic isolation is a widely diffused technique for the seismic protection of bridges. It usually consists on the introduction of isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake. Partially restrained seismically isolated continuous bridges are a particular class of isolated bridges whose transverse motion is restrained at the abutment, in order to avoid the use of expensive bi-directional joints. The present work describes a simplified method for the
evaluation of the seismic response of these bridges which considers the dynamic problem in a variational form and seeks a simplified solution by assuming a sinusoidal transverse deformed shape. Simple formula are derived for estimating the displacement demand, the internal action demand at the piers and at the deck and the abutment reactions. Some validation studies are also carried out in order to evaluate the accuracy of the proposed method in assessing the response of these systems
Influence of FPS bearing properties on the seismic performance of base-isolated structures
No full textThe paper analyzes the influence of friction pendulum system (FPS) isolator properties on the seismic
performance of base-isolated building frames. The behavior of these systems is analyzed by employing a
two-degree-of-freedom model accounting for the superstructure flexibility, whereas the FPS isolator behavior
is described by adopting a widespread model that considers the variation of the friction coefficient with
the velocity. The uncertainty in the seismic input is taken into account by considering a set of natural records
with different characteristics scaled to increasing intensity levels. The variation of the statistics of the
response parameters relevant to the seismic performance is investigated through the nondimensionalization
of the motion equation and an extensive parametric study carried out for different isolator and system properties.
The proposed approach allows to explore a wide range of situations while limiting the required
nonlinear response history analyses.
Two case studies consisting of base-isolated building frames described as shear-type systems are finally
investigated in order to demonstrate the capabilities of the proposed simplified model in unveiling the essential
characteristics of the performance of buildings isolated with FPS bearings
Reliability of systems equipped with viscous dampers with variable properties
No full textViscous dampers are energy dissipation devices widely employed for the seismic control of structures. The performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches. However, these approaches neglect the response dispersion due to the uncertainties in the input as well as in the structural system properties. Some recent works highlighted the important role of these uncertainties in the seismic performance of systems with linear or nonlinear viscous dampers. The present study focuses on the uncertainty in the damper properties and it aims at evaluating its influence on the probabilistic response of the damped system. In particular, the variability of the damper properties is assumed to be constrained by the tolerances allowed in qualification and production control tests. A preliminary study on the damper response is carried out to relate the constitutive damper characteristics to the parameters controlled in the experimental tests and to evaluate the consequences of damper parameter variations on the dissipation properties of the device. In the subsequent part of the study, the response hazard curves, providing the relation between the values of the response parameters of interest and the relevant yearly exceedance probability, are evaluated. In the analyses, a simplified structural system is considered, and the Subset Simulation (SS) algorithm is employed together with the Markov Chain Monte Carlo method to achieve a good estimate of small probabilities of exceedance. A sensitivity analysis, considering the expected variations in the damper properties, is finally carried out by employing the Augmented SS method to study the influence of the device acceptance ranges on the hazard curves
Free vibration problem of PRSI bridges: analytical solution and parametric analysis
No full textThis paper analyzes the dynamic behavior of partially restrained seismically isolated (PRSI) bridges. These are a particular class of multi-span seismically isolated bridges in which isolation bearings are posed only at the top of the piers, while seismic stoppers restrain the transverse motion of the superstructure at the abutments. The transverse dynamic behavior of these partially-restrained bridges is described analytically by considering a two-dimensional simply supported beam model, with intermediate visco-elastic restraints whose properties are calibrated to describe the substructures’ behavior. Particular simplified configurations are considered which allow to identify a minimal set of characteristic problem parameters that completely describe the dynamic response. The properties of the dynamic systems are analyzed by considering separately the undamped and the damped case. The results of the study contribute to improve the understanding of the dynamic behavior of partially restrained seismically isolated bridges and allow to draw some conclusions useful for their preliminary assessment and design
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