Dynamic identification of structures: experimental assessment of modal parameteres through methods in frequency domain, in time-frequency domain and model updating

Among the experimental methods commonly used to define the behaviour of a full scale system, dynamic tests are the most complete and efficient procedures. A dynamic test is an experimental process, which would define a set of characteristic parameters of the dynamic behaviour of the system, such as natural frequencies of the structure, mode shapes and the corresponding modal damping values associated. An assessment of these modal characteristics can be used both to verify the theoretical assumptions of the project, to monitor the performance of the structural system during its operational use. The thesis is structured in the following chapters: The first introductive chapter recalls some basic notions of dynamics of structure, focusing the discussion on the problem of systems with multiply degrees of freedom (MDOF), which can represent a generic real system under study, when it is excited with harmonic force or in free vibration. The second chapter is entirely centred on to the problem of dynamic identification process of a structure, if it is subjected to an experimental test in forced vibrations. It first describes the construction of FRF through classical FFT of the recorded signal. A different method, also in the frequency domain, is subsequently introduced; it allows accurately to compute the FRF using the geometric characteristics of the ellipse that represents the direct input-output comparison. The two methods are compared and then the attention is focused on some advantages of the proposed methodology. The third chapter focuses on the study of real structures when they are subjected to experimental test, where the force is not known, like in an ambient or impact test. In this analysis we decided to use the CWT, which allows a simultaneous investigation in the time and frequency domain of a generic signal x(t). The CWT is first introduced to process free oscillations, with excellent results both in terms of frequencies, dampings and vibration modes. The application in the case of ambient vibrations defines accurate modal parameters of the system, although on the damping some important observations should be made. The fourth chapter is still on the problem of post processing data acquired after a vibration test, but this time through the application of discrete wavelet transform (DWT). In the first part the results obtained by the DWT are compared with those obtained by the application of CWT. Particular attention is given to the use of DWT as a tool for filtering the recorded signal, in fact in case of ambient vibrations the signals are often affected by the presence of a significant level of noise. The fifth chapter focuses on another important aspect of the identification process: the model updating. In this chapter, starting from the modal parameters obtained from some environmental vibration tests, performed by the University of Porto in 2008 and the University of Sheffild on the Humber Bridge in England, a FE model of the bridge is defined, in order to define what type of model is able to capture more accurately the real dynamic behaviour of the bridge. The sixth chapter outlines the necessary conclusions of the presented research. They concern the application of a method in the frequency domain in order to evaluate the modal parameters of a structure and its advantages, the advantages in applying a procedure based on the use of wavelet transforms in the process of identification in tests with unknown input and finally the problem of 3D modeling of systems with many degrees of freedom and with different types of uncertainty.

New catalysts for the water gas shift reaction at middle-temperature

H2 demand is continuously increasing since its many relevant applications, for example, in the ammonia production, refinery processes or fuel cells. The Water Gas Shift (WGS) reaction (CO + H2O = CO2 + H2 DeltaH = -41.1 kJ.mol-1) is a step in the H2 production, reducing significantly the CO content and increasing the H2 one in the gas mixtures obtained from steam reforming. Industrially, the reaction is carried out in two stages with different temperature: the first stage operates at high temperature (350-450 °C) using Fe-based catalysts, while the second one is performed at lower temperature (190-250 °C) over Cu-based catalysts. However, recently, an increasing interest emerges to develop new catalytic formulations, operating in a single-stage at middle temperature (MTS), while maintaining optimum characteristics of activity and stability. These formulations may be obtained by improving activity and selectivity of Fe-based catalysts or increasing thermal stability of Cu-based catalysts. In the present work, Cu-based catalysts (Cu/ZnO/Al2O3) prepared starting from hydrotalcite-type precursors show good homogeneity and very interesting physical properties, which worsen by increasing the Cu content. Among the catalysts with different Cu contents, the catalyst with 20 wt.% of Cu represents the best compromise to obtain high catalytic activity and stability. On these bases, the catalytic performances seem to depend on both metallic Cu surface area and synergetic interactions between Cu and ZnO. The increase of the Al content enhances the homogeneity of the precursors, leading to a higher Cu dispersion and consequent better catalytic performances. The catalyst with 20 wt.% of Cu and a molar ratio M(II)/M(III) of 2 shows a high activity also at 250 °C and a good stability at middle temperature. Thus, it may be considered an optimum catalyst for the WGS reaction at middle temperature (about 300 °C). Finally, by replacing 50 % (as at. ratio) of Zn by Mg (which is not active in the WGS reaction), better physical properties were observed, although associate with poor catalytic performances. This result confirms the important role of ZnO on the catalytic performances, favoring synergetic interactions with metallic Cu.

Operational Modal Analysis: the CEME Skywalk at UBC, Vancouver

Slender and lighter footbridges are becoming more and more popular to meet the transportation demand and the aesthetical requirements of the modern society. The widespread presence of such particular structures has become possible thanks to the availability of new, lightweight and still capable of carrying heavy loads material . Therefore, these kind of structure, are particularly sensitive to vibration serviceability problems, especially induced by human activities. As a consequence, it has been imperative to study the dynamic behaviour of such slender pedestrian bridges in order to define their modal characteristics. As an alternative to a Finite Element Analysis to find natural frequencies, damping and mode shape, a so-called Operational Modal Analysis is a valid tool to obtain these parameters through an ambient vibration test. This work provides a useful insight into the Operational Modal Analysis technique and It reports the investigation of the CEME Skywalk, a pedestrian bridge located at the University of British Columbia, in Vancouver, Canada. Furthermore, human-induced vibration tests have been performed and the dynamic characteristics derived with these tests have been compared with the ones from the ambient vibration tests. The effect of the dynamic properties of the two buildings supporting the CEME Skywalk on the dynamic behaviour of the bridge has been also investigated.

Sistemi catalitici per la reazione di water - gas shift a media temperatura

Negli ultimi anni l’interesse nei confronti dell’H2 è cresciuto notevolmente per l’aumento della richiesta energetica mondiale. Uno dei processi più importanti per la produzione di H2 utilizza la reazione di Water-Gas Shift (WGS) per il trattamento delle correnti in uscita dai processi di steam reforming o di ossidazione parziale catalitica. CO + H2O  CO2 + H2 ∆H0298 = -41,2 KJ/mol Sono quindi stati sviluppati sistemi catalitici attivi nella reazione di WGS a media temperatura (circa 300 °C). Partendo da sistemi catalitici a base di Cu/Zn/Al, ottenuti da precursori idrotalcitici e sviluppati in lavori di tesi precedenti, sono state effettuate modifiche nella composizione al fine di aumentarne l’attività e la stabilità. L’aggiunta di piccole quantità di Mg ha un effetto positivo sull’attività dei sistemi catalitici, con effetti più evidenti a 250 °C. Tuttavia, l’aumento del contenuto di Mg, sebbene migliori le proprietà fisiche del catalizzatore (area superficiale e dispersione del Cu) sia del campione calcinato che di quello scaricato dopo reazione, peggiora drasticamente l’attività catalitica. L’aggiunta di piccole quantità di Mg sembra portare alla stabilizzazione della specie attiva Cu+ e promuovere un meccanismo redox superficiale (Cu0 e Cu+). E’ possibile correlare la conversione del CO con il rapporto ZnO/Cu, confermando il ruolo nella reazione di WGS dell’interazione Cu0/ZnO libero. La sostituzione di Mg con Ba comporta un miglioramento delle prestazioni catalitiche, in particolare nelle condizioni MTS (300 °C), suggerendo una più facile dissociazione dell’acqua legata alla stabilizzazione degli ossidrili da parte dei siti basici. È però accompagnato da una diminuzione della stabilità nelle condizioni di reazione. L’aggiunta di piccole quantità di La, Ce o Zr (con un rapporto Al/R = 50 mol/mol) incrementa la stabilità termica, sia in termini di proprietà fisiche che di attività catalitica. A seguito dei cicli termici di invecchiamento accelerato, infatti, non si riscontrano importanti diminuzioni di attività catalitica, evidenziando un’elevata stabilità della fase attiva.

Non-normal modal logics, quantification, and deontic dilemmas. A study in multi-relational semantics

This dissertation is devoted to the study of non-normal (modal) systems for deontic logics, both on the propositional level, and on the first order one. In particular we developed our study the Multi-relational setting that generalises standard Kripke Semantics. We present new completeness results concerning the semantic setting of several systems which are able to handle normative dilemmas and conflicts. Although primarily driven by issues related to the legal and moral field, these results are also relevant for the more theoretical field of Modal Logic itself, as we propose a syntactical, and semantic study of intermediate systems between the classical propositional calculus CPC and the minimal normal modal logic K.

Studio del comportamento catalitico nella reazione di Water Gas Shift a media ed alta temperatura

Per massimizzare la quantità di H2 nel gas di sintesi ottenuto dal processo di Steam Reforming (SR) si utilizza la reazione di Water Gas Shift (WGS): CO + H2O ⇆ CO2 + H2 ∆H0298 = - 41,2 KJ/mol Sulla base di sistemi catalitici Cu/Zn/Al si è cercato di modificarne la composizione per ottenere catalizzatori attivi e stabili in un intervallo di temperatura tra 350-450 °C, (High Temperature Shift o HTS), al fine di sostituire i tradizionali sistemi a base di Fe/Cr, in relazione alle limitazioni ambientali all’utilizzo del Cr e per poter operare con valori inferiori del rapporto S/DG. Si sono inoltre studiate le caratteristiche dei catalizzatori e le condizioni di reazione che favoriscono la produzione di metilammine ed alcoli nel processo a temperature intermedie, tra 300-350 °C (Middle Temperature Shift o MTS), in relazione alla disattivazione che questi composti comportano nel processo di SR a seguito del riciclo della fase acquosa dal reattore di WGS.

Proof theory of quantified modal logics

We introduce labelled sequent calculi for indexed modal logics. We prove that the structural rules of weakening and contraction are height-preserving admissible, that all rules are invertible, and that cut is admissible. Then we prove that each calculus introduced is sound and complete with respect to the appropriate class of transition frames.

Catalizzatori per la reazione di Water Gas Shift a media ed alta temperatura

L’H2 è un vettore energetico di elevato interesse, utilizzato nell’industria chimica per la produzione di NH3 e CH3OH, oltre che per le reazioni di idrogenazione ed HDS. Un importante processo nella produzione di H2 è la reazione di Water Gas Shift (WGS), usata nel trattamento delle correnti uscenti dal reattore di Steam Reforming (SR) del metano: CO + H2O  CO2 + H2 ∆H0298K = -41,2 KJ/mol. Sulla base di precedenti lavori, sono stati sviluppati nuovi catalizzatori per la reazione WGS ad alta temperatura (HTS), alternativi ai tradizionali sistemi a base di Fe/Cr, in considerazione dei vincoli economici (elevati valori del rapporto vapore/gas secco o S/DG) ed ambientali (formazione di CrVI) di questi sistemi. Partendo da sistemi Cu/Zn/Al con un basso contenuto di rame, ottenuti da precursori tipo idrotalcite (HT), stato studiato l’effetto dell’aggiunta di piccole quantità di alcuni promotori sull’attività e stabilità dei catalizzatori ottenuti, osservando un effetto positivo sulle caratteristiche fisiche, come l’aumento dell’area superficiale e della dispersione della fase attiva. I campioni contenenti i promotori erano inoltre caratterizzati da una maggiore stabilità termica e, in alcuni casi, da un’attività catalitica superiore a quella del catalizzatore di riferimento privo di promotori. L’aggiunta di piccole quantità di alcali alla formulazione con la migliore attività portava ad un ulteriore aumento di attività e di stabilità, attribuibile ad una minore formazione di coke sulla superficie. I sistemi più interessanti potevano operare anche a bassi valori del rapporto S/DG, interessanti dal punto di vista industriale. Lo studio dell’adsorbimento di CO mediante FT-IR ha permesso di ipotizzare la possibile natura della fase attiva nei sistemi. Infine, lo studio è stato esteso a sistemi per la reazione di WGS a media temperatura (MTS), osservando anche in questo caso un positivo effetto legato all’aggiunta di promotori, con un aumento dell’attività catalitica e della stabilità con il tempo di reazione.

Sviluppo di un sistema integrato innovativo per la contemporanea produzione e separazione di H2 ultrapuro, attraverso oxy-reforming, water-gas shift e membrane al Pd

Il presente lavoro di tesi si è focalizzato sullo studio e sulla ottimizzazione di un sistema integrato, che utilizzi la reazione di oxy-reforming del metano al fine di produrre syngas che venga trattato attraverso la water-gas shift al fine di abbattere il contenuto di CO e al tempo stesso aumentare la resa in H2. Con l’obiettivo di ottenere H2 ad elevata purezza (>99%) da poter essere inviato direttamente a celle a combustible ed in impianti di piccola taglia con possibile delocalizzazione della produzione industriale di energia elettrica e termica “pulita”, la miscela reale uscente dal processo di oxy-reforming è stata processata tramite successiva water-gas shift direttamente all’interno di una membrana ceramica al Pd selettiva nella separazione di H2. L’innovativià di questo progetto di studio è data da diversi parametri quali: 1) l’impiego dell’oxy-reforming in alternativa al normale steam-reforming del CH4, che permette di condurre il processo a temperature decisamente inferiori (700-750°C), utilizzando un minor quantitativo di vapore (S/C = 0.7); 2) l’utilizzo di due nuove formulazioni di catalizzatore di WGS per alte temperature, capace di operare in un unico stadio conversioni di CO ottenibili industrialmente solo attraverso i convenzionali due due stadi di reazione (e due diverse formulazioni di catalizzatori a base di Fe/Cr e Cu); 3) l’utilizzo di supporti ceramici con membrana a base di Pd, capaci di ospitare al loro interno un catalizzatore eterogeneo per la reazione di WGS a 400°C, rendendo quindi possibile la produzione e contemporanea separazione di H2 con un ulteriore effetto positivo poiché la membrana rimuovendo H2 dalla zona di reazione favorisce il superamento dell’equilibrio termodinamico per la conversione del CO, abbassandone il contenuto nel flusso uscente dei gas reazione e rendendo non più necessari sistemi aggiuntivi di separazione quali PSA o PROXY.

Boundary condition identification of a bridge pier using experimental data and FEM modal updating

Over the past twenty years, new technologies have required an increasing use of mathematical models in order to understand better the structural behavior: finite element method is the one mostly used. However, the reliability of this method applied to different situations has to be tried each time. Since it is not possible to completely model the reality, different hypothesis must be done: these are the main problems of FE modeling. The following work deals with this problem and tries to figure out a way to identify some of the unknown main parameters of a structure. This main research focuses on a particular path of study and development, but the same concepts can be applied to other objects of research. The main purpose of this work is the identification of unknown boundary conditions of a bridge pier using the data acquired experimentally with field tests and a FEM modal updating process. This work doesn’t want to be new, neither innovative. A lot of work has been done during the past years on this main problem and many solutions have been shown and published. This thesis just want to rework some of the main aspects of the structural optimization process, using a real structure as fitting model.

Education of tobacco use prevention and cessation for dental professionals--a paradigm shift

The use of tobacco continues to be a substantial risk factor in the development and progression of oral cancer, periodontitis, implant failure and poor wound healing. Dental and dental hygiene education providers have made great advances towards the incorporation of tobacco education into their curricula in recent years. Unfortunately, however, both medical and dental education research has consistently reported schools providing only basic knowledge-based curricula that rarely incorporate more effective, behaviourally-based components affecting long-term change. The limited training of oral healthcare students, at least in part, is reflected in practising dental professionals continuing to report offering incomplete tobacco interventions. In order to prepare the next generation of oral healthcare providers, this paper proposes a paradigm shift in how tobacco use prevention and cessation (TUPAC) may be incorporated into existing curricula. It is suggested that schools should carefully consider: to what level of competency should TUPAC be trained in dental and dental hygiene schools; the importance of establishing rapport through good communication skills; the core knowledge level for TUPAC; suggested instructional and assessment strategies; the importance of continuing professional education for the enhancement of TUPAC.

Endothelial Progenitor Cells Induce a Phenotype Shift in Differentiated Endothelial Cells towards PDGF/PDGFR Axis-Mediated Angiogenesis

BACKGROUND: Endothelial Progenitor Cells (EPC) support neovascularization and regeneration of injured endothelium both by providing a proliferative cell pool capable of differentiation into mature vascular endothelial cells and by secretion of angiogenic growth factors. OBJECTIVE: The aim of this study was to investigate the role of PDGF-BB and PDGFR in EPC-mediated angiogenesis of differentiated endothelial cells. METHODS AND RESULTS: Conditioned medium from human EPC (EPC-CM) cultured in hypoxic conditions contained substantially higher levels of PDGF-BB as compared to normoxic conditions (P<0.01). EPC-CM increased proliferation (1.39-fold; P<0.001) and migration (2.13-fold; P<0.001) of isolated human umbilical vein endothelial cells (HUVEC), as well as sprouting of vascular structures from ex vivo cultured aortic rings (2.78-fold increase; P = 0.01). The capacity of EPC-CM to modulate the PDGFR expression in HUVEC was assessed by western blot and RT-PCR. All the pro-angiogenic effects of EPC-CM on HUVEC could be partially inhibited by inactivation of PDGFR (P<0.01). EPC-CM triggered a distinct up-regulation of PDGFR (2.5±0.5; P<0.05) and its phosphorylation (3.6±0.6; P<0.05) in HUVEC. This was not observed after exposure of HUVEC to recombinant human PDGF-BB alone. CONCLUSION: These data indicate that EPC-CM sensitize endothelial cells and induce a pro-angiogenic phenotype including the up-regulation of PDGFR , thereby turning the PDGF/PDGFR signaling-axis into a critical element of EPC-induced endothelial angiogenesis. This finding may be utilized to enhance EPC-based therapy of ischemic tissue in future.