1,720,959 research outputs found
Design of a flowrate measurement system for low-pressure gases
No full textDesign of a flow meter to be used in a low-pressure environment is hereafter presented. The need of this activity comes from the lack of commercial flow meters operating at low pressures due to the unusual working environment, where outgassing and sublimation phenomena becomes relevant for many materials and rarefied atmosphere changes dramatically the heat and mass exchange phenomena. In our case, the need of a low pressure compatible measurement system comes from the need of measuring the flow rate of a rotary vane pump working under an environmental pressure between 10 and 6 mbar, simulating the condition of the Martian atmosphere at the surface. The pump will be the key component of a particle analyzer that should be part of the ExoMars 2020 ESA-Roscosmos mission. The designed measurement system is based on the deformation of a control volume, a stainless-steel bellow, which has been designed on the basis of the expected flow rate. The measurement system has been calibrated at ambient condition and testing in low-pressure has been performed in order to validate the measurement method and derive the flow rate performances within the expected working conditions
Feasibility design of an interface damper for a space borne microbalance
No full textFeasibility design of a damper based on superelastic shape memory alloys (SMAs) is presented. The design wants to develop a passive vibration insulator for the Contamination Assessment Microbalance instrument, a quartz crystal microbalance for monitoring and measuring contamination in space environment. The ability of SMAs to act as efficient vibration insulators comes from their pseudo-elastic capabilities as the hysteretic force versus displacement behavior allows for energy dissipation. A 3D model of the instrument was developed to perform modal and dynamic random analyses aimed to identify the insulator mechanical characteristics and verify the instrument mechanical resistance. Moreover, a setup was designed to measure superelastic damping capacity of a commercial pseudoelastic shape memory alloy wire in dynamic tensile mode. The wire' specific damping capacity was then tested in different conditions, i.e. changing the excitation frequency and the amplitude of the deformation within a range of interest. The experimental activity allowed validation of the selected SMA wire for the intended application
Design of SMA wire based damper for a spaceborne QCM
No full textLAUREA MAGISTRALEIn questo lavoro viene presentata la progettazione di uno smorzatore basato su fili a lega a memoria di forma (SMA) superelastici.
Lo scopo è sviluppare un isolatore passivo di vibrazioni per una Microbilancia per la valutazione della contaminazione, una microbilancia ai cristalli di quarzo per monitorare e misurare la contaminazione in ambiente spaziale (QCM). L’abilità delle leghe SMA di agire come un efficiente isolatore di vibrazioni è data dalla loro capacità pseudoelastica dato che il ciclo di isteresi, visibile nel loro diagramma forza-spostamento, consente la dissipazione di energia.
Uno studio di fattibilità è stato svolto per indentificare le dimensioni del filo che consentano la realizzazione dello smorzamento richiesto.
In seguito a ciò è stato sviluppato un modello 3D per lo smorzatore per eseguire un analisi modale al fine di selezionare gli elementi elastici da usare per la realizzazione di un prototipo dello smorzatore.In this work the design of a damper based on SMA alloy superelastic wires is presented. The design goal is to develop a passive vibration insulator for the Contamination Assessment Microbalance instrument, a quartz crystal microbalance (QCM) for monitoring and measuring contamination in space environment. The ability of SMAs to act as efficient vibration insulators comes from their pseudo-elastic capabilities as the hysteretic force versus displacement behavior allows for energy dissipation.
Feasibility study is performed to identify wire size and mounting that allows achievement of the required damping.
Beside it, a 3D model of the damper is developed to perform modal analyses in order to select elastic elements to be used for the manufacturing of a mockup of the damper
Characterization of the pseudoelastic damping capacity of shape memory alloy wire
No full textThe pseudoelastic hysteresis behavior of shape memory alloy (SMA) elements observed above the austenite finish temperature of the alloy, can be used to provide a large structural damping in different applications. In this work, the pseudoelastic damping capacity (SDC) of a NiTi SMA wire has been characterized using the complex modulus approach through testing under a dynamic tensile condition. A test setup has been specifically designed, built and validated for this measurement since a testing machine with the required performances was not available. Given the dynamic characteristic of the test the structure was designed to behave as a rigid body in the frequency range of interest. Different conditions have been tested, varying the excitation frequency, the amplitude of imposed deformation, and the pre-strain levels. Results show that the SDC has a nearly constant trend of 7.5% for low frequencies until 30 Hz. Moreover, variation of the amplitude of deformation, between 0.3% and 0.8%, causes an increasing of the damping capacity, which varies from 7.7% to 10.4%, respectively. Finally, the measured prestrain amplitude effect is in agreement with existing literature studies
Preliminary design of a shape memory alloy damper for a spaceborne microbalance
No full textLAUREA MAGISTRALEIn questo lavoro si presenta la progettazione preliminare di uno smorzatore basato sull’utilizzo di materiale a memoria di forma con l’obiettivo di ridurre i livelli di vibrazione durante le fasi di lancio per una microbilancia al quarzo utilizzata in ambito spaziale.
Si è sviluppato un modello ad elementi finiti dello strumento con l’obiettivo di valutare il comportamento dinamico e la resistenza meccanica dello stesso al variare delle caratteristiche meccaniche della sospensione.
A valle della fase di modellazione, si è progettato un setup di misura per ricavare il fattore di perdita di un filo a memoria di forma, selezionato per lo sviluppo dello smorzatore. Il filo è stato caratterizzato in differenti condizioni operative ovvero, variando la frequenza di deformazione, l’ampiezza e il valore medio di deformazione.In this work preliminary design of a damper using the effect of superelastic response of shape memory alloys (SMAs) has been performed in order to develop a passive vibration insulator for CAM instrument, a quartz crystal microbalance for thermo-gravimetric measurements in space applications.
The ability of SMAs to act as efficient vibration damper comes from their pseudo-elastic capabilities as the hysteretic force versus displacement behavior allows for energy dissipation. A 3D model of the instrument was developed to perform modal and dynamic random analyses to derive insulator mechanical characteristics and verify the instrument mechanical resistance.
Moreover, a setup has been designed to measure superelastic damping capacity (SDC) of a commercial pseudoelastic shape memory alloy wire in dynamic tensile test. Wire SDC has been tested in different conditions, changing excitation frequency, amplitude of the deformation and pre-strain deformation in a range of interest to validate the usage of the selected SMA wire
Dust monitoring in Martian environment
No full textIn questo lavoro, è stato sviluppato lo schema di misurazione della portata per un analizzatore di particelle progettato per lo studio della polvere sospesa nell’atmosfera marziana. Lo strumento MicroMED è un analizzatore di particelle ottiche con l'obiettivo di misurazione della distribuzione delle dimensioni delle particelle e della densità in termini di particelle per unità di volume dell'atmosfera. Quest'ultimo obiettivo richiede che lo strumento abbia misurato la portata del volume dell'aerosol. Tuttavia, questa misura non è realizzabile nelle condizioni di lavoro previste con sensori disponibili. Poiché il sistema fluidico dello strumento ha delle analogie con un tubo di Venturi, si può prevedere una correlazione significativa tra la portata e la differenza di pressione tra ingresso e sezione ristretta del condotto. Questo punto indica che caratterizzando il circuito fluidico di ingresso-uscita dello strumento nelle condizioni di lavoro, si può derivare la portata del volume dalla misurazione della differenza di pressione.
Per raggiungere questo obiettivo, nella prima fase è stato progettato e realizzato un sistema di misurazione della portata per gas a bassa pressione e per uso di laboratorio. Questo sistema di misurazione dopo la validazione è stato applicato negli esperimenti per le prestazioni della pompa dello strumento e la caratterizzazione del circuito di ingresso-uscita dello strumento nelle condizioni di lavoro previste. D'altra parte, al fine di misurare la differenza di pressione fornita nel sistema ottico dello strumento per correlarla alla portata, sono stati specificati, selezionati e caratterizzati trasduttori di pressione adatti ad operare in condizioni di lavoro marziane.
Il simulatore del circuito fluidico dello strumento, inclusi i condotti di entrata e uscita e il volume di simulazione della testa ottica, è stato utilizzato con CO2 come gas di lavoro, simulando le condizioni di pressione marziana. I dati ottenuti hanno portato alla estrazione delle curve caratteristiche di resistenze fluidiche in entrata-uscita dello strumento che dalla misura di pressione permettono di derivare la portata volumetrica del gas di aspirazione.In this work, the flowrate measurement scheme for a particle analyzer project to do science in Martian atmosphere, was designed and developed. The instrument MicroMED is an optical particle analyzer with measurement target of the particle size distribution and density in terms of particles per unit of atmosphere volume. The latter target requires the instrument to have the aerosol volume flowrate measured. However, this measurement is not feasible in the Martian working conditions by using available sensors. Since the instrument’s fluidic system looks like a Venturi-type one, a good correlation between the flowrate and the pressure difference between the atmosphere and the fluid at the contracted section can be expected. Therefore, by characterizing the instrument’s fluidic circuit in the working conditions, one can derive the volume flowrate from the measurement of the pressure difference.
In order to approach this objective, at first a flowrate measurement system for low-pressure gases and laboratory use was designed and implemented. This reference measurement system after validation was applied in the experiments for the characterization of the instrument’s pump performance and inlet-outlet circuit, in the expected working conditions. On the other hand, in order to measure the provided pressure difference in the instrument’s optical system needed to derive the flowrate, suitable pressure transducers were specified, selected and characterized in Martian working conditions.
The simulator of instrument’s fluidic circuit, including the inlet-outlet ducts and the optical head simulating volume, was characterized with CO2 as working gas in Martian pressure conditions. The obtained data led to derivation of instrument’s inlet-outlet fluidic resistances that allows deriving the volume flowrate of intake gas from one pressure measurement.DIPARTIMENTO DI MECCANICAEngineering Design and Manufacturing for the Industry of the Future32PREVITALI, BARBARAROCCHI, DANIEL
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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