1,720,984 research outputs found
Preliminary Design of the AEGIS Test Facility
No full textThe AEGIS experiment is expected to be installed at the CERN Antiproton Decelerator in a very close future, since the main goal of the AEGIS experiment is the measurement of gravity impact on antihydrogen, which will be produced on the purpose. Antihydrogen production implies very challenging environmental conditions: at the heart of the AEGIS facility 50 mK temperature, 1e-12 mbar pressure and a 1 T magnetic field are required. Interfacing extreme cryogenics with ultra high vacuum will affect very strongly the design of the whole facility, requiring a very careful mechanical design. This paper presents an overview of the actual design of the AEGIS experimental facility, paying special care to mechanical aspects. Each subsystem of the facility – ranging from the positron source to the recombination region and the measurement region – will be shortly described. The ultra cold region, which is the most critical with respect to the antihydrogen formation, will be dealt in detail. The assembly procedures will be considered too, as they are expected to be critical to make the set-up phase easier, as well as to make possible any future improvement of the facility itself
Metodo numerico per la stima degli effetti combinati di tolleranze in un sistema meccanico
No full textA distanza di cinque anni dalla presentazione di un lavoro dedicato allo sviluppo di una procedura originale per valutare la propagazione dell’incertezza in una struttura complessa in ambito aerospaziale, l’entrata in funzione, in orbita, del satellite Planck fornisce una conferma indiretta della correttezza delle conclusioni raggiunte. La presente memoria ripropone la metodologia sviluppata e fornisce alcune informazioni circa possibili sviluppi futuri e programmi di generalizzazione della procedura
Progettazione della struttura di un portale per tomografia muonica di rottami di ferro
No full textLa fusione metallurgica di sorgenti radioattive all'interno di impianti di recupero di rottami di ferro è
estremamente pericolosa sia per gli operatori che per l’ambiente e la salute degli abitanti in una vasta
area attorno all’impianto stesso. Sulla base di incidenti passati, ed i conseguenti danni socioambientali,
le acciaierie sono state attrezzate con sistemi di rilevamento radioattivo in modo da
scongiurare il più possibile delle contaminazioni su larga scala. Si è cercato quindi di limitare le
conseguenze di un eventuale incidente all’interno delle acciaierie stesse, le quali sono comunque
estremamente sensibili all’argomento sia per la salvaguardia della salute dei propri dipendenti sia per
le pesanti conseguenze economiche che una contaminazione radioattiva comporta.
Particolare attenzione viene data all’identificazione preventiva delle sorgenti radioattive prima che
entrino nei processi di fusione con la conseguente compromissione dell’impianto. Le acciaierie che
sfruttano rottami di ferro, infatti, sono già attrezzate con strumenti in grado di rilevare la presenza di
radiazioni, se non schermate, ma sono completamente indifese se la sorgente radioattiva è ben
confinata all'interno di un involucro di materiale appropriato quale ad esempio il piombo. Un gruppo
di lavoro interdisciplinare composto da ingegneri e fisici si è occupato, insieme a due aziende, della
progettazione di un portale dedicato alla scansione di mezzi pesanti carichi di rottame di ferro: il
principio utilizzato per la rilevazione dei rifiuti radioattivi é la tecnologia della radiografia muonica.
Nel presente articolo si descrive il progetto e l'attività svolta dal gruppo di lavoro
In situ compact tensile test device for polymer nanocomposite specimens to be analyzed in an x-ray microdiffractometer
No full textX-ray diffraction is a non-destructive technique for structural analysis of materials. Applications include the evaluation of the residual stresses in real components, wherein the crystalline planes are used as strain gauges. In case of polymer nanocomposites, this technique allows to study the filler structural changes, in particular its orientation as a function of polymer deformation.
A tensile test device to apply uniaxial stretching on polymer nanocomposite specimens has been designed and built to equip a commercial X-ray microdiffractometer.
The main feature of this compact device is allowing setting the specimen strain up to 400% inside the microdiffractometer. X-ray diffraction measurements are carried out at different strains at the same point without removing the sample from the stage. The maximum load applied to the specimen is 100 N.
We report the design phases and the results of preliminary tests on commercial rubber samples
Design of a 6-supports exactly constrained supporting system for superconducting magnets and its application to rotating gantries for cancer therapy
No full textIn particle therapy for cancer treatment, the radiation dose to tissues around the tumour can be reduced by employing a rotating gantry—a mechanical structure allowing the delivery of the particle beam to the patient from various angles. Gantries for ion therapy can benefit from the integration of superconducting magnets to minimize the size and weight of the machine. One significant challenge associated with the supporting system of superconducting elements is related to the management of their accuracy during both alignment and operational phases. Concurrently, heat flow from room temperature to cryogenic temperatures through the supporting system must be restricted as the ratio of power needed to operate the cooling system is around 1000 times the power extracted at cryogenic temperature. The design of the supports must consider the variability of the load during operation, i.e. guarantee accuracy of the cold-mass pose (position and rotation) under its own weight during a 360∘ gantry rotation. A literature review had been done highlighting the possible application of a novel exact-constrained solution for the support of superconducting magnets. Within the framework of the European project HITRIplus (heavy Ion Therapy Research Integration), this study proposes the design and optimization of a support system based on a 6 degrees of freedom parallel mechanism (exactly constrained kinematics). A mathematical model is proposed, referred as “error model”, to estimate the accuracy of the pose of the cold-mass due to major unrecoverable errors. The error model estimates the contribution of main error sources: the elasticity of the supports, the elasticity of the vacuum vessel enclosure and the influence of backlash in the joints. An optimization genetic algorithm has been developed and employed to find the optimal configuration of supports that simultaneously increases the accuracy and minimizes heat-loads to the cold-mass. The error model has been validated by finite element analysis, showing its validity for the optimization process. The optimised solution has been compared to solutions that were proposed initially based on common sense, intuition and had been manually refined: the optimized solution shows considerable improvements in the overall accuracy of the system and a substantial reduction of the heat-loads. The optimized solution also implements a pre-load system to eliminate backlash in the joints: this considerably improves the accuracy of the system. The error model presented allows computationally cheaper optimizations and variations of the designed architecture (i.e. variation in cross sections, change in material, change in geometry, implementation of pre-load etc..) with respect to a classic approach based only on finite element analysis. Furthermore, thanks to the kinematics characteristic of the proposed architecture, the 6-legs design clears the way for a more reliable implementation of an automated positioning system with respect to classical over-constrained architectures
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
Literature Review of Suspension Systems for Superconducting Elements
Full text linkWhen designing suspension systems for superconducting elements, the primary challenge is to strike a balance between limiting the heat load to the cold mass and ensuring the proper mechanical resistance and/or stiffness of the system. This trade-off often leads engineers to choose from a limited set of materials and supporting architectures. The aim of this study is to provide an overview of the different overall designs. Scientific articles were searched within the Google Scholar database using advanced search operators to combine a defined set of keywords. Among the architectures found, the “multi-post” solution and the “8-support” solution are the two most commonly chosen classes. Additionally, a recurrent pattern for the supporting system of superconducting cavities has been identified. The choice of architecture can be correlated with the characteristics of the superconducting element being supported, such as its mass, length, and stiffness. Furthermore, the review provides a conceptual analysis of the possibility of extending these designs to the unconventional environment of rotating machines
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