305,153 research outputs found
Malmquist Productivity Index. Aspetti metodologici
No full textNel lavoro gli autori (Summo D. Quatela P.) analizzano una metodologia non parametrica di tipo frontier-approch che consente di scomporre le variazioni della produttività totale in cambiamenti di efficienza e cambiamenti tecnologici. In particolare si sperimenta una risposta empirica alle esigenze conoscitive della dinamica temporale della produttività del settore bancario italiano adottando un approccio metodologico innovativo rispetto all’impostazione classica. Si tratta di porre in essere indici di produttività di
Malmquist1 che - a differenza di quelli del tipo Laspeyres, Paasche, Fisher, Tornquist, Solow - considerano l’ipotesi di inefficienza delle strutture produttive osservate e consentono di scindere i cambiamenti dovuti alla efficienza tecnica e ai cambiamenti dovuti al progresso tecnologico, noti, nella terminologia anglosassone, come catching-up effect e tecnology schift effect. Questi indici, tuttavia, richiedono la definizione di una metodologia prodromico alla loro generazione: la Data Envelopment Analisys (DEA)
Electrical and all-optical poling of nonlinear optical materials: relaxation dynamics
No full textIl presente lavoro è motivato dalla necessità di trovare nuovi materiali polimerici o ibridi organici-inorganici per la realizzazione di modulatori elettroottici. Per essere utilizzati in un dispositivo reale, i materiali dotati di proprietà ottiche non lineari devono possedere elevata attività non lineare e stabilità temporale. Affinché un materiale esibisca proprietà ottiche non lineari del secondo ordine, esso deve essere sottoposto ad una procedura post-deposizione che definisca una direzione preferenziale in un sistema in partenza centro-simmetrico. A questo scopo sono state utilizzate due diverse tecniche di orientamento: corona e all-optical poling. La prima tecnica, studiata nel laboratorio NeMO, utilizza un campo elettrico statico per orientare le molecole, la cui mobilità viene aumentata innalzandone la temperatura. La seconda, utilizza la sovrapposizione di due sorgenti coerenti alle frequenze ω e 2ω per indurre una polarizzazione su campioni mantenuti a temperatura ambiente. In particolare, questa parte di lavoro è stata sviluppata nel Laboratoire des Propriétés Optiques des Matériaux et Applications (POMA) presso l’Università di Angers, grazie ad una borsa di studio finanziata dal COST P8. Grazie a queste tecniche di poling, i dipoli delle molecole possono essere orientati in una direzione parallela o perpendicolare alla superficie del film. Tale orientazione è stata caratterizzata tramite misure di assorbimento di luce polarizzata (PAS) e di generazione di seconda armonica (SHG). Utilizzando la temperatura come agente degradante, sono stati effettuati test di invecchiamento accelerato su film sottili di materiale polimerico e ibrido organico-inorganico sintetizzato con la tecnica sol-gel. Le curve di decadimento rivelano un andamento doppio esponenziale. Riportando il tempo di rilassamento lento in funzione della temperatura di invecchiamento, è stato possibile estrapolare, tramite un relazione tipo-Arrehnius, il tempo di rilassamento a temperatura ambiente. Due materiali sono risultati promettenti per le applicazioni desiderate: un sistema polimerico basato su una poliimide e un sistema ibrido. La realizzazione di un dispositivo elettroottico verrà realizzata in collaborazione con un’industria italiana. Questo lavoro di tesi rientra nell’ambito di un progetto europeo (ODEON) ed è stato sviluppato principalmente nel laboratorio NeMO presso l’Università di Roma “Tor Vergata”.The present thesis is motivated by the attempt to find polymeric or hybrid organic-inorganic materials for electrooptic modulators. For practical uses, nonlinear optical (NLO) materials must possess both large nonlinearity and temporal stability. Second order NLO properties appear after some additional post-deposition procedures. Indeed, after deposition, these composed materials are centrosymmetric and, as such, not endowed of second order properties. Poling, i.e. the orientation of the molecular dipoles, is necessary in order to break this centrosymmetry. Two different poling methods are investigated and discussed: corona and all-optical poling. The first technique, developed in the NeMO laboratory, involves a dc electric field, used to orient the dipoles of the material at a temperature where the molecule dipoles can rotate. The second one uses two coherent sources possessing different frequencies (ω and 2ω) to induce a reversible static polarization inside the medium at room temperature. This last work was performed in the Laboratoire des Propriétés Optiques des Matériaux et Applications (POMA) at the University of Angers thanks to the COST P8 grant. By poling, the dipoles can be oriented parallel or perpendicular to the film plane. Linear (Polarized Absorption Spectroscopy-PAS) and nonlinear (Second Harmonic Generation-SHG) characterizations are performed on the studied systems in order to reveal the orientation. Accelerated aging tests are performed using temperature as degrading agent and polar order decay monitored by SHG. All the decay curves are well fitted by a double exponential function. An extrapolation of the slower relaxation time using the Arrhenius model, permits to obtain the stability of nonlinear properties at room temperature. Macroscopic second order nonlinearities, orientation mechanisms (raise and decay of the poled order responsible for the nonlinearity) and chemical nature of different systems are discussed. At least two promising materials are found, a polyimide-based and a hybrid sol-gel-based system, and the fabrication of a prototype of electrooptic modulator is envisaged in collaboration with the research centers of some Italian private companies. This work is pursued mainly under the ODEON European project and performed in the NeMO laboratory at the University of Roma "Tor Vergata"
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
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