1,720,977 research outputs found
MULTIFUNCTIONAL NANOSTRUCTURED MATERIALS BASED ON CdSe AND TiO2 NANOPARTICLES
Full text linkNanotechnology has arisen as one of the most important fields in recent research, for the implications in both basic and applied science and technological applications.
The manipulation of matter at the nanoscale is accompanied by the appearance of novel properties and large surface to volume ratio which can be exploited in a number of applications ranging from optics, catalysis and sensing, to name a few.
In this work, we mainly focused on the synthesis and the use of nanomaterials for the preparation of nanocomposites and structures to be employed in the optical field. The main advantage of introducing nanosized inclusions in a host material is that specific functionalities or desired optical change can be imparted while transparency in the visible range can be retained.
The whole activity can be divided in the synthesis and processing of nanoparticles and in their usage for some specific application.
Cadmium selenide (CdSe), Titanium dioxide and layered titanates have been mainly addressed due to PL emission properties and high refractive index. In addition, zinc sulfide (ZnS) nanoparticles have been synthesized.
CdSe nanoparticles (Quantum Dots) have been obtained by colloidal chemistry and part of the work has been spent in the synthesis of core-shell nanoparticles with a CdSe core and a shell of semiconductor materials with wider band gap in order to increase the stability of the emission properties of such materials. These nanoparticles were introduced in sol-gel derived ZrO2 waveguides to obtain materials showing optical gain which was characterized by ASE (Amplified Spontaneous Emission) experiments.
High refractive index materials are useful in many optical applications. High refractive index depositions were obtained introducing Titania nanoparticles in proper matrices.
A sol-gel synthesis for titanium dioxide nanoparticles has been developed yielding to anatase particles in the 3-5 nm range. These were embedded in an epoxy-based hybrid material obtaining transparent depositions with refractive index in the 1.51-1.89 range.
Layered titanates were further addressed since they allowed extending the processing and engineering of titanium oxide materials. A synthetic colloidal procedure was developed, in which titanate nano-sheets are produced by reaction of a titanium alkoxide and an organic base.
These materials allowed to obtained composites with multifumctional properties since materials embedding both titanate sheets and quantum dots could be obtained and applied in PL active waveguide and functional coating for LED devices to improve light extraction and produce white light through down-conversion. Coatings for LED were also developed using conventional sol-gel derived hybrid materials.
The obtained layered titanates could also be modified and treated by UV curing, leading to material’s densification and enhancement of the refractive index at relatively low temperatures (200 °C). This processing behavior has been exploited in Bragg mirror fabrication and vertical optical microcavity incorporating quantum dots. The procedure employed for microcavity fabrication was found to be effective in keeping the optical properties of quantum dots, allowing for optical characterization of this structure.
The properties of titanium dioxide have been exploited for optical gas sensing applications embedding gold nanoparticles in a crystalline TiO2 matrix. Anatase TiO2 particles have been successfully used as matrix material for this application. The employed preparation of such nanocomposites allowed tailoring of porosity and gold-titania interface which could be studied by optical measurements. Optical sensing was evidenced by variation in thin film absorbance at wavelengths near the plasmon resonance of gold nanoparticles caused by the presence of the gas analytes.
Gold nanorods were introduced in the synthesized titanates. Gold nanorods are known to spheroidise upon thermal treatment, losing their peculiar optical properties. We found that the processing treatments developed for titanates resulted in improved thermal stability of such nanostructures as shown by optical measurements. This result is very interesting since it would allow extending gold nanorods’s exploitation in optical applications.
Finally, composites with enhanced refractive index were realized by introducing ZnS nanoparticles in hybrid sol-gel material. A synthesis of ZnS nanoparticles has been developed, which allows nanoparticles functionalization and introduction in a hybrid organic-inorganic sol-gel matrix.Il campo delle nanotecnologie è diventato tra i più importanti nella recente ricerca scientifica. È’ un settore multidisciplinare nelle conoscenze che ne costituiscono le basi e trova applicazione in svariati ambiti della tecnologia.
La manipolazione della materia su nanometrica è accompagnata dalla comparsa di nuove proprietà ed un elevato valore di superficie per unità di volume. Queste proprietà possono essere sfruttate in applicazioni nei campi dell’ottica, della catalisi e della sensoristica, per non citarne che alcuni.
In questo lavoro, l’attività è stata principalmente focalizzata sulla sintesi e l’uso di materiali nanostrutturati per la preparazione di nanocompositi e strutture di interesse nel campo dell’ottica. Il vantaggio principale nell’ introdurre particelle nanometriche in un materiale risiede nella possibilità di introdurre specifiche funzionalità o variazioni nelle proprietà ottiche mantenendo nello stesso tempo la trasparenza nel visibile.
L’intera attività può essere divisa nella sintesi e successiva manipolazione di nanoparticelle e nel loro uso in specifiche applicazioni.
Seleniuro di Cadmio (CdSe), Biossido di Titanio (TiO2) e Titanati a strati sono stati principalmente presi in considerazione per sfruttare specifiche proprietà di fotoluminescenza e di elevato indice di rifrazione. Sono inoltre state sintetizzate nanoparticelle di Solfuro di Zinco (ZnS).
Nanoparticelle di CdSe, anche chiamate Quantum Dots (QDs), sono state ottenute attraverso sintesi di tipo colloidale. Parte del lavoro è stata dedicata al ricoprimento di queste nanoparticelle con semiconduttori a più elevato band gap con lo scopo di aumentare la stabilità delle proprietà di emissione di questi materiali. Queste nanoparticelle sono state introdotte in guide d’onda costituite da Biossido di Zirconio (ZrO2) ottenuto per via sol-gel per ottenere materiali con proprietà di guadagno ottico testate in esperimenti di emissione spontanea amplificata (ASE).
Materiali ad alto indice di rifrazione trovano utilizzo in molte applicazioni ottiche. Deposizioni a elevato indice di rifrazione sono state ottenute introducendo particelle di biossido di titanio in opportune matrici.
E’ stata sviluppata una sintesi di tipo sol-gel in grado di produrre soluzioni colloidali stabili di particelle cristalline con la struttura cristallografica dell’anatase con diametro intorno a 3-5 nm. Queste nanoparticelle sono state introdotte in una matrice ibrida sol-gel ottenendo deposizioni trasparenti con indice di rifrazione variabile tra 1.51 e 1.89.
Sono stati successivamente presi in considerazione i titanati a strati perché permettono di estendere le possibilità di manipolazione ed ingegnerizzazione di materiali a base di ossido di titanio.
È stata sviluppata una sintesi colloidale in cui “foglietti“ nanometrici di titanati sono prodotti per reazione di un alcossido di titanio e una base organica.
Questi materiali hanno permesso di ottenere compositi con proprietà multifunzionali. Infatti, materiali contenenti titanati lamellari e QDs sono stati ottenuti e applicati in guide d’onda con proprietà di fotoluminescenza e ricoprimenti funzionali su dispositivi LED per migliorare la frazione di luce estratta e produrre luce bianca per conversione di parte della luce emessa in luce a lunghezza d’onda maggiore. Ricoprimenti per LED sono inoltre stati sviluppati con materiali ibridi sol-gel più convenzionali.
I titanati stratificati sono stati trattati utilizzando radiazione UV. Questo genere di trattamento porta a una densificazione del materiale con conseguente aumento dell’indice di rifrazione impiegando durante il processo temperature relativamente basse (200 °C). Questo trattamento è stato impiegato nella fabbricazione di specchi multistrato dielettrici e cavità ottiche verticali dove sono stati inseriti QDs come emettitori luminescenti. Il metodo utilizzato è stato verificato essere compatibile con la conservazione delle proprietà di emissione dei Quantum Dots, permettendo la caratterizzazione ottica delle strutture sviluppate.
Sono state inoltre considerate applicazioni sensoristiche per il rilevamento di gas tramite misure ottiche di materiali a base di TiO2 contenenti nanoparticelle d’oro.
Le nanoparticelle di anatase in precedenza menzionate sono state adoperate come matrice, consentendo sia di agire sulla porosità, sia di caratterizzare l’interfaccia oro/titania tramite misure ottiche. La funzionalità sensoristica è stata determinata studiando la variazione nell’assorbanza ottica a lunghezze d’onda vicine alla risonanza plasmonica delle particelle d’oro, causata dalla presenza di uno specifico gas nell’atmosfera.
Nanorods di oro sono stati inseriti in matrici di titanati lamellari. Queste nanostrutture d’oro tendono ad assumere la forma sferica in seguito a trattamento termico perdendo così le loro specifiche proprietà. Il trattamento di densificazione sviluppato per i titanati è stato applicato per questi compositi, fornendo una migliore stabilità termica dei nanorods, come dimostrato da misure ottiche. Questo risultato è interessante poiché potrebbe permettere di estendere l’utilizzo di queste nanostrutture in applicazioni ottiche.
Infine, sono stati realizzati compositi con aumentato indice di rifrazione utilizzando particelle di solfuro di zinco per le quali è stata sviluppata una sintesi colloidale e una procedura di funzionalizzazione per il loro inserimento in matrici ibride sol-gel
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
Spontaneous bleeding or thrombosis in cirrhosis: What should be feared the most?
Full text linkThe more modern and accurate concept of a rebalanced hemostatic status in cirrhosis is slowly replacing the traditional belief of patients with cirrhosis being "auto-anticoagulated", prone only to bleeding complications, and protected from thrombotic events. With greater attention to clinical thrombotic events, their impact on the natural history of cirrhosis, and with the emergence and increased use of point-of-care and global assays, it is now understood that cirrhosis results in profound hemostatic alterations that can lead to thrombosis as well as to bleeding complications. Although many clinical decisions are still based on traditional coagulation parameters such as prothrombin (PT), PT, and international normalized ratio, it is increasingly recognized that these tests do not adequately predict the risk of bleeding, nor they should guide pre-emptive interventions. Moreover, altered coagulation tests should not be considered as a contraindication to the use of anticoagulation, although this therapeutic or prophylactic approach is not at present routinely undertaken. Gastroesophageal variceal bleeding continues to be one of the most feared and deadly complications of cirrhosis and portal hypertension, but great progresses have been made in prevention and treatment strategies. Other bleeding sites that are frequently part of end-stage liver disease are similar to clinical manifestations of thrombocytopenia, with gum bleeding and epistaxis being very common but fortunately only rarely a cause of life-threatening bleeding. On the contrary, manifestations of coagulation factor deficiencies like soft tissue bleeding and hemartrosis are rare in patients with cirrhosis. As far as thrombotic complications are concerned, portal vein thrombosis is the most common event in patients with cirrhosis, but venous thromboembolism is not infrequent, and results in important morbidity and mortality in patients with cirrhosis, especially those with decompensated disease. Future studies and the more widespread use of point-of-care tests in evaluating hemostasis will aid the clinician in decision making when facing the patient with bleeding or with thrombotic complications, with both ends of a continuum being potentially fatal
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
Patterned TiO2 nanostructures fabricated with a novel inorganic resist
No full textThe fabrication of nanostructures is a very intense field of research in material science over the last decades. Overcoming the limit imposed by the diffraction limit in lithography was addressed in several ways: shifting to smaller wavelength, changing radiation and using electrons or ions instead of photons or using non-conventional bottom up techniques like self-assembly. There are few studies on fabrication of ordered TiO2 nanostructures, mostly confined to non-scalable technologies, while nanostructured TiO 2 is a material used in many different fields of applications. In our work we present a hybrid nanofabrication technique based on self-assembly coupled with standard UV lithography. With this method we were able to fabricate in a single step and with the use of inexpensive equipment a 2D Nano Bowl Array of TiO2 with sub wavelength features and easily scalable pattern features
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
