1,721,009 research outputs found
VO2 a prototypical Phase Change Material: spectroscopic study of the orbital contribution across the Metal Insulator Transition
Full text linkIl VO2 è un affascinante sistema con configurazione 3d1 che esibisce una transizione metallo isolane (MIT) a 67°C accompagnata da una transizione strutturale, passando da una fase monoclina isolante a bassa temperatura ad una metallica tetragonale ad alta temperatura. Dalla sua scoperta, la MIT è stata ampiamente studiata sia per il suo potenziale applicativo che per investigarne la natura.
Diversi modelli teorici sono stati proposti in letteratura per spiegare la natura della MIT come una transizione strutturale di Peierls o una transizione Mott-Hubbard innescata dalla repulsione Coulombiana tra gli elettroni. Tuttavia una chiara descrizione teorica non è ancora stata trovata dal momento che le proprietà del VO2 dipendono dalla complessa interazione di diversi gradi di libertà: orbitale, strutturale ed elettronico.
Di conseguenza, al fine di sfruttare le caratteristiche della MIT in applicazioni tecnologiche, uno studio dettagliato dell'interazione tra i vari gradi di libertà è di fondamentale importanza.
Con l'obbiettivo di sciogliere l'intreccio tra ordine reticolare, ordine degli orbitali e interazione elettronica, in questa tesi sono stati studiati quattro campioni di VO2 con proprietà strutturali differenti. Tre film sottili cristallini alla cui struttura reticolare è applicato un diverso grado di strain ed un film nanostrutturato disordinato. Questi campioni sono stati studiati tramite avanzate tecniche spettroscopiche di raggi x quali X-ray Absorption Near Edge Structure (XANES), Resonant Photoemission (ResPES) e Constant Initial State (CIS).
La combinazione di queste tecniche ha permesso di determinare l'influenza dello strain sul contributo multi-orbitale alla MIT. in aggiunta, interessanti proprietà quali il controllo della popolazione del livelo di Fermi possono essere modulate controllando lo strain applicato. nel campione disordinato, in cui il la transizione di Peierls è inibita dalla mancanza di ordine, è stato possibile osservare una transizione puramente elettronica, cioè la prova sperimentale che la transizione strutturale non è strettamente necessaria per innescare la transizione metallo-isolante.VO2 is a fascinating 3d1 system undergoing a temperature triggered (67 °C) Metal Insulator Transition (MIT) coupled with a structural phase transition, from a low temperature monoclinic insulator to a high temperature tetragonal metal. Since its discovery, the MIT has been widely studied with a twofold interest: its applicative potential and its nature.
Different theoretical models have been proposed to explain the occurrence of the insulating phase of VO2 like a structurally driven Peierls transition or a Mott-Hubbard transition triggered by electron mutual Coulomb repulsion. However, a clear theoretical picture is missing since VO2 properties are determined by a complex interplay among lattice, orbital and electronic degrees of freedom. Therefore, in order to exploit the MIT features for technological application, a detailed study of the influence and interplay between the different degrees of freedom is of paramount importance.
With the aim of disentangling the lattice-orbital-electronic intrigue, in this thesis, four samples with different structural properties have been studied. Three thin strained films and one nanostructured disordered VO2 film have been investigated using advanced spectroscopic techniques like X-ray absorption Near Edge Structure (XANES), Resonant Photoemission (ResPES) and Constant Initial State (CIS). The combination of these techniques allowed to determine the strain influence over the multi-orbital contribution to the MIT. In addition, interesting features like Fermi Level population can be modulated tuning the strain. In the disordered sample, in which the Peierls mechanism is quenched, it has been possible observe the occurrence of a purely electronic transition, i.e. structural transition is not necessary to trigger the MIT
Total recovery from Parkinson syndrome after surgical removal of a meningioma: a clinical case.
No full textSigns of parkinsonism, such as resting tremors, rigidity, bradykynesia, and gait disturbance, tipically have a unilateral onset and result from a malfunction in the extrapyramial system involving the basal ganglia. Here we describe a patient who developed a pure bilateral parkinsonism that completely regressed after neurosurgical removal of the patient's tumour
Uterine leiomyosarcoma metastatic to the brain: case report
No full textBackground.We report a leiomyosarcoma of the uterus, an uncommon tumor with a
very aggressive course and poor prognosis due to the fact that, despite complete resection,
it recurs with micrometastases. The most common metastatic sites are the
lung, intraperitoneal, pelvic and paraaortic lymph nodes, and liver. Brain and skull
metastases are very rare.
Case. A 57-year-old woman underwent a hysterectomy and bilateral salpingooophorectomy
for a grade T2N0M0 uterine leiomyosarcoma. There was no evidence
of other lesions. Three months later a total-body PET scan demonstrated the presence
of metastases in both lungs, and the patient was started on chemotherapy. One
year later a cranialMRI demonstrated a brain metastasis to the temporal lobe. Emergency
complete resection of the recurrence was performed, followed by whole-brain
radiation and adjuvant chemotherapy.
Conclusions. Given the limited treatment options, the gold standard for uterine
leiomyosarcoma brain metastasis is total surgical removal. Chemotherapy and radiation
therapy may provide only palliative benefit
Subpial technique in supratentorial glioma resection: state of the art and analysis of costs and effectiveness in a single institute experience
No full textMany neurosurgeons advocate subpial technique as the best technique to remove supratentorial gliomas. However, few authors clearly defined advantages and features of this technique. The aim of our study is to describe microsurgical subpial technique related to glioma surgery, with regard to its safety and cost effectiveness
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
Brain metastases from renal cell carcinoma
No full textBrain metastasis is a major cause of morbidity and mortality in renal cancer patients. Treatment of metastatic renal cancer is difficult because most of RCCs are resistant to several therapeutic strategies: main studies support surgery as a therapeutic option in patients with good performance status, limited systemic disease, single brain metastasis but also in some patients with a limited number of metastases; on the other side, use of whole brain radiotherapy is still controversial
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
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