1,721,049 research outputs found
Spin-Polarization transition inthe two dimensional electron gas
No full textWe present a numerical study of magnetic phases of the 2D electron gas near freezing. The calculations are performed by diffusion;Monte Carlo in the fu;ed-node approximation. At variance with the 3D case we find no evidence for the stability of a partially polarized phase. With plane wave nodes in the trial function, the polarization transition takes place at r(s) = 20, whereas the best available estimates locate Wigner crystallization around r(s) = 35. Using an improved nodal structure. featuring optimized backflow correlations. we confirm the existence of a stability range for the polarized phase, although somewhat shrunk, at densities achievable nowadays in 2-dimensional hole gases in semiconductor heterostructures. The spin susceptibility of the unpolarized phase at the magnetic transition is approximately 30 times the Pauli susceptibility
Spin effects in the 2D electron gas
No full textSpin affects the properties of the electron gas in a subtle way. The quantitative and, in fact, even the qualitative determination of spin dependent properties in this system requires calculations of extreme accuracy. Here, we review predictions of fixed-node diffusion Monte Carlo simulations with Slater-Jastrow as well as backflow nodes for the 2D electron gas at zero temperature, focusing on the spin-polarization dependence of the ground state energy and on the occurrence of spontaneous spin-polarization. We also analyze the enhancement of the spin susceptibility (with respect to the Pauli value), over a wide range of densities. Finally we discuss the form of effective electron-electron interactions that may be used to estimate the possibility of spontaneous superconductivity in the 2D electron gas. (C) 2001 Elsevier Science Ltd. All rights reserved
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
Ettore Majorana a Napoli: la testimonianza dell’allieva Gilda Senatore
No full textGilda Senatore seguì come studentessa il corso di Fisica Teorica che Ettore Majorana, a seguito della nomina a professore ordinario presso la Regia Università di Napoli, svolse tra il 13 Gennaio e la fine di Marzo del 1938 (prima di scomparire in circostanze non ancora chiarite). A lei Majorana lasciò un gruppo di fogli manoscritti, che ora sono depositati presso la Domus Galileiana di Pisa e che sono stati riprodotti nel volume E. Majorana, Lezioni all'Università di Napoli. In questo lavoro è riportata una testimonianza di questa allieva di Majorana che riguarda sia il corso di Fisica Teorica, sia i fogli manoscritti, e che fa piena chiarezza sul numero e sul nome di coloro che erano presenti alle lezioni. Per motivi di completezza, la testimonianza è accompagnata da un nota (a cura di F. Guerra e N. Robotti) sull'attività scientifica e accademica di Majorana, comprensiva anche di un elenco aggiornato delle sue pubblicazioni
Analisi di impatto sul budget di WatchmanTM, dispositivo per la prevenzione tromboembolica nei pazienti con fibrillazione atriale
No full textAtrial fibrillation (AF) is a chronically progressing arrhythmia and an independent risk factor for stroke, leading to a five-fold increased risk of stroke. The available options for stroke prophylaxis are anticoagulant oral drugs, which include warfarin, used in stroke for several decades, the new generation of anticoagulant drugs (Xa inhibitors and direct thrombin inhibitors), anti-platelet drugs, generally recommended for patients in whom anticoagulants are contra-indicated, and left atrial appendage closure technologies implanted via a catheter-based delivery system, including WatchmanTM.
The objective of this research is to estimate the 5-year budget impact for the Italian hospitals funded by the Italian National Health Service adopting WatchmanTM, comparing two scenarios: Scenario A, without the device, and Scenario B, with the device. A Budget Impact Model has been designed adopting a cohort approach, i.e. considering the whole eligible population and assessing the net impact of WatchmanTM (Scenario B versus Scenario A) on health care expenditure. The model has been populated with the relevant data, including the eligible population, the present and future prescribing mix—according to a clinical panel—the cost of the procedure, the cost of pharmacological therapies, follow-up costs, and the effects of thromboembolism and ictus.
The eligible population is represented by patients with non-valvular atrial fibrillation, who are less than 85 years old and with a CHADS2 score ≥1. The budget impact has been firstly estimated for a sub-population of patients with atrial fibrillation, i.e. patients contraindicated or intolerant for chronic anticoagulant therapy. In fact, both the European and Italian Guidelines on atrial fibrillation management strongly support the use of left atrial occlusion in those patients who cannot be treated with this class of drugs. Then, the budget impact analysis has been performed for the overall eligible population of patients with atrial fibrillation.
In the base-case, where data from clinical trials were used, if patients with high thromboembolic risk and contraindications to the use of long-term oral anticoagulant therapy are considered, the device would imply 145 million Euro savings in 5 years compared to treatment with antiplatelet drugs. A break-even point, when the cumulative costs of Scenario A (without the device) outbalance costs of Scenario B (with the device), is reached at the fifth year. The 5-year cumulative cost for Scenario A is over 3.1 billion Euros, while the same cost for Scenario B is under 3.0 billion Euros.
When all eligible patients are included in the model, Scenario B (with WatchmanTM) would imply an additional cumulative cost of 95 million Euros in 5 years. The break-even point is reached at the seventh year, with the 5-year cumulative cost for Scenario A over the period close to 6.0 billion Euros, while for Scenario B this cost approximates 6.1 billion Euros.
Using preliminary and more favourable data on the post-marketing risk-benefit profile of WatchmanTM, additional costs before the break-even point and savings after the break-even are, respectively, lower and higher than in the base-case.
The budget impact analysis should be integrated with a cost-effectiveness analysis, to make decisions based on both value for money and long-term sustainability. Cost-effectiveness would incorporate the circumstance that WatchmanTM shows, if evidence from single trials is considered, a better profile with regard to overall mortality. A recent study shows that the Left Atrial Appendage (LAA) closure technology has, in comparison with warfarin, a lower cost per QALY than dabigatran versus warfarin
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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