1,721,137 research outputs found
Ultrafast relaxation of photoexcited carriers in semiconductor quantum wires: A Monte Carlo approach
Full text linkA detailed analysis of the cooling and thermalization process for photogenerated carriers in semiconductor quantum wires is presented. The energy relaxation of the nonequilibrium carrier distribution is investigated for the ‘‘realistic'' case of a rectangular multisubband quantum-wire structure. By means of a direct ensemble Monte Carlo simulation of both the carrier and the phonon dynamics, all the nonlinear phenomena relevant for the relaxation process, such as carrier-carrier interaction, hot-phonon effects, and degeneracy, are investigated. The results of these simulated experiments show a significant reduction of the carrier-relaxation process compared to the bulk case, which is mainly due to the reduced efficiency of carrier-carrier scattering; on the contrary, the role of hot-phonon effects and degeneracy seems to be not so different from that played in bulk semiconductors
An investigation of carrier dynamics in semiconductor quantum wires following femtosecond laser excitation
No full textA Monte Carlo analysis of the carrier relaxation dynamics in a GaAs quantum wire system following laser photoexcitation is presented. Relaxation mechanisms due to electron-electron and electron-polar optical phonon interaction are included within a multisubband picture taking into account both intrasubband and intersubband scattering mechanisms for the case of rectangular quantum wire structures. Degeneracy and hot-phonon effects are also investigated as a function of carrier density and kinetic energy
Thermalization of Photoexcited Carriers in Bulk and Quantum Wire Semiconductors
No full textA theoretical study of the internal thermalization of high-energy carriers created by laser excitation in bulk and quantum wire semiconductors is presented. For the bulk case the results of our Monte Carlo simulation are compared to luminescence up-conversion experiments used to monitor the spectral and temporal evolution of the photoexcited carrier distributions with a time resolution of about 100 fs. The agreement between theory and experiment is very good and shows that the Coulomb interaction among carriers is responsible for the initial ultrafast thermalization. On the contrary, a much slower thermalization is found theoretically in quantum wires, which can be mainly attributed to the reduced efficiency of intersubband processes and to the reduced effect of electron-electron intrasubband scattering. Available experiments seem to confirm such findings
Exogenous administration of microsomes-associated alpha-synuclein aggregates to primary neurons as a powerful cell model of fibrils formation
Full text linkFor years, the inability of replicating formation of insoluble alpha-synuclein (αS) inclusions in cell cultures has been a great limitation in the study of αS aggregation in Parkinson's Disease (PD). Recently, the development of new animal models through the exogenous inoculation of brain extracts from diseased αS transgenic mice or PD patients has given new hopes to the possibility of creating more adequate cell models of αS aggregation. Unfortunately, when it comes to cells in cultures, administration of raw brain extracts has not proven as successful as in mice and the source of choice of exogenous aggregates is still in vitro preformed αS fibrils. We have developed a method to induce the formation of intracellular αS inclusions in primary neurons through the exogenous administration of native microsomes-associated αS aggregates, a highly toxic αS species isolated from diseased areas of transgenic mice. This fraction of αS aggregates that is associated with the microsomes vesicles, is efficiently internalized and induces the formation of intracellular inclusions positive for aggregated and phosphorylated αS. Compared to in vitro-preformed fibrils which are made from recombinant αS, our method is faster and guarantees that the pathogenic seeding is made with authentic αS aggregates extracted from diseased animal models of PD, mimicking more closely the type of inclusions obtained in vivo. As a result, availability of tissues rich in αS inclusions is mandatory. We believe that this method will provide a versatile cell-based model to study the microscopic aspects of αS aggregation and the related cellular pathophysiology in vivo and will be a starting point for the creation of more accurate and sophisticated cell paradigm of PD
Una tomba di alto rango dell'VIII secolo a.C. da San Marzano sul Sarno
No full textViene pubblicato un importante corredo funerario aristocratico dell'VIII secolo a.C. ritrovato a San Marzano sul Sarno. Grazie a nuovi dati emersi da questo contesto vengono messi a fuoco alcuni rilevanti fenomeni storici, tra cui l'affermazione di una cultura internazionale tra le élites indigene dell'VIII secolo a.C., e l'esistenza di relazioni di scambio intrattenute dai principi indigeni della Valle del Sarno con i Greci e in particolare con Pitecusa fin dal terzo quarto dell'VIII secolo a.C
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
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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