1,721,281 research outputs found
Correlation among structural, electrical, and deep-level properties of Fe centers implanted in InP
No full textThe Fe-related properties in high-temperature Fe implanted and annealed InP were studied by means of PIXE-RBS-channeling and correlated with the results of electrical (current-voltage) measurements. It is found that the point defect mobility, the concentration of substitutional Fe, and the resistivity of the implanted layer, all follow a similar temperature behavior. For annealing temperatures higher than 500degreesC semi-insulating behavior controlled by the Fe2+ deep levels is observed
Breast MR with special focus on DW-MRI and DCE-MRI
No full textThe use of magnetic resonance imaging (MRI) for the assessment of breast lesions was first described in the 1970s;
however, its wide application in clinical routine is relatively recent. The basic principles for diagnosis of a breast lesion
rely on the evaluation of signal intensity in T2-weighted sequences, on morphologic assessment and on the evaluation
of contrast enhancement behaviour. The quantification of dynamic contrast behaviour by dynamic contrast-enhanced
(DCE) MRI and evaluation of the diffusivity of water molecules by means of diffusion-weighted MRI (DW-MRI) have
shown promise in the work-up of breast lesions. Therefore, breast MRI has gained a role for all indications that could
benefit from its high sensitivity, such as detection of multifocal lesions, detection of contralateral carcinoma and in
patients with familial disposition. Breast MRI has been shown to have a role in monitoring of neoadjuvant chemotherapy,
for the evaluation of therapeutic results during the course of therapy. Breast MRI can improve the determination
of the remaining tumour size at the end of therapy in patients with a minor response. DCE-MRI and DW-MRI
have shown potential for improving the early assessment of tumour response to therapy and the assessment of residual
tumour after the end of therapy. Breast MRI is important in the postoperative work-up of breast cancers. High
sensitivity and specificity have been reported for the diagnosis of recurrence; however, pitfalls such as liponecrosis
and changes after radiation therapy have to be carefully considered
Excitation and nonradiative deexcitation processes of Er3+ in crystalline Si
No full textA detailed investigation on the excitation and deexcitation processes of Er3+ in Si is reported. In particular, we explored Er pumping through electron-hole pair recombination and Er deexcitation through Auger processes transferring energy to either free or bound electrons and holes. Since Er donor behavior would result in a free-carrier concentration varying along its profile, experiments have been performed by embedding the whole Er profile within previously prepared n-doped or p-doped regions. Multiple P (B) implants were performed in n-type (p-type) Czochralski Si samples in order to realize uniform dopant concentrations from 4 x 10(16) to 1.2 x 10(18)/cm(3) at depths between 0.5 and 2.5 mu m below the surface. These samples have been subsequently implanted with 4 MeV 3.3 x 10(13) Er/cm(2) and annealed at 900 degrees C for 30 min. Free electrons or holes concentrations in the region where Er sits were measured by spreading resistance profiling. It has been found that the release of electrons or holes from shallow donors and accepters, occurring at temperatures between 15 and 100 K, produces a strong reduction of both time decay and luminescence intensity at 1.54 mu m. These phenomena are produced by Auger deexcitation of the Er3+ intra-4f electrons with energy transfer to free carriers. The Auger coefficient of this process has been measured to be C-A similar to 5 x 10(-13) cm(3) s(-1) for both free electrons and free holes. Moreover, at 15 K (when the free carriers are frozen and the donor and acceptor levels occupied) the Er3+ time decay has been found to depend on the P (or B) concentrations. This is attributed to an impurity Auger deexcitation to electrons (or holes) bound to shallow donors (accepters): the efficiency of this process has been determined to be two orders of magnitude smaller with respect to the Auger deexcitation with free carriers. Furthermore, at temperatures above 100 K a nonradiative back-transfer decay process, characterized by an activation energy of 0.15 eV, is seen to set in for both p-type and n-type samples. This suggests that the back-transfer process, which severely limits the high-temperature luminescence efficiency, is always completed by a thermalization of an electron trapped at an Er-related level to the conduction band. Finally, by analysis of the pump power dependence of time decay and luminescence yield at 15 K, we have found that excitation of Er through the recombination of an electron-hole pair is a very efficient process, characterized by an effective cross section of 3 x 10(-15) cm(2) and able to provide an internal quantum efficiency as high as 10% at low temperatures (15 K) and pump powers (below 1 mW). This efficiency is significantly reduced when, at higher temperatures and/or high pump powers, strong nonradiative decay processes set in. These phenomena are investigated in detail and their impact on device operation perspectives are analyzed and discussed. [S0163-1829(98)01008-X]
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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