1,720,999 research outputs found
Micro-Raman study of free standing porous silicon samples
No full textMicro-Raman spectroscopy has been employed for the characterization of a set of free-standing porous silicon samples with different degrees of porosity, fabricated by electrical anodization of n(+) Si wafers. A broadening and a shift toward lower energy of the transverse optical silicon phonon mode have been clearly observed, indicating the presence of nanometer-sized crystalline structures. In particular, higher porosity samples reveal an inhomogeneous structure characterized by a spread of the nanocrystal size as a function of the region under investigation. The photoluminescence properties of samples produced with similar fabrication parameters, displaying both a blue and a red band, seem to be in agreement with the nanocrystal dimensions derived through micro-Raman spectroscopy. (C) 1999 American Vacuum Society. [S0734-211X(99)07102-4]
Neutron sensing at spallation neutron sources by SERS
No full textNeutron detectors are paramount in many applications from medical science to homeland security and aerospace. A miniaturized solid-state device based on a nanostructured-gold thin film grown by pulsed laser ablation under deposition-controlled conditions and functionalized with a monolayer of 4-mercaptophenyboronic acid (4-MPBA) was fabricated as a neutron dose detector. The device is tested with slow neutron detection in the thermal and epithermal energy range at ISIS spallation neutron source (UK). After the neutron irradiation, 4-MPBA is converted into thiophenol (TP), and the chemical modification is monitored by the intensity of related vibrational bands at 1586 cm−1 (4-MPBA) and 1574 cm−1 (TP). The latter are used as a vibrational signature of the absorbed dose by surface-enhanced Raman spectroscopy (SERS). The conversion of 4-MPBA to TP is due to the loss of the boron-containing group after the absorption of a slow neutron by 10B isotope. The I1574/I1586 ratio is used to estimate the ratio of 10B nuclei absorption reactions due to the thermal and epithermal contributions and it is proposed for the development of neutron dosimetry for nuclear medicine, aerospace, and security applications
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
Electric-field-induced effects on the dipole moment and vibrational modes of the centrosymmetric indigo molecule
No full textIntense static electric fields can strongly perturb chemical bonds and induce frequency shifts of the molecular vibrations in the so-called vibrational Stark effect. Based on a density functional theory (DFT) approach, here, we report a detailed investigation of the influence of oriented external electric fields (OEEFs) on the dipole moment and infrared (IR) spectrum of the nonpolar centrosymmetric indigo molecule. When an OEEF as intense as ∼0.1 V Å-1 is applied, several modifications in the IR spectrum are observed. Besides the notable frequency shift of some modes, we observe the onset of new bands-forbidden by the selection rules in the zero-field case. Such a neat field-induced modification of the vibrational selection rules, and the subsequent variations of the peaks' intensities in the IR spectrum, paves the way toward the design of smart tools employing centrosymmetric molecules as proxies for mapping local electric fields. In fact, here, we show that the ratio between the IR and the Raman intensities of selected modes is proportional to the square of the local field. This indicator can be used to quantitatively measure local fields, not only in condensed matter systems under standard conditions but also in field-emitting-tip apparatus
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
On the role of the ablated mass on the propagation of a laser-generated plasma in an ambient gas
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