1,720,984 research outputs found
Frequency stabilization of a diode laser on the Cs D-2 resonance line by the Zeeman effect in a vapor cell
No full textHyperfine optical pumping of a Cs-vapor cell through a diode laser in frequency standards requires a high purity of the laser emission spectrum, and a high stability of the emission frequency. We present here a frequency-locking scheme that is able to produce a discrimination signal without any modulation, by using the dichroism induced by a magnetic field on the atomic vapor. The larger line-width of the reference signal (Doppler-broadened) is compensated by its larger amplitude, when compared with the saturated absorption signal. As a final result, the slope is similar, and the large line-width warrants a large locking range, making robust the lock against external perturbations. This error signal is used to lock the frequency of an external cavity diode laser, with a grating reflector in Littman configuration. A fast correction band is obtained by changing the cavity length through an intra-cavity electro-optic modulator. The possible sources of instabilities of the locking point are discussed and estimated through a simulation computer program
Effect of Picosecond Postirradiation on Colloidal Suspensions of Differently Capped AuNPs
No full textFifth generation ethylendiamine-core poly(amidoamine) (PAMAM-G5) and poly(ethyleneimine) capped gold nanopartides were prepared by picosecond laser ablation in water, by using the fundamental wavelength of a picosecond Nd:YAG laser. The role of PAMAM-G5 inner cavities in the processes of photofragmentation of the nanoparticles by postirradiation with the second or third harmonic from the same laser is assessed through comparison of the experimental results obtained with the two stabilizers and the shot-by-shot theoretical modeling of the photo-bleaching process. We also show how thorough bleaching of the suspensions by postirradiation with 532 nm causes a strong increase of their fluorescence emission. Such fluorescence, which cannot be attributed to new fluorescent species, such as gold quantum dots, is due to a strong enhancement of the Intrinsic emission bands of both stabilizers and is related to formation of gold subnanometer fragments and their subsequent interactions with the molecular compounds
Sensitive and robust second-harmonic interferometer for measuring the dispersion of the electro-optic coefficients in the bulk materials
No full textTowards the optimization of double-pulse LIBS underwater: effects of experimental parameters on the reproducibility and dynamics of laser-induced cavitation bubble
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Sensitive and robust second-harmonic interferometer for measuring the dispersion of the electro-optic coefficients in bulk materials
No full textSecond-harmonic interferometry (SHI) is proposed for measuring the electro-optic (EO) coefficients of massive media. It combines the advantages of interferometric techniques with the mechanical stability of single-beam methods, simultaneously skimming the wavelength dispersion of the EO response. For demonstrating the effectiveness of the SHI technique, the EO coefficients rT33 and rT13 of the EO crystal lithium niobate are measured simultaneously at 1064 and 532 nm
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
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