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Luminous-flux measurements by an absolute integrating sphere
No full textWe present an original implementation of the absolute-sphere method recently proposed by Ohno. The luminous-flux unit, the lumen, is realized by means of an integrating sphere with an opening calibrated by a luminous-intensity standard placed outside. The adapted experimental setup permits one to measure luminous-flux values between 5 and 2500 lm with a significant improvement with respect to the simulated performances reported in the literature. Traditionally, the luminous-flux unit, the lumen, is realized by goniophotometric techniques in which the luminous-intensity distribution is measured and integrated over the whole solid angle. Thus sphere results are compared with those obtained with the Istituto Elettrotecnico Nazionale goniophotometer. In particular, a set of standards, characterized by luminous-flux values of ~2000 lm, has been calibrated with both techniques. We highlight some of the problems encountered. Experimental results show that the agreement between the two methods is within the estimated uncertainty and suggest promising areas for future research
EXPERIMENTAL EVIDENCE THAT THE ALIGNMENT IN NEMATIC LIQUID CRYSTALS CAN BE DUE TO THE SURFACE-POLARIZATION
No full textLarge area and high sensitivity a-Si:H/a-SiC:H based detectors for visible and ultraviolet light
No full textIn this article we discuss the fabrication and performance of a-Si:H/a-SiC:H based ultraviolet
sensitive devices. They were deposited over a large area (10 cm310 cm) in p-i-n configuration
using a new, multichamber, ultrahigh vacuum plasma enhanced chemical vapor deposition facility.
The intrinsic layer thickness was 10–100 nm. The devices were characterized in the spectral range
365–660 nm and showed good sensitivity in the UV ~365 nm!. A good rejection of visible light was
also measured. Responsivity as high as 0.30 A/W was measured at 365 nm for samples where the
p layer and i layer were 5 and 10 nm thick, respectively. The linearity of the photogenerated current
as a function of photon flux was measured. It was found that over an area of 25 cm 2 the uniformity
was within 15%. Using a laser ~200 mW at 351 and 363 nm! the aging characteristics were
measured and showed a 25% decrease in responsivity after the absorption of 105 J cm22 under
operating conditions
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
Surface polarization effect in the alignment of nematic liquid-crystals
No full textThe change in the orientation of nematic liquid crystals due to the increase of the sample thickness is experimentally analysed. The data show that the phenomenon is a critical one, typical of a second order phase transition. The change in the surface polarization induced by a selective ion-adsorption on the two boundary solid substrates is proposed as the cause of the observed facts and discussed. The considered model is correct for angles of tilt small with respect to the initial homeotropic alignment, and the theoretical curves fit both the interferometric and the voltage-threshold data. A few comments on the obtained results are reported
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
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