1,720,961 research outputs found
Compositional effects on the optical and thermal properties of sodium borophosphate glasses
No full textA series of sodium borophosphate glasses of the composition (1-x)NaPO3-xB2O3 have been synthesised from Na2CO3, B2O3 and P2O5 and their optical and thermal properties investigated. The results show that refractive index (n) and glass transition temperature (Tg) show a maximum at about B/(B+P) = 0.6 while thermal expansion coefficient (α) and thermo-optic coefficient (dn/dT) change monotonically with the B/(B+P) ratio. These observations can be interpreted based on the incorporation of BO3 and BO4 units into the glass structural network
Two-die assembly for the extrusion of glasses with dissimilar thermal properties for fibre optic preforms
No full textExtrusion of a preform based on core and cladding glasses with different thermal properties is demonstrated. The core glass (50BaO-8B) exhibits refractive index of 1.594 and softening temperature of 650 °C. Due to the softer nature of the core glass compared to the cladding glass, a novel two-die assembly method is employed for extrusion. The results show that the core glass flows through the cladding glass and be extruded first before stabilising to enable the extrusion of a cane of core and cladding glasses
Compositional effects on the optical and thermal properties of potassium aluminophosphate glasses
No full textThe K2O–Al2O3–P2O5 glass system has been examined and various compositions have been melted. Their optical and thermal properties have been measured to assess their potential for athermalisation. The addition of alumina (Al2O3) increases the refractive index (n) and glass transition temperature (Tg) and decreases the thermal expansion coefficient (α), consequently leading to positive thermo-optic coefficient (dn/dT). In addition to thermal expansion, polarisability of the glass also affects dn/dT. Generally, glasses must exhibit negative dn/dT to counter thermal expansion, in order to have potential application in athermalisation
Optical and thermal properties of binary calcium phosphate and barium phosphate glasses
No full textBinary calcium phosphate and barium phosphate glasses corresponding to xCaO–(100-x)P2O5 and xBaO–(100-x)P2O5, respectively, have been prepared in the range of 20≤x≤50. Assessment of the optical and thermal properties reveal that refractive index (n) and glass transition temperature (Tg) show a minima while thermal expansion coefficient (α) and thermo-optic coefficient (dn/dT) change monotonically as the amount of modifying oxides, CaO and BaO, increase. α > 9 × 10-6/°C is required for the calcium phosphate and barium phosphate glasses to exhibit negative dn/dT
Thermo-optic coefficients of potassium alumino-metaphosphate glasses
No full textMetaphosphate compositions of the K2O–Al2O3–P2O5 system have been melted and their properties measured to assess their potential for athermalisation. The results show that the addition of alumina (Al2O3) increases the refractive index and glass transition temperature (Tg), decreases the thermal expansion coefficient (α) and leads to a more positive thermo-optic coefficient (dn/dT). Glasses must exhibit negative dn/dT as a requirement for athermalisation purposes
UV-written channel waveguides in Er<sup>3+</sup>-doped Bi<sub>2</sub>O<sub>3</sub>-based glass
No full textThe present paper describes the fabrication of optical channel waveguides in an Er3+-doped Bi2O3-based glass using direct laser writing with a UV beam at 244 nm. A buried positive refractive index change was achieved through this method and a description of the observed phenomena is given, based on optical and electron microscopy
Thulium-doped tellurite fiber amplifier
No full textGain in the S-band is demonstrated in a thulium-doped tellurite fiber amplifier using dual pump and bidirectional pumping schemes. Two pump schemes were employed: 795/1064 and 1047/1550 nm. The gain profile is broader than achieved in a fluoride fiber and overlaps with the C-band of the erbium-doped fiber amplifier. We reach a fiber-to-fiber gain of 11 dB and an internal gain of 35 dB
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
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