1,720,958 research outputs found
Fabrication of submicrometer high refractive index tantalum pentoxide waveguides for optical propulsion of microparticles
No full textDesign, fabrication, and optimization of tantalum pentoxide (Ta2O5) waveguides to obtain low-loss guidance at a wavelength of 1070 nm are reported. The high-refractive index contrast (Δn ~ 0.65, compared to silicon oxide) of Ta2O5 allows strong confinement of light in waveguides of submicrometer thickness (200 nm), with enhanced intensity in the evanescent field. We have employed the strong evanescent field from the waveguide to propel micro-particles with higher velocity than previously reported. An optical propelling velocity of 50 µm/s was obtained for 8 µm polystyrene particles with guided power of only 20 mW
Structured surface wetting of a PTFE flow-cell for terahertz spectroscopy of proteins
No full textWe have fabricated a terahertz compatible polytetrafluoroethylene (PTFE) based microfluidic flow-cell, in which terahertz time-domain spectroscopy of a range of concentrations of aqueous bovine serum albumin (BSA) was performed, demonstrating the device's suitability for future studies of biomolecular interactions. The novel combination of oxygen plasma treatments and milling was used to both increase and decrease the wettability of the channel and surrounding substrate (to superhydrophobic levels) respectively, producing a stark contrast in contact angles allowing surface tension effects to confine liquid in the channel. PTFE is a chemically inert, bio-compatible material with ideal spectroscopic properties at sub-millimetre wavelengths.</p
A thulium-doped tantalum pentoxide waveguide laser
No full textTm-doped Ta2O5 films, deposited on thermally oxidized silicon substrates, were etched to form rib waveguides. Optically pumped (793 nm) multimode lasing at 1.9 µm is demonstrated from bare facets, producing 24-mW output, 46% slope efficiency.</p
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
THz Spectroscopy of BSA in a Surface-Tension Confined Flow-Cell
No full textA novel combination of oxygen plasma treatments and machining was used to modify the surface wetting of polytetrafluorethylene (PTFE) to develop a terahertz compatible microfluidic flow-cell that confines aqueous samples with surface tension forces. By increasing the wettability of the water channel and creating superhydrophobic nanostructures on the surrounding substrate, a stark contrast in contact angles was produced that leads to the principle confinement effect. Terahertz time-domain spectroscopy (THz-TDS) was performed on a range of bovine serum albumin (BSA) concentrations, demonstrating the potential for using this chemically inert, bio-compatible material for investigating protein hydration dynamics with THz spectroscopy.</p
Fabrication and optimization of Tantalum Pentoxide waveguides for optical micro-propulsion
No full textDesign, fabrication and optimization of high refractive index (2.1 @ 1070 nm), sub-micron thickness (200 nm) Tantalum Pentoxide waveguides is reported. Optimization of fabrication parameters reduces the propagation loss to ~ 1 dB/cm @ 1070 nm for Ta2O5 waveguides. Ta2O5 waveguides were found to be stable for high power application with no significant absorption peaks over a large range of wavelengths (600-1700 nm). Ta2O5 waveguides provide high intensity in the evanescent field, which is useful for efficient optical propelling of micro-particles. We have employed Ta2O5 waveguide to propel polystyrene micro-particles with 50 µm/s velocity
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
Optical fiber nanowires and microwires: fabrication and applications
No full textMicrowires and nanowires have been manufactured by using a wide range of bottom-up techniques such as chemical or physical vapor deposition and top-down processes such as fiber drawing. Among these techniques, the manufacture of wires from optical fibers provides the longest, most uniform and robust nanowires. Critically, the small surface roughness and the high-homogeneity associated with optical fiber nanowires (OFNs) provide low optical loss and allow the use of nanowires for a wide range of new applications for communications, sensing, lasers, biology, and chemistry. OFNs offer a number of outstanding optical and mechanical properties, including (1) large evanescent fields, (2) high-nonlinearity, (3) strong confinement, and (4) low-loss interconnection to other optical fibers and fiberized components. OFNs are fabricated by adiabatically stretching optical fibers and thus preserve the original optical fiber dimensions at their input and output, allowing ready splicing to standard fibers. A review of the manufacture of OFNs is presented, with a particular emphasis on their applications. Three different groups of applications have been envisaged: (1) devices based on the strong confinement or nonlinearity, (2) applications exploiting the large evanescent field, and (3) devices involving the taper transition regions. The first group includes supercontinuum generators, a range of nonlinear optical devices, and optical trapping. The second group comprises knot, loop, and coil resonators and their applications, sensing and particle propulsion by optical pressure. Finally, mode filtering and mode conversion represent applications based on the taper transition regions. Among these groups of applications, devices exploiting the OFN-based resonators are possibly the most interesting; because of the large evanescent field, when OFNs are coiled onto themselves the mode propagating in the wire interferes with itself to give a resonator. In contrast with the majority of high-Q resonators manufactured by other means, the OFN microresonator does not have major issues with input-output coupling and presents a completely integrated fiberized solution. OFNs can be used to manufacture loop and coil resonators with Q factors that, although still far from the predicted value of 10. The input-output pigtails play a major role in shaping the resonator response and can be used to maximize the Q factor over a wide range of coupling parameters. Finally, temporal stability and robustness issues are discussed, and a solution to optical degradation issues is presented
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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