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Slippery when dry – Eliminating friction on the nanoscale
No full textThe present thesis is meant to be part of the research project ‘Slippery when dry –
Eliminating friction on the nanoscale’ from TU Delft 3mE PME department, leadered by W.
M. van Spengen and in cooperation with F. Buja.
Concerning the research project as a whole, MEMS/NEMS (micro-/nano-electromechanical
systems) are small, moving mechanical microstructures, like micromotors, accelerometers
and chemical sensors. Although there have been scientific and commercial successes,
reliability problems related to friction and wear prevent designers from taking full advantage
of this technology. In this project, we will use a two-pronged approach towards solving friction
and wear in MEMS: 1. the use of diamond-like carbon (DLC) coatings, and 2. films formed by
vapour phase lubrication (VPL). Some DLC films macroscopically show almost vanishing
friction (‘superlubricity’), which is not well understood. However, at the scale of MEMS,
superlubric DLC has not been demonstrated. VPL involves carbon-containing molecules that
condense between the contacting points of sliding surfaces and form a hard tribofilm. The
basic physical principles are believed to be the same for the tribological behaviour of both
DLC and VPL. It should be possible to induce superlubricity using VPL instead of DLC by
tailoring the molecular composition of the vapour. This would be the best of both worlds,
because VPL has the advantage over a DLC layer that it can be applied more easily in many
complex MEMS devices.
Since this research project requires making measurements with different devices in order to
understand the friction on the nanoscale, the present thesis will focus on the resolution of
such devices. Raman spectrometer and MEMS comb drive are examples of devices whose
noise level can be studied, although the noise background theory is applicable to other kind
of measurements.Outgoin
Slippery when dry – Eliminating friction on the nanoscale
No full textThe present thesis is meant to be part of the research project ‘Slippery when dry –
Eliminating friction on the nanoscale’ from TU Delft 3mE PME department, leadered by W.
M. van Spengen and in cooperation with F. Buja.
Concerning the research project as a whole, MEMS/NEMS (micro-/nano-electromechanical
systems) are small, moving mechanical microstructures, like micromotors, accelerometers
and chemical sensors. Although there have been scientific and commercial successes,
reliability problems related to friction and wear prevent designers from taking full advantage
of this technology. In this project, we will use a two-pronged approach towards solving friction
and wear in MEMS: 1. the use of diamond-like carbon (DLC) coatings, and 2. films formed by
vapour phase lubrication (VPL). Some DLC films macroscopically show almost vanishing
friction (‘superlubricity’), which is not well understood. However, at the scale of MEMS,
superlubric DLC has not been demonstrated. VPL involves carbon-containing molecules that
condense between the contacting points of sliding surfaces and form a hard tribofilm. The
basic physical principles are believed to be the same for the tribological behaviour of both
DLC and VPL. It should be possible to induce superlubricity using VPL instead of DLC by
tailoring the molecular composition of the vapour. This would be the best of both worlds,
because VPL has the advantage over a DLC layer that it can be applied more easily in many
complex MEMS devices.
Since this research project requires making measurements with different devices in order to
understand the friction on the nanoscale, the present thesis will focus on the resolution of
such devices. Raman spectrometer and MEMS comb drive are examples of devices whose
noise level can be studied, although the noise background theory is applicable to other kind
of measurements.Outgoin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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