1,720,963 research outputs found
Transient contact opening forces in a MEMS switch using Au/MWCNT composite
No full textMost failures in micro electromechanical system (MEMS) switches can be attributed to the degradation of contact surfaces and sticking contacts. A wear-tolerant composite contact material, composed of a Au film supported by multi walled carbon nanotubes (Au/MWCNT), has been engineered to provide wear resistance and enhanced switching lifetime with conductive properties close to pure Au. Switching lifetimes of billions of cycles have been demonstrated, representing greatly increased performance over thin film Au. Below the arcing threshold (~12 V) the wear mechanism has been shown to be a combination of the fine transfer of contact material by the molten metal bridge (MMB) phenomenon and a delamination of the Au. In this study, the composite contact is hot switched at low current DC conditions (4 V DC and 20 mA) while the contact force is measured at the micro Newton scale in nanosecond resolution. The characteristic voltage waveform associated with the MMB is observed with forces detected as the contact softens, melts, and separates. The presence of a delamination event (DE) is also observed, where the contact opens abruptly with no MMB phenomenon apparent. The DE contact openings are associated with a transient peak force of 21.6 ± 2.3 µN while the MMBs are linked to a lower peak force of 18.1 ± 2.5 µN
Puite indian, [sic] Chief Bull Tom
No full textPaiuteNative American (Paiute) man identified as Chief Bull Tom is seated on a wooden chair out of doors. He wears light and dark feathers attached to a headband with a beaded rosette in the front, a kerchief, white shirt, a pelt across his shoulder with feathers and silver, and a wool vest and pants
3D surface roughness of a partial free form dental surface after enamel loss due to acidic erosion using optical and X-Ray CT metrology
No full textA partial human natural unprocessed dental sample was submerged in Citric Acid (0.3% pH.3.2), for 1 hour, without agitation, over a selected region (diameter 1.5 mm). The sample was measured using the TaiCaan XYRIS 2020 H instrument “before and after” the test and measured using X-Ray CT (XCT) in the “after” condition, for direct comparison with the optical measurement. The analysis of the sample was conducted using a 80 µm 3D gaussian filter to remove the surface form while maintaining the surface roughness. The 3 surfaces were compared and co-located to allow comparison of 3D surface roughness (Sa). A square region (0.6 x 0.6 mm) of the surface is segmented into 16 measurement regions (0.15 x 0.15 mm) and the roughness of each region compared. Results demonstrate that the “after” optical measurement shows a reduction of surface roughness proportional to the initial roughness of the surface. A comparison with the “after” XCT indicates a similar result to the optical data with a further reduction in roughness values when compared to the optical. We show that XCT generated surface data can be used to measure the surface changes on free form surfaces
Experimental study of arc motion near splitter plates in low voltage switching devices
No full textSwitching performance of a low-voltage switching device (LVSD) is determined by limiting current and stopping re-ignition. This is strongly influenced by how the arc moves inside the LVSD quenching chamber during the switching process. Improved switching performance is achieved when the arc quickly enters and stays inside the splitter plates of the LVSD, with the arc attached to the surface of the plates. This article studies arc motion around splitter plates in LVSDs and the correlation with arc voltage. Arc motion is investigated using a high-speed optical arc imaging system (AIS). It is observed that the arc fluctuates as it enters the splitter plates, with periods inside the plates followed by sudden re-strikes of the arc roots outside the plates. The AIS system allows the measurement of arc displacement and a correlation with the arc voltage. The results show two phases, with a narrow correlation while the arc in the chamber out of the splitter plates and a distributed correlation while in the splitter plates. Further, a new performance parameter the splitter time (ST) ratio is defined. The influence of the ST ratio on the chamber vent design is investigated. It is found that with wider and well-distributed vent apertures, the ST ratio is higher than with a closed vent, and arc motion on entry to the plates is improved.</p
Volumetric erosion of a structured electrical contact surface using X-Ray Computed Tomography
No full textThe use of 3D optical scanning methods is well established for the evaluation of volumetric wear on electrical contact surfaces. A longstanding limitation of these methods has been the accuracy to which the underlying form of the surface prior to the wear process is determined. Electrical contact surfaces are never perfectly flat, in many applications the underlying surface is nominally spherical or a freeform surface. This paper introduces newly developed methodes to enhance the capability of resolving volumetric wear on a surface with complex shape (form). These methods are applicable to a wide range of applications, but the focus here is on arcing elec-trical contacts. The paper investigates wear on a nominally spherical AgNi contact used in low voltage switch-ing applications and compares this to the wear on a surface modified using electron beam process to create a highly structured surface; under the same switching conditions. The spherical contact is analysed using a new 3D optical metrology solution using a data fusion method, which combines both metrology data and surface photographic image data. The 3D optical scanning data is then compared with surface data from X-Ray comput-ed tomography (X-CT) of the structured electrical contact surface
The effective resistivity of dissimilar contact materials using an automated MEMS switching test platform.
No full textAn automated in-situ contact evolution (ICE) apparatus is used to study contact performance for a low contact force (<1 mN) MEMS switching application. The ICE system uses a metrology frame to combine the controlled switching of surfaces with the ability to measure the surface changes in-situ. After a defined number of switching cycles, the surfaces are separated within the metrology frame and measured, then replaced to the same physical location with a precision of 50 nm to continue the switching process. In this study the contact force, resistance relationship is investigated for the evaluation of the effective resistivity of a dissimilar surface combination. In the study a Gold coated hemisphere (radius 1 mm) is used with a Gold Coated (500 nm), multiwalled forest of vertically aligned carbon nanotubes (50 μm), referred to as Au/CNT. In this work we consider the measurement of effective resistivity by the ICE system and 3 other methods, using a nano-indentation system as a reference
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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