1,721,111 research outputs found
Variable polarisation compensator using artificial dielectrics for millimetre and submillimetre waves
No full textA variable polarisation compensator has been designed and demonstrated experimentally at 100 GHz. The device uses two silicon plates with interlocking artificial dielectric surfaces to produce a birefringence that varies with the separation distance. The experimental results indicate a maximum differential phase-shift of 74°, and show good agreement with computer simulation
Artificial dielectric devices for variable polarization compensation at millimeter and submillimeter wavelengths
Get PDFVariable polarization compensation has been demonstrated at 100 GHz. The device consists of two interlocking V-groove artificial dielectric gratings that produce a birefringence that varies with the separation distance. A maximum retardance of 74/spl deg/ has been obtained experimentally in a silicon device, in good agreement with rigorous coupled-wave computer simulations. Further simulations predict that adding quarter wave dielectric antireflection (AR) coatings to the outer surfaces of the device can reduce the insertion loss to below 4 dB. The use of rectangular grooved gratings provides increased retardance and reduced loss. It is predicted that a coupled device with rectangular grooved gratings will be capable of maximum retardance in excess of 180/spl deg/, with low insertion loss (<0.6 dB). The sensitivity of the wave retardation as a function of mechanical separation has a peak value of 485/spl deg//mm. The design and micromachining fabrication techniques scale for operation at submillimeter wavelengths
Controlling acoustic streaming in an ultrasonic heptagonal tweezers with application to cell manipulation
Get PDFAcoustic radiation force has been demonstrated as a method for manipulating micron-scale particles, but is frequently affected by unwanted streaming. In this paper the streaming in a multi-transducer quasi-standing wave acoustic particle manipulation device is assessed, and found to be dominated by a form of Eckart streaming. The experimentally observed streaming takes the form of two main vortices that have their highest velocity in the region where the standing wave is established. A finite element model is developed that agrees well with experimental results, and shows that the Reynolds stresses that give rise to the fluid motion are strongest in the high velocity region. A technical solution to reduce the streaming is explored that entails the introduction of a biocompatible agar gel layer at the bottom of the chamber so as to reduce the fluid depth and volume. By this means, we reduce the region of fluid that experiences the Reynolds stresses; the viscous drag per unit volume of fluid is also increased. Particle Image Velocimetry data is used to observe the streaming as a function of agar-modified cavity depth. It was found that, in an optimised structure, Eckart streaming could be reduced to negligible levels so that we could make a sonotweezers device with a large working area of up to 13 mm × 13 mm
Circuits and systems for biosensing with microultrasound
No full textUltrasound imaging is a well-established, noninvasive imaging modality used in many clinical procedures. New developments in high-resolution microultrasound are well suited to biosensing, including applications such as material characterisation, biometrics and chemical sensing. Electronic system design for ultrasound and microultrasound is most commonly associated with the use of piezoelectric transducers to generate and sense the ultrasonic pressure waves. This chapter covers the basics of ultrasound physics and piezoelectric transducers as well as their context within the larger field of biosensing. An example of an ultrasound imaging system is presented, and the availability and suitability of commercial solutions are discussed in comparison to individual approaches seen in the research domain. Finally, possible variations in ultrasound device characteristics are discussed, and the impact of these and overall system concerns on ASIC development is considered
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
A micromechanical beam-steering device for terahertz systems
Get PDFBeam-steering techniques are required to fully exploit terahertz imaging systems. We propose and model a device employing artificial dielectric techniques to provide a variable phase-control medium. The device consists of two interlocking artificial dielectric surfaces that are initially aligned parallel to each other. By mechanically introducing a relative tilt between the plates, a transmitted wave is subjected to a graded phase delay and thus the beam is steered away from the normal. Continuous and large steering angles are possible. We predict a practical device constructed from a silicon substrate could steer TE beams by up to 4.6 degrees
Efficient sensor for robust low-power design in nano-CMOS technologies
No full textConventional design methods add pessimistic safety margins to mitigate increased variability in scaled technologies that incur high power and performance losses. An efficient sensor design is presented that can significantly reduce design margins yet provide robust circuit operation. The proposed design uses the delay of the master latch of a conventional flip-flop to predetect timing failures and enable low-power error-free operation. HSPICE simulation of a 45 nm 16 x 16 carry save multiplier indicates a 37% reduction in the total power consumption for the proposed design compared to a conventional worst case design when subjected to high statistical variability. Similarly, gate level simulations show a 26% reduction in the total power consumption of a 32 nm 32-bit carry select adder when subjected to temperature variation
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