1,720,972 research outputs found
Ultrasonic microsystems for bacterial cell manipulation
No full textThis chapter introduces the concept of using ultrasound for the manipulation of small particles in fluids for in vitro systems, and in particular how this can be applied to bacterial cells in suspension. The physical phenomena that lead to this effect are discussed, including radiation forces, cavitation, and streaming, thus allowing an appreciation of the limitations and applicability of the technique. Methods for generating ultrasound are described, together with practical examples of how to construct manipulation systems, and detailed examples are given of the current practical techniques of particle manipulation. These include filtration of particles for both batch and continuous systems, concentration of particles, cell washing from one fluid into another, fractionation of cellular populations, and trapping of material against flow. Concluding remarks discuss potential future applications of ultrasonic technology in microfluidic bacterial analysis and predict that it will be a significant tool in cell sample processing, with significant integration potential for Lab-On-Chip technologies
Modelling for the robust design of layered resonators for ultrasonic particle manipulation
Full text linkSeveral approaches have been described for the manipulation of particles within an
ultrasonic field. Of those based on standing waves, devices in which the critical dimension of
the resonant chamber is less than a wavelength are particularly well suited to microfluidic, or
“lab on a chip” applications. These might include pre-processing or fractionation of samples
prior to analysis, formation of monolayers for cell interaction studies, or the enhancement of
biosensor detection capability.
The small size of microfluidic resonators typically places tight tolerances on the positioning
of the acoustic node, and such systems are required to have high transduction efficiencies, for
reasons of power availability and temperature stability. Further, the expense of many
microfabrication methods precludes an iterative experimental approach to their development.
Hence, the ability to design sub-wavelength resonators that are efficient, robust and have the
appropriate acoustic energy distribution is extremely important.
This paper discusses one-dimensional modelling used in the design of ultrasonic resonators
for particle manipulation and gives example of their uses to predict and explain resonator
behaviour. Particular difficulties in designing quarter wave systems are highlighted, and
modelling is used to explain observed trends and predict performance of such resonators,
including their performance with different coupling layer materials
An Ultrasonic MEMS Particle Separator with Thick Film Piezoelectric Actuation
No full textAn ultrasonic resonator has been microfabricated from layers of silicon and Pyrex. A fluid channel of approximately 200?m in depth is etched into the Pyrex and allows particles within the fluid to be moved by acoustic radiation forces into the pressure nodal planes of the ultrasonic standing wave. Depending on the required application this can be used to generate a particle-free fluid sample, to concentrate particles prior to analysis, or to move particles to a surface within the resonator to aid analysis. In previously published work this resonator has been driven using a thickness mode bulk piezoceramic. While this has provided reasonable performance, the adhesion of the piezoceramic plate to the silicon has proved both the least repeatable and the least reliable element of the fabrication process. It has also been a factor in the long-term failure of test devices. To overcome these issues, multilayer thickfilm printed actuators have been developed to replace the bulk piezoceramic. Thick-film processing offers an effective means of depositing active materials onto substrates, and the technique is compatible with the microfabrication process, allowing multiple actuators to be printed onto a wafer comprising multiple devices. A variety of structures has been tested on ceramic substrates and shown to provide acceptable acoustic outputs when compared with bulk transducers mounted on identical substrates. A two layer actuator provides a good performance without excessive complexity and this configuration has been used on the resonator. Further acoustic and flow modeling of the device is described, and this has been used both to improve the channel geometry and to select better operating conditions for the system. It is shown that the thick-film actuated device working at the new operating conditions provides significantly improved performance when compared with the bulk piezoceramic device, and in particular is able to offer a five-fold reduction in concentration for 1?m latex particles, which had previously proved difficult to manipulate successfully
Mode-switching: a new technique for electronically varying the agglomeration position in an acoustic particle manipulator
No full textAcoustic radiation forces offer a means of manipulating particles within a fluid. Much interest in recent years has focussed on the use of radiation forces in microfluidic (or “lab on a chip”) devices. Such devices are well matched to the use of ultrasonic standing waves in which the resonant dimensions of the chamber are smaller than the ultrasonic wavelength in use. However, such devices have typically been limited to moving particles to one or two predetermined planes, whose positions are determined by acoustic pressure nodes/anti-nodes set up in the ultrasonic standing wave. In most cases devices have been designed to move particles to either the centre or (more recently) the side of a flow channel using ultrasonic frequencies that produce a half or quarter wavelength over the channel, respectively.It is demonstrated here that by rapidly switching back and forth between half and quarter wavelength frequencies – mode-switching – a new agglomeration position is established that permits beads to be brought to any arbitrary point between the half and quarter-wave nodes. This new agglomeration position is effectively a position of stable equilibrium. This has many potential applications, particularly in cell sorting and manipulation. It should also enable precise control of agglomeration position to be maintained regardless of manufacturing tolerances, temperature variations, fluid medium characteristics and particle concentration
Micromanipulation of cells and particles using ultrasonic fields
No full textUltrasonic standing waves allow concentration, washing, fractionation, or trapping against a flow of cells in microfluidic environments and can potentially enhance biosensor performance
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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