9,521 research outputs found
An active viscoelastic metamaterial for isolation applications
No full textMetamaterials are of interest due to their ability to produce novel acoustic behaviour beyond that seen in naturally occurring media. Of particular interest is the appearance of band gaps which lead to very high levels of attenuation within narrow frequency ranges. Resonant elements within metamaterials allow band gaps to form within the long wavelength limit at low frequencies where traditional passive isolation solutions suffer poor performance. Hence metamaterials may provide a path to high performance, low frequency isolation. Two metamaterials are presented here. An acoustic material consisting of an array of split hollow spheres is developed, and its performance is validated experimentally. The application of an acoustic/mechanical analogy allows the development of an elastodynamic metamaterial that could be employed as a high performance vibration isolator at low frequencies. A prototype isolator is manufactured, and its performance is measured. The passively occurring band gap is enhanced using an active control architecture. The use of the active control system in conjunction with the natural passive behaviour of the metamaterial enables high levels of isolation across a broad frequency range. An eventual goal of the work is to produce such materials on a small scale, and as such the metamaterials developed are designed for, and produced using, additive layer manufacturing technique
An active viscoelastic metamaterial with enhanced band gap properties
No full textMetamaterials have been the subject of significant interest over the past decade due to their ability to produce novel acoustic behaviour beyond that seen in naturally occurring media. Of particular interest is the appearance of band gaps which lead to very high levels of attenuation across the material within narrow frequency ranges. Unlike traditional periodic materials which have been employed at high frequencies, the resonant elements within metamaterials allow band gaps to form within the long wavelength limit. It is at low frequencies where it is most difficult to design satisfactory passive isolation solutions, and hence metamaterials may provide a useful path to high performance, low frequency isolation. A locally resonant, periodic metamaterial is presented that could be employed as a high performance vibration isolator at low frequencies. The passively occurring band gap is enhanced using an active control architecture. The use of the active control system in conjunction with the natural passive behaviour of the metamaterial enables high levels of isolation across a broad frequency range. An eventual goal of the work is to produce such materials on a small scale, and as such the metamaterial developed has been designed for, and produced using, additive layer manufacturing techniques
Matthew Henry: The Bible, Prayer, and Piety – A Tercentenary Celebration
No full textThe summer of 2014 marked the tercentenary of the death of Matthew Henry (1662–1714), a leading figure among early eighteenth-century Dissenters and author of the six-volume Exposition of the Old and New Testaments (1707–1714/25). This monumental work, which by 1855 had already been published in twenty-five different editions, attempted a peculiarly practical approach to the biblical text and continues to be widely used and readily accessible even today in both print and online versions. The theme of foreign (or ‘strange’) wives and Israelite intermarriage is one which occurs throughout the Hebrew Bible and, accordingly, throughout Matthew Henry’s commentary upon it. Where it appears, the practice of intermarriage is characterized by Henry as (at best) unwise and (at worst) a very real threat to both social and religious cohesion. This essay explores how Henry deals with the issue of ‘strange wives’, why he believes they continue to pose a threat, and (in view of the overall intention of his commentary) what ‘practical observations’ he offers to his reader as a result. In doing so it is argued that Henry’s commentary traces a thematic thread from the ante-diluvian age to the post-exilic period of calamities resulting from mixed marriages between ‘professors of religion’ and their ‘strange wives’
Active elastic metamaterials with applications in vibration and acoustics
No full textElastic metamaterials provide a new approach to solving existing problems in vibration and acoustics. They have also been associated with novel concepts such as acoustic invisibility and subwavelength imaging. To be applied to many of the proposed applications a metamaterial would need to have the desired mass density and elastic moduli over a prescribed frequency band. Importantly active metamaterials provide a degree of adaptability. This paper will focus on extending a previous theoretical concept to a more realistic experimental design. This will include a consideration of the problems which arise when the theory and simulation are developed into an experimental demonstration, including the role which the control system dynamics play in the achievable performance. The adaptability of the bandwidth in which the properties achieve their desired values will also be investigated
Performance and stability constraints of an active acoustic metamaterial
No full textMetamaterials are the subject of significant interest due to their ability to reproduce behaviour beyond what is possible with naturally occurring media such as the appearance of high levels of wave attenuation at specified frequencies, known as band gaps. These band gaps can be tuned to appear at low frequencies, providing isolation performance at long wavelengths where the performance of traditional passive isolation techniques is generally poor. However, due to the resonant nature of the band gaps they tend to only extend over a very narrow frequency range. The application of active control within a metamaterial structure can provide an effective solution to this since the natural material response can be modified to enable attenuation over a much broader frequency region. This paper presents an active acoustic metamaterial, consisting of an array of active Helmholtz resonators. An actuator embedded within the resonators is used with a feedback controller to regulate the velocity of the air within the neck of the resonator elements, thereby enhancing their natural performance. The attainable performance of such an active metamaterial, however, is constrained by the requirement to maintain closed loop stability and formal constraints are presented and illustrated in the paper. Constrained non-linear optimisation is then employed to design a practical feedback controller consisting of an FIR filter, and its performance analysed
Enhancing the band gap of an active metamaterial
No full textMetamaterials have been the subject of significant interest over the past decade due to their ability to produce novel acoustic behaviour beyond that seen in naturally occurring media. As well as their potential in acoustic cloaks and lenses, of particular interest is the appearance of band gaps which lead to very high levels of attenuation across the material within narrow frequency ranges. Unlike traditional periodic materials which have been employed at high frequencies, the resonant elements within metamaterials allow band gaps to form within the long wavelength limit; at low frequencies where it is most difficult to design satisfactory passive isolation solutions. Hence, metamaterials may provide a path to high-performance isolation at low frequencies. Passively these band gaps occur over a narrow bandwidth, however the inclusion of active elements provide a method for enhancing this behaviour and producing attenuation over a broad band. A new type of active viscoelastic metamaterial is presented that achieves double negativity and could be employed as a high-performance vibration isolator at low frequencies. A mathematical method for manipulating the band gap profile is developed and a prototype is produced. The passive band gap is confirmed in the laboratory, and then by applying active control using optimised feedback filters it is shown that the region at which attenuation occurs around the band gap could be greatly enhanced whilst retaining the peak passive band gap performance. The active metamaterial demonstrates that a unified design philosophy matching the best features of active and passive functionality can achieve high levels of attenuation over wide frequency bands
Controller architectures for optimum performance in practical active acoustic metamaterials
No full textOver the last decade there has been significant interest in the design and production of acoustic metamaterials with physical qualities not seen in naturally occurring media. Progress in this area has been stimulated by the desire to create materials that exhibit novel behaviour when subject to acoustic waves,such as negative refraction or the appearance of band gaps in the frequency response of the material. Proposed designs range from locally resonant phononic crystals to arrays of Helmholtz resonators within ducts and past research has investigated both passive and active materials. Much of the research into active acoustic metamaterials remains theoretical, therefore to determine whether such materials are physically realisable and of potentially practical use it is important to understand the physical constraints that may arise in a produced active metamaterial. In this paper a 1-dimensional active acoustic metamaterial derived from a passive, Helmholtz resonator based design is considered where the applied control forces produce controllable double negative behaviour. The physical dimensions and active forces required to achieve the desired novel behaviour are explored for different architectures and any trade-offs that might have to be considered when producing a practically useful active metamaterial are identifie
Citation expectations: are they realized? Study of the Matthew index for Russian papers published abroad
Get PDFWe consider the "Matthew effect" in the citation process which leads to reallocation (or misallocation) of the citations received by scientific papers within the same journals. The case when such reallocation correlates with a country where an author works is investigated. Russian papers in chemistry and physics published abroad were examined. We found that in both disciplines in about 60% of journals Russian papers are cited less than average ones. However, if we consider each discipline as a whole, citedness of a Russian paper in physics will be on the average level, while chemistry publications receive about 16% citations less than one may expect from the citedness of the journals where they appear. Moreover, Russian chemistry papers mostly become undercited in the leading journals of the field. Characteristics of a "Matthew index" indicator and its significance for scientometric studies are also discussed
In the wake of disaster : the Lake Carriers' Association, welfare capitalism, and Lake Erie's Black Friday Storm of 1916
No full textDr. Matthew Daley, Grand Valley State University professor of history, delivers a talk entitled "In the Wake of Disaster: The Lake Carriers' Association, Welfare Capitalism, and Lake Erie's Black Friday Storm of 1916." Daley talks about the shipping industry on the Great Lakes and about ships caught up in the October 20, 1916 storm. He explains how the industry was vertically integrated; corporations owned the iron mines, the ships and the steel mills. Daley gives a history of efforts by seamen to form labor unions and strategies used by the shipping companies to neutralize those efforts using a combination of force, intimidation and corporate paternalism. He explains how the Lake Carriers' Association functioned to effectively self regulate the industry. Daley answers questions from the audience. He is introduced by John Beck, Michigan State University Professor of Human Resources and Labor Relations. Part of the "Our Daily Work/Our Daily Lives" Brown Bag series sponsored by the MSU School of Human Resources and Labor Relations and the MSU Museum. Held at the MSU Museum
An Interview with Matthew Kaiser on Competition and Play
No full textAn Interview with Matthew Kaiser on Competition and Play, by Sean Scanlan. Matthew Kaiser, the author of The World in Play: Portraits of a Victorian Concept (Stanford UP, 2012) says that “[c]ompetition is the disease from which modern life suffers,” and that “[c]ompetition is the only cure” for this suffering. This contradictory pairing seems to get at the heart of his thesis: play, as a totalizing, umbrella-like concept, emanates from a host of philosophical, political, and scientific work produced by Victorians who posed many of their ideas of play in sports metaphors, competitive logics, and narratives of struggle. Kaiser goes beyond the dichotomy of competition and play/competition or play, by stating “I’m interested in the totalizing potential of both concepts, the way that play, or competition for that matter, swallows the world whole, becomes in the minds of so many people, the organizing principle of reality, whether of culture or nature or consciousness, or of all three.
- …
