841 research outputs found
Acoustic scattering from an infinitely long cylindrical shell with an internal mass attached by multiple axisymmetrically distributed stiffeners
No full textA thin infinitely long elastic shell is stiffened by J in number identical lengthwise ribs distributed uniformly around the circumference and joined to a rod in the center. The 2D model of the substructure is a rigid central mass supported by J axisymmetrically placed linear springs. The response of the shell-spring-mass system is quite different from a fluid filled shell or that of a solid cylinder due to the discrete number of contact points which couple the displacement of the shell at different locations. Exterior acoustic scattering due to normal plane wave incidence is solved in closed form for arbitrary J. The scattering matrix associated with the normal mode solution displays a simple structure, composed of distinct sub-matrices which decouple the incident and scattered fields into J families. The presence of a springs-mass substructure causes resonances which are shown to be related to the subsonic shell flexural waves, and an approximate analytic expression is derived for the quasi-flexural resonance frequencies. Numerical simulations indicate that the new solution for three or more springs results in a complicated scattering response for plane wave incidence. As the number of springs becomes large enough, the total scattering cross-section is asymptotically zero at low frequencies and slightly increased compared to the empty shell at moderate frequencies due to the added stiffness and mass. It is also observed that the sensitivity to the angle of incidence diminishes as the number of springs is increased. This system can be tuned by selecting the shell thickness, spring stiffness and added mass to yield desired quasi-static effective properties making it a candidate element for graded index sonic crystals
Acoustic scattering from an infinitely long cylindrical shell with an internal mass attached by multiple axisymmetrically distributed stiffeners
No full textA thin infinitely long elastic shell is stiffened by J in number identical lengthwise ribs distributed uniformly around the circumference and joined to a rod in the center. The 2D model of the substructure is a rigid central mass supported by J axisymmetrically placed linear springs. The response of the shellspring-mass system is quite different from a fluid filled shell or that of a solid cylinder due to the discrete number of contact points which couple the displacement of the shell at different locations. Exterior acoustic scattering due to normal plane wave incidence is solved in closed form for arbitrary J. The scattering matrix associated with the normal mode solution displays a simple structure, composed of distinct sub-matrices which decouple the incident and scattered fields into J families. The presence of a springs-mass substructure causes resonances which are shown to be related to the subsonic shell flexural waves, and an approximate analytic expression is derived for the quasi-flexural resonance frequencies. Numerical simulations indicate that the new solution for J ≥ 3 springs results in a complicated scattering response for plane wave incidence. As the number of springs becomes large enough, the total scattering cross-section is asymptotically zero at low frequencies and slightly increased compared to the empty shell at moderate frequencies due to the added stiffness and mass. It is also observed that the sensitivity to the angle of incidence diminishes as the number of springs is increased. This system can be tuned by selecting the shell thickness, spring stiffness and added mass to yield desired quasi-static effective properties making it a candidate element for graded index sonic crystals.Peer reviewed"Received 9 October 2013, Revised 18 July 2014, Accepted 24 October 2014, Available online 25 November 2014."--Publisher's website
Tunable cylindrical shell as an element in acoustic metamaterial
No full textElastic cylindrical shells are fitted with an internal mechanism which is optimized so that, in the quasi-static regime, the combined system exhibits prescribed effective acoustic properties. The mechanism consists of a central mass supported by an axisymmetric distribution of elastic stiffeners. By appropriate selection of the mass and stiffness of the internal mechanism, the shells effective acoustic properties (bulk modulus and density) can be tuned as desired. Subsonic flexural waves excited in the shell by the attachment of stiffeners are suppressed by including a sufficiently large number of such stiffeners. Effectiveness of the proposed metamaterial is demonstrated by matching the properties of a thin aluminum shell with a polymer insert to those of water. The scattering cross section in water is nearly zero over a broad range of frequencies at the lower end of the spectrum. By arranging the tuned shells in an array the resulting acoustic metamaterial is capable of steering waves. As an example, a cylindrical-to-plane wave lens is designed by varying the bulk modulus in the array according to the conformal mapping of a unit circle to a square
Green's functions for symmetric loading of an elastic sphere with application to contact problems
No full textA compact form for the static Green’s function for symmetric loading of an elastic sphere is derived. The expression captures the singularity in closed form using standard functions and quickly convergent series. Applications to problems involving contact between elastic spheres are discussed. An exact solution for a point load on a sphere is presented and subsequently generalized for distributed loads. Examples for constant and Hertzian-type distributed loads are provided, where the latter is also compared to the Hertz contact theory for identical spheres. The results show that the form of the loading assumed in Hertz contact theory is valid for contact angles up to about 10 degrees. For larger angles, the actual displacement is smaller and the contact surface is no longer flat.Peer reviewe
The Face of the Other in Emmanuel Levinas and Alexey Uhktomsky
No full textThe author compares ethical concepts of a Russian physiologist and philosopher Alexey A. Ukhtomsky and a French philosopher Emmanuel Levinas. Both use the word “face” as a philosophical term. The paper examines the “face” as a key image in the work of both authors which helped them understand the meaning of dialogue and social interaction. The fact that the Russian word “litzo” (“face”) has two different meanings (a “person” and a “human face”) was very important for Ukhtomsky. For the better understanding of Levinas, it is necessary to take in account the interaction of Russian, Hebrew, and French languages as part of the linguistic consciousness of this author. Both philosophers considered ethics to be philosophia prima. The encounter with the face of the Other is the central event in the personality development for both Levinas and Ukhtomsky. For Levinas, the study of the face was a way to transcend the limits of phenomenology because the face is not a “common” phenomenon. For Ukhtomsky, the image of the face pointed at the problematic character of sciences. It was part of his search for the non-theoretical knowledge, e. g. knowledge that accounts not only for the universal but also for the individual and is capable of describing not only impersonal structures and objects but also individual and unique events. Both thinkers thus were seeking to reconsider religious tradition in the context of contemporary science and philosophy. Ukhtomsky arrives at the idea of asymmetrical relationship between the “I” and the “Other” independently of Levinas. Whereas Levinas describes the experience of the encounter with the Other as a kind of epiphany, Ukhtomsky calls God “the First and the Ultimate Interlocutor.” The encounter with the Other for both philosophers is, namely, a mundane, everyday analogue of the Revelation
“MYSLENNYI VOLK” (“MENTAL WOLF”) BY ALEXEY VARLAMOV AS A SYMBOLIST NOVEL
No full textThe author of the article analyzes poetics of the novel by Alexey Varlamov - a contemporary author, a successor of the traditions of Russian Classic literature of the XIX century. The plot covers the last years of the Russian Empire and the Red Terror that followed the Great October Socialist Revolution of 1917. The novel depicts life and fate of many historical and fictional characters. Analyzing the plot, the composition, the motifs of the novel, the author of the article reveals typological parallels between its poetics and the poetics of Russian Symbolism of the early twentieth century, novels written by Fedor Sologub, Valery Bryusov, and Andrey Bely and his novel «Petersburg». The author concludes the novel written by Alexey Varlamov is an example of symbolism prose
Communication Technologies for Vehicles: Third International Workshop, Nets4Cars/Nets4Trains 2011 Oberpfaffenhofen, Germany, March 23-24, 2011 Proceedings
No full textThe Communication Technologies for Vehicles workshop series provides an international forum on latest technologies and research in the field of intra- and inter-vehicle communications in which to present original research results in all areas relating to communication protocols and standards, mobility and traffic models, experimental and field operational testing, and performance analysis
An Irreparable Loss. The Memory of Alexey V. Yablokov
No full textIn this short article, the co-author of Alexey V. Yablokov tells the story of acquaintance with him, about the features of the character of this outstanding scientist, moreover about how he worked with
Yablokov the last few years. Fragments of discussions by e-mail which concern a few actual biological problems (in particular cooperation in nature, evolution and controlled evolution) are given in the articl
Author Correction: A high-throughput screening platform for Polycystic Kidney Disease (PKD) drug repurposing utilizing murine and human ADPKD cells
No full textThe original version of this Article contained an error in the spelling of the author Alexey Zakharov which was incorrectly given as Alexey Zahkarov. The original Article and accompanying Supplementary Information 1 file have been corrected
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