1,721,095 research outputs found
Динамические эффективные параметры упругой сверхрешетки с акустически различными компонентами
No full textAnalytical formulas are obtained for frequency-dependent effective elastic modulus and effective mass density for a periodic layered structure. The proposed homogenization procedure is valid at sufficiently high frequencies well above the lowest band gap in the acoustic spectrum of the structure. It is shown that frequencydependent effective parameters may take negative values either in different regions of frequencies or in the same
quite narrow region. This property demonstrates that 1D elastic structure may behave in the limit of small Bloch
wave vectors as a double-negative acoustic metamaterial.Отримано аналітичні формули для частотно-залежних ефективного модуля пружності та ефективної щільності періодичної шаруватої структури. Запропонована процедура гомогенізації справедлива при досить високих частотах, що
перевищують частоту першої забороненої зони в акустичному
спектрі структури. Показано, що залежні від частоти ефективні параметри можуть набувати від’ємних значень або в
різних частотних областях, або в одній досить вузькій області. Ця властивість показує, що одновимірна пружна структура в межі малих блоховських хвильових векторів може поводитися як акустичний метаматериал, у якого обидва ефективні параметри від’ємні.Получены аналитические формулы для частотнозависимых эффективного модуля упругости и эффективной
плотности периодической слоистой структуры. Предложенная процедура гомогенизации справедлива при достаточно
высоких частотах, превышающих частоту первой запрещенной зоны в акустическом спектре структуры. Показано, что
зависящие от частоты эффективные параметры могут принимать отрицательные значения либо в различных частотных
областях, либо в одной достаточно узкой области. Данное
свойство показывает, что одномерная упругая структура в
пределе малых блоховских волновых векторов может вести
себя как акустический метаматериал, у которого оба эффективных параметра отрицательны.This work is supported by an Emerging Frontiers in Research and Innovation grant from the National Science
Foundation (Grant No. 1741677)
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
Fundamental Properties of Phononic Crystal
No full textInternational audiencePhononic crystals are periodic composite structures where the elastic and acoustic properties display a periodic variation in space. They are in general constituted by a periodic array of inclusions in a matrix. Due to their periodicity, they can exhibit absolute band gaps in which the propagation of elastic waves is prohibited in any direction of the space. More generally, tailoring their band structure allows the control and manipulation of elastic waves and pave the way to several functionalities ranging from sound isolation to filtering and signal processing, negative refraction and high resolution imaging, nanoscale thermal transport managing, quantum information processing. In this chapter, we discuss some basic properties of the phononic crystals, in particular the dependence of the band gaps with the nature of the constituent materials (solid or fluid), the contrast between the elastic properties of the constituents, the shape and the filling fraction of the inclusions, the crystal lattice. We discuss the existence of gaps resulting from Bragg interference or from local resonances. The localized modes associated with defects such as cavities and waveguides are presented and their functionalities in filtering and multiplexing applications are discussed
Preface to Special Topic: Selected Articles from Phononics 2015: The Third International Conference on Phononic Crystals/Metamaterials, Phonon Transport and Phonon Coupling, 31 May-5 June 2015, Paris, France
No full text- …
