1,720,983 research outputs found
Tuning and hybridization of surface phonon polaritons in α-MoO3 based metamaterials.
Full text linkWe propose an effective medium approach to tune and control surface phonon polariton dispersion relations along the three main crystallographic directions of α-phase molybdenum trioxide. We show that a metamaterial consisting of subwavelength air inclusions into the α-MoO3 matrix displays new absorption modes producing a split of the Reststrahlen bands of the crystal and creating new branches of phonon polaritons. In particular, we report hybridization of bulk and surface polariton modes by tailoring metamaterials' structural parameters. Theoretical predictions obtained with the effective medium approach are validated by full-field electromagnetic simulations using finite difference time domain method. Our study sheds light on the use of effective medium theory for modeling and predicting wavefront polaritons. Our simple yet effective approach could potentially enable different functionalities for hyperbolic infrared metasurface devices and circuits on a single compact platform for on-chip infrared photonics
Hybrid thermal Yagi-Uda nanoantennas for directional and narrow band long-wavelength IR radiation sources
Full text linkWe investigate the possibility of spatially and spectrally controlling the thermal infrared emission by exploitation of the Yagi-Uda antenna design. Hybrid antennas composed of both SiC and Au rods are considered and the contributions of emission from all the elements, at a given equilibrium temperature, are taken into account. We show that the detrimental effect due to thermal emission from the not ideal parasitic elements drastically affect the performances of conventional thermal Au antennas in the 12 μm wavelength range. Nevertheless, our results show that the hybrid approach allows the development of efficient narrow-band and high directivity sources. The possibility of exploiting the Yagi-Uda design both in transmission and in reception modes, may open the way to the realization of miniaturized, efficient, robust and cheap sensor devices for mass-market applications. 2020 Optical Society of America
Advances in photothermal science and techniques: a route for NDT from macro to nanoscale
No full textHeat transfer can differ distinctly at the nanoscale from that at the macroscale. Recent advancement in experimental techniques has enabled a large number of interesting observations and understanding of heat transfer processes at the nanoscale
Transparent films for electromagnetic shielding of plastics
No full textThe interest in the development of lightweight transparent electromagnetic (EM) shields for the radio frequency range has been growing up in the last years together with the expansion of the electronic market and the increasing use of plastics. Example of industrial applications are video displays of electrical and electronic apparatus, of electromedical devices, of portable electronic equipment. Applications in the aerospace sector are also very attractive, such as in protecting the electronic systems of aircrafts from the high-intensity electromagnetic fields emitted by radio emitters, TV, radars and telecommunication systems. Moreover, the recent limits of radio frequency electromagnetic fields suggest the use of transparent shields for building windows. Thin films can provide an effective solution in EM shielding of plastic substrates or enclosures. In particular, the use of 1-D photonic band gap structures named as 'transparent metals' has been recently investigated and tested for EM shielding applications in the radiofrequency range, by using physical vapor deposition technique. In this work, the design method and the technological issues concerhing the realization and electromagnetic testing of the shields will be described. Some recent results will be presented, and both perspectives and limits of the proposed technique will be discussed and compared with other solutions
Enhanced stability of the second order optical properties of high-Tg fluorinated electro-optic copolymer
No full textMetamaterials approach for infrared radiation manipulation in dispersed nanowires systems
No full textIn recent years, much effort has been expended upon managing and tuning the radiative properties of structures and material surfaces in the infrared (IR) wavelength range for several applications, such as thermal radiation control as well as IR sensing. Metamaterials are artificial electromagnetic materials, composed by periodically or randomly arranged, subwavelength elements. Since the typical dimensions of the constitutive elements of a metamaterials are smaller than the interaction wavelengths, they behave as an effective medium and may give rise to peculiar electromagnetic properties, such as negative refraction, superlensing and cloaking, to name some. In the present work we review the use of metamaterials composed by dispersed nanowires systems into a dielectric matrix, for managing and tuning of the infrared emission. The main homogenization techniques effective medium approach are presented and discussed, along with several parameters such as filling factor, inclusions orientations and shape. We finally show some examples with different materials (metallic or polar nanowires) and many configurations in order to get spectral and/or spatial modulation of the resulting infrared emissivity. Taming and tuning the infrared radiation of a metamaterial allows the design of versatile optical elements as basic elements for further developments of infrared filters, thermal diodes and thermal logic gates
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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