1,720,982 research outputs found
Study of proper and improper microwave dielectric losses by means of teraherz and infrared spectroscopy
Get PDFTitle: Study ol"proper and improper microwave dielectric tosses by means of tcrahcrz and infrared speetroseopy Author: Ondfej Tkac Department: Department of Dielectrics. Institute of Physics, Academy of Sciences of C/ech Republic Supervisor: RNDr. Slanislav Kamba.C'Sc.. Na Slovance 2. Prague 8 Supervisor's e-mail adress: kambawT/u.c/ Abstract: In the llrst part of this thesis there is described relevant theory, especially we pay our attention to the principles of infrared speetroseopy and fitting models, then to the explanation of the terms proper and improper dielectric losses and we also discuss dielectrics and ferroelectrics. By means of Fourier transform infrared speetroseopy we measured infrared spectra at room temperature in the range of 30 - 3000 em"1. We lilted the spectra and then we extrapolated the final complex permit!vity into the microwave range. This enabled us to estimate the proportion of improper dielectric losses on total microwave losses. By the ceramic SiVxPlxCeVfinO-^ (.\0 to 9) we studied the impact of amount of lead on dielectric properties. We found out that the substitution of strontium with lead causes the increase of permitivity up lo several thousands and forces ferroelectric transition for x>2. With perovskitc Ca/n, jNb^ :,-xVx(.)1 (.v=0 to 0,01) we examined the inlluence of..
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
Study of multiferroics with hexaferrite crystal structure
No full textPráce se zabývá charakterizací fyzikálních vlastností polykrystalických hexaferitů strukturních typů M, Y a Z, které vykazují magnetoelektrický jev potenciálně využitelný v pamětech pro informační technologie. Infračervené reflektivity byly měřeny v závislosti na teplotě od 300 do 10 K, THz spektra byla studována v závislosti na teplotě i na magnetickém poli do 7 T. Pozorovali jsme jak mřížkové, tak i spinové excitace s výrazně odlišným chováním v závislosti na strukturním typu hexaferitu. V případě (Ba0,2Sr0,8)3Co2Fe24O41 (Z-hexaferitová struktura) jsme navíc provedli statická magnetická a magnetodielektrická měření, která kvalitativně prokázala magnetoelektrický jev. Také jsme změřili infračervenou reflektivitu monokrystalu Ba0,5Sr2,5Co2Fe24O41 a porovnali ji s reflektivitou keramiky.The work deals with characterization of physical properties of polycrystalline hexaferrrites of the structural types M, Y and Z, which exhibit magnetoelectric effect, potentially applicable in the memories for IT. Infrared reflectivities were measured from 300 to 10 K. THz spectra were studied depending on temperature and magnetic field up to 7 T. Lattice and spin excitations with different behaviour dependent on the crystal structure were observed. In case of (Ba0.2Sr0.8)3Co2Fe24O41 with Z-hexaferrite structure, we performed static magnetic and magnetodielectric measurements to qualitatively prove magnetoelectric effect. We also measured infrared reflectivity of Ba0.5Sr2.5Co2Fe24O41 single crystal and compared it with spectra of ceramic
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
Study of electrical and dielectric properties of conducting polymers
No full textTitle: Study of electrical and dielectric properties of conducting polymers Author: Mgr. Martin Varga Department: Department of Macromolecular Physics Supervisor: RNDr. Jan Prokeš, CSc., Department of Macromolecular Physics Abstract: Charge transport in polyaniline (PANI) and polypyrrole (PPy) was studied in respect to various oxidants, dopants, morphology, and other modifica- tions in their synthesis. The mechanism of transport was discussed in the frame- work of combination of several models characteristic for disordered solids due to inherent heterogeneous structure of conducting polymers. Effect of drying on conductivity was studied and the long-time limit was explained with the diffusion- based model for bulk materials. For PPy nanotubes stability in strong alkaline media and aging were studied by AC and DC techniques. While conductivity of naturally aged samples after two years remained in the same order of magni- tude, after exposure to alkaline media or accelerated aging at high temperatures, conductivity decreased several orders of magnitude. Degraded material exhibited strong disorder and the transport model was completely changed. Despite severe treatment electrical properties were still comparable to other as-prepared mate- rials. Finally, an application example as ammonia sensor, the response of..
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Morphic effect and anisotropic magnetoelectric coupling in EuTiO3
Get PDFEuTiO3 je incipientně feroelektrický antiferomagnet (pod T_N = 5,3 K), který se vyznačuje silnou magnetoelektrickou vazbou projevující se závislostí permitivity na vnějším magnetickém poli. Práce zkoumá anizotropii magnetoelektrické vazby EuTiO3 keramik vzhledem k vzájemné orientaci elektrického a magnetického pole. Permitivita keramik je spektroskopicky zkoumána v radiofrekvenčním, terahertzovém (THz) a infračerveném oboru. Keramiky jsou též podrobeny dilatometrickým a magnetizačním měřením. Vzorky jsou za nízkých teplot (až 0,3 K) vystaveny silnému magnetickému poli (až do 15 T) orientovanému kolmo či paralelně k poli elektrickému. Práce vysvětluje anizotropii permitivity skrze morfické jevy, magnetostrikci a demagnetizační pole vzorků a porovnává předpovědi s naměřenými daty. Příčinou zdánlivé anizotropie permitivity ve slabém magnetickém poli je nakonec demagnetizační pole keramik. Anizotropie THz indexu lomu je způsobena feromagnetickou rezonancí v subTHz oblasti.EuTiO3 is an incipient ferroelectric antiferromagnet (below T_N = 5.3 K), exhibiting a strong magnetoelectric coupling, characterised by the dependence of permittivity on an external magnetic field. This Thesis aims to examine the EuTiO3 ceramics magnetoelectric-coupling anisotropy with respect to the mutual orienation of the electric and magnetic field. The ceramics are studied spectroscopically in a radio-frequency, terahertz, and infrared region. Moreover, the dilatometric and magnetization measurements are conducted. The samples are subjected to low temperatures down to 0.3 K and magnetic field of up to 15 T, oriented parallelly or perpendicularly to the electric field. The permittivity anisotropy is disccused in terms of the morphic effects, magnetostriction, and the demagnetizing field of the samples. The predictions are compared with the experimental data. The demagnetizing field is found to be the cause of the seeming EuTiO3 permittivity anisotropy in a weak magnetic field. The THz refractive index anisotropy is induced by a ferromagnetic resonance in the subTHz region
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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