1,723,759 research outputs found
Effect of Trisodium Citrate on the Morphology and Luminescence Properties of Hydrothermally Synthesized YVO₄ Phosphor
No full textYVO₄ phosphors with different morphologies were synthesized by trisodium citrate (Na₃cit) surfactant-assisted hydrothermal process. Effects of molar ratio of to and pH value of reaction solution were intensively investigated on the morphologies, structures and luminescence properties of YVO₄ phosphor. The morphologies of the YVO₄ particles can be effectively controlled in strong acidic and strong alkaline environment by affecting the adsorption of on the (001) crystal plane of YVO₄. Strong acidic condition resulted into excessive adsorption of groups on the YVO₄ phosphor, which annihilated the superior luminescence of YVO₄ phosphors. On the contrary, strong alkaline condition does not result into the adsorption of groups. The synthesized YVO₄ phosphor without adsorption of groups showed superior luminescence even though the effective control of the morphology in alkaline condition is not so good as in strong acidic condition
Ein regierungskritischer Staatsrechtler: Yvo Hangartner (1933–2013)
Full text linkYvo Hangartner (1933–2013) spielte als stellvertretender Staatsschreiber, HSG-Professor, rechtspolitischer Kommentator und Experte des öffentlichen Rechts über St. Gallen hinaus eine bedeutende Rolle. Nun wird der Gossauer in einem Buch gewürdigt
Transitions de phase dans le YVO[indice inférieur 3]
No full textDans le mémoire qui suit, les ordres structural, magnétiques et orbital dans le YVO[indice inférieur 3] sont étudiés avec l'aide de la diffraction des rayons X ,de la spectroscopie Raman et de la technique de la cavité résonnante hyperfréquence. L'objectif premier consiste à observer l'évolution de ces ordres en fonction de la température. Le mémoire met ensuite en évidence le couplage entre les différents ordres cohabitants dans le YVO[indice inférieur 3]. Les mesures effectuées par la diffraction des rayons X permettent de mesurer le caractère polycrystallin des échantillons du YVO[indice inférieur 3]. Une comparaison de nos mesures avec des mesures de diffraction des rayons X faites sur la poudre de YVO[indice inférieur 3] indique la faible présence de maclage. Les mesures effectuées avec la technique de résonnance hyperfréquence permettent de suivre l'évolution de la constante diélectrique en fonction de la température. Les changements impliquant l'ordre orbital se manifestent de manière évidente dans la constante diélectrique à 200 K et à 77 K. La transition diélectrique détectée à 77 K est une transition de premier ordre. Un couplage entre les propriétés diélectriques et magnétiques est observable à la température de Néel à 114 K. L'effet d'un champ magnétique fixe sur la température de transition de l'ordre orbital survenant à 77 K est également remarquable. Cela indique un couplage magnétodiélectrique démontrant ainsi le caractère multiferroïque du YVO[indice inférieur 3]. Finalement, l'observation d'un mécanisme de relaxation pouvant être modélisé par le modèle d'Havriliak-Negami est observé en dessous de 77 K. En utilisant le modèle d'Arrhénius et le modèle d'Havriliak-Negami, on peut caractériser le mécanisme avec son énergie d'activation et son temps de relaxation. Les mesures effectuées en spectroscopie Raman permettent de suivre l'évolution de la structure du YVO[indice inférieur 3] en fonction de la température. Les deux changements structuraux survenant à 200 K et 77 K sont observés. Le couplage entre le réseau et l'ordre orbital se manifeste par une augmentation de l'anharmonicité qui se traduit par une augmentation de l'intensité des processus de deuxième et troisième ordres. Les différentes théories expliquant comment l'ordre orbital interagit avec le réseau cristallin seront abordées en mettant l'accent sur la théorie de Van den Brink ['] qui reflète le mieux la réalité. Une comparaison de nos mesures avec d'autres travaux en spectroscopie Raman effectués sur le YVO[indice inférieur 3] sera également effectuée. Le couplage entre le réseau et l'ordre magnétique s'observe par la présence d'excitations magnétiques dans les spectres Raman et par la présence d'un ramollissement/durcissement survenant à la température de Néel. La théorie de Granado expliquant le phénomène de durcissement/ramollissement sera discutée
Far-infrared optical properties of YVO 4 single crystal
No full textNear-normal incident infrared reflectivity spectra of a (001) YVO 4 single crystal have been measured at different temperatures in the frequency region between 100 and 6000 cm -1 . The reflectivity spectra are analyzed with the factorized form of the dielectric function, and the dielectric properties and optical conductivity of the YVO 4 crystal are obtained. From the TO/LO splitting, effective charges at different temperatures are calculated to study the ionicity of YVO 4. The internal modes of the VO 4 3- ion and the external modes of the Y(VO 4) lattice are compared with SiO 4 4- in zircon and with other rare-earth vanadates. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200677.22.Ch Permittivity (dielectric function), 78.20.-e Optical properties of bulk materials and thin films, 63.20.-e Phonons in crystal lattices ,
Perfect Anonymity
No full textFor 35 years, the cryptographic community has created the impression that anonymous communication is always possible. Chaum's dining cryptographer's solution is regarded as achieving unconditional security. Chaum's MIX approach, namely, applying a uniformly random permutation on the plaintexts to be sent, is often given as a definition for anonymity. However, people working in law enforcement know that attempts by whistle-blowers and criminals to remain at large, often fail. The content of the message may reveal the name of the sender or may leak for whom the message is really intended. To understand this issue, we give a definition of perfect anonymity. We contrast our definition with Chaum's approach and discuss the impact on Chaum's dining cryptographer's solution.NSF Grant ANI-0087641.Erik Jonsson School of Engineering and Computer Scienc
Морфология поверхности, оптические и электрофизические свойства пленок ванадата иттрия YVO[4]
Full text linkМетодом высокочастотного импульсно-периодического (f ~ 13 кГц) воздействия лазерного излучения с длиной волны 1.064 мкм и плотностью мощности q = 64 МВт/см{2} на керамику ванадата иттрия YVO[4] при давлении в вакуумной камере р = 3 Па получены наноструктурированные тонкие пленки на кремниевой подложке. Методом атомно-силовой микроскопии изучена морфология тонких пленок YVO[4]. Получены спектры пропускания пленок в видимой, ближней и средней ИК-областях. Проведен анализ электрофизических свойств структуры YVO[4]/Si
Yvo de Boer, "Bm İklim Değişikliği Raporu Uykularınızı Kaçıracak
No full textKopenhag iklim görüşmeleri sırasında BM delegasyonun başkanlığını yapan Yvo de Boer , IPCC tarafından yapılan açıklamada 2013′ün sonu ya da 2014′ün başında yayınlanacak olan BM iklim değişikliği raporunun şok etkisi yaratabileceği konusunda uyarılarda bulundu
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
Structural characterization and photocatalytic properties of novel Bi(2)YVO(8)
No full textBi(2)YVO(8) was prepared by solid-state reaction for the first time. The structural and photocatalytic properties of Bi(2)YVO(8) were studied. The results showed that this compound has the tetragonal crystal system with space group I4/mmm. The band gap of Bi(2)YVO(8) was estimated to be about 2.09 eV by plotting (alpha h nu)(2) versus h nu and obtaining the h nu axis intercept value according to Tauc's equation. For the photocatalytic water splitting reaction, H(2) or O(2) evolution was observed from pure water with Bi(2)YVO(8) as the photocatalyst under ultraviolet light irradiation (wavelength = 390 nm). Degradation of aqueous methylene blue photocatalyzed by this compound was investigated under visible light irradiation. Bi(2)YVO(8) showed higher photocatalytic activity compared to Bi(2)YTaO(7), Bi(2)InTaO(7) or TiO(2) (P-25). Complete removal of aqueous methylene blue was achieved after visible light irradiation for 170 min. The decrease of the total organic carbon and the formation of inorganic products such as SO(4)(2-) and NO(3)(-) revealed the continuous mineralization of aqueous methylene blue during photocatalytic reaction. (c) 2008 Elsevier Ltd. All rights reserved
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