1,721,006 research outputs found
Identität durch Sprache in Grenzregionen
No full textIl lavoro evidenzia come le comunità confinarie costruiscano la propria identità nazionale in base agli usi linguistic
Design guidelines for Thermo-Photo-Voltaic generator: the critical role of the emitter size
No full textIn the last decade, the thermo-photo-voltaic (TPV) generator has gained an increasing attention as cogeneration
system for the distributed generation sector. Nevertheless, these systems are not fully developed
and studied: several aspects need to be further investigated and completely understood.
The aim of this study is to highlight and outline the main design guidelines for a thermo-photo-voltaic
(TPV) generator with a specific attention to the emitter section.
More in details, an investigation of the role of the emitter size will be developed by considering its
influence on spectral efficiency (defined as the ratio between the emitted radiation in the useful range
for photovoltaic conversion and the introduced power with fuel); by using simplified assumptions, the
spectral efficiency as a function of the emitter area in four different TPV configurations will be estimated.
The achieved results show specific power values per unit emitter area significantly larger than in prototypes
realized up to date.
Further, the developed analysis allows to show the role of the optical filter and of the air pre-heating
exchanger in order to increases the spectral efficiency of the system, being equal the considered power
densit
Synthesis mechanism of SiC–SiO2 core/shell nanowires grown by chemical vapor deposition
No full textCore-shell SiC-SiO2 nanowires were grown on silicon substrate with the chemical vapor deposition method using iron nitrate as promoter for the growth and CO as a carbon precursor, under atmospheric pressure and at a temperature of 1100 degrees C. The whole process involves two main stages: promoter conditioning (dewetting) and growth, by reaction with CO. The dewetting phase has been characterized by SEM and TEM techniques, x-ray diffraction and Raman spectroscopy. The results show that at the operating temperature, a solid-state reaction between the substrate and the promoter takes place with the formation of alpha-FeSi2. The growth of the nanowires begins after an induction time of about 5 min from the introduction of CO. The experimental data have been interpreted by considering a nucleation process involving a reaction between FeSi2 and CO. For the nanowires growth phase, a mechanism based on the Vapor-Liquid-Solid theory is proposed, compatible with the morphology of the drop-shaped particles present on the tip of the nanowires
Synthesis and characterization of the layered compounds in the ZnIn2S4 - ZnIn2Se4 system
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A new semimagnetic compound: Cd1-xFexIn 2S4 single crystal grown by CVT
No full textSingle crystals of the Cd1-xFexIn2S 4 compounds were grown by the chemical vapour transport method using iodine as transport agent. The crystals were grown by placing the ampoule in a two zone furnace, keeping the source temperature and the deposition temperature at 850 and 800 °C respectively. The resulting crystals with nominal concentrations: x = 0.25, 0.5, 0.75 were characterized by X-ray powder diffraction, electron probe micro-analysis and magnetic measurements. Electron probe micro-analysis showed that the actual concentration of Fe was lower than the nominal one. X-ray diffractograms were taken at room temperature for each sample, revealing that the compounds form a solid solution in the whole range of compositions and crystallize with cubic symmetry in the space group Fd3m. All samples show a spinel structure with a random arrangement of cations. The magnetic behavior of the samples was investigated by low-field magnetization measurements in the range 5-300 K. The observed magnetic behavior does not show any magnetic transition in the studied temperature range. However an irreversibility has been observed between zero-field-cooled (ZFC) and field-cooled (FC) cycles. High temperature susceptibility data follow the Curie-Weiss law with a negative paramagnetic Curie temperature, indicating the predominance of antiferromagnetic interactions. The optical absorption data for sample with x = 0.75 shows a direct energy gap of 1.28 eV at RT. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Effects of group-III cation substitution in the Raman spectra of some defective chalcopyrites
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