2,536 research outputs found
Numerical solution of stefan problems
No full textThe enthalpy method for two dimensional Stefan problems is outlined, and applied to the numerical solution of a problem involving the solidification of a square cylinder of fluid, for which experimental data have been published. The same technique is then applied to a similar problem, and the results compared with those obtained by other authors
Low-Temperature Sputtering Deposition of Aligned Polycrystalline CaCu3Ti4O12 Nanorods
No full textVertically aligned polycrystalline CaCu3Ti4O12 nanorods were obtained by rf sputtering at low substrate temperatures. The rods grow by electrostatic attraction and aggregation of charged clusters, independently of the substrate used. These nanostructures exhibit a strong nonlinear current x voltage behavior and high losses during cyclic testing, indicating a combination of Schottky's barrier and Joule's heating effects.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNESP Araraquara, Inst Quim, BR-14800900 Araraquara, SP, BrazilJozef Stefan Inst, Adv Mat Dept, Ljubljana 1000, SloveniaUNESP Araraquara, Inst Quim, BR-14800900 Araraquara, SP, Brazi
ZnO varistors from intensively milled powders
No full textTwo ways of application of intensive milling in ZnO varistors processing were compared. First was intensive milling of mixture of previously prepared constituent phases. In this case, intensive milling was applied only to obtain highly activated nanocrystalline varistor powder mixtures. Second application is intensive milling of simple mixture of oxides that could result not only in activation and formation of nanocrystal line powders, but also in mechanochernical reaction and synthesis of constituent phases. Powders and ceramics samples were characterized by XRD and SEM analysis. as well as by de electrical measurements (nonlinearity coefficients, leakage current and breakdown field). Differences in microstructural and electrical properties of obtained varistors were discussed and optimal milling and processing conditions were recommended. The best electrical characteristics were found in sample ZI -DMCP-m, which exhibited leakage current of 2.5 mu A/cm(2), nonlinear coefficient reaching 58 and breakdown field of 8950 V/cm. (c) 2007 Elsevier Ltd. All rights reserved.Ctr Multidisciplinary Studies, Belgrade 11000, SerbiaJozef Stefan Inst, Ljubljana 1000, SloveniaUNESP, Inst Quim, BR-14801970 Araraquara, SP, BrazilUNESP, Inst Quim, BR-14801970 Araraquara, SP, Brazi
The effect of cooling rate during hydrothermal synthesis of ZnO nanorods
No full textThe hydrothermal method was employed in order to obtain zinc oxide nanorods directly on Si/Si02/Ti/ Zn substrates forming brush-like layers. In the final stages of synthesis, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction results showed that all the nanostructures grew [0 0 0 1] oriented perpendicular to the substrate. The influence of the cooling process over the morphology and dimensions of the nanorods was studied by scanning electron microscopy. High-resolution transmission electron microscopy images of the quenched samples showed that the zinc oxide (ZnO) crystal surfaces exhibit a thin-layered coating surrounding the crystal with a high degree of defects, as confirmed by Raman spectroscopy results. Photodetectors made from these samples exhibited enhanced UV photoresponses when compared to the ones based on naturally cooled nanorods. (C) 2009 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNESP, Inst Quim, BR-14800900 Araraquara, SP, BrazilCONICET UNMdP, Inst Invest Ciência & Tecnol Mat INTEMA, Mar Del Plata, Buenos Aires, ArgentinaJozef Stefan Inst, Adv Mat Dept, Ljubljana 1000, SloveniaUniversidade Federal de São Carlos (UFSCar), Dept Quim, BR-13565905 São Carlos, SP, BrazilUNESP, Inst Quim, BR-14800900 Araraquara, SP, Brazi
Leasing-Forum: IAS 17 (rev.) accounting for leases
No full textLeasing-Forum: IAS 17 (rev.) accounting for leases / von Stefan Wotschofsky, Manuel Alvarez & Michaela Miethig. - Augsburg : Inst. für Betriebswirtschaftslehre, 2001. - 34 Bl. - (Betriebswirtschaftliche Steuerlehre ; 2001,1
Untersuchung des unterjährigen Publizitätsverhaltens börsennotierter Unternehmen in Deutschland
No full textUntersuchung des unterjährigen Publizitätsverhaltens börsennotierter Unternehmen in Deutschland / von Stefan Wotschofsky & Manuel Alvarez. - Augsburg : Inst. für Betriebswirtschaftslehre, 1999. - 29 S. - (Betriebswirtschaftliche Steuerlehre ; 1999,5
Influence of Hydrothermal Synthesis Conditions and Device Configuration on the Photoresponse of UV Sensors Based on ZnO Nanorods
No full textZinc oxide nanorods in the form of powder or nanostructured films were synthesized by the hydrothermal method using aqueous solutions. Once the synthesis time was completed, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy techniques were employed to characterize the crystallinity, morphology, and dimensions of the nanorods, as well as their growth direction. Suspensions of powder material were spin-coated over oxidized silicon substrates in order to obtain nanostructured layers. Photodetectors based on in-situ grown and spin-coated films were prepared in order to evaluate the influences of cooling rate and device configuration on the UV sensing characteristics. Spin-coated layers showed an excellent performance (current change by more than four orders of magnitude), better than nanorods grown directly on the substrate during the hydrothermal process. For both configurations, the sensitive layers built from quenched samples exhibited enhanced UV photoresponses when compared to the naturally cooled ones.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Inst Quim UNESP Araraquara, BR-14800900 Araraquara, SP, BrazilCONICET UNMdP, Inst Invest Ciência & Tecnol Mat INTEMA, Mar Del Plata, Buenos Aires, ArgentinaJozef Stefan Inst, Dept Adv Mat, Ljubljana 1000, SloveniaCtr Tecnol Informação Renato Archer, BR-13069901 Campinas, SP, BrazilInst Quim UNESP Araraquara, BR-14800900 Araraquara, SP, BrazilFAPESP: 05/59270-
The modification of structural and optical properties of nano- and submicron ZnO powders by variation of solvothermal syntheses conditions
No full textNano- (30-60 nm) and submicron (100-350 nm) ZnO particles were synthesized using solvothermal method at 200 degrees C from an ethanolic solution of zinc acetate dihydrate, applying different reaction conditions, i.e., pH value of precursor and time of the reaction. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance (DR), Raman spectroscopy, and photoluminescence (PL) spectroscopy have been employed for characterization of synthesized ZnO powders. It was shown that the structural, morphological, and optical properties are largely determined by reaction conditions during solvothermal synthesis. The particle crystallinity improves with the decrease of pH value and/or the increase of time of the reaction. The Raman and PL spectra analyses indicate that the oxygen interstitials are dominant intrinsic defects in solvothermally synthesized ZnO powders. It was observed that concentration of defects in wurtzite ZnO crystal lattices slightly changes with the variation of pH value of the precursor and time of the solvothermal reaction. The correlation between structural ordering and defect structure of particles and corresponding growth processes was discussed.Ministry of Education and Science of Republic of SerbiaUniv Belgrade, Inst Multidisciplinary Res, Belgrade 11030, SerbiaUniv Belgrade, Inst Phys, Ctr Solid State Phys &New Mat, Belgrade 11080, SerbiaUniv Estadual Paulista, Dept Fis Quim IQ, BR-14801907 Araraquara, SP, BrazilJozef Stefan Inst, Ljubljana 1000, SloveniaArgonne Natl Lab, Div Mat Sci, Argonne, IL 60439 USAUniv Estadual Paulista, Dept Fis Quim IQ, BR-14801907 Araraquara, SP, BrazilMinistry of Education and Science of Republic of Serbia: III4500
Ökonomische Analyse der einkommensteuerlichen Behandlung von Lohnersatzleistungen
No full textÖkonomische Analyse der einkommensteuerlichen Behandlung von Lohnersatzleistungen / von Stefan Wotschofsky & Helmut Pasch. - Augsburg : Inst. für Betriebswirtschaftslehre, 2000. - 25 Bl. - (Betriebswirtschaftliche Steuerlehre ; 2000,1
Leasing-Forum: bilanzielle Erfassung von Leasinggeschäften in Frankreich
No full textLeasing-Forum: bilanzielle Erfassung von Leasinggeschäften in Frankreich / von Stefan Wotschofsky & Michaela Miethig. - Augsburg : Inst. für Betriebswirtschaftslehre, 2001. - 17 Bl. - (Betriebswirtschaftliche Steuerlehre ; 2001,2
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