Síntese, sinterização e caracterização de ferritas à base de Ni-Zn

Were synthesized different ferrites NixZn1-xFe2O4 (0,4 ≤ x ≤ 0,6) compositions by using citrate precursor method. Initially, the precursors citrates of iron, nickel and zinc were mixed and homogenized. The stoichiometric compositions were calcined at 350°C without atmosphere control and the calcined powders were pressed in pellets and toroids. The pressed material was sintered from 1100º up to 1200ºC in argon atmosphere. The calcined powders were characterized by XRD, TGA/DTG, FTIR, SEM and vibrating sample magnetometer (VSM). All sintered samples were characterized using XRD, SEM, VSM and measurements of magnetic permeability and loss factor were obtained. It was formed pure ferromagnetic phase at all used temperatures. The Rietveld analyses allowed to calculate the cations level occupation and the crystallite size. The analyses obtained nanometric crystals (12-20 nm) to the calcined powder. By SEM, the sintered samples shows grains sizes from 1 to 10 μm. Sintered densities (ρ) were measured by the Archimedes method and with increasing Zn content, the bulk density decrease. The better magnetization results (105-110 emu/g) were obtained for x=0,6 at all sintering temperatures. The hysteresis shows characteristics of soft magnetic material. Two magnetization processes were considered, superparamagnetism at low temperature and the magnetic domains formation at high temperatures. The sintered toroids presents relative magnetic permeability (μr) from 7 to 32 and loss factor (tanδ) of about 1. The frequency response of toroids range from 0,3 kHz to 0,2 GHz. The composition x=0,5 presents both greater μr and tanδ values and x=0,6 the most broad range of frequency response. Various microstructural factors show influence on the behavior of μr and tanδ, such as: grain size, porosity across grain boundary and inside the grain, grain boundary content and domain walls movement during the process of magnetization at high frequency studies (0,3kKz 0,2 GHz)

Síntese análise das propriedades magnéticas da ferrita de NiMg e características de absorção de radiação

It was synthesized different Ni1-xMgxFe2O4 (0,2 ≤ x ≤ 0,7) compositions by use of citrate precursor method. Initially, the precursory citrates of iron, nickel and magnesium were mixed and homogenized. The stoichiometric compositions were calcined from 350°C to 1200°C at ambient atmosphere or in argon atmosphere. The calcined powders were characterized by XRD, TGA/DTG, FTIR, magnetic measures and reflectivity using the wave guide method. I was observed pure magnetic phase formation between 350°C and 500°C, with formation of ferrite and hematite after 600°C at ambient atmosphere. The calcined powder at argon atmosphere formed pure ferromagnetic phase at 1100°C and 1200°C. The Rietveld analyses calculated the cations level occupation and the crystallite size. The analyses obtained nanometric crystals (11-66 nm), that at 900°C/3h presents micrometric sizes (0,45 - 0,70 Om). The better magnetization results were 54 Am2/Kg for x= 0,2 composition, calcined at 350°C/3h and 30 min, and 55,6 Am2/Kg for x= 0,2 1200°C, calcined in argon. The hysteresis shows characteristics of soft magnetic material. Two magnetization processes were considered, superparamagnetism at low temperature and the magnetic domains formation at high temperatures. The materials presented absorption less or equal the 50 % in ranges specific frequency. As for the 2,0 and 3,0 thickness (in 11,0 - 11,8 GHz), the reflectivity of the x= 0,3, 0,5 and 0,4 compositions, all calcined at 900°C/3h showed agreement with MS and O. Various factors contribute for the final radiation absortion effect, such as, the particle size, the magnetization and the polymer characteristics in the MARE composition. The samples that presented better magnetization does not obtaining high radiation absorption. It is not clear the interrelaction between the magnetization and the radiation absorption in the strip of frequencies studied (8,2 - 12,4 GHz)

Usabilidade da Interface do Sistema Eletrônico de Editoração de Revistas: um estudo da revista BiblioCanto da UFRN

The electronic journals correspond publishing channels and dissemination of scientific information. Through them, users can spread their studies as well as developing new researches. One of the systems used for creation and e-journals management is the Electronic System for Journal Publishing (SEER), used in the construction of periodic portals, as well as the creation of magazines in isolation. In this purport, it is believed that the management systems and creation of e-journals should be developed (internally and externally) according to the needs of its users. In the case of internal development, some of these processes refer to the copyright registration and submission of articles, which, in turn, are relevant tasks in the editorial process. Thus, the proposed study, thematic Usability of scientific journals, aims to analyze the usability of the copyright registration process and submission of articles in the Electronic System for Journal Publishing through BiblioCanto magazine, part of the Electronic Journals Portal of the Federal University of Rio Grande do Norte (UFRN). For the realization of the research, two valuation techniques were used: the Usability Test with a total of twenty participants and the Cooperative Evaluation, with the same number of participants separated in four categories considered target audience of that magazine, namely: undergraduate students, graduate students, teachers and librarians. The results indicated that the two analyzed processes (copyright registration and submission of articles) need improvement. In the case of the registration process, the following needs are: signalizing of the conducting registration ambient; description and exclusion of requested information on the registration form. In the process of article submission, it is emphasized improvement of aspects: the early steps to submission, signaling of required fields, concise description of the steps, minimization and review of the steps. To this end, it is believed that in general idea the SEER partially meets the needs of its users regarding the usability of such software.

Usabilidade da Interface do Sistema Eletrônico de Editoração de Revistas: um estudo da revista BiblioCanto da UFRN

The electronic journals correspond publishing channels and dissemination of scientific information. Through them, users can spread their studies as well as developing new researches. One of the systems used for creation and e-journals management is the Electronic System for Journal Publishing (SEER), used in the construction of periodic portals, as well as the creation of magazines in isolation. In this purport, it is believed that the management systems and creation of e-journals should be developed (internally and externally) according to the needs of its users. In the case of internal development, some of these processes refer to the copyright registration and submission of articles, which, in turn, are relevant tasks in the editorial process. Thus, the proposed study, thematic Usability of scientific journals, aims to analyze the usability of the copyright registration process and submission of articles in the Electronic System for Journal Publishing through BiblioCanto magazine, part of the Electronic Journals Portal of the Federal University of Rio Grande do Norte (UFRN). For the realization of the research, two valuation techniques were used: the Usability Test with a total of twenty participants and the Cooperative Evaluation, with the same number of participants separated in four categories considered target audience of that magazine, namely: undergraduate students, graduate students, teachers and librarians. The results indicated that the two analyzed processes (copyright registration and submission of articles) need improvement. In the case of the registration process, the following needs are: signalizing of the conducting registration ambient; description and exclusion of requested information on the registration form. In the process of article submission, it is emphasized improvement of aspects: the early steps to submission, signaling of required fields, concise description of the steps, minimization and review of the steps. To this end, it is believed that in general idea the SEER partially meets the needs of its users regarding the usability of such software.