Preparation of zinc-oxide and zinc-sulfide powders by controlled precipitation from aqueous-solution

Resumo não disponível..

HST and ground-based eclipse observations of V2051 Ophiuchi: Binary parameters

We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B ~ 16.2 mag. In comparison to the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ~4 and ~5. Flickering activity is mostly suppressed and the lightcurve shows the eclipse of a compact white dwarf at disc centre which contributes ~60 per cent of the total light at 3900--4300 A. We use measurements of contact phases in the eclipse lightcurve to derive the binary geometry and to estimate masses and relevant dimensions. We find a mass ratio of q= 0.19+/-0.03 and an inclination of i= 83+/-2 degrees. The masses of the component stars are M_1 = 0.78+/-0.06 M_dot and M_2 = 0.15+/-0.03 M_dot. Our photometric model predicts K_1 = 83+/-12 km/s and K_2= 435+/-11 km/s. The predicted value of K_1 is in accordance with the velocity amplitude obtained from the emission lines after a correction for asymmetric line emission in the disc is made (Watts et al. 1986). The secondary of V2051 Oph is significantly more massive than the secondaries of the other ultra-short period dwarf novae. V2051 Oph is probably a relatively young system, whose secondary star had not enough time to evolve out of thermal equilibrium.Comment: 16 pages, 7 postscript figures, coded using MNRAS latex style. To appear in Monthly Notices of the Royal Astronomical Society. Revised version with changes in section 4.3. For related papers and files see ftp://fsc01.fsc.ufsc.br/pub/bap and http://www.fsc.ufsc.br/~astr

Germinação de conídios de Microcyclus ulei e sua sensibilidade a fungicidas, "in vitro".

Estudou-se a germinação de conídios de Microcyclus ulei, agente causal do mal-das-folhas da seringueira, em tubos de ensaio de 5mm de diâmetro e placas de Petri de 32mm de diâmetro

Portuguese primary and secondary education in times of COVID-19 pandemic: An exploratory study on teacher training and challenges

The discussion about the use of digital technologies in education is not new. However, the COVID-19 pandemic and the total closure of schools around the world, that forced millions of students to attend their classes from home, has demonstrated the importance of this discussion. It has highlighted the need to revisit debates about the interactions between technology and education, and the added value of digital resources to enhance the educational process. This article, based on an exploratory analysis, aims to understand how the transition from face-to-face to digital was accomplished in Portuguese primary and secondary education, namely regarding teacher training and the difficulties experienced during the emergency remote education period. The data analysed in this article were collected through an online questionnaire, disseminated through online social networks, and answered by 136 Portuguese primary and secondary education teachers. The questions focused on this article were open-ended, and the information collected was analysed using content analysis methodology. The results show how teachers have been forced to modify their pedagogical work, the importance of training, and the inherent challenges and critical reflections associated with the process, as well as the opportunities presented in a post-pandemic educational reality.info:eu-repo/semantics/publishedVersio