The modulation of 7Be-aerosols concentration due to solar activity during the cycle 23 is studied in the present research. For that purpose, was analyzed the differences in the long-term variation of geomagnetic and solar activity to assess the physical effects over the evolution of 7Be during the period 1996–2010. Furthermore, exploratory data analysis was applied to understand better the behavior of 7Be-aerosols in the surface atmosphere. This study shows that there is an inverse relationship among 7Be measured in the near ground air and solar activity. The modulation of 7Be-aerosols during the cycle 23 was divided in two steps. In the first stage, ascending phase, 1996–2002, the solar activity played an important role in the production rate of 7Be, r = ?0.75. However, during the descending phase, 2002–2009, the role of the solar activity was secondary, r = ?0.30, allowing that 7Be-aerosols reached the maximum concentration, 9.33 mBq m?3 in August-09 when the solar activity was zero. Moreover, the remaining solar activity after the end of the ascending phase and the last important solar storm (December-06) caused the slowdown of 7Be production rate from 2001 to 2004 and the rupture of the seasonal behavior of 7Be in 2007, respectively. Finally, this research highlight the necessity to take into account the solar cycle phase, ascending or descending, to model studies of atmospheric process with 7Be as tracer since the contribution of the variables studied are so different in these stages. 相似文献
The environmental impacts associated with the exploitation and transformation of fossil resources aggravate the planet's situation in terms of climate change. Due to this, this paper studies an alternative use of mineral coal as a precursor to obtaining new materials with different properties to the starting coals. The thermal degradation of two Colombian semi-anthracites is analyzed through the thermogravimetry (TG) technique coupled to a Fourier transform infrared spectroscopy (FTIR) equipment from room temperature (25 °C) to 900 °C, at a heating rate of 10 K min?1 in an inert atmosphere. The catalytic effect of the addition of silicon to these samples before being subjected to a carbonization process is evaluated during this process. The results indicated that the primary reaction occurs in the temperature range between 400 and 680 °C, where the highest mass loss rate was observed. At the end of the heating process, the TG profile of the samples with silicon addition showed losses between 14.33 and 18.82% in mass, these values being slightly higher compared to the starting and demineralized samples. The release of water, light gases such as CO2, CH4, and species such as toluene, phenol and formic acid was identified in most of the samples. The presence of silica seems to favor the release of all these species, being more evident in one of the semi-anthracites studied. According to the results obtained, it is proved that the presence of silicon in samples subjected to carbonization processes has a catalytic effect that improves some characteristics of the new materials obtained, thus contributing to the use of carbon to get new materials.
In this study, the synthesis of barium metaborate powder (BaB2O4) was carried out by ultrasound-assisted precipitation using different borate solutions. Different solutions such as borax (Na2B4O7, BD), boric acid (H3BO3, BA), and sodium metaborate (NaBO2, SMB) were used in the synthesis and an ultrasonic immersion horn probe was used as the major source of ultrasound. The effect of reaction temperature and time, pH, and crystallization time on the BaB2O4 yield (%) was investigated. The ultrasound-assisted synthesis up to 90 % yield could be achieved using a 0.2 M BD solution at 80 °C, reacting for 5 min at pH 13 followed by 2 h of crystallization. Following crystallization, the obtained powder was heated up to 140, 250, 650, and 750 °C for 2.5 h, and it was shown that β-BaB2O4 nanometric powders were obtained after the 750 °C heat treatment. 相似文献
