Um produtor rural registrou queda de produtividade numa das áreas de plantio de arroz de sua propriedade. Análises químicas revelaram concentrações elevadas do íon amónio (NH₄⁺) e baixas dos íons nitrito (NO₂^-) e nitrato (NO₃^-) no solo. Esses compostos nitrogenados são necessários para o crescimento dos vegetais e participam do ciclo biogeoquímico do nitrogênio.

Em qual etapa desse ciclo biogeoquímico são formados os compostos que estão em baixa concentração nesse solo?

A obtenção de energia por meio da fissão nuclear do ²³⁵U é muito superior quando comparada à combustão da gasolina. O calor liberado na fissão do ²³⁵U é 8 x 10¹⁰ J/g e na combustão da gasolina é 5 x 10⁴ J/g.

A massa de gasolina necessária para obter a mesma energia na fissão de 1 kg de ²³⁵U é da ordem de

Are Twitter and Facebook Affecting How We Think?

Is constant use of electronic gadgets reshaping our

brains and making our thinking shallower?

By Neil Tweedie

How many times do you click on your email icon in a day? Or look at Facebook, or Twitter? And how many times when reading on the internet do you click on a link navigating away from the text that was the original object of your enquiry? The web, it seems, is like an electronic sweet shop, forever tempting us in different directions. But does this mental promiscuity, this tendency to flit around online, make us, well, thicker?

Nicholas Carr, the American Science writer, has mined this theme for his new book, “The Shallows”, in which he argues that new media are not just changing our habits but our brains. It turns out that the mature human brain is not an immutable seat of personality and intellect but a changeable thing, subject to “neuroplasticity”. When our activities alter, so does the architecture of our brain. Tm not thinking the way I used to think,” writes Carr. “I feel it most stronglywhen l’m reading.”

Disponível em: www.telegraph.co.uk. Acesso em: 27 fev. 2012.

Neil Tweedie levanta vários questionamentos sobre a utilização de diferentes recursos tecnológicos disponíveis hoje em dia. A partir desses questionamentos e dos argumentos do escritor norte-americano Nicholas Carr, o texto sugere que

                         Getting Every Child to School

      Right now 67 million children are missing out on their right to an education. They can’t go to school because they have to work to survive, because they are girls or even because there are no schools where they live.

       Where will these children be when they grow up without the chance to learn?

      We’re working to make sure every child goes to school. We’re helping build schools, train teachers, advocating girl’s education and reaching children who have to work or are caught up in emergencies with learning.

      You can help uphold every child’s right to an education. Make a donation today to not only give children the chance to go to school, but also save their lives and protect their childhoods.

Disponível em: www.supportunicef.org. Acesso em: 20 maio 2013 (adaptado).

Essa campanha pretende contribuir para diminuir a desigualdade social, uma vez que

On the Meaning of Being Chinese

Ethnically speaking, I feel I am complicated to classify, but who isn’t, right? To me, being Chinese-Brazilian in America means a history of living in three opposite cultures, and sometimes feeling that I did not belong in neither, a constant struggle that immigrants, and national citizens, face when their appearance is foreign to natives in the country. Jokingly, I say that I am Asian in America, Brazilian in China, and a “gringa” in Brazil. Nevertheless, 1 believe that dealing with these hard to reconcile extremes have somehow helped me to become more comfortable with my identity.

BELEZA LI. Disponível em: www.aiisf.org. Acesso em: 28 mar. 2014.

Nesse fragmento, Beleza Li resume sua experiência de vida ao descrever a complexidade em