O princípio básico de produção de imagens em equipamentos de ultrassonografia é a produção de ecos. O princípio pulso-eco refere-se à emissão de um pulso curto de ultrassom que atravessa os tecidos do corpo. No processo de interação entre o som e órgãos ou tecidos, umas das grandezas relevantes é a impedância acústica, relacionada à resistência do meio à passagem do som, definida pelo produto da densidade (ρ) do material pela velocidade (v) do som nesse meio. Quanto maior a diferença de impedância acústica entre duas estruturas, maior será a intensidade de reflexão do pulso e mais facilmente sera possível diferenciá-las. A tabela mostra os diferentes valores de densidade e velocidade para alguns órgãos ou tecidos.

Em uma imagem de ultrassom, as estruturas mais facilmente diferenciáveis são 

(UNIFESP) Reducing food waste would mitigate climate change, study shows

April 7, 2016

Reducing food waste around the world would help curb emissions of planet-warming gases, lessening some of the impacts of climate change such as more extreme weather and rising seas, scientists said on Thursday.

Up to  of emissions from agriculture in 2050 could be avoided by managing food use and distribution better, according to a new study from the Potsdam Institute for Climate Impact Research (PIK). “Agriculture is a major driver of climate change, accounting for more than  of overall global greenhouse gas emissions in 2010,” said co-author Prajal Pradhan. “Avoiding food loss and waste would therefore avoid unnecessary greenhouse gas emissions and help mitigate climate change.”

Between  and  of food produced around the world is never eaten, because it is spoiled after harvest and during transportation, or thrown away by shops and consumers. The share of food wasted is expected to increase drastically if emerging economies like China and India adopt western food habits, including a shift to eating more meat, the researchers warned. Richer countries tend to consume more food than is healthy or simply waste it, they noted.

As poorer countries develop and the world’s population grows, emissions associated with food waste could soar from  gigatonnes (GT) of carbon dioxide equivalent per year to between  and  GT annually by mid-century, showed the study published in the Environmental Science & Technology journal. It is widely argued that cutting food waste and distributing the world’s surplus food where it is needed could help tackle hunger in places that do not have enough - especially given that land to expand farming is limited.

But Jürgen Kropp, another of the study’s co-authors and PIK’s head of climate change and development, told the Thomson Reuters Foundation the potential for food waste curbs to reduce emissions should be given more attention. “It is not a strategy of governments at the moment,” he said.

No trecho inicial do quarto parágrafo “As poorer countries develop and the world’s population grows”, o termo em destaque tem sentido equivalente, em português, a

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