Problem is, lithium ion batteries are inherently unstable, so safety systems have to be built in to prevent the batteries from getting too hot from, say, overcharging.

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The number of companies in that predicament tends to swell when economic conditions are weak and credit dries up, but there are also many carriers in countries with unstable economies or political systems who cannot obtain private financing for their aircraft purchases.

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After 30 years of constant warfare, unstable political, civil and governmental systems and a dismal education system, many Afghans look to religious authorities to guide their actions.

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In Arkansas, wind shears and unstable weather conditions suitable for forming super cells, extremely large cloud systems capable of generating powerful tornadoes, were approaching Little Rock.

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