The result is that subsequent structures collapse at increasingly lower heights and require more effort to build.

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The topography also clearly shows the relationship between the scarp of the Olympus Mons, unique on Mars, and structures produced by the collapse of the flanks of the volcano.

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Of those, as many as 2, 500 are deemed dangerous because they may collapse and damage neighboring structures or injure people, Meffert said, and 120 homes -- or what's left of them -- need to be knocked down immediately because they're either in roadways, on sidewalks or on other property.

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Some people think that Nigeria, battered by years of economic decline and the criminalisation of government under military rule, plus a collapse in respect for traditional structures, is on the brink of social breakdown.

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"Unfortunately for the narrow structures in the body (like urethras), they are kind of complex because they tend to collapse, " said Atala, who added that conventional urethra replacement fails more than half the time.

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