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Extra info for [Magazine] Scientific American. Vol. 275. No 4

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Because microorganisms could not have traveled downward from the surface faster than the groundwater descended, some subsurface microbial communities must be at least several million years old. How do microorganisms manage to persevere for so long? In some cases (for example, SLiMEs), bacteria can survive because the essential nutrients are constantly renewed; although in most other sorts of formations, food and energy sources are relatively scarce. NevertheMicrobes Deep inside the Earth JAMES K.

And despite increased allocations for child care, demand will quickly outstrip supply given the new work requirement. According to data from the Congressional Budget Office, states will face shortfalls in child care funding in every year after fiscal year 1998. Even more disturbing is that the legislation reflects a “get tough” attitude that seems to be based on four assumptions that are not supported by empirical findings. The first is that welfare perpetuates dependency rather than serving as a stopgap measure during hard times.

We can now rewrite the laws of friction in a more general way. First, the friction force depends on how easily two surfaces become stuck relative to becoming unstuck: it is proportional to the degree of irreversibility of the force that squeezes the two surfaces together, rather than the outright strength of the force. Second, the friction force is proportional to the actual, rather than apparent, area of contact. Finally, the friction force is directly proportional to the sliding speed of the interface at the true contact points, so long as the surfaces are not allowed to heat up and the sliding speed remains well below the speed of sound.

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[Magazine] Scientific American. Vol. 275. No 4


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