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Additional info for [Magazine] Scientific American. Vol. 275. No 6

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When the enzymes are activated (the blades are unsheathed and wielded), they chop various other proteins in ways that lead to destruction of the cell. Some of the cleaving destroys essential structural components of the cell. And some of the cutting leads directly or indirectly to destruction of the cell’s genetic material, thereby preventing the cell from maintaining itself. In spite of their shared death machinery, cells can differ in the specific signals that induce them to eliminate themselves.

As long as a cell is useful to the body, it will restrain its death machinery. If, however, the cell becomes infected or malignant or otherwise threatens the health of the organism, the lethal proteins will be unleashed. Apoptosis may be set in motion by various triggers, including withdrawal from a cell of the chemical signals (known as growth, or survival, factors) through which cells reassure one another of their importance. Death can also be triggered by a cell’s receipt of external or internal messages that override the reassuring ones or by the cell’s receipt of conflicting directives as to whether it should divide.

We were keen to find out. Julia and I and Northwestern graduate student G. William Nieman set out to make nanophase palladium and copper and to study their strength as a function of grain size. To gauge the strength of the metals, we measured their hardness, testing how easily they could be deformed. As expected, the strength of pure copper increased as its average grain size decreased. When the grains were 50 nanometers in diameter, the copper was twice as hard as usual. Sixnanometer grains—the smallest size we could readily make in our synthesis chamber—yielded copper that was five times harder than normal.

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