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Erica Hill talks to medical contributor Dr. Holly Philips about the FDA's decision to take a closer look at the possible links between the birth control pill, Yaz and increased blood clots.

The FDA is beginning two days of hearings on the possible withdrawal of its approval of the drug Avastin for treating breast cancer. Dr

(PhysOrg.com) -- Although the uncertainty principle is probably the most well-known example of a fundamental limitation of measurement precision in quantum mechanics, it is not the only one. In fact, every physical system is characterized by a number of variables that do not change their values as the system evolves over time; such variables are called conserved quantities and they are said to obey a conservation law. The fact that some quantities cannot change their values suggests that there might be restrictions on the possible ways in which a measurement device can interact with a quantum object and extract information from it.