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Cake day: July 3rd, 2023

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  • The sound is caused by ‘gradient coils’ that are being switched on and off at kHz frequency, which is in the audible range for humans. The sound is caused by those coils vibrating due to the interaction of the magnetic field with the electric current in the coils: they’re non magnetic but they still feel the ‘Lorentz force’. As far as calibration, there is a pre-scan step (which is one reason why MRIs can take awhile) used to optimize the RF settings to each patient. Patients come in many shapes and sizes so the settings have to be tuned to get a good image every time. I’m actually not sure of how often they need to be serviced, but it seems like the manufacturers are here checking on the machines pretty often!




  • Its an electromagnet that they have cooled down to 4 Kelvin with liquid helium. They take time to ‘wind up’ aka ‘ramping up to the desired/max field strength capable of the magnet’. They do this slowly because the magnet itself can crack if done too quickly, and many components are still affected by the strong magnetic field due to Lorentz forces. Also many components may be classified as ‘non-magnetic’ but still have some small amount of magnetism and can move when subjected to the extremely high magnetic fields. So, if the magnet is ‘quenched’ (all the helium shot out through a tube in the roof) then that process occurs in reverse, VERY quickly, potentially destroying many things. So its not like ‘cutting the power’ because the power is stored around the magnet itself by supercooled components creating a superconducting situation. Nonetheless, in case of harm coming to a person, techs should absolutely hit the quench switch. Not sure what happened to allow this guy in that room though




  • From Article: ‘’'She made those comments on a Sunday morning appearance on CBS’s “Face the Nation with Margaret Brennan,” when Brennan asked her if she felt the city was prepared to handle another fire emergency without a permanent chief.

    “No, no, I don’t think that [the lack of a permanent chief is] a problem at all,” Bass said. “Our interim fire chief has 40 years of experience. In fact, he had just recently retired. I called him in, out of retirement, during the fires. He was doing the emergency operation center. So he stepped in, didn’t miss a beat by taking over the fire department. And we are prepared. We do know that it’s fire season.” ‘’’