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September 10, 2021 Archives

Friday, September 10, 2021

CONTINUITY: Selenium Rectifiers—When They Blow Up, It’s Like a Rectal Fire

You'll find these in all kinds of electrical and electronic gear dating from the 1930s through the 1960s. They were the first (kind of) practical solid state rectifier, but had limited reverse voltage capability and required a stack of individual junctions for mains and higher voltage applications. They had a forward voltage drop of around one volt, which would increase as the unit aged. In high voltage and current applications, this could eventually lead to thermal runaway as heat dissipation and resistance increased, ending with a bang and release of hideously malodorous and toxic smoke. At least, when this happened, there was no question about what was wrong.

Posted at 14:11 Permalink

CONTINUITY: Interstellar Visitors in the Oort Cloud

Objects in the Oort cloud orbit the Sun very slowly: some less than 150 metres per second. This means it takes very little delta-v to cancel enough velocity to cause them to plunge into the inner solar system, where we observe them as comets. Interstellar comets, however, pass through the Oort cloud with velocities typical among nearby stars of tens of kilometres per second and continue unperturbed along their paths. This may have the consequence that in the outer Oort cloud interstellar comets outnumber those gravitationally bound to the Sun by a substantial margin.

Posted at 13:28 Permalink

CONTEXT: Ailerons Connected Backwards! The Wild Flight of Air Astana 1388

Here is more about the Air Astana flight 1388 incident.

Posted at 12:13 Permalink

THE HAPPENING WORLD: Radioactive Decay of Xenon-124 Observed: Half-Life 1.8×1022 Years

Xenon-124 decays to stable tellurium-124 by double electron capture with a half life of 1.8×1022 years, which is around a trillion times the present age of the universe. Its observation by the XENON1T detector is the rarest physical phenomenon ever directly detected. This handily exceeds the previous record set in 2003 by the observation of decay of bismuth-209, half life 1.9×1019 years, about which I wrote in “Barely Radioactive Elements”. This isn't, however, the longest-lived known isotope: tellurium-128, with a double beta decay half life of 2.2×1024 years, which is more than 160 trillion times the age of the universe.

Posted at 11:35 Permalink