Esiste una alternativa ActivityPub a LinkedIn?
Sì, si chiama BizzFed ed è ancora agli inizi… È bello vedere che qualcosa si muove nel fediverso anche per l’ambito lavorativo e professionale! 🤩 https://bizzfed.de
🟢 Your smartwatch's green light has a 90-year-old secret origin.
That tiny LED is photoplethysmography (PPG), an optical trick from 1937. Physiologist Alrick Hertzman at St. Louis University pointed a light bulb and photocell at a finger and watched the pulse show up in the changing light passing through the blood.
Same principle, different scale: it now runs hospital pulse oximeters and every fitness wearable. Green light near 520-530nm is strongly absorbed by hemoglobin, so when your heart beats and floods the wrist with blood, less light bounces back to the sensor. Count those dips and you have a heart rate.
One bit of history worth knowing: the rabbit's-ear version of this experiment belongs to Molitor and Kniazuk at the Merck Institute in 1936. Hertzman's landmark 1937 paper measured human fingers and toes, not a rabbit.
The tech also keeps shrinking. In April 2025, SCIVAX and TSLC in Japan announced the world's smallest PPG sensor head at about one square millimeter, a tenth the conventional size. Miniaturization like that is why rings like Oura can get so thin.
It's the first Monday of the month, which is a great time to document something for the first time with a README file https://github.com/ddbeck/readme-checklist
