Daily Archives: January 27, 2011
She Sells CSACS Down by the Seashore
And they are only about $1500. Chip-scale atomic clock approaches performance of modules
Which applications need a CSAC, with GPS-based clocks so available and prevalent? First, there are applications where the GPS-based timing may not be accurate enough. But there are also many applications where GPS is unavailable, such as underwater exploration, underground drilling, geophysical research, and EMI shielded rooms. There are also in-the-field military situations where GPS and all EM waves are deliberately jammed by patrols, to prevent remote triggering of improvised explosive devices (IEDs), yet there is a need for precise communication-equipment synchronization among combat teams.
Knowing, with some precision, what time it is also helps in acquiring a GPS signal, too. The advantage of a soldier not having to stand out in a field for a minute or so while a GPS receiver acquires a signal and gives coordinates is left as an exercise for the student.
I’ve seen some, up close and personal; they’re pretty cool. In fact, we had a prototype and I took a picture of it with my novelty dime (3″ diameter) to make it look really small.
Sarah McLachlan Science
A Mystery: Why Can’t We Walk Straight?
More like building a mystery*. Perhaps I am missing something, but I’m having a hard time understanding the “mystery” behind this. From a physics standpoint, we know that a moving object will travel at constant speed in a straight line if and only if there is no net force acting on it. Forces along that path will change the speed, so we don’t have to worry about that, and vertical forces can be ignored, since we aren’t going to start levitating or submersing ourselves in the ground. Which leaves us with the last component, which is perpendicular to the path. An acceleration perpendicular to the path gives you — ta da — circular motion. Physics 101.
I’m guessing the problem is in the assumption that the human brain could remove all biases in our locomotion and produce only forces along the direction of travel, without visual cues for feedback. Why would you assume that to be true? The surprise might be that there are biases rather than fluctuations, which would lead to a random walk (in the perpendicular component), but that’s still not a straight line. Assuming no noise processes at all is just naive.
*no data on if this effect holds while wearing sandals in the snow