Archive for July, 2011
The chaotic, yet regular sounds of weeping waters and lapping waves inside Lake Superior sea caves
Earlier this month I enjoyed a wonderful sail out of Cornucopia, Wisconsin to Lake Superior’s Mawikwe Sea Caves — described nicely here in a pictorial blog by the Howder family.
Mawikwe means “weeping woman” in Ojibwe. Due to heavy rains in the days leading up to our voyage, the caves were weeping steadily, as you can see and hear in my video. I was fascinated by the cacophony of dripping water combined with the galumphing of the waves into the baby caves at water level. It provided a pleasing mix of randomness and rhythm. Turn up your volume and listen for yourself.
PS. By the way, I learned that by yelling into a sea cave you can (pun intended!) duet yourself.
A Santa Claus machine
Someone just sent me this amazing video of a 3D printer copying a crescent wrench – moving parts and all. The company featured, Z-Corp, is a Stat-Ease client. See this case study showing how their engineers used response surface methods (RSM) to discover a small window of operability.
Another client of Stat-Ease, Stratasys, also offers rapid-prototyping machines, but they make use of another technology called fused deposition modeling (FDM) – explained nicely by this schematic from Ferris State University. I’ve seen these machines at work. They run from plastic line similar to what’s used in a weed whacker. Based on a computerized blueprint, this material (suitable for functional parts, not just prototypes) is melted layer-by-layer into complex shapes. Check out this full-scale turboprop engine produced by FDM.
The next step will be the development of machines that can make whatever you need out of whatever you happen to have nearby that can be shoveled in the hopper. Then people who really want to get away from the crowds can rocket off to any old unoccupied planetismal and set themselves up with house and home.
“It’s possible to imagine a machine that could scoop up material – rocks from the Moon or rocks from asteroids – process them inside and produce just about any product: washing machines or teacups or automobiles or starships. Once such a machine exists it could gather sunlight and materials that it’s sitting on, and produce on call whatever product anybody wants to name, as long as somebody knows how to make it and those instructions can be given to the machine. I think the name Santa Claus Machine for such a device is appropriate.”
– Physicist Theodore Taylor (1978)
Commuting by car or bike: Studies by UK statisticians
This month’s issue (June 2011, volume 8, issue 2) of the Royal Statistical Society magazine Significance [motto “statistics making sense” 🙂 ] features two intriguing articles on commuting.
The first one details Martin Griffiths, a math lecturer at U Manchester, “trying to pull out of the drive” (pp 89-91). This poor fellow must wait upwards of 2 minutes just to get on the road from his property. Imagine the frustration of a somewhat random stream of cars blocking your way out. Then, just as you see a gap, another car comes along to fill it. Griffiths provides a very impressive formula for average wait time based on a Poisson distribution. He factors in the average number of cars passing by as well as the time taken to pull out into the flow. The bottom line: It does not pay to be timid. You’d best mind the gap (inside joke for anyone who’s traveled London’s subways) and make a move!
The second study* comes from a biker, Dr. Jeremy Groves, who spends up to 2 hours or more commuting to his work at Chesterfield Royal Hospital. Thankfully his ride gets considerably shorter in summer when he needn’t wear baggy outerwear, which creates a real drag (Groves estimates 30% more wind resistance). This cycling enthusiast bought a new bicycle recently – one that featured a carbon frame, as opposed to the steel one he’d bought second-hand. Being a fan of randomized (“randomised” in UK spelling) trials, Groves completed a series of runs with one or the other of his bikes – measuring the times taken for the ride from his home in Sheffield to his work at hospital. Seeing his run chart starting off very raggedly at the high end in January, I transcribed only the latter 28 runs (14 of each) for the chart shown. 
Obviously from the overlap in the least-signficant-difference (LSD) bars the results remain inconclusive. (If you have trouble seeing this, click the graph for a larger view of it.) The difference is less than 1 minute in favor of the very costly carbon-framed bicycle. Given a 3.5 minute standard deviation under summer conditions, it would take 400 total runs (200 each) to resolve whether this is a true advantage, according to a power calculation I did with the aid of Design-Expert® software. Dr. Groves has moved on to another experiment for this summer – he plans to randomly load a 4 kg weight on his bicycle (the carbon one, I presume). Aside from being a glutton for punishment, I suppose this fellow wonders how much it slows him down when he must carry in his laptop.
* “Bicycle weight and commuting time: A randomised trial,” pp95-96.