Crazy Eights

My memory was just jogged, bringing this to the fore. A series of cool analemma pictures taken in Greece, showing ruins in the foreground, with the additional feature of some being multiple exposures on a single frame of film.

The analemma — which you can often see on a globe — describes the variation in the position of the sun over the course of the year. Besides the pretty obvious vertical motion you get from the axial tilt of the earth, there is also the effect from the noncircular nature of the earth’s orbit. This causes the earth’s speed to change over the course of the year, so we do not sweep out exactly the same angle from day to day, if you were to assume that noon is when the sun reaches some position in the sky (like straight overhead, or on the vertical line that includes that point). In other words, the time you would read on a sundial will not agree with the time kept by a very good clock. The variation over the course of the year is on order of ± 15 minutes, or almost 4º of arc in each direction. The math that describes this is known as the equation of time.

More detail here or here or many other places on the web.

Traffic

One of the neat things about traffic is how it can be analyzed in terms of some physics parameters. You get density waves that can propagate, and end up getting slowdowns that can persist long after the original cause is gone. Or, as this video shows, there doesn’t have to be a real cause, like an accident or scantily-clad jogger distracting the drivers. Just statistical fluctuation can be enough to send a shockwave through the traffic.

You need to a flashplayer enabled browser to view this YouTube video

There’s a short article as well

(via Cognitive Daily)

UPDATE: more on this at Backreaction. Actual analysis.

The plot shows nicely how the perturbation – the zone of zero velocity (aka the jam) – travels at constant speed in the direction opposite to the traffic flow.

Conferences

FemaleScienceProfessor discusses the pros and cons of talk vs. poster, confounded by the politics of being involved in the conference. Physics conferences in particular have a certain breakdown that’s mentioned over at Uncertain Principles, that being invited talks, contributed talks and posters. It was my impression that posters weren’t nearly as big a thing in the particle physics community vs the AMO community, during my postdoc at an accelerator lab some years back — I was gearing up for an atomic physics conference, to discuss the double-MOT system we had, and how we transferred the atoms, and the particle men acted like they weren’t familiar with the concept of a poster session.

One aspect of talk vs. poster is how important is it to be seen, as opposed to how important it is to get experimental details out (as much as you can do that in 10 minutes or so). In that case it was a description of an apparatus and not any real experimental results, so a poster made sense. When we had some experimental results, I gave a talk, and that gave the attendees a chance to see me and associate my face with that experiment — several or many dozen, as opposed to a smaller number that might have dropped by a poster. (Of course, a smaller number isn’t so bad when it includes a Nobel prize-winner or winner-to-be).

What I remember about that particular talk is that the program listed the talks as being 15 minutes long: 12 minutes of talking, with 3 more for questions. During the announcements preceding the plenary session, we were informed that that was a typo in the program, and the talks were actually just 12 minutes total: 10 for presentation and 2 for questions. The poor people giving talks that day had no chance to revise things and cut down their presentations, and everything ran late. I at least had that evening to make adjustments and drop a slide to bring my talk in in the allotted time.

What Everyone Should Know About Science

The topic being adressed at Uncertain Principles, based on an idea from Michael Nielsen

1) Science is a Process, Not a Collection of Facts

2) Science is an essential human activity.

3) Anyone can do science.

infer some ellipses between those items; Chad goes into some detail about all of them.

Perhaps what science is not is important, too.

– Science doesn’t claim to have all the answers. Good thing, too, since we’d all be doing something else with our lives if everything had been answered.

– Science isn’t about faith (of the religious variety). Related to the above, but it’s important to know that science quantifies certainty and uncertainty. Having some uncertainty is not the same thing as having no certainty at all.

(what everyone should know about blogging: When in doubt, link to someone else)

Having Some Trouble

FYI, I’m having a smidgen of trouble uploading some files to the server for the posts I’m working on. (which is why some posts accessed through RSS won’t show up — they were published and then unpublished as I tried something out that didn’t work)

I know most men wouldn’t admit to having trouble uploading their files, or would try and brag about how many Megabytes they were. But I swear this has only happened once or twice before. It’s not you … it must be the stress.

edit: my “little problem” seems to have been fixed. Though if I keep uploading for four continuous hours, I’m supposed to consult my netdoctor.