European Fuel Economy

Now this's interesting. I'd always heard that European cars in general get higher fuel efficiency than US cars, so I looked it up briefly. Wikipedia, for example, says that a typical European car gets 47 mpg highway, 36 mpg city [Wikipedia: Gas mileage]. But then I checked the Smart Fortwo specifically, since it's got such horrible gas mileage. The exact same model of car the EU rates as 50 mpg while the US rates it as 36 mpg [Wikipedia: Smart Fortwo].

This makes me question our testing methods, and whether European cars really do get better gas mileage than ours. I mean, if we don't test things the same way, it's comparing apples and oranges. Anyone know more about this?

Chocolate, Caffeine, and Theobromine - Oh My!

Branching from a different discussion about migraines, dehydration, and caffeine, I wanted to look up whether caffeine was dehydrating - I knew it was a diuretic, but I wanted to know if it more directly dehydrated. And then I got sidetracked by an article about a parrot dieing from chocolate overdose. So rather than having any sort of coherent picture for you today, I present you with some snippits of facts about chocolate, caffeine, and theobromine.

• "In healthy adults, caffeine's half-life is approximately 3–4 hours. In women taking oral contraceptives this is increased to 5–10 hours" [Wikipedia, original source] In other words, caffeine affects women on the Pill for twice as long as it does for most other adults, but it probably affects people not on the Pill more quickly and more strongly.


• Caffeine on its own is a stimulant in the body. Caffeine metabolizes in the liver into three different other chemicals - most becomes paraxanthine (84%, takes fat out of storage and into the bloodstream, raising blood sugar levels, and sugar is a stimulant), theobromine (12%, diuretic and a stimulant, is present in chocolate and is why most people mistakenly think that chocolate has lots of caffeine), and theophylline (4%, a good asthma treatment, but in much higher concentrations than produced by caffeine metabolism, also raises blood pressure). Each of these by products appears to be created by removing a CH_3 from caffeine and replacing it with a Hydrogen, the only question is which one gets removed; each of them has further stimulant effects. [Wikipedia: Caffeine, Theobromine]


• Chocolate contains both caffeine and theobromine, but significantly more theobromine, and only about as much caffeine as a cup of decaf coffee. Theobromine is often confused with caffeine however, and the media does not distinguish between the two, so the misconception that chocolate is a significant source of caffeine continues to perpetuate.


• One of the ways caffeine works is that it "competes" with adenosine, so that it essentially stops adenosine from working. Adenosine is a depressant in the human nervous system, and its presence is related to the need for sleep; its lack means that dopamine instead begins to dominate - and dopamine is a stimulant, increasing heart rate and blood pressure.


• In humans, theobromine has less of an effect on the nervous system than does caffeine, but has more of an effect on the heart. In addition, theobromine relaxes smooth muscles (ones that act involuntarily), such as dilating blood vessels (and thereby decreasing blood pressure) and bronchial tubes in the lungs (possibly explaining why I've always felt that caffeinated beverages help when I'm feeling allergic, as I also have allergy-triggered asthma).


• For reasons unclear to me, most animals (including dogs, cats, and birds) process theobromine more slowly than humans, with the result that it affects them more strongly, leading to theobromine poisoning. Do NOT feed your pets any of your leftover holiday chocolates. It could be the last thing they eat.

Well, that's a bunch of disorganized facts for you. :-P I warn you of two things though, (1) "damnit Jim, I'm a doctor not an engineer!" I'm a astrophysicist, not a biologist, so it's possible I'm understanding some of this wrong; and (2) since I'm not on the clock, I used Wikipedia as my primary (nearly only) source rather than peer-reviewed journals, or even authoritative/reputable news sources, and as we all know, Wikipedia's biggest strength and weakness is that anyone can edit it. If you wish to contradict or clarify anything I mentioned here, I'd appreciate a concise quote from another source, as well as a link to it - I'm looking to learn! :)

ETA: Another link here to birds and theobromine.

Oh, Arizona

Former AZ governor "comes out" that he believes a famous "sighting" in in 1997 called the Phoenix Lights was an alien spacecraft, and says the burden of proof otherwise is on the DOD. *rolls eyes*

Lunar Eclipse Saturday!

Saturday is a total lunar eclipse (pointed out to me by Sclerotic_Rings as usual).

Man, I just love these things! Notice how Saturday's lunar eclipse is followed in two weeks by a partial solar eclipse. Also note how that happens again later this year (six months later) in August/September. The reason? When the Earth-Moon-Sun are aligned just right for a part of the year (line of nodes, eclipse season), they may cross each others paths for a couple weeks before and after - this means that whenever there's a solar eclipse (at a New Moon), there's a good chance of a lunar one two weeks before or after (at the Full Moon). And if there's one set on a certain date, there's a good chance six months before or after, halfway around the Sun, that it might happen again.

More info on Wikipedia.

Exoplanet data

The furthest discovered exoplanet is OGLE-2005-BLG-390Lb, at 21,500±3,300 ly distance. However, it is an anomaly, as it was discovered using gravitational lensing, which I believe allows us to detect things much further away than the other methods, so the fact that most exoplanets have been discovered by other methods leads me to think I should throw out lensing-detected exoplanets.

Wikipedia also has a list of all 212 exoplanets discovered to date, that I intend to comb though. It occurs to me that if I do a rigorous job of this, I could submit it as a literature review to a peer-reviewed astronomy journal. One problem is (in addition to getting primary sources for the Wikipedia info) it would require me to confirm that no one else has published the same thing. To that effect, a couple links for me (and anyone else curious):

• ADS Abs - a searchable archive of all published peer-reviewed astronomy papers. I think it stands for Astrophysical Database Service Abstracts, but I could be wrong. Hosted by Harvard.


• Astro-ph - another searchable archive of astronomy papers, not as good a search engine, but includes papers that are in the process of peer-review and aren't yet published. Hosted by Los Alamos National Labs.

Climate Change Report

I recently wrote an email to a colleague with whom I've been debating global warming. We both agree that it's happening, but he thinks we do not have sufficient evidence to conclude it's manmade (via CO_2) rather than solar variation.

My email:

FYI, here's a link to a summary of the IPCC report on global warming from Wikipedia.
And here's the full text.

The summary is in a nice bulleted format with section headers, so you can skip to the parts you're most interested in. The report includes data stating that

1) atmospheric CO_2 and methane levels are higher than at any other time in the past 650,000 years, and

2) since 1750, human activities have resulted in "radiative forcing" of 1.6 W/m^2, while solar variations have resulted in only 0.12 W/m^2.

Page 11 of the full text has a graph, Figure SPM-4, which compares the observed temperature increase since 1900 with computer models assuming only natural sources, and natural plus antropogenic sources - search through the full document on the word "solar" to find relevant sections.

I don't have permission to repost his reply, so I'll try and reword it at another time.

See also this paper on ice ages, this discussion of that paper, and this discussion of that discussion.