Wikipedia:Reference desk/Archives/Science/2016 March 31

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March 31

When did the Moon become tidally locked to the Earth ?

Can we put a date on it ? StuRat (talk) 02:14, 31 March 2016 (UTC)

This has some calculations and comes up with an answer for you. --Jayron32 02:29, 31 March 2016 (UTC)

That page in turn cites this one, which states that such estimates can be very far off. --69.159.61.172 (talk) 05:58, 31 March 2016 (UTC)

It's tidally locked everyday. :) --DHeyward (talk) 08:51, 31 March 2016 (UTC)

OK, thanks all. StuRat (talk) 14:54, 4 April 2016 (UTC)

Is it easier for a tornado to make a cow fly or a car or a mobile home/trailer?

The car is several times heavier but it's several times less dense. The trailer might be less dense than the car no? At least when empty. Since it has no engine and more volume to area. It is less aerodynamic and more easily toppled than an SUV. It semi-traps the wind under it as long as the trailer doesn't leave the ground and then increases the area facing the wind (up to a point) as the trapped air effect decreases which should give it some rotational momentum on the long axis for the wind to accelerate. So maybe a mobile home is the easiest of all?

Could a tornado suck up a tank? (high weight, high density). Sagittarian Milky Way (talk) 18:00, 31 March 2016 (UTC)

Tanknado? Now that's scary. You think baseball-sized hail is bad, try HE shells! But why the shells you ask? Because A-Team is coming in for a landing!Wnt (talk) 18:18, 31 March 2016 (UTC)

I believe you have the right ideas, that density matters more than weight, and that the shape also matters quite a bit. The hardest thing to lift is something dense and flat to the ground and attached to it, like pavement. If the pavement is ripped from the ground, you have had a massive tornado. A trailer with no engine would be low density, so would be blown around easily, if not properly anchored to the ground. Cars and trucks would be next, and the cow would be after that, then the tank would be hardest of all to lift. StuRat (talk) 02:02, 1 April 2016 (UTC)

Certainly trailer parks here in Texas are commonly described as "Tornado magnets" - that's because they frequently figure in the news when there are tornadoes touching down. People assume that tornadoes more frequently hit trailer parks - but in truth it's just that they are vastly more likely to be damaged than more substantial (ie denser) structures. The goal when designing such structures is often to enclose the maximum amount of living space with the least amount of material - so they do tend to have low densities when compared to cars and cows. SteveBaker (talk) 13:17, 1 April 2016 (UTC)

Self-driving cars and drafting

I've read that theoretically, a person driving right behind a semi rig can cut gas consumption by as much as half - but he'd have to drive in a suicidal position, within a meter of the back of the rig, and of course it could brake at any time.

However, it strikes me that the self-driving cars being produced should have many advantages - they should have real-time machine-to-machine communication that allows them to coordinate drafting maneuvers from both ends. Do they have enough control via their interfaces to literally dock a specialized fitting to securely link them as a "train"? (Besides reducing the risk of jarring mismatches in position, this would allow the rear cars to deliver their fair share of the energy, so that the front car is not paying full freight when everyone else gets half off) Does the car in front have enough lead time when it sees a hazardous situation that the ones behind can either unhook and evade or else just brake in synchrony?

Has anyone tested anything like this? I'd imagine that you could link any number of self-driving cars together in a train, essentially without limit since each provides its own power. Ideally they should have some kind of specialized structure (maybe even just a set of streamers, or perhaps something more solid) that would make them "one" so that the wind would flow past as if they were a single vehicle. But they'd need some kind of common, manufacturer-independent protocol for communication, docking, and connecting to reduce air resistance, probably other things. Is there any such protocol? Wnt (talk) 18:30, 31 March 2016 (UTC)

I should note I've found some mentions, not very detailed, of "flocking" of self-driving cars [1] but this still implies considerable distance between them. Wnt (talk) 18:38, 31 March 2016 (UTC)

About a month ago, a self driving car found itself unable to avoid hitting a bus when both were traveling at very low speeds: [2]. Given that, I'm not sure the technology exists now to safely allow for self-driving cars to try the maneuvers you are describing. Of course, in the future, who knows? --Jayron32 18:45, 31 March 2016 (UTC)

This was a report about testing self-driving lorries, which would lock into a convoy with just a few feet between vehicles: http://www.bbc.co.uk/news/technology-28834774 217.44.50.87 (talk) 19:24, 31 March 2016 (UTC)

Lockheed Martin has worked on convoys of autonomous vehicles. For example, this 2014 press release, U.S. Army and Lockheed Martin Complete Advanced Autonomous Convoy Demonstration, describes technology for convoys of self-driving military vehicles. I'm pretty sure I've seen presentations from Lockheed Martin and others that describe fuel economies, although wind resistance is not the only advantage. Here's a decent starting place: a 2015 review presentation of interesting technologies investigated by the Army's TARDEC Tank and Automotive Research, Development, and Engineering Center. Fuel economies of modular autonomous vehicles are described. Nimur (talk) 19:28, 31 March 2016 (UTC)

That picture in the first (Lockheed Martin) link shows vehicles quite widely spaced - the convoy doesn't really look like it's worried about fuel, but rather is reducing the number of people exposed to (presumably) potential hostile action. Even the BBC link in the response above that presumes vehicles meant to work together in advance. But what would really seem to make sense is that the car comes onto the freeway, finds a line of other autonomous cars of all descriptions, and they all roll down as one big unit until the next exit where a subset might break off. For which a more universal standardization would be needed. Still -- these are pretty good finds, thanks. Wnt (talk) 21:07, 31 March 2016 (UTC)

They don't have to be self-driving cars. They only have to be self-braking and have some form of communication.Llaanngg (talk) 00:09, 1 April 2016 (UTC)

Well, to physically hitch them I'd expect you'd want robust computer-controlled steering, so that going over a pothole at the wrong time doesn't scratch your pretty chrome bumper (or worse) when you're trying to link up. Wnt (talk) 01:10, 1 April 2016 (UTC)

I'm rather surprised that nobody has mentioned the Mythbusters episode where they figured out that you have to be incredibly close to see any sort of real fuel savings. Dismas|^(talk) 01:23, 1 April 2016 (UTC)

@Dismas: In a way this question was inspired by that episode - I think I remember them getting close to 50% savings at that ridiculously close distance. That's why I was suggesting a physical connection (and even some kind of shell to keep air from getting into the remaining space between vehicles) rather than just a "flock". Wnt (talk) 17:20, 1 April 2016 (UTC)

See also slipstreaming wch cites "a 10% increase in efficiency of certain hybrid vehicles".--Shantavira|^{feed me} 06:52, 1 April 2016 (UTC)

It's worth mentioning that the lead vehicle gets benefits from slipstreaming as well as the one at the rear - but the largest gains are in the middle of the pack.

With intelligent vehicles (even if they aren't 100% self-driving), the communications lag should be a vanishingly small percentage of the time for braking - where mechanical parts have to move. I don't think it would make much difference to stopping distances for all of the vehicles to spend a millisecond be informed by the one in the lead of the intent to brake (or turn, or accelerate, etc) so that it happens at the exact same time. My concern would be about the degree of maintenance of these vehicles. If someone in the middle of the pack has worn brake pads and bald tires - then the possibilities for disaster become rather severe. SteveBaker (talk) 13:09, 1 April 2016 (UTC)

Well, the self-driving car ought to know if it has those mechanical problems, and know whether it can compensate to match the other cars with its current status or not. And the case of the abrupt failure is one of the reasons I suggested a linkage, so that the other cars would physically help the damaged one keep going at the same speed - while, of course, collaborating as a unit to brake it safely as it would with its own self-driving algorithm, even as those not adjacent peel off and reform, until they can leave it safely alongside the road and go on. Wnt (talk) 17:24, 1 April 2016 (UTC)

Perhaps some of this belongs in Platoon (automobile). Jim.henderson (talk) 17:11, 1 April 2016 (UTC)

Now that is a relevant keyword. (though I thought men joined platoons and vehicles joined convoys...) Wnt (talk) 17:27, 1 April 2016 (UTC)

Anti-wart vaccines

Is there a vaccine that prevents one from getting "ordinary" warts on the skin, e.g. plantar warts or the ones pictured in File:Wart ASA animated.gif? Wart#Prevention only really addresses genital warts, ignoring everything else except for a single unsourced statement saying that ordinary anti-genital-wart vaccines don't affect plantar warts. HPV vaccines appears to concern itself entirely with the genital-wart types of viri. Not surprisingly, I can't find anything else on Google. Nyttend (talk) 19:24, 31 March 2016 (UTC)

The Plantar wart article indicates there is no vaccine. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:34, 31 March 2016 (UTC)

See Plural form of words ending in -us#Virus, incidentally. "Viri" is attested - that doesn't mean it's correct. Tevildo (talk) 19:49, 31 March 2016 (UTC)

Hm. I thought all warts were caused by HPV, and wart supports that. But there are hundreds of strains of HPV, so this becomes a very detail-oriented question about how and if vaccines against viral infections have any cross efficacy to closely related strains. There is also the matter that we would never expect a vaccine to do anything much to a current infection. So of course an HPV vaccine will not affect a plantar wart, but it conceptually might still be able to decrease chances of new infection. I'll do more searching of the academic literature to see if I can find any clarification. SemanticMantis (talk) 19:54, 31 March 2016 (UTC)

Here [3] is a research paper that discusses a bit about vaccine development strategies and a little about what works for what. SemanticMantis (talk) 20:20, 31 March 2016 (UTC)

Our entry on Gardasil says it is up to a 9-valent vaccine, i.e. it is a mixture of vaccines against HPV 6, 11, 16, 18, 31, 33, 45, 52, and 58. The bad news is that our wart article blames common warts on "2 and 4 (most common); also types 1, 3, 26, 29, and 57 and others", and plantar warts on "HPV type 1 (most common); also types 2, 3, 4, 27, 28, and 58" - which means that only one (58) is shared with the vaccine. The good news of course is that the vaccine does largely prevent genital warts and cervical cancer caused by them. Which means that it is reasonably likely that a similar 7-valent vaccine could target common warts, or a 10-valent vaccine could target common + plantar warts, and actually provide protection. Wnt (talk) 01:06, 1 April 2016 (UTC)