Wikipedia:Reference desk/Archives/Science/2016 July 26

= July 26 =

Why do some plates fuse and others don't?
Why did all these plates become glued and never break up again? Many of these faults are geologically dead, right? (Kansas is not exactly known for viscous vicious Keweenawan Rift earthquakes) Sagittarian Milky Way (talk) 13:10, 26 July 2016 (UTC)


 * The tectonic status of a geographical area may be extending, thrusting or strike-slipping, see individual articles. While a geologist should never say never, there is no imminent active spreading ridge, fault line or volcanic center on the North American Plate pictured, with the exception of the earthquakes waiting to happen in California as the Pacific Plate departs north westward, see San Andreas Fault. AllBestFaith (talk) 14:44, 26 July 2016 (UTC)
 * Also don't be so quick to dismiss mid-plate quakes. See New Madrid Earthquake.  -- Jayron 32 15:33, 26 July 2016 (UTC)


 * When I was in Rolla, MO, I noticed that the earthquake report showed weekly earthquakes across Missouri, including epicenters outside the state. Most are very tiny and not reported in the news. Every once in a while, a noticeable one happens. I assumed that the nearly constant small ripples keep large earthquakes from happening, not the concept of completely dormant fault lines. 209.149.113.4 (talk) 17:12, 26 July 2016 (UTC)
 * It should also be noted that earthquakes can be man-made; I don't know what the state of fracking and oil extraction is in the Rolla area, but in Oklahoma, petroleum extraction is closely correlated to an increase in seismic activity. See, for example, here which discusses a precipitous rise in large earthquakes in Central Oklahoma correlated to increased petroleum extraction.  -- Jayron 32 17:15, 26 July 2016 (UTC)
 * For the sake of accuracy, note that it is the deep disposal of wastewater that causes almost all of the earthquakes. Mikenorton (talk) 16:10, 30 July 2016 (UTC)


 * The places that old plates join are known as sutures. One of the major sutures on that map is the Iapetus Suture along the Caledonide orogen, long sections of which are now the Atlantic Ocean, so that one broke up very thoroughly. Rifts tend to be localised along old sutures due to their relative weakness and these in turn may become plate boundaries and the sites of new oceanic crust. This is all part of the Wilson Cycle - supercontinents form and then break apart. Mikenorton (talk) 07:45, 30 July 2016 (UTC)

What is an "at-grade road"?
I've seen the term "at-grade road" in several city articles. A search comes up with a multitude of articles that contain the phrase, but we don't have an article At-grade road, or a redirect to a relevant article that explains the term. Roger (Dodger67) (talk) 14:09, 26 July 2016 (UTC)
 * An at-grade intersection is an area where two or more roadways join or cross. AllBestFaith (talk) 14:19, 26 July 2016 (UTC)


 * Have you seen the term just "at-grade road", or was it part of a phrase like "at-grade road crossing"? We have wikt:at-grade (same meaning AllBestFaith found). DMacks (talk) 14:22, 26 July 2016 (UTC)
 * Cape Town is a fairly brief section with a remarkably high number of ocurrences the term. Roger (Dodger67) (talk) 14:28, 26 July 2016 (UTC)


 * In some places, this kind of terminology is used to distinguish between types of highways or main roads: an access-controlled highway has no at-grade crossings (no level-crossings) - it has onramps and interchanges. Certain types of other fast-traffic roadways may still be called a "highway" or "expressway" - but if they have at-grade intersections, the free flow of traffic is necessarily interrupted at each place where cross-traffic can occur or where vehicles can enter the roadway.
 * If you've done all your driving inside the United States (or some parts of, say, Western Europe), it can be a little bit hard to culturally understand why this detail even matters, but that's because we tend to have an absolutely excellent highway system. You might take the assumption that all major highways use controlled access; and you might never have seen a mega-highway with at-grade crossings.  Many other parts of the world have large highways too - but sometimes, their urban planners have simply "promoted" the various large surface streets into the main arteries for commuter traffic, without actually engineering and constructing the roadway for high traffic capacity and high velocity.  So, in many Wikipedia articles about international roadway transportation, the article authors take the time to call out where the major highways that are actually just surface-streets, to distinguish them from modern freeways.
 * I know of a surface street that used to have 10 traffic lanes, 2 parking lanes and 20 at-grade intersections per mile. Is that the kind of road you're taking about? Sagittarian Milky Way (talk) 02:52, 28 July 2016 (UTC)
 * We do sometimes have such roadways in the United States, too - U.S. Route 1 in North Carolina comes to mind - and you can see our editors discussing where the route turns into an expressway.
 * Nimur (talk) 14:42, 26 July 2016 (UTC)
 * In the Cape Town article section, "at grade" is used as a contrast to "highway", which seems in keeping with the idea of it meaning "a road with at-grade intersections". DMacks (talk) 15:27, 26 July 2016 (UTC)
 * There is an article Intersection (road) - and the intersection is the only point at which the "at grade" description applies. Wymspen (talk) 14:58, 26 July 2016 (UTC)
 * Perhaps you have never seen an elevated highway, like I-35 in Austin (and many of the other expressways); or the Expressways of Shanghai? Or a subterranean roadway, like the Prague tunnel complex or the Boston Big Dig?  In some places, the entire roadway is above- or below- grade.  Nimur (talk) 15:05, 26 July 2016 (UTC)
 * Also, the Cross Bronx Expressway in New York, the Vine Street Expressway in Philadelphia and the Eisenhower Expressway in Chicago are all largely below grade, but they are open cuts rather than tunnels. -- Jayron 32 12:22, 27 July 2016 (UTC)


 * Hence the term Grade crossing. ←Baseball Bugs What's up, Doc? carrots→ 18:04, 26 July 2016 (UTC)


 * Sometimes the main highway rises or dipd to go over/under streets that cross its path (often seen where the streets were there first) and sometimes the crossing streets rise or dip to go over/under the main highway (often seen where the highway was there first). See Underpass and Overpass. Places where a road dips below another have a tendency to become temporary swimming pools during storms, so the overpass is more common than the underpass. --Guy Macon (talk) 14:40, 27 July 2016 (UTC)


 * The use of this terminology appears to be US-specific. I first encountered it here on Wikipedia; it's not a common usage in the UK, even (so far as I am aware) in urban planning contexts. I think the underlying reason for this is that the precise nuance of 'grade' required is not common in UK English. AlexTiefling (talk) 15:02, 27 July 2016 (UTC)


 * If you mean simply for a crossing/intersection, I'm pretty sure it's not US specific. See e.g.      for various people referring to grade separated crossings in NZ. Also this question seemed to start due to terminology in South Africa.  Referring to the whole road as above or below grade is perhaps less common in NZ. However there is the added confusion here of the usage that started this question which appears to simply refer to whether the road is grade separated; and the usage of Nimur and Jayron32 are referring to namely whether the road is above or below the surrounding terrain. A road which is above or below the surrounding terrain could not have simple at grade crossings. But a road could be grade separated but also on level with the surrounding terrain if crossings are raised or lowered (or simply excluded other than the beginning and end).  BTW we gave an article Grade separation. Also the last external link above mentions how different terms like highway, expressway and motorway are used in NZ which I think partly enters into Nimur's point.  Nil Einne (talk) 19:45, 27 July 2016 (UTC)

Tying off and cutting arteries in surgery
Books on surgery such as p37 of this 19th century work by Gerster discuss cutting through the skin and underlying tissues until blood vessels appear in the way, then ligating and cutting the vessels. In modern surgical practice "bleeders" sometimes get sealed with an electric cauterization. Are these vessels always veins, are or they sometimes arteries or smaller arterioles? Are these just little negligible unnamed arteries/arterioles or veins? If an artery is thus cut, how does the tissue downstream which it previously supplied get its oxygenated blood supply? (Edited to add: Here I clearly do not include cases of amputation or excision of the supplied tissue. A typical case would be cutting through the abdomenal wall to reach the organs in the abdomen). In the case of the brain or the heart, tissue death seems to result from a blocked artery, as if one volume of tissue is supplied by one single artery. Do arteries network downstream, unlike the nervous system, so that cutting one artery would be analogous to closing one street, where motorists would simply divert to a parallel street and reach the same destination? So how does muscle tissue downstream from an artery, even a small artery or arteriole, survive ligation of its supply? I could not find an answer in Surgery, Artery, Arterial tree or Circulatory system. This is a request for general information and certainly not a request for medical advice. Edison (talk) 17:48, 26 July 2016 (UTC)


 * So part of this is determining whether the arterial tree is a tree_(mathematics). I'm not really sure, but I thought you might like this schematic I found, which makes the topology easier to understand. According to that diagram, it seems there are some closed loops in the arterial tree, but 1) I don't know what is meant by the white nodes and 2)I don't know how reliable the schematic is.  SemanticMantis (talk) 18:03, 26 July 2016 (UTC)
 * Shit, how do I get to fourth toe? Let's see stay on the aorta train to groin, transfer to the femoral train... Sagittarian Milky Way (talk) 18:32, 26 July 2016 (UTC)
 * I left out the obvious concomitant case of arteries severed in some accident. If a patient has a spurting arterial wound on the arm, say, does the surgeon just tie off the upstream and downstream parts of the artery, or does he have to do vascular surgery to reattach the two severed ends. to avoid death of tissue downstream? Is there a size of artery below which it is ok to just tie it off? Again, not a request for advice, just a question for general scientific knowledge. Edison (talk) 18:07, 26 July 2016 (UTC)
 * Anastomoses exist in many tissues; for example the coronary arteries often withstand single blockages, and the brain has the Circle of Willis. See here for a diagram of some important differences; note that an abrupt coronary blockage often can't be compensated for, but a blockage to a tissue with a lower energy requirement might not be as bad.  I don't know about skeletal muscles but should not be surprised.  It's also worth noting that angiogenesis is reactive, and can completely remodel the blood supply for tissue - for example, consider the desperate treatment a century ago for noses lost to syphilis, where the forearm was sutured to the nose for a couple of weeks, then part of the flesh separated entirely from it to form something like a nose. Wnt (talk) 00:59, 28 July 2016 (UTC)
 * That surgery sounds insane but also kind of awesome. SemanticMantis (talk) 13:56, 28 July 2016 (UTC)
 * Actually it was apparently invented in the 1500s, but people tried their best to forget the technique.  This article also mentions a problem that cold winters would kill the nose, suggesting the angiogenesis was less than perfect - I'll wager there was no microsurgery involved! Wnt (talk) 19:59, 28 July 2016 (UTC)

Cross check
You know when you are on a plane, you hear that broadcast "cross-checking". I'm having trouble finding out exactly what it is. Anyone? Anna Frodesiak (talk) 21:45, 26 July 2016 (UTC)
 * According to this, it means one person checking that a task was done by another person. ←Baseball Bugs What's up, Doc? carrots→ 22:18, 26 July 2016 (UTC)
 * As long as neither person is an ice hockey player, I trust. Collect (talk) 22:29, 26 July 2016 (UTC)
 * Yes. That would send the offending flight attendant to the penalty box for two minutes. ←Baseball Bugs What's up, Doc? carrots→ 22:34, 26 July 2016 (UTC)
 * I don't have a source but I believe this specifically refers to cross checking the doors. If one person forgets to lock the door, or if two people think it was the other person's job to do it that time, or whatever, it can cause an aborted takeoff. Also the doors have to be armed before flight and disarmed before disembarkation, I believe that refers to the emergency slides that automatically (and quite explosively) inflate if the door is opened while it is armed. Vespine (talk) 22:40, 26 July 2016 (UTC)

I posted here because I was having trouble understanding here. (Sorry to split up the discussion.) Please feel free to comment further there. Many thanks. Anna Frodesiak (talk) 23:32, 26 July 2016 (UTC)


 * For an official reference from the FAA, see: Advisory Circular 120-51e, Crew Resource Management Training, and Advisory Circular 120-71a, Standard Operating Procedures for Flight Deck Crewmembers. "Several studies of crew performance, incidents and accidents have identified inadequate flight crew monitoring and cross-checking as a problem for aviation safety. Therefore, to ensure the highest levels of safety each flight crewmember must carefully monitor the aircraft’s flight path and systems and actively cross-check the actions of other crew members."
 * Individual airlines or other operators may have additional procedures that exceed FAA guidance.
 * Nimur (talk) 23:54, 26 July 2016 (UTC)
 * On United Airlines, I always hear "cross check and verify straps" right before takeoff. I assume a message to flight attendants to make sure everything is tied down...or something. Someguy1221 (talk) 01:55, 27 July 2016 (UTC)
 * Hi Nimur. I think those FFA pdfs are using cross-checking as meaning simply checking what each other is doing. As explained here, the term is about the "...emergency escape slides, which inflate automatically if the cabin doors are opened with the slides armed to deploy, are disarmed; and the cabin crew then cross-check each other to make sure the disarming has been done properly..." Anna Frodesiak (talk) 02:48, 27 July 2016 (UTC)


 * The definition above is not how I've used the term "cross check". The definition above is "one person checking that a task was done by another person." The definition I've used is "repeating a task done by another person." As an example, suppose you have Alice and Bob. Alice checks the thingamagig. That's a check. Bob is supposed to cross-check it. According to the first definition, if he saw Alice check it, he did the cross-check. According to the definition I've used, he must also check the thingamagig. In other words, a cross-check is not checking a person, it is checking what the other person checked. 209.149.113.4 (talk) 18:26, 27 July 2016 (UTC)


 * Now that I'm prompted by the question, the exact phrasing I always hear (on airlines in South Africa) is "cabin crew, please disarm doors and cross-check". Finally I know what it means, thanks! Zunaid 18:39, 27 July 2016 (UTC)