Wikipedia:Reference desk/Archives/Science/2015 May 18

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May 18

relative refractory period in the heart

Does when the relative refractory period occurs in the heart, that means that there is re-polarization and depolarization in the same time? 149.78.38.232 (talk) 03:15, 18 May 2015 (UTC)

volcanololy/geology

why is sulphur always associated with volcanism?

There is sulfur in solid form in lots of rocks, but it's not very noticeable like that. Only when heated by volcanism and in vapor form does it become noticeable, due to it's pungent odor. StuRat (talk) 15:17, 18 May 2015 (UTC)

To expand on Stu, sulfur has a relatively low boiling point, and hence vaporizes out of lava when it is present in excess It then quickly condenses near the vent, building up pure deposits. μηδείς (talk) 19:51, 19 May 2015 (UTC)

Sleep issue

Hi,

If I sleep for 8 hours, wake up and continue the day, I get tired and I do feel like going to sleep again, and sometimes I do sleep for an hour or two when I feel like I can't take it anymore. But when I sleep for 12 hours, I don't feel like going to sleep at all, I also, can continue over 24 hours... I do wish to sleep for 8 hours as it is suppose to be healthy and I don't want to go to sleep during the next 16 hours... I don't have no desire of sleep for 12 hours as it is suppose to be unhealthy...

What should I do? Any suggestions? I thought of exercising, but it's tiring...

Mr. Prophet (talk) 10:13, 18 May 2015 (UTC)

We shouldn't be giving you medical advice, like it says at the top of the page. And without doing some sort of sleep study, our answers would likely be nothing more than guessing in the dark. That said, you might like to read Circadian rhythm and some of the articles linked from it. Dismas|^(talk) 10:55, 18 May 2015 (UTC)

I know, I'm aware, my English sometimes do come across as something else when I mean something 'else'. I only seek advice, a brainstorm, a guidance and so on, in order to understand a thing better... Sorry for it coming across like that...

I glanced through what you guided, it talks about 'entrainment'. What about this image, the clock and the environment, are they conjoined or can be noted separately according to personal life style? -- Mr. Prophet (talk) 18:24, 18 May 2015 (UTC)

Tasking

When should I start reading/learning or exercising after eating? After how many minute(s)/hour(s)? -- Mr. Prophet (talk) 10:16, 18 May 2015 (UTC)

When you are alert enough. It all depends on you. KägeTorä - (^影_虎) (もしもし！) 12:22, 18 May 2015 (UTC)

Okay, thanks -- Mr. Prophet (talk) 18:27, 18 May 2015 (UTC)

Never heard anyone argue against reading or learning after eating. And the exercising thing I only ever heard about swimming, due to the possibilities of cramps, but I don't know whether to take that seriously. StuRat (talk) 15:13, 18 May 2015 (UTC)

Lol. I was wondering... -- Mr. Prophet (talk) 18:10, 18 May 2015 (UTC)

For a brief moment I thought this section was addressed to me —Tamfang (talk) 09:13, 19 May 2015 (UTC)

• If Russell.mo has a dietary based mental issue he needs to see an endocrinologist ASAP, not be asking strangers on the internet. μηδείς (talk) 19:49, 19 May 2015 (UTC)

@Medeis: Well, I may have excretion problem I'm making love to my bed whenever I'm free, this action dominates my life more than eating, sleeping, walking, name it, whenever I'm not reading/learning/writing, I'm in my bed, having fun. I don't have no control over it I never thought it was a problem because my girlfriend is going crazy to live with me ever since hearing about it...

What do you say? Would you still advice me to visit the endocrinologist? -- Mr. Prophet (talk) 06:05, 20 May 2015 (UTC)

There is little, if any, negative impact on your physical health from exercising immediately after eating, not including overeating. The association with cramps and what else have you, is a results of folk wisdom, and the placebo effect. Plasmic Physics (talk) 05:19, 22 May 2015 (UTC)

I'm guessing, after reading all the comments, 'cramps' might occur if it involves heavy exercising such as swimming, with less fluid (water) inside the body. -- Mr. Prophet (talk) 18:19, 22 May 2015 (UTC)

Age and the amount of sleep

As humans age, they sleep less. I've read that old people don't need less sleep, they just don't (can't?) stay asleep as long as younger adults do. What's the mechanism that causes humans to sleep less as they age. --98.114.146.70 (talk) 11:44, 18 May 2015 (UTC)

Old people are less active. How many 60+ year olds do you see being forced to do sports at school? KägeTorä - (^影_虎) (もしもし！) 12:18, 18 May 2015 (UTC)

There are probably multiple mechanisms, but one of them is that the brain's biological clock, the suprachiasmatic nucleus, generates circadian rhythm signals that decrease in amplitude with age. The result is to leave people feeling less sleepy during the night. See http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3624052/ for a recent review. Looie496 (talk) 13:19, 18 May 2015 (UTC)

ISS

i want to go to international space station and i want to take some pictures of blue marble ,is it possible? well i am not an astronomer,the astronomers who are in space station they are only taking pictures of the outer space ,and doing some experiments i guess. 13:21, 18 May 2015 (UTC) — Preceding unsigned comment added by 178.152.240.42 (talk • contribs)

The space station is too close to Earth. The ISS orbits 200-300 miles above the Earth's surface. You would have to get a few thousand miles from Earth to see it as a blue marble. Looie496 (talk) 13:24, 18 May 2015 (UTC)

However you can easily find many, many photos originating from the ISS of what's visible of earth taken by instruments and by astronauts. E.g. [1]. There is also the famous and somewhat controversial Hyundai ad campaign [2] [3] although this, as with a number of photos was I presume taken with a zoom lens so wasn't trying to maximise the visible portion of earth. Incidently, if you have a very good reason for needing specific new imagery and there is nothing already out there that is good enough, you can even make a request for someone to take a photo for you [4]. (Read what I said again before trying anything like that, if you haven't actually do a good search of existing imagery or don't have a very good reason, your request is likely to be ignored.) In fact in the modern digital camera era, I suspect the majority of astronauts who have been to the ISS have probably taken at least one photo of earth. In fact it wouldn't surprise me if most take far more photos of earth than outer space. BTW, most people who have been to the ISS aren't really astronomers AFAIK. Nil Einne (talk) 13:47, 18 May 2015 (UTC)

Here are some images which show parts of Qatar all apparently taken from the ISS [5], [6], [7] Nil Einne (talk) 14:13, 18 May 2015 (UTC)

Read space tourism and then come back to us whether you think you can make it to the ISS. Your chances are slim indeed, even if you had the money. 131.251.254.154 (talk) 14:44, 18 May 2015 (UTC)

If you have a billion dollars, and are willing to wait a few decades, you can probably go into space in your lifetime. StuRat (talk) 15:11, 18 May 2015 (UTC)

According to the article, you only need to have about $40 million and be willing to wait until later in 2015. -- BenRG (talk) 19:16, 18 May 2015 (UTC)

I can believe some people with $40 million can go up in 2015, but not all of them. StuRat (talk) 19:34, 18 May 2015 (UTC)

Who want's 40 million? Get ready to catch it, cause I'm gonna sneeze it! -- Mr. Prophet (talk) 05:39, 19 May 2015 (UTC)

They were suppose to sink the ISS in 2015, in the 'deep blue sea/ocean', I read this in a newspaper long time ago! What's going on? Does anybody know? -- Mr. Prophet (talk) 18:30, 18 May 2015 (UTC)

Not sure in the case of the ISS, but it's not uncommon for missions to be extended, if the equipment is still functional, still doing good science, and the budgetary and political climate allows it to continue. I even think they may set artificially early mission endings, knowing they are likely to be extended, since extending a mission looks a lot better than ending it "early". This reminds me of Scotty on Star Trek always saying everything is impossible, then getting it done in the next scene. StuRat (talk) 18:40, 18 May 2015 (UTC)

Unsurprisingly, International Space Station program has a fair amount of info on the history of the mission life span, particularly in the #End of Mission section. Nil Einne (talk) 19:21, 18 May 2015 (UTC)

NASA only recently signed a billion-dollar plus contact with SpaceX to make supply trips to the ISS. That would be a very strange thing to do if the plan were to scrap it later this year! That suggests that there is something wrong with this claim. SteveBaker (talk) 20:03, 18 May 2015 (UTC)

From our ISS article's lede: As of January 2014, the American portion of ISS was funded until 2024. Roskosmos has endorsed the continued operation of ISS through 2024, but have proposed using elements of the Russian Orbital Segment to construct a new Russian space station called OPSEK. -- ToE 21:00, 18 May 2015 (UTC)

Sounds like I did read the right info on the newspaper, (like Stu said), otherwise why would they expand the program a year before if it wasn't doing good... -- Mr. Prophet (talk) 05:29, 19 May 2015 (UTC)

Not sure why there remains any confusion. If you read the article which me and others have linked, there was a suggestion once to deorbit the ISS in 2016. Whether or not you remember what you read right, no one can say unless you actually find the specific article you read. Nil Einne (talk) 11:46, 19 May 2015 (UTC)

There's no confusion, others have also defined it, and the article don't say what Stu said!... -- Mr. Prophet (talk) 19:00, 19 May 2015 (UTC)

My point is the extension is largely irrelevant to what you may have read. The question is whether there was ever a stated suggestion to deorbit it in 2015, not whether it was extended. The info suggests there may have been a suggestion to deorbit albeit in 2016 not 2015 (although the mission would have ended in 2015). Also, if you read the article, it strongly suggests StuRat's comment is too simplistic. It isn't just about setting deadlines early because extending sounds better than cutting short, but also very likely to do with the fact budgetary and political elements change over time. As well, trying to guarantee something so far in advance is fairly risky when you can't really predict how these will change in the future. In fact setting a short mission may also be seen as a way to push the budgetary and politics in the desired direction. This is particularly for something as costly, and as internationally complex as the ISS. StuRat mentioned something about budgetary and politics, but seemed to fail to make all these likely connections and instead only mentioned one possibility, which may be true, but is likely to only be one component. Nil Einne (talk) 20:33, 19 May 2015 (UTC)

Acknowledged! I've also read through...

A general thought (don't mind ), conversations do sometimes go round in a circle in order to comprehend the complete picture of a thing 'sometimes', if everything went straight all the time, we wouldn't have needed a brainstorming method, people with ideas, and so on. Discussions open, lead to possibilities, if you take this freedom away from people than we might as well be robots or Pharaohs slaves.

Personally speaking, I can't put my finger on a single comment that deviated, but was relative... I could be wrong. Stu might not have mentioned the complete thing but have some (like you said, one), any project (you name it) do extend due to many reasons, I guess thats why the ISS did not stop deorbiting. You also guided the article, people who are interested can read through the article too... You also gave a summary for correction/complete picture... Everything went step by step. Others also have said things that are 'relative'...you know what I mean. If you still think that I'm wrong than I'll bow to your decision, cause you've helped me a lot, I don't want you to be annoyed with me... -- Mr. Prophet (talk) 18:28, 20 May 2015 (UTC)

'budgetary' and 'politics'? If I get this right from what Stu stated, its about 'money' and 'power', definitely not an uncommon thing to think of when the countries unite. Problems have always occurred between indifferent level group(s), sometimes discreetly sometimes aloud; natural... -- Mr. Prophet (talk) 18:37, 20 May 2015 (UTC)

Species identification: is this a Dark-spotted Frog?

I took this picture in Liaoning, China and want to add it to Commons but I'm not 100% certain of the species. Based on the list at Category:Amphibians_of_China I suspect it is a Dark-spotted frog. Can someone please confirm or reject? DrewHeath (talk) 13:35, 18 May 2015 (UTC)

Kind of hard to tell due to the angle and lighting. Plus the frog has a huge range, so it might show quite some variation. Your best bet would be a process of elimination. If there are only 4 native Ranidae species in the area, and you can rule out the other three, then the identification should be more secure. (Frankly, If I'd found this in the US I'd've assumed it was Rana pipiens without samples of each to compare. μηδείς (talk) 18:13, 18 May 2015 (UTC)

Laser printing process

According to Laser_printing#Printing_process, "A laser beam (...) projects an image of the page to be printed onto an electrically-charged, selenium-coated, rotating, cylindrical drum", " charged electrons (...) fall away from the areas exposed to light."

Why doesn't the charge spread across the selenium, basically deleting the image, once the laser knocks off some electrons and imprints the image? Or, do charges spread from electrically loaded to not electrically loaded locations, but at such slow pace that it does not matter, since the page will be printed before this happens? --Senteni (talk) 17:48, 18 May 2015 (UTC)

Laser Scanner Unit of a Laser Printer
(Click for details)

That's really the clever part. Crystalline selenium has very unusual photoconductivity. When you shine a light onto it, the electrical conductivity goes up by a factor of about 1000! So you shine a light on it - current flows into it easily wherever it's illuminated, yet can only flow exceedingly slowly into the areas that aren't illuminated. Then you can shut off the light and the charge is trapped by the very low conductivity of the material. That's why selenium is used for this purpose.

Clever or what?!  :-) SteveBaker (talk) 19:59, 18 May 2015 (UTC)

There were several photo conducting materials used. Some more robust, some getting scratched from paper, some knows as hazardous. There's a so called corona, a wire connected to a high voltage supply, charging the photo conductor. Light, also laser light is discharging the photo conductor. The laser beam is being moved line by line similar to a the beam in cathode ray tube displaying television. The laser is modulated to apply the latent picture onto the photo conductor. When rubbing a balloon on clothes, it will be electrostatic charge. When moving the charged balloon over your head, it will lift the hair to its surface. Toner is plastic dust. This way the charged photo conductor lifts the toner on its surface. If not charged, not toner will be picked. Now the picture is visible on the photo conductor. Another corona or charged roller transfers the toner onto the paper. The paper is being moved synchronous to the photo conductor. A wiper, similar to a windscreen wiper, cleans the photo conductor from not transferred toner. Some older machines used a lamp to discharge the photoconductor before recharging it. The toner is beeing fused on the paper by heat and some pressure. If paper jams or the machine is being turned of while printing, some toner is not fused, some is on the paper, some on the photo conductor before transfered. --Hans Haase (有问题吗) 23:00, 18 May 2015 (UTC)

Earthquake magnitudes

When magnitude of earthquake is referred to in the news, are they referring to richter magnitude or moment magnitude?

If the news does not cite a source, it's nearly impossible to know. The most common source of data in the United States is the USGS Earthquake program, and they use magnitude for many different purposes. Moment magnitude is the scale that USGS prefers, because it can be used to rate nearly all earthquakes of all sizes for most practical purposes.

Here's the webpage to read: Measuring the Size of an Earthquake, from USGS.

Nimur (talk) 20:45, 18 May 2015 (UTC)

Sitting on Spitfire wings

In the film Malta Story, as Spitfires are being taxied there are sometimes men sitting on the wings - one man at each end. Why was this done? DuncanHill (talk) 21:18, 18 May 2015 (UTC)

There are several stories online (none, that I've found yet, in fully reliable sources) about mechanics sitting on the tail of a Spitfire when taxiing on windy days. In particular, RAF Hibaldstow reiterates the story (from the BBC's People's War project, here) about WAAF mechanic Margaret Horton remaining on the tail for a brief flight. -- Finlay McWalterᚠTalk 21:28, 18 May 2015 (UTC)

It would appear to be for assistance in manouvering the aircraft on the ground. See this contemporary photo, and this forum posting. Tevildo (talk) 21:36, 18 May 2015 (UTC)

Think you might find it was a mater of connivance. Taxing on the ground, the forward field of view of a fighter is blocked by a ruddy great 27 litre engine, requiring one to keep dabbing the left and right hand brakes to swerve the fighter side to side to see where one is going. However, wing riders could guide the pilot, ensuring he did not accidentally run over his commanding officer's bicycle.--Aspro (talk) 22:04, 18 May 2015 (UTC)

Hopefully no tailwheel pilot is taxiing with S-turns by using the brakes! Part of learning to fly a tailwheel aircraft is to learn to steer (on the ground) using the rudder. Some aircraft have a castered tailwheel; others have a rigid attachment to the rudder; still others have a sprung steerable castering tailwheel that is rigged to the rudder with a little bit of flex. Spitfires came in two variants; one that purely castered and one that was rigidly attached to the rudder.

More on this topic: Conventional Gear: Flying a Taildragger; the author has a whole chapter on Hawker Hurricanes the Hawker Sea Fury and I think there's even a brief mention of Spitfires.

Chapter 13 of the Airplane Flying Handbook, Transition to Tailwheel Airplanes, also contains information on how to taxi (and the whole book is available from FAA at no cost). AFH says to "use whatever power or brake is necessary..." but that's amateurish technique! A proper tailwheel pilot doesn't ride the brakes. "While taxiing, the steerable tailwheel should be used for making normal turns and the pilot’s feet kept off the brake pedals to avoid unnecessary wear on the brakes."

Nimur (talk) 22:41, 18 May 2015 (UTC)

I'm not sure there was any good reason for airmen to ride on the wings in the film. It seems likely that these characters were joyriding and that safety rules were being very loosely enforced! If I can find a copy of the movie, or if I can track down any other source of nonfictional information, I'll be happy to report back! Nimur (talk) 22:50, 18 May 2015 (UTC)

• Even moving at slow speeds, the wings provide lift, which weakens the frictional force of the tires, which allows manoeuverability. I have no idea where to find a source, but old planes not equipped with taxiing ailerons could obviously use such support. μηδείς (talk) 23:01, 18 May 2015 (UTC)

What are "taxiing ailerons"? Ailerons roll the aircraft, which is not usually what you want to do when you're taxiing. In fact, when operating a taildragger, the pilot must take care not to roll or weathervane the airplane. Consider reading the sources I linked above. One of the defining characteristics of operating these types of aircraft is the pilot's skillful command of the rudder for directional control, especially on the ground. Trike pilots, who are used to steering with the nosewheel, find this use of the rudder complicated. Nobody steers on the ground using the ailerons!

At low speeds, the weight of the aircraft is not supported by the wing. The weight of the airframe is carried by the landing gear, and the weight of the wing is carried by the airframe. The wing is not producing significantly meaningful lift at such low airspeeds.

Nimur (talk) 01:00, 19 May 2015 (UTC)

I am happy to accept your expertise, but then what are the guys doing sitting on the wings, and can you define "significant" amount of lift to rule out instability while taxiing? μηδείς (talk) 19:36, 19 May 2015 (UTC)

That is explained in lift coefficient. Light aircraft such a Cessna 172 have a lower power to weight ratio. They fly much slower, so need a higher lift coefficient than a high speed fighter (which also have a larger and very much heavy engines). Therefore the climb out speed for a Spit has to be about twice that of a 172. Cessna 172 owners are advised to tie their craft down to dog-anchors in case of high winds tossing them over. A Spit will just rock gently from side-to-side in high winds. They are just way too heavy. Take a Jumbo as another example. The pilot doesn't rotate (lift off) until a speed of about 187 mph. A Cessna 172's wings would be in danger of fall off at this speed. The Jumbo's wings have a much lower lift coefficient though and need the high speed airflow over the wings to obtain the necessary lift. The guys sitting on the wing are there to ensure the pilot does not collide with anything - as the pilot cant see the ground a head - the engine is in his way.--Aspro (talk) 20:51, 19 May 2015 (UTC)

I wonder if it was a particularly windy day. I can imagine a light aircraft with big wings being blown over on such a day, and having people sitting on the wingtips might prevent that. StuRat (talk) 01:06, 19 May 2015 (UTC)

Supermarine Spitfires weighed about six thousand pounds when empty, and had a wing loading of nearly thirty pounds per square foot. They aren't liable to float away, even in a high wind. Nimur (talk) 13:57, 19 May 2015 (UTC)

• Thanks for the answers. Our article does say that taxiing Spitfires was tricky due to the poor visibility, and in the film the airfield had been bombed a lot so help guiding the pilot sounds likely. I don't know how windy it was but that also seems likely. DuncanHill (talk) 11:19, 19 May 2015 (UTC)

I watched the film - it was available on Netflix - and I read about the Siege of Malta (World War II). In this scene, a flight of Spitfires has just landed, and they have only minutes to refuel and rearm, because a German air raid is inbound. Airmen are riding on the wings because they're in such a hurry to get to the fuel depot. Those guys are the ground support - as soon as the aircraft gets to its depot, they're about to jump off and refuel and reload the Spitfire, so it can launch as rapidly as possible. I'm not totally convinced of the historicity of this - I'd never let someone ride on my wing before a flight (or ever)! But the dramatic effect is to emphasize how urgent things are. As Vice Admiral Payne states earlier in the film, the long siege has caused the RAF at Malta to bend procedures a little bit.

My recommendation: track down Air Marshal Lloyd's book Briefed To Attack - on which the film was based. He was there and was commander of the RAF. His version of events is likely to be even more authentic. It looks like you'll have to do some searching to find that book, but maybe a university library near you can help.

Nimur (talk) 13:40, 19 May 2015 (UTC)

Refuelling a Spitfire inside a revetment at RAF Ta Kali in 1942.

If memory serves, the Spitfires in that scene were also new to Malta having just been flown in from a ferry carrier. The airfields on Malta had been very heavily bombed and were a warren of aircraft revetments (a parking bay surrounded by blast walls). The pilots would have needed to be guided into an empty revetment for refuelling - I found this picture of refuelling a Spitfire in a revetment. Alansplodge (talk) 13:20, 20 May 2015 (UTC)

Yes, the film portrays the arrival of the Spitfires from the USS Wasp in 1942. Our article has some historical photographs of these operations in which RAF pilots of No. 603 squadron launched from an American aircraft carrier. Nimur (talk) 13:42, 20 May 2015 (UTC)

USS Wasp took part in two "Club Runs", the first on 20 April 1942, Operation Calendar, when 46 Spitfires arrived on the island, but by the following day only 18 were airworthy due mainly to incessant air raids.[8] The sitting on the wings episode is more likely to be the subsequent Operation Bowery which was more successful; "On arrival, aircraft were dispersed into protected areas and rapidly refuelled and rearmed - one within six minutes of landing" according to our article. Alansplodge (talk) 19:59, 20 May 2015 (UTC)

"9 May 1942: 60 Spitfires to Malta: 1000 hrs - Ta Qali logs the first 22 new Spitfires and their pilots to arrive over the next hour. Each aircraft is numbered ready to be met by an allocated ground crew and taken to a protective pen to refuel, re-arm and repair as necessary, ready for a fresh pilot to take off within 20 minutes as cover for the next arrivals." Malta: War Diary Alansplodge (talk) 22:33, 20 May 2015 (UTC)

Here is a image from inside a spitfires cockpit to show how poor forward visibility was when taxiing [9]. With the tail on the ground, the engine points up and is between the pilot and the visible ground ahead.[10] On a wartime airfield there was a lot of other movements going on at the same time (thats why air craft still have flashing red lights on the top to indicate they are intending to go somewhere). Both the Spitfire and Hurricane had deferential air brakes which had to be dabbed lightly otherwise they would bit and spin one around too far. So (as mentioned above) taxiing by S-turns was not practical nor good practice. As for taxiing air speeds, the control surfaces and wings have precious little effect. Although having said that, one could keep both feet hard on the brakes, increase thrust and get the tail to lift off the ground. Danger with that is, the nose could drop, resulting in a bent fan and a court marshal. --Aspro (talk) 19:07, 19 May 2015 (UTC)

As for a reliable source for ground crew sitting on the tail of a fighter while taxiing, I recently read Force Benedict by Eric Carter, an account of the deployment of the Hawker Hurricanes of No. 151 Wing RAF to an airfield at Vaenga near Murmansk. The airfield there was so waterlogged that the pilots were obliged to open the throttle more than usual to push through the mud, which in turn resulted in several aircraft tipping onto their noses, smashing the propeller. The solution was for two aircraftsmen to "drape themselves over the tail end of the fuselage". Unfortunately, on one aircraft the aircraftsmen left it too late and the slipstream prevented them from getting down before the aircraft took off; the extra weight on the tail caused the aircraft to go into a near vertical climb before stalling and crashing into the ground. The ground crew were both killed and the pilot was pulled unconscious from the wreckage (p. 183). Alansplodge (talk) 20:01, 20 May 2015 (UTC)

In addition, there where many grass air field that were water-logged after heavy rain. Air field need (preferably) flat land and the flat land of natural water meadows were ideal but often duckboards were need under the wheels of parked-up aircraft to save their wheels sinking into the soil. If one looks at say early RAF Northolt , before it had hard runway, one can see that deep culverts had be excavated to carry surface water away. London Heathrow Airport has culverts for the same reason. On modern air ports catering for modern aircraft with trike landing gear, using hard runways, it is not obvious why the ground crew did those thing in all those old photos unless one looks and considers the conditions and environment that they had to operate in.--Aspro (talk) 20:11, 21 May 2015 (UTC)