Wikipedia:Reference desk/Archives/Science/2013 July 11

= July 11 =

Post-operative fever : another Five Ws ?
Hello Learned Ones ! I was inopportunately dozing at the end of Grey's Anatomy (of which I am a late-coming fan), season I, episode 3, & did'nt catch clearly the five causes for post-op. fever as enumerated by Meredith : "wind (splint, ...), water, etc...". Could some of you recall them to me ? , this mnemotechnic line seems quite interesting. As for the term "splint", I infer it means that patient must learn to gently hold his abdomen while coughing ? Thanks beforehand for your answers, t.y. Arapaima (talk) 17:39, 11 July 2013 (UTC)
 * Look at our article on postoperative fever -- hey, presto!, it's right there. Looie496 (talk) 17:50, 11 July 2013 (UTC)
 * Aw, I'm so ashamed : it was just there (& even with the ref. to "Grey's Anatomy" ! ), & I didn't find it !. I swear I looked for it, but I typed "post-operative" , continental way, & it gave me a useless page ([ http://en.wikipedia.org/w/index.php?title=Special%3ASearch&search=post-operative+fever&fulltext=1]

. Thanks Looie for you time & kindness, have a good summer day. T.y. PS : I thought WP could correct a (slight) mispelling in a search statement ? ... And how come Five Ws didn't mention it ? Arapaima (talk) 07:08, 12 July 2013 (UTC)
 * User:Arapaima, you make some good points here! Wikipedia only gets better when people like you notice these things, and take a bit of time to fix them. You can add a "see-also" to the bottom of Five Ws that points to the postoperative fever article. You can also make a "redirect" of post-operative fever and post operative fever to postoperative fever, and that will change the redlinks to blue! If you need help on how to do this, you can ask at the Village Pump or Help desk. SemanticMantis (talk) 14:59, 12 July 2013 (UTC)
 * Actually I found our article by Google-searching. It's better at handling variations than the Wikipedia search facility. Looie496 (talk) 21:32, 12 July 2013 (UTC)

Cricket Revometer
In their coverage of the The Ashes, Sky are showing off a new gadget called the "revometer". It measures the number of revolutions per minute that spin bowlers put onto the cricket ball, which is an indication of the amount of drift and turn they should extract. There's no gadget inside the ball and I don't think the data comes as part of the Hawk-Eye system, although I suspect a specialist (presumably high-speed) camera is involved. Does anyone know how it works? ManyQuestionsFewAnswers (talk) 18:09, 11 July 2013 (UTC)


 * The cricket ball doesn't have a uniform surface. I suspect what it's doing is using computer vision to identify the portion of a ball-tracking camera's image that contains the ball, then checking for a periodic variation in brightness.  The length of that period is determined by the speed the ball is spinning. --Carnildo (talk) 22:48, 11 July 2013 (UTC)
 * That would be kinda tricky because the balls' axis of rotation isn't necessarily perpendicular to the camera - if it were spinning end-on, then there wouldn't be any overall flicker at all. So I suspect it's grabbing two very high resolution photographs close enough together in time and tracking where the seam is moving...that's not *so* difficult and would result in a reasonably accurate spin rate measurement regardless of the axis of spin...providing that the camera has a sufficiently large image of the ball at two consecutive moments in time and a sufficiently short capture time (ie shutter speed) to end up with a reasonably sharp image.  SteveBaker (talk) 01:09, 12 July 2013 (UTC)
 * Ashton Agar in particular has been bowling with some atypical axes of rotation for a spinner - with unusual amounts of topspin or with a scrambled seam. I'm not sure what difference that makes technically. ManyQuestionsFewAnswers (talk) 12:05, 12 July 2013 (UTC)


 * The axis doesn't need to be perpendicular, it just needs to be non-parallel. The closer it is to perpendicular, the stronger the signal is and the better the measurement is, of course. --Carnildo (talk) 01:14, 13 July 2013 (UTC)
 * I would expect doppler effect (radar or sonar) to be the easiest method, techniques are well-known, maybe two or three detectors to get all the angles. No problem with filtering out other objects, the ball will be the only object in the volume being scanned. If we can measure the rotation of Venus using radar on earth (Venus), measuring a ball should be child's play. Ssscienccce (talk) 07:34, 14 July 2013 (UTC)
 * Could you elaborate on the "well-known" technique somewhat? I didn't realise the the doppler effect could be used to measure rates of rotation! ManyQuestionsFewAnswers (talk) 23:30, 15 July 2013 (UTC)

Gastritis
The gastritis article claims that sometimes it can occur after infections but surely this should say during infection? Doesn't the bacterial infection cause the inflammation or gastritis in the first place and after the infection is gone, the inflammation will also go, unless there's another cause? Clover345 (talk) 21:45, 11 July 2013 (UTC)

Boiling water with vending machines... in SECONDS! A miracle!
How do vending machines boil water so quickly to make instant coffee cups or instant noodle cups? I suspect they have some sort of high pressure thingy inside there. Sneazy (talk) 22:17, 11 July 2013 (UTC)
 * Maybe they have a Instant hot water dispenser inside? Vespine (talk) 22:42, 11 July 2013 (UTC)


 * (ec) There are two approaches that can be used, depending on the required flow rate and available electric supply. Some machines maintain a small well-insulated hot water reservoir at close-to-boiling temperatures; this hot water can be dispensed on demand for hot beverages and instant noodle cups.  Having a hot reservoir means that the manufacturer can get by with a smaller heating element, since the heating cycle can last a lot longer than the few seconds that the cup is being filled.   Here's a surprisingly detailed schematic of a hot band cold instant beverage vending machine, featuring a six-liter holding tank with a 900-watt heating element:.
 * It's also possible to heat water on demand, however the electricity requirements are steeper. To heat 1 mL of water from room temperature to boiling takes about 300 joules; to heat a cup (eight ounces or about 250 mL) of water from room temperature requires 75 kJ.  If dispensed over twenty seconds, that's just shy of 4 kilowatts of on-demand heating.  (That is a fairly hefty load, but not impossible to supply if the vending machine location is designed with this type of use in mind; it's comparable to the power drawn by an electric clothes dryer.) TenOfAllTrades(talk) 23:10, 11 July 2013 (UTC)
 * Is that energy source green? Is there a particular company or set of companies that sells these types of products? Do they use greener energy, or do they just don't care about where the energy source come from? Sneazy (talk) 00:52, 12 July 2013 (UTC)
 * I doubt it's anything other than whatever wall socket is handy nearby...so no more or less green than the lights in the area where the machines is situated - or other vending machines at that location. What is "green" is minimising the amount of water that has to be kept hot.  The instant heaters - while they use a lot of power, only do so for a short amount of time.  The total energy they use is less than the type that keep a small tank of hot water because no matter how well insulated that tank is, it's going to be losing some energy over time. SteveBaker (talk) 01:01, 12 July 2013 (UTC)
 * As Steve says, the source is the wall plug of course, so it entirely depends where you are. If you are in Canada or in Sweden, it is likely to be mostly from hydroelectric powerplants. If you are in France, it is 77% nuclear power. If you are in Dubai, it is most likely from burning some sort of fossile fuel like gas. --Lgriot (talk) 08:58, 12 July 2013 (UTC)
 * Well to make this instant heater work anywhere, why they don't just put like a supercapacitor to store the electrical energy so it can distribute the load over a longer time? Modern SMPS have 80+ efficiency so... everyone is happy 140.0.229.26 (talk) 13:51, 12 July 2013 (UTC)
 * A 75kJ supercapacitor isn't cheap, and the existing technology works well and service people are familiar with it. Keeping water warm in a well-insulated tank won't waste that much power, and the machine can be scheduled to shut off at hours it won't be used. Also, many machines are operated by vending services, and they aren't concerned about the amount of power being used unless the owner of the site starts complaining. 209.131.76.183 (talk) 14:53, 12 July 2013 (UTC)


 * Vending machines tend not to be in service very long. So if the OP saw this in the last few years it was probably using a 'flash boiler' with no hot-tank reserve. Yet that can depend on were you live. For instance in North America, most power outlets appear to be split-phase 120 volt sockets. That, (as tenofalltrades points out) would require an aprox 20 sec fill time of your pot noodle with the socket  delivering  its max current.  If you look behind the machine and its pluged in to a full phase (240volt)  socket, it can achieve  a fill time of about half that time. There should be a plate on the back (use a mirror if space is tight) that states both its max amperage and working voltage. If it uses around 3½ to 4 KVA then it likely uses a modern flash boiler. --Aspro (talk) 19:14, 12 July 2013 (UTC)
 * Well if they use a reverse cycle heat pump, they could get more heat for their input power, But due to extra cost, and time delay to heat, this is probably in the same boat as the super capacitor! Graeme Bartlett (talk) 21:16, 12 July 2013 (UTC)