Science desk
< September 4	<< Aug \| September \| Oct >>	September 6 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 5

Beams

Beam engines generally seem to have a particular shape of beam that is wide near the pivot and thinner at the 2 ends. They also seem to generally be made of a vertical plate with wider girders at the edges and centre. Is there a name for this type of beam? After a bit of searching around to me they seem to me to vary somewhere inbetween a lenticular shape and a rhombus / double King post shape. Are the types of beam used on beam engines optimal for the job? What are the principles for calculating the ideal beam shape? Why are the solid beams used rather than a truss only design? JMiall ₰ 00:34, 5 September 2012 (UTC)[reply]

I suspect that the shape is to avoid a weakness where the beam is pierced for the axle. Originally, a straight wooden beam was used[1]. This page says; "...by the end of the 18th Century the elegant BOULTON & WATT engines with their cast‑iron beams..." and the accompanying illustration ("figure H") shows an engine with the rhomboidal shape that you describe. Cast iron is a rather brittle material, and would crack if not thick enough. Alansplodge (talk) 13:17, 5 September 2012 (UTC)[reply]

A Short History of the Steam Engine By Henry Winram Dickinson gives the introduction date of the iron beam as "about 1797" (p.87) but no information on the shape - I'll keep digging. Alansplodge (talk) 13:31, 5 September 2012 (UTC)[reply]

Eureka! Everything you ever wanted to know about the subject in A treatise on the steam engine: historical, practical, and descriptive, Volume 2, By John Farey, London 1827. "In modern engines, the great lever (ie the beam) is always made of cast iron, instead of wood. The depth of the lever in the middle is made equal to the diameter of the cylinder, of nearly so... the depth at each end of the lever is usually one-third of the depth in the middle...". Hopefully, you can read the rest yourself. I would imagine that if you were making one with modern steel, then a truss would be a better solution. Alansplodge (talk) 13:40, 5 September 2012 (UTC)[reply]

Beam engines lasted about 200 years. For the first half of this, they were wooden, and wooden usually implies parallel beams. Kingposts were certainly used. Old Bess is one of the oldest surviving examples and shows a wooden beam that might have had its kingposts added some years after construction, following a fire and damage to the original beam. For the second century of this use, the beams were usually cast iron. In a few cases, wrought iron strapwork was also used to construct the beam as a truss. In one well known survivor from Hammersmith, there's even a cast iron strapwork beam, following the pattern of the wrought iron type.

Don't underestimate Victorian engineers. For about 50 years in the mid-19th century, structural theory (see the works of, or a history of William Fairbairn (just not ours)) progressed to a point where it exceeded manufacturing industry's ability to keep up. Although machines might have looked crude and still been built from the same materials, their stresses were now carefully calculated and beam shapes were being optimised.

Most of the reason was for the increasing speeds of some beam engines as steam pressure increased (mostly the compounds, rather than the Cornish). The hardest loaded portion of a beam engine isn't the beam, it's the supports for the beam pivot. As engine speed increases, this becomes a problem. As well as stiffening the fixed frames supporting this pivot, it was also useful to lighten the beam and so reduce these dynamic forces.

There are a few good beam engine sources around, and the Google copy of Farey is certainly one. The first volume in particular, on the earlier engines - there's not much else available for that period with the same level of detail.

Mostly I'd suggest raising this at talk:beam engine. There's a lot of work still to do on engines of this period. Andy Dingley (talk) 14:36, 5 September 2012 (UTC)[reply]

Also see Walking beam engine for a narrow use of what was probably the ultimate metal "kingpost" beam. Andy Dingley (talk) 14:45, 5 September 2012 (UTC)[reply]

Thanks for the replies. The book looks interesting. I also found this (the bottom 'Beam Development' section) which gives a history of beam types. JMiall ₰ 17:28, 5 September 2012 (UTC)[reply]

Some further comment on the Hammersmith beam, from T E Crowley's book. These cast iron openwork beams appeared in the 1830s, from the work of a William West (not a name I recognise) as a lightweight beam. They weren't popular and the only survivors are the Cruquius engine and the 1854 Hammersmith beam. In 1862, a beam of this type at Hartley colliery broke, blocking the only shaft and leading to the deaths of 204 miners (and 43 pit ponies). Cracked beams weren't that unusual, and the Hammersmith beam has the typical repair bridle added above it (1866), which may have been a safety response to Hartley, as there's no sign of the beam actually having broken. Andy Dingley (talk) 10:27, 6 September 2012 (UTC)[reply]

Another rarity is the "plate" beam, built from riveted plate. Not common (maybe cost, as it should have worked well) and there's a survivor at Clay Mills. Seems that the Clay Mills(1885) engine is late enough for this to be steel plate, rather than wrought iron. That would support the cost theory and explain the rarity. Only for the later beam engines, after steel had become cheap, was a riveted beam cheap enough relative to cast iron. Andy Dingley (talk) 10:31, 6 September 2012 (UTC)[reply]

Black hole accretion disk spectra from ISM

What is the expected accretion disk spectrum peak and luminosity for an ordinary black hole in typical interstellar medium density of about one atom per cubic meter? I've been looking all over the web, arxiv, and specialist publications and can't find this. 199.16.130.122 (talk) 00:44, 5 September 2012 (UTC)[reply]

Would there even be an accretion disk in that density? Accretion requires energy loss, and since the particles are too spread out to interact with each other, there would not be any friction to slow them down. Any other forces that I could think of would be negligible, unless of course the black hole had significant charge (ie. by synchrotron radiation) or rotation (ie. by frame dragging). SamuelRiv (talk) 00:01, 6 September 2012 (UTC)[reply]

Well I found http://arxiv.org/pdf/astro-ph/9712284.pdf which is plenty to get me started for now. Maybe a citation search on it or the papers it cites can find something more recent. 199.16.130.122 (talk) 00:08, 6 September 2012 (UTC)[reply]

hearing loss - age

I'm trying to find a graph that shows the hearing loss (in Hz) by age tnx in advance 217.132.255.144 (talk) 10:22, 5 September 2012 (UTC)[reply]

[2] This page contains such a graph. Note that hearing loss is measured in dB, not Hz. — Preceding unsigned comment added by 194.176.105.145 (talk) 11:41, 5 September 2012 (UTC) (added signature) 194.176.105.145 (talk) 11:45, 5 September 2012 (UTC)[reply]

It is actually lost both ways; that is you lose the ability to hear quiet sounds, but you can also lose the ability to hear certain freqencies, both at the upper and lower ends of the spectrum. Our articles are a bit scattered on the matter, but you can find some information on frequency dependent hearing loss at Audiogram and Hearing range. Oddly, we don't seem to have any good information at Wikipedia on Hearing range of humans, the current article on Hearing range just covers other animals. --Jayron32 15:42, 5 September 2012 (UTC)[reply]

I seriously doubt this graph. I hear dog whistles, and I'm 46. As much as I'd like t5o consider myself spec ial in this regard, it's highly unlikely. Zarnivop (talk) 16:48, 5 September 2012 (UTC)[reply]

Any individual case does not invalidate the graph. Please read the qualification: "In humans the audible range of frequencies is usually said to be 20 Hz (cycles per second) to 20 kHz (20,000 Hz), although there is considerable variation between individuals, especially at the high frequency end, where a gradual decline with age is considered normal." -- ♬ Jack of Oz ♬ ^{[your turn]} 21:12, 5 September 2012 (UTC)[reply]

See The Mosquito for an innovative exploitation of this natural deterioration 194.176.105.145 (talk) 11:35, 6 September 2012 (UTC)[reply]

Semimetallic bonding

What is semimetallic bonding? (It's mentioned in Interchalcogen.) Double sharp (talk) 12:44, 5 September 2012 (UTC)[reply]

See Semimetal which has an explanation and some diagrams that explain the difference between proper metallic bonding and semimetalic bonding, according to band theory, which is the easiest way to think of these sorts of delocalized bonding models. --Jayron32 15:37, 5 September 2012 (UTC)[reply]

Just talking “easy”… it’s like a bounding which acts like a metal bounding in some conditions and like a non-metal in others… see this Iskánder Vigoa Pérez 18:01, 5 September 2012 (UTC) — Preceding — Preceding unsigned comment added by Iskander HFC (talk • contribs)

Malaria in other species besides humans

What adaptations have taken place in other mammals to cope with malaria? Are there adaptations akin to that which leads to sickle cell anemia in humans? I include in my question domestic animals like cattle, and of course other primates. Thanks, Rich Peterson198.189.194.129 (talk) 16:44, 5 September 2012 (UTC)[reply]

The article Malaria doesn't have anything much except a throw-away sentence confirming that Plasmodium does infect lots of other kinds of animals. I did find Plasmodium#Subgenera which covers Plasmodium infections in a wide range of other animals, if you read that section and follow some of the footnotes, it may lead you in the right direction. --Jayron32 16:50, 5 September 2012 (UTC)[reply]

This Nature paper from 2009 looks at malaria resistance in baboons. I didn't spot any other work on non-human animals. Looie496 (talk) 17:44, 5 September 2012 (UTC)[reply]

unsigned comment added by Iskander HFC (talk • contribs)

This paper (a proofed draft, but referenced to its sources) cites research suggesting that a genetic mutation has taken place in orang-utans, gorillas, chimpanzees and crab-eating macaques that offers some protection against Plasmodium, but with an increased risk of thalassemia-type disease. Interestingly, it also refers to research suggesting that the speciation of the crab-eating macaque and the rhesus macaque may have been driven by adaptation in the face of malaria. - Ka renjc 18:17, 5 September 2012 (UTC)[reply]

Star collision

How long do I have to wait for a star collision in the milky way? I know that the center is very different to the rest so I would not count the center few hundred light years. The collision of binary or multiple star systems I would also like to exclude in this estimation. Is it more like years or million years? --Stone (talk) 19:18, 5 September 2012 (UTC)[reply]

The first question is whether you want true star-impacts-star collision or merely a close pass with gravitational effects on the two solar systems. The former is comparatively rare, and per our article on stellar collisions, happens about once every 10000 years within our galaxy. However, that's averaging in the denser portions of the galaxy; for the sun (and similar stars), you're talking about a handful over the full lifespan of the galaxy. For the latter, things are much more common. Our article estimates that sun-like stars (in the sense of location within the galaxy) come within one light year of another star about once every 2 million years. Given the millions of such stars in the galaxy, that sort of occurrence should be quite common. — Lomn 20:23, 5 September 2012 (UTC)[reply]

Thanks! I was waiting for a true collision. So I will wait. A star rogue planet collision will have roughly a similar chance to happen. The number of rogue planets is less defined than that of stars. --Stone (talk) 20:48, 5 September 2012 (UTC)[reply]

Bear in mind that the overwhelming majority of space is just that: empty space. If the sun were the size of a 1/2 inch diameter marble, the closest neighboring star would be about 210 miles away.--Shantavira|^{feed me} 21:03, 5 September 2012 (UTC)[reply]

High voltage and CFLs

My aunt still had mostly incandescent bulbs in her house, and they seemed to burn out very quickly. I suspect she has higher than normal voltage in her home, and this causes the lights to burn more brightly, overheat, and fail. She also had two light sockets damaged from excess heat. I replaced the incandescent bulbs will compact fluorescent bulbs. Will those be better able to withstand higher than normal voltages, since they generate so much less heat ? StuRat (talk) 21:41, 5 September 2012 (UTC)[reply]

The voltage is determined by the local substation, so I doubt high voltage is the problem. There might be some kind of poor connection or interference that causes some variability - that could easily shorten the life of a bulb. --Tango (talk) 22:00, 5 September 2012 (UTC)[reply]

This is a rural area, and they have their own transformer out on the pole. StuRat (talk) 22:07, 5 September 2012 (UTC)[reply]

So measure the line voltage. This is best done with a recording voltmeter, a specialist instrument for just this task (sometimes the voltage spikes when the local steelworks changes shift at 3am). Talk to your electricity company.

CFLs are generally quite good at regulating voltage though, but they do have their own problem that they really don't like thermal overheating. Even hanging some high-power types (like Megaman) as a pendant (hot tubes below their sensitive electronics) will cause early failures when they're perfectly satisfactory used in a table light. Andy Dingley (talk) 22:19, 5 September 2012 (UTC)[reply]

I will bring a meter and measure the voltage the next time I visit, but that won't be until next year. Meanwhile, I told her she should tell the electricity company about the problem, and request that they test her electricity with a recording voltmeter. StuRat (talk) 22:48, 5 September 2012 (UTC)[reply]

The first thing I do (as I'm not in the habit of walking around with a multi-meter) is to look at the brand of the light bulbs. Whatever the voltage turns out to be – some brands of bulbs (incandesent or otherwise) have much shorter life spans. See: [3]--Aspro (talk) 00:23, 6 September 2012 (UTC)[reply]

Other factors that can cause overheating are faulty or worn connections or pins within the light fitting, and using a bulb rated at a higher wattage than the fitting is designed for. Many fittings are rated at 60w max.--Shantavira|^{feed me} 05:56, 6 September 2012 (UTC)[reply]

You cannot just get away with measuring the voltage at one point in time. Instead you have to measure it over a period of weeks to see how it varies. If people off the same circuits are running large electric motors, you may get surges when they vary their load. A few seconds of extreme voltage is much worse than a constanT over 10%. Graeme Bartlett (talk) 09:30, 6 September 2012 (UTC)[reply]