Wikipedia:Reference desk/Archives/Science/2014 February 6

= February 6 =

Housing development road lay-out rules
WHAT ARE THE RULES REGARDING 9M WIDE ROAD IN LAY-OUT DEVELOPING FOR HOUSING DEVELOPMENT? — Preceding unsigned comment added by 117.200.175.136 (talk) 01:44, 6 February 2014 (UTC)
 * Note: this IP geolocates to the state of Maharashtra in India. Looie496 (talk) 02:11, 6 February 2014 (UTC)
 * Whose rules? If you mean something other than "drive on the left", you will need to ask your local highways authority, as the rules may vary from one authority to the next.--Shantavira|feed me 10:51, 6 February 2014 (UTC)
 * In this case it might actually be the municipality or whatever the equivalent is in that particular part of the world. Minimum road widths may be something controlled at that level, with potential requirements for frontages, etc. Mingmingla (talk) 03:17, 7 February 2014 (UTC)

Herbs and flowering plants
I quote from Sukorambi Botanical Garden:"The upper part of the garden, covering some 4.5 hectares (11 acres), includes over 300 species of herbs and 200 species of flowering and fruiting plants."It's sourced to an Indonesian document, which says "300 jenis tanaman herbal atau obat-obatan. Juga ada kebun bunga dan kebun buah yang terdiri atas lebih dari 200 jenis tanaman bunga dan buah". The article's author translates this to:"300 kinds of herbal or medicinal plants. There are also flower gardens and orchards consisting of more than 200 flowering and fruiting plants."Is there really some sort of difference between herbs and flowering plant? "Herb" to me means either a small plant cultivated for its unusual flavor (e.g. mint) or an archaism for all plants in general, "Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field". Some plants are both herbs and flowering plants in my mind, so I'm not sure how to treat this; I'm guessing its a linguistic issue, that Indonesian's concept of "this is an herb; that is a flowering plant" differs from the English conception. I'm not sure what to tell the page's creator, so a more enlightened perons's opinion would help. Nyttend (talk) 06:34, 6 February 2014 (UTC)
 * I second this request. — Crisco 1492 (talk) 06:38, 6 February 2014 (UTC)
 * There is Herbaceous plant, which has a technical meaning, but it's not mutually exclusive with flowering or fruiting. I think there is an English word that means "non-flowering plant", but unfortunately non-flowering plant redirects to our article on Plant reproductive morphology, which is almost entirely about flowering plants.  It's also possible that it just reflects the purpose of growing the plant (e.g. I'd consider chives as a herb rather than a flowering plant, and marigolds as a flowering plant rather than a herb, even though both have edible parts, and both have flowers). MChesterMC (talk) 09:15, 6 February 2014 (UTC)
 * I'm pretty sure that's the distinction they are making, but is there alternative wording other than "medicinal plants" and "decorative plants"? — Crisco 1492 (talk) 09:24, 6 February 2014 (UTC)


 * One biological split is between herbaceous plants and woody plants. This is basically a distinction of morphology and life history. Another key split is between the flowering plants- Angiosperm, and non-flowering plants - the gymnosperms. I cannot at present think of any herbaceous gymnosperms, but there could be some I'm not aware of. All of these are vascular plants, as well as spermatophyta (seed bearing). The non-vascular plants are the bryophyta, including e.g. mosses and liverworts. So, that's the science, but I think MChester has it - they are being described by utility. Also, herbs are often restricted to medicinal/culinary herbaceous plants, and some herbs are not herbaceous (e.g. rosemary can be woody and evergreen, depending on strain and environment).
 * Actually, as it stands, I don't see much of a problem. Or at least, it is unlikely that we could the real story without contacting the botanical garden. It could be salvaged by a parenthetical after your quote, e.g. "...fruiting plants (note that, botanically, most herbs are in fact flowering plants, though other categorizations are also used.) SemanticMantis (talk) 15:11, 6 February 2014 (UTC)
 * The parenthetical works really well, I think. Thank you, SemanticMantis (a quite apt user name indeed!) — Crisco 1492 (talk) 15:17, 6 February 2014 (UTC)


 * I think this is a distinction on the basis of use, not a botanical distinction. "Herb" would be a plant used for flavor or medicine, "flowering plant" and plant used for the beauty of its flowers, and "fruiting plant" a plant used for the fruit it creates. Looie496 (talk) 15:26, 6 February 2014 (UTC)


 * Yes, Looie has it right. Herb has two senses; the traditional meaning of a plant used for flavoring or medicine, and the morphological one of a non-woody plant, usually an annual, with a terminal growth form: herbaceous plant μηδείς (talk) 20:53, 6 February 2014 (UTC)

a term for the doctor who treats a particular patient
Is there a term for the doctor who treats a particular patient? Can "physician-in-charge" be used? — Preceding unsigned comment added by 222.128.181.58 (talk) 07:45, 6 February 2014 (UTC)


 * This question might be more suited to the language desk, but do you mean a personal physician? Being "in charge" wouldn't necessarily associate them with a particular patient.--Shantavira|feed me 09:03, 6 February 2014 (UTC)


 * See the third paragraph of Attending physician. Deor (talk) 10:27, 6 February 2014 (UTC)


 * sometimes, when there is a primary care physician who has to provide referrals to any specialists for a particular insurance plan, that's referred to as a gatekeeper'. Gzuckier (talk) 04:26, 10 February 2014 (UTC)

Cumulative probability for Kaplan-Meier
I have calculated out case burdens for various age bands of a population (for an example, say #strokes in age ranges 15-24, 25-34, 35-44, 45-54 or something like that). I'm trying to work out cumulative probabilities, but I don't think it's right to convert #cases into a %probability. #cases doesn't necessarily correlate with % chance of getting a disease at that age, or does it?

--— Cyclonenim | Chat 10:03, 6 February 2014 (UTC)


 * To get a formula, you will have to define exactly what you mean by cumulative probability. The main question is, when defining the cumulative probability at age N, how do you handle people who have died before reaching age N? Looie496 (talk) 15:22, 6 February 2014 (UTC)


 * Thanks for the reply . In this instance it's recurrent candidal vulvovaginitis so not fatal. The problem is that women can develop the condition at any stage between 15-65, and it can last for any period of time from, say, 1 month through to 15 years. --— Cyclonenim | Chat 11:11, 7 February 2014 (UTC)

Trapping light with just magnetic field
Is there any way by which light can be trapped by magnetic field? Scientist456 (talk) 11:40, 6 February 2014 (UTC)
 * The question is a bit unclear because there is no such thing as a magnetic field without an electric field. I don't think there is any reasonable way of doing it, but if you go to extremes, you could have an electromagnetic field of such enormous energy that its equivalent mass is enough to create a black hole -- which would trap everything, including light. Looie496 (talk) 15:17, 6 February 2014 (UTC)


 * Not under ordinary circumstances. Light is a form of electromagnetic radiation, and hence is almost precisely governed by Maxwell's equations.  Maxwell's equations are linear differential equations, and hence obey the superposition principle.  In simpler terms, in general light passes unaffected through any other electromagnetic field.  However, in an electric field stronger than the Schwinger limit, there are nonlinear effects which in principle might enable you to design a system which traps light in a vacuum with just a carefully designed electromagnetic field produced by the system, for some possible meanings of the phrase "traps light", although that would not be easy.  Red Act (talk) 17:33, 6 February 2014 (UTC)


 * If your "light" is actually a ultra-high-energy gamma ray with enough energy to form antimatter, then it will probably be stopped by a magnetic field such as the earth's. Instead positrons and electrons are formed, these can then make more gamma ray photons, which then cause more positron formation. Graeme Bartlett (talk) 21:39, 8 February 2014 (UTC)

Terrestrial vs satellite TV
Obviously, both services are used, but I'm not sure why.


 * As I understand it, satellite TV signals can carry more data because of the higher frequencies used. But why do we need to use satellites for this? Why can't we use high frequencies for terrestrial transmitters?
 * If the infrastructure used with satellite TV is so much more capable, why do we use terrestrial TV? Is the associated infrastructure cheaper?
 * Why haven't subscription terrestrial TV services made an impact in the UK?

--Leon (talk) 13:04, 6 February 2014 (UTC)


 * Satellites are farther from the surface, so have a wider "spread" for their signal. A single satellite can cover a LOT more ground than an antenna can.  Also, terrestrial antennas are quite expensive in terms of a) material b) maintenance c) land and d) electricity to keep running.  While, hypothetically, you could send the same sort of information through terrestrial antennas as you do through satellites (and ultimately we do; the 4G network works that way), to do so with the same bandwidth, fidelity, and coverage is a LOT more expensive.  To answer the second question, we use terrestrial TV because it is already there.  The system was put in place largely before satellites are; there's nothing to be gained by tearing it all out, so since it already exists, there's no good reason to not use it. -- Jayron  32  13:11, 6 February 2014 (UTC)
 * Likewise with land-line telephone systems vs. wireless. ←Baseball Bugs What's up, Doc? carrots→ 14:15, 6 February 2014 (UTC)
 * The problem with using radio waves for data applications is that the amount of bandwidth available at useful frequencies is strictly limited by the laws of physics...and if you use those radio waves in a non-directional fashion (like a ground-based TV transmitter) then everyone within range has to share the available bandwidth. Wires and optical fibre, on the other hand, can be routed to individual users - and even to individual pieces of equipment - so for a price, you can have as much bandwidth as you need.  Satellites fall partway between those two situations - because you can aim your receiving dish at the known location of the satellite - and you have a directional radio signal.   There can be multiple satellites sharing the same range of frequencies - and so long as your dish is designed to be sufficiently directional - everything works out just fine.
 * With WiFi, you have a similar problem. The number of frequency bands is strictly limited and the bandwidth is consequently kinda bad.   Worse still, you're sharing that limited bandwidth resource with all of your neighbors.  That means that the system has to have artificial limits placed on the amount of transmitter power in order that the available frequencies can be shared.   That's why WiFi has such poor range.   When I last lived in an apartment complex, inhabited mostly by 'tech' people, there were at least 50 WiFi transmitters that I could detect - all fighting over a dozen frequency bands.  The result was terrible data rates.  On the other hand, in our new house, I can only pick up one neighbor's transmitter and we can easily pick different frequencies and not interfere with each other at all.  Sadly, the artificially low power of the WiFi transmitters means that there are lots of 'dead spots' in my home where the WiFi signal hasn't made it through all of the walls and I get drop-outs all the time.


 * TV and broadcast Radio stations are a kinda unique application - lots of people want to consume the exact same data stream. So the lack of bandwidth isn't such a problem.  Suppose one TV transmitter can broadcast ten TV channels and a million people can pick it up.  Contrast that to (say) NetFlix - where the same number of people are watching the same kind of content - but everyone wants to watch something different - or at least the same thing but starting at different times and with the ability to pause, rewind, etc.  You need a 100,000 times as much bandwidth to satisfy a million NetFlix users than people watching broadcast TV!   Clearly you can't satisfy that demand with long-range broadcast TV.


 * Cellular networks can kinda do that - because (like WiFi) they have relatively short range transmitters.  That means that one cell tower only has to have enough bandwidth to keep the people who are within a kilometer or two of it happy...but you'll notice that cellular data companies are very happy to slap bandwidth caps on users in heavily loaded areas, and charge a small fortune for people who need a lot of bandwidth.


 * Satellites could (in principle) do the same kind of thing if people were able to use directional antennae and to point them at different satellites depending on what TV shows they wanted to watch - but that's inconvenient for lots of reasons - so most satellite TV systems employ relatively non-directional dishes...which limits the number of different satellites there can be in the sky that are sharing the same frequencies.


 * Cable TV gets you a lot closer - by laying cable to every house individually - but those wires don't go all the way back to their offices so bandwidth is still a shared resource. If you have cable internet, then the amount of bandwidth you have depends entirely on the degree to which your neighbors are data-hogs.  Fortunately, most people are NOT watching costly pay-per-view stuff - so they can support hundreds of TV channels quite easily.


 * In an ideal world, we'd each have a wire that goes from our homes all the way back to the source of the signals - but that's REALLY expensive.  However, that *is* the way that old-fashioned land-line telephones work.   Unfortunately, the cost of laying all of those wires today is rather prohibitive - so we're stuck with the rather poor quality cables that were laid decades ago, which results in DSL systems that in theory would be really good - but in practice require that you're living close to the telephone exchange - and operate at the very low frequencies that the unshielded copper wires were designed to operate at for analog voice telephony.


 * The idea of using high-altitude unmanned airships to broadcast data is an interesting one - it gives you a system somewhere between satellite and cellular services...midway in cost and midway in performance - but with vastly more flexibility than either of the other approaches. I think this is an idea that's going to start to happen in the not-too-distant future.


 * So there is definitely a place for terrestrial broadcast (no wires, one transmitter for millions of people - so it's cheap!), satellite (not so cheap because you have to launch it, and you can't easily repair it - but more bandwidth available than terrestrial), wired connections (LOTS of bandwidth, if you don't mind digging up the street to lay it) and short-range cellular networks (more transmitters - but more bandwidth).  No one of those is "better" - they each have different cost/bandwidth trade-offs - and much depends on whether people are happy to watch whatever show is currently being broadcast - or whether they want to be able to watch anything they want at any time.


 * SteveBaker (talk) 15:01, 6 February 2014 (UTC)

Mystery Plant


This plant was in my apartment when I first arrived. It was completely ordinary and boring for the first 4 months, but suddenly in the last month, it's grown like crazy. (The first picture was taken Jan. 11; the second was taken today.) The flowers all appeared in the last few days, and it's producing a clear, sticky liquid. It smells overbearingly sweet. Any idea what it is?

If it makes any difference, I live in South Korea, and the previous tenant said she bought it from a random vendor at a subway station...

Also, it's currently Scotch-taped to a chopstick. (I have zero knowledge about gardening whatsoever.) Is that okay, or is there a better way to stake it up? Cherry Red Toenails (talk) 14:32, 6 February 2014 (UTC)


 * Probably a type of Sansevieria. They are very common houseplants, and when they bloom, do have a very sweet aroma. There is a lot of variety to how they look, check out this google image search for the plant, and this one for the flower . When identifying plants, the flower is usually the best part to focus on, and in this case, the matches look pretty good to me. My only reticence is due to the fact that yours is growing in water. Most of the types I'm familiar with are happiest in very small pots, and can go months without water. But again, there is a lot of variety in the genus, and I'm sure the common types in Korea are not the common types I'm familiar with in the USA!
 * That clear, sticky fluid is probably nectar, and, judging by your description, probably from an extrafloral nectary. These exude sweet treats to attract ants, which then defend the plant against herbivorous insects. If it is dripping out from inside the flowers (not the base), then it might be "regular" nectar, used to attract pollinators. I encourage you to taste the nectar, it is quite nice! As for staking, a chopstick is fine, but you'd be better off attaching the plant to it with a loose bit of twine, or a loose elastic band. Oh, and don't be surprised when the bloom stalk (a spike_(botany) in this case) turns brown and dies in a few weeks. That's normal, just snip it off an wait until next bloom (though it might take a year or more to bloom again :) 16:03, 6 February 2014 (UTC)


 * Cool! Thanks! P.S. Should I be worried about the nectar attracting bugs inside my apartment? Cherry Red Toenails (talk) 16:52, 6 February 2014 (UTC)
 * I wouldn't worry. I mean, if you have ants foraging in the apartment already, they will likely find the plant. But if you don't already have bug problems, this plant won't cause them. SemanticMantis (talk) 20:25, 6 February 2014 (UTC)


 * Possibly Sansevieria sambiranensis, Richard Avery (talk) 07:59, 7 February 2014 (UTC)

Can loudspeakers produce infrasound or ultrasound ?
Are they limited to the human hearing range or 20Hz - 200 Mhz? It seems useless, but maybe there is no need to restrict them. Or does avoiding infra and ultrasound generate a better sound somehow? OsmanRF34 (talk) 14:54, 6 February 2014 (UTC)


 * They generally start to lose power as you move away from the range of frequencies for which they were intended to operate. So, yes, you can feed them signals outside of the range of human hearing - but those sounds will play back increasingly quietly as you get further away in frequency.  Good speakers will generally come with a graph of frequency versus sound amplitude that'll allow you to gauge how effective they are.


 * Interestingly, small speakers (such as the ones in phones, tablets and laptops) are pretty good at reproducing ultra-sound - and there have recently been reports of evil-doers using ultrasound to transmit viruses and other malware to computers that are disconnected from the Internet. For that to work, they have to be pretty good at producing sound in frequency ranges where we can't hear it - and the microphones on the receiving machine must be reasonably good at picking it up.


 * You're right though - there is a design cost to having a speaker be able to reproduce sounds over wider ranges of frequency - so avoiding "over-design" is a good thing. I doubt that designing a system that deliberately can't reproduce infra/ultra-sound would improve the audio quality - but it would most likely reduce the cost of the thing.


 * SteveBaker (talk) 15:08, 6 February 2014 (UTC)


 * I found a reference to this at . I may have asked about this before at Reference_desk/Archives/Computing/2012_May_1 (I don't know though; the high-pitched sound I get isn't constant but depends on activities, e.g. scrolling up and down this window makes a distinctive sound according to how fast I do it) but I have to say, even I never imagined that the computers people use routinely could be so riddled with backdoors that they literally sit around waiting for someone to take them over with ultrasonic signals.  There really is no avoiding the next Dark Age, is there? Wnt (talk) 20:07, 6 February 2014 (UTC)
 * Reading the reference, the person that's claiming he has a virus is saying that the virus was installed by some other means, and uses ultrasound for signalling, and the article then jumps to saying that this provides a way to infect a system. It's possible there could be such a vulnerability in some program, but it seems unlikely that you'd be able to get clear enough data to install something. MChesterMC (talk) 09:20, 7 February 2014 (UTC)


 * Adding some detail, good tweeters can generally produce ultrasound, because the high frequencies are the main determinant of perceived sound quality. To get infrasound you need a woofer.  If you put your hand on the woofer and feel it vibrating, that's infrasound. Looie496 (talk) 15:12, 6 February 2014 (UTC)
 * Right, for a neat demonstration of this, this youtube video shows some oobleck on a woofer . SemanticMantis (talk) 15:36, 6 February 2014 (UTC)
 * I remember once having been physically sickened by some hard rock being played real loud -- my abdominal muscles were literally vibrating from the noise, and it felt like the sound waves were going right through me! Was this because of infrasound, like Looie says? 67.169.83.209 (talk) 17:22, 6 February 2014 (UTC)
 * I can't know for sure based on your description (since you could feel non-infrasound and I don't know how you might respond), but it sure sounds like it. Wnt (talk) 20:25, 6 February 2014 (UTC)

As a confirmation that loudspeakers can play ultrasound - The Beatles added a 15-kilohertz high-frequency tone on the run-out groove of the Sgt Pepper's Lonely Hearts Club Band vinyl LP, added at Lennon's suggestion said to be "especially intended to annoy your dog". As for the oobleck experiment - Stephen Fry did it with much more style on QI :-)  Richerman    (talk) 20:16, 6 February 2014 (UTC)
 * Depends on what you mean by ultrasound; I can hear the tone at the end of A Day in the Life just fine, so it can't really be ultra, can it? :) Matt Deres (talk) 21:33, 6 February 2014 (UTC)


 * Oops! yes, it begins at 20 Kilohertz. That's what happens when you think you know what your talking about and don't check your facts. I could never hear it without slowing the record down even when it was first released in 1967 when I was 16. I wouldn't have a chance of hearing it now. Richerman    (talk) 22:44, 6 February 2014 (UTC)
 * I could hear bats quite easily when I was 16 but my mother had much better hearing. I made a device which was generating ultrasonics by mistake and my mother came up the stairs to complain. I was just beside it and heard nothing. Dmcq (talk) 23:42, 6 February 2014 (UTC)
 * I still hear it fine at 40; in fact, by pure serendipity I listened to the song earlier today and could hear the tone above the sound of traffic. 15kHz isn't ultrasonic, but it is on the high end, and if the factory speakers in my Corolla can produce that sound easily, it certainly provides some hope that decent speakers would at least edge into the ultrasonic. Matt Deres (talk) 01:20, 7 February 2014 (UTC)