Wikipedia:Reference desk archive/Science/2006 June 19

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[edit] Arrowroot Flour

I have ground arrowroot and I have flour - in what ratio do I mix these to make 'arrowroot flour'? --Username132 (talk) 02:32, 19 June 2006 (UTC)

Um, I think "arrowroot flour" simply means flour made from arrowroot, not arrowroot mixed with wheat or whatever. So I'd say 100:0. Depends what you want to use it for, though. —Keenan Pepper 03:08, 19 June 2006 (UTC)
Keep in mind that what is sold in the store as "arrowroot flour" is often not real arrowroot (see note in that article). 128.197.81.181 18:41, 19 June 2006 (UTC)

[edit] Is the Wikipedia being censored by the academic guild?

This may seem like a rare problem but I have noticed that some scientific and technical articles are being edited to prevent other users from obtaining a complete and full comprehension of a topic in the same manner as a member of a trade or artisan guild might try to hide techniques or methods or understanding of what the topic actually involves. Such articles are only permitted to have a highly technical version or explanation of the process being presented in the same manner as a tradesman or artisan might withhold simple explanations from a patron for the sole purpose of mystifying the topic and keeping the patron from knowing “too much.” What is the Wikipedia policy on such behavior where simple and accurate explanations are continuously deleted from an article on the false pretense that the article is not about the example although the example fully clarifies the topic? ...IMHO (Talk) 04:36, 19 June 2006 (UTC)

Examples?
Yes, I'd like to see an example too. Of course there's a lot of information difficult for "outsiders" to understand in the 'pedia, but generally it's because of the persons lack of concern for readers with a very low level of understanding. Nothing of what I have seen suggests censorship.  freshofftheufoΓΛĿЌ  04:59, 19 June 2006 (UTC)
I would hope not but then suppose all sysops were also members of the telecom brotherhood or union and certain accurate but simplified technical disclosures were routinely deleted? Would this not make you a bit suspicous? As for examples. Put the Half-life article on your watch list and see over a period of time what conclusion you might reach. ...IMHO (Talk) 05:23, 19 June 2006 (UTC)
I'd say sometimes the medical articles are written in unnecessarily technical language. But I think this is just health professionals failing to consider their audience when writing here rather than a deliberate attempt to obscure. See Hanlon's Razor. There's also the fact that writing both accessibly and accurately about technical is a very difficult skill.
I understand the difficulty for any individual to step far enough away from the field of expertise to see it clearly form a layman's pov but that is why we participate in the Wikipedia in the first place. My concern is that when such experts guard an article with such jealously that any user who is able to bridge the gap between the experts and the layman is prevented from adding simple but accurate explanations. ...IMHO (Talk) 06:30, 19 June 2006 (UTC)
I do think there's scope for stronger attention to be paid to Wikipedia:Explain jargon.--Robert Merkel 05:31, 19 June 2006 (UTC)
In this regard you must unfortunately include mathematical symbols and representations which more often than not require examples of computer code and data in order that the jargon be explained. ...IMHO (Talk) 06:33, 19 June 2006 (UTC)
Perhaps we don't want to sit around and watch the half-life article—did you choose this article as a pun? Why don't you find an example of an edit that removed factually accurate information that made the article harder to understand? My guess would be that incorrect analogies are removed from articles by people who have a definite understanding of the material and that you are simply paranoid. Also, just because a statement is understandable doesn't mean it is true. —Bradley 23:16, 19 June 2006 (UTC)
To have coordinated censorship you'd need coordination among academics in the first place. Which generally does not exist. But as a form of systemic bias, I think it is true that sometimes certain lesser-known topics get monopolized by those who know a lot about them but are not good at explaining it. The better known a topic is, the less likely this can last for long. But there are some articles which reflect a total lack of consideration for the layman (even something as non-technical and narrative-based as our biography of Franz Boas, which is about 3X too long, suffers from this). --Fastfission 13:54, 19 June 2006 (UTC)
I think that in many cases, the technical jargon is used because it saves time--it describes something specific in a way that is easily recognized by people in the field, while using a minimum amount of language. The challenge for Wikipedia, or any widely-used reference source, is how satisfy both "expert" users as well as the public at large. Experts don't want to plod through simplified explanations of what they already know; novices don't want to be frustrated by language they don't understand.
Going back to your question, I believe that there's a policy or guideline or something about how Wikipedia editors should not act as if they "own" a given article. Wikipedia is about reaching consensus and allowing many people to do their bit towards improving an article. --Tachikoma 14:06, 19 June 2006 (UTC)
The problem with reaching consensus is that there is a small group of committed academics who jealously guards some articles, immediately removing any attempt to make them accessible to the general public (which, while far more numerous, lacks the same level of commitment and is thus easily scared off by such actions). The only way I was able to find around this problem was to create a separate article for laymen. For example, the article Boolean algebra suffered from this problem, so I created the simplified version as Boolean logic, and added dabs at the top of each, pointing to the other. StuRat 17:11, 19 June 2006 (UTC)
Yes this possible solution occurred to me as well so I did the same thing and avoided even the temptation of putting a link to the new article in the existing article's "See also" section. Perhaps this way the new article will not be found and deleted before it has gained a few edits from other users who can help fight those who are unsympathetic with the needs of the layman and sometimes experts alike The real scare is that the person standing guard over the article I am concerned about has a false concept of the subject matter. Perhaps it is just as well that a new article be created to give everyone an opportunity to know the truth about the topic. ...IMHO (Talk) 19:43, 19 June 2006 (UTC)
←dragging discussion back a few indents←
Please, please, please don't just create your own fork of an article and try to hide it away somewhere. For one thing, it's very inefficient. Editors may contribute to one branch or the other, allowing both versions to be incomplete. For another, it's frustrating to our readers—they've only got a 50/50 shot of hitting the 'right' article. Finally, it's an ultimately futile effort. Eventually someone will notice the duplication and merge the two articles anyway.
There are several strategies for dealing with an article that you believe is overly technical.
  • Add the {{technical}} template to the article. This flags the article as needing some added detail and description for accessibility, and adds the article to the Category:Wikipedia articles that are too technical category.
  • Open a discussion on the article's talk page, and invite participation from the article's regular editor(s).
  • If an article contains many technical subtopics, it may be appropriate to rewrite it in summary style. (Create a main article with short, accessible descriptions of each subtopic, and link appropriately to technical subarticles.)
  • Seek comment from other editors using a request for comment. We can't help to resolve your dispute if you don't even tell us what article you're talking about.
  • Finally – and most importantly – assume good faith on the part of your fellow editors. Accusing other editors of censorship, or of deliberately concealing information on behalf of some mysterious guild, tends to taint the working relationship a bit. Communication through text alone can be difficult and ambiguous. Other editors might interpret your attempts to make the article more accessible as sloppy or imprecise and be unaware of their own article ownership issues. They might feel attacked by your implications that they are censoring material or trying to hide information.
So do we at least get a hint about what article(s) you're talking about? We can't help you fix things if you won't tell us what the problem is. :D TenOfAllTrades(talk) 00:09, 20 June 2006 (UTC)
See Talk:Half-life starting June 12 and the recently created Half-life computation which has been sent to AFD Wikipedia:Articles for deletion/Half-life computation. Just a hint :-) Vsmith 02:50, 20 June 2006 (UTC)

[edit] First patented form of life...

Hi! The following question is a product of my 'momentary inattentiveness' in class(please don't avoid answering for punishing me).

What is the first 'patented form of life'? I'm quite sure, I heard the name of a scientist- Ananda Mohan Chakrabarty, in this connection(though I doubt its authenticity). How far Super Bug is related to this? Thanks,--Pupunwiki 07:51, 19 June 2006 (UTC)

hi! The first "patented form of life" was invented by the scientist CHAKRABARTY which are nothing but the OIL EATING BACTERIA.... Oil Eating Bacteria are chiefly used to clear oil spills in the process of BIOREMEDIATION In the year 1980 Chakrabarty discovered a bacteria[SUPERBUG] that could digest crude oil. SUPER BUG is said to be a strain of bacteria that is resistant to all antibiotics. It is also said to be a strain that is accidentally imported into florida from the Middle East then spread to California where it is a very serious pest feeding on almost all vegetable crops and poinsettias eg;- Bemisia tabaci, poinsettia strain some oil eating bacteria are also resistant to antibiotics...in this way super bugs are related to oil eating bacteria The oil eating bacteria Pseudomonas species is one such example for a super bug[resistant to antibiotics] --hima 10:27, 19 June 2006 (UTC)

   Thanks a lot, Hima, for clearing my doubts.
                                   --Pupunwiki 10:41, 19 June 2006 (UTC)
Well, the Diamond v. Chakrabarty resulted in the first patent for genetically modified life. But the Plant Patent Act of 1930 allows for the patenting of asexually produced cultivars, which are also "life", technically speaking. --Fastfission 13:47, 19 June 2006 (UTC)

[edit] Ridiculous Information from Wikipedia.

well, i was surfing the "war portal" on wikipedia recently. One of the articles had this link : "http://uncyclopedia.org/wiki/Palestine", under its "external links" section. And i was shocked to visit the link and the contents. And i think that site itself is open for editing, but the content still is shocking. And they have not even deleted it. Can someone help?

Uncyclopedia is in no way affiliated with Wikipedia, the site looks similar beacause they use the same software (and because they are a conscious parody site of Wikipedia). We have no influence on the content of articles on uncyclopedia, if you think their Palestine article is crossing the line of good taste, it's best to take your concerns there. Now, whether or not an external link to an uncyclopedia article is appropriate for a Wikipedia article is another matter...where did you find the link? -- Ferkelparade π 10:04, 19 June 2006 (UTC)
Thank god they don't have a reference desk. Yet. Where is this link? Wikipedia articles shouldn't link to Unencyclopedia (unless they're discussing a topic such as parody). --Shantavira 12:22, 19 June 2006 (UTC)

I read somewhere (maybe in the uncyclopedia) that it was purchased by Wikimedia. Since you can't edit articles who writes them? ...IMHO (Talk) 13:59, 19 June 2006 (UTC)

Uncyclopedia uses MediaWiki software, like Wikipedia. They are not "owned" by the same people. You can edit articles there, just like here - anyone can. What the above poster meant is that the editors here are not responsible for content there, as the majority of users do not overlap between the two sites. -Goldom ‽‽‽ ⁂ 14:32, 19 June 2006 (UTC)
It's a great outlet when you feel like posting nonsense, though! (As long as you keep it funny.) Melchoir 19:27, 19 June 2006 (UTC)
Well you can edit some things but not the majority of things in line with the idea of a contra-wiki. If you could edit everyting then it might actually serve the role of a parody where Wikipedia users could vent steam but as is its more like a spoof than a parody. ...IMHO (Talk) 19:33, 19 June 2006 (UTC)

[edit] Wavefunction, quantum mechanics, electrons etc

Quote from wavefunction -

"The complex square of the wavefunction, |\psi|^2\,, is interpreted as the probability density associated with the particle's position"

I was thinking in terms of an electron though I imagine the specific case is unimportant - my question is - Is there any reasoning or justification behind this relationship, (it seems to be a theorectical assumption used in a model) - and additionally, who originally came up with this idea and are they still alive and sufficiently sentient to be asked how/why they came up with this relationship?HappyVR 14:19, 19 June 2006 (UTC)

(disclaimer: not a physicist) Could you maybe clarify the question? Are you asking why is the complex square not simply a part of the wavefunction so that it evaluates directly to a probability? If so, this is far from a perfect answer, but it is one perspective: consider variance and standard deviation from statistics. Mathematically, variance is the simpler value, in a sense, but its units aren't the same as the original data, they are the square of those units, so the standard deviation is often used, which is simply the square root of the variance, and thus in the same units as the data. Now I'm not saying that's the real answer to your question, I'm just saying sometimes the mathematically easy quantity and the intuitively simple quantity are not the same. A better answer might be that photons/electrons/etc act like complex numbers in a sense (i.e. they follow the same rules when looked at in the right light) and it works out that once you have the complex "amplitude" for an event worked out you can square it and find the actual probability for that event. But perhaps I've only restated your question and added nothing... 128.197.81.181 18:56, 19 June 2006 (UTC)
Well - I'll try to clarify(using electrons) - within the theory, the wavefunction is a property of (an electron), physical properties can be calculated using functions operating on the wavefunction. (A bit like we could have a function describing my velocity at a given time and you could use that function to calculate how far I've gone etc). In this case the probabilty density (thats how likely it is for an electron to be found in a given region - a bit like gas density) is calculated using the complex square of the wave function - thus if the wavefunction is complex eg a+ib the propability density is (a+ib)(a-ib). I was wondering why this function - what reason - why not (for instance) the magnitude of the complex number, or indeed any other function? Whats the reason or reasoning behind it?HappyVR 09:14, 20 June 2006 (UTC)
As Probability amplitude says, this interpretation is due to Max Born who is long dead; he eventually got a Nobel for it though. Melchoir 19:24, 19 June 2006 (UTC)
Thanks for that 'melchoir', god bless Max Born.HappyVR 08:35, 20 June 2006 (UTC)
I wouldn't say it is a "theoretical assumption." It is experimentally verified. (Cj67 22:18, 19 June 2006 (UTC))
?

I have one answer now (Max Born developed this), however maybe a physicist could explain (maybe they have read Borns papers) why this relationship was chosen - is it just for simplicity - I can't see any reason why this relationship has to be right (eg units) - as possible alternatives I could suggest (using a+ib to represent a complex number) the magnitdue sqrt (a^2+b^2) or the square of the magnitude (aa+bb) as two of many possibilities as alternatives to the complex square (aa-bb) being the right answer. Can anyone explain any reason to believe that the complex square should be used as a measure of the probability density.HappyVR 08:35, 20 June 2006 (UTC)

Wavefunctions are a mathematical construction. They provide a convenient mechanism for describing the relationships which ultimately give rise to quantum mechanical observables, but they need not have any tangible meaning themselves and are never directly measured. In fact, you don't need wavefunctions to describe quantum mechanics. Matrix mechanics and mathematical formulation of quantum mechanics describe a number of alternative mathematical formulations that give rise to the same observables and hence must be equally valid descriptions of quantum mechanics. However, for many practical applications, wavefunctions are the easiest approach. In this sense, asking why should | ψ | 2 = | a + bi | 2 = (a + bi) * (a − bi) = a * a + b * b (note, not aa-bb, as you suggest) be a probability density isn't really a sensible question. If it wasn't a probability density then it wouldn't be useful and we would be using some other formalism. However, asking what it means that this relationship holds for the intrepretation of quantum mechanics is an interesting question. In the simplistic way of thinking about things, it means that every particle describable by quantum mechanics can be equated to a wave that has not only an amplitude but also an orientation in space (e.g. a direction in the complex plane) and that determining the interactions between waves depends on considering these oreintations, but ultimately after considering any interactions it is the magnitude, the resulting a*a+b*b, that gives rise to the observable states. Dragons flight 09:13, 20 June 2006 (UTC)
oops - yes bit of a bodge up by me with the 'complex square' - however what I was asking was basically what about sqrt(aa+bb) - (in a simple sense eg addition of vectors this seems to make more sense.HappyVR 10:35, 20 June 2006 (UTC)
Or to put it much simpler - is there someway of showing that using (for instance) |sqrt(aa+bb)| as probability density is wrong?HappyVR
I think Bohm's Quantum Theory has something along these lines. - mako 08:04, 24 June 2006 (UTC)
The page Bohm interpretation doesn't seem to give an answer?HappyVR 14:13, 24 June 2006 (UTC)

[edit] Appropriate Waste Disposal

I have an old computer that I failed to fix. I've salvaged some components but I don't know if the motherboard works properly. It used to run on a 112 W PSU and has no AGP slots (just three PCI and some weird stubby slot). Should I just chuck the mobo and processor in the electrical waste at the tip? Should I keep the processor or PSU? What should I do with the case? Can't it be melted and used in something? There aren't enough provisions for people who want to be environmentally friendly... --Username132 (talk) 14:27, 19 June 2006 (UTC)

You can reuse the case. As for the rest, have you considered an art project? HighInBC 14:32, 19 June 2006 (UTC)
You are correct that computer parts may contain nasty stuff that you don't want ending up in landfill. The best bet is to contant your local recycling company and ask if they have a place to take it. (If your city picks up recycling, ask them, or if not, just another local company). Places like Office Depot often take in things like used-up rechargable batteries for recycling, but I doubt they'd have room to take whole MBs. -Goldom ‽‽‽ ⁂ 14:36, 19 June 2006 (UTC)
The plastic case is probably just that plastic plus some filler - maybe you could put that in any plastic recycling bin you can find. The processor is mostly inert - might contain some gold though but not much - the case will be ceramic or a resin. As far as I know its the glass fibre and the resins gluing it together and the lead used in soldering on the motherboard that are supposed to contain the nasties - no idea what you are supposed to do with this though - burning it is the way to release the chemicals enviromentalist don't like. The PSU contains sufficient scrap metal to be worth at least 50p to a scrap metal merchant - that's most of what I can say to help. (Art project is good idea - maybe you could use the processor as a coaster for small tots of rum)HappyVR 14:38, 19 June 2006 (UTC)
I'm pretty sure you could find a homeless guy that could find some way to use your junk.  freshofftheufoΓΛĿЌ  00:27, 20 June 2006 (UTC)
Why wait for a homeless person? I bet one of your friends would like a hunk of junk. I sort of would, but I'd like it to be in slightly better condition. --M1ss1ontomars2k4 (T | C | @) 04:55, 20 June 2006 (UTC)

[edit] Can medium format (120) film be developed by my local pharmacy?

Is it likely that the neighborhood drugstore would be equipped to develop 120 film? Javguerre 15:28, 19 June 2006 (UTC)

No. It is likely that your local drugstore sends all film to a processing service. It is probably easiest if you just call or visit the drugstore to ask; however you might be better served by searching for a nearby camera store (not a chain like Ritz or its siblings) and asking them for advice. --LarryMac 16:11, 19 June 2006 (UTC)
Right.......and you think getting stuff to an external service and back would allow a 1 hour turnaround? that would be some pretty impressive logistics. Plugwash 01:00, 20 June 2006 (UTC)
Where did anybody ask for 1 hour turnaround? I should have added that many stores do now have the self-contained machines that allow processing of 35MM C-41 process film on premises, but 120 is a whole different animal. --LarryMac 01:03, 20 June 2006 (UTC)

[edit] The Moon

From what points on the Earth does the moon apear largest? Thanks, Lucy Hallam

The Moon would be closest to an Earth-bound observer on Mount Everest, but that's only a 9 km difference versus a sea-level observer. By comparison, the Moon's orbit causes it to vary in distance from the Earth by 40,000 km. So actual size from earth doesn't appreciably vary no matter where you are.
However, there is a well-known Moon illusion where the Moon appears largest near the horizon, though it's simply a trick of the brain's interpretation of the image, not the actual size of the Moon itself. — Lomn | Talk 16:05, 19 June 2006 (UTC)
To be pedantic, you'd be better going up Chimborazo (volcano) than Mount Everest - it's peak is two kilmetres further from the centre of the earth than Everest's. Dmn € Դմն 21:35, 19 June 2006 (UTC)
To add to that, you should wait until perigee occurs near Chimborazo. You could be waiting for a very long time. --M1ss1ontomars2k4 (T | C | @) 04:52, 20 June 2006 (UTC)
Oh yeah. Back to the moon illusion. Due to geometry, shouldn't the moon's actual angular diameter be greatest at the zenith rather than the horizon? --M1ss1ontomars2k4 (T | C | @) 04:54, 20 June 2006 (UTC)
Yes. Moon illusion says "The true angular diameter of the Moon is about 1.5% smaller when it is near the horizon than when it is high in the sky, because it is further away by up to one Earth radius." -- Wikicheng 05:58, 20 June 2006 (UTC)

Thanks for answering that for me, much appreciated! Lucy

[edit] Fish question

What is the name of this fish? It lives deep in the ocean where there is no light. It has an extendor over its eyes that has a bulbuous attachment that glows. It was used in Disney's movie Nemo.

Maybe today you are in luck since this came up on another talk page I was reading - is it Black seadevil - it sounds v. similar. -- HappyVR 17:12, 19 June 2006 (UTC)
and Anglerfish -- HappyVR 17:13, 19 June 2006 (UTC)
It was the angler fish. — The Mac Davis] ⌇☢ ญƛ.

[edit] How much did Apollo 11 cost?

Good afternoon,

Does anyone know how much the first manned mission to land on the moon, Apollo 11, cost?

Thankyou,

Neil

Neil, is your family name Armstrong?
http://www.seds.org/spaceviews/9607/articles.html
TOTAL COST PER APOLLO MISSION:
-----------------------------
              Year   ($M)   (94$M)
Apollo 7      1968   $145    $575
Apollo 8      1968   $310  $1,230
Apollo 9      1969   $340  $1,303
Apollo 10     1969   $350  $1,341
Apollo 11     1969   $355  $1,360
Apollo 12     1970   $375  $1,389
Apollo 13     1970   $375  $1,389
Apollo 14     1971   $400  $1,421
Apollo 15     1971   $445  $1,581
Apollo 16     1972   $445  $1,519
Apollo 17     1972   $450  $1,536
---------------------------------
                   $3,990 $14,644
Have a nice afternoon. -- Toytoy 17:37, 19 June 2006 (UTC)

Thank you very much for your help; no my surname isn't Armstrong I'm afraid!

Thanks,

Neil

I didn't know Space Shuttles are THAT EXPENSIVE!
The data show that over the entire lifetime of the the space shuttle program the cost has been $145 billion, and about $112 billion since the program became operational.
Furthermore, the average cost per flight has been about $1.3 billion over the life of the program and about $750 million over its most recent five years of operations.
Now I think sending people to the moon is cheap. -- Toytoy 01:06, 20 June 2006 (UTC)
Not to get OT, but take into consideration the expanded capability of the STS, in crew capacity, flight duration, and payload. Not to say that $1.3B to gas up a ship and send it around the earth seems cheap, but...
I seem to recall a long discussion of costs at Space Shuttle. There's a lot of ways to define costs -
  • Average Cost ("How much did the total program spend; then divide by number of missions...")
  • Incremental Cost ("How much extra money does it cost to send one more launch, after the program infrastructure exists")
  • Opportunity Cost ("How much could we have earned if we spent money elsewhere...")
... etc. There's no easy way to assign an exact dollar value to spaceflight. Nimur 17:29, 22 June 2006 (UTC)

[edit] Edibility of Cucumis melo leaves

Many cucurbits have edible leaves, but I have not been able to satisfy myself about Cucumis melo. I was surprised at how little information I could find for such a well-studied plant. BioNatural claims that the Pedi and the Sukuma people eat the leaves as a "potherb and relish", but the mention is off-hand and undetailed, and the company sells herbal extracts, so they may have a profit motive in giving this information. An agricultural researcher in Uganda lists the leaf among the plant's edible parts, but again no detail is given. Cucumis melo is not on Leaf for Life's very long list of plant species that have reportedly been eaten by people. Plants for a future reports that "the sprouting seed produces a toxic substance in its embryo", but not what the toxic substance is, where in the plant it is distributed, nor how long it persists as the plant grows.

I have added Cucumis melo to the list of plants with edible leaves, but have not eaten the leaves of the melon vines in my garden. Any further information would be appreciated. Thank you. Leafeater 17:53, 19 June 2006 (UTC)

This is a tough one. All I have to contribute is that Francois Couplan's very comprehensive The Encyclopedia of Edible Plants of North America does not mention the leaf as one of the edible parts of Cucumis melo, and he generally doesn't miss much. — Pekinensis 20:42, 23 June 2006 (UTC)

[edit] EMP nullification

What is the name of the device that nullifies the effect of an electromagnetic pulse on electronic devices? It resembles a cage made of wire. I tried a number of searches under different topics and come up empty. It's driving me crazy. —The preceding unsigned comment was added by 72.54.24.94 (talk • contribs) 19:39, 19 June 2006 UTC.

I'll put you out of your misery. See Faraday cage. --GraemeL (talk) 18:43, 19 June 2006 (UTC)


Thanks much. Now I can sleep at night.

[edit] JPG image problem

I have a group of jpg images which were scanned into the computer under Windows 98 using an HP Scanjet IIcx flatbed scanner. The images seem to be okay except that their widths have been compressed to about 1/3 of the left side of the page with the remainder of the page being solid black. I have never seen this before. Does anyone know what caused this and more importantly how to restore the width of the image without loss of information? Thanks. ...IMHO (Talk) 19:04, 19 June 2006 (UTC)

I guess one question that has to be asked is what did you do with them? Were they copied to a diskette or CD and were they fine when you first scanned them? I've have some problems with scanners before where no matter how many times I scan the same image, it always scans half the image wrong, and I usually assume it to be a scanner problem. If you've used storage media on the images though it might be a different problem, and there are jpeg rebuilders that may be able to fix them. Oh, and for the record, the blank area of the image is usually called the "canvas".  freshofftheufoΓΛĿЌ  00:20, 20 June 2006 (UTC)
Right the programs I have to view and edit call the whole area the canvas but I can't find the one at the moment that actually allows the image on the canvas to be streched by default rather than moved across the canvas. This is the one I had planned to use to restore the images but I am curious as to the cause. The images were fine after scanning and were only transferred from a FAT32 drive to a NTFS drive over a local Ethernet and have been there ever since. ...IMHO (Talk) 08:58, 20 June 2006 (UTC)
Ah, I see what you're getting at now. Any program like Photoshop lets you fiddle with the canvas and size settings, but as you know that's not going to leave you with the same detail as the original 1:1 images. It's not likely that the full quality image is still preserved in the file unless they've been somehow vectorized. Sorry, I can't think of why they would suddenly be compressed like that, since they obviously haven't been simply corrupted.  freshofftheufoΓΛĿЌ  10:21, 20 June 2006 (UTC)

By looking in the subdirectory (I was only looking at the results of a search for jpg files)the reason for the problem may now be revealed although I still do not understand what caused the problems. The image name ends with ....tif.jpg so it looks like they were tif images that got saved as jpg images but that still does not indicate how they were distorted in this manner. After removing the jpg extension the thumbnail image does not change and there is no effect on the edit views of the image as if the extension has been ignored and file type determined by some other means. Anyway I suspect some kind of accidental conversion due to file name change and now possibly even a virus. ...IMHO (Talk) 15:22, 20 June 2006 (UTC)

[edit] Orbit/gravity/weightlessness

I have a question relating to gravity/orbits, etc. Do you know who I can direct it to?

I understand that objects/people in orbit around the earth only appear weightless due to the fact that they are in freefall, and since the spacecraft and everything/everyone aboard are all falling at the same rate of speed around the earth (in orbit), they appear to be weightless.

My question is this:

When the astronauts travelled to the moon, they also experienced weightlessness. Since they left earth orbit on the journey to the moon, and were not in freefall, why were they weightless en route?

Jake Whalen

You should probably check out our article on weightlessness, particularly the discussion on pressure gradients. As a layman, though, here's my attempt:
Weightless freefall isn't dependent on "falling" per se but rather on you and your reference frame (that is, the spacecraft) not resisting gravitational forces, whether or not those forces will eventually cause you to collide with the relevant astronomical body. When you consider "falling" as instead being "coasting without support", weightlessness between the Earth and Moon makes a good bit more sense (to me, at least).
Also, it's a good idea not to post your phone number on the internet. — Lomn | Talk 20:02, 19 June 2006 (UTC)
Please note that weightlessness is experienced only when the spacecraft engines are shut-off (free-fall). Any time the engines are on, they exert a force on the craft and its content, and the reaction, e.g., the force exerted by the astronaut on his seat, is the equivalent of a residual weight. --Michel M Verstraete 00:04, 20 June 2006 (UTC)
Adding to Michel's answer: When the engines are turned off, even if the spacecraft is travelling away from earth, it is still 'free fall' because the only force acting on it is the gravity. So you can say that you will experience weightlessness the moment the engines are turned off, whether the spacecraft is moving away or orbiting earth -- Wikicheng 06:21, 20 June 2006 (UTC)
When you throw a ball it is in freefall from the instant it leaves your hand, even though for half of its trajectory it is "falling" upwards. Tiny astronauts inside the ball would experience "weightlessness" - right up until the point when the ball hits the ground and they are squashed by the deceleration. The Vomit Comet does the same thing, only on a bigger scale (and without the hard landing). Gandalf61 10:36, 20 June 2006 (UTC)


The original poster asked a very good question, and it is fundamental to understand it. Everyone's answer was very well written so I can't add much, but one thing : when I was a child they explained me : you are far away from earth, gravity becomes weak. Well that is simply untrue, in the International Space Station (or Mir) gravity was 9.5 m/s^2 , compared to 9.81 m/s^2 here on earth, I doubt a human would really feel that difference. The correct answer is simple : you experience weightlessness when you and your ship have exactly the same forces that work on them. Evilbu 11:07, 20 June 2006 (UTC)

Just to clarify - it is true that far from the earth the force of gravity due to the earth does become weak; it obeys an inverse square law. Around the distance of the moon, acceleration due to the earth's gravity is less than 0.01 m/s^2. When the astronauts left orbit, they did experience some acceleration due to the ship's rockets, but it was probably pretty small, and once they got far enough out, Earth's gravity became negligible. They were never completely "weightless", but nearly so. --Bmk 17:36, 20 June 2006 (UTC)

There seems to be a confusion here. When an object is orbiting earth, it is again a case of free fall (only that while moving tangentially, the object falls just enough distance, to keep it at the same distance from the earth). As Mir is orbiting earth, the astronauts in Mir experience zero gravity and not 9.5 m/s^2 -- Wikicheng 08:12, 26 June 2006 (UTC)

[edit] Symptoms of long-term oxygen deprivation

What are some possible symptoms of shallow breathing, or mild long-term oxygen deprivation? For instance, someone contracts sleep apnea in conjunction with asthma and allergies, causing generalized shallow breathing and low oxygen intake.

Look under "Symptoms" in the article Sleep apnea. Googling for the term also gives results. --Seejyb 01:39, 20 June 2006 (UTC)

You are actually asking about five sometimes associated, but distinct and independently diagnosable, conditions. Chronic effects, as opposed to acute effects, vary by severity from minimal to marked. At their worst, these conditions can cause some fairly serious effects over time, depending on age and co-morbidities.

  1. asthma: This is usually episodic rather than continual. It usually does not cause hypoxia except in extreme exacerbations. Although it can coincidentally occur in someone with sleep apnea, it is a completely independent condition.
  2. respiratory allergies: The most common of these are simply a stuffy, runny nose, not affecting oxygen level. The most severe kind of respiratory allergy (as distinct from much rarer hypersensitivity reactions) is typically allergen-triggered asthma.
  3. chronic hypoventilation: This can occur from a variety of conditions ranging from genetic defects of breathing drive to congenital brain syndromes to COPD to severe obesity, but not usually from asthma. It typically causes fatigue. In a severe form it can cause chronic hypoxia, and long-term strain on heart leading to cor pulmonale and even death.
  4. sleep apnea: This is most commonly due to upper airway obstruction due to obesity but can have other causes as well. It can cause transient hypoxia during sleep. It can cause daytime fatigue, headache, difficulty concentrating and remembering. There is mounting evidence that obstructive sleep apnea can contribute to the development of insulin resistance and type 2 diabetes.
  5. chronic hypoxia: Chronic hypoxia has many causes ranging from COPD to chronic restrictive lung disease to chronic airway obstruction to cystic fibrosis to cyanotic congenital heart disease. Chronic hypoxia can cause a variety of long-term problems ranging from poor growth in children to fatigue and neurocognitive impairment in adults. In severe cases it can lead to cardiac hypertrophy and congestive heart failure. alteripse 02:17, 20 June 2006 (UTC)
Cigarettes, anyone ? --DLL 20:52, 20 June 2006 (UTC)
Don't forget Chronic_mountain_sickness! — The Mac Davis] ⌇☢ ญƛ.

[edit] Centrifigal Force and Gravity

Since a object on the equator is spinning faster then one on the pole, shouldn't there be a difference in weight between them? Wizrdwarts (T|C|E) 21:19, 19 June 2006 (UTC)

Yep, and there is. See Gravity (Earth) and Apparent weight. moink 21:28, 19 June 2006 (UTC)
Thanks for the quick answer! And according to the timestamp on your post, you replied one minute before I even asked! Do you know how much the actual difference would be? Wizrdwarts (T|C|E) 21:37, 19 June 2006 (UTC)
According to Gravity (Earth), 0.5% (also, Moink's timestamp is 9 minutes after yours). — Lomn | Talk 22:12, 19 June 2006 (UTC)
Must've gotten less than enough sleep today. I misread the "2" as a "1". Thanks! Wizrdwarts (T|C|E) 22:46, 19 June 2006 (UTC)

[edit] Why is AC current prefered over DC?

I've read about the subject, but I have never found a conclusive answer. There must be a major reason, otherwise we would still have both systems. Which reason is that? Afonso Silva 21:20, 19 June 2006 (UTC)

DC power supplies require a power station to be built every fifty miles or so, which becomes very impractical outside large cities. As a result, AC current is used; see the War of Currents article. Andromeda321 21:34, 19 June 2006 (UTC)
Eh, what? There's no problem with transmitting DC over long distances; for long runs high-voltage direct current (HVDC) is actually more efficient than AC. (It has a number of other advantages in certain situations, as well.) AC's major advantage is that its voltage can be easily stepped up and down with a simple transformer, making it possible to transmit current over long distances.
DC transformers are much more complicated and costly than their AC counterparts, rendering them poorly-suited for ubiquitous power grid use. TenOfAllTrades(talk) 22:23, 19 June 2006 (UTC)
There is really no such thing as a "DC transformer." AC voltage can be stepped up and down with two coils of wire and an optional lump of iron (called a transformer). DC voltages are stepped up and down with relatively complex switches and switching circuits referred to as DC-DC converters or through other more involved or less efficient means (e.g., motor-generator hookups). —Bradley 22:59, 19 June 2006 (UTC)

Thanks! I was trying to find an article in Wikipedia about it. The name is strange. Afonso Silva 22:19, 19 June 2006 (UTC)

Yeah, DC transformer is a weird thing, as DC keeps the magnetic field constant. Is that it? At least, it is what I learned. The magnetic flux must change in order to induce a current. Afonso Silva 23:13, 19 June 2006 (UTC)

Correct. As stated above, to change DC voltage levels you need converters such as the flyback converter.
As also mentioned above, there are some cases where DC transmission is used over long distances, with much lower losses, one factor that helps it is the fact that AC currents only "run through" thin layer of the conductor increasing resistance, compared to DC current that flows through the whole section of the conductor. VdSV9•♫ 01:20, 20 June 2006 (UTC)
I think it also has to do with safety purposes. I personally had the "oppurtunity" to get electrocuted by AC and DC voltages, and I found that the AC voltage actually pushes your body away so you have a chance of pulling away your hand or the part that is in contact with the circuit. But try pulling your hand from a 220 V DC (thats the common voltage in India) voltage. I think the death rate would be a lot higher if we had used DC voltage. ;-) Jayant,17 Years, India • contribs 11:55, 20 June 2006 (UTC)
Whatever you prefer, it's not been the same since Bon Scott died. --Dweller 11:59, 20 June 2006 (UTC)

AC offers numerous advantages over DC such as:

  • Voltages can easily and cheaply (compared to DC) be stepped up or down using transformers for diferent transmission and distribution needs
  • Using 3-phase supply allows different voltage levels to be obtained (phase-phase, phase-ground) from the same set of transmission lines
  • Using 3-phase supply, loads on each phase can be balanced in order to reduce or eliminate the need for a conductor to provide the return path to earth. This means less "conductor per kilometer per megawatt", reducing costs. (This is offset by the phenomenon mentioned above about DC current flowing through the whole conductor whereas AC flows only through a thin surface layer). p.s. where is the wikipedia article on the skin depth effect?
  • Protection systems in AC circuits are simpler i.e. cheaper because the current passes through a zero every cycle, which can help to extinguish e.g. a short-circuit arc

Disadvantages of AC include:

  • Line inductance and capacitance to ground may be significant, especially over long distances, causing losses over and above normal resistive losses
  • Power factor becomes one of the main considerations to system stability and power flow. In particular, attention has to be paid to active and reactive power
  • It's just a lot more difficult to understand intuitively than DC. You've got all sorts of messy things such as series and shunt capacitors used for various purposes such as voltage boosting, improved power transmission etc.

In conclusion, the reason most systems are AC is because AC is cheaper. As for the electric shock comment, I simply don't think it is correct. An electric current through your body (AC or DC) causes your muscles to contract involuntarily. When someone touches an exposed electric circuit with their hand, muscle contraction prevents them from letting go, which is why when working on an electrical system, workers will (obviously after making sure everything is earthed!) often touch the device/conductor with the BACK of their hand to test for dangerous induced voltages (muscle contraction would then cause their hand to spasm AWAY from the metal). Zunaid 12:29, 20 June 2006 (UTC)

I think your second point on the advantages of AC – different voltages – isn't valid, as that can be done with DC as well. – b_jonas 11:01, 23 June 2006 (UTC)
Skin effect — The Mac Davis] ⌇☢ ญƛ. 01:38, 21 June 2006 (UTC)


Zunaid gave a great complete answer on the subject. But actually, as for the electric shock, it's much worse in DC, just think of a continuous 220V shock as compared to an intermitent shock. For one thing, the power dissipated by one's body will decrease to 70,7% of the DC, value, not to mention a the reactance of the human body that increases impedance.
This is not the reason "why AC is preferred over DC", I'm just clarifying this electric shock issue. VdSV9•♫ 15:47, 20 June 2006 (UTC)
That's not true. X volts of AC dissipates exactly the same power as X volts of DC in a given resistance, by definition, because AC voltages in this context are specified in RMS. Furthermore, the peak value of X volts AC is 1.41 X volts, so you would get a 41% worse shock, intermittently, from X volts AC than from X volts DC. The current due to capacitive reactance is negligible, only a few microamps (240 V * 2π * 50 Hz * 100 pF). Inductive reactance would make the current smaller. --Heron 21:22, 20 June 2006 (UTC)

Hmmm... right, it slipped my mind. Still, from all I know, the intermitent nature of AC makes the shock less damaging. And resistance and reactance are variable from person to person anyway. -- VdSV9•♫ 18:04, 21 June 2006 (UTC)

allaboutcircuits.com mentions particular hazards of both AC and DC. In summary:
  • Tetanus (muscle spasm): DC worse, because you can't let go
  • Ventricular fibrillation: AC worse, because it interferes with pacemaker
  • Burns: no difference, if exposure time and voltage are equal (for reason given above)
There's no clear winner, which is probably why the dispute won't die. --Heron 20:57, 21 June 2006 (UTC)

Wait a second! AFAIK it is the voltage transition which causes an electric shock. AC current has 50 transitions/sec or 60 transitions/sec depending on where you live and who supplies your electricity. DC only has 2 transitions: 1 when touching the wire, and 1 when releasing it. Didn't Edison hold entire demonstrations on the safety of DC over AC, or am I getting something wrong? You can still get bad burns though. <scratches head> --Kim Bruning (talk) 17:50, 12 January 2008 (UTC) I also seem to remember an episode of junkyard wars where some geeks powered an underwater motor using a dc battery and unshielded leads, and did not die :-P Am I getting something wrong?

Hmm, War_of_Currents, and I was partially right. Online sources say that AC is 3-5 times more dangerous than DC, but at the same time, other sources contradict. So now I'm confused. ^^;; --Kim Bruning (talk) 18:08, 12 January 2008 (UTC)