Wikipedia:Reference desk/Archives/Science/2009 March 21

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March 21

Olaflur

What exactly is olaflur and how effective is it compared with the other forms of fluoride for teeth? Any disadvantages (human toxicity, environmental, etc)? —Preceding unsigned comment added by 79.107.234.164 (talk) 01:25, 21 March 2009 (UTC)

Our article olaflur will tell you exactly what it is (it is N,N,N'-tris(2-hydroxyethyl)-N'-octadecylpropane-1,3-diaminium difluoride) but will not, alas, answer your other questions. Algebraist 01:33, 21 March 2009 (UTC)

Thank you Algebraist, I have read that, as I have searched in many different sites all of which have the excactly same info as in the article you mentioned. I am particularly interested in the advantages/disadvantages that it has, how it compares with the othe fluoride forms for dental use, it's hazard-toxicological profile and any concerns/other issues about its use. Thanks again though! —Preceding unsigned comment added by 79.107.234.164 (talk) 01:41, 21 March 2009 (UTC)

Google coughed this up which might help. [1] Particularly the PubMed study list link. - 76.97.245.5 (talk) 10:44, 21 March 2009 (UTC)

sweetness equivalent of the Scoville scale?

Is there a scale that measures how sweet something tastes, similar to how the Scoville scale measures heat? The closest thing I found is the Brix scale, but that doesn't seem to directly measure sweetness. --Ixfd64 (talk) 02:11, 21 March 2009 (UTC)

For the sweetness scale see e.g. this. I don't think the scale is named after anyone, though; or at least I am not aware of such a name. --Dr Dima (talk) 09:20, 21 March 2009 (UTC)

See Brix. For grapes there's Oechsle scale. - 76.97.245.5 (talk) 10:35, 21 March 2009 (UTC)

Balling, Brix, Oechsle scales all measure specific gravity, and do not measure sweetness directly. In other words, they only indicate concentration of the sugar (sucrose) in the solution, and do not indicate how sweet other substances are compared to sucrose --Dr Dima (talk) 06:46, 22 March 2009 (UTC)

cacti

Can anyone identify these cacti? Scale is that they are about 2.5" across, and the flowering one is 3.5" tall. Also, would these do ok with only office florecent lights, or do they need actual sunlight?

http://i671.photobucket.com/albums/vv76/nod2003/DSCN0034.jpg http://i671.photobucket.com/albums/vv76/nod2003/DSCN0035.jpg

Oh, the not flowering one has cobwebs on it. 12.216.168.198 (talk) 02:31, 21 March 2009 (UTC)

A Mammillaria sp. perhaps? If I remember correctly the species in this genus can sometimes be tricky to identify. One website suggests partial shade (Filtered sunlight or direct sun for only a few hours) and watering it weekly. Sifaka ^talk 06:04, 21 March 2009 (UTC)

The first one is almost certainly Mammillaria, right. The second one looks like a young Melocactus or Cereus, something in the Cereus tribe; but I'm not sure really. --Dr Dima (talk) 09:39, 21 March 2009 (UTC)

[2] looks similar. (Lots of other cacti pix when you click on the sidebar.:-) 76.97.245.5 (talk) 10:29, 21 March 2009 (UTC)

I was thinking maybe the second one was a Echinocactus. That one really has me stumped. 12.216.168.198 (talk) 12:45, 21 March 2009 (UTC)

Depth of Field vs. aperture diameter

Why does the depth of field depend on aperture diameter of a lens? I am a bit confused. Aperture is to control the amount of light entering the lens. If I make my aperture smaller, the less light should enter, but focal length is still the same, so how does it affect the depth of field? Thanks. - DSachan (talk) 16:27, 21 March 2009 (UTC)

It's because aperture appears in the formula for Hyperfocal distance. I have no idea why that is, though! (Our article doesn't seem to explain the formula much.) Hopefully someone more knowledgeable will come along soon... --Tango (talk) 16:40, 21 March 2009 (UTC)

Actually, after thinking about it, I think I have it - the circle of confusion is going to depend on aperture (in fact, I suspect it is proportional to it), since that confusion is caused by light passing through different parts of the lens ending up at different points on the screen. How far apart those points are is going to depend on how far apart the bits of lens in question are, and a bigger lens allows for greater distances between parts of the lens and so greater confusion. --Tango (talk) 16:44, 21 March 2009 (UTC)

Yes, sounds like a good argument. I should have thought about it. Thanks - DSachan (talk) 16:51, 21 March 2009 (UTC)

The diameter of the circle of confusion is proportional to the aperture diameter, and there's an easy way to see that. Assuming an ideal lens, all light rays emitted from a point in the focal plane and passing through the aperture will be focused onto a single point of the detector. Any light emitted elsewhere along the path of that ray, in the same direction, will end up at the same point. So that point on the film will show features lying within a double cone whose base is the aperture and whose apex is the point in the focal plane. A flat object at a certain distance from the focal plane will be blurred by convolution with the aperture scaled by (distance from object to focal plane / distance from aperture to focal plane). This also shows that the "circle" of confusion is really an image of the aperture, and is only circular if the aperture is. -- BenRG (talk) 18:10, 21 March 2009 (UTC)

With a pin-hole camera - which is a lot easier to think about that the ones with lenses and mirrors and stuff - the smaller you make the pinhole, the better the depth-of-field (but the less light you get in - so the longer the exposure times you need). In the limit - if you imagine a pin-hole camera with an infinitely small hole then every ray of light from everywhere in the world would have to pass through that infinitely small hole in order to hit the film. But only ONE path for that ray is possible. Light (basically) travels in straight lines - but you can only draw one line that goes from some point in the world, through that infinitesimal hole and onto the film. So a perfect pinhole camera has perfect focus from zero to infinity for an infinite depth-of-field. But now imagine a pinhole camera with a 1cm "pinhole" (more like an "ice-pick-hole camera!") - now, the light from a particular point in space can go through the extreme left side of the hole, the extreme right, the top, the bottom, through the middle - or anywhere inbetween. Each of those rays hits the film at a different place - so you get a fuzzy image. If the film is very close to the hole - then a 1cm hole will produce a roughly 1cm blur around a point-sized object in the world. If the film is further away from the hole, then the blurry region will be even bigger. But a perfect pinhole camera has perfect depth of field and everything is always in focus...it just takes you an infinite amount of time to capture the image because you have an infinitely small hole for the light to pass through!—Preceding unsigned comment added by SteveBaker (talk • contribs) 14:14, 21 March 2009

Thanks people, it is clear now. - DSachan (talk) 18:17, 21 March 2009 (UTC)

Actually, you are limited by diffraction with smaller pin holes and the amount of detail that is resolvable. Noodle snacks (talk) 07:22, 22 March 2009 (UTC)

True - I was trying to keep it simple for the OP...but yes, you're absolutely right. SteveBaker (talk) 19:32, 22 March 2009 (UTC)

Now you know about that blow your mind out trying to understand Qinitiq's system desribed in [[3]] which can keep the information from different distances sharp. Dmcq (talk) 23:47, 21 March 2009 (UTC)

High Pressure lighting fixtures

Moved from WP:RD/M#High Pressure lighting fixtures, 19:05, 21 March 2009 (UTC)
My question has to do with lighting fixtures. Can a ballast,ignitor & capistor for a high pressure sodiumn light also be used for a metal halide (Ceramic) light if they are the same rated wattage. —Preceding unsigned comment added by 52.129.12.48 (talk) 18:11, 20 March 2009 (UTC)

No, a metal halide light does not need a high voltage pulse to ignite it, but may need a transformer to convert to the correct voltage. Metal halide lamps may work off the full mains voltage. Graeme Bartlett (talk) 21:20, 21 March 2009 (UTC)

That is not correct, Graeme. All HID lamps require a ballast, including HPS and MH/CMH lamps, and all require a high-voltage pulse to strike (initiate) the arc. They do not operate directly off mains voltage. Different ballasts are generally required for MH vs. HPS, because of the different run-up and operating voltage requirements; mixing and matching makes problems ranging from the costly and inconvenient (early failure of lamp and/or ballast) to the extremely dangerous (catastrophic lamp failure). However, there are now on the market various "smart" ballasts compatible with more than one type of lamp, usually HPS and CMH. They detect the current draw characteristics of the lamp during run-up, and since these characteristics are peculiar to the different lamp types, the ballast is thus able to "know" what the lamp wants to see in steady-state operation. We presently have two relevant articles, High-intensity discharge lamp and Gas-discharge lamp, though a merger has been proposed. —Scheinwerfermann ^T·_C22:07, 21 March 2009 (UTC)

Is this Munchausen, or...?

Okay, so if a person knowingly fakes/exaggerates illness/distress, they would be described as having Munchausen disorder; if they create or fabricate illness/distress in a dependent, Munchausen by proxy; do either over the internet, Munchausen by internet. But if a person who engages in all three of the above also mimics real diseases/distresses of their dependents, does that also fall under Munchausen? What if they are a parent who is chronically negligent to an extent that their child(ren) encounter numerous, potentially life-threatening accidents, yet makes no attempt to be less negligent and revels in the attention that results from the child(ren)'s accidents? And what would you call it if said parent, in a fit of new-found religion, demanded that medical personnel announce a miraculous recovery (in the same manner that a standard Munchausener might demand medical treatment), which resulted in the continuation of an injury of the patient that would have otherwise been corrected or at least improved, as a way to self-confirm their religious ideas (note, this would not be in absence of the Munchausen/by proxy/by internet, but rather alongside it...and the treatment avoided by the "miraculous recovery" ultimately causes the injured party permanent disability)?

Thanks in advance for any and all ideas on this. Even if you don't know for sure, please do share your thoughts. bcatt (talk) 19:21, 21 March 2009 (UTC)

Munchausen's, and related diagnoses, are extremely controversial - it's not at all clear what (if anything) distinguishes between someone who abuses themselves or others in a medical context and someone who has Munchhausen's. (In other words, couldn't a diagnosis of "Bank Robber Syndrome" be assigned to anyone who robs banks). There are certainly those who claim that Munchausen's simply does not exist, and others that it is greatly overdiagnosed. At best we can say that empirical diagnostic tools for making even a tentative diagnosis are pretty dismal, so parsing the more complex examples you cite seems beyond current analysis. 87.114.29.204 (talk) 20:20, 21 March 2009 (UTC)

The bible of mental disorders (the DSM-IV) doesn't even list Munchausen - let alone all of these complicated variations. I agree with '87 - this is controversial at best. SteveBaker (talk) 00:36, 22 March 2009 (UTC)

DSM calls it "Factitious Disorder" 87.114.29.204 (talk) 00:40, 22 March 2009 (UTC)

Ah! Thanks - so they have one listing with three sub-classes for the main deal - and one that rolls in all of the "By Proxy" stuff:

• Factitious Disorder with predominantly psychological signs and symptoms.
• Factitious Disorder with predominantly physical signs and symptoms.
• Factitious Disorder with combined psychological and physical signs and symptoms.

...then there is...

• Factitious Disorder Not Otherwise Specified.

...which includes the 'by proxy' thing - and is a vague 'catch all' for things that it describes as "suggested research".

So the answer to our OP is that there is no official term for all of these complicated variations. SteveBaker (talk) 04:09, 22 March 2009 (UTC)

Thanks Steve, do you think the refusal of medical treatment in order to force confirmation of religious beliefs would also fall under that category, though? bcatt (talk) 05:50, 22 March 2009 (UTC)

No! The diagnostic criteria is that the person with the disorder wishes to be treated as if they were sick - or in the "by proxy" version wishes someone they care for be treated as if sick. Refusing treatment to someone who actually IS sick (for whatever reason) doesn't sound to me like the same kind of thing at all. I agree with the subsequent posters - sometimes a jerk is just a jerk. SteveBaker (talk) 19:31, 22 March 2009 (UTC)

Basically we're talking about where you draw the line between a "bad person" and a "mentally ill person that does bad things". I've never really known how that is supposed to work... --Tango (talk) 01:12, 22 March 2009 (UTC)

People who are rich enough to afford doctors who can make a diagnosis are mentally ill. Everyone else are just healthy people who make bad choices. --Jayron32.talk.contribs 02:22, 22 March 2009 (UTC)

That would seem to suggest that everyone who behaves badly in countries with "free" medical care is mentally ill, and there are no healthy people who have made bad choices in such places. One might conclude then that socialized medicine causes mental illmess, or even that it cures choosing badly. // BL \\ (talk) 04:45, 22 March 2009 (UTC)

I am personally in Canada, and we have universal health care. I can assure you that many mentally unstable people access the free health care here. Doctors make money from the pharmaceutical companies every time someone fills a prescription, so it's really not that hard to find a doctor who will play along with a mentally unhealthy person's imaginary problems. Also, BL makes a very good point. And to Tango, I would think that all "bad people" have some sort of mental disorder, no? I don't understand the distinction you're trying to make. bcatt (talk) 05:50, 22 March 2009 (UTC)

Well, you don't have to be sick to be a jerk, you know. -- Captain Disdain (talk) 12:57, 22 March 2009 (UTC)

When people are mentally ill we don't punish them for their actions or put them in secure mental facilities. When people are just bad we throw them in prison. (That's an oversimplification, obviously, but you get the point.) I'm not the one making the distinction. I agree with you that such a distinction doesn't make much sense - that was the point I was trying to make. --Tango (talk) 13:14, 22 March 2009 (UTC)

Of course, my response above was somewhat of an oversimplification, but it comes from a basic problem with the mental health industry, indeed one which Tango has aluded to. The deal with most mental illness is that there is a lack of mechanistic explanation for it. If I have diabetes, its because my pancrease doesn't work right. If I have AIDS, I have a virus in my system which is causing it. If I have ADHD, it means I display a set of behaviors, but what is the underlying physical cause of this?!? See, there's the crux of the problem. Diseases have causes which can be identified. Mental diseases, mostly, are about a set of causeless symptoms; so what sepereates a person who chooses to behave badly from one with a mental illness is simply the existance of a doctor willing to provide the diagnosis. Now, don't get me wrong, there are real mental illnesses. I understand this; however there are also a vast number of people who are overdiagnosed with them, because there is no way to distinguish between people who make bad choices and people who are incapable of making good ones. It;s a shame, because it swamps the system with people who don't need treatment, and reduces the quality of treatment to people who really need it. So people with access to the doctors to make the diagnoses get labeled "unable to make good choices" and those people without get labeled "people who make bad choices". It is unclear what is wrong inside of their bodies that distinguishes one group from the other... --Jayron32.talk.contribs 01:07, 23 March 2009 (UTC)

Ok, I have a lot easier time agreeing with you on these points. Coincidentally (or not), ADD/ADHD appears to be one of the favourite diagnoses of the type of parent that I've described, as well as of every damn teacher out there who expects a child to engage in the completely abnormal behaviour of sitting at a desk for 7 hours 5 days a week...it's simply unnatural. bcatt (talk) 16:19, 23 March 2009 (UTC)