Wikipedia:Reference desk/Archives/Science/2013 June 13

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June 13

Non-circular replacement body joints

There's an ad on TV that shows people riding bicycles or driving cars, comically, with elliptical wheels, then the announcer says "Our replacement knee joints are round, because round is better". Ok, cute ad, but I'm left wondering why the other replacement knee joints are apparently elliptical. Are there advantages to that ? StuRat (talk) 04:36, 13 June 2013 (UTC)

I don't know the ad you are referring to, but are knee joints round? I don't know how anatomically correct an image like this is, but they certainly look quite eliptical to me. As to advantages, the knee doesn't move through 360 degrees, probably only about 140, if you compare a 140 degree arc of a circle to the 140 degrees arc of the kind of "not very eccentric" ellipse we see in the previous image, there's probably very little difference, they're both round arcs, you really need 180 degrees before an arc and a circle look much different (depending which arc you chose of course). One difference I can however imagine is weight distribution and this could play a large factor because wear of artifical knee joints is a main consideration, knee replacement is generally only offered to old people because young people would wear them out too quickly. Vespine (talk) 06:52, 13 June 2013 (UTC)

It's certainly not necessarily or obviously true that "round is better" anyway. Sure, for a wheel on a car, an elliptical wheel results in varying ride height and torque requirements that would be a disaster. But for a limb joint, it's not at all clear that there wouldn't be advantages. Just off the top of my head, I could imagine the following possibilities:

• Firstly, as an elliptically jointed limb rotates, the limb would change in length as the bearing point moves from the major to minor axis of the ellipse - but since the limb is only touching the ground during one part of the arc, that might not matter...but in a car wheel, this would result in massive vibrations at high speeds and sickening lurching at low speeds...also, since the wheels on front and back and either side of a car don't stay lined up - the car would rock from side to side and from front to back - and the suspension would be working continuously.

• Secondly, in a limb joint, when the minor axis of the ellipse is in place against the socket instead of the major axis, some fluid would presumably be trapped in that gap. This would result in fluid being continuously pumped in and out of the socket as you move the limb. That fluid flow might provide a lubrication function - or maybe deposit some material that resurfaces the socket over time - or perhaps have some other important biological function such as delivering oxygen or flushing out bacterial infections. Doing that wouldn't be necessary in an artificial limb - but it could very well be needed in nature.

• Thirdly, with wheels, the driving force is at the central axle - so the torque requirement from the motor would change as the wheel rotates and alternately raises and lowers the body of the car and the effective diameter of the wheel changes - this would clearly be a bad thing. But our limbs are powered by muscles that don't operate at the center of the joint - so the torque requirements wouldn't change significantly - and the idea that the amount of force required to move the limb would change over the arc that it swings through might actually work in favor of efficient motion. You could easily imagine a situation where your leg would be a little longer when in contact with the ground, gradually shortening as you moved it during a stride - this would allow your body weight to help propel the limb during the "power stroke" at the cost of increased torque as the leg is straightened to plant it back on the ground again. That could very easily reduce the load on the muscles and let you run faster.

I don't know whether any of those things are true...but the point is that it's very far from obvious that a round joint would be better than an elliptical one - and the analogy with car wheels is quite utterly bogus.

Since it's much harder to machine and polish an elliptical surface than a round one - I find it hard to believe that the other artificial joint manufacturers would have made elliptical joints if there wasn't good reason to do so.

SteveBaker (talk) 12:48, 13 June 2013 (UTC)

Thanks. Yes, I realize that this is a typical ad which fails to make any real argument to support it's case, so was looking for the real advantages/disadvantages of each. StuRat (talk) 03:58, 14 June 2013 (UTC)

Triple integral integration by parts

We are all familiar with the integration by parts formula:

$\int f{\frac {dg}{dx}}dx=fg-\int g{\frac {df}{dx}}dx.$

Does there exist an "analogous" formula for the following case?

$\iiint f\left({\vec {\nabla }}\cdot g\right)dV=\cdots$

— Trevor K. — 04:46, 13 June 2013 (UTC)

You should post this on the math desk. Someguy1221 (talk) 04:51, 13 June 2013 (UTC)

$f\partial _{k}g_{k}=\partial _{k}\left(fg_{k}\right)-g_{k}\partial _{k}f$ Count Iblis (talk) 12:11, 13 June 2013 (UTC)

And if you're not familiar with the Einstein notation used by Count Iblis in his very concise answer, try

$f{\vec {\nabla }}\cdot {\vec {g}}={\vec {\nabla }}\cdot \left(f{\vec {g}}\right)-{\vec {g}}\cdot {\vec {\nabla }}f$. Dauto (talk) 14:16, 13 June 2013 (UTC)

And don't forget to use Gauss theorem to solve the integral of the divergent. Dauto (talk) 14:20, 13 June 2013 (UTC)

Naming an apple rust (fungus)

The apple tree in front of my work place (middle of Germany) started to look strange and on the under side of the leaves I found nice purple red looking marks. I made a few images and I need some help to give the little fungus the right name . It looks like some rust (fungus), but I could not find any images of a purple red one.

some apple rust

• 
  no magnification
• 
  5x
• 
  10x

--Stone (talk) 07:47, 13 June 2013 (UTC)

I think not. Google images for eriophyid mites. See http://www.whitecanker.net/Maple,%20Norway/Maple,%20Norway.asp and http://www.forestryimages.org/browse/detail.cfm?imgnum=5424246 It seems it is a Gall caused by mites. 196.214.78.114 (talk) 13:56, 13 June 2013 (UTC)

(Awesome pics BTW - hope you add them in the relevant sections.) 196.214.78.114 (talk) 14:02, 13 June 2013 (UTC)

Good call, it does look a little like a fungus, but I think mite gall is correct. Our article is at Eriophyidae, which only has a picture of a much larger type of gall. So the pics could probably be added there, even without a species-level ID. SemanticMantis (talk) 18:22, 13 June 2013 (UTC)

What's wrong with this one-pot synthesis?

Recently I have used orgsyn problems as my crossword puzzles, and I like to find cheaper more feasible alternative routes to known drugs. So what's wrong with this one-pot synthesis -- it seems too simple or else it would have been more popular:

1. Start with any essential oil containing mostly safrole (like the ones on eBay)
2. Markovnikov acid-catalyzed hydration of safrole into a secondary alcohol
3. Oxidize secondary alcohol into ketone using TEMPO and bleach
4. React the ketone with N-Methylformamide (solvent) and formic acid (reagent, 5 equiv?) via the formamide form of the Eschweiler–Clarke reaction. Bleach will be destroyed, chlorine will be released (leave room)
5. Add strong acid to hydrolyze the substituted formamide to release formate and MDMA.

You can then recover the MDMA using the usual workup for amines, purify using chromatography etc.

What's wrong? 71.2.172.65 (talk) 18:42, 13 June 2013 (UTC)

Other than being illegal in many jurisdictions? --Jayron32 19:39, 13 June 2013 (UTC)

"Other than being illegal in many jurisdictions?" - Then what's wrong - LEGAL advice is the kind WP cannot give... ;) — Preceding unsigned comment added by 217.88.169.113 (talk) 12:45, 14 June 2013 (UTC)

They aren't asking for legal advice, but rather chemistry advice (and possibly medical advice, if "What's wrong with..." is meant to include the medical consequences). StuRat (talk) 20:13, 14 June 2013 (UTC)

• This was closed, and any further talk belongs on the talk page. μηδείς (talk) 20:32, 14 June 2013 (UTC)

(apparently most of us disagree with that, fortunately) Wnt (talk) 22:36, 14 June 2013 (UTC)

Alright, this being organic chemistry, I'm hard pressed to unpack the question to begin with. So let's lay it out just to help those of us who want to understand the question! According to the OP:

Reportedly, safrole is subject to acid-catalyzed hydration. (Markovnikov's rule says that the OH ends up on the atom with more alkyl constituents, i.e. the inner one) I'm not so clear on how easy this is - certainly if chemists could just add NH3 across that bond and have it come out the way they want, they'd be done!

With the tail of this molecule now being -CH2-CHOH-CH3 (a secondary alcohol) oxidize it to ketone with TEMPO and bleach, i.e. -CH2-C(=O)-CH3.

The next step ... confuses me. I'm thinking it is basically a Leuckart reaction to convert to -CH2-C(-NH2)-CH3, which is a two step process of adding formamide and then getting rid of the "form" bit.

Now all these do indeed look like they are on the road from A to B; the trick is - is there some incompatibility between the reagents used, or is there something about one of them that would damage the rest of the compound? Wnt (talk) 23:00, 14 June 2013 (UTC)

A minor thing is that I'm seeing TEMPO is "incompatible with strong acids", but I suppose that is gotten around easily enough to not have been the obstacle. Wnt (talk) 04:16, 15 June 2013 (UTC)

And another not-so-minor thing that I see is the release of chlorine gas during the Eschweiler-Clark reaction. Might that (and the consequent coughing and sneezing, or worse) be the obstacle? 24.23.196.85 (talk) 19:22, 15 June 2013 (UTC)

That's something truly mysterious to me. I often see fume hoods presented as if they were some elite technology unavailable to the common experimenter, but I can scarcely think of a simpler apparatus. I would think someone living in a log cabin in Alaska could improvise one using his wood burning stove for draw, an old window, scrap wood, and pine pitch, test for laminar flow with a smoking branch, double check by spilling some aftershave in it. Somebody with access to a fan and electricity ought to have it nailed. Wnt (talk) 18:38, 16 June 2013 (UTC)

Genetic contributions of parentals in haplodiploidy

Resolved

In the haplodiploidy section in the article of sex-determination it states:

"If a queen bee mates with one drone, her daughters share ¾ of their genes with each other, not ½ as in the XY and ZW systems."

The premise is that female bees are diploid and male bees are diploid haploid.

Here is what I do understand:

1. Daughters posses genetic material from both a father bee and a mother bee
2. Sons possess genetic material from a mother only

Here's what I don't understand:

1. If each (diploid) daughter possesses one of each chromosome from father bee and one of each from mother bee, how do they share 3/4 of their genes with each other? According to my calculation, they should have the potential to share 100% of their genes with siblings (if the same chromosome was receveived from mom) or 50% (if a different chromosome was received from mom) because they always have the same chromosomal contribution from haploid dad. Was the comment above meant as an average of 100% and 50%? That seems odd.
2. Do sisters in XY necessarily share only 50% of their genes? They necessarily share at least 50%, but can't they share 100%?
3. So it seems to me that in both haploploidy and XY, sisters can share 50% or 100%, but not 75%.

Thanks! DRosenbach ^{(Talk | Contribs)} 19:39, 13 June 2013 (UTC)

The 3/4 figure is the center of a range, but it isn't all that large of a range. The thing that you are missing is that meiosis (cell division for sexual reproduction) involves genetic recombination -- so the result has 50% of the parent's genome, but each chromosome is a mixture of the two that come from the parent. Looie496 (talk) 19:49, 13 June 2013 (UTC)

1) Yes, the 75% figure is the average, and the 100% or 50% are for each chromosome seperately, and due to interchanging sequences, even a single chromosome can be partly from one parent and partly from the other.

2)Sisters in the XY system (e.g. human sisters) can share anything between 0% and 100% of their genome (not counting the identical X-chromosome that they got from their father), but statistically the similarity is rarely far removed from 50%, except in the case of identical (or semi-identical) twins.

3)As mentioned before, the 75% is the average for the entire genome. - Lindert (talk) 20:20, 13 June 2013 (UTC)

(EC) No, male Hymenoptera are Haploid, females are diploid, that's why it's called haplodiploidy (Oops, I see now you probably just made a typo). Also, as Looie points out, there are ranges. You are correct that these are best viewed as averages, more precisely expected values. Human siblings share 50% of genes on average, but it can be higher and lower in individual cases. It is in fact highly unlikely that a given pair of human siblings share exactly 50% of their genes. And now that I've helped answer, I must point out that we are misusing the term "gene" here. Genes are loci, alleles are the information or "code" present at the loci. So really, we should say that bee sisters share 75% of their alleles, on average. SemanticMantis (talk) 20:23, 13 June 2013 (UTC)

Two things are important: chromosomal crossover in meiosis, which means that each chromosome produced for a gamete is a mixture of parental chromosomes (in the female only in this case, because the male only has one of each). Also note there are 12 chromosomes in the first place, each of which is independently segregated. So 50% or 100% similarity is exceedingly unlikely. Note though that all the male alleles (SemanticMantis is right, though it is so common for "gene" to be misused) go to each offspring, so that 50% of the similarity is reliably so. Wnt (talk) 03:10, 14 June 2013 (UTC)

What kind of microscope do oceanographers use?

Hi, I am from Kiribati, a small country in the Pacific Ocean and I'd love to study oceanography. Thank you. I'm 20 year old. — Preceding unsigned comment added by IchbinKiribatisch (talk • contribs) 22:30, 13 June 2013 (UTC)

Probably optical microscopes. Plasmic Physics (talk) 22:52, 13 June 2013 (UTC)

Oceanography is a very broad discipline, many oceanographers would never touch a microscope. A closely linked field is Marine biology which I imagine is more what you are thinking. Further, microscopy is a field of study in it self and knowing how to use a microscope effectivley takes a bit of practice. You are probably better off buying a general purpose or second hand biological microscope, the kind they use at universities. There are many buying guides online that you should have a look at to give you an idea of what to look for. Vespine (talk) 06:00, 14 June 2013 (UTC)

The article reads that there are subfields within oceanography, which includes biological oceanography. Biological oceanography studies the incidence and distribution of a particular microbe as it relates to the oceanography of a particular site. So, no, I'm not thinking of marine biology. Plasmic Physics (talk) 07:06, 14 June 2013 (UTC)

See WP:Reference desk/Humanities#What's the difference between a marine biologist and an oceanographer? where the OP asked a related question. Roger (Dodger67) (talk) 07:40, 14 June 2013 (UTC)

Sorry I wasn't directly replying to Plasmic, even though that is what it looks like with my indents, I was speaking to the OP, besides I didn't say oceanography was "wrong", i said the linked biological fields like the ones mentioned, were more right.. Vespine (talk) 00:48, 17 June 2013 (UTC)

Spa chemistry

I'm a new home spa owner. (It's a soft-side, if anyone is interested.) I'm kinda confused by how pool chemistry works. I always thought that acidity vs. alkalinity were dependent -- if the pH is 7, adding acid will lower it, adding alkali will increase it. But pool chemistry appears to work not as I expect -- there's a separate number for "total alkalinity" as opposed to "pH". So at the moment, the pool is reading simultaneously too high alkalinity and too high acidity. As a chemist might ask, wtf is going on? What's the science here? --jpgordon^{::==( o )} 22:44, 13 June 2013 (UTC)

Your mistake is in equating alkalinity with pOH. It's not. It's the total capacity of a system to neutralize added acid. Systems at the same pH (or pOH) can have radically different alkalinities. Read our article on it: Alkalinity. Dominus Vobisdu (talk) 22:55, 13 June 2013 (UTC)

OK. That makes sense -- but it doesn't help me figure out what to do to rectify the water when the alkalinity is too high and the pH is way low. Do I need to keep adding more and more acid until the alkalinity starts to drop? But then how do I raise the pH to neutral (or higher) without sending the alkalinity right up again? This goes to applied science, I guess. --jpgordon^{::==( o )}

Yes. If you are starting at pH X and want to bring it down to pH Y, you will have to add more acid to do so if the alkalinity is high.

Generally, high alkalinity is not a common problem in pool water. The main problems associated with it are maintaining a stable pH, and turbidity. If you have problems with high alkalinity, read about how to lower it here: [[1]] and [[2]]. Consult a professional if you can't manage on your own. Dominus Vobisdu (talk) 23:14, 13 June 2013 (UTC)

I might add that high alkalinity at low pH is probably caused by a high CO2 concentration. It takes a lot of time for the CO2 to leave the water, especially in a large pool that doesn't get much use. It can be speeded up somewhat by aeration. Dominus Vobisdu (talk) 23:26, 13 June 2013 (UTC)

This is a 240 gallon spa, not a swimming pool. The general conditions are irrelevant; the specific problem is starting with untreated well water (delicious!) known to have high alkalinity to start with. Anyway, thanks. --jpgordon^{::==( o )} 06:08, 14 June 2013 (UTC)

Alkalinity is almost always caused by CO₂ dissolved as CO₃^2- or HCO₃^-. This can be driven out with heat and aeration, so I would suggest running your spa jets and heater for a few hours a day for a week to solve the issue (if it is really causing you an issue that is). Simply adding acid won't really solve the problem; the CO₂ will be stabilized as H₂CO₃, and the alkalinity will increase as soon as you try to bring the pH back to neutral. This site recommends using soda ash to increase the pH and remove alkalinity. This works because NaCO₃^- is a weak base, but it also forces other carbonate species out of solution via the common ion effect. 202.155.85.18 (talk) 07:57, 14 June 2013 (UTC)