Wikipedia:Reference desk/Archives/Science/2015 January 12

= January 12 =

Poly oxalate
I have heard that Poly oxalate is applied after placing the foam spray in a structure, I want to know what properties does this chemical has? and how is this applied.120.28.45.234 (talk) 05:38, 12 January 2015 (UTC)Garry from Philippines.


 * Are you asking about Polyethoxylated_tallow_amine - it is commonly added as a surfactant to herbicides such as RoundUp - our article has some information about the properties of the chemical. SemanticMantis (talk) 20:03, 12 January 2015 (UTC)

different units used in blood pressure measurement
My doctor measured my blood pressure and told me the result was 18. As he is French and I am English, that meant nothing.Could someone please tell me what that is in pounds,shillings and pence and whether he had reason to be anxious. I am 66, Thank you. — Preceding unsigned comment added by 109.12.62.210 (talk) 12:17, 12 January 2015 (UTC)


 * My first reaction was to comment that you are unlikely to read this reply, but perhaps it depends on where the pressure was measured and in what units. The usual units are millimetres of mercury, but perhaps French doctors use different units (centibars? but 18 would be a bit high).  Alternatively, perhaps the measurement was for systolic pressure measured in the pulmonary artery or right ventricle, then 18 might be normal, but this measurement is an invasive procedure done in a hospital.    D b f i r s   12:31, 12 January 2015 (UTC)


 * You might call them centibars, yes, but the usual term is kilopascal (kPa). There's an online converter here. - Lindert (talk) 12:36, 12 January 2015 (UTC)


 * Oh yes, I should have checked that. You should have been told two figures.  I assume that the 18 is systolic, and equivalent to 135 mm Hg which would be classed as Prehypertension in the USA or just on the high side of normal in the UK (but not serious).  We can't give medical advice, of course, so you should go back to your doctor if you are worried.    D b f i r s   12:50, 12 January 2015 (UTC)


 * I'm hiding ("hatting") this paragraph because it makes an unwarranted assumption with dangerous medical implications if the assumption is wrong. RomanSpa (talk) 13:12, 12 January 2015 (UTC)


 * In France blood pressure is measured in kiloPascals, while in the UK blood pressure is measured in "millimetres of mercury", which is almost exactly the same as another unit called the torr. There are technical differences in the way these different units are defined, and you can read about them here, here and here, but the main thing you need to know is simply the conversion factor, which is 7.5. That is, when your doctor said the result was "18" he meant "18 kPa", so to convert this into the measure you are used to you just multiply by 7.5. So 18kPa = (18 times 7.5)mmHg = 135mmHg. So his "18" is your "135".
 * As you know, Wikipedia is not able to give medical advice, but you will see from our article on blood pressure that doctors usually provide two measures of blood pressure, "systolic" and "diastolic". You can compare your reading with a standard table here, and should clarify with him whether your result was for systolic or diastolic blood pressure. In any case of illness or uncertainty, you should always contact your doctor. RomanSpa (talk) 12:56, 12 January 2015 (UTC)


 * One worrisome thing in this question is that you didn't ask the doctor. If you aren't even comfortable asking him what units your BP reading is in, and whether that's the diastolic or systolic reading, then I doubt if you are asking him any questions at all.  Many studies have shown that such a lack of communication with your doctor is quite bad for your medical outcome.  In the US, we even have a series of PSAs encouraging patients to ask their doctors questions. StuRat (talk) 16:01, 12 January 2015 (UTC)

Thank you to the kind people who answered my question. With regard to asking a doctor questions - there speaks someone who is used to just one language and one system. I have been in France over 2 decades and speak such good French I even write poems in it. Of course I asked questions but, in all honesty, the doctor did not know the answers. He only knows his own system. (To add to the confusion, 18 might have been one word or 10 and 8, which is how the French say 18. So he might have been quoting me one number or two. The latter result would have converted me from hyper to hypo.) This has happened before when, presented with printouts of blood tests or even Xrays taken abroad, the doctor has refused to look at them and insisted all be done again because, in reality, he did not understand them. You might remember that if ever you need the services of any professional not trained in US. — Preceding unsigned comment added by 109.12.62.210 (talk) 09:55, 13 January 2015 (UTC)


 * Well, the doctor certainly knew the answer to whether he was saying one number or two, so you should have at least asked that. It's possible he didn't know the units he was using, but a quick look at the readout on the sphygmomanometer should answer that Q. StuRat (talk) 15:00, 13 January 2015 (UTC)

Why do electric guitars have tunable bridges but acoustic guitar fixed ones
I'm not sure if this is the right forum for this, but I wonder why electric guitars have tunable bridges but acoustic guitars have fixed bridges and saddles. The tunable bridge allows the length of individual strings to be changed. I know that some acoustic guitars have compensated saddles, which come with different lengths set from the factory, but this is just a set and forget.

Also am I right in thinking that even for an electric guitar this won't ever change as long as the strings are uniform in thickness and weight along the length? -- ????


 * The general consensus here is that tunable bridges have too much mass for an acoustic and kill the tone. Also, tunable bridges have moving parts and, because an acoustic works by resonance through the body of the guitar, the moving parts will tend to vibrate against each other and rattle. This doesn't matter with an electric guitar as they have pickups that convert the vibrations of the strings directly above them into an electrical signal, but not vibrations from elsewhere in the guitar body. Richerman    (talk) 14:25, 12 January 2015 (UTC)


 * That makes sense. The weight at the saddle is dead weight at the point where the string needs to vibrate the resonator. The moving parts bit also makes sense. In electric guitars the bridge can be fixed solid to avoid vibration, as the string is the only thing that needs to vibrate -- Q Chris (talk) 16:26, 12 January 2015 (UTC)

TTL IC L293D
I was playing with the TTL IC L293D when something interesting happends.


 * http://www.datasheetcatalog.com/datasheets_pdf/L/2/9/3/L293D.shtml
 * http://img252.imagevenue.com/img.php?image=107212339_L293Dhack_bb_122_552lo.jpg

Here's my layout:


 * 1) Enable 1, 2: **Not connected** presumably LOW
 * 2) Input 1: **Connected to +3V** HIGH
 * 3) Output 1: Connected to a motor
 * 4) GND: Grounded
 * 5) GND
 * 6) Output 2: Connected to a motor
 * 7) Input 2: **Not connected** presumably LOW
 * 8) VCC2: Connected to +3V
 * 9) Enable 3, 4
 * 10) Input 3
 * 11) Output 3
 * 12) GND
 * 13) GND
 * 14) Output 4
 * 15) Input 4
 * 16) VCC1: Connected to +3V

I left pin 1 unconnected.

The motor keeps running while the pin Enable 1, 2 is not connected.

It's alive! It's alive!

I thought the motor must be stopped. What was wrong with this? -- Toytoy (talk) 14:22, 12 January 2015 (UTC)
 * Why do presume "not connected" means "low"? Unless otherwise specified, I would usually assume that a pin not tied one way or another will float to wherever it wants. That why God invented pull-down resistors. --jpgordon:==( o ) 17:03, 12 January 2015 (UTC)
 * Indeed. Looking at the TI datasheet (page 7), the enable inputs have an internal pull-up resistor, so they need to be connected to ground to disable the output.  With no connection, they'll be high and the output will be active. Tevildo (talk) 21:19, 12 January 2015 (UTC)

genetics
thx. I know it is basic, but I seem to have missed this lecture.72.183.121.78 (talk) 22:46, 12 January 2015 (UTC) my question is about the transcription of chromosomes in humans. for example, are all genes on both the maternal chromosome 1 and the paternal chromosome 1 transcribed? Or is either the maternal or paternal chromosome 1 shut down and only the other completely transcribed? or is there partial transcription of both? how does this happen? thx much.72.183.121.78 (talk) 16:32, 12 January 2015 (UTC)


 * The nature of recessive genes tells us that both parent's chromosomes can be used. Once the two haploids come together to make a diploid of genetic material, there is just "the two chromosomes" with zero differentiation between which one came from which parent (with the exception of a male offspring's Y obviously coming from the father). DMacks (talk) 17:25, 12 January 2015 (UTC)

thanks. so at that point are all of the genes of both chromosomes transcribed? if not, then why are some genes transcribed and some not?72.183.121.78 (talk) 17:44, 12 January 2015 (UTC)


 * You get half your genes from each parent (not counting mitochondrial genes, which come exclusively from the mother). So, there is a 50% chance you will inherit a gene from that parent, and a 50% chance you won't get that gene from that parent (although you might still get the same gene from the other parent).  However, not all genes you inherit are activated.  Many remain dormant.  In some cases, you must inherit 2 copies of a gene (one from each parent) for it to be activated (or fully activate, at least).  For example, the gene that causes sickle cell anemia is only a serious problem when 2 copies are present.  Also, mutations can occur, in which case the gene you inherit isn't quite the same as the original in the parent. StuRat (talk) 17:51, 12 January 2015 (UTC)


 * Transvection (genetics) is one of several interesting aspects of the nature of the non-independent nature of the two different chromosomes' copies of some genes. The ABO blood group system is a case where both alleles are transcribed. I don't know much about the general idea of gene silencing in specific relationship to the presence of two copies. DMacks (talk) 18:01, 12 January 2015 (UTC)

thanks. that helps. I am interested in the autosomes.72.183.121.78 (talk) 18:14, 12 January 2015 (UTC)
 * You seem to be talking about X-inactivation. μηδείς (talk) 18:03, 12 January 2015 (UTC)
 * I was confused, I read that as one single chromosome, rather than the first of 23 chromosomes, sorry. μηδείς (talk) 19:12, 12 January 2015 (UTC)


 * Remember, the gene is just the location of the information, the allele is the version or type of information that is carried. For a certain gene X, every human has that gene, insofar as we all have some information in that location of our DNA. However, many of us will have different alleles at that location. It is very common to confuse the two concepts, but we should be clear about the distinction on the reference desk. SemanticMantis (talk) 19:57, 12 January 2015 (UTC)


 * Our article says "locus" is the name of the location. As I understand it, the "gene" would then be something like "eye color", and the "allele" something like "blue eyes". StuRat (talk) 20:07, 12 January 2015 (UTC)
 * The difference is that a locus can be any region, e.g. a gene, a sequence, a portion of a chromosome, etc. Many people prefer to not use the word 'gene' at all, and instead use locus and allele for the separate concepts. This helps to avoid the nonsense of using 'gene' to mean both the region and the information stored at that region (which is what our askers and respondents usually do here on the ref desk). Still, the definition we use for 'gene' in our article makes it clear that it is ultimately a location or region: "a locatable region of genomic sequence, corresponding to a unit of inheritance
 * (emphasis mine) The gene is not the "what" of inheritance, it is the "where." I just think we should make it a habit to use the right words for concepts on the ref desk, instead of perpetuating a common-but-incorrect usage. But your example is basically right (though there are many genes that control eye color) - everyone has genes for eye color, you get one allele from each parent. This also illustrates why it is technically incorrect to say "I got this gene from my father" - you would still have genes for eye color no matter who your father was, but a different father can lead to different alleles. I may seem picky here, but this is basic stuff, and is usually stressed in any intro bio course that covers DNA and inheritance. SemanticMantis (talk) 20:49, 12 January 2015 (UTC)


 * To quibble slightly, you can be missing genes. For example, a woman is simply missing SRY, has no place to put it, like anything on the Y chromosome.  It's also possible that someone is missing both copies of some nonessential gene through deletion mutations, though far less likely.  Where this gets tricky is that a fair number of characteristics, even common ones, are caused by null mutations in which the gene is functionally disrupted; it's as if it isn't even there, for many practical uses.  But since often there is no actual deletion, just a frameshift mutation or a particularly bad point mutation, disrupted enhancer element, etc., the gene still recombines, so it's not really right to say that someone is "missing the gene"; just that what they have isn't active or effective. Wnt (talk) 02:56, 13 January 2015 (UTC)
 * Thanks for the clarification. I was pretty sure truly missing genes were possible as a rare event, but I didn't know the right names. Basically I've noticed that ~95% of the uses of "gene" on ref desk should really be "allele", and decided to start my own mini awareness campaign. I can tolerate the sloppy/incorrect usage on TV or in the bar, but I think we should hold ourselves to a higher standard here ;) SemanticMantis (talk) 15:39, 13 January 2015 (UTC)

thx for above. I realize that I am going to seem really stupid with this question, but I actually have made some effort to find an answer outside of this forum. in a somatic human cell, concerning the conventionally labeled autosome pair number 1, is one of the pair totally from the mother and one totally from the father? thx. — Preceding unsigned comment added by 72.183.121.78 (talk) 16:14, 14 January 2015 (UTC)


 * Concerning your original question, you may want to read about lyonization. Maproom (talk) 19:08, 15 January 2015 (UTC)

thx. will do. what about my second question about autosomes?72.183.121.78 (talk) 20:29, 15 January 2015 (UTC) I read the article. I guess that means that in the autosome pairs also, one is totally from the mother and the other is totally from the father. I guess I just wish you would confirm that. thx much.72.183.121.78 (talk) 13:07, 16 January 2015 (UTC)

Effective Lifetime of Hydrogen Peroxide Solution
If I have a sink filled with 10 gallons of a 4% hydrogen peroxide solution how long will it last? How would I calculate it? The temperature should be "cold" tap water. This would be indoors, but there would probably be some light. I basically want to figure how long it can be used to effectively kill yeast on produce before needing to mix a new batch. Thank you. Any other additional information that you think I should be aware of would be greatly appreciated. David Bradley I (talk) 20:09, 12 January 2015 (UTC)


 * I believe nucleation sites are critical to the formation of oxygen bubbles from hydrogen peroxide, meaning it there are many nucleation sites it won't last nearly as long. Note that washing food with it will "use it up", as well.


 * One rather simple way to test it would be to put a sample in a bottle and shake it. If it foams up (many tiny bubbles), it's still good.  If it reacts like normal water (few, large bubbles), replace it.  After doing this test several times you can get an idea for how long it tends to last, under your conditions. StuRat (talk) 20:15, 12 January 2015 (UTC)


 * Thanks for the tip. Is there a way of estimating how long it should last? I only need it to work for a couple hours. Also, I'll ask another question in another section which is related. David Bradley I (talk) 20:19, 12 January 2015 (UTC)


 * I don't think you could get a good estimate without testing it under your conditions. For example, if you wash produce with lots of surface area, it won't last as long.  Under some conditions, I don't think it would last 2 hours.


 * BTW, in case you don't already know, you should wear gloves and safety glasses when using it. It will hurt a bit on any cuts or hangnails on your hands, and really hurt if it splashes in your eyes. StuRat (talk) 20:21, 12 January 2015 (UTC)


 * Even if it is active, it might not have the desired concentration. It is a conundrum for me. David Bradley I (talk) 20:25, 12 January 2015 (UTC)


 * Maybe I'll buy a cheap bottle of medical hydrogen peroxide and do some tests at home to see how long it lasts. Maybe that would be a good way of estimating how much we'll need. David Bradley I (talk) 20:46, 12 January 2015 (UTC)


 * Have you considered not putting it in a tub, but just pouring it over the produce ? If you keep it in a dark, sealed container, between uses, it will last longer.  However, soaking in a tub will get more of it into contact with the produce (the hidden folds, etc.).  What kind of produce is it, anyway ? StuRat (talk) 20:34, 12 January 2015 (UTC)


 * I think for our setup we couldn't just pour it over. I'm not sure how long the produce should soak in a 4% solution, but I was thinking 10 minutes. Is that too long? It might be possible to cover the sink to keep it fairly dark, but it wouldn't be sealed. David Bradley I (talk) 20:36, 12 January 2015 (UTC)


 * I think 10 mins is good. You might consider portable containers, where you can seal each batch of produce in and let it soak in hydrogen peroxide, then discard it when done.  Ideally you should be able to cram the container full of produce, and invert it or shake it so it all gets wet. StuRat (talk) 20:38, 12 January 2015 (UTC)


 * We're basically talking about a couple hundred of pounds of produce over a period of two hours. The intent is to reuse the solution as much as possible. If we had to discard the solution after each soak then it wouldn't be an economical way of getting rid of the yeast. David Bradley I (talk) 20:55, 12 January 2015 (UTC)


 * I was thinking you could pack it in tightly, to limit the amount of solution used. You probably can't pack it in as tightly in an unsealed container, since some produce will float.  You need the lid to push it down into the solution. StuRat (talk) 21:03, 12 January 2015 (UTC)


 * Another idea: Use some type of rotating wheel to move the produce in and out of the hydrogen peroxide. The same items would be dipped multiple times.  This would have the advantage that the last batch would not encounter a much weaker solution.  This rotating shoe rack might work (it would have to be rotated manually): Reference_desk/Archives/Miscellaneous/2014_December_20. StuRat (talk) 21:07, 12 January 2015 (UTC)


 * Also, if you can "recharge" the solution with a higher concentration of hydrogen peroxide, rather than discarding it, that might be less expensive. There's the cost of the water, but more importantly the remaining potency of the stale batch can be reused then, and you only need to add enough H2O2 to bring it back up to 4%. StuRat (talk) 21:21, 12 January 2015 (UTC)


 * Yes, this is ideal, but I have no idea how to figure out if a solution is 4% after I mix it and it decays. If it is too strong then it might bleach the produce, harm the sink, pipes or workers. If it is too weak then it wouldn't be effective. Acetic acid might be a better solution if only for the fact that I can use litmus paper to test it at various times. It is difficult to find out which substances are effective at killing yeast, while being safe for food and workers. Washing with a food-safe artificial fungicide for the yeast would be fine. We just can't use such ingredients in the product itself. David Bradley I (talk) 18:27, 13 January 2015 (UTC)


 * Erm, given your phrasing and the scale you're talking about here and the question below, it comes across to me as that you're running some kind of commercial operation. If this is the case, I very much doubt you should be seeking advice about your production process from random strangers on the internet. If this is the case, I would strongly advise you to check the relevant legislation. Waste management for starters, if you're talking about hydrogen peroxide. If my assumption is wrong, please ignore! Fgf10 (talk) 22:43, 12 January 2015 (UTC)


 * That's the great thing about hydrogen peroxide, it breaks down into just water and oxygen, so no toxic waste barrels needed. StuRat (talk) 23:37, 12 January 2015 (UTC)

What are the most economical ways of removing or killing yeast on the surface of produce?
I've been looking into using a hydrogen peroxide soak, but perhaps someone else knows a better way of doing it. I'm basically trying to prevent fermentation, but I can't use any unnatural preservatives in the final product so I'm trying to get rid of the yeast on the produce prior to it being processsed. I'm unaware of any natural preservatives that would prevent fermentation. Thank you. David Bradley I (talk) 20:23, 12 January 2015 (UTC)


 * The other method that comes to mind is a UV light, but you would need to rotate the produce so all sides are exposed, and it wouldn't get into hidden folds. With that in mind, your hydrogen peroxide method sounds better, to me.  I am of course assuming that cooking or using ionizing radiation (like gamma rays or X-rays) are both out.  (The radiation method is inexpensive only on a large scale, and many people won't buy food treated with it.)  StuRat (talk) 20:27, 12 January 2015 (UTC)


 * Cooking is out, but if hot tap water could kill the yeast then that might be an option. I know it also grows better in a more acidic environment. Does that mean a basic environment could kill it? It might just inhibit growth which wouldn't work at all, but if it could kill yeast then I'm sure there is an economical and safe way of turning large quantifies of water into a mild base. David Bradley I (talk) 20:33, 12 January 2015 (UTC)


 * Well, yea, I'm sure bleach would kill it, but that's much worse to work with than hydrogen peroxide. StuRat (talk) 20:35, 12 January 2015 (UTC)


 * How about if you plunge the produce into boiling water and then remove it immediately ? StuRat (talk) 20:37, 12 January 2015 (UTC)


 * I think that would work, but the people I work for say the labor cost on that would be too high. I've read that sulfur dioxide kills yeast, but I think it might not be legal to wash produce with a solution of it. Potassium sorbate works, but we aren't allowed to use that preservative. David Bradley I (talk) 20:43, 12 January 2015 (UTC)


 * That wouldn't be economical either, as you'd need breathing masks for your employees and/or a sealed system with an exhaust fan. StuRat (talk) 20:49, 12 January 2015 (UTC)


 * Oh, and don't forget the value of pre-washing it, as that will remove much of the yeast mechanically. The rest will be easier to kill with hydrogen peroxide or some other method.  And if it's some type of produce where you can just discard the outer layers, like an onion, even better. StuRat (talk) 20:40, 12 January 2015 (UTC)


 * The pre-washing hasn't removed it or removed enough of it. Skinning this produce would be far too labor intensive and thus not economical. David Bradley I (talk) 20:43, 12 January 2015 (UTC)


 * David Bradley I, here's a reference: is a detailed discussion of how to sanitize produce. It's published by the US government. A number of different solutions are discussed, including hydrogen peroxide (which is apparently one of the least used commercially, which might be why it's hard to find a source that answers your earlier question about how long it lasts.). Scroll down for a chart comparing the various methods and below that for references to the original studies.Taknaran (talk) 21:20, 12 January 2015 (UTC)


 * Yes, I think the issue is that he wants to do it "organically", and many chemicals don't qualify. StuRat (talk) 21:23, 12 January 2015 (UTC)


 * Non-organically is fine for the cleaning process. "Natural" preservatives may be okay for the final product. I just haven't found any acceptable ones yet. I have actually looked at that link. Most of the methods aren't approved, don't work well, or don't have much info with regards to killing yeast. One of the reasons I went with hydrogen peroxide was because it was my understanding that Lactobacillus acidophilus killed yeast with hydrogen peroxide. I did notice, in that link, that the waxy coating may actually trap the pathogens in it. Would hydrogen peroxide be able to remove it then? Or is this all in vain? David Bradley I (talk) 18:38, 13 January 2015 (UTC)


 * Vinegar (acetic acid) might also work, but I'm thinking that might be more expensive than hydrogen peroxide. StuRat (talk) 21:28, 12 January 2015 (UTC)


 * The way that sulfur dioxide is used to kill yeast is to use a solution of potassium metabisulfite. Home winemakers and brewers use it to sterilize their equipment before use. You would need an extraction system of some sort to draw away the sulfur dioxide that's produced but that would probably be the case with most sterilizing agents. I think the main question would be whether any sulfite would be left on the produce after the washing process. There is some information about the use of sulfites here. Richerman    (talk) 22:36, 12 January 2015 (UTC)


 * Actually that will probably make the problem worse. Yeast grows better in a more acidic environment. Killing it with a wash is most probable with a basic environment. David Bradley I (talk) 18:39, 13 January 2015 (UTC)