Wikipedia:Reference desk/Archives/Science/2015 December 20

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December 20

Electrochemistry of rust restoration by electrolysis

There's a method for restoring rusted items made of steel that can be found on many websites. The method involves immersing the item to be restored in a bath of aqueous Na₂CO₃ solution and connecting the item to the negative terminal of a power supply. A sacrificial iron electrode, also immersed in the solution, is connected to the positive terminal. Can someone provide the chemical equations for the reactions involved? Thanks. --98.115.39.92 (talk) 06:43, 20 December 2015 (UTC)

Not precisely, but it sounds like the idea is that the oxygen in the iron(III) oxide is absorbed into the solution, causing the iron to precipitate out (some back onto the original item). The oxygen then in turn is absorbed by the sacrificial iron electrode to cause it to turn to rust (iron oxide). Hopefully a chemist can confirm this and add in the missing details. I suspect that this technique would work a lot better on the initial stages of rust than after it is already flaking off in big chunks. StuRat (talk) 07:16, 20 December 2015 (UTC)

Never heard of a practical way to restore rusted steel but there are definitely chemicals and sacrificial electrodes (there z zinc one used in steel evaporative coolers also see galvanizing). I believe large industrial cooling towers use similar chemistry to protect pipes and equipments but I've never hear of it being used to repair rusted parts. There are many things that remove an adhesive oxide to make something shiny again though (i.e. remove oxides of silver and copper can be done chemically but it takes the metal with it). --DHeyward (talk) 23:21, 20 December 2015 (UTC)

Rust converter is to prepare before applying the Primer (paint). It is passivation (chemistry), only. The much rust is removed, the better it works. When the rust converter finisted it is being removed by washing and cleaning, before the primer is applied on a dry surface. Phosphoric acid and citric acid in coke can be used to passivation a rusted coffee mill. Coffee for espresso machines with integrated grinder is prepared with an oil film. The oil films also helps to stop the rust on the steel parts of the mill, when the oil is beeing transfered by touching the parts. --Hans Haase (有问题吗) 01:10, 21 December 2015 (UTC)

Snoring

Why do I only snore when I am asleep? Why don't I do it all the time? Is there any benefit to snoring?KägeTorä - (^影_虎) (もしもし！) 12:54, 20 December 2015 (UTC)

The website of the British Snoring & Sleep Apnoea Association has lots of information. Alansplodge (talk) 13:04, 20 December 2015 (UTC)

Thanks. Perfect answer. KägeTorä - (^影_虎) (もしもし！) 13:11, 20 December 2015 (UTC)

Ageing of heart

When does human maximum attainable heart rate start to decline? Is it at age 26? Or 30? — Preceding unsigned comment added by 2A02:C7D:B91D:8000:F968:F108:86EC:A569 (talk) 14:01, 20 December 2015 (UTC)

When I look for details, I find things like this - which references three separate studies, producing three different formulae:

1. The "usual" formula: MHR = 220 - age
2. Tanaka in 2001 looking at a broader age distribution: MHR = 208 – 0.7(age).
3. Gellish in 2007: MHR = 207 – 0.7(age) with a p value of <0.001.

The thing is that none of these studies suggest a peak. They are predicting that MHR is largest at birth and declines fron then on.

That finding seems unlikely - and I very much doubt they did stress testing on little children and newborns. However, I'm also pretty sure they tested people below the age of 26 and over the age of 30 - and none of them reported a peak between those ages.

So I'm doubtful of your premise. SteveBaker (talk) 14:34, 20 December 2015 (UTC)

My guess would be sometime in the late teens when the heart and the organs it supplies are mainly fully grown, but I hope someone else can find some studies to verify or refute this. Dbfirs 16:44, 20 December 2015 (UTC)

On the other hand, smaller animals have faster heart rates - maybe that's true of children & babies too? SteveBaker (talk) 19:31, 20 December 2015 (UTC)

Yes, and the formulas support that. Pediatricians need to know when a baby's heart rate is too fast, so they would have more specific figures, by age, such as these: [1]. StuRat (talk) 19:51, 20 December 2015 (UTC)

Those are way below the figures that the formula gives, but they are averages, not maximum heart rates. My intuition is supported by this article from the Cleveland Clinic, but perhaps someone can find some relevant research? Dbfirs 09:06, 21 December 2015 (UTC)

I thought those tables were mainly for calculating aerobic and anaerobic thresholds and were guidelines. Older people reach anaerobic rates at lower heartrates and the that rate was set at 80% of maximum. There are are studies of EKG by age and how the various peaks spread out as a person ages. A "normal" EKG at 80 would be a concern for a 20 year old even at the same heart rate. The sharpness of the peaks, their distance in time and other variables are all part of how the heart functions. Anecdotally, as I understand it, one of the benefits/dangers of pediatric cases is that they can continue exercising beyond where the imbalance of electrolytes would stop an adult (I think it's similar is small animals like rabbits). A child can jog to death from electrolyte imbalance (adults usually have an underlying heart/artery condition if they die during physical exertion and their skeletal muscles cramp before their heart does). --DHeyward (talk) 23:12, 20 December 2015 (UTC)

Electronics in ovens

Are there electronic devices that can be placed inside ovens, for measuring temperature or humidity wihtout opening the oven?--Jubilujj 2015 (talk) 19:24, 20 December 2015 (UTC)

The way temps are normally measured is by placing a temperature probe (thermistor) in the oven, that doesn't have any electronics in it, but just varies electrical resistance as electricity passes through it: [2]. The wire passes through a small port (hole) to outside the heated area, where electronics are then used to convert the electrical resistance readings into readable form and display them (or to control the temp settings, say by turning the oven down once it reaches cooking temp).

Also note that humidity can be measured by sucking out a small bit of air. I have a microwave oven that does this, but it seems rather unreliable as the humidity varies dramatically in and around the food. And also consider that the temperature alone isn't the only issue that's bad for electronics. There's also splattering grease, etc.. So, best to keep the critical electronics out of the oven. StuRat (talk) 19:37, 20 December 2015 (UTC)

Ours has a thin wire that doesn't significantly impede closing the oven door or getting a good seal. The electronics can sit a few feet away on the countertop and reports temperature and elapsed time - and goes "BING!" as needed. I haven't seen one that measures humidity...but similar principles apply. SteveBaker (talk) 19:49, 20 December 2015 (UTC)

See thermocouple. Two dissimilar metals will create a measurable voltage and can be very accurate. Only the wire needs to be in the oven and it's well below the melting point. Note, that the Peltier effect is used to also drive a voltage on the same junction and forcing a temperature. This is how active cooling is accomplished (those 12DC fridges with no compressor or active heat-sinks on CPUs). I think metallic heat transport makes passive Peltier junctions impractical. Microwave ovens I believe use changes in the cavity impedance matching to determine heating profiles. As water changes phase, the impedance match changes which the micro-controller detects and responds. There might be other types though that don't create field discontinuities though. --DHeyward (talk) 23:01, 20 December 2015 (UTC)

See [3] for measuring temperature. Measuring humidity is not so easy - for a commercial oven you can use something like this but I would imagine it's rather expensive. Richerman (talk) 23:16, 20 December 2015 (UTC)

There is an interesting article about measuring humidity in ovens here. Richerman (talk) 23:27, 20 December 2015 (UTC)

Are you asking just out of curiosity, or is there something you're trying to do? --71.119.131.184 (talk) 13:41, 21 December 2015 (UTC)

Trying to compare across 3 ovens, about how reliable is the temperature they are reporting, how much they are consuming at each temperature, and how well distributed is the heat. Jubilujj 2015 (talk) 19:11, 21 December 2015 (UTC)

For how well distributed the heat is, I suggest a practical food test. Put something in the oven that will brown when heated, like white bread, filling up each shelf. The darker bread got more heat, while the lighter bread got less. Of course, there is the issue that placement of trays on the shelves can interfere with the proper distribution of heat, but that's also the case with real cooking, too. You might come to a conclusion like "Heat is distributed evenly to the bottom shelf, in any case, but only is evenly distributed to the top shelf if the bottom shelf is left empty."StuRat (talk) 20:56, 21 December 2015 (UTC)

Pistol Star magnitude

What is the absolute magnitude of the Pistol Star? I wasn't able to navigate to the full chart that's given in the "list of stars about 30000 ly distant please" section from December 16 (every link I checked failed to download), and I couldn't find any reliable online resources unambiguously giving the figure. Several pages claimed that it was -14.2, but all were unreliable (typical example). I tried searching for <"Pistol Star" "absolute magnitude" 14.2> and found this number appearing on the bottom of page 11 of [4], obviously a reliable source, but I don't know what the authors are talking about in this section. Nyttend (talk) 22:55, 20 December 2015 (UTC)

It should be on one of our Lists of stars. I don't think H-R diagrams even go above magnitude -10 and it would take over 40 of those already rare stars to reach -14.2. So that's bright. Sagittarian Milky Way (talk) 22:59, 20 December 2015 (UTC)

There are many different ways to calculate absolute magnitude. Do you mean the absolute magnitude in visual wavelengths, or the absolute magnitude for all wavelengths? Since almost all of the Pistol Star's radiation is ultraviolet, there is a big difference between the two.

Let's take the visual magnitude first. Our article says that if galactic dust did not exist, the star would appear as magnitude 4 for observers on Earth. The star is 8000 parsecs away. By doing some math, we find that the star's absolute visual magnitude is 4 - log(8000^2/10^2)/log(2.51188) = -10.5.

Let's now consider the bolometric magnitude, which includes all wavelengths. Our article lists the star's luminosity as 1,600,000 solar luminosities. The Sun's absolute bolometric magnitude is arbitrarily set to 4.75, according to our article on absolute magnitude. Doing some math, we find that the Pistol Star has an absolute magnitude of 4.75 - log(1600000)/log(2.51188) = -10.8. --Bowlhover (talk) 01:02, 21 December 2015 (UTC)

I think the 14.2 figure in the arxiv paper is referring to a different star, LBV 1806-20. --Amble (talk) 01:15, 21 December 2015 (UTC)