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April 10

Special relativity. Simultaneity 2.

https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=714473425

Question

Remark

You said the hind clock, when it shows the numerical value $\theta _{0}^{[}$ on its face, is at $t'=\theta _{0}^{[}$. It was not statement , but assumption as I'm not sure it's true (even for previous thread). I've taken it from previous thread (see Remark). So, we shall heve next situation: ε' frame ε frame time coordinate clock reading time coordinate clock reading $t'=0$ $\theta _{0,self}^{[}=-{\tfrac {L'}{2c}}$ $\theta _{0,self}^{]}=-{\tfrac {L'}{2c}}$ $t=0$ $\theta _{0}^{[}=\theta _{1}^{[}-\tau _{1}{\sqrt {...}}$ $=-\tau _{1}{\sqrt {1-u^{2}/c^{2}}}$ $\theta _{0}^{]}=\theta _{2}^{]}-\tau _{2}{\sqrt {...}}$ $=-\tau _{2}{\sqrt {1-u^{2}/c^{2}}}$ $t'=+{\tfrac {L'}{2c}}$ $\theta _{1,self}^{[}=\theta _{2,self}^{[}=0$ $\theta _{2,self}^{]}=\theta _{1,self}^{]}=0$ $t=\tau _{1}={\tfrac {L/2}{c+u}}$ $\theta _{1}^{[}=0$ $t=\tau _{2}={\tfrac {L/2}{c-u}}$ $\theta _{2}^{]}=0$ $t'=\theta _{0}^{[}+{\tfrac {L'}{2c}}$ $\theta _{3,self}^{[}=\theta _{0}^{[}$ $\theta _{3,self}^{]}=\theta _{0}^{[}$ ... $t'=A$ $\theta _{(t'=A),self}^{[}=A-{\tfrac {L'}{2c}}$ $\theta _{(t'=A),self}^{]}=A-{\tfrac {L'}{2c}}$ $t=A$ $\theta _{(t=A)}^{[}=(A-\tau _{1}){\sqrt {..}}$ $\theta _{(t=A)}^{]}=(A-\tau _{2}){\sqrt {..}}$ Correct? Let's check. Hind clock at start is situated in ε in point $(x,t)=(-L/2,0)$ and in ε' in point $(x',t')=(-L'/2,0)$. $(x',t')=({\tfrac {x-ut}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {t-xu/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$; $(x,t)=({\tfrac {x'+ut'}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {t'+x'u/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$. What's next? What to substitute in and what should be compared with result?

https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=713271421 Special relativity. Simultaneity. In your problem, say the light is emitted at (0,0) (in either coordinate system). It reaches the walls at $(x',t')=(\pm L/2,L/2c)$, or equivalently $(x,t)=({\tfrac {\pm Lc}{2(c\pm u)}},{\tfrac {L}{2(c\pm u)}})$. Your first clock has the parametric equation (x,t)(τ) = (0,τ), which you can plug into the Lorentz transformation to find (x',t')(τ). To find the digital reading of that clock at a particular (x,t) or (x',t'), you just solve for τ. Your other three clocks have the parametric equations (x',t')(θ) = (0, θ) and (x',t')(θ[]) = (±L/2, θ[]), and you can plug those into the Lorentz transformation to find (x,t)(θwhatever). Any question you have about what someone sees at a given (place,time) can be answered in this way. They are simple questions about coordinate geometry. -- BenRG (talk) 19:58, 29 March 2016 (UTC)

37.53.235.112 (talk) 12:02, 8 April 2016 (UTC)

OK. According BenRG's suggestions we have:

$(x';t')(A)=(-{\tfrac {L'}{2}};A-{\tfrac {L'}{2c}})$;

$(x,t)=({\tfrac {x'+ut'}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {t'+x'u/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$;

we will substitute x' and t' and should get next

$\color {red}{(x;t)(A)=(-{\tfrac {L}{2}}+uA;(A-\tau _{1}){\sqrt {1-u^{2}/c^{2}}})}$.

After substitution:

$(x,t)(A)=({\tfrac {(-{\tfrac {L'}{2}})+u(A-{\tfrac {L'}{2c}})}{\sqrt {1-u^{2}/c^{2}}}},{\tfrac {(A-{\tfrac {L'}{2c}})+(-{\tfrac {L'}{2}})u/c^{2}}{\sqrt {1-u^{2}/c^{2}}}})$;

$(x,t)(A)=({\tfrac {uA}{\sqrt {1-u^{2}/c^{2}}}}-{\tfrac {L/2}{1-u/c}},{\tfrac {A}{\sqrt {1-u^{2}/c^{2}}}}-{\tfrac {L/2}{c+u}})$.

Why result doesn't match with highlighted equation? 37.53.235.112 (talk) 18:02, 9 April 2016 (UTC)

There's a sign error in the first equation (below the box); it should be $(x';t')(A)=(-{\tfrac {L'}{2}};A+{\tfrac {L'}{2c}})$. With that change, the Lorentz transformation should get you $(x,t)(A)=(u\gamma A-c\tau _{1},\;\gamma A+\tau _{1})$, where I've introduced $\gamma =1/{\sqrt {1-u^{2}/c^{2}}}$ and used your definition of $\tau _{1}$. This is close to the answer you got, and I think the difference is because of the sign error. You should be able to look at this answer and see that it makes sense. For example, if you plug in $A=0$, you get $(-c\tau _{1},\tau _{1})$, which is where the light reaches the clock. Also, the factor of $u$ gives the clock the correct speed, and the factor of $\gamma$ gives it the correct time dilation factor.

Your expected answer (in red) is wrong in several ways. Again, try plugging in $A=0$, think about whether the velocity of the clock (the slope of the line in spacetime) is $u$, and think about whether you should multiply or divide by the time dilation factor. -- BenRG (talk) 05:33, 10 April 2016 (UTC)

Is table ε' frame — ε frame correct? 37.53.235.112 (talk) 07:22, 10 April 2016 (UTC)

Yes, I think so. (Note that where you have $(A-\tau _{1}){\sqrt {..}}$ in that table, it's a clock reading (correct), whereas in your prediction in red, it's a $t$ coordinate (incorrect).) -- BenRG (talk) 07:30, 10 April 2016 (UTC)

How to check table ε' frame — ε frame through Lorentz transformations? Namely, is there correlation between left (ε') and rigth part (ε)? 37.53.235.112 (talk) 09:06, 10 April 2016 (UTC)

The Lorentz transformation will turn the $(x,t)$ of a clock reading into the $(x',t')$ of the same clock reading, or vice versa. In your table you don't have any $x$ or $x'$, and most of the clock readings on the left aren't on the right and vice versa. You could add $x$ and $x'$ coordinates for the points where the clocks read $0$, then check that they match using the Lorentz transformation. But it makes more sense to derive a general equation for the $(x,t)$ and $(x',t')$ coordinates of the clocks as a function of their reading. You just did that for the hind clock (albeit with some errors). Then you can forget about the table, which just gives the values of those functions at certain points. -- BenRG (talk) 17:32, 10 April 2016 (UTC)

Why are images deleted? E.g.

https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=713271421 Special relativity. Simultaneity

https://upload.wikimedia.org/wikipedia/commons/1/17/160329155625UTC.png

https://upload.wikimedia.org/wikipedia/commons/4/49/160329181132UTC.PNG


https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&oldid=714473425 Special relativity. Simultaneity 2

https://upload.wikimedia.org/wikipedia/commons/8/8f/Reference_desk_Science160404140000.PNG

Whati is expiration time of Wikipedia Upload Wizard? Where is this info in rules?<a href="https://archive.org/download/feynmanlectures_631/160414080000_restored.PNG">.</a><a href="https://archive.org/download/feynmanlectures_631/160414080001_restored.PNG">.</a>

Help identify this plant, please

{ Moved from Miscellaneous Ref Desk }

A plant similar to Calycopteris floribunda but with different kind of flowers

A plant similar to Calycopteris floribunda but with different kind of flowers

A climber closely similar to Calycopteris floribunda but never seen to grow as big as that. The plant grows in Kerala, India and flowers during the heights of hard summer. Thrives in wild and don't seem to require watering at all for the flowering. Flowers are fragrant, though not intensely. What is it? — Preceding unsigned comment added by 117.253.195.109 (talk) 02:18, 10 April 2016 (UTC)

The hanging clusters of blossoms opening downward and the leaves resemble Hoya carnosa (familiar name: wax plant, porcelain flower). It's familiar to me as a shrub, possibly cultivated (i.e. not seen in the wild), in the arid subtropic climate zone. -- Deborahjay (talk) 07:34, 10 April 2016 (UTC)

Hoya carnosa is certainly is not by the photos I see on its page. The woody vine and leaves are very similar to Calycopteris floribunda but the flowers are not. --117.253.195.109 (talk) 08:20, 10 April 2016 (UTC)

To me this looks like Combretum indicum, or a closely related species of Quisqualis or Combretum. --Dr Dima (talk) 20:47, 11 April 2016 (UTC)

2016 Mercedes GLE 350d urea injection

My friend says that the 2016 Mercedes GLE 350d doesn't require urea fill-ups anymore unlike the previous version and most diesel cars on the market. Is this actual true?

Our article Mercedes-Benz_M-Class#Engines says "ML 350 BlueTEC 4MATIC", and BlueTEC is Mercedes' branding of urea injection, so just based on the model number I'm inclined to say he's wrong, but I can't find any sources to back me up. Johnson&Johnson&Son (talk) 10:42, 10 April 2016 (UTC)

Ok， so I found three sources[1][2][3] saying that there was a renaming of the model from "ML 350 BlueTEC 4MATIC" to "GLE 350d 4MATIC" back in 2015. Removing "BlueTEC" from the model name could count as circumstantial evidence.

I also found this Mercedes Australia page[4] which names 4 models that require urea injection and the GLE 350d 4MATIC isn't among the four. But this is circumstantial evidence again since it could simply be that the page is outdated or that they don't sell that model in Australia. Johnson&Johnson&Son (talk) 11:12, 10 April 2016 (UTC)

I added a redirect from urea injection to diesel exhaust fluid. StuRat (talk) 14:26, 10 April 2016 (UTC)

This which is about the 2016 Mercedes-Benz GLE 350d 4Matic Coupe [5] says "It involves automatically injecting a liquid called AdBlue into the exhaust stream at pre-determined intervals, breaking the harmful nitrogen oxides into harmless water and nitrogen." Nil Einne (talk) 16:04, 10 April 2016 (UTC)

This description of a very lightly used 2016 Diesel GLE 350d 4Matic AMG Line 5dr 9G-Tronic Auto [6] mentions "BlueTEC diesel emission control system including AdBlue reservoir". The current description doesn't mention that but has also been changed in other ways. This [7] says "The diesel GLE uses injections of AdBlue to reduce harmful emissions" although weirdly it doesn't talk about 350d despite being about the 2016 models. It does mention the GLE300d 4MATIC. This [8] isn't in English but despite not mentioning 2016, from the date and names appears to be about the 2016 models and you can see AdBlue is indicated even without machine translation. This [9] also isn't English but if you scroll right to the 4th of 6th photos at the top it shows an AdBlue tank and the headline machine translates to something like "AdBlue, the only solution for a less harmful diesel". This [10] also isn't in English but a machine translation says something like "Although already new signage does not know about it (déčko is replaced by the CDI, or with a BlueTEC) next to the conventional 93-litre fuel tank is also traditionally the urea tank (AdBlue liquid) that is used for injection into the exhaust system-most of the NOx into nitrogen and water changes". Nil Einne (talk) 16:47, 10 April 2016 (UTC)

The above used car which mentions the manuala got me thinking so I searched for Mercedes manuals and found [11] which is supposed to have 2016 manuals. Looking in the GLE section, there's a a link to [12] which has a filling capacity for the GLE 350 d 4MATIC Coupe for DEF (28.4L). It also links to [13] which has the same filling capacity for the GLE 250 d 4MATIC Sport Utility Vehicle and GLE 350 d 4MATICSport Utility Vehicle. Nil Einne (talk) 17:05, 10 April 2016 (UTC)

Many thanks!!!Johnson&Johnson&Son (talk) 02:41, 11 April 2016 (UTC)

Glad to help. Nil Einne (talk) 14:51, 11 April 2016 (UTC)

Resolved

Sunlight in June

The introduction to June claims that it is the month with greatest amount of daylight, in the Northern Hemisphere. Given the slow per-day changes in amount of daylight around the times of the solstices, how is June the correct answer? May and July both have an additional day, and July in particular is closer to the solstice than May, so how is it that July doesn't have the greatest amount of daylight? Of course, it makes sense for June to have the shortest amount of daylight in the Southern Hemisphere, since it has the winter solstice and one day fewer than either adjoining month. Nyttend (talk) 15:40, 10 April 2016 (UTC)

The quote from our article is "June is the month with the longest daylight hours of the year in the Northern Hemisphere and the shortest daylight hours of the year in the Southern Hemisphere". It's ambiguous if that means per day or the total for the entire month. And if if it does mean per month, there's only 3% more days in July, so even a minor difference per day could be more than that. Also note that how much the length of the day changes from June to July varies with the distance from the equator, so the answer might be different in different locations. StuRat (talk) 16:00, 10 April 2016 (UTC)

(ec)Looks to me like June would be correct. About three-fourths of the longest days of the season occur in June, and the fact of May and June having extra days does not make up for the difference...

The summer solstice typically occurs on June 21, but this year it's the 20th, this being a leap year. Checking my Old Farmer's Almanac for 2016 (which uses Boston, MA as its reference point, about 42 degrees north latitude):

May 1 has only 14 hours and 5 minutes of sunlight. Its first day with 15:00 or more sunlight is the 28th.

June 1 has 15:05 sunlight, peaking at 15:18 on the 20th and 21st, and is 15:14 on the 30th.

July 1 has 15:14, but its last day with 15:00 or more of sunlight is the 14th. The 31st is 14:28.

If the solstice occurred at midnight between June 30 and July 1, then July would have the most daylight, by 1 day. But because it's June 20 or 21, June wins. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:21, 10 April 2016 (UTC)

No, I've got it wrong. See calc's below. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:30, 10 April 2016 (UTC)

Let's do some math with those numbers, just using linear interpolation (hopefully close enough):

May average = {14 hrs 5 mins (14.083) + 15 hrs 3 mins (15.050)} / 2 = 14.567
May daylight hours = 31 × 14.567 = 451.577 hours 

July average = {15 hrs 14 mins (15.233) + 14 hrs 28 mins (14.467)} / 2 = 14.850
July daylight hours = 31 × 14.85 = 460.35 hours

June average, up to solstice =  {15 hrs 5 mins (15.083) + 15 hrs 18 mins (15.300)} / 2 = 15.192
June daylight hours, up to solstice = 21 × 15.192 = 319.025 hours
June average, after to solstice =  {15 hrs 18 mins (15.300) + 15 hrs 14 mins (15.233)} / 2 = 15.267
June daylight hours, after to solstice = 9 × 15.267 = 137.4 hours
June daylight hours = 319.025 + 137.4 hours = 456.425 hours

So, if my math is correct, it does look like July has more total daylight hours in Boston, in July, than in June. StuRat (talk) 16:46, 10 April 2016 (UTC)

[ec] On the other hand, this page (which defaults to the latitude of Ghent) gives a comprehensive list of times. After some work with Excel, it appears that Nyttend's suspicions are correct - the exact figures are: May, 483 hours 37 mins; June, 494 hours 14 mins; July, 495 hours 31 mins. Presumably there's a critical latitude (which varies from year to year) at which June and July are equal, but the unqualified assertion that June has the greatest amount of daylight is apparently not true. Tevildo (talk) 16:40, 10 April 2016 (UTC)

Technically two critical latitudes, as there is also a line near the north pole, above which both June and July have 24 hours of sunlight every day. StuRat (talk) 16:55, 10 April 2016 (UTC)

Using this site,[14] note that at Barrow, Alaska, which is above the Arctic Circle, every day in both June and July is listed as 24 hours of sunlight. So at the North Pole, July beats June by a full 24 hours.[15] ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:44, 10 April 2016 (UTC)

Note further that in Quito, which is very close to the equator,[16] daylight is 12:07 all year, except for two weeks before and after the December solstice, when it's 12:08. So at the equator, July beats June, by 12 hours. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:13, 10 April 2016 (UTC)

But the article actually says "longest daylight hours", not "most hours of daylight". Stu says it's ambiguous; I say the use of "longest" obviously implies that it refers to the average daylight per day. It's still badly phrased, though. As noted, there are latitudes where June and July have continuous daylight. --69.159.61.172 (talk) 19:46, 10 April 2016 (UTC)

I reworded the article to be unambiguous and correct: "June contains the summer solstice, the day with the most daylight hours in the Northern Hemisphere and the fewest daylight hours in the Southern Hemisphere (excluding polar regions in both cases)." StuRat (talk) 20:56, 10 April 2016 (UTC)

You created a further ambiguity by mentioning only the summer solstice, so I have reworded as follows: "June contains the summer solstice in the Northern Hemisphere, the day with the most daylight hours, and the winter solstice in the Southern Hemisphere, the day with the fewest daylight hours (excluding polar regions in both cases)." Akld guy (talk) 22:08, 10 April 2016 (UTC)

Thanks. Even the Jarada would be proud of that. :-) StuRat (talk) 22:16, 10 April 2016 (UTC)

And I have just changed December along the same lines with the same wording. Akld guy (talk) 22:22, 10 April 2016 (UTC)

Unfortunately, "the day with the most daylight hours" implies that it is the only such day. As soon as you get a little way beyond the Arctic Circle, there is more than one day each year with 24-hour daylight. --69.159.61.172 (talk) 23:11, 10 April 2016 (UTC)

But the wording specifically excludes polar regions. Nyttend (talk) 00:04, 11 April 2016 (UTC)

Yes, I thought it was necessary to exclude polar regions, since they would require more explanation than readers would want to read. StuRat (talk) 02:45, 11 April 2016 (UTC)

User:Nyttend, I'm late to this party, but do check out Insolation and refs therein. No need to resort to OR and back of the envelope, this stuff is seriously well-studied. Using that keyword, lat/long, etc can get you very good data, even stuff that includes cloud models and other advanced features if you like. Here's a slightly older but fairly comprehensive overview [17]. SemanticMantis (talk) 14:17, 11 April 2016 (UTC)

It's pretty obvious that the statistic refers to the average amount of daylight per day - and not the total for the month...the latter would be a really useless statistic. SteveBaker (talk) 17:36, 11 April 2016 (UTC)

If that's the approach, June wins: 456.425 / 30 = 15.2 while 460.35 / 31 = 14.8. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:39, 11 April 2016 (UTC)

Criticality and Neutron flux

If I had two pieces of Pu(238) (each weighing 5Kg), one in each hand and brought them togther quickly, how much netron flux would I get and how far away would someone have to be to survive such a criticality incident?--178.101.224.162 (talk) 21:02, 10 April 2016 (UTC)

I think your critical mass for plutonium is off, but in any case see Demon core (which is too mild, come to think of it, since it didn't blow itself apart), and fizzle yield (which is too harsh, since people are trying to jam that together with more effort). Wnt (talk) 21:34, 10 April 2016 (UTC)

Critical mass is between 9 and 10 kg according to our article. So whats wrong with my figures?--178.101.224.162 (talk) 21:39, 10 April 2016 (UTC)

I know you aren't talking about a "weapon" per se, however I think most of the same "issues" would apply as described in this article: Nuclear_weapon_yield#Calculating_yields_and_controversy . Vespine (talk) 23:52, 10 April 2016 (UTC)

No. Not a weapon. Im talking about a criticality 'accident' where the main effect is a large neutron flux and maybe some gamma rays. Definitely not a nuclear explosion as we know it (Jim).--178.101.224.162 (talk) 00:23, 11 April 2016 (UTC)

yes I know, I said I know you aren't talking about a weapon, but my point is that it's very hard to predict, even with accurate models, precisely what will "happen", whether something will reach criticality or not or how much reaction will take place. I recall seeing an article about software that was used for such calculations and a lot of details about it were confidential, except that it was extremely complex, extremely expensive and extremely classified. Vespine (talk) 02:23, 11 April 2016 (UTC)

I stand corrected! I had read some much smaller figures for bombs .... never realized that the critical mass could be changed that much by design considerations. I shoulda RTFA! Wnt (talk) 02:08, 11 April 2016 (UTC)

Yeah I'm not considering use of Neutron reflection, although the water content of my body may have a small effect.--178.101.224.162 (talk) 13:30, 11 April 2016 (UTC)

Why do Electric aircraft have poor thrust to weight ratio?

Is it because of battery limitations or electric motor limitations? Also if electric vehicles have such poor thrust to weight ratios, why is it that the Tesla Model S has such a good 0-60 acceleration time? ScienceApe (talk) 23:30, 10 April 2016 (UTC)

Electric motors are lovely. Small, powerful and efficient. Batteries carry both the fuel and the oxidizer, as rockets do, and don't work on chemicals with as much energy per weight. Power is splendid; thus you can accelerate quicly but batteries are heavy and poor in energy, hence can't go far. Jim.henderson (talk) 23:36, 10 April 2016 (UTC)

Plus, the motors they use have fairly stable "speed-torque" curves. In other words, they give you pretty much the same force whether they're turning slowly or quickly, and they don't generally need a complicated gear/transmission system (a few older electric trains had them). Fuelled vehicles by contrast get the best torque within a relatively narrow range of speeds, and you need a complicated gearbox to get the most out of them. Where acceleration is your biggest concern, electric vehicles are great (look at List of trolleybus systems in the United Kingdom - most electric bus systems were either in very big cities where you have lots of stopping and starting, or in mountainous areas like Yorkshire and the Welsh Valleys. Because it doesn't have the extra weight of batteries, a trolleybus will just fly up a hill almost as if it was flat road). Smurrayinchester 08:06, 11 April 2016 (UTC)

(edit conflict) What makes you think that electric aircraft have poor thrust to weight ratio? I could build you an electric aircraft with a fansastic thrust to weight ratio. It might run the capacitors dead in the first 30 seconds, but until then it would take off like a bat out of hell. Now if you want a good thrust to weight ratio and a decent range, then our article on Energy density has some interesting news about gasoline vs. batteries vs,. capacitors... --Guy Macon (talk) 23:45, 10 April 2016 (UTC)

That's roughly what small electric quadcopters do. Nobody minds the short flights caused by their low energy to weight ratio. Big airplanes, people like to fly far and long. So, they load up with energy storing or making things. This converts the problem to one of power to weight. 108.14.112.81 (talk) 02:24, 11 April 2016 (UTC)

As a bit of interesting trivia, the aircraft with the largest thrust to weight ratios are all blimps or dirigibles. :) --Guy Macon (talk) 04:19, 11 April 2016 (UTC)

Use mass instead. 1989 Goodyear blimp plus pilot, little fuel: 14.4 lb/hp. 1998 world's fastest accelerating production sedan, full tank, empty trunk, four 157 lb men, 4 ¼ lbs clothes (x4): 14.5 lb/hp. City block-sized balloons with 840 horsepower is where it's at. Sagittarian Milky Way (talk) 07:23, 11 April 2016 (UTC)

As for the Tesla, weight isn't as much of a problem in a land vehicle, as you don't need to provide enough lift to offset it. StuRat (talk) 04:28, 11 April 2016 (UTC)

I think to directly answer the question then: battery weight for an airplane is a much more significant issue than it is for a car...but even electric car batteries don't last that long and are very expensive...the limitation is not electric motors themselves (they can be plenty powerful to create great thrust) but powering a powerful electric motor...your flight time could be a matter of minutes instead of hours...68.48.241.158 (talk) 16:48, 11 April 2016 (UTC)

note, too, your tesla car can do what you describe...but will run down the battery in no time...68.48.241.158 (talk) 16:58, 11 April 2016 (UTC)

Besides the huge advantage in fuelefficiency, tru there is way more power stored in 1 kg kerosene then can be loaded into 1 kg of battery, electricity can only use a Propeller (aeronautics), which is limited to many conditions and not very effective in general, to generate reasonable thrust while you have multiple options with fuel, including very powerfull such as turbines (with afterburners), which have the highest thrust to weight ratio of all powermachines (some even excel rockets (which are not machines:)). --Kharon (talk) 17:45, 11 April 2016 (UTC)

I presume we're talking about propeller driven planes here. Jets are different for lots of reasons.

One of the reasons why electric cars have such good acceleration is that electric motors have very flat torque curves - they provide more or less the same torque for any given motor speed below the maximum. Since torque and acceleration are closely related, they have very uniform acceleration at all speeds. So the 0 to 60mph time for a Tesla is almost identical to it's 60 to 120mph time. With fast gasoline powered cars, the torque curve is anything but flat - there is a relatively narrow band of RPM's at which they produce peak torque - and if they have turbochargers, getting uniform torque is even harder.

The (partial) fix for that in a car is to use lots of gears - but there are losses involved in a complex gearbox - and the act of shifting gears (with the requirement to match the engine RPM while shifting) takes time and results in the engine RPM going in and out of the "sweet spot" where all the power is available. Most electric cars don't even have gearboxes.

So - how come gasoline engines for propeller-driven airplanes don't suffer the same problem? They don't even have shiftable gearboxes! Well, generally, they DO have variable pitch propellers - and that's a form of gearbox. It's actually a very efficient one because it has a continually adjustable "gear ratio" and no friction-creating gear teeth or clutch mechanism. This makes it much easier for the plane to keep it's motor running at the optimum RPM's.

Also, when acceleration is most important - on takeoff - the engine can be pushed to the optimum RPM, and the plane held on it's brakes until it needs to start moving. This means that the torque is already at the PERFECT amount when the plane starts rolling. With a car (and especially with a supercharger or a turbo) - the engine has to be at relatively low RPM's when you launch or you'll wreck the clutch or simply spin the wheels without much acceleration.

So many of the disadvantages of a gasoline engine aren't really a problem for airplanes - which makes the advantages of electric power very much less. For a car, the liability of a gasoline engine is a nightmare - and switching to electric motors solves a ton of issues.

Having said all of that - how much better is the acceleration of an electric car? Consider the 2013 BMW 1 series - which is the basis of the BMW ActiveE electric car. Let's consider the stats for a 2013 BMW 1 versus the Active E:

• Weight: BMW1: 1500kg, ActiveE: 1800kg...a 20% overhead for the electric version. Of course a tankful of gasoline adds another 50kg to the BMW1 - so it's a bit less than that.
• Torque: BMW1: 400Nm, ActiveE: 250Nm...oh...not good. But that's the PEAK torque for each car - and the ActiveE maintains that torque over a larger RPM range.
• 0-100kph time: BMW1: 6.3 seconds, ActiveE: 8.6 seconds - actually, better than you'd expect from the numbers given above. With 20% more weight, we'd expect 20% less acceleration for the same torque - but it also has vastly less peak torque. If BMW had put more powerful motors into the ActiveE, it could easily beat the BMW1 in a 0-100kph drag race - but with that much more weight, it's all-important recharge range would be much worse.

So read what you like into that.

SteveBaker (talk) 17:26, 11 April 2016 (UTC)

So the 0 to 60mph time for a Tesla is almost identical to it's 60 to 120mph time. -- I very much doubt that. With constant torque, you can bring constant force onto the road. But you need not double, but 4 times the kinetic energy when you go from 60 mph to 120 mph. --Stephan Schulz (talk) 17:53, 11 April 2016 (UTC)

You may doubt it, but it's correct. Assuming the torque remained constant, which it can do with an electric motor, then the force pushing the car forward is constant. F=ma, therefore the acceleration is constant. v=u+at: therefore constant acceleration gives identical change in velocity in a given time. The power is irrelevant to this: what actually happens is that in order to deliver constant torque, the motor mush deliver increasing power with rotational velocity.--Phil Holmes (talk) 08:31, 12 April 2016 (UTC)

might be true in a vaccum or something...but drag would indeed quadruple, I think...so the car would have less torque available for acceleration and more being used to maintain speed.....68.48.241.158 (talk) 18:14, 11 April 2016 (UTC)

Here's someone's graph of torque vs speed for a Model S. The motor is torque-limited (with power rising linearly) up to a certain speed, then power-limited (with torque dropping inverse-linearly). The crossover point is around 60 km/h ≈ 40 mph. So the Model S's 0–20 time should be similar to its 20–40 time (in a vacuum, at least), but 60–120 is a different matter. -- BenRG (talk) 21:14, 11 April 2016 (UTC)

Thanks to everyone for the responses. In short, batteries are the weakest link for the poor thrust to weight ratios? If we had some kind of super duper capacitor that had the energy density of gasoline, all our thrust to weight issues would be solved? ScienceApe (talk) 01:29, 13 April 2016 (UTC)

Related question, is it possible to have some kind of electric/jet fuel hybrid jet engine where you have an electric motor(s) spinning the turbines and ignite jet fuel to heat the compressed air? ScienceApe (talk) 01:33, 13 April 2016 (UTC)

April 11

Heat of deuteration and tritiation reactions

What are heat of the following reactions of deuteration and tritiation of water or heavy water by neutron capture?

H₂O + n → HOD

HOD + n → D₂O

H₂O + 2n → D₂O

D₂O + n → DOT

D₂O + 2n → T₂O

Are they exothermal or endothermal reactions? Is there some additional experimental complication in measuring the heat of these reactions compared to ordinary chemical reactions?--5.2.200.163 (talk) 13:24, 11 April 2016 (UTC)

This book discusses the mechanisms and energies of neutron capture by protium to form deuterium. --Jayron32 13:42, 11 April 2016 (UTC)

What pages exactly? 391? Are they included in the free preview? Is the mentioned value of 2.23 MeV measured or calculated based on some (semiempirical) formula considering neutron binding energy?--5.2.200.163 (talk) 14:28, 11 April 2016 (UTC)

Is the formation of sodium-23 somehow included in the non-free preview?--5.2.200.163 (talk) 14:31, 11 April 2016 (UTC)

There is a thermodynamic isotope effect, though one hears much more about the rather modest kinetic isotope effect. [18] points me to a review by Galimov about it, only Google is not smiling on me today to tell me what that reference is. I should search on Sci-Hub, but generally prefer to make my interlibrary loans from the library wifi.

As written the reaction seems unlikely to be measured directly, as I assume the velocity of the neutron will blast the proton right out of the water molecule. There are two components: the thermodynamics of making D or T, and the thermodynamics of the exchange. The former is with very high energy and the latter with very low, so I assume that as written, your reactions can be replaced with bare H+, D+, and T+ transmutations for the same result as best as it can be measured. Wnt (talk) 14:38, 11 April 2016 (UTC)

Just to also expand on Wnt's solid answer, and clarify something: the thermodynamic relationships are state functions dependent only on the the starting and ending states, and thus independent of the path taken between the two states. The kinetic relationships DO depend on the path taken. In this case, given the fact that both deuterium and protium are stable, there is likely not a huge difference in potential energy between the two, so I would expect the thermodynamic changes (i.e. if they are exothermic or endothermic) to be relatively low. The kinetics are a different story; there may be a VERY large activation energy for the ¹H + n --> ²H reaction, but this is entirely independent of the thermodynamics. A reaction COULD be exothermic, and still have a very large activation energy. --Jayron32 18:45, 11 April 2016 (UTC)

The activation energy of this reaction is close to zero as even thermal neutrons are easily captured with a cross-section roughly equal to the geometric cross-section of proton. Ruslik_Zero 20:35, 11 April 2016 (UTC)

Well, there ya go. --Jayron32 14:48, 12 April 2016 (UTC)

Hmmm... suppose you softly putt a neutron into a proton. According to [19] and [20], the two should emit a 2.2 MeV gamma ray representing the binding energy. The momentum of this is 2.2 MeV/c = something like 12 x 1000 x 10−28 kg⋅m/s (see electronvolt table). The proton mass is 1.672621777(74)×10−27 kg, so that means the "kick" from this photon emission ought to send the nucleus recoiling just under 4000 m/s - I think. (I'm not 100% sure this logic is valid but I vent it for your delectation) This is faster than generic figures for water motion at room temp [21], but I haven't figured out just yet if it means the molecule will explode. In any case though I suppose it's a "heat of deuteration", if you can figure out what it means. Wnt (talk) 20:19, 13 April 2016 (UTC)

Masturbation and Finasteride

Does masturbation decrease the efficiency of Finasteride? — Preceding unsigned comment added by 182.18.177.78 (talk) 16:29, 11 April 2016 (UTC)

I can't imagine there's any possible reason it would...I've never heard of such reducing the efficacy of any medication...did you read this somewhere and can cite? 68.48.241.158 (talk) 17:49, 11 April 2016 (UTC)

There seems to be a common myth that masturbation can contribute to hair loss [22] [23] [24] (see [25] [26] [27] for some examples of the myth in action). So the idea is perhaps not surprising. However as I said, the link seems to be a myth i.e. there's no scientific evidence for it as with many other rumours about masturbation. Given that there's no evidence masturbation affects hair loss and the mechanism of action of finasteride doesn't suggest any particular reason to think use of the drug will be affected by masturbation in some other way, there's no particular reason to think masturbation will affect efficiency of the drug. P.S. I don't think there's any reason to think testosterone levels will affect finasteride but in any case AFAIK the effect of masturbation on testosterone levels is also fairly complicated [28] [29] [30]. P.P.S. If you are taking finasteride you should speak to an appropriate medical professional if you have concerns about any possible interactions or side effects. P.P.P.S. I should perhaps also clarify I'm mostly thinking of something "resonable". If you're an adult masturbating an average of 20 times a day perhaps while watching a lot of porn and it's causing significant physical and psychological effects, then it's possible it could affect hair loss in some way. Nil Einne (talk) 19:56, 11 April 2016 (UTC)

(ec) Finasteride is a medication primarily for treating enlarged Prostate in men. Its reported possible side effect of diminishing libido is reported by the FDA who advise not to stop taking the medication without first consulting with one's health care provider. Masturbation has been purported to have many harmful effects, especially in the stigmatizing views of the Victorian era but today's medical consensus is that it is a medically healthy and psychologically normal habit. It is considered abnormal only when it inhibits partner-oriented behavior, is done in public, or is sufficiently compulsive to cause distress.(ref.). AllBestFaith (talk) 20:03, 11 April 2016 (UTC)

The question is not about the effect of Finasteride on the body or baldness. But of masturbation on Finasteride.--Scicurious (talk) 23:26, 11 April 2016 (UTC)

But if masturbation increases testosterone levels, and the goal of finasteride is to reduce testosterone level, wouldn't that count as an interference? Scicurious (talk) 21:42, 11 April 2016 (UTC)

Not unless there are citations to that effect. -- Jack of Oz ^{[pleasantries]} 23:06, 11 April 2016 (UTC)

Well there is a link between DHT and baldness: [[31]], and there are some endocrine effects linked to masturbation habits: [[32]]. Add to it that according to finasteride, it "prevents conversion of testosterone to dihydrotestosterone (DHT)." So, it's not too mad of a supposition that it could be a visible effect between masturbation on the effect of Finasteride. Scicurious (talk) 23:26, 11 April 2016 (UTC)

But if masturbation increases testosterone levels, and the goal of finasteride is to reduce testosterone level, wouldn't that count as an interference? Scicurious (talk) 21:42, 11 April 2016 (UTC)

Well, see, there's your first mistake — that's not the goal of finasteride. See the finasteride article. It's not meant to reduce testosterone levels at all. It's meant to inhibit the conversion of testosterone into dihydrotestosterone. --Trovatore (talk) 02:30, 12 April 2016 (UTC)

See response above. -- Jack of Oz ^{[pleasantries]} 02:22, 12 April 2016 (UTC)

But there are two common uses of finasteride. One of them is to reduce hair loss. If masturbation affects hairloss then it's possible that masturbation would also affect the efficiency of finasteride in reducing hair loss. If the OP is under the misapprehesion that there is a correlation (let's ignore for a minute that this doesn't imply causation), then this may be at least part of the reason they ask. So it's important for the OP to understand there's no good reason to think masturbation does affect hair loss i.e there's little scientific evidence despite the common claims.

I don't bring this up in isolation, in fact while I'd heard of propecia (but I didn't know the International Nonproprietary Name) and had a small amount of knowledge of hair loss (in particular the effect of DHT), I'd never heard of this particular rumour before today. The only reason I know now is because I wondered like the first IP to reply why the OP might believe that, and so I searched the two keywords in the OP's question. And from that I found this rumour seems to be the most common reason why people bring up masturbation in relation to finasteride e.g. [33]. (The other reason is some people seem to think they should masturbate or not because of the possible sexual side effects of finasteride. However other than being seriously faulty reasoning, this seems irrelevant unless you're going seriously off-label with your use of finasteride.)

The other relevant point which I also already addresses is whether masturbation will have an effect on the mechanism of action of finasteride. Firstly, as has already been said by others, you're mistaken about the mechanism of action of finasteride. It's purpose is not to reduce testosterone levels. In fact, it may have a small increase because it inhibits the coversion to DHT, although regulation of the human endocrine is complex enough I wouldn't assume this without good evidence. Second, as I already said, the effect of masturbation on testosterone levels is complex and it's too simple to say it increases or decreases them.

Note getting back to the first point, unless there's evidence the changes in testosterone levels that may be caused by masturbation can cause changes in levels of conversion to DHT, there's still no reason to think the efficiency of finasteride will be affected anyway.

P.S. I didn't directly address the other common use of finasteride, although the mechanism of action issue will apply to all uses. I didn't come across any mention of concerns about a connection between masturbation, benign prostatic hyperplasia and masturbation; so it seemed far less likely this would be the cause of the OP's confusion.

Nil Einne (talk) 12:21, 12 April 2016 (UTC)

momentum/weight

If an object (say on dry land, maybe a car) is traveling, the faster it moves it gains more momentum. What happens to the weight of the object (car?) Does the weight become displaced the more momentum the object generates? 199.19.248.20 (talk) 23:20, 11 April 2016 (UTC)

The weight of a car - the force exerted on it by gravity - depends only on its distance from the centre of the Earth, which won't vary significantly if it stays on the ground. The mass of the car depends only on what it's made of - for a car with an internal combustion engine, the mass will steadily decrease as the fuel is used up, but this isn't directly related to its speed. However, the vertical force exerted on the ground by the car - which might be thought of as "weight" - will vary with speed, depending on the aerodynamics of the car's body. Tevildo (talk) 00:09, 12 April 2016 (UTC)

In the strict interpretation of mass energy equivalence, I believe given two identical cars, where one is traveling faster than the other, the faster one will have more kinetic energy and will therefore have more mass and weigh more! Mass_in_special_relativity#Relativistic_mass. However for any speed which is not within an order of magnitude of the speed of light, the increased mass can pretty much be ignored, as it would be infinitesimal. Vespine (talk) 03:43, 12 April 2016 (UTC)

I could be totally wrong, but after a little playing with some online energy calculators, you would need 1,000,000,000 (one thousand million) 1 ton cars traveling at 100km/h to increase the relativistic mass of the whole system by 4 grams. Vespine (talk) 03:50, 12 April 2016 (UTC)

April 12

Methylene diphenyl diisocyanate (MDI)

I was excited yesterday to score three 55 gallon steel drums for five bucks each. I was a little bummed today to see that one, they were filled with MDI, and two, there is still a little left inside of each one. How bad is this stuff? There is probably less than 20 ounces in the bottom of each. It looks like I can treat it with water, ammonia, and detergent, but then how could I dispose of the results? The MSD sheets I've looked at show that this stuff is flammable but it does not appear to be very volatile that I can tell. After treating it I'm hoping it would be safe to use an angle grinder on it with no risk of explosion? Additional, how bad is it that a junk dealer in town has 50 or so of these drums behind his building that have not been cleaned or decontaminated and he is selling them to the public? Beach drifter (talk) 00:07, 12 April 2016 (UTC)

Well, the first thing to do is look up MSDS for it - see [34] for example. There are plenty of sour notes in there, read carefully. There is also an article Methylene diphenyl diisocyanate, though it isn't certified for staking your health on (see disclaimers!) it may help with curiosity. (The MSDS refers you to contact the company if you want to know more about safe disposal ... I dunno, that could be like calling the phone number on the barrel in Return of the Living Dead, in a good or a bad way) Wnt (talk) 00:46, 12 April 2016 (UTC)

Thanks, that MSDS was more informative than the one I had read. I'm satisfied I can clean these barrels well enough to use for some projects, but making a grill or smoker is out for these guys I think. Beach drifter (talk) 01:25, 12 April 2016 (UTC)

It's worrying that the drums were so cheap. Clean 55 gallon steel drums are selling for $20 each on eBay right now. It suggests that the cost of cleaning them out was so high that it was cheaper to (essentially) give them away than it was to clean them and sell them at the going rate. SteveBaker (talk) 13:56, 12 April 2016 (UTC)

Both the junk dealer and the foam insulation company are in a pretty rural area, so this kind of activity might occur more than I realized. Interestingly I have an invoice for the product that the (apparently one man) foam company left taped to one of the drums. Beach drifter (talk) 22:07, 12 April 2016 (UTC)

MDI is water-reactive and will even react with moisture in the air. It is highly likely that if any MDI was left in the drums that it is no longer MDI. ChemNerd (talk) 14:04, 12 April 2016 (UTC)

Well it is definitely not MDI now, as I have added water and sodium carbonate to each drum. The drums were sealed previously. The muck left in the bottom now is definitely different than the liquid I originally saw. Beach drifter (talk) 22:07, 12 April 2016 (UTC)

Sentient nerves

Do they exist in the large intestine?--178.101.224.162 (talk) 00:49, 12 April 2016 (UTC)

Sentience is not a quality that is usually held to be imbued in a given nerve. To be fair, not withstanding the great strides of modern neuroscience, we genuinely have almost no understanding of how the non-physical and nebulously-defined phenomena of consciousness arises out the physical mechanisms of the nervous system (see hard problem of consciousness), although we do have an increasingly detailed understanding of which regions of the nervous system (the brain in particular) are associated with particular mental functions, as a computational matter.

Now, there is a growing trend in neurology/cognitive science to not disassociate the brain from the rest of the body when looking at how the two give rise to a mind. But that being said, the innervation of the enteric nervous system are about as far removed from the mental processes we most associate with sentience as any part of the nervous system broadly. I think what might be causing this confusion is a phrase that has been making the rounds in recent years, that the enteric nervous system is "its own brain". This little piece of apocrypha originates from the fact that its been discovered that the enteric nervous system operates closed circuits which function all on their own, with very little in the way of feedback signals between it and the central nervous system by way of either the sympathetic or parasympathetic nervous sytems, which otherwise govern the body's autonomic functions. That is to say, the enteric nervous system knows how to keep your gut operating and generating peristalsis, even sometimes if there has been severe trauma to the pathways that link it to the rest of the nervous system. So it's a "brain" by way of it's closed functions and modularity, but the nerves within the system are not "thinking" in the traditional sense of cognitive function (though they may, in limited ways, deliver information which may influence the total human sense of self in subtle ways we don't yet appreciate, as with other quasi-somatosensory systems). Snow ^{let's rap} 02:10, 12 April 2016 (UTC)

Is this the same as Autorhythmicity in the heart? DrChrissy ^(talk) 12:37, 12 April 2016 (UTC)

Well, it's an interesting observation that made me pause to consider for at least a moment, so I want to say "yes and no", but the truth is, even drawing the broadest parallels, that the answer is mostly no. The cardiac cells which propagate the action potential are quite distinct in form and function from the cells that make up the enteric nervous system. They don't respond to stimuli, except that which is a part of their own rhythmical, rote function. They don't grow in adaptive networks characterized by weakening and strengthening of associations between given nodes as the result of the influence of need and conditioning, as even small neural circuits will. They achieve their straight-forward mechanical function through chemical channels that, relative to the functions of neurons are fairly simple and predictable (in a healthy heart, anyway). So it can't really be said that the heart has an independent "nervous system" like the ENS, but the comparison is at least on point in that the heart does conduct some of its functions involving propagation of electrical signals with minimal "oversight" from the CNS, which one could say is an accurate description of peristalsis in the intestine as well. It's an elucidating question in any event. Snow ^{let's rap} 04:37, 14 April 2016 (UTC)

Yes I think OP may have been reading pop-sci coverage like this [35]. The claims may be a bit over-sold, but Dr. Michael Gershon and the other researchers named are no quacks. On feature of ENS that stands out to me is that it has memory, e.g. this [36] journal article from 2000 says "The experiments imply that there is molecular memory of synaptic activity, just as there is memory of the effects of distending stimuli in vivo."

Another possibility for what the OP may have heard about is the influence of our gut bacteria on our brains, described e.g. here [37]. SemanticMantis (talk) 13:51, 12 April 2016 (UTC)

We know that someone who has suffered a completely severed spine in an accident is still sentient. So at the very least, it's unnecessary to have those nerves in order to be fully sentient. SteveBaker (talk) 13:53, 12 April 2016 (UTC)

• I am not sure I understand the OP's question exactly, but if you have irritable bowel syndrome, diverticulitis. or tw thirds of your colon removed, and the anastomosis fails, you will be aware enough there's something wrong that you will rather quickly be given narcotics and sedatives. If the question is, does the gut itself consciously reason? I am unaware of evidence for that. μηδείς (talk) 20:54, 12 April 2016 (UTC)

No, just wondering if you can feel a fist/arm 12" up your passage like in some videos.--178.101.224.162 (talk) 23:55, 12 April 2016 (UTC)

Oh, well why didn't you just say so? See e.g. here [38] for a scholarly study, and of course we have an article on fisting. SemanticMantis (talk) 14:46, 13 April 2016 (UTC)

I am fairly certain what's involved in that case is stimulation of the perineum and in men, also the prostate gland--google up how they do semen collection in artificial insemination in cattle. Given that people occasionally get killed by having sex with horses, I suspect there's no pain until the bowel is ruptured, in which case I can assure you there will be a lot of pain. μηδείς (talk) 16:35, 13 April 2016 (UTC)

Compression ratio vs displacement

I'm having a hard time understanding how this can be true. We are comparing 2 vehicles with different variables. Chevy Cobalt has 2.2 liter engine displacement. Mazda 3 has 2.3 liter engine displacement. So the mazda has 0.1 liters larger displacement than the chevy. However the chevy's compression ratio is 10:1 and the mazda's is 9:1. How can an engine have larger cylinder displacement yet a smaller compression ratio? (Both cars have 4 cylinders) 199.19.248.20 (talk) 04:10, 12 April 2016 (UTC)

Why do you think the amount of compression is related to the size of the engine ? There's often the reverse-correlation, because smaller engines need a higher compression ratio and/or turbochargers/superchargers, to produce comparable power to a larger engine. StuRat (talk) 04:29, 12 April 2016 (UTC)

Both cars do NOT have superchargers, tubros, etc. Both cars have dual overhead camshaft valve train configurations. Compression ratio is the ratio of the cylinder volume with the piston at bottom dead center, when compared to the remaining volume with the piston at top dead center. Cylinder displacement is the volume the cylinder holds between bottom dead center and top dead center. With both of these definitions I'm having a hard time understanding (what appears to me) as a contradiction.199.19.248.20 (talk) 05:21, 12 April 2016 (UTC)

I didn't say that turbo/superhchargers were present on that model. I only mentioned them as an alternative way to get more power out of smaller engines, besides a high compression ratio. StuRat (talk) 05:31, 12 April 2016 (UTC)

(ec) This comes down to two factors: bore/stroke, and cylinder head shape. The Chevy may have a smaller bore and longer stroke, thus compressing the combustion gases more, or it may have a less concave cylinder head shape. That is, a smaller combustion chamber into which the gases are more tightly compressed than they are in the Mazda. Or, it may be a combination of those two factors. One engine is not necessarily better than the other on compression ratio alone; there are sound reasons and trade-offs for choosing a particular compression ratio. Akld guy (talk) 05:28, 12 April 2016 (UTC)

The Chevrolet Cobalt has a four cylinder engine. Imagine that we made that a six cylinder engine, keeping the bore, stroke, compression ratio, etc. in each cylinder the same. Larger displacement yet same compression ratio, right? Now imagine that we made that a three cylinder engine, again keeping each cylinder the same. Smaller displacement yet same compression ratio, right? --Guy Macon (talk) 05:38, 12 April 2016 (UTC)

Makes so much sense now. Thanks!! 199.19.248.20 (talk) 06:18, 12 April 2016 (UTC)

Compression ratio is the volume of the cylinder when the piston is at the very bottom of it's travel, divided by the volume when the piston is at the top. So the factors involved are the throw of the piston and the percentage of that space that is above the piston when it's at the top - which relates to the shape of the combustion chamber. None of the other numbers (bore, cubic capacity, number of cylinders, etc) matter. So it's possible (in principle) for an engine of any size and configuration to have any reasonable compression ratio - it's just a matter of design. SteveBaker (talk) 13:49, 12 April 2016 (UTC)

Flamethrowers

In World War 2-era flamethrowers, could the fuel be transferred from one flamethrower to another? So, for example, if an Allied firebat ran out of fuel, could he pick up a discarded German flamethrower and transfer the fuel from that to his own, either by siphoning or by swapping cylinders? And vice versa, could a German soldier do the same with an Allied flamethrower? 2601:646:8E01:515D:8D43:54FA:2E2E:994A (talk) 05:35, 12 April 2016 (UTC)

Even if technically possible, I doubt if the situation would have come up, because flamethrowers were used by the side with near total ground superiority in an area, to "smoke out" any enemy troops hiding in caves or rubble. So, only one side would be likely to use flamethrowers at a time. StuRat (talk) 05:43, 12 April 2016 (UTC)

I agree that one is unlikely to want to do this under live fire conditions, but I could imagine that one side might occasionally capture enemy flamethrowers when they overrun enemy bases or capture enemy soldiers. Captured military equipment was often reused. If you had captured an enemy flamethrower, then it does makes sense to ask whether or not the fuel could be used in your own model of flamethrower. Dragons flight (talk) 07:08, 12 April 2016 (UTC)

A WWII-era flamethrower used gasoline (sometimes mixed with heavy oil) as a fuel and compressed nitrogen as a propellant and small one-time-use "igniter" cylinders of something hydrogen gas to start the flame. It's just barely conceivable that you could use the fuel from one flamethrower in another (although changing the gasoline/oil mixture might screw the whole thing up) - it's not at all reasonable to assume that the propellant could be transferred - and it's as near as dammit certain that the igniters wouldn't be interchangeable.

The nitrogen tanks were pressurized to 2,000 psi - and you'd need some tight-fitting high pressure hoses with connectors compatible with one system on one end going to different connectors on the other in order to connect the two tanks, and even then, you'd only be able to transfer at most half of the nitrogen until the pressure equalized and no more would flow. Since (as previously indicated) there would be almost zero opportunities to use such a contraption - there is no way they'd bother equipping and training their soldiers to perform this tricky operation. Even if this were remotely possible, it's unlikely that the two systems would be designed to work at the same pressure - and it could easily be that you'd risk an exploding nitrogen tank if it were over-pressured - or not having enough pressure left at the end to do any good anyway.

On the fuel side, even if the (unpressurized) fuel could be transferred and would be compatible, it would probably be easier to steal a few of gallons from a jerrycan from a nearby vehicle rather than messing around with a captured enemy flamethrower. But it seems unlikely you'd run out of fuel much before you ran out of propellant gas (why provide a heavy gas cylinder that's larger than it needs to be?) - so refilling just the fuel tank would probably have been pointless because you'd run out of propellant before you could make much use of the extra fuel.

The igniters were also in limited supply. For example, the most common British weapon was provided with enough gasoline and propellant for just 10 seconds of operation - and came equipped with ten igniter cartridges for ten one-second bursts. So again, refilling the fuel and propellant tanks wouldn't help you if you were out of igniters - and getting enemy igniters that you'd somehow kludge together to work might not help if you were out of either fuel or propellant.

So this is a complete bust - not gonna happen. Too many things that would be incompatible - too little benefit in being able to do it. Unless we can find some instances of it actually happening - the answer from the available evidence has to be "No".

Much more likely would be that you'd just pick up the other weapon and use it rather than fiddling around trying to transfer stuff...but even that might be problematic. It takes some degree of skill to operate these dangerous machines - and using one left behind by the enemy might pose an unacceptable risk of the damned thing blowing up in your face if you hadn't been trained on it.

SteveBaker (talk) 13:40, 12 April 2016 (UTC)

Some time ago, I read a paper copy of the Marine report on the Battle of Kwajalein... I'm still looking for the exact title or report number (it was very probably a sub-section of Amphibious Operations bound as a separate booklet... but I recall a lot more narrative descriptions). The take-away message that I had was that you barely wanted to use your own flame weapons, let alone somebody else's. During the war in the Pacific, Japanese booby-traps were commonplace, and a rigged flamethrower would make for a very unpleasant trap. Many horrible things were done during the battle, and the use of flame weapons were probably among the worst.

While I was searching for this specific report on CARL, this came up: Portable flame thrower operations in World War II. It should be cautioned that for uninitiated readers, flame weapons are much less "cool" than Hollywood movies would make them seem. They are usually used as a negotiation tactic when verbal communication is established with a dug-in enemy soldier inside a bunker or fortified position who refuses to surrender.

The United States Army classified flame weapons as chemical warfare and no longer operates those devices in combat. Across the entire Department of Defense, use was phased out by 1978.

Commanders in the American military eventually decided to ban flame weapons.

From the tactical doctrine and training section of the report I linked above: flame soldiers (rather, infantrymen with additional training as flamethrower operators) would be trained in fueling their weapons systems, but in theater, fuel would be managed at the regiment level by a chemical warfare officer, not by an individual soldier during an assault. There are concerns about correct type and filling procedure. That report lists several additional training resource manuals, if you want to conduct deeper research.

Again, it can't be emphasized strongly enough how awful these devices are, and a little historical context might help. In today's world, our whole society stops when a hundred people are gunned down at random... in 1944, 500 American Marines burned in an accidental fuel explosion would be a minor footnote on page 134 of the report. Those were the friendly forces. Regarding enemy dead:

“

"The disposal of enemy dead ashore was a problem for the following reasons:

(a) Some had been dead for several days prior to DOG Day.

(b) Many were wholly or partly covered by debris in bloc houses, under bombproof shelter, etc., and were very difficult to remove.

(c) The stench resulting from the putrefaction of mutilated bodies made the work very obnoxious.

(d) The depth of the soil."

” — Commander Northern Attack Force - Roi Namur

Nimur (talk) 15:10, 12 April 2016 (UTC)

I wonder if the US Army or the DoD has any high level ontologists or taxonomists on staff? Maybe they could use some. Flamethrowers don't meet our WP definition of chemical weapons (hinging on toxic properties), but other definitions are viable, and surely there is some some chemical action involved in a flamethrower. However, if a flamethrower is a chemical weapon, then so is an M16, but somehow I don't think they are going to ban those any time soon. We do have an article on military taxonomy, but it's not very clear on what that's all about. But maybe there are indeed a few wonks out there pushing for better military classification schemes. SemanticMantis (talk) 15:47, 12 April 2016 (UTC)

Indeed they do employ such individuals. From our article on the Chemical Corps, here is one research report, United States Chemical Policy....

If you ever have the misfortune to receive training on, e.g. NBC weapons, the first introduction in your first lecture will likely be a historical review of chemical warfare, beginning with the semi-apocryphal Greek fire flamethrower.

I'll readily grant that "incendiary" and "chemical" are difficult definitions - and that these definitions carry a lot of emotional charge, not to mention legal and treaty ramifications. Nonetheless, in World War II, incendiary weapons such as the man-portable flame thrower were the responsibility of the Army Chemical Warfare Service.

Nimur (talk) 15:56, 12 April 2016 (UTC)

I shouldn't comment when I don't know, but I just want to disagree with the assumption that they shouldn't count as chemical weapons. They may produce fire but they also produce a lot of smoke, probably carbon monoxide etc. - if one is shot down into a bunker, will some soldiers die because of toxic gasses the flame thrower produced? There must be nuanced discussions out there somewhere. Wnt (talk) 16:40, 12 April 2016 (UTC)

Oh no, I didn't mean to say they were (or weren't) chemical weapons. My only point was that this sort of taxonomy can be deceptively difficult, and there are literally lives on the line in some cases (e.g. do I get to use this weapon to legally kill the bad guys, or would that constitute a war crime?). I do make the assertion that most any definition of "chemical weapon" that a flame thrower satisfies would also be satisfied by most any conventional gun. I realize now that Nimur did not say that flamethrowers were banned because they were considered chemical weapons, though that is still the inference I draw from my brief reading. SemanticMantis (talk) 16:46, 12 April 2016 (UTC)

OK, so getting back on topic, the answer would be: don't bother with any of this, just pick up the enemy weapon instead if you need it (or better still, get a spare flamethrower if there are any available)? 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 02:40, 13 April 2016 (UTC)

No, American soldiers during World War II were not trained to use captured weaponry. They were, in fact, trained not to use enemy weaponry. Unlike a video game, actual combat is conducted according to rules, designed to reduce hazard and to abide by law. One can't simply run over to the downed enemy and loot the body before it pixellates out to the respawn point.

Theft of enemy property is a war crime. (UCMJ 903 Art. 103). Enemy weaponry found during combat can be inherently hazardous, or it can be damaged, inoperative, or even rigged as a trap.

In most operations, it is incredibly unlikely that both sides would have brought a flamethrower to the same engagement. Flame weapons, in Allied armies, were specially allocated (although many commanders favored integrating the flamethrower as a regular weapon into infantry units, this never happened). Battle Experiences Against the Japanese, (May 1945). Flame weapons would only be issued to soldiers when specific combat circumstances required them: specifically, when rooting out a dug-in position.

Nimur (talk) 15:06, 13 April 2016 (UTC)

I agree - firstly, you certainly can't move fuel+propellant+igniter from an enemy flamethrower into yours - secondly, moving just fuel won't help you because when you run out of fuel you've almost certainly run out of propellant (and probably igniters) too - thirdly, you probably shouldn't (but theoretically could if life or death circumstances prevailed) pick up an enemy flame thrower and use it - fourthly, it's very unlikely (but not impossible) that both sides would simultaneously be equipped with them anyway.

So the answer is comprehensively and utterly "No!"...are we done now? SteveBaker (talk) 20:22, 13 April 2016 (UTC)

Can trisodium phosphate attack or catalyze the hydrolysis of thioethers or thiolic amino acids (cysteine and methionine, etc.) in a frying pan?

I've been playing around with trisodium phosphate while cooking (I would have gotten dibasic phosphate, but TSP was cheaper and I figured I could be free to add citric acid or vinegar to buffer the cooking process) in order to catalyze caramelization and Maillard reaction processes, and there are different optimal pH's for each chokepoint in the pathway. However, I notice with one route I took, the products *tasted* very delicious at first, intensely bittersweet (as by design) but there was this note that made me intensely nauseous and sick; it wasn't like hydrogen sulfide, but it seemed reminiscent of some sort of thiol or amine. Also, in this process I took, the TSP (in hot oil) ended up breaking down the cell walls of my ginger and garlic and released a lot of water. However, my organic chemistry classes never really informed us about high-temperature frying (oil-water emulsions). What could have happened? Yanping Nora Soong (talk) 16:10, 12 April 2016 (UTC)

To begin with, I do hope this was a food grade additive, and not borrowed from a chemistry lab! Because it's just nice to know there are no toxic impurities, and that some idiot didn't pour something back into the wrong container the week before for that matter. But assuming that, the next question would be whether it could be something extracted from the frying pan. I suppose this could be tested by a mock cook without any protein. The question after that might be what the pH really is, at least to some crude litmus approximation. But cysteine oxidation might be linked more to reactive oxygen species - see [39] - though "moderately alkaline conditions" can increase it. [40] But with several highly intense flavors mentioned, I would wonder if any of those chemicals reacted. You'd need to simplify the experimental process to its bare minimum before trying to name a culprit ... otherwise you're just guessing at culprits. Wnt (talk) 16:36, 12 April 2016 (UTC)

Right, OP would do well to come up with what is essentially a Minimal_Working_Example as part the bug fixing process. SemanticMantis (talk) 17:01, 12 April 2016 (UTC)

I used food-grade TSP from eBay ($11-15 for 2-3 pounds!). Also I have some pH paper I bought for cooking but it's on my storage unit right now (I moved). Yanping Nora Soong (talk) 17:47, 12 April 2016 (UTC)

(EC)So the idea is you were trying to use TSP to... make a steak browner? Or caramelize onions faster? Somehow add umami to your stir fry? It's a little unclear, and it might matter for the question. Anyway, have you thought about TSP's use a a degreaser? What's that mode of action on that? I wonder if you're getting some sort of TSP-driven rancidification or lipid peroxidation of the oil, independent of whatever catalytic role you're looking for. Actually the TSP article directly mentions saponification, so maybe you accidentally made soap. My suggestion is to simplify: see if you get the bad taste with TSP and oil only. SemanticMantis (talk) 16:40, 12 April 2016 (UTC)

To increase the production of advanced glycated end products (mmmm) Yanping Nora Soong (talk) 17:49, 12 April 2016 (UTC)

You don't want to activate too much RAGE though....Fgf10 (talk) 19:15, 12 April 2016 (UTC)

Yeah, but I'm not sure that consumed AGEs stay in the system for very long after first pass metabolism or even get taken up into cells. I think the problem with AGEs comes from endogeneously produced AGEs. Yanping Nora Soong (talk) 16:48, 13 April 2016 (UTC)

calculating the pH-dependent solubility product of phosphate species in the presence of calcium ions

The Ksp of calcium phosphate is 2.0 * 10^-29 and the Ksp of calcium hydrogen phosphate (Dicalcium phosphate) is 1.0 * 10^-7. It's one thing to estimate the amount of phosphate versus hydrogen phosphate from the Henderson-Hasselbalch equation, but how do I set up an expression derived from multiple Ksps, if I want to have an expression for the maximum pH-dependent concentration of any phosphate species (tribasic phosphate and dibasic phosphate?

Right now I have an expression that looks like:

• [Ca(II)] * [phosphate] / [monohydrogen phosphate] = 10^-22
• [phosphate] / [monohydrogen phosphate] = 10^(-12.4+pH)
• [Ca(II)] = 2*10^(-9.6 - pH)

But this expression doesn't give a limit to the presence of how much phosphate impurities there could be, since they were cancelled out.

This isn't related to my above question about TSP in cooking. This question is something I'm thinking about as we add 5-10 mM calcium chloride to our amino-sulfonate (HEPES etc.) buffered immunoassay reagent in an attempt to combat non-selective binding (false positives, etc.) How sensitive our reagent would be to phosphate impurities leftover from the phosphate buffer used to make our solid phase magnetic particle reagent...we already carried out a buffer exchange.) Yanping Nora Soong (talk) 18:10, 12 April 2016 (UTC)

bilateral renal agenesis likelihood an survival

What is the likelihood of survival in the instance of bilateral renal agenesis? It says that most infants don't survive beyond 4 hours, but it doesn't actually tell me the likelihood. Also I'd like to know the likelihood of an infant being born with bilateral renal agenesis, since it was stated that with unilateral renal agenesis the likelihood is 1 in 750. (Also what is the likelihood of survival for unilateral renal agenesis? Something much higher? I'd assume so, but I'd rather KNOW.) — Preceding unsigned comment added by 173.165.123.73 (talk • contribs)

“ At the completion of this study, 114 patients (73%) were alive, and the survival rate was similar to that of age-, sex-matched United States life tables. ”

From "Prognosis of patients with unilateral renal agenesis", here [41]. SemanticMantis (talk) 20:37, 12 April 2016 (UTC)

Are there respectable studies that re-cooked starches are lower in glycemic index?

I have heard this several times since last year (that cold, and reheated pasta raises your bloodsugar less than does freshly cooked). Is there respectable research behind this? Here's an article on the subject from the BBC. μηδείς (talk) 20:36, 12 April 2016 (UTC)

Table 1, here [42] seems to support this notion. Table 3 here [43] shows how time in cold storage seems to decrease glycemic index for tortillas and beans too. Cooking method and storage of potatoes influences their glycemic index too [44]. So yeah, I think that there's respectable studies that at least generally support the notion that longer cooking times and cold storage times decrease glycemic index of many starches. I did not know that, so thanks for asking. SemanticMantis (talk) 20:43, 12 April 2016 (UTC)

You'd think they'd be shouting this from the rooftops. Damned Egg-Council Guy! μηδείς (talk) 16:27, 13 April 2016 (UTC)

How do babies get good bacteria in their digestive tracts ?

Presumably their digestive tract is sterile when they are born, and mother's milk is also sterile (unless mom has an infected duct), is it not ? So, do they get healthy microbes by putting random objects in their mouths ? Do they get them from solid foods they eat later ? StuRat (talk) 20:38, 12 April 2016 (UTC)

Nope, not born sterile. See here [45] [46] for some pop science coverage. Gut_flora#Acquisition_of_gut_flora_in_human_infants indicates that many scientists used to think that infant guts were sterile, but now we know they are not. SemanticMantis (talk) 20:46, 12 April 2016 (UTC)

There is also a degree of contamination with maternal bacteria as the baby passes through the birth canal. There was some recent publicity about research showing that babies born by caesarian section had more immunological problems because they missed out on that, This was being dealt with by taking vaginal fluid from the mother and wiping it over the babies head and body to give the same effect. 81.132.106.10 (talk) 22:15, 12 April 2016 (UTC)

The baby ingests microflora off the mother's skin during breastfeeding. Roger (Dodger67) (talk) 08:01, 13 April 2016 (UTC)

Thanks, all. StuRat (talk) 15:27, 13 April 2016 (UTC)

Animals to be identified

This is another round of animals species to be identified:

• Spider
  Spider
• Insect
  Insect
• 
  Fish

the spider (first image) is very hard to identify at the image resolution provided; a sharper image would be needed. The insect (second image) is a Pentatomid bug ("shield bug"). --Dr Dima (talk) 21:57, 12 April 2016 (UTC)

Yep, could be a green stink bug, but hard to say with only a single blurry picture. SemanticMantis (talk) 14:43, 13 April 2016 (UTC)

The fish could also be any of a wide range of species - especially as there is nothing to indicate size. 81.132.106.10 (talk) 22:17, 12 April 2016 (UTC)

The fish isn't very dissimilar to a zebra fish, if the photo saturation is very washed out, which it looks like it could be. The proportions and fins look similar in any case. Vespine (talk) 22:40, 12 April 2016 (UTC)

They look like yellowtail snapper to me ([47]), though admittedly the morphology of their anterioposterior markings are a little different than anything I've seen with yellowtail before. Perhaps the OP can tell us where the pictures were taken? Snow ^{let's rap} 04:37, 13 April 2016 (UTC)

The fish are labelled 'Peixe Noronha', Portuguese for 'Noronha fish' which implies they may have been in Fernando de Noronha, off the Brazilian coast. and BTW the picture looks upside down to my eyes. Richard Avery (talk)

That would fit with yellowtail snapper, but I wouldn't rule out another species of snapper closely related but not generally classed taxonomically as yellowtail. Snow ^{let's rap} 00:22, 14 April 2016 (UTC)

April 13

Why are flies prevalent in some places and nearly absent from others?

Seems like there are some places where they are numerous and annoying, while other places seem to bereft of them. Perhaps it's just the presence of unburied excrement, but if that's the case how far away do you have to be from the poop in order to avoid the flies? — Preceding unsigned comment added by 50.43.36.155 (talk) 00:09, 13 April 2016 (UTC)

what species of flies are we talking about? --Dr Dima (talk) 01:21, 13 April 2016 (UTC)

The obnoxious ones. — Preceding unsigned comment added by 50.43.36.155 (talk) 02:36, 13 April 2016 (UTC)

They are often frequent with farm animals such as cattle, sheep and pigs. Graeme Bartlett (talk) 04:02, 13 April 2016 (UTC)

There are many ecological factors that can influence where flies thrive and where they are relatively scarce, but arguably the biggest is climate. Like most insect species, most varieties of flies thrive where there is relatively high temperature and humidity. Flies are ectotherms and not very cold resistant even as ectotherms go. The incubations of their eggs and larva are also dependent on a very specific band of temperature and humidity (for most species anyway). Finally, their food sources (which are not limited to excrement, but also all manner of decaying plant and animal life, amongst other sources) are more plentiful, accessible and easier to digest/consume at warmer latitudes. That's not to say that two regions of equal warmth and humidity can't have drastically different amounts of flies because of other factors with their ecological niche, but I think its fair to say that climate is arguably the most important variable. Snow ^{let's rap} 04:27, 13 April 2016 (UTC)

That theory makes perfect sense. But then there's this and this and this. Wnt (talk) 12:58, 13 April 2016 (UTC)

Oh yes, with insecta, there are always outliers (which is why I peppered "most"); in fact, I just recently created this article on a proper arctic ant. Given enough time, species will inevitably adapt to fill any available ecological niche (especially if there is a potential dearth of predation because of an initial lack of species adapted to prey upon them. Because insects are so massively plentiful, in terms of both species variety and individual organisms, and because their generations (mostly) have a short span, they are particularly good at filling those gaps and finding areas where they can have massive population booms, even in areas where they relatively recently (in terms of evolutionary time, which is massive itself, mind you) could not have survived and most of their closest existing relative species still can't. Also, for insects, sometimes the difference between an area being absolutely barred to them and their being able to explode on to the scene is as small as a few degrees, so we live in very interesting times with regard to this aspect of insect ecology and its influence on the wider world. Snow ^{let's rap} 16:11, 13 April 2016 (UTC)

Many fly species, like fruit fly and the house fly, (and the mosquito Aedes aegypti, etc.) are highly human-commensal species, and they are found at higher densities in cities and suburbs than they are in rural or wild areas. SemanticMantis (talk) 14:42, 13 April 2016 (UTC)

housefly, and many carrion-flies (Calliphoridae), are attracted to toilet or decomposing-food odors: indole, trimethylamine, and so on. Just do scholar.google.com search for "housefly odor attractant" and you'll get a ton of papers to read. Alternatively, you can look at the plants that rely on flies for pollination: Amorphophallus titanum, Rafflesia (most species), Bulbophyllum (most species), and so on. They all smell like rotting flesh, or worse. Fruit-flies (e.g. Drosophila) on the other hand are attracted to ethanol, vinegar, amyl acetate, and other compounds associated with fermenting fruit. Different flies are attracted to different odors, but I don't think you're asking about those. Hope this helps. --Dr Dima (talk) 17:41, 13 April 2016 (UTC)

'Distant antagonistic muscles'

I randomly opened a biology dictionary to 'antagonistic muscles' -- muscles that act opposite to each other, and wondered if any of our unconscious or subconscious actions are to move muscles at a distance from consciously moved ones. Are there specific cases anybody is aware of?4.35.219.219 (talk) 01:24, 13 April 2016 (UTC)

I'm not sure I entirely understand your question, but I'll try to give some insight into the general principles involved here. Antagonism in terms of musculature simply refers to the biomechanical arrangement and relationship between muscles and muscle groups. An agonist muscle is simply one which opposes a particular exertion of force by anther muscle, for the purposes of reversing or stabilizing the motion of that other muscle. There are three types of muscle in the human body, anatomically speaking, but only one of these is used in volitional movement, whether through conscious or subconscious exertion--skeletal muscle. Now as to what kind of motor function constitutes "volitional" movement, the rules get really quite fuzzy. Ever walked somewhere and arrived, only to realize you had no memory of getting there, because you were "in your own head"? Well, you'd probably still say you "willed" your body to conduct those movements in some sense, and the truth is that neurophysiology doesn't tell us much about where the borders between "conscious" volition movements and non-conscious movements lie, because we don't really understand much about consciousness in general.

But perhaps you are asking if there are antagonistic muscles which act more or less reflexively to counteract a movement after you've finished with it? The answer there is, sure, in a sense. But these actions are still subject to the weird conceptual issues discussed above. This is further complicated by the fact that agonist muscle can have different degrees of tension, leading to a certain resting position of the part of the body in which they are incorporated. Extend all of your fingers out while holding your hands off of any surface. You probably have to concentrate to keep them perfectly extended; drops your volitional effort with regard to these muscles and your hand goes into a state halfway between a fist and a flat palm (but closer to the latter, probably). But this is the consequence of the arrangement of the muscles and bones to which they are attached as much as a matter of motor function and cognition. Snow ^{let's rap} 03:48, 13 April 2016 (UTC)

Visualize doing any act of bodily balancing in acrobatics, athletics, ballet, sports, standing at military attention, bracing for an impact, etc. Each case identifies physiological sense organs that regulate equilibrium (equilibrioception), such as the Vestibular system in the inner ear, and consciously or unconsciously invokes the appropriate pair(s) of efferent (voluntarily controlled) and reflex-affected muscles. In the skeletal muscles, the muscle spindles report information about muscle extension to assist in maintaining posture. This can be demonstrated by a normal standing person closing their eyes and waving their hand around. At no time will the person lose balance nor awareness of where the hand actually is. AllBestFaith (talk) 22:24, 13 April 2016 (UTC)

Yes, and actually, your example provides a perfect platform for discussing the OP's question. You correctly point out that proprioception is highly refined and can help trigger minute corrections to posture and the relative position of parts of an individuals anatomy, but to what extent can a person be said to be "consciously" aware of incorporating each action of the musculature in that process? They are generally aware of "balancing" or of moving a limb, and have a sense of having instigated that movement "willfully", but they can scarcely be said to know exactly how they are accomplishing the act through each of the countless little corrections necessary. These are controlled by motor pathways which exist somewhere between volition and the triggering of each neurogenic muscle action. The conscious "self" is aware of this process only in a fuzzy sense.

On the flip side, proprioception, and somatosensation, can be "tricked"; create a false image of a person's extremity in a location where it is not in fact located, and the sensory data the brain receives via the eyes can override the sense of where that hand is located. You can even create a false sense of tactile sensation by stroking the false hand/limb/what-have-you. So there you have the opposite of the former example, a perceptual construct overriding actual sensory information from the sensory motor neurons and their associated neural architecture. This is all very confusing, of course, and a source of deep division amongst scientists studying perception and cognition. One possible explanation, that most people find unsatisfying or outright unnerving, is that there is really no such thing as free-will or "decisions" in the classical sense--that we are just chemical machines, responding to stimuli in complex ways and that part of the machinery is the illusion that we willed those actions--which we create after-the-fact. But that's a rabbit hole that, while implicated in the OP's question, we just don't have space to go into here. Snow ^{let's rap} 23:40, 13 April 2016 (UTC)

Memory during sleep

By what mechanism does the brain inhibit recording of dream memories during sleep? I note a couple of things;

• Firstly, that waking memories minutes before entering sleep can be recalled with ease, but immediately upon entering sleep the memory inhibiting is active.
• Memory of events from earlier in a dream can be recalled while still in the dream, but immediately become inhibited upon entering a new dream or waking up.

Both of these strongly suggest that whatever mechanism is at work acts very fast upon the brain. Is it a chemical or hormone? — Preceding unsigned comment added by 182.253.36.220 (talk) 10:39, 13 April 2016 (UTC)

Just on the last point "chemical or hormonal" Those are essentially synonyms, insofar as a hormone is a chemical that is used to communicate signals between different parts of one's body. --Jayron32 11:11, 13 April 2016 (UTC)

archived for the same reason as SemanticMantis notes below. Not relevant to answering OP --Jayron32 18:00, 13 April 2016 (UTC)
The following discussion has been closed. Please do not modify it.
A hormone is always a chemical. But that does not make both synonyms. A chemical can be perfectly something different from a hormone, and communicate signals. Even if a substance is chemically the same as a hormone, it can be a neurotransmitter and not a hormone.--Llaanngg (talk) 12:32, 13 April 2016 (UTC) A hormone is a chemical messenger. A neurotransmitter is a chemical messenger. Ergo, a neurotransmitter is a hormone, QED. The debate over whether a neurotransmitter is a proper hormone, or not, is akin to the stupid debate over whether a hamburger is a sandwich, and such wastes of time are below us here. Or should be. I know the debate exists. It doesn't make it less stupid. --Jayron32 14:50, 13 April 2016 (UTC) A man is a human, a woman is a human, ergo, a man is a woman. Right? Right? And I do not believe there is a hot debate around the difference between hormone/neurotransmitter. Neither do I believe it would be simply a discussion about semantics. Both are different and mutually exclusive. Llaanngg (talk) 15:26, 13 April 2016 (UTC)

Take a look at this Scientific American article: Why Do Memories of Vivid Dreams Disappear Soon After Waking Up?. "Perhaps the most compelling explanation is the absence of the hormone norepinephrine in the cerebral cortex, a brain region that plays a key role in memory, thought, language and consciousness." --Llaanngg (talk) 12:27, 13 April 2016 (UTC)

And, as if to prove my point above, the quote describes norepinephrine as a hormone. It is also a neurotransmitter. --Jayron32 15:16, 13 April 2016 (UTC)

norepinephrine can be released into the bloodstream by the adrenal glands as a hormone or can be released by sympathetic nerve endings as a neurotransmitter. Chemically they may be the same, their function is not. That does not make the statement "neurotransmitters are hormones" a true one. Nor it denies that hormones change the way neurotransmitters operate.Llaanngg (talk) 15:26, 13 April 2016 (UTC)

Note: is it turns out that Jayron is right (he's not, but let's assume he could be right), there are many articles that would need a review. Starting by hormone, neurotransmitter and Comparison with neurotransmitters. Llaanngg (talk) 15:35, 13 April 2016 (UTC)

This discussion means so little to me, you can be correct. I don't need to be right. I'm wrong. I say that uncategorically, so I can end the silly semantic discussion. You are correct. I am wrong. Problem solved. --Jayron32 16:02, 13 April 2016 (UTC)

You say you are wrong categorically? Um...., um... I think I have to think about that...for some time. ;-) 16:24, 13 April 2016 (UTC)

I say that I am completely wrong. There's nothing I said that was correct. You were correct. I was wrong. There's no need to argue, no amount of argument from you will convince me that I am correct. I will continue to have been wrong in what I said no matter how much you try to argue. There's really no point to it. --Jayron32 16:58, 13 April 2016 (UTC)

Well so long as you're wrong, I hope that also extends to being completely wrong about the stupidity of the hamburger-as-sandwich argument. I think that is a fine way to practice one's rhetoric, logic, and persuasion. It also has no place on the reference desks, and is best reserved for beer gardens and similar :) On a more serious note, I'm also collapsing this bit, because it has almost nothing to do with OP. SemanticMantis (talk) 17:55, 13 April 2016 (UTC)

Uncollapsed this, as there is a very clear answer to this (Llaanngg is right, Jayron is wrong). As is explicitly stated in our hormone article, a hormone is by definition secreted to the blood, and as stated in our neurotransmitter article, they signal across a chemical synapse. This means some neurotransmitters also act as hormones, some hormones can act as neurotransmitters, but the overlap between these is fairly small. Fgf10 (talk) 07:34, 14 April 2016 (UTC)

I'm not sure why you removed SemanticMantis's collapsing of this distracting side discussion, since 1) it contains no useful information to help the OP answer their question and 2) You don't add to the discussion by further confirming that I was mistaken in my original assessment, which I have already noted. What do you hope to achieve here? --Jayron32 08:03, 14 April 2016 (UTC)

So, this is a fascinating area of cognition and yours is a question with a lot of implications, but, by way of answering it, allow me to ask one of my own. Are you sure that there was a memory to be "inhibited" in the first place? Dreams are a relatively poorly understood phenomena and the truth is that no one really understands with any empirical certainty what functional purpose they serve for the mind or brain, how exactly they are produced, or, like any other form of qualia, how the arise out of the chemical matter of the brain--other than to say, we know which neuroanatomical regions of the brain tend to be most active while dreaming is occurring.

But in any event, your association between dreams and memory is very much on-point, because the leading contemporary theories about dreaming often posit that their major function is in memory consolidation. In other words, as you sleep, your brain sets about the complicated task of organizing all of the disparate sensory and conceptual information your brain has recently processed and began to integrate into memory, to form strong long-term connections that help to make sense of our experience by connecting it with other elements of our internal semantics (using the term in its broader, rather than strictly linguistic sense). It may be that dreaming is an integral component of how we evolve our outlook, perceptions, perspective and other elements of our selves which change over time.

If this is so, then the experiential components of this process, which we call the dreams themselves, which we feel we bear witness to, are very possibly just a bi-product. To the extent you don't remember them, it's arguably because they weren't experienced in the classic sense and they don't represent information which comport with the kinds of experiences and intuitive concepts which are a part of waking consciousness; in that sense, they didn't exist as elements of the mind's functions that can be remembered, or are only partially composed of such. And this is a somewhat separate issue, but it's also possible that in some cases when people do recall dreams "clearly", they are actual constructing false memories, the way people often do in numerous circumstances when they can't recall all the details in waking life, filling in details until the story makes sense, or at least can be conceptualized in normal terms, no matter how weird the content of the dream was. Snow ^{let's rap} 00:06, 14 April 2016 (UTC)

Metabolic uncoupling medications?

Are there any drugs other than DNP (2,4-dinitrophenol) which are known to increase metabolic uncoupling for the purpose of weight loss? I'd have thought there was a lot of incentive in the west for such interventions. --78.148.105.117 (talk) 11:17, 13 April 2016 (UTC)

There are lots of drugs that help to lose weight, with different risks and mechanisms of action - curbing appetite, making us feel full, or reducing fat absorption. Does it have to use the same mechanism as DNP? --Llaanngg (talk) 12:50, 13 April 2016 (UTC)

Hmmm, we should have an article uncoupling agent ... note that there have been many brilliant ideas for weight loss invented that have been withdrawn after they turned out to kill lots of people. (I can think of amphetamines, Phen-fen and ephedra off hand, but I think there are more!) Wnt (talk) 13:05, 13 April 2016 (UTC)

DNP is also known for killing some people. Anyway, anti-obesity medication is the corresponding article. --Llaanngg (talk) 13:22, 13 April 2016 (UTC)

I believe the goal of increasing metabolic rate so as to lose weight is misguided, regardless of the mechanism used. A higher metabolic rate means more oxidative stress, which causes damage to cells, accelerates aging, and shortens lifespan. Instead we should find ways to suppress appetite, so we can lose weight AND stay younger, longer. StuRat (talk) 15:23, 13 April 2016 (UTC)

Increasing metabolism and increasing metabolic uncoupling are not the same thing. Llaanngg (talk) 16:48, 13 April 2016 (UTC)

April 14

Specific heat of Pepsi

What is the specific heat of Pepsi? It's easy to find pages on Google that address this issue, e.g. [48], but for some reason my browser's throwing a fit and refusing to open anything. It's almost all water, so the answer should be really close to one joule per millilitre, but the corn syrup and other ingredients presumably alter it slightly, and I'm not sure whether they'd raise it or lower it, and I don't know how much. Nyttend (talk) 01:58, 14 April 2016 (UTC)

PS, bonus points if you can also find the specific heat of Coca-Cola. Nyttend (talk) 02:01, 14 April 2016 (UTC)

@Nyttend: The powerpoint you linked mentioned Pepsi One since it has one calorie (4184 J, which can boil 10 ml of water according to the powerpoint). I think you need to specify how much Pepsi you're referring to though. Like one 12oz can? EvergreenFir (talk) Please {{re}} 04:04, 14 April 2016 (UTC)

How would the specific heat change by volume or mass? Isn't the specific heat of water always one joule per millilitre, regardless of the number of millilitres? Nyttend (talk) 04:12, 14 April 2016 (UTC)

Yeah, I think you're right there. Honestly I doubt it differs much from water though. This page says it's 4.16 J/ml (slightly less than water). Found a list of liquids' specific heats here, but no soda (List of foods here if you're interested). This link might be interesting but need to sign up to download the files. EvergreenFir (talk) Please {{re}} 06:13, 14 April 2016 (UTC)

To add, it seems adding things to water lowers the J/ml needed. Compare milk and sea water to fresh water in the list of liquids linked above. EvergreenFir (talk) Please {{re}} 06:19, 14 April 2016 (UTC)

Drugs to reduce inhibition/anxiety when approaching women

Do they exist? Even when a girl seems to show interest I'm still very high inhibition. — Preceding unsigned comment added by Money is tight (talk • contribs) 02:26, 14 April 2016 (UTC)

Are you familiar with ethanol? It has traditionally been used for this purpose. You should be aware that the therapeutic index is narrow. --Trovatore (talk) 02:29, 14 April 2016 (UTC)

I dont do this kind of things at clubs/bars, I can't drink at ordinary places. And I need something a lot stronger — Preceding unsigned comment added by Money is tight (talk • contribs) 02:49, 14 April 2016 (UTC)

Why does it have to be drugs? Seeing a therapist might be helpful. --71.110.8.102 (talk) 03:24, 14 April 2016 (UTC)

Some find the best antidote to this sort of anxiety is self-confidence. Get good at something that can be demonstrated in a social situation (dancing is an excellent choice). It might take quite a while, so pick something you enjoy.

Once you're a good dancer (or whatever), you can invite a woman to dance with confidence. She may or may not end up with a high opinion of you, but at least there's a decent shot that she'll enjoy the dance, and knowing that should reduce your fear when issuing the invitation. --Trovatore (talk) 03:32, 14 April 2016 (UTC)

There are anti-anxiety medications, but the risk of side effects means a doctor isn't likely to prescribe those unless the patient has a severe problem, like vomiting in the presence of girls. For something less than that, self-help books and various confidence building exercises might be in order. For example, you could practice interacting with girls in a formalized environment, like a square dance. It might also help to be friends with a girl you are NOT interested in, to get up the confidence to talk with the ones you are interested in. StuRat (talk) 03:33, 14 April 2016 (UTC)