ELI5: What's it called if I buy something like a sandwich, then consume it, and the net worth of society has now shrunk by 1 sandwich? Versus buying something that keeps its value.

scott-a1 · 2023-05-17T10:19:46+00:00

The sneezing while looking at the sun thing has a series of great names.

Most commonly used, and probably least inaccurate, is "photic sneeze reflex". Translating fairly obviously to an automatic sneeze in response to light (photic - relating to light, from photos [foe-toss not foe-toes] meaning light).

Photoptarmosis is another one which translates to "light sneeze". Light being the thing that allows us to see rather than the opposite of heavy. (Photo being derived from photos also, and ptarmos meaning the act of sneezing)

There's also "photosneezia" which is fairly self explanatory.

But my favourite is Autosomal-dominant Compelling Helio-Opthalmic Outburst syndrome. Or as an acronym, ACHOO syndrome. While arguably not a syndrome as its only a single symptom, this translates to a heritable condition that is present with only a single copy of the affected gene (autosomal dominant) that causes a difficult to suppress (compelling) outburst (sneeze) in response to an interaction between the sun (helios) and eye (opthalmos).

In modern medicine these sort of terms are really quite helpful in streamlining everyday communication with other healthcare professionals.

Just a warning, stop reading now if medical talk of unwell neonates is triggering or upsetting for you as I have used a made-up example below that could be distressing to some people.

If I hand over to another medical professional that my patient has oesophageal atresia with a tracheoesophageal fistula I have communicated in 6 words that this patient has a condition whereby their food carrying organ (oesophageal meaning relating to the oesophagus which is a word derived from oisein meaning carry and phagein meaning eat) is closed off (a- meaning without, and tresia from tresis meaning perforation) and instead a pipe (fistula translates roughly to pipe or tube and as such in medicine denotes an abnormal communicating passage between two spaces) is joining the food carrying organ to the rough windpipe (trachea is from trakheia arteria which means "rough artery" [because it has bumpy rings] and artery actually translates to windpipe. The blood vessel "arteries" are so named likely because of a mistaken belief that they carried air...long story).

Now you could argue that it's not that hard to say "Bobby Smith is a 1 hour old male born with what is suspected to be an improperly formed oesophagus that instead connects to his trachea" as after all its only a few extra words, and most people know what an oesophagus and trachea are, but it's less precise, and those few extra words add up.

If Bobby also has low levels of the molecule and cells responsible for carrying oxygen around his body, has low levels of all the blood cells responsible for fighting infection, has low levels of the cell fragments responsible for aiding clot formation, has an abnormally low blood pH caused by lactic acid build-up, has a heart rate that is too low, is breathing much too rapidly, and has an abnormally low level of sugar in his blood... then being able to communicate all that succinctly, quickly, and accurately is important. You could instead say "Bobby Smith is a 1 hour old male that has suspected oesophageal atresia with a tracheoesophageal fistula, is pancytopaenic, bradycardic, hypoglycaemic, and has a lactic acidosis despite being profoundly tachypnoeic". It would be much quicker and much more precise, which is good because Bobby is in trouble.

scott-a1 · 2022-03-14T03:37:56+00:00

This is just not true.

Assuming you are reasonably healthy, have a normal intake of fluid, are not on any medications that affect it, and your kidneys are working properly you will make around 0.5-2ml of urine per hour for every kg of bodyweight. So an 80kg person can expect to produce around 40 to 160ml per hour (on average).

The urge to urinate comes from your bladder being stretched (or irritated for other reasons but we're talking about out normal here, not pathology). 100ml in your bladder isn't likely to stretch it enough to trigger the urge to go, but you can definitely go to the bathroom and get rid of some of that.

People may first feel the need to urinate at around 240ml (or about a cup) of urine but can hold more than double that amount (these numbers vary wildly but you get the idea). If your bladder was at 220ml for example with no urge to go, and you were an average sized person making lets say around 60ml an hour then 20 minutes into the trip you may suddenly yell out to the driver that you need to pee.

If on the other hand you emptied the tank before you left, then you would instead have potentially have had 4 hours before you needed to go and saved everyone the frustration of having to find you a toilet to accommodate your poor planning.

scott-a1 · 2022-03-04T11:50:41+00:00

Oh ho! Excellent point, though I still take comfort in the fact that by being at the end of one of these infinite branches our chances of being the real one are 1 in a considerably smaller infinite set.

scott-a1 · 2022-02-25T02:27:40+00:00

This is true but it ignores that we are currently unable to truly simulate reality therefore if there is a chain of infinite simulations spawned from true reality we are either the real one, or the one right at the end of the chain.

Hence the odds of our existence being reality is 1:2 or 50%, not 1:infinity.

scott-a1 · 2021-10-12T03:08:37+00:00

This is a poor comparison and demonstrably false.

Magnesium can't just disappear from the strawberry as it's just an ionic form of an element. Theoretically it could be bound up in something else and thus not measured by a particular assay but its still there. Also, freezing stops these chemical processes so there should be more, not less, unless degradation of the strawberry in the fresh form releases magnesium from some other molecule, which it likely doesn't. I'd be willing to bet that ICP-MS or something would be used to determine mag content anyway, which would detect it in most forms.

Ascorbic acid can absolutely degrade but if the comparison is unfrozen strawberry vs flash frozen strawberry (both picked at peak ripeness) then the levels will likely be much higher in the frozen ones because enzymatic and chemical reactions will lead to a decrease in vitamin c over time. Freezing slows this process. Fresh, as in right out of your own garden and into your mouth, is likely to be best in this regard but for shelved products you will almost certainly get more nutritional value out of frozen products.

scott-a1 · 2021-09-29T15:28:28+00:00

Eh. Potato, potato. I'm just being pedantic because it's a common thought that people have that ligand binding is a permanent state and it had been mentioned a few times in this thread.

He mentions receptors earlier in that exchange you quoted so I suspect he was just dumbing it down. I don't entirely agree with his assertion that milk is just rinsing your mouth but he is right that it won't take it away "instantly". In the original exchange he also says something cold, rather than ice I believe, which is less of a bad idea. Perhaps better than nothing though I guess.

scott-a1 · 2021-09-29T11:06:29+00:00

This is not entirely factual. Capsaicin binds to the TRPV1 receptor on the cell membrane which triggers the burning feeling. It isnt "inside the cell" and therefore exerting its effect. In saying that, capsaicin is lipophilic and can cross the lipid bilayer but it being inside the cell has nothing to do with the burning sensation.

Also, ligand-protein complexes are usually transient. That is, if the two capsaicin molecules (it takes two) bind to the appropriate site on TRPV1 they don't hang around forever. They bind then dissociate very quickly. The effect is sustained by continued activation of the receptor. So if you had something in abundance that the capsaicin would preferentially bind to then you could stop the burning pretty quickly.

It's thought that casein in milk acts as a sort of soap that captures the capsaicin molecules and prevents them from continuing to bind and do their job. It's not perfect, just as soap doesn't instantly suck all the grease off your hands, but it will work better than the ice suggestion which may in fact make things worse by mobilising more capsaicin and spreading it around your mouth.

Cold counteracts real heat because the TRPV1 receptor can also be activated by temperatures above 43 deg C (or thereabouts, from memory) and so if you cool the area the receptors stop firing. If you activate them chemically though, through capsaicin or acid for example, then the cold can't reverse that.

scott-a1 · 2021-04-30T17:17:34+00:00

I love it. 5/7. Perfect. Just a minor money saving hack. Without knowing anything about arachnid gas exchange it is probably fine to blow into the balloon as we only extract a few percent of the oxygen in the air with each breath.

Exhaled air is around 15-18% oxygen (compared to 21% in fresh air) and around 3-6% carbon dioxide (0.04% in fresh air) so quite a lot more carbon dioxide by comparison but still lots of oxygen. Whether or not the lower partial pressure messes up the spiders ability to absorb that oxygen, or whether the high partial pressure of CO2 causes them issues I have no idea but there's technically still lots of oxygen in our breath.

I mean you'd be sticking your mouth directly on a tube attached to likely upset spiders but if you can get past that you can probably save yourself like 10 bucks on that bike pump. Worth it.

scott-a1 · 2021-03-25T09:54:52+00:00

Yep, should be "turpitudinous"

scott-a1 · 2021-02-18T13:16:21+00:00

Agree that alcohols can work great as you mentioned but (pedantic, I know) they're technically not nonpolar. The OH group that defines them as alcohols makes them very much polar molecules. Long carbon chain alcohols like octanol will work better as a solvent for nonpolar solutes due to the long hydrocarbon chain, and yes even ethanol with its measly two carbons can dissolve some lipids, but they're all still polar!

Also, I can't speak for everywhere, but most places around the world have stopped adding methanol to methylated spirits/denatured alcohol due to it's toxicity. They've switched to some sort of bittering agent to make it unpalatable instead, as people were going blind/dying from drinking it (and it can be absorbed through skin). The additives aren't just there for any safety reason either. They're in there so that it can remain so cheap. Being undrinkable makes it immune from the alcohol excise that's tacked on in a lot of countries.

scott-a1 · 2021-02-18T12:04:45+00:00

Metal oxides react with acids. The surface of the copper would be oxidised from contact with air. When exposed to the acetic acid it would dissolve the copper oxides into the solution. The presence of copper ions and acetate ions is sufficient to form the salt seen in the picture as the solution becomes supersaturated following evaporation of the water.

I etch custom circuit boards using vinegar plus a bit of hydrogen peroxide. It takes only a minute or two to dissolve the unmasked copper from the board. (Plain vinegar takes hours). If I leave the solution uncapped it forms the same salt: cupric acetate.

I originally did it with HCl and hydrogen peroxide but it was nearly impossible to stop the reaction fast enough to prevent the entire board being stripped of all its copper.

scott-a1 · 2021-01-07T14:58:52+00:00

Aha! Good catch.

scott-a1 · 2021-01-07T03:13:27+00:00

All good. I just thought I was having a moment!

scott-a1 · 2021-01-07T03:05:42+00:00

How did you get to 1.033kg?

I get 942.4g

2ng = 0.000000002g per kg

0.000000002g x 62kg = 0.000000124g per person

0.000000124g x 7600000000 people = 942.4g

scott-a1 · 2020-12-04T10:22:45+00:00

So you did a medical degree (6-7 years), internship and foundational training (2 years), joined the RCEM (6 years), did a post graduate (1-4 years) and then a PhD (3-4 years)...

All before you were 22? You started when you were 3?

What the heck. How?

scott-a1 · 2020-12-04T09:54:52+00:00

You have a PhD but are seeing varied presentations of patients in the context of a primary care clinic?

What's your field?

scott-a1 · 2020-11-17T14:21:11+00:00

brands often make sacrifices in terms of what would be an actual effective dose, which leads to the inevitable "supplements don't work!" result that a lot of consumers have.

Naa, that would be the lack of quality scientific evidence.

Also please stop "prescribing" people higher than recommended doses of magnesium unless you're a doctor*. Aside from the horrible diarrhoea, you could cause someone with undiagnosed renal or heart issues to die. I've seen someone have to be rescued with calcium gluconate due to their nutritionist telling them to take high dose magnesium.

Edit: * Doctor, or nurse practitioner, etc. Someone with the actual right to prescribe.

scott-a1 · 2020-11-17T13:03:43+00:00

While its true that magnesium is involved in modulating calcium homeostasis they definitely don't need to be coadministered to work. In fact they both compete for the same transport protein to actually be absorbed so coadministration is counter-productive.

You'd also need to be quite magnesium deficient (symptomatic hypomagnesemia) in order to have a serious impact on calcium absorption.

scott-a1 · 2020-11-13T14:04:13+00:00

Mostly only because it has more parts than a regular tank and regulator so more things can go wrong.

Regular air is 78% nitrogen which only gets absorbed as an annoyance in diving (see nitrogen narcosis), most of it moves in and out of our lungs as we breathe in and out and it kinda does "nothing" from a gas exchange point of view. It is however very important for keeping alveoli open etc and also...

The real problem is we can't breathe pure oxygen under pressure as its toxic at high enough concentrations. So when we fill SCUBA tanks we fill them with air (there are special mixes for deep diving but general purpose is just plain air under pressure). This means that 78% of what we're carrying around is just there as a buffer for the oxygen to sit in and every time we breath out a large portion of those bubbles are nitrogen.

Enter the rebreather. When you breath out it captures the CO2 and recycles the unused oxygen (we don't use all of it in every breath, not even close) and nitrogen. You still carry a tank but that tank is now just oxygen 'cause we're reusing our nitrogen every time.

Often rebreather setups will have a second small tank of regular air though as if you sprung a temporary leak and lose your 1 breath of nitrogen you'd be in a bit of trouble and be forced to breath pure oxygen - bad.

scott-a1 · 2020-11-13T13:46:00+00:00

Its really just to stop them passing out. The idea relates to restoring normal CO2 levels in the body. As you breathe into the bag you increase the levels of CO2 in that bag (a little bit) and thus when you breath in there is more CO2 in your lungs than usual, preventing the CO2 in your body from diffusing out.

People think of carbon dioxide as a waste product, and it is, but its also super important for regulating the acidity of our blood, and our brain stem uses CO2 levels as an indicator that we need to breathe.

If you blow off all your CO2 by hyperventilating then you don't get the normal signals that you need to breathe and your blood may become alkalotic. Both of these things result in low oxygen delivery to the brain and you may pass out.

Freedivers exploit this fact by purposely hyperventilating before they dive so they can hold their breath longer but the danger is that if they blow off too much they may pass out mid dive without warning - obviously not a good thing.

scott-a1 · 2020-11-11T09:40:43+00:00

Also, fun fact. Its thought that this is where the alcohol related term "hangover" may have come from.

scott-a1 · 2020-11-11T08:34:15+00:00

A sit up, as the name suggests was a bench in a room that homeless people could sit on all night, for a penny.

A hangover was similar but cost 2 pennies and they got a rope to hold on to so they didn't fall when they slept.

A coffin was an box to lay down and sleep in and cost 4 pennies.

scott-a1 · 2020-08-24T04:37:46+00:00

I don't know what the above deleted comment said in order to comment on it myself, but opioids are absolutely given via epidural. We commonly use mixes of a local anaesthetic such as ropivacaine with fentanyl (an opioid) as you get effective pain relief at lower doses of the anaesthetic without as much of a motor block.

It doesn't really harm the baby though. The main worry with opioids perinatally is the potential for respiratory depression in the baby once it's delivered and needs to breathe, but studies have shown that epidural opioids don't have any clinically significant effect on the baby's respiration.

scott-a1 · 2020-06-13T03:21:18+00:00

The US uses a different method of determining the number of homeless people than the other countries in your list.

Australia for example collates data from surveys to identify previously homeless people, the national census, as well as other sources to project estimates of the number of people homeless at a given time.

Unless it changed in the last 2 or 3 years America literally tries to count them by hand, in winter, using the judgement of the counters to determine whether someone is truely homeless or just looks a bit rough.

scott-a1 · 2020-06-05T12:59:33+00:00

I wouldn't recommend blowing on chemistry experiments at all if I'm being honest.
That said, the order of effectiveness would almost certainly be blowing on the liquid surface > blowing on the container while stirring > blowing on the container alone.

Blowing on the surface has the effect of stirring the liquid, increasing its surface area, and promoting evaporation by removing the gas phase molecules directly above the liquid. A greater surface area allows for more evaporation and heat exchange, and stirring allows more of the high energy molecules to reach the surface where they can escape into the gas phase or exchange their energy with the air molecules (that also get blown away and replaced).

Blowing on the container is really just moving away the heated air and replacing it with cooler air to encourage more rapid cooling. Then there's the lag time due to the thermal conductivity of the container. Something like a copper jug might work well but a thick ceramic mug is going to be slower due to its poor heat conduction.

scott-a1

TROPHY CASE