1

Cells, Microbes & Viruses / Re: Is 85 deaths ON AVERAGE a day per 60 milllion a reason to PANIC ?

« on: 13/03/2020 23:45:12 »

Quite a simple one this, yes or no ?

If so should we isolate ourselves from others ? Shun mass gatherings, stop trading ?

No, but the fact that about 100% of the world population is susceptible, and further that it's killing very roughly 1% of those it infects (so it could be expected to kill very roughly 70 million people, comparable or higher than the 1918 Spanish Flu) is.

2

COVID-19 / Re: What is the natural history of Covid-19?

« on: 13/03/2020 21:23:29 »

Unfortunately, it appears that an infected person can spread the virus before they show symptoms, which means the disease will be harder to control.

Not necessarily. If if's (say) one in a thousand, you may be able to stay ahead of it enough with quarantine measures. Like a thousand people have it, and you quarantine them, but one escapes quarantine because they didn't have any symptoms. Oh dear. But then you find and quarantine the few dozen that caught it off them, and then probably nobody catches it off them, so the number of people infected decreases to zero.

3

The Environment / Re: Are average wind speeds increasing with climate change?

« on: 18/02/2020 22:07:20 »

They should be increasing slightly because the equator is warming, but the poles (until they melt entirely) are being kept cool by ice at roughly constant surface temperature, so there's a greater temperature difference which should drive faster winds.

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Physics, Astronomy & Cosmology / Re: Do rockets work due to conservation of momentum theory or imbalanced forces?

« on: 06/02/2020 04:36:50 »

Yes but the imbalanced force is created by the gas pushing on the front of the rocket. It is because the exiting gas is not pushing on the rocket is what causes the imbalanced force.

Of course there are no imbalanced forces in physics. That's Newton's Third Law. You may have heard of it. The force that pushes on the rocket (from the gas pressure times the cross-sectional area it acts over) causes an equal and opposite force on the exhaust which accelerates the exhaust in the opposite direction; and so the rate of change of the momentum of the rocket is always equal to the rate of change in momentum of the exhaust.

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Technology / Re: Could regenerative braking help with air pollution from car brakes?

« on: 31/01/2020 22:56:45 »

Brake dust apparently makes up 20% of pm2.5 pollution:

https://www.dailymail.co.uk/health/article-7864855/Metal-particles-vehicle-brake-dust-damage-immune-diesel-pollution.html

Certainly brakes on vehicles with regenerative braking tend to last many fold longer, so you would expect a lot less pollution to be released.

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Technology / Re: Would it be possible to 3D print housing using waste plastic?

« on: 31/01/2020 22:41:10 »

Tarmac pretty much occupies that space just fine. Plastic roads sound to me like a terrible idea- they would wear and all the ground-up plastic will end up getting washed out to sea. Building plastic into a permanent structure is at least the opposite of single-use plastic.

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Technology / Re: Would it be possible to 3D print housing using waste plastic?

« on: 31/01/2020 00:19:32 »

So far as I can tell, the compressive strength is similarish to normal concrete, but it has one key advantage- it actually has some tensile strength without further reinforcement, so it's quite robust and not brittle, and the other obvious advantage is that unlike normal concrete it sets off very quickly.

There were some caveats I found, you possibly can't just use any thermoplastic, it has to actually stick the aggregate together, so it probably can't be (for example) polyethylene- polyethylene has a really slippery, "low energy" surface. IRC polyamide worked, those 'glue sticks' work really well for obvious reasons. I tried polycaprolactone and that worked OK because it gets sticky when hot. That was fun because you can mold it with your hands.

Although it's probably significantly more expensive than normal concrete, you probably don't need as much of it because you can put it right where you need it, and you can corrugate it and print it with spaces in the middle.

The real problem is whether there's a killer app for it. I mean you could easily print domes and things with it. Is that something people need though?

Oh yeah, and UV is an issue. Mixing in a tonne of carbon black and painting it would help a lot though.

Edit: graded aggregate is a very, very good idea, but perhaps not in the way you'd initially think- it minimises the amount of plastic you need, because you just have to fill in the gaps between the bigger aggregate, but with graded aggregate most of that is filled with smaller aggregate. Plastic is actually one of the more expensive materials in constructions so anything you can do to reduce it is super helpful.

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Technology / Re: Would it be possible to 3D print housing using waste plastic?

« on: 29/01/2020 02:21:01 »

I mixed up some thermoplastic polymer concrete a year or two ago. To make it I found all you have to do is just heat a thermoplastic, stir in some sharp sand and then let it cool. I tried a few different polymers and they seemed to all more or less work. It seemed to be potentially 3D printable, although it looked like it was going to be quite abrasive on nozzles. Polymer concretes are actually quite strong.

If the waste plastic is cheaper than portland cement, then it could be quite good; normally plastic is relatively expensive. What kind of cost per kg can you get?

The upsides are that polymer concrete is usually waterproof, but the downsides of concrete is that it's a good thermal conductor; in most cases you want poor thermal conductors for structures, and the flammability is an issue, but with the right additives or polymers might not be an issue.

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Physiology & Medicine / Re: H2O2 good for mouthwash?

« on: 17/11/2018 16:23:17 »

Peroxide mouthwashes are widely available. They're rather acidic though, IRC similar to orange juice.

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New Theories / Re: Reactionless Drives Possible ?

« on: 08/11/2018 02:56:48 »

Nope. They violate both conservation of energy and conservation of momentum. If you could build them, then you have created a potentially infinite power source.

11

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 16/10/2018 16:19:11 »

FWIW the 'flying bum' Airlander has a top speed of 92 miles per hour, so provided the wind isn't as fast as that, it can still make headway. Airships often fly lower in the atmosphere than most aircraft, (well below the jet streams) where there's lower wind speeds.

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Physiology & Medicine / Re: Can Cataract be Cured without Surgery?

« on: 06/10/2018 03:34:19 »

Most of the advice on 'antioxidants' is bunk. However cataracts is one of the conditions that it might help for:

https://www.allaboutvision.com/nutrition/cataracts.htm

To the extent this is right, you want a diet high in antioxidants, vitamins A, C, E, lutein and zeaxanthin. So, not so much carrots, more Kale. Also you don't want a super high carbohydrate diet; glucose can react with proteins in the eye and can trigger or accelerate cataracts. If you're overweight, lose it, because that will improve your insulin sensitivity.

But no, so far as I know, it can't be reversed, you might be able to halt it though.

13

General Science / Re: What term describes a solid that has melted to become a liquid?

« on: 06/10/2018 03:12:52 »

Yeah, as Bored Chemist already noted, it's just a 'melt':

https://en.wiktionary.org/wiki/melt#Noun

As in snow melt, chocolate melt, cheese melt etc.

14

Physiology & Medicine / Re: Is the shingles vaccine still useful if I've recently had shingles?

« on: 29/09/2018 02:46:46 »

Most likely the symptoms you have are not due to a current shingles attack, but is the nerve damage caused by the attack. Your immune system would likely have rebuilt antibodies to it, but a vaccination wouldn't do any harm. In about 85% of cases the pain goes away within a year.

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Physiology & Medicine / Re: Would identical twins fool a paternity test?

« on: 29/09/2018 02:38:14 »

I wonder if epigenetics might be employed- presumably the child's epigenetics would match the father's better than the twin's.

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General Science / Re: Why no other similar energy to electricity?

« on: 26/09/2018 23:41:24 »

The main advantage of electricity is that it's a low entropy, very highly ordered form of energy.

But other forms of secondary energy could potentially work also; compressed air has somewhat similar properties, but it's probably a much more dangerous way to deliver large amounts of energy for things like lighting.

17

Physics, Astronomy & Cosmology / Re: Magnetic force per distance?

« on: 24/09/2018 20:37:50 »

Either a rectangular Halbach array or just alternate N-S-N-S magnets work (alternate magnets are more or less self stable, whereas the Halbach array is constantly trying to push itself apart.)

18

Physics, Astronomy & Cosmology / Re: Magnetic force per distance?

« on: 24/09/2018 01:49:06 »

Are there magnets that they repel so strong when they are extremely close together, so that you can virtually not make them touch each other, but when they are in a distance of few millimeters, there's barely no interaction?

Thanks

Yes, magnets arranged in an opposing checkerboard pattern do that. The smaller the checkerboard squares are, the more short range it is. from a distance you get virtually no force.

19

General Science / Re: If I wear ANY battery watch, within a week the battery is dead. Why?

« on: 24/09/2018 01:00:46 »

To be fair to him, the lower carats of gold do corrode somewhat, and even 24 carat gold can rub off and create a black mark, if there's anything abrasive on the skin (some cosmetics do that for example). It would be worth checking the hallmarks.

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Physics, Astronomy & Cosmology / Re: Is it possible to secure a magnetic particle in a specific position?

« on: 23/09/2018 20:02:37 »

Diamagnetism. It's a weak form of magnetism that most things have to a degree. In a sufficiently strong magnetic field, of the right shape, stuff floats. Like, live frogs. Also, pyrolitic graphite is particularly diamagnetic and you can float it on supermagnets.

Iron doesn't work, because it's highly ferromagnetic, that means that the attraction increases as it approaches a magnet, which is the opposite of what you want.