1

Question of the Week / Re: QotW - 24.09.20 - What will wind farms mean for the weather?

« on: 14/09/2024 14:51:32 »

The total amount of energy present in weather phenomena, all provided by solar energy, is so great in comparison to the tiny pittance harvested by man that I reckon there would be no measureable effects even with the projected increase in wind farms. Possibly short range effects in the local vicinity of wind farms is all there would be.

I think solar could have quite an effect, hose black panels absorb the suns enery and only 20 percent is converted to leccy.

Lol

What do you think usually happens to the radiation from the sun?

Some of it gets reflected, but less if the albedo changes.

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Physiology & Medicine / Re: What liquid solution is best for a portable commode?

« on: 08/09/2024 13:13:30 »

I used a commode in hospital once, and there wasn't anything in it other than what I deposited. Commodes are emptied immediately after use, unlike chemical toilets. I've been splashed by the water in an ordinary toilet on occasion, I wouldn't want that if it was corrosive.

3

Physiology & Medicine / Re: What Is The Role Of Bread In Human Nutrition?

« on: 23/08/2024 18:42:43 »

Medical Research Council nutrition recommendations from their DAPA toolkit. (No more than 50% of total calories from carbs.)

Data from the European Food Standards Agency here.

Bread is high in salt (the biggest source of salt in my diet), and unless it's baked by a local artisan baker it's classed as 'Ultra Processed' because of the preservatives in it. I recently switched to supermarket loaf which has no preservatives, but it does tend to feel more stale as a result. Wholemeal is better because it's higher in fibre.

Beer used to be safer than water because it's boiled during the brewing process, famously, it was the absence of cholera among brewery workers that led John Snow to the cause of the Broad Street cholera outbreak.

4

That CAN'T be true! / Re: Is potassium chloride explosive

« on: 20/08/2024 18:19:34 »

Another use for urine here:
https://twitter.com/twitrkshukla/status/1825936930334454106

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New Theories / Re: What's the unit of Torque?

« on: 11/08/2024 18:56:24 »

If you have a spring that follows Hooke's law, the displacement, s is proportional to the force, f, and the area under the graph is the energy stored: E=fs/2, or E=TΘ/2 (ie the area of a triangle).

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General Science / Re: Is the Curie Effect Reversible

« on: 06/08/2024 13:39:22 »

Some confusion, I think. A permanent magnet will become permanently demagnetised above the  Curie temperature but a piece of soft iron simply changes from ferromagnetic to paramagnetic, and this change is reversible.

Yes, of course, this. It's the armature attached to the stat contacts in the iron that's magnetised, not the calibrated pellet on the back of the bit.

I have two bits for this iron, one with a fine tip which barely gets hot enough to solder and one which is far too hot and actually glows faintly in the dark

Size and temperature are two independent variables. My bit of choice is the PTF-7: 600F is too cool and slow, and 800F just burns off the flux and oxidises too quickly, 700F is the Goldilocks temperature. The PTF is fine enough to solder SMDs, but short and stubby enough that it's thermal resistance isn't so high that the tip temperature drops when you solder something the size of a BNC socket.

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General Science / Is the Curie Effect Reversible

« on: 30/07/2024 14:50:14 »

So this website says that the Curie Effect is not reversible: heating above the Curie point results in a permanent loss of magnetism.

This seems to contradict the operation of the Weller soldering irons that I spent my whole working life using: they have bits with a magnetic pellet that it releases a spring-loaded armature to open the switch contacts when the bit reaches it's set temperature and attracts it again as it cools.

Reading Wikipedia, they make no mention of whether it's reversible or not, and Chat GPT starts by saying that it is, then agrees with the site that says it isn't, then when I point out it's contradicting itself says that there are two Curie Effects: one reversible and the other not.

I see that the original site makes note of a separate effect that's not the Curie Effect, but which causes a reversible loss of magnetism which is progressive not sudden, but I'm sceptical that's what Weller are using, as without a sudden loss at a particular temperature, the switching point would be dependent on the armature spring as well as the bit, and much more difficult to calibrate. Weller call their system Magnastat without reference to Curie, and although they don't explain in any detail how it works, they do refer to a change in characteristics at a specific temperature.

8

General Science / Re: Why Are Red And Yellow Most Visible?

« on: 25/07/2024 11:15:02 »

Red is the longest wavelength, lowest frequency, violet the shortest wavelength highest frequency. The peak in the spectrum of sunlight is green, in the middle of the visible spectrum, so green is the colour that the human eye is the most sensitive to. The eye is also quite sensitive to yellow, which is next to green on the spectrum. I assume red has always been associated with danger because blood is red.

9

Physiology & Medicine / What tissue is this?

« on: 23/07/2024 13:33:59 »

Behind my ear is a groove where the arm of my spex rests. The force it exerts must have all on to be even as much as a gram, so you'd think the tissue it's making an impression in would be soft to the touch, but it ain't so. If I press it with my finger it's so hard and permanent it feels as if someone has machined the groove into my skull.

Yesterday I found a similar groove in my knee where it had been resting against the table leg, and again, it felt so hard it's as if the groove has been filed into my kneecap even though it can't have taken much more than an hour or so to develop. I didn't notice how long it took to disappear again.

What tissue's developing these impressions? It's not soft like pitting oedema, the way sustained gentle pressure deforms it but sudden hard pressure doesn't makes it seem like a non-Newtonian liquid.

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COVID-19 / Re: Was the Covid Pandemic Panic justified?

« on: 22/07/2024 12:05:18 »

the population explosion in North Africa/middle east.

Population growth is fixed, the increase in births has already ceased, and the remaining increase in total population is just what's already baked into the system as today's children grow up and have children of their own.

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COVID-19 / Re: Was the Covid Pandemic Panic justified?

« on: 21/07/2024 17:01:56 »

don't forget the "long covid " sufferers, there are thousands of people whose lives have been severely disrupted

Only thousands? This neuroscientist who specialises in Long Covid says the figure may be as high as 10 million, and that we have no way of knowing because the data isn't being recorded adequately.

https://threadreaderapp.com/thread/1814824165272080546.html

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General Science / Re: Why don't hands get sunburnt?

« on: 18/07/2024 18:56:24 »

Depends on which side of the hand you are thinking of. The palms have very low melanocyte levels compared with the rest of the body and tanning rarely occurs to any significant degree- people with very dark skin colour usually have palms which are quite pale in comparison. The other side, ie the back of the hand, will tan as normal, mine certainly do.  Ps: I didn't read your question properly and the answer I gave is for the question "why do hands not TAN". Any unprotected area of the skin will suffer burns with sufficient sun exposure. Try exposing the palms of your hands to strong sunlight for 3-4 hours and I think you will achieve a burn. 

I've spent many years indulging in outdoor activities like fellwalking and cycle touring that involve being out in the hottest sun all day every day, and discovered numerous ways of getting sunburnt, even when using sun cream. In all that time, the backs of my hands have never been burnt, despite the fact that I never put sun cream on them. Tanned yes, burnt no. (I wash my hands after applying sun cream otherwise it makes a greasy mess of everything I touch, particularly the bike handlebars.) My hands don't face upwards towards the sun when I'm walking, but they do when I cycle.

13

General Science / Why don't hands get sunburnt?

« on: 17/07/2024 15:00:41 »

Mine seem immune.

14

Physiology & Medicine / Going Deaf

« on: 08/07/2024 14:01:59 »

As deafness develops, does the threshold of damage rise in step with the threshold of hearing, or does the safe zone between loud enough and too loud shrink?

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Physiology & Medicine / Re: What Is Junk Food?

« on: 28/06/2024 09:00:24 »

For some time, the orthodox view has been that foodstuffs high in salt, fat & sugar are unhealthy, but recently the idea that foods that are highly processed are damaging to health is gaining some traction.

If you're looking for an objective definition, the Food Standards Agency Nutrient Profile Score is a system that was originally devised for legislating which foodstuffs are allowed to be advertised during children's TV programmes. It creates an index number based primarily on salt, fat & sugar content, but also takes into account fruit, & veg content, and the higher the score the more unhealthy the food, with a healthy/unhealthy threshold being set at 4.

These are some general nutrition guidelines from the FSA.

Regarding processed foodstuffs, the Nova system defines four categories:

Group 1: Unprocessed or minimally processed.
Unprocessed (or natural) foods are edible parts of plants (seeds, fruits, leaves, stems, roots) or of animals (muscle, offal, eggs, milk), and also fungi, algae and water, after separation from nature.

Minimally processed foods are natural foods altered by processes such as removal of inedible or unwanted parts, drying, crushing, grinding, fractioning, filtering, roasting, boiling, pasteurisation, refrigeration, freezing, placing in containers, vacuum packaging, or non￾alcoholic fermentation. None of these processes adds substances such as salt, sugar, oils or fats to the original food.

Group 2: Processed culinary ingredients.
These are substances obtained directly from group 1 foods or from nature by processes such as pressing, refining, grinding, milling, and spray drying.

Group 3: Processed.
These are relatively simple products made by adding sugar, oil, salt or other group 2 substances to group 1 foods. Most processed foods have two or three ingredients. Processes include various preservation or cooking methods, and, in the case of breads and cheese, non-alcoholic fermentation.

Group 4: Ultra-processed.
These are industrial formulations typically with five or more and usually many ingredients. Such ingredients often include those also used in processed foods, such as sugar, oils, fats, salt, anti-oxidants, stabilisers, and preservatives. Ingredients only found in ultra-processed products include substances not commonly used in culinary preparations, and additives whose purpose is to imitate sensory qualities of group 1 foods or of culinary preparations of these foods, or to disguise undesirable sensory qualities of the final product. Group 1 foods are a small proportion of or are even absent from ultra-processed products.

The general idea here is that it is the Ultra-Processed Foods which are harmful, and consumption of them should be reduced as far as possible.

Monteiro et al go into more detail on how UPF are defined.
Lane et al is a review of the current evidence of the effect of UPF on health outcomes.

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Physiology & Medicine / What Causes Saccadic Dysmetria

« on: 24/06/2024 17:10:10 »

??

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Physiology & Medicine / Re: What isotope to commit murder undetectably?

« on: 22/06/2024 18:39:59 »

Incidentally, if anyone is looking at this for ideas, try these folks.

https://www.samaritans.org/how-we-can-help/contact-samaritan/

They don't have any ideas either.

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Physiology & Medicine / Re: What isotope to commit murder undetectably?

« on: 14/06/2024 16:59:45 »

wouldn't be the first thing a pathologist would look for.

From an episode of Silent Witness:

"How would you commit the perfect murder?"

"First find out what ails them, then use that to kill them."

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Question of the Week / Re: QotW - 24.06.21 - Why aren't wind turbine blades designed liked windmills?

« on: 14/06/2024 16:48:41 »

The span limit for any kind of windmill (including helicopters and propellors) is the point at which the tip approaches the speed of sound

What about the Harvard, which famously had propeller tips that went supersonic and made a raucous rasping noise.

20

General Science / Do germinating tomatoes kill off competing plants?

« on: 10/06/2024 11:52:32 »

What's going on here, it looks like the 'winning' shoot kills off all its competitors.
https://www.youtube.com/shorts/6gRBjN9SiTw