1

Physiology & Medicine / Re: Why do brain tumours (and blood clots) cause headaches.......

« on: 16/08/2021 23:27:19 »

The meninges are a sack in which the brain floats. The meninges do have pain receptors, so increased pressure within the brain will affect them. Various veins and arteries also have pain receptors, as do muscles outside the brain case.
see: https://en.wikipedia.org/wiki/Headache#Pathophysiology

2

Technology / Re: Does electric transportation cause greater pollution than conventional means?

« on: 30/06/2021 17:19:14 »

So whether you use a bike or car or EV it is all the same CO2 will increase with population.

Bollocks.
If we were able to stop using fossil fuels- for example, buy switching to renewables like solar power, where would the CO2 come from?

3

Physiology & Medicine / Re: How much use is pulse oximetry?

« on: 29/03/2021 21:27:37 »

When I was looking at the pulse oximetry devices available on display, I saw another device which did pulse oximetry, but also claimed to be able to detect atherosclerosis.
- The implication on the box was that it analyzed the pattern of the pulse of blood reaching your finger to determine the stiffness of the arteries between the heart and finger.
- The aorta acts as a shock absorber between the heart and the rest of the circulatory system
- Furring of the arteries in your arm would conceivably change the waveform too.

But because it was almost 4 times the price, I didn't bother with this one.

4

Physiology & Medicine / Re: How much use is pulse oximetry?

« on: 29/03/2021 14:29:54 »

I've only tried it on myself 3 times in a day, and got a range of 95-98%.

I was just curious whether it varies between consecutive display updates as you sit and watch it, like mine does.

You might be interested in this https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5539125/

5

Physiology & Medicine / Re: How much use is pulse oximetry?

« on: 29/03/2021 10:57:30 »

Is it giving consistent readings?

I've only tried it on myself 3 times in a day, and got a range of 95-98%.

This averages in the recommended range - nothing to worry about!

6

Physiology & Medicine / Re: How much use is pulse oximetry?

« on: 27/03/2021 00:09:17 »

The breathing reflex is prompted by a rise of carbon dioxide levels in the blood.
- That's why nitrogen asphyxiation is so dangerous, as it doesn't lead to increase in carbon dioxide in the blood.

You don't want to breathe too deeply for too long. Hyperventilation can cause dizziness, loss of vision and fainting.
It's also hard work, so your body does not naturally breathe too much.
See: https://en.wikipedia.org/wiki/Hyperventilation

Scarring of lung tissue due to COVID-19 infection reduces oxygen flow across the alveoli, and reduces blood oxygen levels.
- But because this scarring occurs gradually over a period of days to weeks, your body adapts to the reduced oxygen levels, and you may not notice it around the house
- You are more likely to notice it if you exercise; normal levels of exercise may leave you unusually breathless
- A pulse oximeter will pick up the reduced oxygen levels, even if you don't feel breathless
- This slow adaptation to reduced oxygen is similar to the process when mountain climbers spend a week or two at Everest base camp to acclimatize

With an average SpO2 of 93%, it sounds like you should mention it to your doctor, next time you visit.
- It SpO2 stays consistently below 92% (but you still feel ok), make an immediate medical appointment - a chest X-Ray will reveal if you have the "ground glass" pattern indicative of COVID scarring, or other respiratory problems.
See: https://en.wikipedia.org/wiki/Ground-glass_opacity

7

That CAN'T be true! / Re: Can this microwave boiler heat your home?

« on: 18/03/2021 19:20:16 »

...and uses no harmful chemicals....powered by renewable electricity....

Except that a microwave boiler is an exterior heat source, not an immersion heater. So "no dangerous electricity inside your water tank..." and unlike the resistive heater it delivers  "...a precisely defined energy spectrum that is uniquely absorbed by water molecules" and was "developed from the top-secret magnetron that won the Battle of Britain"

8

That CAN'T be true! / Re: Can this microwave boiler heat your home?

« on: 18/03/2021 19:12:38 »

I could sell an ordinary immersion heater as "works via microwaves".
Presumably I could then stick an extra zero or two on the price tag and still undercut the supplier in the OP.

Yes, you could be onto a winner there,  but I'd suggest a few enhancements to increase  appeal and earning power:

1  Replace "microwaves" by "quantum effects".  After all can that be scientifically incorrect?  Doesn't everything in the Universe ultimately result from these effects, so you can't be proved wrong and sued in any court;

2. Incorporate the word "natural"  Again, everything in the Natural Universe, is by nature, "Natural", so you can't be sued for that either.

3. Also incorporate words like "modern", "latest" and "safely"  - none of which can be pinned down in court.

So, that leads to your new immersion heater being advertised as:

" A  modern boiler which uses the latest quantum technology to warm your home safely and naturally"

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That CAN'T be true! / Re: Can this microwave boiler heat your home?

« on: 17/03/2021 18:51:48 »

Just a thought.
If I put a resistor in a tank of water, I could make the case that, at least some of, the heat transfer would be via microwaves being emitted from the resistor and (without having to travel very far) being absorbed by the water.

In which case, I could sell an ordinary immersion heater as "works via microwaves".
Presumably I could then stick an extra zero or two on the price tag and still undercut the supplier in the OP.

(even if I bought my immersion heaters from RS.)
https://uk.rs-online.com/web/p/heating-elements/0273034/?cm_mmc=UK-PLA-DS3A-_-google-_-PLA_UK_EN_Automation_%26_Control_Gear_Whoop-_-Water%20Heater%20Elements_Whoop-_-273034&gclid=Cj0KCQjw0caCBhCIARIsAGAfuMxPY265L9n3KJHLhI7EbvUXRwBbWEMy0mfvarWiGM-b4qXHJ8bQ02MaAg6TEALw_wcB&gclsrc=aw.ds&matchtype=&pla-296206105570

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That CAN'T be true! / Re: Can this microwave boiler heat your home?

« on: 17/03/2021 17:32:58 »

No need to read the article. "Could help cut emissions" is the magic phrase that opens wallets without actually promising anything in return.

11

Physiology & Medicine / Re: CT Scanner Operation

« on: 15/02/2021 18:17:23 »

The difference between the head scan and the abdominal scans is like chalk & cheese.

Yes. We spend several years teaching radiographers the difference between an arse and an elbow - but they still get it wrong sometimes.

The abdominal scout scan is more often needed than for a head because the bits inside (to use the technical term) tend to float around between different patients, but the brain is nearly always located in the skull (apart from teenagers, where it is located in the pelvic region). It takes time for the contrast agent to reach wherever it is going and if you are looking for differential flow as a diagnostic, you may need a few scans  to measure it, whereas a brain hemorrhage will be fairly static so you either see it in a single shot or you don't.  I'm pleased they didn't.

12

Physiology & Medicine / Re: CT Scanner Operation

« on: 13/02/2021 11:36:20 »

A multislice CT scanner can take up to 64 parallel slices in a single rotation of the tube head (or more for some cardiac research units) so in principle can cover a small 3D volume without moving the patient. If you want really high spatial resolution it's a good idea to shift by half a slice width and scan again, then interpolate the images to "smooth over the joins". Scan time can be down to tens of milliseconds for a conventional system or microseconds for a single slice "electron beam CT."

There are clinical advantages in MRI scanning to have the patient standing or sitting, and I've owned a few such systems, but I haven't persuaded anyone of the diagnostic value of upright CT: a pity, because,  like MRI, my design involves a stationary patient and a moving scan field.

You can also use "cone beam" CT  for small volumes. These systems are very popular in dentistry, essentially taking several hundred complete images up to 10 x 10 cm  in a single 10 second rotation and interpolating the reconstruction. Resolution of around 2.5 lines per mm is standard but the software and x-ray spectrum are usually optimised for hard tissue (bones and teeth) as against medical CT which is optimised for resolving soft tissue inside a skull. 

13

Physiology & Medicine / Re: CT Scanner Operation

« on: 13/02/2021 00:10:59 »

If you just wanted a single slice through the head, I guess you could do that
- Although I understand that the beam shape is somewhat fan-shaped
- And the imaging algorithms are probably optimized to deal with a helical scan (moving patient)

But why would you want just a single slice?
- Most medical problems exist in 3 dimensions
- The exact location of medical problem is somewhat uncertain, so aligning this 2D slice is difficult
- And most doctors are 3-dimensional, so they will disrupt things around this 2D slice.
- So imaging a 3D volume has real advantages for the doctor
- Even if it means a slightly higher X-Ray dose for the patient

14

Technology / Re: Why do videos of same length and resolution have such contrasting sizes?

« on: 22/12/2020 13:29:48 »

... The achievable degree of compression is strongly dependent on the video content.
- Large areas of uniform colour compress more easily than areas of great image detail
- Stationary or slowly-moving video content compresses better than fast-moving content

15

COVID-19 / Re: Anyone know the details of the new coronavirus variant?

« on: 21/12/2020 23:22:21 »

One of the staff said that they were having quite a few people refusing the vaccine, not because of safety worries, or even Bill Gates' microchips, but because it's made by them forriners, and not British.

Nice to know there are still people willing to die for their country

16

Technology / Re: What happens to unused electricity?

« on: 20/06/2020 00:07:21 »

When I went round Bradwell in the late 70s they had two clocks on the wall in the control room, one running of the mains, and a battery one adjusted to the Greenwich time signal. They just adjusted the frequency to keep the clocks reading the same time.

If it works, it works.
Is that what they mean by an "atomic clock"?

17

Physics, Astronomy & Cosmology / Re: How does static electricity work?

« on: 04/06/2020 23:58:42 »

But, like wood, earth isn't a great conductor.
So, you really can't need a good conductivity to earth something.

It's true that some rock types like granite have low conductivity, and safety earth connections in granite country need alternative methods (eg relying more on the Neutral wire). But most rock types give reasonable protection.

I agree that rock would not be good to make long, thin wires. But in its protective/electrical safety role, it is used to make short, really fat wires, and it's not too bad at this - 1 Ohm resistance is often achievable, especially in areas using "Multiple Earthed Neutral", where every house has its own earth stake.

The other important role of "Earth" is as a capacitor.
- This is why the old-fashioned "wireless" had a terminal for an antenna wire and an earth wire - the Earth is able to absorb the radio-frequency currents picked up by the antenna wire.
- Most of the capacitors we put in electronics have two plates, spaced very close together. This allows high capacitance in a small volume.
- But there is another form of capacitor which has just a single conductive element. It doesn't pack nearly as much capacitance into the same volume as a two-plate capacitor.
- A doorknob insulated by the door can act as a small capacitor, and can cause a spark when you touch it
- A car, somewhat insulated by its tyres can act as a larger capacitor, and can cause a spark when you touch it
- An earthed object is connected to the Earth as a much larger capacitor, and can cause a significant spark when you touch it
- I remember at university calculating the capacitance of the Earth - I don't remember the technique, but I do remember that I wasn't impressed with the comparison with what I could get at my local electronics store...

Of course, the Earth, insulated by the vacuum of space, has a higher breakdown voltage compared to a capacitor I could hold in my hand!

Even for an "Earthed" object, the inductance of the Earth wire and skin effect in the wire significantly reduces the current in an impulse with a fast rise and fall time, like an electrostatic discharge.

PS: These MIT lecture notes calculate that the Earth has a capacitance of around 0.0007 Farads, or 700 microFarads.
http://web.mit.edu/sahughes/www/8.022/lec06.pdf

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Physics, Astronomy & Cosmology / Re: How does static electricity work?

« on: 04/06/2020 19:34:43 »

Wood is NOT an insulator and therefore is not an alternate route for electrical current.

Pardon?

19

COVID-19 / Re: Are we testing the wrong people for coronavirus infection?

« on: 23/05/2020 11:33:34 »

I heard a suggestion that authorities could use a "sniff test" to supplement temperature checks.
- Some standard sniff tests already exist
- Presumably, such a test would be quicker to manufacture than a vaccine

Symptoms are not very uniform with this virus - temperature is not always a good indicator.
- For some people, a loss of a sense of smell is an early symptom
- A sniff test is not as quick as a temperature test, but it may detect another subset of infected individuals
- Without a baseline sniff test (before infection), it would be hard to tell if someone had lost their sense of smell, or were always poor at detecting scents.

See: https://en.wikipedia.org/wiki/University_of_Pennsylvania_Smell_Identification_Test

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COVID-19 / Re: Latest Report From SAGE

« on: 14/05/2020 01:32:10 »

There's plenty more where that came from ... https://rationalwiki.org/wiki/Kookmobile#Kookmobile_gallery