1

General Science / Dry Docks

« on: 23/03/2023 13:10:42 »

Having seen ships in dry dock from time to time, and been struck by how precarious the supports looked, I'm having difficulty in being surprised at the "capsize" of the Petrel.

The system I recall seeing has the keel, and I presume the majority of the weight, supported on blocks on the floor, with props at the sides holding the ship upright. With the ship balanced on the keel and minimal load on the props, since they were wedged and in compression only it would take relatively little force from a gust of wind to momentarily release the compression at the windward side, at which point all the props fall out.

It looks like there's about 900m² of windage, which would give about 20 tons at 45mph, perhaps that's enough if the props were put in carelessly, especially if there are repeated nudges from repeated gusts over a long period of time.


Petrel.png (4.86 kB . 707x677 - viewed 144 times)

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General Science / Do You Dream in Monochrome or Colour?

« on: 08/12/2022 12:22:00 »

On Radio 4 this morning someone was saying that in the days of B&W TV only 9% of the population dreamt in colour, but now in an era of colour TV the ratio is reversed. That reminded me of a news story a few years ago in which a blind man who had just been given an operation to restore his sight said that he was now dreaming in colour instead of B&W.

At the time, that set me wondering about whether I dream in colour or B&W, and after much thought I realised it's neither. My dreams are like memory, they occur in terms of salient points: if I think of a rectangle or a circle they're not in in colour or B&W, they just 'are', unless I think of a no enty sign, in which case I see a red circle and a white rectangle.

In the most recent dream I recall, I was talking to someone. I don't know who I was talking to, what they said, or what they looked like, but they were trying to show me something, and I don't know what they were trying to show me either, I just recall telling them that I couldn't see it because I was having an ocular migraine.

Then I woke up and found I was having an ocular migraine. That's all I rememeber/saw, because that's all that was salient.

3

General Science / BP Monitor Cuff Inflation

« on: 26/11/2022 12:19:35 »

The pressure to which my BP monitor inflates the cuff varies widely. It would seem reasonable to suppose it would inflate until the pressure exceeds systolic by a sufficient margin, but if you look below, the data is grouped into two distinct clusters pretty much independent of systolic bp.


BP mon.png (17.69 kB . 704x385 - viewed 989 times)

Is it inflating for a preset time? No.
Is it inflating until it exceeds sys bp for a predetermined time? No.
Is it inflating until it exceeds sys bp for a predetermined number of pulses? No.
Is inflation pressure dependent on how tightly the cuff is wrapped? No.

So what are the criteria?

(Monitor: Omron M2 Basic, HEM-7120-E))

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General Science / How much water vapour in human breath

« on: 25/11/2022 12:01:24 »

It occurs to me that if oxygen consumption is directly proportional to energy metabolised, then water produced must also be. Wikipedia just gives typical levels, not the relationship to metabolic rate.

5

Geek Speak / How do you remove malware that commercial antivirus won't find?

« on: 07/10/2022 16:43:18 »

As per the title, if antivirus like Norton, McAfee, & Malwarebytes won't find the malware, how do you go about removing it?

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General Science / Stats question: who's most likely to be at fault?

« on: 16/06/2022 17:22:28 »

Referring to this page, there are 3782 cyclists at fault for failing to look properly, and 7565 non-cyclists. If we assume that there are 8 times as many non-cycling road users as cyclists, does it follow that:

1.   Cyclists are four times more likely to be at fault because they’re producing half as many incidents from 8 times fewer vehicles.
2.   Cyclists are 16 times less likely to be at fault because non-cyclists are still producing twice the incidents despite having 8 times fewer potential targets for careless road users to collide with.
3.   From the product of 1&2 above, cyclists are four times less likely to be at fault overall.
4.   Cyclists are just half as likely to be at fault, because those who haven’t crashed are not relevant.
5.   None of the above.

Personally, I’m inclined to think it’s (3), because the probability of an accident must be the probability of finding a careless road user multiplied by the probability of them finding something to hit.

7

COVID-19 / Deaths vs Vaccination Rate

« on: 23/11/2021 15:20:45 »

This seems interesting. I'm assuming that a high proportion of African deaths are going unrecorded, and that African countries without the resources to collect death stats also have fewer resources to administer vaccines.

Vaccine temp.png (8.79 kB . 481x287 - viewed 1715 times)
https://ourworldindata.org/coronavirus

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

« on: 16/08/2021 18:15:51 »

.....if there are no pain receptors in the brain?

I've found this:

"The headaches are not caused directly by the tumour itself, as the brain has no pain receptors, but by a build-up of pressure on pain-sensitive blood vessels and nerves within the brain."

So what's a "pain-sensitive nerve within the brain" if it's not a pain receptor?

https://www.thebraintumourcharity.org/brain-tumour-signs-symptoms/adult-brain-tumour-symptoms/headaches/#:~:text=Headaches%20are%20one%20of%20the%20most%20common%20symptoms,pain-sensitive%20blood%20vessels%20and%20nerves%20within%20the%20brain.

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Physiology & Medicine / Anaesthetics - what's the difference?

« on: 23/07/2021 12:15:56 »

One anaesthetic: injected into the arm, count down 10 9 8 7.....gone.
Another: injection in the arm, remain awake for several minutes, then a mask on, inhale a solvent smelling gas for several more minutes, then gone.

What's the difference here, because according to the record they're both sevoflurane?

10

Just Chat! / The Gas Man Cometh

« on: 10/06/2021 18:00:08 »

There's a gas leak on the main road near here, they've only been trying to find it for the last 15 months.

They came out in March last year and stayed until June, then they were back July - September, then Nov/Dec, then January - March. By that time it looked like they'd finally fixed it, but I've just walked past this afternoon, and they're back again.

As far as I can tell, the nub of their problem is that the gas would appear to be leaking into the BT cable duct, and then by the time it's travelled for hundreds of yards up & down the duct, it's effectively disguised the location of the leak. They started poking sniffer probes down boreholes drilled in the road, then digging holes looking for it, then after a few months they seemed to be just speculatively replacing sections of pipe and waiting to see what happens.

They could have renewed the main along the whole street in all the time they've been there.

11

COVID-19 / Can we get herd immunity?

« on: 24/05/2021 13:25:27 »

So can the vaccine give us herd immunity if enough of the population have it, or will the virus continue to circulate anyway until a vaccine-resistant mutant emerges?

12

Physiology & Medicine / How much use is pulse oximetry?

« on: 26/03/2021 14:51:07 »

Since covid made pulse oximeters toy of the moment, the published advice seems to be:

>=95%: You're fine.
92% - 95%: ask your doctor for advice.
<92%: Call 999.

So from this, it would appear that the higher the oxygen saturation the better, IE there's no 'optimum', nor any homeostasis striving to achieve it.

Of the pulse oximeters on the consumer market, it would appear that the accuracy of most, if not all, is ±2%, but professional machines don't seem to quote any accuracy at all in the specifications. So if your SpO2 were 93.5% for example, your course of action upon checking it with a pulse oximeter would be either do nothing at all or call an ambulance, depending only on whether your instrument lays at the top or bottom of its tolerance range.

I have a pair of oximeters, both the same model, and the difference between them is 1.16%, based on an average of 80 pairs of readings, which is well within tolerance, but the instantaneous difference between any one pair of readings is ±6%, so you might reasonably wonder whether they're of any use at all.

My own SpO2 is all over the shop, varying from 88% to 98%, but usually 93%. If I make an effort to breathe more deeply it will rise to 95%, but if I continue it then falls back to 93%, which rather seems to suggest that there's some sort of homeostasis at work. If I breathe hard enough for long enough it makes me go dizzy, which also suggests that more isn't necessarily better.

Any thoughts?

13

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

« on: 16/03/2021 16:40:16 »

There's a company here wanting to take £3500 of your hard earned cash for a revolutionary new central heating boiler that uses a magnetron to heat the water. They're claiming 96% efficiency, a wonderful improvement on the mere 100% efficiency to be had from a much more expensive and complicated resistor immersed in the water.

https://www.theguardian.com/environment/2021/mar/16/first-microwave-powered-home-boiler-could-help-cut-emissions

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COVID-19 / Pfizer Side Effects, but what's the denominator?

« on: 16/02/2021 15:37:38 »

20,000 reports of 60,000 side effects, and 143 deaths, but no denominator.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/960150/COVID-19_mRNA_Pfizer_BioNTech_vaccine_analysis_print.pdf
Anyone know how many people have had a Pfizer vaccine?

15

Physiology & Medicine / CT Scanner Operation

« on: 12/02/2021 14:53:37 »

Is it possible to get a CT scan of the head with the patient table stationary, and not traversing through the scanner? How long does a head scan typically take.

16

Just Chat! / Questions pertaining to Notifications on TheNakedScientists.

« on: 04/01/2021 12:32:42 »

Questions pertaining to Notifications on TheNakedScientists

17

Technology / Anyone noticed the variability in Freeview audio?

« on: 22/12/2020 21:25:57 »

Has anyone else noticed how the bandwidth of Freeview audio keeps varying from one mic to another?

The recent Panorama documentary on the development of the vaccine would be a case in point, Fergal Walsh would be sat interviewing someone, and whilst the mic of the interviewee was crisp, sharp and sibilant, Walsh's mic was woolly, muffled and lacking in any HF response. By comparison, Walsh's commentary dubbed over the program was clear and sharp.

I'm not just talking about one program, it's a common problem. Two news presenters in a studio for example, one with a clear mic, the other muffled. Absurd, but it makes it look like half the microphones in the BBC are faulty whilst nobody has noticed.

18

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

« on: 22/05/2020 14:46:39 »

If you're not a key worker but have symptoms, you can apply for a test (https://www.nhs.uk/conditions/coronavirus-covid-19/testing-for-coronavirus/ask-for-a-test-to-check-if-you-have-coronavirus/), but if you're already symptomatic that's reason enough to isolate, the people we need to find are the asymptomatic ones. According to the stats on the news, 40% of those in care homes are positive, and 50% of those are asymptomatic. Among staff, 80% of those infected are asymptomatic.

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Physiology & Medicine / AF, Anticoagulation, Stroke, Haemorrhage

« on: 20/05/2020 18:20:01 »

AF risks blood clots, clots cause strokes, anticoagulants reduce the risk of clots but increase the risk of haemorrhage.

CHA2DS2-VASc estimates the risk of additional ischaemic strokes incurred by AF patients, and HASBLED estimates the increased risk of haemorrhagic strokes to patients taking anticoagulants. So, from the data in the NICE guidelines, it's possible to tabulate the net risk of stroke for each combination of Chads & Hasbled (below).


Nice Anticoag.JPG (53.64 kB . 682x407 - viewed 4024 times)

Both NICE and ESC guidelines seem inline with this:

NICE clinical guideline 180: Atrial fibrillation: the management of atrial fibrillation
"1.5.2 Consider anticoagulation for men with a CHA2DS2-VASc score of 1. Take the
bleeding risk into account.

1.5.3 Offer anticoagulation to people with a CHA2DS2-VASc score of 2 or above,
taking bleeding risk into account."

2016 ESC Guidelines for the management of atrial Fibrillation
"9.1.1 In general, patients without clinical stroke risk factors do not need
antithrombotic therapy"

However, the ESC guidelines then go on to say:
"9.1.3 A high bleeding risk score should generally not result in withholding OAC. Rather, bleeding risk factors should be identified and treatable factors corrected"

This seems contrary to me. If HASBLED has been calculated from patients whose treatable risks haven't been treated, what's the point of it, or alternatively, if it's been calculated from patients whose risks are being managed, what's the point of the advice in 9.1.3?

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COVID-19 / Latest Report From SAGE

« on: 12/05/2020 16:53:54 »

Sounds interesting.