1

Physics, Astronomy & Cosmology / Re: How did Andrei Sakharov acheive such a "clean" explosion?

« on: 03/10/2022 23:28:45 »

ALL the original particles were still there after the [fission] reaction!

I guess you could say that there is the same number of baryons (protons+neutrons) after the reaction as before.

However, a nuclear fission reaction releases an immediate burst of neutrons from the Uranium/Plutonium atoms during the fission chain reaction.
- Plus gamma rays, X-Rays and light (which were not physically present in the original lump of fissile material)
- If not absorbed by another atom, the neutrons will decay into protons, releasing an electron and neutrino (which were not physically present in the original bomb)
- The daughter nuclei are also radioactive and will emit a variety of particles as they decay over time

Overall, the number of electrons and neutrinos increases after the explosion (there is a net conversion of neutrons into protons + electrons + neutrinos)
- And a change in the mix of quarks, as neutrons (1 up + 2 down quarks) gets turned into protons (2 up+1 down quarks)

The loss of mass comes from the nuclear binding energy, much of it in the form of kinetic energy of the daughter products in the explosion, plus gamma rays as the baryons shuffle into a more stable form
- If you ignore the gamma rays, and slow down the daughter products to a halt, you will find that the mass of the products is less than the mass of the original Uranium nucleus.
- It is this "missing mass" that is converted to energy

2

Geek Speak / Re: Can you copy paste windows 7 programs folder into windows 8.1 programs folder

« on: 03/10/2022 23:08:35 »

i never had a hacker hack me

I have had a hacker hack me.
- He/she/it did not have to download my entire hard disk - they just encrypted all my files, and sent me a ransom demand for BitCoin.
- I did not pay it, so I lost all the files that I had not backed up yet
- I hope you don't leave your 6 TBytes of storage permanently attached to your computer, or they will all be encrypted, too!

3

Geek Speak / Re: Can you copy paste windows 7 programs folder into windows 8.1 programs folder

« on: 02/10/2022 21:11:22 »

According to Microsoft, they will no longer support Windows 7 & Windows 8.1 beyond 10th January 2023.
- That means no bug fixes, and no security updates
- It will be less than 6 months before some vulnerability appears and a successful hack becomes available.
https://www.microsoft.com/en-us/windows/end-of-support?r=1

You may not want Windows 10 or Windows 11, but the hackers definitely want your Windows 8.1!

4

General Science / Re: Looking for basic theory on mixing of gases

« on: 01/10/2022 22:09:12 »

Numerical simulations are probably ok for laminar flow, but become extremely difficult with turbulent flow.
- The Navier-Stokes equations describe the behaviour quite well
- In turbulent flow, the behaviour at large scales depends strongly on the behaviour at small scales, which makes it difficult to select a suitable granularity for the simulation in both time and space.
- In practise, aerodynamic simulation for aircraft design, weather and climate use experimentally-derived approximations for the behaviour at small scales. But it still needs to run on a supercomputer.
- There is a $1 million prize for finding a solution to some fundamental questions about the Navier-Stokes equations.
https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_existence_and_smoothness

Turbulence brings the two gases into intimate contact in a way that laminar flow does not.
- Since the two gases are closer together, Graham's Law operates over much shorter distances to achieve good mixing.

For practical use, I recommend a vortex mixer, and using empirical measurements of the mixing efficiency.
- For an exercise in learning how to do numerical simulation, stick with laminar flow and apply Graham's Law. You will need to take into account the near-parabolic distribution of flow speed across the pipe - fastest in the center, almost stationary on the walls.

https://en.wikipedia.org/wiki/Turbulence

5

General Science / Re: Hurricanes and Car Washes

« on: 30/09/2022 22:55:37 »

A hurricane, with heavy rain, would dilute any acid rain.

However, winds can blow chemical pollutants from one part of the country to another, relieving one part, and harming another.

One city that suffers from winds is Los Angeles, where onshore winds, the inland mountains and a temperature inversion frequently conspire to trap pollution over the city, causing quite severe smog. Perhaps that is why California leads the USA in terms of regulations for pollution reduction?

6

General Science / Re: How inexpensive is to identify an individual using a droplet of blood as ID?

« on: 27/09/2022 08:45:49 »

$300 is the cost of a genetic test, if done in bulk on pure samples of significant size.
- However, in forensic work, the perpetrator's DNA is often mixed with that of the victim, or spread thinly on surfaces already contaminated by other people. This requires careful extraction of multiple samples, and complicates the analysis considerably.
- The samples need to be collected, stored, processed and the results analysed in a rigorous and traceable manner, which will be cross-examined in court
- It gets a whole lot more complicated if you don't already have a DNA sample from the perpetrator in your database
- You could guess a forensic cost from thousands of dollars to ten times that amount.

However, unlike fingerprinting, if you have a relative of the perpetrator in the database, you can identify the link, and zero in on the identity of the perpetrator.

7

Question of the Week / Re: QotW - 22.09.19 - Do nuclear bombs cause global warming?

« on: 25/09/2022 22:56:39 »

Can the American continent survive a potential nuclear war if it is on the European continent?

NATO (North Atlantic Treaty Organisation) is a defence pact between Europe and North America.

If there is a nuclear war in Europe, the USA will be automatically drawn into it (and not just by the global circulation of the fallout).
- A trigger for the current Russian invasion of Ukraine was the threat that Ukraine might become a member of NATO, effectively allowing nuclear missiles on the Russian border.
- Perhaps a negotiated resolution may be to allow Ukraine to join the European Union (a trade pact), but not NATO (a military pact)? Effectively the Ukraine would become a buffer state.

https://en.wikipedia.org/wiki/NATO
Of course, the French think the rest of the world has NATO backwards, and calls it OTAN (Organisation du traité de l'Atlantique nord). But it has a nice symmetry to it...

8

General Science / Re: How inexpensive is to identify an individual using a droplet of blood as ID?

« on: 24/09/2022 12:07:24 »

The first case where DNA sequencing played a major role in identifying the killer was a serial killer called the "Golden State Killer".
- The police had DNA samples from the crime scenes. This is ennough to confirm a suspect is or is not the criminal.
- However, in this case, there was no suspect, and this man did not have his DNA on record, so the police couldn't find an exact match
- However, public DNA databases (Ancestry.com, 21andme etc) did have DNA checks on several third cousins - and also family trees, so the police could easily spot people with the right amount of relatedness
- They found a man with an exact match on their second guess.
- These DNA sites don't do a complete DNA sequence, but instead use short sections of DNA that have many variants in the community (some of them selected because they have been linked to risk for some disease, or because they are indicative of certain ancestor population groups)
- The more points of comparison, the more likely that you can find a match
https://en.wikipedia.org/wiki/Single-nucleotide_polymorphism
https://www.forbes.com/sites/jvchamary/2020/06/30/genetic-genealogy-golden-state-killer/?sh=49433be95a6d

9

Physics, Astronomy & Cosmology / Re: How much precession is observed in Parker Solar Probe's orbit?

« on: 15/09/2022 22:46:49 »

Parker Solar Probe's orbital period is similar to Mercury's

NASA planned the orbit of the Parker Probe so that it will periodically meet up with Venus.
- That means the aphelion is just outside the orbit of Venus (allowing 2 potential encounters)
- They ensure that the orbital period of the probe is a simple fraction of the orbital period of Venus (but this fraction changes on every encounter).
- This is so they can use a gravitational slingshot from Venus to reduce the perihelion of the Parker probe.
- It takes a huge delta-V to bring the orbit close to the Sun, and it is impractical to provide this much delta-V with chemical propellants

How does it affect its precession?

It would be interesting if NASA used Einstein's corrections to Newton's equations in planning the orbit of this space probe.
- For trips to Mercury, Venus, the Moon and farther out, Newton's equations are fine.
- Einstein's corrections apply on the order of centuries, while the planned lifetime of this space probe is just 7 years

https://en.wikipedia.org/wiki/Parker_Solar_Probe#Mission

10

Technology / Re: Shower Chairs

« on: 14/09/2022 00:38:49 »

Because if you aren't very stable on your feet at the best of times, adding a slippery floor is a recipe for disaster!
- Osteoporosis (weak bones) is common in older people, and in people who don't get enough exercise
- A broken hip is a common trigger for people to move from independent living into a nursing home
- And months of confinement to bed only causes weaker bones - leading to a downward spiral

On the other hand, being seated frees up your hands for showering, instead of supporting yourself (eg on a Zimmer frame).

11

Question of the Week / Re: QotW - 22.08.15 - How do drugs affect the balance of sodium in the body?

« on: 13/08/2022 11:17:36 »

Does (hyponatremia) have any danger to health?

Your body carefully regulates the levels of salts in your body, as a severe imbalance can cause death:
- Nerves use sodium and potassium ions to transmit nerve impulses. Mental confusion can result from an imbalance.
- Muscles use sodium and potassium ions to coordinate contraction. Cramps can result from an imbalance
- The salt levels affect osmotic pressure, which is important in all cells
- Brain swelling can result from an imbalance, producing possible brain damage
- Hyponatremia often affects amateur long-distance runners
See: https://en.wikipedia.org/wiki/Hyponatremia

The "ideal" level of salt inside our cells is quite different from the levels outside our cells (eg in the blood & lymphatic fluid).
- It is much higher than in fresh water,
- and much lower osmotic pressure than in the sea today (except for sponges & jellyfish).
- Some have suggested that the level of salt is indicative of salt levels in the sea when the first cells were formed.
- Marine creatures have to do work to keep the salt levels at the correct level, despite higher salt concentrations in the surrounding sea water.
- Freshwater creatures have to do work to keep the salt levels at the correct level, despite lower salt concentrations in the surrounding sea water.
See: https://biology.stackexchange.com/questions/88338/does-animal-blood-esp-human-really-have-similar-salinity-as-ocean-water-and

12

Plant Sciences, Zoology & Evolution / Re: Evolutionary DNA Leaps in Chromosome counts?

« on: 06/08/2022 01:42:49 »

Chromosomes can merge (reducing the count of chromosomes) or split (increasing the number of chromosomes).
- Recent research has found that use of CRISPR can chop up a chromosome, leaving a "spare" bit floating around in a cell nucleus
- Neither of these processes need be immediately fatal to a cell, since you still have the same number of genes
- The problem comes when the cell divides - does each "daughter" cell still have a full set of genes?
- And in the next generation of organism - do they still have a full set of genes?

The centromere is a structure in the center of each chromosome that plays a vital role in duplicating DNA into each daughter cell.
- A split-off portion of a chromosome may lack a centromere, inhibiting gene replication (or sometimes, a new centromere may appear)
- Two joined chromosomes may have two centromeres, which leads to chromosome breakage
- So most cases of chromosome splitting or joining are bad for the individual organism (often leading to cancer) and the descendents (who will suffer high rates of genetic disease and infertility with the parent species)
- But in rare cases, a descendent will receive two copies of the same mutation, allowing speciation
- Gene sequencing can identify cases where chromosomes have split or joined, since biologists can compare which genes occur on which chromosome.
See: https://en.wikipedia.org/wiki/Centromere

The leap from 46 or 44 Chromosomes to a working group of 48 chromosomes in the new species to be Gorillas

The human genome appears to be the result of the fusion of two chromosomes that remained separate in other primates (ie humans went from 48 to 46, while gorillas & chimpanzees remained at 48).
- So "progress" (new species) do not always come from splitting chromosomes (fission).
- New species can come from fusion, too.
https://www.mun.ca/biology/scarr/Human_Ape_chromosomes.htm

13

Physics, Astronomy & Cosmology / Re: What images do you most want to see from JWST?

« on: 04/08/2022 22:54:04 »

I would like to see stars circling the supermassive black hole at the center of our galaxy.
- At infra-red wavelengths, it should be possible to see more stars than we can see with ground-based telescopes
- and see how active the accretion disk is now
- By watching nearby stars move over a period of years, we should be able to predict when the accretion disk might fire up again.

14

Physics, Astronomy & Cosmology / Re: How many levels of orbit can a planetary system sustain?

« on: 31/07/2022 22:08:05 »

Could we have something orbit the moon that is 1/(1.2x10^2) the mass of the moon?

The Moon/Earth system is very "similar" in size: The Moon is 1/80 the mass of the Earth. Some have called it a "twin planet"
- Probably due to the method of formation: The current popular theory is a Mars-sized body smashing into the Earth.
- But other ratios in our Solar system are more extreme:
- Mars has the tiny Phobos & Deimos
- Jupiter & Saturn have significant sized moons, but the planet is huge.

When we come to smaller objects:
- Pluto & Charon are fairly similar in size
- There are a number of double asteroids
- Some comets look like they were originally two objects which stuck together, with descriptions like "duck" and "snowman"

15

Cells, Microbes & Viruses / Re: 'When' would you use nucleotides to construct phylogenetic trees?

« on: 30/07/2022 02:01:06 »

You might use protein amino-acid sequences when:
- Temperatures are so high that fossil DNA has been corrupted beyond our ability to read, but there is some intact protein available.
- When you are looking for functional changes in a protein, rather than non-functional genetic changes in the protein.
- But untangling and reading the sequence of a protein is not easy, and different techniques need to be developed for every different protein

In most cases, if you can recover intact DNA, you would use it, because:
- You can read the sequence of every protein in the same way, without having to develop a new technique for every protein
- You can read changes in "non-protein-coding" DNA, which often changes more rapidly than protein-coding segments, allowing the researcher to chart even very close family relationships
- Techniques for reading DNA have accelerated exponentially over the past few decades, making it the cheapest and fastest method available
- COVID-19 has resulted in the deployment of far more PCR machines and DNA sequencers than ever before...
- If you can't read nuclear DNA, mitochondrial DNA will also give some clues (there are more copies of mitochondrial DNA in each cell than nuclear DNA)

16

New Theories / Re: What makes Riemann's Hypothesis Hard to Prove?

« on: 23/07/2022 23:53:27 »

the thing about Mathematics:   It often looks easy when you know how to do it

I have heard that the mathematician Gauss had a reputation for working on a mathematical problem until he solved it. And then, knowing it was true, he looked for the most elegant way of showing that it was true - but in a way that made it difficult for other mathematicians to use the learnings he had gained in discovering the result.
https://mathworld.wolfram.com/NonconstructiveProof.html

17

Physics, Astronomy & Cosmology / Re: Star distance appearences

« on: 20/07/2022 00:26:16 »

It is a well known fact that stars that we see don't exist anymore

It is a well known expectation that most of the stars we see with our eyes do still exist.
- There are a few exceptions, such as a few stars that are thought to be nearing the end of their lives, and displaying some instability. They are very bright, so we see them from far away, and it is possible that they have already gone supernova.
- But most of the stars we can see have life expectancies far in excess of the light-travel time.

18

Physics, Astronomy & Cosmology / Re: Star distance appearences

« on: 13/07/2022 02:27:00 »

You have to admit - the constellations do not look much like their names, at first glance.

I heard that some researchers had extrapolated stellar proper motions backward in time to see what the constellations would have looked like thousands of years ago. They came up with some date that they thought the familiar Ancient Greek constellations looked "most like" their name. From this they deduced a date when these constellations may have been originally named.
- I've not heard of the same thing being done for Australian Aboriginal constellations, which are apparently more about galactic dust clouds, and it would be much harder to measure a proper motion (compared to an individual star)..

Of course there is another explanation that I heard, about some Ancient Greek astronomers spending the night outside, with a very large amphora of ouzo...

19

New Theories / Re: What makes Riemann's Hypothesis Hard to Prove?

« on: 03/07/2022 10:45:45 »

some problems are impossible to solve- That's the incompleteness theorem

The Incompleteness Theorem applies within a specific domain of mathematics - it may be impossible to prove some true statements within the axioms of that system.

However, some mathematical breakthroughs occur when applying results from a quite different domain of mathematics.
- Effectively, this extends the original set of axioms with an additional set of axioms over a different domain
- There may be additional true statements within the new, extended set of axioms that are unproveable within that extended set of axioms.

20

General Science / Re: How much of me is original?

« on: 29/06/2022 22:53:11 »

Some cells are not replaced during your lifetime. This applies to the lens of your eye, and brain cells.
- Most parts of the cell are generated from instructions in the DNA, using new raw materials from your diet
- But if the cell does not divide after birth (eg brain), it can continue to use the same DNA with which you were born
- Some parts of the brain do generate new cells (eg hippocampus), but this does not apply to most of the brain
- There will be spot repairs to DNA when it is damaged by natural radioactivity or metabolic stress, and these repairs would be made from "new" atoms in your diet.

I understand that some of these DNA ages were determined by measuring the radioactive content of DNA from different tissues. The isotopic mix in the diet changed noticeably in the years that atmospheric nuclear testing was underway.
https://www.sciencefocus.com/the-human-body/what-cells-in-the-human-body-live-the-longest/