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Physics, Astronomy & Cosmology / Re: Why isn't my salt water evaporating?

« on: 15/09/2023 09:09:02 »

May be hygroscopic salts in there - they absorb moisture from the atmosphere (which BC was alluding to).
https://en.wikipedia.org/wiki/Hygroscopy

In extreme cases, this becomes "deliquescence" - these compounds absorb water from the atmosphere, and dissolve in the extracted water.
https://en.wikipedia.org/wiki/Hygroscopy#Deliquescence

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Physics, Astronomy & Cosmology / Re: Could the James Webb telescope had saved NASA hundreds of millions?

« on: 29/08/2023 22:16:29 »

The James Webb Space Telescope cost $US10 billion. It was a gross budget blow-out!
- They considered canceling it several times, but then it became "too big to fail"

The JWST cannot take pictures of Pluto/Charon in anywhere near the same detail as an up-close fly-by.
- And it cannot take pictures of farther objects, either, like Arrakoth in the Kuiper Belt
- JWST is an infra-red telescope, and you need a much larger dish to get the same resolution as a visible-light telescope like Hubble. JWST has similar resolution to Hubble.
- Hubble was used in selecting Arrakoth as a target to visit beyond Pluto. Hubble can only see it as a faint dot of light, which moves against the background stars as Earth goes around its orbit.
- But New Horizons took high-resolution images of Arrakoth from up-close. Not possible with Hubble.

https://en.wikipedia.org/wiki/486958_Arrokoth

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Physics, Astronomy & Cosmology / Re: Why Is The Oooooooort Cloud Spherical ? ..and Not an Accretion Disc

« on: 08/08/2023 23:11:19 »

I expect it is because:
- The temperature is so low this far from the Sun, that most of the volatiles have condensed onto compact icy comets and asteroids. So there is effectively no wind resistance out there.
- The density of the icy bodies this far from the Sun is so low that they hardly ever collide with each other.
- The average size of the bodies is pretty low (eg Pluto-sized and smaller), so they don't interact strongly via gravity (we do see the occasional long-period comet)
- That means they don't exchange angular momentum, and so they stay on their original, random trajectories, forming a diffuse ball.

In contrast, the inner accretion disk (nearer the Sun) was full of hot gas, with asteroids frequently running into each other and exchanging angular momentum through collisions and (for the bigger objects) through gravitational interactions.
- As a result of gravitational interactions, many objects would have plunged into the Sun, or been thrown out of the Solar system altogether
- Eventually, after many interactions, the whole inner solar system would have settled down to the average angular momentum of the original cloud from which the inner solar system formed.
- This resulted in a planar arrangement of the planets with a common axis. This then minimised subsequent interactions, and is a fairly stable arrangement (if isolated from outside influences).

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Plant Sciences, Zoology & Evolution / Re: Has natural selection been nullified in humans ?

« on: 03/07/2023 10:46:26 »

Some Australian crows carry burning twigs from forest fires

In Australia, I have heard them called "fire eagles", rather than crows/corvids.
- The Wikipedia link describes it as a "black kite"
https://en.wikipedia.org/wiki/Fire_adaptations#Animal_use_of_fire

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COVID-19 / Re: Is it all over in Brazil?

« on: 27/06/2023 10:33:46 »

The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known.

You can make some guesstimates based on:
- R₀: The average number of other people who will be infected by one infected individual
- Vaccine Efficacy: The percentage of people who will be protected if they are given the vaccine. Call it E

The original Wuhan virus had R₀ ≈ 2.5, and RNA vaccine efficacy E ≈ 90%.
- The minimum number to be vaccinated = 1-E/R₀ ≈ 1-0.9/2.5 = 64% of the population
- That is why early predictions said that if most people had the vaccine, it would protect the population as a whole against the spread of the virus

Two years later: It is thought that some of the more recent COVID variants have R₀ ≈ 12.
- Against these variants, the original vaccine against Wuhan strain had efficacy E ≈ 40%.
- The minimum number to be vaccinated = 1-E/R₀ ≈ 1-0.4/12 = 97% of the population
- Even well-vaccinated countries have trouble meeting this high target for vaccination
- Throw in the fact that vaccine protection declines with time, so E reduces significantly 5 months after previous vaccination or exposure

Which is why there are now bivalent vaccines available, which provide a higher efficacy against the recent variants
- And people are encouraged to get a booster every 6 months
- And still wear a mask if there is an outbreak in your area.

The COVID emergency may be over, but COVID is not over.
- A significant difference between COVID and smallpox is that smallpox only infects humans
- COVID infects many mammal species, so there is an animal reservoir of the virus that will continue mutating, and potentially jumping back into the human population. That makes elimination practically impossible with our current technologies.

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General Science / Re: Horizontal Lightning Conductors

« on: 22/06/2023 23:05:48 »

Lightning consists of one or a few closely-spaced DC impulses. A Fourier analysis shows that many frequencies make up this DC impulse.

I have done lightning testing on telecommunications equipment with a test generator that could generate several waveforms that corresponded to various standards, with peak voltages around 10,000 Volts or so. As I recall, two of them were DC impulses like the graph shown by BC (with rapid rise and slower fall, but different time constants). A third had an AC component, which you might get if the surge were inductively/capacitively coupled from an adjacent wire; in this case you don't get such a strong DC component, the higher frequencies are enhanced compared to the lower frequencies, and you get some "ringing" from the inductive/capacitive resonance.

The most spectacular example of lightning testing was at a visit to a national lightning test facility, which could generate impulses over a million volts. Understandably, the test engineer checked everything over very carefully before he took his hands out of his pockets!

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General Science / Re: Horizontal Lightning Conductors

« on: 22/06/2023 09:47:52 »

old-fashioned heavy iron down-pipes from the gutters

"Skin effect" means that high-frequency components (like lightning impulses) only travel through a thin skin on the outside of the conductor.
- That is why lightning down-conductors are made of a braid of many fine wires (with a large surface area) instead of one big conductor.
- Iron has poor conductivity
- I expect the magnetic interaction with iron would also impair the ability to handle high-frequency components...
https://en.wikipedia.org/wiki/Skin_effect

Horizontal Lightning Conductors

There is another instance where you get horizontal lightning conduction, with Fulgurites on a beach.
- The lightning turns the sand into a glassy tube
- When the lightning reaches the more conductive water, it sometimes turns into a branching pattern at the level of the water table...
https://en.wikipedia.org/wiki/Fulgurite

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General Science / Re: How does ChatGPT work?

« on: 19/06/2023 09:36:51 »

I volunteer at a group providing computer skills for retirees, and today's topic was "AI".

The guy presenting on AI today asked ChatGPT and Bard to provide a description of AI. One of them even produced a lesson plan, with a time allocation for each topic!

One thing we discovered is that when a large number of people try to contact ChatGPT simultaneously from the same IP@, it gets suspicious, and starts asking for birthdates, email addresses and phone numbers (for 2-Factor Authentication).
- It obviously suspects an AI robot attack!

PS: Bard was a lot more forgiving - we ended up with half the group on ChatGPT, and half on Bard.

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Geology, Palaeontology & Archaeology / Re: What are Rocks & Sand?

« on: 06/06/2023 10:16:46 »

sand is Valuable, besides We got soo much of it,

Sand is quite valuable, forming a large component of our roads and reinforced concrete buildings.

But not any sand will do:
- There are huge deserts in the world, but apparently wind-blown sand is too "smooth", and does not form a strong bond
- There are huge oceans in the world, but the salt in marine sand causes "concrete cancer"
- So that basically leaves river sand, of which there is a very limited supply. Dredging river sand disrupts ecosystems and is unsightly for the people who live near the rivers.

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Geology, Palaeontology & Archaeology / Re: Is there enough lithium?

« on: 01/06/2023 10:16:30 »

Apparently, Lithium has no significant new sources in the whole universe...
- Lithium was produced in the early universe, making up 10^-9 of matter from the Big Bang
- When Lithium finds its way into the core of stars, it is rapidly fused into heavier elements (ie the amount is reducing)
- When stars fuse lighter elements, they "skip over" Lithium, so no new Lithium is being produced in stars

So, it is important to wisely use what Lithium we have (and recycle what we no longer use)...
- Lithium is great for mobile applications, due to its low density
- But for stationary power storage, other chemistries are becoming competitive, like flow batteries

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COVID-19 / Re: What's included in protein-based vaccines?

« on: 29/05/2023 11:11:36 »

Every virus has a different set of proteins, so vaccines for different viruses need to emulate different proteins in order to create an effective immune response.
- But a useful target is the protein by which a virus enters the human (or animal) cell. Gum that up with antibodies, and the virus can't infect a cell - these are called neutralising antibodies.

Ultimately, the mRNA vaccines are also protein vaccines - they expose a protein to the immune system, which then targets that protein with antibodies.
- The difference is that the mRNA sequence provides the template from which the target protein is manufactured by ribosomes.

If you are talking about COVID specifically:

Like other coronaviruses, SARS-CoV-2 has four structural proteins, known as the S (spike), E (envelope), M (membrane), and N (nucleocapsid) proteins; the N protein holds the RNA genome, and the S, E, and M proteins together create the viral envelope.

The only proteins exposed to the immune system are S, E & M.
- Most existing vaccines target the Spike (S) protein, to create neutralising antibodies.
- Someone who has been infected will also develop antibodies to E & M proteins. These won't neutralise the virus, but they will draw the attention of the immune system to an infection.

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Chemistry / Re: Silicon based Life?

« on: 18/05/2023 10:41:48 »

Why haven't We seen any Fossilised Evidence of of (Silicon based Life) as Yet?

How do you know? We walk on silicon-based rocks all the time! We don't have any criteria for recognising any that may once have been alive.

As BC mentions above, at room temperature, silicates are solid, but 100km or so beneath our feet, they become plastic, and might show characteristics like movement, metabolism, reproduction, etc.
- Volcanic action can bring up rock samples from these depths, but we would just see it as a solid volcanic rock.
       - What would limit life is the amount of available energy:
       - At the surface of the Earth, we have a solar energy input of about 700W/m²
       - Under the oceans, heat flow is around 0.1 W/m² (and only 0.6 W/m² through the crust), although there are big variations, such as at volcanoes and mid-oceanic ridges.
       - This 4 orders of magnitude difference in available energy suggests that any life processes down there might be extremely slow

Perhaps we could keep our eyes out for some form of information storage: a silicate-based genetic code in rocks, which would provide the instructions for reproducing a silicate-based life form?

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Physics, Astronomy & Cosmology / Re: BLC 1 Signal from Proxima Centauri?

« on: 17/05/2023 22:45:07 »

Radio Telescopes in Deep space?
Or on the ' Other ' side of the Moon?

If you put a radiotelescope on the other side of the Moon, there is no line-of-sight back to Earth, so no easy way to relay back results for detailed analysis.

In practise, various countries are putting relay satellites in orbit around the Moon, so they can relay messages from experiments on the other side of the Moon back to Earth (eg China's Yutu-2 rover). If it is simultaneously visible from Earth and the Far side of the Moon, then it is in view of a conceptual radiotelescope there.

But perhaps technology will come to our aid - various satellite operators are using optical communications to carry the increasing flood of data collected from space, including LEO broadband satellite constellations, NASA missions, and military satellites.

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Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 15/05/2023 09:56:05 »

in an expanding universe, light will be redshifted...a photon experiences time because it does have a property that can change

That is a fairly slow rate of change, not easily observable within a lab.

Another property that can change more rapidly with time is the amplitude of the electric and magnetic fields of a coherent light beam. In the absence of any measurable expansion of the local universe in the time that light takes to cross the lab, a light beam in a vacuum will keep the same amplitude, frequency and direction (ok - you need to ignore Earth's gravity too!). Since these are the main characteristics of light, the light itself is not changed by the passage of time.

Similarly, if you slow down light by putting it through glass or water, any light that managed to avoid absorption, scattering or reflection will be effectively identical to what went in, so they are unchanged by the "experience". Since there is no change, there is no experience of time (for the light itself).

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Question of the Week / QotW - 23.05.05 - How fast does evolution happen?

« on: 06/05/2023 03:43:41 »

On today's podcast, a listener asked how long does it take a mutation to spread through a population?
In summary, the answer was: Evolution can be very fast or very slow.

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Physics, Astronomy & Cosmology / Re: Forgotten vocabulary - a thing being pulled apart by tidal forces.

« on: 09/04/2023 10:00:27 »

A month ago, I had the privilege of seeing 47 Tucanae (in the Toucan constellation) from a dark-sky park - it's a spectacular globular cluster.
- It's about 7% of the distance to the small Magellenic Cloud, which means that tidal effects from the Milky Way will be around 3,000 times stronger.
- However, this very dense concentration of stars has (so far) resisted tidal disruption, perhaps aided by the presence of a central black hole (not yet firmly established).
- It is possible that this is the core of a small galaxy, and that all of the outer stars have already been stripped off.
- The Gaia satellite has been able to spot stellar streams from other torn-apart globular clusters, but to date none have been detected from 47 Tucanae

This video from ESA starts with the Small Magellanic Cloud, and then zooms in on 47 Tucanae

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Physics, Astronomy & Cosmology / Re: Forgotten vocabulary - a thing being pulled apart by tidal forces.

« on: 07/04/2023 11:25:29 »

Roche Limit.

There is a series of science fiction stories set on "Rocheworld" - a double planet which almost at the point of being torn apart, set against the very peculiar geography that might result...

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

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General Science / Re: [Asking ChatGPT] Why would LED ligths in cargo ship is a good idea?

« on: 28/03/2023 09:49:54 »

Today I heard a story about someone who became an editor at a major newspaper, just 2 years after graduation...
- She was editor of AI
- It turns out that the AI was writing the news stories, and her editors job was to detect and correct (or delete) the AI hallucinations...

The story is here: https://www.scientificamerican.com/podcast/episode/if-ai-starts-making-music-on-its-own-what-happens-to-musicians/#transcripts-body

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Physiology & Medicine / Re: Marburg?

« on: 27/03/2023 20:33:01 »

Monkeys are closely related to humans, so whatever infects monkeys can easily infect us (especially if humans eat the monkeys!).

Among mammals, bats have a very unusual immune system - perhaps tied to their very high metabolic rate (needed for flight).
- They harbour a lot of viruses (eg coronaviruses), but they don't seem to be severely affected.
- Bats are not closely related to humans, so these viruses are less likely to infect humans (or be transmitted amongst humans)
- But humans in rural areas of Asia do go into bat caves to collect guano as fertiliser (and often don't wear masks) - antibody testing have shown that many villagers  have antibodies against coronaviruses - even before COVID!
- Humans also eat bats

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Technology / Re: How did they make the first screw?

« on: 19/03/2023 19:52:09 »

You have just invented CNC machining.

North Korea discovered CNC machining - and wax lyrical about it (the chorus is recognizable by English-speakers, and starts at 24 seconds).
- A decade ago, this was one of their most popular songs...