41

Physics, Astronomy & Cosmology / Re: Star distance appearences

« on: 20/07/2022 22:34:55 »

a few stars that are thought to be nearing the end of their lives

Here is a "Top 10" list of stars thought to be ready to "pop their top", along with a short bio of each...
For many of them, light takes over 1,000 years to reach us,
https://naturenoon.com/next-star-supernova/

Here is a more technical list (with a lot less description):
https://en.wikipedia.org/wiki/List_of_supernova_candidates

Astronomers expect 1 supernova in our galaxy about every 50 years, but historical records suggest that we only can see a naked-eye supernova about every 400 years (theories for the discrepancy vary...).
Overall, out of the roughly 7,000 individual stars visible in the night sky, probably all of them will still be visible next year.

42

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.

43

Physiology & Medicine / Re: The crucial ingredients of CBD:

« on: 19/07/2022 10:23:23 »

You can click on the user's name, which will take you to their profile page.
Select Actions > Send Personal Message

If they are banned, you will get a message like "User 'XYZ can not receive personal messages."

Unfortunately, you have to put yourself out there to see if they are banned

44

Physiology & Medicine / Re: How often do multiple fertilization's result in only one birth

« on: 19/07/2022 09:34:56 »

As techniques for detecting pregnancy/fertilization get more sensitive, the fraction of fertilizations that does not go to full term keeps increasing. Recent figures I heard put it at around 75% (and that does not include the scenario mentioned by SeanB).

45

Plant Sciences, Zoology & Evolution / Re: Why doesn't evolution revert when environments change back?

« on: 18/07/2022 23:12:17 »

The longest experiment on cellular evolution has now passed 70,000 generations of E.Coli.
- One result that made news was the "evolution" of a gene that could metabolize citrate in an oxygenated environment.
- In fact, E.Coli have all the cellular machinery to metabolize citrate in both aerobic & anaerobic environments, but it is normally turned off if there is oxygen but no glucose. What occurred was a series of (probably 3) changes in gene regulation which allowed one population of E.Coli to metabolize the abundant citrate in their growth medium. The other 11 populations have not developed a set of mutations that allow this capability.

There are suggestions that there have been mutations in unused parts of the genome, that disabled those genes. So if these E.Coli were returned to a more natural environment, it is unlikely that they would fully regain the lost functions (barring horizontal gene transfer..).

So the "1-way traffic" of genetic evolution is a function of entropy interacting with natural selection.
https://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment#Evolution_of_aerobic_citrate_usage_in_one_population

There is a similar regulatory mutation in humans - mammal babies have the ability to digest lactose, an ability which is usually lost after weaning. However, independent changes in gene regulation in several human populations enable lactose metabolism even in adult humans. It is thought that these regulatory changes were beneficial after the development of agriculture, when a ready supply of milk from cows and goats became available.
https://en.wikipedia.org/wiki/Lactase_persistence

46

Just Chat! / Re: Should a film from 1929 still be copyrighted?

« on: 17/07/2022 22:21:04 »

There was an extension to the copyright laws in the USA, enacted just before the copyright on Mickey Mouse would have expired. A similar law was passed in Europe.
- So I am afraid that the copyright owners want to keep milking that cash cow forever...

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

47

Plant Sciences, Zoology & Evolution / Re: Is ant behaviour instinctive?

« on: 15/07/2022 00:51:47 »

Ants may have pre-programmed behaviors, but they are flexible to a certain extent:
- The mix of behaviors can be controlled by the queen, using pheromones
- Some learning is possible, such as rapidly finding new food sources (also assisted by pheromones)

48

Plant Sciences, Zoology & Evolution / Re: Why Are There No Freshwater Cephalopods?

« on: 15/07/2022 00:49:00 »

sodium pump is a very basic structure every living being could develop with time

But you can lose a functioning gene much more rapidly than you can regain a lost gene.

49

Just Chat! / Re: Are the concept of heatwavwes relative

« on: 15/07/2022 00:42:53 »

I once spent a few days in the United Arab Emirates - it was extremely hot, and extremely humid, so washing did not dry well.

Reverse-cycle air-conditioners are pretty new, but passive (convective) building air conditioners have been around for quite a while.
- An activity pattern of resting in the shade in the middle of the day (like a siesta) would certainly help...

If you don't need light/windows: I recently visited these "magnetic" termite mounds in Litchfield National Park (Australia's Northern Territory), which apparently achieve quite good thermal regulation by minimizing sun exposure at midday, while increasing it at dawn and sunset.

Magnetic_Termite_Mounds_Litchfield_NP_small.JPG (58.64 kB . 591x443 - viewed 663 times)

50

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...

51

Physiology & Medicine / Re: How do testosterone levels affect runners?

« on: 13/07/2022 02:17:20 »

RadioLab do their usual great story-telling on this topic (47 minutes). As I recall, from a few months ago:
- They bring in offbeat topics like some women have a trace of testes-like tissue that produces testosterone.
- After a court case, the Olympics athletics committee analyzed the data, comparing testosterone levels to actual performance, and found that higher testosterone helped in certain events, but not others, so they introduced a testosterone test for certain events.
https://radiolab.org/episodes/dutee

52

Question of the Week / Re: QotW - 22.07.18 - Can pet faeces make good fertiliser?

« on: 11/07/2022 23:43:48 »

Bird poop (guano) has been used as a fertilizer for many years, as has cave deposits of bat feces.
https://en.wikipedia.org/wiki/Guano

53

General Science / Re: Can a white LED be powered by the same size of it collecting radiation energy?

« on: 11/07/2022 11:09:43 »

LEDs wired in parallel arrays. There are PBC tracks connecting them.

I understand that there are electrical tracks between the LEDs.
But an illuminated LED producing slightly less than the bandgap voltage at its terminals will have trouble applying a voltage slightly greater than the same bandgap voltage to another LED through said conductive tracks.

54

Physics, Astronomy & Cosmology / Re: Has the distance between the sun & earth changed?

« on: 11/07/2022 11:04:44 »

the delta of the suns field across the Earth, due to the inverse square law

A delta on an inverse square law for gravitation gives you an inverse cube law for tidal effects.

55

General Science / Re: Can a white LED be powered by the same size of it collecting radiation energy?

« on: 11/07/2022 01:34:58 »

The others also seem to light (dimly)

The yellow phosphor powder would be quite good at scattering the yellow and violet light, providing an optical path between illuminated and non-illuminated pixels.
You can test this hypothesis by looking at the spectrum from the other pixels.
- If there is violet present, it is scattered light from your laser
- If there is yellow light present, it is probably fluorescence from scattered violet light and/or scattered yellow light
- It is only if you see blue light from the other pixels that you know there is enough electrical energy from one blue diode to light up other blue diodes.

I find a significant electrical path between illuminated and non-illuminated pixels unlikely:
- Any excess optical energy above the bandgap is lost as heat (eg violet/UV photons striking a blue LED)
- Any voltage less than the bandgap will not produce significant light from the LED (current flow/LED output is an exponential function of voltage above the bandgap)
- There are resistances in the circuit inherent in the semiconductor and wiring, and also load-sharing resistors to even-up power distribution between the LEDs. These will cause a voltage drop between the laser-illuminated LED and any electrically-illuminated LEDs.
- It is best to drive LEDs with a voltage above the bandgap voltage, rather than one slightly below the bandgap voltage.

56

New Theories / Re: Why Evolution Is Wrong In Biology And What is Right?

« on: 09/07/2022 23:29:33 »

it  has been found that no solvent, other than water, is able to pack protein properly

That is what you would expect for water-based life.

If we imagine some other form of life, based on (say) ammonia, I expect that no solvent, other than ammonia, would be able to pack their proteins properly.

The current approach places the DNA at the top of the food chain

In a sense, the cell is DNA's way of reproducing itself. This is the concept behind "The Selfish Gene".

There are various views about which came first: Data storage (DNA or RNA), structure (proteins), process (enzymes) or energy/metabolism.
- To some extent, they are all required for life as we know it
- But the origins are now lost to the sands of time.
- Perhaps we might discover more on Europa....

57

Just Chat! / Re: What where the sins of Boris Johnson?

« on: 09/07/2022 08:29:13 »

Now Trump's "mini-me" in the UK has also exited the stage.

Will he stage a come-back?

58

Question of the Week / Re: QotW - 22.07.11 - How dangerous is an explosion on the moon?

« on: 09/07/2022 08:26:55 »

For explosions of the more nuclear type, the Earth's atmosphere attenuates the X-Ray, Gamma Ray and neutron radiation more than the Moon's vacuum.

59

General Science / Re: Is there any quick Probabilities tutorial?

« on: 09/07/2022 04:34:31 »

Khan Academy have courses for all levels of skill. You could start here, and pick an introductory course:
https://www.khanacademy.org/math/probability

60

Chemistry / Re: What things can block x-ray imaging at airport customs?

« on: 09/07/2022 04:30:28 »

On a recent flight from Sydney, I saw that the airport scanners were now taking 3D images of the bags.
- The security staff had touch screens, and could reorient the image of the bag in any axis, allowing them to look "behind" obstructions.
- Unfortunately, the security staff were all wearing black gloves that did not activate the touch screens, so they had to remove one glove to look at the image, and put the gloves back on to look inside the bags
- I think the security staff should use those gloves with a fingertip coating that allows them to activate touch-screens.