Genady
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Joined
Posts posted by Genady
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15 minutes ago, CharonY said: You know, it struck me that the development of all these things just shows how tech is helping us to be even more disconnected from each other. I mean, one could have a system which where actual humans are checking on the elderly.
We have exactly such system where I live. Hospital nurses visit daily elderly living alone.
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8 minutes ago, KJW said: the connection is more subtle (rather than non-existent).
The only such connection I see is, if the ASA for triangles depends on the parallel axiom. I don't know if it does.
12 minutes ago, KJW said: The assumption in bold is the assumption that the parallel axiom is valid for a+b equal to two right angles.
It seems that "it follows" of Stillwell is misleading, and all he wants to demonstrate is why Euclid postulates the case of a+b being less than two right angles.
P.S. Nope, this understanding is also not right, because the next he says, "Thus Euclid’s axiom about non-parallel lines implies that parallel lines exist." How?
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2 minutes ago, KJW said: Without the validity of the parallel axiom for α + β less than two right angles, you could not make the assumption that the parallel axiom is valid for α + β equal to two right angles, and therefore would be unable to obtain the contradiction for α + β equal to two right angles.
Where is an assumption that the parallel axiom is valid for a+b equal two right angles made?
The only assumption made is that when a+b equal two right angles the lines meet, and this assumption leads to contradiction.
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2 minutes ago, KJW said: Yeah, I understand the point you're making, which is why I said your question was a good question, and why my reply was almost but not quite an answer to it. However, you are using the validity of the parallel axiom for α + β less than two right angles to formulate the case where α + β is equal to two right angles that leads to the contradiction.
IOW, you also think that this statement of the parallel axiom does not apply in this deduction of the two described lines not meeting.
There is no question of extending the parallel axiom statement to the case of straight angle.
The question is, why Stillwell says, "it follows"?
1 minute ago, studiot said: The deduction is:- If the sum of alpha and beta is not less than two right angles then l and m do not meet on the same side of the line as alpha and beta.
And this deduction does not use the axiom that if the sum of alpha and beta is less than two right angles then m and n meet. Or does it?
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1 minute ago, studiot said: The version of theaxiom you state is Euclid's own original.
Even in his time there were several altbernative versions (eg Proclus, Arisole) aand much debate about he subject.
What should be remembered is that Euclid built a coherent structure for Geometry and offered his version in line with the posiion in that buildup postulate 5 occurs.
All the properties of parallel lines (apart from not meeting) are deduced by triangles after this raher as in your 'deducion' paragraph.
What is your interest in his ?
Many books have been written about this subject.
Sorry, I don't understand your question and its relevance to my question.
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21 minutes ago, KJW said: This is actually a good question. The best answer I can come up with is that the parallel axiom is being proven not to extend to the case where α + β is equal to two right angles (that for the parallel axiom, α + β is strictly less than two right angles). Note that this is a proof by contradiction (reductio ad absurdum) where the parallel axiom is assumed to be true for α + β equal to two right angles, then shown to contradict the uniqueness of a line through any two points.
But it, supposedly, shows that not meeting of the lines in the case when sum of the angles is straight follows from the parallel axiom, which describes a case when sum of the angles is less that straight. How come?
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This movie caused some heated debates in my youth.
I was firmly in the sceptics' camp.
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12 minutes ago, tar said: The description matches the 2012 study titled "Helicospiral Growth in the Whip Black Coral Cirrhipathes sp. (Antipatharia, Antipathidae)" by Giorgio Bavestrello, Riccardo Cattaneo-Vietti, Carlo Cerrano, Antonella Cerrano, and Stefano Schiaparelli, published in the Biological Bulletin (Volume 222, Issue 1, pages 17-25).
Key details from the study:
It examines the coiling pattern in Cirrhipathes (whip black coral) colonies from Bunaken Marine Park, Indonesia.
The helix forms due to the irregular arrangement of polyps on the convex side of the stem, creating a "helicospiral" growth where whorls tilt predominantly to the right (clockwise when viewed from the base).
This chirality is attributed to innate cellular/molecular asymmetries, similar to how chiral molecules influence right-handed structures in calcium carbonate (e.g., in mollusks or coral analogs).
The study notes that colonies grow fast initially to escape the bottom, then extend into currents for plankton capture, but the right-handed bias is consistent across samples.
If this isn't the exact study you meant (or if it's a paraphrase from another source), provide more details for a refined search!
This study does not mention at all the sense of rotation. It does not relate to the topic in question, i.e., is irrelevant and does not help.
Other suggestions in
49 minutes ago, tar said: The "Wire Black Coral" you're referring to is likely Cirrhipathes sp. (commonly called whip or wire black coral), a species in the Antipatharia order. These are deep-water corals known for their long, thin, unbranched skeletons that often form spiraling or helical shapes, resembling coiled wire. They have a jet-black chitin skeleton covered in polyps, and they're more closely related to anemones than true stony corals.Why the Right-Handed Helix?From your observation (and similar reports from divers/scientists), Cirrhipathes indeed predominantly forms right-handed helices (counterclockwise spiral when viewed from above). This chirality (handedness) is not unique to this coral but common in biology (e.g., most seashells spiral right-handed). Based on research:
Biochemical Origin: Chirality in living structures often stems from molecular asymmetry. For example, L-amino acids (the dominant form in proteins) can induce right-handed spirals in growing structures like coral skeletons. A study on helicospiral growth in Cirrhipathes suggests the helix forms from the relationship between the growing stem and polyp placement intensity — whorls tilt right due to innate cellular chirality, similar to how chiral molecules in calcium carbonate (a coral analog) create right-handed toroids.
Adaptive Feature?: Possibly. The helix may enhance stability in currents (like a screw anchor) or optimize nutrient flow/water circulation around polyps. However, it's more likely a developmental byproduct of genetic/biochemical handedness rather than direct adaptation — left-handed forms might occur rarely but be less viable or unobserved. No widespread reports of left-handed Cirrhipathes, supporting your dozens of sightings.
General Causes: Biological chirality breaks symmetry via genes/proteins (e.g., in ciliates, global handedness sets cortical structures). In corals, it could tie to embryonic development or environmental cues, but molecular bias is key. No symmetry-breaking external force (like Earth's rotation) is needed for such small scales.
If you've seen dozens without a left-hander, it reinforces strong bias — perhaps report to marine biologists for confirmation (e.g., via ReefBuilders or a journal like Coral Reefs).
are not helpful as well.
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14 minutes ago, tar said: A study on helicospiral growth in Cirrhipathes suggests the helix forms from the relationship between the growing stem and polyp placement intensity — whorls tilt right due to innate cellular chirality, similar to how chiral molecules in calcium carbonate (a coral analog) create right-handed toroids.
Which study is this?
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30 minutes ago, Moon99 said: But what do these drugs do like how do drugs work that it has side effects.
Answers on the Internet: Explainer: how do drugs work?
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Using Grok as a tool.
in The Lounge
Yes, the galactic North Pole and our North Pole do not coincide, but this doesn't change the sense of rotation. Important fact is that the galactic North Pole lies in our northern hemisphere.
AFAIK, our galaxy rotates clockwise as viewed from the galactic North Pole.
This is what I remember from my astronomy class years ago.