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 2020-10-11, 07:31 #34 tuckerkao   Jan 2020 3×41 Posts Barack Obama has won more popular votes in 2008 than any of other U.S. presidential candidates before Nov 2020.
2020-10-11, 13:01   #35
LaurV
Romulan Interpreter

Jun 2011
Thailand

22·2,239 Posts

Quote:
 Originally Posted by wildrabbitt A triangle can be divided into two triangles whose area sums to the area of the original triangle. EDIT : not sure if the triangle has to be right angled or not.
Ha ha ha ha, this is precious! Any geometric figure can be divided in any amount of other figures, whose total area is the area of the original figure, but I am not sure if those figures must have one or more right angles...

Last fiddled with by LaurV on 2020-10-11 at 13:03

2020-10-11, 13:22   #36
xilman
Bamboozled!

"πΊππ·π·π­"
May 2003
Down not across

2×5,197 Posts

Quote:
 Originally Posted by Dr Sardonicus Yes, which places what you posted firmly in the realm of speculation, not fact. The least you could do is give a plausible means of surviving the prevailing conditions before the core collapse supernova commenced. I'm also not sure of the sequence of events when the supernova commences. Photons created by the reactions which create the neutrinos might be delayed by all the stuff in their way, while the neutrinos would go merrily zipping off into the ether. So, I'm not sure whether the blast of neutrinos might not hit you before the blast of EM.
OK. Orbit at a safe distance until you detect that the core collapse is about to occur. Dive in on a high-speed orbit in a spacecraft fitted with a refrigeration unit sufficient to keep you alive for the time it takes to reach 1 AU. A sufficiently thick layer of phase-change material (melting ice, for instance) will do the trick.

The neutrinos are only held up for a minute or so whereas the bulk of the photons take the best part of a day to get through the collapsing material. You are very likely to be dead before that happens.

Last fiddled with by xilman on 2020-10-11 at 13:25

2020-10-11, 13:52   #37
Dr Sardonicus

Feb 2017
Nowhere

74578 Posts

Quote:
 Originally Posted by wildrabbitt A triangle can be divided into two triangles whose area sums to the area of the original triangle. EDIT : not sure if the triangle has to be right angled or not.
A segment from any vertex to any point on the opposite side (other than its endpoints) does the trick for any triangle.

The Wallace-Bolyai-Gerwien Theorem says that two polygons (polygonal regions) are "congruent by dissection" if and only if they have the same area.

2020-10-11, 14:07   #38
Dr Sardonicus

Feb 2017
Nowhere

132×23 Posts

Quote:
 Originally Posted by xilman OK. Orbit at a safe distance until you detect that the core collapse is about to occur. Dive in on a high-speed orbit in a spacecraft fitted with a refrigeration unit sufficient to keep you alive for the time it takes to reach 1 AU. A sufficiently thick layer of phase-change material (melting ice, for instance) will do the trick. The neutrinos are only held up for a minute or so whereas the bulk of the photons take the best part of a day to get through the collapsing material. You are very likely to be dead before that happens.
So -- you're saying that if you survive the pre-supernova conditions at 1 AU, the slug of neutrinos from the supernova will kill you before the blast of EM arrives and completely obliterates your remains.

Haw, haw, I love it!

2020-10-11, 14:14   #39
xilman
Bamboozled!

"πΊππ·π·π­"
May 2003
Down not across

101000100110102 Posts

Quote:
 Originally Posted by Uncwilly Turkey has mainland territories in Europe and Asia. As does Kazakhstan. Egypt has territory in Africa and Asia. Panama is on both North America and South America. If it is in the area near North America it is a Hurricane. There have been hurricanes that were in the Atlantic and moved into the Pacific and vice versa.
France has territories in North America (St Pierre & MIquelon), South America, the Carribean and in the Indian Ocean.

None of these are mainland territories but they are internationally recognized as being parrt of France. Take a look at β¬ denominated banknotes for some evidence.

Spanish and Portuguese territories in the North Atlantic (which are politically part of Europe but not geographically so) have also been included.

2020-10-11, 14:22   #40
xilman
Bamboozled!

"πΊππ·π·π­"
May 2003
Down not across

2×5,197 Posts

Quote:
 Originally Posted by Dr Sardonicus So -- you're saying that if you survive the pre-supernova conditions at 1 AU, the slug of neutrinos from the supernova will kill you before the blast of EM arrives and completely obliterates your remains. Haw, haw, I love it!
That is exactly what I have been saying.

I am pleased that you have found it surprising.

Neutrinos are nasty little buggers in sufficient quantities.

You will be hit by a solar neutrino about once or twice a month on average. All the rest (about a quadrillion every second) will go straight through you.

The SN1987a event resulted in 20-30 detected neutrinos. If you multiply the mass of a human eyeball by the number of eyeballs around at the time by the neutrino reaction cros-section it turns out that there was a 50-50 chance of the Cerenkov radiation being visible.

2020-10-11, 16:31   #41
Dr Sardonicus

Feb 2017
Nowhere

132×23 Posts

Quote:
 Originally Posted by xilman I am pleased that you have found it surprising.
I was mildly surprised about what the slug of neutrinos would do. I was much more surprised/bemused at the idea of being at 1 AU from a star about to nova.

In 1987, the question of whether neutrinos were massive or traveled at the speed of light was unanswered. IIRC the arrival time of the detected neutrinos WRT the light helped put bounds on the possible mass.

Since then, of course, the question has been answered. There is clear evidence that neutrinos "change their stripes," between electron, muon, and tau neutrinos. Particles traveling at the speed of light can't do that. The result also solved the "solar neutrino problem," which was that only a third of the number of neutrinos predicted by theory were being detected.

 2020-10-11, 16:35 #42 Dr Sardonicus     Feb 2017 Nowhere 132×23 Posts There is a counterintuitive fact of probability called the "birthday paradox." If you assume that all birthdays are equally likely (they aren't, but close enough) and the people in a group are "randomly selected" with respect to birthday, and February 29 is excluded so there are 365 possible dates, then the probability of two people in the group having the same birthday is greater than 1/2 if the group has at least 23 people. I was teaching a class one time, and was on the topic of probability. There were 22 students in the class, so I had each of them write their birthday on a slip of paper. No two of the birthdays matched. But one of them matched my birthday! There is another curious fact, having to do with permutations. A permutation which does not map any element to itself is called a derangement. The number of derangements of a set of n elements is sometimes called "subfactorial n" or nΒ‘ and may be expressed as $n!\sum_{i=0}^n\frac{(-1)^{i}}{i!}$. The sum is well known to be a partial sum for the usual series for 1/e. Thus, for example, if a deck of cards is shuffled "randomly," the probability that none of the cards will be in its original position is extremely close to 1/e.
 2020-10-11, 17:48 #43 Uncwilly 6809 > 6502     """"""""""""""""""" Aug 2003 101Γ103 Posts 5·1,787 Posts A family had exactly 5 children, each born on the same day of the year in different years. This was thought to be the greatest coincidence (highest odds against). But a family with exactly 3 children each born on the same day of the year in different years beat those odds. Each was delivered (not induced) on Feb 29th.
2020-10-11, 22:46   #44

"Kieren"
Jul 2011
In My Own Galaxy!

2·5,059 Posts

Quote:
 Originally Posted by chalsall Helium is a non-renewable resource, and yet we still use it for party balloons.
I fume at that. Don't superconducting magnets have a more productive claim?
As I thought, helium is produced via distillation from natural gas.
https://en.wikipedia.org/wiki/Helium...d_distribution
Quote:
 For large-scale use, helium is extracted by fractional distillation from natural gas, which can contain as much as 7% helium.[132] Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and methane). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture.

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