Cumulative General Science/Technology Quiz

[peter grimes]

So Brennan got the answer several days ago!

 

[Perfection]

Yeah, dutchfire just didn't do his homework.

DO YOUR HOMEWORK BEFORE ASKING, PEEPS!

 

[Mise]

Moderators are different from control rods. Moderators slow down the neutrons so that they can participate in further fission reactions, since slower neutrons can't be absorbed by U-238, and will therefore go on to react with U-235. Control rods absorb excess neutrons, as Dutchfire described.

The name "moderator" makes it sound like they should be doing what the control rods are doing, though.

 

[Perfection]

Oh NEVER MIND then!

 

[dutchfire]

Moderators are different from control rods. Moderators slow down the neutrons so that they can participate in further fission reactions, since slower neutrons can't be absorbed by U-238, and will therefore go on to react with U-235. Control rods absorb excess neutrons, as Dutchfire described.

The name "moderator" makes it sound like they should be doing what the control rods are doing, though.

Yeah, dutchfire just didn't do his homework.

DO YOUR HOMEWORK BEFORE ASKING, PEEPS!

DO YOUR HOMEWORK BEFORE TELLING PEEPS TO DO THEIR HOMEWORK, PEEPS!

What Mise said is correct.

The moderator in a nuclear reactor is usually water, while the control rods are usually some sort of metal, alloy, compound or sometimes graphite.

 

[Perfection]

PEEPS STILL SHOULD DO THEY'S HOMEWORK BEFORE ASKING QUESTIONS!

It's just that you already did!

 

[dutchfire]

PEEPS STILL SHOULD DO THEY'S HOMEWORK BEFORE ASKING QUESTIONS!

It's just that you already did!

And I'm glad I did, as this was the first question at my physics exam

 

[peter grimes]

...so who's up then?

 

[Brighteye]

It's Dutchfire again, but if he doesn't post in the next day, it's open.

 

[dutchfire]

peter grimes had it right, so he can ask the next question if he wants.

 

[brennan]

I must be getting out of date, control rods (esp boron) is exactly what I was thinking of. I'm sure they were called moderator rods in my day.

 

[Perfection]

I was just following Brennan's lead.

 

[Sidhe]

72 hours is stupid, should be 48, or 24. If you aint going to log before 72 hours then presumably you'd have the courtesy to notify someone, unless you got eaten by friggin' sharks with laser beams.

Just my two cents. Catharsis should change the rules, they don't make sense for such a high turnover thread/ forum.

Still nm, I'm sure this only happens once in a blue moon right?

 

[Genocidicbunny]

The rules are what they are, so stop complaining about them. They're fine as is.

 

[peter grimes]

List 4 interesting properties of the number Phi.

 

[Mise]

Phi is the golden ratio, so it makes for very pretty rectangles and such. Greek architects used to use it for building stuff too I think. Not sure if that counts as "four" or "interesting"...

 

[Perfection]

phi - 1 =1 / phi

the ratio of cn/cn-1 for the fibonocci sequence converges to phi.

The ratio of segments in a pentagram is phi

The sides of a golden rectangle have a ratio of phi

 

[peter grimes]

Perfection got it - I didn't even know about the pentagon one. I assume that means that the ratio of diagonals to sides, right?

The one that always baffles me is how Phi relates both to quantum physics as well as prime numbers
Here's sort of an abstract - I can't find the original anymore.

 

[Perfection]

Perfection got it - I didn't even know about the pentagon one. I assume that means that the ratio of diagonals to sides, right?

http://en.wikipedia.org/wiki/Image:Pentagram-phi.svg

It's all the segments.

Perfy knows pentagons


Speaking of pentagons...

Regular Triangles, Squares, and Hexagons can all form grids (as shown below), why can't pentagons? (I'm looking for an informal mathematical proof).

 

[Brighteye]

The sum of the angles around where they join must be 360, but pentagons have internal angles of 108 degrees, which doesn't fit into 360.