## Search found 3683 matches

Tue Feb 16, 2016 8:30 am UTC
Forum: Mathematics
Topic: Infinite Inscribed Squares
Replies: 10
Views: 3162

### Re: Infinite Inscribed Squares

Let the circle be centered at the origin, with radius 1. We'll construct the sequence of squares along the positive X axis. Let (x, y) be the coordinates of the top right corner of a square, so for each square x² + y² = 1 by Pythagoras' theorem. Let s be the side of a square. The first square has x ...
Sun Feb 14, 2016 4:26 am UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 8965

### Re: LIGO Gravity Waves: Questions and Answers

Also: with detector arms in the X and y directions, a wave passing through in the z direction gives the largest signal - take a look at the GIFs on the "gravitational wave" wiki page. A wave travelling in the z direction that passes through the xy plane causes a ring of free particles in ...
Sat Feb 13, 2016 6:28 am UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 8965

### Re: LIGO Gravity Waves: Questions and Answers

@p1t1o: I Am Not a Real Physicist, so I might be totally wrong, but this is my take on how LIGO works. The LIGO interferometer has two "rulers" that are perpendicular to one another. Let's call the direction of one path X and the other path Y, with Z the direction perpendicular to both X &...
Sat Jan 30, 2016 6:04 am UTC
Forum: Mathematics
Topic: How many pencils and how many jars I have?
Replies: 7
Views: 3140

### Re: How many pencils and how many jars I have?

Pity you don't have two more jars: you could put a certain number of pencils into each jar, with no pencils left over.
Fri Jan 29, 2016 7:18 am UTC
Forum: Science
Topic: Mixing things with different melting points
Replies: 6
Views: 3906

### Re: Mixing things with different melting points

Mixtures tend to have broad melting points. Waxes are generally mixtures of compounds, and even if your wax sample is supposed to be a pure compound it's likely to consist of a mixture of isomers with slightly different melting points. A conventional way of dealing with this problem when assigning a...
Tue Jan 26, 2016 6:42 am UTC
Forum: Language/Linguistics
Topic: most words with fewest different letters
Replies: 16
Views: 8427

### Re: most words with fewest different letters

There are links to various free word lists at The National Puzzlers League, but I don't know if any of them have part of speech data.
Fri Jan 22, 2016 11:15 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

From SO Python Chat:
F4z wrote:hello, I keep getting confused with TypeError and ValueError, can someone kindly simplify for me what those two are?

bereal wrote:Ok, you go to bed and see another girl instead of your gf - that's ValueError. You see a raccoon - that's TypeError.
Mon Jan 18, 2016 5:58 am UTC
Replies: 34
Views: 7139

I have, of course, succumbed to the law of physics stating that anyone posting a grammatical correction will make a grammatical mistake themselves. On another forum I frequent we call it the Law of Recursive Pedantry. Wikipedia says it's Muphry's Law , along with a few other terms. Also, Any correc...
Wed Jan 13, 2016 10:34 am UTC
Forum: Science
Topic: Theory of black hole composition
Replies: 50
Views: 7383

### Re: Theory of black hole composition

FWIW, the Kugelblitz blog of David Horgan has lots of info about black holes made from photons. Note that you need a very high energy density to get photons to collapse gravitationally: the photon gas needs to have a temperature greater than the Planck temperature.
Sun Jan 03, 2016 5:13 am UTC
Forum: Mathematics
Topic: Recursive Circle Packing
Replies: 4
Views: 1595

### Re: Recursive Circle Packing

Descartes theorem is useful to find the radius and location of these circles.

Mon Dec 28, 2015 8:01 am UTC
Topic: 1621: "Fixion"
Replies: 19
Views: 6731

### Re: 1621: "Fixion"

OP Tipping wrote:Surely 'fixion would be more appropriate at Easter.

Crucially.
Tue Dec 22, 2015 6:13 am UTC
Forum: Science
Topic: Wendelstein 7-X
Replies: 43
Views: 8499

### Re: Wendelstein 7-X

There's a lot more to plasma control than mere containment. Plasmas are tricky things. A sample of gas can (generally) be adequately modeled by the ideal gas equation, PV = nRT, where P is pressure, V is volume, T is temperature, n is the number of moles of gas, and R is the ideal gas constant . Thi...
Tue Dec 15, 2015 6:10 am UTC
Forum: Science
Topic: Unbihexium density?
Replies: 11
Views: 3311

### Re: Unbihexium density?

I don't know where you can get tungsten cylinders, but Forge Solid do tungsten cubes at a reasonable price. They also sell magnesium alloy cubes of the same size as their tungsten cubes so you can do a tangible density comparison.
Sun Dec 13, 2015 8:15 am UTC
Forum: Science
Topic: Unbihexium density?
Replies: 11
Views: 3311

### Re: Unbihexium density?

It was formerly believed that element 126 was the centre of an island stability but according to Fricke et al more recent calculations indicate that the superactinides (Z=121 to 155) are extremely unstable; see Superheavy elements a prediction of their chemical and physical properties . That article...
Fri Dec 11, 2015 2:58 pm UTC
Forum: Science
Topic: Many, many worlds (no relation to QM)
Replies: 20
Views: 3687

### Re: Many, many worlds (no relation to QM)

FWIW, there are stable multi-body orbits that don't have a central primary: one of the best-known is the beautiful figure-8 orbit, first announced by Cris Moore in 1993: http://tuvalu.santafe.edu/~moore/figure8-3.loop.gif This system is stable to minor perturbations of position and velocity, but it'...
Sat Dec 05, 2015 1:21 am UTC
Topic: 1389: "Surface Area"
Replies: 125
Views: 36816

### Re: 1389: "Surface Area"

Do we not know the surface area of the solid mass at the center of Jupiter? Or is there still debate as to whether such a mass exists? (Sorry for necro -- reverse archive crawl.) We're still not sure what the center of Jupiter is like. It may have a rocky / metallic core: it's suspected that Jupite...
Thu Dec 03, 2015 12:09 pm UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

Understood about the Python stuff, by the way. I did only a tiny bit of perl about 8 years ago, before I had enough grounding in computer science in general to have a clue what I was doing, but the one thing I learned really well is perl regexes. I can read ridiculously long, obtuse regexes almost ...
Thu Dec 03, 2015 11:29 am UTC
Topic: 1611: "Baking Soda and Vinegar"
Replies: 43
Views: 10307

### Re: 1611: "Baking Soda and Vinegar"

FWIW, "dried vinegar" is sodium acetate, the salt produced when you react vinegar with sodium bicarbonate. Wikipedia says : "Vinegar is roughly 3–9% acetic acid by volume, making acetic acid the main component of vinegar apart from water". Pure acetic acid can be prepared in crys...
Tue Dec 01, 2015 8:18 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

@Wildcard The C Programming Language by K&R is a very decent course. Thanks; I actually hadn't realized that book is online for free. In that case I'll *definitely* be using it; I've heard it referenced all over the place. It's an excellent book, and even though I don't use C much these days I ...
Mon Nov 30, 2015 8:13 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

On a totally unrelated note, I have now learned bash, sed, and awk thoroughly and using them all the time. Nice. I hope you're quoting your bash parameter expansions (except when you do explicitly want word splitting etc). :) Just in case you don't know about it, here's a link to the Shellcheck she...
Mon Nov 30, 2015 7:13 am UTC
Forum: Science
Topic: convert bits to J/K -- and more entropy mischief
Replies: 14
Views: 3229

### Re: convert bits to J/K -- and more entropy mischief

I guess it's just a coincidence that it's within an order of magnitude of Avogadro's number: To clarify, it's not a coincidence at all: the boltzmann constant is defined as R/N A . So that 0.17 must be some combination of ln2 and the gas constant (in J/K/mol). Ah, of course. :oops: R = 8.3144598 jo...
Fri Nov 27, 2015 7:42 am UTC
Forum: Science
Topic: convert bits to J/K -- and more entropy mischief
Replies: 14
Views: 3229

### Re: convert bits to J/K -- and more entropy mischief

FWIW, Google Calculator can do that calculation: (1 joule / kelvin) / (ln(2) * boltzmann constant) 1.04494013 × 10 23 I guess it's just a coincidence that it's within an order of magnitude of Avogadro's number: ((1 joule / kelvin) / (ln(2) * boltzmann constant)) / (avogadros number) 0.173516388 whic...
Sat Nov 21, 2015 10:34 am UTC
Forum: Mathematics
Topic: Least numbers discarded when dealing cards
Replies: 30
Views: 6449

### Re: Least numbers discarded when dealing cards

Unfortunately, converting those digit sequences to card sequences is a little tedious, and (AFAICT) you have to generate the whole 20 digit sequence before you can decide that it's invalid. Actually, you don't have to generate the whole sequence before you can decide that it's invalid; I should kno...
Fri Nov 20, 2015 11:42 am UTC
Forum: Mathematics
Topic: Least numbers discarded when dealing cards
Replies: 30
Views: 6449

### Re: Least numbers discarded when dealing cards

Am I missing something or are people way overthinking this? Just put the numbers 1 through 52 in an array and shuffle it. Dealing cards is as simple as pulling out elements starting from the first index and working your way down. The problem is that the OP's TRNG (true random number generator) only...
Wed Nov 18, 2015 10:40 pm UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

Inside the electrons are quarks, [...] In the Standard Model, electrons, like all leptons , are fundamental particles in their own right, they aren't composed of quarks. Quarks (and gluons), and particles composed of quarks, feel the strong nuclear force, but leptons are oblivious to that force. Ho...
Sat Nov 14, 2015 4:18 pm UTC
Forum: Mathematics
Topic: Numbers are cool. Is there a proof/theorem for this?
Replies: 2
Views: 1431

### Re: Numbers are cool. Is there a proof/theorem for this?

This is related to the topic of perfect numbers and aliquot sequences . If we continue your sequence that starts with 62447, the next number after 15505 is 5807, which is prime, so it must be followed by 1. If we start at a perfect number, eg 6 or 28, then the next number is the same number we start...
Fri Nov 06, 2015 7:45 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2934
Views: 700378

### Re: RELATIVITY QUESTIONS! (and other common queries)

If quantum field theory in curved space could be reasoned about successfully with fractions, I'd have gotten my PhD in fourth grade. :D If you want to know what Hawking radiation looks like to an infalling observer rather than one at infinity, just do the Bogolyubov transformation for that intrepid...
Fri Nov 06, 2015 6:41 am UTC
Forum: News & Articles
Topic: In other news... (humorous news items)
Replies: 15136
Views: 2590160

### Re: In other news... (humorous news items, etc)

Here's a pertinent quote from Yes, Minister (Series One, Episode Six: The Right to Know): Sir Humphrey : Minister, I have something to say to you which you may not like to hear. Jim Hacker: Why should today be any different? Sir Humphrey: Minister, the traditional allocation of executive responsibil...
Wed Oct 28, 2015 10:31 am UTC
Forum: Mathematics
Topic: hard geometry homework problem
Replies: 7
Views: 2789

### Re: hard geometry homework problem

Yes, it is a tough one. And I was about to start writing some GeographicLib code before I noticed that this question is 5 years old. :) The OP mentioned Vincenty's formulae, which are commonly used for ellipsoid geodesic calculations. However, for the benefit of other readers who might find this thr...
Tue Oct 27, 2015 6:01 am UTC
Topic: 1595: "30 Days Hath September"
Replies: 132
Views: 27023

### Re: 1595: "30 Days Hath September"

This is the integer division thing I was talking about. I love the way it seems to make sense to begin with, with recognisable numbers like 52 and 365... but then you start getting crazy shit like 306 and 10. All division is integer division, operator % is modulus. Given integer y, m, d, calculate ...
Fri Oct 16, 2015 6:21 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

New to OOP - quick question. [...] What is the canonical way to implement a function that is identical in a bunch of unrelated classes? And does python implement this? Just a quick note on terminology. A function that's defined inside a class is called a method. As Flumble said, if these classes al...
Mon Oct 12, 2015 10:17 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9968
Views: 1950135

### Re: Coding: Fleeting Thoughts

What phlip said. It's definitely a much better strategy these days to learn Python 3. You should start with the official Python tutorial , since it's aimed at people who already know how to program. If you want to be able to read old code &/or use old libraries properly you will eventually need ...
Sat Oct 10, 2015 6:20 am UTC
Forum: Mathematics
Topic: Set of particular numbers
Replies: 14
Views: 2768

### Re: Set of particular numbers

Are those sequences related to any other problem in number theory? Probably not. As Conman said earlier, sequences like this don't usually reveal anything particularly deep about the numbers involved because the results depend on the base you're using to represent the numbers. There's nothing of pa...
Wed Oct 07, 2015 7:17 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2934
Views: 700378

### Re: RELATIVITY QUESTIONS! (and other common queries)

FWIW, Greg Egan created some nice diagrams, images, and a Java applet illustrating the neighbourhood of a pure GR Schwarzschild black hole to accompany his short story the Planck Dive . I guess it'd be nice to have graphics that somehow illustrated Hawking radiation, but it's not exactly easy to see...
Mon Oct 05, 2015 6:52 am UTC
Forum: Mathematics
Topic: Composite numbers and polynomials
Replies: 9
Views: 2719

### Re: Composite numbers and polynomials

If we can build a diophantine equation giving all the prime numbers even if it is not workable then why not trying to build functions or sequences or polynomials giving ONLY all the composite numbers. I started some ideas to find such way to solve this problem using some binary partition. A much si...
Fri Oct 02, 2015 8:35 am UTC
Forum: Fictional Science
Topic: Superpower gives control over water - can they fly?
Replies: 42
Views: 12526

### Re: Superpower gives control over water - can they fly?

Conservation of momentum is very native and natural to us, much moreso than conservation of energy. So in fiction, conservation of energy often goes out the window but conservation of momentum will be preserved to a degree, since things would look strange without it. I guess so. OTOH, it's because ...
Fri Oct 02, 2015 8:21 am UTC
Forum: Mathematics
Topic: Composite numbers and polynomials
Replies: 9
Views: 2719

### Re: Composite numbers and polynomials

I don't believe that it's possible to do what you want with a finite degree polynomial without overlapping: the structure of the primes is too rich for that. On a closely related note, there is the Diophantine Representation of the Set of Prime Numbers by James P. Jones, Daihachiro Sato, Hideo Wada ...
Thu Oct 01, 2015 7:01 am UTC
Forum: Science
Topic: Speed of waves in water
Replies: 8
Views: 5679

### Re: Speed of waves in water

I'm used to the concept that, say, sound waves and light waves travel at a constant speed in a constant medium, unaffected by either frequency or amplitude That's not true: wave speeds in a given medium generally are dependent on frequency / wavelength. One well-known manifestation of this is the d...
Fri Sep 18, 2015 10:50 am UTC
Forum: Coding
Replies: 62
Views: 10693

Your password page could have an embedded client-side password hasher, eg Xanthir's SHA-1 password hasher , (maybe with a slightly simplified, more user-friendly UI), with clear instructions on how to use it. And I guess you could include a brief explanation of why it's secure: it does its calculati...
Sat Sep 12, 2015 9:25 am UTC
Forum: Computer Science
Topic: A formula based approach to Arithmetic Coding
Replies: 4
Views: 7114

### Re: A formula based approach to Arithmetic Coding

siara wrote:By the way, how were you able to post URL in the reply? I couldn't.

The answer to that question can be found in the xkcd Forum Rules, along with other useful information.