2,865 reputation
1119
bio website vyznev.net
location Helsinki, Finland
age
visits member for 2 years, 9 months
seen yesterday

I like programming in Perl and C. I know Java and PHP too (I'm a MediaWiki developer), but I can't really say I like them. I keep meaning to learn Python some day, but never seem to get around to it.

I'm working on a Ph.D. in biomathematics. I also like programming puzzles and cryptography.

Please consider any (original) code I post to Stack Overflow (and other Stack Exchange sites) to be released under CC-Zero unless stated otherwise. You may do whatever you want with it and don't have to credit me in any way, although of course that would be nice.


Apr
20
comment Birds sitting on electric wires: potential difference between their feet
Having the bird spread its legs will (very slightly) increase both the current and the voltage through the bird (as one would intuitively expect), not decrease them: increasing $R_{wire}$ increases both $I_{bird} = I_{wire} \dfrac{R_{wire}}{R_{bird}}$ and $V_{bird} = V_{wire}$.
Apr
16
comment Does the mass of a star change as it collapses into a black hole?
@trysis: On the surface. And no, it doesn't account for the presence of the atmosphere, so it's not actually sufficient to escape the Earth's gravity if you're starting from the surface. (In fact, an object moving at 11.2 km/s or faster near the Earth's surface would most likely shortly turn into a ball of incandescent gas due to aerodynamic heating. To actually get into space from the Earth's surface, you need to start relatively slowly until you've cleared most of the atmosphere.)
Mar
29
comment Where does a string tighten when you pull it?
The behavior you describe is fairly typical if the string is lying on the ground, so that there's significant static friction resisting its movement. If the string is in free-fall, or, say, floating on/in water, things can be very different.
Mar
9
comment If I take a bottle of air into space, and open it, where does it go?
@XièJìléi: That just means you need a stronger balloon.
Mar
7
comment How does a half-life work?
Dammit, accepted. And just when I was this close to getting a Populist badge... ;-)
Feb
18
comment Does space curvature automatically imply extra dimensions?
@SantiBailors: Maybe this math.SE thread might help a little.
Feb
12
comment Is there a delay in the effect of gravitational force?
Just blow up the large object into two pieces, with enough energy to send them off (orthogonally to the line between the original objects) at a good fraction of $c$. (I believe the technical term is "rapid change in the quadrupole moment," but for popular science, "blowing up" will do.) It's not quite magic teleportation, but it's a pretty fair approximation.
Feb
8
comment What justifies dimensional analysis?
+1 for "consider the units to be variables."
Jan
19
comment Very strange shadow phenomenon
I don't think this is the full answer. The thing is, convolution (including blurring) and multiplication don't commute, so you'll get different results if you merge the layers before you blur them (which is closer to the real situation, assuming the book and elbow are at approximately the same distance from the wall). And indeed, doing it "correctly" should generally make the "bridge" region between the shapes darker than in your example.
Dec
16
comment How to measure resistance of a piece of wire?
@BrandonEnright: So use insulated wire?
Dec
1
comment Rotation of a slipping ladder
@ja72: Perhaps we're coming from different viewpoints here. I agree that the DoF reduction trick is neat here (and gave you a +1 for it), but coming from a numerics background, for general use I'd rather prefer a representation of motion that a) did not change in the absence of external forces, b) worked for all rotation rates, including zero, and c) was easy to (approximately) integrate over time. Translation + rotation around the CoM fits those criteria.
Dec
1
comment Rotation of a slipping ladder
@ja72: Only if you insist on describing the (instantaneous) motion as a pure rotation, rather than as a rotation plus a translation. Admittedly, that's what the OP seems to be asking for (since otherwise their question doesn't make much sense), but in general it doesn't seem to me like a very useful way to model rigid body dynamics.
Nov
29
comment Is there a way for an astronaut to rotate?
@EmilioPisanty: Yeah, but it's about as close an approximation as you can get without actually going into space. In practice, those chairs tend to have pretty low friction (at least if well maintained), so unless you do the exercise at a snail's pace, it can be mostly neglected. (As a double check, you can try holding the object at a constant distance, but moving it left and right at different speeds. If you don't observe any significant net rotation, that means the effect of friction was negligible.)
Sep
16
comment What is vacuum to DC flow?
Does a vacuum tube still count as "common circuitry"? Because, you know...
Sep
13
comment What is the difference between the Balmer series of hydrogen and deuterium?
A minor nitpick on an otherwise excellent answer: while high concentrations of heavy water do indeed inhibit eukaryotic cell division, at least some bacteria and other prokaryotes will grow just fine even in 100% heavy water. That's how perdeuterated biochemicals are produced.
Sep
2
comment Why does blowing on a candle put it out but sucking doesn't?
Also related: What happens, if a rocket is filled with a vacuum instead of high pressured air?
Aug
30
comment Why is a hard sphere gas correlated?
@MichaelBrown: No, of course I don't mind. My answer is really just an extension of gatsu's, anyway.
Aug
29
comment Why is a hard sphere gas correlated?
@MichaelBrown: I guess the point it that if the particles are less than two diameters apart, then the closer they are the smaller the gap between them is, and so the more room there is for other particles. Basically, looking at the possible locations of the centers of each particle, each of them excludes other particles from a sphere of radius $a$ around it. But if you bring two particles closer than $2a$ apart, then their exclusion radii overlap, leaving more room for other particles elsewhere.
Aug
28
comment Why do chimneys have these spiral “wings”?
@Kaz: Yes, it's the same effect.
Aug
28
comment Why do chimneys have these spiral “wings”?
@AlbeyAmakiir: To be honest, I don't know, but I'd guess they might be of stiffer construction, and thus less vulnerable to being damaged by wind-induced oscillations. Really big smokestacks are often built out of reinforced concrete, which doesn't flex much at all; smaller ones are often just thin-walled steel tubes, which do. Or maybe the engineers who designed them just used different safety margins.