## Search found 20 matches

Thu May 06, 2010 6:06 pm UTC
Forum: Science
Topic: mean free path of electrons in air?
Replies: 4
Views: 3155

### Re: mean free path of electrons in air?

that looks alot more legit
approximating the e- <-> air crosssection by the nitrogen atom radius seems crude but was basically just what i was looking for .

gonna find one of those spare turbo-pumps tomorrow and see how far we can get that vacuum .

thanks alot!
Thu May 06, 2010 2:41 pm UTC
Forum: Science
Topic: mean free path of electrons in air?
Replies: 4
Views: 3155

### Re: mean free path of electrons in air?

sorry, but i'll need something at least a BIT more accurate. i found the value of 520nm somewhere, also 0,1µm (which is 100nm). that should be roughly right, but without any citation i can't just accept that ;-). any further clues? i know there is a really simple heuristic formula for that regarding...
Thu May 06, 2010 2:03 pm UTC
Forum: Science
Topic: mean free path of electrons in air?
Replies: 4
Views: 3155

### mean free path of electrons in air?

hey there, does anyone happen to know a roundabout value for the mean free path of electrons in air? electrons are "slow" (300eV max) and the pressure is about 5E-2mbar. as this only needs to be a crude approximation, a standard value for thermic electrons at normal pressure would suffice ...
Fri Mar 20, 2009 2:09 am UTC
Forum: Coding
Topic: Sort-of dynamic array
Replies: 17
Views: 1345

### Re: Sort-of dynamic array

c++ convention would be to use the "new" operator, giving something like: int* a = new int[n*(n+1)]; when you don't need that array "a" anymore simply call delete [] a; the "[]" after delete being necessary as "a" points to an array. e: oh yeah, beat me to it....
Sat Feb 14, 2009 1:30 pm UTC
Forum: Mathematics
Topic: 0/0=?
Replies: 24
Views: 2274

### Re: 0/0=?

0/0 = 5

Thu Feb 12, 2009 12:43 am UTC
Forum: Science
Topic: Home Theatre Projector Optics
Replies: 8
Views: 1130

### Re: Home Theatre Projector Optics

well that's the reason why they turn off the light in cinemas while you see the film. ;-) as you already realized, there is no "black light" coming out the projector, so a black spot is nothing else than an unlit piece of canvas. a white spot would be a fully-lit piece of canvas. our eyes ...
Wed Feb 04, 2009 6:14 pm UTC
Forum: Coding
Topic: anything fundamentally wrong with...?
Replies: 26
Views: 2388

### Re: anything fundamentally wrong with...?

AFAIR it's mandatory in ANSI C.
Sun Dec 14, 2008 3:12 am UTC
Forum: Science
Topic: Space Lightning
Replies: 28
Views: 2835

### Re: Space Lightning

as previously stated: there would be no visible lightning-strike in the good-as-vacuum between earth and the moon, nevertheless current would flow - in the form of "free flying electrons". as they have (nearly) nothing to collide with on their way though space there will be no optically vi...
Sun Sep 14, 2008 3:55 am UTC
Forum: Science
Topic: Physicists don't lock their doors
Replies: 17
Views: 2687

### Re: Physicists don't lock their doors

in the german uni that i attend every classroom is open all the time - if it's not used by anyone you can freely walk in and use it for groupwork or whatever you like. also the library is open daily 'til 10pm (don't know about sundays) and you can also hang around or work there if you like to... if ...
Mon Sep 08, 2008 10:55 pm UTC
Forum: Science
Topic: Research
Replies: 31
Views: 3625

### Re: Research

i'm a physics/CS student just starting into my second year. I'm currently working on an algorithm to improve the human perceived signal/noise ratio in high-stress intercom appliances. it's not part of my university studies (i'm doing it "for fun and if it turns out to work profit"), althou...
Sun Aug 03, 2008 2:05 am UTC
Forum: Coding
Topic: Good programming music
Replies: 93
Views: 15945

### Re: Good programming music

i really like some liquid-funk-flavor drum&bass for programming :) e: i figured someone who hasn't ever heard of "liquid funk" probably couldn't imagine what kind of music i was referring to, so some artists for research ;): high contrast danny byrd london elektricity you'll figure the...
Mon Jul 07, 2008 6:36 pm UTC
Forum: Mathematics
Topic: Euler's Formula
Replies: 8
Views: 1489

### Re: Euler's Formula

z4lis wrote:I realize it's trivial, which is exactly why I'm curious as to why we don't use the more general form. It seems sort of bizarre to me.

because your "more general form" uses ln() - which is the logarithm to the base e, therefore being not a bit "more general".
Fri Jul 04, 2008 2:53 pm UTC
Forum: Science
Topic: The possibility of bullet-bending -- WANTED
Replies: 49
Views: 10420

### Re: The possibility of bullet-bending -- WANTED

shooting at a downwards/upwards angle and letting coriolis "force" do the rest
Wed Jul 02, 2008 12:56 am UTC
Forum: Science
Topic: a question regarding AC voltage, power, and interference
Replies: 22
Views: 2313

### Re: a question regarding AC voltage, power, and interference

no the variable transformer won't have that problem - at least not in principal. so does phase angle control or the switching method. of course every regulatory action will warm up, though orders of magnitude less than just burning away the unnecessary energy. if you would tell us more about what yo...
Wed Jul 02, 2008 12:36 am UTC
Forum: Science
Topic: Physics Tattoo Ideas
Replies: 63
Views: 17922

### Re: Physics Tattoo Ideas

it's not particularly physics, but somewhere on the mighty intarwebs i once saw the transistor-symbol tattoed on the inside of someones wrist. really liked that one, although i wouldn't have tattoo which is not unique.
Wed Jul 02, 2008 12:28 am UTC
Forum: Science
Topic: a question regarding AC voltage, power, and interference
Replies: 22
Views: 2313

### Re: a question regarding AC voltage, power, and interference

look up "phase angle control", that's how most light-dimmers work and it will probably work out for your application. you can also get a standard lightdimmer from a hardware store and use it. (as usual be VERY careful around such voltages, btw how do you americans call the eletric power co...
Fri Jun 27, 2008 3:39 pm UTC
Topic: 0442: "xkcd Loves the Discovery Channel"
Replies: 372
Views: 89559

### Re: "xkcd Loves the Discovery Channel" discussion

this is one of the best xkcd comics i have ever seen.

really cracked me up on so many levels.

pure greatness. thanks
Mon May 26, 2008 6:05 pm UTC
Forum: Science
Topic: Sound Wave Frequencies
Replies: 27
Views: 3916

### Re: Sound Wave Frequencies

just to make it clear: if you are stuck with giving a frequency and have it played you will not be able to have something like chords coming out of the speaker. you would need the buffer-playback thing for that. it might be worth trying to play two rapidly alternating frequencies, but i have no idea...
Sun Mar 09, 2008 8:17 pm UTC
Forum: Science
Topic: Maglev Car
Replies: 10
Views: 1973

### Re: Maglev Car

there will be no extra-acceleration to your car, although the car's "ability to levitate" will be impaired. imagine a closed-circles track with tilted magnets; with your idea the cars would accelerate on and on - a perpetuum mobile which we all know is impossible. also please don't take it...
Sat Mar 08, 2008 12:49 pm UTC
Forum: General
Topic: Who the dickens are you?
Replies: 10922
Views: 2422089

### Re: INTRO THREAD THE THIRD

hi, i'm a 20 years old student (physics/computer science) from germany who's been reading the comics for some time now. although i had seen the fancy "forum" link before i never bothered actually clicking, as in some way i thought those were mostly about the comics themselves... now that i...