# Recent content by xaratustra

1. ### NASA NASA's Ephemerides

I was wondering, how does NASA actually calculate their super exact Ephemerides?
2. ### I Vector addition and Newton's law

I know that n-body problem can be complicated, but that's for the dynamics. What about a static case: e.g. if I have the distances of several bodies A, B and C etc. and their distance to a reference mass m, can I just use the vector addition of the Newton's gravitational force to add up all of...
3. ### I Foucault pendulum and a round globe

cool. then all pendula must be installed at the same altitude to guarantee smoothness. :smile:
4. ### I Foucault pendulum and a round globe

Imagine we are all cavemen without satellite technology and just discovered the Foucault pendulum! As we know the angle of presession depends on the latitude. This can be used to prove that the earth is rotating, right? Now by putting several Foucault pendula around the Earth, at equidistant...
5. ### Same physics, two theories?

true. Thanks. Now I have to think more... o_O
6. ### Same physics, two theories?

Was just thinking, is it ever possible that the same phenomenon can be fully explained by two theories that are not subset of each other? :rolleyes:

ok, the concept of DDC is explained here nicely by T. Schilcher starting from page 249: http://cdsweb.cern.ch/record/1003726/files/full_document.pdf [Broken] :oldwink:

Thanks so far for replies. After checking the above mentioned document written by Lyons, I also found another doc from him here http://www.ece.ucsb.edu/Faculty/rodwell/Classes/ece218b/tutorials_etc/sampling.pdf'][/PLAIN] [Broken]...

thanks for the explanation. Yes, I know the nice article by R. Lyons. But I checked it again. There he shows the ADCs to be placed after the quadrature oscillators. i.e. you already have 2 ADCs sampling at a fixed frequency fs, signals which come from the I branch and Q branch. All is good here...

Hey everyone! Can anyone explain, why quadrature sampling works the way it does? i.e. taking 2 samples for the I and 2 samples for the Q. I mean I can understand if one tries to sample one mono frequency signal, say 40 Hz sine wave, on 0, 90, 180, 270 degrees, that is a sampling frequency of...
11. ### Name of a geometrical shape

Found it! I think it is called a superellipse. I found a formula and an octave program on Wikipedia. The one I was looking for is the one with parameters "3 6 6 6", the table on the right side. The plot in octave also works by using the following command: sf2d([3 6 6 6],[1 1]) anyway...
12. ### Name of a geometrical shape

What is the geometrical shape called, when combining 3 ellipses together, such that each two share one focal point and together form a kind of 60 degree triangular shape? It will look similar to Reuleaux triangle, but it is not formed out of a triangle, but 3 ellipses, as if you are gluing...
13. ### PF is getting a face lift!

Oh, cool. I like the new design. :-)
14. ### Energy of light vs energy of photon

this has become a wonderful thread thanks to you all, I love it! :approve: In fact Darwin123 made a wonderful description, which I can now relate to what I have read in a book. Maybe the answer to Crazymechanic is also here. Near field effects seem to be the result of the interaction of 2...
15. ### Energy of light vs energy of photon

Great! thanks. o:)