petschge

33 ms·

331.
by petschge 7y ago
To get good precision you need to remove the effect of electrons in the ionosphere. These basically change the index of refraction and therefore the propagation speed of the radio waves. The delayed signal makes your receiver think it is fu
332.
by petschge 7y ago
MSVC is hilariously bad and not used in HPC code. Not sure how much high performance game code is compiled with it.
333.
by petschge 7y ago
By hitting the compose key [1] followed by "<" and "-". 1: https://en.wikipedia.org/wiki/Compose_key
334.
by petschge 7y ago
That is at best a convention. You can multiply the Lagrangian by -1, without changing the equations of motion or the resulting trajectories. So physically nothing changes, but maxima and minima swap.
335.
by petschge 7y ago
The article claims "In Lagrangian Mechanics you minimize the total energy of a system to find its motion". But if you actually look into it, you derive Lagrangian Mechanics by minimizing (or maximizing) the _action_. Action in thi
336.
by petschge 7y ago
Because the solar system is moving relative to the local interstellar medium. So effectively you get a "headwind".
337.
by petschge 7y ago
The rocket equation is dv = isp * g0 * ln(m0/mf) [1]. For dv we assume 10% the speed of light, isp of a ion thruster is say 19300 s [2], for g0 I will use 9.80665m/s^2 and mf is 1kg. For m0 this gives us m0 = mf * exp(0.1 c /
338.
by petschge 7y ago
Voyager 1 is 0.00234 light years from Earth, Voyager 2 is 0.00194 ly. Or in more useful units: 20.5 and 17 light hours. Also we do not receive images any more (the cameras were made for planetary encounters and have been turned off long ago
339.
by petschge 7y ago
The split is actually much more uneven, and heavily on the side of kinetic energy. An orbit at 200 km altitude has an orbital velocity of 7.79 km/s. Potential energy is given by m * g * h (to good approximation, as h is much smaller th
340.
by petschge 7y ago
That is true until you have to so many photons that you hit the QED regime where photons interact with each other and electrodynamics becomes non-linear. However at that point no just the nucleii notice, but you start to get all kinds of ot
341.
by petschge 7y ago
The mpg of reactors (or rather the burnup) is measured by the energy extracted from the primary fuel. In practice that is not limited by neutron flux, but by accumulation of gaseous fission products inside the fuel or the cladding. They do
342.
by petschge 7y ago
Sorry, that was a horrible typo for "Schwinger limit" that is now fixed. An explanation can be found at [1]. The limit comes from the following process: Thanks to quantum mechanics there is an uncertainty principle between positio
343.
by petschge 7y ago
Maybe. It is hard to find any scientifically accurate information on his proposal. But if you say he wants laser intensities that are directly sufficient to get 1 MeV (typical nuclear energies) across the 10fm of a nucleus he would need int
344.
by petschge 7y ago
For all we know this is possible but not at all practical. The NIF [1] already does experiments with lasers that start nuclear processes in the ICF [2] capsule. An exeptionally good shot produces 2e16 neutrons [3], from (about) 2e16 nuclear
345.
by petschge 7y ago
Nope, they are quite different exactly because "something you are" is attached to you and "something you have" is not. One can be swapped out if compromised or get lost. The other can not (intentionally or unintentionall
346.
by petschge 7y ago
Print with a laserjet onto overhead projector foil, spread a suitable kind of wood glue, dry, peel and apply to own finger tip. It is actually very straight forward.
347.
by petschge 7y ago
You are right. But note that I never said that faces where any better.
348.
by petschge 7y ago
Cosmological simulations already take up month of run time on worlds largest supercomputers. (astro-)Physicists were the first users of large computations, in many cases inventing the computers along side with the physical theory the were t
349.
by petschge 7y ago
No, observations of galaxies that seem to have little dark matter are an argument for the existence of dark matter (over the competing theory of a modified gravitational interaction). And here is why: If you have two galaxies with about the
350.
by petschge 7y ago
What I meant is: you can not change it and you can not keep it secret so it makes a poor password replacement. Usernames do not have to kept secret (you know that my username on HN is petschge), so finger prints might be slightly more usabl
351.
by petschge 7y ago
A fingerprint is never a secure password. It is a username at best.
352.
by petschge 7y ago
My favourite scheduler is still "Son of Grid Engine", the open source continuation of the "Sun Grid Engine". I never had much trouble setting it up, but it is not really maintained at this point. PBS as suggested by othe
353.
by petschge 7y ago
A lot of US based startups make a lot more sense to us Europeans in case we move to the US and notice how broken all infrastructure is. Banking still uses cheques, so you have Paypal, Venmo, CashApp and so on. Public transport is bad or eve
354.
by petschge 7y ago
Tiny comment: I think the sentence "However, in practice the overhead needed to correctly avoid locks is greater than just using a mutex." should be part of footnote 1, not the main text.
355.
by petschge 7y ago
That is true for the spherical part of the lens. When you start to look into the correction of astigmatism (done by the cylindrical component of the lens) it become a whole lot more complicated.
356.
by petschge 7y ago
So the government and BBC being (unfairly perhaps) pro-remain is a reason to vote leave? Yes, you can argue "both sides were unfair". But one side was unfair by lying, the other was unfair by using their position of power to sprea
357.
by petschge 7y ago
Random imagined example: Two files with different names being created in the same directory. The race decides which one gets which inode number, but both are created correctly and successfully. That would be a race condition, but as long as
358.
by petschge 7y ago
syncthing[1] works nicely for me. [1] https://syncthing.net/
359.
by petschge 7y ago
Can confirm that the Southern sky is great from my time in South Africa. We had a nicer view of the milky way during many braais in a small town backyard than I have seen in the Northern hemisphere (including back country camping in Yellows
360.
by petschge 7y ago
I will repeat a comment that I have made on HN before: 50% of the US population live in just 35 metropolitan areas (Los Angeles, CA; New York, NY; Chicago, IL; Philadelphia, PA; Washington, DC; Detroit, MI; Houston, TX; Atlanta, GA; Dallas,

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