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visits member for 2 years, 8 months
seen Apr 18 '13 at 6:08

Aug
18
awarded  Yearling
Apr
5
comment How does a thermal temperature gun work?
A minor correction - thermometers also have to be calibrated for the type of surface being measured, as Planck's law is inexact for surfaces that are not perfectly 'black'. I imagine that most are calibrated for water. (Materials that reflect some of the incident radiation necessarily emit less in that region than a blackbody would).
Jan
14
awarded  Announcer
Sep
12
awarded  Necromancer
Aug
18
awarded  Yearling
Jul
10
comment Is a hard drive heavier when it is full?
The interesting question is if it is heavier or it is lighter... need to look up how the data is encoded for storage to answer this one. With some encodings one may have expected energy that will be identical for the hard drive storing a file of zeroes and the one storing a file of ones or 010101s. The coding is rather complicated. edit: see en.wikipedia.org/wiki/Modified_Frequency_Modulation for more information.
Jul
10
answered How to deal with conflicting “no-slip” Navier-Stokes boundary value constraints?
Jul
10
answered Why does a semiconductor hole have a mass?
Jul
8
awarded  Critic
May
29
comment Has any permanent magnet motor been proven to run?
A ferromagnetic material consists of many small magnetic domains, which are, themselves, magnetized (quantum mechanical phenomenon). A piece of steel that is magnetized, has those domains in alignment, which is a higher energy configuration, while the piece of steel that is not magnetized, has those domains out of alignment, which is a lower energy configuration. It is very common to store some energy in the magnetic field inside the ferromagnetic material; the device which does so is called 'inductor', and most inductors use field inside ferromagnetic material.
May
28
comment Has any permanent magnet motor been proven to run?
Put a pair of magnets together side to side, north up south down, parallel, like !! , as you'd do to make a bigger magnet. Remove hands. One of the magnets will flip over, resulting in lower energy state of !i (the ! is meant to represent up arrow and i down arrow). Yes, the lowest energy state is magnetized, but the magnetic domains are not aligned (and external magnetic field is very small). edit: found an image en.wikipedia.org/wiki/File:Powstawanie_domen_by_Zureks.png
May
27
answered Has any permanent magnet motor been proven to run?
May
27
revised Cyclist's electrical tingling under power lines
clarified calculations
May
27
comment Cyclist's electrical tingling under power lines
LuboŇ° Motl: There would not be enough zap. The physiological zap is a complicated function of pulse duration, current, and voltage. In this scenario the total charge that goes through the body on each zap is no bigger than if you get zapped taking off a sweater or stroking a cat (which can also generate several kilovolts), and the pulse duration is so short and energy so low that neither the current nor the voltage are relevant, but the total charge (integral of current by time).
May
27
answered Cyclist's electrical tingling under power lines
May
19
comment Getting from $E^2 - p^2c^2 = m^2c^4$ to $E = \gamma mc^2$
Ya, having every formula peppered with multiplications and divisions by c when you could of just done it in the beginning, results in great deal of confusion and is just plain bad for readability (I would not want such in software code, let alone in text that is written for humans). I think though its bit like hard to read code written by clever programmers - not a sign of incompetence, just a nasty habit - it is easy to read if you have done that stuff a lot.
May
18
answered Voltage and current of positive lightning
May
6
revised Why don't modern spacecraft use nuclear power?
added 471 characters in body
May
6
answered Why don't modern spacecraft use nuclear power?
May
6
answered Apparent non-aberration of gravity waves