Dmytry

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	526 reputation	bio	website	dmytry.com	visits	member for	1 year, 10 months
27 badges		location			seen	Apr 18 at 6:08

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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 Luboš 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
Apr 20	comment	Is the efficiency of a stirling engine affected by dead volumes? There is no real-world uniform temperatures like this in a real-world Stirling engine. Temperatures vary in the gas. Ultimately, the one thing that can be said in general is that for same amount of heat going from same temperature heat source to same temperature heat sink, the engine with dead volumes would have lower efficiency. Any more requires to specify the type of Stirling engine in question, the placement of dead volumes, and how much mixing does happen.