# Search results

1. ### I Relativistic doppler shifted blackbody color?

I'm trying to render the sky as it would appear from a starship moving at some large part of the speed of light. Geometry was straightforward, but colors are the problem. How would the doppler effect change the color of a star? The expectation is that the stars behind are red and the ones ahead...
2. ### I Is there a point during star formation when gas is 1 atm?

I have been reading about and contemplating the early stages of star formation lately. An interstellar cloud collapses under it's own gravity to form a star. There is much data about what could trigger it, and what happens when the gas heats up or starts fusing. However, i couldn't find...
3. ### Ray transformation of a 3d lens?

Greetings. I'm working on a raytracer, and got stuck with trying to model a lens analytically. Given is a thin lens at position p with the axis n, radius r and a focal distance f, a ray hits it at position p1 going in the direction d. Which way would the ray be going on the other side of the...
4. ### Article on texture generation - can't get the math

There is an article on procedural texture generation by example. I'm trying to implement it, and got lost in the mathematics. http://graphics.cs.kuleuven.be/publications/LVLD10PISTE/ The outline of the algorithm is thus: We start with a noise-like photo. Do a 2D DFT of it: Compute the power...
5. ### How to convert air flow into pressure?

Let's say i have an air pump which produce plenty of air flow, but almost no pressure. Is there a simple way to turn this high flow, low pressure into high pressure, low flow? I'm thinking something akin to a gearbox turning fast spin, low torque of a motor into a high torque, slow spin output...
6. ### Calculating optical properties of an arbitrary gas?

Hello. Is there a way to calculate properties of a gas, given only it's composition? I.e. let's say i want to know what would a planet look like with an atmosphere of a mix of 50% gaseous sulphur and 50% gaseous mercury, at 500*C and surface pressure of half that of Earth. How would i go about...
7. ### Decoding AM station from SDR into sound?

In short, how do you decode AM signal from I/Q samples into sound? In details, i made a software defined radio that uses a PC sound card as ADC. The local oscillator on it is set to 700KHz, there is a radio station at 731KHz. With existing software i verified that the hardware works - the...
8. ### What can be used to measure liquid nitrogen temperature?

Hi. I'm looking for a common electronic component that can be used to determine a temperature between room temperature and that of liquid nitrogen. -Multimetre probe failed, getting stuck at -135*C -Common NTC thermistors rapidly ascent past gigaohm range, even from 1Ω-5Ω initial values...
9. ### Axial flux alternators and motors design?

Axial flux alternator is an easy to make pancake of stationary coils between spinning permanent magnets. Having made one and played with it, i ended up with a few questions. Would it make a good motor? There are axial flux motors for sale, and my alternator spins nicely when hooked up to a...
10. ### Constant current boost converter problems

Hi. I want to make a constant current driver for a Xenon arc lamp. It takes 12V as input, should give out 8A at 15 - 20V, and maintain 50V idle voltage. I used a TL494 to control it, single-ended output driving a boost converter. 100KHz frequency. Schematics attached below. It...
11. ### Would a lithium-ion store a current pulse?

Let's say i have a 2-3Ah LiPo RC battery pack, rated at 80C discharge, and 2C charge. It gets connected to an inductor for several milliseconds, allowing a current of about 200A to build up. Then it gets disconnected, and a set of diodes rectify the current from the inductor back into the...
12. ### Li-ion protection breakdown voltage?

Li-ion cells come with undervoltage protection circuits - little integrated thingies that open up the circuit when the voltage across the cell drops below 2.7V or so. What sort of a switch is that? I've been thinking, if a cell is inside a large series pack - a dozen of cells for a hobbyist...
13. ### Electrolysis of baking soda solution?

What is being produced in electrolysis of water with baking soda (NaHCO3) dissolved in it, and carbon electrodes? Seems to be an extremely simple question, but every place i google up have a different answer. In practice, there is hydrogen on the cathode - it burns - but on the anode i get...
14. ### Boost converter switch node spiking

Greetings. I'm making a high power boost converter, supposed to deliver constant current at 15-50V from about 12V input. 100KHz frequency. There are problems, however. There was a lot of ringing at the switch node - meeting point of the diode, inductor and MOSFET. 5.8Mhz clear decaying...
15. ### Filtering ultraviolet from Xenon arc lamp

Hello. What sort of commonly accessible material can block harmful UV from a 150W Xenon arc lamp, without blocking much of visible light? Lamp relative spectrum (a bit around 250nm, growing to a lot at 400nm): Enough UV should be blocked for the lamp to be usable as a regular...
16. ### Charging a capacitor with solar panel?

A solar panel have a certain voltage at which it produces the most power. Below this voltage it's a current source - giving about the same current all the way down to short circuit. Right? On the other hand, a capacitor sucks up as much current as is available (ignoring ESR), slowly...
17. ### Solar panel aging and other weird behaviour

Given: a ~3W monocrystalline solar panel, originally from a panel+battery+light pack from early 90s, spent a decade in a box, then a decade on the roof under the sun and elements, unconnected to anything. I wanted to finally put it to some use. The circuit is straightforward - the panel...
18. ### Failure to make a Mach–Zehnder interferometer?

Hello. I'm trying to make a "Mach–Zehnder interferometer", that would show a same-named paradox. In plain words: Two half-silvered mirrors, two full mirrors, the beam is split, then merged together. At the merge point one way the photon is cancelled out, while the other way it is combined...
19. ### Erasing a powered EPROM with UV?

Hello. I was curious on how the content of an UV-eraseable EPROM chip degrade when it's being erased. So, i put a picture into a chip from a TV test signal generator (M27C512), powered it up, and put an UV erasing lamp next to it, expecting pixels to go pop.... pop... pop pop popopopopop or...
20. ### Tesla coil with voltage doubler?

I want to power a small-ish tesla coil from a 8KV 500W transformer with a voltage doubler to raise that to 16KV. Problem is - it works considerably worse (shorter sparks, LOUD gap) than with a 30KV 100W flyback, spark gap being the same, set at about 12KV. One issue appears to be that...
21. ### How to measure a capacitance of an isolated object?

How can you measure a capacitance of an isolated object, like a conductive sphere or a coil? Can it be done using a typical RLC meter? I've tried touching only one end of the probe to the object in question, and that seems to give sporadic readings, but within the order of magnitude of the...
22. ### Zero voltage, non-zero current?

Reading about solar panels i came across a peculiar description - "When the panel is short circuited, there is current but no voltage, so no power is being generated." How does that work? What does the current represent in that case, and what moves the needle of an ammeter? Another...
23. ### Relative and absolute potential?

Hello. I've been thinking about potential on charged capacitors, and got confused. A charge is AFAIK absolute - there is a balance of electrons and protons in matter, which can be biased one way or another. However, voltage is defined as difference of potential, not an absolute value. So...
24. ### PWM controlled fan responds unexpectedly

Hello. I'm trying to control the speed of a fan (12V cpu cooler) with PWM (555 + MOSFET). Should be quite straightforward, but i noticed that the speed of the fan does not seem to always change in the same way the duty cycle does. With an optical RPM meter i'm seeing that the lowest RPM...
25. ### Xray refraction and UV refraction border?

Xray in any matter have a slightly below one refraction index. Ultraviolet still have materials with above 1 refraction index. Where in the spectrum between them does >1 index cease to be possible, and what is the nature of this threshold?
26. ### Why light does not travel in wires?

Asking in most general shape, why do signals from upper Ghz and above don't seem to travel in wires? Radio frequency waves can propagate in wires - you can have a signal like that being induced from the wave interacting with the wire, being generated, measured directly, and so on. But...
27. ### Induction heating of non-magnetic metal?

I'm experimenting with induction heating, and made a simple ~100W device. Royer oscillator type, 200kHz frequency. It readily heats a steel blade to the point of incandescence. However, a piece of aluminium of a similar size doesn't even get warm. I understand that magnetic hysteresis...
28. ### Boosting 0.3V to 2V or higher?

Hello. I want to get about 2-5 volt out of a 0.3V DC source, at µA levels, or get power out of it in any other way that would allow to charge a capacitor up to the said 5V. Any leads on how can this be done?
29. ### Melting NaCl (table salt)?

I was thinking of making an MWIR lens from table salt, which is quite transparent for it. That needs a big, monolithic cylinder of salt - 3x1 cm. Now, growing it the classic-oversaturated-solution way would take forever, if feasible at all. And i want to try to just melt some salt and cast...
30. ### Pinhole camera optimal resolution?

For a given pinhole size in a camera, and camera size, what would be the optimal pixel size to get the maximum resolution at maximum light intensity? i.e. the larger the hole, the more light enters through it, but eventually the sharpness would drop below the resolution. Conversely, the...