Slashdot is powered by your submissions, so send in your scoop

 



Forgot your password?
typodupeerror

Comment: silentpcreview.com (Score 1) 720

by Michael Woodhams (#48487263) Attached to: Ask Slashdot: Making a 'Wife Friendly' Gaming PC?

silentpcreview.com is a web site dedicated to quiet and silent computing, with extensive reviews and forums. They have very recently posted a sample build of a quiet gaming PC.

You can take that as a base and adjust according to taste. (For example, I'm more obsessed by quiet and less by frames per second, so my gaming PC has a single GTX760Ti GPU.) If you have questions, take them to the forums.

Comment: Re:Some details from the paper (Score 1) 145

by Michael Woodhams (#48480853) Attached to: Scientists Develop "Paint" To Help Cool the Planet

Emissivity and absorptivity are the same thing. One way to look at this is the time-reversibility of physics on a microscopic scale, another is that something that was really absorptive but not emissive or vice-versa would give you a really easy way to beat the 2nd law of thermodynamics. Emissivity can, however, vary with wavelength, which is the trick here.

Comment: Re:Some details from the paper (Score 2) 145

by Michael Woodhams (#48476975) Attached to: Scientists Develop "Paint" To Help Cool the Planet

Not really - the 40Wm^2 of cooling is only useful if it is in contact with something that can move that cold to where it is needed. (Hand-wavy explanation, really we are shifting heat to the film.) It also needs to see mostly sky, which windows usually don't.
You'd put it on your roof and run water behind it to shift the heat around.

Comment: Re:the law (Score 2) 145

by Michael Woodhams (#48476929) Attached to: Scientists Develop "Paint" To Help Cool the Planet

Would you care to be more specific? My explanation is pop-science simplified, but I don't see an error in it.

More detailed explanation:
In the 8-13 micron (wavelength) window, atmospheric transmittance averages about 80% (estimated from a plot in the paper.) So the energy received is about 20% of what you'd get from a black body at atmospheric temperature (plus 80% of what you'd get from space, which is negligible in comparison.) So the brightness temperature at 8-13 microns is lower than ground level atmospheric temperature. How much lower depends on the average temperature of the atmosphere along the line of sight, and where 8-13 microns falls on the black body curve at that temperature (even this is oversimplifying) and I can't be bothered figuring that out. However, if we can reflect/insulate all energy except 8-13 micron radiation, then our thermal equilibrium temperature will be the brightness temperature at 8-13 microns to which we are exposed. This is, as noted, less than atmospheric temperature at ground level.

Comment: Re:the law (Score 1) 145

by Michael Woodhams (#48476743) Attached to: Scientists Develop "Paint" To Help Cool the Planet

It is possible, because the environment is not in thermal equilibrium. In particular, the film 'sees' colder temperatures at some wavelengths than at others.

Did you not think before you posted that just maybe a bunch of scientists publishing in this area and the reviewers for one of the worlds top scientific journals might possibly have a better understanding of thermodynamics than you do?

Comment: Some details from the paper (Score 5, Informative) 145

by Michael Woodhams (#48476691) Attached to: Scientists Develop "Paint" To Help Cool the Planet

For those fortunate enough to have institutional access, the research paper is here.

Quickly picking some highlights:
The atmospheric transmission window is between 8 and 13 microns. They achieved 4.9C below ambient in direct sunlight at 850 watts per square metre. Cooling power was 40.1 watts per square metre. Emissivity (equivalently absorptivity) averages about 70% in the 8-13 micron window (estimated from a plot.)

Here's a quick back-of-the-envelope calculation
90% reflective white paint: absorbs 85W/m^2
97% reflective foil: absorbs 25.5W/m^2, an improvement over white paint of ~60W/m^2
This film: emits 40W/m^2, an improvement over simple foil of ~60W/m^2.
So in this scenario, the special film gives twice the benefit compared to just going for something simple and reflective. (The 90% for white paint is guess-work. The 97% for 'foil' is just matching the special film. Perhaps someone can update the calculations with better founded values.)

The summary title is highly misleading.

It is not paint, it is a manufactured film. It cools buildings, not planets. Yes, with enough you could cool the planet, but if you wanted to take that route, it would be much more cost effective to just use aluminium foil and use a marginally larger area of it (or, indeed, white paint.) Back in the real world, the way this invention cools the planet is by reducing electricity demand for air conditioning. (I saw another article about this in which one of the authors makes exactly this point.)

Comment: Every single transaction is broadcast to the world (Score 2, Informative) 115

by Michael Woodhams (#48470685) Attached to: Bitcoin Is Not Anonymous After All

And you can absolutely guarantee that the three letter agencies remember every one of them. They can look at who you've made transactions with and usually get a very good idea just from that who you are. I imagine they get more from fronts and hacked/infiltrated organizations. If they need more and you've ever transacted with a commercial entity within their jurisdiction, you are a National Security Letter or local equivalent away from being identified.

This IP address thing is like discovering that the back door is unlocked and open when the front door is secured by a piece of string.

The clash of ideas is the sound of freedom.

Working...