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Comment: Re:The image formation process is still the same (Score 1) 60

by dak664 (#46685383) Attached to: How To Build a Quantum Telescope

That's the infinite plane wave approximation for lattices of infinite extent. Scattered spherical waves from finite objects will result in some energy passing through the aperture for every spatial frequency. Although it could be difficult to sort out which frequencies are contributing (aliasing). Analysis of the through focal series can do that, also changing the convergence of incident illumination.

But if the source is known to be two points, accurate measurement of the spacing between the resulting PSFs is limited only by signal to noise.

Comment: Re:The image formation process is still the same (Score 3, Insightful) 60

by dak664 (#46683631) Attached to: How To Build a Quantum Telescope

Yes, and what's more diffraction causes no fundamental limit to resolution, it just happens to be the distance between the first zeroes of an interference function. For two point sources of equal intensity that leads to an easily seen contrast difference of around 25% but trained observers can detect 5%. On electronic displays the contrast can be cranked up arbitrarily.

The fundamental limit to resolution is signal-to-nose.

Comment: Re:Can someone explain this theft? (Score 1) 232

by dak664 (#46347469) Attached to: Mt. Gox Shuts Down: Collapse Should Come As No Surprise

Isn't the history of a bitcoin included in the block chain? And the stolen bitcoins identifiable?

If so whoever tries to use one risks being traced, moreover the recipient could be considered as knowingly accepting stolen goods..

Sort of like the haul from a bank robbery having an indelible "This money stolen from Bank X" printed on every bill.

+ - WhatsApp Founder used Nonchangable Airline Ticket to Pressure Facebook-> 1

Submitted by McGruber
McGruber (1417641) writes "In a post on the Flyertalk website (http://www.flyertalk.com/forum/22387891-post72.html), WhatsApp Founder Jan Koum provides another interesting detail about how he steered Whatsapp into a $16 Billion Deal with Facebook (http://mobile.slashdot.org/story/14/02/20/1344218/how-jan-koum-steered-whatsapp-into-16b-facebook-deal):

we announced the deal with Facebook on wednesday after the market closed. during the process, we realized there was a chance we might not be able to get the deal wrapped up and signed on wednesday and it could delay. when the risk of the delay became real, i said: "if we don't get it done on wednesday, it probably wont get done. i have tickets on thursday to fly out to Barcelona which i bought with miles and they are not easily refundable or even possible to change. this has to be done by wednesday or else!!!" ...and so one of the biggest deals in tech history had to be scheduled around my M&M award ticket

"

Link to Original Source

Comment: Re:idle time (Score 1) 533

by dak664 (#46004945) Attached to: Ask Slashdot: What's the Most Often-Run Piece of Code -- Ever?

The idle loop is alive and well in embedded systems. In some cases energy use is minimized by using a slow clock chosen for some small fraction of idle time, in others by sleeping between bursts of fast processing.

x86 idle power reduction under unix started sometime in the late 1990s
https://blogs.oracle.com/bholler/entry/the_most_executed_code_in

Other OS starting using it around 2000
http://en.wikipedia.org/wiki/System_Idle_Process

Thus seti@home launched in 1999 could legitimately claim it made use of otherwise wasted CPU cycles on the Mac and Windows 95 clients.

Comment: Re:ethics of killing and warfare (Score 3, Interesting) 153

by dak664 (#45753401) Attached to: How Asimov's Three Laws Ran Out of Steam

Moral killing may not be that hard to define. Convert the three laws of robotics into three laws of human morals by taking them in reverse order:

1) Self-preservation
2) Obey orders if no conflict with 1
3) Don't harm others if no conflict with 1 or 2

To be useful in war an AI would have to have to follow those laws, except that self-preservation would apply to whichever human overlords constructed them.

Comment: Re:Vacuum (Score 1) 332

by dak664 (#45579837) Attached to: The Quietest Place On Earth Will Cause You To Hallucinate In 45 Minutes

I confess to being stupid but endeavor to learn. Your blind spot seems to be the assumption that in equilibrium the radiation from an object must re-emit the same energy per Hz as acquired from the absorption spectrum. Classical thermodynamics, while powerful, leads to an incomplete picture. Statistical thermodynamics says the incoming energy is rapidly randomized among probable states (fortunately for life some of those may start the electron transport chain). The excess energy populates an increasing number of available states until enough of them dissipate (or in vacuum radiate) the excess energy away. Which has very little connection with some hypothetical temperature of the incoming radiation.

Comment: Re:Vacuum (Score 1) 332

by dak664 (#45578183) Attached to: The Quietest Place On Earth Will Cause You To Hallucinate In 45 Minutes

In thermal equilibrium with the environment, not with each other. An object absorbing more high frequency radiation has to get hotter to radiate that energy at the lower frequencies. Thus any measurable temperature is a property of the object, not the radiation field. You could define the temperature of vacuum as that of a gray body in equilibrium with the local radiation if that makes you happy. Not sure how useful such a definition would be.

Comment: Re:Vacuum (Score 2) 332

by dak664 (#45576337) Attached to: The Quietest Place On Earth Will Cause You To Hallucinate In 45 Minutes

A thermometer coating with high absorption for solar wavelengths and low emissivity at longer wavelengths would get hotter than one with the opposite characteristic when placed near the Sun. Indeed you could run a heat engine off this temperature difference and as you say it would ultimately be powered by the continuing incident radiation. But the vacuum environment has no inherent temperature of its own, rather a radiation flux which can heat different objects to different temperatures even when both are in thermal equilibrium.

If you enclose a vacuum in a black box with walls at 1 kelvin what is the temperature of the vacuum? If you heat one wall to 5000 kelvin what is the temperature of the vacuum? Is there a gradient? Does it become anisotropic and depend on the orientation of the thermometer?

Comment: Re:Vacuum (Score 2) 332

by dak664 (#45574369) Attached to: The Quietest Place On Earth Will Cause You To Hallucinate In 45 Minutes

But in that case the thermometer is measuring its own temperature, not "the temperature of the vacuum", whatever that means. And selective coatings with different absorption and emission spectra could change the reading of the thermometer. Does that change the "temperature of the vacuum"?

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