Become a fan of Slashdot on Facebook


Forgot your password?
DEAL: For $25 - Add A Second Phone Number To Your Smartphone for life! Use promo code SLASHDOT25. Also, Slashdot's Facebook page has a chat bot now. Message it for stories and more. Check out the new SourceForge HTML5 internet speed test! ×

Comment Re:sounds overly optimistic (Score 1) 79

... it's a UV diode with a phosphor on it, not a blue diode.

Nope. Just look at the spectrum of some white LEDs, they clearly peak around 450 nm plus what the phosphor delivers. UV is very problematic as it quickly degrades the plastic optics which are predominantly used with LEDs. Plus, you would only get the yellow light from the phosphor, not white light. It's the mixture of blue and yellow that's necessary where the ratio determines the correlated color temperature.

Comment Re:Beware of too many LEDs (Score 1) 113

What they did is they compared the light of LEDs and HID to that of sodium lamps, mostly found in outdoor lighting (for those who don't RTFA). The blue light, which is missing in the sodium spectrum, supresses the melatonin production. The same process happens every morning when you get up and turn on the light or go outside. As sodium lamps are mostly used in streetlighting etc. I think this is actually a benefit instead of being dangerous. Supressing the melatonin fights the fatigue which might prevent some car accidents, although I'm not sure if this effect is high enough for this.

Comment Re:Self Cleaning (Score 1) 388

Not really. With high power lasers you really should make sure your optics are clean. Not so much for the energy loss of the beam but for damage of the optics. Any dirt on a lens or mirror will partially reflect some light which propagates back into the lens and is eventually being focused therein. For low power lasers this is harmless but when you go to high power this little amount of light is able to form a plasma when focused and hence destroy the optics. Since they try to ignite the gasoline I assume it is a somewhat powerful laser. If it is the optics might be damaged by soot, if not the soot will just stay there and you'll have to remove it manually.

Comment Re:Longer lifetimes is the answer (Score 1) 627

Nitpick... the time dilation for a constant relative velocity is, as the term 'relative velocity' suggests, symmetrical. People on earth see the ships clocks go slower as the crew sees the clocks on earth go slower. Both age at the same rate, that's the Twin Paradoxon of special relativity.
A constant high velocity is not the reason why this works, you have to take the acceleration into account a real ship would have to undergo.

Comment Re:Achem (Score 1) 234

I blindly assume you have not read the pdf either you have linked, or did you? No relation to thermodynamics in it.

Wrong and wrong. Did you read it? The first part is about magnetism in general which is later used to define the partition function of a paramagnet and calculate thermodynamic properties it, i.e. heat capacity or entropy.

In other words: the famous 1st, 2nd and 3rd law of thermodynamics have no relation to magnetic or electric or other fields.

You forgot the 0st law...
Anyway, the laws of thermodynamics only account for the macroscopic features of an ensemble. They define relations between these properties independently of the microscopic nature of the ensemble. But to use this on any real system the microscopic interaction has to be described to derive the first set of macroscopic properties. And this has to include the magnetic or electric forces if present.

Comment Re:Aside from that... that isn't scientific litera (Score 1) 1038

I beg to differ. We do have quite some evidence. The human evolution can be traced back to about 3 million years where the Australopithecine lived. Only after that the Homo genus appeared and its remains could be found. There might still be some links missing and you could give or take a million years due to undiscovered specimens for the first appearance of the Homo genus. But the overall picture is consistent and to assume there have been human ancestors 65 millions back in time together with the dinosaurs is just absurd.

We have a consistent picture of human evolution which starts 60 million years after the dinosaurs became extinct. Of course you might doubt the extinction but for that we have quite some good arguments, too. On the one hand how likely would it be that you find all kinds of skeletons only up to the point of extinction but not afterwards? Unless all remainung dinosaurs gathered together in a yet undiscovered spot on earth this cannot be explained plausibly. But that's not real evidence, granted. At the same time the dinosaurs stopped to exist we also see that remains of many species stopped to appear afterwards, leading to the assumption of global mass extinction. And last but not least an impact crater of a meteor dating back to the very time the assumed extinction took place has been found. All in all this picture is pretty consistent, too.

Slashdot Top Deals

"In matters of principle, stand like a rock; in matters of taste, swim with the current." -- Thomas Jefferson