Voltage drop across a white LED is 3-4 V. Who ever heard of germanium LEDs with 0.8V drop?
And if you have a power LED used for lighting, you don't use a resistor to limit the current; you use a small switchmode power supply.
If you design a good one, you can have electrical efficiency of >90% running from 12V, wasting less than 10%.
Ok, here we go again:
LHCb sees where the antimatter's gone
ALICE looks at collisions of lead ions
CMS and ATLAS are two of a kind
They're looking for whatever new particles they can find
The LHC accelerates the protons and the lead
And the things that it discovers will rock you in the head.
Or, for the full version: http://www.youtube.com/watch?v=j50ZssEojtM
Whatever it is, I got a prompt saying that an extension that I want to use would be disabled if I upgraded to 8.
Would it be disabled because it is incompatible, or because you did not install it yourself?
In the latter case, you can just enable the checkmark before it, and continue using it.
Many programs install, if you don't pay attention, extensions that you may not be totally happy with ('Ask'-toolbar, anyone?)
Firefox now disables these by default, but gives you the option to keep them enabled if you want them.
I find this a useful feature.
On the other hand, there may be extensions that refuse to load after a major version number change, That is a pain, but in many cases, this will be remedied quickly.
In Suriname / Dutch slang, "doekoe" (pronounced as "duku") means money.
So, what would be the ultimate purpose of "Duqu"?
To make heaps of money with it!
A double din android car stereo
Hey, yours is the second one I heard of!
A friend of mine made one too for his car.
Took a standard cradle, which has just about the right size, and mounted it over the double-din car stereo slot.
He had one problem, if I remember correctly.
When you put the Droid tablet into the cradle, I think you could either charge, or have sound output, or something like that.
Stupid limitation by Samsung who had not foreseen creative uses of their product.
I don't think it took him a week to make, however.
You forgot the "GET OFF MY LAWN" part... *sigh*
Hey, that's implied by my low UID. It shouldn't have to be explcit.
If your UID really would be low, then OK, maybe.
But to be considered 'low', I would guess that it would have 4 digits. Or less.
A claim like this requires some explanation of how it could be done, and such an explanation is obviously missing from the article. You shouldn't try to make up explanations for them (although that is how this nonsense continues to thrive).
Or to put it another way, if this thing can go through the point where it is going at the speed of the wind to then go faster than the wind the, assuming that it isn't storing energy from some time in the past and that the wind doesn't slow down, then it could also sit in zero mph wind and start going forward all by itself, just powered by a zero mph (non-existent) wind. Perhaps you believe that. I don't.
Parent has been moderated "Troll" but I think he is sincere.
And, at first, I did not believe this to be possible either.
I now understand how it works.
The propellor is used as a sail.
As long as there is pressue on the back of the 'sail' it can accelerate the cart.
If the sail were fixed w.r.t. the cart, it would stop receiving back pressure as soon as you reach wind speed. When you pass wind speed, you would get wind pressure from the front, and you would slow down.
So, what do they do: they drive the propellor from the wheels, so the surface of the propellor gets a forward speed that is lower than the forward speed of the cart itself.
In that way, even when the cart itself has passed wind speed, the surface of the propellor hasn't, and the wind can keep pushing the propellor forward, and thus, the cart.
The cart itself will feel the wind coming from the front, but the surface of the propellor, because it is turning, will still feel the wind force from the back.
Then a last question remains: will this force on the back of the propellor be greater than the force in the opposite direction on the wheels (that causes the turning of the propellor)?
This depends on the gear ratio. If you choose the gear ratio 'wrong' you will create a cart that will propel itself against the wind instead of along with it.
Notice that this is something that has been done earlier many times.
If it would be stationary, it would get close to wind speed, but never be able to pass it.
But the propellor is being driven by the wheels.
This gives the surface of the propellor blades a speed forward (wrt the ground) that is lower than the wind speed, even when the cart itself is already above wind speed.
In this way, the wind can still exert a forward force on the blades, and thus propel the cart.
That would make the total energy 30 kW * 4 h = 120 kW * h, not 120 kW / h.
The units are multiplied / divided the same way as the numbers.
If you would have a power that was linearly increasing from zero to 30 kW in 15 minutes, then you would have an increase of 30 kW / 0.25h, or 120 kW/h.
As you see, the unit kilowatt per hour is rarely encountered.
When you speak of energy, you have kilowatthours, not kilowatts per hour.
Normally I wouldn't mind so much, but further down in the thread, people are quoting your GW number, and basing their conclusions on it.
And I think your physics prof would take more offence from the nonsensical kilowatt-per-hour (that's a factor of hours squared off!) than from the capitalization
Anyway, in the end you are right, more than a megawatt _is_ a lot of power.
say a car would need 30kw to maintain motorway speed (say 50, for ease of calculation), and ranges 200 miles, that means you need 120 KW/h of stored energy, pack 90% of that in five minutes, and you end up with roughly 1.3 Gigawatt of drain sustained over 5 minutes...
IT'S OVER 1.21 GIGAWAT!! (yeah i know, i got my meme's mixed)
That would be 30 kW (not kw), 120 kWh (not KW/h), 1.3 MW (not GW)
So no, it's not over 1.21 gigawatt, just a factor 997 lower...
I cannot find anywhere how this system interconnects the components.
They write about the issues of current technology (solder containing lead, chemicals for etching PCB boards), but don't give an insight how their technology works around these problems. Encasing your whole device in plastic is neat, but the components will still have to be interconnected.
How? I cannot find it in the article, nor on the site of Griffith University.
To pick one more nit:
I wasn't correct myself when writing the equations.
It should be
Ic = Is ( exp(Vbe/Vth) - 1 )
In practice, Is is so small that you will not see the difference except for very small collector currents, but it's just bad style to correct errors of others when you are not correct yourself
I really like the simplicity of the circuit, and the way they try to explain the basics of transistor design. Nowadays, there is an integrated circuit for about anything, but just using that doesn't make you learn anything, and - in my opinion - takes away the fun of creating something from scratch.
But am I the only one to see the huge error in the equations they are using?
They state
Ic = Ib * beta
Ib = Is exp(Vbe/Vth)
where it should be
Ic = Is exp(Vbe/Vth)
Ib = Ic / beta
or, their equations are off by a factor of beta!
That does not seem too important, it appears you could compensate for this in Is, but in practice, that is not so straightforward.
The exponential relation between Ic and Vbe holds over many decades, whereas beta is not nearly as constant as we sould like.
So, if these are really MIT students, I'd like a word with their professors...
E = MC ** 2 +- 3db
