Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

Comment Re:Another energy-diffuse, capital-intensive syste (Score 2, Interesting) 203

Like windmills, PV solar (and arguably, thermal solar), this will use a ton of capital (in multiple dimensions -- energetic, costs, and materials) to harvest very diffuse energy.

Kites use two orders of magnitude less material than a turbine of equivalent swept area. Water is two orders of magnitude denser than air.

This is starting to add up to something that doesn't sound so diffuse any more.

Comment Re:Payback period? (Score 1) 562

Thermodynamics governs the maximum efficiency of all powerplants, end of story. We can approach but we can't exceed their maximum efficiencies.

Thermodynamics governs the maximum efficiency of powerplants based on thermodynamic cycles. IIUC, electrochemical powerplants like this fuel cell can exceed thermodynamic efficiency limits (but not the conservation-of-energy limits based on potential chemical energy of the fuel, of course).

Comment Lomborg is not a climate change skeptic (Score 2, Interesting) 807

I challenge anyone to find a quote from Lomborg suggesting that he questions climate change or its anthropogenic origin.
He does, however, make a pretty convincing case that focusing on it diverts resources and attention away from some other very serious issues. But I guess it's easier to vilify him than to actually LISTEN to him.

Comment Re:On Hybrid Vehicles (Score 1) 594

How come there is no hybrid vehicle that is in the form of Diesel / Battery ?

Do you know that diesel engines is much more efficient than that of the gasoline engine ?

The Chevy Volt is a series hybrid. The gasoline engine runs a generator and is not directly connected to the wheels. This means that it's always running at its optimal RPM and under these conditions the difference in efficiency between gasoline and diesel can be minimal.

Comment Floating point representation (Score 3, Interesting) 158

The floating point representation issue could be resolved the same way it is handled in Python 3.1 by using the shortest decimal representation that is rounded to the exact same binary floating fraction.

With this solution 1.1 + 2.2 will show as 3.3 (it doesn't now) but it will not test as equal to 3.3. It's not as complete a solution as using IEEE 754r but it handles the most commonly reported problem - the display of floating point numbers.

See What's New In Python 3.1 and search for "shortest".

Comment Sorry, Cringely (Score 1) 221

The idea of deriving some energy and momentum from the captured debris is interesting. But I'm pretty sure it will not stand up to critical analysis. The relative speeds of orbits crossing through the same area in space at different inclinations or eccentricities are faster than a bullet. Even if the net survives this many types of debris captured certainly won't - they will shatter and generate lots of smaller pieces of debris. If you somehow manage to choose only encounters with speeds low enough to survive the impact it will be too slow to derive any useful energy or momentum from. This idea might be sound in principle (though I wouldn't bet on it) but wrong by several orders of magnitude in practice.

And no, Cringely, you can't simply "trade altitude for speed" (potential energy for kinetic energy) in space to change to a different orbit. While it does not break the law of conservation of energy it definitely violates conservation of momentum. You could change momentum without spending energy via gravity assist with a third body (nothing available with enough mass in the vicinity but the moon) or using a tether. Otherwise you need to spend energy and reaction mass to change to a different orbit even if it has the same orbital energy. Space tethers are sometimes proposed for collecting space junk by people who actually understand a bit of orbital mechanics. Tethers are a very complex and mostly untested space technology we haven't mastered yet.

Capturing all 18000+ objects in a single net?!?!? What are you smoking? Have you any idea how much mass you are talking about? Moving all this mass to all the target orbits is an unimaginable waste of delta V. Even if you could somehow derive some momentum from the captured debris the 100th piece captured will barely change the vector of this huge collected mass.

Yes, as you say, this is a crazy idea. But it's not crazy in the "crazy enough that it might just work" kind of way. It's just plain crazy, dumb and ignorant.

Sorry, Cringely. You have just lost whatever remains of professional respect I still had for you.

Comment Energy from salinity gradients (Score 1) 128

Just like it takes energy to desalinate water the opposite is also true: energy can be produced from salinating water.
See http://en.wikipedia.org/wiki/Osmotic_power

What this system does is to concentrate seawater by evaporation and then use the salinity gradient between that concentrated brine and normal seawater to produce energy. This energy is then used to desalinate another stream of seawater. In principle, there is no reason to use this energy specifically for desalination. It could also be fed to the grid.

Is there anything inherently more efficient in using energy derived from osmotic power for desalination compared to using electricity from any other source? The answer to this question will probably determine whether this process can have any real benefits over the alternatives.

One potential advantage is that this system uses only ion flows and not electron flows. AFAIU, using electricity would have resulted in unwanted electrolysis byproducts which this system elegantly avoids. There is also no need for any power conversion circuits, wires, etc.

Comment Re:How is this different than now? (Score 1) 219

The market is still not mature for human-capable launch vehicles (Atlas and Delta aren't man-rated)

If it was YOUR ass on the line, would you rather fly on the "man rated" shuttle with its track record of one crash with complete loss of crew and vehicle every sixty-something flights and no means of emergency escape or an EELV as-is with no "man rating" and a decent escape system?

Man rating is largely a red herring. The sad truth is that there really isn't that much you could do for an astronaut that you wouldn't do for a multibillion dollar spy bird. A few sensors to detect failure a bit sooner to trigger the escape system and you are ready to go.

Comment Already done. Nearly 20 years ago. (Score 1) 559

The reason this works is that the surface is modified at the nanoscale to suppress emissions in the infrared spectrum where most of the energy of an incandescent light bulb is wasted. Guess what? This has already been done nearly 20 years ago.

U.S. Patent 5,123,868 describes a filament with nanoscale tuned resonant cavities that suppress the emission of infrared. No fancy femtosecond lasers - it was manufactured using centuries-old metalworking techniques of repeatedly drawing wires to make them thinner, followed by acid etching. It works. It improves the efficiency about twofold. Unfortunately, nanostructures can't withstand these high temperatures very long, even when made of tungsten. They deteriorate in less than 100 hours and efficiency drops to that of a conventional bulb. I'm pretty sure happens here, too.

Comment Re:Model M Keyboard (Score 2, Informative) 622

Ignore my post. Jumped the gun. While I do have 2 keyboards, they are for IBM terminals and not adaptable for PC use.

I assume you mean they cannot be directly plugged in. This is not the same as "adaptable". Depending on the amount of effort you are willing to spend, almost anything/a. is adaptable for use as a PC keboard.

Slashdot Top Deals

FORTUNE'S FUN FACTS TO KNOW AND TELL: #44 Zebras are colored with dark stripes on a light background.