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

 



Forgot your password?
typodupeerror
What's the story with these ads on Slashdot? Check out our new blog post to find out. ×

Comment Calculations (Score 5, Interesting) 93

So you harpoon a comet with a velocity relative to you of 10 km/s. You have 1000km of tether. That means that if you didn't apply any braking, you'd have just 100s before your tether ran out. With little bit of physics, I find that the probe would need to accelerate at 50m/s^2 (over 5g) to match velocity with the comet before running out of tether (which takes 200s because now it is accelerating). So the tether and the harpoon need to withstand a tension of 5 times the earth-weight of the probe, without breaking or pulling the harpoon out of the comet. Now assume the probe is 1000kg. (For simplicity I'll ignore the mass of the tether and the rotation of the tether reel, although that would probably be a deal breaker too.) Force = 1000kg x 50m/s^2 = 50000N. Distance acted over = 1000km = 10^6 m, so work = 5x10^4 x 10^6 = 5 x 10^10 J. It is 200 s before the tether runs out, so power = 5x10^10/200 = 2.5x10^8W = 250 MW. That power has to be stored and/or dissipated, and you have at best 1000kg with which to do it.

It all gets very much easier if your relative velocity with the comet is much lower, but then you're not gaining much, and intercepting a comet with only few km/s relative velocity is very hard in itself.

It is a pretty idea, but I can't see it working with anything vaguely like current technology.

Does anyone care to poke holes in my reasoning?

Comment Re: Yay for price drop (Score 1) 130

Crude is the raw material. You still ned to manufacture and distribute the gasoline. As a guess, the refinery capacity hasn't increased in your area of the world. Nor is it likely to, as the trend is toward hybrids and all-electrics. Projected future consumption is not likely to support a large refinery project for the next 30-50 years.

Comment Everything in your life will be a governance gizmo (Score 4, Insightful) 149

I've been trying to keep my job skills fresh so I can keep up with the "next big thing". But I'll be damned if I can figure out what the hell IoT really is and why it's taking off. Yes, I know it's connecting things to the internet. But to what end?

It will allow Apple, Microsoft, Google, the US Government, and others to turn every device in your home into a governance/surveillance device. It won't just be your TV watching you a la 1984, it will be your thermostat, your keyboard, your couch, your bedside lamp, hell, not just your bed but your baby's crib and the baby's rattle.

That is why they are so keen on the "Internet of Things." What? You thought it was to benefit you? Really? Then I've got a bridge in Brooklyn I'd like to sell you.

Comment A step forward, but... (Score 4, Insightful) 396

Achieving practical nuclear fusion for power generation would be a very nice step forward. But "holy grail" is rather overselling it, I suspect.

Even when practical, we're still talking very big, very expensive plants that depend on a long supply chain for all its parts, the high-purity fuel and so on. When you consider the building, running and maintenance costs, and the cost of dealing with the spent fuel (much better than for fission plants of course) the energy won't be all that cheap. Hopefully cheaper than fossil fuels at least, but I would not be surprised if a first generation of plants, at least, become more expensive than that.

And they'll be competing with rapidly dropping costs for solar and other renewables. A big, expensive plant like that will need a 40-50 year lifetime to pay for itself. If you can't show that it will likely run profitably for that time period few or no companies will be willing to take on the very major investment. We may well see a technical breakthrough for fusion, and still get no plants actually built.

Comment Re:From TFA: bit-exact or not? (Score 1) 172

There used to be a web page called "Your Eyes Suck at Blue". You might find it on the Wayback machine.

You can tell the luminance of each individual channel more precisely than you can perceive differences in mixed color. This is due to the difference between rod and cone cells. Your perception of the color gamut is, sorry, imprecise. I'm sure that you really can't discriminate 256 bits of blue in the presence of other, varying, colors.

Comment Re:From TFA: bit-exact or not? (Score 5, Insightful) 172

Rather than abuse every commenter who has not joined your specialty on Slashdot, please take the source and write about what you find.

Given that CPU and memory get less expensive over time, it is no surprise that algorithms work practically today that would not have when various standards groups started meeting. Ultimately, someone like you can state what the trade-offs are in clear English, and indeed whether they work at all, which is more productive than trading naah-naahs.

Comment Re:truth is... (Score 1) 93

Yea, because open-source software is famous for having well-designed, easy-to-use comprehensive instructions. ;>)

It often sucks, certainly. But there is one compelling advantage, in the case of unusual stuff such as this. The developers themselves are happy to talk about and answer questions around their tools. And open source tools tend to attract hobbyists that do things for fun, and are happy talking about what they do, and not just commercial developers that won't publicly say a word.

So with open source tools you're much more likely to find blog posts, forums and so on with information to help you along. There's a chance there's be people out there that had the same trouble you do, and wrote about it in public. With commercial tools - and especially tools with a userbase in the hundreds rather than tens or hundreds of thousands - there may simply be no public information out there at all beyond the docs written by the provider.

Comment Re:Might want to read the fine print... (Score 4, Interesting) 165

This is fine - they're not pretending those impacts don't happen, they are just not what they're studying. They are asking "What does the fallout do to people some distance from the accident?"

The exposure people get early in the accident and very close to the reactors depends hugely on the nature of the accident. At Chernobyl, there were many firefighters within meters of an exposed critical core, resulting in a large toll from acute radiation sickness. At Fukushima, the cores ceased to be critical seconds after the quake and tens of minutes before the tsunami, and radiation was only released days later, so there was no acute radiation sickness.

By contrast, the effect of the fallout is much less dependent on the nature of the accident, just on how much radioactive material was released*. It can sensibly be studied without specifying details of how the accident happened.

* There is some dependence: the relative quantity of short lived isotopes such as Iodine-131 in the fallout depends somewhat on how long the radioactive material was contained prior to release.

PLUG IT IN!!!

Working...