Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



Forgot your password?
typodupeerror
×

Comment Build WHAT in California? (Score 1) 619

Build WHAT?!

Not in California. Not even if the central valley is a dust bowl to save the river smelt. Not even if the state paid the highest electric rates in the nation due to horribly botched deregulation. Not even if the manufactured crisis was easy to trigger because the total electric power available is very close to peak usage.

And yes, if California seceded from the Union, the only liquid flowing in most of California would be untreated sewage and contaminated field run-off. Water quality regulations are only important when they impact voters.

Comment NJ nicknames (Score 2, Insightful) 240

I think that some people do not know why NJ is called "the armpit of America". It's not just the smell of its refineries and chemical plants along the coast. Look at its position on the map.

Most visitors just see the part of NJ along I95, missing the sections further inland which gave it the name "The Garden State".

Comment Re:G-forces ???? (Score 1) 384

Hitting escape velocity won't help -- whatever is sent out will be unrecoverable. It will roughly be on Earth's orbit around the Sun, but likely won't coincide.

There is some flexibility by shooting the object past the moon, and getting a little bit of a 'slingshot' effect to modify the resulting orbit. But it would still require steering rockets because even a slight error in the initial path or orbital calculation would make a huge different in the resulting orbit.

This topic would make for a great physics and geometry lesson. Why inertial orbits starting from the surface always intersect the surface (the original topic). Why going from a one-body system to a two-body system might be able to change this, but at the expense of extreme sensitivity. How the complexity of potential orbits vastly increases as you add more bodies.

Even more interesting, is the extreme state sensitivity of the "interesting" configurations. A few seconds of arc difference in the initial course can put you someplace completely different. Simple orbital calculations assume point sources of gravity. That's not a bad approximation if you are far enough away, but a "slingshot" breaks that assumption. You can't even model the objects as uniform spheres -- the earth isn't spherical, and it doesn't have a uniform mass distribution. And for objects such as the Earth that have significant magnetic fields, there will be a deflection on approach and departure.

Bottom line is that anything done in space requires a significant ability to steer, and most operations require the ability to dynamically navigate.

Comment Prolog Assignment (Score 4, Interesting) 683

That's completely understandable in this case of programming in Prolog.

Prolog is a declarative language.

You declare the rules, and the system figures out a result that matches those rules.

The problem is that this basically doesn't work. So a Prolog programmer has to write the "declarative" rules in a procedural order so that the run-time system doesn't have to try every possible combination to find (or fail to find) a matching result.

The proper ordering of declarations can be quite subtle. With a modestly complex program you can make a seemingly unimportant change in the order of the declarations and have the runtime go from a second to a week.

In this case the professor didn't (couldn't) know how long a Prolog program to solve this problem should take. He just assumed that you had found a more efficient ordering for the declarations. He might even have thought it was luck rather than deep insight that your program was faster than his. But you have to a decent understanding of the limits of Prolog to get a complex program to complete in a reasonable time, so you had to be good before you could get that lucky.

If you couldn't already tell, I have a low opinion of Prolog and declarative languages. They are "parlor tricks". Much like computer 'Life' and neural networks, simple programs can produce unexpected seemingly-sophisticated results. But they don't get better from those initial results. To compute the answers or results you want in a reasonable time, you end up with at least the complexity of writing things in the traditional explicitly procedural method.

The promoters of declarative language typically don't mention that you end up writing rules in an explicitly procedural order if you want the program to work. If you press them on the issue, they then say "well, OK, it's not actually any easier to write, but it's easier to verify that you've correctly specified the desired result." But if you have to carefully shuffle declarations around, and even then some results unpredictably take centuries to compute, pretty much no one cares.

Comment Power isn't a problem (Score 1) 274

How much energy does it take to get out of earth orbit? How much power capacity needs to be held in reserve for unexpected events?

I don't expect that power usage for entertainment communications is an issue. The ship will no doubt have antennas and transmitters large enough to transmit video and telemetry both for control and for the benefit of the citizens that paid for the mission. The bits needed to request something is trivial in comparison.

On the other side, there is plenty of power on earth to transmit por... entertainment during the slow periods.

I also don't see any problem with the latency. You obviously wouldn't be able to play online games, but most of what you view in a day could be pre-cached or just waited for without a problem.

Comment This is the real reason that this story is bunk. (Score 1) 323

For the first year or two of a policy 'mistake' like this, contractors make extra money. After that the increase in profitability is taken into account on the next bid. So at most there was a temporary extra expenditure four decades ago.

If the rates were changed today, the market reaction would be almost instant. Contractors would insist on the old terms for existing contracts, and increase the rates for new contracts. And charge a little extra to compensate for the new risk of additional changes. (If you make your suppliers nervous, they rationally will spend extra to mitigate their new risk and will pass that cost onto you.)

Comment That's the beauty of this scheme! (Score 1) 119

The RIAA gathers license fees, and distributes them among the record companies and artists.. after taking out an administrative fee (100% in some cases).

The payments for "covenants not to sue" are not license fees.

No doubt some small fraction will be treated as a license fee, just to put a veneer of legitimacy on the scheme. But I've no doubt that the RIAA will use the extra layers of administration to make reduce the amount and skew the payout distribution to record companies that play the game.

Comment Why rent payments are less than mortgage payments (Score 1) 695

It's not uncommon for rent payments to be less than the mortgage in high cost areas like San Francisco. The owners are hoping to make their money on rapid property value increases. The renters are just there to keep the place occupied and help qualify for the mortgage.

If a $700K house will be worth $800K next year, you aren't that concerned if the renters are paying $2K/month or $3K/month.

Everything changes when the $800K house will be worth $750K next year. The owner can't sell. They would probably need to get rid of the tenants to put the house on the market, but they can't afford to pay the full mortgage when the house doesn't sell in the slow market. They can't raise the rent much, until all of the other rental properties go up as well.

Slashdot Top Deals

Those who can, do; those who can't, write. Those who can't write work for the Bell Labs Record.

Working...