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

 



Forgot your password?
typodupeerror

Comment So put it under a freeway! (Score 3, Interesting) 110

Each hole might be of manageable size. But the array would be on the order of the same size as the town. That's a lot of holes and a lot of property you are going to be perforating.

It must be on the scale of the town IN ONE DIMENSION. Linear-square law: The bigger the area you're protecting, the lower the percentage of the area you need to perforate.

So you need to perforate a strip around the town to do this? Do it while you're ALREADY perforating such a strip. Like when you're building (or revamping) the next beltway-freeway around the city of interest, or approving a rezoning for the construction of a new outer subdivision.

Comment Or send it back out to sea. (Score 1) 110

divert tsunamis from strategic buildings and towards some poor fishing village full of primitive natives nobody cares about.

You can also use this to send the wave back out to sea - and defocus it while you're at it, so it's just a slightly higher wave than usual when it finally gets to another piece of land.

This is what happens to it when it hits shore: Some of it bounces and is diffused - or possibly focussed. By doing this intelligently we can make it SMALLER when it hits the "secon

Comment Energy level doesn't matter in this case. (Score 1) 110

You are talking about redirecting amounts of energy in a wall of water than may be 10-20 feet high or more, yet it comes in as a solid wave and the elevation stays at that height causing water to move inland extremely fast for a long time.

It would be easy to calculate what amount of energy that would be in a width of a town: ...

Yes, you are. So what? That energy is spread out over a very wide area. You're talking about building a "lens" over a similarly wide area - out where the "tsunami" is a gentle (though fast-moving) rise of a couple inches to a foot - representing a water current that's comparable to other wave action. The only thing special about a tsunami is that it's a very low frequency wave.

A mirror, lens, or metamaterial doesn't care HOW much energy it's handling, until the energy density gets high enough to start damaging it. The energy density of a tsunami, spread out over those same several miles or whatever, is quite low.

In fact, it's a similar structure acting on the wave - the gradual rise of the seabed as you approach the beach - that concentrates the energy of the tsunami, along its direction of propagation, into a destructive, abrupt, wavefront.

Comment Industrial-grade vanadium redox. (Score 1) 579

Hawaii has basically hit the saturation point of renewable energy until a decent storage system is developed.

A fine, industrial scale, storage system has already been developed and deployed. It's the "vanadium redox" battery.

Think of it as a battery built something like a liquid-fueled fuel cell, with chemical solutions pumped across the two sides of a membrane going through oxidation-state changes, and the electrons going the long way around via conductors on the surfaces of the membrane to cross the potential difference. In this case the solutions on BOTH sides are the same soluble vanadium compounds (except for the different oxidation state of the vanadium), so minor leakage doesn't contaminate the solutions.

Pumping the liquid "electrodes" of this battery decouples power and energy storage rating. Size the cells for the power requirement, size the tanks for the energy storage requirement.

This has already been developed and deployed for utility energy storage. As I understand it: It's quite cost effective and the limited deployment is mainly because it's still under patent protection and the one manufacturer isn't big enough (yet) to make a dent in the power grid's potential market. (Of course it's also new, so it's not yet time-proven.)

Comment Re: There must be a very good reason... (Score 4, Insightful) 579

Solar goes from zero to max out put from dawn to solar noon back to zero at sunset. ... You need a huge amount of peaking plants to keep the grid stable. You do not want large voltage and or frequencies swings.

Except that renewable energy largely feeds during the peaks, REDUCING the need for peaking generation. Solar generates more during sunny times, closely tracking air conditioning requirements. Wind peaks in afternoon/evening, along with classical peak load, due to "lake effect" wind at good sites (i.e. Altamont pass, with the Pacific for the "lake" and California's central valley for the "land") and also tracks heating requirements, due both to lower temperatures during stormy times and greater thermal transfer through walls during windy times. A mix of solar and wind is normally a close match to the grid's peak cycle.

Meanwhile, generation-affecting weather phenomena, like storm shadows and weather-related winds and gusting, make output vary quickly at any given site, but with both solar and wind generation spread out over many square miles and grid-connected these variations are smoothed out. They're also predictable days in advance.

So solar and wind DECREASE the need for peaking generation.

Comment Because there are also wiring losses. (Score 1) 579

... as home lighting is trying to become more efficient, LED lighting wants to work on lower power but efficiency is actually harmed with each AC-DC conversion for each LED lamp. So why not start by going DC in the home?

Because you have to include the (square law!) resistive losses of the wiring, too. For every factor of two you drop the voltage you must multiply the amount of metal in your wriing by by a factor of four to get the same percentage loss for a given amount of powe4r transferred., Going low-voltage DC means putting in a LOT of new VERY HEAVY copper wire, and copper is currently so expensive that thieves are actually breaking into empty houses and ripping open the walls to steal it.

Meanwhile, semiconductor-based switching-type voltage converters have become very cheap and very efficient - to the point that modern commercial computer and networking equipment puts individual voltage converters next to the major chips, to save a substantial amount of power (mainly to reduce cooling requirements) from transporting the power across a few inches of power-plane printed circuit layer.

By substantial, I mean that, by feeding the boards 48V and regulating it beside the chips, rather than using a single regulator where the power enters the board, they more that cut their heat losses IN HALF. The resistive losses at low voltage were bigger than the load AND its regulator. It's the same story as using high voltage transmission lines cross-country. But now switching regulators are substantially more efficient than line-frequency transformers.

So you want the regulators at the load, to keep your efficiency up and your house wiring costs and losses down. The last step: Switch to DC at high voltage for the house wiring? Why bother? You don't lose enough extra power or add enough extra cost by including a couple diodes and a filter capacitor to make up for the trouble of retooling ALL THE APPLIANCES for AC/DC capability, and failing to do that means you still need both AC and DC wiring in the home (doubling the wiring again) or to only be able to use DC-capable devices. How many gadgets do you have powered by transformer-based "wall warts"?

Comment Make me think twice? Sure does! (Score 1) 579

... does this make you think twice about it?

It sure does. Here's the relevant sentence:

Efficiency gains and cost reductions has brought the price of solar energy to within parity of traditional power generation in states like California and Hawaii.

I.e. places with enough sun (5ish or so solar hours) to make it worthwhile. (It's not just the subsidies.)

What's new is that the breakeven point is finally being crossed. So it's finally time to look into actually getting off the grid.

Comment Re:Did Civilization Create Beer? (Score 2) 89

Anthropologists are currently documenting another way it may have led to civilization: Tribes brewing batches of beer and, when it's ready, throwing beer parties and inviting the neighboring tribes (who reciprocate when THEIR beer is ready - or do some other valuable thing for the partygivers). This leads to alliances and good relations between polities.

Comment Do it to code and get it inspected. (Score 3, Insightful) 148

Now many home improvements can be a DYI project, but wiring a 240V-50A line is NOT one of those things.

The HELL it's not. I did the wiring on my home improvement - including upgrading the drop to 200A service - and (unlike my uncle) I'm not a licensed electrician or electrical contractor.

Here's the drill:
  - Read up on the subject. Use several sources. One should be the electrical code itself.
  - Do some initial planning, then talk to your local code inspectors BEFORE you TAKE OUT THE building permit and start the project, and adjust the plans accordingly
.
  - Do it WITH a building permit and inspections. (The fee for the permit pays for the inspectors!)
  - Try to get it right, or as right as possible, the first time. Inspectors don't like to find a bunch of problems to be repaired. (It makes them worry that there are more they might have missed.) Fix whatever they spot, don't argue about it. Answer all their questions and be helpful.
  - DON'T use aluminum wire, EVER! Use copper and pay the extra price. (Getting aluminum wiring right is hard, requires special tools, and you can't really tell if you goofed. If you get it wrong, it wil burn you down in a year or a decade.)
  - When the code offers you options, go for the better approach, rather than the corner-cutting way.
  - Look for the UL label (or your country's equivalent) - on EVERYTHING you use.

Things to remember about the electrical code:
  - The national code is a model. Some cities adopt it verbatim, some with changes, a few roll their own. But the REAL code is the way your inspector interprets it.
  - Be nice and helpful with the inspector. Don't argue. (Feel free to ask what you misunderstood about the code, what you're doing wrong, what the purpose of some fine point is. But don't take TOO much of his time.) He has the authority to shut down your project. Respect that.
  - If you DON'T do it to code, and with a permit and inspections in locations that require it (almost all of 'em), and your house then burns down (even if your work didn't start the fire), your fire insurance can pay you nothing (and keep all the premiums you paid over the years, too.)

Comment Designed to WOUND. (Score 1) 283

Modern (i.e. WW II and later) military small arms are mainly designed to WOUND. Yes, they sometimes kill. But wounding is better for winning battles, wars, and avoiding their resumption.

Kill a soldier and the enemy loses one effective soldier. Wound him and he loses, for a time, SEVERAL effectives and a lot of other resources, hauling the wounded warrior off the field, treating him, feeding him, etc.

More survivors also means fewer vendettas and an easier time making and maintaining peace, rebuilding both sides once the disagreement is over, and forming alliances and trading partnerships with former enemy countries.

Comment Re:And they ARE compromised. (Score 1) 213

But we know it keeps its wired link active.

In fact, on an older laptop I have had (a Toshiba Tecra M5) you can see it:
  - Power it down.
  - Plug it into a live ethernet switch.
  - Green light comes on, yellow light flickers with traffic.

Of course there's no need for those lights to blink, either. So I wouldn't take the ABSENSE of activity, especially in a newer model that might be trying to be stealthy, to indicate it's NOT talking and listening. (Look at the switch, instead, which I'd consider more likely to show such activity since it doesn't have any easy way to know that the device was trying to be stealthy.)

Comment Re:And they ARE compromised. (Score 1) 213

Some of what you say may be true, but a normal laptop generally doesn't have its WiFi active when it's switched off.

And you know this how?

(By "switched off" do you mean laptop power or the WiFi/Bluetooth switch?)

Suppose it's listening passively, possibly also intermittently, and not transmitting unless it observes a properly authenticated request from the "remote administrator" or a specialized beacon (since most WiFi networks won't know how to send it traffic if it's not responding). How could you tell the difference? There'd be no external sign - no light, no radio emission - unless it was actively being probed RIGHT THEN, and even then there'd only be the acknowledgements and other handshaking, with no need to light the lamp.

Yes there are issues with trying to establish a link through the ordinary WiFi network when you're being passive, and the documentation claims WiFi configuration doesn't work in power-down mode (but the wired connection does). Nevertheless, who knows what that firmware is up to, besides Intel and the NSA?

Comment While they're at it: Integrate with tow/haul mode (Score 3, Informative) 112

On my recent model F150 there's a very handy feature: "Tow/Haul" mode. It changes the transmission shift behavior so that touching the brakes makes it downshift and STAY downshifted (and doing it again downshifts another step on the many-gear-ratios transmission), while touching the accelerator lets it shift back up. This is GREAT for long downgrades in mountains, even if you're NOT towing.

But it doesn't interact well with the cruise control. The speed control raises the throttle setting to keep you from going under the setpoint. But when you're over it just goes down to idle and lets your speed runaway. Touch the brakes to enable engine braking and the cruise control disengages. No automatic speed control for YOU on the downgrade. When the grade starts to level out the speed drops, and even before that you're back to watching the speedometer and doing manual adjustments,

Result: On mountain roads you're constantly disengaging and re-engaging the speed control.

They should integrate the two: When tow/haul mode is engaged, the speed control should send downshift signals to the transmission to control too-fast as well as too-slow conditions.
When tow-haul is on the speed control should signal the transmission to downshift when necessary, to keep the speed from running away and requiring the driver to brake. (The speed control's acceleration when too-slow will handle the upshift correctly.)

You'll still have to touch the brakes or tap-down the speed setting for curves and other locally slow zones. But then you'd just hit "resume" or tap-up the setting. Meanwhile the automation would handle the non-exceptional condition of preventing overspeed and runaway on downgrades.

Slashdot Top Deals

This system will self-destruct in five minutes.

Working...