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US Navy Authorizes Use of Laser In Combat

joe_frisch Re:This might alienate anti-ISI* Muslims. (225 comments)

The only demo I saw of one of these was against a small boat.

Missiles might be a valid target, but they could be designed to be very laser resistant - picture a reentry shield......

I don't really see much use for these anyway - "won't work in rain and fog" is a pretty big problem.

about a week ago
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US Navy Authorizes Use of Laser In Combat

joe_frisch Re: This might alienate anti-ISI* Muslims. (225 comments)

A modestly shiny piece of metal will do quite a good job of reflecting. You won't get a coherent beam but a diffuse spot that will still blind at a long distance. think of the sun reflecting off of a modestly well polished metal surface. Something you could easily get with a buffing wheel.

Or for more humor value - a disco ball......

about a week ago
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US Navy Authorizes Use of Laser In Combat

joe_frisch Re:This might alienate anti-ISI* Muslims. (225 comments)

I'm worried about a reflector on the target ship. If I were planning a terrorist attack on a US navy ship, after reading this, I'd mount an optical retro-reflectors. (though of course that makes you more radar-visible... The retroreflectors are a big hazard to crew on the firing ship. They don't need to be very good if you are just trying to blind, not do physical damage.

The blinding problem is more an issue if the ship is in harbor somewhere. There is also the risk of a clever terrorist on a boat reflecting the beam toward a nearby (few kilometers) set of civilians - say a crowded beach.......

Reasonable precautions can avoid these scenarios, but the precautions need to be taken very seriously. I don't want to hear that we accidentally blinded hundreds of innocent families on a beach somewhere.....

(I just hope that the US realizes the risk before the terrorists recognize the opportunity). Otherwise I wouldn't even post ideas like this on a public board.

about a week ago
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US Navy Authorizes Use of Laser In Combat

joe_frisch Re:This might alienate anti-ISI* Muslims. (225 comments)

This could get sticky. The most effective property of the lasers may be that they blind, even though that isn't their stated function. Similarly to using white phosphorus against humans, the legality is debated.

Everyone on a ship with the laser will need eye protection all the time. Crude metal corner cubes will be pretty effective and since the goal of the weapon is rapid response, the crew will need to always be ready, or they risk blinding their own people. It will have a really tough time burning through a 1/4" thick aluminum corner cube.

Note - it isn't clear from the article whether the laser operates at a wavelength that is likely to cause blindness. Various hints suggest it is Nd (or maybe Yb) based which would be ~1um and is in a wavelength range that can easily cause blindness (it is focused by the eye). The powers required for blinding are dramatically lower then the power required to do physical damage, so its range as a blinding weapon (intentional or not) will be much longer than its range for physical damage. The risk of blinding bystanders from scatter may be significant.

If it is ~1um micron wavelength the beam will be invisible and targets may not be aware of how they were damaged or blinded.

about a week ago
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CIA Lied Over Brutal Interrogations

joe_frisch Re:Effectiveness doesn't matter (768 comments)

Are you so sure?
How many lives were lost in WWII to protect freedom? Would we allow an authoritarian government that didn't support human rights to take over the US because fighting would mean we would lose millions of lives?

about two weeks ago
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CIA Lied Over Brutal Interrogations

joe_frisch Re:It's allowed... (768 comments)

Generally fighting fire with water or other fire retardants is the preferred method.

It is in the very nature of evil that it "gets results". The entire point of morality is that there are things you will not do even if they are in your interest.

As an American citizen, I do not in any way approve of the use of torture. I am willing to accept the higher risk of death by terrorism, assuming the risk even is higher, in return for the country behaving in a moral fashion. I am willing to trade my safety for doing what is right. No torture, no indefinite detention, no extra-judicial killings.

  If I knew a legal way to stop the US from using torture, I would.

We have become the things we always claimed that we opposed in the world.

about two weeks ago
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Berkeley Lab Builds World Record Tabletop-Size Particle Accelerator

joe_frisch Re:What about efficiency? (90 comments)

Superconducting linacs can be quite efficient - 10s of %. Electric costs are not a major driver for most accelerators so typically they are not that good in order to save construction costs. You could probably design >50% wall plug -> beam efficiency accelerator if you wanted to.

Laser accelerators are not that good at converting laser energy to beam energy. I don't know the numbers, but above ~10% would surprise me. Then the high drive lasers are very inefficient (these are not diode laesrs!). Both those can be improved, but I would be surprised if the final efficiency were as high as for a conventional superconducting linac.

For low power beam applications that may not be a significant disadvantage and the short length is of course a big advantage. (though the drive laser is big).

about two weeks ago
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Orion Capsule Safely Recovered, Complete With 12-Year-Old Computer Guts

joe_frisch Engineering == use the correct technology (197 comments)

If older computers can do the job and are known to be reliable in this environment, then using them is the correct choice. We sent people to the moon, and Voyager to multiple outer planets with much older computer technology.

If newer computers would provide improved performance IN THIS APPLICATION then they are worth considering.

about two weeks ago
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Trains May Soon Come Equipped With Debris-Zapping Lasers

joe_frisch Re:Even if their wet? (194 comments)

We need to test all the competing technologies for this to pick the best:

1) high power lasers.
2). Flame throwers
3). High power plasma discharges.
4). rocket-propelled Anti-leaf attack drones
5). Jets of ClF3
6) Anti-proton beams.
7). Brushes
8) US only: a guy walking ahead of the train with a broom.

then we can see which is the most cost effective and safe - and get some cool youtube videos as well.

about two weeks ago
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The Sony Pictures Hack Was Even Worse Than Everyone Thought

joe_frisch Re:Sauce for the goose; sauce for the gander (528 comments)

I wonder if Sony knows that they are still losing business over this - probably no way for them to find out. I know they've lost >$10K in sales from me since then (I had all Sony stuff at home until then, now nothing).

about two weeks ago
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The Sony Pictures Hack Was Even Worse Than Everyone Thought

joe_frisch Re:Sauce for the goose; sauce for the gander (528 comments)

I feel sorry for their employees who's information was compromised, but I can't say the same about the company. They are still on my "do not buy" list, and I buy a lot of the sort of things that they sell. Still waiting for an apology for the rootkit.

about two weeks ago
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Physicist Kip Thorne On the Physics of "Interstellar"

joe_frisch Re:You will not go to wormhole today. (289 comments)

Depends on what you mean by "small scales". Relativity works to the length scales accessible by accelerators (1 TeV, or something like 1e-18M - and probably extrapolated a lot further). There are issues with quantum gravity but they only become significant at energy scales approaching plank energy - far beyond any conceivable technology. There are also possible issues with relativity at cosmological scales.

The problem is that relativity seems completely under all technologically reachable conditions. Star drives just don't seem possible.

We *could* be missing something, but it is very difficult to imagine a set of rules that allow FTL or other fun stuff, but which would not have been noticed in present day measurements that range for accelerator scales to cosmological scales.

about two weeks ago
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Drone Sightings Near Other Aircraft Up Dramatically

joe_frisch Re:These idiots are going to ruin it for everyone (132 comments)

Maybe this suggests a technical solution.
Equip drones with GPS and nav databases so that they will not fly in controlled airspace. (with the ability to override with some sort of approval).

There are flights in uncontrolled airspace but it is much less of an issue.

about a month ago
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New Particle Collider Is One Foot Long

joe_frisch Re:SLAC FACET accelerator (161 comments)

Unfortunately for ion drives you want high current but very low energy. The amount of electric power required by an ion drive increases as the exhaust velocity increases, and for present day space applications you are better off with less particle energy, not more.

about a month and a half ago
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New Particle Collider Is One Foot Long

joe_frisch Re:Not exactly (161 comments)

Its a good question .
I don't understand astrophysical shocks, but see: http://www.slac.stanford.edu/e...
As far as I can tell the rely on magnetic fields bending the particles back into the shock.

When relativistic particle trajectories are bent by magnetic fields, they emit synchrotron radiation which increases rapidly with increasing particle energy.

Longitudinal fields don't do the same thing. There is a tiny amount of radiation, but it is not strongly dependent on particle energy. I believe this is because Lorentz contraction increases transverse, but not longitudinal electromagnetic fields: http://en.wikipedia.org/wiki/C...

Ideally the fields in the plasma accelerator are longitudinal on axis. If the particle enters slightly off axis it will get a transverse kick and will radiate synchrotron radiation, and we do see that. For very high energies that radiation might be large, but the effect would be to damp the transverse motion of the particle, but not affect the longitudinal acceleration.

  I know that the plasma wakefield people are seriously thinking about TeV scale machines: https://accelconf.web.cern.ch/...

It is possible that the concept fails at some much higher energy.

about a month and a half ago
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New Particle Collider Is One Foot Long

joe_frisch Re:SLAC FACET accelerator (161 comments)

That is a slightly different concept. This uses a medium-energy (20GeV), high current electron beam to drive the plasma, which then accelerates a high energy beam.

There is also a scheme to use a high energy proton beam to drive the plasma, and a scheme to use a high power (Peta-watt) laser to drive the plasma.

All are being seriously considered / developed by various laboratories.

This type of scheme probably doesn't apply well to a circular machine like LHC because the energy limit there is the magnets used to bend the beam into a ring .You might accelerate the protons at the end, but you wouldn't be able to send them back for re-use and you would not get enough collisions to get interesting physics.

about a month and a half ago
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New Particle Collider Is One Foot Long

joe_frisch Re:Not exactly (161 comments)

If you do everything right, you should get the same added energy from each section. So a 10 GeV input beam woudl go to 11.6, and a 1000 GeV beam would go to 1001.6. The beams are ultra-relativistic - for all practical purposes speed of light (off by only a part in a billion) and this acceleration mechanism doesn't depend on the beam energy .

about a month and a half ago
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New Particle Collider Is One Foot Long

joe_frisch Re:Not exactly (161 comments)

Yes - in principal. You will need a separate bunch of 20 GeV drive electrons for each section, but that is not very difficult to do with a single accelerator. You need to separate the waste beam from the previous stage and the magnetic system to do that may be inconveniently long unless there is a beam-optics trick (which there may be).

Staging two sections together is on the list of things that they are going to try. The eventual goal is to put together a lot of stages to get to TeV scale energies.

about a month and a half ago
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New Particle Collider Is One Foot Long

joe_frisch Re:Not exactly (161 comments)

If you do a Google search on

SLAC PUB plasma wakefield
you will find a lot of non-paywalled papers on this and related plasma accelerator experiments at SLAC.

about a month and a half ago
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New Particle Collider Is One Foot Long

joe_frisch SLAC FACET accelerator (161 comments)

I am peripherally involved in the SLAC plasma wakefield accelerator described in the article.

It provides a very high energy gain in a short distance, but needs to be driven by a high energy drive beam. The present design uses a 20GeV drive beam (using part of the old high energy physics accelerator).The required drive beam energy could be reduced to ~10GeV but probably not a whole lot lower. So this is a way to build a relatively short very high energy accelerator, but not a way to build a very short low-medium energy machine.

Other labs are working on laser driven plasma accelerators that do not need to start with a high energy beam, but do need an enormous laser system and are presently limited to much lower average beam powers .

Plasmas are very promising for future accelerators and there was some excellent work done at SLAC as well as laser / plasma accelerators at other labs. There is still a lot to do. There are issues with staging multiple plasma cells to get high energies, beam quality and stability issues etc.

about a month and a half ago

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Ask Slashdot: Computers for the elderly

joe_frisch joe_frisch writes  |  more than 2 years ago

joe_frisch (1366229) writes "There is a growing group of elderly computer users who have learned to be productive with a particular interface, say windows XP and office 2003, and who do not have the interest or energy to learn something new like Windows 7 or the office "ribbon". They continue to use aging and unreliable computers because they do not know how to order new computers with the older interface. Many of these users are relatively wealthy so this is potentially a valuable market.

While it it possible to cobble something together, with time it becomes increasingly difficult, especially for the often minimally computer-literate people in this market. In addition, as older software is no longer supported it will be increasingly susceptible to viruses. What would be ideal is a old style interface to updated programs and operating systems.

What are the options — and remember the target market is NOT people who read slashdot, suggesting that they use Debian is not going to work."

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