The other limit is finding a suitably reflective material that is cheap enough to be used as media. X rays pass easily through plastics, and they are absorbed by lead. Gamma rays pass through most kinds of material. You need something that reflects well, and doesn't absorb the radiation, that can also be used to store distinct states and be mass produced easily.
If you can produce a finely focused x-ray beam in the reader, you could probably factory-produce extremely high density discs by coating the discs in a material that fluoresced in x-rays, and using an electron beam to etch pits in it. Or stamping, coating, and CMP to leave only the filled pits, but that's probably just as expensive as e-beam writing. Data is read by scanning the disk with the x-ray beam and looking for spots where it doesn't fluoresce.
If you're willing to mount the disc and read/write head in vacuum, you could use a low-energy electron beam as the probe beam and get resolution as fine as you like, though that means carrying your factory-stamped discs in a vacuum caddy the whole time.
The article only discusses write techniques. I'd like to hear if there are any peculiarities involved in reading it before I make guesses as to the delay before production. I'd also like to know if they only have a tube or if they have a diode already.
You need a laser with comparable or finer wavelength to the writing laser in order to read an optical disc.
This is almost certainly a frequency-doubled or even frequency-tripled laser, which means it's very power-inefficient (I believe there were old green laser pointers that were frequency-doubled IR; they got awfully warm, as most of the pump beam stayed as IR, and was wasted).
Source laser isn't mentioned in the short blurb (and the full blurb is subscribers-only), but I'd guess it's an excimer laser similar to the kind used for EUV photolithography, if it can make 70 nm holes. In fact, it wouldn't surprise me to learn that it's _exactly_ that type of laser, and that this experiment was done in a photolithography clean room. Excimer lasers are gas lasers that produce output in the near-UV. The 193 nm light used for photolithography a generation or so ago was from frequency-doubled argon fluoride excimer lasers.
We have UV LEDs, and so presumably low-power UV laser diodes are available in research labs, but getting something that can reliably make holes 70 nm wide would probably take frequency _tripling_ at this point. So I'd put money on a gas laser at the moment, with a tripled blue or violet diode or a doubled intermediate UV diode laser "some time really soon now, honest".
Producing light of the needed wavelength without frequency doubling would take a pretty exotic material with a bandgap that puts it well into the "insulator with extreme prejudice" range (lots of doping required).
I would like to point out that tournament fighting has absolutely nothing to do with real-world fighting.
Tournament sparring at tournaments is typically non-contact. Practice sparring at the dojo is "light contact", for varying values of "light" (that at one point involved me landing in a weapons rack a few feet away, giving me a healthy respect for kicks). Clean footage of that would be harder to dig up, as less of this was filmed.
In a real-world fight, a 97lb man punching a 194lb man in the stomach will probably hurt his hand, inflict very little damage to his opponent, and be summarily pummeled.
All I can say is, I'm 160 lbs, and have had little girls half my weight hit me hard enough to give me pause. See my other response in this thread for a longer discussion on this.
I am in no way saying that a little guy can't kick a big guy's ass. But if the two are equally skilled, the little guy is probably going to take a severe beating, at least outside of the artificial rules of a tournament.
I'd actually expect the little guy to block, counterattack, and then run like heck:). If it was tooth and nail between two equally skilled opponents... I'd perhaps give better odds for the big guy, but it would by no means be a sure thing. And, per my previous comments, equal skill is a very unusual situation even among black belts (perhaps especially so).
Furthermore, all of the real-world fights between martial artists that I have seen tend to involve very little "art" after the first few seconds.
Fair enough, though arguably those first few seconds are pretty important.
First, he couldn't get close enough to get a good hit on me. I could kick at him from a much farther distance. He had to leave a lot of room between myself and him if he wanted to catch his breath.
I'm puzzled as to why he didn't block or dodge your kick and move in to counter before you recovered from throwing it. A smaller person is going to have a lot of trouble throwing the first technique against someone who has longer reach, so reacting to attacks (and ideally, provoking attacks that leave your opponent exposed) is the lion's share of the smaller person's strategy.
Was I slower than him? No, not really. I was bigger, but I had a lot more strength as well. My feet and fists could move at least as fast as his.
Same speed, and longer distance, means more travel time. Ditto with the "same acceleration" scenario if you assume the same strength to weight ratio instead of the same speed. Square/cube law means that it's hard for the larger person to have the same strength-to-weight ratio as the smaller person, meaning generally lower acceleration, and an even larger time difference (as well as a time difference even for moving the same distance, and for doing things like changing the direction your body is moving). Exceptions exist - level of physical conditioning varies as greatly as skill level between arbitrary individuals - but if you can throw techniques as quickly as your instructor, or change direction as quickly, it represents a very unusual case. Everything I've seen among the people who train at my own dojo bears this out.
Third, the sheer mass of my body left his attacks wanting. My forearm weighed enough that I could stop his strongest kicks before they reached my body. My attacks could not be repelled. When I put my weight behind an attack, his only option was to dodge it. Sure, he was fast, but not that fast. And one good knock and he would've been done.
This is why "strength on strength" techniques are generally discouraged in favour of deflection and evasion techniques, even against an opponent who doesn't out-mass you, as I'm sure you're aware. For a few weeks my regular training partner was a young lady two thirds my weight, who nonetheless could block (sincere) punches and kicks from me without an unmanageable amount of effort.
I've also been hit enough times by people smaller than me to have a healthy respect for their power, but I'm perhaps a bad example, as in sparring I seem to have a knack for leaving myself exposed. For a more general argument, consider a sledgehammer. It only weighs 8 lbs, and it moves slower than a punch, but you still wouldn't want to get hit by it. The same applies to techniques thrown by most of the black belts I know (of all sizes); enough parts are moving, in the right direction, that that technique will hurt.
A small person won't take a large person down in one shot, while the opposite could still happen, but the large person is still going to have considerable trouble landing that one shot, and can easily leave themselves open in the process.
The last fighting game I played was "killer instinct". I can do the Cranky Kong rant about bit-planes too, if you like.
On the other hand, I watch sparring pretty frequently (and spar myself, but I'm not nearly good enough at it to use my own approaches as examples). For smaller people, speed and maneuverability win. For large people, capitalizing on longer reach and effectively countering the small person's attacks wins, because they aren't going to out-race or easily out-maneuver the small guy.
Very true. Which is why I didn't say "green belt" or "random punk." When our meter of skill is "black belt", we can assume identical values for skill given identical variables.
Um, black belt generally represents the beginning of serious training, as opposed to an endpoint. Depending on how high the school sets the bar, getting to black belt takes 3-6 years or so. That leaves another few decades to continue to improve one's technique.
Even among the shodans at our school, there is a very wide skill variation.
I know some 97 pound black belts who can kick your ass through the room.
And when they meet a 194 lbs black belt, they probably get thrown in turn. "All else being equal, the stronger man wins."
This is not obvious to me. As the previous poster pointed out, small fighters are _fast_. While the smaller black belt would be toast if the heavier one managed to grapple, the heavier one will have a hard time successfully counterattacking as long as the lighter one is on their toes.
Strength matters, and reach matters, but skill matters considerably more than either.
Unfortunately none of the footage from tournaments our school has attended is online, or I'd link a few video clips as examples. Skill is very rarely equal, making the other factors less relevant.
I think it's important to distinguish between skepticism and self-sabotage. When you find a claim that sounds unbelievable, do you always say "that sounds too good to be true, it can't possibly work", or do you sometimes investigate further to see if there's anything to it?
Every 20+% return investment I've seen has been the result of investors getting lucky enough to ride a bubble. In the early 1990s this was mutual funds, around here. More recently, this was tech stocks. In both cases, it didn't last.
In theory, if you can consistently pick the right investments all the time, you can sustain this. In practice, you can't even come close to that. I'll stick with conservative or at least moderate investments, thank you.
To succeed in the markets, you need more than wisdom. You need training in all the components of a trading system (not just the stock pick du jour).
You also need a very large amount of luck, which no amount of training will provide.
Very few people have all of these.
But very many people can afford to hire them.
Think about it - I'm Joe Caviar with a few $million to invest. I'm going to hire the best investment portfolio manager money can buy, because I'd much rather eat with gold-plated cutlery than silver! I'm also going to be buying far more stocks than Joe Average, magnifying the fraction of stocks that are held by my demographic. And yet, I still don't consistently make scads of money with my investments...
I am not convinced that 20% yields are sustainable. Too many people would have the means and the desire to access these investment strategies if they worked. We'd either see them getting rich, or there would be enough of them to poison the well.
If you get some decent investment system training, you can make your own investment plan that regularly makes you 20% a year.
I am skeptical of claims that wise people can consistently outperform index growth by that much, simply because if any significant number of people tried it, it would cease to be true (they'd be fighting for the same money when they tried to cash in). Therefore, only a small fraction of people can actually see this kind of return - which means odds are I won't be one of them no matter who my broker or portfolio manager is.
The numbers I hear for return rates sustained over the long term are on the order of 10%, and even these investments will be vulnerable to serious economic downturns (which seem to happen every decade or two).
Fortunately, you don't live forever. You can actually withdraw a portion of that principle each month as well, and live decently for a million, or less.
That depends on how early I want to retire, how long I think I'll live, and what I think the average rate of inflation will be. If I'm looking at living for another 40+ years, and especially if I expect big expenses near the end of that period, I don't want to eat into my principal early on.
Aircraft take time to arrive, unless they are already in the area. They can get shot at, shot down, interfered with, break down, require jamming support, tanker support, etc., etc., etc. It just isn't that easy.
Satellites will take quite some time to get over the target region - remember, a satellite in LEO can only target an area a few hundred kilometres wide, so you either need a very large number of satellites, or live with it taking a while for a crowbar sat to get into position to drop things.
If the satellite is what's doing the targetting, it's easy to jam - shine a light at it, or set a fire big enough to serve as a smoke screen for the area, or just use a camo tarp and keep equipment cool, and it can't target you accurately enough to hit you.
If ground troops are doing the targetting, a ground-level smokescreen or any other means of fouling line-of-sight will work just fine. As will return fire.
Remember the first Gulf War? Scud busting was the big thing then, and the Air Force - even though based next door - couldn't get anywhere. Orbital artillery would.
The problem was not weapons - the problem was that you didn't know a Scud launcher existed until they took the tarps off it and fired it. Hitting the launcher after the fact is questionably useful. Hitting the missiles is _more_ difficult from orbit than it is from the ground, and that was hard enough (Patriot, a repurposed anti-aircraft missile, had a zero percent success rate last I heard, though I'm told a newer version worked marginally better in the current war).
And now, I realize just how pathetically little, a million dollars really is. I look at movies from the 1970's where the plot was someone pulling off a robbery, or murder, for like $10,000. Dude, $1 million won't change your life in a way that's measurable 5 years out.
$1 million put into safe but low-yield investments would give me my current pittance of an income _forever_, _after_ inflation. $2 million would let me retire in modest comfort.
So, while $1M won't make you _rich_, it's still a very respectable amount.
As it is, it appears to be little more than a light sensor attatched to a rapid-fire nerf gun. i.e. Dumb-fire, no aiming.
These are still quite fun. You can buy the pressure-hose equivalent from hardware stores to keep raccoons/cats/etc. away from your garbage, flower garden, or whatever.
I was quite impressed when I saw one of these, though in hindsight it's just a combination of two widely-available existing devices (automatic sprinkler and motion-sensor light). Impressively elegant.
With space based weapons, you don't have to get an aircraft into the area. You look at the area from space, and drop a crowbar on them.
a) The poster this was in reply to was suggesting using satellites as artillery support, which both involves lots of crowbars, and presupposes an area you can get other troops/what-have-you to.
b) My point across this whole thread has been that to do anything serious, you're probably going to be able to accomplish it more cheaply by ICBM than by satellite. There is nowhere that's out of missile range to a nation with ground-to-orbit rockets, which means your satellite scenarios are quite limited (basically, cases where you want to deliver a small payload at high cost and for some reason can't use a big missile to do it).
Not if you have a 50-ton nickel-iron asteroid in orbit.
At present, the only cheap way to get a 50-ton slug into orbit is to lift it from Earth. We can't _see_ the asteroids that are that small, and a craft capable of moving the ones that we _can_ see would cost more than a lifetime supply of orbit-dropped crowbars.
A smelter and manufacturing facility capable of turning a chunk of impure iron into rod-shaped slugs with good de-orbiting characteristics is also big and heavy enough to be impractical to lift with chemical rockets.
Remember, all of this has to compete with the cost of either firing a long-range missile, or inserting an artillery team close enough to do the same job from the ground.
Until there's a cheap road to orbit, ground-side solutions tend to win.
What I think the OP was getting at is the idea of using a rail gun to accelerate large chunks of metal to very high velocities. Upon impact they would easily take out something like a ship or tank, and probably most bunkers. Especially if you fire three or four in rapid succession. Aricraft would be mince meat if you could hit one.
I don't know how well this would, but I have read stories about how the Air Force has tested some of the concepts in labs.
It turns out not to be practical to put a railgun that powerful in orbit. The power storage required and the practical constraints on acceleration would require a structure many kilometres long at minimum (and probably more like many hundreds of kilometres, if you want velocities much higher than you'd already get by dropping things).
The navy railguns linked from previous articles have muzzle velocities of a few km/sec. Anything in this range (or dropped from orbital height) has more kinetic energy than an equivalent mass of explosive, but that's a far cry from being able to demolish a ship using a crowbar's worth of mass.
Ship-mounted railguns can also be far heavier than something you'd put in space, and have a nice, heavy nuclear plant or gigantic diesel engine to power them. An upper limit to the mass of any killer sattelite is about 10-30 tonnes, depending on what it's launched with.
Is 500 lbs of TNT enough to crack a buried bunker designed to be safe from tactical nuclear weapons?
It likely is if it's a focused shaped charge to a single 1" circle....which is basically the entire idea of the crowbar-dropped-from-orbit idea.
I seriously doubt this, if the bunker is deep enough to resist conventional explosive attack (or tactical nuclear warheads). Remember, the 1/e velocity distance is the distance at which the penetrator has displaced an amount of material comparable to its own mass. That'd be at most 10-20 metres of earth for your crowbar. By comparison, the bunker would be on the order of 100 metres down.
The idea isn't to demolish the bunker, it's to kill a single person *despite* that person being in a bunker
This requires demolishing the bunker, as you don't know where they are inside it. If you have a spy in there, there are far cheaper ways of killing the target.
And I'm completely agreed with that idea- but NEITHER can fortified targets or conventional armies stop an attack from space. Multiply that crobar by thousands- even millions- of similar crowbars taking out *specific* ground based targets (of the command and communications variety) and your ground-based army gets one heck of a lot easier to defeat.
The problem is that it's ludicrously expensive to stock that much mass in space. You'd be better off carpet-bombing with napalm and raining down conventional missiles on hardened targets. Space weapons only make practical sense vs. missile-delivered weapons if they use very little mass per shot, as would be the case for anti-satellite weapons or perhaps very energetic particle beam weapons (which are too expensive to lift with chemical rockets).
A very cheap launch technology, like a space elevator, would change all of this, but as long as we're stuck with conventional launch techniques, space is only useful for surveillance and for anti-space weapons.
OK then... How about if the British (or anyone else with the required steel foundry infrastructure) resurrected the Tallboy or Grand Slam bombs used in WW2? Put a few of these into space in orbits that give decent time-to-target, and all you have to do is de-orbit them at the right time. If you can drop them from low earth orbit, then you don't even need any explosive. A ten-ton half-molten ingot dropping on a concrete bunker at several times the speed of sound has got to hurt.
While this would work, it requires a large amount of mass in space. Until something like the space elevator comes along, it'll probably be cheaper to send the payload by ICBM or medium-range missile than from orbit (which requires bringing it into orbit in the first place, which is at _least_ as expensive as sending it by ICBM; comparable delta-v required).
It would also be unlikely to work against tacnuke-rated bunkers, which are deeper than even the grand slam bomb can penetrate.
Oh, I don't know - guided 2 meter crowbars would make a handy anti-tank weopon. Clusters of them could be used as "artillery support" - I imagine it would be a very useful capability to be able to support a small airborne combat team ANYWHERE in the world with what amounts to heavy artillery. Make a nice force multiplier.
The thing is, if you can get an aircraft into the combat zone, you can probably get missiles into it too. This is cheaper than re-stocking the orbital crowbar carpet-bomber's ammunition stores.
I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.
Ooo, good point. Unless they do something to the spent fuel that I don't know about, I've never heard of a worry about the spent fuel restarting itself.
The spent fuel is dissolved in glass (vitrified), which is then encapsulated as glass pellets sheathed in carbon composites for structural strength, to limit possible accidents during handling. These are put in extremely strong barrels, and the plan is to put these in deep mine shafts in non-porus rock and plug the holes with clay.
What's actually done now is storing them as fuel bundles in pools of water, as an interim measure until we can agree on whose mine shaft the waste gets dumped into, but that's another discussion.
Upshot is that the short-term storage doesn't have to worry about the fuel reactivating, and the long-term storage doesn't have enough in one place, and has enough other crud around it, to not have to worry about reactivation.
A construct amounting to a several-mile sphere of radioactive waste, on the other hand, probably _would_ have to worry about it, though a more plausible scenario is a steady-state burn where the rate of outward diffusion of lighter wastes matches their rate of production.
ObDisclaimer about having to run lots of numbers before being able to say what would actually happen in a situation like this.
Hmm- would my favortie space based weapon- guided 2-meter crowbars as a Weapon of Minimal Distruction- be legal then because it's specifically designed only for assasination inside of reinforced concrete bunkers?
Anything dropped from space has kinetic energy equivalent to about 15 times its weight in TNT, at most.
Your 2-meter crowbar will weigh maybe 30 lbs.
Is 500 lbs of TNT enough to crack a buried bunker designed to be safe from tactical nuclear weapons?
I don't think so either.
Space-based weapons are very nice as terror weapons, and tolerably adequate as assasination tools if you know where the target is but don't have weapon platforms nearby. They're ok for knocking out other satellites or even spacecraft, if suitably armed. What they're not good at is defeating conventional armies or cracking fortified targets.
Actually, it is complete trivial to handcode it so no images come up for certain searches.
I'm betting you don't do much filtering.
Short answer is, it's a very large amount of work to both cover all of the search terms that might bring up the material you want suppressed, and find, flag, and isolate _all_ of the material you don't want to be searchable.
As an exercise, try listing all sources of the images that you can think of, and all possible search queries you might use to find them. Once you've gone through several sheets of paper, you'll start to see my point.
We still don't know if there's a core. The problem is that we don't have a good equation of state for materials at those pressures and temperatures and that the data from the Voyager flybys and Galileo orbits isn't that strong a constraint. (You're forced to use minor deflections in the trajectories to determine the deep interior structure. But that structure is, of course, shielded by many Earth-masses of overlying hydrogen and helium.)
Out of curiosity, did anyone manage to get seismic data by looking at how Jupiter's envelope moved after Shoemaker-Levy 9's fragments hit?
Even using a fast-neutron raction, I'd wager (feel free to fill in the nuclear physics here, though) that if the daughter isotopes moderate the reaction enough to stop it, then their daughter products probably will as well Lighter elements aren't necessarily incapable of this, after all. (Carbon is a good moderator, as I recall.)
Actually, moderation (thermalizing of neutrons by a light material that scatters neutrons more readily than it absorbs them) could even speed it up. It's absorption that's the problem. There isn't a strong relation between the absorption characteristics of the initial daughter products and what they alpha or beta decay to. I'd either have to crunch through an ungodly-huge number of possible decay chains, or find a nuclear physicist who has.
I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.
I'd like to see your sources on the core of Jupiter. I can cite a lot of sources to back up my statement, if you like. "The New Solar System" is an easily accessable book that covers the topic adequately. If you want something more detailed, "Protostars and Planets IV" has a nice discussion of this. I'd bet that the new Jupiter book from Cambridge University Press covers it, but my copy hasn't arrived yet.
If you're not finding references that say that the core is mainly ice, I'm curious where you're looking. (No, really: I'm curious.)
About half an hour of looking for all of the web sources I could find (starting with Nasa, then moving to wikipedia and then exhaustive Googling). I figured that if that if there was a new or at least more detailed model that asserted that there were definitely light elements in the core, that at least one page on Jupiter's structure would mention it. Everything I could find said rocky core, then metallic hydrogen, then supercritical fluid hydrogen, then gaseous hydrogen mixed with small amounts of icy material and trace amounts of things like phosphine and hydrogen sulphide.
Any of the books I have lying around that talk about gas giant structure are old enough that they're still speculating about whether a rocky core exists at all, so they weren't much help.
I'm not disputing your sources, as you appear to have ones that are both more recent and more detailed than what I could dig up. Crawling through an astronomy publication archive would have taken me longer than half an hour:).
What's worse is that you need a lot more uranium than Earth has to generate your heat that way.
I realize that. My older sources on Jupiter mainly say that its heat source is from things like latent heat of fusion as materials continue to fraction out. Is this still thought to be the case?
While I'm at it, is heat of crystallization still thought to be making any significant contribution to Earth's heating? I recall that that was the competing model for Earth's heat generation before radioactive decay became widely accepted.
And you can't restart the reactor by letting the uranium daughter istopes decay. What do you think that they decay into? Lead, mainly. If thorium stops the reactions, I'm pretty sure that lead will, too.
If the core is conjectured to be a ball of mostly-pure uranium, you actually get a fast-neutron reactor type of process, which means most of your material is fissioned instead of decaying by alpha emission. This gives you all kinds of junk lighter than lead, instead of the slow decay chain you'd find in a subcritical radiothermal source.
Even a slow-neutron reactor should breed U238 and thorium into things that will fission. The whole point of a reactor is to speed up the rate of decay by either triggering it directly (as with fissile materials in a slow-neutron reactor or any material in a fast-neutron reactor) or by transmuting materials into ones that can be induced to decay rapidly (breeder reactors of all types). Mostly the end result is fission, again giving light daughter products.
Basically, what the reactor model does is speed the burn rate. Which means, since we know the present heating rate of the Earth pretty well, you have to make it a lot hotter in the past with the reactor model than with pure decay.
As I understand it, the universe has only one megnetic field and the Earth (and other masses) merely distorts that field. Same goes for gravity. Is this not true? I realize this doesn't change the sense of the article at all, but it always bothers me to hear people talk of the "Earth's" magnetic field like it is somehow unconnected to anything else.
The answer to this is "sort of".
The short answer is, the Earth's magnetic field is best thought of as belonging to Earth, as opposed to being a disturbance in a larger universal field. ObCaveats about the interaction between the Earth's field and the Sun's field and the Milky Way's field giving important effects; all of these can still be considered fields local to the objects generating them.
The long answer is that the electromagnetic force can be thought of as charges disturbing a field of virtual photons that does indeed fill the universe. However, saying that there's a magnetic field pervading the universe doesn't really make sense, as the measured magnetic and electric field strengths without charges and currents disturbing the virtual photon field will be zero, and these disturbances for unchanging fields have a very limited range of effect (or rather, an unlimited range but a strength that drops off very fast with distance).
In summary, "Earth's magnetic field" is probably the best description.
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The other limit is finding a suitably reflective material that is cheap enough to be used as media. X rays pass easily through plastics, and they are absorbed by lead. Gamma rays pass through most kinds of material. You need something that reflects well, and doesn't absorb the radiation, that can also be used to store distinct states and be mass produced easily.
If you can produce a finely focused x-ray beam in the reader, you could probably factory-produce extremely high density discs by coating the discs in a material that fluoresced in x-rays, and using an electron beam to etch pits in it. Or stamping, coating, and CMP to leave only the filled pits, but that's probably just as expensive as e-beam writing. Data is read by scanning the disk with the x-ray beam and looking for spots where it doesn't fluoresce.
If you're willing to mount the disc and read/write head in vacuum, you could use a low-energy electron beam as the probe beam and get resolution as fine as you like, though that means carrying your factory-stamped discs in a vacuum caddy the whole time.
The article only discusses write techniques. I'd like to hear if there are any peculiarities involved in reading it before I make guesses as to the delay before production. I'd also like to know if they only have a tube or if they have a diode already.
You need a laser with comparable or finer wavelength to the writing laser in order to read an optical disc.
This is almost certainly a frequency-doubled or even frequency-tripled laser, which means it's very power-inefficient (I believe there were old green laser pointers that were frequency-doubled IR; they got awfully warm, as most of the pump beam stayed as IR, and was wasted).
Source laser isn't mentioned in the short blurb (and the full blurb is subscribers-only), but I'd guess it's an excimer laser similar to the kind used for EUV photolithography, if it can make 70 nm holes. In fact, it wouldn't surprise me to learn that it's _exactly_ that type of laser, and that this experiment was done in a photolithography clean room. Excimer lasers are gas lasers that produce output in the near-UV. The 193 nm light used for photolithography a generation or so ago was from frequency-doubled argon fluoride excimer lasers.
We have UV LEDs, and so presumably low-power UV laser diodes are available in research labs, but getting something that can reliably make holes 70 nm wide would probably take frequency _tripling_ at this point. So I'd put money on a gas laser at the moment, with a tripled blue or violet diode or a doubled intermediate UV diode laser "some time really soon now, honest".
Producing light of the needed wavelength without frequency doubling would take a pretty exotic material with a bandgap that puts it well into the "insulator with extreme prejudice" range (lots of doping required).
I would like to point out that tournament fighting has absolutely nothing to do with real-world fighting.
:). If it was tooth and nail between two equally skilled opponents... I'd perhaps give better odds for the big guy, but it would by no means be a sure thing. And, per my previous comments, equal skill is a very unusual situation even among black belts (perhaps especially so).
Tournament sparring at tournaments is typically non-contact. Practice sparring at the dojo is "light contact", for varying values of "light" (that at one point involved me landing in a weapons rack a few feet away, giving me a healthy respect for kicks). Clean footage of that would be harder to dig up, as less of this was filmed.
In a real-world fight, a 97lb man punching a 194lb man in the stomach will probably hurt his hand, inflict very little damage to his opponent, and be summarily pummeled.
All I can say is, I'm 160 lbs, and have had little girls half my weight hit me hard enough to give me pause. See my other response in this thread for a longer discussion on this.
I am in no way saying that a little guy can't kick a big guy's ass. But if the two are equally skilled, the little guy is probably going to take a severe beating, at least outside of the artificial rules of a tournament.
I'd actually expect the little guy to block, counterattack, and then run like heck
Furthermore, all of the real-world fights between martial artists that I have seen tend to involve very little "art" after the first few seconds.
Fair enough, though arguably those first few seconds are pretty important.
First, he couldn't get close enough to get a good hit on me. I could kick at him from a much farther distance. He had to leave a lot of room between myself and him if he wanted to catch his breath.
I'm puzzled as to why he didn't block or dodge your kick and move in to counter before you recovered from throwing it. A smaller person is going to have a lot of trouble throwing the first technique against someone who has longer reach, so reacting to attacks (and ideally, provoking attacks that leave your opponent exposed) is the lion's share of the smaller person's strategy.
Was I slower than him? No, not really. I was bigger, but I had a lot more strength as well. My feet and fists could move at least as fast as his.
Same speed, and longer distance, means more travel time. Ditto with the "same acceleration" scenario if you assume the same strength to weight ratio instead of the same speed. Square/cube law means that it's hard for the larger person to have the same strength-to-weight ratio as the smaller person, meaning generally lower acceleration, and an even larger time difference (as well as a time difference even for moving the same distance, and for doing things like changing the direction your body is moving). Exceptions exist - level of physical conditioning varies as greatly as skill level between arbitrary individuals - but if you can throw techniques as quickly as your instructor, or change direction as quickly, it represents a very unusual case. Everything I've seen among the people who train at my own dojo bears this out.
Third, the sheer mass of my body left his attacks wanting. My forearm weighed enough that I could stop his strongest kicks before they reached my body. My attacks could not be repelled. When I put my weight behind an attack, his only option was to dodge it. Sure, he was fast, but not that fast. And one good knock and he would've been done.
This is why "strength on strength" techniques are generally discouraged in favour of deflection and evasion techniques, even against an opponent who doesn't out-mass you, as I'm sure you're aware. For a few weeks my regular training partner was a young lady two thirds my weight, who nonetheless could block (sincere) punches and kicks from me without an unmanageable amount of effort.
I've also been hit enough times by people smaller than me to have a healthy respect for their power, but I'm perhaps a bad example, as in sparring I seem to have a knack for leaving myself exposed. For a more general argument, consider a sledgehammer. It only weighs 8 lbs, and it moves slower than a punch, but you still wouldn't want to get hit by it. The same applies to techniques thrown by most of the black belts I know (of all sizes); enough parts are moving, in the right direction, that that technique will hurt.
A small person won't take a large person down in one shot, while the opposite could still happen, but the large person is still going to have considerable trouble landing that one shot, and can easily leave themselves open in the process.
Large != slow.
You've been playing too many fighting games.
The last fighting game I played was "killer instinct". I can do the Cranky Kong rant about bit-planes too, if you like.
On the other hand, I watch sparring pretty frequently (and spar myself, but I'm not nearly good enough at it to use my own approaches as examples). For smaller people, speed and maneuverability win. For large people, capitalizing on longer reach and effectively countering the small person's attacks wins, because they aren't going to out-race or easily out-maneuver the small guy.
Very true. Which is why I didn't say "green belt" or "random punk." When our meter of skill is "black belt", we can assume identical values for skill given identical variables.
Um, black belt generally represents the beginning of serious training, as opposed to an endpoint. Depending on how high the school sets the bar, getting to black belt takes 3-6 years or so. That leaves another few decades to continue to improve one's technique.
Even among the shodans at our school, there is a very wide skill variation.
I know some 97 pound black belts who can kick your ass through the room.
And when they meet a 194 lbs black belt, they probably get thrown in turn. "All else being equal, the stronger man wins."
This is not obvious to me. As the previous poster pointed out, small fighters are _fast_. While the smaller black belt would be toast if the heavier one managed to grapple, the heavier one will have a hard time successfully counterattacking as long as the lighter one is on their toes.
Strength matters, and reach matters, but skill matters considerably more than either.
Unfortunately none of the footage from tournaments our school has attended is online, or I'd link a few video clips as examples. Skill is very rarely equal, making the other factors less relevant.
I think it's important to distinguish between skepticism and self-sabotage. When you find a claim that sounds unbelievable, do you always say "that sounds too good to be true, it can't possibly work", or do you sometimes investigate further to see if there's anything to it?
Every 20+% return investment I've seen has been the result of investors getting lucky enough to ride a bubble. In the early 1990s this was mutual funds, around here. More recently, this was tech stocks. In both cases, it didn't last.
In theory, if you can consistently pick the right investments all the time, you can sustain this. In practice, you can't even come close to that. I'll stick with conservative or at least moderate investments, thank you.
To succeed in the markets, you need more than wisdom. You need training in all the components of a trading system (not just the stock pick du jour).
You also need a very large amount of luck, which no amount of training will provide.
Very few people have all of these.
But very many people can afford to hire them.
Think about it - I'm Joe Caviar with a few $million to invest. I'm going to hire the best investment portfolio manager money can buy, because I'd much rather eat with gold-plated cutlery than silver! I'm also going to be buying far more stocks than Joe Average, magnifying the fraction of stocks that are held by my demographic. And yet, I still don't consistently make scads of money with my investments...
I am not convinced that 20% yields are sustainable. Too many people would have the means and the desire to access these investment strategies if they worked. We'd either see them getting rich, or there would be enough of them to poison the well.
If you get some decent investment system training, you can make your own investment plan that regularly makes you 20% a year.
I am skeptical of claims that wise people can consistently outperform index growth by that much, simply because if any significant number of people tried it, it would cease to be true (they'd be fighting for the same money when they tried to cash in). Therefore, only a small fraction of people can actually see this kind of return - which means odds are I won't be one of them no matter who my broker or portfolio manager is.
The numbers I hear for return rates sustained over the long term are on the order of 10%, and even these investments will be vulnerable to serious economic downturns (which seem to happen every decade or two).
Fortunately, you don't live forever. You can actually withdraw a portion of that principle each month as well, and live decently for a million, or less.
That depends on how early I want to retire, how long I think I'll live, and what I think the average rate of inflation will be. If I'm looking at living for another 40+ years, and especially if I expect big expenses near the end of that period, I don't want to eat into my principal early on.
Aircraft take time to arrive, unless they are already in the area. They can get shot at, shot down, interfered with, break down, require jamming support, tanker support, etc., etc., etc. It just isn't that easy.
Satellites will take quite some time to get over the target region - remember, a satellite in LEO can only target an area a few hundred kilometres wide, so you either need a very large number of satellites, or live with it taking a while for a crowbar sat to get into position to drop things.
If the satellite is what's doing the targetting, it's easy to jam - shine a light at it, or set a fire big enough to serve as a smoke screen for the area, or just use a camo tarp and keep equipment cool, and it can't target you accurately enough to hit you.
If ground troops are doing the targetting, a ground-level smokescreen or any other means of fouling line-of-sight will work just fine. As will return fire.
Remember the first Gulf War? Scud busting was the big thing then, and the Air Force - even though based next door - couldn't get anywhere. Orbital artillery would.
The problem was not weapons - the problem was that you didn't know a Scud launcher existed until they took the tarps off it and fired it. Hitting the launcher after the fact is questionably useful. Hitting the missiles is _more_ difficult from orbit than it is from the ground, and that was hard enough (Patriot, a repurposed anti-aircraft missile, had a zero percent success rate last I heard, though I'm told a newer version worked marginally better in the current war).
And now, I realize just how pathetically little, a million dollars really is. I look at movies from the 1970's where the plot was someone pulling off a robbery, or murder, for like $10,000. Dude, $1 million won't change your life in a way that's measurable 5 years out.
$1 million put into safe but low-yield investments would give me my current pittance of an income _forever_, _after_ inflation. $2 million would let me retire in modest comfort.
So, while $1M won't make you _rich_, it's still a very respectable amount.
As it is, it appears to be little more than a light sensor attatched to a rapid-fire nerf gun. i.e. Dumb-fire, no aiming.
These are still quite fun. You can buy the pressure-hose equivalent from hardware stores to keep raccoons/cats/etc. away from your garbage, flower garden, or whatever.
I was quite impressed when I saw one of these, though in hindsight it's just a combination of two widely-available existing devices (automatic sprinkler and motion-sensor light). Impressively elegant.
With space based weapons, you don't have to get an aircraft into the area. You look at the area from space, and drop a crowbar on them.
a) The poster this was in reply to was suggesting using satellites as artillery support, which both involves lots of crowbars, and presupposes an area you can get other troops/what-have-you to.
b) My point across this whole thread has been that to do anything serious, you're probably going to be able to accomplish it more cheaply by ICBM than by satellite. There is nowhere that's out of missile range to a nation with ground-to-orbit rockets, which means your satellite scenarios are quite limited (basically, cases where you want to deliver a small payload at high cost and for some reason can't use a big missile to do it).
Not if you have a 50-ton nickel-iron asteroid in orbit.
At present, the only cheap way to get a 50-ton slug into orbit is to lift it from Earth. We can't _see_ the asteroids that are that small, and a craft capable of moving the ones that we _can_ see would cost more than a lifetime supply of orbit-dropped crowbars.
A smelter and manufacturing facility capable of turning a chunk of impure iron into rod-shaped slugs with good de-orbiting characteristics is also big and heavy enough to be impractical to lift with chemical rockets.
Remember, all of this has to compete with the cost of either firing a long-range missile, or inserting an artillery team close enough to do the same job from the ground.
Until there's a cheap road to orbit, ground-side solutions tend to win.
What I think the OP was getting at is the idea of using a rail gun to accelerate large chunks of metal to very high velocities. Upon impact they would easily take out something like a ship or tank, and probably most bunkers. Especially if you fire three or four in rapid succession. Aricraft would be mince meat if you could hit one.
I don't know how well this would, but I have read stories about how the Air Force has tested some of the concepts in labs.
It turns out not to be practical to put a railgun that powerful in orbit. The power storage required and the practical constraints on acceleration would require a structure many kilometres long at minimum (and probably more like many hundreds of kilometres, if you want velocities much higher than you'd already get by dropping things).
The navy railguns linked from previous articles have muzzle velocities of a few km/sec. Anything in this range (or dropped from orbital height) has more kinetic energy than an equivalent mass of explosive, but that's a far cry from being able to demolish a ship using a crowbar's worth of mass.
Ship-mounted railguns can also be far heavier than something you'd put in space, and have a nice, heavy nuclear plant or gigantic diesel engine to power them. An upper limit to the mass of any killer sattelite is about 10-30 tonnes, depending on what it's launched with.
Is 500 lbs of TNT enough to crack a buried bunker designed to be safe from tactical nuclear weapons?
It likely is if it's a focused shaped charge to a single 1" circle....which is basically the entire idea of the crowbar-dropped-from-orbit idea.
I seriously doubt this, if the bunker is deep enough to resist conventional explosive attack (or tactical nuclear warheads). Remember, the 1/e velocity distance is the distance at which the penetrator has displaced an amount of material comparable to its own mass. That'd be at most 10-20 metres of earth for your crowbar. By comparison, the bunker would be on the order of 100 metres down.
The idea isn't to demolish the bunker, it's to kill a single person *despite* that person being in a bunker
This requires demolishing the bunker, as you don't know where they are inside it. If you have a spy in there, there are far cheaper ways of killing the target.
And I'm completely agreed with that idea- but NEITHER can fortified targets or conventional armies stop an attack from space. Multiply that crobar by thousands- even millions- of similar crowbars taking out *specific* ground based targets (of the command and communications variety) and your ground-based army gets one heck of a lot easier to defeat.
The problem is that it's ludicrously expensive to stock that much mass in space. You'd be better off carpet-bombing with napalm and raining down conventional missiles on hardened targets. Space weapons only make practical sense vs. missile-delivered weapons if they use very little mass per shot, as would be the case for anti-satellite weapons or perhaps very energetic particle beam weapons (which are too expensive to lift with chemical rockets).
A very cheap launch technology, like a space elevator, would change all of this, but as long as we're stuck with conventional launch techniques, space is only useful for surveillance and for anti-space weapons.
OK then... How about if the British (or anyone else with the required steel foundry infrastructure) resurrected the Tallboy or Grand Slam bombs used in WW2? Put a few of these into space in orbits that give decent time-to-target, and all you have to do is de-orbit them at the right time. If you can drop them from low earth orbit, then you don't even need any explosive. A ten-ton half-molten ingot dropping on a concrete bunker at several times the speed of sound has got to hurt.
While this would work, it requires a large amount of mass in space. Until something like the space elevator comes along, it'll probably be cheaper to send the payload by ICBM or medium-range missile than from orbit (which requires bringing it into orbit in the first place, which is at _least_ as expensive as sending it by ICBM; comparable delta-v required).
It would also be unlikely to work against tacnuke-rated bunkers, which are deeper than even the grand slam bomb can penetrate.
Oh, I don't know - guided 2 meter crowbars would make a handy anti-tank weopon. Clusters of them could be used as "artillery support" - I imagine it would be a very useful capability to be able to support a small airborne combat team ANYWHERE in the world with what amounts to heavy artillery. Make a nice force multiplier.
The thing is, if you can get an aircraft into the combat zone, you can probably get missiles into it too. This is cheaper than re-stocking the orbital crowbar carpet-bomber's ammunition stores.
I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.
Ooo, good point. Unless they do something to the spent fuel that I don't know about, I've never heard of a worry about the spent fuel restarting itself.
The spent fuel is dissolved in glass (vitrified), which is then encapsulated as glass pellets sheathed in carbon composites for structural strength, to limit possible accidents during handling. These are put in extremely strong barrels, and the plan is to put these in deep mine shafts in non-porus rock and plug the holes with clay.
What's actually done now is storing them as fuel bundles in pools of water, as an interim measure until we can agree on whose mine shaft the waste gets dumped into, but that's another discussion.
Upshot is that the short-term storage doesn't have to worry about the fuel reactivating, and the long-term storage doesn't have enough in one place, and has enough other crud around it, to not have to worry about reactivation.
A construct amounting to a several-mile sphere of radioactive waste, on the other hand, probably _would_ have to worry about it, though a more plausible scenario is a steady-state burn where the rate of outward diffusion of lighter wastes matches their rate of production.
ObDisclaimer about having to run lots of numbers before being able to say what would actually happen in a situation like this.
Hmm- would my favortie space based weapon- guided 2-meter crowbars as a Weapon of Minimal Distruction- be legal then because it's specifically designed only for assasination inside of reinforced concrete bunkers?
Anything dropped from space has kinetic energy equivalent to about 15 times its weight in TNT, at most.
Your 2-meter crowbar will weigh maybe 30 lbs.
Is 500 lbs of TNT enough to crack a buried bunker designed to be safe from tactical nuclear weapons?
I don't think so either.
Space-based weapons are very nice as terror weapons, and tolerably adequate as assasination tools if you know where the target is but don't have weapon platforms nearby. They're ok for knocking out other satellites or even spacecraft, if suitably armed. What they're not good at is defeating conventional armies or cracking fortified targets.
Actually, it is complete trivial to handcode it so no images come up for certain searches.
I'm betting you don't do much filtering.
Short answer is, it's a very large amount of work to both cover all of the search terms that might bring up the material you want suppressed, and find, flag, and isolate _all_ of the material you don't want to be searchable.
As an exercise, try listing all sources of the images that you can think of, and all possible search queries you might use to find them. Once you've gone through several sheets of paper, you'll start to see my point.
We still don't know if there's a core. The problem is that we don't have a good equation of state for materials at those pressures and temperatures and that the data from the Voyager flybys and Galileo orbits isn't that strong a constraint. (You're forced to use minor deflections in the trajectories to determine the deep interior structure. But that structure is, of course, shielded by many Earth-masses of overlying hydrogen and helium.)
Out of curiosity, did anyone manage to get seismic data by looking at how Jupiter's envelope moved after Shoemaker-Levy 9's fragments hit?
Even using a fast-neutron raction, I'd wager (feel free to fill in the nuclear physics here, though) that if the daughter isotopes moderate the reaction enough to stop it, then their daughter products probably will as well Lighter elements aren't necessarily incapable of this, after all. (Carbon is a good moderator, as I recall.)
Actually, moderation (thermalizing of neutrons by a light material that scatters neutrons more readily than it absorbs them) could even speed it up. It's absorption that's the problem. There isn't a strong relation between the absorption characteristics of the initial daughter products and what they alpha or beta decay to. I'd either have to crunch through an ungodly-huge number of possible decay chains, or find a nuclear physicist who has.
I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.
I'd like to see your sources on the core of Jupiter. I can cite a lot of sources to back up my statement, if you like. "The New Solar System" is an easily accessable book that covers the topic adequately. If you want something more detailed, "Protostars and Planets IV" has a nice discussion of this. I'd bet that the new Jupiter book from Cambridge University Press covers it, but my copy hasn't arrived yet.
:).
If you're not finding references that say that the core is mainly ice, I'm curious where you're looking. (No, really: I'm curious.)
About half an hour of looking for all of the web sources I could find (starting with Nasa, then moving to wikipedia and then exhaustive Googling). I figured that if that if there was a new or at least more detailed model that asserted that there were definitely light elements in the core, that at least one page on Jupiter's structure would mention it. Everything I could find said rocky core, then metallic hydrogen, then supercritical fluid hydrogen, then gaseous hydrogen mixed with small amounts of icy material and trace amounts of things like phosphine and hydrogen sulphide.
Any of the books I have lying around that talk about gas giant structure are old enough that they're still speculating about whether a rocky core exists at all, so they weren't much help.
I'm not disputing your sources, as you appear to have ones that are both more recent and more detailed than what I could dig up. Crawling through an astronomy publication archive would have taken me longer than half an hour
What's worse is that you need a lot more uranium than Earth has to generate your heat that way.
I realize that. My older sources on Jupiter mainly say that its heat source is from things like latent heat of fusion as materials continue to fraction out. Is this still thought to be the case?
While I'm at it, is heat of crystallization still thought to be making any significant contribution to Earth's heating? I recall that that was the competing model for Earth's heat generation before radioactive decay became widely accepted.
And you can't restart the reactor by letting the uranium daughter istopes decay. What do you think that they decay into? Lead, mainly. If thorium stops the reactions, I'm pretty sure that lead will, too.
If the core is conjectured to be a ball of mostly-pure uranium, you actually get a fast-neutron reactor type of process, which means most of your material is fissioned instead of decaying by alpha emission. This gives you all kinds of junk lighter than lead, instead of the slow decay chain you'd find in a subcritical radiothermal source.
Even a slow-neutron reactor should breed U238 and thorium into things that will fission. The whole point of a reactor is to speed up the rate of decay by either triggering it directly (as with fissile materials in a slow-neutron reactor or any material in a fast-neutron reactor) or by transmuting materials into ones that can be induced to decay rapidly (breeder reactors of all types). Mostly the end result is fission, again giving light daughter products.
Basically, what the reactor model does is speed the burn rate. Which means, since we know the present heating rate of the Earth pretty well, you have to make it a lot hotter in the past with the reactor model than with pure decay.
Quite a valid objection.
As I understand it, the universe has only one megnetic field and the Earth (and other masses) merely distorts that field. Same goes for gravity. Is this not true? I realize this doesn't change the sense of the article at all, but it always bothers me to hear people talk of the "Earth's" magnetic field like it is somehow unconnected to anything else.
The answer to this is "sort of".
The short answer is, the Earth's magnetic field is best thought of as belonging to Earth, as opposed to being a disturbance in a larger universal field. ObCaveats about the interaction between the Earth's field and the Sun's field and the Milky Way's field giving important effects; all of these can still be considered fields local to the objects generating them.
The long answer is that the electromagnetic force can be thought of as charges disturbing a field of virtual photons that does indeed fill the universe. However, saying that there's a magnetic field pervading the universe doesn't really make sense, as the measured magnetic and electric field strengths without charges and currents disturbing the virtual photon field will be zero, and these disturbances for unchanging fields have a very limited range of effect (or rather, an unlimited range but a strength that drops off very fast with distance).
In summary, "Earth's magnetic field" is probably the best description.