I believe the fact that no letter mapped onto itself was known long before Alan Turing came on the scene. In fact, all sorts of things that happened at beltchley are commonly attributed to him, which is an intriguing demonstration of how fame works. His major controbution to the code-cracking effort was to devise a decibel-like probablity weighting system that estimated the likelyhood of occurrence of certain words depending on the current news or anticipated news, the current type of message, the writer's style, and so on.
The basic facts are still accurate. Anyone who had rigid patterns in the way they worked could have their code content guessed. There was an airstrip in the alps that used to send a weather report every day that was word for word the same - "Weather fine, skies clear, visibility good" etc. Bletchley knew from the number of letters in the message that it was the same today as yesterday.
There is another important moral here. The fact that no letter mapped onto itself - a weak property but exploitable if you have enough text - arose because some engineer reckoned if you sent the electrical signal back through the rotors again, then it would be like having twice as many rotors. if didn't - it made the code weaker. You can make everyone have long passwords with random characters, but there is little benefit in this unless you are sure all your ports are protected, and your computer does not have any of the standard service or administration accounts still enabled. If the password is really the limiting security weakness, then maybe it is time to go to something more advanced, like a USB dongle to prove you are who you say you are.
Yep, there are ways around that, too. But every little helps...
Usually this sort of discussion relies on hypothetical arguments. However, there are real cases where software has been created under controlled conditions, and then analysed for similarity. The Phoenix BIOS was written by people with coding experience but with no prior knowledge of the BIOS used in the IBM PC. They were given a functional description of what the BIOS should do. Care was taken to ensure they could not reverse engineer the IBM BIOS or directly compare their code to the IBM code.
What they wrote ended up having large bursts of code that was identical to the IBM PC BIOS. Sometimes there is only one good way of doing something.
Well, this is what I remembered reading years ago. It was an unusual exercise because the actual amount of code was small, so the potential legal cost per byte was very high. If there is someone out there who actually was part of this project, maybe they can post their experiences, and say whether I have got it vaguely right.
I think this was researched in the sixties. Apparently, if you stick brandy or sherry into a high neutron flux reactor, then it comes out having all the symptoms of having been aged. However, there was no market for Nuits St Three Mile Island, or rather (as many other people have pointed out) if you take away the exclusivity of the product, then your profit margins disappear.
This neutron stuff may seem like an urban myth, but I know some people who repeated the experiment in the eighties with a Ministry of Defence reactor that is sometimes used for colouring sapphires, and other strange jobs to earn a buck. They lowered in a bottle of Spanish rotgut brandy, left it there for a fortnight, and what they pulled out was a lot lighter, and smoother tasting. So, it can be done.
Absolutely. This dates from the days when it was though a good idea to let off groundburst megaton weapons in bits of Australia or the on bits of wasteground with 450,000 servicemen in slit trenches watching, so they could get an idea of what a nuclear bang looks like. If the UK could not let them off in Australia or the US, there were plans to test them in Scotland. There were bombers with nukes continuously in the air going to and from the USSR all through my childhood 24-7. If you want to see some really hairy stuff, look for webpages on the US nuclear powered aircraft (I kid you not). Major scary stuff.
At least radioactivity goes away eventually. Chemical stuff can sit around forever. The up-and-coming madman of today fools around with genetic stuff that multiplies and hops species. Progress, I guess.
Back to the original idea, though. Chucking it in the sea is only a good idea if it really gets mixed and thoroughly dispersed. But it can be done.
Well, exactly. Stick it in solid form a hole in an earthquake zone. It starts leaking before it's halfway gone. You can't dig it up and re-seal it. We are all stuffed.
The UK Windscale nuclear plant - now the Sellafield reprocessing plant, and soon probably to be re-badged the Ravengalss Wildlife park or something like that has a pipeline that put dissolved low-level waste into the sea. At first this sounds like a really, really bad idea. However, the Atlantic has about 10^13 curies of mixed radioactive stuff in it - a lot of it a duterium, tritium, C14, and a mess of heavy metals. You could dump all the waste that had ever been produced into the Atlantic, and provided you mixed it in well, you would never be able to detect the difference. The 1950's solution was to stick a pipe far enough into the ocean to get the waste into some of the fast currents in the north Irish sea, which should sweep it out into the Atlantic. It has been argued since that this did not qork quite as designed, but at the time this bit of the Irish Sea had been surveyed as well as anywhere. The other UK solution was to stick the stuff into drums and drop it into the mid-Atlantic. The drums were designed to burst half-way down, again dispersing the material into the fast ocean currents.
Compare this to the US idea of chucking solid waste into a concreted drum, and sending it right to the bottom. The bottom of the oceans are often quiet places where the water hardly moves. Fish and crustacea live in the rusting cans, and lay their eggs on the concrete. We are trawling for deep sea fish like grenadiers these days as the cod has virtually gone, so we may be getting it all back again - we don't know.
We seem to have lived through an age when Science was trusted to do anything, and the nuclear budget could be underwritten by weapons work; then through an age when Science was not trusted at all, and anything nuclear was controlled by evil warmongers. We might actually be heading for a balanced view. Coo!
The devices are made of "Gallium, Aluminium, and Arsenide". The stuff may be called Gallium Aluminium Arsenide, but the element is called Arsenic. If they send you down to stores to get a jar of Arsenide, expect to get left-handed screwdrivers and tartan paint too.
So, the reporter doesn't know his periodic table? I bet he's red-hot at quantum physics, though. Really brilliant and highly trained minds sometimes skip over the basic stuff, yerknow.
There were commercial DCT-based image processing methods in production in 1984. I worked on the Crosfield Electronics 'Rabbit' system for image archives. The consultant used on this system had written a book describing most of the techniques, so that was easily in the public domain.
Huffmann coding was not considered patented at the time. The LZW algorithm had patent issues, but I reckoned at the time we could do LZW-compatible coding with a two-pass algorithm: the only unique feature of LZW was the reoptimization of the compression tables as the data was being processed.
There is a 1935 Italian patent on the compression of images, including colour images, for fax using variable length codes for different picture elements. The claims are sufficiently general the invalidate a lot of run-length compression schemes.
That's just what I can remember while writing this. I am not impressed by their patent. There are lots of dud patents in there. It is easy to search the patent database, and become convinced there is a claim. Look at prior art in products and in theliterature, and it is a different story.
I think the quotes around 'encrypted' are trying to tell us something...
What does 'encrypted' data look like? You have a file that seems to contain random digits. The better the encryption, the less structure your encrypted file will have. In the end, a securely encrypted file becomes indistinguishable from a file containing random data.
If the police - or whoever it is doing the searching, this isn't an anti-police thing as such - find some file containing ramdom data, and demand the key, you should be able to say "There is no key. That is random data". This might sound deeply suspicious if only one of us does it. If many of us keep a few files of random data on our hard disk as a mark of passive resistence, then it will become plausible. And the number of encrypted messages, if there are such things, may be outnumbered by the false random data files.
Have things really come to this? I don't honestly know. But I have just made a small, random file and stuck it on my hard drive. Now, we need lots of other people to do the same.
Bright sunlight is about 120 000 lux. We can see some detail in starlight at about 0.0003 lux. If you want to cover the entire range of the eye, then about 10^9:1 ought to do it.
This, of course, is rather silly. We cannot see simultaneous contrast of a billion to one. Our retina is not black, so the light will scatter around in the eye, and give us a flare signal of about a percent or so. We are used to rejecting a low light level like that. That would give us a sensible contrast ratio of 100:1. But this is not the whole story either - if you have a scene on a monitor with only 100:1 contrast, it might look OK in office lighting, but the shadows will look very 'milky' in a darkened room.
In our experience, people using monitors or digital projectors to simulate film will need something like a 1500:1 contrast ratio. There seems to be a point somewhere a bit beneath 2000:1 where the blacks come convincing, and the viewer will accept the simulation. There is some point about 1200:1 where the blacks stop looking convincing, and start looking grey.
If you are trying to match a display to a projector, it is nice to have another factor of two, so you can match the absolute brightness without having to go to the display white. You may want to get this because you sometimes have to drive the RGB channels beyond the white point to get bright and clean looking pastel colours.
You will want to have a continuous tone curve. Field-emission devices will have a cube-type power law down to a point, and then they will cut off exponentially. This may give good-looking greys down to a point, and then plunge into black, crushing all the shadow detail. That does not look as nasty as 'milky' shadows, but it is not that much better.
So - about 3500:1 is good for simulating colour film. However, colour film is pretty dim - 16 ft-lamberts (50 cd/m2) is standard. Images look a lot more colourful if they are brighter. If you want really high-contrast images, you need something like a LCD monitor with a variable LED blacklight, which gives you your local 100:1 contrast and a huge overall contrast ratio. Have a look at http://www.brightsidetech.com/tech/bstech.php.
I can't find the note I once did on this, so this is largely from memory...
My thesis was that there is a long history of 3D photography and cinema, with the level of interest bouncing up and down on about a 20 year cycle - about the expiry time of a patent. The 3D views had a short-term novelty value, but they always lost out in the long run to conventional photographs with sightly better resolution.
Wheatstone produced the first hand-drawn stereographs in about 1834.When his friend, Fox Talbot introduced the Daguerrotype process to the UK in 1835, they got together and made some stereo photographs, which were exhibited the same year.
Stereographs were mass-produced from about 1845 onwards (Queen Victoria got given one, then everyone had to try it). In Europe, people often used transmission stereographs, while in the US, the Homes stereograph used reflection prints. Some of Brady's Civil war photographs were stereo pairs. No special camera was necessary: when emulsion speeds allowed hand-held cameras, you had two plates, and you took one with your weight on the right foot, and the second with your weight on the left foot. This moved the camera by something like the intra-ocular distance. This meant that anyone who could take a conventional photograph could take a stereograph, and some people amassed huge private stereo collections (over 100,000 pairs).
The heyday of stereo photography was bought to an end by advances in lens design. The old 'bullseye' lens gave a very limited field of view. The Right Rectilinear lens gave less abberation at the edges, so you could take wider views. Panoramic cameras extended this by moving the emulsion as the photo was taken. You could have 3D panoramas if you made a special spectrograph, but if the parallax offset went through a minimum in the centre of view, then you ended up squinting at the edges.
Two-colour printing for book plates in the late 1800's allowed the red-blue anaglyph stereo images. You could get a wide field of view without special optics because the two images appeared on the same sheeet of paper. Magenta and cyan glasses, and a full-colour print with a common, defocussed, yellow image culd give the appearance of full colour.
Conventional stereographs were combined with flicker-book animation in 3-D 'What the Butler Saw' machines in the late 1800 - early 1900s. Later innovations included anaglyph 3D films and colour still image viewers (View-Master) within a year or so of the first colour films in the 1930s. There were polarized 3D films in the 1950's, a year or so after Polaroid became available in reasonable amounts. Experimental 3D TV was also tried in the 1950's. There were adapters for 35mm cameras and slider projectors in the 1970's, and printable polarized images (the Xograph). There were also lenticular sheet images, the Nimslo camera, and so on. In the 1990 there were liquid-crystal shuttered glasses 3D on colour TVs using the Pulfrich effect (the BBC's Doctor Who in Eastenders episode). It goes on, and on - I am sure there are others that I have forgotten in my original collection. However, they tended to peak on odd-numbered decades. Perhaps the most recent is the IMAX 3D films - the International Space Station (keep your head really level or you see the other images), and New York in 3D (keep your head over the bucket, so you don't miss it when the motion sickness kicks in).
I reckon we are now on a low: there will be a flurry of 3D work in about 2010, peaking at about 2015 at exhibitions, and then disappearing for good a few years later. It's sort-of fun at the time, but it never seems to last.
If you go to Tokyo, you will meet women who seem to do nothing all day but bow and say "irashimase!" in a high-pitched cartoon-mouse type voice. They do it in shops, by lifts, and in some offices. The best looking ones are promoted to 'office flowers' - people who apparently do nothing but look nice. ATM and ticket machines often have an animation of a bowing woman. Getting Joo Puburicu-san to treat an automaton like a woman may be no big deal - some of them have been tresting women like automata for years.
And while we're on the subject, some of our fellow slashdotters could clean up their act a bit too...
I remember seeing a German periodic table from the 1930's. The long lanthanide and actinide loops were racetrack-shaped, so most of the elements has a squarish block of the chart where they wrote useful weight, number, and isotope data. It was not as minimal as the charts we used to have at school from the Mond Nickel company, but it worked.
Suppose we had a set of rings tilted up so they were perpendicular to the sun's rays. If it is made of millimeter-sized particles and we can set the spacing between the rings right to a few mm, then we ought to be able to use it as a giant phase plate to focus the sun's infra-red on Mars. Of course, we will have to terraform Mars a bit before there is enough oxygen to set fire to things. Giant ants too.
Maybe not as appealing as writing rude words in the aurora borealis using a thin beam of microwaves, but still, top laffs, eh?
Is the gravitational force really significant?
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Glass In Spaaaaace
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If you are drawing glass fibres, then you are pulling a long bit of thin stuff from a much fatter melt. This implies the stuff must be accelerating, because the stuff must be coming out a lot faster than it went in if you are conserving volume. So, the drawing region must have a lot of acceleration, shear, and so forth. The physicist C.V. Boys in the 1920s used to make the best sapphire fibres for galvonometers, and for experiments to measure the gravitational constant by heating a glass rod and throwing one end of it down an evacuated tube using a giant crossbow. So there is plenty of acceleration and shear in the drawing process.
This in essence shows you how the fibres might be made on earth. If you keep the melt region small then the convective forces should be small, and have little time to redistibute the components by shear thinning. If you have a rod of the material which you locally heat to melting point using an RF furnace, and you draw the fibre upwards, then you ought to get comparable results. Or am I missing something here?
Ages ago, I used to work on this sort of thing too. Railguns as weapons were experimented with in the fifties - perhaps earlier for all I know (some Tesla fan will probably tell me he had one). You cannot make a shell go faster than the propellant's natural velocity, and you only get so many joules per gram with chemicals. To get close to this limit you have to stick the bangy stuff (tm) not only at the bottom of the barrel but at various intervals along its length, as in the V4 supergun. Driving a projectile with a magnetic field (energy but no mass, hooray) seems to offer limitless muzzle velocities. However, they have a history of throwing their breech into the ground at mach 2, rather than putting a bullet in the air when anyone over the rank of major is watching (I forget who I have to thank for this matchless description, but they worked on these, not I).
Rail guns are unlkely to be useful for driving implosions. It would be very hard to focus a symmetric implosion with a railgun. However, you could use the same pulsed power to drive an implosion like a plasma gun. Get a thin gold tube, fill it with DT, and whack in a pulse. The pulse goes up the outside of the tube. The gold outside goes directly to plasma, stops conducting, and so the current can move inward. If you can get the shockwave reaction from the expanding plasma to approximately match the speed of the current penetration, then a nice, cylindrically symmetrical implosion should be yours, and the small burst of annoying penetrative radiation and the hair loss that goes with it.
There is another effect - the Z-pinch - that is a bit railgun-ish. This gets a lot of mention in the Sandia webpage. People used to have great hopes for that - it was quite the thing in the seventies, when people could still use phrases like 'everlasting power from seawater' without laughing - but it is hard to get a symmetrical pinch before instabilities run riot.
Don't take my word for it. Maybe, I'm too old, and things have moved forward since I last was in this field. Sandia is a seriously cool place, even if the people who write their webpages are a bit too keen now and then.
Salty water is heaver than fresh water. If you have a column filled with fresh water and you sink it in the ocean until the top is level with the sea surface, then the column of fresh water will have a lower pressure at the bottom than the surrounding sea, provided there is something across the end of your column to stop the salt water rushing in. If you make the tube deep enough (8000m approx) then the pressure difference will be 25 atmospheres. If you cap the thing with a semi-permeable menbrane, then the pressure difference will be enough to force water through, with a bit of pressure left over to allow the water to squirt out of the top end. If you don't want fresh water, just run through a turbine, and dump it back in the sea. Hooray for perpetual motion!
As usual, thermodynamics manages to muck things up. If it were energetically favourable for water to do this sort of thing, then it would have already done it. If you have a column of salty water at uniform temnperature, then the salt concentration takes up a Boltzmann distribution. The bottom of the oceans are saltier than the top, and so the pressure is never enough to force the reverse osmosis.
A similar truth exists for heat. We will need to force the cold water to the surface, or the hot water to the depths. If there were lots of energy to be got from warming the deep oceans, then this would probably have already happened.
This does not mean the proposal is not sound. If you are close to deep oceans, then keeping stuff cool is a lot cheaper and more energy efficient then your typical closed cycle refrigerator, or water evaporator.
Getting dew from the air may not be easy. The driest town in the world is in Chile, on the coast.
Thanks for the link. Seriously fun. However, isn't this something between the conventional chemical rocket (low exit velocity, so lots of momentum per unit energy, but you run out of stuff to chuck out the back end quick) and the ion drive (tiny thrust for the wattage, but the same weight lasts for ages)? The Prometheus could use the waste heat of the reactor to drive this way, but then they would have to pack extra propellant mass, which takes away the whole point. This is why they have radiative heat sinks instead of evaporative cooling. I don't think this is the sort of thing that would leave its motor on for the months it would take to get to Mars, but it could accelerate a large craft for some hours, and decelerate it at the other end, which would amount to the same thing.
With a nuclear source and/or solar panels we can get lots of energy. The problem is always getting enough mass to check away to get momentum. There is not a lot of stuff out in space, but there is enough to drive a solar sail. If we can trap a bit of this, then we can use this as propellant. I dimly remember a proposal for a craft with an electromagnetic scoop for interstellar hydrogen (the Daedalus, I think it was called). If we can scoop enough to keep a gaseous core reactor busy, then we would be cruising indeed.
PS.
If it blows up in the atmosphere, the uranium might not be a huge problem, but the fluorine you get when the UF6 splits up in the UV would do in the ozone layer something rotten. Be prepared for considerable community service slapping factor 30 suncream on angry emperor penguins.
Re:Voyeger is more important
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Hope for Hubble
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There are arguments for cheaper replacements for Voyager too. The Voyager craft would be overtaken by a solar sail with just the instruments needed to measure what's out in deep space. The sail could perhaps double as a parabolic reflector for the radio signals.
For people with sentimental attachments to Hubble, such as myself, maybe we could leave it in orbit when it dies, so future generations can get it down and stuff it in a museum.
This is a cute design, but it will only work at scales where gravity dominates. You do not find bacteria using this because surface tension and chemical forces at their scale will be so much greater. It will start working at about ant sizes, I guess.
However, supposing you were into designing something that distorted its shape, so it overbalances in a controlled way, but perhaps without shaking the load it carries so much. So, you might want a wheel that propelled itself using an off-center load. However most of the wheel is doing nothing useful at any given time - except, perhaps, keeping the mechanical integrity of the wheel itself- so you only need two spokes of the wheel with little arcs at the end instead of the tyre, with some action that causes the weight to transfer from the back segment to the front one, then whipping the back segment around to the front again. Hang on, you've just invented walking, damn, no patents there...
Okay, this isn't quite bipedal walking; it is more like a tai chi exercise if you are going to be balanced at all times. Or you can opt for true walking, which is harder to control safely. Or for safety you can always opt for a suitcase with lots of little legs, which I think puts the right Terry Pratchett sort of look and feel to the whole exercise.
I find there are three different sorts of test you can run...
(1) Designed tests:
You know what is supposed to happen, and you design a test to fit the extreme conditions. If you are processing images, you might include an image with just extreme black-white edges to check for integer overflows, and stuff like that. These take time and thought to develop. They are usually informative if they fail. If the person who designed the code designs the tests, their coverage is likely to be poor.
(2) Real tests:
If you can get some real data, such as scanned images, then you can eyeball the results and see whether they look right. The coverage is better, but the pass/fail test is more arbitrary. Sometimes you may have important failures but they only have a faint effect on your particular images. The coverage will be incomplete, but it will be different to (1). These are very useful for regression tests, because they can be easy to develop, and the pass/fail test is limited to checking that you get exactly the same result.
(3) Random tests:
Fill the image buffer with white noise and use that. This is useful to test that two implementations are identical. I have used random tests to show that hardware and software implementations of the same algorithm are identical. The coverage is still not good, but it complements (1) which will have flat regions, and (2) which will typically have small differences between adjacent pixels. However, if you get a difference, then it is very hard to trace the cause.
I would guess any good testing strategy ought to include all three types. If you can think of a fourth type, please post.
I remember when you used to have a radio licence in the UK. These were per household rather than per set, and I don't think they were ever enforced the way TV licences were. The thinking was that the general public should not have to pay for a rich man's toy, plus a bit of public enterprise would pump the UK valve industry. When radios became generally available, there was, fortunately a new toy - first 405-line TV, and then colour TV (there was a different licence for 625-line colour). We wanted a broadcasting company with independence, so the licence fees went to the BBC, but central government picked up the costs for collecting the licences.
Now most people have a TV. The people who need TV most may be the poorest amongst us - Open University Students, parents, and carers, and so on. You can make a TV by putting a card in your computer. The TV detector vans do not work any longer (if they ever did, which I doubt). The licence costs more to collect then it is worth. The whole TV licence scheme is getting beyond its useful life. Basically, the only thing it has going for it is its long history.
If you can come up with a reliable alternative that can give the BBC a secure income that does not depend on central government or market forces, then we would love to hear about it. But coming up with a general way of making being nice finiancially rewarding would be a bit of a social breakthrough.
The transmission electron microscope (or TEM) is not the gadget that gives the lovely looking photographs of 3D objects - that's a scanning electron microscope (or SEM). The transmission electron microscope passes a beam of highly collimated electrons though a thin film sample, and then projects the beam onto a phosphor screen at the bottom of the column, much like a slide projector for electrons. The TEM is a lot simpler than the SEM, and it used to be the standard way of getting a really close look at your microstructure back in the 1970's, if you could make it thin enough, and avoid it getting cooked by the electrons.
You actually see the image on the phosphor screen yourself through a window at the base of the column. The image is a bit dim, you you have to have the lights out, but what you see is being imaged directly.
The electrons all have roughly the same energy - a million eV or so - so they are the equivalent of nearly monochromatic light. If your target film varies in thickness, then you get electron Newton's rings because of reflections from the top and bottom surfaces. You can get lots of fringes - out to the 50th or 100th order because the electrons are pretty monochromatic.
Suppose you have a 1 MeV electron beam travelling about 50 cms from your target to the screen. You cannot put more than a few hundred picoamps through your target without frying it. Now you do not get many electrons per second in a picoamp, and they are moving very fast at 1 MeV. I remember doing the sums, and finding out that the whole TEM column for my beam current spent 97% of its time completely empty. The film is only a few nm of this 50 cms, so the odds of it having two transmitting electrons in it at once is really tiny.
You actually see the image on the phosphor screen yourself through a window at the base of the column. The image is a bit dim, so you you have to have all the lights out, but what you see is being imaged directly by the electrons. Or electron, rather, because what you are looking it is the image formed by a single electron interfering fifty or a hundred times with itself after having passed through every point of the target film, and reflecting (or not reflecting) multiple times off each surface.
This as much as anything got me to believe in the wave equations. Trust in the sums and leave your common sense by the door, and it all seems to work.
Ordinary newsprint paper can reflect less than 85% of the light falling on it. Really white colour printer paper can reflect over 97% of the light. Some papers help this along a bit by adding 'optical brightners' - stuff that absorbs UV and flouresces in the blue to counter the natural yellowness of the paper. This suggests if you use a really white background, you can occupy over 10% of the surface with non-active black components, and the white will still look acceptable. This display uses TiO2, the white in white paint (not usually the white in paper), but it looks more like newsprint.
(2) Blackness
A typical print black may be a density of about 1.8. Against a good white, 2% reflectance can look pretty black. It is hard to know what they are getting here because this is a multilayered device , and we are seeing reflections from the other layers. Judging by eye, we do not have quite this constrast. A cholesteric LCD has similar storage properties, but loks contrasty (though the ones I have seen always look blue-black).
(3) Flatness
I guess the pixels are 0.1mm or larger. The device looks rectangular in cross-section from the diagram (NB: this diagram has no dimensions, and the test suggests it was churned out by marketing droids, rather than the engineers who developed it - caveat lector). This suggests the device may appear deep, and may cast shadows. This is not necessarily a problem: light can diffuse 0.1mm within paper to give things like the Yule-Neilsen effect, but we do not notice a dark halo around print. However, if the thing casts a sharp shadow like some LCDs, then this can look disturbing, particularly when you get moire with halftoning patterns. This depth problem will get a lot worse with a colour display.
(4) Resolution
A display is not likely to equal the typical 1800 pixels per inch (70 pixels per mm) for decent looking text. However, this is an unreasonable demand for a refreshable display.
Print on paper is a tough act to follow. This display looks okay, but no more than that. I would look for a flatter device (though I have little real detail on how flat this is). I worry about the switching time, and lifetime problems that dogged earlier electrochromic displays.
Disclaimer: my personal favourite technology is electrostrictive gels, which is why I could trot out these numbers.
Some enterprising guy once bought out a set of composing cards. With these and a die, an unskilled person could use randomness to compose an aria in the style of Mozart. Apparently Mozart himself bought a copy and was delighted by it.
Weirdly enough, I was in Canon Research Europe in the late nineties, and we suggested using edible inks in printer cartridges to write on rice paper. You can then stick this down to cake tops with egg white or something. We wondered whether to patent it but decided not to. I expect there is an earlier Japanese patent, but we didn't bother to dig too deeply.
Later that year, a company in Texas started printing direct to cake icing using a travelling printer head.
When I was young we had none of this fancy technology. A slice of bread in the typewriter had to suffice...
Slashdot Mirror
The basic facts are still accurate. Anyone who had rigid patterns in the way they worked could have their code content guessed. There was an airstrip in the alps that used to send a weather report every day that was word for word the same - "Weather fine, skies clear, visibility good" etc. Bletchley knew from the number of letters in the message that it was the same today as yesterday.
There is another important moral here. The fact that no letter mapped onto itself - a weak property but exploitable if you have enough text - arose because some engineer reckoned if you sent the electrical signal back through the rotors again, then it would be like having twice as many rotors. if didn't - it made the code weaker. You can make everyone have long passwords with random characters, but there is little benefit in this unless you are sure all your ports are protected, and your computer does not have any of the standard service or administration accounts still enabled. If the password is really the limiting security weakness, then maybe it is time to go to something more advanced, like a USB dongle to prove you are who you say you are.
Yep, there are ways around that, too. But every little helps...
What they wrote ended up having large bursts of code that was identical to the IBM PC BIOS. Sometimes there is only one good way of doing something.
Well, this is what I remembered reading years ago. It was an unusual exercise because the actual amount of code was small, so the potential legal cost per byte was very high. If there is someone out there who actually was part of this project, maybe they can post their experiences, and say whether I have got it vaguely right.
This neutron stuff may seem like an urban myth, but I know some people who repeated the experiment in the eighties with a Ministry of Defence reactor that is sometimes used for colouring sapphires, and other strange jobs to earn a buck. They lowered in a bottle of Spanish rotgut brandy, left it there for a fortnight, and what they pulled out was a lot lighter, and smoother tasting. So, it can be done.
At least radioactivity goes away eventually. Chemical stuff can sit around forever. The up-and-coming madman of today fools around with genetic stuff that multiplies and hops species. Progress, I guess.
Back to the original idea, though. Chucking it in the sea is only a good idea if it really gets mixed and thoroughly dispersed. But it can be done.
The UK Windscale nuclear plant - now the Sellafield reprocessing plant, and soon probably to be re-badged the Ravengalss Wildlife park or something like that has a pipeline that put dissolved low-level waste into the sea. At first this sounds like a really, really bad idea. However, the Atlantic has about 10^13 curies of mixed radioactive stuff in it - a lot of it a duterium, tritium, C14, and a mess of heavy metals. You could dump all the waste that had ever been produced into the Atlantic, and provided you mixed it in well, you would never be able to detect the difference. The 1950's solution was to stick a pipe far enough into the ocean to get the waste into some of the fast currents in the north Irish sea, which should sweep it out into the Atlantic. It has been argued since that this did not qork quite as designed, but at the time this bit of the Irish Sea had been surveyed as well as anywhere. The other UK solution was to stick the stuff into drums and drop it into the mid-Atlantic. The drums were designed to burst half-way down, again dispersing the material into the fast ocean currents.
Compare this to the US idea of chucking solid waste into a concreted drum, and sending it right to the bottom. The bottom of the oceans are often quiet places where the water hardly moves. Fish and crustacea live in the rusting cans, and lay their eggs on the concrete. We are trawling for deep sea fish like grenadiers these days as the cod has virtually gone, so we may be getting it all back again - we don't know.
We seem to have lived through an age when Science was trusted to do anything, and the nuclear budget could be underwritten by weapons work; then through an age when Science was not trusted at all, and anything nuclear was controlled by evil warmongers. We might actually be heading for a balanced view. Coo!
So, the reporter doesn't know his periodic table? I bet he's red-hot at quantum physics, though. Really brilliant and highly trained minds sometimes skip over the basic stuff, yerknow.
Bah.
Huffmann coding was not considered patented at the time. The LZW algorithm had patent issues, but I reckoned at the time we could do LZW-compatible coding with a two-pass algorithm: the only unique feature of LZW was the reoptimization of the compression tables as the data was being processed.
There is a 1935 Italian patent on the compression of images, including colour images, for fax using variable length codes for different picture elements. The claims are sufficiently general the invalidate a lot of run-length compression schemes.
That's just what I can remember while writing this. I am not impressed by their patent. There are lots of dud patents in there. It is easy to search the patent database, and become convinced there is a claim. Look at prior art in products and in theliterature, and it is a different story.
What does 'encrypted' data look like? You have a file that seems to contain random digits. The better the encryption, the less structure your encrypted file will have. In the end, a securely encrypted file becomes indistinguishable from a file containing random data.
If the police - or whoever it is doing the searching, this isn't an anti-police thing as such - find some file containing ramdom data, and demand the key, you should be able to say "There is no key. That is random data". This might sound deeply suspicious if only one of us does it. If many of us keep a few files of random data on our hard disk as a mark of passive resistence, then it will become plausible. And the number of encrypted messages, if there are such things, may be outnumbered by the false random data files.
Have things really come to this? I don't honestly know. But I have just made a small, random file and stuck it on my hard drive. Now, we need lots of other people to do the same.
This, of course, is rather silly. We cannot see simultaneous contrast of a billion to one. Our retina is not black, so the light will scatter around in the eye, and give us a flare signal of about a percent or so. We are used to rejecting a low light level like that. That would give us a sensible contrast ratio of 100:1. But this is not the whole story either - if you have a scene on a monitor with only 100:1 contrast, it might look OK in office lighting, but the shadows will look very 'milky' in a darkened room.
In our experience, people using monitors or digital projectors to simulate film will need something like a 1500:1 contrast ratio. There seems to be a point somewhere a bit beneath 2000:1 where the blacks come convincing, and the viewer will accept the simulation. There is some point about 1200:1 where the blacks stop looking convincing, and start looking grey.
If you are trying to match a display to a projector, it is nice to have another factor of two, so you can match the absolute brightness without having to go to the display white. You may want to get this because you sometimes have to drive the RGB channels beyond the white point to get bright and clean looking pastel colours.
You will want to have a continuous tone curve. Field-emission devices will have a cube-type power law down to a point, and then they will cut off exponentially. This may give good-looking greys down to a point, and then plunge into black, crushing all the shadow detail. That does not look as nasty as 'milky' shadows, but it is not that much better.
So - about 3500:1 is good for simulating colour film. However, colour film is pretty dim - 16 ft-lamberts (50 cd/m2) is standard. Images look a lot more colourful if they are brighter. If you want really high-contrast images, you need something like a LCD monitor with a variable LED blacklight, which gives you your local 100:1 contrast and a huge overall contrast ratio. Have a look at http://www.brightsidetech.com/tech/bstech.php.
My thesis was that there is a long history of 3D photography and cinema, with the level of interest bouncing up and down on about a 20 year cycle - about the expiry time of a patent. The 3D views had a short-term novelty value, but they always lost out in the long run to conventional photographs with sightly better resolution.
Wheatstone produced the first hand-drawn stereographs in about 1834.When his friend, Fox Talbot introduced the Daguerrotype process to the UK in 1835, they got together and made some stereo photographs, which were exhibited the same year.
Stereographs were mass-produced from about 1845 onwards (Queen Victoria got given one, then everyone had to try it). In Europe, people often used transmission stereographs, while in the US, the Homes stereograph used reflection prints. Some of Brady's Civil war photographs were stereo pairs. No special camera was necessary: when emulsion speeds allowed hand-held cameras, you had two plates, and you took one with your weight on the right foot, and the second with your weight on the left foot. This moved the camera by something like the intra-ocular distance. This meant that anyone who could take a conventional photograph could take a stereograph, and some people amassed huge private stereo collections (over 100,000 pairs).
The heyday of stereo photography was bought to an end by advances in lens design. The old 'bullseye' lens gave a very limited field of view. The Right Rectilinear lens gave less abberation at the edges, so you could take wider views. Panoramic cameras extended this by moving the emulsion as the photo was taken. You could have 3D panoramas if you made a special spectrograph, but if the parallax offset went through a minimum in the centre of view, then you ended up squinting at the edges.
Two-colour printing for book plates in the late 1800's allowed the red-blue anaglyph stereo images. You could get a wide field of view without special optics because the two images appeared on the same sheeet of paper. Magenta and cyan glasses, and a full-colour print with a common, defocussed, yellow image culd give the appearance of full colour.
Conventional stereographs were combined with flicker-book animation in 3-D 'What the Butler Saw' machines in the late 1800 - early 1900s. Later innovations included anaglyph 3D films and colour still image viewers (View-Master) within a year or so of the first colour films in the 1930s. There were polarized 3D films in the 1950's, a year or so after Polaroid became available in reasonable amounts. Experimental 3D TV was also tried in the 1950's. There were adapters for 35mm cameras and slider projectors in the 1970's, and printable polarized images (the Xograph). There were also lenticular sheet images, the Nimslo camera, and so on. In the 1990 there were liquid-crystal shuttered glasses 3D on colour TVs using the Pulfrich effect (the BBC's Doctor Who in Eastenders episode). It goes on, and on - I am sure there are others that I have forgotten in my original collection. However, they tended to peak on odd-numbered decades. Perhaps the most recent is the IMAX 3D films - the International Space Station (keep your head really level or you see the other images), and New York in 3D (keep your head over the bucket, so you don't miss it when the motion sickness kicks in).
I reckon we are now on a low: there will be a flurry of 3D work in about 2010, peaking at about 2015 at exhibitions, and then disappearing for good a few years later. It's sort-of fun at the time, but it never seems to last.
And while we're on the subject, some of our fellow slashdotters could clean up their act a bit too...
I remember seeing a German periodic table from the 1930's. The long lanthanide and actinide loops were racetrack-shaped, so most of the elements has a squarish block of the chart where they wrote useful weight, number, and isotope data. It was not as minimal as the charts we used to have at school from the Mond Nickel company, but it worked.
Maybe not as appealing as writing rude words in the aurora borealis using a thin beam of microwaves, but still, top laffs, eh?
This in essence shows you how the fibres might be made on earth. If you keep the melt region small then the convective forces should be small, and have little time to redistibute the components by shear thinning. If you have a rod of the material which you locally heat to melting point using an RF furnace, and you draw the fibre upwards, then you ought to get comparable results. Or am I missing something here?
Rail guns are unlkely to be useful for driving implosions. It would be very hard to focus a symmetric implosion with a railgun. However, you could use the same pulsed power to drive an implosion like a plasma gun. Get a thin gold tube, fill it with DT, and whack in a pulse. The pulse goes up the outside of the tube. The gold outside goes directly to plasma, stops conducting, and so the current can move inward. If you can get the shockwave reaction from the expanding plasma to approximately match the speed of the current penetration, then a nice, cylindrically symmetrical implosion should be yours, and the small burst of annoying penetrative radiation and the hair loss that goes with it.
There is another effect - the Z-pinch - that is a bit railgun-ish. This gets a lot of mention in the Sandia webpage. People used to have great hopes for that - it was quite the thing in the seventies, when people could still use phrases like 'everlasting power from seawater' without laughing - but it is hard to get a symmetrical pinch before instabilities run riot.
Don't take my word for it. Maybe, I'm too old, and things have moved forward since I last was in this field. Sandia is a seriously cool place, even if the people who write their webpages are a bit too keen now and then.
As usual, thermodynamics manages to muck things up. If it were energetically favourable for water to do this sort of thing, then it would have already done it. If you have a column of salty water at uniform temnperature, then the salt concentration takes up a Boltzmann distribution. The bottom of the oceans are saltier than the top, and so the pressure is never enough to force the reverse osmosis.
A similar truth exists for heat. We will need to force the cold water to the surface, or the hot water to the depths. If there were lots of energy to be got from warming the deep oceans, then this would probably have already happened.
This does not mean the proposal is not sound. If you are close to deep oceans, then keeping stuff cool is a lot cheaper and more energy efficient then your typical closed cycle refrigerator, or water evaporator.
Getting dew from the air may not be easy. The driest town in the world is in Chile, on the coast.
With a nuclear source and/or solar panels we can get lots of energy. The problem is always getting enough mass to check away to get momentum. There is not a lot of stuff out in space, but there is enough to drive a solar sail. If we can trap a bit of this, then we can use this as propellant. I dimly remember a proposal for a craft with an electromagnetic scoop for interstellar hydrogen (the Daedalus, I think it was called). If we can scoop enough to keep a gaseous core reactor busy, then we would be cruising indeed.
PS.
If it blows up in the atmosphere, the uranium might not be a huge problem, but the fluorine you get when the UF6 splits up in the UV would do in the ozone layer something rotten. Be prepared for considerable community service slapping factor 30 suncream on angry emperor penguins.
For people with sentimental attachments to Hubble, such as myself, maybe we could leave it in orbit when it dies, so future generations can get it down and stuff it in a museum.
However, supposing you were into designing something that distorted its shape, so it overbalances in a controlled way, but perhaps without shaking the load it carries so much. So, you might want a wheel that propelled itself using an off-center load. However most of the wheel is doing nothing useful at any given time - except, perhaps, keeping the mechanical integrity of the wheel itself- so you only need two spokes of the wheel with little arcs at the end instead of the tyre, with some action that causes the weight to transfer from the back segment to the front one, then whipping the back segment around to the front again. Hang on, you've just invented walking, damn, no patents there...
Okay, this isn't quite bipedal walking; it is more like a tai chi exercise if you are going to be balanced at all times. Or you can opt for true walking, which is harder to control safely. Or for safety you can always opt for a suitcase with lots of little legs, which I think puts the right Terry Pratchett sort of look and feel to the whole exercise.
(1) Designed tests: You know what is supposed to happen, and you design a test to fit the extreme conditions. If you are processing images, you might include an image with just extreme black-white edges to check for integer overflows, and stuff like that. These take time and thought to develop. They are usually informative if they fail. If the person who designed the code designs the tests, their coverage is likely to be poor.
(2) Real tests: If you can get some real data, such as scanned images, then you can eyeball the results and see whether they look right. The coverage is better, but the pass/fail test is more arbitrary. Sometimes you may have important failures but they only have a faint effect on your particular images. The coverage will be incomplete, but it will be different to (1). These are very useful for regression tests, because they can be easy to develop, and the pass/fail test is limited to checking that you get exactly the same result.
(3) Random tests: Fill the image buffer with white noise and use that. This is useful to test that two implementations are identical. I have used random tests to show that hardware and software implementations of the same algorithm are identical. The coverage is still not good, but it complements (1) which will have flat regions, and (2) which will typically have small differences between adjacent pixels. However, if you get a difference, then it is very hard to trace the cause.
I would guess any good testing strategy ought to include all three types. If you can think of a fourth type, please post.
Now most people have a TV. The people who need TV most may be the poorest amongst us - Open University Students, parents, and carers, and so on. You can make a TV by putting a card in your computer. The TV detector vans do not work any longer (if they ever did, which I doubt). The licence costs more to collect then it is worth. The whole TV licence scheme is getting beyond its useful life. Basically, the only thing it has going for it is its long history.
If you can come up with a reliable alternative that can give the BBC a secure income that does not depend on central government or market forces, then we would love to hear about it. But coming up with a general way of making being nice finiancially rewarding would be a bit of a social breakthrough.
You actually see the image on the phosphor screen yourself through a window at the base of the column. The image is a bit dim, you you have to have the lights out, but what you see is being imaged directly.
The electrons all have roughly the same energy - a million eV or so - so they are the equivalent of nearly monochromatic light. If your target film varies in thickness, then you get electron Newton's rings because of reflections from the top and bottom surfaces. You can get lots of fringes - out to the 50th or 100th order because the electrons are pretty monochromatic.
Suppose you have a 1 MeV electron beam travelling about 50 cms from your target to the screen. You cannot put more than a few hundred picoamps through your target without frying it. Now you do not get many electrons per second in a picoamp, and they are moving very fast at 1 MeV. I remember doing the sums, and finding out that the whole TEM column for my beam current spent 97% of its time completely empty. The film is only a few nm of this 50 cms, so the odds of it having two transmitting electrons in it at once is really tiny.
You actually see the image on the phosphor screen yourself through a window at the base of the column. The image is a bit dim, so you you have to have all the lights out, but what you see is being imaged directly by the electrons. Or electron, rather, because what you are looking it is the image formed by a single electron interfering fifty or a hundred times with itself after having passed through every point of the target film, and reflecting (or not reflecting) multiple times off each surface.
This as much as anything got me to believe in the wave equations. Trust in the sums and leave your common sense by the door, and it all seems to work.
Ordinary newsprint paper can reflect less than 85% of the light falling on it. Really white colour printer paper can reflect over 97% of the light. Some papers help this along a bit by adding 'optical brightners' - stuff that absorbs UV and flouresces in the blue to counter the natural yellowness of the paper. This suggests if you use a really white background, you can occupy over 10% of the surface with non-active black components, and the white will still look acceptable. This display uses TiO2, the white in white paint (not usually the white in paper), but it looks more like newsprint.
(2) Blackness
A typical print black may be a density of about 1.8. Against a good white, 2% reflectance can look pretty black. It is hard to know what they are getting here because this is a multilayered device , and we are seeing reflections from the other layers. Judging by eye, we do not have quite this constrast. A cholesteric LCD has similar storage properties, but loks contrasty (though the ones I have seen always look blue-black).
(3) Flatness
I guess the pixels are 0.1mm or larger. The device looks rectangular in cross-section from the diagram (NB: this diagram has no dimensions, and the test suggests it was churned out by marketing droids, rather than the engineers who developed it - caveat lector). This suggests the device may appear deep, and may cast shadows. This is not necessarily a problem: light can diffuse 0.1mm within paper to give things like the Yule-Neilsen effect, but we do not notice a dark halo around print. However, if the thing casts a sharp shadow like some LCDs, then this can look disturbing, particularly when you get moire with halftoning patterns. This depth problem will get a lot worse with a colour display.
(4) Resolution
A display is not likely to equal the typical 1800 pixels per inch (70 pixels per mm) for decent looking text. However, this is an unreasonable demand for a refreshable display.
Print on paper is a tough act to follow. This display looks okay, but no more than that. I would look for a flatter device (though I have little real detail on how flat this is). I worry about the switching time, and lifetime problems that dogged earlier electrochromic displays.
Disclaimer: my personal favourite technology is electrostrictive gels, which is why I could trot out these numbers.
Some enterprising guy once bought out a set of composing cards. With these and a die, an unskilled person could use randomness to compose an aria in the style of Mozart. Apparently Mozart himself bought a copy and was delighted by it.
Later that year, a company in Texas started printing direct to cake icing using a travelling printer head.
When I was young we had none of this fancy technology. A slice of bread in the typewriter had to suffice...