The key issue is how little of the radio waves are reflected.
Indeed, I couldn't agree more, and this is a property which rarely seems to be mentioned in meta-material discussions. Supposing that such a material passed 95% of the energy undisturbed and only reflected 5%. I think that this would rightly be regarded as an excellent technical achievement, and after all some glass isn't that good, but it would seem to be of limited military value. As we know from the radar equation's R^4 term, this will only reduce detection range by a little more than 50%, and you can easily buy commercial radar absorbing materials which will do much better than this.
Of course, your absorbing/transmitting solution also has to meet many other criteria. It needs to work over a wide range of frequencies, polarisations and angles; be rugged enough to survive on the outside of a military vehicle without needing maintenance every five minutes; not be so heavy that your aeroplane can't take off and most of all, be affordable (I appreciate that military affordability is not the same as normal affordability, but never the less budgets are much tighter these days). Of course, progress is probably being made in all these area's but my feeling is that there is still a long way to go.
My other big problem with meta-materials is seeing how they can possibly be applied in real life. As I see it, they are basically being used to make a sort of cunning lens which diffracts the wavefront around the object to be concealed. Sadly, the geometry of the situation seems to result in devices which have a high degree of symmetry (for example, cylinders). I can imagine how this might be extended to a sphere (great if we need stealthy cannon balls) or maybe even a prolate spheroid (which perhaps we could fashion into some sort of missile), but to deal with the complex shape of an aircraft in such a way that the different parts of the wavefront passing around different parts of the wings and fuselage all add up correctly in phase over a useful range of angles seems to me to be an extremely difficult problem.
Still, I am not going to sit here and say that it can't be done. The people working on these problems are no doubt very brainy and may come up with a practical solution, but presumably the paint and shape solution is also being advanced and it is my feeling that this older simpler technology is going to stay ahead for a considerable period of time.
Sigh, here we go again! Radars and optical vision do not work in remotely the same way. Creating invisibility in the two different realms is a completely different problem.
In most vision situations there are two critical factors which don't occur in the great majority of radars. The first is illumination of the target from angles other than the viewing angle (OK, there are bistatic radars, but they are not common) and the other is a background which is illuminated. Try to think about this for just a few moments. Why can't we all make ourselves invisible just by wearing matt black clothing? Well, obviously because we will stand out against the background unless we happen to be standing in front of black wall or wandering around in a coal mine. The whole point of the fictional 'invisibility cloak' is that it works in all circumstances. We can already be invisible in certain carefully controlled environments, that after all is what camouflage is all about.
But, a radar is rather like wandering about in the above mentioned coal mine, or perhaps a dark forest with a miner's lamp fixed to your head. The background is basically black and the illumination comes from the viewing direction. In this scenario, someone dress entirely in black would be effectively invisible. And that is the key point to grasp. In the world or radar we can achieve invisibility simply by making sufficiently 'black' 'paint'. The weird ability of these meta-materials to allow the illumination to pass through the target un-disturbed is of no benefit. Since we don't have a receiver on the other side of the target to detect this energy it isn't relevant. Now, sure, we can all dream up complex bistatic radars which rely on the obscuration of the signal to detect the target, but I remain to be convinced that such a thing can be made sufficiently versatile to be useful.
Can I stress that I am not suggesting the these meta-materials don't have an application in the world of radar. They seem to me to be particularly useful where one wants to remove a fixed object which obscures the view of your radar. For example, consider a radar on a ship. It may well find that in some directions its view is obscured by other parts of the superstructure. If the could cover these other bits of the ship with meta-materials such that the radar pulses could pass 'through' and back again undisturbed, then our radar's field of view would be increased. Such an application would work perfectly well with even the relatively narrow band materials presented previously.
Basically it's paint that is "black" at radar frequencies.
The fact that the main feature of the paint can be summarised in a pithy sentence does not mean that it is not exotic or hard to make. Example: "A time machine is just a gadget that lets you visit people from history". There, that was easy wasn't it!
Making an really militarily effective radar absorbing paint is very difficult. Why? Well, if we wish to attenuate a radio wave, we must absorb either the electric or the magnetic fields or both. Absorbing the electric field is easy with the aid of a resistive material, but there is a snag. Recall, that electric fields are always perpendicular to a conductor (e.g. the steel surface of our tank). If we attempt to absorb this field with a thin material such as paint then only a tiny portion of the field will be within the paint and there will be little effect (especially at lower frequencies). Returning to basic physics, we observe that the magnetic field is parallel to our conducting tank, and therefore much more likely to interact with our thin paint. Sadly, again, if we wish to attenuate magnetic fields we need something like iron filings (as has been suggested above) and plenty of them. This makes the paint extremely heavy (never mind stopping the iron filings from settling to the bottom of the tin!). It might just about to practical to cover a tank with such a paint, but a thick enough coat on a lighter vehicle will seriously slow it down, and for aircraft, which it always where the real stealth action is, it is completely impractical to use other than in very small amounts.
So, we can all mix iron filings into various resins and absorb some radar waves. The tough challenge is making it light enough to be useful, particularly on aircraft. I agree that in cases where weight doesn't matter (e.g. buildings) the problem is well understood. That is why EMC chambers designed for low frequency use are lined with ferrite tiles. The weight is terrific, but you just have to make the walls a bit stronger.
Now, I have no idea if this chap in the desert has managed to make a thin, light RAM paint which works well, but if he has he can expect some serious interest and money to be coming his way.
My reading of the story may be wrong, but I can't find anywhere in it where it says that he was prosecuted. Perhaps this is a transatlantic definition problem. Here in the UK, there are basically four stages to a criminal prosecution (yes, I have simplified).
- Arrest: The police suspect that you might have committed a crime.
- Charging: The police decide that their suspicions were correct and ask for the case to go to trial.
- Prosecution: The Crown Prosecution Service (a body independent from the police) decide that the case is likely to succeed and will be in the public interest. They prepare the prosecution case and go to the courts.
- Conviction or aquital: A court decided whether or not the defendant is guilty and if guilty imposes a penalty.
So far as I can tell, in this case Mr Bunce only passed through the first stage. The police eventually decided that he had not committed a crime and therefore didn't charge him. Now, that is not to minimise his suffering. He has clearly been very badly treated and he hope he succeeds with legal action against not only the web site, but also the police and his ex-employers. I should also point out that here in the UK police state, he will have had his finger prints and DNA taken and that these will now be retained forever (even after his death) even thought the police accept that he did nothing wrong.
Under the terms of the Schengen Agreement there are no longer any border controls between the vast majority of European countries. It is possible to drive all the way from Estonia to Portugal without needing to show your passport once.
Of course things are not quite as open as they may be in the USA. Firstly, not all countries are covered (notably missing are the UK and Ireland). Secondly, some countries require citizens to carry ID cards and visitors to carry passports, but the agreement means that you don't have to show them at the border (and you couldn't if you wanted to, since in most places there simply isn't any form of border post at all). Finally, it really only makes a big difference for land travel. Airlines and Ferry companies are still required to check identity documents for all of their passengers, and that usually means a passport.
Do they really think censoring that sort of information on the web will stop anyone who wants to build a bomb?
No, of course they don't, that is not the real purpose of the exercise. Let me try to explain.
Suppose that you are a politician and you are being interviewed on the TV. The interviewer says "Minister, what steps is your government taking to stop terrorists acquiring bomb making instructions?". Now, you basically have two options:
Patiently try to explain that this would be a pointless waste of time.
Say, "We are introducing legislation forcing ISPs to block access to such reprehensible material"
If you try option 1, then 1% of the viewers will understand the technical impossibility and agree with you, whilst the other 99% will get the vague impression that you are soft on terrorism or, at best, hear a strange buzzing noise. With option 2, OTOH, 1% of viewers will be outraged by such a pointless and stupid idea, whilst the rest will get the impression that you are tough on terrorists.
Now, you are a smart politician and wish to be re-elected. Which one are you going to choose?
Of course, you know full well that in a few years time you will get a question like "Minister, in the recent terrorism trial it was revealed that the terrorists obtained their bomb instructions from the internet. I thought that you had introduced legislation to prevent this?", but fortunately there are lots of ways out of this:
Blame "evil hackers" and announce even more draconian restrictions.
Blame ISPs for not implementing the law and announce increased penalties.
Count on the fact that by then you will have moved on or retired and it will be someone else's problem.
Here in the UK we don't have any of these problems of TV listing availability and complicated html parsing scripts which break every week. The BBC have a special web page just for XMLTV downloads, and it doesn't just cover BBC channels, but practically every channel you can receive in the UK (check the channels.dat file for a full list). The only restriction is that the data can only be used for private non-commercial purposes.
Of course, most of this is probably being paid for from our TV license fees which I know many Americans regard as being a terrible communist plot (some funding may come from the cover price of the Radio Times magazine).
Here in the UK, you practically never see a Red cross used anywhere outside of the British Red Cross society and the various military medical services. The Red Cross don't even have to go to the expense of enforcing this, since the government do it for them via (I believe) an office in the Ministry of Defence. We don't have Red Crosses on first aid kits (they are all green and white), ambulances (other than military and the voluntary Red Cross ones), signs for hospitals etc.
A remember a political dust up many years ago when the ruling labour party (who I think were in opposition at the time) printed a campaign leaflet about health with a Red Cross on the cover. The other parties jumped on this with glee and they had to stop distributing the leaflets.*
Clearly, there are some sensible exceptions to this otherwise total ban. You can buy models of military ambulances with red crosses on them, and clearly there is some sort of exception for people making films and TV programmes.
*Although I remember this event distinctly, I can't find any links to reports about it (it was more than 10 years ago). If anyone can find such a link I would be most grateful.
Well, I don't know about the USA, but here in the UK and I believe the rest of Europe, all first aid kits are green with a white cross. Furthermore, in commercial use (i.e. kits in public buildings and work places) those colours are compulsory.
Can someone please explain to me why allegedly prestigious law firms would use anonymous and clearly libelous postings as any sort of basis to decide whether to employ someone? Especially when many of the comments appear to be unrelated to legal ability (breast size, sexual orientation etc).
Surely, if these women are indeed excellent graduates, they will have completely non-anonymous references from prestigious law professors saying so. Why would a potential employer need anything else.
Perhaps this problem could best be solved by some sort of automated system which publishes random derogatory comments about all law graduates. Then, these law firms would not be able to employ any new graduates and would eventually go out of business!!
Currently, people making and using their own biofuels in the UK have to register and pay fuel tax, but this is about to change. The government has agreed a new limit of 2500 litres per annum below which there will be no need to register or pay tax.
As always, one is amazed to see a sensible suggestion from government!
Now, as to your main point, whilst I agree with the main thrust, I think that you may have missed the key point. I think we all agree that if Uri Geller owns some copyright in some material and someone in the USA breaches that copyright in some way which doesn't constitute fair use then Geller can in principle sue them in the US courts for breach of copyright, but that is not the situation under debate.
The Bern convention does not extend copyright transnationaly in quite the way you are perhaps implying (i.e. completely equal rules everywhere). It lays down certain minimal requirements, but the details vary from country to country. The UK and USA are both signatories, but never the less there are differences in what is protected. Examples include the period of protection (50 years for music in the UK, significantly longer in the USA) and what exactly is defined as 'fair use' (in this latter case US rules seem to be rather less stringent). I agree however that Geller probably has the same right to sue in the USA as US citizens have.
But the key point here is that Geller is not suing anyone. He issued a DMCA takedown notice. A concept which I don't believe the Bern convention addresses at all. It may well be that anyone in the world is allowed to issue such a notice in the USA, but the presence of the Bern convention doesn't demonstrate that this is necessarily the case, hence my question. I suggest that it would be perfectly legal for the USA or any other country to have a DMCA like law which says "Only our citizens may issue takedown notices" without any fear of breaching the terms of the Bern convention, because those who were not citizens would still be able to exercise their Bern rights by initiating a conventional suit for copyright infringement.
On your final point, it has been discussed here on many previous occasions that extradition law only applies to criminal cases and not civil ones such as this. Hence my suggestion that breaching an injunction may be a criminal act (I don't know, IANAL) capable of invoking extradition proceedings.
I am a supporter of EFF but having read the compaint, I am (as usual) a little confused. It says that both Geller and his company are based in the UK (paras 4 and 5) and then goes on to say that the court has jurisdiction (para 8). Isn't this going to end up rather like the SpamHaus case but possibly with better management from the UK end?
I can see how the EFF might prevail with relief A (declaratory judgment) and possibly B (injunctive relief) although its not clear what would happen if Geller broke the injunction. Would that be a criminal offence for which he could be extradited? But reliefs C to F all seem to boil down to Geller handing over some money. What is going to happen when the court rules against him and he ignores them?
So far as I can see, YouTube shouldn't have had to accept a DMCA takedown request from outside the USA in the first place. Perhaps they didn't have to? Does the DMCA say anything about this? What's to stop some bored teenager from (for example) China sending dozens of takedown notices every day in the certain knowledge that no-one can stop him?
I live in the UK and have recently purchased a 'naked' Laptop from Transtec. I also had the option to have it supplied with SuSE. The naked and SuSE machines were cheaper than the Windows ones (once you get the hardware configuration the same). I understand that they will supply desktops without Windows as well.
They are a smaller supplier, but not tiny. They are an approved supplier for some central government departments.
If the big companies don't want to sell me a naked or Linux machine then that is fine by me. I will take my custom elsewhere and they are the ones who will lose out.
I run Gentoo on five different systems, including a laptop and an Alpha. For me one of the big advantages is that it doesn't fill up with dozens of unwanted libraries. Let me explain: In an RPM based distribution (I have used Mandrake and SuSE) when one installs an application, it will often bring in a host of other dependent RPMs. That's just fine, and Gentoo does something similar, but what happens when you decide that you don't want the application any longer? I often install something to try it out and then decide that it doesn't do what I want. You can remove the application itself, but what about all those libxxxxx.rpm packages which it depended on. I can remove them if I can remember which ones they were, but otherwise they just hang around getting in the way.
"Disks are cheap you Bozo!" Yes, I know, but I keep my systems up to date and unwanted libraries mean unwanted security updates. With Gentoo, this problem is entirely solved with the 'emerge --depclean' command. When I emerge an application its name is added to the world file (/var/lib/portage/world) but not the names of it's dependencies. So, emerge --depclean simply looks for packages which which are not in world (or the base system list) and aren't depended on by any installed packages.
Related points: The wonder of USE flags means that many libraries never get installed at all because I can tell the application that I am not interested in that functionality. My general point also applies to cases where one upgrades an application and the new version no longer depends on a particular library.
If there are RPM (or apt) based distributions which have a similar scheme then I would love to know about it. Mandrake has (or at least used to have) a script called something like 'urpmi_rpm-find-leaves' which gave a list of RPMs which were not depended upon. By filtering the output through 'grep lib' one could get part of the way there, but it would still leave quite a few RPMs to locate by hand.
I just bought an OS free laptop in the UK from Transtec. I could have had it with SuSE pre-installed for a bit extra. The default hardware spec is different for the OS free machines, but if you configure them to be the same as the Windows ones then they are cheaper (i.e. there is no negative Windows cost as others have reported). Although Transtec mostly supply business customers, they will sell to individuals. I am happy with the machine and it is now running Gentoo just fine.
There are very few UK companies who will see you a Linux or OS free laptop. One of the others told me that they get theirs from Lenovo, but can only occasionally get one without an OS. In other cases they remove Windows and try to claim back the cost from their wholesaler. Occasionally, this works. So, in most cases money is still going to Microsoft. I don't like this idea, so I was pleased when Transtec told me that their OS free machines have never had any OS installed and so none of my money would go to Redmond. This might be a point worth checking if you are looking for a linux laptop.
For any given size of coax there is a maximum permitted frequency. This occurs when the average circumference of the dielectric equals the wavelength in that dielectric material. This means that as the frequency goes up the diameter of the cable must go down. We see this clearly in the development of coax connectors for mmwave applications, where diameters are now around 1mm in some cases. If one operates above the maximum frequency, then the outer of the coax will start to act as a circular waveguide. Some of the energy will start to switch from the conventional coax TEM mode (where the E and H fields are always transverse to the direction to travel) into a weird waveguide mode. If this happens then a) you will get serious dispersions since the group velocity of the modes will be different and b) the energy in the waveguide mode won't all come out when it gets to the other end. So, if you want to fit a signal with an extremely small wavelength (such as light) down coax then you need to get that average circumference down to a similar size.
There is no issue of minimizing impedance. You can make coax work at any impedance you like, although making it at high impedances gets difficult because the inner becomes very thin and delicate. The important thing is to have a constant impedance throughout your cables, connectors etc in order not to get reflections and standing wave problems. The choice of impedance is not arbitrary however, since loss and maximum power handling both vary with this parameter. Minimum loss occurs around 75 ohms, which is why this impedance is used for TV cables. Maximum power handling (due to flashover) occurs at around 30 ohms. In practice, very few people generate enough power for this to be an issue, so the world has settled on 50 ohms as a handy compromise for most cables.
Hmm, interesting. Exciting though it may be for me to try out one of these, there are some serious obstacles, including:
Neither the bulbs or the holders appear to be available in the UK.
I can't even try one out in a standard lamp holder since we have bayonet rather than screw fittings here (although Edison screw lamp holders are relatively easy to get hold of since they are used in Europe).
I would need to dig out a transformer to reduce our 240V supply to 110V.
I think that the best plan would be to go with something like the Estonian scheme and I have toyed with re-wiring some of the light fittings when I move to a new house in a year or so's time.
Amazing! I have never seen anything like this in the UK and I presume that they are not available. I don't believe that you can get them in Estonia either, but I'll ask my Mother-in-law.
Can someone tell me how they connect, since I couldn't find a picture of the base of any? I presume that there is an additional ring which provides the third connection. What happens if you screw one into an ordinary socket or visa versa
Many of the other replies to this post are at best mis-informed. So, here are the facts.
1) Reducing the power to incandescent bulbs via a dimmer does not save money. It is true that you use less power, but as you reduce the voltage the efficiency of the bulb goes down. Wikipedia has an article on this with some handy power laws. If we apply these to the example case (75% of the voltage, assume 100W bulb) we get only 38% of the light (i.e. about what we would get from a 40W bulb), but we consume 63W of electricity. Of course, the bulb will now last for about 100 times as long. Perhaps the original post didn't mean 75% of the voltage, but instead 75% of the light. Doing the maths for this case we get: 88W and 3.8 times lifetime.
Note that the above lifetime extensions are purely a result of the lower voltage and nothing to do with flipping on and off. You will get the advantage even if you leave the bulb on all the time. But, since bulbs cost more to run than they do to buy and replace (except in special cases such as traffic lights) then reducing the voltage is a false economy. You would be better off simply buying some lower wattage bulbs or better still getting some compact flourescent lamps instead.
When I first knew my wife she lived in Estonia and her bedroom was fitted with a very clever scheme for dimming the lights (something which I often wanted to do!). Her light fitting had three bulbs connected to a double wall switch. One switch operated a single bulb and the other controlled the other two. One could therefore have 1, 2 or 3 bulbs and they would always be running at optimum efficiency. I suspect that limited Soviet domestic technology was the motivation behind this scheme rather than power efficiency, but it worked very well. Sadly, although several of the rooms in the flat are still wired for this scheme, you can no longer buy the special multi-wired fittings. I have offered to modify my mother-in-laws new lights, but she is reluctant.
Finally, can I point out that dimmer switches do not rely on resistance. If they did then they would get very hot! Most use electronic components called triacs, which are essentialy switches which can be controlled in such a way as to permit current to flow for only part of each half cycle of the AC voltage. This reduces the average voltage and for incandescent bulbs this is what matters.
As it says in the BBC article, only some devices will be legal.
Now certain FM transmitters, which can be tuned to spare frequencies, will be legal from 8 December.
However, many devices currently on the market will remain illegal as they do not meet the legally required technical specifications and could interfere with radio broadcasts.
All approved transmitters will carry a CE mark indicating approval for sale in the European Union.
So, as I see it, legal transmitters will not only have to meet strict power limits, but also be tunable only to certain spare frequencies in the FM band. I spent some time searching the Ofcom web site to try and find exact details of the regulations (e.g. which frequencies exactly), but without success. If anyone else can find them then I for one would be interested.
After a great deal of thought, I have come up with a possible application for the current 2D, limited bandwidth version.
Suppose that you have a radar on, for example, a ship. It is often the case that since only one radar can be on top of the tallest mast, the others have some of their field of view partly obscured by other masts. If nearby masts were covered in this stuff then the radar should be able to see right through them and thus maintain a 360 deg field of view. In this case the 2D nature is fine for wrapping around the mast, and the limited bandwidth doesn't matter since we presumably know the frequency on which our radar operates.
Well, yes and no. Clearly, the current system is entirely detectable by such methods because it doesn't do very much, but I think you are asking "What if we could make one which worked over a broad range of frequencies and angles". In that case it probably would work against passive (i.e. bistatic) radars and indeed that is apparently the whole point. If we only want to defeat conventional monostatic radars then covering the whole thing in some sort of absorbing material (i.e. RAM) would be just as effective, cheaper and more practical (for example, you wouldn't need to invent a spherical airoplane with no inlets of exhausts).
I have to say that although this is an interesting trick, it doesn't seem to be quite as useful as people might at first imagine. For a kick off, it seems to be round and one would therefore suppose that a 3D one would need to be a sphere. Is that useful? I suppose that you could put your tank inside a huge sphere and roll it around, but guiding it and firing the gun sounds a bit tricky. Somehow I don't think that making a none-spherical one which works over a broad range of incident angles is going to be at all easy. I suppose that you might be able to make a spherical bomb.
Next, as the article mentions, what about bandwidth. For it to be useful against radars you are going to need at least a 10:1 bandwidth which again, doesn't sound easy. There is slightly better news for visible light, where a bit less than 2:1 will work.
Finally, I can't believe that it doesn't reflect any radar energy back. It might only reflect 10% or maybe even only 1%, but when you consider the dreaded R^4 factor in the radar equation that still doesn't buy you a lot of stealth.
Why precisely is it illegal to finance a lawsuit? Although I am not in favour of Microsoft's alledged actions in financing SCO, I often see circumstances where someone seems to have suffered an injustice, but can't claim redress because they can't afford the legal costs. I think to myself "If I were rich, perhaps I would offer to help them out". Do I understand that such philanthropy would be illegal? Is it all part of a scheme to maintain the legal system as a means for the rich to oppress the poor?
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The key issue is how little of the radio waves are reflected.
Indeed, I couldn't agree more, and this is a property which rarely seems to be mentioned in meta-material discussions. Supposing that such a material passed 95% of the energy undisturbed and only reflected 5%. I think that this would rightly be regarded as an excellent technical achievement, and after all some glass isn't that good, but it would seem to be of limited military value. As we know from the radar equation's R^4 term, this will only reduce detection range by a little more than 50%, and you can easily buy commercial radar absorbing materials which will do much better than this.
Of course, your absorbing/transmitting solution also has to meet many other criteria. It needs to work over a wide range of frequencies, polarisations and angles; be rugged enough to survive on the outside of a military vehicle without needing maintenance every five minutes; not be so heavy that your aeroplane can't take off and most of all, be affordable (I appreciate that military affordability is not the same as normal affordability, but never the less budgets are much tighter these days). Of course, progress is probably being made in all these area's but my feeling is that there is still a long way to go.
My other big problem with meta-materials is seeing how they can possibly be applied in real life. As I see it, they are basically being used to make a sort of cunning lens which diffracts the wavefront around the object to be concealed. Sadly, the geometry of the situation seems to result in devices which have a high degree of symmetry (for example, cylinders). I can imagine how this might be extended to a sphere (great if we need stealthy cannon balls) or maybe even a prolate spheroid (which perhaps we could fashion into some sort of missile), but to deal with the complex shape of an aircraft in such a way that the different parts of the wavefront passing around different parts of the wings and fuselage all add up correctly in phase over a useful range of angles seems to me to be an extremely difficult problem.
Still, I am not going to sit here and say that it can't be done. The people working on these problems are no doubt very brainy and may come up with a practical solution, but presumably the paint and shape solution is also being advanced and it is my feeling that this older simpler technology is going to stay ahead for a considerable period of time.
Sigh, here we go again! Radars and optical vision do not work in remotely the same way. Creating invisibility in the two different realms is a completely different problem.
In most vision situations there are two critical factors which don't occur in the great majority of radars. The first is illumination of the target from angles other than the viewing angle (OK, there are bistatic radars, but they are not common) and the other is a background which is illuminated. Try to think about this for just a few moments. Why can't we all make ourselves invisible just by wearing matt black clothing? Well, obviously because we will stand out against the background unless we happen to be standing in front of black wall or wandering around in a coal mine. The whole point of the fictional 'invisibility cloak' is that it works in all circumstances. We can already be invisible in certain carefully controlled environments, that after all is what camouflage is all about.
But, a radar is rather like wandering about in the above mentioned coal mine, or perhaps a dark forest with a miner's lamp fixed to your head. The background is basically black and the illumination comes from the viewing direction. In this scenario, someone dress entirely in black would be effectively invisible. And that is the key point to grasp. In the world or radar we can achieve invisibility simply by making sufficiently 'black' 'paint'. The weird ability of these meta-materials to allow the illumination to pass through the target un-disturbed is of no benefit. Since we don't have a receiver on the other side of the target to detect this energy it isn't relevant. Now, sure, we can all dream up complex bistatic radars which rely on the obscuration of the signal to detect the target, but I remain to be convinced that such a thing can be made sufficiently versatile to be useful.
Can I stress that I am not suggesting the these meta-materials don't have an application in the world of radar. They seem to me to be particularly useful where one wants to remove a fixed object which obscures the view of your radar. For example, consider a radar on a ship. It may well find that in some directions its view is obscured by other parts of the superstructure. If the could cover these other bits of the ship with meta-materials such that the radar pulses could pass 'through' and back again undisturbed, then our radar's field of view would be increased. Such an application would work perfectly well with even the relatively narrow band materials presented previously.
The fact that the main feature of the paint can be summarised in a pithy sentence does not mean that it is not exotic or hard to make. Example: "A time machine is just a gadget that lets you visit people from history". There, that was easy wasn't it!
Making an really militarily effective radar absorbing paint is very difficult. Why? Well, if we wish to attenuate a radio wave, we must absorb either the electric or the magnetic fields or both. Absorbing the electric field is easy with the aid of a resistive material, but there is a snag. Recall, that electric fields are always perpendicular to a conductor (e.g. the steel surface of our tank). If we attempt to absorb this field with a thin material such as paint then only a tiny portion of the field will be within the paint and there will be little effect (especially at lower frequencies). Returning to basic physics, we observe that the magnetic field is parallel to our conducting tank, and therefore much more likely to interact with our thin paint. Sadly, again, if we wish to attenuate magnetic fields we need something like iron filings (as has been suggested above) and plenty of them. This makes the paint extremely heavy (never mind stopping the iron filings from settling to the bottom of the tin!). It might just about to practical to cover a tank with such a paint, but a thick enough coat on a lighter vehicle will seriously slow it down, and for aircraft, which it always where the real stealth action is, it is completely impractical to use other than in very small amounts.
So, we can all mix iron filings into various resins and absorb some radar waves. The tough challenge is making it light enough to be useful, particularly on aircraft. I agree that in cases where weight doesn't matter (e.g. buildings) the problem is well understood. That is why EMC chambers designed for low frequency use are lined with ferrite tiles. The weight is terrific, but you just have to make the walls a bit stronger.
Now, I have no idea if this chap in the desert has managed to make a thin, light RAM paint which works well, but if he has he can expect some serious interest and money to be coming his way.
My reading of the story may be wrong, but I can't find anywhere in it where it says that he was prosecuted. Perhaps this is a transatlantic definition problem. Here in the UK, there are basically four stages to a criminal prosecution (yes, I have simplified).
- Arrest: The police suspect that you might have committed a crime.
- Charging: The police decide that their suspicions were correct and ask for the case to go to trial.
- Prosecution: The Crown Prosecution Service (a body independent from the police) decide that the case is likely to succeed and will be in the public interest. They prepare the prosecution case and go to the courts.
- Conviction or aquital: A court decided whether or not the defendant is guilty and if guilty imposes a penalty.
So far as I can tell, in this case Mr Bunce only passed through the first stage. The police eventually decided that he had not committed a crime and therefore didn't charge him. Now, that is not to minimise his suffering. He has clearly been very badly treated and he hope he succeeds with legal action against not only the web site, but also the police and his ex-employers. I should also point out that here in the UK police state, he will have had his finger prints and DNA taken and that these will now be retained forever (even after his death) even thought the police accept that he did nothing wrong.
Under the terms of the Schengen Agreement there are no longer any border controls between the vast majority of European countries. It is possible to drive all the way from Estonia to Portugal without needing to show your passport once.
Of course things are not quite as open as they may be in the USA. Firstly, not all countries are covered (notably missing are the UK and Ireland). Secondly, some countries require citizens to carry ID cards and visitors to carry passports, but the agreement means that you don't have to show them at the border (and you couldn't if you wanted to, since in most places there simply isn't any form of border post at all). Finally, it really only makes a big difference for land travel. Airlines and Ferry companies are still required to check identity documents for all of their passengers, and that usually means a passport.
No, of course they don't, that is not the real purpose of the exercise. Let me try to explain.
Suppose that you are a politician and you are being interviewed on the TV. The interviewer says "Minister, what steps is your government taking to stop terrorists acquiring bomb making instructions?". Now, you basically have two options:
If you try option 1, then 1% of the viewers will understand the technical impossibility and agree with you, whilst the other 99% will get the vague impression that you are soft on terrorism or, at best, hear a strange buzzing noise. With option 2, OTOH, 1% of viewers will be outraged by such a pointless and stupid idea, whilst the rest will get the impression that you are tough on terrorists.
Now, you are a smart politician and wish to be re-elected. Which one are you going to choose?
Of course, you know full well that in a few years time you will get a question like "Minister, in the recent terrorism trial it was revealed that the terrorists obtained their bomb instructions from the internet. I thought that you had introduced legislation to prevent this?", but fortunately there are lots of ways out of this:
Here in the UK we don't have any of these problems of TV listing availability and complicated html parsing scripts which break every week. The BBC have a special web page just for XMLTV downloads, and it doesn't just cover BBC channels, but practically every channel you can receive in the UK (check the channels.dat file for a full list). The only restriction is that the data can only be used for private non-commercial purposes.
Of course, most of this is probably being paid for from our TV license fees which I know many Americans regard as being a terrible communist plot (some funding may come from the cover price of the Radio Times magazine).
Here in the UK, you practically never see a Red cross used anywhere outside of the British Red Cross society and the various military medical services. The Red Cross don't even have to go to the expense of enforcing this, since the government do it for them via (I believe) an office in the Ministry of Defence. We don't have Red Crosses on first aid kits (they are all green and white), ambulances (other than military and the voluntary Red Cross ones), signs for hospitals etc.
A remember a political dust up many years ago when the ruling labour party (who I think were in opposition at the time) printed a campaign leaflet about health with a Red Cross on the cover. The other parties jumped on this with glee and they had to stop distributing the leaflets.*
Clearly, there are some sensible exceptions to this otherwise total ban. You can buy models of military ambulances with red crosses on them, and clearly there is some sort of exception for people making films and TV programmes.
*Although I remember this event distinctly, I can't find any links to reports about it (it was more than 10 years ago). If anyone can find such a link I would be most grateful.
Well, I don't know about the USA, but here in the UK and I believe the rest of Europe, all first aid kits are green with a white cross. Furthermore, in commercial use (i.e. kits in public buildings and work places) those colours are compulsory.
Can someone please explain to me why allegedly prestigious law firms would use anonymous and clearly libelous postings as any sort of basis to decide whether to employ someone? Especially when many of the comments appear to be unrelated to legal ability (breast size, sexual orientation etc).
Surely, if these women are indeed excellent graduates, they will have completely non-anonymous references from prestigious law professors saying so. Why would a potential employer need anything else.
Perhaps this problem could best be solved by some sort of automated system which publishes random derogatory comments about all law graduates. Then, these law firms would not be able to employ any new graduates and would eventually go out of business!!
Currently, people making and using their own biofuels in the UK have to register and pay fuel tax, but this is about to change. The government has agreed a new limit of 2500 litres per annum below which there will be no need to register or pay tax.
As always, one is amazed to see a sensible suggestion from government!
Well, first of all I am also a UK citizen.
Now, as to your main point, whilst I agree with the main thrust, I think that you may have missed the key point. I think we all agree that if Uri Geller owns some copyright in some material and someone in the USA breaches that copyright in some way which doesn't constitute fair use then Geller can in principle sue them in the US courts for breach of copyright, but that is not the situation under debate.
The Bern convention does not extend copyright transnationaly in quite the way you are perhaps implying (i.e. completely equal rules everywhere). It lays down certain minimal requirements, but the details vary from country to country. The UK and USA are both signatories, but never the less there are differences in what is protected. Examples include the period of protection (50 years for music in the UK, significantly longer in the USA) and what exactly is defined as 'fair use' (in this latter case US rules seem to be rather less stringent). I agree however that Geller probably has the same right to sue in the USA as US citizens have.
But the key point here is that Geller is not suing anyone. He issued a DMCA takedown notice. A concept which I don't believe the Bern convention addresses at all. It may well be that anyone in the world is allowed to issue such a notice in the USA, but the presence of the Bern convention doesn't demonstrate that this is necessarily the case, hence my question. I suggest that it would be perfectly legal for the USA or any other country to have a DMCA like law which says "Only our citizens may issue takedown notices" without any fear of breaching the terms of the Bern convention, because those who were not citizens would still be able to exercise their Bern rights by initiating a conventional suit for copyright infringement.
On your final point, it has been discussed here on many previous occasions that extradition law only applies to criminal cases and not civil ones such as this. Hence my suggestion that breaching an injunction may be a criminal act (I don't know, IANAL) capable of invoking extradition proceedings.
I am a supporter of EFF but having read the compaint, I am (as usual) a little confused. It says that both Geller and his company are based in the UK (paras 4 and 5) and then goes on to say that the court has jurisdiction (para 8). Isn't this going to end up rather like the SpamHaus case but possibly with better management from the UK end?
I can see how the EFF might prevail with relief A (declaratory judgment) and possibly B (injunctive relief) although its not clear what would happen if Geller broke the injunction. Would that be a criminal offence for which he could be extradited? But reliefs C to F all seem to boil down to Geller handing over some money. What is going to happen when the court rules against him and he ignores them?
So far as I can see, YouTube shouldn't have had to accept a DMCA takedown request from outside the USA in the first place. Perhaps they didn't have to? Does the DMCA say anything about this? What's to stop some bored teenager from (for example) China sending dozens of takedown notices every day in the certain knowledge that no-one can stop him?
I live in the UK and have recently purchased a 'naked' Laptop from Transtec. I also had the option to have it supplied with SuSE. The naked and SuSE machines were cheaper than the Windows ones (once you get the hardware configuration the same). I understand that they will supply desktops without Windows as well.
They are a smaller supplier, but not tiny. They are an approved supplier for some central government departments.
If the big companies don't want to sell me a naked or Linux machine then that is fine by me. I will take my custom elsewhere and they are the ones who will lose out.
I run Gentoo on five different systems, including a laptop and an Alpha. For me one of the big advantages is that it doesn't fill up with dozens of unwanted libraries. Let me explain: In an RPM based distribution (I have used Mandrake and SuSE) when one installs an application, it will often bring in a host of other dependent RPMs. That's just fine, and Gentoo does something similar, but what happens when you decide that you don't want the application any longer? I often install something to try it out and then decide that it doesn't do what I want. You can remove the application itself, but what about all those libxxxxx.rpm packages which it depended on. I can remove them if I can remember which ones they were, but otherwise they just hang around getting in the way.
"Disks are cheap you Bozo!" Yes, I know, but I keep my systems up to date and unwanted libraries mean unwanted security updates. With Gentoo, this problem is entirely solved with the 'emerge --depclean' command. When I emerge an application its name is added to the world file (/var/lib/portage/world) but not the names of it's dependencies. So, emerge --depclean simply looks for packages which which are not in world (or the base system list) and aren't depended on by any installed packages.
Related points: The wonder of USE flags means that many libraries never get installed at all because I can tell the application that I am not interested in that functionality. My general point also applies to cases where one upgrades an application and the new version no longer depends on a particular library.
If there are RPM (or apt) based distributions which have a similar scheme then I would love to know about it. Mandrake has (or at least used to have) a script called something like 'urpmi_rpm-find-leaves' which gave a list of RPMs which were not depended upon. By filtering the output through 'grep lib' one could get part of the way there, but it would still leave quite a few RPMs to locate by hand.
There are very few UK companies who will see you a Linux or OS free laptop. One of the others told me that they get theirs from Lenovo, but can only occasionally get one without an OS. In other cases they remove Windows and try to claim back the cost from their wholesaler. Occasionally, this works. So, in most cases money is still going to Microsoft. I don't like this idea, so I was pleased when Transtec told me that their OS free machines have never had any OS installed and so none of my money would go to Redmond. This might be a point worth checking if you are looking for a linux laptop.
OK, two important points about coax.
Hmm, interesting. Exciting though it may be for me to try out one of these, there are some serious obstacles, including:
I think that the best plan would be to go with something like the Estonian scheme and I have toyed with re-wiring some of the light fittings when I move to a new house in a year or so's time.
Amazing! I have never seen anything like this in the UK and I presume that they are not available. I don't believe that you can get them in Estonia either, but I'll ask my Mother-in-law.
Can someone tell me how they connect, since I couldn't find a picture of the base of any? I presume that there is an additional ring which provides the third connection. What happens if you screw one into an ordinary socket or visa versa
Many of the other replies to this post are at best mis-informed. So, here are the facts.
1) Reducing the power to incandescent bulbs via a dimmer does not save money. It is true that you use less power, but as you reduce the voltage the efficiency of the bulb goes down. Wikipedia has an article on this with some handy power laws. If we apply these to the example case (75% of the voltage, assume 100W bulb) we get only 38% of the light (i.e. about what we would get from a 40W bulb), but we consume 63W of electricity. Of course, the bulb will now last for about 100 times as long. Perhaps the original post didn't mean 75% of the voltage, but instead 75% of the light. Doing the maths for this case we get: 88W and 3.8 times lifetime.
Note that the above lifetime extensions are purely a result of the lower voltage and nothing to do with flipping on and off. You will get the advantage even if you leave the bulb on all the time. But, since bulbs cost more to run than they do to buy and replace (except in special cases such as traffic lights) then reducing the voltage is a false economy. You would be better off simply buying some lower wattage bulbs or better still getting some compact flourescent lamps instead.
When I first knew my wife she lived in Estonia and her bedroom was fitted with a very clever scheme for dimming the lights (something which I often wanted to do!). Her light fitting had three bulbs connected to a double wall switch. One switch operated a single bulb and the other controlled the other two. One could therefore have 1, 2 or 3 bulbs and they would always be running at optimum efficiency. I suspect that limited Soviet domestic technology was the motivation behind this scheme rather than power efficiency, but it worked very well. Sadly, although several of the rooms in the flat are still wired for this scheme, you can no longer buy the special multi-wired fittings. I have offered to modify my mother-in-laws new lights, but she is reluctant.
Finally, can I point out that dimmer switches do not rely on resistance. If they did then they would get very hot! Most use electronic components called triacs, which are essentialy switches which can be controlled in such a way as to permit current to flow for only part of each half cycle of the AC voltage. This reduces the average voltage and for incandescent bulbs this is what matters.
As it says in the BBC article, only some devices will be legal.
Now certain FM transmitters, which can be tuned to spare frequencies, will be legal from 8 December.
However, many devices currently on the market will remain illegal as they do not meet the legally required technical specifications and could interfere with radio broadcasts.
All approved transmitters will carry a CE mark indicating approval for sale in the European Union.
So, as I see it, legal transmitters will not only have to meet strict power limits, but also be tunable only to certain spare frequencies in the FM band. I spent some time searching the Ofcom web site to try and find exact details of the regulations (e.g. which frequencies exactly), but without success. If anyone else can find them then I for one would be interested.
After a great deal of thought, I have come up with a possible application for the current 2D, limited bandwidth version.
Suppose that you have a radar on, for example, a ship. It is often the case that since only one radar can be on top of the tallest mast, the others have some of their field of view partly obscured by other masts. If nearby masts were covered in this stuff then the radar should be able to see right through them and thus maintain a 360 deg field of view. In this case the 2D nature is fine for wrapping around the mast, and the limited bandwidth doesn't matter since we presumably know the frequency on which our radar operates.
Well, yes and no. Clearly, the current system is entirely detectable by such methods because it doesn't do very much, but I think you are asking "What if we could make one which worked over a broad range of frequencies and angles". In that case it probably would work against passive (i.e. bistatic) radars and indeed that is apparently the whole point. If we only want to defeat conventional monostatic radars then covering the whole thing in some sort of absorbing material (i.e. RAM) would be just as effective, cheaper and more practical (for example, you wouldn't need to invent a spherical airoplane with no inlets of exhausts).
I have to say that although this is an interesting trick, it doesn't seem to be quite as useful as people might at first imagine. For a kick off, it seems to be round and one would therefore suppose that a 3D one would need to be a sphere. Is that useful? I suppose that you could put your tank inside a huge sphere and roll it around, but guiding it and firing the gun sounds a bit tricky. Somehow I don't think that making a none-spherical one which works over a broad range of incident angles is going to be at all easy. I suppose that you might be able to make a spherical bomb.
Next, as the article mentions, what about bandwidth. For it to be useful against radars you are going to need at least a 10:1 bandwidth which again, doesn't sound easy. There is slightly better news for visible light, where a bit less than 2:1 will work.
Finally, I can't believe that it doesn't reflect any radar energy back. It might only reflect 10% or maybe even only 1%, but when you consider the dreaded R^4 factor in the radar equation that still doesn't buy you a lot of stealth.
Why precisely is it illegal to finance a lawsuit? Although I am not in favour of Microsoft's alledged actions in financing SCO, I often see circumstances where someone seems to have suffered an injustice, but can't claim redress because they can't afford the legal costs. I think to myself "If I were rich, perhaps I would offer to help them out". Do I understand that such philanthropy would be illegal? Is it all part of a scheme to maintain the legal system as a means for the rich to oppress the poor?