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General Science / Re: How does radiation exposure affect free carrier electrons in a material?

« on: 13/06/2013 12:39:45 »

Just to add to evan_au's reply... In general, any radiation "particle" (not just a photon) will generate electron-hole pairs as it gives up its energy within the crystal lattice of Silicon. This is a problem for memory devices, especially for aerospace use, where cosmic rays can generate enough electron-hole pairs in the depletion region (between a p-doped and n-doped regions) to neutralise any charge that may be stored on a capacitor for which one of the regions is a part. A good deal of error correction circuits need to be deployed. Generally this does not damage the device but just produces a "soft" error. This was a particular problem with Dynamic Memories (DRAMs) in the 1980s which was traced to material within the device package which was slightly radioactive and emitted alpha particles. These caused soft errors, particularly as the radioactive material was part of the filler in the package seal which meant it penetrated the device's memory cells at just the right angle to maximise the number of electron hole pairs within the depletion region within the memory cells. The alpha particle energy was such that in typically penetrated about 20 microns. It was solved by applying a polyimide coating to the die although now this type of package is not used so the polyimide is unnecessary.

In high levels of radiation semiconductor devices can be permantly damaged and devices for aerospace use have to be designed with this in mind. Typically the transistor characteristics change and eventually will prevent a device from working. Devices have to be designed to tolerate this change which can be done by use of specific technology which is less susceptible to damage and also designing with wide tolerances. Earth-bound aerospace (unless military) is usually OK with fairly conventional processes but Space use (or military where it has to work despite nuclear attack) has to tolerate a very large radiation - often 1 Mrad.

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Just Chat! / Re: Describe to me your thoughts on a Direct Democracy within a Socialistic emphasis

« on: 11/06/2013 17:36:45 »

A necessary requirement for a proper democracy to work is that you need a well informed population. I feel that, even more than today, there would be too much power in those with the ability to influence and have control of the media. On neutral decisions it can be a very good method; I think this is shown by how the odds vary on spot betting - it is surprising how the net results of lots of bets come close to predicting a result. But where there is some vested interest by those who can weight the arguments in their favour then it will not be fair or balanced.

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Physics, Astronomy & Cosmology / Re: How can fibre optics send data further with lower losses?

« on: 11/06/2013 17:21:18 »

There are quite a few modulation schemes that can be used. The more complex ones enable more bits per second to be carried withing a particular bandwidth. In fibre, keeping the bandwidth narrow is useful as it reduces the effects of dispersion. In RF it is useful mainly useful so that more of the available spectrum is utilised. In both cases, the more bits/second you send the shorter is the range however. However, if the aim is to just get as much data tranferred as possible (and the distance between repeaters is not a factor) then elaborate modulation schemes are worthwhile. It makes a lot of sense to send two signals differentially because any "common mode" distortions can be cancelled effectively improving the Signal to Noise+Distortion ratio. It has been a long time since I worked on fibre transmission so it is interesting to see the latest developments.

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Technology / Re: Why switch to digital radio?

« on: 15/05/2013 17:23:34 »

I agree with Imatfaal; digital TV provides a much better service - more channels (of course that does not always translate to better programs), better quality, TVs which can accept broadcast signal inputs or WiFi so you can see high quality downloaded or streamed video. The broadcast cost in the power used is not a significant cost compared with everything else. The advantage is in better usage of available bandwidth, of which there is much demand now.

Analogue systems are all inherently a compromise to get acceptable quality. PAL is not quite as good as NTSC in an ideal situation but NTSC is rarely ideal and used to be nicknamed "Never The Same Colour". Digital processing in a TV is also much more easily cost reduced with technological advances than are analogue systems.

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Technology / Re: How can technology help farmers keep track of their livestock?

« on: 15/05/2013 09:37:51 »

Yes, absolutely. There are other systems so that animals can be given small electric shocks (based on GPS data) so that they can be kept on a patch of grazing without the need to build and move expensive fences. This may seem cruel but the animals can learn to avoid this by providing some sort of recognisable boundary. It is no worse than an electric fence and very simple to construct and move about.

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Technology / Re: Can the flow of ionised air be controlled by an electric field?

« on: 15/05/2013 09:29:02 »

Yes. Ionised particles will move in an electric field.

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Technology / Re: Google glass

« on: 15/05/2013 09:25:30 »

Probably. However the power levels used when transmitting would be much lower than with a mobile phone. The operating frequencies are also higher (typically 2.4GHz and around 5GHz I think) which maybe less penetrative. 2.4GHz does not pass through water very well (near absorption resonance) so this may also help though I expect it may be argued that this causes more heating locally.

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General Science / Re: Are the words "natural" and "supernatural" actually meaningless?

« on: 15/05/2013 09:16:53 »

I think you are choosing a narrow meaning of the word natural. There are many shades of meaning that are useful to use within the English language...

http://www.merriam-webster.com/dictionary/natural

gives examples.

With the particular meaning you are attributing you may be right. If everything is natural then the word unnatural cannot be applied to anything. Another example of this is the use of the word "selfish". In a very strict meaning everyone is selfish (by definition) which makes the use of the word redundant. So Mother Teresa was selfish because she was helping poor people merely to please her own desires to feel better about her actions and to satisfy herself that she was acting in a way to put her in a way to please her God. It is not a generally useful interprertation of the word's meaning though.

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General Science / Re: Are irrational numbers separated by an infinite number of rationals?

« on: 14/05/2013 15:21:02 »

I think it can be understood by non-pure-maths-people (most of us) by the idea that there are different sized infinities! The infinity of irrationals is bigger that the infinity of rationals. I'm sure a mathematician can express this more rigorously.

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General Science / Re: Numbers Rational and Irrational

« on: 08/05/2013 10:25:47 »

Furthermore, there are more irrational numbers than rational numbers.

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Technology / Re: Did you know that grid frequency can be used to authenticate CCTV timestamps?

« on: 06/05/2013 10:49:45 »

I did not know they did this. What a great idea. I can see it is quite possible and very reasonable but I'm not sure I would ever of thought of it!

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Physics, Astronomy & Cosmology / Re: How long do you have to accellerate at G to reach the speed of light?

« on: 01/05/2013 15:03:22 »

Yes. Forward Shields to maximum please Mr Scott :-)

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Physics, Astronomy & Cosmology / Re: How can we create Earth-like gravity on the Moon?

« on: 01/05/2013 13:06:27 »

There is no known way to emulate gravity perfectly. The only way to do this approximately is to create an acceleration of your reference frame. This is shown in the classic rotating space stations as in Arthur C. Clarkes 2001 so that your "floor" is the inside of this rotating ring. It is not perfect because your head and feet experience a different gravitational force which only lessens the bigger the space station but is always there to some extent. I expect this could be done on the moon with a ring parallel to the moons surface (like a big roundabout) so that the net force from the rotation (in your rotating frame of reference) and gravity would sum. The resulting gravity would be outwards from the ring but also somewhat downwards from the moon's gravity. It may be somewhat disturbing to live in such a body though and, of course, restricts you to only moving on the inner surface of this rotating ring, but it may serve as a living/sleeping area.

Magnetic devices would only act on the parts of your body equipped with magnetic material (like magnetic boots). This does not give an emulation of gravity and I think can take some getting used to. Your magnetic boots would only work on a floor made of some material like iron of course. On the moon this would be harder to get used to that just managing the lower gravity I think.

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Physics, Astronomy & Cosmology / Re: How long do you have to accellerate at G to reach the speed of light?

« on: 01/05/2013 12:48:44 »

It will never reach the speed of light. It would take an infinite amount of energy. This results from Einstein's theory of Special Relativity. However, from the perspective of anyone travelling on this craft, they will experience a contraction in the distances in their direction of travel. So although they can never get to 186,000 miles per second they can (theoretically), nonetheless, achieve a speed such that they can travel a distance that they may initially have measured (before accelerating) as 186,000 miles in less that 1 second as measured on their clocks. If I remember correctly this turns out to be the same time (to get to this speed) as would be calculated by Newtonian mechanics - I would need to check this with some maths to be sure. There are some unfortunate consequences of travelling this fast resulting from time dilation so that should return at some point you would find the earth you left having aged considerably compared to yourself.

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Physics, Astronomy & Cosmology / Re: How are current and internal resistance related?

« on: 01/05/2013 09:05:01 »

Hi Lily. I am not sure of what the circuit is that you are looking at or where you are measuring the Voltages V and E. However, I will make a guess that you are somehow applying a voltage from some power supply or battery across a resistive load and measuring the current. If you do this then Ohm's Law will apply and V=IR where 'V' is the voltage across the terminals of the load, 'I' will be the measured current and 'R' is the resistance of the load. When you speak of "internal resistance" I am guessing you mean the resistance of the power supply which may include that of the ammeter measuring the current. For low currents this "internal resistance" of the power supply is usually negligible as it is much smaller than the resistance of the load. If the the current is high, however, the voltage applied to the load may not be exactly what you think because of the supply's internal resistance, any ammeter in series and the resistance of the connecting wires.

I don't know if this is exactly what you mean, however. You can often neglect these effects but if making accurate measurements in certain situations you may need to take precautions to eliminate the effects of internal resistance of supplies and ammeters (the resistance is ideally zero but is finite in practice) or of voltmeters (the resistance is ideally infinite but, of course, isn't in practice).

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Technology / Re: My Phone slowly slides off my tablet

« on: 28/04/2013 15:05:29 »

Apple are very devious. They have clearly incorporated a device that detects and disposes of Samsung's products :-)

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General Science / Re: A weapon detector; how do companies get away with selling this?

« on: 28/04/2013 15:01:47 »

Yes, you may be right. I am just thinking of people who sell lucky charms or magic crystals or, when it comes to it, a lot of products that are advertised on the media. How can people claim that their washing powder washes whiter that other powders or their brand of toothpaste, shampoo, baldness cure etc. are in someway superior to others (or in the case of baldness cure, work at all). Maybe it is down to exactly how they word their ads.

In this case I hope the bloke gets a significant time in prison and has his ill-gotten wealth confiscated (though I doubt this will happen).

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Technology / Re: Why is there not no institution on earth preventing loss of scientific knowledge

« on: 25/04/2013 09:32:43 »

The point I was making there was that, as you say, we have the ability to record every possible idea that people can have by many different means. The problem is how does anyone notice the really good idea or invention from the large amount of rubbish. For example, in electronics I would say that 99% of patent claims are invalid beacuse they are either prior art or someone reasonably versed in the art would devised the (obvious) solution being patented. Unfortunately the field is so vast now that patent lawyers are simply not up to the task of deciding such issues and there is huge pressure from large organisations to patent everything they can to have a sufficient weight of patents (valueless or not) to counter-sue any company making a claim on them which acts as a deterrent; the companies know that the big winners in ant patent war is usually just the lawyers.

Many "learned" papers are similarly worthless though at least more genuine in their attempts to be original. Success at a university is measured by the the number of papers it gets accepted by journals. There is strong incentives to publish and get a paper past peer reviews (and at least this has to happen for the better publications). The number of these that turn out to say something really new and important is unfortunately not large and it is also hard to find the good ones from the average to poor except to wait (often some years) to find a particular paper referenced a lot by other papers - a good sign.

You are right to imply that it is sometimes difficult to tell a good idea from a bad one but I have to say that if you have a situation where only 1 in 1000 is good (say) then I, for one, would like to see a good deal of pre-filtering. Life is too short. It would be wrong if there were no record of these adjudged "bad" ideas, but there does need to be a practical method of sifting. Sites that try to promote "alternative" science are packed with loonies building anti-gravity machines (for example)! I would love to believe that someone will produce one that works but, despite the high interest in such sites, none have emerged.

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General Science / Re: A weapon detector; how do companies get away with selling this?

« on: 25/04/2013 09:04:40 »

Clifford, I think you missed my point. I know it would be easy to prove the efficacy of such a device (or lack of it) scientifically but I just wondered where the law stands on whether he is committing a crime by selling something like this unless it can be proved, beyond reasonable doubt, that he knew it did not work and was committing an act of deception. There are plenty of "snake oil" salesmen (and companies) out there, where the consequences of their deception is, admittedly, not so great, but where nothing is done to prevent them promoting their wares and accepting the idea of Caveat Emptor.

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Technology / Re: Why is there not no institution on earth preventing loss of scientific knowledge

« on: 24/04/2013 15:18:22 »

It's not my field but to me your inventions are impressive and seem quite original. I am sorry to hear how you were either ignored or exploited by a corrupt and inefficient regime. To go back to your question, I think it is true that many ideas and inventions have been lost in the past (the destruction of the library at Alexandria must be a key event here) but I think the world is getting better at (at least) preserving ideas. I think the problem now is often how to recognise the good ideas from the vast numbers of bad ones (or simply ones that are not as good). Often the only way to promote an idea is to get sufficient funding to promote and manufacture some item that exploits the concepts. There are arguably quite a few cases where the less good concept wins just because it has had better promotion. If it is more of a theoretical concept there may be, at the time, no means to exploit it for any practical use. I think this is true particularly in the "pure" sciences and mathematics. New ideas have to be recorded and (hopefully) recognised in the future.

I work in the semiconductor industry where I think, generally, new ideas are exploited quickly although this is also not without problems. I had an internet conversation once with a guy who claimed to be an electronics engineer but who believed the advances in semiconductors had to have come from aliens (i.e. from beings on other planets). Yes, he really believed this! But having been in the business for over 40 years I have experienced the advances of technology step by step and can say there is no magic, just a lot of good engineering, determination and a lot of money.