studiot

In post 56 I said hello and pointed out that the Lorenz force fails in the Hall effect in semiconductors. You can find the theory in any good intermediate solid state physics book, such as Ashcroft and Mermin. You thanked me in the following post. However I have not seen further reference. Did I waste my effort?

Look here under the section marked Euclidean Plane. There is an example calculation of the type you are trying to perform. http://en.wikipedia.org/wiki/Covariance_and_contravariance_of_vectors

[math]{V^\mu } = {V_\upsilon }[/math] Well that wasn't what you said in the first post, which was why I asked about your notation. Are you talking about contravarient and covarient or column vectors and row vectors? To premultiply by the square matrix you need a column vector.

Why do you want to throw anything at your teacher?

I am unsure of your convention. What are you signifying by upper and lower are they transposed?

Like all old sayings it has its domain of applicability and is invalid outside that domain. which is why there is often a counter saying. Such as 'if a job is worth doing it is worth doing properly'. I expect there are others. I remember someone when I was at university has this beat up old philips tape recorder and a huge selection of music of poor sound quality recorded of the radio or anywhere he could get it. To the Avant Garde students, who were trying to get HiFi the sound was unacceptably poor. But to this person ignorance was indeed bliss - he genuinely didn't know any better and was much happier than those who were never satisfied.

Is there a crop that doesn't? Perhaps you can enlighten us by naming one that ripens instantaneously.

In their proper season golden delicious are not too bad. Braeburn on the other hand. Absolutely 100% certain. I can pick decent apples, that have never been near a cold stroage facility off a tree! If anything most crops in supermarkets are harvested far too early!

Thank you, I was not referring to our earlier discussion in this thread. I can only use the knowledge and reasoning powers I possess to evaluate propositions that are put. When someone else with greater knowledge or insight comes along I am grateful and accept their statement, as I did earlier with yours. My style may be somewhat flambouyant, but it is not ludicrous. At least on your side of the pond you don't have a bunch of beaurocrats on grater than 100K per year (of your money) trying to tell you that bananas must be straight to be sold. Yes it truly was an EU regulation for a while. or that apples must be greater than a certain diameter to be graded as first class. I live in an apple growing area and am sick of the mushy, tasteless excuses for apples that are offered as a result of modern 'improvements' in varieties. go well

Thank you imatfaal. Now all we need is for respondents to address the points made by others rather than going off on a frolic of their own in discussion Let me try this again in the face of substantial nasturtiums being cast against my person rather than proper discussion of my logic. Earlier in this thread it was stated (not by me) that the progenitor of modern potato crops were poisonous. It was also stated (again not by me) that this poisonous characteristic was removed or reduced to tolerable levels by selective breeding by native americans up to a thousand years ago. So, quite naturally, I questioned whether they also wanted their improved potato to be unable to be planted to yield a crop on a year by year or generation by generation basis. I think those early practitioners of GM did not want to prevent a % of each year's harvest being saved as 'seed' to plant for the next year - in fac that is what the wanted and they wanted the subsequent harvest to grow at least as well as the previous. So I am making the point that the idea of actively preventing this by further and more sophisticated exploitation of GM techniques, not originally employed. I don't see how you can breed infertility into a strain by selection. I am further questioning whether the motives for these later developments are as purely virtuous as the original ones. As such I do not appreciate being mocked for my views.

Ludicrous huh? Then why have others here taken great pains to describe the creation of non poisonous potatato tubers by selective breeding? Are you trying to tell me that these potatoes we deliberately bred for sterility?

Rather than reviving and continuing a discussion already done to death how about discussing duality in the light of the following http://www.bbc.co.uk/news/science-environment-18833386 http://en.wikipedia.org/wiki/Scattering

Once again too-open minded posted where I was heading before I arrived. We are discussing the reasons behind genetic manipulation. First the pros stated that it was to provide enhanced yield, quality and disease/pest resistance as the only reasons and the only manipulations. When pushed they admited that another manipulation has been sterility to prevent transfer to existing species. Now I have consistently discussed potatoes and several hers have stated that potatoes are not grown from seed. So why does sterility matter if some manipulated genes spread beyond their field? The result if not sterile would not result in a new generation of potatoes anyway. My underlying question is since getting all the reasons out in the open is like drawing sharks teeth, what else are they hiding? A further observation is that the deliberate sterility demanded nowadays is the exact opposite of the reuqirement of traditional selective breeding where the product is of little use if it cannot breed true. What I am seeking is an open and honest debate leading to the best deployment of the technology.

Statement 1 How is this a mechanism? I asked for a reason why you made this statement or an explanation of it. Statement 2 and I stated that I understood this one - I understand it to be a reason for not wanting the cross tranfer, not a mechanicsm for it. So I am still awaiting an explanation of the first statement.

Yes, Arete, I am not dumb. You stated two reasons joined by the conjuction and. I agreed with the second reason and asked for an explanation of the first. Repeating the explanation of the second does not constitute an explanation of the first.

Don't ever be afraid to ask questions. If you want to learn 'science'on your own look out some booksor internet stuff on 'engineering science'. This is basic stuff designed for auto mechnaics, plumbers, electricians and other practical trades to understand enough science and maths for their needs. It is a very good introduction over a wide range. By the way what dis you think of my post in your voltage thread?

As an electrician you need to be aware of 'electrode boilers', which are often three phase. Google is your friend. There's lots there.

I can see the reason for the second clause (I have not italicised) although I cannot see why it would be any worse than old farmer M'ginty's scabby potaotoes spreading. However I cannot see an overt reason for the first italicised clause so please explain the good scientific reason for this.

And starting fires.

That's exactly what I'm talking about. You can't buy a decent tomato/apple/runnerbean/potato/........ in the supermarket because they decent varieties are not available. They have been bred for one purpose and one purpose only. Profit. And we have seen with bankers in recent weeks and years who profits and who looses.

Well here are photos of my LED unit. The delta suppressor does not work - it's really for mains borne interference. The lamp totally wipes out AM and FM radio within about a 7metre radius. Not good. I also had recent experience of some 24 volt recessed ceiling units in the barge. They were supposedly replacement fittings for low energy units but the light output is disappointing. I think the source is too far up inside the can, remembering how intense it is because of its small size. So the light can't get out so easily.

Going back to potatoes, what is the reason for the sterility of Maris Piper? It can have nothing to do with modern gene manipulation.

Both things are not the same they are just measured in the same units - volts. It works like this. I have an 18inch ruler and a 6 inch ruler. That is the length of ruler A is 18 inches and the length of ruler B is 6 inches. But the length difference between the two rulers is 12 inches. Both length and length difference are measured in inches. So it is with EMF and Potential Difference which are both measured in volts. If it is any further help, neither are any form of energy. However an EMF is a way of introducing electrical energy into a circuit whereas a PD is a way of dissipating electrical energy out of a circuit as heat.

I was just about to strip down my Robus lamps to get some photos and try a delta filter. http://www.scienceforums.net/topic/67711-led-and-other-light-sources/page__pid__690581#entry690581

The last thread on light sources was in politics So here's a start for a technical thread.