# Thread: Imaginary part in the second Fick's low

1. Hello!

Could anyone answer this question: https://physics.stackexchange.com/qu...-the-ficks-low
I am sorry for such a form, but I don't know how to handle LaTeX here.

Thank you for any help.  2. Originally Posted by Boro Hello!

Could anyone answer this question: https://physics.stackexchange.com/qu...-the-ficks-low
I am sorry for such a form, but I don't know how to handle LaTeX here.

Thank you for any help. So, there will be two solutions, one dependent of and one dependent of   3. But what these solutions describes since there is only one diffusion process? Describes the magnetization vector in NMR and I want to get the signal attenuation due to diffusion. Under the standard asumption about gradient linearity, the imaginary part is equal to zero, but I wanted to calculate it for more genaral case. Can I just reject the imaginary part as devoided of the physical meaning?  4. Originally Posted by Boro But what these solutions describes since there is only one diffusion process? Describes the magnetization vector in NMR and I want to get the signal attenuation due to diffusion. Under the standard asumption about gradient linearity, the imaginary part is equal to zero, but I wanted to calculate it for more genaral case. Can I just reject the imaginary part as devoided of the physical meaning?
No, you can't, because there are TWO solutions, both valid, not one.  5. Ok. But what is the physical meaning of the existence two solutions?  6. Originally Posted by Boro Ok. But what is the physical meaning of the existence two solutions?
There are actually two equations, hence two solutions. One dependent on , the other dependent on , as already explained. Using complex functions simply reduces the two equations to solving one, it is a well known mathematical trick.  7. So, if the real part coresponds to x direction and the imaginary part to y direction on the plane on which the vector is spinning, there are separate solutions for x and y? It doesn't make sense for me. Thank you for answers anyway.  8. Originally Posted by Boro So, if the real part coresponds to x direction and the imaginary part to y direction
This is not true (and it is not what I have been trying to explain).

on the plane on which the vector is spinning, there are separate solutions for x and y? It doesn't make sense for me. Thank you for answers anyway.
No, this is not what I meant. You need to study differential equations, this is not working, you lack the fundamentals.  9. I know that it is not what you meant, but it is true, because it is my assumption. I wrote: "Psi describes the magnetization vector in NMR". The vector is rotation on the xy plane and is given by the complex number. Perhaps I did not make it clear enough in the previous posts.  Tags for this Thread Posting Permissions
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