Recent content by xfshi2000

Thank you all for the reply. When we apply some window function on discrete sampled data, we can make the sampled tail data signal to be zero. Under the point of view of discrete FFT algorithm, This window-filtered sampled data will repeat themselves from minus infinity to positive infinity...

Hi all: I have one confused question. one continuous exponential decay function f=exp(-lamda*t) start from t=0 to infinity. I sample 1024 data points from the decay function. time variable (t) ranges from 0 to 1 second. the tail data of this exponential function is zero. I apply discret FFT on...

Thanks. I do not really understand your answer. After I search the internet and get some explanation, for diffusion tensor matrix, each component of matrix represents an apparent diffusion coefficient. These diffusion coefficient are not real diffusion coefficient. After we calculate the...

Thank you. Could you tell me what the meaning of each component of diffusion tensor matrix is ? For example, what do off-diagonal terms represent? What do diagonal terms represent? thanks

Hi all: Does anyone explain why we call diffusion as the second rank tensor variable? I understand Based on the tensor definition, we know tensor expresses the relationship between input vector and output vector. How about diffusion? what is its input vector? what is its output vector? thanks...

Hi all: I am confused about one question. When we detect signal from human brain using coil in Nuclear Magnetic Resonance, two source contribute noise to our signal. One is coil itself. The other is human brain. Why can we think the noise from human brain is white noise? Can we compare the...

Thank you Bob. I got it. xf

Hi all: In magnetic resonance imaging such as human brain head image, I select several regions of interest (ROI) with the size of 8 pixel. Thus the average value and standard deviation are computed for each ROI. Now I want to evaluate the average value over different ROIs. For example...

Hi all: One system consists of two neutrons. both spin magnetic moments are 1/2. At a instant time, neutron 1 locates position 1 and neutron 2 is in position. As we know, spin magnetic moment is kind of dipole moment. They can generate magnetic field (not electric field). The interaction can be...

Thanks for your advice and answer. I found one possible answer. The only reason to make Gd3+ ion change its total magnetic moment is due to collision of inter-molecule(diffusion). You can imagine that in water solution, the average distance between two water molecules are 3x10^-10 meter. Violent...

Hi all: I have one confused concept about T1 relaxation time in nuclear magnetic resonance field. As we know, fluctuation of local magnetic field inside the sample causes T1 decay in the following RF excitation. Imagine one simple mode, near a gadolinium ion (Gd3+), there is one water...

Thank you for your reply. I agree with you. As I know there are infinite paths for particle from one position to another position(path integral). Classical path is the one with maximum probability. We indeed have no chance to observe it at zero probability density at a node point. But we don't...

Hi I have a question about zero point of probability density of particle. In general we say if probability density is zero at a certain position, the particle never arrive there. But I also read some post in this forum. They said zero probability density means you have zero chance of seeing the...

HI all: I have one confused question. a infinitely long wire carrying constant direct current is placed in the space. One particle with charge q and velocity v is moving in the magnetic field which is created by current-carrying wire. We know in the lab frame. particle will accelerate in this...

thank you all.