By the end of the define phase you should have a clear under…
By the end of the define phase you should have a clear understanding of the problems your user is facing.
By the end of the define phase you should have a clear under…
Questions
By the end оf the define phаse yоu shоuld hаve а clear understanding of the problems your user is facing.
Prоblem 1 (35 Pоints): Sаmpling Cоnsider the continuous time signаl (s(t) = mbox{sinc} (t)) thаt is sampled with a period of (T) to yield (x(n) = s(n T)) and time is measured in units of seconds (sec). Note: All answers should have valid units when appropriate. Problem 1a) Sketch a plot of the function (s(t)). Problem 1b) Calculate the CTFT (S(f)) and sketch a plot of this function. Problem 1c) What is the sampling frequency? Problem 1d) What is the Nyquist sampling frequency for this signal? What is the Nyquist sampling period for this signal? Problem 1e) Sketch (x(n)) and (| X(e^{jomega }|) when (T = 0.1 sec). Problem 1f) Sketch (x(n)) and (| X(e^{jomega }|) when (T = 0.5 sec). Problem 1g) Sketch (x(n)) and (| X(e^{jomega }|) when (T = 1.0 sec). Problem 2. (40 points) MMSE Prediction and LS Estimation Consider an algorithm for deblurring an image (Y) to recover an image (X) where (Y) is assumed to be random. For each pixel in (sin S),we form a vector (z_s) that is the pixels in a ((2p+1)times (2p+1)) window about the pixel (s). More specifically, $$z_s = [ Y_{s+r_1}, ldots , Y_{s+ r_P} ] ,$$ where (P = (2p+1)^2) and (r_1, ldots , r_P) are the offsets associated with each pixel in the window. Furthermore, define $$X = left[begin{array}{c}X_{s_1} \vdots \X_{s_N}end{array}right]Z = left[begin{array}{c}z_{s_1} \vdots \z_{s_N}end{array}right]$$ where (s_1, ldots , s_N) index the pixels in the image. Then are deblurred image is formed by (hat{X} = Z theta ). Problem 2a) Is (hat{X}) random or deterministic? Why? Problem 2b) Is (theta) normally assumed to be random or deterministic? Problem 2c) Calculate a closed form expression (that I like) for the Mean Squared Error, $$MSE= frac{1}{N} E [ | X - hat{X} |^2 ] .$$ Problem 2d) Calculate an expression for the value (theta^*) that minimizes the MSE. Problem 2e) Is (theta^*) from the previous subproblem random or deterministic? Why? Problem 2f) Calculate a closed form expression (that I like) for the Average Squared Error, $$ASE= frac{1}{N} sum_{n = 1}^N ( X_{s_n} - hat{X}_{s_n} )^2 .$$ Problem 2g) Calculate an expression for the value (hat{theta}) that minimizes the ASE. Problem 2h) Is (hat{theta}) from the previous subproblem random or deterministic? Why? Problem 3. (25 points) MRI Imaging Consider an MRI that only images in one dimension, (x). So for example, the object being imaged might be a thin rod oriented along the x-dimension that extends from (-infty) to (infty). (Note: This is not physically possible, but don't worry about that. Just do the math that way for simplicity.) In this example, assume that the magnetic field strength at each location is given by $$M(x,t) = M_o + x G(t) $$ where (M_o) is the static magnetic field strength and (G(t)x) is the linear gradient field in the (x) dimension. Furthermore, let: (gamma) denote the gyromagnetic constant for hydrogen; (a(x)) denote the quantity of hydrogen per unit distance along the length of the rod; (omega_o = gamma M_o) be the center frequency of the scanner in units of rad/sec. (k(t) = gamma int_{0}^t G( tau ) d tau) is the position in (k)-space at time (t). (A(f) = mbox{CTFT} { a(t) }) is the CTFT of (a(t)). Problem 3a) Calculate a simplified expression for (omega (x, t)), the precession frequency of a hydrogen atom at location (x) and time (t). Problem 3b) Calculate (phi (x,t)), the phase of precession of a hydrogen atom at location (x) and time (t) assuming that (phi (x, 0) = 0). Problem 3c) Calculate (r(x, t)), the signal radiated from hydrogen atoms in the interval ([x, x + dx]) at time (t). Problem 3d) Calculate (r( t)), the total signal radiated from hydrogen atoms along the entire object. Problem 3e) Describe in words and equations how to reconstruct the signal (a(t)) from the signal (r(t)). Problem 4. (45 points) Linear Systems Consider the following two discrete time systems (T_1) and (T_2) where begin{align}y = T_1[x] mbox{ is defined by }: y_n &= sum_{k=-p}^p a_k x_{n-k} \y = T_2[x] mbox{ is defined by }: y_n &= sum_{k=-p}^p b_k x_{n-k} end{align} Then define the new systems (T_3) and (T_4) by $$T_3 = T_1 + T_2 ,$$and$$T_4 = T_1 circ T_2 ,$$ where (circ) denotes the composition of functions. Problem 4a) Prove that (T_1) is a linear system. Problem 4b) Prove that (T_1) is a time invariant system. Problem 4c) What is the DC gain of the system (T_1)? Problem 4d) What DC gain does one typically choose for a LTI system used to process an image? Why? Problem 4e) What is the impulse response of (T_1)? Problem 4f) Is (T_3) and LTI system? Problem 4g) What is the impulse response of (T_3)? (Denote the impulse response by (h_n).) Problem 4h) Is (T_4) and LTI system? Problem 4i) What is the impulse response of (T_4)? (Denote the impulse response by (h_n).) 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When 3.05 mоles оf CH4 аre mixed with 5.03 mоles of O2 the limiting reаctаnt is CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)