複選題

20. Consider the autonomous system
(A) the system is linear
(B) the system has two equilibria
(C) (x1, x2) = (2, 2), (-2, -2) are equilibria of the system
(D) (x₁, x₂) = (-2, -2) is the only stable equilibrium of the system
(E) (x₁, x₂) = (2, -2) is a saddle equilibrium of the system.

複選題16. Let A = be a nonzero matrix of size n×n with its real part and imaginary part being denoted by B and C, respectively. Moreover, let Ω be a symmetric matrix with A and C as its four blocks. Which of the following statements are true? (A) Matrix C has at least one real eigenvalues. (B) Let λ and μ be any two eigenvalues of B and C, respectively. Then λ + μ ≠ 0. (C) Any eigenvalue of A is also an eigenvalue of Ω. (D) Any eigenvalue of Ω is also an eigenvalue of A. (E) Let be an eigenvalue-eigenvector-pair of Ω. Then (λ, x+iy) is an eigenvalue- eigenvector-pair of A.

複選題17. Let L(.) denote the Laplace transform. Which of the followings are true? (A) L(a1 f1 + a2 ⋅ f2) = a1 ⋅ L(f1) + a2 ⋅ L(f2), for all a1, a2 ∈ and for all functions f1, f2 (B) if L(f) = F(s), then = sF(s) (C) if L(f) = F(s), then L( ⋅ f) = F(s)/(s+a) (D) if L(f) = F(s), then L(t² ⋅ f) =  (E) if L(f) = F(s) and L(g) = G(s), then L(f * g) = (F * G)(s), where * denotes convolution operation

複選題18. Consider the differential equation + kx(t) = u(t). Suppose sin(2t) is a solution when u(t) = 4 cos(2t). Which of the followings are true? (A) m = 1 (B) b = 0 (C) k = 8 (D) 2tsin(t) is a solution when u(t) = 8cos(2t) (E) )sin(2t - 1) is a solution when u(t) = 4cos(2t - 1)

複選題19. Consider the homogeneous system , where A = (A) the system is linear (B) the system is time invariant (C) the system has more than one equilibrium (D) when a ＜ -4, any initial condition results in a solution which diverges to infinity (E) when -4 ＜ a ＜ -1, any initial condition results in a solution which converges to the origin

1. What processing is often utilized to enhance the mechanical properties of metal during fabrication procedures? (A) grain growth, (B) thickness thinning, (C) recrystallization, (D) strain hardening, and (E) high-temperature annealing

2. When two atoms are separated in an equilibrium status in a solid, which description for the potential energy of the solid is correct? (A) at lowest, (B) at highest, (C) at the middle, (D) uncertain, and (E) none of the above.

3. Which is the slip system for the Face-Centered Cubic (FCC) structure? (A) {100}(110),(B) {100}(111), (C) {110}(110), (D) {110}(111), and (E) {111}(110)

4. Which one is correct in the following description about diffusion: (A) interstitial diffusion is usually not as fast as vacancy diffusion； (B) interstitial atoms are smaller, so their mobility is less； (C) copper-nickel interdiffusion belongs to interstitial diffusion, (D) carbon-iron interdiffusion belongs to interstitial diffusion, and (E) interstitial diffusion cannot occur at concentration equilibrium.

5. If it is hard to move the dislocation in metal, the metal may be (A) heavy, (B) fragile,(C) deformable, (D) at high-temperature annealing, and (E) immersion in oil.

6. Which one among the descriptions about deformation is correct: (A) elastic deformation is time-dependent and permanent, (B) elastic deformation is time- dependent and temporary, (C) inelastic deformation is time-independent and permanent, (D) inelastic deformation is time-dependent and temporary, and (E) none of the above.