AE	acoustic emission
b-AE	burst-type AE
c-AE	continuous-type AE
CNN	convolution neural network
LSTM	long short-term memory
$x\left(t\right)$	AE signal
$\omega$	frequency factor
$X_{half}\left(\omega \right)$	Fourier transform of $x\left(t\right)$ (the positive-frequency part)
$e$	the base of natural logarithms
$\delta$	the delta function
$u\left(t\right)$	the unit step signal
$\alpha$	the damping factor
$A$	the amplitude of b-AE
$h_t$	the output of LSTM cells
$c_t$	the internal state of LSTM cells
$x_t$	the input of LSTM cells
$f_t$	the output of the Sigmoid gate of forgetting
$i_t$	the output of the Sigmoid gate of input
$o_t$	the output of the Sigmoid gate of output
${\tilde{c}}_t$	the output of the tanh gate
$b_f$	the bias parameter of the Sigmoid gate of forgetting
$b_i$	the bias parameter of the Sigmoid gate of input
$b_c$	the bias parameter of the tanh gate of the LSTM cell
$b_o$	the bias parameter of the Sigmoid gate of output
$W_f$	the forgetting weight matrix
$W_i$	the input weight matrix
$W_o$	the output weight matrix
$W_c$	the state weight matrix of the LSTM cell
$\sigma$	the Sigmoid function
${\sigma }_f$	the Sigmoid gate of forgetting
${\sigma }_i$	the Sigmoid gate of input
${\sigma }_o$	the Sigmoid gate of output