@staticmethod
def T1_ps(p, s):
    """function T1_ps = T1_ps(p, s)

        5 Equations for Region 1, Section. 5.1 Basic Equation, 5.2.2 The Backward Equation T (p, s)

        Eqution 13, Table 8, Page 11
        """
    I1 = [0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 4]
    J1 = [0, 1, 2, 3, 11, 31, 0, 1, 2, 3, 12, 31, 0, 1, 2, 9, 31, 10, 32, 32]
    n1 = [174.78268058307, 34.806930892873, 6.5292584978455, 
        0.33039981775489, -1.9281382923196e-07, -2.4909197244573e-23, -
        0.26107636489332, 0.22592965981586, -0.064256463395226, 
        0.0078876289270526, 3.5672110607366e-10, 1.7332496994895e-24, 
        0.00056608900654837, -0.00032635483139717, 4.4778286690632e-05, -
        5.1322156908507e-10, -4.2522657042207e-26, 2.6400441360689e-13, 
        7.8124600459723e-29, -3.0732199903668e-31]
    Pi = p / 1
    Sigma = s / 1
    T = 0
    for i in range(0, 20):
        T = T + n1[i] * Pi ** I1[i] * (Sigma + 2) ** J1[i]
    return T
