
import numpy as np

EPS_WATER = 78.54              # relative permittivity water
EPS_ZERO = 8.8541878128e-12            # permittivity vacuum
EPS_ZW = EPS_ZERO * EPS_WATER  # often together
E_CHARGE = 1.602e-19             # elementary charge
BOLTZ_T = 1.380649e-23 * 298  # Boltzmann constant x temperature
N_AVO = 6.022e23                 # Avogadro's number
ETA_VISC = 0.89e-3             # viscosity water
TWOPI = 2.0 * np.pi
RHO_W = 1000                   # density water [kg/m^3]
KAPPA2_ZERO = (np.square(E_CHARGE) * N_AVO) / (EPS_ZW * BOLTZ_T)  # in m^{-2}

