(a), (b) and (c) are the droplet size distributions produced from stable cone-jet mode under nozzle voltages of 5.0, 5.5 and 5.6 kV, respectively. The droplet sizes are fitted with Gaussian and Poisson distributions, and the goodness of fit is evaluated using the chi-squared statistic test at a 5% significance level. The mean and standard deviation for the fitted distribution is indicated above. For (a), the p values for the Gaussian and Poisson distribution fits are 0.154 and 0.027, respectively. For (b), the p values for the Gaussian and Poisson distribution fits are 0.628 and 0.016, respectively. For (c), the p values for the Gaussian and Poisson distribution fits are 0.962 and 0.037, respectively. In all cases, the core/shell flow rates (1.0/3.5 ml/h) and the nozzle-to-collector distance (15 cm) are maintained.