Onset of Marangoni convection for evaporating sessile droplets

We have generated stability parameters using a linear stability analysis to predict the onset criteria for Marangoni convection in evaporating sessile droplets for two types of substrates, insulating and conducting. The stability problem was formulated with boundary conditions that allow for a temperature discontinuity at the liquid-vapour interface and the inclusion of an expression for the evaporation flux that considers this temperature discontinuity. We introduce no fitting coefficients; therefore, the stability parameters we generate contain only physical variables. The results indicate that spherical sessile droplets evaporating on insulating substrates are predicted to have a similar onset criteria with sessile droplets evaporating on conducting substrates. The onset prediction for sessile droplets evaporating on insulating substrates is found to be considerably different than the case of liquids evaporating from conical funnels constructed of insulating materials owing to the modification of the boundary condition from the geometrical shift and the corresponding retention of modes in the solution. A parametric analysis demonstrates how the input variables impact the stability of evaporating sessile droplets.     

Contact shape and the strength of the electron-phonon interaction determined by point contact spectroscopy

The signal in point contact spectroscopy contains information on the absolute strength of the electron-phonon interaction in a metal. In order to determine this strength, however, it is necessary to compare the strength of ohmic and non-ohmic parts of the current and to make some assumption concerning the shape of the contact. In this article we show that the usual assumption of a circular contact would lead to an underestimate of the electron-phonon coupling strength if the actual contact were of more irregular shape. This observation is quantified by explicit calculations for rectangular contacts.