An apparatus for applying a stress voltage to a device under test includes a stress voltage source, a constant voltage circuit having an input connected to the stress voltage source and an output connected to a control circuit for removing stress when current exceeds a predetermined level which is connected to the device under test. Lip-engaging members are attached to the articulating arms opposite the primary hinge and are also attached to the articulating arms in a hinged manner. Each of the discharge cells has upper and lower substrates. Electrical charge is concentrated on the particle as the microdroplet evaporates. The sensor is spring-loaded to insure solid contact with the cutting element, and thus, accurate temperature measurements. The compounds of this invention have the structure, wherein R1a, R1b, R1c, R1d, R2, R2a, and A are as defined herein, including stereoisomers, esters, solvates and pharmaceutically acceptable salts thereof.