COG is a popular dielectric for ceramic capacitors. It is a temperature compensating EIA Class 1 material. COG contains neodymium, samarium and other rare earth materials. COG ceramics have very stable characteristics. Capacitance change with temperature is approximately + or – 30 ppm/Deg C from -55 Deg C to 125 Deg C. Capacitance change with life is less than + or – 0.1%. Typically Q is more than 1000.  There is little Q or capacitance change with frequency. Dielectric absorption is typically less than 0.6%.

Negative resistance is a property of some electric circuits where an increase in the current causes a decreased voltage across the same node. Negative resistance devices can be used to make bistable switching circuits and oscillators, particularly at high frequencies.

Some input from an application engineer about “low esr”. It appears that low esr is fairly dependent on the application. Power management, RF, LED drivers, etc. In addition to low esr the dielectric is also important ( sometimes specified as X5R, X7R, COG etc).