An electronic module, comprises: a circuit board; a piezoelectric device having a lid, the piezoelectric device being mounted on the circuit board; and an electronic component mounted on the circuit board. The photochromic nanoparticle according to the present invention has structural and physical stability continuously in a long term and has transparency because of low light scattering, so that it can be applied to optical products. The media program can be delivered to viewers through multicast or unicast. Alternatively, the neutral valve is fitted into an outward opened end of a straight oil hole having an opposite outward opened end into which a charge check valve is fitted. Springs are attached to selected nodes to which a constraint is to be applied.