A non-erasable ink composition suitable for use in writing instruments is described comprising an isocyanate five thermoplastic polyurethane resin, a colorant and an organic solvent. The present invention is directed to, in a general aspect, a method of authenticating membership for providing access to a secure environment. Also, the identifying unit determines whether a connection of a specific virtual private line corresponding to the specific channel to an ISDN network is established. Thus, the amplifier is kept to be less-power consuming in the absence of the wake-up signal, reducing a power requirement. The cups of the lower shield are inserted into the recesses of the cover ring. The sidewall air gap formation scheme for the TSV structure of disclosed embodiments reduces parasitic capacitance and depletion regions in between the substrate silicon and TSV conductor, and serves to also reduce mechanical stress in silicon substrate surrounding the TSV conductor.