A method and apparatus for classifying signals into a multiplicity of signal classes which employs discriminant functions of low-complexity discriminant variables that are computed directly from the passband signal. The method may also include converting the compensated digital signal into a wireless communication signal. The computer system includes an RF identification tag registration device operable to acquire user physical information and communicate the physical information to a computer, wherein the computer verifies that a valid user is wearing the tag. The air barrier may be permanently secured to or removable from the welding helmet. An elongated tire support bracket is connected to the outer end of the cable and has opposite inclined straight surfaces for self-centering wheels with center holes of different diameters. Polymers and resists of the invention are particularly useful for imaging with short wavelength radiation, such as sub-200 nm and preferably about 157 nm.