ABSTRACT
The characteristics of the spectrum can give clues to the nature and origin of the cosmic ray radiation. The chapter discusses possible acceleration mechanisms in relation to the power law spectrum. The original proposal for a cosmic ray acceleration mechanism yielding a power law spectrum is due to Fermi. Good candidate sources for direct acceleration are rotating high magnetic field objects such as neutron stars. These typically have 10 gauss surface fields and radii of a few kilometers and they rotate at approximately 30 revolutions per second. This implies an induced electromotive force of on the order of 10 volts. Cosmic strings are thought to be loops or topological defects in the universe produced by processes in the expansion of the universe Certain models lead to a picture of strings composed of super heavy charged fermions which pair up so as to be effectively massless.
