Polyvinylfluoride plastic films exhibit a normalized detectivity, D* (500 K, 1, 1), of 3×108 cm Hz1/2/W. This value for the infrared-detector figure of merit is close to the highest available from other pyroelectric materials. A pyroelectric coefficient of 1 nC/cm2K was obtained from the optical response, and a material figure of merit of 1.3×10−9 C cm/J was determined.
IRREVERSIBILITY IN HEISENBERG SPIN SYSTEMS. II 325 For explicit calculations, we have averaged (A8) over all directions of the vector q; this gives {I q ) av =2J 2 Z(sinqb/qb). (A9)Here, / is the exchange integral between two neighboring spins, and b is the lattice parameter. It may be worthwhile remarking that this usual averaging procedure, which is consistent with the experimental situation, has the nontrivial effect of destroying the periodicity of I q in different Brillouin zones.The nuclear hexadecapole matrix elements for the static and the one-phonon nuclear interactions are developed and are evaluated for Am -±3 and Am = ±4 nuclear transitions involving a spin-| nucleus in a crystal with 43m symmetry. An expression for the saturation factor for a general interaction which gives rise to nuclear-spin transitions involving the change in the z component of the spin by any amount Am = -±.n is developed and is used to derive the angular variation of the one-phonon, Am -±3 and Aw = ±4 nuclear hexadecapole interactions. Finally a way to end the speculation about the observation of the hexadecapole interaction is presented.
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