Excitation localization effects in nanoscale molecular clusters (J-aggregates)
An analysis of experimental data from low-temperature selective spectroscopy and single J-aggregate spectroscopy reveals a hierarchy of exciton states within the confines of the absorption band of J-aggregates which are formed by relaxation of an excited state. For J-aggregates, which are characterized by substantial static disorder, strongly localized excitons are found in the long-wavelength edge of the absorption band; they have a discrete energy spectrum and jump mobility, and are not subject to strong relaxation. Delocalized (spatially extended) excitons are excited within the absorption band of the J-aggregates, except at its long-wavelength edge. They are characterized by coherent exciton transport and are the source of self-localized excitons.
An instruction-level simulator for IBM 3090 with VF (vector facility) has been developed for studying the performance of vector processors and their memory hierarchies. Results of a study of the locality of several large scientific applications are presented. The cache miss ratios of vectorized applications are found to be almost equal to those of their original scalar executions. Moreover, both the spatial and temporal locality of these applications (in scalar and vector executions) are strong enough to show a sufficiently high hit ratio on conventional cache structures.<<ETX>>