A Model of Stimulus-Specific Adaptation in Neuromorphic Analog VLSI.

Stimulus-specific adaptation (SSA) is a phenomenon observed in neural systems which occurs when the spike count elicited in a single neuron decreases with repetitions of the same stimulus, and recovers when a different stimulus is presented. SSA therefore effectively highlights rare events in stimulus sequences, and suppresses responses to repetitive ones. In this paper we present a model of SSA based on synaptic depression and describe its implementation in neuromorphic analog very-large-scale integration (VLSI). The hardware system is evaluated using biologically realistic spike trains with parameters chosen to reflect those of the stimuli used in physiological experiments. We examine the effect of input parameters and stimulus history upon SSA and show that the trends apparent in the results obtained in silico compare favorably with those observed in biological neurons.

High variation and strong phylogeographic pattern among cpDNA haplotypes in Taxus wallichiana (Taxaceae) in China and North Vietnam.

We studied the phylogeography of Chinese yew (Taxus wallichiana), a tree species distributed over most of southern China and adjacent regions. A total of 1235 individuals from 50 populations from China and North Vietnam were analysed for chloroplast DNA variation using polymerase chain reaction-restriction fragment length polymorphism of the trnL-F intron-spacer region. A total of 19 different haplotypes were distinguished. We found a very high level of population differentiation and a strong phylogeographic pattern, suggesting low levels of recurrent gene flow among populations. Haplotype differentiation was most marked along the boundary between the Sino-Himalayan and Sino-Japanese Forest floristic subkingdoms, with only one haplotype being shared among these two subkingdoms. The Malesian and Sino-Himalayan Forest subkingdoms had five and 10 haplotypes, respectively, while the relatively large Sino-Japanese Forest subkingdom had only eight. The strong geography-haplotype correlation persisted at the regional floristic level, with most regions possessing a unique set of haplotypes, except for the central China region. Strong landscape effects were observed in the Hengduan and Dabashan mountains, where steep mountains and valleys might have been natural dispersal barriers. The molecular phylogenetic data, together with the geographic distribution of the haplotypes, suggest the existence of several localized refugia during the last glaciation from which the present-day distribution may be derived. The pattern of haplotype distribution across China and North Vietnam corresponded well with the current taxonomic delineation of the three intraspecific varieties of T. wallichiana.

A priority system model for sanitation management in food service establishments.

We set out to develop a sanitation management scheme that will enable health regulatory authorities to utilize available personnel more efficiently in the regulation of the food service industry given the current budgetary and manpower constraints. Previous analyses of the Annual Food Service Establishment Sanitation Inspection Summary records from a large County Department of Health for fiscal years 1979, 1980, and 1981 indicated a cut-off point at about two to four visits for a productive follow-up sanitation inspection of food service establishments. Revisits after this point seemed counter-productive. Revisits of up to 13 times in some establishments and a high uninspection rate of others were noted. The above data, the population at risk for each establishment (generated by a prescribed method), and various control criteria were integrated into the model. Application of the model to a sample of 82 food service establishments was successful in ensuring that those operations that pose high risk to patrons are given priority in a sanitation management program while also facilitating the inspection of all food service establishments within a jurisdiction at some point.