Parallel scheduling of recursively defined arrays

A new method of automatic generation of concurrent programs which constructs arrays defined by sets of recursive equations is described. It is assumed that the time of computation of an array element is a linear combination of its indices, and integer programming is used to seek a succession of hyperplanes along which array elements can be computed concurrently. The method can be used to schedule equations involving variable length dependency vectors and mutually recursive arrays. Portions of the work reported here have been implemented in the PS automatic program generation system

Growth kinetics effects on self-assembled InAs/InP quantum dots

A systematic manipulation of the morphology and the optical emission properties of MOVPE grown ensembles of InAs/InP quantum dots is demonstrated by changing the growth kinetics parameters. Under non-equilibrium conditions of a comparatively higher growth rate and low growth temperature, the quantum dot density, their average size and hence the peak emission wavelength can be tuned by changing efficiency of the surface diffusion (determined by the growth temperature) relative to the growth flux. We further observe that the distribution of quantum dot heights, for samples grown under varying conditions, if normalized to the mean height, can be nearly collapsed onto a single Gaussian curve.Comment: 2 figure

On the fitness of informative cues in complex environments

To be able to deal with uncertainty is of primary importance to all organisms. When cues provide information about the state of the environment, organisms can use them to respond flexibly. Thus information can provide fitness advantages. Without environmental cues, an organism can reduce the risks of environmental uncertainty by hedging its bets across different scenarios. Risk mitigation is then possible by adopting a life-history of bet-hedging, either randomly switching between phenotypes (diversifying bet-hedging) or adopting intermediate phenotypes (conservative bet-hedging). Hence, understanding patterns of bet-hedging is necessary in order to quantify the fitness benefit of environmental cues, since it provides a baseline fitness in the absence of informative cues. Quantifying fitness benefits in terms of mutual information reveals deep connections between Darwinian evolution and information theory. However, physiological constraints or complex ecological scenarios often lead to the number of environmental states to exceed that of potential phenotypes, or a single intermediate phenotype is adopted, as in the case of conservative bet-hedging. Incorporating these biological complexities, we generalise the relationship between information theory and Darwinian fitness. Sophisticated bet-hedging strategies combining diversifying and conservative bet-hedging - can then evolve. We show that, counterintuitively, environmental complexity can reduce, rather than increase, the number of phenotypes that an organism can adopt. In conclusion, we develop an information-theoretic extensible approach for investigating and quantifying fitness in ecological studies

Collective narratives catalyse cooperation

Humans invest in fantastic stories—mythologies. Recent evolutionary theories suggest that cultural selection may favour moralising stories that motivate prosocial behaviours. A key challenge is to explain the emergence of mythologies that lack explicit moral exemplars or directives. Here, we resolve this puzzle with an evolutionary model in which arbitrary mythologies transform a collection of egoistic individuals into a cooperative. We show how these otherwise puzzling amoral, nonsensical, and fictional narratives act as exquisitely functional coordination devices and facilitate the emergence of trust and cooperativeness in both large and small populations. Especially, in small populations, reflecting earlier hunter- gatherers communities, relative to our contemporary community sizes, the model is robust to the cognitive costs in adopting fictions