Opinion is strongly divided on whether life arose on earth under hot or cold conditions, the hot-start and cold-start scenarios, respectively. The origin of life close to deep thermal vents appears as the majority opinion among biologists, but there is considerable biochemical evidence that high temperatures are incompatible with an RNA world. To be functional, RNA has to fold into a three-dimensional structure. We report both theoretical and experimental results on RNA folding and show that (as expected) hot conditions strongly reduce RNA folding. The theoretical results come from energy-minimization calculations of the average extent of folding of RNA, mainly from 0-90 degrees C, for both random sequences and tRNA sequences. The experimental results are from circular-dichroism measurements of tRNA over a similar range of temperatures. The quantitative agreement between calculations and experiment is remarkable, even to the shape of the curves indicating the cooperative nature of RNA folding and unfolding. These results provide additional evidence for a lower temperature stage being necessary in the origin of life.
Parallel and distributed languages specify computations on multiple processors and have a computation language to describe the algorithm, i.e. what to compute, and a coordination language to describe how to organise the computations across the processors. Haskell has been used as the computation language for a wide variety of parallel and distributed languages, and this paper is a comprehensive survey of implemented languages. We outline parallel and distributed language concepts and classify Haskell extensions using them. Similar example programs are used to illustrate and contrast the coordination languages, and the comparison is facilitated by the common computation language. A lazy language is not an obvious choice for parallel or distributed computation, and we address the question of why Haskell is a common functional computation language.
Complexity in concurrent or distributed systems can be managed by dividing component into smaller components. For example, suppose component D is replaced by an assembly of sub components D1 to D4:While the new assembly may have the same functional correctness properties as the original component, the coordination properties of the whole system may have changed radically, as the additional processes must now be scheduled with attendant impact on the scheduling of the original processes. If the original system is non-deterministic or time dependent, then the system's functional properties may also change. A well known solution for managing large systems is to structure the components into sub-parts, an approach that was first taken by Harel [2] for finite state automata (FSA). By illustrating with the Hume programming language, we will argue for a similar approach for program transformation, where the overall structure is preserved by nesting new components inside a super-component.Hume[1] explicitly separates coordination and computation concerns. It is based on autonomous boxes linked by wires, which are defined in the finite state coordination language. Transitions within a box is defined in the expression language by a list of matches, each of the form pattern → expression where each pattern is matched against the box input and the associated expression generates output by associated recursive actions. Hume targets safety-critical resource bounded * This work has been supported by EU FP6 EmBounded and a James Watt Scholarship. A full version of the paper is available at
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