56,836 research outputs found
How to Do Things with Words: Tolkienâs Theory of Fantasy in Practice
After his St Andrews lecture on âFairy Storiesâ Tolkien projected his theory of sub-creation into his legendarium. In this projection the theory of what the human sub-creator does with thought and words became a model for what miraculous and magical beings can do with spirit and matter. For example, FĂ«anorâs making of the Silmarils and Sauronâs forging of the Ring were conceived (or in the first case, re-conceived) as acts analogous to human fantasy. Middle-earth thus became a world in which the magical potential of human words is revealed in the visible being of magical things
Does Advice Help to Prove Propositional Tautologies?
One of the starting points of propositional proof complexity is the seminal paper by Cook and Reckhow [6], where they defined propositional proof systems as poly-time computable functions which have all propositional tautologies as their range. Motivated by provability consequences in bounded arithmetic, Cook and KrajĂÄek [5] have recently started the investigation of proof systems which are computed by poly-time functions using advice. While this yields a more powerful model, it is also less directly applicable in practice. In this note we investigate the question whether the usage of advice in propositional proof systems can be simplified or even eliminated. While in principle, the advice can be very complex, we show that proof systems with logarithmic advice are also computable in poly-time with access to a sparse NP-oracle. In addition, we show that if advice is ânot very helpfulâ for proving tautologies, then there exists an optimal propositional proof system without advice. In our main result, we prove that advice can be transferred from the proof to the formula, leading to an easier computational model. We obtain this result by employing a recent technique by Buhrman and Hitchcock [4]
The impacts of new A8 migration in Leeds
New arrivals from Eastern Europe have made regular headlines in the popular press in recent times, not only for the unprecedented magnitude of the flows involved, but also for their impacts â positive and negative â on regions and localities up and down the country. This paper reports on a recently completed research project aimed at finding out more about A8 migrants in Leeds
The Role of Lactose Tolerance in Pre-Colonial Development
This paper establishes a link between natural selection since the Neolithic Revolution and economic conditions in the pre-colonial era. The ability to digest milk, or to be lactose tolerant, is conferred by a gene variant, which is unequally distributed across the Old World. Digesting milk conferred qualitative and quantitative advantages to early farmers's diets, which ultimately, led to differences in the carrying capacities of respective countries. It is shown through a number of specifications that country level variation in the frequency of the ability to consume milk is positively and significantly related to population densities in 1500 CE; specifically, a one standard deviation in- crease in the frequency of lactose tolerant individuals (24% points) is associated with roughly a 60% increase in pre-colonial population densities. This relationship remains while controlling for agricultural transition dates, other measures of genetic distance, and a wide array of environmental controls. Additionally, the basis for the relation- ship between dairying and population density is confirmed with the use of instrumental variables estimation.
Testing a Simplified Version of Einstein's Equations for Numerical Relativity
Solving dynamical problems in general relativity requires the full machinery
of numerical relativity. Wilson has proposed a simpler but approximate scheme
for systems near equilibrium, like binary neutron stars. We test the scheme on
isolated, rapidly rotating, relativistic stars. Since these objects are in
equilibrium, it is crucial that the approximation work well if we are to
believe its predictions for more complicated systems like binaries. Our results
are very encouraging.Comment: 9 pages (RevTeX 3.0 with 6 uuencoded figures), CRSR-107
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