7,983 research outputs found
Why it is important to build robots capable of doing science
Science, like any other cognitive activity, is grounded in the sensorimotor interaction of our bodies with the environment. Human embodiment thus constrains the class of scientific concepts and theories which are accessible to us. The paper explores the possibility of doing science with artificial cognitive agents, in the framework of an interactivist-constructivist cognitive model of science. Intelligent robots, by virtue of having different sensorimotor capabilities, may overcome the fundamental limitations of human science and provide important technological innovations. Mathematics and nanophysics are prime candidates for being studied by artificial scientists
On Instability of Certain Bi-Metric and Massive-Gravity Theories
Stability about cosmological background solutions to the bi-metric
Hassan-Rosen theory is studied. The results of this analysis are presented, and
it is shown that a large class of cosmological backgrounds is classically
unstable. This sets serious doubts on the physical viability of the
Hassan-Rosen theory - and in turn also of the de Rham-Gadabaze-Tolley model, to
which the mentioned theory is parent. A way to overcome this instability by
means of curvature-type deformations is discussed.Comment: 4 pages, 2 figures; v2: minor changes to match PRD versio
Millennial Variability in an Idealized Ocean Model: Predicting the AMOC Regime Shifts
A salient feature of paleorecords of the last glacial interval in the North Atlantic is pronounced millennial variability, commonly known as DansgaardâOeschger events. It is believed that these events are related to variations in the Atlantic meridional overturning circulation and heat transport. Here, the authors formulate a new low-order model, based on the HowardâMalkus loop representation of ocean circulation, capable of reproducing millennial variability and its chaotic dynamics realistically. It is shown that even in this chaotic model changes in the state of the meridional overturning circulation are predictable. Accordingly, the authors define two predictive indices which give accurate predictions for the time the circulation should remain in the on phase and then stay in the subsequent off phase. These indices depend mainly on ocean stratification and describe the linear growth of small perturbations in the system. Thus, monitoring particular indices of the ocean state could help predict a potential shutdown of the overturning circulation
âIneffectiveâ competition: a puzzle?
Conventionally, we think of an increase in competition as weakly decreasing prices, increasing the number of consumers served, thus increasing consumer surplus, decreasing firms profits, etc. Here, we demonstrate that, under some tame circumstances, an increase in competition may lead to a price increase in a horizontally differentiated market. We show this relationship for the petrol market in German cities
Comparing visible and less visible costs of the Habitats Directive: The case of hamster conservation in Germany
The EU Habitats Directive provides in Annexes II and IV a list of species needing to be conserved. Member States have implemented a variety of conservation measures in response to this obligation. These measures include the rejection, modification or delay of land development plans, payments for landowners to perform conservation measures and management actions such as breeding programmes. The costs of the various conservation measures are not always apparent. There may be an underestimation of the resulting costs when land development plans are altered, because there is no visible flow of financial resources. Such a biased perception may result in selecting conservation measures with high but less visible costs, whereas conservation measures with low but more visible costs are neglected. The purpose of this paper is to contribute to avoiding a biased selection of conservation measures by presenting a framework which captures a broad variety of costs relevant to the conservation of species protected by the Habitats Directive. We also demonstrate the relevance of a biased selection of conservation measures by using the framework to empirically estimate the costs of protecting the common hamster (Cricetus cricetus) in the region of Mannheim, Germany. We find that the less visible costs of changes in development plans are significantly higher than the more visible costs of payments to landowners and management actions. This result suggests that measures with visible costs should be given more attention in the future. --Common hamster,Cost assessment,Cost-effectiveness,EU Habitats Directive,Land use,Spatial planning,Species conservation
ĂąâŹĆIneffectiveù⏠competition: a puzzle?
Conventionally, we think of an increase in competition as weakly decreasing prices, increasing the number of consumers served, thus increasing consumer surplus, decreasing firms profits, etc. Here, we demonstrate that, under some tame circumstances, an increase in competition may lead to a price increase in a horizontally differentiated market. We show this relationship for the petrol market in German cities.
Cosmic String Loops, Large and Small
We extend our earlier model of the small scale structure of cosmic string
networks through an improved treatment of the separation of long and short
scales. We find that the production of small loops (at the gravitational
radiation scale) is a robust feature of string networks, in addition to a
population of loops near the horizon scale. We obtain quantitative agreement
with the scaling of loop production functions as found in simulations by two
groups.Comment: 13 pages, 3 jpg figures. v2: reference moved, note adde
Quantum geometry from phase space reduction
In this work we give an explicit isomorphism between the usual spin network
basis and the direct quantization of the reduced phase space of tetrahedra. The
main outcome is a formula that describes the space of SU(2) invariant states by
an integral over coherent states satisfying the closure constraint exactly, or
equivalently, as an integral over the space of classical tetrahedra. This
provides an explicit realization of theorems by Guillemin--Sternberg and Hall
that describe the commutation of quantization and reduction. In the final part
of the paper, we use our result to express the FK spin foam model as an
integral over classical tetrahedra and the asymptotics of the vertex amplitude
is determined.Comment: 33 pages, 1 figur
- âŠ