Quantum probe and design for a chemical compass with magnetic nanostructures

Magnetic fields as weak as Earth's may affect the outcome of certain photochemical reactions that go through a radical pair intermediate. When the reaction environment is anisotropic, this phenomenon can form the basis of a chemical compass and has been proposed as a mechanism for animal magnetoreception. Here, we demonstrate how to optimize the design of a chemical compass with a much better directional sensitivity simply by a gradient field, e.g. from a magnetic nanostructure. We propose an experimental test of these predictions, and suggest design principles for a hybrid metallic-organic chemical compass. In addition to the practical interest in designing a biomimetic weak magnetic field sensor, our result shows that gradient fields can server as powerful tools to probe spin correlations in radical pair reactions.Comment: 8 pages, 6 figures, comments are welcom

Toward Efficient Urban Form in China

Land efficiency in urban China is examined, using Tianjin as a case study, from the perspective of agricultural land conservation; reduction in energy use, conventional pollution, and greenhouse gas emissions; and human time savings. Issues addressed include increased scatter on the periphery, over-consumption of industrial land, over fiscal dependence on land sales, and loss of valuable agricultural and environmental services land. Policy implications discussed include the need for greater variation in urban densities (leveraging already high densities in urban China – one-third the global median), less broad-brush agricultural land conservation policies, higher floor area ratios near rapid transit stations, etc.China, land conversion, land efficiency, land use policy, urban density