Laurent Freidel
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Laurent Freidel is a physicist, working at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. He is working in loop quantum gravity and spin foam models of quantum gravity. He has recently coauthored a series of papers on the Ponzano-Regge model, a spin foam model of 3-dimensional Riemannian quantum gravity, in which he explains how point particles naturally arise in this theory. He is also working with Artem Starodubtsev on a perturbative spin foam model of 4-dimensional quantum gravity.
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Directivity is also defined for directional couplers and similiar devices for RF and Microwave measurements. It is the properof the device couple power in one direction while rejecting in other direction. Higher the rejection, higher the directivity. For example in a directional coupler if the directivity of a measuring port is 40 dB, it means the power coupled in this port from desired direction will be 40 dB higher than the undesired power coupled from other direction.
