We introduce quantum point contact microscopy (QPCM) as a novel method for surface characterization, where the conductance through a quantum point contact formed by a metal atom between the tip of a scanning tunneling microscope and the surface is mapped across the surface. Application of QPCM to copper and gold (111) shows reproducibly atomic resolution, on gold (111) the alternating atomic st...

The basic quantum mechanical relation between fluctuations of transported charge and current correlators is discussed. It is found that, as a rule, the correlators are to be time-ordered in an unusual way. Instances where the difference with the conventional ordering matters are illustrated by means of a simple scattering model. We apply the results to resolve a discrepancy concerning the third...

Qualitative reasoning can, and should, be decomposed into a model-building task, which creates a qualitative differential equation (QDE) as a model of a physical situation, and a qualitative simulation task, which starts with a QDE . and predicts the possible behaviors following from the model . In support of this claim, we present QPC, a model builder that takes the general approach of Qualita...

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