9,442 research outputs found
Achieving the Theoretical Depairing Current Limit in Superconducting Nanomesh Films
We show the theoretical depairing current limit can be achieved in a robust fashion in highly ordered superconductor nanomesh films having spatial periodicities smaller than both the superconducting coherence length and the magnetic penetration depth. For a niobium nanomesh film with 34 nm spatial periodicity, the experimental critical current density is enhanced by more than 17 times over the continuous film and is in good agreement with the depairing limit over the entire measured temperature range. The nanomesh superconductors are also less susceptible to thermal fluctuations when compared to nanowire superconductors. T_c values similar to the bulk film are achieved, and the nanomeshes are capable of retaining superconductivity to higher fields relative to the bulk. In addition, periodic oscillations in T_c are observed as a function of field, reflecting the highly ordered nanomesh structure
Scanning Tunneling Microscopy Characterization of the Electrical Properties of Wrinkles in Exfoliated Graphene Monolayers
We report on the scanning tunneling microscopy study of a new class of corrugations in exfoliated monolayer graphene sheets, that is, wrinkles ~10 nm in width and ~3 nm in height. We found such corrugations to be ubiquitous in graphene and have distinctly different properties when compared to other regions of graphene. In particular, a “three-for-six” triangular pattern of atoms is exclusively and consistently observed on wrinkles, suggesting the local curvature of the wrinkle provides a sufficient perturbation to break the 6-fold symmetry of the graphene lattice. Through scanning tunneling spectroscopy, we further demonstrate that the wrinkles have lower electrical conductance and are characterized by the presence of midgap states, which is in agreement with recent theoretical predictions. The observed wrinkles are likely important for understanding the electrical properties of graphene
Robust Dynamic Selection of Tested Modules in Software Testing for Maximizing Delivered Reliability
Software testing is aimed to improve the delivered reliability of the users.
Delivered reliability is the reliability of using the software after it is
delivered to the users. Usually the software consists of many modules. Thus,
the delivered reliability is dependent on the operational profile which
specifies how the users will use these modules as well as the defect number
remaining in each module. Therefore, a good testing policy should take the
operational profile into account and dynamically select tested modules
according to the current state of the software during the testing process. This
paper discusses how to dynamically select tested modules in order to maximize
delivered reliability by formulating the selection problem as a dynamic
programming problem. As the testing process is performed only once, risk must
be considered during the testing process, which is described by the tester's
utility function in this paper. Besides, since usually the tester has no
accurate estimate of the operational profile, by employing robust optimization
technique, we analysis the selection problem in the worst case, given the
uncertainty set of operational profile. By numerical examples, we show the
necessity of maximizing delivered reliability directly and using robust
optimization technique when the tester has no clear idea of the operational
profile. Moreover, it is shown that the risk averse behavior of the tester has
a major influence on the delivered reliability.Comment: 19 pages, 4 figure
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