18,702 research outputs found
Approaching a topological phase transition in Majorana nanowires
Recent experiments have produced mounting evidence of Majorana zero modes in
nanowire-superconductor hybrids. Signatures of an expected topological phase
transition accompanying the onset of these modes nevertheless remain elusive.
We investigate a fundamental question concerning this issue: Do well-formed
Majorana modes necessarily entail a sharp phase transition in these setups?
Assuming reasonable parameters, we argue that finite-size effects can
dramatically smooth this putative transition into a crossover, even in systems
large enough to support well-localized Majorana modes. We propose overcoming
such finite-size effects by examining the behavior of low-lying excited states
through tunneling spectroscopy. In particular, the excited-state energies
exhibit characteristic field and density dependence, and scaling with system
size, that expose an approaching topological phase transition. We suggest
several experiments for extracting the predicted behavior. As a useful
byproduct, the protocols also allow one to measure the wire's spin-orbit
coupling directly in its superconducting environment.Comment: 13 pages, 8 figure
ARGES: an Expert System for Fault Diagnosis Within Space-Based ECLS Systems
ARGES (Atmospheric Revitalization Group Expert System) is a demonstration prototype expert system for fault management for the Solid Amine, Water Desorbed (SAWD) CO2 removal assembly, associated with the Environmental Control and Life Support (ECLS) System. ARGES monitors and reduces data in real time from either the SAWD controller or a simulation of the SAWD assembly. It can detect gradual degradations or predict failures. This allows graceful shutdown and scheduled maintenance, which reduces crew maintenance overhead. Status and fault information is presented in a user interface that simulates what would be seen by a crewperson. The user interface employs animated color graphics and an object oriented approach to provide detailed status information, fault identification, and explanation of reasoning in a rapidly assimulated manner. In addition, ARGES recommends possible courses of action for predicted and actual faults. ARGES is seen as a forerunner of AI-based fault management systems for manned space systems
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