Parity-time electromagnetic diodes in a two-dimensional nonreciprocal photonic crystal

We propose a kind of electromagnetic (EM) diode based on a two-dimensional nonreciprocal gyrotropic photonic crystal. This periodic microstructure has separately broken symmetries in both parity (P) and time-reversal (T) but obeys parity-time (PT) symmetry. This kind of diode could support bulk one-way propagating modes either for group velocity or phase velocity with various types of negative and positive refraction. This symmetry-broken system could be a platform to realize abnormal photoelectronic devices, and it may be analogous to an electron counterpart with one-way features

An online fault-diagnosis of electromagnetic actuator based on variation characteristics of load current

Accurate and fast fault-diagnosis is the foundation of fault-tolerance. To develop the fault-tolerance of magnetic-levitated bearing system, this paper presents an online fault-diagnosis approach of electromagnetic actuator based on variation characteristics of sampled load current in the modulation to identify the time constant of the electromagnetic coil, and then to diagnose the broken circuit or partial short-circuit faults. After analysing the variation characteristics of the load current theoretically, the simulation is constructed to verify the effectiveness of the proposed approach. Considering the real-time requirement of fault-diagnosis, we develop a fast sampling and calculating method for the equivalent slope of the load current in the modulation, which represents the variation characteristics of the load current. The experimental results demonstrate that the proposed approach is effective for diagnosing broken circuit and partial short-circuit faults, and the execution time for the fault-diagnosis is about 2 ms, proving its excellent real-time performance

First-principles studies on K-promoted porous iron oxide catalysts

AbstractPorous potassium-promoted iron oxide, with the potassium content of 8 wt% can produce dense hydrogen materials as a catalyst. In this letter, we use density functional theory (DFT) and the generalized gradient approximation (GGA) to study this catalyst. Rhombohedral α-Fe2O3 is used to build a porous model. We randomly put potassium atoms in the clean porous structure and iron-vacant defective structure. The results show that potassium atoms eventually exist in the form of clusters in the two samples. To further study the effect of potassium, clean and two K-promoted models are filled with the same quantity of H2. We obtain that the existence of potassium clusters prevents hydrogen molecules to dissociate into atoms in non-defective porous iron oxide. Most of the hydrogen atoms still exist in the form of hydrogen molecules in three models. The structures of potassium clusters for 2 ≤ N ≤ 8 in the porous model are also discussed, in contrast to the isolated clusters

An Ohta-Kawasaki Model set on the space

We examine a non-local diffuse interface energy with Coulomb repulsion in three dimensions inspired by the Thomas-Fermi-Dirac-von Weizs\"{a}cker, and the Ohta-Kawasaki models. We consider the corresponding mass-constrained variational problem and show the existence of minimizers for small masses, and the absence of minimizers for large masses