Low-density parity-check (LDPC) codes exhibit excellent error correcting capability. However, small trapping sets in the Tanner graph are harmful to the iterative decoding algorithm. In this letter, we present a method of constructing (3, n) girth-eight quasi-cyclic LDPC codes with low error floor by removing the small trapping sets from the Tanner graph. To address this issue, we analyze the relationship between eight-cycles and small trapping sets of Tanner graphs based on fully connected base graphs without parallel edges. We find that if some eight-cycles are not found in the Tanner graphs, any elementary trapping set in the range of a ≤ 8 and b ≤ 3 is removed naturally. We also derive a lower bound on the permutation size for the construction of such codes. The experimental simulation shows a favorable error rate performance with lower error floor over additive white Gaussian noise channels.

Epitaxial Ba_xSr_1−xTiO₃ (BST) films are grown on SrTiO₃:Nb (NSTO) substrates by hydrothermal means. A Pt/BST/NSTO device exhibits typical rectification characteristics under relatively low voltage and forming-free bipolar resistive switching under relatively high voltage, with the resistance ratio between the high and low resistance states exceeding four orders of magnitude. Furthermore, negative differential resistance arises during the reset process, and multilevel resistive switching is achieved under various reset voltages. These behaviors in the Pt/BST/NSTO device are likely due to trapping/detrapping of electrons by oxygen vacancies at the Pt/BST interface.

Phase change memory (PCM) is an important element in the development and realization of new forms of brain-like computing. In this article, a three-dimensional finite element method simulation is carried out to study the temperature profiles within PCM cells for a better understanding of switching operations. On the basis of a finite difference method, the simulation consists of phase transition kinetics, electrical, thermal, percolation effect, as well as thermoelectric effects, using temperature-dependent material parameters. The Thomson effect within the phase-change material and the Peltier effect at the electrode contact are respectively considered for a detailed analysis of the impact on the temperature profiles and the programming current for switching processes. The simulation results show that switching operations are primarily implemented by the melting and quenching of the phase-change material close to the contact between the bottom electrode and phase change material, and its final phase distribution is determined by the cooling rate. With positive current polarity, thermoelectric effects improve heating efficiency and then reduce the programming current. Because of the different occurrence region, the Peltier effect significantly changes the temperature profile, which is more influential in switching operations. Additionally, the contribution of thermoelectric effects decreases with the cell size scaling because of the weakening of the Peltier effect. This paper aims at providing a more precise description of the thermoelectric phenomena taking place in switching operations for future PCM design.

Conventional finite control set model predictive control (FCS-MPC) for permanent magnet synchronous motor (PMSM) drives suffers from a fundamental trade-off: shortening the control period improves current tracking but increases switching frequency and losses. This paper proposes a hysteresis-based variable control period MPC (HBVCP-MPC) to break this compromise. Unlike methods like direct torque control (DTC) and model predictive direct torque control (MPDTC) that use hysteresis to select voltage vectors (VV), our approach first selects the optimal VV via a cost function that balances current tracking accuracy and switching frequency. Hysteresis on the $dq$-axis currents is then employed solely to dynamically determine the application time of this pre-selected VV, which defines the variable control period. This grants continuous adjustment over the VV duration, enabling superior current tracking without a proportional rise in switching frequency. Experimental results confirm that the proposed method achieves enhanced steady-state performance at a comparable switching frequency.

Phase change memory (PCM) is one of the most promising emerging non-volatile memory technologies. This paper simulates phase change memory devices (PCMDs) with careful attention to the scaling and its resulting impact on programming current during the switching operation, while Thomson heating within the phase change material and Peltier heating at the electrode interface are considered. The simulation results show that the device scaling has an influence on temperature distribution, volume of the molten region, heat diffusion and switching operation of PCMDs. The programming current decreases with smaller electrode size, greater thickness of phase change material and deeper isotropic scaling. The heat diffusion becomes more serious when the thickness of phase change materials decreases and the size of PCMD is isotropically scaled down. The scaling arguments also indicate that the impact of thermoelectric phenomena weakens with smaller dimensions due to the influence of programming current, heat diffusion and action area. This simulation provides useful insights to understand the switching operation of the PCMDs under the impact of thermoelectric effects. The process is instrumental for a complete understanding of device operation and hence provides valuable feedback for fine-tuning the device design so as to enhance its efficiency.