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Vortex domain configuration for energy-storage ferroelectric ceramics design: A phase-field simulation
No full textThe utilization of ferroelectrics in forms of ceramics, films, and composites toward energy-storage applications is of great interest recent years. However, the simultaneous achievement of high polarization, high breakdown strength, low energy loss, and weakly nonlinear polarization-electric field (P-E) correlation has been a huge challenge, which impedes progress in energy storage performance. In this work, a vortex domain engineering constructed via the core-shell structure in ferroelectric ceramics is proposed. The formation and the switching characteristics of vortex domains (VDs) were validated through a phase-field simulation based on the time-dependent Ginzburg-Landau kinetic equation. Benefiting from the smaller depth of a potential well in the energy profiles, the switching of VDs was much easier than that of conventional large-sized domains, which was found to be the origin of the lower coercive field, lower remanent polarization, and weaker nonlinear P-E correlation. Choosing BaTiO3 (BT) as a representative of ferroelectric ceramics, the shell fractions and permittivity values were varied in our phase-field simulation to optimize the energy storage performance. As a result, a large discharge energy of 6.5 J/cm3 was obtained in BT ferroelectric ceramics with a shell fraction of 5% and a shell permittivity of 20 under the applied electric field of 100 kV/mm, which is almost 140% higher than that with no shell structure. In general, the vortex domain engineering proposed in this work can serve as a universal method in designing high-performance ferroelectrics with simultaneous high breakdown strength, high discharge energy density, and high energy efficiency
A Simplified Model of the Field Dependence for HTS Conductor on Round Core (CORC) Cables
No full textThis article presents a simplified mathematical model the anisotropic magnetic field dependence (AMFD) for simulating the High-Temperature superconducting (HTS) Conductor on Round Core (CORC) Cables. All these simulations of HTS CORC Cable were performed based on the finite-element method (FEM) H-formulation model merged into the numerical platform COMSOL Multi-physics. The simplified model of AMFD was implemented into both the 2D and 3D H-formulation models of HTS CORC cables. Their results were studied with different conditions, such as the increasing transport current, as well as the gap angle between the superconducting tapes in a single layer. This new simplified AMFD model can give a proper approximation of the actual electromagnetic behaviours of the HTS CORC, but also establish the upper limit of the AC loss calculation, which can be fairly useful for designing future HTS CORC cables
Charging an HTS Coil: Flux Pump with an HTS Square Bridge
No full textIn recent years, along with the unceasing development of High-Temperature Superconductor (HTS) technology, the performance of HTS tape has been improved significantly, including the higher critical current, lower joint resistance, and longer tape length etc. To use HTS instead of Low-Temperature Superconductor (LTS) in Magnetic Resonance Imaging (MRI) applications, the flux pumping method with travelling wave has been investigated. In this paper, our new experimental results were regarding to the frequency, amplitude, and wavelength characteristics of charging an HTS coil with an HTS square bridge, using an electromagnetic flux pump designed at the University of Cambridge
Wind turbine blade wastes and the environmental impacts in Canada
No full textElectricity production by wind turbines is considered a clean energy technology, but the life cycle of wind turbines could introduce environmental risks due to waste generation, especially at the decommissioning process. This study predicts the future wind turbine blade waste arising in Canada, throughout all life cycle stages, from manufacturing until end of life, based on the installed capacities of existing Canadian wind farms and projected future installations. Five alternative strategies for managing this waste stream are assessed in terms of life cycle greenhouse gas emissions and primary energy demand, including landfilling, incineration, and mechanical recycling. For the base case scenario, it is observed that the total cumulative waste until 2050 is 275,299 tonnes, with on-site waste accounting for around 75% of this total. Waste generation is concentrated in provinces with greater wind power deployment: Ontario and Quebec alone account for 70% of total blade waste. Life cycle environmental impacts of waste management strategies are dependent on background energy systems, with incineration a significant source of greenhouse gas emissions, particularly when displacing low-carbon grid mixes. Cement kiln coprocessing achieves net zero emission by converting waste into energy and raw materials for the cement. Mechanical recycling can achieve substantial reductions in primary energy demand and greenhouse gas emissions but achieving financial viability would likely require substantial regulatory support
Multi-Chiplet System Architecture with Shared Uniform Access Memory Based on Board-Level Optical Interconnects
No full textWe propose a new multi-chiplet system architecture based on shared uniform memory access and on-board optical interconnects. System-level simulation results demonstrate that such systems offer improved execution times and energy efficiency over conventional computing architectures
The FinFET effect in Silicon Carbide MOSFETs
No full textIn ISPSD 2020 it has been shown that the effective mobility of a lateral 4H-SiC MOSFET could be increased by an order of magnitude through using an ultra-narrow-body design. Thus, this work presents further experimental results on a wide set of fin widths, ranging from conventional (860nm) to ultra-narrow (35nm). Furthermore, a 3D TCAD model, employing quantum corrections, is matched to experiment and applied to study these designs. It is thereby shown that the FinFET effect can have a strong impact in SiC devices and may allow for up to an 18x increase of the mobility relative to a reference width of 280nm. Finally, an optimization window of ~30-50nm is predicted for the fin width, below which the FinFET effect becomes detrimental
A tool for generation of stochastic occupant-based internal loads using a functional data analysis approach to re-define ‘activity’
No full textIn building energy simulation (BES), internal loads are typically defined as hourly schedules based on occupant-related ‘activities’ assigned to each building zone. In this paper, a data-centric bottom-up functional data analysis model is used to examine how activities in a building correlate with energy demand for plug loads and lighting. Functional principal component analysis and hierarchical clustering of the principal component scores have been used to explore the links between the data and zone activity. The results show that plug loads show limited links to activity to the extent that the activity determines the variability of the data. The lighting loads show little correlation with zone activity but instead are determined primarily by the building control system. A novel methodology is proposed for the generation of stochastic load data for input into BES. This methodology has been developed into a tool for stochastic load generation which is available online
Identification of a driver model incorporating sensory dynamics, with nonlinear vehicle dynamics and transient disturbances
No full textIn earlier work, a driver model incorporating sensory dynamics was identified from driving simulator experiments involving random disturbances, random target paths and linear vehicle dynamics. In the present paper, the driver model and experiments are extended to include transient disturbances, discrete target paths and nonlinear vehicle dynamics. The predictions of the model are compared with measurements from the experiments. Simulator motion is found to have a significant beneficial effect on drivers' responses, giving faster driver reaction times and more successful disturbance rejection and path following. The driver model predicts the measured responses well. The model suggests that drivers are unable to develop an accurate internal model of motion cueing filters, perceiving phase and gain distortions introduced by filtering as disturbances. Drivers are found able to account for the time-varying operating point of a nonlinear vehicle. The driver model is also able to match the behaviour of experienced drivers near the friction limit of the tyres, however, further work is necessary to understand how an inaccurate internal model impedes the performance of less experienced drivers. The findings contribute new knowledge to the fields of driver simulation and motion cueing
Machine learning force fields based on local parametrization of dispersion interactions: Application to the phase diagram of C60
No full textWe present a comprehensive methodology to enable the addition of van der Waals (vdW) corrections to machine learning (ML) atomistic force fields. Using a Gaussian approximation potential (GAP) [Bartók et al., Phys. Rev. Lett. 104, 136403 (2010)10.1103/PhysRevLett.104.136403] as a baseline, we accurately machine learn a local model of atomic polarizabilities based on Hirshfeld volume partitioning of the charge density [Tkatchenko and Scheffler, Phys. Rev. Lett. 102, 073005 (2009)10.1103/PhysRevLett.102.073005]. These environment-dependent polarizabilities are then used to parametrize a screened London-dispersion approximation to the vdW interactions. Our ML vdW model only needs to learn the charge density partitioning implicitly by learning the reference Hirshfeld volumes from density functional theory (DFT). In practice, we can predict accurate Hirshfeld volumes from the knowledge of the local atomic environment (atomic positions) alone, making the model highly computationally efficient. For additional efficiency, our ML model of atomic polarizabilities reuses the same many-body atomic descriptors used for the underlying GAP learning of bonded interatomic interactions. We also show how the method enables straightforward computation of gradients of the observables, even when these remain challenging for the reference method (e.g., calculating gradients of the Hirshfeld volumes in DFT). Finally, we demonstrate the approach by studying the phase diagram of C60, where vdW effects are important. The need for a highly accurate vdW-inclusive reactive force field is highlighted by modeling the decomposition of the C60 molecules taking place at high pressures and temperatures
A Recursive Quantizer Design Algorithm for Binary-Input Discrete Memoryless Channels
No full textThe optimal quantization of output binary-input discrete memoryless channels is considered, whereby the optimal quantizer preserves at least a constant \alpha -fraction of the original mutual information, with the smallest output cardinality. Two recursive methods with top-down and bottom-up approaches are developed; these methods lead to a new necessary condition for the recursive quantizer design. An efficient algorithm with linear complexity, based on dynamic programming and the new necessary optimality condition, is proposed