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In this article, an improved variable switching frequency zero-voltage switching (ZVS) control strategy is proposed for two parallel interleaved three-phase inverters. Discontinuous pulsewidth modulation is adopted and full-range ZVS can be achieved at any load or modulation ratio. The critical switching frequency can be easily calculated in a digital controller based on current ripple prediction instead of current zero-crossing detection. No additional high-frequency sensor or auxiliary circuit is needed. Compared with the continuous pulsewidth modulation, the switching frequency variation range is narrower and the frequency calculation equation is simplified. In addition, lower peak current ripple leads to lower current stress. Owing to the high switching frequency and the low inductance, the size and the cost of the inverter can be significantly reduced. A 6.6-kW experimental prototype with SiC MOSFETs interfacing 400-V dc with three-phase 110-V ac grid is developed to verify the effectiveness of the proposed control strategy.

Zirconium carbide hollow microspheres (ZrC HMs) were fabricated via spray drying process and polymer-derived ceramics technique. The stable and homogeneous ZrC precursor solution can be prepared by mixing polyzirconoxane (PZO), phenolic resin (PR), curing agent p-toluenesulfonic acid (TsOH) and solvent n-propanol. The precursor solution was spray-dried to form hollow precursor microspheres. During the spray drying process, morphology of the hollow precursor microspheres can be regulated by adjusting temperature of inlet hot N2, concentration of precursor solution and the amount of curing agent TsOH. The prepared hollow precursor microspheres were carbonized at 700 °C and then converted into ZrC HMs by carbothermal reduction reaction above 1500 °C. During the pyrolysis process, nanosized ZrO2 grains produced by PZO decomposition are evenly dispersed, so is the carbon produced by PR pyrolysis, as prevents overgrowth of ZrO2 grains in the following process, even when it is changed to ZrC. ZrC HMs maintained excellent spherical morphology at temperatures of 1500–1900 °C, with particle size Dv(50)=16.4–18.7 μm, which enable their promising applications in ultra-high temperature insulation material. This preparation method is simple and can be prepared on a large scale.

Multiphase ceramics like ZrC/SiC are promising candidates as ultra-high temperature ceramics for applications in extreme environments. In this work, non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics were synthesized by a one-pot reaction of three components – metal source, silicon source, and activating reagent. Molecular structures of the precursors were identified by 1H NMR and FTIR. Transformation process of the precursors to the ZrC/SiC ceramics was investigated via XRD and SEM. After heat-treatment at 1600 °C under argon, the obtained ZrC/SiC and HfC/SiC ceramics features a particle size of 100–200 nm and high metal content without excess carbon. The elemental composition of pyrolyzed ceramics can be tuned by varying the ratio of the reagents in the synthesis of precursors. This strategy also inspires a facile fabrication of composite ceramics with other elemental compositions.

Polymeric precursor for HfTaC2 ceramic was prepared by coordination reaction between metal alkoxides and acetylacetone, subsequent hydrolysis, and blend with oligomeric novolac carbon sources. The phase analysis and microstructure study were conducted using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). It showed that after pyrolyzed at 1450 °C for 90 min, HfTaC2 was obtained with particle size ~50 nm and uniform elemental distribution. Phase transition from precursor to ceramic was studied by in situ XRD measurements at temperatures from 800 to 1200 °C. In the early stage, oxide solid solution Hf6Ta2O17 was firstly detected at ~950 °C, followed by Ta2O5 and TaO. As temperature was raised, signals for TaO and Hf6Ta2O17 gradually weakened and disappeared, while those for other phases strongly strengthened. Furthermore, formation of HfxTayCz solid solution was monitored and confirmed by peak migration during 1300 °C isothermal treatment. When the sample was pyrolyzed at 1450 °C, solid solution HfxTayCz was detected at different holding time. Phase structure at 90 min was the closest to standard HfTaC2 with particle size Dv (90) ~ 200 nm.

The application of advanced ceramic materials is limited by their brittleness and complicated manufacturing methods. Three-dimensional (3D) printing has emerged as a new method for the fabrication of complex-shaped ceramics. Herein, a type of printable slurry composed of SiBCN preceramic polymers and high-volume fractions of Si3N4 whiskers (up to 60 wt% of polymer) was prepared, and subsequently printed via digital light processing (DLP) technology. We successfully manufactured complex-structured ceramic composites and achieved high bending strength (∼180 MPa). The linear shrinkage and mass loss of the ceramic material were both significantly reduced after the introduction of whiskers. The properties and structure of the printed parts pyrolyzed at different temperatures were compared, and the relationship between the microstructure and mechanical properties discussed.

In this work, the continuous Nextel™ 720 fiber reinforced alumina ceramic matrix composites (CMCs) were prepared by the prepreg process. The alumina matrix derived from aqueous slurry, which consisted of organic glue, alumina sol, nanometer alumina powder and micrometer alumina powder. This combination endowed the ceramic matrix composite with the prepreg processing capability, making the low-cost fabrication of complex shape components possible. The ratio of different alumina sources in aqueous slurry was optimized to offer good sintering activity, high thermal resistance, and excellent mechanical properties simultaneously. Furthermore, the preceramic polymer of mullite was used to strengthen the ceramic matrix through multiple impregnation process. The final CMC sample achieved a high flexural strength of 255 MPa and a good high-temperature stability. The maximum flexural strength of the CMC sample still remained 85% after heat-treatment at 1100 ℃ for 24 h.

Multi-chiplet systems are a new design paradigm to mitigate the chip design cost and improve yield for complex SoCs. The design space of multi-chiplet systems is much larger compared to a single chip SoC system. To support early stage design space exploration, simulators are of paramount importance. However, existing open-source multi-/many-core simulators are not suitable for simulating large-scale multi-chiplet systems due to the following reasons: 1) lack of accurate inter-chiplet interconnection model, and 2) incapable of supporting large-scale parallel simulation with accurate interconnection modelling. Therefore, we propose a methodology for building up a simulator for multi-chiplet systems using open-source simulators like gem5, sniper, gpgpu-sim, etc. This simulation methodology mimics the reuse and integration idea of chiplets, that is, these existing open-source simulators are reused to simulate individual chiplets, and an inter-simulator-process communication and synchronization protocol is proposed to simulate inter-chiplet communication. The proposed simulation methodology has the following features: 1) Parallel simulation for large-scale systems is supported with inter- and intra-chiplet interconnection accurately modelled. 2) Both distributed and shared memory models are supported for multi-chiplet systems. We also provide a method to modify the code of the open-source simulators like gem5, sniper, gpgpu-sim, etc. for multi-chiplet simulation, and we have released the source code of multi-chiplet simulators based on gem5, sniper, gpgpu-sim at https://github.com/FCAS-SCUT/chiplet_simulators. In the future we will port more applications/benchmarks and integrate more open-source simulators.

Variable frequency and phase shift modulation can achieve zero-voltage switching (ZVS) of dual active bridge series resonant DC-DC converters(DABSRCs) over a wide operating range so as to effectively improving system efficiency and reliability. In order to study the dynamics of DABSRCs and provide the basis for the closed-loop compensator design, a continuous-time small-signal model is proposed. The generalized average modelling approach is adopted, in which the DC component of the output voltage and the fundamental component of the inductor current and resonant capacitor voltage are selected as the state variables, precisely describing impacts of the resonance on the system dynamics. On the above-mentioned basis, a closed-loop compensator is designed, which achieves the stable operation with the ZVS variable frequency and phase shift modulation. The analysis results are verified by the simulation and experimental results.

Electrification of transportation offers clear national energy security benefits but unclear climate benefits. With the current heterogeneity of grid electricity mix in China, greenhouse gas (GHG) benefits of battery electric vehicles (BEVs) vary dramatically with location. Currently, compared to baseline conventional gasoline vehicles, BEVs in north and northeastern Chinese provinces have very modest (∼10-20%) well-to-wheel (WTW) GHG benefits, whereas BEVs in southern provinces have substantial benefits (∼50%). With the expected transition to a more renewable electricity mix documented here, regional effects will largely disappear and the benefits of BEVs will be substantial (∼60-70% lower than current internal combustion engine vehicles (ICEVs) and ∼10-40% lower than 2030 advanced hybrid electric vehicles (HEVs)) across the whole of China by 2030. GHG emissions from BEVs in Chinese cities (Beijing, Shanghai, Chongqing, and Pearl River Delta) and United States cities and regions (New York; Washington, DC; Chicago; New England; Texas; and California) in 2015 and 2030 are evaluated and compared. BEVs in Chinese cities will still have substantially higher WTW GHG emissions than those in New York, New England, and California in 2030.

Soluble Hf-containing polymers are significant processable precursors for the fabrication of ultra-high temperature ceramics. In this work, cyclic Hf-Schiff base polymers were synthesized via direct polymerization of hafnium alkoxide and bis-salen monomers. The defined structure and molecular weight of the polymers were characterized by NMR spectroscopy, gel permeation chromatography and MALDI-TOF mass spectroscopy. The feed ratio of monomers regulated the molecular weight and solubility of the polymers. This synthetic strategy features simple operation under ambient conditions, efficient reaction with high yield and cyclic polymers as the main products. The Hf-Schiff base polymers were converted to HfC/C materials after pyrolysis under argon at 1600 °C, which was identified by XRD measurements, elemental analyses and Raman spectroscopy. This work will inspire more precise and efficient synthesis and applications of metallopolymers.

In the present study, the quasi-static and fatigue behavior of chopped glass fiber reinforced sheet molding compound composite was investigated. Considering the stochastic meso-structure induced by processing, fiber orientation within specimens was analyzed based on the sectional images obtained by X-ray Computerized Tomography (XCT). Quasi-static tensile and compressive tests were conducted, in which the strain distribution was recorded by Digital Image Correlation (DIC) system. The fatigue behavior of material was evaluated under tension–tension (R = 0.1) and tension–compression (R = -1) loading. Interrupted fatigue test was conducted to investigate the damage evolution on the side surface of specimen using optical microscopy. A modeling method based on Representative Volume Element (RVE) was modified and applied to predict the fatigue behavior of glass fiber SMC. The simulation result showed a good consistency with experimental results on both prediction of the fatigue life and the damage mechanisms under cyclic loading.

Given the growing popularity of wearable smart watch with the capability to detect human hand movements, this paper studies the potential to recognize fatigue driving based on steering operation by using a wearable smart watch. The sensor data used includes acceleration and angular velocity data related to drivers’ operation behavior. We analyze the sensors’ data features of smart watch under drivers’ fatigue and normal states, and select 13 principal characteristic parameters by using the method of principal component analysis (PCA). Then the recognition model of fatigue driving based on support vector machine (SVM) is established. The results show that the proposed method recognizes the drivers’ fatigue or normal state more effectively than other methods and its accuracy can reach 83.29%.

We present a novel method to fabricate SiBCN ceramic components with complex shapes from preceramic polymers by using digital light processing (DLP) 3D printing technology in this research work. The photocurable precursor for 3D printing was prepared by blending high ceramic yield polyborosilazane with photosensitive acrylate monomers. The material formulation and printing parameters were optimized to fabricate complicated SiBCN ceramic components with high precision. The printed SiBCN ceramic materials were pyrolyzed at different temperatures, and retained their fine features after pyrolysis. Their microstructures were characterized by FTIR, XRD and TEM respectively. Furthermore, the thermal stability and mechanical properties of the SiBCN ceramic samples were investigated and discussed in detail. The 3D printed SiBCN ceramic material exhibited excellent thermal stability and resistance to high temperature oxidation up to 1500 °C.

Monolithic titania (TiO2) aerogel was fabricated by using bacterial cellulose (BC) as the bio-template and preceramic polymer as titanium resource, via freeze-drying and two-step calcination process. As-prepared TiO2 aerogel BCTi-air-2 h possessed low bulk density (0.04 g/cm3) and moderate mechanical strength. SEM images showed that TiO2 aerogel was composed of 3D reticulate TiO2 nanofibers. The anatase crystalline structure of TiO2 with crystal size around several nanometers was revealed by XRD measurements. N2 adsorption/desorption analysis indicated that TiO2 aerogel possessed high specific area (115 m2/g) and macroporous structure, which contributed to the high photocatalytic activity. Most importantly, the monolithic state will ease the usage, recycling, and regeneration of TiO2 aerogel as photocatalyst.

Preceramic oligosilazane was applied as a waterproof hydrophobic surface coating for electromagnetic wave-transmitting material (silica cloth-reinforced bismaleimide laminated composite). Oligosilazane spread readily on the surface of the material, due to its good wetting ability, enabling formation of silazane coatings using various processing methods such as spraying, dipping, wiping, etc. When using oligosilazane containing micrometer-sized silica particles as filler, a hydrophobic surface was realized after moisture curing under ambient condition. The hydrophobic surface with oligosilazane coating inhibited water absorption shows promise for application as a waterproof surface coating of electromagnetic wave-transmitting materials.

Casting pores are regarded as the main factor causing stress/strain concentrations, facilitating the initiation of microcracks and shortening the plasticity of a cast component. The influence of pore characteristics (i.e., size, morphology, and position) on local stress concentration in a High Pressure Die Cast (HPDC) AM60 sample is studied utilizing X-ray tomography (XRT) and image-based finite element (FE) techniques. Heterogeneous porosity distribution is identified in terms of volume fraction and projected area ratio per segment. Statistically results demonstrate that small pores (volume 0.01 mm3) account for a very low number frequency (0.3%), and complex shape. The present study addresses the local stress/strain behavior in a cast-pore containing HPDC AM60 sample during tensile loading investigated using 3D image-based models which consider the actual size, morphology, and spatial distribution of pores based on XRT images and consider the actual material properties of the AM60 alloy. Simulation results show that the local stress/strain around a pore evolves progressively with deformation. The strain at a certain pore location may be amplified or reduced in the presence of other pores, depending on the specific location of the concerning pores. Also, the ratio between the projected area of a pore and its shortest distance to the free surface (PA/SD) could give a good indication of the max local stress concentration around the pore surface. The weakening of K t pl values of pores found in defect bands are principally due to the pore orientation concerning the load direction. These findings may be extended to provide additional insight into the damage mechanisms in material containing casting pores and to enhance understanding of the ductility variation in terms of local deformation fields around pores and their interactions.