This paper presents a spherical robot driven by flywheels with low control torque, which combines terrain adaptability with flexible steering capability. The robot's center of mass is located below the sphere center, enabling sustained oscillations on the ground. Meanwhile, by periodically swinging its heading from side to side, the robot walks forward, eventually achieving locomotion along a zigzag trajectory. The robot can accumulate energy via oscillation under flywheel excitation, reducing the torque requirement and enabling a small actuator to drive a relatively heavy system. Experiments validate the robot's locomotion performance across various scenarios. The proposed actuation scheme demonstrates balanced performance while achieving lower torque demand under comparable normalized conditions.

Low-Mach thrust vectoring control for micro turbojet powered low-altitude manned air vehicles requires an externally attached conical vector nozzle that redirects the exhaust flow. However, the geometric rules governing the compromise between thrust retention and vectoring effectiveness remain insufficiently quantified. In this study, a three-dimensional steady compressible Reynolds-averaged Navier-Stokes model was established for the engine aft section, vector nozzle, and near-field flow region. The diameter ratio 7D and length-to-diameter ratio 7L were used to characterize the outlet expansion level and streamwise development length of the vector nozzle, respectively. A total of 128 non-deflected configurations were first calculated, and representative deflected cases were further analyzed at B = 5 degrees, 10 degrees, 15 degrees, 20 degrees. The numerical setup was supported by grid independence, engineering consistency, and turbulence model sensitivity checks. The results show that the nozzle thrust first increases and then decreases with increasing 7D, with the maximum thrust appearing at 7D = 1.0 similar to 1.2 under non-deflected conditions. The thrust also exhibits a non-monotonic variation with 7L, indicating that outlet expansion and internal flow development must be geometrically matched. Under deflected conditions, the thrust optimal and thrust vectoring efficiency optimal 7D are different: 7D approximate to 1.2 favors thrust retention, whereas 7D approximate to 0.8 improves flow turning and vectoring efficiency. It provides a favorable balance between wall guided momentum redirection and suppression of separated asymmetric flow at 7L approximate to 1.8. Flow field analysis indicates that the performance variation is governed by outlet expansion matching, asymmetric pressure redistribution, wall attachment, and separation development. Within the investigated operating and geometric range, 7D = 0.8 and 7L = 1.8 are identified as a favorable design candidate rather than a universal optimum, providing an important reference for vector nozzle parameter selection in micro turbojet vector control applications.

Ti(C,N)-based cermets are important materials for cutting tools and wear-resistant applications because of their excellent hardness, and thermal stability. Nevertheless, enhancing their efficiency by improving the microstructure, mechanical properties, and wear resistance is still complicated. This work examined how La2O3 addition affects the microstructure, mechanical properties, thermal stability, and tribological performance of Ti (C,N)-based cermets. Ball milling and vacuum sintering were used to produce the samples containing various La2O3 contents. Ball-on-disk wear tests were used to examine the tribological properties of Ti(C,N)-based cermets. The incorporation of La2O3 improved the microstructure of samples by refining the grain size of hard phase. La2O3 enhanced the mechanical properties of Ti(C,N)-based cermets, achieving a maximum Vicker's hardness of 1640 Kgf/mm2 (L1 cermet with 0.5 wt% La2O3) and fracture toughness of 10.0 MPa.m1/2 (L3 cermet with 1.5 wt% La2O3). However, the incorporation of excessive La2O3 minimizes transverse rupture strength (TRS) from 1495 MPa (T sample) to 900 MPa (L3 cermet). Among these three La2O3 contents, Ti(C,N)-based cermet incorporated with 1.0 wt% La2O3 (L2 cermet) has the highest wear resistance, with a wear rate of 2.49 x 10-6 mm3/(Nm).

Due to the advantages of reduced torque ripple, enhanced fault tolerance, and superior power density, dual three-phase permanent magnet synchronous motors (DTPPMSMs) systems are widely adopted in high-power applications. However, during motors operation, critical parameters exhibit time-varying characteristics due to multi-factor influences such as temperature rise effects and magnetic saturation effects, leading to degradation of control performance. To achieve realtime acquisition of motor parameters, this paper proposes a novel online parameter identification method based on highfrequency harmonic voltage injection. By utilizing the inherent harmonic subspace of space vector decoupling (VSD), voltage signals are injected into the torque-insensitive harmonic plane to prevent coupling with fundamental plane excitation. Through extraction of current responses at the injection frequency, harmonic impedance components are derived via frequencydomain demodulation, enabling precise estimation of stator resistance and leakage inductance. This method effectively isolates identification parameter from non-ideal error sources by frequency-selective processing.

Silicon carbide (SiC) mosfets with Kelvin-source connection are widely used in power converters based on a bridge configuration circuit, but crosstalk significantly impacts reliability and limits their application potential. For this problem, this article presents an active gate driver (AGD) based on hardware closed-loop control. A simple hardware closed-loop controller is designed to regulate the gate-source voltage of SiC mosfets. For aspect one, the closed-loop structure can reduce the peak voltage of crosstalk online. For aspect two, since the closed-loop structure can ensure the convergence of the gate-source voltage, a higher drive voltage is then permitted to shorten switching time and power loss. Compared with conventional methods, the proposed AGD can suppress crosstalk without adding switching loss. Experimental results verify the superiority of the proposed AGD for the SiC mosfet-based bridge configuration circuit.

This article provides a tradeoff study of torque and rotor losses, including the permanent magnet (PM) loss and core loss, in permanent magnet vernier machines (PMVMs), for in-wheel traction. Firstly, the analytical models of PM loss, core loss, and torque are established, and the core loss is calculated by three methods. Besides, the influencing factors on toque and losses are extracted. Secondly, the influence of stator and rotor topologies on torque and losses is studied, and the contribution of flux density harmonic on PM loss, core loss, and torque in various topologies and slot-pole combinations are calculated and compared, where both sub-harmonics and slot harmonics are mostly responsible for core loss and PM loss. Next, the rotor flux barrier in d-axis path is introduced. The influence of flux barrier dimensions on air-gap flux density, core loss, PM loss, and torque is carried out, and it shows that the modulated flux density is reduced with flux barrier, which helps to reduce PM loss. Moreover, the decay rates of losses and torque under the typical conditions are extracted. The PM loss has the dramatic decrease compared with the other ones, but the torque also decreases slightly, which can validate the applicability and correctness of the rotor flux barrier. Finally, a PMVM and a benchmark PMSM are manufactured and tested to validate the theoretical analysis and finite-element analysis (FEA). This article aims to provide the tradeoff design between torque and losses, and introduce a flux barrier solution to alleviate the design conflicts in PMVM for in-wheel traction applications.

In this paper, we developed models for 21 quinary high-entropy transition metal carbide ceramics (HETMCCs), composed of carbon and the transition metals Ti, Zr, Mo, V, Nb, W, and Ta, employing the Special Quasirandom Structures (SQS) method. We investigated how the transition metal elements influence lattice distortion, mixing enthalpy, Gibbs free energy of mixing, and the electronic structure of the systems through first-principles calculations. The calculations show that 21 systems can form a stable single phase, among which (TiMoVNbTa)C5, (ZrMoNbWTa)C5, and (MoVNbWTa)C5 exhibit superior stability. The formation energy and migration energy of carbon vacancies in systems with strong single-phase stability were calculated to predict their radiation resistance. The formation energy of carbon vacancies is closely related to the types of surrounding transition metal elements, with values ranging between the maximum and minimum formation energies observed in binary transition metal carbides (TMCs). The range of migration energy for carbon vacancies is wider than that observed in TMCs, which can hinder their long-range migration and enhance the radiation resistance of the materials.

The solid solution is a widely used and effective approach at a low cost to achieve desirable properties. Here, we performed theoretical investigation on a series of binary-A solid solution MAX (SS-MAX) phases, i.e., Ti3(Al1-xAx) C2 SS (A = Ga, In, Tl, Si, P, and S; x = 0-1 in 0.25 increments). Under the insight of the mixing enthalpy Delta H mix Gibbs free energy Delta G mix , and formation enthalpy H cp , S-alloyed MAX phases were evaluated to be unstable and are further corroborated by experiments. Interestingly, the bulk modulus of Ti3(Al0.75AGa0.25)C2 (Ti3(A- l 0.75 In 0.25 )C 2 ) unusually showed an approximate 12.8 % (11.1 %) enhancement than that of Ti3AlC2 and 11.0 (17.1 %) enhancement than that of Ti3GaC2 (Ti3InC2). Moreover, the elastic moduli were exclusively enhanced by A elements capable of reducing triangular prism distortions. The anisotropic behavior was also revealed and interpreted as that the group IIIA elements (Ga, In, Tl) showed a pronouncedly strengthened effect on the intralayer bonding states, while Si and P acted on the interlayer interaction. Ti3(Al1-xSix)C2 presented strong resistance to phonon scattering, resulting in their similar lattice thermal conductivities. The phenomena and the underlying physics driven by the MX-A interlayer interaction will not only provide insights into manipulation multi-site/lattice materials but also pave the way for accelerating the developments and applications of high entropy MAX phases.

By regulating the proportion of large and small boron nitride particles, BN-ZrO2-SiC composites with particle gradation are designed. Through the strategy of particle grading, small particles could be filled into the "cardhouse structure" formed by h-BN with large particle size, promoting the densification process. At the same time, this also shortens the mass transfer distance between particles, which is conducive to the mass transfer during the hot-pressing sintering. On the basis of achieving the second phase strengthening effect, the performance of hexagonal boron nitride composite has been further improved. The results demonstrate that by a volumetric proportionality of 6:4 between the constituent large particle (7 mu m) and small (1 mu m) particle. Thus, the BN-ZrO2SiC composite with high density has been successfully fabricated at a sintering temperature of 1700 degrees C under 25 MPa. The optimization mechanical properties of BN-ZrO2-SiC composites are achieved when the volumetric ratio of large particle (7 mu m) to small (1 mu m) particle is 6:4. The optimal flexural strength, fracture toughness, Vickers' hardness and elastic modulus is 187 f 4 MPa, 2.2 f 0.3 MPa m1/2, 0.74 f 0.06 GPa, and 57 f 1.1 GPa, respectively. Comparing to the h10 and H10 sample, the thermal conductivity of samples with particle size gradation has been improved, especially the H8h2 and H4h6 samples. The thermal conductivity is significantly enhanced from 14.79 W/(m center dot K) to 16.83 W/(m center dot K).

A novel alpha/beta SiC-(Ti, Nb)B-2 toughened (Ti, Nb)C-based composites was fabricated by reactive hot pressing with TiC, NbB2 and Si powders at 1500 degrees C and 1600 degrees C, respectively. The influence of NbB2, Si content, and sintering temperature on the microstructure and mechanical properties of the composite was investigated. The intermediate product NbC reacts with Si to form NbSi2 and beta-SiC phases. With addition of 10 mol% NbB2, a toughening phase alpha-SiC was formed. During the reaction process, insufficient diffusion of Nb atoms in TiC leads to the formation of a specific "core-shell" microstructure, which improves the flexural strength of the composite ceramics. The (Ti, Nb)C has a specific crystallographic orientation relationship with NbSi2 and alpha-SiC. The high-density stacking faults and ordered structures in beta-SiC crystals enhances its hardness. The rod-shaped alpha-SiC and plate-like (Ti, Nb)B-2 by in situ reactions effectively improve the fracture toughness of the composites. TiC-32 mol% Si-10 mol% NbB2 (raw powder composition) sintered at 1600 degrees C has excellent comprehensive mechanical properties, with fracture toughness, flexural strength, and Vickers hardness of 5.45 MPam(1/2), 665 MPa, and 22 GPa, respectively, which provide a new insight into the optimization strength and toughness of TiC-based composites. In addition, under high temperature oxidation of 1000 similar to 1200 degrees C, the 30NB (54 mol% TiC-16 mol% Si-30 mol% NbB2) sample has better high-temperature oxidation resistance than the 30ZB (54 mol% TiC-16 mol% Si-30 mol% ZrB2) sample.

This work investigates the effect of preheating air temperature on the sooting tendency in the laminar co-flow diffusion flames of n-heptane. A modified co-flow burner was employed to produce steady n-heptane laminar diffusion flames with the preheating temperatures of co-flow air varying from 344 K to 588 K. The planar laser-induced incandescence (LII) calibrated by the line-of-sight attenuation (LOSA) was performed to quantitatively measure the soot volume fraction and the soot yield in flames and an ICCD camera was used to capture the flame luminosity images. The results reveal that the visible flame height is decreased with the preheating co-flow air temperature, and it is hardly affected by the air velocity with a constant air temperature. As the co-flow air temperature increases, the soot inception and oxidation and the peak soot concentration initiate at the lower positions in flames, and the soot loading in flames has a remarkable increasing trend by assessing the evolution of the soot volume fraction and the soot yield. However, the enhancement rate of total soot loading in flames with the co-flow air temperature below the initial fuel temperature is lower than that for the co-flow air temperature above the initial fuel temperature. In addition, the temperature sensitivity of soot loading is assessed by the maximum soot volume fraction, which is in accordance with those of the alkane in previous research. According to the response of the maximum soot yield to the co-flow air temperature and adiabatic flame temperature, the temperature sensitivity of sooting tendency in n-heptane flames is further confirmed.(c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

•The dual-phase high-entropy ceramics (HECs) were first designed and fabricated using reaction-driven inter-diffusion processes among ZrB2, HfB2, NbB2, TaB2, and TiC.•The inhomogeneity of element distribution in boride and carbide phases was quantitatively investigated.•The novel diboride-carbide HECs showed outstanding mechanical properties as compared with other single-phase HEC samples.

The grain growth kinetics and densification mechanism of (TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work. A single phase carbide with a rock-salt structure is formed until 2300 °C, below which an apparent aggregation of V, Zr and Hf exists. It is associated with the slow diffusion rate of V element as well as the relatively poor solubility of VC in HfC (as well as ZrC). The grain growth mechanism gradually changes from surface diffusion to volume diffusion and then grain boundary diffusion with increasing sintering temperature. This is attributed to the variation of activation energy of grain growth. The densification mechanism is principally dominated by the mass transport through lattice diffusion with the activation energy of 839 ± 53 kJ/mol. Through the design of two-step sintering, it is verified that the solid solution formation can effectively promote the densification process.

Dense (Zr, Ti) (C, N) ceramics were fabricated by spark plasma sintering (SPS) at 1900-2000 degrees C using ZrC, TiCN and ZrH2 powders as raw materials. A single Zr-rich (Zr, Ti)(C, N) solid solution was formed in Zr0.95Ti0.05C0.975N0.025 and Zr0.80Ti0.20C0.90N0.10 ceramics (nominal composition). A Ti-rich solid solution appears in Zr0.50Ti0.50C0.75N0.25 ceramics. The coaddition of TiCN and ZrH2 promoted the densification of (Zr, Ti) (C, N) ceramics by forming solid solutions and carbon vacancies, which could reduce critical resolved shear stress (CRSS) and promote carbon and metal atom diffusion. ZrC-45 mol% TiCN-10 mol% ZrH2 (raw powder composition) possesses good comprehensive mechanical properties (Vickers hardness of 24.5 +/- 0.9 GPa, flexural strength of 503 +/- 51 MPa, and fracture toughness of 4.3 +/- 0.2 MPamiddotm(1/2)), which reach or exceed most ZrC-based (Zr, Ti) C and (Zr, Ti) (C, N) ceramics in previous reports.

(TiZrHfVNbTa)C-x with variable stoichiometry are fabricated by pressureless sintering utilizing self-synthesized carbide powders via carbothermal reduction reaction. The densification behavior and microstructure evolution coupled with corresponding adjustable mechanical properties are investigated. The single-phase rock-salt crystal structure is retained despite the carbon stoichiometry approaching 0.6, indicating (TiZrHfVNbTa)C-x can maintain structural stability even containing high carbon vacancy. The carbon vacancy is beneficial for promoting densification procedure. The relative density of (TiZrHfVNbTa)C-0.6 sintered at 2150 degrees C can reach 97.9 %, while the similar value for (TiZrHfVNbTa)C-1.0 is obtained even at 2400 degrees C. While, remarkable grain growth accompanied by decline in relative density also occurs for lower carbon stoichiometry. With the variation of carbon content, the concentration of carbon-metal bonds changes gradually, leading to the adjustable mechanical properties. This work provides a potential approach to synthesize non-stoichiometric high-entropy carbides with high carbon vacancy via low-temperature pressureless sintering.

In this paper, a permanent magnet vernier motor (PMVM) topology with flux barriers that can suppress the permanent magnet eddy current (EC) loss is proposed. Through the combination of theoretical analysis and finite element analysis (FEA), it is revealed that flux barriers can suppress permanent magnet eddy current loss by reducing the amplitude of the modulated harmonic flux density. By establishing a series of finite element analysis models of permanent magnet vernier motors and permanent magnet synchronous motors (PMSMs), it is verified that flux barriers can greatly reduce the permanent magnet eddy current loss and iron loss while having less effect on the torque. The influence of flux barriers on the torque and loss of the motors with different motor types and different slot-pole combinations under different working conditions is compared, and the influence of flux barrier width variation on torque and loss is studied. Finally, the application of flux barriers in different type vernier motors and different operating conditions is summarized.

Under simulated flue gas conditions, the effect of the residence time of different chars on the evolution of physiochemical structures during the NO reduction process was evaluated. The experimental data proved that the acid-soaking treatment contributed to the development of char structures. Both biomass chars and H-form chars showed better reactivity on NO reduction, which may be related to smaller average pore diameters, larger BET surface areas and larger pore volumes. The increasing of residence time increased the graphitization degree of all chars, and main reductions of structural defects were from within and between carbon graphene layers. Besides, with the residence time increasing, N-6 and N-5 of R-form Shenmu chars were transformed into N-Q and N-X, while N-X and N-Q (and some N-5) of R-form and H-form sawdust chars were transformed into N-6, which is related to the oxidation or reduction reaction for different chars.

A multicomponent (TiZrHfNbTaMo)C ceramic has been fabricated by pressureless sintering at temperatures from 2100 °C to 2500 °C, using an equimolar multicomponent carbide powder synthesized by carbothermal reduction as the starting material. Influence of sintering temperature on densification, microstructure and mechanical properties of the ceramics was investigated. The relative density increases with increasing sintering temperature, and a nearly fully dense sample is achieved by pressureless sintering at 2500 °C. Average grain size increases from 3.7 to 15.2 μm with increasing sintering temperature from 2300 to 2500 °C. The (TiZrHfNbTaMo)C ceramic sintered at 2400 °C exhibits a single phase fcc structure with homogeneous chemical composition, an average grain size of 7.0 μm and a relative density of 96.5%, while its measured hardness is 33.2 GPa at 100 mN and 23.2 GPa at 9.8 N.

The char reactivity generally determines the overall efficiency of the whole gasification process of coal, so it is of great significance to deeply understand the factors influencing the char reactivity and the coupling mechanism between them. This study aims to investigate the combined impacts of intrinsic alkali and alkaline earth metals (AAEMs) and chemical structure of organic matter on char reactivity, and provide new evidence for confirming the controversial role of water-soluble AAEMs during char gasification. Four series of char samples prepared from Zhundong coal containing different forms of intrinsic AAEMs were isothermally gasified by air in TGA, obtaining the specific reaction-rate curves, and a reasonable evaluation index of char reactivity was established. The carbon skeleton structure of char surfaces was analyzed by Raman spectroscopy. The comprehensive discussion of chemical structure, AAEMs state and char reactivity indicates that the water-soluble AAEMs reduce the char reactivity in the early part of gasification process, which is due to the catalytic cracking of aromatic C-H caused by these substances on char surfaces during pyrolysis, while improving the char reactivity in the later part because of the original catalysis of these substances on gasification; the ion-exchangeable AAEMs significantly catalyze the opening of aromatic rings in char during gasification, especially the small rings, which weakens the reaction priority of aliphatic structures; the increasing pyrolysis temperature results in the ordering of chemical structure and the enrichment of ion-exchangeable AAEMs, and the former reduces the char reactivity, while the latter has the opposite effect; at the pyrolysis temperature of 400-600 degrees C, the enrichment of ion-exchangeable AAEMs is the main factor controlling the char reactivity, while at 700-1000 degrees C, the ordering of chemical structure plays a dominant role.