Search

Side-chain alkylation of toluene with methanol is a green pathway to realize the one-step production of styrene under mild conditions, but the low selectivity of styrene is difficult to be improved with by-products of ethylbenzene and xylene. In this study, a new way is introduced to improve the catalytic performance by means of assisting basic compounds as co-catalysts during the toluene side-chain alkylation with methanol to styrene. As a result, high activity of side-chain alkylation appears over the basic Cs-modified zeolite catalysts prepared by ion exchange and impregnation methods. This high performance should be mainly attributed to two co-catalysis actions: (1) the promotion of basic compounds for methanol dehydrogenation to formaldehyde as the intermediate for side-chain alkylation; (2) the suppression of the styrene transfer hydrogenation on basic Cs-modified zeolites to avoid the formation of ethylbenzene. Especially for Cs2O/CsX-ex catalyst, the addition of 2 mol% 2-picoline in reaction mixture could achieve both 12.3% toluene conversion and 84.1% styrene selectivity. Whereas the higher concentration of 2-picoline (>6 mol%) caused an inhibition to the catalytic activity because the excessive basic compound poisoned the combined acid-base pathway required for the side-chain alkylation process. In addition, two possible side-chain alkylation reaction routes on Cs-modified zeolite under the different 2-picoline absorption were described.

Excellent radiation resistance is a prerequisite for pressure-sensitive hydrogels to be used in high-energy radiation environments. In this work, tannic acid-modified boron nitride nanosheet (BNNS-TA) is first prepared as the radiation-resistant additive by a facile one-step ball milling of hexagonal boron nitride and tannic acid. Then, polyacrylamide (PAAm)-based pressure-sensitive hydrogel doped with BNNS-TA and Fe3+ ions is fabricated. The ternary BNNS-TA/Fe3+/PAAm hydrogel exhibits excellent compressive strength (at least four times the compressive strength of unfilled pure PAAm hydrogel), pressure-sensitive performance (gauge factor is up to 1.4), and performance recovery due to the combination of multiple intermolecular interactions, such as covalent crosslinking, hydrogen bonds, and ion coordination interactions. The BNNS-TA/Fe3+/PAAm hydrogel can be made as a pressure sensor installed in the control circuit or attached on the human body to detect human activities accurately. More importantly, the compressive strength and the pressure-sensitive performance of the BNNS-TA/Fe3+/PAAm hydrogel can be maintained after the hydrogel is irradiated by 60Co gamma-ray at an absorbed dose of 15 kGy. As a comparison, the compressive strength of the unfilled PAAm hydrogel is only a quarter of that before irradiation. This work not only reveals a facile method to achieve the preparation of chemically modified BNNS as a promising radiation-resistant additive but also provides a novel strategy for the development of pressure-sensitive hydrogel devices in radiation environments.

The broad learning system (BLS) is designed based on the technology of compressed sensing and pseudo-inverse theory, and consists of feature nodes and enhancement nodes, has been proposed recently. Compared with the popular deep learning structures, such as deep neural networks, BLS has the ability of rapid incremental learning and can remodel the system without the usual tedious retraining process. However, given that BLS is still in its infancy, it still needs analysis, improvements, and verification. In this article, we first analyze the principle of fast incremental learning ability of BLS in depth. Second, in order to provide an in-depth analysis of the BLS structure, according to the novel structure design concept of deep neural networks, we present four brand-new BLS variant networks and their incremental realizations. Third, based on our analysis of the effect of feature nodes and enhancement nodes, a new BLS structure with a semantic feature extraction layer has been proposed, which is called SFEBLS. The experimental results show that SFEBLS and its variants can increase the accuracy rate on the NORB dataset 6.18%, Fashion-MNIST dataset by 3.15%, ORL data by 5.00%, street view house number dataset by 12.88%, and CIFAR-10 dataset by 18.42%, respectively, and the four brand-new BLS variant networks also obviously outperform the original BLS.

The last mile relief network is the final stage of the relief chain but the most critical stage for ensuring the timely delivery of relief supplies after a disaster. Due to the suddenness of the di...

In the single-point diamond turning (SPDT) of optical spherical/aspheric surface, tool deviating from the spindle rotation center significantly deteriorates the form accuracy of the spherical/aspherical surface and its optical performance. In this study, the influence of tool deviation on the form accuracy of a convex spherical surface and the cutting force forms during the turning process were studied first, following which a force-based tool deviation model was derived to identify the tool deviation using cutting force. Finally, by analyzing the influence of tool deviation on the three-dimensional (3D) form of residual structures at the center of the convex spherical surface, the 3D form of the convex spherical surface was predicted online. Results indicate the existence of a mapping relation between the tool deviation and the cutting force form, which could be further used to online predict the 3D form of the machined convex spherical surface in SPDT through the established geometric model.

This paper investigates the adaptive neural tracking control of the strict-feedback nonlinear systems, where the states are measured in an event-triggered manner so as to save the communication resources. As the neural networks (NNs) account for the unknown dynamics of the system, the minimum learning parameters (MLPs) are extracted from the weights of the NNs and the upper bounds of the disturbances. The estimates of the MLPs are updated in an event-triggered manner to ensure the approximation ability of the NNs and the stability of the closed-loop system. An adaptive neural model is established to substitute for the original strict-feedback system and direct the design of the backstepping-based control laws. The states of this adaptive model are reset to the measured states of the original system when the triggering condition is violated. The triggering condition is constructed in the compound form and with the adaptive threshold. The dead-zone operator is involved to avoid the accumulation of triggering instants. In this paper, we notice the problem of "jumps of virtual control laws" for the event-triggered control (ETC) in the backstepping frame, and a detailed formulaic definition is given in section 2.2. To solve this problem, the first-order filters are fabricated to provide the continuous substitutes for virtual control laws. In addition, the "complexity explosion" generated by direct differentiating of virtual control laws can be averted. Through the proposed scheme, the closed-loop system can be viewed as an impulsive dynamic system, and the semi-globally uniformly ultimate boundedness (SGUUB) of all the errors is proved. Finally, two examples validate the feasibility of the proposed control scheme.

With the large-scale grid connection of wind and photovoltaic power, the contradiction between renewable energy and thermal power is becoming more and more serious. To solve this problem, this paper comprehensively considers the construction and operation costs of power plants, and constructs an optimal generation expansion planning model of a combined thermal–wind–photovoltaic​ power system with the objective of minimizing total cost. The planning is calculated under the boundary conditions of ensuring the safe operation of the power grid and taking into account the share requirement, utilization requirements and construction requirements for renewable energy. The model is applied to the self-use and supporting power plants in Xinjiang. The results show that the proposed generation expansion plan can realize the coordinated development of three types of power sources under multiple boundary conditions, which has good applicability.

Lack of electricity networks in remote areas and also the high cost of connecting these areas to national networks due to the unfavorable geographical situation of the region leads to the use of other energy sources independent of the network in these areas. Today, the use of distributed generation sources is increasing due to the reduction of fossil fuel sources and heat problems. The output power of distributed generation sources, especially renewable energy sources, fluctuates under the influence of atmospheric conditions. The main purpose of the present study is to present a new optimal configuration for a hybrid photovoltaic/diesel generator/battery system to refine the load demand of a rural area in Hoxtolgay, China. The idea is to minimize the CO2 emissions value, the annualized cost, and the loss of load probability of the system. To simplify this system, e -constraint method is performed. The problem has been solved by an adaptive version of Marine Predators Algorithm (AMPA) to improve the optimization results. The total ACS for the optimal system is achieved 8224.15 $. Also, an optimal value of 451.30 kW for diesel generator, 4266$ for battery storage, and 2670.53 $ for PV generator are achieved. The initial capital cost of the system is achieved 47940 $ that is less than the NPC. In this case, the maximum cost of the system with 43.12% belongs to the PV system of total cost of the system. Finally, CO2 emission by the suggested AMPA with 1624 kg/year shows the minimum value with cleanest result among the others. Final results of the proposed technique are compared with PSO method and HOMER-based optimization to indicate its effectiveness. Sensitivity analysis has been also performed to determine the system efficiency.

As a novel method to reduce the temperature during electron beam welding, and to subsequently inhibit interfacial reaction between SiC and Al matrix, the electron beam surface heating - diffusion bonding is proposed for joining SiC particle reinforced aluminum alloy metal - matrix composite of 45 vol.% SiC/2024 Al. The defocused electron beam was used to heat the base metal surface, and the simultaneous pressure was applied to the butt surface to achieve bonding. The base metals were successfully joined by diffusion. The maximum temperature of the whole joint was effectively decreased to less than 650 ℃. The Gibbs free energy change of interfacial reaction was calculated, meaning a positive value reaching 218 kJ/mol and a consequently prominent inhibitory effect on the formation of brittle Al4C3 that was proved by microstructural observation. The tensile strength for the bonded joint was increased by 35 % compared to that for ordinary welded joint. When the TC4 layer was added, TiC strengthening particles were formed with the deficiency of Al4C3, corresponding to the significantly increased tensile strength of 63 % of base metal (154 MPa).

The use of a biological dust suppressant for the prevention of mine dust was explored. A biological dust suppressant was prepared with Bacillus pasteurii, CaCl2 and urea as raw materials. The results show that the surface tension of the bacterial solution and the CaCl2-urea solution was 32.517 and 32.595 mN/m, respectively, which had a good effect on wetting coal dust. When the concentration of CaCl2-urea solution was 0.6 mol/L, the yield of mineralized products was the highest. In addition, the urease activity was the strongest. According to the wind resistance test, when the volume ratio of the bacterial solution to the CaCl2-urea solution was 1:1 and the CaCl2-urea solution was 0.6 mol/L, the dust suppression effect was the best. The above results show that MICP is a mine dust control technology with strong development prospects.

The booming development of online social media has changed the way people post and access information. The authenticity of content is weakened, and all kinds of misinformation on social media spread rapidly. In Online Social Networks (OSN), users arbitrarily form private groups/communities, which greatly increase the exposure rate of misinformation. Considering that echo chamber effect of groups wildly exists, this paper studies the disbanding strategy of private groups in OSNs to Minimize the Spread of Misinformation under the effect of Echo chamber effect (MSME). Given a directed acyclic OSN G ( V , E , C ) , C denotes a set of private groups, the problem of MSME is to select K groups from C , such that the spread of misinformation will be minimized by disbanding these groups. We prove the problem of MSME is NP-hard, then prove that the objective function computation of the problem of MSME is #P-hard. It is proved that the objective function of the problem of MSME is neither a submodular nor a supermodular. A greedy algorithm is constructed and several heuristic algorithms are proposed to solve the objective function which is non-submodular and non-supermodular. Our experimental simulation on four real world datasets verifies the effectiveness of our constructed algorithm.

Natural disasters not only inflict massive life and economic losses but also result in psychological damage to survivors, at times even causing social unrest. It is necessary to design a sustainable last mile relief network for distributing relief supplies regarding social factors, disaster relief efficiency as well as the economic cost of three perspectives in terms of sustainability. We establish a multi-objective distributionally robust optimization model for a sustainable last mile relief network problem that maximizes the equitable distribution of relief supplies and simultaneously minimizes the transportation time and operation cost. Under the partial probability information of uncertainties, such as the disaster situation, transportation time, freight, road capacity, and demand, we characterize the uncertain variables in an ambiguity set incorporating the bounds, means and the mean absolute deviations. Then, the bounds on the objective values and the safe approximations of the chance constraints are deduced under the ambiguity sets. Based on a revised multi-choice goal programming approach, we obtain a computationally tractable framework of the multi-objective model. To verify the effectiveness of the model and methods, a case study of the Banten tsunami is illustrated. The results demonstrate our proposed model can obtain a trade-off between the equitability, timeliness and economics for relief distribution in a relief network.

In this article, a new command filtered backstepping based finite-time adaptive fuzzy tracking control scheme for a class of unknown nonlinear systems with full-state constraints is established. First, the proposed finite-time command filter will filtering the virtual control signal and get the intermediate control signal within finite-time, so the problem of calculating complexity will not occur in the backstepping process. Then, the fraction-power-based error compensate signal is set up, which can eliminate the influence of filtering error on the control performance. Considering that the unknown nonlinearities exist in the system, the fuzzy logic system based adaptive control technique is used to deal with them, and only one parameter needs to be estimated. It is shown that the states will not violate the prescribed constrains, all the signals in the closed-loop system are bounded in finite-time and the tracking error can converge to the desired neighborhood of the origin in finite time under the barrier Lyapunov function and fraction-power-based virtual control signals. Finally, the effectiveness of the control method is shown by the simulations.

The Al–Al2O3 composites were prepared by fused alumina, α-Al2O3 micropowders, and metal aluminum powder. The samples with 3% carbon black (N330), 3% resin powder and α-Al2O3 micropowder, 10% α-Al2O3 micropowder were named S1, S2, and S3, respectively. They were oxidized at 1500 °C for 3 h in a box-type electric furnace, and then the unoxidized areas were analyzed by X-ray diffraction and scanning electron microscopy. It was found that the aluminum oxycarbonitride formed in situ during the oxidation resistance test inhibited further oxidation of S2. The in situ formation mechanism of aluminum oxycarbonitride in the unoxidized zone is believed to be 7Al + 3Al3C4 + 12AlN + 4Al2O3 = 12Al3CON, which is also verified and proven by XRD, SEM and EDS in this work. The oxidation depth of S2 is 46.7% lower than that of S3. Sample S2 hardly has any linear change after fired at 1500 °C × 3 h in coke, which benefits to improve the volume stability and prolongs the service life. Among the three batches, S2 exhibits the minimum creep rate, from 0% to 0.026% at 1500 °C, and the HMOR at 1500 °C in a N2 atmosphere of S2 is 58 MPa. The Al–Al2O3 composites combined with resin strengthened by in situ formed aluminum oxycarbonitride give the composites excellent high-temperature strength owing to the fiber-intersected reinforced microstructure of Al3CON crystals at high temperature. In the Al–C–N–O system, it was found that the general formula of aluminum oxycarbonitride is expressed by Al4n+m(C,O,N)3n+m, and the (n, m) values are (0, 3) for Al3CON.

Fly ash has been widely explored in alkali-activated concrete technology as a precursor; however, it suffers sudden brittle failure and requires heat activation for early-strength development. Previous studies have demonstrated that these shortcomings can be overcome by adding nanosilica and various types of fibers. However, they were mainly focused on improving the mechanical properties, but there is no clear understanding of the durability and microstructural changes. Therefore, this study systematically addresses the effects of nanosilica sol and hybrid fibers (steel and polypropylene fibers) on the workability, porosity, flexural/compressive strength development, flexural toughness, crack resistance, and durability (subjected to sulfuric acid of pH = 1, 5% sodium sulfate, and 3.5% seawater attacks) of fly ash-based mortars cured at ambient environments. The results demonstrate that nanosilica and hybrid fibers have acceptable simultaneous effects on the properties of mortar. Although they both reduce fluidity, nanosilica improves the pore enlargement caused by fiber materials; thus, it greatly improves the mechanical properties of mortar. The flexural toughness of the mortar with nanosilica and hybrid fibers was approximately 200% higher than that of the pure-fly ash. Only approximately 58.25 mm2 microcracks were observed during the early crack detection, and the residual strength also improved under chemical solution attack. The microstructures were studied by field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction/Rietveld method, and nanoscale 3D X-ray microscopy. The nanosilica enhanced the reactivity of the precursors and refined the pore structure of the mortar due to the changes in the crystalline and amorphous phases, and the hybrid fibers produced composites with good internal characteristics and strong fiber/matrix interfacial bonding.

To analyze the influence of a curved ceiling and fire location on the combustion characteristics in a utility tunnel, the burning rate and temperature profile produced by a pool fire beneath a curved ceiling were investigated experimentally and theoretically. The results showed that oxygen supply and heat feedback from the surrounding form a competitive mechanism, determining the evolution of the burning rate. A qualitative analysis was performed to elucidate this competitive mechanism. With the fire source moving close to the sidewall, the positive influence from the heat feedback is is gradually compensated for by the negative influence from oxygen supply limitation. Moreover, it was inferred that the magnitude of decline of the burning rate near the wall has a positive correlation with heat release rate of the fire source. A characteristic inclined angle was defined to replace the changing angle of the curved ceiling along the ceiling jet path. Based on the definition of the characteristic ‘inclined angle’ concept, the relationship between the temperature profile beneath the curved ceiling centerline, tunnel height and horizontal position from fire source was unified by an empirical model. The maximum temperature delay beneath the curved ceiling centerline produced by the pool fire was analyzed by radial flow and one-dimensional flow. The proposed models for radial flow and one-dimensional flow were validated and could effectively predict the maximum temperature delay, which can be applied in utility tunnel’s fire protection engineering.

Distribution uniformity is critical to achieve high performance for proton exchange membrane fuel cell (PEMFC) stacks. In this work, air flow distribution of a 30 kW “U-type” stack of 100 unit cells is investigated by computational fluid dynamics (CFD) simulation, Burgers vortex model is introduced to describe the mechanism of flow maldistribution. Three cases are presented to evaluate the effects of vortexes on the distribution uniformity under various average current densities, and obtain optimized design for better uniformity. The results show that the vortexes usually generate in the feed header, the flow vortex structures are governed by the feed header’s configuration. The distribution uniformity reduces dramatically with the increase of current density and the generation of vortexes. The cells that locate in the positions of vortexes get less flow allocation than other cells, distribution uniformity can improve by optimizing the feed header’s configuration to change the vortex structure of flow field.

Hydratable magnesium carboxylate (HMC), which is similar to the properties of cement, can be used as a potential binder for refractory castables. However, its decomposition may lead to poor mechanical properties at medium temperatures (300 °C–1100 °C). This work investigated the effects of boric acid on the mechanical properties and microstructural evolution of castables bonded with hydratable magnesium carboxylate. The mechanical strength, bulk density, apparent porosity, thermal shock resistance, and sintering properties of the castables were evaluated. The results showed that the mechanical properties of HMC-bonded castables (HMCC) at various temperatures can be improved by adding boric acid. Boric acid reacts with HMC to form magnesium carboxylate borate ester (MCBE), which improves the bonding strength between HMC molecules. Thus, the cold modulus of rupture of HMCC containing boric acid dried at 110 °C are higher than that of calcium aluminate cement-bonded refractory castables (CACC). The decomposition temperature of MCBE is 77 °C higher than that of HMC, so MCBE can endow castables with better mechanical properties at 110 °C–500 °C. The B4C obtained by MCBE pyrolysis could form a boron-rich liquid phase, which can accelerate the structural densification of castables via transient liquid phase sintering, thus improving the mechanical properties of castables at 500 °C–1100 °C. Moreover, boric acid can improve the thermal shock resistance of HMCC. The residual strength rate first increases and then decreases with an increasing boric acid, and reaches a maximum value of 29.7% (1 wt% boric acid is added), which is 2.3 times that of the CACC. The nanoindentation test showed that the microcracks in the matrix of 1 wt% boric acid castables are easy to initiate but difficult to propagate, so the microcracks are many and wavy.

Since the production process in manufacturing industry is one of the main sources of carbon emissions, most governments have enacted relevant carbon policies to encourage manufacturers to invest in green production technology and reduce carbon emissions. However, the effectiveness of the carbon policy deserves further investigation because the manufacturers focus more on economic profits in actual operations. For this purpose, this paper proposes a dual-channel supply chain network (DCSCN) equilibrium model based on variational inequality theory to examine progressive carbon tax mechanism design of the government and its impacts on the production/pricing and abatement level decisions of the manufacturers in the DCSCN. In addition, this paper also examines the influences of the online channel introduction on supply chain network equilibrium decisions, carbon emissions and profits. We employ the modified projection and contraction algorithm to obtain the numerical solutions for several examples, and analyze the impacts of the key parameters on the equilibrium decisions and derive several managerial insights. The results show that if the government sets the high-level carbon tax and the cut-off value in progressive carbon tax policy appropriately, it can induce the manufacturers to improve abatement level actively; meanwhile the profit maximization goal of the manufacturer and the whole DCSCN can be consistent with the government's low-carbon emission target. Moreover, the introduction of online channel may depress the economic activities and lead to profit loss for the supply chain network but contributes to reducing the carbon emissions under progressive carbon tax policy. The conclusions may be useful for reference in the study of the low-carbon supply chain and the design of carbon emission reduction policy for government.

The complex mixed feeding process for the binary mixture of coal and cylindroid biomass particles in a screw feeder was numerically studied by the discrete element method (DEM). The effects of biomass feeding ratio, feeding rate, and screw rotational speed on the feeding performance were investigated with the continuity, uniformity, and stability of the mixed feeding process being emphatically discussed. The results reveal that the stability of real-time mass flow rate and biomass blending ratio performs better at higher biomass feeding ratios. A larger variability of real-time biomass blending ratio is found at low feeding rate, while increasing the feeding rate reduces the stability of real-time mass flow rate and the too high feeding rate would cause some cylindroid biomass particles being hindered by the front wall surface of the hopper. Moreover, increasing the screw rotational speed significantly increases the stability of the mixed feeding process.

An applicable method to improve the tensile properties of 2219-T8 aluminum alloy TIG welding joints is attractive in manufacturing of large propellant tanks. In this work, tensile properties of 2219-T8 TIG welded joints was improved by adjusting the weld geometry using multi -pass welding with swing. The effects of weld geometry on the tensile properties of joint were investigated. And the geometry parameters were optimized by an orthogonal experiment design. The joints with tensile strength coefficient of 70 % and elongation over 4% were acquired after weld geometry optimization. The improvement mechanisms of weld geometry attributed to the reduced strain variation rate and stress concentration at the weld toe.

Sulfur-doped carbon nanotubes (SCNTs) exhibit better conductivity and hydrophilicity, as compared to the undoped carbon nanotubes (CNTs). Low cost mass production of SCNTs is highly desirable for their real application at an industrial scale. Here, scalable green syntheses of SCNTs and S, N dual doped CNTs (SNCNTs) are demonstrated based on the gaseous S doping using SO2 as dopant. The process not only significantly promotes the hydrophilicity and conductivity of CNTs due to the incorporation of S atoms in carbon framework, but also purifies the final product due to burning off the carbon coatings of metal particles. SO2 is generated by CaSO3 pyrolysis and absorbed by CaO, thus realize the recycling of S species. The LiFePO4 cathodes using the as-prepared SCNTs and SNCNTs as conductive additive exhibit enhanced capacity and rate performance than the electrodes prepared with the pristine CNTs, not matter using N-methyl pyrrolidone or water as solvent.

Kondo effect is an interesting phenomenon in quantum many-body physics. Niobium (Nb) is a conventional superconductor important for many superconducting device applications. It was long thought that the Kondo effect cannot be observed in Nb because the magnetic moment of a magnetic impurity, e.g. iron (Fe), would have been quenched in Nb. Here we report an observation of the Kondo effect in a Nb thin film structure. We found that by co-annealing Nb films with Fe in Argon gas at above 400 $$^{\circ }$$ ∘ C for an hour, one can induce a Kondo effect in Nb. The Kondo effect is more pronounced at higher annealing temperature. The temperature dependence of the resistance suggests existence of remnant superconductivity at low temperatures even though the system never becomes superconducting. We find that the Hamann theory for the Kondo resistivity gives a satisfactory fitting to the result. The Hamann analysis gives a Kondo temperature for this Nb–Fe system at $$\sim $$ ∼ 16 K, well above the superconducting transition onset temperature 9 K of the starting Nb film, suggesting that the screening of the impurity spins is effective to allow Cooper pairs to form at low temperatures. We suggest that the mechanism by which the Fe impurities retain partially their magnetic moment is that they are located at the grain boundaries, not fully dissolved into the bcc lattice of Nb.

Tin dioxide (SnO2) has been demonstrated as one of the promising electron transport layers for high-efficiency perovskite solar cells (PSCs). However, scalable fabrication of SnO2 films with uniform coverage, desirable thickness and a low defect density in perovskite solar modules (PSMs) is still challenging. Here, we report preparation of high-quality large-area SnO2 films by chemical bath deposition (CBD) with the addition of KMnO4. The strong oxidizing nature of KMnO4 promotes the conversion from Sn(II) to Sn(VI), leading to reduced trap defects and a higher carrier mobility of SnO2. In addition, K ions diffuse into the perovskite film resulting in larger grain sizes, passivated grain boundaries, and reduced hysteresis of PSCs. Furthermore, Mn ion doping improves both the crystallinity and the phase stability of the perovskite film. Such a multifunctional interface engineering strategy enabled us to achieve a power conversion efficiency (PCE) of 21.70% with less hysteresis for lab-scale PSCs. Using this method, we also fabricated 5 × 5 and 10 × 10 cm2 PSMs, which showed PCEs of 15.62% and 11.80% (active area PCEs are 17.26% and 13.72%), respectively. For the encapsulated 5 × 5 cm2 PSM, we obtained a T80 operation lifetime (the lifespan during which the solar module PCE drops to 80% of its initial value) exceeding 1000 h in ambient condition.

In single-point diamond turning (SPDT), two-dimensional (2D) tool centre error is caused by the tool deviating from the workpiece rotation centre both in the horizontal direction (tool feed direction) and vertical direction (perpendicular to tool feed direction). This greatly affects the form accuracy of the machined surface and its optical function. Traditional tool centre error identification is usually performed off-machine manually with high-precision instruments, which is time-consuming and labour-dependent. In this paper, a novel force-based 2D tool centre error identification method in SPDT is introduced. First, according to the relative position between the tool and workpiece centre, the tool centre error is classified into nine cases. The relation between the cutting force profiles and the tool centre error is analysed for each case. Then, a numerical fitting model and a geometric model are established to identify tool-above-centre and tool-below-centre errors, respectively. Additionally, a geometric model is established to calculate the normal distance from the tool interference/exit cutting to the workpiece centre, which serves as a reference for the horizontal tool centre error identification. Finally, the on-machine identification results of the 2D tool centre error are verified by experiments. Theoretical and experimental results show that the proposed on-machine 2D tool centre error identification method is effective and accurate, which greatly improves the cutting efficiency in SPDT.

The addition of C/MgAl2O4 composite powders can improve the thermal shock resistance of low-carbon Al2O3–C refractories attribute to the formation of microcracks in the agglomerated structure, thus consuming more thermal stress and strain energy. Moreover, C/MgAl2O4 composite powders additive promote the formation of short fibrous ceramic phases in the refractories, which suggest a bridging role in the interior of the refractories and increase its toughness. Furthermore, the C/MgAl2O4 composite powders also result in a remarkable enhancement of the slag corrosion resistance in the refractories.

To achieve an ideal drug delivery platform with precise composition and high tumor selectivity, the PEGylated dual-drug backboned prodrug was synthesized via the copolymerization between diamine monomer of ortho ester and cisplatin- demethylcantharidin conjugate (Pt(IV)-1), and then terminated by mPEG550-active ester. The amphipathic prodrug could self-assemble into nano-prodrugs, which endowed the precise structure and high drug loading. Moreover, the nano-prodrugs exhibited physicochemical stability at physiological pH (7.4) for stable blood circulation, DePEGylation and dynamic size change for selective tumor accumulation and enhanced cellular internalization at tumoral extracellular pH (6.8), and efficient drug release for synergetic apoptosis and cytotoxicity at tumoral intracellular pH (5.0)/glutathione. Thus, the precise dual-drug backboned nano-prodrugs with detachable PEGylation, dynamic size change and efficient drug release could be potentially translated for clinically selective cancer treatment. Statement of significance Few nanomedicines have been clinically used for cancer treatment and little progress has been made in the last decades due to the unprecise composition and unsatisfactory tumor selectivity. Herein, the PEGylated dual-drug backboned nano-prodrugs were successfully constructed by rational design and endowed the defined structure, precise drug ratio, extraordinary high drug loading and reduction/pH dual sensitivity. The nano-prodrugs further exhibited the stable storage and blood circulation through PEGylation and low critical micelle concentration, enhanced tumor accumulation and cellular uptake via extracellular DePEGylation and dynamic size translation, and synergetic cytotoxicity via intracellular efficient drug release, respectively. This study can open a new avenue for easy industrial manufacture and quality control, and highly selective chemotherapy appealing for clinical translation. .

The low-cost and high-capacity micron silicon is identified as the suitable anode material for high-performance lithium-ion batteries (LIBs). However, the particle fracture and severe capacity fading during electrochemical cycling greatly impede the practical application of LIBs. Herein, we first proposed an in situ reduction and template assembly strategy to attain a weave cage-like carbon nanostructure, composed of short carbon nanotubes and small graphene flakes, as a flexible nanotemplate that closely wrapped micron-sized mesoporous silicon (PSi) to form a robust composite construction. The in situ formed weave cage-like carbon nanostructure can remarkably improve the electrochemical property and structural stability of micron-sized PSi during deep galvanostatic cycling and high electric current density owing to multiple attractive advantages. As a result, the rechargeable LIB applying this anode material exhibits improved initial Coulombic efficiency (ICE), excellent rate performance, and cyclic stability in the existing micron-sized PSi/nanocarbon system. Moreover, this anode reached an approximation of 100% ICE after only three cycles and maintains this level in subsequent cycles. This design of flexible nanotemplated platform wrapped micron-sized PSi anode provides a steerable nanoengineering strategy toward conquering the challenge of long-term reliable LIB application.

To improve the pyrolytic carbon (PyC) deposition rate of Carbon/Carbon (C/C) composites prepared by the traditional chemical vapor infiltration (CVI) method, the 3D Ni/wood-carbon (3D Ni/C) catalyst was introduced into the CVI process. The effects of catalyst on the density of C/C composites were studied, and the deposition rate and morphologies of PyC were investigated after catalytic CVI. The morphologies of catalyst and PyC were characterized by scanning electron microscope and polarized light microscopy. The catalytic deposition mechanism of PyC was studied by density functional theory. The experimental results show that the initial carbon deposition efficiency of the catalytic pyrolysis process was 3–4 times that of the noncatalytic process. The catalyst reduced the energy barrier in the first step of deposition reaction from 382.55 to 171.67 kJ/mol according to simulation results. The pyrolysis reaction energy with Ni catalyst is reduced by 54% than that without the catalyst.

Intertwining quantum order and non-trivial topology is at the frontier of condensed matter physics1–4. A charge-density-wave-like order with orbital currents has been proposed for achieving the quantum anomalous Hall effect5,6 in topological materials and for the hidden phase in cuprate high-temperature superconductors7,8. However, the experimental realization of such an order is challenging. Here we use high-resolution scanning tunnelling microscopy to discover an unconventional chiral charge order in a kagome material, KV3Sb5, with both a topological band structure and a superconducting ground state. Through both topography and spectroscopic imaging, we observe a robust 2 × 2 superlattice. Spectroscopically, an energy gap opens at the Fermi level, across which the 2 × 2 charge modulation exhibits an intensity reversal in real space, signalling charge ordering. At the impurity-pinning-free region, the strength of intrinsic charge modulations further exhibits chiral anisotropy with unusual magnetic field response. Theoretical analysis of our experiments suggests a tantalizing unconventional chiral charge density wave in the frustrated kagome lattice, which can not only lead to a large anomalous Hall effect with orbital magnetism, but also be a precursor of unconventional superconductivity. An unconventional chiral charge order is observed in a kagome superconductor by scanning tunnelling microscopy. This charge order has unusual magnetic tunability and intertwines with electronic topology.

Melamine has been illegally adulterated in dairy food because of the rich nitrogen content and stable chemical properties in recent years. Therefore, the detection of melamine is of great significance for food safety supervision and human health protection. As melamine is a weak fluorescent substance, it is difficult to detect melamine directly by fluorescence spectroscopy. In this work, we found that melamine can significantly enhance the emission of the tetracycline–europium (EuTC) complex at 616 nm. Therefore, we took EuTC complex as a fluorescent probe to detect melamine. According to the characterizations of absorption spectra, molecular electrostatic potential distribution, and the time-resolved spectra, we speculated that tetracycline and melamine may form a complex through hydrogen bonding interaction in the melamine-EuTC reaction system, causing the melamine closer approach to Eu3+ and reducing the non-radiative energy loss of water molecules to Eu3+, which significantly enhanced the fluorescence intensity of EuTC. The fluorescence intensity of EuTC complex with melamine concentration in the range of 0.5–40.0 μM shows a good linear relationship, and the correlation coefficient is 0.9951 with the detection limit of 7.85 × 10−8 M. It shows a high sensitivity for the EuTC complex as a fluorescent probe to detect melamine, which provides a supplement and extension for the detection of melamine by fluorescence spectroscopy.

This note focuses on the leader–follower formation control problem of underactuated surface vehicles (USVs) with the unknown environmental disturbance. Especially, due to the ocean environmental disturbance, the vehicle’s desired-heading angle is altered violently. To address the constraint, a reduced-order extended state observer (ESO) is introduced. The sideslip angle of the vehicle is estimated online to amend the reference heading angle by virtue of the proposed observer. Furthermore, a novel adaptive formation control algorithm is presented to stabilize the dynamic error system. For the merits of the radial basis function neural networks (RBF NNs) and the minimal learning parameter (MLP) techniques, only two adaptive parameters require to be updated online to compensate for the perturbation from the model uncertainty and the environmental disturbance. Based on the proposed controller, it is illustrated that the desired formation pattern can be maintained without the effect of the sideslip angle. Meanwhile, all signals in the closed-loop system are proved to be with the semi-global uniformly ultimately bounded (SGUUB) stability. Finally, numerical simulations are conducted to demonstrate the effectiveness of the proposed algorithm.

Detection of AC magnetic fields at the nanoscale is critical in applications ranging from fundamental physics to materials science. Isolated quantum spin defects, such as the nitrogen-vacancy center in diamond, can achieve the desired spatial resolution with high sensitivity. Still, vector AC magnetometry currently relies on using different orientations of an ensemble of sensors, with degraded spatial resolution, and a protocol based on a single NV is lacking. Here we propose and experimentally demonstrate a protocol that exploits a single NV to reconstruct the vectorial components of an AC magnetic field by tuning a continuous driving to distinct resonance conditions. We map the spatial distribution of an AC field generated by a copper wire on the surface of the diamond. The proposed protocol combines high sensitivity, broad dynamic range, and sensitivity to both coherent and stochastic signals, with broad applications in condensed matter physics, such as probing spin fluctuations.

This paper investigates the problem of parameter identification for ship nonlinear Nomoto model with small test data, a nonlinear innovation-based identification algorithm is presented by embedding sigmoid function in the stochastic gradient algorithm. To demonstrate the validity of the algorithm, an identification test is carried out on the ship ‘SWAN’ with only 26 sets of test data. Furthermore, the identification effects of the least squares algorithm, original stochastic gradient algorithm and the improved stochastic gradient algorithm based on nonlinear innovation are compared. Generally, the stochastic gradient algorithm is not suitable for the condition of small test data. The simulation results indicate that the improved stochastic gradient algorithm with sigmoid function greatly increases its accuracy of parameter identification and has 14.2% up compared with the least squares algorithm. Then the effectiveness of the algorithm is verified by another identification test on the ship ‘Galaxy’, the accuracy of parameter identification can reach more than 95% which can be used in ship motion simulation and controller design. The proposed algorithm has advantages of the small test data, fast speed and high accuracy of identification, which can be extended to other parameter identification systems with less sample data.

In the permafrost regions of the Qinghai-Tibet Plateau (QTP), the permafrost table has a significant effect on the stability of geotechnical engineering. The thermal boundaries and soil properties are the key factors affecting the permafrost table. Complex geological environments and human activities can lead to the uncertainties of thermal boundaries and soil properties. In this paper, an array of field experiments and Monte Carlo (MC) simulations of thermal boundaries and soil properties are carried out. The coefficient of variation (COV), scale of fluctuation (SOF), and autocorrelation distance (ACD) of uncertainties of thermal boundaries and soil properties are investigated. A stochastic analysis method of the probabilistic permafrost table is then proposed, and the statistical properties of permafrost table on the QTP are computed by self-compiled program. The proposed stochastic analysis method is verified with the calculated and measured temperature observations. According to the relationship between ACD and SOF for the five theoretical autocorrelation functions (ACFs), the effects of ACF, COV, and ACD of soil properties and the COV of thermal boundaries on the permafrost tables are analyzed. The results show that the effects of different ACFs of soil properties on the standard deviation (SD) of permafrost table depth are not obvious. The SD of permafrost table depth increases with time, and the larger the COVs of thermal boundaries and soil properties, the deeper the SD of permafrost table; the longer the ACD of soil properties, the shallower the SD of permafrost table. This study can provide a reference for the stability analysis of geotechnical engineering on the QTP considering the uncertainties of thermal boundaries and soil properties.

With the development of power electronics technology, power modules delivery considerably greater power density, which makes junction temperature an important parameter for reliable operation. Existing thermal models often ignore the influence of the thermal boundary conditions on the thermal parameter and cannot accurately predict junction temperature in various operating conditions. This article proposes a three-dimensional compact thermal network model that considers the thermal boundary conditions and can be obtained by the finite-element method (FEM). A novel two-step method for thermal parameter extraction is presented and the effects of boundary conditions on thermal network parameters are discussed in detail. The experimental results and FEM simulation show that the proposed thermal network model can accurately estimate the junction temperature in different thermal boundary conditions.

To improve the wettability of coal, a combination of nonionic and anionic surfactants was used to improve the dust removal efficiency of water spray. The sedimentation test shows that the dust suppressant solution prepared by SDBS, DSS and CDEA has a good wetting effect on coal dust. The results show that the effect of a SDBS:DSS:CDEA ratio of 3:1:12 on the wettability of coal is stronger than that of other allocation methods. FTIR was used to explore the changes in the functional groups of experimental coal samples treated with different concentrations of new dust suppressants. With the FTIR results, a correlation analysis between sedimentation time and functional groups was carried out. In addition, the mechanism of the gas-liquid interface and solid-liquid interface in the coal dust adsorption process was analysed.

Low gravity fields have been simulated through magnetic acceleration to conduct experimental study on bearing capacity of circular footings on a type of crushable planetary regolith simulant, which has comparable density and particle size distribution of lunar soil. The load–settlement responses of surface spread footings are obtained by investigating the relative density, footing size and gravity effects. Applying the hyperbolic asymptote method, normalised foundation stiffness and ultimate bearing capacity are obtained by curve fitting and predicted by power functions using multivariate nonlinear regression. The results show that the nonlinear gravity effect is not negligible, related to stress condition, soil dilatancy and mobilised friction angle. A cone penetration test (CPT)-based method for prediction of bearing capacity is proposed with correlations between ultimate bearing capacity of footings and shallow penetration stiffness of CPTs, avoiding the uncertainties of soil property estimations. Analyses of allowable bearing capacity and footing influence zone in consideration of footing size and gravity effects could therefore improve the design of shallow foundations on the Moon and Mars, and provide new understandings and potential implications to the bearing capacity of shallow foundations on crushable granular material in both terrestrial and extraterrestrial geotechnical engineering.

Non-uniformity is a common phenomenon in infrared imaging system, which seriously affects imaging quality. In view of the problems of existing non-uniformity correction of infrared images, such as loss of image details and blurred edge of image, an improved non-uniformity correction method of infrared images based on convolution neural network using long-short connections (LSC-CNN) is proposed. The proposed method designs a long-short connection residual network structure suitable for non-uniformity correction of infrared image.The network depth is increased to fully learn the noise by short connections, image sizes are adjusted to reduce the number of parameters, the long connection is used to solve the problem of image information loss caused by transposed convolution, and a multiply operation is carried out to enhance the contrast of corrected images. Besides, batch normalization is utilized to improve the training speed. The experimental results show that LSC-CNN has excellent performance in non-uniformity correction of infrared images whether qualitative evaluation or quantitative evaluation. LSC-CNN is especially effective in image detail preservation and image edge protection whose average PSNR exceeds 37.5 dB and the average SSIM is greater than 0.98.

Transition zones between railway tracks and bridge decks can cause higher dynamic impacts. A solution is smoothly changing the track stiffness by gradually mixing steel furnace slag into the stone ballast. A nominated bridge transition zone is divided into 5 blocks of 7 meters long, with the mixing percentages of 0%, 25%, 50%, 75% and 100%. The mechanical behaviors of furnace slag-ballast combinations (FS-BCs) were studied using experiments of shear strength test, Los Angles abrasion index and plate load test. Furthermore, the dynamic behavior of bridge transition zone with FS-BCs blocks was investigated using a field validated FEM model. Results show that the 100%, 75%, 50% and 25% furnace slag by weight of ballast can increase the shear strength and ballast layer bending modulus by 13%, 12%, 9% and 7% at speed of 300 km/h compared with those of the stone ballast. The FEM study shows that rail deflections are reduced about 20%, 14%, 21% and 16% at speed of 300 km/h corresponding to 100%, 75%, 50% and 25% FS-BCs and accelerations are significantly reduced as well as increasing FS content of each block in bridge transition zone so that a smooth bridge transition zone can be achieved.

Rubber concrete (RC) has been confirmed to be suitable for concrete sleeper production. This paper studies the cracking behaviour of conventional and rubber-reinforced concrete sleepers based on the results of an experimental program. The cracking behaviour in the pure bending zone was analysed up to a load of 140 kN. The crack mouth opening displacement (CMOD) was accordingly measured using a digital image correlation (DIC) method. The DIC results show that the rubber prestressed concrete sleeper (RPCS) has a resistance against crack initiation that is 20% greater than that of the conventional prestressed concrete sleeper (CPCS) under the same loading condition; however, due to the higher crack growth rate of the RPCS, the first crack detected by the operator forms at 60 kN, which corresponds to a strength approximately 9% lower compared with the 65 kN load at which the first crack is detected in the CPCS. Before the first crack (60 kN), the RPCS has a deflection 35% lower than that of the CPCS, but after cracking, at loads of 80 kN, 100 kN and 140 kN, the RPCS has a deflection 15%, 4% and 24% higher than that of the CPCS, respectively.

University students always suffer from technostress and experience burnout during technology-enhanced learning (TEL). Research revealing whether and how university support contributes to eliminate them lacks. This study aims to investigate the structural relationship among university support (i.e., administration support and peer support), students’ ICT competence, technostress, and learning burnout. Altogether 1,785 students studying at three Chinese universities participated in this study by filling out a self-reported questionnaire revised from previous literatures and validated with confirmatory factor analysis (CFA). Structural equation modelling (SEM) revealed that: (a) university students’ technostress significantly predicted their learning burnout in TEL; (b) administration support was essential in alleviating students’ technostress and burnout; (c) peer support negatively predicted students’ learning burnout but did not predict their technostress; (d) ICT competence alone had no significant effects on technostress. Moreover, multiple group comparisons based on genders found that females benefited more from administrator support in alleviating learning burnout than males. In contrast, males benefit more from peer support in improving their ICT competence than females. Implications for alleviating university students’ technostress and learning burnout in TEL were discussed.

Artificial skins with sensing ability have great potential in applications of wearable devices and soft robotics. Inspired by the functions of human skins including sensing stimuli via electrical signal and bruising for injury indication, an ionic conductive and mechanochromic organohydrogel is synthesized and demonstrated as ionic skin (I-skin). The gel consisting of mechanochromophore cross-linked micelles is mechanically robust, stretchable, and deformation durable with minor hysteresis, and it also displays good solvent retention. The change of relative resistance during elongation and compression suggests a high sensitivity. An optical change from pale yellow to bruise-like blue-purple color is observed under a large deformation. The ionic conductive organohydrogel as I-skin is attached to different parts of the human body with movements mimicking various body-bruising scenarios, demonstrating successful perception and visualization of mechanical stimuli. The work vividly presents a strain sensor with the functions of injury visualization and damage warning for mechanical impacts. The I-skin can be potentially used in the applications including prosthetic devices, wearable electronics, and intelligent robots.

Sodium-ion batteries (SIBs), being an attractive candidate of lithium-ion batteries, have attracted widespread attention as a result of sufficient sodium resource with low price and their comparable suitability in the field of energy storage. However, one of the main challenges for their wide-scale application is to develop suitable anode materials with excellent electrochemical performance. Herein, a novel orderly layered VMoS2 (OL-VMS) anode material was synthesized through a facile hydrothermal self-assembly approach followed by a heating procedure. As the anode material of the SIBs, the unique structure of OL-VMS not only facilitated the rapid migration of sodium ions between the stacked layers but also provided a stable framework for the volume change in the process of intercalation/deintercalation. In addition, vanadium mediating in the framework caused more defects to produce abundant storage sites for Na+. As such, the obtained OL-VMS-based anode exhibited high reversible capacities of 602.9 mAh g-1 at 0.2 mA g-1 and 534 mAh g-1 even after 190-cycle operation at 2 A g-1. Furthermore, the OL-VMS-based anode delivered an outstanding specific capacity of 626.4 mAh g-1 after 100-cycle testing at 2 A g-1 in a voltage range from 0.01 to 3 V. In particular, even in the absence of conductive carbon, it still showed an excellent specific capacity of 260 mAh g-1 at 1 A g-1 after 130 cycles in a 0.3-3 V voltage range, which should contribute to the cost reduction and energy density increase.

In order to explore the influence of internal water on the seismic response of hydraulic tunnel, the combined mechanical analysis models of multimaterial including surrounding rock, lining structure, and internal water are built. Based on the explicit central difference method, the dynamic finite element analysis methods for rock, lining, and water are discussed, respectively. The dynamic contact force method is used to simulate the rock-lining contact interaction, and the arbitrary Lagrange-Euler (ALE) method is used to simulate the lining-water coupling interaction. Then a numerical simulation analysis method for combined seismic response of rock-lining-water system in hydraulic tunnel is proposed, and the detailed solving steps are given. This method is used to study the seismic stability characteristics of the water diversion tunnel in a hydropower station, and the displacement, stress, and damage failure characteristics of the lining structure under the conditions of no water, static water, and dynamic water are comparatively analyzed. The results show that the hydrostatic pressure restricts the seismic response of the lining, while the hydrodynamic pressure exacerbates its seismic response and leads to damage, separation, and slip failure appearing on the haunch, which can provide a scientific reference for the seismic design of hydraulic tunnel with high water head and large diameter.

Numerical simulations are performed to investigate the effects of different RPM (revolutions per minute) and different diameter on aerodynamic performances of tiltrotor in both hovering and cruise flight modes. The CLORNS code based on embedded grid and Reynold averaged Navier–Stokes equations is employed. According to the flight state of the tiltrotor, the corresponding comprehensive performance evaluation criteria and aerodynamic trimming strategy are established. On these bases, the numerical investigations on figure of merit and cruise efficiency of XV-15 tiltrotor with different RPM and diameter are conducted, and the results indicate that a large RPM is good for improving the hovering efficiency of tiltrotor, while in cruise mode, tiltrotor with small diameter (root-cut) and RPM helps to enhance the cruise efficiency.

SummarySpontaneous imbibition (SI) is regarded as an effective method to improve the oil recovery in a tight sandstone reservoir, which leads to a significant change in fracturing design and flowback treatment. However, a longtime shut-in period would aggravate the retention of fracturing fluid, which is in contradiction with high production in the field. It is imperative to understand how SI works during shut-in time, so as to maximize the effect of imbibition in oil recovery enhancement. In this study, a series of experiments were conducted to simulate the status of residual oil saturation so that the inner mechanism of imbibition on oil recovery can be investigated. Low-field nuclear magnetic resonance (LF-NMR) was used to provide direct observation of phase changes in different pore sizes. The experimental results show a positive effect of imbibition on residual oil reduction. This phenomenon further elucidates the observations made during the well shut-in, soaking period, and low flowback efficiency. This study aims to understand the mechanism of SI behavior and help to improve the accuracy of production prediction.

This study investigates the course-tracking problem for the unmanned surface vehicle in the presence of constraints of the actuator faults, control gain uncertainties, and environmental disturbance. A novel event-triggered robust neural control algorithm is proposed by fusing the robust neural damping technique and the event-triggered input mechanism. In the algorithm, no prior information of the system model about the unknown yawing dynamic parameters and unknown external disturbances is required. The transmission burden between the controller and the actuator could be relieved. Moreover, the control gain-related uncertainties and the unknown actuator faults are compensated through two updated online adaptive parameters. Sufficient effort has been made to verify the semi-global uniform ultimate bounded stability for the closed-loop system based on Lyapunov stability theory. Finally, simulation results are presented to illustrate the effectiveness and superiority of the proposed algorithm.

With the gradual reduction of mineral resources, marine mining has increasingly been developed as a method of exploiting resources. However, the cutting efficiency of submarine mineral deposits requires additional improvement. Investigating the preferable cutting efficiency in marine mining, it is important to establish a theoretical model of predicting the peak cutting force for polymetallic sulfide. The polymetallic sulfide was taken from the floor of the Indian Ocean and maintained at constant temperature and humidity conditions during transportation. In the paper, some experiments were conducted to study the physicomechanical properties of polymetallic sulfide. And the cutting experiments were conducted to investigate the cutting force at room temperature and atmosphere pressure, preliminarily. Then, based on maximum tensile stress theory, the theoretical equation of predicting the peak cutting force was derived, and an improved high-precision theoretical model was established. The reliability and accuracy of this model was verified using the experimental data. Based on the improved theoretical model, the brittleness index and the cutting depth, which influenced the peak cutting force, were investigated. Results show that the established model improved the accuracy of predictions. The peak cutting force decreased with the increase of the brittleness index, but it increased with the increase of the depth, which followed the power-law pattern. The power-law coefficient was generally at 1-2. The experiments verified that this improved theoretical model and the related conclusions can predict the peak cutting force. It is significant for the design and study of conical picks and cutting mechanisms in marine mining.

In this paper, the initiation characteristics of the oblique detonation flow field induced by single- and double-wedge surfaces of finite length in a confined space are investigated. Numerical simulations with a detailed H2/air reaction and theoretical shock polar analyses are combined to study the influence mechanism of a complex wave system structure on the characteristics of the oblique detonation. The effects of expansion waves on the oblique detonation waves (ODWs) and their flow field characteristics for different equivalent ratios and geometric sizes are analyzed in single-wedge and double-wedge structures with the same inflow parameters. The results show that the length of the induced ODW is shorter in the double-wedge structure than in the single-wedge structure. For the single-wedge structure, the strength of the expansion wave increases, the wall temperature drops, and the characteristic length of the induction zone decreases with increasing deflection angle of the second wedge. If the strength of the expansion wave is sufficiently large, the ODW is initiated. For the double-wedge structure, the ODWs interact and form a complex wave system structure, consisting of a Mach stem, two reflected detonation waves and slip lines. The length and the temperature before and after the Mach stem decrease with an increase in the strength of the expansion waves. The effects of the expansion waves on the flow field of the ODW are relatively small at a large equivalent ratio and significantly larger at a small equivalent ratio.