Abstract: According to the elastic wave theory combined with the propagation law of shock waves in rock or rock-like media, a slotted pipe wall is assumed to be elastic, irrespective of the attenuation process of detonation and shock waves in the coupling medium. The reflection of detonation and shock waves at the slotted pipe and blasthole walls is also assumed to be positive reflections, and the flow rate and internal energy constantly change with time. The proportional relationship between the peak stress of the hole wall, the range of the crushing area, and the fracture area in the cutting and non-cutting directions was established in this study. Moreover, AUTODYN software was used to establish a slit charge blasting model. Five measuring points were set at equal intervals in slit and non-slit directions. The peak stress, peak blasting vibration velocity, and peak arrival time at the measuring points were analyzed. Thereafter, based on the tunnel blasting test of the Gubei Coal Mine in the Huainan mining area, blasting tests of ordinary charge packs, slit charge packs, and varying peripheral hole spacing were performed. The crack state of the surrounding rock before and after blasting was tested through drilling peeping. Then, a two-dimensional graph of the crack development of the surrounding rock before and after blasting was imported into the customized MATLAB box dimension calculation program for calculation. The results before and after blasting were obtained based on the linear fitting curve and the box-counting dimension of the pixel information matrix of the surrounding image of rock burst cracks after blasting. The influence of the size of the slit charge and the surrounding hole spacing on the damage degree of the surrounding rock was also investigated. The results indicate that when the slit charge is used for blasting, the detonation product jet and stress concentration are produced in the slit direction. Further, the stress peak value and blasting vibration speed in the non-slit direction decline, the energy propagation speed in the non-slit direction decreases, and the energy propagation size in the non-slit direction decreases to achieve the goal of directional fracture. The results of the field test indicate that the degree of damage of the surrounding rock is reduced by >30% after using slit charge blasting compared with ordinary charge blasting. When the slit charge is used for blasting, the degree of damage to the surrounding rock reduces with an increase in the distance between the surrounding holes.
Abstract: Selective flocculation separation is one of the most efficient methods for fine mineral separation. To enhance the flocculation selectivity on the surfaces of hydrophilic and hydrophobic minerals, a hydrophobic group such as cetyldimethyl allyl ammonium chloride (C16DMAAC) was introduced within the molecular chain of polyacrylamide (PAM) to synthesize hydrophobically modified polyacrylamide (HMPAM). The effects of different K+ and Ca2+ concentrations on the in situ adsorption behavior of dispersants such as sodium hexametaphosphate (SHMP) and HMPAM and their effect on hydrophilic and hydrophobic surfaces were studied using dissipative quartz crystal microbalance (QCM-D). The effects of SHMP and HMPAM on the particle size distribution of silicon powder and hydrophobically modified silicon powder with different salinity were analyzed using a laser particle size analyzer. Results indicated that HMPAM exhibited good flocculation selectivity at varying salinity concentrations. When the background solutions were 10 mmol?L?1, 100 mmol?L?1 KCl, and 1 mmol?L?1 CaCl2, the QCM-D results indicated that no adsorption layer of SHMP was formed on the hydrophobic surface; moreover, the HMPAM was adsorbed on the hydrophobic surface in sequence. With an increase in salinity, the adsorption of HMPAM increased, and the dissipation of the adsorption layer decreased. Moreover, in the background solution of 10 mmol?L?1 CaCl2, SHMP did not inhibit the adsorption of HMPAM on hydrophobic surfaces, and an adsorption layer with the change of resonant frequency (Δf) of ?18.3 Hz was formed. Conversely, a thin and dense adsorption layer of SHMP was generated on the surface of SiO2 in 100 mmol?L?1 KCl, which inhibited the adsorption of HMPAM. In 10 mmol?L?1 CaCl2, a dissipative adsorption layer of SHMP was detected on the surface of SiO2. Furthermore, a relatively dense adsorption layer was deposited after the injection of 10 mmol?L?1 CaCl2 solution, which also inhibited the adsorption of HMPAM. The results of floc size measurements revealed that the position and shape of the floc size distribution peak of the silica powder did not change with the effect of SHMP and HMPAM in the background solutions of 100 mmol?L?1 KCl and 10 mmol?L?1 CaCl2, thus indicating that the SHMP inhibited the flocculation of silica powder by HMPAM. The floc size of the hydrophobically modified silica powder increased with the effect of SHMP and HMPAM. Summarily, the effects of SHMP and HMPAM on the particle size distribution of silicon micro powder and hydrophobic silicon micro powder under different salinity were consistent with the results of QCM-D measurements. This study is an important research basis for selecting and developing flocculants for selective flocculation separation.
Abstract: A specific columnar crystal structure is obtained using the directional solidification technique, which has a substantial effect on the optimization of the axial mechanical properties of the alloy. Additionally, the convection phenomenon in the melt changes the temperature field and concentration field at the front of the solid–liquid interface, affecting the shape of this interface. Thus, the influence on alloy properties cannot be ignored. Although the phase field method has more research on the microdendrite growth morphology, the results of coupling the flow field into the phase field and exploring the microdendrite morphology of directional solidification are still scarce. In this paper, the phase field model of a coupled flow field is used to simulate dendritic growth during directional solidification. The effects of the anisotropy coefficient and interfacial energy on the growth of directionally solidified dendrites and the growth behavior of dendrites under forced convection were studied. For the numerical solution procedure, a uniform grid of the finite difference method was used to discretize the governing equations. A combined solution of the MAC algorithm and a phase field discrete calculation was realized. When addressing the coupling of the microvelocity and pressure fields, the MAC algorithm was used to solve the Navier–Stokes equation and pressure Poisson equation, and the interlocked grid method was applied to handle the complex free interface. The results show that the growth rate of the dendrite tip increases, and the radius of curvature and the solute concentration at the root of the dendrite decrease with an increasing anisotropy coefficient. When the anisotropy coefficient is a maximum of 0.065, the wall of the dendrite tends to develop toward a secondary dendrite because of the influence of the anisotropy coefficient; with increasing interfacial energy, the radius of curvature of the dendrite tip increases. When the interfacial energy is a maximum of 0.6 J·m?2, the solidification shows a flat interface advancing mode; forced convection has a great influence on the growth direction of directional solidification dendrites. The directional solidification of dendrites in the upstream direction is coarse and grows faster with increasing flow rate. Additionally, the dendrite growth morphology observed using an optical microscope agrees well with the experimental results.
Abstract: Molybdenum carbide (Mo2C), as an alternative to platinum group metals, has been widely used in the hydrocarbon and hydrogen evolution reactions due to its excellent catalytic performance. The exploitation of its preparation method with high efficiency and low cost, therefore, received increasing attention in recent decades. In the current work, the preparation method of Mo2C by reducing MoO2 with CO–15%CO2 mixed gases was proposed, in which the main focus was laid in the reaction kinetics and reduction mechanism studies of the reduction-carburization processes. To determine the isothermal reaction temperature, the nonisothermal reactions of MoO2 in CO–15%CO2 mixed gases under different heating rates (2, 5, 10, and 15 K·min–1) were conducted first. After that, the isothermal reactions in the temperature range from 993 to 1153 K were carried out. Different analytical technologies, such as the thermodynamic calculation, Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Thermogravimetric (TG), Brunauer-Emmett-Teller (BET), and model fitting methods were adopted to analyze the experimental data. The results revealed that both the beginning (953 to 997, 1015, and 1031 K) and ending reaction temperatures (1100 to 1201, 1318, and 1383 K) were gradually increased with the increase of the heating rate (2 to 5, 10, and 15 K·min–1); besides, the reaction rate increased with increasing the temperature was also obtained. Phase transformation process of MoO2 to Mo2C was found to proceed by a one-step reaction (MoO2→Mo2C) without the formation of intermediate product Mo. The study also discovered that both Mo2C and MoO2 maintained the similar platelet-shaped morphology during the reaction process, but partial micro-pores and cracks were formed on the product surface because of the entry of reaction gases and escape of the product gases as well as the shrinking of the molar volume, increasing the specific surface area of the as-obtained Mo2C by nearly 20 times when compared to that of the raw material. Kinetics analysis revealed that the reduction-carburization process of MoO2 to Mo2C were not controlled by a one-step reaction mechanism but by the co-action of nucleation growth and interfacial chemical reactions. It was also discovered that the nucleation growth accounted for 68.9% and the chemical reaction accounted for 31.1%, with the extracted activation energies of 80.651 and 121.002 kJ·mol–1, respectively. The work would make a better understanding of the reaction processes of MoO2 to Mo2C in CO–15%CO2 mixed gases.
Abstract: Selective laser melting (SLM), a rising additive manufacturing technology, has extensive application potential because of its advantage in fabricating components with individual and complex shapes. During the SLM progress, the laser molten pool cools very quickly, leading to non-equilibrium microstructure formation and high thermal residual stress in the SLM components. Therefore, a suitable heat treatment is required to reduce the residual thermal stress and obtain excellent mechanical properties after the SLM process. In this paper, the 316L stainless steel fabricated by SLM (SLM-316L SS) is first heat-treated at 900 ℃ for 0, 0.5, 1.0, 3.0, and 5.0 h. Then, the microstructures of SLM-316L SS treated at different times are investigated using SEM, TEM, and EDS, and their corrosion resistance is estimated through electrochemical measurements. Finally, the microstructure evolution of SLM-316L SS during heat treatment at 900 ℃ is discussed based on the experimental data, and the effect of the microstructure on the formation kinetics and properties of the passive film on SLM-316L SS is explained. The results of the microstructure analysis reveal that the dislocations and sub-grain boundaries in SLM-316L SS disappeared with increasing holding time, accompanied by the precipitation of MnS inclusions, carbides, and σ phases along the grain boundaries. The potentiodynamic polarization in the buffer solution with 0.1 mol·L-1 NaCl reveals that a sample with a longer holding time shows a more negative pitting potential. According to the EIS test results, the shape of the curve in Nyquist diagram is not completely circular. The calculated film thicknesses decrease with increasing holding time. The potentiostat polarization under 0.1, 0.2, 0.3, 0.4, and 0.5 V vs SCE was used to form passive films on SLM-316L SS after heat treatments. By fitting the Mott-Schottky curves, the negative slopes demonstrate that the passive films formed on the samples are an n-type semiconductor, and the calculated point defect densities in the sample increase with the holding time. In addition, a logarithmic relationship holds between the carrier densities and the formation potentials of the passive films, and, using this relationship, the calculated diffusion coefficient of point defects across the passive film of SLM-316L SS increases with the holding time. A theoretical model related to the energy band structure and space charge layer is obtained based on the Mott-Schottky results to explain the electrochemical reaction on the passive film/solution interface.
Abstract: Because of its high strength and good fracture toughness, 6013 aluminum alloy is widely used in auto and aircraft parts, such as the outer hood, outer decklid, and outer fuselage skin. An aluminum alloy must have good plastic forming ability in forming auto and aircraft parts and must have high deformation resistance in service. These performance requirements mainly depend on the yield ratio, that is, the ratio of yield strength to tensile strength. A lower yield ratio means larger deformation from the start of plastic deformation to the final fracture, which benefits formability. A higher yield ratio means higher plastic deformation resistance, which benefits service safety. In this paper, the mechanical properties and microstructure of the extruded 6013 aluminum alloy after natural aging, artificial aging, and retrogression re-aging are studied using microhardness tests, tensile tests, scanning electron microscopy, and transmission electron microscopy. The samples after the solid solution were naturally aged at room temperature and artificially aged at 170, 180, and 190 °C to determine the peak aging time. Then, after natural peak aging, the samples were heat-treated using the retrogression and re-aging process (retrogression at 200/210 °C for 0.5 h and re-aging at 170 °C). The results show that the tensile strength was 286 MPa, the yield strength was 158 MPa, and the yield ratio was 0.54 after natural peak aging for 16 d, which is suitable for plastic forming. The tensile strength was 362 MPa, the yield strength was 336 MPa, and the yield ratio reached 0.92 after the retrogression and re-aging process (retrogression at 210 °C for 0.5 h and peak re-aging at 170 °C for 2 h); the plastic deformation resistance was considerably enhanced. Compared with single-stage artificial aging, retrogression and re-aging can enhance the yield strength of 6013 aluminum alloy more substantially to break through the yield ratio limit in single-stage aging. Because the size of the precipitated phase decreases and the number density increases considerably after retrogression and re-aging, the precipitation strengthening effect is considerably enhanced. Precipitation strengthening has different effects on yield strength and tensile strength, so the yield strength ratio can be regulated by aging heat treatment. In other words, the plastic deformation and anti-deformation abilities of the alloy can be improved by natural peak aging and the retrogression and re-aging process, respectively.
Abstract: To date, the recycling technology of common solid waste (blast furnace iron slag) in the iron and steel industry has made important progress. However, persisting, stubborn solid waste problems urgently need to be solved. With the continuous growth of stainless steel production in China, the total amount of stainless steel slag has reached more than 10 million tons. This slag contains a lot of CaO, MgO, and SiO2, which are suitable building material additives. However, the harmful element chromium (Cr) in the slag and the dissolution characteristics of Cr6+ ions limit its large-scale application. For a long time, no effective, harmless disposal method has been available for Cr-containing slag, which brings great hidden danger to the environment. Given the characteristics of stainless steel slag, the current detoxification methods mainly include the solidification method, wet reduction, high-temperature ferrosilicon reduction, and high-temperature modification–crystallization control processes. Among these methods, high-temperature modification–crystallization control can promote Cr-containing spinel phase formation by adjusting steel slag compositions (e.g., basicity and oxidation-reduction properties) to improve the enrichment degree of Cr in the spinel phase. At the same time, by adjusting the slag cooling system (e.g., the quenching temperature and holding time) and reducing the slag viscosity, the nucleation and growth of the Cr-containing spinel phase can be improved, the precipitation amounts of the spinel phase are increased, and the occurrence probability of chromium in the matrix phase is reduced; thus, the detoxification of stainless steel slag can be achieved. Compared with the other three detoxification treatment methods, high-temperature modification–crystallization control has the advantages of a simple process, stable treatment effect, and large scale. In particular, solid wastes containing silicon, aluminum, and magnesium can be used as additives to adjust the composition of steel slag to realize a coordinated treatment of various solid wastes, which has very high economic value. In addition, using waste heat to modify steel slag directly after slag picking can substantially reduce energy consumption, should become one of the most promising harmless treatment approaches, and has recently attracted extensive attention. In this paper, the research progress of high-temperature modification and detoxification of stainless steel slag is reviewed according to its thermodynamic mechanism and crystallization kinetics principles. On the basis of the core problem of melt modification-selective crystallization, the methods and measures for improving the detoxification effect are emphasized. In addition, aiming at the existing problems in the high-temperature modification–crystallization control detoxification of stainless steel slag, development directions are proposed.
Abstract: Human health and environmental concerns caused by the massive volatile organic compound (VOC) emission have attracted widespread attention recently. VOCs are toxic and difficult to eliminate; moreover, they come from a wide variety of sources. Efficient and environmentally friendly removal of VOCs has always been one of the primary concerns in the catalytic chemical industry. Presently, the commonly used methods for VOC removal include absorption?adsorption, biodegradation, thermal catalysis, and membrane separation. However, these methods have several drawbacks, such as high initial investment, expensive materials, high energy consumption, low catalyst efficiency, and incomplete treatment. Photocatalytic oxidation (PCO) technology is considered to be one of the effective methods of environmental pollution control. PCO can directly use solar energy to remove various environmental pollutants. Thus, PCO has inherent advantages such as low consumption, environmental protection, no secondary pollution, and convenience. Photocatalyst is a core step in the PCO process, and as aphotocatalyst studied for the longest time, titanium dioxide (TiO2) has the advantages of high cost-effectiveness, good stability, strong photocatalytic degradation capability, and producing no harmful byproducts. However, bottleneck problems such as the inability to utilize visible light and low separation efficiency of photoexcited charge carriers have always restricted its advancement. Thus, the inherent limitations of TiO2 need to be overcome, and its capability to degrade VOCs via PCO needs to be improved. These modifications can improve the PCO performance through the following mechanisms: (1) By introducing electron trapping levels in the bandgap, which will create some defects in the TiO2 lattice and help trap charge carriers, and (2) by slowing down the electron carrier loading rate to increase VOC degradation. Thus, considering the basic principle of TiO2 photocatalytic removal of VOCs, this study focuses on the key factors affecting the photocatalytic reaction. Beginning with aspects such as metal/nonmetal doping, semiconductor recombination, defect engineering, crystal plane engineering, carrier adsorption, and morphology control, the research on the design of TiO2-based materials and their application in the field of photocatalytic degradation of VOCs in recent years are systematically summarized; moreover, a brief introduction of its control parameters and applications in practical engineering and prospects on how to further improve the use of TiO2-based materials for the PCO technology of VOCs is provided. This review will provide parameter support and optimization suggestions for the research on the degradation of VOCs by TiO2-based photocatalytic materials to help researchers lay the foundation for future research.
Abstract: In this study, the surface modification of titanium plates was performed using in situ nitriding via plasma-enhanced chemical vapor deposition to improve the conductivity and corrosion resistance of the plates. A series of titanium nitride (TiN) coatings were synthesized at different nitriding temperatures and durations. The influence of nitriding temperatures and durations on the surface morphology, hydrophobicity, interfacial conductivity, and corrosion resistance of the as-prepared coatings was investigated. The results indicated that faster growth and larger particle size of TiN are observed at higher temperatures. However, lower temperatures are unfavorable for surface reactions; thus, the coating cannot entirely cover the titanium substrate. Moreover, a shorter nitriding time results in irregular nanogrowth nuclei on the surface, leading to an uneven coating and bare titanium substrate. Conversely, longer nitriding time encourages the continuous accumulation of TiN nanoparticles and forms a uniform coating of the titanium substrate but decreases the flatness because of the stacking of the coatings due to the long nitriding time (120 min). The TiN coating prepared by nitriding at 650 °C for 90 min (TiN-650-90) is relatively compact and smooth with the composition of TiN0.26 and has an increased water contact angle of 105.4°. The change from hydrophilicity to hydrophobicity in TiN is beneficial to fuel cell water resistance. At a loading pressure of 1.5 MPa, the contact resistances of the coatings prepared at a nitriding time of 60 min can satisfy the U.S. Department of Energy requirement of less than 10 mΩ·cm2. Despite a contact resistance of 13.2 mΩ·cm2 for the TiN-650-90 coating, the contact resistance decreases with increasing loading pressure and is stable at 6.5 mΩ·cm2 under a loading pressure of 2.75 MPa. The corrosion current density of the TiN-650-90 coating is 0.56 μA·cm?2, and the corrosion potential positively shifts from ?0.37 to ?0.05 V at room temperature. The corrosion current density tested in the simulated operating environment of fuel cells is higher than that at room temperature but much lower than that of titanium (4.2 μA·cm?2). Furthermore, the current density is stable at 0.67 μA·cm?2 and at a ?0.1 V constant potential, indicating superior corrosion resistance and stability than titanium. The titanium bipolar plates modified by this method exhibit the advantages of relatively low deposition temperature, quick deposition speed, and good hydrophobicity, conductivity, and corrosion resistance. This work can pave the way for efficient surface modification of metal bipolar plates.
Abstract: A more-electric aircraft refers to an aircraft whose secondary power is unified from the traditional multi-energy, such as mechanical energy, hydraulic energy, and pneumatic energy, to the electrical energy, which has the advantages of a simple system structure, high reliability, high maintainability, and high energy efficiency. The most advanced architecture of its power system is the 360–800 Hz variable frequency AC power supply and the 270 V high-voltage DC power supply, which have been applied in the Airbus A380, Boeing B787, F-22, and other more-electric aircraft. As power consumption increases, the power distribution, power network, and cable layout in a more-electric aircraft become more complex, and the probability of electrical faults such as short circuits increases. The arc generated by fault current not only severely affects the life, reliability, and safety of cable and electrical equipment but also limits the capacity expansion of an aviation power system and the improvement of flight performance. The circuit breaker in a more-electric aircraft is a key device for arc extinguishing. Analyzing the complex mechanism of the arc-discharging process in a circuit breaker helps improve the arc-extinguishing performance. To further promote research on the arc mechanism and extinguishing technology of circuit breakers in more-electric aircraft power systems, in this paper, the structure of civilian and military more-electric aircraft power systems and the difficulties in the electrical fault and protection are first analyzed. Then, the research status of the arc-extinguishing technology of the aviation variable frequency AC circuit breaker and the 270 V high-voltage DC circuit breaker are summarized. For an intermediate-frequency vacuum arc, the instantaneous input power inside the gap and at the anode increases with the current frequency, which indicates that the half-wave input power increases with the frequency and proves that the transition state arc is an important source of anode ablation during intermediate-frequency arcing. Under the same current condition, the frequency increases. On the one hand, when the value of di/dt increases, the arc-extinguishing ability decreases with increasing frequency. On the other hand, intensifying the skin effect leads to an increase in the arc center pressure, arc contraction, and magnetic field hysteresis, which is not conducive to arc extinguishing. In addition, the metal vapor density vaporized by droplets reduces the recovery strength of the dielectric after the current zero, which is not conducive to arc extinguishing. For the 270 V DC arc, air, nitrogen, helium, hydrogen, and other gas are presently used in aviation power systems, among which hydrogen is the research hotspot. Finally, future research trends of arc extinguishing technology for aviation circuit breakers are predicted.
Abstract: Ore is an essential industrial raw material and strategic resource that plays an important role in China’s economic construction. The smart mine aims to build an unmanned, efficient, intelligent, and remote factory to improve quality, reduce cost, save energy, and increase the efficiency of mineral resource extraction. Ore image processing technology can automatically and efficiently complete a series of difficult and repetitive tasks, which constitutes an important part of smart mine construction. However, open-air operation modes, high-dust environments, and ore diversity have brought great challenges to ore image processing. Benefiting from its strong automatic feature extraction ability, deep learning can deeply perceive a complex environment, which enables it to play an important role in the ore image processing field and help traditional mining companies transform into efficient, green, and intelligent enterprises. This paper focuses on two production stages, including ore prospecting and belt transportation. We systematically summarize the main applications of deep learning in ore image processing, including ore classification, particle size analysis, and foreign material recognition, sort out the corresponding algorithms, and analyze their advantages and disadvantages. Specifically, according to the number of ores in an image, ore classification is divided into single-object and multi-object classifications. Single-object classification is mostly addressed by image classification networks, while multi-object classification is mostly accomplished by object detection and semantic segmentation networks. Single-object classification plays an important role in geological prospecting. Particle size refers to the size information of ores in an image. Generally, it can be divided into three modes: particle size statistics, particle size classification, and large block detection. Among these modes, the first and the third are mainly used in actual industrial production. Particle size statistics are determined mostly using semantic segmentation networks and can provide a reference for the control of crushers and conveyor belts. Large block detection is performed mostly by adopting object detection networks and can identify the oversized ore on an ore feeding belt and prevent material blockage accidents in the transfer buffer bin between the ore feeding belt and the ore receiving belt. Foreign material recognition detects harmful objects mixed in the ores on the belt to ensure product quality and prevent the belt from tearing. Object detection technology is often used to complete the task of foreign material recognition.
Abstract: As a legally binding computer program, smart contracts are stored on the blockchain and can be automatically executed according to the contract terms. These features of smart contracts provide a trusted execution environment for the electronic voting system. However, since the contract is deployed on an open and transparent blockchain, this causes a considerable threat to the validity and privacy of the voting content. However, due to the openness of the blockchain network, any node linked to the network can obtain information concerning contract transactions on the chain without restriction, which greatly threatens the validity and privacy of the voting content. To address this problem, a smart-contract voting system has been designed. First, we construct a new interactive zero-knowledge set membership proof protocol (ZSMPP) based on the discrete logarithm problem. Using ZSMPP in the design of the smart-contract voting system, the voter can verify the voting content validity to the initiator without disclosing the voting content itself to avoid the impact of invalid votes. Moreover, we prove that the proposed protocol is complete and has zero knowledge. Second, we describe the voting contract by the specification language of smart-contract (SPESC) and limit the trigger conditions of stages of the voting system through contract terms. By deploying the voting contract to the blockchain as a JAR file, the proposed smart-contract voting system can be automatically executed in accordance with the predefined contract terms. Additionally, we further introduce the execution process and related algorithms of the four stages of the proposed voting system and show the related execution results in the form of contract transactions. Furthermore, we analyzed five security features of the proposed voting protocol. Particularly, the validity of the ballot content is ensured by the zero-knowledge of our protocol, which can prevent invalid votes from affecting the system. The privacy of the ballot ensures that the voting content is undisclosed either in the verification or counting stage. Uniqueness ensures that each voter can only vote once. Supervision-free means that there are no trusted supervisors in the proposed voting protocol. Self-counting indicates that smart-contract programs automatically implement the counting process. Finally, the performance of the proposed smart-contract voting system is analyzed. The experimental results show that both the voting and counting stages of our voting system can be implemented efficiently. Moreover, our smart-contract voting system can provide a reference for effectively combining the cryptographic protocol construction technology and smart-contract voting system.
Abstract: This study analyzes the feed-in tariff strategy of steel enterprises in the context of the steel industry’s electricity market, which is composed of waste heat and pressure (WHP) power generation and traditional thermal power generation. A Stackelberg game model was developed to compare three pricing strategies (i.e., fixed price, fixed premium, and variable premium) for the feed-in tariff of WHP power generation technology among steel enterprises, traditional fossil fuel power generators, and local governments. Three pricing strategies for WHP generation feed-in tariffs are compared, and numerical simulations are run to examine the effects of market size, WHP generation cost coefficients, and steel firm environmental costs on optimal regulated prices, optimal steel firm profits, and optimal total social welfare, respectively. The following findings are obtained. (1) For optimal price regulation, increasing the market size and the coefficient of WHP generation cost has little effect on the optimal price regulation under the fixed price policy. The only way to increase the price of the fixed price policy is to increase the environmental cost of steel enterprises. Moreover, increasing the market size and the coefficient of WHP generation cost will reduce the price of fixed premia. Additionally, increasing the market size and the coefficient of WHP generation cost will reduce the price of fixed premia. Increases in market size and WHP generation costs will raise the price of variable premium insurance, whereas increases in enterprise environmental costs will lower and maintain the price of variable premium policy. (2) For optimal steel enterprise profit, increasing the market size and the cost coefficient of WHP generation will increase the profit of steel enterprises under the fixed premium policy. However, it will have little effect on the profit of the fixed price and variable premium policies. Moreover, increasing the environmental cost of enterprises will reduce the profit of the fixed premium policy, but it will have little effect on the profit of the fixed price and variable premium policy. (3) For optimal total social welfare, increasing the market size and environmental cost of steel enterprises can increase total social welfare under the fixed price policy. Moreover, increasing the coefficient of WHP generation cost has little effect on the fixed price policy welfare; increasing both the market size and the coefficient of WHP generation cost has little effect on the fixed premium policy welfare. Additionally, increasing the environmental cost of enterprises can increase the fixed premium policy welfare, and increasing the market size can increase the total variable premium policy welfare. Meanwhile, increasing the coefficient of WHP generation cost and the environmental cost of steel enterprises can reduce the variable premium policy welfare and finally level off. (4) Depending on the decision maker’s preferences, various optimal decisions can be made. Higher subsidies imply higher optimal regulation prices, which are accompanied by market riskiness, thus influencing the rate of market development of waste heat and waste pressure power feed-in tariffs. In optimal rule prices, low riskiness and low subsidies are fixed price strategies, high riskiness and moderate subsidies are fixed premium strategies, and high riskiness and high subsidies are variable premium strategies. In optimal steel firm profit, low riskiness and low subsidy, high riskiness and high subsidy, and low riskiness and high subsidy are fixed price, fixed premium, and variable premium strategies, respectively. In optimal total social welfare, moderate riskiness and moderate subsidy, low riskiness and low subsidy, and high riskiness and high subsidy are fixed price, fixed premium, and variable premium strategies, respectively.
Abstract: Aircraft landing with low fuel is usually caused by diversion decision changes in the air. It could lead to an unsafe event. To solve the problem of collective alternate landings of multiple flights in the area, the most complex situation is selected, that is, when the weather in the route or terminal area is dangerous. However, in this situation, when the pilot announces diversion, many are unacceptable by the airport due to limited aircraft stand. Therefore, this study establishes a decision-making approach to help air traffic controllers and airlines choose suitable alternate airports since accurate fly limit zone conditions can keep the aircraft out of dangerous weather and a short diversion route can avoid the low fuel situation, both of which can increase the safety of the diversion process. The basic conditions of the fly limit zone under dangerous weather are obtained by combining meteorological data and historic tracks. Here, A* and the improved gray wolf Dijkstra algorithm are used to plan the diversion path for two different routes to the alternate aerodrome: maneuvering flight and flying along the route. First, considering the shortest total flight time of alternate flight as the single objective and subsequently integrating the expectations of flight, control, airport, and airline, a multi-objective function is constructed, the dynamic decision-making time interval is defined, and a dynamic optimization scheme of multi-flight alternate in the region based on a single objective and multi-objective is proposed. The single-objective scheme focuses on the safe aspect of diversion, while the multi-objective scheme focuses on preventing airport rejection. The multi-objective scheme can enable the flight to land quickly, ensure safety, and consider the expectations of multiple parties to avoid diverting simultaneously. Using the “8.12” North China large area alternate landing data, the total flight time obtained by selecting the direct flight A* algorithm is reduced by 100 and 62 min, respectively, and the total flight time obtained by the improved gray wolf Dijkstra algorithm based on the route is reduced by 73 and 14 min. Moreover, in the multi-objective scheme, the overall time of flight resumption to the original destination is 63 min earlier, and the total cost is reduced by 62900 yuan. Although multiple diversion still occurs on CA991, the process is within the safety range. Therefore, results indicate that the scheme considers the needs of multiple parties and improves the economy to ensure the safety of flight alternate landing.
Abstract: Power system is one of the largest and complex artificial engineering in the modern society. With the development of intelligence, digitization and long-distance technology, a large number of multi-source, multi-state and heterogeneous operational data have emerged. As a new trend direction of machine learning, deep learning has shown potential in data feature extraction and pattern recognition. Because of its excellent ability in data analysis and prediction, it is widely used in power system, which has a significant impact on optimizing power production planning, improving power production efficiency and energy utilization, and ensuring the smooth operation of the system influence. Based on massive quantities of data and by means of deep learning, it can better fit the nonlinear relationship between the factors affecting the subsequent operational state of the system, so as to further improve the prediction accuracy. Power system prediction includes load forecasting, new energy power prediction and state-of-health prediction. Power production planning can be optimized using load forecasting; thus, electrical energy can be finely dispatched. The capacity of new energy power consumption is improved through power prediction to reasonably use electrical energy. Potential equipment hazards can be timely found using power equipment health state prediction, thereby ensuring safe and smooth operation. First, in this paper, the characteristics and applicable scenarios of typical deep learning models are introduced, among them, deep belief network and stacked auto encoder belong to stack structure, so the structure is flexible and easy to expand, which is suitable for the modeling and feature extraction of unrelated data type; convolutional neural network shares convolution kernel internally to reduce the number of network parameters and is good at processing high-dimensional data type; recurrent neural network has feedforward and feedback connections, so it is suitable for processing sequence data with pre and post dependence. Second, the application frontiers of predictive power systems based on deep learning are reviewed, which include civil and industrial scenarios, photovoltaic and wind power, mechanical and non-mechanical equipment health state prediction. Finally, facing the challenges of power system in energy efficient allocation, high proportion of new energy power consumption, highly stable operation of power equipment and so on, the key problems and future development trends are presented.
Abstract: Hydrogen production of biomass via microwaves is an efficient, rapid, and environmentally friendly chemical engineering technology. Lignin is the only renewable aromatic hydrocarbon resource in the nature, and thus, the lignin-based forest biomass, which has the advantages of low sulfur, is a good raw material for hydrogen production. However, the microwave hot spot effect restricts the industrial application of hydrogen production by microwave. In this study, the reactor was carried out based on the penetration depth of biomass under different microwave frequencies was designed by modeling. Orthogonal design simulation, CFD, and HYSYS were used to obtain the distribution of temperature field with different microwave power density, the radius of biomass particles, bulk density, and the coefficient of variation. Based on the results, the optimal microwave power density was 30 W·g–1, the optimal radius of biomass particles was 4 mm, and the optimal bulk density was 800 kg·m–3, at which a favorable uniform temperature field was achieved, and its coefficient of variation was only 0.009, less than the standard value of 0.01. Then, to reduce energy consumption and improve product economy, the Computational Fluid Dynamics (CFD) method was used to analyze the cloud image of hydrogen production with different height to diameter ratio of the reactor. It was found that when the height to diameter ratio of the reactor was 2.0, the hydrogen-flow could not only fully contact with the falling materials, but also achieve thermal energy circulation by using its own high temperature. Finally, the industrial process of hydrogen production of biomass via microwave was added into HYSYS, and the operating parameters of the maximum hydrogen yield of the 10000-ton industrial device were simulated and optimized. In the reforming reaction, by adding steam in the mid-piece and the end-piece, the production yield of hydrogen can be maximized and the temperature of the reactor can be maintained continuously after the heat energy of hydrogen was recovered. Under the conditions optimized, when the mid-piece and end-piece fluxes of steam were 290 and 1230 m3·h–1, respectively, a favorable hydrogen production of biomass was achieved. The output of hydrogen, the mole fraction and the yield of hydrogen production were 922.98 m3·h–1, 0.4781 and 82.49%, respectively. Moreover, the hydrogen product can reach the high standard of 6.592 g hydrogen/ 100 g biomass, which was far superior to the industry level.
Abstract: Caproic acid is a value-added product that has many uses in the preservation and synthesis of bio-energy. It is obtained via reverse β-oxidation reaction using electron donors and acceptors through the process of carbon chain elongation. The short-chain fatty acids are converted to high-value medium-chain fatty acids (such as caproic acid with six carbon chains). To improve the production yield of caproic acid, it is essential to clarify the relationship between reductase and energy supply, as well as the appropriate range of influencing factors and their mechanism in the biosynthesis process. This review paper describes the mechanisms of carbon chain elongation with lactic acid and ethanol as electron donors. Excessive ethanol oxidation, methanogenesis, and the lactate–acrylate pathways were introduced as competitive pathways during electron donor oxidation, and the corresponding inhibition methods were also reviewed. The reductase supply relationship between electron donor oxidation and electron acceptor reduction during the reverse β oxidation was discussed. In addition, this study clarified the utilization of energy by anaerobic microorganisms during the biosynthesis of caproic acid and two types of ATP synthesis: substrate level phosphorylation and electron transport phosphorylation. Electron bifurcation in the reverse β oxidation (a phenomenon in which two electrons from the same molecule are separated and redox potential is converted into energy to drive thermodynamically adverse reactions) and the role of different electron bifurcations in the production of caproic acid were evaluated. The influence of pH on the production of caproic acid driven by different electron donors was analyzed from the perspectives of competitive pathways, the growth range of functional microorganisms, and product inhibition. Regulating the collaboration between different bacterial communities and exploiting product separation techniques may enhance the production of caproic acid, and this should be investigated in the future. The role of CO2 and H2 as headspace in reverse β oxidation was investigated from the perspectives of substrates, competitive pathways, and thermodynamics. Relevant studies of the CO2 loading rate and H2 partial pressure were also reviewed. The development and current status of bioelectrochemical enhancement in the synthesis of caproic acid were examined, with emphasis on the fixation of CO2. Future research should focus on synthesizing caproic acid using lactic acid as an electron donor and organic wastewater as a substrate by bioelectrochemistry. This review summarized the advantages and disadvantages of the biosynthesis of caproic acid, providing theoretical guidance on how to produce it and improve its yield.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
