To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology,the propagation characteristics of Rayleigh surface w...To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology,the propagation characteristics of Rayleigh surface waves in an elastic half-space attached by a nanoscale piezoelectric semiconductor(PSC)thin layer with flexoelectricity and size-effects are systematically investigated.Based on the Hamiltonian principle,the elastic dynamic equations and Gauss's theorem of electrostatics are obtained.The eigenvalue problem is numerically solved with a genetic algorithm in MATLAB,and the dispersion properties are obtained.The effects of various key factors,including the flexoelectricity,inertia gradients,strain gradients,electric field gradients,PSC layer thickness,steady-state carrier concentration,and bias electric fields,on the propagation and attenuation characteristics of Rayleigh surface waves are analyzed.The results demonstrate that the increases in the flexoelectric coefficient and strain gradient characteristic length lead to an increase in the real part of the complex phase velocity,while the increases in the inertia gradient characteristic length,electric field gradient characteristic length,PSC layer thickness,and steady-state carrier concentration result in a decrease.Additionally,the bias electric fields significantly influence the Rayleigh surface wave attenuation.The present findings are crucial for the accurate property evaluation of miniaturized highfrequency Rayleigh wave devices,and provide valuable theoretical support for their design and optimization.展开更多
Treatment of lake sediments with salts is a promising approach for preventing phosphorus release from sediments. Five 35-d treatments of undisturbed sediment cores in the East Lake, Wuhan, China were applied under ano...Treatment of lake sediments with salts is a promising approach for preventing phosphorus release from sediments. Five 35-d treatments of undisturbed sediment cores in the East Lake, Wuhan, China were applied under anoxic conditions： nothing added （control）, Al2（SO4）3 added, FeCl3 added, CaCl2 added, and NaNO3 added. To identify changes in the P binding sites in the sediment caused by the treatments, different P binding forms were extracted from the sediment before and after the treatments. We found that the mean P release rates for anoxic treatments with Al2（SO4）3, FeCl3, CaCl2 and NaNO3 were -0.6, 0.03, 0.6 and 2.6 mg/（m^2·d）, respectively, while the P release rate with no additives was 7.3 mg/（m^2·d）. In suboxic conditions, the concentration of total phosphorus （TP ge 657 mg/kg） in sediment was much lower than that of untreated sediment （TPaverage 688 mg/kg） and treatments with salts （TP（Al2（SO4）3） 793 mg/kg, TP（FeCl3） 781 mg/kg, TP（NaNO3） 802 mg/kg, TP（CaCl2） 747 mg/kg）. We also found that adding CaCl2 prevented P release because of apatite formation and because PCa （Ca bound P） increased at the sediment surface. Addition of Fe^3＋ and NO3^- to the sediment increased the amounts of PFe. Mn （Redox-sensitive P, mostly Fe and Mn compounds）, since iron oxide has the ability to combine P. Addition of Al2（SO4）3 increased the fraction of PAl, Fe （P bound to metal oxides （Al, Fe）） and decreased the P and Fe in the water above the anoxic sediment, showing the greater ability orAl in binding P. The results showed that Al2（SO4）3, FeCl3, CaCl2 and NaNO3 all had an effect in controlling phosphorus release. The effect was related to the forms of phosphorus existing in the sediment before treatment and the forms resulting after adding the four reagents. The combination of Al^3＋ or Fe^3＋ with NO3^- promises to be a reasonable chemical treatment for increasing the P retention capacity of sediments in eutrophic lakes. If chemical treatment is combined with bioremediation, the aim of environmental repair may be achieved.展开更多
Recently,magnesium and its alloys have attracted more and more attention as promising implant materials due to their excellent properties such as good biocompatibility,biodegradation,non-toxicity and comparable mechan...Recently,magnesium and its alloys have attracted more and more attention as promising implant materials due to their excellent properties such as good biocompatibility,biodegradation,non-toxicity and comparable mechanical properties with natural bone.They can be gradually degraded and absorbed so as to avoid the second surgery for implants removal after the tissues are healed completely.In addition,they are also able to prevent the stress shielding effect in human body environment because of the density,elastic modulus and yield strength of magnesium closer to the bone.Unfortunately,the high corrosion rate which causes early mechanical failure of the implants in physiological environment limits the widespread use of magnesium alloys for clinical application in biology.And the high corrosion process usually causes huge hydrogen evolution and alkalinization,resulting in problems against the implants as well as the surrounding tissues.In order to enhance the corrosion resistance of magnesium alloys,in this study,the ZEK100 magnesium alloy was pre-deformed with a highpressure torsion(HPT)process and then fabricated hydroxyapatite(HA)coatings with different contents of Mg(OH)2 nanopowder via hydrothermal method.The specimens were characterized by scanning electron microscope(SEM)and X-ray diffraction(XRD).At the same time,prior and after the HPT procedure,the metallography,microhardness and tensile tests of specimens were characterized.Meanwhile,the corrosion behavior of the specimens was evaluated by electrochemical impedance spectroscopy(EIS)and hydrogen evolution tests.And the interface bonding strength of the HA coating on the magnesium alloy substrate was evaluated by a tape adhesion test/scratch test.Results showed that HPT processing refined the grain size and introduced a great number of twins,resulting in the enhancement of microhardness and Young’s modulus of ZEK100 magnesium alloy,but hardness values at the edge were higher than those at the center due to the uneven shear strain.At the same conditions,the HA coating on HPT-ZEK was denser,thicker than that on ZEK sample and the crystal sizes of HA were smaller on HPT-ZEK.These were attributed to fine,uniform distributed secondary phases and lots of fine grains,twins,grain boundaries in HPT-ZEK substrates which can provide more nucleation sites for the HA crystal.In terms of the amount of Mg(OH)2 nanopowder,Mg(OH)2 nanopowder significantly influenced the microstructure and thickness of the HA coating.And at a 0.3 mg/mL content of Mg(OH)2 nanopowder,there was the densest,thickest HA coating on magnesium alloys,and the crystal size of HA was minimum.Specifically,the HA coating thickness on ZEK-03(0.3 mg/mL Mg(OH)2 nanopowder)was 1.8 times of that on ZEK-00(0 mg/mL Mg(OH)2 nanopowder),while the HA coating thickness on HPT-03 was 2.6 times of that on ZEK-00.And the adhesion strength of HA coating on HPT-03 substrate was better than that on ZEK-03.In addition,HPT technology and surface modification by HA coating simultaneously increased the corrosion resistance of ZEK100 magnesium alloy and the corrosion of HPT-ZEK samples occurred in a more uniform manner,while it was pitting on the surface of ZEK100 magnesium alloy.Therefore,there was the best corrosion resistance on HPT-03 sample,which could promote the application of magnesium alloys in biomedical fields.展开更多
The paper presents an improved support vector machine （SVM） by combining principal component analysis （PCA） and particle swarm optimization （PSO）. Then, the improved SVM is applied to the intrusion detection sys...The paper presents an improved support vector machine （SVM） by combining principal component analysis （PCA） and particle swarm optimization （PSO）. Then, the improved SVM is applied to the intrusion detection system （IDS） to improve the detection rate. First, PCA is used to reduce the dimension of feature vectors. Second, we use the PSO algorithm to optimize the punishment factor C and kernel parameters oin SVM. The experimental results indicate that the intrusion detection rate （97.752 8%） of improved SVM by combining PCA and PSO is higher than those （95.635 5%） of PSO-SVM and those （90.476 2%） of standard SVM with KDD Cup 1999 data set.展开更多
Both parallel and staggered plate fin arrays have shown promise for use inhigh performance heatsinks regard of its individual manufacturing costs. The geometrical andoperational parameters are very important to their ...Both parallel and staggered plate fin arrays have shown promise for use inhigh performance heatsinks regard of its individual manufacturing costs. The geometrical andoperational parameters are very important to their cooling performance as heatsinks in practicalapplications. Fluent 5.0 commercial CFD (computational fluid dynamic) code is used to simulate theflow and heat transfer of those heatsinks of different realistic parameters. Based on thosesimulations, two correlations, concerning Nusselt number and friction factor as the functions ofgeometrical and operational parameters, FB (fin-base area ratio), PR' (ratio of spanwise pitch tolengthwise pitch) and Re, were developed. From the both, the performance comparisons for optimizinggeometrical and operational parameters of a fixed dimension heatsink are shown at constant pumpingpower and constant thermal resistance. Several optimized parameters were obtained can out performthe staggered ones.展开更多
This paper presents the results of a research into capacitor discharge percussion welding （CDPW） of pure aluminum wires and pure copper sheets, using percussion welding power and special welding device. A lot of CDP...This paper presents the results of a research into capacitor discharge percussion welding （CDPW） of pure aluminum wires and pure copper sheets, using percussion welding power and special welding device. A lot of CDPW factors, which will affect aluminum and copper dissimilar bonding, are described and these parameters have also been optimized. The fracture pull, interface compounds, microstructure and hardness are all studied. The results show that aluminum wire welding to copper sheet can form a sound weld and in some conditions the fracture pull is similar to that of the pure aluminum wires. The capacitance, discharge voltage, wire taper angle and machine oil as welding assistant medium affect fracture pull. The intermetaUic compounds A12 Cu appears on the copper side of joint. Narrower heat-affected zone is observed.展开更多
The paper submits a method to calculate thermal deformation and manufacture error in surface grinding. The author established a simplified temperature field model, and derived the thermal deformation of the ground wor...The paper submits a method to calculate thermal deformation and manufacture error in surface grinding. The author established a simplified temperature field model, and derived the thermal deformation of the ground workpiece. It is found that there exists not only a upwarp thermal deformation, but also a parallel expansion thermal deformation. A upwarp thermal deformation causes a concave shape error on the profile of the workpiece, and a parallel expansion thermal deformation causes a dimension error in height. The calculations of examples are given and compared with presented experiment data.展开更多
Surface classification, 3D parting line, parting surface generation and demoldability analysis which is helpful to select optimal parting direction and optimal parting line are involved in auto-matic cavity design bas...Surface classification, 3D parting line, parting surface generation and demoldability analysis which is helpful to select optimal parting direction and optimal parting line are involved in auto-matic cavity design based on the my-testing model. A new ray-testing approach is presented to classify the part surfaces to core/cavity surfaces and undercut surfaces by automatic identifying the visibility of surfaces. A simple, direct and efficient algorithm to identify surface visibility is developed. The algorithm is robust and adapted to rather complicated geometry, so it is valuable in computer-aided mold design systems. To validate the efficiency of the approach, an experimental program is implemented. Case studies show that the approach is practical and valuable in automatic parting line and parting surface generation.展开更多
Computer aided design of heat treatment for AISI P20 mold steel with good machinability is attempted to proceed by the commercial software package Thermo-Calc (TCP+DICTRA). Through experimental and theoretical analysi...Computer aided design of heat treatment for AISI P20 mold steel with good machinability is attempted to proceed by the commercial software package Thermo-Calc (TCP+DICTRA). Through experimental and theoretical analysis of phase transformation during heat treatment, further knowledge of designing proper heat treatment is obtained. Then the machinability of AISI P20+Ni steel under given heat treatment condition is studied and the influencing factors to their machinability are analyzed. It is shown that heat treatment designed by computer simulation of carbide transformation is applicable to AISI P20+Ni steel with good machinability; AISI P20+Ni steel with tempered sorbite treated by quenching & tempering has optimal machinability; normalizing at the temperature of 910°C & tempering can avoid cracking and result in acceptable machinability in small thickness module.展开更多
A mathematical model, surface-particle-emulsion heat transfer model, ispresented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heattransfer near the surface is treated by disperse...A mathematical model, surface-particle-emulsion heat transfer model, ispresented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heattransfer near the surface is treated by dispersed particles touching the surface and through theemulsion when the distance from the surface is greater than the diameter of a particle. A film withan adjustable thickness which separates particles from the surface is not introduced in this model.The coverage ratio of particles on the surface is calculated by a stochastic model of particlepacking density on a surface. By comparison of theoretical solutions with experimental data fromsome references, the mathematical model shows better qualitative and quantitative prediction forlocal heat transfer coefficients around a horizontal immersed tube in a fluidized bed.展开更多
IntroductionBone defect caused by specific diseases or medications is very common. Autologous bone, allogeneic bone or xenogeneic bone transplantation is commonly used in clinical practice. However, autologous bone so...IntroductionBone defect caused by specific diseases or medications is very common. Autologous bone, allogeneic bone or xenogeneic bone transplantation is commonly used in clinical practice. However, autologous bone sources are limited. Xenogeneic bone cannot participate in metabolism. Because of the development of bone tissue engineering, the transplantation of new scaffold materials and autologous cells has opened up new treatment options for bone defects. The bone tissue engineering principle is applied to construct a degradable porous bone scaffold, which is implanted into the human body after loading bone cells, growth factors, etc.展开更多
This paper presents a modeling procedure for deriving a single value measurebased on a regression model, and a method for determining a statistical threshold value asidentification criterion of normal or abnormal stat...This paper presents a modeling procedure for deriving a single value measurebased on a regression model, and a method for determining a statistical threshold value asidentification criterion of normal or abnormal states of machine wear. A real numerical example isexamined by the method and identification criterion presented. The results indicate that thejudgments by the presented methods are basically consistent with the real facts, and therefore themethod and identification criterion are valuable for judging the normal or abnormal state of machinewear based on oil analysis.展开更多
Hydrogen(H_(2))sensors are of great significance in hydrogen energy development and hydrogen safety monitoring.However,achieving fast and effective detection of low concentrations of hydrogen is a key problem to be so...Hydrogen(H_(2))sensors are of great significance in hydrogen energy development and hydrogen safety monitoring.However,achieving fast and effective detection of low concentrations of hydrogen is a key problem to be solved in hydrogen sensing.In this work,we combined the excellent gas sensing properties of tin(IV)oxide(SnO_(2))and zinc oxide(ZnO)with the outstanding electrical properties of reduced graphene oxide(rGO)and prepared palladium(Pd)-doped rGO/ZnO-SnO_(2)nanocomposites by a hydrothermal method.The crystal structure,structural morphology,and elemental composition of the material were characterized by FE-SEM,TEM,xRD,XPS,Raman spectroscopy,and N2 adsorption-desorption.The results showed that the Pd-doped ZnO-SnO_(2)composites were successfully synthesized and uniformly coated on the surface of the rGO.The hydrogen gas sensing performance of the sensor prepared in this work was investigated,and the results showed that,compared with the pure Pd-doped ZnO-SnO_(2)sensor,the Pddoped rGO/ZnO-SnO_(2)sensor modified with 3 wt%rGO had better hydrogen(H_(2))-sensing response of 9.4-100 ppm H_(2)at 380℃.In addition,this sensor had extremely low time parameters(the response time and recovery time for 100 ppm H_(2)at 380℃were 4 s and 8 s,respectively)and an extremely low detection limit(50 ppb).Moreover,the sensor exhibited outstanding repeatability and restoration.According to the analysis of the sensing mechanism of this nanocomposite,the enhanced sensing performance of the Pd-doped rGO/ZnO-SnO_(2)sensor is mainly due to the heterostructure of rGO,Zno,and SnO_(2),the excellent electrical and physical properties of rGO and the synergy between rGO and Pd.展开更多
Power maximization has always been a practical consideration in wind turbines. The question of how to address optimal power capture, especially when the system dynamics are nonlinear and the actuators are subject to u...Power maximization has always been a practical consideration in wind turbines. The question of how to address optimal power capture, especially when the system dynamics are nonlinear and the actuators are subject to unknown faults, is significant. This paper studies the control methodology for variable-speed variable-pitch wind turbines including the effects of uncertain nonlinear dynamics, system fault uncertainties, and unknown external disturbances. The nonlinear model of the wind turbine is presented, and the problem of maximizing extracted energy is formulated by designing the optimal desired states. With the known system, a model-based nonlinear controller is designed; then, to handle uncertainties, the unknown nonlinearities of the wind turbine are estimated by utilizing radial basis function neural networks. The adaptive neural fault tolerant control is designed passively to be robust on model uncertainties, disturbances including wind speed and model noises, and completely unknown actuator faults including generator torque and pitch actuator torque. The Lyapunov direct method is employed to prove that the closed-loop system is uniformly bounded. Simulation studies are performed to verify the effectiveness of the proposed method.展开更多
Solar multiple （SM） and thermal storage capacity are two key design parameters for revealing the performance of direct steam generation （DSG） solar power tower plant. In the case of settled land area, SM and therm...Solar multiple （SM） and thermal storage capacity are two key design parameters for revealing the performance of direct steam generation （DSG） solar power tower plant. In the case of settled land area, SM and thermal storage capacity can be optimized to obtain the minimum levelized cost of electricity （LCOE） by adjusting the power generation output. Taking the dual-receiver DSG solar power tower plant with a given size of solar field equivalent electricity of 100 MWe in Sevilla as a reference case, the minimum LCOE is 21.77 /kWhe with an SM of 1.7 and a thermal storage capacity of 3 h. Besides Sevilla, two other sites are also introduced to discuss the influence of annual DNI. When compared with the case of Sevilla, the minimum LCOE and optimal SM of the San Jose site change just slightly, while the minimum LCOE of the Bishop site decreases by 32.8% and the optimal SM is reduced to 1.3. The influence of the size of solar field equivalent electricity is studied as well. The minimum LCOE decreases with the size of solar field, while the optimal SM and thermal storage capacity still remain unchanged. In addition, the sensitivity of different investment in sub-system is investigated. In terms ofoptimal SM and thermal storage capacity, they can decrease with the cost of thermal storage system but increase with the cost of power generation unit.展开更多
Heterogeneous vehicular clustering integrates multiple types of communication networks to work efficiently for various vehicular applications.One popular form of heterogeneous network is the integration of long-term e...Heterogeneous vehicular clustering integrates multiple types of communication networks to work efficiently for various vehicular applications.One popular form of heterogeneous network is the integration of long-term evolution(LTE)and dedicated short-range communication.The heterogeneity of such a network infrastructure and the non-cooperation involved in sharing cost/data are potential problems to solve.A vehicular clustering framework is one solution to these problems,but the framework should be formally verified and validated before being deployed in the real world.To solve these issues,first,we present a het-erogeneous framework,named destination and interest-aware clustering,for vehicular clustering that integrates vehicular ad hoc networks with the LTE network for improving road traffic efficiency.Then,we specify a model system of the proposed framework.The model is formally verified to evaluate its performance at the functional level using a model checking technique.To evaluate the performance of the proposed framework at the micro-level,a heterogeneous simulation environment is created by integrating state-of-the-art tools.The comparison of the simulation results with those of other known approaches shows that our proposed framework performs better.展开更多
The immune response to ultra-high molecular weight polyethylene wear debris is thought to beone of the majorcauses of osteolysis and aseptic loosening.An in-vitro methodfor the measurement of the response is necessary...The immune response to ultra-high molecular weight polyethylene wear debris is thought to beone of the majorcauses of osteolysis and aseptic loosening.An in-vitro methodfor the measurement of the response is necessary in orderto priori estimate the lifespan of the implants.lt is of importance to distinguish the bioactivity of various polyethylenebiomaterials.The current research focused on the inverse culturing process,which was shown to be effective toevaluate the biological reaction of mouse macrophages and wear particles by estimating the amount of inflammatorycytokines.In this study,several improvements were carried out through trial quantification.Silicon sheet wasintroduced instead of PVC seal to remove air bubbles and to eliminate the influence of potentially-attached endotoxin.Calculations along with experiments according to Stokes'law were also performed to determine the reaction time andthe minimum particle size that can be phagocytosed by macrophages in the improved method.The authorsco-incubated mouse macrophages and polyethylene particles in different sizes,densities and molecular weights usingthe new method.The result suggests that the amount of tumour necrosis factor-α(TNF-α)generated is dosagedependent on the total surface area of particles added regardless of particle size,density and molecular weight ofpolyethylene.展开更多
基金supported by the Singapore Ministry of Education(MOE)Academic Research Fund(AcRF)Tier 1(Nos.RG145/23 and RG78/24)the National Natural Science Foundation of China(No.U24A2005)Ningbo Natural Science Foundation(No.2024J183)。
文摘To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology,the propagation characteristics of Rayleigh surface waves in an elastic half-space attached by a nanoscale piezoelectric semiconductor(PSC)thin layer with flexoelectricity and size-effects are systematically investigated.Based on the Hamiltonian principle,the elastic dynamic equations and Gauss's theorem of electrostatics are obtained.The eigenvalue problem is numerically solved with a genetic algorithm in MATLAB,and the dispersion properties are obtained.The effects of various key factors,including the flexoelectricity,inertia gradients,strain gradients,electric field gradients,PSC layer thickness,steady-state carrier concentration,and bias electric fields,on the propagation and attenuation characteristics of Rayleigh surface waves are analyzed.The results demonstrate that the increases in the flexoelectric coefficient and strain gradient characteristic length lead to an increase in the real part of the complex phase velocity,while the increases in the inertia gradient characteristic length,electric field gradient characteristic length,PSC layer thickness,and steady-state carrier concentration result in a decrease.Additionally,the bias electric fields significantly influence the Rayleigh surface wave attenuation.The present findings are crucial for the accurate property evaluation of miniaturized highfrequency Rayleigh wave devices,and provide valuable theoretical support for their design and optimization.
文摘Treatment of lake sediments with salts is a promising approach for preventing phosphorus release from sediments. Five 35-d treatments of undisturbed sediment cores in the East Lake, Wuhan, China were applied under anoxic conditions： nothing added （control）, Al2（SO4）3 added, FeCl3 added, CaCl2 added, and NaNO3 added. To identify changes in the P binding sites in the sediment caused by the treatments, different P binding forms were extracted from the sediment before and after the treatments. We found that the mean P release rates for anoxic treatments with Al2（SO4）3, FeCl3, CaCl2 and NaNO3 were -0.6, 0.03, 0.6 and 2.6 mg/（m^2·d）, respectively, while the P release rate with no additives was 7.3 mg/（m^2·d）. In suboxic conditions, the concentration of total phosphorus （TP ge 657 mg/kg） in sediment was much lower than that of untreated sediment （TPaverage 688 mg/kg） and treatments with salts （TP（Al2（SO4）3） 793 mg/kg, TP（FeCl3） 781 mg/kg, TP（NaNO3） 802 mg/kg, TP（CaCl2） 747 mg/kg）. We also found that adding CaCl2 prevented P release because of apatite formation and because PCa （Ca bound P） increased at the sediment surface. Addition of Fe^3＋ and NO3^- to the sediment increased the amounts of PFe. Mn （Redox-sensitive P, mostly Fe and Mn compounds）, since iron oxide has the ability to combine P. Addition of Al2（SO4）3 increased the fraction of PAl, Fe （P bound to metal oxides （Al, Fe）） and decreased the P and Fe in the water above the anoxic sediment, showing the greater ability orAl in binding P. The results showed that Al2（SO4）3, FeCl3, CaCl2 and NaNO3 all had an effect in controlling phosphorus release. The effect was related to the forms of phosphorus existing in the sediment before treatment and the forms resulting after adding the four reagents. The combination of Al^3＋ or Fe^3＋ with NO3^- promises to be a reasonable chemical treatment for increasing the P retention capacity of sediments in eutrophic lakes. If chemical treatment is combined with bioremediation, the aim of environmental repair may be achieved.
基金sponsored by the National Natural Science Foundation of China ( 51571150,11572222)Tianjin Natural Science Foundation ( 14JCYBJC16900)
文摘Recently,magnesium and its alloys have attracted more and more attention as promising implant materials due to their excellent properties such as good biocompatibility,biodegradation,non-toxicity and comparable mechanical properties with natural bone.They can be gradually degraded and absorbed so as to avoid the second surgery for implants removal after the tissues are healed completely.In addition,they are also able to prevent the stress shielding effect in human body environment because of the density,elastic modulus and yield strength of magnesium closer to the bone.Unfortunately,the high corrosion rate which causes early mechanical failure of the implants in physiological environment limits the widespread use of magnesium alloys for clinical application in biology.And the high corrosion process usually causes huge hydrogen evolution and alkalinization,resulting in problems against the implants as well as the surrounding tissues.In order to enhance the corrosion resistance of magnesium alloys,in this study,the ZEK100 magnesium alloy was pre-deformed with a highpressure torsion(HPT)process and then fabricated hydroxyapatite(HA)coatings with different contents of Mg(OH)2 nanopowder via hydrothermal method.The specimens were characterized by scanning electron microscope(SEM)and X-ray diffraction(XRD).At the same time,prior and after the HPT procedure,the metallography,microhardness and tensile tests of specimens were characterized.Meanwhile,the corrosion behavior of the specimens was evaluated by electrochemical impedance spectroscopy(EIS)and hydrogen evolution tests.And the interface bonding strength of the HA coating on the magnesium alloy substrate was evaluated by a tape adhesion test/scratch test.Results showed that HPT processing refined the grain size and introduced a great number of twins,resulting in the enhancement of microhardness and Young’s modulus of ZEK100 magnesium alloy,but hardness values at the edge were higher than those at the center due to the uneven shear strain.At the same conditions,the HA coating on HPT-ZEK was denser,thicker than that on ZEK sample and the crystal sizes of HA were smaller on HPT-ZEK.These were attributed to fine,uniform distributed secondary phases and lots of fine grains,twins,grain boundaries in HPT-ZEK substrates which can provide more nucleation sites for the HA crystal.In terms of the amount of Mg(OH)2 nanopowder,Mg(OH)2 nanopowder significantly influenced the microstructure and thickness of the HA coating.And at a 0.3 mg/mL content of Mg(OH)2 nanopowder,there was the densest,thickest HA coating on magnesium alloys,and the crystal size of HA was minimum.Specifically,the HA coating thickness on ZEK-03(0.3 mg/mL Mg(OH)2 nanopowder)was 1.8 times of that on ZEK-00(0 mg/mL Mg(OH)2 nanopowder),while the HA coating thickness on HPT-03 was 2.6 times of that on ZEK-00.And the adhesion strength of HA coating on HPT-03 substrate was better than that on ZEK-03.In addition,HPT technology and surface modification by HA coating simultaneously increased the corrosion resistance of ZEK100 magnesium alloy and the corrosion of HPT-ZEK samples occurred in a more uniform manner,while it was pitting on the surface of ZEK100 magnesium alloy.Therefore,there was the best corrosion resistance on HPT-03 sample,which could promote the application of magnesium alloys in biomedical fields.
基金Supported by the Introduction of Key Discipline Talented People in the 11th Five-Year Plan of Tianjin (20090047)
文摘The paper presents an improved support vector machine （SVM） by combining principal component analysis （PCA） and particle swarm optimization （PSO）. Then, the improved SVM is applied to the intrusion detection system （IDS） to improve the detection rate. First, PCA is used to reduce the dimension of feature vectors. Second, we use the PSO algorithm to optimize the punishment factor C and kernel parameters oin SVM. The experimental results indicate that the intrusion detection rate （97.752 8%） of improved SVM by combining PCA and PSO is higher than those （95.635 5%） of PSO-SVM and those （90.476 2%） of standard SVM with KDD Cup 1999 data set.
文摘Both parallel and staggered plate fin arrays have shown promise for use inhigh performance heatsinks regard of its individual manufacturing costs. The geometrical andoperational parameters are very important to their cooling performance as heatsinks in practicalapplications. Fluent 5.0 commercial CFD (computational fluid dynamic) code is used to simulate theflow and heat transfer of those heatsinks of different realistic parameters. Based on thosesimulations, two correlations, concerning Nusselt number and friction factor as the functions ofgeometrical and operational parameters, FB (fin-base area ratio), PR' (ratio of spanwise pitch tolengthwise pitch) and Re, were developed. From the both, the performance comparisons for optimizinggeometrical and operational parameters of a fixed dimension heatsink are shown at constant pumpingpower and constant thermal resistance. Several optimized parameters were obtained can out performthe staggered ones.
文摘This paper presents the results of a research into capacitor discharge percussion welding （CDPW） of pure aluminum wires and pure copper sheets, using percussion welding power and special welding device. A lot of CDPW factors, which will affect aluminum and copper dissimilar bonding, are described and these parameters have also been optimized. The fracture pull, interface compounds, microstructure and hardness are all studied. The results show that aluminum wire welding to copper sheet can form a sound weld and in some conditions the fracture pull is similar to that of the pure aluminum wires. The capacitance, discharge voltage, wire taper angle and machine oil as welding assistant medium affect fracture pull. The intermetaUic compounds A12 Cu appears on the copper side of joint. Narrower heat-affected zone is observed.
文摘The paper submits a method to calculate thermal deformation and manufacture error in surface grinding. The author established a simplified temperature field model, and derived the thermal deformation of the ground workpiece. It is found that there exists not only a upwarp thermal deformation, but also a parallel expansion thermal deformation. A upwarp thermal deformation causes a concave shape error on the profile of the workpiece, and a parallel expansion thermal deformation causes a dimension error in height. The calculations of examples are given and compared with presented experiment data.
文摘Surface classification, 3D parting line, parting surface generation and demoldability analysis which is helpful to select optimal parting direction and optimal parting line are involved in auto-matic cavity design based on the my-testing model. A new ray-testing approach is presented to classify the part surfaces to core/cavity surfaces and undercut surfaces by automatic identifying the visibility of surfaces. A simple, direct and efficient algorithm to identify surface visibility is developed. The algorithm is robust and adapted to rather complicated geometry, so it is valuable in computer-aided mold design systems. To validate the efficiency of the approach, an experimental program is implemented. Case studies show that the approach is practical and valuable in automatic parting line and parting surface generation.
基金supported by the key project of Science and Technology Commission of Shanghai Local Government(015211010)
文摘Computer aided design of heat treatment for AISI P20 mold steel with good machinability is attempted to proceed by the commercial software package Thermo-Calc (TCP+DICTRA). Through experimental and theoretical analysis of phase transformation during heat treatment, further knowledge of designing proper heat treatment is obtained. Then the machinability of AISI P20+Ni steel under given heat treatment condition is studied and the influencing factors to their machinability are analyzed. It is shown that heat treatment designed by computer simulation of carbide transformation is applicable to AISI P20+Ni steel with good machinability; AISI P20+Ni steel with tempered sorbite treated by quenching & tempering has optimal machinability; normalizing at the temperature of 910°C & tempering can avoid cracking and result in acceptable machinability in small thickness module.
基金This work was financially supported by the Education Ministry of China
文摘A mathematical model, surface-particle-emulsion heat transfer model, ispresented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heattransfer near the surface is treated by dispersed particles touching the surface and through theemulsion when the distance from the surface is greater than the diameter of a particle. A film withan adjustable thickness which separates particles from the surface is not introduced in this model.The coverage ratio of particles on the surface is calculated by a stochastic model of particlepacking density on a surface. By comparison of theoretical solutions with experimental data fromsome references, the mathematical model shows better qualitative and quantitative prediction forlocal heat transfer coefficients around a horizontal immersed tube in a fluidized bed.
文摘IntroductionBone defect caused by specific diseases or medications is very common. Autologous bone, allogeneic bone or xenogeneic bone transplantation is commonly used in clinical practice. However, autologous bone sources are limited. Xenogeneic bone cannot participate in metabolism. Because of the development of bone tissue engineering, the transplantation of new scaffold materials and autologous cells has opened up new treatment options for bone defects. The bone tissue engineering principle is applied to construct a degradable porous bone scaffold, which is implanted into the human body after loading bone cells, growth factors, etc.
文摘This paper presents a modeling procedure for deriving a single value measurebased on a regression model, and a method for determining a statistical threshold value asidentification criterion of normal or abnormal states of machine wear. A real numerical example isexamined by the method and identification criterion presented. The results indicate that thejudgments by the presented methods are basically consistent with the real facts, and therefore themethod and identification criterion are valuable for judging the normal or abnormal state of machinewear based on oil analysis.
基金funded by the National Basic Research Program of China(grant No.2021YFB2012502)the National Science Foundation of China Project(grant numbers 62174163,61874121,61874012).
文摘Hydrogen(H_(2))sensors are of great significance in hydrogen energy development and hydrogen safety monitoring.However,achieving fast and effective detection of low concentrations of hydrogen is a key problem to be solved in hydrogen sensing.In this work,we combined the excellent gas sensing properties of tin(IV)oxide(SnO_(2))and zinc oxide(ZnO)with the outstanding electrical properties of reduced graphene oxide(rGO)and prepared palladium(Pd)-doped rGO/ZnO-SnO_(2)nanocomposites by a hydrothermal method.The crystal structure,structural morphology,and elemental composition of the material were characterized by FE-SEM,TEM,xRD,XPS,Raman spectroscopy,and N2 adsorption-desorption.The results showed that the Pd-doped ZnO-SnO_(2)composites were successfully synthesized and uniformly coated on the surface of the rGO.The hydrogen gas sensing performance of the sensor prepared in this work was investigated,and the results showed that,compared with the pure Pd-doped ZnO-SnO_(2)sensor,the Pddoped rGO/ZnO-SnO_(2)sensor modified with 3 wt%rGO had better hydrogen(H_(2))-sensing response of 9.4-100 ppm H_(2)at 380℃.In addition,this sensor had extremely low time parameters(the response time and recovery time for 100 ppm H_(2)at 380℃were 4 s and 8 s,respectively)and an extremely low detection limit(50 ppb).Moreover,the sensor exhibited outstanding repeatability and restoration.According to the analysis of the sensing mechanism of this nanocomposite,the enhanced sensing performance of the Pd-doped rGO/ZnO-SnO_(2)sensor is mainly due to the heterostructure of rGO,Zno,and SnO_(2),the excellent electrical and physical properties of rGO and the synergy between rGO and Pd.
文摘Power maximization has always been a practical consideration in wind turbines. The question of how to address optimal power capture, especially when the system dynamics are nonlinear and the actuators are subject to unknown faults, is significant. This paper studies the control methodology for variable-speed variable-pitch wind turbines including the effects of uncertain nonlinear dynamics, system fault uncertainties, and unknown external disturbances. The nonlinear model of the wind turbine is presented, and the problem of maximizing extracted energy is formulated by designing the optimal desired states. With the known system, a model-based nonlinear controller is designed; then, to handle uncertainties, the unknown nonlinearities of the wind turbine are estimated by utilizing radial basis function neural networks. The adaptive neural fault tolerant control is designed passively to be robust on model uncertainties, disturbances including wind speed and model noises, and completely unknown actuator faults including generator torque and pitch actuator torque. The Lyapunov direct method is employed to prove that the closed-loop system is uniformly bounded. Simulation studies are performed to verify the effectiveness of the proposed method.
基金This research was supported by the National Natural Science Foundation of China （Grant No. 51676069）, the 111 Project （1312034）, and the Fundamental Research Funds for the Central Universities （Grant No. 2016XS30）.
文摘Solar multiple （SM） and thermal storage capacity are two key design parameters for revealing the performance of direct steam generation （DSG） solar power tower plant. In the case of settled land area, SM and thermal storage capacity can be optimized to obtain the minimum levelized cost of electricity （LCOE） by adjusting the power generation output. Taking the dual-receiver DSG solar power tower plant with a given size of solar field equivalent electricity of 100 MWe in Sevilla as a reference case, the minimum LCOE is 21.77 /kWhe with an SM of 1.7 and a thermal storage capacity of 3 h. Besides Sevilla, two other sites are also introduced to discuss the influence of annual DNI. When compared with the case of Sevilla, the minimum LCOE and optimal SM of the San Jose site change just slightly, while the minimum LCOE of the Bishop site decreases by 32.8% and the optimal SM is reduced to 1.3. The influence of the size of solar field equivalent electricity is studied as well. The minimum LCOE decreases with the size of solar field, while the optimal SM and thermal storage capacity still remain unchanged. In addition, the sensitivity of different investment in sub-system is investigated. In terms ofoptimal SM and thermal storage capacity, they can decrease with the cost of thermal storage system but increase with the cost of power generation unit.
基金the European Project H2020(No.H2020-MG-2018-2019-2020,ENDURUNS).Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature。
文摘Heterogeneous vehicular clustering integrates multiple types of communication networks to work efficiently for various vehicular applications.One popular form of heterogeneous network is the integration of long-term evolution(LTE)and dedicated short-range communication.The heterogeneity of such a network infrastructure and the non-cooperation involved in sharing cost/data are potential problems to solve.A vehicular clustering framework is one solution to these problems,but the framework should be formally verified and validated before being deployed in the real world.To solve these issues,first,we present a het-erogeneous framework,named destination and interest-aware clustering,for vehicular clustering that integrates vehicular ad hoc networks with the LTE network for improving road traffic efficiency.Then,we specify a model system of the proposed framework.The model is formally verified to evaluate its performance at the functional level using a model checking technique.To evaluate the performance of the proposed framework at the micro-level,a heterogeneous simulation environment is created by integrating state-of-the-art tools.The comparison of the simulation results with those of other known approaches shows that our proposed framework performs better.
基金an extension of a conference paper presentedat the 10th International Biotribology Forum and the 38th Biotribology Symposium,held at Kumamoto University,Japan.
文摘The immune response to ultra-high molecular weight polyethylene wear debris is thought to beone of the majorcauses of osteolysis and aseptic loosening.An in-vitro methodfor the measurement of the response is necessary in orderto priori estimate the lifespan of the implants.lt is of importance to distinguish the bioactivity of various polyethylenebiomaterials.The current research focused on the inverse culturing process,which was shown to be effective toevaluate the biological reaction of mouse macrophages and wear particles by estimating the amount of inflammatorycytokines.In this study,several improvements were carried out through trial quantification.Silicon sheet wasintroduced instead of PVC seal to remove air bubbles and to eliminate the influence of potentially-attached endotoxin.Calculations along with experiments according to Stokes'law were also performed to determine the reaction time andthe minimum particle size that can be phagocytosed by macrophages in the improved method.The authorsco-incubated mouse macrophages and polyethylene particles in different sizes,densities and molecular weights usingthe new method.The result suggests that the amount of tumour necrosis factor-α(TNF-α)generated is dosagedependent on the total surface area of particles added regardless of particle size,density and molecular weight ofpolyethylene.
