One great surprise discovered in modern physics is that all elementary particles exhibit the property of wave-particle duality. We investigated this problem recently and found a simple way to explain this puzzle. We p...One great surprise discovered in modern physics is that all elementary particles exhibit the property of wave-particle duality. We investigated this problem recently and found a simple way to explain this puzzle. We proposed that all particles, including massless particles such as photon and massive particles such as electron, can be treated as excitation waves in the vacuum, which behaves like a physical medium. Using such a model, the phenomenon of wave-particle duality can be explained naturally. The key question now is to find out what kind of physical properties this vacuum medium may have. In this paper, we investigate if the vacuum can be modeled as an elastic solid or a dielectric medium as envisioned in the Maxwell theory of electricity and magnetism. We show that a similar form of wave equation can be derived in three cases: (1) By modelling the vacuum medium as an elastic solid;(2) By constructing a simple Lagrangian density that is a 3-D extension of a stretched string or a vibrating membrane;(3) By assuming that the vacuum is a dielectric medium, from which the wave equation can be derived directly from Maxwell’s equations. Similarity between results of these three systems suggests that the vacuum can be modelled as a mechanical continuum, and the excitation wave in the vacuum behaves like some of the excitation waves in a physical medium.展开更多
An internal solitary wave of elevation in a two-layer density stratified system of an incompressible, viscous and homogeneous fluid was studied. The run-up of a wave of elevation encountering different slopes was inve...An internal solitary wave of elevation in a two-layer density stratified system of an incompressible, viscous and homogeneous fluid was studied. The run-up of a wave of elevation encountering different slopes was investigated numerically based on solving the continuity, Navier-Stokes and convective-diffusion equations within the Boussinesq approximation. The commercial software COMSOL Multiphysics was used to conduct the numerical simulations. For gradual shoals, a bolus formed that transported dense fluid up the shoal. The bolus disappeared when it reached its maximum height on the slope due to the draining of the dense fluid. Various shoal angles were simulated to detect the critical angle above which a bolus does not form. An angle of 30 or less resulted in the formation of a bolus. In addition, the simulations demonstrated that the size of the bolus induced by shallower slopes was larger and that the vertical height traveled by the bolus was insensitive to the slope of the shoal.展开更多
Ni60-WC particles are used to improve the wear resistance of hard-facing steel due to their high hardness. An emerging technology that combines laser with cold spraying to deposit the hard-facing coatings is known as ...Ni60-WC particles are used to improve the wear resistance of hard-facing steel due to their high hardness. An emerging technology that combines laser with cold spraying to deposit the hard-facing coatings is known as supersonic laser deposition. In this study, Ni60-WC is deposited on low-carbon steel using SLD. The microstructure and performance of the coatings are investigated through SEM, optical microscopy, EDS, XRD, microhardness and pin-on-disc wear tests. The experimental results of the coating processed with the optimal parameters are compared to those of the coating deposited using laser cladding.展开更多
Accurate estimation of stiffness loss is a challenging problem in structural health monitoring.In this studyorthogonal wavelet decomposition is used for identifying the stiffness loss in a single degree of freedom spr...Accurate estimation of stiffness loss is a challenging problem in structural health monitoring.In this studyorthogonal wavelet decomposition is used for identifying the stiffness loss in a single degree of freedom spring-mass-dampersystem.The effects of excitation frequency on accuracy of damage detection is investigated.Results show that pseudo-aliaseffects caused by the orthogonal wavelet decomposition(OWD),affect damage detectability.It is demonstrated that theproposed approach is sunable for damage detection when the excitation frequency is relatively low.This study shows how apriori knowledge about the signal and ability to control the sampling frequency can enhance damage detectability.展开更多
Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, whic...Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.展开更多
In this work, bulk acoustic wave propagation properties of langasite single crystal excited by lateral electric field have been investigated. Three important crystal cuts have been identified for different operational...In this work, bulk acoustic wave propagation properties of langasite single crystal excited by lateral electric field have been investigated. Three important crystal cuts have been identified for different operational modes of lateral field excitation （LFE） on langasite substrate, namely the （yxl）65° （pure-LFE mode）, （yxl）45° （quasi-LFE mode）, and （yxl）0° （pseudo-LFE mode）. Devices on langasite substrate with the above cuts were fabricated and tested, and the experimental results agree well with the theoretical analysis. It is found that a pure thickness shear mode exists in the （yxl）65° langasite LFE device with the bare side facing liquid, and no spurious mode is found due to its moderately large piezoelectric coupling factor. In addition, （yxl）0° langasite LFE device is also found suitable for liquid phase sensing applications.展开更多
Modern metropolises are increasingly affected by air quality problems. Transportation is one of the largest sources of several pollutants emissions, such as nitrogen oxides (NOx) and carbon monoxide (CO). Today in the...Modern metropolises are increasingly affected by air quality problems. Transportation is one of the largest sources of several pollutants emissions, such as nitrogen oxides (NOx) and carbon monoxide (CO). Today in the EU, vehicles' emissions are strictly limited by Euro 6 norm-Euro VI for heavy-duty vehicles-which is periodically upgraded. To match such limits, manufacturers are forced in developing new technologies to perform new sustainable vehicles design strategies, such as EVs and HEVs. Present work's aim is to provide the design of series-hybrid urban transportation bus, equipped with a novel thermal power unit, namely a small gas turbine, to exploit its cleaner combustion process in comparison with an ICE. The control logic is described, while the main drivetrain components are chosen, and suitable models from suppliers are selected as well. Then, some simulations of the resulting vehicle are performed on opportune drive cycles, using Advisor, a free software based on Matlab-Simulink environment, published by US' National Renewable Energy Laboratory (NREL). Two different final configurations are environmentally and economically analysed, with the thermal power unit being respectively fuelled by compressed natural gas (CNG) and liquefied petroleum gas (LPG). Both satisfy the Euro VI norms, showing a substantial emission reduction (-89% and -43% in CO and THC releases respectively) in comparison to pollutants' threshold values.展开更多
Fiber-reinforced polymer composite materials have become materials of choice for manufacturing application due to their high specific stiffness, strength and fatigue life, low density and thermal expansion coefficient...Fiber-reinforced polymer composite materials have become materials of choice for manufacturing application due to their high specific stiffness, strength and fatigue life, low density and thermal expansion coefficient. However, there are some types of defects such as porosity that form during the manufacturing processes of composites and alter their mechanical behavior and material properties. In his study, hand lay-up was conducted to fabricate samples of carbon fiber-reinforced polymer composites with three different vacuum levels in order to vary porosity content. Nondestructive evaluation, destructive techniques and mechanical testing were conducted. Nondestructive evaluation results showed the trend in percentages of porosity through-thickness. Serial sectioning images revealed significant details about the composite’s internal structure such as the volume, morphology and distribution of porosity. Mechanical testing results showed that porosity led to a decrease in both Mode I static interlaminar fracture toughness and Mode I cyclic strain energy release rate fatigue life. The fractographic micrographs showed that porosity content increased as the vacuum decreased, and it drew a relationship between fracture mechanisms and mechanical properties of the composite under different modes of loading as a result of the porosity effects. Finally, in order to accurately quantify porosity percentages included in the samples of different vacuum levels, a comparison was made between the parameters and percentages resulted from the nondestructive evaluation and mechanical testing and the features resulted from fractography and serial sectioning.展开更多
To solve the problems of poor forming and easy adhesion of the stainless steel,Cu alloyed layer on the stainless steels was prepared by the double glow plasma surface alloying technique.The experimentalresults indicat...To solve the problems of poor forming and easy adhesion of the stainless steel,Cu alloyed layer on the stainless steels was prepared by the double glow plasma surface alloying technique.The experimentalresults indicated that the supersaturated copper dispersedly precipitated in grain interior and crystalboundaries and formed the vermicular structure.The tribologicaltests indicated that the friction coefficient of the Cu alloyed layer was lower than that of the stainless steels.The wear rate of stainless steelin the presence of Cu alloyed layer was approximately 2-fold lower than that in the absence of the alloyed layer.The results of the incrementalforming indicated that the ploughing phenomenon was not observed on the stainless steelin the presence of Cu alloyed layer during the incrementalforming,while the stainless steelpresented the deep ploughing.Therefore,Cu alloyed layer on stainless steelexhibited excellent self-lubrication and forming properties.展开更多
Glow discharge was utilized to add oxygen functional groups to the graphene platelets sample produced in chemical exfoliation synthesis. It was concluded based on Raman spectra that the graphene sample treated with th...Glow discharge was utilized to add oxygen functional groups to the graphene platelets sample produced in chemical exfoliation synthesis. It was concluded based on Raman spectra that the graphene sample treated with the glow discharge preserves specific graphene features while no transformation to amorphous carbon is happening. SEM and EDS results indicated the increases of oxygen content in the graphene sample after the exposure to the glow discharge. Raman spectra also support the fact that the graphene platelets have been decorated with oxygen as the result of the glow discharge treatment.展开更多
The primary purpose of this study is to exploit the effect of Earth＇s non-sphericity perturbation, particularly due to the J2 term, in order to optimize the capture sequence of potential orbital debris, that is the c...The primary purpose of this study is to exploit the effect of Earth＇s non-sphericity perturbation, particularly due to the J2 term, in order to optimize the capture sequence of potential orbital debris, that is the cumulative AV associated to the transfers between one object and the others. As results of several researches and model predictions, many international agencies agree that the growing population of objects and debris in LEO （low earth orbits）, will follow a diverging trend in the future. This, in turn, would constitute a serious threat to circum-terrestrial space safety and sustainability. In LEO, the ,J disturbance is prevailing over the others, and it acts by affecting the longitude of the ascending node （Ω）, the argument of perigee （ω） and, accordingly, the true anomaly （v）. Therefore, the goal of optimizing the AV is achieved by taking advantage of the rate of variation of Ω and ω, thereby compensating for the △Ω and △ω, present between the orbital transfer vehicle （chaser） and the debris to be captured （target）. Obviously, the perturbation will lead to favourable variations of the orbital parameters only for some combinations of Ω and ω. Yet the presence of a debris population with random distribution of Ω and ω, makes this application particularly suited to the problem. The single maneuver has been modelled with a 4-impulse time fixed rendezvous and the optimization problem has been addressed by implementing a hybrid evolutionary algorithm, which adopts, in parallel, three different strategies, namely, genetic algorithm, differential evolution and particle swarm optimization.展开更多
Quartz crystal resonators （QCRs） with circular electrodes have been widely used for various liquid and gas sensing applications. In this work, quartz crystal resonators with elliptical electrodes were studied and te...Quartz crystal resonators （QCRs） with circular electrodes have been widely used for various liquid and gas sensing applications. In this work, quartz crystal resonators with elliptical electrodes were studied and tested for liquid property measurement. Mindlin＇s theory was used to optimize the dimension and geometry of the electrodes and a 5-MHz QCR with minimum series resistance and without any spurious modes was obtained. A series of AT-cut QCRs with elliptical electrodes of different sizes were fabricated and their sensing performances were compared to devices with circular electrodes. The experimental result shows that the device with elliptical electrodes can obtain lower resonance impedance and a higher Q factor, which results in a better loading capability. Even though the sensitivities of devices with elliptical and circular electrodes are found to be similar, the sensor with elliptical electrodes has much higher resolution due to a better frequency stability. The study indicates that the performance of QCRs with elliptical electrodes is superior to that of traditional QCRs with circular electrodes.展开更多
This paper presents a novel concept, the Hybrid Power Pack (HPP), which consists of a hybridization kit for transforming small city cars, powered by an original diesel engine, into a parallel hybrid vehicle. The study...This paper presents a novel concept, the Hybrid Power Pack (HPP), which consists of a hybridization kit for transforming small city cars, powered by an original diesel engine, into a parallel hybrid vehicle. The study was jointly conducted by the University of Rome “Sapienza” and the Enea Casaccia research center. The idea is to design a hybrid powertrain that can be installed in a typical microcar, which means that all systems and components will be influenced by the limited space available in the motor compartment of the vehicle. In this paper the details of the mechanical and electrical realization of the powertrain will be discussed and the simulation of a small city car equipped with HPP will be presented and the results discussed and analyzed. The hybrid system also includes the battery pack which is composed of twenty-four Li-ion cells made by EIG, connected in series. The storage system is controlled as regards the voltage and temperature by a Battery Management System (BMS). All the above components are connected and managed by a control unit. The HPP presented in this paper obtains a reduction in fuel consumption higher than 20%. The solution presented with the HPP with its management strategy and the addition of the “plug-in function” makes the hybrid vehicle suitable in terms of performance and consumption in every driving conditions. The ideal strategy behind the “plug-in function” could represent a guideline for further achievements and experimentations, because it offers a simple hardware layout and a real reduction in fuel consumption.展开更多
The gas-kinetic theory based flux splitting method has been successfully proposed for solving one-and two-dimensional ideal magnetohydrodynamics by Xu et al. [J.Comput.Phys.,1999;2000],respectively.This paper extends ...The gas-kinetic theory based flux splitting method has been successfully proposed for solving one-and two-dimensional ideal magnetohydrodynamics by Xu et al. [J.Comput.Phys.,1999;2000],respectively.This paper extends the kinetic method to solve three-dimensional ideal magnetohydrodynamics equations,where an adaptive parameter 17 is used to control the numerical dissipation in the flux splitting method. Several numerical examples are given to demonstrate that the proposed method can achieve high numerical accuracy and resolve strong discontinuous waves in three dimensional ideal MHD problems.展开更多
This paper describes a ZnO-nanotaper array sacrificial templated synthetic approach for the fabrication of the arrays of nanotubes with tube-walls assembled by building-blocks of Ag-nanoplates, Au-nanorods, Pt-nanotho...This paper describes a ZnO-nanotaper array sacrificial templated synthetic approach for the fabrication of the arrays of nanotubes with tube-walls assembled by building-blocks of Ag-nanoplates, Au-nanorods, Pt-nanothorns or Pd-nanopyramids, thus possessing high-density 3D ＂hot spots＂ in sub-10-nm gaps of neighboring building blocks with nano-tips, -corners or -edges. Additionally, these hierarchical nanostructure arrays possess high surface area with rich surface chemistry, being beneficial to capturing the analyte. The Ag-nanoplate- assembled nanotube arrays can be used as sensitive surface-enhanced Raman scattering （SERS） substrates with good signal uniformity and reproducibility. Using such Ag hierarchical nanostructure arrays as SERS-substrates, not only has 10-14 M rhodamine 6G been identified, but also 10-7 M polychlorinated biphenyls （PCBs, a notorious class of persistent organic pollutants） are recognized, and even two congeners of PCBs can be identified in a mixture, showing the potential applications of the materials in SERS-based rapid detection of environmental organic pollutants.展开更多
Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. ...Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. During a single pass of the friction stir welding （FSW） process, the nano-lamellar structure of the parent material （PM） was retained but was observed to fragment into equiaxed grains during the second pass. FSW has been modeled as a severe deformation process in which the material is subjected to an instantaneous high shear strain rate followed by extreme shear strains. The loss of the nano-lamellar layers was attributed to the increased strain and longer time at temperature resulting from the second pass of the FSW process. Kinematic modeling was used to predict the global average shear strain and shear strain rates experienced by the ARB material during the FSW process. The results of this study indicate that through careful selection of FSW parameters, the nano-lamellar structure and its associated higher strength can be maintained using FSW to join ARB NLC panels.展开更多
Graphene platelet networks (GPNs) were deposited onto silicon substrates by means of anodic arc discharge ignited between two graphite electrodes.Substrate temperature and pressure of helium atmosphere were optimized ...Graphene platelet networks (GPNs) were deposited onto silicon substrates by means of anodic arc discharge ignited between two graphite electrodes.Substrate temperature and pressure of helium atmosphere were optimized for the production of the carbon nanomaterials.The samples were modified or destroyed with different methods to mimic typical environments responsible of severe surface degradation.The emulated conditions were performed by four surface treatments,namely thermal oxidation,substrate overheating,exposition to glow discharge,and metal coating due to arc plasma.In the next step,the samples were regenerated on the same substrates with identical deposition technique.Damaging and re-growth of GPN samples were systematically characterized by scanning electron microscopy and Raman spectroscopy.The full regeneration of the structural and morphological properties of the samples has proven that this healing method by arc plasma is adequate for restoring the functionality of2D nanostructures exposed to harsh environments.展开更多
Natural gas, whose primary constituent is methane, has been considered a convincing alternative for the growth of the energy supply worldwide. Adsorbed natural gas （ANG）, the most promising methane storage method, h...Natural gas, whose primary constituent is methane, has been considered a convincing alternative for the growth of the energy supply worldwide. Adsorbed natural gas （ANG）, the most promising methane storage method, has been an active field of study in the past two decades. ANG constitutes a safe and low-cost way to store methane for natural gas vehicles at an acceptable energy density while working at substantially low pressures （3.5- 4.0 MPa）, allowing for conformable store tank. This work serves to review the state-of-the-art development reported in the scientific literature on adsorbents, adsorption theories, ANG conformable tanks, and related technolo- gies on ANG vehicles. Patent literature has also been searched and discussed. The review aims at illustrating both achievements and problems of the ANG technologies-based vehicles, as well as forecasting the development trends and critical issues to be resolved of these technologies.展开更多
Laminar flow design is one of the most effective ways to reduce the drag of a commercial aircraft by expanding the laminar flow region on the surface of the aircraft. As material science develops, the emergence of new...Laminar flow design is one of the most effective ways to reduce the drag of a commercial aircraft by expanding the laminar flow region on the surface of the aircraft. As material science develops, the emergence of new materials such as low surface energy materials has offered new choices for laminar flow design of commercial aircraft. Different types of low surface energy micro-nano coatings are prepared to verify the effects on the boundary layer transition position and the drag of the airfoil through wind tunnel tests. The infrared thermal imaging technology is adopted for measuring the boundary layer transition, while the momentum integral approach is employed to measure the drag coefficient through a wake rake. Infrared thermal imaging results indicate that the coatings are capable of moving backward the boundary layer transition position at both a low velocity of Mach number 0.15 and a high velocity of Mach number 0.785. Results of the momentum integral approach demonstrate that the drag coefficients are reduced obviously within the cruising angle of attack range from 1° and 5° by introducing the low surface energy micro-nano coating technology.展开更多
文摘One great surprise discovered in modern physics is that all elementary particles exhibit the property of wave-particle duality. We investigated this problem recently and found a simple way to explain this puzzle. We proposed that all particles, including massless particles such as photon and massive particles such as electron, can be treated as excitation waves in the vacuum, which behaves like a physical medium. Using such a model, the phenomenon of wave-particle duality can be explained naturally. The key question now is to find out what kind of physical properties this vacuum medium may have. In this paper, we investigate if the vacuum can be modeled as an elastic solid or a dielectric medium as envisioned in the Maxwell theory of electricity and magnetism. We show that a similar form of wave equation can be derived in three cases: (1) By modelling the vacuum medium as an elastic solid;(2) By constructing a simple Lagrangian density that is a 3-D extension of a stretched string or a vibrating membrane;(3) By assuming that the vacuum is a dielectric medium, from which the wave equation can be derived directly from Maxwell’s equations. Similarity between results of these three systems suggests that the vacuum can be modelled as a mechanical continuum, and the excitation wave in the vacuum behaves like some of the excitation waves in a physical medium.
文摘An internal solitary wave of elevation in a two-layer density stratified system of an incompressible, viscous and homogeneous fluid was studied. The run-up of a wave of elevation encountering different slopes was investigated numerically based on solving the continuity, Navier-Stokes and convective-diffusion equations within the Boussinesq approximation. The commercial software COMSOL Multiphysics was used to conduct the numerical simulations. For gradual shoals, a bolus formed that transported dense fluid up the shoal. The bolus disappeared when it reached its maximum height on the slope due to the draining of the dense fluid. Various shoal angles were simulated to detect the critical angle above which a bolus does not form. An angle of 30 or less resulted in the formation of a bolus. In addition, the simulations demonstrated that the size of the bolus induced by shallower slopes was larger and that the vertical height traveled by the bolus was insensitive to the slope of the shoal.
基金sponsored by the Centre for Industrial Photonics, Institute for Manufacture, Department of Engineering, University of Cambridgethe Natural Science Foundation of China (51271170)+1 种基金China International Science and Technology Cooperation Project (2011DFR50540)Major Scientific and Technological Special Key Industrial Project of Zhejiang Province (2012C11001)
文摘Ni60-WC particles are used to improve the wear resistance of hard-facing steel due to their high hardness. An emerging technology that combines laser with cold spraying to deposit the hard-facing coatings is known as supersonic laser deposition. In this study, Ni60-WC is deposited on low-carbon steel using SLD. The microstructure and performance of the coatings are investigated through SEM, optical microscopy, EDS, XRD, microhardness and pin-on-disc wear tests. The experimental results of the coating processed with the optimal parameters are compared to those of the coating deposited using laser cladding.
文摘Accurate estimation of stiffness loss is a challenging problem in structural health monitoring.In this studyorthogonal wavelet decomposition is used for identifying the stiffness loss in a single degree of freedom spring-mass-dampersystem.The effects of excitation frequency on accuracy of damage detection is investigated.Results show that pseudo-aliaseffects caused by the orthogonal wavelet decomposition(OWD),affect damage detectability.It is demonstrated that theproposed approach is sunable for damage detection when the excitation frequency is relatively low.This study shows how apriori knowledge about the signal and ability to control the sampling frequency can enhance damage detectability.
基金supported by the 973 program under grant 2012CB825601the Chinese Academy of Sciences (KZZD-EW-01-4)+3 种基金the National Natural Science Foundation of China (Nos.41204126,41231068,41274192,41031066 and 41374176)the Specialized Research Fund for State Key Laboratoriessupported by NSFAGS1153323 and AGS1062050support by the Youth Innovation Promotion Association of CAS (2015122)
文摘Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.
基金Project supported by the National Natural Science Foundation of China(Grant No.60571014)
文摘In this work, bulk acoustic wave propagation properties of langasite single crystal excited by lateral electric field have been investigated. Three important crystal cuts have been identified for different operational modes of lateral field excitation （LFE） on langasite substrate, namely the （yxl）65° （pure-LFE mode）, （yxl）45° （quasi-LFE mode）, and （yxl）0° （pseudo-LFE mode）. Devices on langasite substrate with the above cuts were fabricated and tested, and the experimental results agree well with the theoretical analysis. It is found that a pure thickness shear mode exists in the （yxl）65° langasite LFE device with the bare side facing liquid, and no spurious mode is found due to its moderately large piezoelectric coupling factor. In addition, （yxl）0° langasite LFE device is also found suitable for liquid phase sensing applications.
文摘Modern metropolises are increasingly affected by air quality problems. Transportation is one of the largest sources of several pollutants emissions, such as nitrogen oxides (NOx) and carbon monoxide (CO). Today in the EU, vehicles' emissions are strictly limited by Euro 6 norm-Euro VI for heavy-duty vehicles-which is periodically upgraded. To match such limits, manufacturers are forced in developing new technologies to perform new sustainable vehicles design strategies, such as EVs and HEVs. Present work's aim is to provide the design of series-hybrid urban transportation bus, equipped with a novel thermal power unit, namely a small gas turbine, to exploit its cleaner combustion process in comparison with an ICE. The control logic is described, while the main drivetrain components are chosen, and suitable models from suppliers are selected as well. Then, some simulations of the resulting vehicle are performed on opportune drive cycles, using Advisor, a free software based on Matlab-Simulink environment, published by US' National Renewable Energy Laboratory (NREL). Two different final configurations are environmentally and economically analysed, with the thermal power unit being respectively fuelled by compressed natural gas (CNG) and liquefied petroleum gas (LPG). Both satisfy the Euro VI norms, showing a substantial emission reduction (-89% and -43% in CO and THC releases respectively) in comparison to pollutants' threshold values.
文摘Fiber-reinforced polymer composite materials have become materials of choice for manufacturing application due to their high specific stiffness, strength and fatigue life, low density and thermal expansion coefficient. However, there are some types of defects such as porosity that form during the manufacturing processes of composites and alter their mechanical behavior and material properties. In his study, hand lay-up was conducted to fabricate samples of carbon fiber-reinforced polymer composites with three different vacuum levels in order to vary porosity content. Nondestructive evaluation, destructive techniques and mechanical testing were conducted. Nondestructive evaluation results showed the trend in percentages of porosity through-thickness. Serial sectioning images revealed significant details about the composite’s internal structure such as the volume, morphology and distribution of porosity. Mechanical testing results showed that porosity led to a decrease in both Mode I static interlaminar fracture toughness and Mode I cyclic strain energy release rate fatigue life. The fractographic micrographs showed that porosity content increased as the vacuum decreased, and it drew a relationship between fracture mechanisms and mechanical properties of the composite under different modes of loading as a result of the porosity effects. Finally, in order to accurately quantify porosity percentages included in the samples of different vacuum levels, a comparison was made between the parameters and percentages resulted from the nondestructive evaluation and mechanical testing and the features resulted from fractography and serial sectioning.
基金Funded by the National Natural Science Foundation of China(Nos.51245010 and 51405242)the Natural Science Foundation of Jiangsu Province,China(No.BK2012463)
文摘To solve the problems of poor forming and easy adhesion of the stainless steel,Cu alloyed layer on the stainless steels was prepared by the double glow plasma surface alloying technique.The experimentalresults indicated that the supersaturated copper dispersedly precipitated in grain interior and crystalboundaries and formed the vermicular structure.The tribologicaltests indicated that the friction coefficient of the Cu alloyed layer was lower than that of the stainless steels.The wear rate of stainless steelin the presence of Cu alloyed layer was approximately 2-fold lower than that in the absence of the alloyed layer.The results of the incrementalforming indicated that the ploughing phenomenon was not observed on the stainless steelin the presence of Cu alloyed layer during the incrementalforming,while the stainless steelpresented the deep ploughing.Therefore,Cu alloyed layer on stainless steelexhibited excellent self-lubrication and forming properties.
文摘Glow discharge was utilized to add oxygen functional groups to the graphene platelets sample produced in chemical exfoliation synthesis. It was concluded based on Raman spectra that the graphene sample treated with the glow discharge preserves specific graphene features while no transformation to amorphous carbon is happening. SEM and EDS results indicated the increases of oxygen content in the graphene sample after the exposure to the glow discharge. Raman spectra also support the fact that the graphene platelets have been decorated with oxygen as the result of the glow discharge treatment.
文摘The primary purpose of this study is to exploit the effect of Earth＇s non-sphericity perturbation, particularly due to the J2 term, in order to optimize the capture sequence of potential orbital debris, that is the cumulative AV associated to the transfers between one object and the others. As results of several researches and model predictions, many international agencies agree that the growing population of objects and debris in LEO （low earth orbits）, will follow a diverging trend in the future. This, in turn, would constitute a serious threat to circum-terrestrial space safety and sustainability. In LEO, the ,J disturbance is prevailing over the others, and it acts by affecting the longitude of the ascending node （Ω）, the argument of perigee （ω） and, accordingly, the true anomaly （v）. Therefore, the goal of optimizing the AV is achieved by taking advantage of the rate of variation of Ω and ω, thereby compensating for the △Ω and △ω, present between the orbital transfer vehicle （chaser） and the debris to be captured （target）. Obviously, the perturbation will lead to favourable variations of the orbital parameters only for some combinations of Ω and ω. Yet the presence of a debris population with random distribution of Ω and ω, makes this application particularly suited to the problem. The single maneuver has been modelled with a 4-impulse time fixed rendezvous and the optimization problem has been addressed by implementing a hybrid evolutionary algorithm, which adopts, in parallel, three different strategies, namely, genetic algorithm, differential evolution and particle swarm optimization.
基金supported by the National Natural Science Foundation of China (Grant No.60571014)
文摘Quartz crystal resonators （QCRs） with circular electrodes have been widely used for various liquid and gas sensing applications. In this work, quartz crystal resonators with elliptical electrodes were studied and tested for liquid property measurement. Mindlin＇s theory was used to optimize the dimension and geometry of the electrodes and a 5-MHz QCR with minimum series resistance and without any spurious modes was obtained. A series of AT-cut QCRs with elliptical electrodes of different sizes were fabricated and their sensing performances were compared to devices with circular electrodes. The experimental result shows that the device with elliptical electrodes can obtain lower resonance impedance and a higher Q factor, which results in a better loading capability. Even though the sensitivities of devices with elliptical and circular electrodes are found to be similar, the sensor with elliptical electrodes has much higher resolution due to a better frequency stability. The study indicates that the performance of QCRs with elliptical electrodes is superior to that of traditional QCRs with circular electrodes.
文摘This paper presents a novel concept, the Hybrid Power Pack (HPP), which consists of a hybridization kit for transforming small city cars, powered by an original diesel engine, into a parallel hybrid vehicle. The study was jointly conducted by the University of Rome “Sapienza” and the Enea Casaccia research center. The idea is to design a hybrid powertrain that can be installed in a typical microcar, which means that all systems and components will be influenced by the limited space available in the motor compartment of the vehicle. In this paper the details of the mechanical and electrical realization of the powertrain will be discussed and the simulation of a small city car equipped with HPP will be presented and the results discussed and analyzed. The hybrid system also includes the battery pack which is composed of twenty-four Li-ion cells made by EIG, connected in series. The storage system is controlled as regards the voltage and temperature by a Battery Management System (BMS). All the above components are connected and managed by a control unit. The HPP presented in this paper obtains a reduction in fuel consumption higher than 20%. The solution presented with the HPP with its management strategy and the addition of the “plug-in function” makes the hybrid vehicle suitable in terms of performance and consumption in every driving conditions. The ideal strategy behind the “plug-in function” could represent a guideline for further achievements and experimentations, because it offers a simple hardware layout and a real reduction in fuel consumption.
基金supported by the National Basic Research Program under the Grant 2005CB321703the National Natural Science Foundation of China(No.10925101 and No.10828101)+4 种基金the Doctoral Program of the Education Ministry of China(No.20070001036)the Program for New Century Excellent Talents in University(No.NCET-07-0022)supported by Hong Kong Research Grant Council 621709National Natural Science Foundation of China(Project No.10928205)National Key Basic Research Program(2009CB724101)
文摘The gas-kinetic theory based flux splitting method has been successfully proposed for solving one-and two-dimensional ideal magnetohydrodynamics by Xu et al. [J.Comput.Phys.,1999;2000],respectively.This paper extends the kinetic method to solve three-dimensional ideal magnetohydrodynamics equations,where an adaptive parameter 17 is used to control the numerical dissipation in the flux splitting method. Several numerical examples are given to demonstrate that the proposed method can achieve high numerical accuracy and resolve strong discontinuous waves in three dimensional ideal MHD problems.
文摘This paper describes a ZnO-nanotaper array sacrificial templated synthetic approach for the fabrication of the arrays of nanotubes with tube-walls assembled by building-blocks of Ag-nanoplates, Au-nanorods, Pt-nanothorns or Pd-nanopyramids, thus possessing high-density 3D ＂hot spots＂ in sub-10-nm gaps of neighboring building blocks with nano-tips, -corners or -edges. Additionally, these hierarchical nanostructure arrays possess high surface area with rich surface chemistry, being beneficial to capturing the analyte. The Ag-nanoplate- assembled nanotube arrays can be used as sensitive surface-enhanced Raman scattering （SERS） substrates with good signal uniformity and reproducibility. Using such Ag hierarchical nanostructure arrays as SERS-substrates, not only has 10-14 M rhodamine 6G been identified, but also 10-7 M polychlorinated biphenyls （PCBs, a notorious class of persistent organic pollutants） are recognized, and even two congeners of PCBs can be identified in a mixture, showing the potential applications of the materials in SERS-based rapid detection of environmental organic pollutants.
基金supported by the Los Alamos National Laboratory Directed Research and Development (LDRD) project 20130764ECR
文摘Accumulative roll bonded （ARB） Copper Niobium （Cu-Nb） nano-lamellar composite （NLC） panels were friction stir welded （FSWed） to evaluate the ability to join panels while retaining the nano-lamellar structure. During a single pass of the friction stir welding （FSW） process, the nano-lamellar structure of the parent material （PM） was retained but was observed to fragment into equiaxed grains during the second pass. FSW has been modeled as a severe deformation process in which the material is subjected to an instantaneous high shear strain rate followed by extreme shear strains. The loss of the nano-lamellar layers was attributed to the increased strain and longer time at temperature resulting from the second pass of the FSW process. Kinematic modeling was used to predict the global average shear strain and shear strain rates experienced by the ARB material during the FSW process. The results of this study indicate that through careful selection of FSW parameters, the nano-lamellar structure and its associated higher strength can be maintained using FSW to join ARB NLC panels.
文摘Graphene platelet networks (GPNs) were deposited onto silicon substrates by means of anodic arc discharge ignited between two graphite electrodes.Substrate temperature and pressure of helium atmosphere were optimized for the production of the carbon nanomaterials.The samples were modified or destroyed with different methods to mimic typical environments responsible of severe surface degradation.The emulated conditions were performed by four surface treatments,namely thermal oxidation,substrate overheating,exposition to glow discharge,and metal coating due to arc plasma.In the next step,the samples were regenerated on the same substrates with identical deposition technique.Damaging and re-growth of GPN samples were systematically characterized by scanning electron microscopy and Raman spectroscopy.The full regeneration of the structural and morphological properties of the samples has proven that this healing method by arc plasma is adequate for restoring the functionality of2D nanostructures exposed to harsh environments.
文摘Natural gas, whose primary constituent is methane, has been considered a convincing alternative for the growth of the energy supply worldwide. Adsorbed natural gas （ANG）, the most promising methane storage method, has been an active field of study in the past two decades. ANG constitutes a safe and low-cost way to store methane for natural gas vehicles at an acceptable energy density while working at substantially low pressures （3.5- 4.0 MPa）, allowing for conformable store tank. This work serves to review the state-of-the-art development reported in the scientific literature on adsorbents, adsorption theories, ANG conformable tanks, and related technolo- gies on ANG vehicles. Patent literature has also been searched and discussed. The review aims at illustrating both achievements and problems of the ANG technologies-based vehicles, as well as forecasting the development trends and critical issues to be resolved of these technologies.
基金support by the United Innovation Program of Shanghai Commercial Aircraft Engine, which was founded by Shanghai Municipal Commission of Economy and Informatization, Shanghai Municipal Education Commission, and AECC Commercial Aircraft Engine Co., Ltd. (No. AR909)the Aeronautical Science Foundation of China (No. 2015ZBP9002)the China Scholarship Council
文摘Laminar flow design is one of the most effective ways to reduce the drag of a commercial aircraft by expanding the laminar flow region on the surface of the aircraft. As material science develops, the emergence of new materials such as low surface energy materials has offered new choices for laminar flow design of commercial aircraft. Different types of low surface energy micro-nano coatings are prepared to verify the effects on the boundary layer transition position and the drag of the airfoil through wind tunnel tests. The infrared thermal imaging technology is adopted for measuring the boundary layer transition, while the momentum integral approach is employed to measure the drag coefficient through a wake rake. Infrared thermal imaging results indicate that the coatings are capable of moving backward the boundary layer transition position at both a low velocity of Mach number 0.15 and a high velocity of Mach number 0.785. Results of the momentum integral approach demonstrate that the drag coefficients are reduced obviously within the cruising angle of attack range from 1° and 5° by introducing the low surface energy micro-nano coating technology.
