Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achi...Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achieved by hot stamping process.However,the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement.To reduce this kind of risk,recent research efforts have been focused on various ways to optimize the microstructure of PHS.The present review intends to summarize these efforts,to highlight present solutions to address hydrogen embrittlement,and to shed light on directions for future improvement.The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition.The substrate part covers the influence of martensite,carbides,inclusions,and retained austenite,while the surface part covers decarburization and oxidation,pre-coating,and trimming.展开更多
The surface waves generated by unsteady concentrated disturbances in an initially quiescent fluid of infinite depth with an inertial surface are analytically investigated for two- and three-dimensional cases. The flui...The surface waves generated by unsteady concentrated disturbances in an initially quiescent fluid of infinite depth with an inertial surface are analytically investigated for two- and three-dimensional cases. The fluid is assumed to be inviscid, incompressible and homogenous. The inertial surface represents the effect of a thin uniform distribution of non-interacting floating matter. Four types of unsteady concentrated disturbances and two kinds of initial values are considered, namely an instantaneous/oscillating mass source immersed in the fluid, an instantaneous/oscillating impulse on the surface, an initial impulse on the surface of the fluid, and an initial displacement of the surface. The linearized initial-boundary-value problem is formulated within the framework of potential flow. The solutions in integral form for the surface elevation are obtained by means of a joint Laplace-Fourier transform. The asymptotic representations of the wave motion for large time with a fixed distance- to-time ratio are derived by using the method of stationary phase. The effect of the presence of an inertial surface on the wave motion is analyzed. It is found that the wavelengths of the transient dispersive waves increase while those of the steady-state progressive waves decrease. All the wave amplitudes decrease in comparison with those of conventional free-surface waves. The explicit expressions for the freesurface gravity waves can readily be recovered by the present results as the inertial surface disappears.展开更多
This paper studied the changing principles of carbon content in direct reduction iron (DRI) and liquid iron in the COREX melting gasifier. Under the normal working conditions of experimental equipment, liquid nitrogen...This paper studied the changing principles of carbon content in direct reduction iron (DRI) and liquid iron in the COREX melting gasifier. Under the normal working conditions of experimental equipment, liquid nitrogen was poured into the melting gasifier from its tuyere to cool down quickly. And then seven cross sections were made to study the carburization reaction and its characteristics of the solid iron and the liquid iron, and also the reaction of carbon between the slag and the metal. According to the results, the influences of the thickness of the semi-coke layer and the temperature on the carbon content of liquid iron in the COREX melting gasifier were confirmed.展开更多
The establishment of a possible connection between neutrino emission and gravitational-wave(GW)bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge.In t...The establishment of a possible connection between neutrino emission and gravitational-wave(GW)bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge.In the Daya Bay experiment,using the data collected from December 2011 to August 2017,a search was per-formed for electron-antineutrino signals that coincided with detected GW events,including GW150914,GW151012,GW151226,GW170104,GW170608,GW 170814,and GW 170817.We used three time windows of±10,±500,and±1000 s relative to the occurrence of the GW events and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates.The detected electron-antineutrino candidates were consistent with the expected background rates for all the three time windows.Assuming monochromatic spectra,we found upper limits(90%confidence level)of the electron-antineutrino fluence of(1.13-2.44)×10^(11)cm^(-2)at 5 MeV to 8.0×10^(7)cm^(-2)at 100 MeV for the three time w indows.Under the assumption of a Fermi-Dirac spectrum,the upper limits were found to be(5.4-7.0)×10^(9)cm^(2)for the three time windows.展开更多
The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by ...The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment,in combination with the fission rates of fissile isotopes in the reactor,is used to extract the positron energy spectra resulting from the fission of specific isotopes.This information can be used to produce a precise,data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay.The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method.Consistent results are obtained with other unfolding methods.A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated.Given the reactor fission fractions,the technique can predict the energy spectrum to a 2%precision.In addition,we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.展开更多
The deformation and failure of soft rock affected by hydro-mechanical（HM） effect are one of the most concerns in geotechnical engineering, which are basically attributed to the grain sliding of soft rock. This study...The deformation and failure of soft rock affected by hydro-mechanical（HM） effect are one of the most concerns in geotechnical engineering, which are basically attributed to the grain sliding of soft rock. This study tried to develop a dissolution-diffusion sliding model for the typical red bed soft rock in South China. Based on hydration film, mineral dissolution and diffusion theory, and geochemical thermodynamics, a dissolution-diffusion sliding model with the HM effect was established to account for the sliding rate. Combined with the digital image processing technology, the relationship between the grain size of soft rock and the amplitude of sliding surface was presented. An equation for the strain rate of soft rocks under steady state was also derived. The reliability of the dissolution-diffusion sliding model was verified by triaxial creep tests on the soft rock with the HM coupling effect and by the relationship between the inversion average disjoining pressure and the average thickness of the hydration film. The results showed that the sliding rate of the soft rock grains was affected significantly by the waviness of sliding surface, the shear stress, and the average thickness of hydration film. The average grain size is essential for controlling the steady-state creep rate of soft rock. This study provides a new idea for investigating the deformation and failure of soft rock with the HM effect.展开更多
The mesoporous nanoscale zircoina zeolite was firstly synthesized via solid state —— Structure directing method without addition of any stabilizer. The sample bears lamellar or worm pore structures, relatively high ...The mesoporous nanoscale zircoina zeolite was firstly synthesized via solid state —— Structure directing method without addition of any stabilizer. The sample bears lamellar or worm pore structures, relatively high surface area compared with that reported. The mesoporous nanosize structure can also resist higher calcination temperature. The introduction of above zirconia to the catalyst of methanol synthesis dedicates the nanosize particle size to the catalyst, which significantly changes the physical structure and elec-tronic effect of the catalyst. The catalyst shows higher catalytic activity and selectivity to methanol. The active sites for methanol synthesis are demonstrated over various cata-lysts in this paper.展开更多
Analytical solutions for the flexural-gravity wave resistances due to a line source steadily moving on the surface of an infinitely deep fluid are investigated within the framework of the linear po- tential theory. Th...Analytical solutions for the flexural-gravity wave resistances due to a line source steadily moving on the surface of an infinitely deep fluid are investigated within the framework of the linear po- tential theory. The homogenous fluid, covered by a thin elastic plate, is assumed to be incompressible and inviscid, and the motion to be irrotational. The solution in integral form for the wave resistance is obtained by means of the Fourier transform and the explicitly analytical solutions are derived with the aid of the residue theorem. The dispersion relation shows that there is a minimal phase speed cmin, a threshold for the existence of the wave resistance. No wave is generated when the moving speed of the source V is less than emin while the wave resistances firstly increase to their peak values and then decrease when V ~〉 Crnin. The effects of the flexural rigidity and the inertia of the plate are studied. @ 2013 The Chinese Society of Theoretical and Applied Mechanics. [doi：10.1063/2.1302202]展开更多
ZrO 2-Al 2O 3 composite oxides and supported Ni catalysts were prepared, and characterized by N 2 adsorption /desorption, X-ray diffraction(XRD) an d X-ray photoelectron spectroscopy(XPS) techniques. The catalytic...ZrO 2-Al 2O 3 composite oxides and supported Ni catalysts were prepared, and characterized by N 2 adsorption /desorption, X-ray diffraction(XRD) an d X-ray photoelectron spectroscopy(XPS) techniques. The catalytic performance and carbon deposition was also investigated. This mesoporous composite oxide is shown to be a promising catalyst support. An increase in the catalytic activity and stability of methane and carbon dioxide reforming reaction was resulted from the zirconia addition, especially at 5wt% ZrO 2 content. The Ni catalyst supported ZrO 2-Al 2O 3 has a strong resistance to sintering and the carbon deposition in a relatively long-term reaction.展开更多
Head-on collision between two hydroelastic solitary waves propagating at the surface of an incompressible and ideal fluid covered by a thin ice sheet is analytically studied by means of a singular perturbation method....Head-on collision between two hydroelastic solitary waves propagating at the surface of an incompressible and ideal fluid covered by a thin ice sheet is analytically studied by means of a singular perturbation method. The ice sheet is represented by the Plotnikov-Toland model with the help of the special Cosserat theory of hyperelastic shells and the Kirchhoff-Love plate theory,which yields the nonlinear and conservative expression for the bending forces. The shallow water assumption is taken for the fluid motion with the Boussinesq approximation. The resulting governing equations are solved asymptotically with the aid of the Poincaré-Lighthill-Kuo method,and the solutions up to the third order are explicitly presented. It is observed that solitary waves after collision do not change their shapes and amplitudes. The wave profile is symmetric before collision, and it becomes, after collision, unsymmetric and titled backward in the direction of wave propagation. The wave profile significantly reduces due to greater impacts of elastic plate and surface tension. A graphical comparison is presented with published results, and the graphical comparison between linear and nonlinear elastic plate models is also shown as a special case of our study.展开更多
ABSTRACT： Three trials were conducted to analyze a multi-enzyme compound produced by Aspergillus sulphureus in solid-state fermentation （SSF） as a po- tential feed additive. The results of the first trial showed th...ABSTRACT： Three trials were conducted to analyze a multi-enzyme compound produced by Aspergillus sulphureus in solid-state fermentation （SSF） as a po- tential feed additive. The results of the first trial showed that there were at least 5 non-starch polysac- charide enzymes： xylanase, 13-ghicanase, pectinase, mannase and carboxy methyl cellulase （CMCase） contained in the compound. Xylanase and fl-glucanase showed good activities at pH 2.5-7.0, which were in the range of 649-1046 U/g and 444-648 U/g, respec- tively. Pectinase showed good activity in acidic solu- tion （pH 2.5-3.0）,which ranged from 195 to 917 U/g. Mannase showed high activity of 235-298 U/g at pH 3.5-4.5 and the activity of CMCase was relatively constant at pH 2.5-7.0, which was in the range of 38.2-78.6 U/g. The second trial was aimed to test the stability of the enzymes in gastric liquor （pH 2.6） of finishing pigs and Na2 HPO4-gastric liquor （ pH 5.5 ）.After 6 h incubation at 40℃ in gastric liquor,the re- tained activity of xylanase, 13-glucanase, pectinase, mannase and CMCase was 26.3% ,65.0% ,71.0%, 74.8% and 85.6%, respectively. While after 6 h in- cubation at 40℃ in Na2I-IPO4-gastric liquor, the re- tained activity of xylanase, [3-glucanase, pectinase, mannase and CMCase was 87.9% ,91.1% ,92.3%, 95.0%, and 97.5%, respectively. The third trial was carried out in a jejunum liquor （ pH 5.8,200 mL）, which contained 0.2 g of the multi-enzyme compound and 10 g of soybean hull or wheat bran, respectively. After 8 h incubation at 40℃, 18.7% of soybean hull and 20.1% of wheat bran could be degraded to solu- ble saccharide, respectively. Compared with the tradi- tional methods for feed enzyme testing which involve feeding animals for 1-3 months, enzyme assay in this way was relatively convenient.展开更多
The reliability of quasi integrable and non-resonant Hamiltonian system under fractional Gaussian noise(fGn)excitation is studied.Noting rather flat fGn power spectral density(PSD)in most part of frequency band,the fG...The reliability of quasi integrable and non-resonant Hamiltonian system under fractional Gaussian noise(fGn)excitation is studied.Noting rather flat fGn power spectral density(PSD)in most part of frequency band,the fGn is innovatively regarded as a wide-band process.Then,the stochastic averaging method for quasi integrable Hamiltonian systems under wide-band noise excitation is applied to reduce 2n-dimensional original system into n-dimensional averaged ltd stochastic differential equations(SDEs).Reliability function and mean first passage time are obtained by solving the associated backward Kolmogorov equation and Pontryagin equation.The validity of the proposed procedure is tested by applying it to an example and comparing the numerical results with those from Monte Carlo simulation.展开更多
Linear machines(LMs)produce linear motion without any intermediate transmission mechanisms,thus the whole electromechanical system has simple structure and its efficiency is high.Because of such merits,linear machines...Linear machines(LMs)produce linear motion without any intermediate transmission mechanisms,thus the whole electromechanical system has simple structure and its efficiency is high.Because of such merits,linear machines have been studied for a long time and rapidly developed in recent years.Due to the characteristic of open structure,linear machines have more diversity than rotary machines in terms of machine topologies.Accounting for the wide applications of linear machines,e.g.Maglev train,precision machine tools,semiconductor processing device,automatic equipment,logistic transport line,ropeless lifter,compressor,etc.,this paper reviews the most applied linear machines including machine topologies,operating principle and features.In addition,the influence of end effects and the corresponding reduction methods are also summarized.Finally,several commercial applications are exemplified.展开更多
基金M.X.Huang acknowledges the support from Guangzhou Municipal Science and Technology Project(No.202007020007)Guangdong Basic and Applied Basic Research Foundation of China(No.2020B1515130007).
文摘Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achieved by hot stamping process.However,the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement.To reduce this kind of risk,recent research efforts have been focused on various ways to optimize the microstructure of PHS.The present review intends to summarize these efforts,to highlight present solutions to address hydrogen embrittlement,and to shed light on directions for future improvement.The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition.The substrate part covers the influence of martensite,carbides,inclusions,and retained austenite,while the surface part covers decarburization and oxidation,pre-coating,and trimming.
基金the National Natural Science Foundation of China(10602032)the Shanghai Rising-Star Program(07QA14022)the Shanghai Leading Academic Discipline Project(Y0103)
文摘The surface waves generated by unsteady concentrated disturbances in an initially quiescent fluid of infinite depth with an inertial surface are analytically investigated for two- and three-dimensional cases. The fluid is assumed to be inviscid, incompressible and homogenous. The inertial surface represents the effect of a thin uniform distribution of non-interacting floating matter. Four types of unsteady concentrated disturbances and two kinds of initial values are considered, namely an instantaneous/oscillating mass source immersed in the fluid, an instantaneous/oscillating impulse on the surface, an initial impulse on the surface of the fluid, and an initial displacement of the surface. The linearized initial-boundary-value problem is formulated within the framework of potential flow. The solutions in integral form for the surface elevation are obtained by means of a joint Laplace-Fourier transform. The asymptotic representations of the wave motion for large time with a fixed distance- to-time ratio are derived by using the method of stationary phase. The effect of the presence of an inertial surface on the wave motion is analyzed. It is found that the wavelengths of the transient dispersive waves increase while those of the steady-state progressive waves decrease. All the wave amplitudes decrease in comparison with those of conventional free-surface waves. The explicit expressions for the freesurface gravity waves can readily be recovered by the present results as the inertial surface disappears.
文摘This paper studied the changing principles of carbon content in direct reduction iron (DRI) and liquid iron in the COREX melting gasifier. Under the normal working conditions of experimental equipment, liquid nitrogen was poured into the melting gasifier from its tuyere to cool down quickly. And then seven cross sections were made to study the carburization reaction and its characteristics of the solid iron and the liquid iron, and also the reaction of carbon between the slag and the metal. According to the results, the influences of the thickness of the semi-coke layer and the temperature on the carbon content of liquid iron in the COREX melting gasifier were confirmed.
基金Daya Bay is supported in part by the Ministry of Science and Technology o f China, the U.S. Department o f Energy, the Chinese Academy of Sciences, the CASCenter for Excellence in Particle Physics, the National Natural Science Foundation of China, the Guangdong provincial government, the Shenzhen municipal government,the China General Nuclear Power Group, Key Laboratory of Particle and Radiation Imaging (Tsinghua University), the Ministry of Education, Key Laboratory ofParticle Physics and Particle Irradiation (Shandong University), the Ministry o f Education, Shanghai Laboratory for Particle Physics and Cosmology, the ResearchGrants Council o f the Hong Kong Special Administrative Region of China, the University Development Fund of the University of Hong Kong, the MOE program forResearch of Excellence at National Taiwan University, National Chiao-Tung University, NSC fund support from Taiwan, the U.S. National Science Foundation, the AlfredP. Sloan Foundation, the Ministry o f Education, Youth, and Sports of the Czech Republic, the Charles University GAUK (284317), the Joint Institute o f NuclearResearch in Dubna, Russia, the National Commission of Scientific and Technological Research of Chile, and the Tsinghua University Initiative Scientific Research Program.
文摘The establishment of a possible connection between neutrino emission and gravitational-wave(GW)bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge.In the Daya Bay experiment,using the data collected from December 2011 to August 2017,a search was per-formed for electron-antineutrino signals that coincided with detected GW events,including GW150914,GW151012,GW151226,GW170104,GW170608,GW 170814,and GW 170817.We used three time windows of±10,±500,and±1000 s relative to the occurrence of the GW events and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates.The detected electron-antineutrino candidates were consistent with the expected background rates for all the three time windows.Assuming monochromatic spectra,we found upper limits(90%confidence level)of the electron-antineutrino fluence of(1.13-2.44)×10^(11)cm^(-2)at 5 MeV to 8.0×10^(7)cm^(-2)at 100 MeV for the three time w indows.Under the assumption of a Fermi-Dirac spectrum,the upper limits were found to be(5.4-7.0)×10^(9)cm^(2)for the three time windows.
基金Supported in part by the Ministry of Science and Technology of Chinathe U.S.Department of Energy,the Chinese Academy of Sciences,the CAS Center for Excellence in Particle Physics,the National Natural Science Foundation of China+3 种基金the Guangdong provincial governmentthe Shenzhen municipal government,the China General Nuclear Power Group,the Research Grants Council of the Hong Kong Special Administrative Region of China,the Ministry of Education in TWthe U.S.National Science Foundation,the Ministry of Education,Youth,and Sports of the Czech Republic,the Charles University Research Centre UNCE,the Joint Institute of Nuclear Research in Dubna,Russiathe National Commission of Scientific and Technological Research of Chile。
文摘The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment,in combination with the fission rates of fissile isotopes in the reactor,is used to extract the positron energy spectra resulting from the fission of specific isotopes.This information can be used to produce a precise,data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay.The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method.Consistent results are obtained with other unfolding methods.A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated.Given the reactor fission fractions,the technique can predict the energy spectrum to a 2%precision.In addition,we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.
基金supported by the National Key Research and Development Project (Grant No. SQ2017YFSF060085)the National Natural Science Foundation of China (NSFC)(Grant Nos. 41472257, 41530638, and 41372302)+1 种基金the Special Fund Key Project of Applied Science and Technology Research and Development in Guangdong (Grant No. 2016B010124007)the Special Support Program for High Level Talents in Guangdong (Grant No. 2015TQ01Z344)
文摘The deformation and failure of soft rock affected by hydro-mechanical（HM） effect are one of the most concerns in geotechnical engineering, which are basically attributed to the grain sliding of soft rock. This study tried to develop a dissolution-diffusion sliding model for the typical red bed soft rock in South China. Based on hydration film, mineral dissolution and diffusion theory, and geochemical thermodynamics, a dissolution-diffusion sliding model with the HM effect was established to account for the sliding rate. Combined with the digital image processing technology, the relationship between the grain size of soft rock and the amplitude of sliding surface was presented. An equation for the strain rate of soft rocks under steady state was also derived. The reliability of the dissolution-diffusion sliding model was verified by triaxial creep tests on the soft rock with the HM coupling effect and by the relationship between the inversion average disjoining pressure and the average thickness of the hydration film. The results showed that the sliding rate of the soft rock grains was affected significantly by the waviness of sliding surface, the shear stress, and the average thickness of hydration film. The average grain size is essential for controlling the steady-state creep rate of soft rock. This study provides a new idea for investigating the deformation and failure of soft rock with the HM effect.
文摘The mesoporous nanoscale zircoina zeolite was firstly synthesized via solid state —— Structure directing method without addition of any stabilizer. The sample bears lamellar or worm pore structures, relatively high surface area compared with that reported. The mesoporous nanosize structure can also resist higher calcination temperature. The introduction of above zirconia to the catalyst of methanol synthesis dedicates the nanosize particle size to the catalyst, which significantly changes the physical structure and elec-tronic effect of the catalyst. The catalyst shows higher catalytic activity and selectivity to methanol. The active sites for methanol synthesis are demonstrated over various cata-lysts in this paper.
基金supported by the National Natural Science Foundation of China (11072140)the State Key Laboratory of Ocean Engineering (Shanghai Jiao Tong University) (0803)The Shanghai Program for Innovative Research Team in Universities
文摘Analytical solutions for the flexural-gravity wave resistances due to a line source steadily moving on the surface of an infinitely deep fluid are investigated within the framework of the linear po- tential theory. The homogenous fluid, covered by a thin elastic plate, is assumed to be incompressible and inviscid, and the motion to be irrotational. The solution in integral form for the wave resistance is obtained by means of the Fourier transform and the explicitly analytical solutions are derived with the aid of the residue theorem. The dispersion relation shows that there is a minimal phase speed cmin, a threshold for the existence of the wave resistance. No wave is generated when the moving speed of the source V is less than emin while the wave resistances firstly increase to their peak values and then decrease when V ~〉 Crnin. The effects of the flexural rigidity and the inertia of the plate are studied. @ 2013 The Chinese Society of Theoretical and Applied Mechanics. [doi：10.1063/2.1302202]
文摘ZrO 2-Al 2O 3 composite oxides and supported Ni catalysts were prepared, and characterized by N 2 adsorption /desorption, X-ray diffraction(XRD) an d X-ray photoelectron spectroscopy(XPS) techniques. The catalytic performance and carbon deposition was also investigated. This mesoporous composite oxide is shown to be a promising catalyst support. An increase in the catalytic activity and stability of methane and carbon dioxide reforming reaction was resulted from the zirconia addition, especially at 5wt% ZrO 2 content. The Ni catalyst supported ZrO 2-Al 2O 3 has a strong resistance to sintering and the carbon deposition in a relatively long-term reaction.
基金sponsored by the National Natural Science Foundation of China (No. 11472166)
文摘Head-on collision between two hydroelastic solitary waves propagating at the surface of an incompressible and ideal fluid covered by a thin ice sheet is analytically studied by means of a singular perturbation method. The ice sheet is represented by the Plotnikov-Toland model with the help of the special Cosserat theory of hyperelastic shells and the Kirchhoff-Love plate theory,which yields the nonlinear and conservative expression for the bending forces. The shallow water assumption is taken for the fluid motion with the Boussinesq approximation. The resulting governing equations are solved asymptotically with the aid of the Poincaré-Lighthill-Kuo method,and the solutions up to the third order are explicitly presented. It is observed that solitary waves after collision do not change their shapes and amplitudes. The wave profile is symmetric before collision, and it becomes, after collision, unsymmetric and titled backward in the direction of wave propagation. The wave profile significantly reduces due to greater impacts of elastic plate and surface tension. A graphical comparison is presented with published results, and the graphical comparison between linear and nonlinear elastic plate models is also shown as a special case of our study.
基金supported by New Century Excellent Talent in University (NCET-07-0807)the National High Technology Research and Development Program of China (2007AA100601)the Projectof State Key Laboratory of Animal Nutrition(2004DA125184(team)0806)
文摘ABSTRACT： Three trials were conducted to analyze a multi-enzyme compound produced by Aspergillus sulphureus in solid-state fermentation （SSF） as a po- tential feed additive. The results of the first trial showed that there were at least 5 non-starch polysac- charide enzymes： xylanase, 13-ghicanase, pectinase, mannase and carboxy methyl cellulase （CMCase） contained in the compound. Xylanase and fl-glucanase showed good activities at pH 2.5-7.0, which were in the range of 649-1046 U/g and 444-648 U/g, respec- tively. Pectinase showed good activity in acidic solu- tion （pH 2.5-3.0）,which ranged from 195 to 917 U/g. Mannase showed high activity of 235-298 U/g at pH 3.5-4.5 and the activity of CMCase was relatively constant at pH 2.5-7.0, which was in the range of 38.2-78.6 U/g. The second trial was aimed to test the stability of the enzymes in gastric liquor （pH 2.6） of finishing pigs and Na2 HPO4-gastric liquor （ pH 5.5 ）.After 6 h incubation at 40℃ in gastric liquor,the re- tained activity of xylanase, 13-glucanase, pectinase, mannase and CMCase was 26.3% ,65.0% ,71.0%, 74.8% and 85.6%, respectively. While after 6 h in- cubation at 40℃ in Na2I-IPO4-gastric liquor, the re- tained activity of xylanase, [3-glucanase, pectinase, mannase and CMCase was 87.9% ,91.1% ,92.3%, 95.0%, and 97.5%, respectively. The third trial was carried out in a jejunum liquor （ pH 5.8,200 mL）, which contained 0.2 g of the multi-enzyme compound and 10 g of soybean hull or wheat bran, respectively. After 8 h incubation at 40℃, 18.7% of soybean hull and 20.1% of wheat bran could be degraded to solu- ble saccharide, respectively. Compared with the tradi- tional methods for feed enzyme testing which involve feeding animals for 1-3 months, enzyme assay in this way was relatively convenient.
基金supported by National Key R&D Program of China(Grant No.2018 YFC0809400)Zhejiang Provincial Natural Science Foundation of China(Grant No.LY16A020001)National Natural Science Foundation of China(Grant No.11802267).
文摘The reliability of quasi integrable and non-resonant Hamiltonian system under fractional Gaussian noise(fGn)excitation is studied.Noting rather flat fGn power spectral density(PSD)in most part of frequency band,the fGn is innovatively regarded as a wide-band process.Then,the stochastic averaging method for quasi integrable Hamiltonian systems under wide-band noise excitation is applied to reduce 2n-dimensional original system into n-dimensional averaged ltd stochastic differential equations(SDEs).Reliability function and mean first passage time are obtained by solving the associated backward Kolmogorov equation and Pontryagin equation.The validity of the proposed procedure is tested by applying it to an example and comparing the numerical results with those from Monte Carlo simulation.
基金This work is supported by National Natural Science Foundation of China(NSFC51777190,NSFC51477150),China.
文摘Linear machines(LMs)produce linear motion without any intermediate transmission mechanisms,thus the whole electromechanical system has simple structure and its efficiency is high.Because of such merits,linear machines have been studied for a long time and rapidly developed in recent years.Due to the characteristic of open structure,linear machines have more diversity than rotary machines in terms of machine topologies.Accounting for the wide applications of linear machines,e.g.Maglev train,precision machine tools,semiconductor processing device,automatic equipment,logistic transport line,ropeless lifter,compressor,etc.,this paper reviews the most applied linear machines including machine topologies,operating principle and features.In addition,the influence of end effects and the corresponding reduction methods are also summarized.Finally,several commercial applications are exemplified.
