We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose-Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions....We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose-Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions. The cavity frequency is harmonically modulated in time for both the cases. The main quantity of interest is the number of intracavity scattered photons. The system has been investigated under the weak and strong modulations. It has been observed that the amplitude of the scattered photons is more for the classical mirror motion than the quantized mirror motion. Also, initially, the amplitude of scattered photons is high for lower modulation amplitude than higher modulation amplitude. We also found that the behavior of the plots are similar under strong and weak modulations for the quantized mirror motion.展开更多
In the previous paper (JMP 2014) we showed that there exists a NeoMinkowskian Gravitational Expanding Solution of GR (General Relativity) with CC (Cosmological Constant). We prove now that NeoMinkowskian Vacuum (non-b...In the previous paper (JMP 2014) we showed that there exists a NeoMinkowskian Gravitational Expanding Solution of GR (General Relativity) with CC (Cosmological Constant). We prove now that NeoMinkowskian Vacuum (non-baryonic Fluid), with gravitational (first) density (dark energy) and gravitational waves (at light speed), corresponds to the Gravitation Field of a Cosmological Black Hole (CBH). The latter predicts furthermore a basic emission of Radiation (CBR) from Hubble spherical singular Horizon to the inside of CBH (unlike Hawking’s emission) at an initial singular time. Our solution is then compatible with a well-tempered Big Bang and Expanding Universe (Escher’s Figure, see Penrose, 3) but incompatible with inflation. The latter is based on Hypothesis of a so-called Planck’s particle (Lemaitre’s primitive atom) characterized by a so-called Planck length. We prove that we can short-circuit this unstable particle with a stable cosmological Poincaré’s electron with gravific pressure. It is well known that electron is a stranger in usual Minkowskian vacuum (dixit Einstein). The stranger electron can be perfectly integrated in NeoMinkowskian Radiation fluid and then also (with its mass, charge and wavelength) in (second density of) CBR. Everything happens as if the leptonic mass of the electron were induced by our cosmological field. The unexpected cosmological model proposed here is the only one that predicts numerical values of (second) density and temperature of CBR very close to the observed (COBE) values.展开更多
Two central schemes of finite difference (FD) up to different accuracy orders of space sampling step Dx (Fourth order and Sixth order respectively) were used to study the 1-D nonlinear P-wave propagation in the nonlin...Two central schemes of finite difference (FD) up to different accuracy orders of space sampling step Dx (Fourth order and Sixth order respectively) were used to study the 1-D nonlinear P-wave propagation in the nonlinear solid media by the numerical method. Distinctly different from the case of numerical modeling of linear elastic wave, there may be several difficulties in the numerical treatment to the nonlinear partial differential equation, such as the steep gradients, shocks and unphysical oscillations. All of them are the great obstacles to the stability and conver-gence of numerical calculation. Fortunately, the comparative study on the modeling of nonlinear wave by the two FD schemes presented in the paper can provide us with an easy method to keep the stability and convergence in the calculation field when the product of the absolute value of nonlinear coefficient and the value of u/x are small enough, namely, the value of bu/x is much smaller than 1. Several results are founded in the numerical study of nonlinear P-wave propagation, such as the waveform aberration, the generation and growth of harmonic wave and the energy redistribution among different frequency components. All of them will be more violent when the initial amplitude A0 is larger or the nonlinearity of medium is stronger. Correspondingly, we have found that the nonlinear P-wave propagation velocity will change with different initial frequency f of source wave or the wave velocity c (equal to the P-wave velocity in the same medium without considering nonlinearity).展开更多
This study was conducted to investigate the characteristics of meso-scale combustion.The technique of electrical capacitance tomography(ECT) was used to locate flame position and monitor the effect corresponding to va...This study was conducted to investigate the characteristics of meso-scale combustion.The technique of electrical capacitance tomography(ECT) was used to locate flame position and monitor the effect corresponding to varied air/fuel ratio in a meso-scale combustor.Combustion phenomena including igniting,quenching and unsteady combustion have been visualized using ECT.The method of metallization protecting ECT sensor from high temperature damage and the novel calibration method adapted to ECT monitoring of unknown permittivity flame have been shown to be successful.At the same time,electrical nature of combustion and dielectric characteristics of hy-drocarbon flame were studied.The relationship between flame permittivity and state parameters of combustion gas was demonstrated preliminarily.展开更多
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic ...In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic ＂pillar＂ structure and a nacreous ＂brick and mortar＂ structure. The prismatic layer looks like a ＂pillar forest＂ with variationsection pillars sized on the order of several tens of microns. The nacreous material looks like a ＂brick wall＂ with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively. The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material. In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.展开更多
The existing analytical formulas to calculate the temperature field distribution of artificial frozen soil walls are all based on the conditions that the surface temperatures of all freezing pipes are equivalent. In t...The existing analytical formulas to calculate the temperature field distribution of artificial frozen soil walls are all based on the conditions that the surface temperatures of all freezing pipes are equivalent. In this paper, analytical solution of steady state temperature field of two freezing pipes with diferent temperatures is deduced based on thermal potential superposition method. The correctness of the analytical formulas is verified by comparing the temperature field distributions of the analytical formulas and those of the numerical simulations in the same conditions. And discussions are made to analyze the influence of some parameters on temperature field distribution of this condition.展开更多
The problem of steady laminar magnetohydrodynamic （MHD） mixed con- vection stagnation-point flow of an incompressible viscous fluid over a vertical stretch- ing sheet is studied. The effect of an externally magnetic...The problem of steady laminar magnetohydrodynamic （MHD） mixed con- vection stagnation-point flow of an incompressible viscous fluid over a vertical stretch- ing sheet is studied. The effect of an externally magnetic field is taken into account. The transformed boundary layer equations are solved numerically by using an implicit finite-difference scheme. Numerical results are obtained for various values of the mixed convection parameter, Hartmann number, and Prandtl number. The effects of an exter- nally magnetic field on the skin friction coefficient, local Nusselt number, velocity, and temperature profiles for both A 〉 1 and A ~ 1, where A is the velocity ratio parameter, are presented graphically and discussed in detail. Both assisting and opposing flows are considered, and it is found that dual solutions exist for the opposing flow.展开更多
Furnace lining erosion is closely related to the operation stability and safety. The detection technology for hearth lining thickness of blast furnace was introduced.By using the data of thermocouples installed in the...Furnace lining erosion is closely related to the operation stability and safety. The detection technology for hearth lining thickness of blast furnace was introduced.By using the data of thermocouples installed in the bottom of furnace hearth,a mathematical model of erosion was established; the real state of the hearth and bottom erosion was studied; the erosion condition was followed,serving for the furnace longevity.展开更多
On a self-developed circular-translation polishing machine,the influence of different electric potentials on the friction coefficient and wear properties of SiC/HT200 friction pair,which contacted as one electrode,wer...On a self-developed circular-translation polishing machine,the influence of different electric potentials on the friction coefficient and wear properties of SiC/HT200 friction pair,which contacted as one electrode,were studied in NaOH solutions.The results show that the friction coefficient of SiC/HT200 pair is 0.25 under no externally applied potential;but it decreases to 0.23 while applying +3 V polarization potential on the pair;in contrast,it increases to 0.30 when applying-3 V polarization potential on the pair.And the polished SiC surface under + 3 V potential is much smoother,while there are clear ploughing marks and adhesive region on the polished SiC surface under zero and-3 V potential,respectively.The mixed triboelectrochemical friction model has been proposed and the mechanisms of the electric effects on the tribological properties of SiC/HT200 friction pair in NaOH electrolyte are addressed.Results and discussion show that the anodic passivation technique may be used for hastening the running-in process of SiC/Fe friction pairs,as well as for polishing SiC to increase its materials removal efficiency while maintaining good surface quality.展开更多
Objective: The aim of this study was to describe the use of the postpartum intrauterine device in the maternity ward of the Ratoma communal medical center in Conakry. Methods: This was a descriptive cross-sectional st...Objective: The aim of this study was to describe the use of the postpartum intrauterine device in the maternity ward of the Ratoma communal medical center in Conakry. Methods: This was a descriptive cross-sectional study carried out between July 1<sup>st</sup> 2015 and June 30 2016, i.e. a duration of one year. Results: A total of 551 patients received advice on various contraceptive methods. Most of this advice was given in the post-partum period (40.2%) and during antenatal care (39.1%). Of the patients advised, 87 (15.8%) used the intrauterine device. The majority of users (93%) were married and uneducated (63.2%), and 39.1% were poor. The majority (56.3%) of intra-uterine devices were inserted in the immediate post-partum period. The majority of women had no adverse events either during the first six weeks (n = 57;65.5%) or at 3<sup>rd</sup> months (n = 75;86.2%) or 6<sup>th</sup> months (n = 76;87.4%) after IUD insertion. Most users remained complication-free throughout the follow-up period (n = 76;87.4% at 6<sup>th</sup> weeks and 3<sup>rd</sup> months, and n = 77;88.5% at 6<sup>th</sup> months). The continuation rate was 89.7% at 6 weeks and 3<sup>rd</sup> months, and 87.4% at 6<sup>th</sup> months after insertion. The majority of users (87.0%) were satisfied with the care they received. Conclusion: This study showed very few complications among intrauterine device users, and high continuation and satisfaction rates. The intrauterine device is a long-acting, effective, reversible and safe contraceptive that can be used by most women for birth spacing in Guinea, where women do not regularly visit health facilities.展开更多
Carbon materials featuring hierarchical pores and atomically dispersed metal sites are promising catalysts for energy storage and conversion applications.Herein,we developed a facile strategy to construct functional c...Carbon materials featuring hierarchical pores and atomically dispersed metal sites are promising catalysts for energy storage and conversion applications.Herein,we developed a facile strategy to construct functional carbon materials with a fluffy peony-like structure and dense binary FeCo-Nx active sites(termed as f-FeCo-CNT).By regulating the metal content in precursors,a three-dimensional(3D)interconnected conductive carbon nanotubes network was in-situ formed throughout the atomically dispersed FeCo-NC matrix during pyrolysis.Taking advantage of rich pore hierarchy and co-existence of highly active FeCo-Nx sites and beneficial FeCo alloy nanoparticles,the f-FeCo-CNT material exhibited excellent bifunctional performance towards oxygen reduction reaction/oxygen evolution reactions(ORR/OER)with respect to the atomically dispersed FeCo-NC(SA-f-FeCo-NC)and commercial Pt/C+Ru02 mixture,surpassing the SA-f-FeCo-NC with a 20 mV higher ORR half-wave potential and a 100 mV lower OER overpotential(at 10.0 mA/cm^2).Remarkably,the f-FeCo-CNT-assembled Zn-air battery(ZAB)possessed a maximum specific power of 195.8 mW/cm^2,excellent rate capability,and very good cycling stability at large current density of 20.0 mA/cm^2.This work provides a facile and feasible synthetic strategy of constructing low-cost cathode materials with excellent comprehensive ZAB performance.展开更多
In this paper, by constructing the one-to-one correspondence between its IFS and the quaternary fractional expansion, the n-th iteration analytical expression and the limit representation of the family of the Koch-typ...In this paper, by constructing the one-to-one correspondence between its IFS and the quaternary fractional expansion, the n-th iteration analytical expression and the limit representation of the family of the Koch-type curves with arbitrary angles are obtained. The distinction between our method and that of H. Sagan is that we provide the generation process analytically and represent it as a graph of a series function which looks like the Weierstrass function. With these arithmetic expressions, we further analyze and prove some of the fractal properties of the Koch-type curves such as the self-similarity, the HSlder exponent and with the property of continuous everywhere but differentiable nowhere. Then, we will show that the Koch- type curves can be approximated by different constructed generators. Based on the analytic transformation of the Koch-type curves, we also constructed more continuous but nowhere-differentiable curves represented by arithmetic expressions. This result implies that the analytical expression of a fractal has theoretical and practical significance.展开更多
By X-ray diffraction and high pressure Mossbauer spectroscopy, the structure and the hyperfine parameters of Ni substituted γ-Fe4N were investigated. The results of X-ray diffraction indicate that single phase γ’-(...By X-ray diffraction and high pressure Mossbauer spectroscopy, the structure and the hyperfine parameters of Ni substituted γ-Fe4N were investigated. The results of X-ray diffraction indicate that single phase γ’-(Fe1-xNix)4N compounds can be prepared in the composition range of 0≤x≤0.6, and with the increase of Ni content the lattice parameter is fit for the relationship a0(x) = 3.790 5-0.021 57x-0.031 67x2. By high pressure Mossbauer spectra, effects of magnetovolume and chemical bonding of Ni atom on hyperfine magnetic field and isomer shift of iron were distinguished for the first time, and their composition dependences for different lattice sites were studied simultaneously. It is found that the magnetovolume and chemical bonding have different influences on the properties of γ’-(Fe1-xNix)4N, and the latter one plays a key role in the property changes of γ-(Fe1-xNix)4N.展开更多
文摘We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose-Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions. The cavity frequency is harmonically modulated in time for both the cases. The main quantity of interest is the number of intracavity scattered photons. The system has been investigated under the weak and strong modulations. It has been observed that the amplitude of the scattered photons is more for the classical mirror motion than the quantized mirror motion. Also, initially, the amplitude of scattered photons is high for lower modulation amplitude than higher modulation amplitude. We also found that the behavior of the plots are similar under strong and weak modulations for the quantized mirror motion.
文摘In the previous paper (JMP 2014) we showed that there exists a NeoMinkowskian Gravitational Expanding Solution of GR (General Relativity) with CC (Cosmological Constant). We prove now that NeoMinkowskian Vacuum (non-baryonic Fluid), with gravitational (first) density (dark energy) and gravitational waves (at light speed), corresponds to the Gravitation Field of a Cosmological Black Hole (CBH). The latter predicts furthermore a basic emission of Radiation (CBR) from Hubble spherical singular Horizon to the inside of CBH (unlike Hawking’s emission) at an initial singular time. Our solution is then compatible with a well-tempered Big Bang and Expanding Universe (Escher’s Figure, see Penrose, 3) but incompatible with inflation. The latter is based on Hypothesis of a so-called Planck’s particle (Lemaitre’s primitive atom) characterized by a so-called Planck length. We prove that we can short-circuit this unstable particle with a stable cosmological Poincaré’s electron with gravific pressure. It is well known that electron is a stranger in usual Minkowskian vacuum (dixit Einstein). The stranger electron can be perfectly integrated in NeoMinkowskian Radiation fluid and then also (with its mass, charge and wavelength) in (second density of) CBR. Everything happens as if the leptonic mass of the electron were induced by our cosmological field. The unexpected cosmological model proposed here is the only one that predicts numerical values of (second) density and temperature of CBR very close to the observed (COBE) values.
基金Project of Knowledge Innovation Program from Chinese Academy of Sciences (KZCX2-109).
文摘Two central schemes of finite difference (FD) up to different accuracy orders of space sampling step Dx (Fourth order and Sixth order respectively) were used to study the 1-D nonlinear P-wave propagation in the nonlinear solid media by the numerical method. Distinctly different from the case of numerical modeling of linear elastic wave, there may be several difficulties in the numerical treatment to the nonlinear partial differential equation, such as the steep gradients, shocks and unphysical oscillations. All of them are the great obstacles to the stability and conver-gence of numerical calculation. Fortunately, the comparative study on the modeling of nonlinear wave by the two FD schemes presented in the paper can provide us with an easy method to keep the stability and convergence in the calculation field when the product of the absolute value of nonlinear coefficient and the value of u/x are small enough, namely, the value of bu/x is much smaller than 1. Several results are founded in the numerical study of nonlinear P-wave propagation, such as the waveform aberration, the generation and growth of harmonic wave and the energy redistribution among different frequency components. All of them will be more violent when the initial amplitude A0 is larger or the nonlinearity of medium is stronger. Correspondingly, we have found that the nonlinear P-wave propagation velocity will change with different initial frequency f of source wave or the wave velocity c (equal to the P-wave velocity in the same medium without considering nonlinearity).
基金Supported by the National Natural Science Foundation of China (50806005,50736002,61072005)
文摘This study was conducted to investigate the characteristics of meso-scale combustion.The technique of electrical capacitance tomography(ECT) was used to locate flame position and monitor the effect corresponding to varied air/fuel ratio in a meso-scale combustor.Combustion phenomena including igniting,quenching and unsteady combustion have been visualized using ECT.The method of metallization protecting ECT sensor from high temperature damage and the novel calibration method adapted to ECT monitoring of unknown permittivity flame have been shown to be successful.At the same time,electrical nature of combustion and dielectric characteristics of hy-drocarbon flame were studied.The relationship between flame permittivity and state parameters of combustion gas was demonstrated preliminarily.
基金The research was supported by the National Basic Research Program of China (Grant 2012CB937500),the National Natural Science Foundation of China (Grants 91216108,11432014),and the CAS/SAFEA International Partnership Program for Creative Reserch Teams
文摘In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic ＂pillar＂ structure and a nacreous ＂brick and mortar＂ structure. The prismatic layer looks like a ＂pillar forest＂ with variationsection pillars sized on the order of several tens of microns. The nacreous material looks like a ＂brick wall＂ with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively. The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material. In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.
基金the National Natural Science Foundation of China(Nos.50578120 and 51178336)the Science and Technology Project of the Zhejiang Department of Transportation(No.2010H02)
文摘The existing analytical formulas to calculate the temperature field distribution of artificial frozen soil walls are all based on the conditions that the surface temperatures of all freezing pipes are equivalent. In this paper, analytical solution of steady state temperature field of two freezing pipes with diferent temperatures is deduced based on thermal potential superposition method. The correctness of the analytical formulas is verified by comparing the temperature field distributions of the analytical formulas and those of the numerical simulations in the same conditions. And discussions are made to analyze the influence of some parameters on temperature field distribution of this condition.
基金supported by the Fundamental Research Grant Scheme(FRGS)from the Ministry of HigherEducation in Malaysia(No.5524295)the Research University Grant from the Universiti Kebangsaan Malaysia(No.GUP-2013-040)
文摘The problem of steady laminar magnetohydrodynamic （MHD） mixed con- vection stagnation-point flow of an incompressible viscous fluid over a vertical stretch- ing sheet is studied. The effect of an externally magnetic field is taken into account. The transformed boundary layer equations are solved numerically by using an implicit finite-difference scheme. Numerical results are obtained for various values of the mixed convection parameter, Hartmann number, and Prandtl number. The effects of an exter- nally magnetic field on the skin friction coefficient, local Nusselt number, velocity, and temperature profiles for both A 〉 1 and A ~ 1, where A is the velocity ratio parameter, are presented graphically and discussed in detail. Both assisting and opposing flows are considered, and it is found that dual solutions exist for the opposing flow.
文摘Furnace lining erosion is closely related to the operation stability and safety. The detection technology for hearth lining thickness of blast furnace was introduced.By using the data of thermocouples installed in the bottom of furnace hearth,a mathematical model of erosion was established; the real state of the hearth and bottom erosion was studied; the erosion condition was followed,serving for the furnace longevity.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51475119)the National Program on Key Basic Research Project of China(Grant No.2011CB013202)
文摘On a self-developed circular-translation polishing machine,the influence of different electric potentials on the friction coefficient and wear properties of SiC/HT200 friction pair,which contacted as one electrode,were studied in NaOH solutions.The results show that the friction coefficient of SiC/HT200 pair is 0.25 under no externally applied potential;but it decreases to 0.23 while applying +3 V polarization potential on the pair;in contrast,it increases to 0.30 when applying-3 V polarization potential on the pair.And the polished SiC surface under + 3 V potential is much smoother,while there are clear ploughing marks and adhesive region on the polished SiC surface under zero and-3 V potential,respectively.The mixed triboelectrochemical friction model has been proposed and the mechanisms of the electric effects on the tribological properties of SiC/HT200 friction pair in NaOH electrolyte are addressed.Results and discussion show that the anodic passivation technique may be used for hastening the running-in process of SiC/Fe friction pairs,as well as for polishing SiC to increase its materials removal efficiency while maintaining good surface quality.
文摘Objective: The aim of this study was to describe the use of the postpartum intrauterine device in the maternity ward of the Ratoma communal medical center in Conakry. Methods: This was a descriptive cross-sectional study carried out between July 1<sup>st</sup> 2015 and June 30 2016, i.e. a duration of one year. Results: A total of 551 patients received advice on various contraceptive methods. Most of this advice was given in the post-partum period (40.2%) and during antenatal care (39.1%). Of the patients advised, 87 (15.8%) used the intrauterine device. The majority of users (93%) were married and uneducated (63.2%), and 39.1% were poor. The majority (56.3%) of intra-uterine devices were inserted in the immediate post-partum period. The majority of women had no adverse events either during the first six weeks (n = 57;65.5%) or at 3<sup>rd</sup> months (n = 75;86.2%) or 6<sup>th</sup> months (n = 76;87.4%) after IUD insertion. Most users remained complication-free throughout the follow-up period (n = 76;87.4% at 6<sup>th</sup> weeks and 3<sup>rd</sup> months, and n = 77;88.5% at 6<sup>th</sup> months). The continuation rate was 89.7% at 6 weeks and 3<sup>rd</sup> months, and 87.4% at 6<sup>th</sup> months after insertion. The majority of users (87.0%) were satisfied with the care they received. Conclusion: This study showed very few complications among intrauterine device users, and high continuation and satisfaction rates. The intrauterine device is a long-acting, effective, reversible and safe contraceptive that can be used by most women for birth spacing in Guinea, where women do not regularly visit health facilities.
基金This work was financially supported by the National Natural Science Foundation of China(No.21701101)the National Key Research and Development Project(Nos.2018YFE0118200,2016YFF0204402)+5 种基金the Fundamental Research Funds for the Central Universities(No.18CX06063A)the Long-Term Subsidy Mechanism from the Ministry of Finance and the Ministry of Education of China,the Shandong Key Research and Development Project(No.2019JZZY010506)the Shandong Scientific Research Awards Foundation for Outstanding Young Scientists(No.ZR2018JL010)the Shandong Joint Fund of Outstanding Young Talents(No.ZR2017BB018)the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents(No.2017RCJJ059)the Program for Tsingtao Al-ion Power and Energy-Storage Battery Research Team in the University(No.17-2-1-1-zhc).
文摘Carbon materials featuring hierarchical pores and atomically dispersed metal sites are promising catalysts for energy storage and conversion applications.Herein,we developed a facile strategy to construct functional carbon materials with a fluffy peony-like structure and dense binary FeCo-Nx active sites(termed as f-FeCo-CNT).By regulating the metal content in precursors,a three-dimensional(3D)interconnected conductive carbon nanotubes network was in-situ formed throughout the atomically dispersed FeCo-NC matrix during pyrolysis.Taking advantage of rich pore hierarchy and co-existence of highly active FeCo-Nx sites and beneficial FeCo alloy nanoparticles,the f-FeCo-CNT material exhibited excellent bifunctional performance towards oxygen reduction reaction/oxygen evolution reactions(ORR/OER)with respect to the atomically dispersed FeCo-NC(SA-f-FeCo-NC)and commercial Pt/C+Ru02 mixture,surpassing the SA-f-FeCo-NC with a 20 mV higher ORR half-wave potential and a 100 mV lower OER overpotential(at 10.0 mA/cm^2).Remarkably,the f-FeCo-CNT-assembled Zn-air battery(ZAB)possessed a maximum specific power of 195.8 mW/cm^2,excellent rate capability,and very good cycling stability at large current density of 20.0 mA/cm^2.This work provides a facile and feasible synthetic strategy of constructing low-cost cathode materials with excellent comprehensive ZAB performance.
基金Supported partly by National Natural Science Foundation of China(No.60962009)
文摘In this paper, by constructing the one-to-one correspondence between its IFS and the quaternary fractional expansion, the n-th iteration analytical expression and the limit representation of the family of the Koch-type curves with arbitrary angles are obtained. The distinction between our method and that of H. Sagan is that we provide the generation process analytically and represent it as a graph of a series function which looks like the Weierstrass function. With these arithmetic expressions, we further analyze and prove some of the fractal properties of the Koch-type curves such as the self-similarity, the HSlder exponent and with the property of continuous everywhere but differentiable nowhere. Then, we will show that the Koch- type curves can be approximated by different constructed generators. Based on the analytic transformation of the Koch-type curves, we also constructed more continuous but nowhere-differentiable curves represented by arithmetic expressions. This result implies that the analytical expression of a fractal has theoretical and practical significance.
基金Project supported by the National Natural Science Foundation of China,the Natural Science Fund of Gansu Province and the Postdoctoral Fund of China.
文摘By X-ray diffraction and high pressure Mossbauer spectroscopy, the structure and the hyperfine parameters of Ni substituted γ-Fe4N were investigated. The results of X-ray diffraction indicate that single phase γ’-(Fe1-xNix)4N compounds can be prepared in the composition range of 0≤x≤0.6, and with the increase of Ni content the lattice parameter is fit for the relationship a0(x) = 3.790 5-0.021 57x-0.031 67x2. By high pressure Mossbauer spectra, effects of magnetovolume and chemical bonding of Ni atom on hyperfine magnetic field and isomer shift of iron were distinguished for the first time, and their composition dependences for different lattice sites were studied simultaneously. It is found that the magnetovolume and chemical bonding have different influences on the properties of γ’-(Fe1-xNix)4N, and the latter one plays a key role in the property changes of γ-(Fe1-xNix)4N.
