调制解调法是一种常用的微弱信号检测方法,高精度、低复杂度的解调方法的实现对于调制解调法的应用具有重要的意义.传统坐标旋转数字计算(coordinate rotation digital computer,CORDIC)算法具有占用资源多,需要缩放因子补偿等问题.因...调制解调法是一种常用的微弱信号检测方法,高精度、低复杂度的解调方法的实现对于调制解调法的应用具有重要的意义.传统坐标旋转数字计算(coordinate rotation digital computer,CORDIC)算法具有占用资源多,需要缩放因子补偿等问题.因此设计并实现了一种基于改进CORDIC算法的离散傅里叶变换(discrete Fourier transform,DFT)解调方法用于微弱信号的检测.首先改进了传统的CORDIC算法用于正余弦函数值的计算,该方法不仅免除了缩放因子,而且不需要进行旋转角度的判断,降低了算法的资源占用;然后基于该CORDIC算法设计了DFT解调算法,避免了乘法器与大量查找表的使用.最终仿真结果表明,设计的DFT解调方法在整周期采样的情况下能够实现对调制信号的高精度解调,并且具备良好的抗噪声性能,能够满足微弱信号检测的要求.展开更多
It is advisable to look into efficient and environmentally friendly materials that have the ability to turn lost energy into electricity in order to mitigate the rapid depletion of fossil fuels and the ensuing environ...It is advisable to look into efficient and environmentally friendly materials that have the ability to turn lost energy into electricity in order to mitigate the rapid depletion of fossil fuels and the ensuing environmental damage.In the present work density functional theory(DFT)was employed to analyze the structural,optical,electronic,and thermoelectric characteristics of novel half-Heusler AMnSb(A=La,Lu)materials.The structural stability of both compounds under consideration was verified by using the Birch-Murnaghan equations of states,which indicate that both compounds have structural stability due to ground-state energy levels being negative.Band structure and total density of state analysis display that LaMnSb has an energy band gap of 0.96 eV for spin-up(↑)and 0.21 eV for spin-down(↓)configurations.LuMnSb has band gap of 0.47 eV for spin-up and an indirect band gap of 0.3 eV for spin-down channel.In terms of its optical properties,LuMnSb exhibits maximal conductivity and absorption of electromagnetic radiation in the ultraviolet range(99-462 nm),which makes it a desirable material for optoelectronic applications.Moreover,the transport characteristics of the examined materials were computed by means of the Boltztrap code based on Boltzmann transport theory.The thermoelectric parameters,like the thermal conductivity,Seebeck coefficient,and electrical conductivity are computed in the 200-1200 K temperature range.These anticipated results suggest that AMnSb(A=La,Lu)compounds would be the best choice for thermoelectric and green energy applications.展开更多
Our study employed self-consistent ab-initio calculations using highly precise spin-polarized density functional theory with both GGA and GGA+U approaches,coupled with the Boltzmann transport scheme.This co mprehensiv...Our study employed self-consistent ab-initio calculations using highly precise spin-polarized density functional theory with both GGA and GGA+U approaches,coupled with the Boltzmann transport scheme.This co mprehensive approach investigated the structural stability,magneto-electronic behavior,thermophysical characteristics,and thermoelectric transport properties of Co_(2)TiRE(RE=Nd,Tb)Heusler alloys.Through structural optimizations,we confirm that these materials exhibit fe rromagnetic behavior.Analysis of band occupation and density of states using GGA and GGA+U methods reveals that both compounds are metallic in both spin configurations.We evaluated key transport properties such as the Seebeck coefficient,electrical and thermal conductivity and the figure of merit to understand their potential in thermoelectric applications.Conservative estimates of the Seebeck coefficient and the figure of merit suggest promising applications in thermoelectric energy harvesting technologies.Additionally,we provide a comprehensive analysis of the thermophysical behavior,including the Debye temperature,thermal expansion,and specific heat,to assess the alloys thermodynamic stability across varying temperature and pressure conditions.展开更多
To achieve selective leaching of ion adsorption rare earth,it is necessary to thoroughly reveal the differences in the adsorption mechanisms of aluminum and rare earth elements.In this study,we investigated the adsorp...To achieve selective leaching of ion adsorption rare earth,it is necessary to thoroughly reveal the differences in the adsorption mechanisms of aluminum and rare earth elements.In this study,we investigated the adsorption processes of Dy and Al on the surface of K–homoionic kaolinite using batch experiments and sequential chemical extractions.The results revealed that the adsorption of Dy and Al,as well as the desorption of K,followed the Langmuir model.The maximum ion-exchangeable capacity of Dy was higher(9.39 mmol.kg^(-1))than that of Al(6.30 mmol.kg^(-1)).The ion exchange stoichiometry ratios of Dy–K and Al–K derived from the Langmuir model were2.0 and 2.6.The analysis of X-ray absorption fine structure(XAFS)and density functional theory(DFT)revealed that Dy and Al were adsorbed onto kaolinite as outer-sphere hydrated complexes via hydrogen bonds.Dy was adsorbed as[Dy(H_(2)O)_(10)]^(3+),and Al was adsorbed as[Al(OH)_(2)(H_(2)O)_(4)]^(+).In particular,the adsorption of Al resulted in protonation of the hydroxyl groups on the surface of the kaolinite.Based on the above insights,the higher ion exchange stoichiometry ratios are attributed to closer adsorption distances(6.04 A for Dy and 3.69 A for Al)and lower adsorption energies(-223.72 kJ.mol^(-1)for Dy and-268.33 kJ.mol^(-1)for Al).The maximum ionexchangeable capacity is related to the change of the surface electrical properties of kaolinite.The zeta potential was increased to-7.3 mV as the protonation resulted from aluminum adsorption,while Dy adsorption had a minor effect,maintaining a value of-17.5 m V.展开更多
Density(p)and speed of sound(u)findings on the binary liquid mixtures consisting of cyclohexanol(CH—OH),with aniline(A),ortho-chloroaniline(o-CA),and meta-chloroaniline(m-CA)were gathered at the various temperatures ...Density(p)and speed of sound(u)findings on the binary liquid mixtures consisting of cyclohexanol(CH—OH),with aniline(A),ortho-chloroaniline(o-CA),and meta-chloroaniline(m-CA)were gathered at the various temperatures spanning the entire concentration range.303.15,308.15,313.15 and 318.15 K at atmospheric pressure.The information measured there was utilized to compute excess molar volume(V_(m)^(E)),excess isentropic compressibility(K_(S)^(E)),excess of speed of sound(u^(F)),excess intermolecular free length(L_(f)^(F))and excess acoustic impedance(Z^(F)).Further,the partial molar volumes(^(-)V°_(m,1).^(-)V°_(φ,1).^(-)V°_(m,2).^(-)V°_(φ,2)),partial molar compressibilities(K°_(m,1).^(-)K°_(φ,1).^(-)K°_(m,2).^(-)K°_(φ,2))and their excess values(^(-)V^(E)_(m,1).^(-)V^(°E)_(φ,1).^(-)V^(E)_(m,2).^(-)V^(°E)_(φ,2)),(K^(E)_(m,1).^(-)K^(°E)_(φ,1).^(-)K^(E)_(m,2).^(-)K^(°E)_(φ,2))were also computed to perceive more information on molecular interaction and structural effects in these mixtures.Applying the theory of Prigogine-Flory-Patterson(PFP)as a framework,the V_(m)^(E)data of the current liquid mixtures were examined.The analysis of the experimental data took into consideration the interactions that occur between the individual molecules that make up liquid mixtures.By using density functional theory DFT(B3LYP)of 6-31++G(d,P)to analyze the geometries,bond characteristics,interaction energies,and hydrogen bonded complexes in organic solvent phase,quantum chemical calculations were able to further confirm the hydrogen bonding that predominates between cyclohexanol with aniline and chlorosubstituted anilines.展开更多
A corrosion discoloration model for copper-nickel alloys in Cl^(−)environments was established using CIE-Lab,UV-VIS absorption spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion discolor...A corrosion discoloration model for copper-nickel alloys in Cl^(−)environments was established using CIE-Lab,UV-VIS absorption spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion discoloration process and the corresponding main corrosion products can be summarized as follows:silver-white(Cu+Ni)→green(NiO)→reddishbrown(NiO+Cu_(2)O)→black(NiO+Cu_(2)O+CuO).Density functional theory was employed to explain the corrosion process of copper-nickel alloys and the detrimental effect of Cl^(−).The results indicate that adsorbates preferentially bind to nickel,leading to the preferential formation of NiO,which imparts a green appearance to the surface.Furthermore,the difficulty in forming nickel cation vacancies and the higher diffusion barrier for nickel inhibit the migration of species within the oxide layer.Notably,nickel also suppresses carrier migration within the oxide layer,reducing the charge transfer rate.In contrast,the promotion of corrosion by Cl^(−)is primarily attributed to the reduction in surface work function and the formation energy of cation vacancies.展开更多
Two pairs of novel 6/6/6/9 tetracyclic merosesquiterpenoid enantiomers,dauroxonanols A(1)and B(2),possessing an unprecedented 9,15-dioxatetracyclo[8.5.3.0^(4.17).0^(14.18)]octadecane core skeleton,were isolated from R...Two pairs of novel 6/6/6/9 tetracyclic merosesquiterpenoid enantiomers,dauroxonanols A(1)and B(2),possessing an unprecedented 9,15-dioxatetracyclo[8.5.3.0^(4.17).0^(14.18)]octadecane core skeleton,were isolated from Rhododendron dauricum.The nuclear magnetic resonance(NMR)spectra of 1 and 2 showed very broad resonances,and^(13)C NMR spectrum of 1 exhibited only 13 instead of 22 carbon resonances.These broadening or missing NMR resonances led to a great challenge to elucidate their structures using NMR data analysis.Their structures and absolute configurations of 1 and 2 were finally determined by single crystal X-ray diffraction analysis,chiral separation,and electronic circular dichroism(ECD)calculations.Plausible biosynthetic pathways for 1 and 2 are proposed.Conformational analysis,density functional theory(DFT)calculations,and dynamic NMR assigned the coalescent NMR phenomena of 1 and 2 to the conformational changes of the flexible oxonane ring.Dauroxonanols A(1)and B(2)showed potentα-glucosidase inhibitory activities,2-8 times potent than acarbose,an antidiabetic drug targetingα-glucosidase in clinic.展开更多
基金the Deanship of Research and Graduate studies at King Khalid University for funding this work through a large group research project under grant number RGP2/96/45。
文摘It is advisable to look into efficient and environmentally friendly materials that have the ability to turn lost energy into electricity in order to mitigate the rapid depletion of fossil fuels and the ensuing environmental damage.In the present work density functional theory(DFT)was employed to analyze the structural,optical,electronic,and thermoelectric characteristics of novel half-Heusler AMnSb(A=La,Lu)materials.The structural stability of both compounds under consideration was verified by using the Birch-Murnaghan equations of states,which indicate that both compounds have structural stability due to ground-state energy levels being negative.Band structure and total density of state analysis display that LaMnSb has an energy band gap of 0.96 eV for spin-up(↑)and 0.21 eV for spin-down(↓)configurations.LuMnSb has band gap of 0.47 eV for spin-up and an indirect band gap of 0.3 eV for spin-down channel.In terms of its optical properties,LuMnSb exhibits maximal conductivity and absorption of electromagnetic radiation in the ultraviolet range(99-462 nm),which makes it a desirable material for optoelectronic applications.Moreover,the transport characteristics of the examined materials were computed by means of the Boltztrap code based on Boltzmann transport theory.The thermoelectric parameters,like the thermal conductivity,Seebeck coefficient,and electrical conductivity are computed in the 200-1200 K temperature range.These anticipated results suggest that AMnSb(A=La,Lu)compounds would be the best choice for thermoelectric and green energy applications.
文摘Our study employed self-consistent ab-initio calculations using highly precise spin-polarized density functional theory with both GGA and GGA+U approaches,coupled with the Boltzmann transport scheme.This co mprehensive approach investigated the structural stability,magneto-electronic behavior,thermophysical characteristics,and thermoelectric transport properties of Co_(2)TiRE(RE=Nd,Tb)Heusler alloys.Through structural optimizations,we confirm that these materials exhibit fe rromagnetic behavior.Analysis of band occupation and density of states using GGA and GGA+U methods reveals that both compounds are metallic in both spin configurations.We evaluated key transport properties such as the Seebeck coefficient,electrical and thermal conductivity and the figure of merit to understand their potential in thermoelectric applications.Conservative estimates of the Seebeck coefficient and the figure of merit suggest promising applications in thermoelectric energy harvesting technologies.Additionally,we provide a comprehensive analysis of the thermophysical behavior,including the Debye temperature,thermal expansion,and specific heat,to assess the alloys thermodynamic stability across varying temperature and pressure conditions.
基金financially supported by the National Key Research and Development Program of China(No.2021YFC2902203)the Key Research and Development Program of Guangxi Province(No.Guike-AB22080056)+2 种基金Beijing Nova Program(No.20230484379)the Science and Technology Innovation Fund of GRINM(No.2022PD0102)the Central Government Guides Local Science and Technology Development Fund Project(No.246Z4005G)。
文摘To achieve selective leaching of ion adsorption rare earth,it is necessary to thoroughly reveal the differences in the adsorption mechanisms of aluminum and rare earth elements.In this study,we investigated the adsorption processes of Dy and Al on the surface of K–homoionic kaolinite using batch experiments and sequential chemical extractions.The results revealed that the adsorption of Dy and Al,as well as the desorption of K,followed the Langmuir model.The maximum ion-exchangeable capacity of Dy was higher(9.39 mmol.kg^(-1))than that of Al(6.30 mmol.kg^(-1)).The ion exchange stoichiometry ratios of Dy–K and Al–K derived from the Langmuir model were2.0 and 2.6.The analysis of X-ray absorption fine structure(XAFS)and density functional theory(DFT)revealed that Dy and Al were adsorbed onto kaolinite as outer-sphere hydrated complexes via hydrogen bonds.Dy was adsorbed as[Dy(H_(2)O)_(10)]^(3+),and Al was adsorbed as[Al(OH)_(2)(H_(2)O)_(4)]^(+).In particular,the adsorption of Al resulted in protonation of the hydroxyl groups on the surface of the kaolinite.Based on the above insights,the higher ion exchange stoichiometry ratios are attributed to closer adsorption distances(6.04 A for Dy and 3.69 A for Al)and lower adsorption energies(-223.72 kJ.mol^(-1)for Dy and-268.33 kJ.mol^(-1)for Al).The maximum ionexchangeable capacity is related to the change of the surface electrical properties of kaolinite.The zeta potential was increased to-7.3 mV as the protonation resulted from aluminum adsorption,while Dy adsorption had a minor effect,maintaining a value of-17.5 m V.
文摘Density(p)and speed of sound(u)findings on the binary liquid mixtures consisting of cyclohexanol(CH—OH),with aniline(A),ortho-chloroaniline(o-CA),and meta-chloroaniline(m-CA)were gathered at the various temperatures spanning the entire concentration range.303.15,308.15,313.15 and 318.15 K at atmospheric pressure.The information measured there was utilized to compute excess molar volume(V_(m)^(E)),excess isentropic compressibility(K_(S)^(E)),excess of speed of sound(u^(F)),excess intermolecular free length(L_(f)^(F))and excess acoustic impedance(Z^(F)).Further,the partial molar volumes(^(-)V°_(m,1).^(-)V°_(φ,1).^(-)V°_(m,2).^(-)V°_(φ,2)),partial molar compressibilities(K°_(m,1).^(-)K°_(φ,1).^(-)K°_(m,2).^(-)K°_(φ,2))and their excess values(^(-)V^(E)_(m,1).^(-)V^(°E)_(φ,1).^(-)V^(E)_(m,2).^(-)V^(°E)_(φ,2)),(K^(E)_(m,1).^(-)K^(°E)_(φ,1).^(-)K^(E)_(m,2).^(-)K^(°E)_(φ,2))were also computed to perceive more information on molecular interaction and structural effects in these mixtures.Applying the theory of Prigogine-Flory-Patterson(PFP)as a framework,the V_(m)^(E)data of the current liquid mixtures were examined.The analysis of the experimental data took into consideration the interactions that occur between the individual molecules that make up liquid mixtures.By using density functional theory DFT(B3LYP)of 6-31++G(d,P)to analyze the geometries,bond characteristics,interaction energies,and hydrogen bonded complexes in organic solvent phase,quantum chemical calculations were able to further confirm the hydrogen bonding that predominates between cyclohexanol with aniline and chlorosubstituted anilines.
基金supported by the Key Program of the National Natural Science Foundation of China(Grant No.51131007)the National Key Research and Development Program of China(Grant No.2021YFC2803102).
文摘A corrosion discoloration model for copper-nickel alloys in Cl^(−)environments was established using CIE-Lab,UV-VIS absorption spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion discoloration process and the corresponding main corrosion products can be summarized as follows:silver-white(Cu+Ni)→green(NiO)→reddishbrown(NiO+Cu_(2)O)→black(NiO+Cu_(2)O+CuO).Density functional theory was employed to explain the corrosion process of copper-nickel alloys and the detrimental effect of Cl^(−).The results indicate that adsorbates preferentially bind to nickel,leading to the preferential formation of NiO,which imparts a green appearance to the surface.Furthermore,the difficulty in forming nickel cation vacancies and the higher diffusion barrier for nickel inhibit the migration of species within the oxide layer.Notably,nickel also suppresses carrier migration within the oxide layer,reducing the charge transfer rate.In contrast,the promotion of corrosion by Cl^(−)is primarily attributed to the reduction in surface work function and the formation energy of cation vacancies.
基金supported by the National Natural Science Foundation of China(Nos.22207036,22277034,22477034,and 22107033)Interdisciplinary Research Program of Huazhong University of Science and Technology(No.2023JCYJ037)International Cooperation Project of Hubei Provincial Key R&D Plan(No.2023EHA040)。
文摘Two pairs of novel 6/6/6/9 tetracyclic merosesquiterpenoid enantiomers,dauroxonanols A(1)and B(2),possessing an unprecedented 9,15-dioxatetracyclo[8.5.3.0^(4.17).0^(14.18)]octadecane core skeleton,were isolated from Rhododendron dauricum.The nuclear magnetic resonance(NMR)spectra of 1 and 2 showed very broad resonances,and^(13)C NMR spectrum of 1 exhibited only 13 instead of 22 carbon resonances.These broadening or missing NMR resonances led to a great challenge to elucidate their structures using NMR data analysis.Their structures and absolute configurations of 1 and 2 were finally determined by single crystal X-ray diffraction analysis,chiral separation,and electronic circular dichroism(ECD)calculations.Plausible biosynthetic pathways for 1 and 2 are proposed.Conformational analysis,density functional theory(DFT)calculations,and dynamic NMR assigned the coalescent NMR phenomena of 1 and 2 to the conformational changes of the flexible oxonane ring.Dauroxonanols A(1)and B(2)showed potentα-glucosidase inhibitory activities,2-8 times potent than acarbose,an antidiabetic drug targetingα-glucosidase in clinic.
