In this article,we conduct a study on mixed quasi-martingale Hardy spaces that are defined by means of the mixed L_(p)-norm.By utilizing Doob’s inequalities,we explore the atomic decomposition and quasi-martingale in...In this article,we conduct a study on mixed quasi-martingale Hardy spaces that are defined by means of the mixed L_(p)-norm.By utilizing Doob’s inequalities,we explore the atomic decomposition and quasi-martingale inequalities of mixed quasi-martingale Hardy spaces.Moreover,we furnish sufficient conditions for the boundedness ofσ-sublinear operators in these spaces.These findings extend the existing conclusions regarding mixed quasi-martingale Hardy spaces defined with the help of the mixed L_(p)-norm.展开更多
The process of decomposion of the bastnasite and monazite rare earth concentrates by alkali solutions was investigated. The mixed slurries of the rare earth concentrates and the alkali solutions were calcined at diffe...The process of decomposion of the bastnasite and monazite rare earth concentrates by alkali solutions was investigated. The mixed slurries of the rare earth concentrates and the alkali solutions were calcined at different temperatures in a rotary tubular electric furnace. The effects of calcination temperature on the decomposing ratio of rare earth, the oxidation ratio of cerium, the stripping of fluorine and phospho-rous after calcinations, and the adaptability of the process to the mixed rare earth concentrates of different grade were studied. The results showed that the decomposition ratio of rare earth and the oxidation ratio of cerium could reach 95.8% and 93.7%, respectively, while the cal-cinating temperature was above 300℃.展开更多
Ce-modified Mn-Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction,Raman,N2 adsorption-desorption,infrared spectra H2 temperature-programmed reduction and ther...Ce-modified Mn-Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction,Raman,N2 adsorption-desorption,infrared spectra H2 temperature-programmed reduction and thermogravimetric analyses.Their catalytic properties were investigated in ozone(O3)decomposition reaction.Results show that the small amount of rare earth metal Ce added during Mn-Fe(FM) mixed-oxide synthesis greatly improves the catalytic performance in O3 decomposition.Among the prepared catalysts.the C0.04(FM)0.96 mixed-oxide catalyst exhibits the highest catalytic activity and stability.The O3 conversion over C0.04(FM)0.96 is 98% after 24 h reaction at 25℃ under dry condition,and that over FM decreases to 90% after 16 h reaction.At 0℃,the O3 conversion over C0.04(FM)0.96 is 95% after 7 h reaction under dry condition.and that over FM slows down to 70%.Under humid condition(RH 65%),the O3 conversion over C0.04(FM)0.96 is 63% after 6.5 h reaction at 25℃.while that over FM decreases to 55%.When Ce is doped into Mn-Fe mixed oxides,the small amount of Ce enters the crystal lattice of MnO2.and partial Fe is separated to form Fe2O3.This changes cause lattice distortion and increase defects and enable the as-synthesized Ce-Fe-Mn ternary mixed-oxide catalysts to acquire additional oxygen vacancies and increase their specific surface area,thereby increasing the number of reaction sites and enhancing the catalytic performance of the catalysts for O3 decomposition.展开更多
When used for separating multi-component non-stationary signals, the adaptive time-varying filter(ATF) based on multi-scale chirplet sparse signal decomposition(MCSSD) generates phase shift and signal distortion. To o...When used for separating multi-component non-stationary signals, the adaptive time-varying filter(ATF) based on multi-scale chirplet sparse signal decomposition(MCSSD) generates phase shift and signal distortion. To overcome this drawback, the zero phase filter is introduced to the mentioned filter, and a fault diagnosis method for speed-changing gearbox is proposed. Firstly, the gear meshing frequency of each gearbox is estimated by chirplet path pursuit. Then, according to the estimated gear meshing frequencies, an adaptive zero phase time-varying filter(AZPTF) is designed to filter the original signal. Finally, the basis for fault diagnosis is acquired by the envelope order analysis to the filtered signal. The signal consisting of two time-varying amplitude modulation and frequency modulation(AM-FM) signals is respectively analyzed by ATF and AZPTF based on MCSSD. The simulation results show the variances between the original signals and the filtered signals yielded by AZPTF based on MCSSD are 13.67 and 41.14, which are far less than variances (323.45 and 482.86) between the original signals and the filtered signals obtained by ATF based on MCSSD. The experiment results on the vibration signals of gearboxes indicate that the vibration signals of the two speed-changing gearboxes installed on one foundation bed can be separated by AZPTF effectively. Based on the demodulation information of the vibration signal of each gearbox, the fault diagnosis can be implemented. Both simulation and experiment examples prove that the proposed filter can extract a mono-component time-varying AM-FM signal from the multi-component time-varying AM-FM signal without distortion.展开更多
The thermal decomposition behavior and nonisothermal reaction kinetics of the double-base gun propellants containing the mixed ester of triethyleneglycol dinitrate（TEGDN） and nitroglycerin（NG） were investigated by...The thermal decomposition behavior and nonisothermal reaction kinetics of the double-base gun propellants containing the mixed ester of triethyleneglycol dinitrate（TEGDN） and nitroglycerin（NG） were investigated by thermogravimetry（TG） and differential thermogravimetry（DTG）, and differential scanning calorimetry（DSC） under the high-pressure dynamic ambience. The results show that the thermal decomposition processes of the mixed nitric ester gun propellants have two mass-loss stages. Nitric ester evaporates and decomposes in the first stage, and nitrocellulose and centralite II（C2） decompose in the second stage. The mass loss, the DTG peak points, and the terminated temperatures of the two stages are changeable with the difference of the mass ratio of TEGDN to NG. There is only one obvious exothermic peak in the DSC curves under the different pressures. With the increase in the furnace pressure, the peak temperature decreases, and the decomposition heat increases. With the increase in the content of TEGDN, the decomposition heat decreases at 0.1 MPa and rises at high pressure. The variety of mass ratio of TEGDN to NG makes few effect on the exothermic peak temperatures in the DSC curves at different pressures. The kinetic equation of the main exothermal decomposition reaction of the gun propellant TG0601 was determined as： dα/dt=1021.59（1-α）3e-2.60×104/T. The reaction mechanism of the process can be classified as chemical reaction. The critical temperatures of the thermal explosion（Tbe and Tbp） obtained from the onset temperature（Te） and the peak temperature（Tp） are 456.46 and 473.40 K, respectively. ΔS≠, ΔH≠, and ΔG≠ of the decomposition reaction are 163.57 J·mol^-1·K^-1, 209.54 kJ·mol^-1, and 133.55 kJ·mol^-1, respectively.展开更多
The relationships between soil total nitrogen(STN)and influencing factors are scale-dependent.The objective of this study was to identify the multi-scale spatial relationships of STN with selected environmental factor...The relationships between soil total nitrogen(STN)and influencing factors are scale-dependent.The objective of this study was to identify the multi-scale spatial relationships of STN with selected environmental factors(elevation,slope and topographic wetness index),intrinsic soil factors(soil bulk density,sand content,silt content,and clay content)and combined environmental factors(including the first two principal components(PC1 and PC2)of the Vis-NIR soil spectra)along three sampling transects located at the upstream,midstream and downstream of Taiyuan Basin on the Chinese Loess Plateau.We separated the multivariate data series of STN and influencing factors at each transect into six intrinsic mode functions(IMFs)and one residue by multivariate empirical mode decomposition(MEMD).Meanwhile,we obtained the predicted equations of STN based on MEMD by stepwise multiple linear regression(SMLR).The results indicated that the dominant scales of explained variance in STN were at scale 995 m for transect 1,at scales 956 and 8852 m for transect 2,and at scales 972,5716 and 12,317 m for transect 3.Multi-scale correlation coefficients between STN and influencing factors were less significant in transect 3 than in transects 1 and 2.The goodness of fit root mean square error(RMSE),normalized root mean square error(NRMSE),and coefficient of determination(R2)indicated that the prediction of STN at the sampling scale by summing all of the predicted IMFs and residue was more accurate than that by SMLR directly.Therefore,the multi-scale method of MEMD has a good potential in characterizing the multi-scale spatial relationships between STN and influencing factors at the basin landscape scale.展开更多
During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three differ...During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three different plant species tissues (Stipa baicalensis: Sb, Leymus chinensis: Lc and Artemisia frigid: Af), endemic to Stipa baicalensis Steppe, and measured the mass loss of mixtures over 417 days under the N addition treatment. We studied the effect of N addition (N0: no N addition;N15: 1.5 g N/m<sup>2</sup>·a;N30: 3.0 g N/m<sup>2</sup>·a;N50: 5.0 g N/m<sup>2</sup>·a;N100: 10.0 g N/m<sup>2</sup>·a;N150: 15.0 g N/m<sup>2</sup>·a) on the rate of mixed litter decomposition and nutrient dynamics change. The decomposition constant (k) of leaf mixtures was higher than that of root mixtures. The k values of leaf mixed combinations were 0.880 (Sb + Lc), 1.231 (Lc + Af), 1.027 (Sb + Lc + Af), respectively. The k value of stem was 0.806 (Lc + Af) and the root mixed combinations were 0.665 (Sb + Lc), 0.979 (Lc + Af) and 1.164 (Sb + Lc + Af), respectively. The results indicated that N addition had significantly effect on the mixed litter decomposition and nutrient releasing. The rate of plant tissues litter decomposition had different response to N addition. In the context of N addition, litter decomposition rate and nutrient dynamics were changed by synthetic effect of decaying time, specie types and N addition dose. Our findings suggested that prairie plants may adapt to environmental change by adjusting litter quality, thus retaining the stability of the steppe ecosystem.展开更多
A series of LnSrNiO_4(A_2BO_4, Ln=La, Pr, Nd, Sm, Gd) mixed oxides with K_2NiF_4 structure, in which Asite(Sr) was partly substituted by individual light rare earth element, was prepared. The solid state physicochemic...A series of LnSrNiO_4(A_2BO_4, Ln=La, Pr, Nd, Sm, Gd) mixed oxides with K_2NiF_4 structure, in which Asite(Sr) was partly substituted by individual light rare earth element, was prepared. The solid state physicochemical properties including crystal structure, defect structure, IR spectrum, valence state of Bsite ion, nonstoichiometric oxygen, oxygenous species, the properties of oxidation and reduction etc. as well as the catalytic behavior for NO decomposition on these mixed oxides were investigated. The results show that all of these mixed oxide catalysts have high activity for the direct decomposition of NO(at 900 ℃ the conversion of NO is more than 90%). The effect of the substitution of light rare earth elements at Asite on catalytic behavior for NO decomposition was elucidated.展开更多
This paper presents non-Darcy mixed convective flow of an incompressible and viscous fluid in a differentially heated vertical channel filled with a porous material in the presence of a temperature dependent source/si...This paper presents non-Darcy mixed convective flow of an incompressible and viscous fluid in a differentially heated vertical channel filled with a porous material in the presence of a temperature dependent source/sink. The analytical solution of fourth order non-linear ordinary differential equation for temperature field, which is formed by eliminating velocity field from system of governing equations in non-dimensional form, is obtained by using new modified Adomian decomposition method (NMADM) in terms of various parameters. In order to illustrate the interactive influences of governing parameters on the temperature and velocity fields, a numerical study of the analytical solution is performed with respect to three categories of transport processes i) when forced convection is dominated, ii) when forced and natural convection are equal and iii) when natural convection is dominated. Analysis of all categories has revealed that the temperature and velocity profiles are increasing function of modified Darcy number while decreasing function of Forchheimer number.展开更多
On the basis of the absolute and relative gravity observations in North China,spatial dynamic variation of regional gravity fields is obtained. A multi-scale decomposition technique is used to separate anomalies at di...On the basis of the absolute and relative gravity observations in North China,spatial dynamic variation of regional gravity fields is obtained. A multi-scale decomposition technique is used to separate anomalies at different depths,and give some explanation to gravity variation at different time space scales. Gravity variation trends in North China are improved. Based on this result and the analysis of wavelet power spectrum,the images of the depth of wavelet approximation and detail are obtained. The results obtained are of scientific significance for the deep understanding of potential seismic risk in North China from gravity variations in different time space scales.展开更多
The mirror extending approach proposed by Zhao and Huang in EMD method is improved in this paper. Mirror extending manner of data is kept unchanged, but the approach for determining envelopes is changed. When the end ...The mirror extending approach proposed by Zhao and Huang in EMD method is improved in this paper. Mirror extending manner of data is kept unchanged, but the approach for determining envelopes is changed. When the end of data is obviously not extremum, the envelope is determined by the first inner extremum and the image value in the mirror, ignoring the value on the end. This improvement eliminates the frequency compression near the end and decreases the error. Meanwhile, tridiagonal equations are used and the calculation speed is much increased. The temporal process curve is more important in reflecting the real physical process and comparable with other phenomena. Frequency mixing in IMFs makes it impossible. A high frequency reconstruction (HFR) approach is proposed to eliminate common frequency mixing and reconstruct an IMF with all high frequency portions. By this approach, the IMFs without frequency mixing are obtained to express significative processes. The high frequency information restored in high frequency IMF can be extracted by general spectrum method. After obtaining IMFs by EMD method, some of the theoretical and technological issues still exist when using the IMFs. The consistency of IMFs with real physical process is discussed in detail. By virtue of the approach proposed in this paper, the EMD method can be widely used in various fields.展开更多
Noise is generated in a two-dimensional mixing layer due to the growing of instability waves and vortex pairings. The adjoint-based control methodology has shown to be a robust tool to suppress noise radiation. The mo...Noise is generated in a two-dimensional mixing layer due to the growing of instability waves and vortex pairings. The adjoint-based control methodology has shown to be a robust tool to suppress noise radiation. The mode decomposition algorithms such as the compressible version of proper orthogonal decomposition （POD） and dynamic mode decomposition （DMD） are employed to analyze the spatial/spatial-temporal coherent structures for a consecutive data sets of the controlled mixing layer and its uncontrolled counterpart. The analyses of POD indicate that the y-direction body force control mainly modify the most energetic spatial structures, and increase the uniformity of the flow. The analyses of DMD show us prevalent frequencies and corresponding mode structures, and the stability characteristics of each mode can be obtained from DMD-spectrum. The spectral signatures illustrate that a lot of neutral/slightly damping modes emerging in uncontrolled flow within the frequency range （w 〈 0.4） are suppressed due to control, relevant spatial-temporal structures are also varied, which is coincident with the change of far-field noise spectra. From the view of mode decomposition, the action of control redistribute the energy for frequency components of ~ 〈 0.4 by weakening nonlinearities and regularizing corresponding dynamic structures in streamwise direction, and thus suppress the noise radiation. Moreover, the POD- and DMD-analysis in this study demon- strate that DMD can serve as an important supplement for POD in analyzing a time-resolved physical process.展开更多
Cover cropping is a diversifying agricultural practice that can improve soil structure and function by altering the underground litter diversity and soil microbial communities.Here,we tested how a wheat cover crop alt...Cover cropping is a diversifying agricultural practice that can improve soil structure and function by altering the underground litter diversity and soil microbial communities.Here,we tested how a wheat cover crop alters the decomposition of cucumber root litter.A three-year greenhouse litterbag decomposition experiment showed that a wheat cover crop accelerates the decomposition of cucumber root litter.A microcosm litterbag experiment further showed that wheat litter and the soil microbial community could improve cucumber root litter decomposition.Moreover,the wheat cover crop altered the abundances and diversities of soil bacterial and fungal communities,and enriched several putative keystone operational taxonomic units(OTUs),such as Bacillus sp.OTU1837 and Mortierella sp.OTU1236,that were positively related to the mass loss of cucumber root litter.The representative bacterial and fungal strains B186 and M3 were isolated and cultured.In vitro decomposition tests demonstrated that both B186 and M3 had cucumber root litter decomposition activity and a stronger effect was found when they were co-incubated.Overall,a wheat cover crop accelerated cucumber root litter decomposition by altering the soil microbial communities,particularly by stimulating certain putative keystone taxa,which provides a theoretical basis for using cover crops to promote sustainable agricultural development.展开更多
For increasing reaction rate and reducing decomposing temperature,TG-DTA,XRD,SEM and Chemical analysis were used to study the kinetics of mixed rar e earths minerals decomposed by CaO with NaCl-CaCl2. The results show...For increasing reaction rate and reducing decomposing temperature,TG-DTA,XRD,SEM and Chemical analysis were used to study the kinetics of mixed rar e earths minerals decomposed by CaO with NaCl-CaCl2. The results showed that the reaction rate increased with increasing of NaC-CaCl2 addition,CaO addition,an d decomposition temperature. The kinetics of mixed rare earths minerals decompos ed by CaO conformed to 1-2/3X-(1-X) 2/3=kdt mode. The decomposition reaction rate was controlled by two steps,and the activation energy was decreased with addin g of NaCl-CaCl2 melting salt. The micro-pattern of products was loosening and po rous with NaCl-CaCl2 in decomposition system.展开更多
A decomposition experiment of Populus purdomii litter,a commonly used afforestation species in the Qinling Mountains,China,was conducted.Water extracts of five conifer litters were used to treat P.purdomii litter and ...A decomposition experiment of Populus purdomii litter,a commonly used afforestation species in the Qinling Mountains,China,was conducted.Water extracts of five conifer litters were used to treat P.purdomii litter and its soil.The P.purdomii litter was incubated at room temperature(20–25℃)and constant soil moisture for 6 months.During the decomposition period,the dynamics of litter mass and nutrient contents were detected to investigate the impacts of plant secondary metabolites.The results indicate that litter extracts of Pinus tabuliformis,Platycladus orientalis,Pinus armandii and Larix principisrupprechtii significantly inhibited the overall nutrient release of P.purdomii litter,while the last three types of litter extracts simultaneously inhibited its decomposition.Conversely,the litter extracts of Picea asperata significantly accelerated the overall nutrient release of P.purdomii.Generally,most of the conifer species,whose litter released terpenoids,phenolics,steroids,and aliphatic acids,will inhibit the decomposition and/or nutrient release from P.purdomii litter.Their negative effects on the decomposers and soil enzymatic activities indicates that planting diversity should be lower when mixed planted with P.purdomii.展开更多
Noise has traditionally been suppressed or eliminated in seismic data sets by the use of Fourier filters and, to a lesser degree, nonlinear statistical filters. Although these methods are quite useful under specific c...Noise has traditionally been suppressed or eliminated in seismic data sets by the use of Fourier filters and, to a lesser degree, nonlinear statistical filters. Although these methods are quite useful under specific conditions, they may produce undesirable effects for the low signal to noise ratio data. In this paper, a new method, multi-scale ridgelet transform, is used in the light of the theory of ridgelet transform. We employ wavelet transform to do sub-band decomposition for the signals and then use non-linear thresholding in ridgelet domain for every block. In other words, it is based on the idea of partition, at sufficiently fine scale, a curving singularity looks straight, and so ridgelet transform can work well in such cases. Applications on both synthetic data and actual seismic data from Sichuan basin, South China, show that the new method eliminates the noise portion of the signal more efficiently and retains a greater amount of geologic data than other methods, the quality and consecutiveness of seismic event are improved obviously as well as the quality of section is improved.展开更多
Neurons in the pre-B6tzinger complex within the mammalian brain stem play important roles in the generation of respiratory rhythms. Experimental observations show that some neurons can exhibit novel mixed bursting act...Neurons in the pre-B6tzinger complex within the mammalian brain stem play important roles in the generation of respiratory rhythms. Experimental observations show that some neurons can exhibit novel mixed bursting activities. In this paper, based on a mathematical model proposed by Butera, we show how the mixed bursting activities depend on the potassium current in the coupled pre-Botzinger complex. Using fast-slow decomposition and bifurcation analysis, we investigate the dynamics of mixed bursting, as well as the mechanisms of transition between different mixed bursting patterns. We find that mixed bursting involves different bistability, and it is the transition state of two types of regular burstings.展开更多
The decomposition reactions of monazite and bastnaesite mixed rare earth minerals calcined by CaO-NaCl-CaCl2 were studied by means of TG-DTA and XRD. The results show that the process of the minerals decomposed by CaO...The decomposition reactions of monazite and bastnaesite mixed rare earth minerals calcined by CaO-NaCl-CaCl2 were studied by means of TG-DTA and XRD. The results show that the process of the minerals decomposed by CaO involves two steps. The first step occurs in the temperature range of 425-540 ℃, and the main reactions are bastnaesite decomposition, i.e. REOF reacts with CaO to produce RE2O3 and CaF2, and Ce2O3 is oxidized to CeO2. During this step, CaCO3 is formed at about 500 ℃. The second step takes place in the temperature range of 610-700 ℃, and the reactions are monazite decomposition into RE2O3, Ca5F(PO4)3 and Ca3(PO4)2 by CaO and CaF2. In this process, the decomposition ability is improved because CaO from CaCO3 decomposing has high chemical activity. In calcining process, the new formed Ca5F(PO4)3 restrains fluorine that can escape in form of gaseous compound. The decomposition ratio of the mixed rare earth minerals reaches 90.8% at 700 ℃.展开更多
In this paper, we extend the reliable modification of the Adomian Decom-position Method coupled to the Lesnic’s approach to solve boundary value problems and initial boundary value problems with mixed boundary condit...In this paper, we extend the reliable modification of the Adomian Decom-position Method coupled to the Lesnic’s approach to solve boundary value problems and initial boundary value problems with mixed boundary conditions for linear and nonlinear partial differential equations. The method is applied to different forms of heat and wave equations as illustrative examples to exhibit the effectiveness of the method. The method provides the solution in a rapidly convergent series with components that can be computed iteratively. The numerical results for the illustrative examples obtained show remarkable agreement with the exact solutions. We also provide some graphical representations for clear-cut comparisons between the solutions using Maple software.展开更多
Aimed at the problem that Fourier decomposition method(FDM)is sensitive to noise and existing mode mixing cannot accurately extract gearbox fault features,a gear fault feature extraction method combining compound dict...Aimed at the problem that Fourier decomposition method(FDM)is sensitive to noise and existing mode mixing cannot accurately extract gearbox fault features,a gear fault feature extraction method combining compound dictionary noise reduction and optimized FDM(OFDM)is proposed.Firstly,the characteristics of the gear signals are used to construct a compound dictionary,and the orthogonal matching pursuit algorithm(OMP)is combined to reduce the noise of the vibration signal.Secondly,in order to overcome the mode mixing phenomenon occuring during the decomposition of FDM,a method of frequency band division based on the extremum of the spectrum is proposed to optimize the decomposition quality.Then,the OFDM is used to decompose the signal into several analytic Fourier intrinsic band functions(AFIBFs).Finally,the AFIBF with the largest correlation coefficient is selected for Hilbert envelope spectrum analysis.The fault feature frequencies of the vibration signal can be accurately extracted.The proposed method is validated through analyzing the gearbox fault simulation signal and the real vibration signals collected from an experimental gearbox.展开更多
基金Supported by the National Natural Science Foundation of China(11871195)。
文摘In this article,we conduct a study on mixed quasi-martingale Hardy spaces that are defined by means of the mixed L_(p)-norm.By utilizing Doob’s inequalities,we explore the atomic decomposition and quasi-martingale inequalities of mixed quasi-martingale Hardy spaces.Moreover,we furnish sufficient conditions for the boundedness ofσ-sublinear operators in these spaces.These findings extend the existing conclusions regarding mixed quasi-martingale Hardy spaces defined with the help of the mixed L_(p)-norm.
基金Project supported by Key Scientific Projects of Baotou Science and Technology Bureau Intellectual Property (2010Z2003)
文摘The process of decomposion of the bastnasite and monazite rare earth concentrates by alkali solutions was investigated. The mixed slurries of the rare earth concentrates and the alkali solutions were calcined at different temperatures in a rotary tubular electric furnace. The effects of calcination temperature on the decomposing ratio of rare earth, the oxidation ratio of cerium, the stripping of fluorine and phospho-rous after calcinations, and the adaptability of the process to the mixed rare earth concentrates of different grade were studied. The results showed that the decomposition ratio of rare earth and the oxidation ratio of cerium could reach 95.8% and 93.7%, respectively, while the cal-cinating temperature was above 300℃.
基金supported by the National Natural Science Foundation of China(21506194,21676255)the Natural Science Foundation of Zhejiang Province(Y16B070011)the Commission of Science and Technology of Zhejiang province(2017C03007,2017C33106).
文摘Ce-modified Mn-Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction,Raman,N2 adsorption-desorption,infrared spectra H2 temperature-programmed reduction and thermogravimetric analyses.Their catalytic properties were investigated in ozone(O3)decomposition reaction.Results show that the small amount of rare earth metal Ce added during Mn-Fe(FM) mixed-oxide synthesis greatly improves the catalytic performance in O3 decomposition.Among the prepared catalysts.the C0.04(FM)0.96 mixed-oxide catalyst exhibits the highest catalytic activity and stability.The O3 conversion over C0.04(FM)0.96 is 98% after 24 h reaction at 25℃ under dry condition,and that over FM decreases to 90% after 16 h reaction.At 0℃,the O3 conversion over C0.04(FM)0.96 is 95% after 7 h reaction under dry condition.and that over FM slows down to 70%.Under humid condition(RH 65%),the O3 conversion over C0.04(FM)0.96 is 63% after 6.5 h reaction at 25℃.while that over FM decreases to 55%.When Ce is doped into Mn-Fe mixed oxides,the small amount of Ce enters the crystal lattice of MnO2.and partial Fe is separated to form Fe2O3.This changes cause lattice distortion and increase defects and enable the as-synthesized Ce-Fe-Mn ternary mixed-oxide catalysts to acquire additional oxygen vacancies and increase their specific surface area,thereby increasing the number of reaction sites and enhancing the catalytic performance of the catalysts for O3 decomposition.
基金supported by National Natural Science Foundation of China (Grant No. 71271078)National Hi-tech Research and Development Program of China (863 Program, Grant No. 2009AA04Z414)Integration of Industry, Education and Research of Guangdong Province, and Ministry of Education of China (Grant No. 2009B090300312)
文摘When used for separating multi-component non-stationary signals, the adaptive time-varying filter(ATF) based on multi-scale chirplet sparse signal decomposition(MCSSD) generates phase shift and signal distortion. To overcome this drawback, the zero phase filter is introduced to the mentioned filter, and a fault diagnosis method for speed-changing gearbox is proposed. Firstly, the gear meshing frequency of each gearbox is estimated by chirplet path pursuit. Then, according to the estimated gear meshing frequencies, an adaptive zero phase time-varying filter(AZPTF) is designed to filter the original signal. Finally, the basis for fault diagnosis is acquired by the envelope order analysis to the filtered signal. The signal consisting of two time-varying amplitude modulation and frequency modulation(AM-FM) signals is respectively analyzed by ATF and AZPTF based on MCSSD. The simulation results show the variances between the original signals and the filtered signals yielded by AZPTF based on MCSSD are 13.67 and 41.14, which are far less than variances (323.45 and 482.86) between the original signals and the filtered signals obtained by ATF based on MCSSD. The experiment results on the vibration signals of gearboxes indicate that the vibration signals of the two speed-changing gearboxes installed on one foundation bed can be separated by AZPTF effectively. Based on the demodulation information of the vibration signal of each gearbox, the fault diagnosis can be implemented. Both simulation and experiment examples prove that the proposed filter can extract a mono-component time-varying AM-FM signal from the multi-component time-varying AM-FM signal without distortion.
基金the National Natural Science Foundation of China(No.20573098)the Foundation of Key Laboratory of Science and Technology for National Defence of Propellant and Explosive of China(No.9140C3503020605).
文摘The thermal decomposition behavior and nonisothermal reaction kinetics of the double-base gun propellants containing the mixed ester of triethyleneglycol dinitrate（TEGDN） and nitroglycerin（NG） were investigated by thermogravimetry（TG） and differential thermogravimetry（DTG）, and differential scanning calorimetry（DSC） under the high-pressure dynamic ambience. The results show that the thermal decomposition processes of the mixed nitric ester gun propellants have two mass-loss stages. Nitric ester evaporates and decomposes in the first stage, and nitrocellulose and centralite II（C2） decompose in the second stage. The mass loss, the DTG peak points, and the terminated temperatures of the two stages are changeable with the difference of the mass ratio of TEGDN to NG. There is only one obvious exothermic peak in the DSC curves under the different pressures. With the increase in the furnace pressure, the peak temperature decreases, and the decomposition heat increases. With the increase in the content of TEGDN, the decomposition heat decreases at 0.1 MPa and rises at high pressure. The variety of mass ratio of TEGDN to NG makes few effect on the exothermic peak temperatures in the DSC curves at different pressures. The kinetic equation of the main exothermal decomposition reaction of the gun propellant TG0601 was determined as： dα/dt=1021.59（1-α）3e-2.60×104/T. The reaction mechanism of the process can be classified as chemical reaction. The critical temperatures of the thermal explosion（Tbe and Tbp） obtained from the onset temperature（Te） and the peak temperature（Tp） are 456.46 and 473.40 K, respectively. ΔS≠, ΔH≠, and ΔG≠ of the decomposition reaction are 163.57 J·mol^-1·K^-1, 209.54 kJ·mol^-1, and 133.55 kJ·mol^-1, respectively.
基金financially supported by the Research Project of Shanxi Scholarship Council of China (2017– 075)the Natural Science foundation for Young Scientists of Shanxi Province (201801D221103)the Innovation Grant of Shanxi Agricultural University (2017ZZ07)
文摘The relationships between soil total nitrogen(STN)and influencing factors are scale-dependent.The objective of this study was to identify the multi-scale spatial relationships of STN with selected environmental factors(elevation,slope and topographic wetness index),intrinsic soil factors(soil bulk density,sand content,silt content,and clay content)and combined environmental factors(including the first two principal components(PC1 and PC2)of the Vis-NIR soil spectra)along three sampling transects located at the upstream,midstream and downstream of Taiyuan Basin on the Chinese Loess Plateau.We separated the multivariate data series of STN and influencing factors at each transect into six intrinsic mode functions(IMFs)and one residue by multivariate empirical mode decomposition(MEMD).Meanwhile,we obtained the predicted equations of STN based on MEMD by stepwise multiple linear regression(SMLR).The results indicated that the dominant scales of explained variance in STN were at scale 995 m for transect 1,at scales 956 and 8852 m for transect 2,and at scales 972,5716 and 12,317 m for transect 3.Multi-scale correlation coefficients between STN and influencing factors were less significant in transect 3 than in transects 1 and 2.The goodness of fit root mean square error(RMSE),normalized root mean square error(NRMSE),and coefficient of determination(R2)indicated that the prediction of STN at the sampling scale by summing all of the predicted IMFs and residue was more accurate than that by SMLR directly.Therefore,the multi-scale method of MEMD has a good potential in characterizing the multi-scale spatial relationships between STN and influencing factors at the basin landscape scale.
文摘During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three different plant species tissues (Stipa baicalensis: Sb, Leymus chinensis: Lc and Artemisia frigid: Af), endemic to Stipa baicalensis Steppe, and measured the mass loss of mixtures over 417 days under the N addition treatment. We studied the effect of N addition (N0: no N addition;N15: 1.5 g N/m<sup>2</sup>·a;N30: 3.0 g N/m<sup>2</sup>·a;N50: 5.0 g N/m<sup>2</sup>·a;N100: 10.0 g N/m<sup>2</sup>·a;N150: 15.0 g N/m<sup>2</sup>·a) on the rate of mixed litter decomposition and nutrient dynamics change. The decomposition constant (k) of leaf mixtures was higher than that of root mixtures. The k values of leaf mixed combinations were 0.880 (Sb + Lc), 1.231 (Lc + Af), 1.027 (Sb + Lc + Af), respectively. The k value of stem was 0.806 (Lc + Af) and the root mixed combinations were 0.665 (Sb + Lc), 0.979 (Lc + Af) and 1.164 (Sb + Lc + Af), respectively. The results indicated that N addition had significantly effect on the mixed litter decomposition and nutrient releasing. The rate of plant tissues litter decomposition had different response to N addition. In the context of N addition, litter decomposition rate and nutrient dynamics were changed by synthetic effect of decaying time, specie types and N addition dose. Our findings suggested that prairie plants may adapt to environmental change by adjusting litter quality, thus retaining the stability of the steppe ecosystem.
文摘A series of LnSrNiO_4(A_2BO_4, Ln=La, Pr, Nd, Sm, Gd) mixed oxides with K_2NiF_4 structure, in which Asite(Sr) was partly substituted by individual light rare earth element, was prepared. The solid state physicochemical properties including crystal structure, defect structure, IR spectrum, valence state of Bsite ion, nonstoichiometric oxygen, oxygenous species, the properties of oxidation and reduction etc. as well as the catalytic behavior for NO decomposition on these mixed oxides were investigated. The results show that all of these mixed oxide catalysts have high activity for the direct decomposition of NO(at 900 ℃ the conversion of NO is more than 90%). The effect of the substitution of light rare earth elements at Asite on catalytic behavior for NO decomposition was elucidated.
文摘This paper presents non-Darcy mixed convective flow of an incompressible and viscous fluid in a differentially heated vertical channel filled with a porous material in the presence of a temperature dependent source/sink. The analytical solution of fourth order non-linear ordinary differential equation for temperature field, which is formed by eliminating velocity field from system of governing equations in non-dimensional form, is obtained by using new modified Adomian decomposition method (NMADM) in terms of various parameters. In order to illustrate the interactive influences of governing parameters on the temperature and velocity fields, a numerical study of the analytical solution is performed with respect to three categories of transport processes i) when forced convection is dominated, ii) when forced and natural convection are equal and iii) when natural convection is dominated. Analysis of all categories has revealed that the temperature and velocity profiles are increasing function of modified Darcy number while decreasing function of Forchheimer number.
基金funded by the Special Fund for Earthquake Scientific Research of China(201308004,201308009)
文摘On the basis of the absolute and relative gravity observations in North China,spatial dynamic variation of regional gravity fields is obtained. A multi-scale decomposition technique is used to separate anomalies at different depths,and give some explanation to gravity variation at different time space scales. Gravity variation trends in North China are improved. Based on this result and the analysis of wavelet power spectrum,the images of the depth of wavelet approximation and detail are obtained. The results obtained are of scientific significance for the deep understanding of potential seismic risk in North China from gravity variations in different time space scales.
文摘The mirror extending approach proposed by Zhao and Huang in EMD method is improved in this paper. Mirror extending manner of data is kept unchanged, but the approach for determining envelopes is changed. When the end of data is obviously not extremum, the envelope is determined by the first inner extremum and the image value in the mirror, ignoring the value on the end. This improvement eliminates the frequency compression near the end and decreases the error. Meanwhile, tridiagonal equations are used and the calculation speed is much increased. The temporal process curve is more important in reflecting the real physical process and comparable with other phenomena. Frequency mixing in IMFs makes it impossible. A high frequency reconstruction (HFR) approach is proposed to eliminate common frequency mixing and reconstruct an IMF with all high frequency portions. By this approach, the IMFs without frequency mixing are obtained to express significative processes. The high frequency information restored in high frequency IMF can be extracted by general spectrum method. After obtaining IMFs by EMD method, some of the theoretical and technological issues still exist when using the IMFs. The consistency of IMFs with real physical process is discussed in detail. By virtue of the approach proposed in this paper, the EMD method can be widely used in various fields.
基金supported by the National Natural Science Foundation of China (11072238, 11232011)111 project (B07033)
文摘Noise is generated in a two-dimensional mixing layer due to the growing of instability waves and vortex pairings. The adjoint-based control methodology has shown to be a robust tool to suppress noise radiation. The mode decomposition algorithms such as the compressible version of proper orthogonal decomposition （POD） and dynamic mode decomposition （DMD） are employed to analyze the spatial/spatial-temporal coherent structures for a consecutive data sets of the controlled mixing layer and its uncontrolled counterpart. The analyses of POD indicate that the y-direction body force control mainly modify the most energetic spatial structures, and increase the uniformity of the flow. The analyses of DMD show us prevalent frequencies and corresponding mode structures, and the stability characteristics of each mode can be obtained from DMD-spectrum. The spectral signatures illustrate that a lot of neutral/slightly damping modes emerging in uncontrolled flow within the frequency range （w 〈 0.4） are suppressed due to control, relevant spatial-temporal structures are also varied, which is coincident with the change of far-field noise spectra. From the view of mode decomposition, the action of control redistribute the energy for frequency components of ~ 〈 0.4 by weakening nonlinearities and regularizing corresponding dynamic structures in streamwise direction, and thus suppress the noise radiation. Moreover, the POD- and DMD-analysis in this study demon- strate that DMD can serve as an important supplement for POD in analyzing a time-resolved physical process.
基金supported by the National Natural Science Foundation of China(32072655 and 32272792)。
文摘Cover cropping is a diversifying agricultural practice that can improve soil structure and function by altering the underground litter diversity and soil microbial communities.Here,we tested how a wheat cover crop alters the decomposition of cucumber root litter.A three-year greenhouse litterbag decomposition experiment showed that a wheat cover crop accelerates the decomposition of cucumber root litter.A microcosm litterbag experiment further showed that wheat litter and the soil microbial community could improve cucumber root litter decomposition.Moreover,the wheat cover crop altered the abundances and diversities of soil bacterial and fungal communities,and enriched several putative keystone operational taxonomic units(OTUs),such as Bacillus sp.OTU1837 and Mortierella sp.OTU1236,that were positively related to the mass loss of cucumber root litter.The representative bacterial and fungal strains B186 and M3 were isolated and cultured.In vitro decomposition tests demonstrated that both B186 and M3 had cucumber root litter decomposition activity and a stronger effect was found when they were co-incubated.Overall,a wheat cover crop accelerated cucumber root litter decomposition by altering the soil microbial communities,particularly by stimulating certain putative keystone taxa,which provides a theoretical basis for using cover crops to promote sustainable agricultural development.
基金Project supported by the National Natural Science Foundation of China (50974042)Scientific Research Special Foundation of Doctor Subject of Chinese Universities (20090042120015)The Fundamental Research Funds for the Central Universities (N090302007)
文摘For increasing reaction rate and reducing decomposing temperature,TG-DTA,XRD,SEM and Chemical analysis were used to study the kinetics of mixed rar e earths minerals decomposed by CaO with NaCl-CaCl2. The results showed that the reaction rate increased with increasing of NaC-CaCl2 addition,CaO addition,an d decomposition temperature. The kinetics of mixed rare earths minerals decompos ed by CaO conformed to 1-2/3X-(1-X) 2/3=kdt mode. The decomposition reaction rate was controlled by two steps,and the activation energy was decreased with addin g of NaCl-CaCl2 melting salt. The micro-pattern of products was loosening and po rous with NaCl-CaCl2 in decomposition system.
基金supported by the Specialized Research Fund for the Doctoral Program of Yan’an University(YDBK2017-26)the Natural Science Basic Research Plan in Shaanxi Province of China(2018JQ4047)the Young Talent fund of University Association for Science and Technology in Shaanxi,China(20170704)
文摘A decomposition experiment of Populus purdomii litter,a commonly used afforestation species in the Qinling Mountains,China,was conducted.Water extracts of five conifer litters were used to treat P.purdomii litter and its soil.The P.purdomii litter was incubated at room temperature(20–25℃)and constant soil moisture for 6 months.During the decomposition period,the dynamics of litter mass and nutrient contents were detected to investigate the impacts of plant secondary metabolites.The results indicate that litter extracts of Pinus tabuliformis,Platycladus orientalis,Pinus armandii and Larix principisrupprechtii significantly inhibited the overall nutrient release of P.purdomii litter,while the last three types of litter extracts simultaneously inhibited its decomposition.Conversely,the litter extracts of Picea asperata significantly accelerated the overall nutrient release of P.purdomii.Generally,most of the conifer species,whose litter released terpenoids,phenolics,steroids,and aliphatic acids,will inhibit the decomposition and/or nutrient release from P.purdomii litter.Their negative effects on the decomposers and soil enzymatic activities indicates that planting diversity should be lower when mixed planted with P.purdomii.
基金supported by China Petrochemical key project during the 11th Five-year Plan as well as the Doctorate Fund of Ministry of Education of China (No.20050491504)
文摘Noise has traditionally been suppressed or eliminated in seismic data sets by the use of Fourier filters and, to a lesser degree, nonlinear statistical filters. Although these methods are quite useful under specific conditions, they may produce undesirable effects for the low signal to noise ratio data. In this paper, a new method, multi-scale ridgelet transform, is used in the light of the theory of ridgelet transform. We employ wavelet transform to do sub-band decomposition for the signals and then use non-linear thresholding in ridgelet domain for every block. In other words, it is based on the idea of partition, at sufficiently fine scale, a curving singularity looks straight, and so ridgelet transform can work well in such cases. Applications on both synthetic data and actual seismic data from Sichuan basin, South China, show that the new method eliminates the noise portion of the signal more efficiently and retains a greater amount of geologic data than other methods, the quality and consecutiveness of seismic event are improved obviously as well as the quality of section is improved.
基金Project supported by the National Natural Science Foundation of China(Grant No.11472009)Construction Plan for Innovative Research Team of North China University of Technology(Grant No.XN018010)Scientific Research for Undergraduate of North China University of Technology
文摘Neurons in the pre-B6tzinger complex within the mammalian brain stem play important roles in the generation of respiratory rhythms. Experimental observations show that some neurons can exhibit novel mixed bursting activities. In this paper, based on a mathematical model proposed by Butera, we show how the mixed bursting activities depend on the potassium current in the coupled pre-Botzinger complex. Using fast-slow decomposition and bifurcation analysis, we investigate the dynamics of mixed bursting, as well as the mechanisms of transition between different mixed bursting patterns. We find that mixed bursting involves different bistability, and it is the transition state of two types of regular burstings.
基金Project(50574031) supported by the National Natural Science Foundation of ChinaProject(20030145015) supported by the Scientific Research Special Foundation of Doctoral Subject of Chinese University
文摘The decomposition reactions of monazite and bastnaesite mixed rare earth minerals calcined by CaO-NaCl-CaCl2 were studied by means of TG-DTA and XRD. The results show that the process of the minerals decomposed by CaO involves two steps. The first step occurs in the temperature range of 425-540 ℃, and the main reactions are bastnaesite decomposition, i.e. REOF reacts with CaO to produce RE2O3 and CaF2, and Ce2O3 is oxidized to CeO2. During this step, CaCO3 is formed at about 500 ℃. The second step takes place in the temperature range of 610-700 ℃, and the reactions are monazite decomposition into RE2O3, Ca5F(PO4)3 and Ca3(PO4)2 by CaO and CaF2. In this process, the decomposition ability is improved because CaO from CaCO3 decomposing has high chemical activity. In calcining process, the new formed Ca5F(PO4)3 restrains fluorine that can escape in form of gaseous compound. The decomposition ratio of the mixed rare earth minerals reaches 90.8% at 700 ℃.
文摘In this paper, we extend the reliable modification of the Adomian Decom-position Method coupled to the Lesnic’s approach to solve boundary value problems and initial boundary value problems with mixed boundary conditions for linear and nonlinear partial differential equations. The method is applied to different forms of heat and wave equations as illustrative examples to exhibit the effectiveness of the method. The method provides the solution in a rapidly convergent series with components that can be computed iteratively. The numerical results for the illustrative examples obtained show remarkable agreement with the exact solutions. We also provide some graphical representations for clear-cut comparisons between the solutions using Maple software.
基金The National Natural Science Foundation of China(No.51975117)the Key Research&Development Program of Jiangsu Province(No.BE2019086).
文摘Aimed at the problem that Fourier decomposition method(FDM)is sensitive to noise and existing mode mixing cannot accurately extract gearbox fault features,a gear fault feature extraction method combining compound dictionary noise reduction and optimized FDM(OFDM)is proposed.Firstly,the characteristics of the gear signals are used to construct a compound dictionary,and the orthogonal matching pursuit algorithm(OMP)is combined to reduce the noise of the vibration signal.Secondly,in order to overcome the mode mixing phenomenon occuring during the decomposition of FDM,a method of frequency band division based on the extremum of the spectrum is proposed to optimize the decomposition quality.Then,the OFDM is used to decompose the signal into several analytic Fourier intrinsic band functions(AFIBFs).Finally,the AFIBF with the largest correlation coefficient is selected for Hilbert envelope spectrum analysis.The fault feature frequencies of the vibration signal can be accurately extracted.The proposed method is validated through analyzing the gearbox fault simulation signal and the real vibration signals collected from an experimental gearbox.
