The effects of galvanic interaction between galena and pyrite on their flotation and electrochemical characters were studied by electrochemical,adsorption,flotation and FTIR techniques,respectively.Electrochemical tes...The effects of galvanic interaction between galena and pyrite on their flotation and electrochemical characters were studied by electrochemical,adsorption,flotation and FTIR techniques,respectively.Electrochemical tests indicate that galena is electrochemically more active than pyrite and serves as an anode in galvanic combination with pyrite.The galvanic current density from a mixture of galena and pyrite is 4 times as high as the self corrosion current density of galena,which indicates that the corrosion rate of galena is accelerated.Adsorption tests show that the adsorption of butyl xanthate on galena surface is enhanced,and affected by a combination of pyrite-galena mixtures and conditioning time.Compared with individual mineral particles,galvanic interaction reduces the floatability difference between galena and pyrite.The flotation recovery of galena decreases while that of pyrite increases when two minerals are mixed together due to the influence of galvanic interaction on the formation of hydrophilic/hydrophobic product.The FTIR results show that the formation of dixanthogen on pyrite surface is depressed due to the galvanic interaction.展开更多
A differential equation that is generally effective for squeeze film air damping of perforated plate and non perforated plate as well as in MEMS devices is developed.For perforated plate,the thickness and the dimens...A differential equation that is generally effective for squeeze film air damping of perforated plate and non perforated plate as well as in MEMS devices is developed.For perforated plate,the thickness and the dimensions of the plate are not limited.With boundary conditions,pressure distribution and the damping force on the plate can be found by solving the differential equation.Analytical expressions for damping pressure and damping force of a long strip holeplate are presented with a finite thickness and a finite width.To the extreme conditions of very thin plate and very thin hole,the results are reduced to the corresponding results of the conventional Reynolds' equation.Thus, the effectiveness of the generalized differential equation is justified.Therefore,the generalized Reynolds' equation will be a useful tool of design for damping structures in MEMS.展开更多
The accelerating factor (AF) method is a simple and appropriate way to investigate the atomic long-time deep diffusion at solid-solid interface. In the framework of AF hyperdynamics (HD) simulation, the relationsh...The accelerating factor (AF) method is a simple and appropriate way to investigate the atomic long-time deep diffusion at solid-solid interface. In the framework of AF hyperdynamics (HD) simulation, the relationship between the diffusion coefficient along the direction of z-axis which is normal to the Mg/Zn interface and temperature was investigated, and the AF's impact on the diffusion constant (D0) and activation energy (Q^*) was studied. Then, two steps were taken to simulate the atomic diffusion process and the formation of new phases: one for acceleration and the other for equilibration. The results show that: the Arrhenius equation works well for the description of Dz with different accelerating factors; the AF has no effect on the diffusion constant Do in the case of no phase transition; and the relationship between Q* and Q conforms to Q^*=Q/A. Then, the new Arrhenius equation for AFHD is successfully constructed as Dz=Doexp[-Q/(ART)]. Meanwhile, the authentic equilibrium conformations at any dynamic moment can only be reproduced by the equilibration simulation of the HD-simulated configurations. Key words: accelerating factor method; Arrhenius equation; two-steps scheme; Mg/Zn interface; hyperdynamic simulation展开更多
To solve the inaccuracy problem caused by the two existing methods (averageend-area method and prismoidal method) used for the calculation of roadway earthwork volume, thispaper puts forward a new concept of the 3-dim...To solve the inaccuracy problem caused by the two existing methods (averageend-area method and prismoidal method) used for the calculation of roadway earthwork volume, thispaper puts forward a new concept of the 3-dimensional algorithm that takes all the roadway geometricdesign procedures as a kind of geometrical operation between the ground model (original terrainmodel) and the roadway model (designed model) under certain constraints, and then presents acomplete 3-dimensional algorithm of roadway earthwork volume as well as its executable computerprogram. The algorithm benefits from the re-triangulation technique of constrained delaunaytriangulation (CDT), which can yield a true volume value theoretically. Through a number ofpractical testscovering varied intervals between adjacent cross sections, it is proven to possess ahigher accuracy compared with that of traditional methods. All the work involved in this paperindicates that the 3-dimensional calculation of roadway earthwork volumeis feasible, more accurateand should have further application in practice.展开更多
The dynamic responses of any floating platform arc dependent on the mass, stiffness and damping characteristics of the body as well as mooring system. Therefore, it is very essential to study the effect of individual ...The dynamic responses of any floating platform arc dependent on the mass, stiffness and damping characteristics of the body as well as mooring system. Therefore, it is very essential to study the effect of individual contributions to the system that can finally help to economise their cost. This paper focuses on the effect of mooring stiffness on the responses of a truss spar platform, obtained by different grouping of lines. The study is part of our present researches on mooring systems which include the effect of line pretension, diameter and azimuth angles. The platform is modelled as a rigid body with three degrees-of-freedom and its motions are analyzed in time-domain using the implicit Newmark Beta technique. The mooring lines restoring force-excursion relationship is evaluated using a quasi-static approach. It is observed that the mooring system with lines arranged in less number of groups exhibits better performance in terms of the restoring forces as well as mean position of platform. However, the dynamic motions of platform remain unaffected for different line groups.展开更多
China has implemented a series of emission reduction policies since 2013,and the concentration of air pollutants has consequently decreased significantly.However,PM_(2.5)(particulate matter with an aerodynamic diamete...China has implemented a series of emission reduction policies since 2013,and the concentration of air pollutants has consequently decreased significantly.However,PM_(2.5)(particulate matter with an aerodynamic diameter less than_(2.5)μm)pollution still occurs in China in relation to the interannual variations in meteorological conditions.Considering that El Nino-Southern Oscillation(ENSO)is the strongest signalmodulating the interannual variation in the atmosphere-ocean system,in this study the authors investigate the variations in PM_(2.5)concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021.Results show that the wintertime PM_(2.5) concentrations in the Beijing-Tianjin-Hebei and Fenwei Plain regions during El Nino years are higher than those during La Nina years,which can be explained by the anomalous southerly(northerly)winds during El Nino(La Nina) favoring PM_(2.5) accumulation(diffusion).In the Pearl River Delta region,PM_(2.5)concentrations decrease in El Nino relative to La Nina years owing to the enhanced water vapor flux and precipitation,removing more PM_(2.5)from the atmosphere.The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_(2.5)over the Yangtze River Delta region,which should be analyzed case by case.展开更多
The objective of the study is to examine the relationship between environmental accounting audit decision and firm's profitability in Nigeria. Specifically, the authors hypothesize that profitability is a determinant...The objective of the study is to examine the relationship between environmental accounting audit decision and firm's profitability in Nigeria. Specifically, the authors hypothesize that profitability is a determinant of company's decision to disclose quantitative environmental information for external audits. The population of this research is made up of both quoted and non-quoted companies. The sample size for this study was selected using the simple random sampling technique. The selected companies included companies from the following sectors: agriculture, automobile and tyre, breweries, building materials, chemical and paints, conglomerates companies, food/beverages and tobacco, construction, healthcare, industrial/domestic products, packaging, printing and publishing, textiles, petroleum marketing companies, banking, insurance, and others. A sample of 160 companies with audited final accounts for 2009 financial year was eventually selected. The binary logit regression technique was utilized as the data analysis method. The finding reveals that profitability is a positive and significant determinant in evaluating the probability that a firm includes environmental information for external audits. The study concludes that finn-specific factors may provide incentives for corporate environmentalism in Nigeria.展开更多
In this paper, the problem of determining the largest possible set of symmetries for an important nonlinear dynamical system: the two-dimensional damped Kuramoto-Sivashinsky ((21)) DKS ) equation is studied. By ...In this paper, the problem of determining the largest possible set of symmetries for an important nonlinear dynamical system: the two-dimensional damped Kuramoto-Sivashinsky ((21)) DKS ) equation is studied. By applying the basic Lie symmetry method for the (217)) DKS equation, the classical Lie point symmetry operators are obtained. Also, the optimal system of one-dimensional subalgebras of the equation is constructed. The Lie invariants as well as similarity reduced equations corresponding to infinitesimal symmetries are obtained. The nonclassicaJ symmetries of the (2D) DKS equation are also investigated.展开更多
Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitu...Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitutive model of fiber bundles, statistical constitutive equations of aramid fiber bundles are derived from statistical analysis of test data at different strain rates. Comparison between the theoretical predictions and experimental data indicates statistical constitutive equations fit well with the experimental data, and statistical constitutive equations of fiber bundles at different strain rates are valid.展开更多
Previous studies have revealed a connection between springtime sea surface temperature (SST) in the tropical northern Atlantic (TNA) and the succeeding wintertime El Nino-Southern Oscillation (ENSO). The present...Previous studies have revealed a connection between springtime sea surface temperature (SST) in the tropical northern Atlantic (TNA) and the succeeding wintertime El Nino-Southern Oscillation (ENSO). The present analysis demonstrates that the linkage between springtime TNA SST and the following ENSO experiences an obvious interdecadal change around the early 1980s, with the connection being weak before but significant after. After the early 1980s, springtime positive TNA SST anomalies induce an anomalous cyclone over the northeastern subtropical Pacific and an anomalous Walker circulation with a descending branch over the tropical central-eastern Pacific. This leads to anomalous cold SST in the northeastern Pacific and an anomalous anticyclone over the western-central tropical Pacific, with anomalous easterlies to the equatorward side. As such, springtime TNA SST anomalies are followed by wintertime ENSO after the early 1980s. In contrast, before the early 1980s, anomalous cold SST in the northeastern Pacific and related anomalous easterlies over the western-central tropical Pacific are weak, corresponding to springtime positive TNA SST anomalies and resulting in a weak linkage between springtimeTNA SST and the succeeding wintertime ENSO. Further investigation implies that the change in the TNA SST-ENSO relationship is probably due to a change in springtime mean precipitation over the tropical Atlantic and South America.展开更多
Frequency-domain airborne electromagnetics is a proven geophysical exploration method.Presently,the interpretation is mainly based on resistivity-depth imaging and onedimensional layered inversion;nevertheless,it is d...Frequency-domain airborne electromagnetics is a proven geophysical exploration method.Presently,the interpretation is mainly based on resistivity-depth imaging and onedimensional layered inversion;nevertheless,it is difficult to obtain satisfactory results for two- or three-dimensional complex earth structures using 1D methods.3D forward modeling and inversion can be used but are hampered by computational limitations because of the large number of data.Thus,we developed a 2.5D frequency-domain airborne electromagnetic forward modeling and inversion algorithm.To eliminate the source singularities in the numerical simulations,we split the fields into primary and secondary fields.The primary fields are calculated using homogeneous or layered models with analytical solutions,and the secondary(scattered) fields are solved by the finite-element method.The linear system of equations is solved by using the large-scale sparse matrix parallel direct solver,which greatly improves the computational efficiency.The inversion algorithm was based on damping leastsquares and singular value decomposition and combined the pseudo forward modeling and reciprocity principle to compute the Jacobian matrix.Synthetic and field data were used to test the effectiveness of the proposed method.展开更多
This study employed an innovative meth- odological framework that combines geomatics and conventional survey methods to monitor changes in forest conditions and examine their associations with local forest governance ...This study employed an innovative meth- odological framework that combines geomatics and conventional survey methods to monitor changes in forest conditions and examine their associations with local forest governance parameters in a mountain watershed covering 153.3 km2 in the middle moun- tains of Nepal. The study involved two spatial scales and analytical steps. First, geomatics techniques were used to map and detect changes in major land cover types in the watershed between 1976 and 2000 and to analyze relationships between forest cover changes and governance arrangements. This was followed by micro-level analysis of the relationships between the biological conditions of selected forests within the watershed and their governance arrangements, using conventional survey methods and analytical tools. The findings show that forest cover in the watershed in- creased by about 15 per cent during the period. The rate of increase in forest cover was highest in areas under a semi-government type of governance ar- rangement, while the community forests were gener- ally better in terms of current biological conditions compared to the semi-government forests. This in- consistency between the findings from the two analy- ses does not allow us to draw any firm conclusions regarding the role of property rights in determining forest condition, but it indicates that the outcomes of local forest management initiatives may be more de-pendent on local institutional arrangements regulat- ing forest use and maintenance of forest resources than on the type of property rights arrangements. The findings also provide evidence of the methodological suitability of the research approach adopted, which may be useful for addressing many other research questions related to forestry and natural resources management, particularly those involving multiple spatial scales.展开更多
Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problem...Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method (DEM) provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional (a-D) finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.展开更多
The study examined the levels of resource-use efficiency of rice farmers unde,r irrigation method in Dadinkowa, Gombe state of Nigeria. Using questionnaire, data were collected during the year 2010 irrigation season f...The study examined the levels of resource-use efficiency of rice farmers unde,r irrigation method in Dadinkowa, Gombe state of Nigeria. Using questionnaire, data were collected during the year 2010 irrigation season from 120 randomly sampled rice irrigators and the data were analyzed using multiple regression and marginal analyses. Results showed that significant factors influencing irrigated rice production were labour (P 〈 0.001), land and fertilizer (P 〈 0.01). In addition, the coefficient of determination (R2), the F-ratio and the standard error of the mean (S) were found to be 0.471, 16.37*** and 8.908, respectively. The results also indicated that efficiency values of land, seeds, fertilizer and labour were 1.234, 0.498, 2.352 and 1.620, respectively. Finally, it was found that resource-use among the farmers were not efficient thus equipment, land, fertilizer and labour inputs shall be increased by 78.3%, 18.9%, 57.5% and 38.3%, respectively, while seed input shall be reduced by 50.2% for the farmers to attain optimal resource utilization.展开更多
Several oscillation criteria are given for the second order nonlinear differential equation with damped term of the form [α(t)(y'(t))σ]' +p(t)(y'(t))σ+ q(t)f(y(t)) = 0, where α∈C(R, (0,∞)), p(t) and ...Several oscillation criteria are given for the second order nonlinear differential equation with damped term of the form [α(t)(y'(t))σ]' +p(t)(y'(t))σ+ q(t)f(y(t)) = 0, where α∈C(R, (0,∞)), p(t) and q(t) are allowed to change sign on [t0, ∞), and f∈C1 (R, R) such that xf(x) > 0 for x ≠0. Our results improve and extend some known oscillation criteria. Examples are inserted to illustrate our results.展开更多
The relationship between Indian and East Asian summer rainfall variations is non-stationary in observations as well as in historical simulations of climate models.Is this non-stationarity due to changes in effects of ...The relationship between Indian and East Asian summer rainfall variations is non-stationary in observations as well as in historical simulations of climate models.Is this non-stationarity due to changes in effects of external forcing or internal atmospheric processes? Whilst ENSO is an important oceanic forcing of Indian and East Asian summer rainfall variations,its impacts cannot explain the observed long-term changes in the Indian-East Asian summer rainfall relationship.Monte Carlo test indicates that the role of random processes cannot be totally excluded in the observed longterm changes of the relationship.Analysis of climate model outputs shows that the Indian-North China summer rainfall relationship displays obvious temporal variations in both individual and ensemble mean model simulations and large differences among model simulations.This suggests an important role played by atmospheric internal variability in changes of the Indian-East Asian summer rainfall relationship.This point of view is supported by results from a 100-years AGCM simulation with climatological SST specified in the global ocean.The correlation between Indian and North China or southern Japan summer rainfall variations displays large fluctuations in the AGCM simulation展开更多
基金Project(51274255)supported by the National Natural Science Foundation of ChinaProject supported by the Co-innovation Center for Clean and Efficient Utilization of Strategic Metal Mineral Resources,China
文摘The effects of galvanic interaction between galena and pyrite on their flotation and electrochemical characters were studied by electrochemical,adsorption,flotation and FTIR techniques,respectively.Electrochemical tests indicate that galena is electrochemically more active than pyrite and serves as an anode in galvanic combination with pyrite.The galvanic current density from a mixture of galena and pyrite is 4 times as high as the self corrosion current density of galena,which indicates that the corrosion rate of galena is accelerated.Adsorption tests show that the adsorption of butyl xanthate on galena surface is enhanced,and affected by a combination of pyrite-galena mixtures and conditioning time.Compared with individual mineral particles,galvanic interaction reduces the floatability difference between galena and pyrite.The flotation recovery of galena decreases while that of pyrite increases when two minerals are mixed together due to the influence of galvanic interaction on the formation of hydrophilic/hydrophobic product.The FTIR results show that the formation of dixanthogen on pyrite surface is depressed due to the galvanic interaction.
文摘A differential equation that is generally effective for squeeze film air damping of perforated plate and non perforated plate as well as in MEMS devices is developed.For perforated plate,the thickness and the dimensions of the plate are not limited.With boundary conditions,pressure distribution and the damping force on the plate can be found by solving the differential equation.Analytical expressions for damping pressure and damping force of a long strip holeplate are presented with a finite thickness and a finite width.To the extreme conditions of very thin plate and very thin hole,the results are reduced to the corresponding results of the conventional Reynolds' equation.Thus, the effectiveness of the generalized differential equation is justified.Therefore,the generalized Reynolds' equation will be a useful tool of design for damping structures in MEMS.
基金Project (2012CB722805) supported by the National Basic Research Program of ChinaProjects (50974083, 51174131) supported by the National Natural Science Foundation of China+1 种基金Project (50774112) supported by the Joint Fund of NSFC and Baosteel, ChinaProject(07QA4021) supported by the Shanghai "Phosphor" Science Foundation, China
文摘The accelerating factor (AF) method is a simple and appropriate way to investigate the atomic long-time deep diffusion at solid-solid interface. In the framework of AF hyperdynamics (HD) simulation, the relationship between the diffusion coefficient along the direction of z-axis which is normal to the Mg/Zn interface and temperature was investigated, and the AF's impact on the diffusion constant (D0) and activation energy (Q^*) was studied. Then, two steps were taken to simulate the atomic diffusion process and the formation of new phases: one for acceleration and the other for equilibration. The results show that: the Arrhenius equation works well for the description of Dz with different accelerating factors; the AF has no effect on the diffusion constant Do in the case of no phase transition; and the relationship between Q* and Q conforms to Q^*=Q/A. Then, the new Arrhenius equation for AFHD is successfully constructed as Dz=Doexp[-Q/(ART)]. Meanwhile, the authentic equilibrium conformations at any dynamic moment can only be reproduced by the equilibration simulation of the HD-simulated configurations. Key words: accelerating factor method; Arrhenius equation; two-steps scheme; Mg/Zn interface; hyperdynamic simulation
文摘To solve the inaccuracy problem caused by the two existing methods (averageend-area method and prismoidal method) used for the calculation of roadway earthwork volume, thispaper puts forward a new concept of the 3-dimensional algorithm that takes all the roadway geometricdesign procedures as a kind of geometrical operation between the ground model (original terrainmodel) and the roadway model (designed model) under certain constraints, and then presents acomplete 3-dimensional algorithm of roadway earthwork volume as well as its executable computerprogram. The algorithm benefits from the re-triangulation technique of constrained delaunaytriangulation (CDT), which can yield a true volume value theoretically. Through a number ofpractical testscovering varied intervals between adjacent cross sections, it is proven to possess ahigher accuracy compared with that of traditional methods. All the work involved in this paperindicates that the 3-dimensional calculation of roadway earthwork volumeis feasible, more accurateand should have further application in practice.
文摘The dynamic responses of any floating platform arc dependent on the mass, stiffness and damping characteristics of the body as well as mooring system. Therefore, it is very essential to study the effect of individual contributions to the system that can finally help to economise their cost. This paper focuses on the effect of mooring stiffness on the responses of a truss spar platform, obtained by different grouping of lines. The study is part of our present researches on mooring systems which include the effect of line pretension, diameter and azimuth angles. The platform is modelled as a rigid body with three degrees-of-freedom and its motions are analyzed in time-domain using the implicit Newmark Beta technique. The mooring lines restoring force-excursion relationship is evaluated using a quasi-static approach. It is observed that the mooring system with lines arranged in less number of groups exhibits better performance in terms of the restoring forces as well as mean position of platform. However, the dynamic motions of platform remain unaffected for different line groups.
基金This study was supported by the National Natural Science Foundation of China[grant number 41975159]the National Key Research and Development Program of China[grant numbers 2020YFA0607803 and 2019YFA0606800].
文摘China has implemented a series of emission reduction policies since 2013,and the concentration of air pollutants has consequently decreased significantly.However,PM_(2.5)(particulate matter with an aerodynamic diameter less than_(2.5)μm)pollution still occurs in China in relation to the interannual variations in meteorological conditions.Considering that El Nino-Southern Oscillation(ENSO)is the strongest signalmodulating the interannual variation in the atmosphere-ocean system,in this study the authors investigate the variations in PM_(2.5)concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021.Results show that the wintertime PM_(2.5) concentrations in the Beijing-Tianjin-Hebei and Fenwei Plain regions during El Nino years are higher than those during La Nina years,which can be explained by the anomalous southerly(northerly)winds during El Nino(La Nina) favoring PM_(2.5) accumulation(diffusion).In the Pearl River Delta region,PM_(2.5)concentrations decrease in El Nino relative to La Nina years owing to the enhanced water vapor flux and precipitation,removing more PM_(2.5)from the atmosphere.The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_(2.5)over the Yangtze River Delta region,which should be analyzed case by case.
文摘The objective of the study is to examine the relationship between environmental accounting audit decision and firm's profitability in Nigeria. Specifically, the authors hypothesize that profitability is a determinant of company's decision to disclose quantitative environmental information for external audits. The population of this research is made up of both quoted and non-quoted companies. The sample size for this study was selected using the simple random sampling technique. The selected companies included companies from the following sectors: agriculture, automobile and tyre, breweries, building materials, chemical and paints, conglomerates companies, food/beverages and tobacco, construction, healthcare, industrial/domestic products, packaging, printing and publishing, textiles, petroleum marketing companies, banking, insurance, and others. A sample of 160 companies with audited final accounts for 2009 financial year was eventually selected. The binary logit regression technique was utilized as the data analysis method. The finding reveals that profitability is a positive and significant determinant in evaluating the probability that a firm includes environmental information for external audits. The study concludes that finn-specific factors may provide incentives for corporate environmentalism in Nigeria.
文摘In this paper, the problem of determining the largest possible set of symmetries for an important nonlinear dynamical system: the two-dimensional damped Kuramoto-Sivashinsky ((21)) DKS ) equation is studied. By applying the basic Lie symmetry method for the (217)) DKS equation, the classical Lie point symmetry operators are obtained. Also, the optimal system of one-dimensional subalgebras of the equation is constructed. The Lie invariants as well as similarity reduced equations corresponding to infinitesimal symmetries are obtained. The nonclassicaJ symmetries of the (2D) DKS equation are also investigated.
基金The project is supported by Zhejiang Provincial Natural Science Foundaion of China(599113)Science and Technology Foundation of Ministy of Educationd of China(DF 02064)
文摘Tensile impact tests of aramid (Twaron) fiber bundles were carried out under high strain rates with a wide range of 0. 01/s -1 000/s by using MTS and bar-bar tensile impact apparatus. Based on the statistical constitutive model of fiber bundles, statistical constitutive equations of aramid fiber bundles are derived from statistical analysis of test data at different strain rates. Comparison between the theoretical predictions and experimental data indicates statistical constitutive equations fit well with the experimental data, and statistical constitutive equations of fiber bundles at different strain rates are valid.
基金supported by the National Natural Science Foundation of China[grant numbers 41530425 and 41605050]the China Postdoctoral Science Foundation[grant number2015M581151]
文摘Previous studies have revealed a connection between springtime sea surface temperature (SST) in the tropical northern Atlantic (TNA) and the succeeding wintertime El Nino-Southern Oscillation (ENSO). The present analysis demonstrates that the linkage between springtime TNA SST and the following ENSO experiences an obvious interdecadal change around the early 1980s, with the connection being weak before but significant after. After the early 1980s, springtime positive TNA SST anomalies induce an anomalous cyclone over the northeastern subtropical Pacific and an anomalous Walker circulation with a descending branch over the tropical central-eastern Pacific. This leads to anomalous cold SST in the northeastern Pacific and an anomalous anticyclone over the western-central tropical Pacific, with anomalous easterlies to the equatorward side. As such, springtime TNA SST anomalies are followed by wintertime ENSO after the early 1980s. In contrast, before the early 1980s, anomalous cold SST in the northeastern Pacific and related anomalous easterlies over the western-central tropical Pacific are weak, corresponding to springtime positive TNA SST anomalies and resulting in a weak linkage between springtimeTNA SST and the succeeding wintertime ENSO. Further investigation implies that the change in the TNA SST-ENSO relationship is probably due to a change in springtime mean precipitation over the tropical Atlantic and South America.
基金supported by the Doctoral Fund Project of the Ministry of Education(No.20130061110060 class tutors)the National Natural Science Foundation of China(No.41504083)National Basic Research Program of China(973Program)(No.2013CB429805)
文摘Frequency-domain airborne electromagnetics is a proven geophysical exploration method.Presently,the interpretation is mainly based on resistivity-depth imaging and onedimensional layered inversion;nevertheless,it is difficult to obtain satisfactory results for two- or three-dimensional complex earth structures using 1D methods.3D forward modeling and inversion can be used but are hampered by computational limitations because of the large number of data.Thus,we developed a 2.5D frequency-domain airborne electromagnetic forward modeling and inversion algorithm.To eliminate the source singularities in the numerical simulations,we split the fields into primary and secondary fields.The primary fields are calculated using homogeneous or layered models with analytical solutions,and the secondary(scattered) fields are solved by the finite-element method.The linear system of equations is solved by using the large-scale sparse matrix parallel direct solver,which greatly improves the computational efficiency.The inversion algorithm was based on damping leastsquares and singular value decomposition and combined the pseudo forward modeling and reciprocity principle to compute the Jacobian matrix.Synthetic and field data were used to test the effectiveness of the proposed method.
文摘This study employed an innovative meth- odological framework that combines geomatics and conventional survey methods to monitor changes in forest conditions and examine their associations with local forest governance parameters in a mountain watershed covering 153.3 km2 in the middle moun- tains of Nepal. The study involved two spatial scales and analytical steps. First, geomatics techniques were used to map and detect changes in major land cover types in the watershed between 1976 and 2000 and to analyze relationships between forest cover changes and governance arrangements. This was followed by micro-level analysis of the relationships between the biological conditions of selected forests within the watershed and their governance arrangements, using conventional survey methods and analytical tools. The findings show that forest cover in the watershed in- creased by about 15 per cent during the period. The rate of increase in forest cover was highest in areas under a semi-government type of governance ar- rangement, while the community forests were gener- ally better in terms of current biological conditions compared to the semi-government forests. This in- consistency between the findings from the two analy- ses does not allow us to draw any firm conclusions regarding the role of property rights in determining forest condition, but it indicates that the outcomes of local forest management initiatives may be more de-pendent on local institutional arrangements regulat- ing forest use and maintenance of forest resources than on the type of property rights arrangements. The findings also provide evidence of the methodological suitability of the research approach adopted, which may be useful for addressing many other research questions related to forestry and natural resources management, particularly those involving multiple spatial scales.
基金the National Basic Research Program of China (Grant No. 2008CB425802)
文摘Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method (DEM) provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional (a-D) finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.
文摘The study examined the levels of resource-use efficiency of rice farmers unde,r irrigation method in Dadinkowa, Gombe state of Nigeria. Using questionnaire, data were collected during the year 2010 irrigation season from 120 randomly sampled rice irrigators and the data were analyzed using multiple regression and marginal analyses. Results showed that significant factors influencing irrigated rice production were labour (P 〈 0.001), land and fertilizer (P 〈 0.01). In addition, the coefficient of determination (R2), the F-ratio and the standard error of the mean (S) were found to be 0.471, 16.37*** and 8.908, respectively. The results also indicated that efficiency values of land, seeds, fertilizer and labour were 1.234, 0.498, 2.352 and 1.620, respectively. Finally, it was found that resource-use among the farmers were not efficient thus equipment, land, fertilizer and labour inputs shall be increased by 78.3%, 18.9%, 57.5% and 38.3%, respectively, while seed input shall be reduced by 50.2% for the farmers to attain optimal resource utilization.
文摘Several oscillation criteria are given for the second order nonlinear differential equation with damped term of the form [α(t)(y'(t))σ]' +p(t)(y'(t))σ+ q(t)f(y(t)) = 0, where α∈C(R, (0,∞)), p(t) and q(t) are allowed to change sign on [t0, ∞), and f∈C1 (R, R) such that xf(x) > 0 for x ≠0. Our results improve and extend some known oscillation criteria. Examples are inserted to illustrate our results.
基金supported by the National Key Research and Development Program of China[grant number 2016YFA0600603]the National Key Basic Research Program of China[grant number 2014CB953902]the National Natural Science Foundation of China[grant number 41661144016],[grant number 41530425],[grant number 41475081],and[grant number 41275081]
文摘The relationship between Indian and East Asian summer rainfall variations is non-stationary in observations as well as in historical simulations of climate models.Is this non-stationarity due to changes in effects of external forcing or internal atmospheric processes? Whilst ENSO is an important oceanic forcing of Indian and East Asian summer rainfall variations,its impacts cannot explain the observed long-term changes in the Indian-East Asian summer rainfall relationship.Monte Carlo test indicates that the role of random processes cannot be totally excluded in the observed longterm changes of the relationship.Analysis of climate model outputs shows that the Indian-North China summer rainfall relationship displays obvious temporal variations in both individual and ensemble mean model simulations and large differences among model simulations.This suggests an important role played by atmospheric internal variability in changes of the Indian-East Asian summer rainfall relationship.This point of view is supported by results from a 100-years AGCM simulation with climatological SST specified in the global ocean.The correlation between Indian and North China or southern Japan summer rainfall variations displays large fluctuations in the AGCM simulation