The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based...The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based on the low-cost alloy composition design,the corro-sion behavior of commercial Mg-3Al-1Zn(AZ31)alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy,hydrogen evolution,electrochemical measurements,and corrosion morphology analysis.Results revealed that the potential differ-ence of Al_(2)Ca/α-Mg and Mg_(2)Sn/α-Mg was(230±19)mV and(80±6)mV,respectively,much lower than that of Al_(8)Mn_(5)/α-Mg(430±31)mV in AZ31 alloy,which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance,followed by AZ31-0.2Ca,while AZ31 al-loy exhibited the worst corrosion resistance.Moreover,Sn dissolved into matrix obviously increased the potential ofα-Mg and participated in the formation of dense SnO_(2) film at the interface of matrix,while Ca element was enriched in the corrosion product layer,resulting in the cor-rosion product layer of AZ31-0.2Ca/Sn alloys more compact,stable,and protective than AZ31 alloy.Therefore,AZ31 alloy bearing 0.2wt%Ca or Sn element exhibited excellent balanced properties,which is potential to be applied in commercial more comprehensively.展开更多
The role of the rare earth element Sm in as-cast Zn-5AI alloy was studied in this work.A three times higher improvement than the control group on corrosion resistance was found with rare earth Sm adding(0.15 wt%).By u...The role of the rare earth element Sm in as-cast Zn-5AI alloy was studied in this work.A three times higher improvement than the control group on corrosion resistance was found with rare earth Sm adding(0.15 wt%).By using an electron prove micro analyzer(EPMA),focused ion beam(FIB)and scanning Kelvin probe force microscopy(SKPFM)techniques,two main mechanisms of the premium performance of the Sm adding were revealed.One was that the non-uniform nucleation and component undercooling induced by Sm adding,reduced theα-AI layer spacing thus improved the covering efficiency of the Al_(2)O_(3)film.The other was that the dissolved Sm in the Zn/Al eutectic structure modulated the electron work function thus induced the attenuation of Volta potential discrepancy.The experimental results show that when the addition of Sm is 0.15 wt%,the minimum Volta potential difference betweenα-AI andη-Zn phases is achieved,and excessive or deficient Sm addition will increase the Volta potential difference.展开更多
The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that...The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that Mg_(2)Ca corroded easier thanα-Mg,indicating that Mg_(2)Ca acted as an anode.The work function(Φ)for Mg_(2)Ca calculated by first-principles is significantly lower compared to that forα-Mg.The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg_(2)Ca had a relatively low Volta potential(ψ)value.The lowerΦandψvalues for Mg_(2)Ca indicate a lower electrochemical nobility,which is consistent with the experimental phenomenon.展开更多
Quinones are common organic compounds frequently used as model dissolved organic matters in water, and their redox properties are usually characterized by either electrochemical or spectroscopic methods separately. In...Quinones are common organic compounds frequently used as model dissolved organic matters in water, and their redox properties are usually characterized by either electrochemical or spectroscopic methods separately. In this work, electrochemical methodology was combined with two fluorescence spectroelectrochemical techniques, cyclic voltafluorescence spectrometry （CVF） and derivative cyclic voltafluorescence spectrometry （DCVF）, to determine the electrochemical properties of p-benzoQuinone in dimethvl sulfoxide, an aprotic solution. The CVF results show that the electrochemical reduction ofp-benzoquinone resulted in the formation of radical anion and dianion, which exhibited a lower fluorescence intensity and red-shift of the emission spectra compared to that of p-benzoauinone. The fluorescence intensity was found to vary along with the electrochemical oxidation and reduction ofp-benzoquinone. The CVF and DCVF results were in good consistence. Thus, the combined method offers a powerful tool to investigate the electrochemical process of p-benzoquinone and other natural organic compounds.展开更多
In regional water resources management and disaster preparedness, the analysis of extreme rainfall events is essential. The need to investigate drought and flood conditions is now heightened within the context of clim...In regional water resources management and disaster preparedness, the analysis of extreme rainfall events is essential. The need to investigate drought and flood conditions is now heightened within the context of climate change and variability. The Standardised Precipitation Index (SPI) was employed to assess the extreme rainfall event on Tordzie watershed using precipitation data from 1984-2014. The SPI on the time scale of 3, 6, 9 and 12 months were determined using “DrinC” software. The drought was characterised into magnitude, duration, intensity, frequency, commencement and termination at the time scales of SPI-3, SPI-6, SPI-9 and SPI-12. Results indicated that the middle reaches (Kpetoe) of the watershed experienced less severe drought condition compared to the lower reaches (Tordzinu). Mann-Kendall (MK) test and Sen’s slope (SS) revealed general increasing drought trend but insignificant at 95% confidence interval. The SS indicated change in magnitude of 0.016 mm/year, 0.012 mm/year, 0.026 mm/year and 0.016 mm/year respectively at the mentioned time scales at 95% confidence interval at the Tordzinu and that of Kpetoe were 0.006 mm/year, 0.009 mm/year, 0.014 mm/year and 0.003 mm/year. These changes could have implication for agriculture and water resources management and engender food insecurity among smallholder farmers.展开更多
This research was carried out at two locations, Ada and Aveglo at the Volta Estuary, Ghana to evaluate the importance of sediments as regulatory media in controlling the levels of four metals, Manganese (Mn), Zinc (Zn...This research was carried out at two locations, Ada and Aveglo at the Volta Estuary, Ghana to evaluate the importance of sediments as regulatory media in controlling the levels of four metals, Manganese (Mn), Zinc (Zn), Iron (Fe) and Mercury (Hg) in the tissues of the clam, Galatea paradoxa (Born 1778) and to investigate the possible relationships between the concentrations of the metals in the sediments and the clams. The clams were categorized into three size classes as follows: small (25 - 40 mm), medium (41 - 55 mm), and large (above 55 mm). To understand the possible relationships between the concentrations of the studied metals in the sediments and in the tissues of the three clam size classes, the monthly concentrations of the studied metals were graphed and subjected to Pearson correlation analyses (p < 0.05) to identify metal accumulation patterns and determine whether or not positive relationship patterns existed between the concentrations in the clams and sediment samples. The correlation revealed no simple linear relationships between the concentrations of four heavy metals in the clam tissues and the sediments at the two sampling stations although some distinct trends were observed. Mn concentrations in the clams and sediments from the two stations showed some clear positive relationship patterns with some increments in monthly sediment concentrations resulting in increments in clam tissue concentrations. This relationship though, was not too clear-cut.展开更多
In order to study the effect of intermaetallics on the corrosion behaviour of 7A52 aluminum alloy, the alloy was characterized by means of SEM-EDS and scanning Kelvin probe force microscopy（SKPFM）. The experimental ...In order to study the effect of intermaetallics on the corrosion behaviour of 7A52 aluminum alloy, the alloy was characterized by means of SEM-EDS and scanning Kelvin probe force microscopy（SKPFM）. The experimental results indicate that there are two different intermetallics：A1-Mn-Fe and Mg2Si. Both intermetallics exhibite the negative volta potential relative to the matrix indicating an anodic behaviour. Hereby, they are easy to be dissolved and corroded under the erosive environment, and there become the corrosion initiation sites. The A1-Mn-Fe intermetallics show stronger anodic behaviour than those of Mg2Si intermetalics. It means that A1-Mn-Fe intermetalics are easier to be corroded.展开更多
River discharge data offer a rich source of information for reservoir management and flood control, if modelling can separate out the effects of rainfall, land use, soil type, relief, and weather conditions. In this p...River discharge data offer a rich source of information for reservoir management and flood control, if modelling can separate out the effects of rainfall, land use, soil type, relief, and weather conditions. In this paper, we model river discharge data from the Black Volta River, using Generalised Additive Mixed Models (GAMMs) with a space-time interaction represented via a tensor product of continuous time and discrete space. River discharge data from January 2000 to December 2009 for the four gauge stations along the Black Volta River namely, Lawra, Chache, Bui and Bamboi were obtained from the hydrological services department of Ghana and used for model fitting. Four GAMMs were explored, two with space-time interactions and two without space-time interactions. The comparison of the performance of the models with space-time interactions and those without space-time interactions based on Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) suggests that in this application, the former is better overall and in particular for modelling local variations. Further, a model with space and time main effects performed better compared with one without space and time main effects. After model selection, checking and validation, there is evidence for increasing river discharge from the most upstream gauge station to the most downstream gauge station for the study period.展开更多
The corrosion performances of rolled AZ31 alloy with addition of Y and Gd were comparatively investigated. The corrosion rates of AZ31 alloy modified with Y and Gd were 3.3 and 3.7 mm/y immersing for 24 h in 3.5 wt% N...The corrosion performances of rolled AZ31 alloy with addition of Y and Gd were comparatively investigated. The corrosion rates of AZ31 alloy modified with Y and Gd were 3.3 and 3.7 mm/y immersing for 24 h in 3.5 wt% NaCl solution, respectively, which were much lower than that of AZ31 alloy(23.6 mm/y). The remarkable improvement in corrosion performance by adding Y or Gd was ascribed to preferentially form less noble Al_(2)Y or Al_(6)GdMn_(6) and more protective corrosion product layer, resulting in the reduction in H_(2) evolution rate and the enhancement of passivity.展开更多
It was K. B. Oldham who developed a semi-integral polarographie method in 1972 to record the curve of the semi-integral value of current against the electrode potential. M. Goto presented subsequently a semidifferenti...It was K. B. Oldham who developed a semi-integral polarographie method in 1972 to record the curve of the semi-integral value of current against the electrode potential. M. Goto presented subsequently a semidifferential polarographic method to record the curve of the semidifferential value of current against the electrode potential. On the basis of these methods, the 1.5th order (e^n) and 2.5th order (e″)展开更多
05001 On the Reflection Coefficient Expressed inTerms of the Conjugate Impedances. Huang Zhixun:1(1). 1980. pp.63--76.This paper discusses the power waves and theirapplications. These waves are related to the availabl...05001 On the Reflection Coefficient Expressed inTerms of the Conjugate Impedances. Huang Zhixun:1(1). 1980. pp.63--76.This paper discusses the power waves and theirapplications. These waves are related to the availablepower of the generator. The reflection coefficient ofthe power waves is different from the conventionaltravelling waves. and it can lead to more precisethinking and measurements. Using this theory. we ex-展开更多
This paper has examined how the resources of the White Volta River are enhancing food availability for riparian communities in northern Ghana despite climate change and its associated effects on food security. Using p...This paper has examined how the resources of the White Volta River are enhancing food availability for riparian communities in northern Ghana despite climate change and its associated effects on food security. Using participatory methods such as focus group discussions and interviews, data was collected from households and institutions in three riparian communities. The result of the study indicates that, all things been equal, cultivation of food crops along the river bank in the rainy season gives significantly high yields as compared to yields from farms farthest from the river under rain fed agriculture. Higher organic content and moisture retention capacity of river bank soils explains the yield differential and adaptability to climate change. In addition, farmers now irrigate cereal crops which were hitherto, reserved for only rainy season production. However, inappropriate irrigation practices are accelerating erosion and sedimentation of the river and thus, threaten the sustainability of agriculture and food security in the White Volta Basin. The paper therefore, recommends the adoption of IWRM （integrated water resources management） and the participation of local communities, Government and Civil Society organisations for sustaining the productive capacity of the White Volta Basin for enabling adaptation of agriculture to climate change in the riparian communities of the basin.展开更多
Some stations for the following spectes are pointed out:Anagallis tenella.Aster squamatus, Cistus salvifolitts,Cypripedium calceolus.Euphorbia villosa.Galium glaucum,G.montis-arerae,Humulus scan- dens.Ornitltogalum py...Some stations for the following spectes are pointed out:Anagallis tenella.Aster squamatus, Cistus salvifolitts,Cypripedium calceolus.Euphorbia villosa.Galium glaucum,G.montis-arerae,Humulus scan- dens.Ornitltogalum pyramidale,Phacelia tanacetifolia,Plantago indica.Polypodium australe,Potentilla norvegi- ca.Si(?)vos angulatus.Thlaspi alpestre.Veratrum album subsp.lobelianum,Viola clatior.展开更多
In this letter, the rotating ring-disc electrodes are used to study corrosion. The influence of K2CrO4 and Na3S on electrochemical corrosion of A3 steel in concentrated alkaline solution has been investigated. The pro...In this letter, the rotating ring-disc electrodes are used to study corrosion. The influence of K2CrO4 and Na3S on electrochemical corrosion of A3 steel in concentrated alkaline solution has been investigated. The products formed in liquid phase were distinguished, using silver ring-A3 steel disc elec-展开更多
The authors investigated plant species selected for charcoal production. Then, they compared these species with those exploited for charcoal production in Togo, another West African country. The study in Ghana took pl...The authors investigated plant species selected for charcoal production. Then, they compared these species with those exploited for charcoal production in Togo, another West African country. The study in Ghana took place in six localities in the Volta Region. Simple ranking was used in the analysis of the species. A total of 35 species belonging to 31 genera were used. Five of these are non-traditional charcoal-making species, implying the increasing diversity of the plants used. Anogeissus leiocarpus ranked first with over 79% of the producers exploiting it and was reported as a preferred or a category 1 species for charcoal production in Togo. Out of the 34 woody species exploited in Togo, 10 are similar to those used in the study area. The ranking used are compared favourably with the categorization used in the Togolese studies.展开更多
Through a series of precise measurements of the EMF of acid H-type cells (there is Pb, Sn, or Pb-Sn in the amalgam) provided by three factories, the characteristics of these cells were studied. The measuring apparatus...Through a series of precise measurements of the EMF of acid H-type cells (there is Pb, Sn, or Pb-Sn in the amalgam) provided by three factories, the characteristics of these cells were studied. The measuring apparatus and temperature control system are basically similar to those used in the experiment of 1974. The temperature graclient of oil bath was measured by a precision platinum resistance thermometer. It was found that the horizontal temperature gradient of the bath was less than 0.001℃ under any temperature and the gradient between any two points in the working region was less than 0.002℃.展开更多
The knowledge about groundwater flow conditions within Volta river basin in Benin, has restricted information coming to piezometry, water storage time, water path, and water quality. A good groundwater resources asses...The knowledge about groundwater flow conditions within Volta river basin in Benin, has restricted information coming to piezometry, water storage time, water path, and water quality. A good groundwater resources assessment of this sudano-sahelian area, is a huge condition for the sustainable management of water resources, which since the part of the 20th century is facing a severe drought that leads to a greater aridity. This article provides a summary with the main elements of carbon isotope (13C and 14C) as well as tritium (3H) coupled with hydrogeological and hydrochemical data. The goal is to improve the initial water recharging and the groundwater flow system within the aquifer. Two main results can be produced from the groundwater chemistry. First, the interactions between groundwater and clay minerals related to the residence time of groundwater are indicated by a slight evolution of Ca-HCO3 and Ca-Mg-HCO3 to Na-HCO3. Beside that towards water types Cl-NO3 indicates the anthropogenic influence on groundwater, related to agricultural activities and sanitation conditions. The carbon-14 activity measured on the TDIC is between 17.29 and 85.47 pmC. Therefore, it contains some samples covering a wide period of time from now to the Holocene implying a continuous system recharging over time. All the data confirm the assumption of a homogeneous, largely unified aquifer system with a multi-layer structure, but it also points out the low resource sustainability and a strong anthropogenic contamination of the most superficial horizons.展开更多
基金This work is financially supported by the Fundamental Research Funds for the Central Universities,China(Nos.2302017FRF-IC-17-001,2302018FRF-IC-18-004,232019 FRF-IC-19-018,and 2302020FRF-IC-20-10)the China Postdoctoral Science Foundation(No.2021M700378).
文摘The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based on the low-cost alloy composition design,the corro-sion behavior of commercial Mg-3Al-1Zn(AZ31)alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy,hydrogen evolution,electrochemical measurements,and corrosion morphology analysis.Results revealed that the potential differ-ence of Al_(2)Ca/α-Mg and Mg_(2)Sn/α-Mg was(230±19)mV and(80±6)mV,respectively,much lower than that of Al_(8)Mn_(5)/α-Mg(430±31)mV in AZ31 alloy,which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance,followed by AZ31-0.2Ca,while AZ31 al-loy exhibited the worst corrosion resistance.Moreover,Sn dissolved into matrix obviously increased the potential ofα-Mg and participated in the formation of dense SnO_(2) film at the interface of matrix,while Ca element was enriched in the corrosion product layer,resulting in the cor-rosion product layer of AZ31-0.2Ca/Sn alloys more compact,stable,and protective than AZ31 alloy.Therefore,AZ31 alloy bearing 0.2wt%Ca or Sn element exhibited excellent balanced properties,which is potential to be applied in commercial more comprehensively.
基金the National Natural Science Foundation of China(51974097,52161010)Central Government Guides Local Science and Technology Development Special Projects(20194011)+1 种基金the Program of"One Hundred Talented People"of Guizhou Province(20164014)Guizhou Province Science and Technology Project(20175656,20175788,20191414,20192162)。
文摘The role of the rare earth element Sm in as-cast Zn-5AI alloy was studied in this work.A three times higher improvement than the control group on corrosion resistance was found with rare earth Sm adding(0.15 wt%).By using an electron prove micro analyzer(EPMA),focused ion beam(FIB)and scanning Kelvin probe force microscopy(SKPFM)techniques,two main mechanisms of the premium performance of the Sm adding were revealed.One was that the non-uniform nucleation and component undercooling induced by Sm adding,reduced theα-AI layer spacing thus improved the covering efficiency of the Al_(2)O_(3)film.The other was that the dissolved Sm in the Zn/Al eutectic structure modulated the electron work function thus induced the attenuation of Volta potential discrepancy.The experimental results show that when the addition of Sm is 0.15 wt%,the minimum Volta potential difference betweenα-AI andη-Zn phases is achieved,and excessive or deficient Sm addition will increase the Volta potential difference.
基金funded by the National Key Research and Development Program of China(No.2017YFB0702504)
文摘The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that Mg_(2)Ca corroded easier thanα-Mg,indicating that Mg_(2)Ca acted as an anode.The work function(Φ)for Mg_(2)Ca calculated by first-principles is significantly lower compared to that forα-Mg.The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg_(2)Ca had a relatively low Volta potential(ψ)value.The lowerΦandψvalues for Mg_(2)Ca indicate a lower electrochemical nobility,which is consistent with the experimental phenomenon.
基金Acknowledgements The authors wish to thank the National Natural Science Foundation of China （Grant Nos. 21505074 and 21477120） and the Natural Science Foundation of Jiangsu Province （BK20140781） for partial support of this study.
文摘Quinones are common organic compounds frequently used as model dissolved organic matters in water, and their redox properties are usually characterized by either electrochemical or spectroscopic methods separately. In this work, electrochemical methodology was combined with two fluorescence spectroelectrochemical techniques, cyclic voltafluorescence spectrometry （CVF） and derivative cyclic voltafluorescence spectrometry （DCVF）, to determine the electrochemical properties of p-benzoQuinone in dimethvl sulfoxide, an aprotic solution. The CVF results show that the electrochemical reduction ofp-benzoquinone resulted in the formation of radical anion and dianion, which exhibited a lower fluorescence intensity and red-shift of the emission spectra compared to that of p-benzoauinone. The fluorescence intensity was found to vary along with the electrochemical oxidation and reduction ofp-benzoquinone. The CVF and DCVF results were in good consistence. Thus, the combined method offers a powerful tool to investigate the electrochemical process of p-benzoquinone and other natural organic compounds.
文摘In regional water resources management and disaster preparedness, the analysis of extreme rainfall events is essential. The need to investigate drought and flood conditions is now heightened within the context of climate change and variability. The Standardised Precipitation Index (SPI) was employed to assess the extreme rainfall event on Tordzie watershed using precipitation data from 1984-2014. The SPI on the time scale of 3, 6, 9 and 12 months were determined using “DrinC” software. The drought was characterised into magnitude, duration, intensity, frequency, commencement and termination at the time scales of SPI-3, SPI-6, SPI-9 and SPI-12. Results indicated that the middle reaches (Kpetoe) of the watershed experienced less severe drought condition compared to the lower reaches (Tordzinu). Mann-Kendall (MK) test and Sen’s slope (SS) revealed general increasing drought trend but insignificant at 95% confidence interval. The SS indicated change in magnitude of 0.016 mm/year, 0.012 mm/year, 0.026 mm/year and 0.016 mm/year respectively at the mentioned time scales at 95% confidence interval at the Tordzinu and that of Kpetoe were 0.006 mm/year, 0.009 mm/year, 0.014 mm/year and 0.003 mm/year. These changes could have implication for agriculture and water resources management and engender food insecurity among smallholder farmers.
文摘This research was carried out at two locations, Ada and Aveglo at the Volta Estuary, Ghana to evaluate the importance of sediments as regulatory media in controlling the levels of four metals, Manganese (Mn), Zinc (Zn), Iron (Fe) and Mercury (Hg) in the tissues of the clam, Galatea paradoxa (Born 1778) and to investigate the possible relationships between the concentrations of the metals in the sediments and the clams. The clams were categorized into three size classes as follows: small (25 - 40 mm), medium (41 - 55 mm), and large (above 55 mm). To understand the possible relationships between the concentrations of the studied metals in the sediments and in the tissues of the three clam size classes, the monthly concentrations of the studied metals were graphed and subjected to Pearson correlation analyses (p < 0.05) to identify metal accumulation patterns and determine whether or not positive relationship patterns existed between the concentrations in the clams and sediment samples. The correlation revealed no simple linear relationships between the concentrations of four heavy metals in the clam tissues and the sediments at the two sampling stations although some distinct trends were observed. Mn concentrations in the clams and sediments from the two stations showed some clear positive relationship patterns with some increments in monthly sediment concentrations resulting in increments in clam tissue concentrations. This relationship though, was not too clear-cut.
基金Funded by the National Natural Science Foundation of China(No.50801066)
文摘In order to study the effect of intermaetallics on the corrosion behaviour of 7A52 aluminum alloy, the alloy was characterized by means of SEM-EDS and scanning Kelvin probe force microscopy（SKPFM）. The experimental results indicate that there are two different intermetallics：A1-Mn-Fe and Mg2Si. Both intermetallics exhibite the negative volta potential relative to the matrix indicating an anodic behaviour. Hereby, they are easy to be dissolved and corroded under the erosive environment, and there become the corrosion initiation sites. The A1-Mn-Fe intermetallics show stronger anodic behaviour than those of Mg2Si intermetalics. It means that A1-Mn-Fe intermetalics are easier to be corroded.
文摘River discharge data offer a rich source of information for reservoir management and flood control, if modelling can separate out the effects of rainfall, land use, soil type, relief, and weather conditions. In this paper, we model river discharge data from the Black Volta River, using Generalised Additive Mixed Models (GAMMs) with a space-time interaction represented via a tensor product of continuous time and discrete space. River discharge data from January 2000 to December 2009 for the four gauge stations along the Black Volta River namely, Lawra, Chache, Bui and Bamboi were obtained from the hydrological services department of Ghana and used for model fitting. Four GAMMs were explored, two with space-time interactions and two without space-time interactions. The comparison of the performance of the models with space-time interactions and those without space-time interactions based on Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) suggests that in this application, the former is better overall and in particular for modelling local variations. Further, a model with space and time main effects performed better compared with one without space and time main effects. After model selection, checking and validation, there is evidence for increasing river discharge from the most upstream gauge station to the most downstream gauge station for the study period.
基金financially supported by the Fundamental Research Funds for the Central Universities(No.FRF-IC-20-10)。
文摘The corrosion performances of rolled AZ31 alloy with addition of Y and Gd were comparatively investigated. The corrosion rates of AZ31 alloy modified with Y and Gd were 3.3 and 3.7 mm/y immersing for 24 h in 3.5 wt% NaCl solution, respectively, which were much lower than that of AZ31 alloy(23.6 mm/y). The remarkable improvement in corrosion performance by adding Y or Gd was ascribed to preferentially form less noble Al_(2)Y or Al_(6)GdMn_(6) and more protective corrosion product layer, resulting in the reduction in H_(2) evolution rate and the enhancement of passivity.
文摘It was K. B. Oldham who developed a semi-integral polarographie method in 1972 to record the curve of the semi-integral value of current against the electrode potential. M. Goto presented subsequently a semidifferential polarographic method to record the curve of the semidifferential value of current against the electrode potential. On the basis of these methods, the 1.5th order (e^n) and 2.5th order (e″)
文摘05001 On the Reflection Coefficient Expressed inTerms of the Conjugate Impedances. Huang Zhixun:1(1). 1980. pp.63--76.This paper discusses the power waves and theirapplications. These waves are related to the availablepower of the generator. The reflection coefficient ofthe power waves is different from the conventionaltravelling waves. and it can lead to more precisethinking and measurements. Using this theory. we ex-
文摘This paper has examined how the resources of the White Volta River are enhancing food availability for riparian communities in northern Ghana despite climate change and its associated effects on food security. Using participatory methods such as focus group discussions and interviews, data was collected from households and institutions in three riparian communities. The result of the study indicates that, all things been equal, cultivation of food crops along the river bank in the rainy season gives significantly high yields as compared to yields from farms farthest from the river under rain fed agriculture. Higher organic content and moisture retention capacity of river bank soils explains the yield differential and adaptability to climate change. In addition, farmers now irrigate cereal crops which were hitherto, reserved for only rainy season production. However, inappropriate irrigation practices are accelerating erosion and sedimentation of the river and thus, threaten the sustainability of agriculture and food security in the White Volta Basin. The paper therefore, recommends the adoption of IWRM （integrated water resources management） and the participation of local communities, Government and Civil Society organisations for sustaining the productive capacity of the White Volta Basin for enabling adaptation of agriculture to climate change in the riparian communities of the basin.
文摘In this letter, the rotating ring-disc electrodes are used to study corrosion. The influence of K2CrO4 and Na3S on electrochemical corrosion of A3 steel in concentrated alkaline solution has been investigated. The products formed in liquid phase were distinguished, using silver ring-A3 steel disc elec-
文摘The authors investigated plant species selected for charcoal production. Then, they compared these species with those exploited for charcoal production in Togo, another West African country. The study in Ghana took place in six localities in the Volta Region. Simple ranking was used in the analysis of the species. A total of 35 species belonging to 31 genera were used. Five of these are non-traditional charcoal-making species, implying the increasing diversity of the plants used. Anogeissus leiocarpus ranked first with over 79% of the producers exploiting it and was reported as a preferred or a category 1 species for charcoal production in Togo. Out of the 34 woody species exploited in Togo, 10 are similar to those used in the study area. The ranking used are compared favourably with the categorization used in the Togolese studies.
文摘Through a series of precise measurements of the EMF of acid H-type cells (there is Pb, Sn, or Pb-Sn in the amalgam) provided by three factories, the characteristics of these cells were studied. The measuring apparatus and temperature control system are basically similar to those used in the experiment of 1974. The temperature graclient of oil bath was measured by a precision platinum resistance thermometer. It was found that the horizontal temperature gradient of the bath was less than 0.001℃ under any temperature and the gradient between any two points in the working region was less than 0.002℃.
基金the framework of the International Atomic Energy Agency(IAEA)Regional Project RAF-7011,Vienna,Austria
文摘The knowledge about groundwater flow conditions within Volta river basin in Benin, has restricted information coming to piezometry, water storage time, water path, and water quality. A good groundwater resources assessment of this sudano-sahelian area, is a huge condition for the sustainable management of water resources, which since the part of the 20th century is facing a severe drought that leads to a greater aridity. This article provides a summary with the main elements of carbon isotope (13C and 14C) as well as tritium (3H) coupled with hydrogeological and hydrochemical data. The goal is to improve the initial water recharging and the groundwater flow system within the aquifer. Two main results can be produced from the groundwater chemistry. First, the interactions between groundwater and clay minerals related to the residence time of groundwater are indicated by a slight evolution of Ca-HCO3 and Ca-Mg-HCO3 to Na-HCO3. Beside that towards water types Cl-NO3 indicates the anthropogenic influence on groundwater, related to agricultural activities and sanitation conditions. The carbon-14 activity measured on the TDIC is between 17.29 and 85.47 pmC. Therefore, it contains some samples covering a wide period of time from now to the Holocene implying a continuous system recharging over time. All the data confirm the assumption of a homogeneous, largely unified aquifer system with a multi-layer structure, but it also points out the low resource sustainability and a strong anthropogenic contamination of the most superficial horizons.
