Since the D-band center theory was proposed,it has been widely used in the fields of surface chemistry by almost all researchers,due to its easy understanding,convenient operation and relative accuracy.However,with th...Since the D-band center theory was proposed,it has been widely used in the fields of surface chemistry by almost all researchers,due to its easy understanding,convenient operation and relative accuracy.However,with the continuous development of material systems and modification strategies,researchers have gradually found that D-band center theory is usually effective for large metal particle systems,but for small metal particle systems or semiconductors,such as single atom systems,the opposite conclusion to the D-band center theory is often obtained.To solve the issue above,here we propose a bonding and anti-bonding orbitals stable electron intensity difference(BASED)theory for surface chemistry.The newly-proposed BASED theory can not only successfully explain the abnormal phenomena of D-band center theory,but also exhibits a higher accuracy for prediction of adsorption energy and bond length of intermediates on active sites.Importantly,a new phenomenon of the spin transition state in the adsorption process is observed based on the BASED theory,where the active center atom usually yields an unstable high spin transition state to enhance its adsorption capability in the adsorption process of intermediates when their distance is about 2.5Å.In short,the BASED theory can be considered as a general principle to understand catalytic mechanism of intermediates on surfaces.展开更多
Background,aim,and scope Solar radiation is the main source of energy for terrestrial ecosystems.Small changes in the absorption of solar radiation at the ground surface can have a significant impact on the climatic e...Background,aim,and scope Solar radiation is the main source of energy for terrestrial ecosystems.Small changes in the absorption of solar radiation at the ground surface can have a significant impact on the climatic environment.Natural and anthropogenic changes in ground cover are important factors affecting the absorption of solar radiation at the ground surface.This phenomenon is particularly pronounced in the mid and high latitudes.In order to quantify the inf luence of surface cover change on the absorption of solar radiation at the surface and to provide a scientific basis for changes in the climatic environment,this paper analyzed ground cover change,ground absorbed solar radiation change and the effect of ground cover change on ground absorbed solar radiation in the Three Northeastern Provinces of China from 2001 to 2018.Materials and methods In this study,the Three Northeastern Provinces of China were used as the study area.Firstly,satellite remote sensing data were used to obtain land cover data and albedo data for Aug.1st of each year in 2001,2005,2010,2015 and 2018.The albedo data were further used to calculate the absorbed solar radiation data at the ground surface.Next,the land cover data were used to count the area changes and shifts of different land classes over the five-year period.The land cover data were overlaid with the surface absorbed solar radiation data to obtain the mean and standard deviation of radiation absorption for different ground classes.The surface absorbed solar radiation data were subtracted to obtain the changes in surface absorbed solar radiation for 2001-2005,2005-2010,2010-2015 and 2015-2018.Ultimately,we used a combination of shifted changes in ground classes and changes in surface absorbed solar radiation data,with unchanged ground classes as a baseline and data such as slope orientation as an aid.We analyzed the effect of ground cover change on surface absorbed solar radiation at regional and pixel point scales.Results(1)The area of woodland and waters in the Three Northeastern Provinces of China increased and then decreased from 2001 to 2018,with an overall increase of 3.96%and 10.51%respectively.Cropland decreased and then increased,with a total decrease of 1.22%.Grassland continued to decrease,with an overall decrease of 19.36%.Building sites increased all the time,with a total increase of 11.08%.The main types of ground cover shifted were woodland,cropland and grassland.The main factors for the change in ground cover were China’s woodland protection policy and the saturation of the total woodland stock.(2)The five ground types absorb solar radiation in the order of waters>building sites>woodland>grassland>cropland.The surface absorption of solar radiation in the Songnen Plain,the Sanjiang Plain and the Songhua River Basin flowing through the Songnen Plain and the Sanjiang Plain varies significantly,by more than 25 W·m^(-2).(3)Changes in the ground cover type affected the absorption of solar radiation energy by the ground surface.There was a clear trend of interconversion between waters and cropland/grassland,cropland and woodland/grassland.In particular,the conversion of waters to both cropland and grassland radiation absorption values decreased significantly,while the opposite increased.The absolute difference between waters and cropland was a maximum of -156.66 W·m^(-2)in 2010-2015,and between waters and grassland was a maximum of 102.36 W·m^(-2) in 2005-2010.The radiative absorption values of woodland and grassland reclamation declined and conversely increased.The absolute difference between woodland and cropland was a maximum of-13.94 W·m^(-2) in 2010-2015 when woodland converted to cropland,and between grassland and cropland was a maximum of 22.36 W·m^(-2) in 2001-2005 when cropland converted to grassland,respectively.Discussion Ground cover changes in the Three Northeastern Provinces of China from 2001-2018 were inextricably linked to natural factors and the inf luence of Chinese national policies.The main inf luencing factors were China’s woodland protection policy,restoration of woodland fire sites,saturation of total woodland,optimization of cropland patterns,sanding of grassland,expansion of water conservancy projects,and urbanization expansion.There were differences in the radiation absorption characteristics of different ground cover types.This was due to the nature of the ground type itself and the regional environment.When ground cover types changed,their ability to absorb solar radiation also changed.The degree of change could be inf luenced by different ground types and different environmental factors.Different spatial scales can also produce variability.We need to consider the effects of ground cover change on the absorption of solar radiation at the surface in an integrated and comprehensive way.Conclusions The Three Northeastern Provinces of China had frequent changes in ground cover from 2001-2018,with the area of grassland decreased by almost 20%.These changes were due to natural environmental change and policies issued by China since the 21st century.The extent to which solar radiation was absorbed by different ground cover types was different,with grassland being the strongest and cropland the least.In the past few years,the Songnen Plain and Sanjiang Plain regions were the most significant changes in the absorption of solar radiation by the ground cover.The change in ground cover type led to a change in solar radiation absorption at the ground surface,with the conversion of waters to cropland or grassland and the conversion of cropland to woodland or grassland showing the greatest change in radiation absorption values,and vice versa.Of these,the absolute difference in the conversion of waters to cropland amounts to-156.66 W·m^(-2) in 2010-2015.The variation in the absorption of solar radiation at the ground surface was related to the characteristics of the ground class itself,but was also limited by the regional environment.Recommendations and perspectives This study showed that surface cover change can affect the absorption of solar radiation at the surface to varying degrees.The unchanged land classes were used as a comparative analysis in this paper,and it was clear from the paper that some of the unchanged land classes showed significant changes in radiation absorption that should be of interest in future studies.展开更多
Under the condition of high temperature, the effects of five cover patterns （clean tillage, film mulching, weed covering, branches and leaves covering and growing grass covering） on soil properties in young Phoebe b...Under the condition of high temperature, the effects of five cover patterns （clean tillage, film mulching, weed covering, branches and leaves covering and growing grass covering） on soil properties in young Phoebe boumei forest were in- vestigated. The results showed that the five cover patterns all showed significant ef- fects on soil properties in young Phoebe bournei forest under the condition of high temperature. Land cover increased land temperature in Phoebe boumei forest. Un- der the film mulching, the land temperature was increased most rapidly with the largest increment. However, weed covering, branches and leaves covering and growing grass covering decreased land temperature. Among them, growing grass covering showed the best cooling effect. The film mulching, weed covering, branch- es and leaves covering and growing grass covering all increased land humidity. The film mulching showed the best moisture-preserving effect in the early period, but in the late period, the humidity in the film mulching treatment group was lower than that in the clean tillage treatment group. Among the five mulching patterns, moisture loss in the film mulching treatment group was slowest and least, followed by those in the weed covering and branches and leaves covering treatment groups, and moisture loss in the growing grass covering treatment group was fastest and most.展开更多
Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool ...Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool wear status. Results show that good surface integrity of TC21 can be obtained in high speed milling. In addition, even in acutely worn stages, there is no so-called serious hardening layer （or white layer） according to the studies on microhardness and metallurgical structure.展开更多
The surface and interfacial properties of polymeric bonding agents and nitramine crystal fillers were studied. The surface free energy and adhesion work of polymeric bonding agents and nitramine fillers were calculate...The surface and interfacial properties of polymeric bonding agents and nitramine crystal fillers were studied. The surface free energy and adhesion work of polymeric bonding agents and nitramine fillers were calculated by using Kaeble′s equations. It was observed that the hydroxyl values of neutral polymeric bonding agents (NPBA) correlate well with the polar components of surface free energies. On the basis of the measurements of swelling ratio and initial modulus, the interfacial bonding through highly crosslinked polymeric shell formation around the nitramine particles and generating interfacial reinforcement were rationalized. The application of Tapping Mode AFM (atomic force micro scope) to observing the surface morphology of NPBA reveals that methyl acrylate monomer appears to play a role for aiding the formation of network like structure when nanometer scale images of NPBA are created.展开更多
High-speed milling of titanium alloys is widely used in aviation and aerospace industries for its high efficiency and good quality.In order to optimize the machining parameters in high-speed milling TB6 titanium alloy...High-speed milling of titanium alloys is widely used in aviation and aerospace industries for its high efficiency and good quality.In order to optimize the machining parameters in high-speed milling TB6 titanium alloy,experiments of high-speed milling and fatigue were conducted to investigate the effect of parameters on 3D surface topography and fatigue life.Based on the fatigue fracture,the effect mechanism of surface topography on the fatigue crack initiation was proposed.The experiment results show that when the milling speed ranged from 100 m/min to 140 m/min,and the feed per tooth ranged from 0.02 mm/z to 0.06 mm/z,the obtained surface roughness were within the limit（0.8 μm）.Fatigue life decreased sharply with the increase of surface equivalent stress concentration factor.The average error of fatigue life between the established model and the experimental results was 6.25%.The fatigue cracks nucleated at the intersection edge of machined surface.展开更多
X-ray diffraction was used to measure the unit cell parameters of chalcopyrite crystal.The results showed that the chalcopyrite crystal is perfect,and the arrangement of its atoms is regular.A qualitative analysis of ...X-ray diffraction was used to measure the unit cell parameters of chalcopyrite crystal.The results showed that the chalcopyrite crystal is perfect,and the arrangement of its atoms is regular.A qualitative analysis of molecular mechanics showed that surface relaxation causes the chalcopyrite surface to be sulfur enriched.Atomic force microscope（AFM） was used to obtain both a microscopic three-dimensional topological map of chalcopyrite surface and a two-dimensional topological map of its electron cloud.The AFM results revealed that the horizontal and longitudinal arrangements of atoms on the chalcopyrite surface change dramatically compared with those in the interior of the crystal.Longitudinal shifts occur among the copper,iron and sulfur atoms relative to their original positions,namely,surface relaxation occurs,causing sulfur atoms to appear on the outermost surface.Horizontally,AFM spectrum showed that the interatomic distance is irregular and that a reconstruction occurs on the surface.One result of this reconstruction is that two or more atoms can be positioned sufficiently close so as to form atomic aggregates.The lattice properties of these models were calculated based on DFT theory and compared with the experimental results and those of previous theoretical works.On analyzing the results,the atomic arrangement on the（001） surface of chalcopyrite is observed to become irregular,S atoms move outward along the Z-axis,and the lengths of Cu—S and Fe—S bonds are enlarged after geometry optimization because of the surface relaxation and reconstruction.The sulfur-rich surface and irregular atomic aggregates caused by the surface relaxation and reconstruction greatly influence the bulk flotation properties of chalcopyrite.展开更多
Anisotropic surface broken bond densities of six different surfaces of calcite and three surfaces of fluorite were calculated. In terms of the calculated results, the commonly exposed surfaces of the two minerals were...Anisotropic surface broken bond densities of six different surfaces of calcite and three surfaces of fluorite were calculated. In terms of the calculated results, the commonly exposed surfaces of the two minerals were predicted and the relations between surface broken bonds densities and surface energies were analyzed. Then the anisotropic wettability of the commonly exposed surfaces was studied by means of contact angle measurement. The calculation results show that the （101^-4）, （213^-4）and （01 1^-8）surfaces for calcite and （111） for fluorite are the most commonly exposed surfaces and there is a good rectilinear relation between surface broken bond density and surface energy with correlation of determination （R^2） of 0.9613 and 0.9969, respectively. The anisotropic wettability of different surfaces after immersing in distilled water and sodium oleate solutions at different concentrations can be explained by anisotropic surface broken bond densities and active Ca sites densities, respectively.展开更多
A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting proc...A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting process were first plated with a coarse copper coating layer by electroless plating process.A low-temperature sintering process was then completed at about 800 °C for 1 h under the protection of hydrogen atmosphere.The results show that a novel SMFM with complex surface morphology and high specific surface area（0.2 m2/g） can be obtained in this way.The effect of sintering temperature on the surface morphology and specific surface area of SMFM was studied by means of scanning electron microscopy and Brunauer-Emmett-Teller.The damage of micro-structure during the sintering process mainly contributed to the loss of specific surface area of SMFM and the optimal sintering temperature was 800 °C.展开更多
The effect of concentration of hydrogen peroxide （H2O2） on the surface properties of Ni-Cr alloys was studied. Surface roughness and surface morphology of Ni-Cr alloys were evaluated by surface profiler and scanning...The effect of concentration of hydrogen peroxide （H2O2） on the surface properties of Ni-Cr alloys was studied. Surface roughness and surface morphology of Ni-Cr alloys were evaluated by surface profiler and scanning electron microscopy after being immersed in different concentrations of H2O2 for 112 h. Surface corrosion products of Ni-Cr alloys were analyzed by photoelectron spectrograph after being immersed in 0% and 30% H2O2. The order of increasing surface roughness of Ni-Cr alloys after being immersed in different concentrations of H2O2 was 0〈3.6%〈10%〈30%. As the concentration of hydrogen peroxide increased, the surface roughness of Ni-Cr alloys increased and the surface morphology showed different degrees of corrosion. According to the XPS results, the corrosion products formed on the outmost surface layer of the studied samples are Ni（OH）2 and BeO.展开更多
Sex determination is composed of somatic and germ-line sex differentiation hierarchies whose interaction is poorly understood. A single gene known to control somatic sex determination, the DM-domain containing （Doubl...Sex determination is composed of somatic and germ-line sex differentiation hierarchies whose interaction is poorly understood. A single gene known to control somatic sex determination, the DM-domain containing （Doublesex/Mab-3 DNA-binding motif） gene, is highly conserved across species. Vertebrate DMRT1 （DM-related transcription factor 1） expression occurs predominantly in the testis. Here, however, isolated two distinct DM-domain cDNA from Oreochromis aurea ovary and testis have been named DMRT4 （DM-related transcription factor 4） and DMRT1 by BLAST, respectively. Despite high homology in the DM-domain there is little similarity outside the DM-domain.To better understand the structure, function, and possible roles of DMRT4 and DMRT1 as potential candidates for sex differentiation and sex determination, the intact regions encoding DMRT4 and DMRT1 obtained by PCR were sub-cloned into the vector pMAL-c2x and introduced into the Escherichia coli TB1 cell for efficient fusion expression. After purification and cleavage, DMRT4 and DMRT1 proteins were used to immunize adult rabbits following standard protocols. Consequently, it was found by using Western blot analysis that polyclonal antibodies against DMRT4 and DMRT1 had high specificity. The relative expression levels of DMRT4 and DMRT1 mRNA were determined by fluorescent Real-time RT-PCR in female and male Oreochromis aurea with 13-actin as the internal standard. DMRT1 was expressed only in testis, whereas DMRT4 was over expressed in the ovary, but in both female and male, a slight expression in the brain was also detected. Statistical analysis showed that in the brain, mean DMRT4 mRNA levels in female were significantly higher than in male. Meanwhile, the expression of DMRT4 and DMRT1 protein was also analyzed using the purified antibodies through Western blot and immunohistochemistry. It was found that DMRT4 was exclusively expressed in the ovary and DMRT1 in the testis. Study on DMRT4 and DMRT1 expression facilitated the elucidation of their roles and the understanding of sex differentiation of fish.展开更多
Land use/land cover change (LUCC) mapping and analysis using multi-temporal normalize difference vegetation index (NDVI) data have been well documented. Recent empirical studies have documented that many new methods w...Land use/land cover change (LUCC) mapping and analysis using multi-temporal normalize difference vegetation index (NDVI) data have been well documented. Recent empirical studies have documented that many new methods with high accuracy of retrieved land surface temperature ( Ts) have been developed. Thus, the combination of land surface temperature and NDVI has the greatest potential to improve the surface vegetation dynamic monitoring. In this study, the following objectives are pursued to: (1) introduce the practical method to produce the Ts, NDVI and Ts/NDVI based on remotely sensed data; (2) investigate the different retrieved result of vegetation cover information from NDVI, Ts and Ts/NDVI data sets, and analyze the intra-annual time trajectories of different vegetation cover categories in the NDVI- Ts space for farming-pastoral zone in North China, and (3) quantitative analysis the difference in using NDVI, Ts and Ts/NDVI data sets to express information based on the indices (information entropy and averaged information grads), and evaluate the relative role of Ts/NDVI data set in the discrimination of different vegetation cover categories through comparison to traditional NDVI data set.展开更多
文摘Since the D-band center theory was proposed,it has been widely used in the fields of surface chemistry by almost all researchers,due to its easy understanding,convenient operation and relative accuracy.However,with the continuous development of material systems and modification strategies,researchers have gradually found that D-band center theory is usually effective for large metal particle systems,but for small metal particle systems or semiconductors,such as single atom systems,the opposite conclusion to the D-band center theory is often obtained.To solve the issue above,here we propose a bonding and anti-bonding orbitals stable electron intensity difference(BASED)theory for surface chemistry.The newly-proposed BASED theory can not only successfully explain the abnormal phenomena of D-band center theory,but also exhibits a higher accuracy for prediction of adsorption energy and bond length of intermediates on active sites.Importantly,a new phenomenon of the spin transition state in the adsorption process is observed based on the BASED theory,where the active center atom usually yields an unstable high spin transition state to enhance its adsorption capability in the adsorption process of intermediates when their distance is about 2.5Å.In short,the BASED theory can be considered as a general principle to understand catalytic mechanism of intermediates on surfaces.
文摘Background,aim,and scope Solar radiation is the main source of energy for terrestrial ecosystems.Small changes in the absorption of solar radiation at the ground surface can have a significant impact on the climatic environment.Natural and anthropogenic changes in ground cover are important factors affecting the absorption of solar radiation at the ground surface.This phenomenon is particularly pronounced in the mid and high latitudes.In order to quantify the inf luence of surface cover change on the absorption of solar radiation at the surface and to provide a scientific basis for changes in the climatic environment,this paper analyzed ground cover change,ground absorbed solar radiation change and the effect of ground cover change on ground absorbed solar radiation in the Three Northeastern Provinces of China from 2001 to 2018.Materials and methods In this study,the Three Northeastern Provinces of China were used as the study area.Firstly,satellite remote sensing data were used to obtain land cover data and albedo data for Aug.1st of each year in 2001,2005,2010,2015 and 2018.The albedo data were further used to calculate the absorbed solar radiation data at the ground surface.Next,the land cover data were used to count the area changes and shifts of different land classes over the five-year period.The land cover data were overlaid with the surface absorbed solar radiation data to obtain the mean and standard deviation of radiation absorption for different ground classes.The surface absorbed solar radiation data were subtracted to obtain the changes in surface absorbed solar radiation for 2001-2005,2005-2010,2010-2015 and 2015-2018.Ultimately,we used a combination of shifted changes in ground classes and changes in surface absorbed solar radiation data,with unchanged ground classes as a baseline and data such as slope orientation as an aid.We analyzed the effect of ground cover change on surface absorbed solar radiation at regional and pixel point scales.Results(1)The area of woodland and waters in the Three Northeastern Provinces of China increased and then decreased from 2001 to 2018,with an overall increase of 3.96%and 10.51%respectively.Cropland decreased and then increased,with a total decrease of 1.22%.Grassland continued to decrease,with an overall decrease of 19.36%.Building sites increased all the time,with a total increase of 11.08%.The main types of ground cover shifted were woodland,cropland and grassland.The main factors for the change in ground cover were China’s woodland protection policy and the saturation of the total woodland stock.(2)The five ground types absorb solar radiation in the order of waters>building sites>woodland>grassland>cropland.The surface absorption of solar radiation in the Songnen Plain,the Sanjiang Plain and the Songhua River Basin flowing through the Songnen Plain and the Sanjiang Plain varies significantly,by more than 25 W·m^(-2).(3)Changes in the ground cover type affected the absorption of solar radiation energy by the ground surface.There was a clear trend of interconversion between waters and cropland/grassland,cropland and woodland/grassland.In particular,the conversion of waters to both cropland and grassland radiation absorption values decreased significantly,while the opposite increased.The absolute difference between waters and cropland was a maximum of -156.66 W·m^(-2)in 2010-2015,and between waters and grassland was a maximum of 102.36 W·m^(-2) in 2005-2010.The radiative absorption values of woodland and grassland reclamation declined and conversely increased.The absolute difference between woodland and cropland was a maximum of-13.94 W·m^(-2) in 2010-2015 when woodland converted to cropland,and between grassland and cropland was a maximum of 22.36 W·m^(-2) in 2001-2005 when cropland converted to grassland,respectively.Discussion Ground cover changes in the Three Northeastern Provinces of China from 2001-2018 were inextricably linked to natural factors and the inf luence of Chinese national policies.The main inf luencing factors were China’s woodland protection policy,restoration of woodland fire sites,saturation of total woodland,optimization of cropland patterns,sanding of grassland,expansion of water conservancy projects,and urbanization expansion.There were differences in the radiation absorption characteristics of different ground cover types.This was due to the nature of the ground type itself and the regional environment.When ground cover types changed,their ability to absorb solar radiation also changed.The degree of change could be inf luenced by different ground types and different environmental factors.Different spatial scales can also produce variability.We need to consider the effects of ground cover change on the absorption of solar radiation at the surface in an integrated and comprehensive way.Conclusions The Three Northeastern Provinces of China had frequent changes in ground cover from 2001-2018,with the area of grassland decreased by almost 20%.These changes were due to natural environmental change and policies issued by China since the 21st century.The extent to which solar radiation was absorbed by different ground cover types was different,with grassland being the strongest and cropland the least.In the past few years,the Songnen Plain and Sanjiang Plain regions were the most significant changes in the absorption of solar radiation by the ground cover.The change in ground cover type led to a change in solar radiation absorption at the ground surface,with the conversion of waters to cropland or grassland and the conversion of cropland to woodland or grassland showing the greatest change in radiation absorption values,and vice versa.Of these,the absolute difference in the conversion of waters to cropland amounts to-156.66 W·m^(-2) in 2010-2015.The variation in the absorption of solar radiation at the ground surface was related to the characteristics of the ground class itself,but was also limited by the regional environment.Recommendations and perspectives This study showed that surface cover change can affect the absorption of solar radiation at the surface to varying degrees.The unchanged land classes were used as a comparative analysis in this paper,and it was clear from the paper that some of the unchanged land classes showed significant changes in radiation absorption that should be of interest in future studies.
基金Supported by Forestry Science and Technology Program of Hunan Province(XLK201406)~~
文摘Under the condition of high temperature, the effects of five cover patterns （clean tillage, film mulching, weed covering, branches and leaves covering and growing grass covering） on soil properties in young Phoebe boumei forest were in- vestigated. The results showed that the five cover patterns all showed significant ef- fects on soil properties in young Phoebe bournei forest under the condition of high temperature. Land cover increased land temperature in Phoebe boumei forest. Un- der the film mulching, the land temperature was increased most rapidly with the largest increment. However, weed covering, branches and leaves covering and growing grass covering decreased land temperature. Among them, growing grass covering showed the best cooling effect. The film mulching, weed covering, branch- es and leaves covering and growing grass covering all increased land humidity. The film mulching showed the best moisture-preserving effect in the early period, but in the late period, the humidity in the film mulching treatment group was lower than that in the clean tillage treatment group. Among the five mulching patterns, moisture loss in the film mulching treatment group was slowest and least, followed by those in the weed covering and branches and leaves covering treatment groups, and moisture loss in the growing grass covering treatment group was fastest and most.
基金Supported by the National Natural Science Foundation of China(50975141)the National Scienceand Technology Major Project(2010ZX04012-042)the Aeronautical Science Foundation(2010352005)~~
文摘Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool wear status. Results show that good surface integrity of TC21 can be obtained in high speed milling. In addition, even in acutely worn stages, there is no so-called serious hardening layer （or white layer） according to the studies on microhardness and metallurgical structure.
文摘The surface and interfacial properties of polymeric bonding agents and nitramine crystal fillers were studied. The surface free energy and adhesion work of polymeric bonding agents and nitramine fillers were calculated by using Kaeble′s equations. It was observed that the hydroxyl values of neutral polymeric bonding agents (NPBA) correlate well with the polar components of surface free energies. On the basis of the measurements of swelling ratio and initial modulus, the interfacial bonding through highly crosslinked polymeric shell formation around the nitramine particles and generating interfacial reinforcement were rationalized. The application of Tapping Mode AFM (atomic force micro scope) to observing the surface morphology of NPBA reveals that methyl acrylate monomer appears to play a role for aiding the formation of network like structure when nanometer scale images of NPBA are created.
基金Projects(50975237,51005184) supported by the National Natural Science Foundation of China
文摘High-speed milling of titanium alloys is widely used in aviation and aerospace industries for its high efficiency and good quality.In order to optimize the machining parameters in high-speed milling TB6 titanium alloy,experiments of high-speed milling and fatigue were conducted to investigate the effect of parameters on 3D surface topography and fatigue life.Based on the fatigue fracture,the effect mechanism of surface topography on the fatigue crack initiation was proposed.The experiment results show that when the milling speed ranged from 100 m/min to 140 m/min,and the feed per tooth ranged from 0.02 mm/z to 0.06 mm/z,the obtained surface roughness were within the limit（0.8 μm）.Fatigue life decreased sharply with the increase of surface equivalent stress concentration factor.The average error of fatigue life between the established model and the experimental results was 6.25%.The fatigue cracks nucleated at the intersection edge of machined surface.
基金Project(u0837602) supported by the Key Program of the National Natural Science Foundation of ChinaProject(2010J056) supported by the Natural Science Foundation of Education Department of Yunnan Province,China+1 种基金Projects(2009113,2011464) supported by the Analysis and Testing Foundation of Kunming University of Science and TechnologyProject(41118011) supported by the Excellent Doctoral Dissertation to Cultivate Foundation of Kunming University of Science and Technology
文摘X-ray diffraction was used to measure the unit cell parameters of chalcopyrite crystal.The results showed that the chalcopyrite crystal is perfect,and the arrangement of its atoms is regular.A qualitative analysis of molecular mechanics showed that surface relaxation causes the chalcopyrite surface to be sulfur enriched.Atomic force microscope（AFM） was used to obtain both a microscopic three-dimensional topological map of chalcopyrite surface and a two-dimensional topological map of its electron cloud.The AFM results revealed that the horizontal and longitudinal arrangements of atoms on the chalcopyrite surface change dramatically compared with those in the interior of the crystal.Longitudinal shifts occur among the copper,iron and sulfur atoms relative to their original positions,namely,surface relaxation occurs,causing sulfur atoms to appear on the outermost surface.Horizontally,AFM spectrum showed that the interatomic distance is irregular and that a reconstruction occurs on the surface.One result of this reconstruction is that two or more atoms can be positioned sufficiently close so as to form atomic aggregates.The lattice properties of these models were calculated based on DFT theory and compared with the experimental results and those of previous theoretical works.On analyzing the results,the atomic arrangement on the（001） surface of chalcopyrite is observed to become irregular,S atoms move outward along the Z-axis,and the lengths of Cu—S and Fe—S bonds are enlarged after geometry optimization because of the surface relaxation and reconstruction.The sulfur-rich surface and irregular atomic aggregates caused by the surface relaxation and reconstruction greatly influence the bulk flotation properties of chalcopyrite.
基金Project (50834006) supported by the National Natural Science Foundation of ChinaProject (CX2011B122) supported by Hunan Provincial Innovation Foundation for PostgraduateProject (2011ybjz045) supported by Graduate Degree Thesis Innovation Foundation of Central South University
文摘Anisotropic surface broken bond densities of six different surfaces of calcite and three surfaces of fluorite were calculated. In terms of the calculated results, the commonly exposed surfaces of the two minerals were predicted and the relations between surface broken bonds densities and surface energies were analyzed. Then the anisotropic wettability of the commonly exposed surfaces was studied by means of contact angle measurement. The calculation results show that the （101^-4）, （213^-4）and （01 1^-8）surfaces for calcite and （111） for fluorite are the most commonly exposed surfaces and there is a good rectilinear relation between surface broken bond density and surface energy with correlation of determination （R^2） of 0.9613 and 0.9969, respectively. The anisotropic wettability of different surfaces after immersing in distilled water and sodium oleate solutions at different concentrations can be explained by anisotropic surface broken bond densities and active Ca sites densities, respectively.
基金Project (50930005) supported by the National Natural Science Foundation of ChinaProject (U0834002) supported by the Key Programof NSFC-Guangdong Joint Funds of China+1 种基金Project (LYM09024) supported by Training Program for Excellent Young Teachers withInnovation of Guangdong University, ChinaProject (2009ZM0121) supported by the Fundamental Research Funds for the CentralUniversities of South China University of Technology,China
文摘A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting process were first plated with a coarse copper coating layer by electroless plating process.A low-temperature sintering process was then completed at about 800 °C for 1 h under the protection of hydrogen atmosphere.The results show that a novel SMFM with complex surface morphology and high specific surface area（0.2 m2/g） can be obtained in this way.The effect of sintering temperature on the surface morphology and specific surface area of SMFM was studied by means of scanning electron microscopy and Brunauer-Emmett-Teller.The damage of micro-structure during the sintering process mainly contributed to the loss of specific surface area of SMFM and the optimal sintering temperature was 800 °C.
基金Projects(13ZR1427700,13ZR1427900)supported by the Natural Science Foundation of Shanghai,ChinaProject(51304136)supported by the National Natural Science Foundation of ChinaProjects(Slgl4049,Slgl4050)supported by the Shanghai Education Development Foundation"Selection and Training the Excellent Young College Teacher"Project,China
文摘The effect of concentration of hydrogen peroxide （H2O2） on the surface properties of Ni-Cr alloys was studied. Surface roughness and surface morphology of Ni-Cr alloys were evaluated by surface profiler and scanning electron microscopy after being immersed in different concentrations of H2O2 for 112 h. Surface corrosion products of Ni-Cr alloys were analyzed by photoelectron spectrograph after being immersed in 0% and 30% H2O2. The order of increasing surface roughness of Ni-Cr alloys after being immersed in different concentrations of H2O2 was 0〈3.6%〈10%〈30%. As the concentration of hydrogen peroxide increased, the surface roughness of Ni-Cr alloys increased and the surface morphology showed different degrees of corrosion. According to the XPS results, the corrosion products formed on the outmost surface layer of the studied samples are Ni（OH）2 and BeO.
基金This work was supported by the National Basic Research Program of China(No.2004CB117401)Chinese National Programsfor High Technology Research and Development(No.2004AA243060).
文摘Sex determination is composed of somatic and germ-line sex differentiation hierarchies whose interaction is poorly understood. A single gene known to control somatic sex determination, the DM-domain containing （Doublesex/Mab-3 DNA-binding motif） gene, is highly conserved across species. Vertebrate DMRT1 （DM-related transcription factor 1） expression occurs predominantly in the testis. Here, however, isolated two distinct DM-domain cDNA from Oreochromis aurea ovary and testis have been named DMRT4 （DM-related transcription factor 4） and DMRT1 by BLAST, respectively. Despite high homology in the DM-domain there is little similarity outside the DM-domain.To better understand the structure, function, and possible roles of DMRT4 and DMRT1 as potential candidates for sex differentiation and sex determination, the intact regions encoding DMRT4 and DMRT1 obtained by PCR were sub-cloned into the vector pMAL-c2x and introduced into the Escherichia coli TB1 cell for efficient fusion expression. After purification and cleavage, DMRT4 and DMRT1 proteins were used to immunize adult rabbits following standard protocols. Consequently, it was found by using Western blot analysis that polyclonal antibodies against DMRT4 and DMRT1 had high specificity. The relative expression levels of DMRT4 and DMRT1 mRNA were determined by fluorescent Real-time RT-PCR in female and male Oreochromis aurea with 13-actin as the internal standard. DMRT1 was expressed only in testis, whereas DMRT4 was over expressed in the ovary, but in both female and male, a slight expression in the brain was also detected. Statistical analysis showed that in the brain, mean DMRT4 mRNA levels in female were significantly higher than in male. Meanwhile, the expression of DMRT4 and DMRT1 protein was also analyzed using the purified antibodies through Western blot and immunohistochemistry. It was found that DMRT4 was exclusively expressed in the ovary and DMRT1 in the testis. Study on DMRT4 and DMRT1 expression facilitated the elucidation of their roles and the understanding of sex differentiation of fish.
文摘Land use/land cover change (LUCC) mapping and analysis using multi-temporal normalize difference vegetation index (NDVI) data have been well documented. Recent empirical studies have documented that many new methods with high accuracy of retrieved land surface temperature ( Ts) have been developed. Thus, the combination of land surface temperature and NDVI has the greatest potential to improve the surface vegetation dynamic monitoring. In this study, the following objectives are pursued to: (1) introduce the practical method to produce the Ts, NDVI and Ts/NDVI based on remotely sensed data; (2) investigate the different retrieved result of vegetation cover information from NDVI, Ts and Ts/NDVI data sets, and analyze the intra-annual time trajectories of different vegetation cover categories in the NDVI- Ts space for farming-pastoral zone in North China, and (3) quantitative analysis the difference in using NDVI, Ts and Ts/NDVI data sets to express information based on the indices (information entropy and averaged information grads), and evaluate the relative role of Ts/NDVI data set in the discrimination of different vegetation cover categories through comparison to traditional NDVI data set.
