The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasi...The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasive wheel was developed for grinding steel bonded carbide GT35. Factors affecting ELID grinding performance were analyzed by an atomic force microscope (AFM). Based on the analysis of AFM topography of the fine ground mirror surface of the steel bonded carbide, a schematic diagram of the mechanism of micro-removal of the ground surface was described. The AFM topography also shows that the hard brittle carbide particles, on the surface of steel bonded carbide, were machined out by ductile cutting. Since the grinding cracks in the ground surface are due to temperature gradient, temperature distribution in the grinding area was analyzed by finite element method (FEM). Experimental results indicate that a good mirror surface with Ra<0.02pm can be obtained by the developed ELID grinding system.展开更多
Electrosorption of oxygen and CO on Ru(0001) surface were investigated by ex-situ electron diffraction (LEED/RHEED), AES and electrochemical data. The Ru(0001) surface exhibited a strongly affinity for oxygen which g...Electrosorption of oxygen and CO on Ru(0001) surface were investigated by ex-situ electron diffraction (LEED/RHEED), AES and electrochemical data. The Ru(0001) surface exhibited a strongly affinity for oxygen which gave preference to form a (22)-O phase. However, anodization of Ru(0001) electrode produced a (11)-O phase. A coadsorption structure (2CO+O)(22) / Ru(0001) was performed from electrosorption of CO on Ru(0001) surface in electrolyte solution.展开更多
Combined with recent historical climate data and two periods of land use datasets from remote sensing data, we test the net primary productivity (NPP) data sets in North Chinamodelled by the satellite data-driven Glob...Combined with recent historical climate data and two periods of land use datasets from remote sensing data, we test the net primary productivity (NPP) data sets in North Chinamodelled by the satellite data-driven Global Production Efficiency Model (GLO-PEM) for detecting thewidespread spatial and temporal characteristics of the impacts of climate and land use change onthe regional NPP. Our results show that over the past 20 years, the mean annual temperature in thestudy region has remarkably increased by more than 0.064 ℃, but over the same period, there hasbeen a 1.49 mm decrease in annual precipitation and decrease in NPP by an annual rate of 6.9 TgC.The NPP changes in the study region were greatly affected by the average temperature andprecipitation by ten-day periods as well as the seasonal temperature and precipitation in the studyregion. The correlation between seasonal NPP and seasonal precipitation and temperature is highlyconsistent with land cover spatially, and the correlation coefficient changes with the changes ofvegetation types. The analysis reveals that the related areas in land use change only take up 5.45%of the whole studied region, so the climate changes dominate the impacts on the NPP in the wholestudy region (90% of the total). However, land use plays an absolute dominative role in areas withland cover changes, accounting for 97% of the total. From 1981 to 2000, the NPP in the whole studyregion remarkably reduced due to obvious precipitation decrease and temperature rise. Between twoperiods of land use (about 10 years), the changes in climate are predicted to promote a decrease inNPP by 78 ( + -0.6) TgC, and integrated impacts of climate changes and land use to promote adecrease in NPP by 87(+-0.8) TgC.展开更多
Dipyrido [3, 2-a:2,3-c] phenazine moiety has been introduced as neutral ligand in europium complex. Therefore, a new europium complex with saturated emission, strong fluorescent intensity and good solubility was desi...Dipyrido [3, 2-a:2,3-c] phenazine moiety has been introduced as neutral ligand in europium complex. Therefore, a new europium complex with saturated emission, strong fluorescent intensity and good solubility was designed and synthesized for the first time. Its photoluminescence and UV properties were examined. The experimental results showed that this new Eu-complex could be used as red electroluminescent materials.展开更多
Ashort amateur2 video of two kids smoking on a train was uploaded3 to one of China’s YouTube-like video sharing web sites4 Tuesday, quickly igniting an outcry5 and a lively discussion about China’s smoking problem ...Ashort amateur2 video of two kids smoking on a train was uploaded3 to one of China’s YouTube-like video sharing web sites4 Tuesday, quickly igniting an outcry5 and a lively discussion about China’s smoking problem — which seems almost impossible to tackle6. In the minute-long video, two young boys — probably three or four years old — are seen puffing7 and giggling while standing in the space connecting two cars on a moving train （Such connections are usually a default8 smoking section on Chinese trains, although the doors connecting the cars are normally open）.展开更多
A new ionic conductor La2-xNdxMo2O9 (x=0.0-2.0) has been synthesized by wet- chemistry method. The precursors and the resultant oxide powders were characterized by DTA/TG, DSC, XRD and XPS techniques. Effect of subs...A new ionic conductor La2-xNdxMo2O9 (x=0.0-2.0) has been synthesized by wet- chemistry method. The precursors and the resultant oxide powders were characterized by DTA/TG, DSC, XRD and XPS techniques. Effect of substituting Nd for La reveals that the phase transition which occurs in La2Mo2O9 around 565℃ disappears when x>0.2. And the maximum amount of Nd stabilized the high temperature phase of βLa2Mo2O9 from cubic to tetragonal is about x =1.6. The measurements of impedance spectroscopy indicate that the ionic conductivity becomes considerably higher in comparison to that of La2Mo2O9.展开更多
Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinf...Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinforcement properties, this paper describes some new phenomenon of the helical and twisted reinforcement in concrete and other matrix by experimental studies, and then discusses on mechanism of helical effect of strengthening. This paper also discusses the mechanism of accessional helical effect of strengthening and its significance in industrial practice. Extensive tests indicate that twisting is the most effective way to improve reinforcement mechanical properties. The main results are： （1） They can greatly enhance bond anchorage in base material. In some pull-out tests, the pull-out resistance increases with reinforcement slip within the specimens, which results not only in a higher pull-out load but also a larger slip up to 70%-80% of reinforcement embedded length. （2） Concrete reinforced by twisted bars demonstrates certain ductility at failure. （3） The bond strength depends on the pitch space directly. （4） The twisted effect on material strengthening is from a three-dimensional interlocking force which is formed from material untwisting when they were pulled out from base specimens.展开更多
An easy preparation of controlled alumina nanoparticles by the solution precipitate method has been carried out using dendrimer as surfactant. The effects of the amount and size of surfactant on morphological control...An easy preparation of controlled alumina nanoparticles by the solution precipitate method has been carried out using dendrimer as surfactant. The effects of the amount and size of surfactant on morphological control of powder have also been discussed.展开更多
Within a wireless opportunistic network,one of the lucky users gets an opportunity to utilize thewhole radio resource.However some of the unlucky users keep silent during an unexpected period result-ing from severe wi...Within a wireless opportunistic network,one of the lucky users gets an opportunity to utilize thewhole radio resource.However some of the unlucky users keep silent during an unexpected period result-ing from severe wireless environment and imperfect scheduling algorithms .An opportunistic cooperationprotocol is proposed that can achieve equivalent performance measured in terms of outage probability,inwhich scheme the opportunistic user helps to relay what need retransmitting indicated by the destinationand selects the appropriate power allocation to pursue fairness.The proposed scheme deploys superposi-tion coding and successive interference cancellation at relay and destination,respectively .To improve thespectral efficiency,the modified cooperation architecture involves two opportunistic users which work inturn.The simulation results demonstrate that the protocol obtains better performance compared with theconventional methods.展开更多
A support vector machine （SVM） based multiuser detection （MUD） scheme in code-division multi- ple-access （CDMA） system is proposed. In this scheme, the equivalent support vector （SV） is obtained through a kern...A support vector machine （SVM） based multiuser detection （MUD） scheme in code-division multi- ple-access （CDMA） system is proposed. In this scheme, the equivalent support vector （SV） is obtained through a kernel sparsity approximation algorithm, which avoids the conventional costly quadratic pro-gramming （QP） procedure in SVM. Besides, the coefficient of the SV is attained through the solution to a generalized eigenproblem. Simulation results show that the proposed scheme has almost the same bit er-ror rate （BER） as the standard SVM and is better than minimum mean square error （MMSE） scheme. Meanwhile, it has a low comoutation complexity.展开更多
This paper presents a new inductive learning algorithm, HGR (Version 2.0), based on the newly-developed extension matrix theory. The basic idea is to partition the positive examples of a specific class in a given exam...This paper presents a new inductive learning algorithm, HGR (Version 2.0), based on the newly-developed extension matrix theory. The basic idea is to partition the positive examples of a specific class in a given example set into consistent groups, and each group corresponds to a consistent rule which covers all the examples in this group and none of the negative examples. Then a performance comparison of the HGR algorithm with other inductive algorithms, such as C4.5, OC1, HCV and SVM, is given in the paper. The authors not only selected 15 databases from the famous UCI machine learning repository, but also considered a real world problem. Experimental results show that their method achieves higher accuracy and fewer rules as compared with other algorithms.展开更多
We study several quintessence models which are exotic at Q = 0, and use a simple constraint Q H/2π to check when they enter the tracking regime, disregarding the details of inflation. We find that it can also give st...We study several quintessence models which are exotic at Q = 0, and use a simple constraint Q H/2π to check when they enter the tracking regime, disregarding the details of inflation. We find that it can also give strong constraints for V = VoQ-α, which has to enter the tracking regime after Inz - 10, while for the supergravity model V = V0Q-αexp(kQ2/2), the constraint is much weaker. For the exponential form of inverse power-law potential V = V0exp(λ/Q), it exhibits no constraints.展开更多
We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range -4.0 <[Fe/H]< 0.5. Based on the observed data of Ba and Eu, we evaluated the...We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range -4.0 <[Fe/H]< 0.5. Based on the observed data of Ba and Eu, we evaluated the least-squares regressions of [Ba/Fe] on [Fe/H], and [Eu/H] on [Ba/H]. Assuming that the heavy elements (heavier than Ba) are produced by a combination of the main components of s- and r-processes in metal-poor stars, and choosing Ba and Eu as respective representative elements of the main s- and the main r-processes, a statistical model for predicting the Galactic chemical evolution of the heavy elements is presented. With this model, we calculate the mean abundance trends of the heavy elements La, Ce, Pr, Nd, Sm, and Dy with the metallicity. We compare our results with the observed data at various metallicities, showing that the predicted trends are in good agreement with the observed trends, at least for the metallicity range [Fe/H]≥ -2.5. Finally, we discuss our results and deduce some important information about the Galactic chemical evolution.展开更多
文摘The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasive wheel was developed for grinding steel bonded carbide GT35. Factors affecting ELID grinding performance were analyzed by an atomic force microscope (AFM). Based on the analysis of AFM topography of the fine ground mirror surface of the steel bonded carbide, a schematic diagram of the mechanism of micro-removal of the ground surface was described. The AFM topography also shows that the hard brittle carbide particles, on the surface of steel bonded carbide, were machined out by ductile cutting. Since the grinding cracks in the ground surface are due to temperature gradient, temperature distribution in the grinding area was analyzed by finite element method (FEM). Experimental results indicate that a good mirror surface with Ra<0.02pm can be obtained by the developed ELID grinding system.
基金W.B.Wang is grateful for a fellowship from the Max-Planck-Gesellschaft(MPG). We also thank Prof. G. Ertl for helpful suggestions and discussions.
文摘Electrosorption of oxygen and CO on Ru(0001) surface were investigated by ex-situ electron diffraction (LEED/RHEED), AES and electrochemical data. The Ru(0001) surface exhibited a strongly affinity for oxygen which gave preference to form a (22)-O phase. However, anodization of Ru(0001) electrode produced a (11)-O phase. A coadsorption structure (2CO+O)(22) / Ru(0001) was performed from electrosorption of CO on Ru(0001) surface in electrolyte solution.
基金National 973 Project No.2002CB412507+5 种基金 National Natural Science Foundation of China No.90202002 Knowledge Innovation Project of IGSNRR CAS No.CXIOG-E01-02-04 One Hundred Talents Program of CAS.
文摘Combined with recent historical climate data and two periods of land use datasets from remote sensing data, we test the net primary productivity (NPP) data sets in North Chinamodelled by the satellite data-driven Global Production Efficiency Model (GLO-PEM) for detecting thewidespread spatial and temporal characteristics of the impacts of climate and land use change onthe regional NPP. Our results show that over the past 20 years, the mean annual temperature in thestudy region has remarkably increased by more than 0.064 ℃, but over the same period, there hasbeen a 1.49 mm decrease in annual precipitation and decrease in NPP by an annual rate of 6.9 TgC.The NPP changes in the study region were greatly affected by the average temperature andprecipitation by ten-day periods as well as the seasonal temperature and precipitation in the studyregion. The correlation between seasonal NPP and seasonal precipitation and temperature is highlyconsistent with land cover spatially, and the correlation coefficient changes with the changes ofvegetation types. The analysis reveals that the related areas in land use change only take up 5.45%of the whole studied region, so the climate changes dominate the impacts on the NPP in the wholestudy region (90% of the total). However, land use plays an absolute dominative role in areas withland cover changes, accounting for 97% of the total. From 1981 to 2000, the NPP in the whole studyregion remarkably reduced due to obvious precipitation decrease and temperature rise. Between twoperiods of land use (about 10 years), the changes in climate are predicted to promote a decrease inNPP by 78 ( + -0.6) TgC, and integrated impacts of climate changes and land use to promote adecrease in NPP by 87(+-0.8) TgC.
基金This work was supported by the National Natural Science Foundation of China (No29992530-6) and Provincial Natural Science Foundation of Hunan (00JJY2043).
文摘Dipyrido [3, 2-a:2,3-c] phenazine moiety has been introduced as neutral ligand in europium complex. Therefore, a new europium complex with saturated emission, strong fluorescent intensity and good solubility was designed and synthesized for the first time. Its photoluminescence and UV properties were examined. The experimental results showed that this new Eu-complex could be used as red electroluminescent materials.
文摘Ashort amateur2 video of two kids smoking on a train was uploaded3 to one of China’s YouTube-like video sharing web sites4 Tuesday, quickly igniting an outcry5 and a lively discussion about China’s smoking problem — which seems almost impossible to tackle6. In the minute-long video, two young boys — probably three or four years old — are seen puffing7 and giggling while standing in the space connecting two cars on a moving train （Such connections are usually a default8 smoking section on Chinese trains, although the doors connecting the cars are normally open）.
基金supported by the State Key Program of Basic Research (G1998061311) and the National Natural Science Foundation of China (29831010).
文摘A new ionic conductor La2-xNdxMo2O9 (x=0.0-2.0) has been synthesized by wet- chemistry method. The precursors and the resultant oxide powders were characterized by DTA/TG, DSC, XRD and XPS techniques. Effect of substituting Nd for La reveals that the phase transition which occurs in La2Mo2O9 around 565℃ disappears when x>0.2. And the maximum amount of Nd stabilized the high temperature phase of βLa2Mo2O9 from cubic to tetragonal is about x =1.6. The measurements of impedance spectroscopy indicate that the ionic conductivity becomes considerably higher in comparison to that of La2Mo2O9.
基金the National Natural Science Foundation of China(No.50578119)
文摘Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinforcement properties, this paper describes some new phenomenon of the helical and twisted reinforcement in concrete and other matrix by experimental studies, and then discusses on mechanism of helical effect of strengthening. This paper also discusses the mechanism of accessional helical effect of strengthening and its significance in industrial practice. Extensive tests indicate that twisting is the most effective way to improve reinforcement mechanical properties. The main results are： （1） They can greatly enhance bond anchorage in base material. In some pull-out tests, the pull-out resistance increases with reinforcement slip within the specimens, which results not only in a higher pull-out load but also a larger slip up to 70%-80% of reinforcement embedded length. （2） Concrete reinforced by twisted bars demonstrates certain ductility at failure. （3） The bond strength depends on the pitch space directly. （4） The twisted effect on material strengthening is from a three-dimensional interlocking force which is formed from material untwisting when they were pulled out from base specimens.
基金This work was partially supported by a Grant in Aid (for returned student) for Science Research from the Ministry of Education of China ( 2000 ) and by the Research Fund for the Doctoral Program of Higher Education of China (No. 20010141004).
文摘An easy preparation of controlled alumina nanoparticles by the solution precipitate method has been carried out using dendrimer as surfactant. The effects of the amount and size of surfactant on morphological control of powder have also been discussed.
基金supported by the National Nature Science Foundation of China(No.60674009)the High Technology Research and Development Programme of China(No.2006AA01Z270)
文摘Within a wireless opportunistic network,one of the lucky users gets an opportunity to utilize thewhole radio resource.However some of the unlucky users keep silent during an unexpected period result-ing from severe wireless environment and imperfect scheduling algorithms .An opportunistic cooperationprotocol is proposed that can achieve equivalent performance measured in terms of outage probability,inwhich scheme the opportunistic user helps to relay what need retransmitting indicated by the destinationand selects the appropriate power allocation to pursue fairness.The proposed scheme deploys superposi-tion coding and successive interference cancellation at relay and destination,respectively .To improve thespectral efficiency,the modified cooperation architecture involves two opportunistic users which work inturn.The simulation results demonstrate that the protocol obtains better performance compared with theconventional methods.
文摘A support vector machine （SVM） based multiuser detection （MUD） scheme in code-division multi- ple-access （CDMA） system is proposed. In this scheme, the equivalent support vector （SV） is obtained through a kernel sparsity approximation algorithm, which avoids the conventional costly quadratic pro-gramming （QP） procedure in SVM. Besides, the coefficient of the SV is attained through the solution to a generalized eigenproblem. Simulation results show that the proposed scheme has almost the same bit er-ror rate （BER） as the standard SVM and is better than minimum mean square error （MMSE） scheme. Meanwhile, it has a low comoutation complexity.
文摘This paper presents a new inductive learning algorithm, HGR (Version 2.0), based on the newly-developed extension matrix theory. The basic idea is to partition the positive examples of a specific class in a given example set into consistent groups, and each group corresponds to a consistent rule which covers all the examples in this group and none of the negative examples. Then a performance comparison of the HGR algorithm with other inductive algorithms, such as C4.5, OC1, HCV and SVM, is given in the paper. The authors not only selected 15 databases from the famous UCI machine learning repository, but also considered a real world problem. Experimental results show that their method achieves higher accuracy and fewer rules as compared with other algorithms.
基金Supported by the National Natural Science Foundation of China.
文摘We study several quintessence models which are exotic at Q = 0, and use a simple constraint Q H/2π to check when they enter the tracking regime, disregarding the details of inflation. We find that it can also give strong constraints for V = VoQ-α, which has to enter the tracking regime after Inz - 10, while for the supergravity model V = V0Q-αexp(kQ2/2), the constraint is much weaker. For the exponential form of inverse power-law potential V = V0exp(λ/Q), it exhibits no constraints.
基金This research has been supported by the National Natural Science Foundation of China through grant No.19973002 Chinese Academy of Sciences-Peking University Joint Beijing Astrophysical Center.
文摘We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range -4.0 <[Fe/H]< 0.5. Based on the observed data of Ba and Eu, we evaluated the least-squares regressions of [Ba/Fe] on [Fe/H], and [Eu/H] on [Ba/H]. Assuming that the heavy elements (heavier than Ba) are produced by a combination of the main components of s- and r-processes in metal-poor stars, and choosing Ba and Eu as respective representative elements of the main s- and the main r-processes, a statistical model for predicting the Galactic chemical evolution of the heavy elements is presented. With this model, we calculate the mean abundance trends of the heavy elements La, Ce, Pr, Nd, Sm, and Dy with the metallicity. We compare our results with the observed data at various metallicities, showing that the predicted trends are in good agreement with the observed trends, at least for the metallicity range [Fe/H]≥ -2.5. Finally, we discuss our results and deduce some important information about the Galactic chemical evolution.
