Al-5Ti-0.5C-8Sr (mass fraction,%) master alloy was prepared using a melt reaction method.The microstructure and synthetic process of the master alloy were investigated by optical microscopy,X-ray diffraction,scanning ...Al-5Ti-0.5C-8Sr (mass fraction,%) master alloy was prepared using a melt reaction method.The microstructure and synthetic process of the master alloy were investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and X-ray energy-dispersive spectrum.The results show that the master alloy is composed of α(Al),TiAl3,TiC,Al4Sr and Al-Ti-Sr phases.The synthesis mechanisms of the master alloy are as follows:TiAl3 is formed through the reaction between K2TiF6 and Al melt at 850 ℃;when the melt was heated up to 1 200?1 300 ℃,TiC was formed through the reaction:Ti+C(s)=TiC(s);Al4Sr was formed through the binary uniform reaction when Sr was added into the melt;after the following solidification process in the peritectic reaction:L(Al,Sr)+α(TiAl3)→β(Al-Ti-Sr),the enwrapped structure was formed with the outer layer of Al-Ti-Sr phase and the internal layer of TiAl3 phase.展开更多
Heterovalent Sn2O3 nanosheets were fabricated via an oxidation annealing process and the formation mechanism was investigated. The temperature required to complete the phase transformation from Sn3O4 to Sn2O3was consi...Heterovalent Sn2O3 nanosheets were fabricated via an oxidation annealing process and the formation mechanism was investigated. The temperature required to complete the phase transformation from Sn3O4 to Sn2O3was considered.Two contrasting experiments showed that both oxygen and heating were not necessary conditions for the phase transition.Sn2O3 was formed under an argon protective atmosphere by annealing and could also be obtained at room temperature by exposing Sn3O4 in atmosphere or dispersing in ethanol. The synthesis mechanism was proposed and discussed. This fundamental research is important for the technological applications of intermediate tin oxide materials.展开更多
The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scannin...The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.展开更多
3,4-Bis（4＇-aminofurazano-3＇）furoxan（DATF）, one of a new generation of high energy density materials, shows lots of interesting properties such as lower sensitivity, excellent thermal stability and superior deton...3,4-Bis（4＇-aminofurazano-3＇）furoxan（DATF）, one of a new generation of high energy density materials, shows lots of interesting properties such as lower sensitivity, excellent thermal stability and superior detonation perfor- mance in chemistry and physics. In this paper, on-line infrared（IR） spectroscopy was used to monitor the synthesis process of DATF. The concentration profiles and IR spectra of the components were determined by analyzing the IR data via principal component analysis（PCA）, evolving factor analysis（EFA） and multivariate curve resolution-alternating least squares（MCR-ALS）. The geometric configurations of reactant, intermediates and product were optimized with the density functional theory（DFT） at B3LYP/6-3 l＋G（d, p） level. Their vibrational frequencies and IR spectra were obtained on the basis of vibrational analysis. The result obtained by the chemometric resolution methods agreed well with that obtained by quantum chemical calculation method, which demonstrated the reliability of the proposed chemometric resolution methods. The unstable intermediate 3-amino-4-oxycyanofurazan（AOF） was confirmed via comparing the IR spectra resloved by chemometric resolution methods with those calculated by B3LYP/6-3 l＋G（d,p） and analyzed by MCR-ALS. Finally, the possible synthesis mechanism of DATF was deduced by analyzing the above IR spectra.展开更多
The reaction mechanism of glyoxal （G） with urea （U） under weak acid condition was theoretically investigated at PW91/DNP/COSMO of quantum chemistry using density functional theory （DFT） method. The results show ...The reaction mechanism of glyoxal （G） with urea （U） under weak acid condition was theoretically investigated at PW91/DNP/COSMO of quantum chemistry using density functional theory （DFT） method. The results show that the addition reaction of G with U under the conditions mainly involves the reactions of U with protonated glyoxal （p-G）, protonated 2,2-dihy- droxyacetaldehyde （p-G 1） and protonated bis-hemdiol （p-G2） to form two important carbocation reactive intermediates of C-p-UG and C-p-UG1, and two important hydroxyl compounds of UG and UG1. These compounds play important roles in the formation of UG resin. According to the result of quantum chemical calculation, UG resin was synthesized successfully under weak acid conditions. The UG resin was characterized by matrix assisted laser desorption ionization time of flight mass spectrometry （MALDI-TOF-MS）, ultraviolet and visible spectroscopy （UV-vis）, Fourier transform infrared spectroscopy （FT1R） and nuclear magnetic resonance spectroscopy （13CNMR and 1HNMR）. These instrumental analytical results agree with each other and further confirm the addition reaction pathway of glyoxal with urea proposed by quantum chemical calculation.展开更多
Conventional overconstrained parallel manipulators have been widely studied both in industry and academia,however the structural synthesis of hybrid mechanisms with additional constraints is seldom studied,especially ...Conventional overconstrained parallel manipulators have been widely studied both in industry and academia,however the structural synthesis of hybrid mechanisms with additional constraints is seldom studied,especially for the four degrees of freedom（DOF） hybrid mechanisms.In order to develop a manipulator with additional constraints,a class of important spatial mechanisms with coupling chains（CCs） whose motion type is two rotations and two translations（2R2T） is presented.Based on screw theory,the combination of different types of limbs which are used to construct parallel mechanisms and coupling chains is proposed.The basic types of the general parallel mechanisms and geometric conditions of the kinematic chains are given using constraint synthesis method.Moreover,the 2R2T motion pattern hybrid mechanisms which are derived by adding coupling chains between different serial kinematic chains（SKCs） of the corresponding parallel mechanisms are presented.According to the constraint analysis of the mechanisms,the movement relationship of the moving platform and the kinematic chains is derived by disassembling the coupling chains.At last,fourteen novel hybrid mechanisms with two or three serial kinematic chains are presented.The proposed novel hybrid mechanisms and construction method enrich the family of the spatial mechanisms and provide an instruction to design more complex hybrid mechanisms.展开更多
The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration...The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.展开更多
Through the experiments and the numerical simulation of temperature field in multi-heatsource synthesis Si C furnace, in order to research the feature point in multi-heat-source synthesis furnace, the variation law of...Through the experiments and the numerical simulation of temperature field in multi-heatsource synthesis Si C furnace, in order to research the feature point in multi-heat-source synthesis furnace, the variation law of heat fl ux was studied and the multi-directional energy fl ow diffusion mechanism was revealed. The results show that, due to the shielding action between the heat-source and the superposition effect of thermal fields, the insulating effect is best in multi-heat-source synthesis furnace. The heat emission effect is good outside the common area between heat-sources, but the heat storage is poor. Compared with the synthesis furnace that heat source is parallelly arranged, the furnace of stereoscopic arrangement has a more obvious heat stacking effect and better heat preservation effect, but the air permeability of heat source connecting regions is worse. In the case with the same ingredients, the resistance to thermal diffusion and mass diffusion is higher in heat source connecting regions.展开更多
In order to enhance the effect of comeal grafting, an assisting microsurgical robot has been developed. As one of principal issues for the robotic system design, type and size synthesis of the robotic mechanism is dis...In order to enhance the effect of comeal grafting, an assisting microsurgical robot has been developed. As one of principal issues for the robotic system design, type and size synthesis of the robotic mechanism is discussed. For this purpose, timeline subtask is analyzed with surgical component motion in manual comeal grafting microsurgery, as the reference of robotic mechanism synthesis. On the basis of study on the kinematic correlation between the arm structures and the wrist structures, configuration of joint is determined for the surgical task and motion in type synthesis of the mechanism. The objective for size synthesis of robotic mechanism is optimization of the mechanism dexterity as a manipulation capability. The condition number based on Jacob matrix is chosen as dexterity measure of the mechanism. The prototype is developed.展开更多
A series of boron- and phosphorus-doped silicon wafers are used to prepare a series of doped silicon nanocrystals （nc-Si） by high-energy ball milling with carboxylic acid-terminated surface. The sizes of the nc-Si s...A series of boron- and phosphorus-doped silicon wafers are used to prepare a series of doped silicon nanocrystals （nc-Si） by high-energy ball milling with carboxylic acid-terminated surface. The sizes of the nc-Si samples are demonstrated to be 〈 S nm. The doping levels of the nc-Si are found to be nonlinearly dependent on the original doping level of the wafers by x-ray photoelectron spectroscopy measurement. It is found that the nonlinear doping process will lead to the nonlinear chemical passivation and photoluminescence （I3L） intensity evolution. The doping, chemical passivation and PL mechanisms of the doped nc-Si samples prepared by mechanochemical synthesis are analyzed in detail.展开更多
Perovskite-type oxide nanocrystalline LaCoO3-λ was prepared using the citrate method. The structure and morphology of the sampies were characterized by powder X-ray diffraction （XRD） and transmission electron micro...Perovskite-type oxide nanocrystalline LaCoO3-λ was prepared using the citrate method. The structure and morphology of the sampies were characterized by powder X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The intermediate products were analyzed by thermal gravimetric and differential thermal analysis （TG-DTA） technology. The results showed that nanocrystalline LaCoO3-λ with a granula of 30-50 nm had a cubic perovskite structure. The reaction mechanism of low temperature preparation was suggested as follows： the metal complex was first formed by the combination of metal ion and citric acid; and then it decomposed into an aconitic acid complex, followed by an oxycarbonate, and finally a perovskite-type oxide.展开更多
Submicron copper microcrystal was synthesized by reducing Cu2O with hydrazine hydrate as reducer in aqueous solution,and was characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The sha...Submicron copper microcrystal was synthesized by reducing Cu2O with hydrazine hydrate as reducer in aqueous solution,and was characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The shapes of copper microcrystal depend on additives. Cubic copper particles were observed when the inorganic salt containing Cl^-,such as NH4Cl,NaCl,or KCl,was added into the reaction system. By combined use of NH4Cl and polyvinylpyrrolidone （PVP）,the proportion of cubic copper particle number exceeded 90%,and the particle size is 0.1-0.5μrn. While other inorganic salt without Cl^-,such as Na2SO4 or （NH4）2SO4,had little effect on the shapes of the copper particles. The growth mechanism of metallic copper crystal in aqueous solution was analyzed. It is suggested that the formation of cubic copper crystals is ascribed to the selective adsorption of Cl^-on copper crystal （100） faces.展开更多
It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of ...It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of seedling pickup mechanism with planetary gear train was studied based on the data of given key points and the trajectory of the endpoint of seedling pick-up mechanism.Given the positions and orientations requirements of the five key points,the study first conducted a dimensional synthesis of the linkage size and center of rotation.The next steps were to select a reasonable solution and optimize the data values based on the ideal seedling trajectory.The link motion was driven by the planetary gear train of the two-stage gear.Four pitch curves of noncircular gears were obtained by calculating and distributing the transmission ratio according to the data.For the pitch curve with two convex points,the tooth profile design method of incomplete noncircular gear was applied.The seedling pick-up mechanism was tested by a virtual prototype and a physical prototype designed with the obtained parameter values.The results were consistent with the theoretical design requirements,confirming that the mechanism meets the expected requirements for picking seedlings up.This paper presents a new design method of vegetable pot seedling pick-up mechanism for an automatic vegetable transplanter.展开更多
The production. characteristics. and commercialization of monolithic and composite titanium aluminides are summanzed with emphasis on use in the demanding aerospace industry. The attractive elevated temperature proper...The production. characteristics. and commercialization of monolithic and composite titanium aluminides are summanzed with emphasis on use in the demanding aerospace industry. The attractive elevated temperature properties combined with alow density make these materials of great interest, but inherently low 'forgiveness', and environmental concerns, must be overcome before widespread use will occur One synthesis method for the production of monolithic titanium aluminides-mechanical alloying- will be discussed in detail展开更多
A new iterating method based on homotopy function is developed in this paper. All solutions can be found easily without the need of choosing proper initial values. Compared to the homotopy continuation method, the sol...A new iterating method based on homotopy function is developed in this paper. All solutions can be found easily without the need of choosing proper initial values. Compared to the homotopy continuation method, the solution process of the present method is simplified, and the computation efficiency as well as the reliability for obtaining all solutions is also improved. By application of the method to the mechanisms problems, the results are satisfactory.展开更多
In this study, the winter-summer-winter seasonal variation characteristics of the atmospheric temperature in northern East Asia(NEA) during the past 60 years are analyzed. The results revealed a type of new seasonal v...In this study, the winter-summer-winter seasonal variation characteristics of the atmospheric temperature in northern East Asia(NEA) during the past 60 years are analyzed. The results revealed a type of new seasonal variation mechanism of temperature: winter-winter recurrence(WWR). This study initially discussed the formation mechanism of WWR from the angle of the relationship between the WWR and the atmospheric internal factors and external forcing.The main conclusions are summarized as follows:(1) The winter-summer-winter continuous variation of the AO anomaly index has consistent characteristics with the atmospheric variation of the WWR in the NEA, and their 60-year correlation coefficient reaches 0.43, passing the 95% significance level. It is indicated that the seasonal anomaly of the AO has a certain influence on the WWR;(2) Overall, the PDO maintains a negative phase in the negative WWR years,while it displays the opposite feature in the positive WWR years. The negative(positive) anomaly of PDO is favourable to the occurrence of sustainable low(high) temperatures in the NEA, and may be the important external driving factor for motivating the WWR in the NEA;(3) The binary regression, based on the PDO and AO indexes successfully reproduces the curve of T_(WWR-HG), which is significantly correlated with the WWR index TWWR, and can reproduce the time-height profile of the WWR characteristics from 400 to 1,000 hPa. Therefore, it is concluded that the WWR of the atmospheric temperatures in the NEA is the result of the combined action of the PDO and AO.展开更多
The AB-crosslinked polymers (i.e. ABCP) with polystyrene as chain A and vinyl group blocked prepolymers of polyurethanes (PU) as chain B were synthesized and studied. The results of dynamic mechanical spectrometry (DM...The AB-crosslinked polymers (i.e. ABCP) with polystyrene as chain A and vinyl group blocked prepolymers of polyurethanes (PU) as chain B were synthesized and studied. The results of dynamic mechanical spectrometry (DMS) show that the compatibility between the components A and B can be improved greatly through chemical crosslinking during the formation of ABCPs. This effect is especially pronounced when short chain prepolymers is chosen as one of the components. It is apparent that the degree of crosslinking between the two components plays a major role in determining their compatibility. Copolymerizafion of styrene with maleic anhydride in chain A can improve the compatibility and broaden the damping temperature range. Mechanical properties of the sythesized ABCPs were also studied.展开更多
Revealing the relations among robotic comprehensive performance,configuration,scales and working tasks is the basis to optimize robotic mechanism. Due to the correlation and diversity of the single performance indexes...Revealing the relations among robotic comprehensive performance,configuration,scales and working tasks is the basis to optimize robotic mechanism. Due to the correlation and diversity of the single performance indexes,statistical principles of linear dimension reduction and nonlinear dimension reduction are introduced into comprehensive performance analysis and evaluation for typical serial robot. The robotic mechanism's configuration,scales and task with the best comprehensive performance can be obtained by principal component analysis( PCA) and kernel principal component analysis( KPCA) respectively. The results show that KPCA can reveal the nonlinear relations among different single performance indexes more effectively and provide more comprehensive performance information than PCA. Thus,task-oriented method of serial robot for mechanism analysis and evaluation is proposed,which also provides scientific research basis for the mechanism synthesis and optimum task order.展开更多
In order to solve four-bar straight-line guidance mechanism synthesis problem for the arbitrarily given straight-line’s"angle requirement"and"point-position requirement",a numerical comparison syn...In order to solve four-bar straight-line guidance mechanism synthesis problem for the arbitrarily given straight-line’s"angle requirement"and"point-position requirement",a numerical comparison synthesis method for single and double straight-line guidance mechanism is presented,which is convenient to realize by computer program.The basic idea of this method is:to select a four-bar linkage whose relative bar length of crank is 1 as a basic four-bar linkage.Then the other three relative bars’length is changed,and a lot of basic four-bar linkage can be obtained.There are many single and double ball-points of each basic four-bar linkage.With the motion of a basic four-bar linkage,there is straight-line segment of each Ball-point’s path.The data of these basic four-bar linkages is saved to a database.When designing a four-bar straight-line guidance mechanism,the design data is compared with the data in database and a satisfactory four-bar linkage can be obtained.The method effectively solves the straight-line guidance mechanism synthesis problem.展开更多
In this study,the mechanism of the reduction-diffusion reaction in a Sm-Fe binary system at low temperature was studied to investigate the possibility of synthesis of a Fe-rich TbCu_(7)-type SmFe_(x)(x>9)by the low...In this study,the mechanism of the reduction-diffusion reaction in a Sm-Fe binary system at low temperature was studied to investigate the possibility of synthesis of a Fe-rich TbCu_(7)-type SmFe_(x)(x>9)by the low-temperature diffusion-reduction(LTRD)process using LiCl-KCl eutectic molten salts.Firstly,the Sm-Fe phase transformation depending on the Sm-Fe composition,the LTRD temperature,and time was investigated,and it is found that the obtained metastable phase is only TbCu_(7)-type SmFe_(~8.5),which is not a Fe-rich phase.This Fe content does not change even after an expended LTRD process,and the metastable TbCu_(7)-type SmFe_(~8.5)tends to transform to the stable Sm_(2)Fe_(17)phase.In addition,it is found that the Sm-Fe phase starts to synthesize from the Sm-rich phase in the order of SmFe_(2),SmFe_(3),and SmFe_(8.5)as the LTRD temperature increases(when the time was 10 h)or the LTRD time increases(when the temperature was 550℃).Core-shell-like particles are observed in the case of a short LTRD time,and the core and the shell are Fe and the Sm-rich Sm-Fe phase,respectively,indicating that the Sm-rich phase begins to produce on the surface of the Fe particles.It is difficult to synthesize a Fe-rich TbCu_(7)-type SmFe_(x)(x>9)phase with the Sm-Fe binary system,suggesting that a different approach,such as addition of other elements,will be necessary.展开更多
文摘Al-5Ti-0.5C-8Sr (mass fraction,%) master alloy was prepared using a melt reaction method.The microstructure and synthetic process of the master alloy were investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and X-ray energy-dispersive spectrum.The results show that the master alloy is composed of α(Al),TiAl3,TiC,Al4Sr and Al-Ti-Sr phases.The synthesis mechanisms of the master alloy are as follows:TiAl3 is formed through the reaction between K2TiF6 and Al melt at 850 ℃;when the melt was heated up to 1 200?1 300 ℃,TiC was formed through the reaction:Ti+C(s)=TiC(s);Al4Sr was formed through the binary uniform reaction when Sr was added into the melt;after the following solidification process in the peritectic reaction:L(Al,Sr)+α(TiAl3)→β(Al-Ti-Sr),the enwrapped structure was formed with the outer layer of Al-Ti-Sr phase and the internal layer of TiAl3 phase.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21377063,51102250,21203226,and 21205127)the Personnel Training Foundation of Quzhou University,China(Grant No.BSYJ201412)
文摘Heterovalent Sn2O3 nanosheets were fabricated via an oxidation annealing process and the formation mechanism was investigated. The temperature required to complete the phase transformation from Sn3O4 to Sn2O3was considered.Two contrasting experiments showed that both oxygen and heating were not necessary conditions for the phase transition.Sn2O3 was formed under an argon protective atmosphere by annealing and could also be obtained at room temperature by exposing Sn3O4 in atmosphere or dispersing in ethanol. The synthesis mechanism was proposed and discussed. This fundamental research is important for the technological applications of intermediate tin oxide materials.
基金This work was financially supported by the Natural Science Foundation of Shaanxi Province, China (No.2004E107)
文摘The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.
基金Supported by the National Natural Science Foundation of China（No.21175106） and the Specialized Research Fund for the Doctoral Program of Higher Education, China（No.20126101110019）.
文摘3,4-Bis（4＇-aminofurazano-3＇）furoxan（DATF）, one of a new generation of high energy density materials, shows lots of interesting properties such as lower sensitivity, excellent thermal stability and superior detonation perfor- mance in chemistry and physics. In this paper, on-line infrared（IR） spectroscopy was used to monitor the synthesis process of DATF. The concentration profiles and IR spectra of the components were determined by analyzing the IR data via principal component analysis（PCA）, evolving factor analysis（EFA） and multivariate curve resolution-alternating least squares（MCR-ALS）. The geometric configurations of reactant, intermediates and product were optimized with the density functional theory（DFT） at B3LYP/6-3 l＋G（d, p） level. Their vibrational frequencies and IR spectra were obtained on the basis of vibrational analysis. The result obtained by the chemometric resolution methods agreed well with that obtained by quantum chemical calculation method, which demonstrated the reliability of the proposed chemometric resolution methods. The unstable intermediate 3-amino-4-oxycyanofurazan（AOF） was confirmed via comparing the IR spectra resloved by chemometric resolution methods with those calculated by B3LYP/6-3 l＋G（d,p） and analyzed by MCR-ALS. Finally, the possible synthesis mechanism of DATF was deduced by analyzing the above IR spectra.
基金Supported by the Key Program of the National Natural Science Foundation of China(No.30930074)National Natural Science Foundation of China(No.31260160)
文摘The reaction mechanism of glyoxal （G） with urea （U） under weak acid condition was theoretically investigated at PW91/DNP/COSMO of quantum chemistry using density functional theory （DFT） method. The results show that the addition reaction of G with U under the conditions mainly involves the reactions of U with protonated glyoxal （p-G）, protonated 2,2-dihy- droxyacetaldehyde （p-G 1） and protonated bis-hemdiol （p-G2） to form two important carbocation reactive intermediates of C-p-UG and C-p-UG1, and two important hydroxyl compounds of UG and UG1. These compounds play important roles in the formation of UG resin. According to the result of quantum chemical calculation, UG resin was synthesized successfully under weak acid conditions. The UG resin was characterized by matrix assisted laser desorption ionization time of flight mass spectrometry （MALDI-TOF-MS）, ultraviolet and visible spectroscopy （UV-vis）, Fourier transform infrared spectroscopy （FT1R） and nuclear magnetic resonance spectroscopy （13CNMR and 1HNMR）. These instrumental analytical results agree with each other and further confirm the addition reaction pathway of glyoxal with urea proposed by quantum chemical calculation.
基金Supported by National Natural Science Foundation of China(Grant Nos.51175029,51475035)
文摘Conventional overconstrained parallel manipulators have been widely studied both in industry and academia,however the structural synthesis of hybrid mechanisms with additional constraints is seldom studied,especially for the four degrees of freedom（DOF） hybrid mechanisms.In order to develop a manipulator with additional constraints,a class of important spatial mechanisms with coupling chains（CCs） whose motion type is two rotations and two translations（2R2T） is presented.Based on screw theory,the combination of different types of limbs which are used to construct parallel mechanisms and coupling chains is proposed.The basic types of the general parallel mechanisms and geometric conditions of the kinematic chains are given using constraint synthesis method.Moreover,the 2R2T motion pattern hybrid mechanisms which are derived by adding coupling chains between different serial kinematic chains（SKCs） of the corresponding parallel mechanisms are presented.According to the constraint analysis of the mechanisms,the movement relationship of the moving platform and the kinematic chains is derived by disassembling the coupling chains.At last,fourteen novel hybrid mechanisms with two or three serial kinematic chains are presented.The proposed novel hybrid mechanisms and construction method enrich the family of the spatial mechanisms and provide an instruction to design more complex hybrid mechanisms.
基金Supported by National Natural Science Foundation of China(Grant No.51405425)Hebei Provincial Natural Science Foundation of China(Grant No.E2014203255)Independent Research Program Topics of Young Teachers in Yanshan University,China(Grant No.13LGA001)
文摘The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.
基金Funded by the National Natural Science Foundation of China(No.51074123)the Scientif ic Research Program Funded by Shaanxi Provincial Education Department(No.12JK0785)+1 种基金the Cooperation Project of Industry,Academe and Research of Yulin City(2011)the Ph D Foundation of Xi’an University of Science and Technology(No.2011QDJ022)
文摘Through the experiments and the numerical simulation of temperature field in multi-heatsource synthesis Si C furnace, in order to research the feature point in multi-heat-source synthesis furnace, the variation law of heat fl ux was studied and the multi-directional energy fl ow diffusion mechanism was revealed. The results show that, due to the shielding action between the heat-source and the superposition effect of thermal fields, the insulating effect is best in multi-heat-source synthesis furnace. The heat emission effect is good outside the common area between heat-sources, but the heat storage is poor. Compared with the synthesis furnace that heat source is parallelly arranged, the furnace of stereoscopic arrangement has a more obvious heat stacking effect and better heat preservation effect, but the air permeability of heat source connecting regions is worse. In the case with the same ingredients, the resistance to thermal diffusion and mass diffusion is higher in heat source connecting regions.
基金This project is supported by National Hi-tech Research and DevelopmentProgram of China (863 Program, No.2002AA420110).
文摘In order to enhance the effect of comeal grafting, an assisting microsurgical robot has been developed. As one of principal issues for the robotic system design, type and size synthesis of the robotic mechanism is discussed. For this purpose, timeline subtask is analyzed with surgical component motion in manual comeal grafting microsurgery, as the reference of robotic mechanism synthesis. On the basis of study on the kinematic correlation between the arm structures and the wrist structures, configuration of joint is determined for the surgical task and motion in type synthesis of the mechanism. The objective for size synthesis of robotic mechanism is optimization of the mechanism dexterity as a manipulation capability. The condition number based on Jacob matrix is chosen as dexterity measure of the mechanism. The prototype is developed.
基金Supported by the National Natural Science Foundation of China under Grant No 61575216
文摘A series of boron- and phosphorus-doped silicon wafers are used to prepare a series of doped silicon nanocrystals （nc-Si） by high-energy ball milling with carboxylic acid-terminated surface. The sizes of the nc-Si samples are demonstrated to be 〈 S nm. The doping levels of the nc-Si are found to be nonlinearly dependent on the original doping level of the wafers by x-ray photoelectron spectroscopy measurement. It is found that the nonlinear doping process will lead to the nonlinear chemical passivation and photoluminescence （I3L） intensity evolution. The doping, chemical passivation and PL mechanisms of the doped nc-Si samples prepared by mechanochemical synthesis are analyzed in detail.
基金the National Natural Science Foundation of China (20671069)
文摘Perovskite-type oxide nanocrystalline LaCoO3-λ was prepared using the citrate method. The structure and morphology of the sampies were characterized by powder X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The intermediate products were analyzed by thermal gravimetric and differential thermal analysis （TG-DTA） technology. The results showed that nanocrystalline LaCoO3-λ with a granula of 30-50 nm had a cubic perovskite structure. The reaction mechanism of low temperature preparation was suggested as follows： the metal complex was first formed by the combination of metal ion and citric acid; and then it decomposed into an aconitic acid complex, followed by an oxycarbonate, and finally a perovskite-type oxide.
文摘Submicron copper microcrystal was synthesized by reducing Cu2O with hydrazine hydrate as reducer in aqueous solution,and was characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The shapes of copper microcrystal depend on additives. Cubic copper particles were observed when the inorganic salt containing Cl^-,such as NH4Cl,NaCl,or KCl,was added into the reaction system. By combined use of NH4Cl and polyvinylpyrrolidone （PVP）,the proportion of cubic copper particle number exceeded 90%,and the particle size is 0.1-0.5μrn. While other inorganic salt without Cl^-,such as Na2SO4 or （NH4）2SO4,had little effect on the shapes of the copper particles. The growth mechanism of metallic copper crystal in aqueous solution was analyzed. It is suggested that the formation of cubic copper crystals is ascribed to the selective adsorption of Cl^-on copper crystal （100） faces.
基金National Key Research and Development Program of China(Grant No.2017YFD0700800)National Science Foundation of China(Grant Nos.51775512,51575496)Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ16E050003).
文摘It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of seedling pickup mechanism with planetary gear train was studied based on the data of given key points and the trajectory of the endpoint of seedling pick-up mechanism.Given the positions and orientations requirements of the five key points,the study first conducted a dimensional synthesis of the linkage size and center of rotation.The next steps were to select a reasonable solution and optimize the data values based on the ideal seedling trajectory.The link motion was driven by the planetary gear train of the two-stage gear.Four pitch curves of noncircular gears were obtained by calculating and distributing the transmission ratio according to the data.For the pitch curve with two convex points,the tooth profile design method of incomplete noncircular gear was applied.The seedling pick-up mechanism was tested by a virtual prototype and a physical prototype designed with the obtained parameter values.The results were consistent with the theoretical design requirements,confirming that the mechanism meets the expected requirements for picking seedlings up.This paper presents a new design method of vegetable pot seedling pick-up mechanism for an automatic vegetable transplanter.
文摘The production. characteristics. and commercialization of monolithic and composite titanium aluminides are summanzed with emphasis on use in the demanding aerospace industry. The attractive elevated temperature properties combined with alow density make these materials of great interest, but inherently low 'forgiveness', and environmental concerns, must be overcome before widespread use will occur One synthesis method for the production of monolithic titanium aluminides-mechanical alloying- will be discussed in detail
文摘A new iterating method based on homotopy function is developed in this paper. All solutions can be found easily without the need of choosing proper initial values. Compared to the homotopy continuation method, the solution process of the present method is simplified, and the computation efficiency as well as the reliability for obtaining all solutions is also improved. By application of the method to the mechanisms problems, the results are satisfactory.
基金State Key development program for Basic Research(2017YFC15023003)National Natural Science Foundation of China(41575082,41530531)Special Scientific Research Project for Public Interest(GYHY201306021)
文摘In this study, the winter-summer-winter seasonal variation characteristics of the atmospheric temperature in northern East Asia(NEA) during the past 60 years are analyzed. The results revealed a type of new seasonal variation mechanism of temperature: winter-winter recurrence(WWR). This study initially discussed the formation mechanism of WWR from the angle of the relationship between the WWR and the atmospheric internal factors and external forcing.The main conclusions are summarized as follows:(1) The winter-summer-winter continuous variation of the AO anomaly index has consistent characteristics with the atmospheric variation of the WWR in the NEA, and their 60-year correlation coefficient reaches 0.43, passing the 95% significance level. It is indicated that the seasonal anomaly of the AO has a certain influence on the WWR;(2) Overall, the PDO maintains a negative phase in the negative WWR years,while it displays the opposite feature in the positive WWR years. The negative(positive) anomaly of PDO is favourable to the occurrence of sustainable low(high) temperatures in the NEA, and may be the important external driving factor for motivating the WWR in the NEA;(3) The binary regression, based on the PDO and AO indexes successfully reproduces the curve of T_(WWR-HG), which is significantly correlated with the WWR index TWWR, and can reproduce the time-height profile of the WWR characteristics from 400 to 1,000 hPa. Therefore, it is concluded that the WWR of the atmospheric temperatures in the NEA is the result of the combined action of the PDO and AO.
文摘The AB-crosslinked polymers (i.e. ABCP) with polystyrene as chain A and vinyl group blocked prepolymers of polyurethanes (PU) as chain B were synthesized and studied. The results of dynamic mechanical spectrometry (DMS) show that the compatibility between the components A and B can be improved greatly through chemical crosslinking during the formation of ABCPs. This effect is especially pronounced when short chain prepolymers is chosen as one of the components. It is apparent that the degree of crosslinking between the two components plays a major role in determining their compatibility. Copolymerizafion of styrene with maleic anhydride in chain A can improve the compatibility and broaden the damping temperature range. Mechanical properties of the sythesized ABCPs were also studied.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51075005)the Beijing City Science and Technology Project(Grant No.Z131100005313009)
文摘Revealing the relations among robotic comprehensive performance,configuration,scales and working tasks is the basis to optimize robotic mechanism. Due to the correlation and diversity of the single performance indexes,statistical principles of linear dimension reduction and nonlinear dimension reduction are introduced into comprehensive performance analysis and evaluation for typical serial robot. The robotic mechanism's configuration,scales and task with the best comprehensive performance can be obtained by principal component analysis( PCA) and kernel principal component analysis( KPCA) respectively. The results show that KPCA can reveal the nonlinear relations among different single performance indexes more effectively and provide more comprehensive performance information than PCA. Thus,task-oriented method of serial robot for mechanism analysis and evaluation is proposed,which also provides scientific research basis for the mechanism synthesis and optimum task order.
文摘In order to solve four-bar straight-line guidance mechanism synthesis problem for the arbitrarily given straight-line’s"angle requirement"and"point-position requirement",a numerical comparison synthesis method for single and double straight-line guidance mechanism is presented,which is convenient to realize by computer program.The basic idea of this method is:to select a four-bar linkage whose relative bar length of crank is 1 as a basic four-bar linkage.Then the other three relative bars’length is changed,and a lot of basic four-bar linkage can be obtained.There are many single and double ball-points of each basic four-bar linkage.With the motion of a basic four-bar linkage,there is straight-line segment of each Ball-point’s path.The data of these basic four-bar linkages is saved to a database.When designing a four-bar straight-line guidance mechanism,the design data is compared with the data in database and a satisfactory four-bar linkage can be obtained.The method effectively solves the straight-line guidance mechanism synthesis problem.
文摘In this study,the mechanism of the reduction-diffusion reaction in a Sm-Fe binary system at low temperature was studied to investigate the possibility of synthesis of a Fe-rich TbCu_(7)-type SmFe_(x)(x>9)by the low-temperature diffusion-reduction(LTRD)process using LiCl-KCl eutectic molten salts.Firstly,the Sm-Fe phase transformation depending on the Sm-Fe composition,the LTRD temperature,and time was investigated,and it is found that the obtained metastable phase is only TbCu_(7)-type SmFe_(~8.5),which is not a Fe-rich phase.This Fe content does not change even after an expended LTRD process,and the metastable TbCu_(7)-type SmFe_(~8.5)tends to transform to the stable Sm_(2)Fe_(17)phase.In addition,it is found that the Sm-Fe phase starts to synthesize from the Sm-rich phase in the order of SmFe_(2),SmFe_(3),and SmFe_(8.5)as the LTRD temperature increases(when the time was 10 h)or the LTRD time increases(when the temperature was 550℃).Core-shell-like particles are observed in the case of a short LTRD time,and the core and the shell are Fe and the Sm-rich Sm-Fe phase,respectively,indicating that the Sm-rich phase begins to produce on the surface of the Fe particles.It is difficult to synthesize a Fe-rich TbCu_(7)-type SmFe_(x)(x>9)phase with the Sm-Fe binary system,suggesting that a different approach,such as addition of other elements,will be necessary.
