Four-factor and three-level orthogonal experimental design(L9(34))was used in the experiment.The effects of three genotypes:Germany SAB three-bred-cross rabbits(S2),New Zealand purebred(N),and crossbred rabbits(ON);th...Four-factor and three-level orthogonal experimental design(L9(34))was used in the experiment.The effects of three genotypes:Germany SAB three-bred-cross rabbits(S2),New Zealand purebred(N),and crossbred rabbits(ON);three levels of Clenbuterol treatment: 1 ng.g-1,2 ng.g-1and 3 ng.g-1,and three feeding methods:5-day,7-day and 10-day withdrawal period after two weeks of feeding Clenbuterol(CL)on bodyweight gain were evaluated.CL apparently improved average daily gain(ADG)of rabbits.70-day ADG of 5-day and 10-day withdrawal were higher than that of 7-day withdrawal,70-day ADG of S2 genotype was significantly higher than that of the control and N genotype was significant.Genotype,additive dose and feeding method had significant effects on overall-stage ADG.ON genotype,2 ng.g-1 dose and 5-day withdrawal feeding method was the best.Responses of different genotype to Clenbuterol appeared different at experimental prophase or whole experimental period.展开更多
An experimental installation of cold model simulation was set up to study the bed pressure drop in different regions of fixed fluidized bed reactor during top feeding and bottom feeding, respectively, at various gas v...An experimental installation of cold model simulation was set up to study the bed pressure drop in different regions of fixed fluidized bed reactor during top feeding and bottom feeding, respectively, at various gas velocities with the fluidization image of solid particles monitored at the same time. By comparing the changes in bed density and operating gas velocity in different regions of fixed fluidized bed reactor, the influence of top feeding and bottom feeding patterns on fluidization behavior could be investigated. The results showed that the bed density in top feeding reactor responded more stably to the change in gas velocity along with the advantage of working in a wider range of operating gas velocities. Based on this study, it is concluded that existing bottom feeding reactor configurations cannot meet the fluidization requirements; and optimization of bottom feeding reactor will be needed.展开更多
In order to adopt Billings Method for fertility regulation during the period of breast feeding, cervical mucus was observed and monitored in 61 breast feeding mothers.Urine estrogen and /or pregnanediol ...In order to adopt Billings Method for fertility regulation during the period of breast feeding, cervical mucus was observed and monitored in 61 breast feeding mothers.Urine estrogen and /or pregnanediol were/was measured in 15 breast feeding mothers. Observations on cervical mucus during 244 months were collected. The type of dry or no mucus was observed in 75.27% fully breast feeding mothers. Constant unchanging mucus was observed in 69.39% partially breast feeding mothers. Developmental changing mucus was observed in 79.25% of mothers bottle feeding their infants. According to the record on cervical mucus within 6 months postpartum, 97.14% of the cervical mucus was consistent with normal menstrual cycles. Urine estrogen and /or pregnanediol were/was measured in 15 breast feeding mothers. The level of estrogen in urine averaged 0.08 μmol/24 h in fully breast feeding mothers and 0.14 μmol/24 h in partially breast feeding mothers.The peak level averaged 0.21 μmol/24 h in bottle feeding mothers.The pregnanediol level was determined to confirm ovulation in bottle feeding mothers. The average levels of cut off and the period of ovulation in 6 bottle feeding mother were 7 μmol/24 h and 9 μmol/24 h respectively.Measurement of urine estrogen and pregnanediol level all matched with cervical mucus appearances. Conclusion: Billings Method is a simple, scientific method for contraception without side effects during breast feeding period.展开更多
Based on the evaluation of dynamic performance for feed drives in machine tools, this paper presents a two-stage tuning method of servo parameters. In the first stage, the evaluation of dynamic performance, parameter ...Based on the evaluation of dynamic performance for feed drives in machine tools, this paper presents a two-stage tuning method of servo parameters. In the first stage, the evaluation of dynamic performance, parameter tuning and optimization on a mechatronic integrated system simulation platform of feed drives are performed. As a result, a servo parameter combination is acquired. In the second stage, the servo parameter combination from the first stage is set and tuned further in a real machine tool whose dynamic performance is measured and evaluated using the cross grid encoder developed by Heidenhain GmbH. A case study shows that this method simplifies the test process effectively and results in a good dynamic performance in a real machine tool.展开更多
A definition of combined phase center for horn feeds is given.Formulas of E-planeand H-plane combined phase center for conical horns and the corresponding Optimal model arepresented,and a fast optimization method for ...A definition of combined phase center for horn feeds is given.Formulas of E-planeand H-plane combined phase center for conical horns and the corresponding Optimal model arepresented,and a fast optimization method for solving this model is described.By using thismethod,the phase center of corrugated horn is discussed and calculated,and the variation of thephase center with distance and operating frequency is given.展开更多
Ring patch antennas have the characteristics of electrically small size as decreasing the width of the conducting portion compared to those of conventional patch antennas.In the ring patch antenna,using capacitive fee...Ring patch antennas have the characteristics of electrically small size as decreasing the width of the conducting portion compared to those of conventional patch antennas.In the ring patch antenna,using capacitive feed method is suitable for impedance matching.The effect of the size of the feed patch on the input impedance of the square ring patch antennas are analyzed and radiation patterns of the square ring patch antennas are compared to that of a square conventional patch antenna by the simulated results.展开更多
During radial-axial ring rolling process, cooperative strategy of the radial axial feed is critical for dimensional accuracy and thermo mechanical parameters distribution of the formed ring. In order to improve the co...During radial-axial ring rolling process, cooperative strategy of the radial axial feed is critical for dimensional accuracy and thermo mechanical parameters distribution of the formed ring. In order to improve the comprehensive quality of the ring parts, response surface method （RSM） is employed for the first time to optimize the cooperative feed strategy for radial-axial ring rolling process by combining it with an improved and verified 3D coupled thermo-mechanical finite element model. The feed trajectory is put forward to describe cooperative relationship of the radial- axial feed and three variables are designed based on the feed trajectory. In order to achieve multi- objective optimization, four responses including thermo mechanical parameters distribution and rolling force are proposed. Based on the FEM results, RSM is used to establish a response model to depict the function relationship between the objective response and design variables. Through this approximate model, effects of different variables on ring rolling process are analyzed connect- edly and optimal feed strategy is obtained by resorting to the optimal chart specific to a constraint condition.展开更多
Fluorescent silk is fundamentally important for the development of future tissue engineering scaffolds.Despite great progress in the preparation of a variety of colored silks,fluorescent silk with enhanced mechanical ...Fluorescent silk is fundamentally important for the development of future tissue engineering scaffolds.Despite great progress in the preparation of a variety of colored silks,fluorescent silk with enhanced mechanical properties has yet to be explored.In this study,we report on the fabrication of intrinsically super-strong fluorescent silk by feeding Bombyx mori silkworm carbon nanodots(CNDs).The CNDs were incorporated into silk fibroin,hindering the conformation transformation,confining crystallization,and inducing orientation of mesophase.The resultant silk exhibited super-strong mechanical properties with breaking strength of 521.9±82.7 MPa and breaking elongation of 19.2±4.3%,improvements of 55.1%and 53.6%,respectively,in comparison with regular silk.The CNDs-reinforced silk displayed intrinsic blue fluorescence when exposed to 405 nm laser and exhibited no cytotoxic effect on cells,suggesting that multi-functional silks would be potentially useful in bioimaging and other applications.展开更多
[Objectives]This study was conducted to establish a qualitative method for rapid detection of pesticide residues in feed.[Methods]A rapid screening method for 82 pesticide residues in feed was established using ultra ...[Objectives]This study was conducted to establish a qualitative method for rapid detection of pesticide residues in feed.[Methods]A rapid screening method for 82 pesticide residues in feed was established using ultra liquid chromatography coupled with quadrupole-time of flight mass spectrometry(UPLC-Q-TOF-MS)combined with optimized pretreatment methods.[Results]Feed samples were extracted with 0.2%formic acid-acetonitrile solution,shaken,centrifuged,and re-centrifuged,and the supernatant was filtered with a 0.22μm filter membrane for determination.The samples were separated on a Waters ACQUITY UPLC HSS T3 chromatographic column(2.1 mm×50 mm,1.8μm),and subjected to gradient elution with methanol-water solution as the mobile phase,and scanning was performed in ESI+mode.82 compounds could be accurately qualitatively detected in 13 min.[Conclusions]This method is simple to operate,time-saving,and can be applied to rapid screening of large-scale feed.This study provides a theoretical basis for the development of new methods in the future.展开更多
The finite element modeling of three dimensional structures is important for researchers especially in the field of antennas and other domains of electromagnetic waves. This paper presents a finite element calculation...The finite element modeling of three dimensional structures is important for researchers especially in the field of antennas and other domains of electromagnetic waves. This paper presents a finite element calculations and numerical analysis for the microstrip patch antennas. In this paper, two different designs have been modelled and analyzed and both designs are based on the rectangular patches. The feeding point of one design is inside the patch while the other design contains feeding point outside the patch is T shaped. The computational analysis showed some interesting results for radiation pattern and far field domain. For these designs, the characteristic impedance taken is 50 Ω and the operating frequency domain is 1.4 to 1.7 GHz. The microstrip patch antennas are encapsulated in the inert spherical atmosphere of 20 mm thickness containing air inside it.展开更多
A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopt...A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States(CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.展开更多
The medium -large caliber naval gun is still playing an important role in modern war. The development of highly automatic Shell Raising and Feeding System (SRFS) in the world has been briefly outlined. Several typical...The medium -large caliber naval gun is still playing an important role in modern war. The development of highly automatic Shell Raising and Feeding System (SRFS) in the world has been briefly outlined. Several typical SRFS of medium-large caliber naval guns have been analyzed. A re-design of the system is introduced, in which systematic design method has been used to demonstrate its feasibility. The design goal of the system is to realize rapid shell feeding, with application to many types of shells, quick change of shell types , accurate and reliable feeding operation, simple mechanical structure and easy realization of shell withdrawing.展开更多
A flexible technique of hot working of bars by axial feed rolling was introduced. The process deformation, strain field, stress field, and temperature fie M of the parts are analyzed by finite element method （ FEM）-...A flexible technique of hot working of bars by axial feed rolling was introduced. The process deformation, strain field, stress field, and temperature fie M of the parts are analyzed by finite element method （ FEM）-simulation software DEFORM-3D. The material flow rule and tool load have been investigated.展开更多
A numerical control (NC) tool path of digital CAD model is widely generated as a set of short line segments in machining. However, there are three shortcomings in the linear tool path, such as discontinuities of tange...A numerical control (NC) tool path of digital CAD model is widely generated as a set of short line segments in machining. However, there are three shortcomings in the linear tool path, such as discontinuities of tangency and curvature, huge number of line segments, and short lengths of line segments. These disadvantages hinder the development of high speed machining. To smooth the linear tool path and improve machining efficiency of short line segments, this paper presents an optimal feed interpolator based on G^2 continuous Bézier curves for the linear tool path. First, the areas suitable for fitting are screened out based on the geometric characteristics of continuous short segments (CSSs). CSSs in every area are compressed and fitted into a G^2 Continuous Bézier curve by using the least square method. Then a series of cubic Bézier curves are generated. However, the junction between adjacent Bézier curves is only G^0 continuous. By adjusting the control points and inserting Bézier transition curves between adjacent Bézier curves, the G^2 continuous tool path is constructed. The fitting error is estimated by the second-order Taylor formula. Without iteration, the fitting algorithm can be implemented in real-time environment. Second, the optimal feed interpolator considering the comprehensive constraints (such as the chord error constraint, the maximum normal acceleration, servo capacity of each axis, etc.) is proposed. Simulation and experiment are conducted. The results shows that the proposed method can generate smooth path, decrease the amount of segments and reduce machining time for machining of linear tool path. The proposed research provides an effective method for high-speed machining of complex 2-D/3-D profiles described by short line segments.展开更多
To improve the accuracy of fault location system, several short-circuit tests need to be conducted before being brought into service in autotransformer （AT） feeding systems for high-speed railways in China. However,...To improve the accuracy of fault location system, several short-circuit tests need to be conducted before being brought into service in autotransformer （AT） feeding systems for high-speed railways in China. However, no systematic algorithm yet exists to evaluate the consistency of the current distribution of short-circuit tests. A methodology is proposed in this paper to address this problem. Based on Kirchhoff’s current law and the generalized method of symmetrical components, the current deviations of the AT feeding systems are analysed and then normalized with the short-circuit current as they vary greatly with systems and short-circuit sites. It is also found that the short-circuit current varies with the calculation methods, and its unbiased standard deviation also reflects the consistency of the short-circuit test. The mean and maximum of the current deviations, as well as the unbiased standard deviation of the short-circuit current, show the consistency of the short-circuit test from different aspects,although the last two items are highly relevant. Therefore, a unified evaluation index is defined as the sum of the three items, and then applied in two case studies to test its performance. The results show that, the proposed index canclearly distinguish the consistency of the short-circuit tests and may be used to sort the short-circuit tests for fault location systems. Besides, some short-circuit tests may have very poor consistency indices, and thus are not applicable to the tuning of fault location systems. In the authors’ opinion, the determination of the threshold of the proposed index needs further investigation.展开更多
文摘Four-factor and three-level orthogonal experimental design(L9(34))was used in the experiment.The effects of three genotypes:Germany SAB three-bred-cross rabbits(S2),New Zealand purebred(N),and crossbred rabbits(ON);three levels of Clenbuterol treatment: 1 ng.g-1,2 ng.g-1and 3 ng.g-1,and three feeding methods:5-day,7-day and 10-day withdrawal period after two weeks of feeding Clenbuterol(CL)on bodyweight gain were evaluated.CL apparently improved average daily gain(ADG)of rabbits.70-day ADG of 5-day and 10-day withdrawal were higher than that of 7-day withdrawal,70-day ADG of S2 genotype was significantly higher than that of the control and N genotype was significant.Genotype,additive dose and feeding method had significant effects on overall-stage ADG.ON genotype,2 ng.g-1 dose and 5-day withdrawal feeding method was the best.Responses of different genotype to Clenbuterol appeared different at experimental prophase or whole experimental period.
文摘An experimental installation of cold model simulation was set up to study the bed pressure drop in different regions of fixed fluidized bed reactor during top feeding and bottom feeding, respectively, at various gas velocities with the fluidization image of solid particles monitored at the same time. By comparing the changes in bed density and operating gas velocity in different regions of fixed fluidized bed reactor, the influence of top feeding and bottom feeding patterns on fluidization behavior could be investigated. The results showed that the bed density in top feeding reactor responded more stably to the change in gas velocity along with the advantage of working in a wider range of operating gas velocities. Based on this study, it is concluded that existing bottom feeding reactor configurations cannot meet the fluidization requirements; and optimization of bottom feeding reactor will be needed.
文摘In order to adopt Billings Method for fertility regulation during the period of breast feeding, cervical mucus was observed and monitored in 61 breast feeding mothers.Urine estrogen and /or pregnanediol were/was measured in 15 breast feeding mothers. Observations on cervical mucus during 244 months were collected. The type of dry or no mucus was observed in 75.27% fully breast feeding mothers. Constant unchanging mucus was observed in 69.39% partially breast feeding mothers. Developmental changing mucus was observed in 79.25% of mothers bottle feeding their infants. According to the record on cervical mucus within 6 months postpartum, 97.14% of the cervical mucus was consistent with normal menstrual cycles. Urine estrogen and /or pregnanediol were/was measured in 15 breast feeding mothers. The level of estrogen in urine averaged 0.08 μmol/24 h in fully breast feeding mothers and 0.14 μmol/24 h in partially breast feeding mothers.The peak level averaged 0.21 μmol/24 h in bottle feeding mothers.The pregnanediol level was determined to confirm ovulation in bottle feeding mothers. The average levels of cut off and the period of ovulation in 6 bottle feeding mother were 7 μmol/24 h and 9 μmol/24 h respectively.Measurement of urine estrogen and pregnanediol level all matched with cervical mucus appearances. Conclusion: Billings Method is a simple, scientific method for contraception without side effects during breast feeding period.
基金This paper is supported by the Major State Basic Research Development Program of China under Grant No2005CB724101the Key Items Program of International Science and Technology Cooperation of China under Grant No2003DF000021
文摘Based on the evaluation of dynamic performance for feed drives in machine tools, this paper presents a two-stage tuning method of servo parameters. In the first stage, the evaluation of dynamic performance, parameter tuning and optimization on a mechatronic integrated system simulation platform of feed drives are performed. As a result, a servo parameter combination is acquired. In the second stage, the servo parameter combination from the first stage is set and tuned further in a real machine tool whose dynamic performance is measured and evaluated using the cross grid encoder developed by Heidenhain GmbH. A case study shows that this method simplifies the test process effectively and results in a good dynamic performance in a real machine tool.
文摘A definition of combined phase center for horn feeds is given.Formulas of E-planeand H-plane combined phase center for conical horns and the corresponding Optimal model arepresented,and a fast optimization method for solving this model is described.By using thismethod,the phase center of corrugated horn is discussed and calculated,and the variation of thephase center with distance and operating frequency is given.
文摘Ring patch antennas have the characteristics of electrically small size as decreasing the width of the conducting portion compared to those of conventional patch antennas.In the ring patch antenna,using capacitive feed method is suitable for impedance matching.The effect of the size of the feed patch on the input impedance of the square ring patch antennas are analyzed and radiation patterns of the square ring patch antennas are compared to that of a square conventional patch antenna by the simulated results.
基金Specialized Research Fund for the Doctoral Program of Higher Education(No.20126102120022) of ChinaNorthwestern Polytechnical University(NPU) Foundation for Fundamental Research(NPU-FFR-JC200822) of China for the support given to the research
文摘During radial-axial ring rolling process, cooperative strategy of the radial axial feed is critical for dimensional accuracy and thermo mechanical parameters distribution of the formed ring. In order to improve the comprehensive quality of the ring parts, response surface method （RSM） is employed for the first time to optimize the cooperative feed strategy for radial-axial ring rolling process by combining it with an improved and verified 3D coupled thermo-mechanical finite element model. The feed trajectory is put forward to describe cooperative relationship of the radial- axial feed and three variables are designed based on the feed trajectory. In order to achieve multi- objective optimization, four responses including thermo mechanical parameters distribution and rolling force are proposed. Based on the FEM results, RSM is used to establish a response model to depict the function relationship between the objective response and design variables. Through this approximate model, effects of different variables on ring rolling process are analyzed connect- edly and optimal feed strategy is obtained by resorting to the optimal chart specific to a constraint condition.
基金sponsored by the National Key Research and Development Program of China(2016YFA0201700,2016YFA0201702)the Fundamental Research Funds for the Central Universities(2232019A3-06,2232019D3-02)+2 种基金the National Key Research and Development Program of China(2018YFC1105800)the National Natural Science Foundation of China(21674018,51903045)the Shanghai Belt and Road Joint Laboratory of Advanced Fiber and Low-Dimension Materials(18520750400).
文摘Fluorescent silk is fundamentally important for the development of future tissue engineering scaffolds.Despite great progress in the preparation of a variety of colored silks,fluorescent silk with enhanced mechanical properties has yet to be explored.In this study,we report on the fabrication of intrinsically super-strong fluorescent silk by feeding Bombyx mori silkworm carbon nanodots(CNDs).The CNDs were incorporated into silk fibroin,hindering the conformation transformation,confining crystallization,and inducing orientation of mesophase.The resultant silk exhibited super-strong mechanical properties with breaking strength of 521.9±82.7 MPa and breaking elongation of 19.2±4.3%,improvements of 55.1%and 53.6%,respectively,in comparison with regular silk.The CNDs-reinforced silk displayed intrinsic blue fluorescence when exposed to 405 nm laser and exhibited no cytotoxic effect on cells,suggesting that multi-functional silks would be potentially useful in bioimaging and other applications.
基金Supported by Key R&D Project in Hebei Province(19227516D)Hebei Provincial Phase II Modern Agricultural Industry Technology System Innovation Team Building Project(HBCT2018120207)+2 种基金Hebei Provincial Phase II Modern Agricultural Industry Technology System Forage Industry Innovation Team Building Project(HBCT2018160403)Tangshan Science and Technology Planning Project(21130243A)The Fourth Batch of High-end Talent Project in Hebei Province。
文摘[Objectives]This study was conducted to establish a qualitative method for rapid detection of pesticide residues in feed.[Methods]A rapid screening method for 82 pesticide residues in feed was established using ultra liquid chromatography coupled with quadrupole-time of flight mass spectrometry(UPLC-Q-TOF-MS)combined with optimized pretreatment methods.[Results]Feed samples were extracted with 0.2%formic acid-acetonitrile solution,shaken,centrifuged,and re-centrifuged,and the supernatant was filtered with a 0.22μm filter membrane for determination.The samples were separated on a Waters ACQUITY UPLC HSS T3 chromatographic column(2.1 mm×50 mm,1.8μm),and subjected to gradient elution with methanol-water solution as the mobile phase,and scanning was performed in ESI+mode.82 compounds could be accurately qualitatively detected in 13 min.[Conclusions]This method is simple to operate,time-saving,and can be applied to rapid screening of large-scale feed.This study provides a theoretical basis for the development of new methods in the future.
文摘The finite element modeling of three dimensional structures is important for researchers especially in the field of antennas and other domains of electromagnetic waves. This paper presents a finite element calculations and numerical analysis for the microstrip patch antennas. In this paper, two different designs have been modelled and analyzed and both designs are based on the rectangular patches. The feeding point of one design is inside the patch while the other design contains feeding point outside the patch is T shaped. The computational analysis showed some interesting results for radiation pattern and far field domain. For these designs, the characteristic impedance taken is 50 Ω and the operating frequency domain is 1.4 to 1.7 GHz. The microstrip patch antennas are encapsulated in the inert spherical atmosphere of 20 mm thickness containing air inside it.
基金supported by the National Natural Science Foundation of China(51805399)the Fundamental Research Funds for the Central Universities(JB180403)+2 种基金the Chinese Academy of Sciences(CAS)"Light of West China" Program(2017-XBQNXZ-B-024)the National Basic Research Program of China(973 Program)(2015CB857100)the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the CAS
文摘A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States(CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.
文摘The medium -large caliber naval gun is still playing an important role in modern war. The development of highly automatic Shell Raising and Feeding System (SRFS) in the world has been briefly outlined. Several typical SRFS of medium-large caliber naval guns have been analyzed. A re-design of the system is introduced, in which systematic design method has been used to demonstrate its feasibility. The design goal of the system is to realize rapid shell feeding, with application to many types of shells, quick change of shell types , accurate and reliable feeding operation, simple mechanical structure and easy realization of shell withdrawing.
基金the National Natural Science Foundation of China （Nos. 50205003 ,50675014）.
文摘A flexible technique of hot working of bars by axial feed rolling was introduced. The process deformation, strain field, stress field, and temperature fie M of the parts are analyzed by finite element method （ FEM）-simulation software DEFORM-3D. The material flow rule and tool load have been investigated.
基金Supported by National Natural Science Foundation of China(Grant No.50875171)National Hi-tech Research and Development Program of China(863 Program,Grant No.2009AA04Z150)
文摘A numerical control (NC) tool path of digital CAD model is widely generated as a set of short line segments in machining. However, there are three shortcomings in the linear tool path, such as discontinuities of tangency and curvature, huge number of line segments, and short lengths of line segments. These disadvantages hinder the development of high speed machining. To smooth the linear tool path and improve machining efficiency of short line segments, this paper presents an optimal feed interpolator based on G^2 continuous Bézier curves for the linear tool path. First, the areas suitable for fitting are screened out based on the geometric characteristics of continuous short segments (CSSs). CSSs in every area are compressed and fitted into a G^2 Continuous Bézier curve by using the least square method. Then a series of cubic Bézier curves are generated. However, the junction between adjacent Bézier curves is only G^0 continuous. By adjusting the control points and inserting Bézier transition curves between adjacent Bézier curves, the G^2 continuous tool path is constructed. The fitting error is estimated by the second-order Taylor formula. Without iteration, the fitting algorithm can be implemented in real-time environment. Second, the optimal feed interpolator considering the comprehensive constraints (such as the chord error constraint, the maximum normal acceleration, servo capacity of each axis, etc.) is proposed. Simulation and experiment are conducted. The results shows that the proposed method can generate smooth path, decrease the amount of segments and reduce machining time for machining of linear tool path. The proposed research provides an effective method for high-speed machining of complex 2-D/3-D profiles described by short line segments.
文摘To improve the accuracy of fault location system, several short-circuit tests need to be conducted before being brought into service in autotransformer （AT） feeding systems for high-speed railways in China. However, no systematic algorithm yet exists to evaluate the consistency of the current distribution of short-circuit tests. A methodology is proposed in this paper to address this problem. Based on Kirchhoff’s current law and the generalized method of symmetrical components, the current deviations of the AT feeding systems are analysed and then normalized with the short-circuit current as they vary greatly with systems and short-circuit sites. It is also found that the short-circuit current varies with the calculation methods, and its unbiased standard deviation also reflects the consistency of the short-circuit test. The mean and maximum of the current deviations, as well as the unbiased standard deviation of the short-circuit current, show the consistency of the short-circuit test from different aspects,although the last two items are highly relevant. Therefore, a unified evaluation index is defined as the sum of the three items, and then applied in two case studies to test its performance. The results show that, the proposed index canclearly distinguish the consistency of the short-circuit tests and may be used to sort the short-circuit tests for fault location systems. Besides, some short-circuit tests may have very poor consistency indices, and thus are not applicable to the tuning of fault location systems. In the authors’ opinion, the determination of the threshold of the proposed index needs further investigation.
