Background: Whether premature infants should be fed by bolus or continuous gavage feeding, is still a matter of debate. A recent Cochrane analysis revealed no difference. Study design and methods: We carried out a ran...Background: Whether premature infants should be fed by bolus or continuous gavage feeding, is still a matter of debate. A recent Cochrane analysis revealed no difference. Study design and methods: We carried out a randomized controlled trial in premature infants on continuous versus bolus nasogastric tube feeding, to search for differences with respect to number of incidents, growth, and time to reach full oral feeding. In total, 110 premature neonates (gestational age 27 - 34 weeks) were randomly assigned to receive either continuous or bolus nasogastric tube feeding. Basic characteristics were comparable in both groups. Results: No significant difference in weight gain could be detected between the two groups, mean weight gain amounting 151.6 (108.9 - 194.3) and 152.4 (102.2 - 202.6) grams per week in the continuous and bolus group, respectively. No significant differences were found between both groups in the time needed to achieve full oral feeding (8 oral feedings per day), full oral feeding being achieved at day 31 (range 19 - 43) and day 29 (range 18 - 40) of life in the continuous and bolus group, respectively. We also found no significant differences in the number of 'incident-days' (three or more incidents a day): 3.5 (0 - 9) versus 2.7 (0 - 6.5) days in the continuous and bolus group, respectively. Conclusion: No significant differences were found in weight gain, time to achieve full oral feeding and number of incident-days between preterm infants enterally fed by nasogastric tube, according to either the bolus or continuous method.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
This paper studies the problem of robust controller design for linear perturbed continuous stochasticsystems with variance constraints via output feedback. The goal is to design static output feedback controllers such...This paper studies the problem of robust controller design for linear perturbed continuous stochasticsystems with variance constraints via output feedback. The goal is to design static output feedback controllers suchthat the uncertain system has the desil'ed stability margin and the steady-state variance constraints. The existenceconditions for the desired controllers are discussed, and the analytical expression of these controllers is alsocharacterized. A numerical example is provided to demonstrate the directness and effectiveness of the proposedmethod.展开更多
Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-pa...Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-path running trajectory error is significant during high-feed-speed machining, which seriously restricts the machining precision for such parts with varied curvature features. In order to reduce the continuous-path running trajectory error without sacrificing the machining efficiency, a pre-compensation method for the trajectory error is proposed. Based on the formation mechanism of the continuous-path running trajectory error analyzed, this error is estimated in advance by approximating the desired toolpath with spline curves. Then, an iterative error pre-compensation method is presented. By machining with the regenerated toolpath after pre-compensation instead of the uncompensated toolpath, the continuous-path running trajectory error can be effectively decreased without the reduction of the feed speed. To demonstrate the feasibility of the proposed pre-compensation method, a heart curve toolpath that possesses varied curvature features is employed. Experimental results indicate that compared with the uncompensated processing trajectory, the maximum and average machining errors for the pre-compensated processing trajectory are reduced by 67.19% and 82.30%, respectively. An easy to implement solution for high efficiency and high precision machining of the parts with varied curvature features is provided.展开更多
Steel strip feeding into the mold during continuous casting is known as an innovative technology.The newly applied technology is designed to further improve the slab quality.To analyze the complex phase change process...Steel strip feeding into the mold during continuous casting is known as an innovative technology.The newly applied technology is designed to further improve the slab quality.To analyze the complex phase change processes,molten sodium thiosulphate(Na2S2O3-5H2O)was used in the experimental investigation as a transparent analog for metallic alloys.Then,a numerical model incorporating fluid flow,heat transfer and phase change during strip feeding into the mold process was developed.The generalized enthalpy-based method was applied to describe the phase change behavior,and the porous media theory was used to model the blockage of fluid flow by the dendrites in the mushy zone between the strip and melt as well as the solidified shell and melt.The validated model was then used for the simulation of the real strip feeding into the mold process in an industrial scale.The whole shape of the strip under the effect of jet flow from the submerged entry nozzle(SEN)was presented.Results show that the strip will reach a pseudo-steady state after experiencing steel sheath formation,steel sheath melting and strip melting processes.When using the feeding method that is the strip narrow side toward the SEN in the present condition,the strip immersion length can reach 4.5 m below the meniscus and the slab centerline temperature can be decreased by 21 K to a maximum.When the strip feeding speed increased from 0.3 to 0.5 m/s,the minimum temperature of the centerline could be lowered by 4 K or so.展开更多
文摘Background: Whether premature infants should be fed by bolus or continuous gavage feeding, is still a matter of debate. A recent Cochrane analysis revealed no difference. Study design and methods: We carried out a randomized controlled trial in premature infants on continuous versus bolus nasogastric tube feeding, to search for differences with respect to number of incidents, growth, and time to reach full oral feeding. In total, 110 premature neonates (gestational age 27 - 34 weeks) were randomly assigned to receive either continuous or bolus nasogastric tube feeding. Basic characteristics were comparable in both groups. Results: No significant difference in weight gain could be detected between the two groups, mean weight gain amounting 151.6 (108.9 - 194.3) and 152.4 (102.2 - 202.6) grams per week in the continuous and bolus group, respectively. No significant differences were found between both groups in the time needed to achieve full oral feeding (8 oral feedings per day), full oral feeding being achieved at day 31 (range 19 - 43) and day 29 (range 18 - 40) of life in the continuous and bolus group, respectively. We also found no significant differences in the number of 'incident-days' (three or more incidents a day): 3.5 (0 - 9) versus 2.7 (0 - 6.5) days in the continuous and bolus group, respectively. Conclusion: No significant differences were found in weight gain, time to achieve full oral feeding and number of incident-days between preterm infants enterally fed by nasogastric tube, according to either the bolus or continuous method.
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This paper studies the problem of robust controller design for linear perturbed continuous stochasticsystems with variance constraints via output feedback. The goal is to design static output feedback controllers suchthat the uncertain system has the desil'ed stability margin and the steady-state variance constraints. The existenceconditions for the desired controllers are discussed, and the analytical expression of these controllers is alsocharacterized. A numerical example is provided to demonstrate the directness and effectiveness of the proposedmethod.
基金Supported by National Natural Science Foundation of China(Grant Nos.51575087,51205041)Science Fund for Creative Research Groups(Grant No.51321004)+1 种基金Basic Research Foundation of Key Laboratory of Liaoning Educational Committee,China(Grant No.LZ2014003)Research Project of Ministry of Education of China(Grant No.113018A)
文摘Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-path running trajectory error is significant during high-feed-speed machining, which seriously restricts the machining precision for such parts with varied curvature features. In order to reduce the continuous-path running trajectory error without sacrificing the machining efficiency, a pre-compensation method for the trajectory error is proposed. Based on the formation mechanism of the continuous-path running trajectory error analyzed, this error is estimated in advance by approximating the desired toolpath with spline curves. Then, an iterative error pre-compensation method is presented. By machining with the regenerated toolpath after pre-compensation instead of the uncompensated toolpath, the continuous-path running trajectory error can be effectively decreased without the reduction of the feed speed. To demonstrate the feasibility of the proposed pre-compensation method, a heart curve toolpath that possesses varied curvature features is employed. Experimental results indicate that compared with the uncompensated processing trajectory, the maximum and average machining errors for the pre-compensated processing trajectory are reduced by 67.19% and 82.30%, respectively. An easy to implement solution for high efficiency and high precision machining of the parts with varied curvature features is provided.
基金This work was funded by the National Natural Science Foundation of China(Nos.51574068 and 51974071)Yong Elite Scientists Sponsorship Program by China Association for Science and Technology(No.2018QNRC001).
文摘Steel strip feeding into the mold during continuous casting is known as an innovative technology.The newly applied technology is designed to further improve the slab quality.To analyze the complex phase change processes,molten sodium thiosulphate(Na2S2O3-5H2O)was used in the experimental investigation as a transparent analog for metallic alloys.Then,a numerical model incorporating fluid flow,heat transfer and phase change during strip feeding into the mold process was developed.The generalized enthalpy-based method was applied to describe the phase change behavior,and the porous media theory was used to model the blockage of fluid flow by the dendrites in the mushy zone between the strip and melt as well as the solidified shell and melt.The validated model was then used for the simulation of the real strip feeding into the mold process in an industrial scale.The whole shape of the strip under the effect of jet flow from the submerged entry nozzle(SEN)was presented.Results show that the strip will reach a pseudo-steady state after experiencing steel sheath formation,steel sheath melting and strip melting processes.When using the feeding method that is the strip narrow side toward the SEN in the present condition,the strip immersion length can reach 4.5 m below the meniscus and the slab centerline temperature can be decreased by 21 K to a maximum.When the strip feeding speed increased from 0.3 to 0.5 m/s,the minimum temperature of the centerline could be lowered by 4 K or so.
