We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure ...We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δn_(eff) between the adjacent guided modes could be kept larger than 1.32 × 10^(-4) over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF(14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.展开更多
Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external ...Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external radius （ρ） under different loading rates. The results show that the dynamic tensile strength of disc rock specimen is approximately five times its static tensile strength. The failure modes of ring specimens are related to the dimension of the internal hole and loading rate. Under static loading tests, when the ratio of internal radius to external radius of the rock ring is small enough （ρ〈0.3）, specimens mostly split along the diametral loading line. With the increase of the ratio, the secondary cracks are formed in the direction perpendicular to the loading line. Under dynamic loading tests, specimens usually break up into four pieces. When the ratio ρreaches 0.5, the secondary cracks are formed near the input bar. The tensile strength calculated by Hobbs’ formula is greater than the Brazilian splitting strength. The peak load and the radius ratio show a negative exponential relationship under static test. Using ring specimen to determine tensile strength of rock material is more like a test indicator rather than the material properties.展开更多
The short lifespan of most commercial plastics as disposables and the failure to adequately address the end-of-life issues of synthetic polymers have led to outrageous global plastic pollution and resource depletion.T...The short lifespan of most commercial plastics as disposables and the failure to adequately address the end-of-life issues of synthetic polymers have led to outrageous global plastic pollution and resource depletion.To solve the problem,one of the most effective strategies is to develop circular polymers and thus establish a new circular material economy.Polymers from ring-opening polymerization of five-membered(thio)lactones contribute greatly to this field due to their excellent material performance and recyclability.The emerging topic emphasizes on the monomer design strategies based on five-membered(thio)lactones,and compares the thermal and mechanical properties and depolymerizability of the resulting polymers with different structures.展开更多
The influences of circular-ring turbulators （CRT） and twisted tape （TT） swirl generators on the heat transfer enhancement, pressure drop and thermal performance factor characteristics in a round tube are reported....The influences of circular-ring turbulators （CRT） and twisted tape （TT） swirl generators on the heat transfer enhancement, pressure drop and thermal performance factor characteristics in a round tube are reported. The circular-ring turbulators were individually employed and together with the twisted tape swirl generators in the heated section of the tube. Three different pitch ratios （I/D = 1.0, 1.5, and 2.0） of the CRT and three different twist ratios （y/W= 3, 4, and 5） of the TT were introduced. The experiments were conducted using air as the working fluid under a uniform wall heat flux condition, for the Reynolds number between 6000 and 20000. The experimental results reveal that the heat transfer rate, friction factor and thermal performance factor of the combined CRT and qT are considerably higher than those of CRT alone. For the range examined, the Sncreases of mean Nusselt number, friction factor and thermal performance, in the tube equipped with combined devices, respectively, are 25.8%, 82.8% and 6.3% over those in the tube with the CRT alone. The highest thermal performance factor of 1.42 is found for the combined device consisting of the CRT with l/D = 1.0 and TT with y/W= 3. The correlations of the Nusselt number, friction factor and thermal performance factor of the tubes with combined devices are also developed in terms of Reynolds number, Prandtl number, twist ratio and pitch ratio.展开更多
The influence of the width of the circular ring of a car cooling fan on the aerodynamic noise is investigated numerically through the determination of the overall sound pressure level(OASPL).The results demonstrate th...The influence of the width of the circular ring of a car cooling fan on the aerodynamic noise is investigated numerically through the determination of the overall sound pressure level(OASPL).The results demonstrate that when the circular rings cover near 2/3 of the width of the blade tips of the rotor in the axis direction,the rotor has the lowest OASPL and the related total pressure efficiency and flow mass rate are better than the corresponding values obtained for a reference rotor without a circular ring.With increasing the width of the circular ring in the axis direction,the tip vortex around the trailing edge of the blade tip becomes smaller and finally disappears.Meanwhile,a separated flow field arises gradually and then grows in size around the middle of the junction of the blade tips with the ring.When the circular rings cover nearly 2/3 s of the width of the blade tips of the fan in the axis direction,the extension of the separated flow around the blade’s tip attains a minimum.展开更多
基金National Natural Science Foundation of China(NSFC)(61331010,61205063)863 High Technology plan(2015AA016904)Program for New Century Excellent Talents in University(NCET)(NCET-13-0235)
文摘We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δn_(eff) between the adjacent guided modes could be kept larger than 1.32 × 10^(-4) over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF(14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.
基金Project(2015CB060200)supported by the National Basic Research Program of ChinaProject(51474250)supported by the National Natural Science Foundation of ChinaProject(2015JJ3166)supported by the Natural Science Foundation of Hunan Province,China
文摘Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external radius （ρ） under different loading rates. The results show that the dynamic tensile strength of disc rock specimen is approximately five times its static tensile strength. The failure modes of ring specimens are related to the dimension of the internal hole and loading rate. Under static loading tests, when the ratio of internal radius to external radius of the rock ring is small enough （ρ〈0.3）, specimens mostly split along the diametral loading line. With the increase of the ratio, the secondary cracks are formed in the direction perpendicular to the loading line. Under dynamic loading tests, specimens usually break up into four pieces. When the ratio ρreaches 0.5, the secondary cracks are formed near the input bar. The tensile strength calculated by Hobbs’ formula is greater than the Brazilian splitting strength. The peak load and the radius ratio show a negative exponential relationship under static test. Using ring specimen to determine tensile strength of rock material is more like a test indicator rather than the material properties.
基金supported by the National Natural Science Foundation of China(No.52173093)Peking University Ge Li and Ning Zhao Life Science Research Fund for Young Scientists.
文摘The short lifespan of most commercial plastics as disposables and the failure to adequately address the end-of-life issues of synthetic polymers have led to outrageous global plastic pollution and resource depletion.To solve the problem,one of the most effective strategies is to develop circular polymers and thus establish a new circular material economy.Polymers from ring-opening polymerization of five-membered(thio)lactones contribute greatly to this field due to their excellent material performance and recyclability.The emerging topic emphasizes on the monomer design strategies based on five-membered(thio)lactones,and compares the thermal and mechanical properties and depolymerizability of the resulting polymers with different structures.
文摘The influences of circular-ring turbulators （CRT） and twisted tape （TT） swirl generators on the heat transfer enhancement, pressure drop and thermal performance factor characteristics in a round tube are reported. The circular-ring turbulators were individually employed and together with the twisted tape swirl generators in the heated section of the tube. Three different pitch ratios （I/D = 1.0, 1.5, and 2.0） of the CRT and three different twist ratios （y/W= 3, 4, and 5） of the TT were introduced. The experiments were conducted using air as the working fluid under a uniform wall heat flux condition, for the Reynolds number between 6000 and 20000. The experimental results reveal that the heat transfer rate, friction factor and thermal performance factor of the combined CRT and qT are considerably higher than those of CRT alone. For the range examined, the Sncreases of mean Nusselt number, friction factor and thermal performance, in the tube equipped with combined devices, respectively, are 25.8%, 82.8% and 6.3% over those in the tube with the CRT alone. The highest thermal performance factor of 1.42 is found for the combined device consisting of the CRT with l/D = 1.0 and TT with y/W= 3. The correlations of the Nusselt number, friction factor and thermal performance factor of the tubes with combined devices are also developed in terms of Reynolds number, Prandtl number, twist ratio and pitch ratio.
基金supported by the Guiding Project of Scientific Research Plan of Hubei Education Department of China[Grant No.B2020227].
文摘The influence of the width of the circular ring of a car cooling fan on the aerodynamic noise is investigated numerically through the determination of the overall sound pressure level(OASPL).The results demonstrate that when the circular rings cover near 2/3 of the width of the blade tips of the rotor in the axis direction,the rotor has the lowest OASPL and the related total pressure efficiency and flow mass rate are better than the corresponding values obtained for a reference rotor without a circular ring.With increasing the width of the circular ring in the axis direction,the tip vortex around the trailing edge of the blade tip becomes smaller and finally disappears.Meanwhile,a separated flow field arises gradually and then grows in size around the middle of the junction of the blade tips with the ring.When the circular rings cover nearly 2/3 s of the width of the blade tips of the fan in the axis direction,the extension of the separated flow around the blade’s tip attains a minimum.
