Spin effect of the small diameter shaped charge results in the centrifugal stress during the jet stretching process. Consequently, the jet scatters, which deceases the jet penetration capability. In the present study,...Spin effect of the small diameter shaped charge results in the centrifugal stress during the jet stretching process. Consequently, the jet scatters, which deceases the jet penetration capability. In the present study, a multi-section method was proposed to design the spin-compensation liner. The spincompensation rate(SCR) of the liner was defined as the specific angular velocity that a fluted liner can offset. Based on the plain stress theory, SPH numerical method was applied to study the converging process of the 2D fluted structure. The spin-compensation mechanism of the fluted structure was illustrated. Then, nine cross sections were chosen along the liner axis equidistantly. On each of the section, a 2D fluted structure was designed to offset a given initial angular velocity. After, the optimized fluted structures were integrated into a 3D fluted liner. Jet appearances of the normal liner and the fluted liners under different initial angular velocities were compared, which verifies the practicality of the multi-sectional method. The multi-section optimization method provides a new efficient method of designing the shaped charge liner for a specific usage.展开更多
Fluted pumpkin(FP;Telfairia occidentalis)is an edible vegetable,grown in West Africa,that is used in traditional medicine for its regulatory effects on the male gonads.Scientific articles concerning the effects of FP ...Fluted pumpkin(FP;Telfairia occidentalis)is an edible vegetable,grown in West Africa,that is used in traditional medicine for its regulatory effects on the male gonads.Scientific articles concerning the effects of FP were identified by searching PubMed,PubChem,Scopus,Springer,ResearchGate,Google Scholar and Web of Science;this literature was to better understand the effects of FP seed(FPS)and leaf(FPL)extracts on the testes.Data showed that in experimental animals extracts of FPL and FPS at 1/100 of the lethal dose promoted testis regeneration and improved testosterone concentration and sperm quality,while at higher doses they had antifertility effects.Several extracts of FPS and FPL,including ethanol,aqueous,methanol and hydroethanolic,had protective effects on the testes of study animals at lower doses(>50 mg/kg body weight),but at higher doses(>200 mg/kg body weight)they inhibited hormone synthesis,sperm quality and histomorphological structure,under both normal and disease conditions.The posttreatment effects of FPS on the gonads were reversible in young mature rats and FPS had slight systemic toxic effects.Although,there are inconsistencies in some of the published results,the current evidence suggests that FPS and FPL have both profertility and reversible antifertility effects in experimental animals.展开更多
To improve the uniformity and accuracy of fertilizing amount for fertilizer applicators with spiral fluted roller,this paper experimentally studied the influence of major structural parameters on the fertilizing perfo...To improve the uniformity and accuracy of fertilizing amount for fertilizer applicators with spiral fluted roller,this paper experimentally studied the influence of major structural parameters on the fertilizing performance.Through two sets of orthogonal tests,it is found that the helix angle and installation angle of spiral fluted rollers are the main factors,which affect the uniformity of fertilizer discharge and the linear relationship between fertilizing amount and opening,respectively.Based on these findings,the experiment and analysis were carried out to determine the optimal helix angle and installation angle for the spiral fluted roller The experimental results of fertilizing performance show that:when the helix angle is 45°,it able to achieve satisfactory uniformity of fertilizer discharge and linear relationship between fertilizing amount and rotational speed;when the installation angle is 40°,it enhances the accuracy of fertilizer discharge with good linear relationship between fertilizing amount and opening.Compared with the fertilizing performance of traditional fertilizer applicators with horizontally installed straight fluted roller,in the aspect of uniformity,the optimized fertilizer applicators reduce the variation coefficient of fertilizing amount within 0.2 s at low speed(10-30 r/min)from 5.1%-52.5%to 4.2%-14.7%;in the aspect of accuracy;and increase the correlation coefficient square R2 between fertilizing amount and opening from 0.93-0.97 to no less than 0.996,and the regression intercept in the fitting equation is reduced from larger than 10.0 to less than 1.0.展开更多
The turbulence kinetic energy and heat transfer performance of air in spirally fluted tube were numerically studied at a constant wall temperature with Reynolds number(Re)between 5000 and 45000.Furthermore,the flow dy...The turbulence kinetic energy and heat transfer performance of air in spirally fluted tube were numerically studied at a constant wall temperature with Reynolds number(Re)between 5000 and 45000.Furthermore,the flow dynamics and heat transfer performance of spirally fluted tubes with five different geometric parameters as well as the effects of separation vortex and swirling wake flow on heat transfer and flow resistance were analyzed.According to the results,heat transfer is enhanced mainly because the fluid hit the windward side of the flute,thus generating a strong turbulence kinetic energy to further reconstruct the boundary layer.The second reason is that the formation of the recirculation zone between the flutes disturbs the boundary layer caused by the flow separation.With the increase of flute depth ratio(L_(d)/D),the separation vortex will become stronger and larger on the leeward side of flute.The separation vortex will break the boundary layer and improve the heat transfer capacity which is accompanied with the increase of fluid resistance.As the flute pitch length ratio(L_(p)/D)decreases,the spiral flow is strengthened,and meanwhile more wake flow is generated.The spiral flow causes little impact on enhancing heat transfer but inhibits the development of the separation vortex and fluid pulsation;in addition,the fluid resistance is reduced at the same time.The maximum value of the average Nusselt number appears when Re=5000,L_(d)/D=0.25 and L_(p)/D=1.00,which is 2.53 times the value of smooth tube.In view of the whole range of Reynolds number,the thermal performance enhancement factor indicates that L_(d)/D=0.15 and L_(p)/D=1.00 are the optimal geometric design parameters.展开更多
I have a wonderful family.We all like music very much.My mother is a music teacher.She is good at playing the piano and the violin.She also likes singing and she can sing many songs.My father is a doctor.He likes musi...I have a wonderful family.We all like music very much.My mother is a music teacher.She is good at playing the piano and the violin.She also likes singing and she can sing many songs.My father is a doctor.He likes music,too.After he comes back from work,he often listens to music.In fact,playing the flute and the erhu are his favorites.I enjoy playing the guitar though it's difficult to play.I practice playing it every day,so I can play it very well.I once won the second prize at a guitar concert in the city.But my sister thinks playing theguitar is boring.展开更多
Ammonia corrosion in copper tube will affect the safety of boiler running in power plant. Therefore, no copper in heating system has become a technical orientation in heat exchanger reconstruction, This paper analy...Ammonia corrosion in copper tube will affect the safety of boiler running in power plant. Therefore, no copper in heating system has become a technical orientation in heat exchanger reconstruction, This paper analyzes the condition and mechanism of ammonia corrosion occurring in copper tube used in coal-fired power plants. Using a general steam condensation testing equipment only for horizontal single tube, with water vapor and water as working fluid, on two types of steel tube with 2-side enhancement heat transfer, namely, a spirally fluted tube and a ratchet tube with internal spiral groove （RISG tube） which was developed recently, a set of experimental tests are conducted to investigate the characteristics of heat transfer and hydromeehanics. In order to compare easily, both one copper smooth tube and one steel smooth tube are also used in the experiment. The experimental results, which get from single horizontal tube, show that the overall heat transfer coefficient of steel spirally fluted tube are improved by 10%o to 17%, and that of the steel RISG tube（22%-28%） is better than steel spirally fluted tube, its flow resistance coefficient is only increased by 22% to 66% when compared with smooth tube. Based on a lot of experimental data, the steel spirally fluted tube and the steel RISG tube were applied in a low pressure preheater and an oil-cooler of some or other power plant respectively. The field testing results showed that their heat transfer coefficient with each types of enhancement heat transfer tubes were improved by 2.5% and 21%-45% comparing with copper smooth tube heat exchangers. Both basic and field experiment indicates that the steel tube with 2-side enhancement heat transfer is an ideal choice for heat exchanger reconstruction in no copper issue in power plants.展开更多
An evaluation of the incidence of Crypticerya multicicatrices and Maconellicoccus hirsutus in Colombian Seaflower Biosphere Reserve in San Andrés, Providence and Santa Catalina islands, from mid-August to mid-Nov...An evaluation of the incidence of Crypticerya multicicatrices and Maconellicoccus hirsutus in Colombian Seaflower Biosphere Reserve in San Andrés, Providence and Santa Catalina islands, from mid-August to mid-November 2012 was made. 38 locations were sampled, and 34% of sites tested show an incidence of C. multicicatrices oscillating between a range of 80%-100%, 24% with 40%-80% of incidence, 18% between 10%-40% and 24% with a range of 0%-10%. The occurrence of M. hirsutus fluctuated between 0.5% and 17%. There were seven genera of ants associated C. multicicatrices and 94 hosts of this agriculturally important insect and we found high incidence of associated sooty mold in C. multicicatrices hosts. Observations also contained some developmental stages of C. multicatrices.展开更多
To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear,the rake angles of the teeth on the pitch circle should be reduced.A method of forming the spiral flutes by ...To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear,the rake angles of the teeth on the pitch circle should be reduced.A method of forming the spiral flutes by using a variable transmission ratio was developed.This method ensures that the rake angles on the indexing torus of each tooth are approximately 0°.Based on the gear meshing theory and the hourglass worm forming method,the discretization mathematical model of the rake face of a planar double enveloping worm gear hob was established by using cylindrical generating surface,and the feed parameters for machining the rake face for a variable transmission ratio were obtained.The spiral flute was simulated and the hob was machined on a four axis CNC milling machine.A contourgraph was used to measure the rake angle.The measurement results showed that the proposed method can reduce the absolute value of the rake angle on both sides of the cutting teeth,which can be used for machining the spiral flute rake face of an hourglass worm gear hob.展开更多
The article is devoted to the study of spreading of the twisted yarn in a spinning cell. The article presents the scheme and principle of operation of the effective design of the yarn-output tube of pneumomechanical s...The article is devoted to the study of spreading of the twisted yarn in a spinning cell. The article presents the scheme and principle of operation of the effective design of the yarn-output tube of pneumomechanical spinning machine. To determine the law of motion of a roller installed in a yarn-output tube, the tension of the thread enveloping the surface of the rotating roller was studied, as a result of which the equation of its motion was obtained. As a result of solving the equation, the values of the thread tension on the surface of the rotating roller are obtained. The dependences of the change in the tension of the thread in time are obtained depending on the angle of rotation and the mass of the roller. The recommended design of the yarn-output tube allows increasing the strength characteristics of the pneumomechanical yarn.展开更多
Arthur Miller's Death of a Salesman takes advantage of the flute music to strengthen the atmosphere of stage, thus acoustically making people immerse the scene of the drama. The paper explores the conflicts and co...Arthur Miller's Death of a Salesman takes advantage of the flute music to strengthen the atmosphere of stage, thus acoustically making people immerse the scene of the drama. The paper explores the conflicts and connections in this drama through the flute music, such as work and family, agriculture and business, work and family.展开更多
The integration of reliable Video-on-Demand (VoD) broadcasting schemes in the DVB-h transmission system is studied, exemplary for Pyramid Broadcasting (PB). Sophisticated VoD broadcasting schemes such as PB allow rece...The integration of reliable Video-on-Demand (VoD) broadcasting schemes in the DVB-h transmission system is studied, exemplary for Pyramid Broadcasting (PB). Sophisticated VoD broadcasting schemes such as PB allow receivers to tune into the ongoing transmission of a video-stream at arbitrary time, while still being able to receive the multimedia sequence from the beginning to end, after a short initial playout latency. Raptor coding, integrated in the FLUTE protocol, is combined with the traditional PB scheme in order to provide high service and presentation reliability. We give a short overview on the DVB-h transmission system as well as on the FLUTE protocol. We present and discuss options for the integration of VoD broadcasting schemes in combination with Raptor coding. We achieve backward-compatibility even with terminals not supporting Raptor coding. Simulation results show the benefits of the discussed VoD scheme compared to existing carousel approaches in DVB-h.展开更多
Geometry of end mill cutters plays a vital role in the stability of the flexible parts milling.The present study considers helix angle and number of flutes.Multi-frequency solution is established to draw stability Lob...Geometry of end mill cutters plays a vital role in the stability of the flexible parts milling.The present study considers helix angle and number of flutes.Multi-frequency solution is established to draw stability Lobe diagram(SLD)for different helix angles and number of flutes.SLD for the two cases shows that the greater the value of helix angle,the more stable the milling process will be,and conversely increasing the number of flutes degrades the stability of flexible parts milling.A simple empirical methodology is adopted to employ the inclined plane workpiece geometry offering agradual increase of the axial depth of cut in the feed direction.Surface roughness is used as a measure of stability.Test results corroborate the model conclusions very well.展开更多
The manafacturing theory proposed in this paper is composed of the se-lection of the machining type(motions and adjustments)and the determination of thefunctions of motion parameters.The paper shows that the special r...The manafacturing theory proposed in this paper is composed of the se-lection of the machining type(motions and adjustments)and the determination of thefunctions of motion parameters.The paper shows that the special revolving tools withconstant spiral angled egdes can be ground in the[x y (?)]or[x y z (?)]systembased on the conjugate theory and differential geometry.The functions of motion pa-rameters in these two systems are deduced.展开更多
基金supported by the project of National Natural Science Foundation of China (NSFC, Grant No. 12032006)。
文摘Spin effect of the small diameter shaped charge results in the centrifugal stress during the jet stretching process. Consequently, the jet scatters, which deceases the jet penetration capability. In the present study, a multi-section method was proposed to design the spin-compensation liner. The spincompensation rate(SCR) of the liner was defined as the specific angular velocity that a fluted liner can offset. Based on the plain stress theory, SPH numerical method was applied to study the converging process of the 2D fluted structure. The spin-compensation mechanism of the fluted structure was illustrated. Then, nine cross sections were chosen along the liner axis equidistantly. On each of the section, a 2D fluted structure was designed to offset a given initial angular velocity. After, the optimized fluted structures were integrated into a 3D fluted liner. Jet appearances of the normal liner and the fluted liners under different initial angular velocities were compared, which verifies the practicality of the multi-sectional method. The multi-section optimization method provides a new efficient method of designing the shaped charge liner for a specific usage.
文摘Fluted pumpkin(FP;Telfairia occidentalis)is an edible vegetable,grown in West Africa,that is used in traditional medicine for its regulatory effects on the male gonads.Scientific articles concerning the effects of FP were identified by searching PubMed,PubChem,Scopus,Springer,ResearchGate,Google Scholar and Web of Science;this literature was to better understand the effects of FP seed(FPS)and leaf(FPL)extracts on the testes.Data showed that in experimental animals extracts of FPL and FPS at 1/100 of the lethal dose promoted testis regeneration and improved testosterone concentration and sperm quality,while at higher doses they had antifertility effects.Several extracts of FPS and FPL,including ethanol,aqueous,methanol and hydroethanolic,had protective effects on the testes of study animals at lower doses(>50 mg/kg body weight),but at higher doses(>200 mg/kg body weight)they inhibited hormone synthesis,sperm quality and histomorphological structure,under both normal and disease conditions.The posttreatment effects of FPS on the gonads were reversible in young mature rats and FPS had slight systemic toxic effects.Although,there are inconsistencies in some of the published results,the current evidence suggests that FPS and FPL have both profertility and reversible antifertility effects in experimental animals.
基金that this work was financially supported by the National Key Research and Development Program of China(Grant No.2021YFD2000403)the National Natural Science Foundation of China(Grant No.32372002)Guangzhou Basic and Applied Basic Research Project(Grant No.202102020870).
文摘To improve the uniformity and accuracy of fertilizing amount for fertilizer applicators with spiral fluted roller,this paper experimentally studied the influence of major structural parameters on the fertilizing performance.Through two sets of orthogonal tests,it is found that the helix angle and installation angle of spiral fluted rollers are the main factors,which affect the uniformity of fertilizer discharge and the linear relationship between fertilizing amount and opening,respectively.Based on these findings,the experiment and analysis were carried out to determine the optimal helix angle and installation angle for the spiral fluted roller The experimental results of fertilizing performance show that:when the helix angle is 45°,it able to achieve satisfactory uniformity of fertilizer discharge and linear relationship between fertilizing amount and rotational speed;when the installation angle is 40°,it enhances the accuracy of fertilizer discharge with good linear relationship between fertilizing amount and opening.Compared with the fertilizing performance of traditional fertilizer applicators with horizontally installed straight fluted roller,in the aspect of uniformity,the optimized fertilizer applicators reduce the variation coefficient of fertilizing amount within 0.2 s at low speed(10-30 r/min)from 5.1%-52.5%to 4.2%-14.7%;in the aspect of accuracy;and increase the correlation coefficient square R2 between fertilizing amount and opening from 0.93-0.97 to no less than 0.996,and the regression intercept in the fitting equation is reduced from larger than 10.0 to less than 1.0.
基金This work was supported by the National Key Research and Development Program of China(Grant No.2018YFE0196000)IWHR Basic Scientific Research Projects(No.MK2018J09,No.MK2020J06).
文摘The turbulence kinetic energy and heat transfer performance of air in spirally fluted tube were numerically studied at a constant wall temperature with Reynolds number(Re)between 5000 and 45000.Furthermore,the flow dynamics and heat transfer performance of spirally fluted tubes with five different geometric parameters as well as the effects of separation vortex and swirling wake flow on heat transfer and flow resistance were analyzed.According to the results,heat transfer is enhanced mainly because the fluid hit the windward side of the flute,thus generating a strong turbulence kinetic energy to further reconstruct the boundary layer.The second reason is that the formation of the recirculation zone between the flutes disturbs the boundary layer caused by the flow separation.With the increase of flute depth ratio(L_(d)/D),the separation vortex will become stronger and larger on the leeward side of flute.The separation vortex will break the boundary layer and improve the heat transfer capacity which is accompanied with the increase of fluid resistance.As the flute pitch length ratio(L_(p)/D)decreases,the spiral flow is strengthened,and meanwhile more wake flow is generated.The spiral flow causes little impact on enhancing heat transfer but inhibits the development of the separation vortex and fluid pulsation;in addition,the fluid resistance is reduced at the same time.The maximum value of the average Nusselt number appears when Re=5000,L_(d)/D=0.25 and L_(p)/D=1.00,which is 2.53 times the value of smooth tube.In view of the whole range of Reynolds number,the thermal performance enhancement factor indicates that L_(d)/D=0.15 and L_(p)/D=1.00 are the optimal geometric design parameters.
文摘I have a wonderful family.We all like music very much.My mother is a music teacher.She is good at playing the piano and the violin.She also likes singing and she can sing many songs.My father is a doctor.He likes music,too.After he comes back from work,he often listens to music.In fact,playing the flute and the erhu are his favorites.I enjoy playing the guitar though it's difficult to play.I practice playing it every day,so I can play it very well.I once won the second prize at a guitar concert in the city.But my sister thinks playing theguitar is boring.
文摘Ammonia corrosion in copper tube will affect the safety of boiler running in power plant. Therefore, no copper in heating system has become a technical orientation in heat exchanger reconstruction, This paper analyzes the condition and mechanism of ammonia corrosion occurring in copper tube used in coal-fired power plants. Using a general steam condensation testing equipment only for horizontal single tube, with water vapor and water as working fluid, on two types of steel tube with 2-side enhancement heat transfer, namely, a spirally fluted tube and a ratchet tube with internal spiral groove （RISG tube） which was developed recently, a set of experimental tests are conducted to investigate the characteristics of heat transfer and hydromeehanics. In order to compare easily, both one copper smooth tube and one steel smooth tube are also used in the experiment. The experimental results, which get from single horizontal tube, show that the overall heat transfer coefficient of steel spirally fluted tube are improved by 10%o to 17%, and that of the steel RISG tube（22%-28%） is better than steel spirally fluted tube, its flow resistance coefficient is only increased by 22% to 66% when compared with smooth tube. Based on a lot of experimental data, the steel spirally fluted tube and the steel RISG tube were applied in a low pressure preheater and an oil-cooler of some or other power plant respectively. The field testing results showed that their heat transfer coefficient with each types of enhancement heat transfer tubes were improved by 2.5% and 21%-45% comparing with copper smooth tube heat exchangers. Both basic and field experiment indicates that the steel tube with 2-side enhancement heat transfer is an ideal choice for heat exchanger reconstruction in no copper issue in power plants.
文摘An evaluation of the incidence of Crypticerya multicicatrices and Maconellicoccus hirsutus in Colombian Seaflower Biosphere Reserve in San Andrés, Providence and Santa Catalina islands, from mid-August to mid-November 2012 was made. 38 locations were sampled, and 34% of sites tested show an incidence of C. multicicatrices oscillating between a range of 80%-100%, 24% with 40%-80% of incidence, 18% between 10%-40% and 24% with a range of 0%-10%. The occurrence of M. hirsutus fluctuated between 0.5% and 17%. There were seven genera of ants associated C. multicicatrices and 94 hosts of this agriculturally important insect and we found high incidence of associated sooty mold in C. multicicatrices hosts. Observations also contained some developmental stages of C. multicatrices.
基金supported by the National Natural Science Foundation of China (No. 51475460)
文摘To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear,the rake angles of the teeth on the pitch circle should be reduced.A method of forming the spiral flutes by using a variable transmission ratio was developed.This method ensures that the rake angles on the indexing torus of each tooth are approximately 0°.Based on the gear meshing theory and the hourglass worm forming method,the discretization mathematical model of the rake face of a planar double enveloping worm gear hob was established by using cylindrical generating surface,and the feed parameters for machining the rake face for a variable transmission ratio were obtained.The spiral flute was simulated and the hob was machined on a four axis CNC milling machine.A contourgraph was used to measure the rake angle.The measurement results showed that the proposed method can reduce the absolute value of the rake angle on both sides of the cutting teeth,which can be used for machining the spiral flute rake face of an hourglass worm gear hob.
文摘The article is devoted to the study of spreading of the twisted yarn in a spinning cell. The article presents the scheme and principle of operation of the effective design of the yarn-output tube of pneumomechanical spinning machine. To determine the law of motion of a roller installed in a yarn-output tube, the tension of the thread enveloping the surface of the rotating roller was studied, as a result of which the equation of its motion was obtained. As a result of solving the equation, the values of the thread tension on the surface of the rotating roller are obtained. The dependences of the change in the tension of the thread in time are obtained depending on the angle of rotation and the mass of the roller. The recommended design of the yarn-output tube allows increasing the strength characteristics of the pneumomechanical yarn.
文摘Arthur Miller's Death of a Salesman takes advantage of the flute music to strengthen the atmosphere of stage, thus acoustically making people immerse the scene of the drama. The paper explores the conflicts and connections in this drama through the flute music, such as work and family, agriculture and business, work and family.
文摘The integration of reliable Video-on-Demand (VoD) broadcasting schemes in the DVB-h transmission system is studied, exemplary for Pyramid Broadcasting (PB). Sophisticated VoD broadcasting schemes such as PB allow receivers to tune into the ongoing transmission of a video-stream at arbitrary time, while still being able to receive the multimedia sequence from the beginning to end, after a short initial playout latency. Raptor coding, integrated in the FLUTE protocol, is combined with the traditional PB scheme in order to provide high service and presentation reliability. We give a short overview on the DVB-h transmission system as well as on the FLUTE protocol. We present and discuss options for the integration of VoD broadcasting schemes in combination with Raptor coding. We achieve backward-compatibility even with terminals not supporting Raptor coding. Simulation results show the benefits of the discussed VoD scheme compared to existing carousel approaches in DVB-h.
文摘Geometry of end mill cutters plays a vital role in the stability of the flexible parts milling.The present study considers helix angle and number of flutes.Multi-frequency solution is established to draw stability Lobe diagram(SLD)for different helix angles and number of flutes.SLD for the two cases shows that the greater the value of helix angle,the more stable the milling process will be,and conversely increasing the number of flutes degrades the stability of flexible parts milling.A simple empirical methodology is adopted to employ the inclined plane workpiece geometry offering agradual increase of the axial depth of cut in the feed direction.Surface roughness is used as a measure of stability.Test results corroborate the model conclusions very well.
文摘The manafacturing theory proposed in this paper is composed of the se-lection of the machining type(motions and adjustments)and the determination of thefunctions of motion parameters.The paper shows that the special revolving tools withconstant spiral angled egdes can be ground in the[x y (?)]or[x y z (?)]systembased on the conjugate theory and differential geometry.The functions of motion pa-rameters in these two systems are deduced.
