The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducin...The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducing the energy consumption of reproduction or other costly tissues should compensate for the cost of a large brain.Egg production in birds requires a large proportion of the total energy budget,and a clutch mass in some bird species can outweigh the body mass of the female.To date,this hypothesis has mainly been tested in mammals and ectothermic animals such as anurans and fishes.We collated data on adult brain size,body mass and eggproduction traits such as clutch size,egg mass and annual broods from published studies,and conducted a phylogenetic comparative test of the interplay between egg-production investment and brain size evolution across bird species.After controlling for phylogenetic relationships and body size,we find a negative correlation between brain size and clutch size across 1395 species,which favored ETH.However,when egg mass was integrated in models,positive associations were detected between brain size and mass of eggs(via egg mass,clutch mass and annual total egg mass).Our results suggest that brain size trades off against egg-production only via certain aspects(e.g.,clutch size).By contrast,a positive relationship between brain size and total egg reproduction(e.g.,clutch mass and annual total egg mass) implied increased total energy budget outweighing energy allocation across bird species.Our study shows that there is no general energy trade-off between brain size and eggreproduction investment,and suggests that brain size evolution follows mixed strategies across bird species.展开更多
Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equiva...Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equivalent radius is a function of clutch speed and flow rate. The drag torque achieves its peak at a critical speed. Above this speed, drag torque drops due to the shrinking of the oil film. The model also points out that viscosity and flow rate effects on drag torque. Experimental results indicate that the model is reason-able and it performs well for predicting the drag torque peak.展开更多
Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the fricti...Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the friction behavior may occur and make the actuation of the clutch challenging.This transcript describes the typical running-in behavior of wet multi-plate clutches and gives a general definition for running-in of clutches.Moreover,a new test method to systematically investigate the running-in behavior of clutches is introduced.This test method contains a test procedure to characterize the running-in behavior on different load levels.Furthermore,a multi-stage procedure to evaluate and characterize the running-in behavior of clutches with mathematical approaches and new characteristic values is given.The quality of the test method is demonstrated on the example of three different tribological systems from dual clutch transmissions(DCT)and automatic transmissions(AT)application using paper friction linings.展开更多
The diaphragm spring clutch static characteristics to improve the starting quality for cars equipped with automated mechanical transmission （AMT） were modeled and simulated. First, axial stiffness of clutch cushion ...The diaphragm spring clutch static characteristics to improve the starting quality for cars equipped with automated mechanical transmission （AMT） were modeled and simulated. First, axial stiffness of clutch cushion spring and characteristic curves of diaphragm spring were theoretically and experimentally studied. Then, model of transfer characteristics of the normal force was built, with special conscen on the abrasion of friction discs and the influence of temperature to diaphragm spring. Finally, the model was tested in practical starting for cars equipped with AMT, which showed that the starting quality was significantly improved. The experimental results showed that the proposed model was precise enough to be implemented conveniently.展开更多
The effects of contact surface on dynamic wedging behavior of the roller and inner-ring of the overrunning clutch in a dual-turbine torque converter were investigated to reveal the friction self- locking mechanism and...The effects of contact surface on dynamic wedging behavior of the roller and inner-ring of the overrunning clutch in a dual-turbine torque converter were investigated to reveal the friction self- locking mechanism and dynamic process. Planar strain clutch models including roller, inner-ring and outer-ring were built, and transient wedging process was analyzed with an explicit dynamics meth- od. The modeling of stress and strain distribution and variation of two kinds of contact surfaces show that there are three stages named slipping, wedging and binding respectively during whole wed- ging process. Meanwhile the geometric structures of contact surfaces greatly influence the peak stress and strain distribution of the wedging process of the roller and inner-ring. The load bearing performance of contact surfaces with logarithmic spiral curve is better than that with straight line. Our study provides theoretical foundation for design and further optimization of wedging contact surface of an overrunning clutch in a dual-turbine hydrodynamic torque converter.展开更多
Traditional mathematical models cannot predict and explain the phenomenon by which the drag torque(DT)in wet clutches rises in the high-speed zone.In order to evaluate the DT in such conditions,a two-phase air-fluid m...Traditional mathematical models cannot predict and explain the phenomenon by which the drag torque(DT)in wet clutches rises in the high-speed zone.In order to evaluate the DT in such conditions,a two-phase air-fluid mathematical model for a DT with grooves was elaborated.The mathematical model was based on the theory of viscous fluid flow.A two-phase volume of fluid model was also used to investigate the distribution and volume fraction of air and fluid.Experiments on three friction plates with different grooves were conducted to validate the resulting mathematical model.It was found that the gap between plates decreased in the high-speed zone,thereby producing an increase of the DT in the high-speed zone.These results support the understanding of the physical phenomena relating to disengaged wet clutches,and provide a theoretical basis for the future improvement of drive systems.展开更多
Weather conditions play a pivotal role in embryo development and parental incubation costs,potentially impacting the clutch size and incubation behavior of birds.Understanding these effects is crucial for bird conserv...Weather conditions play a pivotal role in embryo development and parental incubation costs,potentially impacting the clutch size and incubation behavior of birds.Understanding these effects is crucial for bird conservation.Reeves’ s Pheasant(Syrmaticus reevesii) is a threatened species endemic to China,which is characterized by female-only incubation.However,there is a lack of information regarding the impact of weather conditions on clutch size and incubation behavior in this species.Using satellite tracking,we tracked 27 wild female Reeves’ s Pheasants from 2020 to 2023 in Hubei Province,China.We explored their clutch size and incubation behavior,as well as their responses to ambient temperature and precipitation.Clutch size averaged 7.75 ±1.36,had an association with average ambient temperature and average daily precipitation during the egglaying period,and was potentially linked to female breeding attempts.Throughout the incubation period,females took an average of 0.73 ±0.46 recesses every 24 h,with an average recess duration of 100.80 ±73.37 min and an average nest attendance of 92.98 ±5.27%.They showed a unimodal recess pattern in which nest departures peaked primarily between 13:00 and 16:00.Furthermore,females rarely left nests when daily precipitation was high.Recess duration and nest attendance were influenced by the interaction between daily mean ambient temperature and daily precipitation,as well as day of incubation.Additionally,there was a positive correlation between clutch size and recess duration.These results contribute valuable insights into the lifehistory features of this endangered species.展开更多
According to the statistics, there are about 90 auto clutch assembly and its main parts manufacturers now in China. Before 1985, the main products of these clutch plants were helical spring clutches for truck OE and s...According to the statistics, there are about 90 auto clutch assembly and its main parts manufacturers now in China. Before 1985, the main products of these clutch plants were helical spring clutches for truck OE and service markets. Their production scale was limited and facilities and technological process level were low. Since 1985, Changchun No.228 Factory, Clutch Plant of Nanjing Automobile Works, Shanghai General Plant of Auto展开更多
A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphr...A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral-derivative(PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.展开更多
The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline.In this research,the judder characteristics of automobile clutch friction materials and experimental ...The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline.In this research,the judder characteristics of automobile clutch friction materials and experimental verification are studied.First,considering the stick-slip phenomenon in the clutch engagement process,a detailed 9-degrees-of-freedom(DOF)model including the body,each cylinder of the engine,clutch and friction lining,torsional damper,transmission and other driveline parts is established,and the calculation formula of friction torque in the clutch engagement process is determined.Second,the influence of the friction gradient characteristics on the amplification or attenuation of the automobile friction judder is analyzed,and the corresponding stability analysis and the numerical simulation of different friction gradient values are carried out with MATLAB/Simulink software.Finally,judder bench test equipment and a corresponding damping test program are developed,and the relationship between the friction coefficient gradient characteristics and the system damping is analyzed.After a large number of tests,the evaluation basis of the test is determined.The research results show that the friction lining with negative gradient characteristics of the friction coefficient will have a judder signal.When the friction gradient value is less than-0.005 s/m,the judder signal of the measured clutch cannot be completely attenuated,and the judder phenomenon occurs.When the friction gradient is greater than-0.005 s/m,the judder signal can be significantly suppressed and the system connection tends to be stable.展开更多
The breeding traits of Sporophila seedeaters have been relatively well studied in recent years;nevertheless,a group of ten species in the genus,known as southern capuchinos,remain understudied.That is the case with Ch...The breeding traits of Sporophila seedeaters have been relatively well studied in recent years;nevertheless,a group of ten species in the genus,known as southern capuchinos,remain understudied.That is the case with Chestnut Seedeater(Sporophila cinnamomea),a species vulnerable to extinction,which breeds in the grasslands of southeast South America and,after reproduction,migrates towards the Cerrado region in central Brazil.Here,we investigated breeding ecology and calculated average clutch size,productivity,the sex ratio of nestlings,and estimated nest success.Then we tested(1)whether there is a relationship between the number of active nests and environmental variables,(2)whether the nestling sex ratio deviates from the 1:1 ratio,(3)whether clutch size varies between breeding seasons,and(4)whether the nest success is related to starting date,nest age,plant support,nest height from the ground,and clutch size.During two breeding seasons(October-March 2018-2020),we monitored 98 nests.We generated survival models with five interacting covariates to assess the survival of the nests.We recorded the entire breeding period for Chestnut Seedeater,which was estimated to be 4.6 months,similar to other migratory seedeaters.Clutch size did not differ between breeding seasons.The sex ratio of nestlings was not significantly different from the 1:1 ratio.Nest success was 31%,and predation was the leading cause of unsuccessful nests(83%).The daily survival rate was 0.95±0.01.The main predictor of nest survival was the covariate starting date.These findings,added to other aspects of the species’natural history described here,may help illuminate the ecology and behavior of Chestnut Seedeater and other southern endangered capuchinos,and grassland-dependent species of South America.展开更多
Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the di...Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates.Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model.Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force,but was also based on full oil film in the gap,which resulted difference between model prediction and experimental data.The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification.An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate.A high speed camera was used to record the flow pattern through transparent quartz disk plate.The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking.Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking.Meanwhile,drag torque decreases sharply due to little contact area between the stationary plate and the oil.A three-dimensional Navier-Stokes （N-S） equation based on laminar flow is presented to model the drag torque.Pressure distributions in radial and circumferential directions as well as speed distributions are deduced.The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate.An approach to descript flow pattern was presented on the basis of visual observation.The drag torque predicted by the model agrees well with test data for non-grooved wet clutch.The proposed model enhances the precision for predicting drag torque,and lays down a framework on which some subsequent models are developed.展开更多
The present study aims to determine,by histological examination,the female reproductive cycle of specimens of Kulzer’s rock lizards collected in a mountainous region in Lebanon.Females of Phoenicolacerta kulzeri foll...The present study aims to determine,by histological examination,the female reproductive cycle of specimens of Kulzer’s rock lizards collected in a mountainous region in Lebanon.Females of Phoenicolacerta kulzeri followed a seasonal reproductive pattern.Winter hibernation period lasted for 5 months.Females of P.Kulzeri exhibited a reproductive activity during spring characterized by the presence of vitellogenic follicles in the ovaries and eggs in the oviducts.Oviposition occurred throughout the springtime.Up to two clutches were produced with an average clutch size of 2.9 eggs.Clutch size was significantly correlated to female body size.The attainment of sexual maturity was at a minimum size of 46 mm snout-vent length.The mean body size of adult females was 55.0 mm and did not differ significantly from that of adult males.Females showed a period of sexual rest in summer and none of them showed a reproductive activity in autumn.The female reproductive activity of P.kulzeri was well-synchronized with that of the males in spring;however,an autumnal asynchrony was observed between the female and male reproductive cycles,since males continued to exhibit a spermatogenetic activity.展开更多
Start-up working condition is the key to the research of optimal engagementof automatic clutch for AMT. In order to guarantee an ideal dynamic performance of the clutchengagement, an optimal controller is designed by ...Start-up working condition is the key to the research of optimal engagementof automatic clutch for AMT. In order to guarantee an ideal dynamic performance of the clutchengagement, an optimal controller is designed by considering throttle angle, engine speed, gearratio, vehicle acceleration and road condition. The minimum value principle is also introduced toachieve an optimal dynamic performance of the nonlinear system compromised in friction plate wearand vehicle drive quality. The optimal trajectory of the clutch engagement can be described in theform of explicit and analytical expressions and characterized by the deterministic and accuratecontrol strategy in stead of indeterministic and soft control techniques which need thousands ofexperiments. For validation of the controller, test work is carried out for the automated clutchengagements in a commercial car with an traditional mechanical transmission, a hydraulic actuator, agroup of sensors and a portable computer system. It is shown through experiments that dynamicbehaviors of the clutch engagement operated by the optimal control are more effective and efficientthan those by fuzzy control.展开更多
基金National Natural Science Foun-dation of China(Grant No.32170481 and Grant No.3221153042).
文摘The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducing the energy consumption of reproduction or other costly tissues should compensate for the cost of a large brain.Egg production in birds requires a large proportion of the total energy budget,and a clutch mass in some bird species can outweigh the body mass of the female.To date,this hypothesis has mainly been tested in mammals and ectothermic animals such as anurans and fishes.We collated data on adult brain size,body mass and eggproduction traits such as clutch size,egg mass and annual broods from published studies,and conducted a phylogenetic comparative test of the interplay between egg-production investment and brain size evolution across bird species.After controlling for phylogenetic relationships and body size,we find a negative correlation between brain size and clutch size across 1395 species,which favored ETH.However,when egg mass was integrated in models,positive associations were detected between brain size and mass of eggs(via egg mass,clutch mass and annual total egg mass).Our results suggest that brain size trades off against egg-production only via certain aspects(e.g.,clutch size).By contrast,a positive relationship between brain size and total egg reproduction(e.g.,clutch mass and annual total egg mass) implied increased total energy budget outweighing energy allocation across bird species.Our study shows that there is no general energy trade-off between brain size and eggreproduction investment,and suggests that brain size evolution follows mixed strategies across bird species.
基金Sponsored by the Ministerial Level Advanced Research Foundation(10506024)
文摘Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equivalent radius is a function of clutch speed and flow rate. The drag torque achieves its peak at a critical speed. Above this speed, drag torque drops due to the shrinking of the oil film. The model also points out that viscosity and flow rate effects on drag torque. Experimental results indicate that the model is reason-able and it performs well for predicting the drag torque peak.
基金The presented results are based on the research project FVA no.343/Ⅲ undertaken by the Research Association for Drive Technology e.V.(FVA).
文摘Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the friction behavior may occur and make the actuation of the clutch challenging.This transcript describes the typical running-in behavior of wet multi-plate clutches and gives a general definition for running-in of clutches.Moreover,a new test method to systematically investigate the running-in behavior of clutches is introduced.This test method contains a test procedure to characterize the running-in behavior on different load levels.Furthermore,a multi-stage procedure to evaluate and characterize the running-in behavior of clutches with mathematical approaches and new characteristic values is given.The quality of the test method is demonstrated on the example of three different tribological systems from dual clutch transmissions(DCT)and automatic transmissions(AT)application using paper friction linings.
基金Supported by the National Natural Science Foundation of China(51275038)
文摘The diaphragm spring clutch static characteristics to improve the starting quality for cars equipped with automated mechanical transmission （AMT） were modeled and simulated. First, axial stiffness of clutch cushion spring and characteristic curves of diaphragm spring were theoretically and experimentally studied. Then, model of transfer characteristics of the normal force was built, with special conscen on the abrasion of friction discs and the influence of temperature to diaphragm spring. Finally, the model was tested in practical starting for cars equipped with AMT, which showed that the starting quality was significantly improved. The experimental results showed that the proposed model was precise enough to be implemented conveniently.
基金Supported by the National Natural Science Foundation of China(51475041)the Ministerial Level Advanced Research Foundation(40402060103)the Ministerial Basic Products Innovation Program(VTDP2104)
文摘The effects of contact surface on dynamic wedging behavior of the roller and inner-ring of the overrunning clutch in a dual-turbine torque converter were investigated to reveal the friction self- locking mechanism and dynamic process. Planar strain clutch models including roller, inner-ring and outer-ring were built, and transient wedging process was analyzed with an explicit dynamics meth- od. The modeling of stress and strain distribution and variation of two kinds of contact surfaces show that there are three stages named slipping, wedging and binding respectively during whole wed- ging process. Meanwhile the geometric structures of contact surfaces greatly influence the peak stress and strain distribution of the wedging process of the roller and inner-ring. The load bearing performance of contact surfaces with logarithmic spiral curve is better than that with straight line. Our study provides theoretical foundation for design and further optimization of wedging contact surface of an overrunning clutch in a dual-turbine hydrodynamic torque converter.
基金support from the research project of basic product innovation of MIIT(VTDP3203).
文摘Traditional mathematical models cannot predict and explain the phenomenon by which the drag torque(DT)in wet clutches rises in the high-speed zone.In order to evaluate the DT in such conditions,a two-phase air-fluid mathematical model for a DT with grooves was elaborated.The mathematical model was based on the theory of viscous fluid flow.A two-phase volume of fluid model was also used to investigate the distribution and volume fraction of air and fluid.Experiments on three friction plates with different grooves were conducted to validate the resulting mathematical model.It was found that the gap between plates decreased in the high-speed zone,thereby producing an increase of the DT in the high-speed zone.These results support the understanding of the physical phenomena relating to disengaged wet clutches,and provide a theoretical basis for the future improvement of drive systems.
基金supported by the National Natural Science Foundation of China (grant number 31872240)。
文摘Weather conditions play a pivotal role in embryo development and parental incubation costs,potentially impacting the clutch size and incubation behavior of birds.Understanding these effects is crucial for bird conservation.Reeves’ s Pheasant(Syrmaticus reevesii) is a threatened species endemic to China,which is characterized by female-only incubation.However,there is a lack of information regarding the impact of weather conditions on clutch size and incubation behavior in this species.Using satellite tracking,we tracked 27 wild female Reeves’ s Pheasants from 2020 to 2023 in Hubei Province,China.We explored their clutch size and incubation behavior,as well as their responses to ambient temperature and precipitation.Clutch size averaged 7.75 ±1.36,had an association with average ambient temperature and average daily precipitation during the egglaying period,and was potentially linked to female breeding attempts.Throughout the incubation period,females took an average of 0.73 ±0.46 recesses every 24 h,with an average recess duration of 100.80 ±73.37 min and an average nest attendance of 92.98 ±5.27%.They showed a unimodal recess pattern in which nest departures peaked primarily between 13:00 and 16:00.Furthermore,females rarely left nests when daily precipitation was high.Recess duration and nest attendance were influenced by the interaction between daily mean ambient temperature and daily precipitation,as well as day of incubation.Additionally,there was a positive correlation between clutch size and recess duration.These results contribute valuable insights into the lifehistory features of this endangered species.
文摘According to the statistics, there are about 90 auto clutch assembly and its main parts manufacturers now in China. Before 1985, the main products of these clutch plants were helical spring clutches for truck OE and service markets. Their production scale was limited and facilities and technological process level were low. Since 1985, Changchun No.228 Factory, Clutch Plant of Nanjing Automobile Works, Shanghai General Plant of Auto
基金the National Natural Science Foundation of China(No.51475284)
文摘A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral-derivative(PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.
基金Supported by National Natural Science Foundation of China (Grant No.51775249)。
文摘The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline.In this research,the judder characteristics of automobile clutch friction materials and experimental verification are studied.First,considering the stick-slip phenomenon in the clutch engagement process,a detailed 9-degrees-of-freedom(DOF)model including the body,each cylinder of the engine,clutch and friction lining,torsional damper,transmission and other driveline parts is established,and the calculation formula of friction torque in the clutch engagement process is determined.Second,the influence of the friction gradient characteristics on the amplification or attenuation of the automobile friction judder is analyzed,and the corresponding stability analysis and the numerical simulation of different friction gradient values are carried out with MATLAB/Simulink software.Finally,judder bench test equipment and a corresponding damping test program are developed,and the relationship between the friction coefficient gradient characteristics and the system damping is analyzed.After a large number of tests,the evaluation basis of the test is determined.The research results show that the friction lining with negative gradient characteristics of the friction coefficient will have a judder signal.When the friction gradient value is less than-0.005 s/m,the judder signal of the measured clutch cannot be completely attenuated,and the judder phenomenon occurs.When the friction gradient is greater than-0.005 s/m,the judder signal can be significantly suppressed and the system connection tends to be stable.
基金part of the project"Neotropical Grasslands Connection:Ecology,Migration,and Conservation of the Threatened Chestnut Seedeater Sporophila cinnamomea",supported by the Rufford Foundation,United Kingdom(ID 270441)supported by grants to JRRR and CJC,who received doctoral and postdoctoral fellowships,respectively,from the Coordenacão de Aperfeicoamento de Pessoal de Nível Superior-CAPES(88882.439380/2019-01 and 88882.316294/2019-01)a research grant from the Conselho Nacional de Desenvolvimento Científico e Tecnológico-CNPq(310608/2019-8)。
文摘The breeding traits of Sporophila seedeaters have been relatively well studied in recent years;nevertheless,a group of ten species in the genus,known as southern capuchinos,remain understudied.That is the case with Chestnut Seedeater(Sporophila cinnamomea),a species vulnerable to extinction,which breeds in the grasslands of southeast South America and,after reproduction,migrates towards the Cerrado region in central Brazil.Here,we investigated breeding ecology and calculated average clutch size,productivity,the sex ratio of nestlings,and estimated nest success.Then we tested(1)whether there is a relationship between the number of active nests and environmental variables,(2)whether the nestling sex ratio deviates from the 1:1 ratio,(3)whether clutch size varies between breeding seasons,and(4)whether the nest success is related to starting date,nest age,plant support,nest height from the ground,and clutch size.During two breeding seasons(October-March 2018-2020),we monitored 98 nests.We generated survival models with five interacting covariates to assess the survival of the nests.We recorded the entire breeding period for Chestnut Seedeater,which was estimated to be 4.6 months,similar to other migratory seedeaters.Clutch size did not differ between breeding seasons.The sex ratio of nestlings was not significantly different from the 1:1 ratio.Nest success was 31%,and predation was the leading cause of unsuccessful nests(83%).The daily survival rate was 0.95±0.01.The main predictor of nest survival was the covariate starting date.These findings,added to other aspects of the species’natural history described here,may help illuminate the ecology and behavior of Chestnut Seedeater and other southern endangered capuchinos,and grassland-dependent species of South America.
基金supported by National Defense Arming Pre-researching Project of China(Grant No.40402060102)
文摘Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates.Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model.Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force,but was also based on full oil film in the gap,which resulted difference between model prediction and experimental data.The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification.An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate.A high speed camera was used to record the flow pattern through transparent quartz disk plate.The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking.Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking.Meanwhile,drag torque decreases sharply due to little contact area between the stationary plate and the oil.A three-dimensional Navier-Stokes （N-S） equation based on laminar flow is presented to model the drag torque.Pressure distributions in radial and circumferential directions as well as speed distributions are deduced.The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate.An approach to descript flow pattern was presented on the basis of visual observation.The drag torque predicted by the model agrees well with test data for non-grooved wet clutch.The proposed model enhances the precision for predicting drag torque,and lays down a framework on which some subsequent models are developed.
文摘The present study aims to determine,by histological examination,the female reproductive cycle of specimens of Kulzer’s rock lizards collected in a mountainous region in Lebanon.Females of Phoenicolacerta kulzeri followed a seasonal reproductive pattern.Winter hibernation period lasted for 5 months.Females of P.Kulzeri exhibited a reproductive activity during spring characterized by the presence of vitellogenic follicles in the ovaries and eggs in the oviducts.Oviposition occurred throughout the springtime.Up to two clutches were produced with an average clutch size of 2.9 eggs.Clutch size was significantly correlated to female body size.The attainment of sexual maturity was at a minimum size of 46 mm snout-vent length.The mean body size of adult females was 55.0 mm and did not differ significantly from that of adult males.Females showed a period of sexual rest in summer and none of them showed a reproductive activity in autumn.The female reproductive activity of P.kulzeri was well-synchronized with that of the males in spring;however,an autumnal asynchrony was observed between the female and male reproductive cycles,since males continued to exhibit a spermatogenetic activity.
文摘Start-up working condition is the key to the research of optimal engagementof automatic clutch for AMT. In order to guarantee an ideal dynamic performance of the clutchengagement, an optimal controller is designed by considering throttle angle, engine speed, gearratio, vehicle acceleration and road condition. The minimum value principle is also introduced toachieve an optimal dynamic performance of the nonlinear system compromised in friction plate wearand vehicle drive quality. The optimal trajectory of the clutch engagement can be described in theform of explicit and analytical expressions and characterized by the deterministic and accuratecontrol strategy in stead of indeterministic and soft control techniques which need thousands ofexperiments. For validation of the controller, test work is carried out for the automated clutchengagements in a commercial car with an traditional mechanical transmission, a hydraulic actuator, agroup of sensors and a portable computer system. It is shown through experiments that dynamicbehaviors of the clutch engagement operated by the optimal control are more effective and efficientthan those by fuzzy control.
