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关键词： 拖拉机齿轮箱   行星齿轮传动系统   故障特性   啮合刚度  

摘要： 以拖拉机齿轮箱为研究对象,针对行星齿轮传动系统设计过程中出现的不足,以行星齿轮传动系统最小总体积为设计目标,确定设计目标函数约束条件和设计过程约束条件,建立设计过程的数学模型并将其最优化。在MatLab中将建立的最优化的数学模型求解,得到设计参数最优值,使行星齿轮传动系统机构的体积达到最小值,进一步提高设计过程质量。同时,采用动力学对行星齿轮传动系统进行建模,考虑振动传递路径时变效应及振动信号对传动系统动力学的影响,推导了单个行星齿轮在发生故障时的啮合刚度表达式,进一步得出多个行星齿轮发生故障时的啮合刚度变化表达式,得到行星齿轮传动系统在不同故障程度下的啮合刚度。研究可为拖拉机行星齿轮传动系统机构的故障监测提供参考依据。

关键词： 汽车离合器   分离不彻底   故障分析  

摘要： 离合器作为汽车动力系统中最频繁使用的重要部件之一,其在使用过程中出现的问题也是广大车主最为关注的焦点。通常离合器分离不彻底的原因有很多,给车主们带来最大的不便就是行驶途中换档困难或者起步时挂不上档等。由于离合器控制的是动力与发动机之间的切断与连接,所以离合器的使用能直接反应出驾驶水平的高低以及对车保养的好坏程度。

关键词： Post-traumatic stress disorder   TSST   Neuropeptides   HPA axis   Prefrontal cortex   FKBP5 knockout mice   PTSD biomarkers  

摘要： This study aimed to identify yet unavailable blood biomarkers for the responsive and the hyporesponsive hypothalamic-pituitary-adrenal (HPA) axis subtypes of posttraumatic stress disorder (PTSD). As, I, we recently discovered the intranasal neuropeptide oxytocin to reduce experimentally provoked PTSD symptoms, II, expression of its receptor (OXTR) has hitherto not been assessed in PTSD patients, and III, oxytocin and OXTR have previously been related to the HPA axis, we considered both as suitable candidates. During a Trier Social Stress Test (TSST), we compared serum oxytocin and blood OXTR mRNA concentrations between female PTSD patients, their HPA axis reactivity subtypes and sex and age-matched healthy controls (HC). At baseline, both candidates differentiated the hyporesponsive HPA axis subtype from HC, however, only baseline OXTR mRNA discriminated also between subtypes. Furthermore, in the hyporesponsive HPA axis subgroup, OXTR mRNA levels correlated with PTSD symptoms and changed markedly during the TSST. To assess the influence of (traumatic) stress on the cerebral expression of oxytocin and its receptor and to test their suitability as biomarkers for the mouse PTSD-like syndrome, we then analyzed oxytocin, its mRNA (Oxt) and Oxtr mRNA in three relevant brain regions and Oxt in blood of a PTSD mouse model. To further explore the HPA axis reactivity subtype dependency of OXTR, we compared cerebral OXTR protein expression between mice exhibiting two different HPA axis reactivity traits, i.e., FK506 binding protein 51 knockout vs. wildtype mice. In summary, blood OXTR mRNA emerged as a potential biomarker of the hyporesponsive HPA axis PTSD subtype and prefrontal cortical Oxtr and Oxt of the mouse PTSD-like syndrome. Moreover, we found first translational evidence for a HPA axis responsivity trait-dependent regulation of OXTR expression. The lack of a cohort of the (relatively rare) hyporesponsive HPA axis subtype of HC is a limitation of our study.

关键词： Great Tit   hatching asynchrony   nest attentiveness   nocturnal incubation   partial incubation   Parus major  

摘要： Ambient temperature is assumed to be the major cue used by passerines to synchronize their laying and hatching dates to the expected peak of prey availability. While laying eggs, females are still able to fine-tune their hatching date following increasing or decreasing patterns of ambient temperature, mostly via changes in incubation onset. The onset of incubation behaviour in relation to the laying sequence could have later consequences for the duration of the incubation period and the extent of hatching asynchrony. Clutch size is also known to affect incubation patterns and might therefore condition potential responses to changing temperatures. In this study we assessed the association of ambient temperature and clutch size with the onset of four different incubation behaviours: partial and full nocturnal incubation, and partial and full diurnal incubation. We also evaluated how the onset and duration of each incubation behaviour might predict the duration of diurnal full incubation and the extent of hatching asynchrony. To achieve our aims, we monitored incubation behaviour using temperature data loggers during the egg-laying period in three Mediterranean Great Tit Parus major populations in three consecutive years. Our results showed that increasing temperatures were related to an advance of diurnal partial incubation, but not its duration or the onset of full incubation behaviour. We did not find any effect of ambient temperatures on nocturnal incubation. However, females lengthened nocturnal partial incubation and delayed the onset of nocturnal full and diurnal partial incubation when laying larger clutches. Longer diurnal incubation before clutch completion was associated with greater hatching asynchrony. Moreover, longer diurnal partial incubation shortened the duration of the full incubation period. In conclusion, increasing ambient temperatures during the egg-laying period advanced diurnal partial incubation, indirectly shortening the full incubation perio

关键词： magnetorheological fluid   clutch   twin-driven actuator   haptics  

摘要： Magnetorheological fluids are composite materials made of ferromagnetic particles, medium oils, and several types of additives. We have developed actuation systems for the fine haptic control of master-slave robots. In this study, we proposed a new structure of a magnetorheological fluid-based actuator suitable for haptic devices. For the basic structure of the actuator, we proposed a twin-driven magnetorheological fluid actuator using two multi-layered disc-type magnetorheological fluid clutches for haptics. We conducted performance measures for the magnetorheological fluid clutches for haptics with three commercially available magnetorheological fluids (i.e. 122EG, 132DG, and 140CG from Lord Corp.). The experimental results show that 132DG is a better material for force control. Then, we proposed two types of twin-driven magnetorheological fluid actuators (i.e. link type and belt type) and compared their performance. The results show that the averages of the time constant are 19.1 and 16.1 ms for the link type and belt type, respectively. Furthermore, the averages of torque error are 0.033 and 0.068 N m for the link type and belt type, respectively. However, the belt-type twin-driven magnetorheological fluid actuator is better if a large range of motion is required, while the link-type twin-driven magnetorheological fluid actuator is better if accurate torque control is required.

关键词： breeding date   long‐   term study   parental investment   sex allocation  

摘要： Mothers may produce more of one sex to maximize their fitness if there are differences in the cost of producing each sex or there are differences in their relative reproductive value. Breeding date and clutch size are known to influence offspring sex ratios in birds through sex differences in dispersal, social behaviours, differential mortality and available food resources. We tested whether breeding date, clutch size and drought conditions influenced offspring sex ratios in a sexually size-monomorphic species, the Western Bluebird Sialia mexicana, by interrogating a 21-year dataset. After controlling for differential mortality, we found that hatch dates late in the breeding season were associated with the production of more females, suggesting that the value of producing males declines as the breeding season progresses. When clutch size was taken into account, small clutches yielded significantly more females late in the breeding season than in the early and middle parts of the breeding season, which produced significantly more males. Large clutches early in the season tended to produce more females, although this was not significant. Drought severity was not correlated with sex ratio adjustment. We propose and discuss several explanations for these patterns, including male offspring, but not female offspring, acting as helpers, increased female nestling provisioning late in the breeding season, differences in food abundance and egg-laying order. Future work will help to uncover the mechanisms leading to these patterns. Identifying patterns and mechanisms of sex ratio skew from long-term datasets is important for informing predictions regarding life-history trade-offs in wildlife populations.

关键词： magneto-rheological fluid   dual-clutch   finite element analysis   two-speed transmission   electric vehicles  

摘要： The dual-clutch transmission (DCT) in electric vehicles can significantly decrease the torque interruption and improve the shifting comfort. The magneto-rheological fluid (MRF) is a kind of intelligent material commonly used for torque transmission devices with high control accuracy and fast response, e.g. MRF clutch. This paper proposes a novel MRF dual-clutch (MRFDC) design for the two-speed transmission of EVs combining the DCT and MRF clutch advantages. The MRFDC is composed of an internal clutch and an external clutch. The two clutches with the same input shaft and different output shaft can shift between two gears by controlling the input current through the coils in the two clutches. The relationship between the input current and the magnetic flux density is obtained by the finite element analysis of the magnetic field under different input current. Theoretical analysis is carried out to estimate the output torque of MRFDC according to the geometric dimensions of MRFDC structure and rheological properties of MRF. The Herschel-Bulkley model is applied to describe the MRF behaviour because the shear rate of MRF is relatively high. The output torque model is built considering the magnetic flux density. Therefore, the relationship between the transmissible torque and applied input current is determined. Finally, the MRFDC model is experimentally verified on the testbed;besides, the transmissible torque tests and response time tests for internal and external MRF clutches are carried out, respectively. The test results agree with the simulation results, and the differences are within 2 N m. It is suggested that the MRFDC can be applied in EVs to improve vehicle performance.

关键词： Graphene   Epitaxy   CVD   Silicon carbide   Homoepitaxy   Raman spectroscopy   X-ray diffraction   Transport properties  

摘要： In this report we investigate structural and electrical properties of epitaxial Chemical Vapor Deposition quasifree-standing graphene on an unintentionally-doped homoepitaxial layer grown on a conducting 4H-SiC substrate 4-off-axis from the basal [0001] direction towards [11-20]. Due to high density of SiC vicinal surfaces the deposited graphene is densely stepped and gains unique characteristics. Its morphology is studied with atomic force and scanning electron microscopy. Its few-layer character and p-type conductance are deduced from a Raman map and its layers structure determined from a high-resolution X-ray diffraction pattern. Transport properties of the graphene are estimated through Hall effect measurements between 100 and 350 K. The results reveal an unusually low sheet resistance below 100 omega/sq and high hole concentration of the order of 1015 cm(-2). We find that the material's electrical properties resemble those of an epitaxially-grown SiC PIN diode, making it an attractive platform for the semiconductor devices technology.

关键词： Series-parallel hybrid electric vehicle   Permanent magnet synchronous motor   Mode switches   Instability analysis  

摘要： Variable driving conditions can cause an integrated starter generator hybrid powertrain to switch between multiple drive modes. The addition of a permanent magnet synchronous motor (PMSM) gives hybrid powertrains complex electromechanical coupling characteristics. The effects of excitation sources, such as the engine and PMSM, may cause unstable behavior in the drive system, such as speed fluctuations during mode switches due to electromechanical coupling characteristics. Although traditional mode switch strategies and methods have achieved measurable results, they are difficult to improve. To solve this problem, we first considered the combination and separation of the clutch and establish a nonlinear model of mode switches for series-parallel hybrid electric vehicles. Then, we predicted the instability boundary of the drive system during mode switches. Experimental results indicated that the proposed instability boundary has higher accuracy. Numerical results showed that the three-mode switches have different thresholds of instability for the clutch structure gap. The decrease in electromagnetic torque and the increase in load excitation amplitude will improve the critical value of the clutch structure gap. The increase in load excitation frequency causes the critical value of the clutch structure gap to drop first and then rise.