BackgroundThe C4 photosynthetic cycle supercharges photosynthesis by concentrating CO2 around ribulose-1,5-bisphosphate carboxylase and significantly reduces the oxygenation reaction. Therefore engineering C4 feature into C3 plants has been suggested as a feasible way to increase photosynthesis and yield of C3 plants, such as rice, wheat, and potato. To identify the possible transition from C3 to C4 plants, the systematic comparison of C3 and C4 metabolism is necessary.ResultsWe compared C3 and C4 metabolic networks using the improved constraint-based models for Arabidopsis and maize. By graph theory, we found the C3 network exhibit more dense topology structure than C4. The simulation of enzyme knockouts demonstrated that both C3 and C4 networks are very robust, especially when optimizing CO2 fixation. Moreover, C4 plant has better robustness no matter the objective function is biomass synthesis or CO2 fixation. In addition, all the essential reactions in C3 network are also essential for C4, while there are some other reactions specifically essential for C4, which validated that the basic metabolism of C4 plant is similar to C3, but C4 is more complex. We also identified more correlated reaction sets in C4, and demonstrated C4 plants have better modularity with complex mechanism coordinates the reactions and pathways than that of C3 plants. We also found the increase of both biomass production and CO2 fixation with light intensity and CO2 concentration in C4 is faster than that in C3, which reflected more efficient use of light and CO2 in C4 plant. Finally, we explored the contribution of different C4 subtypes to biomass production by setting specific constraints.ConclusionsAll results are consistent with the actual situation, which indicate that Flux Balance Analysis is a powerful method to study plant metabolism at systems level. We demonstrated that in contrast to C3, C4 plants have less dense topology, higher robustness, better modularity, and higher CO2 and radiation use efficiency. In addition, preliminary analysis indicated that the rate of CO2 fixation and biomass production in PCK subtype are superior to NADP-ME and NAD-ME subtypes under enough supply of water and nitrogen.

Using bibliometric methods, we investigate China's international scientific collaboration from 3 levels of collaborating countries, institutions and individuals. We design a database in SQL Server, and make analysis of Chinese SCI papers based on the corresponding author field. We find that China's international scientific collaboration is focused on a handful of countries. Nearly 95% international co-authored papers are collaborated with only 20 countries, among which the USA account for more than 40% of all. Results also show that Chinese lineage in the international co-authorship is obvious, which means Chinese immigrant scientists are playing an important role in China's international scientific collaboration, especially in English-speaking countries.

A novel method is proposed to monitor and record scientists' working timetable. We record the downloads information of scientific papers real-timely from Springer round the clock, and try to explore scientists' working habits. As our observation demonstrates, many scientists are still engaged in their research after working hours every day. Many of them work far into the night, even till next morning. In addition, research work also intrudes into their weekends. Different working time patterns are revealed. In the US, overnight work is more prevalent among scientists, while Chinese scientists mostly have busy weekends with their scientific research.

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Based on the external compaction return mechanism of a balanced double-row axial piston pump and the vector coordinate transformation principle, a mathematical model of the relative motion relation within the external return spherical bearing pair was built. The influence of slant inclination of the external swash plate and of pump shaft rotating speed and eccentricity on the relative motion trail, movement speed and acceleration was analysed. The relative motion velocity and acceleration between external retainer plate and external spherical hinge, at top and bottom dead centres, were discussed. By increasing the slant inclination of the external swash plate, the relative motion trail increased correspondingly, leading to a larger size of the pump integral structure. The relative speed and acceleration increased with the pump shaft speed and the slant inclination of the external swash plate, leading to a larger fluctuation of the slipper pair oil film. The increase of eccentricity slightly influenced the relative velocity and acceleration along the x-axis, without significantly increasing the fluctuation of the slipper pair oil film. Increasing the pump shaft speed, the external swash plate slant inclination and the eccentricity all caused fluctuations in the relative velocity and acceleration along the y- and z-axes, deepening the grinding crack on the compaction surface of the external retainer plate. In case of eccentricity and a 0° rotation angle of the principal axis, the related acceleration of the radial friction surface of the retainer plate showed the largest fluctuation amplitude, and a scratch could easily occur.

The closed-loop nature of the Gough-Stewart platform generates complex singular configurations inside the workspace and makes its workspace smaller compared to the serial mechanism. It is desirable to obtain a non-singular workspace based on describing the constraint workspace and representing the singularities inside the constraint workspace. Some algorithms have been proposed by researchers to find the workspace boundary, but cannot locate the voids inside the workspace and are not applicable to the generation of a workspace with more than one zone. In this paper, the position-singularity expression in ℜ 3 and the orientation-singularity expression in SO(3) are obtained, respectively. The new algorithms of the two types of constraint workspace in ℜ 3 and in SO(3) are developed considering the limitations of the kinematic pairs. It can be shown that the singularities may exist inside the constraint workspace. Based on the singularity representation and the abovementioned constraint workspace determination, the two types of procedures of the non-singular workspace in ℜ 3 and in SO(3) are further addressed, respectively. When the moving platform translates inside the non-singular position-workspace in ℜ 3 for a constant-orientation or rotates inside the non-singular orientation-workspace in SO(3) for a given position, the mechanism is not singular. The two types of non-singular workspace representations in ℜ 3 and SO(3) can help the designers to explore the singularity-free path planning, on which our next work will be focused. The novel method of workspace determination of the mechanism can also be used for the workspace analysis of the other types of parallel mechanisms.

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The digital valve distribution axial piston pump is a swashplate rotary piston pump, the force on slippers is different from that of traditional axial piston pump. At the same time, the control strategy of the distribution valve will affect the pressure in the piston cavity, and then affect the oil film lubrication. According to these characteristics, the modeling method of oil film thickness field was proposed, and the force model of slipper pair and the numerical solution model of oil film lubrication of digital valve distribution axial piston pump were further established. The influence of swashplate rotation speed, swashplate inclination angle, and distribution valve control strategy on the characteristics of oil film lubrication were solved. The results show that the established thickness field model of oil film conforms to the stress characteristics of the slipper of the valve distribution pump. Increasing the swashplate rotation speed and the swashplate inclination angle is beneficial to optimize the oil film lubrication performance. The discharge valve should be opened in advance or closed in delay, which is beneficial to prevent eccentric wear and adhesion wear of slippers. The research results can provide theoretical basis for the optimal design of valve distribution axial piston pump.