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Cardiomyocytes are critically responsible for heart contraction and the pumping of blood through the circulatory system. In adult mice and humans, the rate of cardiomyocyte division is extremely low. In addition, dedicated cardiac stem cells that support myocardial renewal do not exist. Therefore, cardiomyocytes that are lost upon heart damage cannot be replenished. The inability to recover from cardiac injury, such as a myocardial infarction, is a leading cause of morbidity and mortality worldwide. Obviously, it is of great biomedical interest to find ways for enabling heart regeneration by restoration of lost cardiomyocytes. Previous reports have suggested that dedifferentiation of adult cardiomyocytes, which concurs with reactivation of fetal gene expression programs, is a prerequisite to enable adult cardiomyocytes to reenter the cell-cycle. Continuous forced expression of reprogramming factors known as OSKM (Oct4, Sox2, Klf4 and c-Myc) causes stepwise dedifferentiation of somatic cells and acquisition of pluripotency. More recently, it was shown that short-term OSKM-expression allows partial reprogramming of cells without the loss of cellular identity, improving the regenerative potential of tissues. The aim of this thesis was to investigate whether OSKM-expression in cardiomyocytes enforces cardiomyocyte dedifferentiation and proliferation, and to establish a cardiomyocyte-specific partial reprogramming strategy that might enable heart regeneration. To this end, two transgenic mouse lines designated i4FHeart and i4FHeart/mCherry were generated and analyzed in this study. These animal models allow control of OSKM expression specifically in fluorescently labelled cardiomyocytes. Here, it was found that OSKM-expression facilitates division of both neonatal and adult cardiomyocytes in vitro. Furthermore, cardiomyocyte-specific OSKM-expression results in dedifferentiation and enhanced proliferation of cardiomyocytes in neonatal, juvenile and adult hearts in vivo. Sustained OSKM-expression leads to complete cardiomyocyte reprogramming and heart tumor formation. Transient OSKM-expression in the adult heart dedifferentiates adult cardiomyocytes to fetal-like cardiomyocytes and allows subsequent reversion to the previous differentiated state. Transient OSKM-expression in juvenile mice enables heart regeneration after resection of the heart apex. In adult mice, transient OSKM-expression before and during myocardial infarction facilitates heart regeneration and ameliorates heart failure.

The theory of sampling method for measuring the mean parameters of quasi-periodic signal is analyzed, and the condition without introducing measurement errors is given. The reason of measuring error caused by non-synchronous sampling and the mechanism of window weighted method to suppress measurement error are analyzed. In particular, the analytical formulas of rectangular convolution window and measurement errors are given. Aiming at the DC component in the input signal of the practical analog-to-digital conversion (ADC) circuit, a series of formulas for parameter measurement of quasi-periodic signal in engineering implementation are derived.

In order to analyze soybean stalk using mechanics index, five kinds of soybean stalks were selected as experimental materials. The shear test and bending test were did by means of 1000N electronic universal testing machine. Loading position, loading velocity and moisture content were selected as experimental factor and the maximum loading force, stress and other mechanics indexs of the 5 kinds of soybean stalks in the shear test and bending test were measured. The relationship between mechanical properties of stalk and experimental factors were analyzed by statistical software and the function relationship were also be fitted using the software of matlab. The research results showed that the maximum shear force and bending force of stalk increased with the hight increase. The maximum shear force decreased with the increased of loading speed and moisture content. And the maximum bending force increased with the loading speed increased. But with the moisture content of the stalk increased, the maximum bending force increased first and then decreased. The research results can be used as theoretical fundation and reference to improve the soybean threshing and transport machine. It can also be used to confirm the best mechanical harvest time of soybean and other technological parameters.

In order to improve the screening effect of grain combine harvester, it is necessary to study the influence of different screening parameters on screening performance.In this paper, discrete element method was used to simulate the screening process of soybean and short stems by selecting different screening parameters, and dynamic screening efficiency and the number of short stems under screening were introduced as evaluation criteria.The results show that under certain other conditions, the vibration frequency, amplitude and direction angle have significant influence on the screening performance, while the inclination angle of the upper screen has little influence on the screening performance. With the increase of vibration frequency, amplitude and direction angle, screening efficiency increased first and then decreased, while the number of short stalks under screening increased first and then decreased. Considering the screening efficiency and the number of short stalks under the screening, it is concluded that the screening performance is better when the amplitude is 25 mm, the vibration frequency is 4 Hz, the vibration direction angle is 25 degrees and the upper screening angle is 3 degrees. The simulation results are verified by field experiments, and the simulation results meet the requirements of field experiments.