RESUMO
Objective To develop a sinusoidal alternating magnetic field therapy system in order to overcome the disadvantages of the single output frequency and the low effective value of the output magnetic field strength of the alternating magnetic field therapy system in the market,of which the frequency and magnetic density both were continuously adjustable. Methods Multi winding Helmholtz coil was used as the magnetic field generator.On the basis of inverter technology,bipolar equivalent area method considering dead zone and variable speed integral incremental PID control algorithm were used to achieve the accuracy control of magnetic frequency and density in the coil.The accuracy of the resulting waveform and the accuracy of the magnetic field strength was verified by simulation calculation and system current and magnetic field strength test.Results The magnetic field treatment system gained high performance,total harmonic distortion (THD)of sine wave met the requirements of international standards.The obtained magnetic density was as expected of the simulation and calculation. Conclusion The device provides continuously adjustable magnetic field,which has a positive effect on the research for the medical staff, and technical references are provided to the research of magnetic field therapy system.
RESUMO
This study was aimed to investigate the effect of GATA-2 over-expression on function of mouse fetal liver hematopoietic stem cells. GATA-2 was introduced into mouse fetal liver cells via retrovirus mediated transduction with GFP as a detecting marker. Flow cytometry, colony-forming assay and cell cycle assay were used to detect the biologic changes of these retrovirus infected mouse fetal liver hematopoietic stem cells. The results showed that GATA-2 over-expression increased the Lin(-)Sca1(+)C-Kit(+) (LSK) population dramatically. Cell cycle of LSK cells didn't show abnormal, while colony forming ability decreased significantly. These data indicated that GATA-2 over-expression inhibited definitive differentiation of mouse fetal liver hematopoietic stem cells. It is concluded that over-expression of GATA-2 can significantly raise the LSK cell proportion in mouse fetal liver and inhibit the differentiation capability, the underlying mechanisms may be related to up-regulation of Hes-1, which may lead to the blocking of cell differentiation at the stem/progenitor cell stage.