ABSTRACT
With the continuous exploration of the bioelectric effect, nanosecond and picosecond pulsed electric fields used in cancer therapy and drug introduction have attracted great attention. In this paper, an ultrashort pulsed electric field generator is proposed, which connects two photoconductive semiconductor switches in parallel to generate unipolar and bipolar pulses. We described the experimental scheme of the generator and the simulation of the radio frequency combiner. A 532 nm laser with pulse widths of 1 ns and 500 ps is used to trigger the photoconductive semiconductor switches. The experimental results show that the scheme can achieve adjustments of 357 and 720 MHz for the center frequency and the 3 dB bandwidth, respectively. The results confirm that this proposed scheme can be used for unipolar/bipolar frequency-adjustable ultra-wideband pulse generation.
ABSTRACT
High power microwave (HPM) sources usually require a well-defined rectangular pulse waveform, which is especially true for the case of long pulse (>100 ns), stable, and high efficiency operation. Most long pulse HPM drivers are realized with pulse forming networks. This paper presents a long pulse driver composed of a conventional Marx generator and metal-oxide varistors (MOVs), utilizing the MOV's nonlinear V-I characteristic. This method is easy to implement, and it has an additional benefit that the voltage can be stabilized even if the load's impedance changes slightly. A low inductance zig-zag folding structure of the MOV is designed to decrease its size and self-inductance. An LC filter is used to reduce the energy loss in the MOV. In the experiment, a 400 kV, 800 ns long pulse is achieved at a foil-less electron diode, and longer than 300 ns HPM generation is obtained.
ABSTRACT
An attenuated strain of Salmonella typhimurium was used as a vehicle for oral gene therapy against murine tumor. Eukaryotic expression vectors containing genes of human interleukin-12 (hIL-12), human granulocyte/macrophage colony-stimulating factor (hGM-CSF), mouse (m)IL-12, mGM-CSF and green fluorescent protein (GFP) were used to transform attenuated Salmonella (SL3261), and such transformants were administered orally to BALB/c and C57BL/6 mice. As a reporter gene, GFP expression in murine liver, spleen, tumor, intestine and kidney was confirmed by confocal and flow cytometry. Soluble cytokines were detected in murine sera, and the concentrations were much higher than those of the control, which contributed to the increased number of cytotoxic T cells and prolongation of survival. Oral cytokine gene therapy using live attenuated Salmonella demonstrated a significant protection against the development of two unrelated murine tumors. These results suggest that such gene therapy has the potential to be simple, effective and (above all) safe against tumor.
