The effects of <i>astragalus</i>polysaccharide on zebrafish cell apoptosis and senescence

Astragalus polysaccharide (AP) is the extraction of astragalus, which is a plant used in traditional Chinese herb medicine and may increase an orgainism’s resistance to stress. Several earlier studies in vitro have indicated that AP has anti-aging activities, however the mechanism underlyling these activities was unclear and remained to be elucidated. In this study, Using the zebrafish (Danio rerio), we evaluated molecular mechanism of the effect of AP on zebrafish growth, development and apoptosis. 30 zebrafish embryos (24 hours post fertilization (hpf)) were exposed to varying concentrations of AP (from 0.125 mg/ml to 0. 5 mg/ml) continuously for 3 days. The results of β-galactosidase (SA-β-gal) and acridine orange fluorescence showed that AP can delay zebrafish embryos apoptosis under the concentration of 0.125 mg/ml. In addition, the differential gene expression of AP treated zebrafish embryos was examined by RT-PCR analysis. We found that the gene expression of mdm2 and tert were up-regulated while bax, p21 and p53 gene expression were down-regulated during early apoptosis of the zebrafish embryos mediated by AP. These results demonstrated that AP may play a role during the induction of senescence and this function might by p53-mediated pathway.

Numerical study of the grid erosion of field emission electric propulsion

In this paper, the immersed finite element particle-in-cell Monte Carlo collision(IFE-PIC-MCC)model is used to study the cause of the grid erosion in field emission electric propulsion(FEEP).The simulation results show that charge exchange(CEX) ions are the main cause of the grid erosion, while beam ions basically do not impinge on the grid. The CEX ions are mainly generated near the grid. Some of these CEX ions return to the upper surface, lower surface and notch side surface of the grid. The impact angle of CEX ions returning to the upper and side surfaces is large, but their energy is low, while the impact angle of CEX ions returning to the lower surface is small, but their energy is high. The above characteristics lead to the similar erosion rates of these three surfaces.

Preparation of N-doped graphite oxide for supercapacitors by NH_(3) cold plasma

In this work,N-doped graphite oxide(GO-P)was prepared by cold plasma treatment of GO using a mixture of NH_(3) and Ar as the working gas.When the ratios of NH_(3):Ar were 1:2,1:3,and 1:4,the specific capacitances of the GO-P(NH_(3):Ar=1:2),GO-P(NH_(3):Ar=1:3),and GO-P(NH_(3):Ar=1:4)were 124.5,187.7,and 134.6 F·g^(-1),respectively,which were 4.7,7.1,and 5.1 times that of GO at the current density of 1 A·g^(-1).The capacitance retention of the GO-P(NH_(3):Ar=1:3)was 80%when it was cycled 1000 times.The characterization results showed that the NH_(3)cold plasma could effectively produce N-doped GO and generate more active defects.The N/C ratio and the contents of pyridinic nitrogen and graphitic nitrogen of the GO-P(NH_(3):Ar=1:3)were the highest.These were conducive to providing pseudocapacitance and reducing the internal resistance of the electrode.In addition,the ID/IGof the GO-P(NH_(3):Ar=1:3)(1.088)was also the highest,indicating the highest number of defects.The results of discharge parameters measurement and in situ optical emission spectroscopy diagnosis of NH_(3) plasma showed that the discharge is the strongest when the ratio of NH_(3):Ar was 1:3,thereby the generated nitrogen active species can effectively promote N-doping.The N-doping and abundant defects were the keys to the excellent electrochemical performance of the GO-P(NH_(3):Ar=1:3).NH_(3) cold plasma is a simple and rapid method to prepare N-doped GO and regulate the N-doping to prepare high-performance supercapacitors.

Plasma transport simulation under different conditions and optimization analysis of dual-stage grid ion thruster

In order to study the extraction and acceleration mechanism of the dual-stage grid,a three-dimensional model based on the Particle-In-Cell/Monte Carlo Collision(PIC/MCC)method is performed.Dual-stage grid ion thruster is a new type of electrostatic ion thruster,which can break through the limitations of traditional gridded ion thrusters,and greatly improve the specific impulse.The high performance also makes the grid sensitive to operating parameters.In this paper,the influence of grid parameters on xenon ion thruster’s performance in a wide range is systematically simulated,and the optimal operating condition is given.Both the over-focusing of the plume,and the transparency of the screen grid are improved,and the grid corrosion is reduced through simulation optimization.The specific impulse under the given working conditions is 9877.24 s and the thrust is 7.28 mN.Based on the simulation optimization,the limitation of the dual-stage grid is discussed.The grid performs well under high voltage conditions(>3000 V)but not well under low voltage conditions(<2000 V).Finally,since argon is cheaper and more advantageous in future engineering applications,the plasma distribution and grid extraction ability under xenon and argon are analyzed and compared to study the flexibility of the dual-stage grid ion thruster.The simulation results show that a set of optimal parameters is only applicable to the corresponding propellant,which needs to be optimized for different propellant types.

Ion thruster accelerator grid erosion mechanism under extreme conditions of cylindrical erosion and chamfer erosion

In this paper,the abnormal experimental phenomenon on barrel erosion under extreme working conditions in the ultra-long life experiment(>10000 h)of ion thruster ion optics is studied by the Immersed-Finite-Element Particle-In-Cell Monte-Carlo-Collision(IFE-PIC-MCC)method and the grid erosion evaluation model.The transport process of beam ions and Charge Exchange(CEX)ions in the grid system,and the characteristics and mechanisms of the aperture barrel erosion under extreme erosion conditions(i.e.the cylindrical erosion and chamfer erosion)were systematically studied.Thanks to the advantage of the IFE method for dealing with complex boundaries in structured mesh,the aperture barrel erosion morphology of the accelerator grid is reconstructed accurately based on the experimental results.The results show that,with the evolution of working conditions,the mechanism of the aperture barrel erosion changes significantly,which relies heavily on the accelerator grid morphology.The change of the accelerator grid aperture barrel morphology has a significant effect on the behavior of CEX ions,and only affects the local electric field distribution,but has no effect on the upstream plasma sheath.As the erosion progresses,the erosion position moves downstream along the grid aperture axis direction,and the erosion range becomes narrower.Regardless of the erosion phase,the erosion rate of the CEX ions located downstream of the decelerator grid is the largest.The erosion rate is related to the mean incident energy and angle,and their variation is closely related to the position and trajectory of CEXions.

Simulation of plasma behavior for medium propellant mass and pulsed energy of small scale pulsed inductive thruster

The pulsed inductive thruster is characterized of no electrode corruption and wide propellant choice.To give insight into the propulsion mechanism of small scale thruster at different propellant mass(m)and energy(E)levels,the transient Magneto Hydro Dynamics(MHD)method,completed by high temperature thermodynamic and transport,and plasma electrical models,is developed to study argon plasma response under the excitation of current of high rise rate.By calculating the two-dimensional expansion properties of the thruster with conical pylon,the simulations find that the main energy deposition occurs during the initial pulse rise stage,and the energy density of Joule heat is two magnitudes higher than the deposition in the down side.At propellant mass of 2 mg,average axial velocity of the current sheet increases from about 15 km/s at 750 J to about 21 km/s at 1470 J within the decoupling distance.The velocity variation synchronizes with the pulsed rise in the initial.The monotonically decrease of the temperature along axis results in the growth of low ionization level ions and reducing of high levels.The current sheet maintains the structure formed during the initial pulse rise when moving beyond the decoupling distance.Besides the change in forward velocity,the main difference is the dimension compared with that in the first half period,caused by thermal conduction and particle diffusion.The variations of total impulse It in the range of m from 2 mg to8 mg and E from 750 J to 1470 J show that It is proportional to m1/2 when E is determined.

Particle simulation of grid system for krypton ion thrusters

The transport processes of plasmas in grid systems of krypton（Kr） ion thrusters at different acceleration voltages were simulated with a 3 D-PIC model, and the result was compared with xenon（Xe） ion thrusters. The variation of the screen grid transparency, the accelerator grid current ratio and the divergence loss were explored. It is found that the screen grid transparency increases with the acceleration voltage and decreases with the beam current, while the accelerator grid current ratio and divergence loss decrease first and then increase with the beam current. This result is the same with Xe ion thrusters. Simulation results also show that Kr ion thrusters have more advantages than Xe ion thrusters, such as higher screen grid transparency, smaller accelerator grid current ratio, larger cut-off current threshold, and better divergence loss characteristic. These advantages mean that Kr ion thrusters have the ability of operating in a wide range of current. Through comprehensive analyses, it can be concluded that using Kr as propellant is very suitable for a multimode ion thruster design.

A finite-time 3D guidance law based on fixed-time convergence disturbance observer

In order to achieve accurate interception of high-speed maneuvering targets,this paper presents a relative Line-of-Sight(LOS)velocity based finite-time three-dimensional guidance law design framework,and discusses the application of fixed-time convergence disturbance observer in this framework.Firstly,a simple Lyapunov function is provided to show that the coupled terms in the relative kinematics can be ignored in the proposed guidance law design framework.Secondly,the realizations of several classical guidance laws are analyzed with the proposed framework,including TPN guidance law,finite-time Input-to-State Stability(ISS)guidance law,and sliding mode guidance law.Thirdly,fixed-time convergence disturbance observers are introduced to design the composite finite-time 3D guidance law,and Lyapunov method is employed to show the stability of the guidance system.Numerical simulations with different scenarios show that the proposed generalized guidance law performs high interception accuracy.

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster(PIT)has the advantages of repeatable startup,no corruption and in-situ propellant feed.To study the flow expansion and circuit characteristics of PITs,the circuit-fluid model is developed,and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters.The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 k V are simulated.Comparison of the flow fields of argon and helium propellants suggests that,the flow field structures are similar.Slight differences exist on the magnitude of the density and magnetic field,caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels.Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current,the larger the ratio,the greater the rise rate and the better the following characteristic.The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained;self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Confinement characteristic of primary electrons with the variation of channel width in the discharge chamber of annular ion thruster

In this paper,the confinement characteristic of primary electrons in the non-axisymmetric discharge chamber of annular ion thruster is investigated by a three-dimensional(3 D)non-self-consistent particle tracking model with Monte Carlo Collision(MCC)method.The results show that:The density of primary electrons upstream of ion optics on cathode axis is about 5–50 times higher than that of the other side,which means that the density of primary electrons is obviously non-axisymmetric.The channel width has a significant effect on the average density and uniformity of primary electrons.The average density can be increased by nearly 1.5 times under the appropriate channel width,meanwhile,the variance of density distribution can be reduced by more than 2 times.This is because that increasing the channel width can improve the average confinement length of primary electrons greatly.Furthermore,there is an infection point in the increase of primary electron average confinement length with the channel width,which caused by the significant change of magnetic field structure.Under the case after the inflection point,primary electron mainly(more than 50%)moves to the channel center,which makes the average confinement length of primary electrons and their number in the discharge chamber increase largely.