A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed S...A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthMpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.展开更多
Designing low power sensor networks has been the general goal of design engineers, scientist and end users. It is desired to have a wireless sensor network (WSN) that will run on little power (if possible, none at all...Designing low power sensor networks has been the general goal of design engineers, scientist and end users. It is desired to have a wireless sensor network (WSN) that will run on little power (if possible, none at all) thereby saving cost, and the inconveniences of having to replace batteries in some difficult to access areas of usage. Previous researches on WSN energy models have focused less on the aggregate transceiver energy consumption models as compared to studies on other components of the node, hence a large portion of energy in a WSN still get depleted through data transmission. By studying the energy consumption map of the transceiver of a WSN node in different states and within state transitions, we propose in this paper the energy consumption model of the transceiver unit of a typical sensor node and the transceiver design parameters that significantly influences this energy consumption. The contribution of this paper is an innovative energy consumption model based on simple finite automata which reveals the relationship between the aggregate energy consumption and important power parameters that characterize the energy consumption map of the transceiver in a WSN;an ideal tool to design low power WSN.展开更多
This study investigates the stopping power of a mammalian cell for low energy ions. The energy equation of the incident ion has been conducted based on the elastic collision between the pairs of nuclei in order to est...This study investigates the stopping power of a mammalian cell for low energy ions. The energy equation of the incident ion has been conducted based on the elastic collision between the pairs of nuclei in order to establish the stopping powers of the mammalian cell for low energy ion implantation. Based on the biological structure of the mammalian cell and the measured thickness of the V79 cell, a physical structural model is proposed that the attached cell is approximately of a model of a constringent multi-membrane structure （C-2M model） in order to analyse the stopping power of the mammalian cell for low energy ions. With this model we have determined the mean line energy transfer, and roughly estimated the depth of ion implantation on the selected Chinese hamster V79 cell for 30 keV N^＋ ions at a flux of 1 × 10^15 ion/cm^2, which is in agreement with those by using Monte Carlo methods.展开更多
基金supported by National Natural Science Foundation of China (Nos.50836007, 10921062)
文摘A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthMpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.
文摘Designing low power sensor networks has been the general goal of design engineers, scientist and end users. It is desired to have a wireless sensor network (WSN) that will run on little power (if possible, none at all) thereby saving cost, and the inconveniences of having to replace batteries in some difficult to access areas of usage. Previous researches on WSN energy models have focused less on the aggregate transceiver energy consumption models as compared to studies on other components of the node, hence a large portion of energy in a WSN still get depleted through data transmission. By studying the energy consumption map of the transceiver of a WSN node in different states and within state transitions, we propose in this paper the energy consumption model of the transceiver unit of a typical sensor node and the transceiver design parameters that significantly influences this energy consumption. The contribution of this paper is an innovative energy consumption model based on simple finite automata which reveals the relationship between the aggregate energy consumption and important power parameters that characterize the energy consumption map of the transceiver in a WSN;an ideal tool to design low power WSN.
基金supported by the Innovation Project of the Chinese Academy of Sciences(No.KSCX2-SW-324)the Human Resource Development Project of Anhui Province(No.20052024)
文摘This study investigates the stopping power of a mammalian cell for low energy ions. The energy equation of the incident ion has been conducted based on the elastic collision between the pairs of nuclei in order to establish the stopping powers of the mammalian cell for low energy ion implantation. Based on the biological structure of the mammalian cell and the measured thickness of the V79 cell, a physical structural model is proposed that the attached cell is approximately of a model of a constringent multi-membrane structure （C-2M model） in order to analyse the stopping power of the mammalian cell for low energy ions. With this model we have determined the mean line energy transfer, and roughly estimated the depth of ion implantation on the selected Chinese hamster V79 cell for 30 keV N^＋ ions at a flux of 1 × 10^15 ion/cm^2, which is in agreement with those by using Monte Carlo methods.
