Propagation Velocity of Pulsed Streamer Discharges in Atmospheric Air

Pulsed streamer discharges have been extensively used in many applications such as control of NO/sub X/ and SO/sub 2/ from exhaust gases, treatment of dioxins, removal of volatile organic compounds, generation of ozone, and laser excitation. An operation with a high energy efficiency is necessary for practical applications. It is very important to know the propagation mechanism of streamer discharges in order to improve the energy efficiency of pulsed discharge systems. In this paper, the emission from pulsed streamer discharges in a coaxial electrode system in air at 0.1 MPa was observed using a high-speed gated intensified charge-coupled display camera. A concentric wire-cylinder electrodes configuration was used. A positive pulsed voltage having a width of about 100 ns was applied to the central electrode. The streamer discharges were initiated at the inner electrode and terminated at the outer electrode. The propagation velocity of the streamer discharges was 1.8-3.3 mm/ns

The Reactor Design for Diesel Exhaust Control Using a Magnetic Pulse Compressor

A magnetic pulse compressor (MPC) was used to control the exhaust gases from a diesel generator employing a wire-to-plate plasma reactor in this work. To obtain efficient NO/sub X/ removal, the energy transfer efficiency from the MPC to the plasma reactor and the pulse streamer discharge physics were investigated by varying the number of anode wires and wire-to-wire distance of the reactor. It was experimentally confirmed that the number of wires and the neighboring wire distance affected the energy transfer efficiency. The optimal reactor design for efficient diesel exhaust processing using an MPC can be achieved by employing large numbers of wires and long wire-to-wire distances for the wire-to-plate reactor

Novel Dual Marx Generator for Microplasma Applications

Micrometer size plasmas, or microplasmas, find applications in pollution control, reduction, and prevention. The required nonthermal plasmas can be generated by either an electron beam or an electric discharge. The pulse widths and voltages necessary to generate these nonthermal plasmas are 10- 10-10-8 s, and 103-104 V, respectively, depending on the application. The required energy is typically in the low 10-3 J range. This paper presents a novel circuit design to generate high-voltage pulses with variable pulse widths and pulse rise and fall times in the low 10-9 s regime. The circuit employs two parallel Marx Generators utilizing bipolar junction transistors (BJTs) as closing switches. The BJTs are operated in the avalanche mode to yield fast rise times. The design allows for positive or negative polarity pulses, and can easily be changed to yield higher or lower output voltage

Production of Nitric Monoxide Using Pulsed Discharges for a Medical Application

Nitric monoxide (NO) is widely used in medical treatment of acute respiratory distress syndrome (ARDS). The production of NO is of interest to the medical community. In the present work, NO is generated by pulsed discharges between two rod electrodes in a mixture of nitrogen and oxygen. An arc discharge having a temperature of about 10000K was produced, which was sufficient to generate NO. Some of the important parameters affecting the production of NO have been investigated. These include the percentage of O2 (6-94%) in the mixture of N2 and O2, the energy of the discharge (0.5-12 J/pulse), the pulse repetition rate (0.5-4.5 pps) and the flow rate (1.35-5.4 l/min) of the gas mixture. NO2 produced in the discharge was successfully changed to NO using a heated molybdenum tube. NO2 must be extracted from the gas before clinical inhalation. The concentration of ozone was completely eliminated by bubbling the gas mixture through water. A maximum of NO and a minimum of NO2 concentrations were generated when the proportion of O2 in the gas mixture was in the range of 20-27%. The concentrations of NO and NO2 increased with increasing pulse repetition rate and with decreasing flow rate of the mixture. In all cases, NO2 was effectively removed using a heated molybdenum tube

Improvement of NOX removal efficiency using short-width pulsed power

Pulsed power has been used to remove nitric oxide (NO) in a mixture of nitrogen, oxygen, and water vapor simulating the flue gases from a power station stack. The effect of the pulsewidth at a fixed applied voltage on NO removal concentration was studied. The dependence of the energy efficiency of the removal of NO at a fixed applied voltage on the pulsewidth, on the removal ratio of NO and on the discharge current was investigated. This removal energy efficiency increases with decreasing pulsewidth and decreasing removal ratio of NO

The Effects of Pulsed Streamerlike Discharge on Cyanobacteria Cells

Recently, cyanobacteria blooms (or water blooms) occurred on the surface of water bodies frequently and extensively due to eutrophia of the water. That has posed more and more serious environmental problems worldwide. In this paper, the effects of pulsed streamerlike discharge on M. aeruginosa cells are reported, which are one genus of cyanobacteria and ease to form water blooms. A stainless needle with a diameter of 30 mum was employed as a point discharge electrode, which is 15-cm apart from the cylinder cathode, and a 2-mus 160-kV pulse was applied. A pulsed streamerlike discharge was obtained in the water filled with cyanobacteria cells (named as sample water in this paper). From the experimental result, it can be found that the discharge collapsed the intracellular-structure gas vesicles in the M. aeruginosa cells, and the colonies of the cells sank to the bottom of the discharge chamber and rotten gradually

An ant involving pollination system——pollination biology of three orchids of Listera and Neottia

蚂蚁和被子植物之间存在广泛、普遍和多样的关系，但蚂蚁为被子植物传粉的报道却很少。本文通过对分布于四川省黄龙寺自然保护区黄龙沟内鸟巢兰属和对叶兰属的三种花结构十分相似的植物(高山鸟巢兰Neottia listeroides、小叶对叶兰Listera smithii以及花叶对叶兰L. puberula var. maculata)的传粉生态学研究，首次在国内报道高山鸟巢兰和花叶对叶兰中蚂蚁参与的传粉现象，并探讨了蚂蚁参与的传粉系统中蚂蚁传粉的特点、传粉效率、蚂蚁活动特点与防止自花授粉的关系、以及蚂蚁传粉的作用等问题。同时通过蚂蚁参与传粉的高山鸟巢兰和花叶对叶兰以及没有蚂蚁参与传粉的小叶对叶兰的生境对比，初步分析了蚂蚁参与传粉的生境条件。 黄龙沟内小叶对叶兰、高山鸟巢兰和花叶对叶兰居群水平的花期分别可持续27 d、40 d和50 d，大量开花期(～60%)分别在6月下旬到7月上旬、7月中下旬和8月。这3种植物都具暴露的花蜜，花蜜位于唇瓣中央不明显蜜槽内，花蜜量很小。访问小叶对叶兰的昆虫非常少，2005年和2007年均没有观察到传粉者。在2005年，姬蜂和瘿蜂为花叶对叶兰主要传粉者。在2007年，蚂蚁(包括细胸蚁和立毛蚁)分别是高山鸟巢兰和花叶对叶兰最主要的传粉者，其单花访问次数、携粉次数以及授粉次数分别在这2种植物的所有访问昆虫中是最高的。蚂蚁沿唇瓣蜜槽取食花蜜，到达唇瓣基部后，在高山鸟巢兰上，一般情况下蚂蚁头部不能接触到蕊喙先端，只有当蚂蚁头部向上抬起，才能触碰到蕊喙，花粉团通过蕊喙先端释放的粘滴粘在蚂蚁头部最顶端；而在花叶对叶兰上，只要蚂蚁在唇瓣基部活动就可以触碰到蕊喙，花粉团粘在蚂蚁头部的前额处。当小叶对叶兰、高山鸟巢兰和花叶对叶兰的蕊喙先端被触碰后，立即向下运动盖住柱头，分别约9 h、21 h和23 h重新抬起至药帽位置。蕊喙的这种运动可以避免因蚂蚁的重复访问而引起自花授粉的发生。繁育系统实验表明，这3种植物是自交亲和的，但必须依靠昆虫进行传粉。自然条件下，小叶对叶兰的自然结实率在2005和2007年分别为18.03%和14.42%，花叶对叶兰在2005和2007年分别为17.05%和43.20%，高山鸟巢兰在2007年为19.77%。 细胸蚁和立毛蚁在高山鸟巢兰和花叶对叶兰上的访问频率差异不大，前者略低于后者，但高山鸟巢兰的结实率却远低于花叶对叶兰。这主要是由于高山鸟巢兰与细胸蚁和立毛蚁之间形态上的不完全适应，而花叶对叶兰与2种蚂蚁之间形态上却较为适应的缘故。虽然2007年2种蚂蚁是高山鸟巢兰和花叶对叶兰最有效的传粉者，但这种传粉关系可能只是在特定时间和独特生态环境中出现的。生境干旱可能是导致蚂蚁访花和传粉的重要因素。我们的研究结果也初步表明当环境变化导致原有的主要传粉者缺失时，蚂蚁可以起到补充传粉的作用