6,097 research outputs found
Positive- and negative-pulsed argon plasma plumes in the open air
Cold atmospheric pressure plasma plumes have obtained great interests for their attractive features and application potentials. In this work, cold argon plasma plumes were generated in the open air by a single medical-needle excited by a high-power pulsed excitation source. Characteristic comparision was carried out in the plasmas under different polarties of applied voltages. The results showed that the positive pulsed plasma plume performed a larger discharge current and stronger optical emission than the negative case. Gas temperature of the plasmas were obtained by the Boltzmann plot method and fitting the syntheric-to-experimental spectrum of the OH (A-X) transition emission bands. It is found that both the positive and negative pulsed plasma plumes are under a relative low gas temperature about 400 K. Through the high-speed imaging, an interesting propagation process was observed for the positive pulsed plasma plume, during which the plasma first propagates in the form of plasma ‘bullets’, and then transits into typical stream propagation as soon as the ‘bullets’ disappears in the open air, which is much different with the negative case
Propagation dynamics of a room-temperature pulsed argon plasma plume through a simple dispersion-grating diagnostic method
In this paper, a novel grating-ICCD camera dispersion diagnostic method was designed to investigate the propagation behaviors of an open-air pulsed argon plasma plume. Based on the dispersion feature of gratings, the irradiative plasma plume was dispersed into several emission-volumes corresponding to different wavelengths. And a series of high-speed dispersed emission-image sequences were captured by the ICCD camera. From these sub-microsecond emission-images at different wavelengths, the temporal and spatial propagation behaviors of excited species in the plasma plume were observed clearly
Hydrogen peroxide generation by DC and pulsed underwater discharge in air bubbles
The generation of H(2)O(2) in underwater discharge in air bubbles is studied with consideration of the influence of electrodes polarity, input power, solution conductivity and the inter-electrode distance. The efficiency of hydrogen peroxide generation strongly depends on the polarity, input power and the inter-electrode distance. Discharges in air bubbles with water as a cathode have significantly higher energy yield of hydrogen peroxide in comparison with negative DC or pulsed discharges. The generation of hydrogen peroxide by DC discharge increases with decrease in the inter-electrode distance, but it is opposite for pulsed discharges. Different efficiency of H(2)O(2) production is explained based on physical processes which result to formation of OH radicals
Topology, connectivity and electronic structure of C and B cages and the corresponding nanotubes
After a brief discussion of the structural trends which appear with
increasing number of atoms in B cages, a one-to one correspondence between the
connectivity of B cages and C cage structures will be proposed. The electronic
level spectra of both systems from Hartree-Fock calculations is given and
discussed. The relation of curvature introduced into an originally planar
graphitic fragment to pentagonal 'defects' such as are present in
buckminsterfullerene is also briefly treated.
A study of the structure and electronic properties of B nanotubes will then
be introduced. We start by presenting a solution of the free-electron network
approach for a 'model boron' planar lattice with local coordination number 6.
In particular the dispersion relation E(k) for the pi-electron bands, together
with the corresponding electronic Density Of States (DOS), will be exhibited.
This is then used within the zone folding scheme to obtain information about
the electronic DOS of different nanotubes obtained by folding this model boron
sheet.
To obtain the self-consistent potential in which the valence electrons move
in a nanotube, 'the March model' in its original form was invoked and results
are reported for a carbon nanotube.
Finally, heterostructures, such as BN cages and fluorinated
buckminsterfullerene, will be briefly treated, the new feature here being
electronegativity difference.Comment: 22 pages (revtex4) 12 figure
Similarity and contrasts between thermodynamic properties at the critical point of liquid alkali metals and of electron-hole droplets
The recent experimental study by means of time-resolved luminescence
measurements of an electron-hole liquid (EHL) in diamond by Shimano et al.
[Phys. Rev. Lett. 88 (2002) 057404] prompts us to compare and contrast critical
temperature T_c and critical density n_c relations in liquid alkali metals with
those in electron-hole liquids. The conclusion drawn is that these systems have
similarities with regard to critical properties. In both cases the critical
temperature is related to the cube root of the critical density. The existence
of this relation is traced to Coulomb interactions and to systematic trends in
the dielectric constant of the electron-hole systems. Finally a brief
comparison between the alkalis and EHLs of the critical values for the
compressibility ratio Z_c is also given
A branching streamer propagation argon plasma plume
Cold atmospheric-pressure plasma plumes have obtained great interests for their attractive features and application potentials. In this paper, a pulsed argon plasma plume was generated in the open air. Characteristic propagation of the argon plasma plume was carried out through high-speed imaging by an ICCD camera. An interesting propagation process was observed for the plasma plume, during which the plasma first propagated in a single streamer channel, and then with side branching as the applied voltage increased. The side branches are generated surrounding the main plasma channel but not split from the anode tip. This branching streamer propagation behavior was much different from the bulletlike development of typical plasma jets or streamers in point-wire or point-plane gaps
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