Axial Distribution Of Electron Density Research Articles

Observation of the dynamic evolution process of vacuum arc microscopic particles based on the emission spectrum principle

The distribution of microscopic particles directly affects the recovery of the post arc insulating medium and determines whether the fault current can be interrupted. Based on the principle of vacuum arc emission spectrum, a high-speed spectrum observation platform was built to study the distribution of microscopic particles during the arc burning, and the axial and radial spectral line intensity and density distributions of atoms and ions under different current amplitudes were obtained. The results show that the CuI spectral line intensity has two peaks near the cathode and anode, while in the arc column it is relatively low. The peak of the CuI spectral line intensity near the electrode is caused by electrode evaporation. The peak duration of the CuI spectral line intensity near the cathode is always longer than that near the anode. The CuII spectral line intensity is lower, appears later and disappears earlier, which in the arc column increased obviously, compared with CuI. The CuII density near the cathode is higher than that near the anode, and the CuII density in the arc column is higher than in the two electrodes, which is similar to the axial distribution of electron density. The radial distribution curve of CuI and CuII density is similar to the radial distribution curve of spectral line intensity, and displays the characteristics of a high center and low edge in the radial direction of the arc gap. The difference is that the width of the atomic spectral line is larger than that of the corresponding ionic spectral line, the distribution curve of the ionic spectral line is smooth and symmetrical, and the radial attenuation rate of the CuII density is larger than that of the corresponding CuI. This reflects the ionization of atoms and the effect of magnetic fields. The radial and axial distribution of the particle density is opposite to that of the excitation temperature. Electrode emission will first affect the atom formation.

An estimation of the axial structure of surface-wave produced plasma column

An analytical expression to predict the axial distribution of electron density along the surface-wave sustained plasma column has been derived. The model is based on the square root approximation of the dispersion relation that gives a linear roll-off of electron density distribution in the plasma column. The point is to use a more tractable analytical approximation of dispersion relation of surface waves. An expression of attenuation coefficient, which includes the collisional loss, has been applied in studying the structure of the surface-wave produced plasma column. The derived attenuation model predicts a linear axial attenuation of electron density, as well as a nonlinear relation between the glass permittivity dependent frequency sensitivity and the wavenumber. The nonlinearity arises from non-negligible dielectric thickness. This result is consistent with early Aliev's results of the electron density profile, which correspond to the volume collisional absorption regime of surface wave sustained plasmas. The combined effects of surface-wave amplitude attenuation due to collisions and frequency dependence of group velocity cause an axial decrease in the surface wave axial power flux as the wave moves away from the launcher. A short analysis of the sensitivity of the normalized frequency to the permittivity of the glass based on the quasistatic approximation of the dispersion relation of surface waves is given.

Experimental studies on DC axial virtual cathode electric discharge

A new modification is carried out on axial virtual cathode oscillator to improve the device performance. The device operates by virtual cathode theory to generate high power microwave from the interaction between energetic electron beam and virtual cathode field. The electrical parameters are measured to understand the behavior of the discharge by using nitrogen gas. The breakdown potential Vb against Pd is investigated. A single electric probe is used to measure and estimate the plasma parameters. The virtual cathode position is defined from the axial distribution of electron density, axial distribution of electric field and axial distribution of plasma potential. The position of virtual cathode has been estimated to be at about 2cm from the mesh anode which can be confirmed from the electric field changing its direction and from the maximum value of plasma density at that position. The exposed samples to microwave radiation ensure the effects of the microwave radiation on them.

Direct evidence supporting the existence of a helical dislocation in protofilament packing in the intermediate filaments of oxidized trichocyte keratin.

The X-ray diffraction patterns of quill and hair, as well as other trichocyte keratin appendages, contain meridional reflections that can be indexed on an axial repeat of 470 Å. Unusually, however, many of the expected orders are not observed. A possible explanation, proposed by Fraser and MacRae (1983), was that the intermediate filaments (IF) that constitute the fibrillar component of the filament/matrix texture consist of 4-chain protofilaments arranged on a surface lattice subject to a helical dislocation. The radial projection of the resulting 8-protofilament ribbon was defined in terms of a two-dimensional unit cell characterized by vectors (a, b) with axial projections za ∼ 74 Å and zb ∼ 198 Å. This situation resembles that found in microtubules, where helical dislocations in subunit packing are also encountered, leading to a so-called "seam" along their length (Metoz and Wade, 1997). In keratin, however, the protofilaments are helical so the seam is inclined to the axis of the IF. Here we report details of the Patterson function that provides independent evidence for both the helical dislocation and the dimensions of the surface lattice. In addition, the observed meridional X-ray amplitudes have been compared with those predicted by various models of the axial distribution of electron density. A new model, adapted from one previously proposed, fits the data significantly better than has heretofore proved possible. An interpretation of the model in terms of either specific keratin-associated-protein (KAP) binding or the retention of IF symmetry by a portion of the head and/or tail domains is suggested.

Gas temperature and electron density profiles in an argon dc microdischarge measured by optical emission spectroscopy

Optical emisssion spectroscopy was employed to study a high pressure (100 s of Torr), slot-type (600 μm interelectrode gap), argon dc microdischarge, with added traces of nitrogen. Spatially resolved gas temperature profiles were obtained by analyzing rovibrational bands of the N2 first positive system. The gas temperature peaked near the cathode and increased with current. The contribution of Stark broadening to the hydrogen Hβ emission lineshape was used to extract the electron density. The axial distribution of electron density as well as visual observation revealed that the microdischarge positive column was highly constricted. The electron density near the sheath edge increased with both pressure and current.

Structural changes in the trichocyte intermediate filaments accompanying the transition from the reduced to the oxidized form

Earlier studies established that substantial changes take place in the three-dimensional structure of the newly assembled trichocyte keratin intermediate filament (IF) during the oxidation process (Wang, H., Parry, D.A.D., Jones, L.N., Idler, W.W., Marekov, L.N., Steinert, P.M. 2000. In vitro assembly and structure of trichocyte keratin intermediate filaments: A novel role for stabilization by disulfide bonding. J. Cell Biol. 151, 1459–1468). The present contribution describes a re-examination of previous data in which more accurate values for the axial dispositions of the molecules have been obtained to yield the most detailed picture yet available of the structural changes that occur in vivo. In particular, it is shown that in the newly assembled (reduced) IF the crosslinking data are consistent with the detailed (8 + 0) model suggested earlier (Fraser, R.D.B., Parry, D.A.D. 2005. The three-dimensional structure of trichocyte (hard α-) keratin intermediate filaments: Features of the molecular packing deduced from the sites of induced crosslinks. J. Struct. Biol. 151, 171–181), in which eight four-chain protofilaments are arranged on an annular ring. For oxidized IF, however, the existing X-ray data require a periodic imperfection in the surface lattice which is substantial in the case of an (8 + 0) model and hence difficult to explain. In contrast, an alternative (7 + 1) model (Fraser, R.D.B., MacRae, T.P., Parry, D.A.D., Suzuki, E. 1986. Intermediate filaments in α-keratin. Proc. Natl. Acad. Sci. USA 83, 1179–1183) requires only a minor imperfection, and it is suggested that this is associated with the central protofilament. This suggestion is shown to be compatible with both the crosslinking data and a model for the axial distribution of electron density derived from the meridional X-ray pattern. In addition, evidence from an X-ray diffraction study of the follicle (Er Rafik, M., Briki, F., Burghammer, M., Doucet, J. 2006. In vivo formation of the hard α-keratin intermediate filament along a hair follicle: Evidence for structural polymorphism. J. Struct. Biol. 154, 79–88) and electron microscope studies of isolated reduced IF (Watts, N.R., Jones, L.N., Cheng, N., Wall, J.S., Parry, D.A.D., Steven, A.C. 2002. Cryo-electron microscopy of trichocyte (hard α-keratin) intermediate filaments reveals a low-density core. J. Struct. Biol. 137, 109–118) have been combined with earlier X-ray studies to give an estimate of the reduction in diameter that occurs in the IF due to the lateral reorganization of the protofilaments during the oxidation process. It has also been shown that the local coiled-coil geometry in the immediate vicinity of the contributing cysteine residues is necessarily disrupted, a feature consistent with the breadths of the near-equatorial layer lines in the X-ray diffraction pattern that indicate an average coherent length of coiled coil of only about 5 nm.

Surface Wave Plasma Production Employing High-Permittivity Discharge Tube for Material Processing

As a novel method of plasma production, microwave-sustained discharge was studied, particularly focusing on the permittivity effect on the axial distributions of the plasma in the discharge column with the two discharge tube materials. In the alumina discharge tube with a high permittivity, the axial distribution of electron density showed to be very localized in the upstream, nearby the microwave launcher, while in the quartz with a low permittivity a higher density region appeared further downstream. This difference in the axial distribution of the electron density could be explained by the behavior of the surface wave. It was stressed that this property could be one of the biggest advantages in its application to material processing on the industrial level, particularly in achieving a low-damage plasma process, such as low-damage silicon etching.

Low temperature formation of microcrystalline silicon films using high-density SiH 4 microwave plasma

A microwave discharge utilizing a spokewise antenna was successfully applied for high rate deposition of microcrystalline silicon (μc-Si:H) film at low substrate temperatures of 200–250°C. Systematic deposition studies were carried out with the total pressure, H 2 dilution ratio and flow rate of SiH 4, Fr(SiH 4), as variables, combined with optical emission spectroscopy (OES) and Langmuir probe characterizations. It was revealed that the total pressure was the most important parameter for determining the deposition rate, which exhibited a maximum at 40–50 mtorr along with good crystallinity. By optimizing the plasma parameters together with the axial distribution of electron density, n e, a high deposition rate of ∼47 Å/s is achieved in the highly crystallinitzed and photoconductive μc-Si:H growth. A correlation among OES signal intensity, SiH, the intensity ratio, I Hα/ I Si*, deposition rate and film crystallinity is demonstrated.

空気吹付け平板状消弧室内の電子密度分布とその遮断能力に及ぼすノズルの形状と位置の効果

空気吹付け平板状消弧室内の電子密度分布とその遮断能力に及ぼすノズルの形状と位置の効果

容量結合型RF放電プラズマの軸方向電子密度分布

容量結合型RF放電プラズマの軸方向電子密度分布

The modelling of a discharge sustained by a standing surface wave

Presents a model of a microwave discharge sustained by a standing surface wave. An experimental verification of the model is made by carrying out a discharge in argon gas. The model is based on the solution of an electron diffusion equation in a gas, assuming that electrons are the sole particles causing the ionisation of gas, disappearing on the walls of the discharge tube during the process of recombination. The calculated and experimentally determined values of the axial distribution of electron density, the intensities of electric and magnetic fields and the axial distribution of intensities of neutral and ion lines are compared. This comparison shows good agreement of the model with the experiment.

Glutaraldehyde-induced changes in the axially projected fine structure of collagen fibrils

The fine structure of the collagen fibril, as seen in axial projection, is changed by treatment with glutaraldehyde. The changes are detectable in electron-optical staining patterns and in the intensities of the low-angle meridional X-ray diffraction maxima. Current knowledge of the amino acid sequence of collagen and of the axial arrangement of molecules in fibrils permits interpretation in terms of specific alterations to the axial distribution of electron density along the fibril. Analysis of fibril staining patterns from glutaraldehyde-treated calf skin collagen shows that uptake of staining ions in positive staining patterns is inhibited at residues known to interact with glutaraldehyde (lysyl, hydroxylysyl and probably histidyl side-chains) and on other charged residues in the immediate neighbourhood of the glutaraldehyde-reactive residues. This can be seen as a “stain-exclusion effect” due to the presence of bulky polymeric complexes of glutaraldehyde molecules at cross-linking sites. Such stain exclusion accounts for the drastic changes in the negative staining pattern following treatment with glutaraldehyde. The intensity changes observed in the low-angle meridional X-ray reflections from rat tail tendon, similarly treated, also can be explained by the presence of these bulky complexes. Existing data have been used to predict a model of the altered electron density profile indicating the axial distribution of glutaraldehyde along a D-period of moist tendon collagen.