Characteristics Of Streamers Research Articles

Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Context. Investigating the physical properties of solar coronal streamers is important for understanding their role in the global magnetic structure of the extended solar atmosphere, as well as in the generation of the slow solar wind. Aims. We hope to contribute as completely as possible to the ongoing SOHO instruments campaign devoted to the study of the physical characteristics of coronal streamers at various heliocentric distances. Methods. We analyzed ultraviolet H i Lyα and O vi resonance doublet lines observed by UVCS/SOHO in a narrow, mid-latitude streamer structure along different lines of sight during a week in May 2004 and made nearly simultaneous white-light polarized brightness measurements from the LASCO/SOHO C2 coronagraph. Results. Electron densities and temperatures, H i and O vi kinetic temperatures, and outflow velocities were derived from the line

Characteristics of DC Corona Streamers Induced by UV Laser Irradiation in Non-Thermal Plasma

AbstractPositive corona streamers are widely used in the field of air pollution control such as NOx or SOx removal and VOCs decomposition based on non-thermal plasma chemical process. In this study, the characteristics of DC positive corona streamers induced by UV laser irradiation are investigated in the tube-to-plane electrode configuration with electrode gap spacing of 3 cm. The streamer images were recorded using an ICCD camera with a nanosecond order time resolution. During the DC corona discharge, regular streamers appear with tens of ms intervals, the duration of which considerably fluctuates. This makes time resolved streamer observation by the ICCD camera extremely difficult. However, additional streamers with a predictable inception time can be induced by UV laser irradiation. As a result, the current waveform characteristics of the laser-induced streamers were obtained. In this work, three-dimensional streamer structures including the streamer propagation and branching were studied. Also the streamer propagation velocity was evaluated.

A transition from negative to positive streamers under a guiding field

A transition from a negative regime to positive streamers in a guiding field has been studied. The apparatus is a simple parallel plane electrode arrangement that provides the uniform guiding field. Negative streamers were generated by a pulsed negative voltage of magnitude ≈5 kV and duration ≈270 ns applied to a trigger pin electrode placed in an aperture at the centre of the grounded electrode and insulated from it by air. It has been shown that the velocities of streamers was between 4×104 and 1.5×105 m s−1 over an external guiding field range of 5.5–6.3 kV cm−1. Results have been presented showing the variation of field in the mid-gap region and the characteristics of streamers. Optical observations have shown the light emission from the developing discharge to be non-linear.

Oscillation characteristics of biofilm streamers in turbulent flowing water as related to drag and pressure drop.

Mixed population biofilms consisting of Pseudomonas aeruginosa, P. fluorescens, and Klebsiella pneumoniae were grown in a flow cell under turbulent conditions with a water flow velocity of 18 cm/s (Reynolds number, Re, =1192). After 7 days the biofilms were patchy and consisted of cell clusters and streamers (filamentous structures attached to the downstream edge of the clusters) separated by interstitial channels. The cell clusters ranged in size from 25 to 750 microm in diameter. The largest clusters were approximately 85 microm thick. The streamers, which were up to 3 mm long, oscillated laterally in the flow. The motion of the streamers was recorded at various flow velocities up to 50.5 cm/s (Re 3351) using confocal scanning laser microscopy. The resulting time traces were evaluated by image analysis and fast Fourier transform analysis (FFT). The amplitude of the motion increased with flow velocity in a sigmoidal shaped curve, reaching a plateau at an average fluid flow velocity of approximately 25 cm/s (Re 1656). The motion of the streamers was possibly limited by the flexibility of the biofilm material. FFT indicated that the frequency of oscillation was directly proportional to the average flow velocity (u(ave)) below 9.5 cm/s (Re 629). At u(ave) greater than 9.5 cm/s, oscillation frequencies were above our measurable frequency range (0.12-6.7 Hz). The oscillation frequency was related to the flow velocity by the Strouhal relationship, suggesting that the oscillations were possibly caused by vortex shedding from the upstream biofilm clusters. A loss coefficient (k) was used to assess the influence of biofilm accumulation on pressure drop. The k across the flow cell colonized with biofilm was 2.2 times greater than the k across a clean flow cell.

Repetition rate of streamers as a measure of content of electronegative additives in the air

This paper demonstrates that the positive streamer corona may be useful for the detection of electronegative impurities in gas (ambient air). The measurements of the repetition rate of streamers are carried out in a point-to-coaxial cylinder gap where DC voltage and AC voltage at a frequency of up to some kilohertz (the so-called `mixed voltage') are applied simultaneously. The repetition rate of streamers is investigated depending on the airflow rate, on the amplitude and frequency of the AC voltage, on the level of gas preionization and on the amount of moisture and impurities of different kinds in air. Results presented in the form of counting-rate characteristics of streamers show that under the action of halogens the detectable changes in characteristics take place if the halogen concentration exceeds 1 - 10 ppb. Principles of operation of the proposed detector and possible basic physical mechanisms of the influence of impurities on the counting response are discussed. It has been demonstrated that a simple statistical model for the inception of streamers under the conditions of a mixed voltage enables calculation of the counting-rate characteristics of streamers in satisfactory agreement with the experimental results.

Simulation of negative-streamer dynamics in nitrogen.

In this paper we consider how the dynamical characteristics of streamers are determined by their multidimensional structure. Results from two-dimensional (three-dimensional, cylindrically symmetric) simulations are presented at atmospheric pressure for ${\mathrm{N}}_{2}$ and plane-parallel electrodes. Our high-spatial-resolution simulations are based on a numerical model which is able to treat a wide range of electrode configurations (including point-to-plane and other complex configurations). This model has allowed us to make a more thorough investigation of streamer morphology than has been attempted previously. Detailed knowledge of the streamer morphology and its evolution are vital to the application of streamer discharges to processes such as the destruction of airborne toxic chemicals. We find that the morphology is complex, even for plane-parallel electrodes, with a range of radial structures that become evident at different phases of the streamer evolution. Several distinct phases of evolution are clearly discernible. We demonstrate the transition between these phases, showing how the self-consistent radial and axial structure varies with time.

Morphological and physiological characteristics of streamers in acid mine drainage water from a pyritic mine.

The occurrence of vast amounts of streamers was observed widely in acid mine drainage water from the abandoned Matsuo sulfur and iron sulfide mine area. The acid streamers were commonly white or cream colored and gelatinous, and were composed of many fine fibers. The streamers showed strong oxidizing activity of ferrous iron, sulfur and thiosulfate in an inorganic acid environment. Microscopic examinations of the streamers indicated that morphologically-similar bacterial rods multiplied in a long oriented cell chain and that a great number of the bacterial cell chains were combined in a zoogleal big conglomeration. The acid streamers were a mass of acidophilic, obligately chemolithotrophic iron-oxidizing bacteria, proved to be Thiobacillus ferrooxidans, which were embedded in a gelatinous matrix.

Plasma characteristics of streamers in neon

On the basis of electron-optical and oscillographic investigations of streamer breakdown in neon, calculations are made of the plasma density, conduction, and field strength at the ends of the streamer and inside it. It is shown that the streamer is a highly conducting plasma formation.

Multiple Contrail Streamers Observed by Radar

An unusual case of multiple streamers or filaments with the characteristic mare's tail pattern in vertical section has been observed by radar where the generating elements were condensation trails laid by high-altitude aircraft. The contrails were laid perpendicular to the wind, and, as they drifted, a multitude of streamers formed along each trail. The streamers extended from 9 km to the ground. RHI and PPI photographs at X and S band taken over a 2-hr period show the three-dimensional shape of the streamers due to the wind shear. Doppler measurements were also taken. The resulting velocity spectra are very narrow indicating little or no turbulence. Reflectivity factors were measured at various altitudes and show a decrease in reflectivity with distance from the generating line. Fall velocities based on the slopes of the streamer patterns varied from 0.4 to 1.4 m/sec. In general, the characteristics of the precipitation streamers were quite similar to those previously measured in naturally occurring cloud forms such as cirrus uncinus.