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Electrode erosion caused by dense plasma in constrictive discharge channel is one of the fundamentally detrimental effects existing in pulsed discharge switches. An enhanced plasma expansion in pseudospark discharge assisted by a magnetic switch (MS) is observed from ICCD images in this paper, accompanied by reduced commutation loss, and the mechanisms are revealed by experiments and simulations. The characteristics of the discharge waveforms and channel images of the pseudospark discharge with and without a series-connected MS are compared, and the influence of the number of magnetic cores is studied. As the loop current increases, the discharge channel expands radically and reaches the maximum as the current rising rate reaches the maximum. As the number of magnetic cores increases from 0 to 8, the maximum diameter of the discharge channel increases from 16 mm to about 38 mm, and the commutation loss is reduced from 30 mJ to 11 mJ. The electrode erosion rate of the case with a MS is lower than that without a MS. A particle in cell/Monte Carlo collision model coupling to nonlinear external circuit elements is established. The simulation results fit well with the experiment phenomena, including the discharge waveforms and the profiles of the discharge channel. The distribution of ions shows more diffused features than that of electrons, while the distribution of electrons is more similar to the discharge channel observed in experiments. The enhanced plasma expansion is mainly caused by the higher radial acceleration component of the charged particles during the magnetically delayed time. [ABSTRACT FROM AUTHOR]

Electrode erosion caused by dense plasma in constrictive discharge channel is one of the fundamentally detrimental effects existing in pulsed discharge switches. An enhanced plasma expansion in pseudospark discharge assisted by a magnetic switch (MS) is observed from ICCD images in this paper, accompanied by reduced commutation loss, and the mechanisms are revealed by experiments and simulations. The characteristics of the discharge waveforms and channel images of the pseudospark discharge with and without a series-connected MS are compared, and the influence of the number of magnetic cores is studied. As the loop current increases, the discharge channel expands radically and reaches the maximum as the current rising rate reaches the maximum. As the number of magnetic cores increases from 0 to 8, the maximum diameter of the discharge channel increases from 16 mm to about 38 mm, and the commutation loss is reduced from 30 mJ to 11 mJ. The electrode erosion rate of the case with a MS is lower than that without a MS. A particle in cell/Monte Carlo collision model coupling to nonlinear external circuit elements is established. The simulation results fit well with the experiment phenomena, including the discharge waveforms and the profiles of the discharge channel. The distribution of ions shows more diffused features than that of electrons, while the distribution of electrons is more similar to the discharge channel observed in experiments. The enhanced plasma expansion is mainly caused by the higher radial acceleration component of the charged particles during the magnetically delayed time. [ABSTRACT FROM AUTHOR]

With colorimetric characterization, digital cameras can be used as image-based tristimulus colorimeters for color communication. In order to overcome the restriction of fixed capture settings adopted in the conventional colorimetric characterization procedures, a novel method was proposed considering capture settings. The method calculating colorimetric value of the measured image contains five main steps, including conversion from RGB values to equivalent ones of training settings through factors based on imaging system model so as to build the bridge between different settings, scaling factors involved in preparation steps for transformation mapping to avoid errors resulted from nonlinearity of polynomial mapping for different ranges of illumination levels. The experiment results indicate that the prediction error of the proposed method, which was measured by CIELAB color difference formula, reaches less than 2 CIELAB units under different illumination levels and different correlated color temperatures. This prediction accuracy for different capture settings remains the same level as the conventional method for particular lighting condition. [ABSTRACT FROM AUTHOR]

RF ion thruster has a broad prospect of development via its simple structure, high specific impulse and electrode-less discharge. During the RF operating process, an important but ignored generally issue is that the high-energy metal particles generated by sputtering grid system can diffuse towards the ionization chamber and then deposit on the wall to form a conductive film. As a result, the RF power feed can be significantly inhibited which affects the thruster perform and reliability. In this work, the axial distribution of film thickness on the ionization chamber has been measured which has the characteristic of nonlinear distribution. And the film roughness can be significantly affected due to the gradient of film thickness and deposition temperature. Another corresponding measurement of plasma parameter evolutions in the ionization chamber has been carried out within 6000 min of thruster operation. Results shows that the presence of the deposited film can result in a ∼30 % decrease in the plasma density, which weakens the grid sputtering erosion and subsequently leads to a decrease in film growth rate. The combination of contributed to the degradation of the thruster performance, with the effect of deposited film accounting for about 41 %. [ABSTRACT FROM AUTHOR]

Due to the high flexibility of the spectral shape generated by a spectrally tunable multichannel LED light source, the traditional spectral estimation by a digital camera has difficulty in the training procedure and cannot reach a satisfactory accuracy. Considering the characteristics of the linear system for both lighting and imaging equipment, a method based on matrix factorization was proposed by capturing a standard color chart with its known reflectance illuminated under the individual channels of the multichannel LED light source. The experimental results indicate that the proposed method outperforms the traditional one, in terms of spectral accuracy and colorimetric difference, with the upper bound performance being higher than 0.999 goodness of fit coefficient (GFC) and less than 1.0 CIELAB unit, respectively. [ABSTRACT FROM AUTHOR]

High dynamic range (HDR) image acquisition techniques can record both bright and dark areas of the real scene. In order to acquire accurate colorimetric information as well as the luminance of the HDR scene, a reconstruction method in CIEXYZ device-independent color space based on camera colorimetric method was proposed in this paper. The camera RGB values of individual pictures are firstly transformed into the corresponding CIEXYZ values by colorimetric characterization with unrestricted capture settings. Then the XYZ values are fused by the weighting function determined according to the characterization accuracy. The prediction accuracy of the proposed method was verified by two phases of experiments to outperform the traditional one, with the color difference being less than 2 CIELAB units under the constant relative spectral power distribution (SPD) of lighting and 3.5 CIELAB units for the illuminations of different correlated color temperatures (CCTs), respectively. [ABSTRACT FROM AUTHOR]

Spectral estimation of fluorescent lamps is important in practical applications. Using an RGB digital camera and a standard color chart can be regarded as a multispectral way to recover lamp spectral characteristics that contain spikes or spectral lines. In this study, a new method for estimating the spectral power distribution (SPD) of fluorescent lamps was proposed with a workflow by applying two improvements to the existing reflectance recovery methods. The first improvement is to classify the estimated SPD into the corresponding type of fluorescent illuminant defined by CIE based on the spectral correlation distance, and the second one is to choose the optimized number of color patches for lamp SPD recovery with less error. The workflow consists of three modules, i.e. training, testing and optimization procedures. Compared with the traditional recovery method, the training procedure using synthetic data reduces the tremendous workload in practical measurements of different light sources. The testing results from synthetic and real data both indicate that these proposed modifications can significantly improve the accuracy of the existing recovery methods on colorimetric and spectral metrics. And by comparing their experimental results, three among five different methods are suggested to be suitable for the fluorescent lamp spectral estimation. [ABSTRACT FROM AUTHOR]

Correlated color temperature (CCT) is one of the most important lighting factors to influence the subjective perceptions, while there currently are few researches involving a wide range of CCT to study the comfort and preference within specific indoor scenarios. Therefore a psychophysical experiment with the method of forced choice was carried out in a light-emitting diode (LED) light booth with a panel of twelve observers to evaluate these estimations with different combinations of CCT and illuminance. The results show that Kruithof’s rule is just a qualitative conclusion rather than an accurate expression about pleasing combination of CCT and illuminance, and that illuminance is not a significant factor to influence the estimations if it is limited within a moderate range. The detailed analysis indicates that CCT has significant impact on the subjective comfort and preference, and a set of models were proposed to predict these subjective perceptions for the scenarios of relaxing and working. [ABSTRACT FROM AUTHOR]