Xiangen Zhao

Branching is a common feature in positive leader development, which changes the channel topology and significantly influences discharge behavior. However, the factors associated with its occurrence remain poorly understood. In this study, an event‐based analytical framework was established using synchronized optical observations and electrical measurements. Five physically motivated variables were constructed, including the injected charge Q , the rise rate of applied voltage dU / dt , the background field E , the background‐field direction angle θ ₁ , and the prior‐channel deflection angle θ ₂ . Their independent, nonlinear, and interaction effects were analyzed using multivariable logistic regression, restricted cubic splines, and random‐forest‐assisted interaction mining with regression validation. Primary and sensitivity analyses show that Q , dU / dt , and E are consistently and positively associated with branching occurrence, whereas θ ₁ and θ ₂ provide weaker and less stable information. Q shows the most reproducible nonlinear association, although its curve shape is partly affected by original‐scale skewness. The interaction rule of E > 275 kV/m and dU / dt > 8.1 kV/μs is identified as the most reproducible candidate interaction signal, suggesting that branching is more likely when stronger background‐field conditions coincide with faster dU / dt ; however, its statistical support is sensitive to variable definition and sample composition. These results suggest that positive leader branching is associated with multiple interacting field‐related factors rather than a single fixed threshold. The proposed event‐based proxy‐variable framework provides a feasible approach for quantitatively analyzing branching‐related factors under the resolution limits of the present experiments.

Understanding arc‐flow interactions is crucial for optimizing CO ₂ conversion in magnetically driven gliding arc reactors. In this study, a comprehensive diagnostic platform integrating electrical, high‐speed optical, and Schlieren imaging is developed to investigate arc‐flow dynamic under purely flow‐driven, magnetically‐accelerated, and magnetically‐decelerated configurations. Although the magnetically‐accelerated configuration expands the plasma region, it minimizes the arc‐flow slip velocity, thereby degrading CO ₂ conversion due to a weakened gas‐sweeping effect and enhanced thermalization. Conversely, the magnetically‐decelerated configuration sustains a large relative slip velocity, which effectively dissipates heat and preserves a strong non‐equilibrium state. Consequently, it significantly improves CO ₂ conversion performance by facilitating efficient mixing between the active plasma and feedstock.

This work proposes an updated set of electron-impact cross sections (CSs) for carbon dioxide (CO₂) by quantitatively identifying CO₂ dissociation within the two electronic excitation channels proposed by Phelps. In particular, the CS with energy threshold at 7 eV is considered with a 15% dissociation branching ratio and is associated with dissociation into O(¹D) + CO(X), while the one with threshold at 10.5 eV is used entirely for dissociation into O(³P) + CO(a³Π_r). Experimental data on CO₂ dissociation rate coefficients at moderate reduced electric field (E/N), CO₂ conversion efficiencies at high E/N, and electron transport coefficients for E/N∈[10⁻², 10³] Td are used to validate the updated set and demonstrate its completeness and consistency over a wide range of E/N. Notably, the updated CS set enables the full coupling between the electron and chemical kinetics, a feature lacking in most existing CS sets. The updated set is applied to study electron kinetics in CO₂–Ar and CO₂–N₂ mixtures, revealing significant modifications in the electron energy distribution function and CO₂ dissociation rate coefficient due to mixture composition. The updated CS set is made available at the IST-Lisbon database within LXCat.

Droplet transport assumes a crucial role in domains such as atmospheric governance, water resource development, drug delivery, medical analysis and detection, as well as the development of biosensors. Currently, droplet transport is accomplished through established chemical environments and structural gradients, yet it fails to precisely control the motion state of droplets. This paper presents an innovative approach for transporting droplets by means of discharge plasma, which governs the start, stop, and velocity of the droplets by modulating the discharge power. We employ discharge plasma to charge and polarize droplets and form gradient electric fields and gradient charges in space for driving droplets. Eventually, we achieved directional transport of diverse droplets via this method, which holds significant potential application value for controlling droplet motion.

To prevent incidents caused by AC series arc faults, arc fault detection devices or arc-fault circuit interrupters have been introduced into the Chinese market where these products must pass the IEC62606 or GB31143 tests, which are developed to ensure the device's capabilities with resistance to missed tripping and unwanted tripping. However, the performance of representative products in realistic domestic environments is not as good as it should be. This paper presents a comprehensive investigation into these devices experimentally on the ability to clear the arcing fault under series arc faults and avoid unwanted trips in a normal circuit with mixed loads. It is found that less than half of the selected products passed the standard tests. The products passing the standard test failed in one or more additional tests with more diverse appliances or more complicated circuit configurations. Through analyzing the current waveforms collected in failure cases, realistic experiments with diverse appliances and complex load configurations were provided for inclusion in the dataset creation for detection algorithm development and in the standard for certification.

To study the mechanism of space stem formation, the high‐speed direct imaging technique and Schlieren photography are used to simultaneously observe the space stems in a 1.35‐m air gap under the lightning impulse voltage. It is found that the average length and diameter of the space stem is approximately 5 and 0.5 mm, which is about 1/3 of the length and 1/10 of the diameter of the local luminous region respectively. Moreover, the space stem exhibits a non‐uniform distributed temperature with a maximum value of several hundred Kelvin for tens of microseconds. Accordingly, a possible mechanism is proposed that the space stem is formed at the primary corona streamer boundary as a result of the propagation of a secondary ionization wave from the HV electrode and survives long enough (to finish the polarization) due to the fast gas heating and production of atomic oxygen.