1,720,978 research outputs found
Experimental study on the life and performance of an improved DC arc plasma torch
No full textA novel DC arc plasma torch is designed in this paper in order to reduce the electrode erosion, and a series of experiments are carried out to investigate how to improve the lifetime and performance of the nitrogen DC arc plasma torch. The analysis of voltage characteristics of the plasma torch indicates that the interelectrode insert can increase the average arc voltage and the sudden expansion structure can reduce the voltage fluctuation, which is helpful to improve the working stability to some extent. The spectrum characteristics at the plasma torch outlet and the cold flow simulations show that the dual shielding gas mainly act near the anode and can effectively cover the entire anode wall. Combining the shielding gas distribution with anode heat transfer processes in argon and nitrogen plasma torch, it is inferred that argon shielding gas plays an important role on reducing the anode heat transfer processes in nitrogen plasma torch, which can effectively suppress the anode erosion. The life testing experimental results find that there is no significant erosion of the cathode, anode, and interelectrode insert after cumulative working time exceeding 20 h. The maximum nitrogen plasma jet length can reach similar to 35 mm with the outlet jet temperature of about 20 000 K at the current of 100 A and nitrogen gas flow rate of 10 slm. The maximum average specific enthalpy and thermal efficiency are respectively about 14 MJ kg-1 and 75% in the nitrogen plasma torch. Therefore, this newly designed DC arc plasma torch not only can suppress the electrode erosion but also has good working performance, which is expected to have excellent application prospects
Experimental study on the full cycle evolution of high-intensity atmospheric dc arc discharge from breakdown to extinguishment
No full textIn this study, the spatiotemporal evolution of full cycle of high-intensity dc argon arc discharge at atmospheric pressure is investigated by using a transferred arc device, which is easy to be directly observed in the experiment. Combining the voltage and current waveforms with high-speed images, the full cycle evolution process of high-intensity atmospheric dc arc can be divided into five different stages: breakdown pulse stage, cathode heating stage, current climbing stage, stable arc discharge stage, and finally arc extinguishing stage. The characteristics of each different stage are analyzed in detail through the electrical properties, high-speed pictures, and spectroscopic measurements. The results show that the strong luminescence region develops from the vicinity of cathode and anode to the middle in the breakdown pulse stage, which is explained from the spatiotemporal evolution of distributions of excited argon atom and ions. The development velocity of emission intensity of argon ions is mainly determined by the dominant stepwise ionization process. Then the cathode heating stage appears with many bright and nonuniformly distributed light spots on the cathode surface, and the electron emission mechanism of cathode gradually changes to the thermionic emission as the surface temperature rises. With the increase of arc current, the discharge channel significantly expands, then becomes stable due to the increment of the Lorentz force. The characteristics of arc extinguishing stage are clarified in terms of the decay of charged particles density
Experimental study of liquid aluminum droplet breakup characteristics based on a Drop-on-demand (DOD) magnetohydrodynamic actuation
No full textIn magnetohydrodynamic (MHD) drop-on-demand (DOD) actuation, Lorentz force generated in different excitation stages are exerted on the liquid metal jet to form a "push-pull" mechanism, which is crucial for generating accurate and repeatable metal droplets. In this study, the important parameters of the excitation current waveform in the magnetohydrodynamic (MHD) process, including the influence of the excitation voltage pulse width ratio and current amplitude on the velocity, energy, volume, and breakup length of aluminum droplets are studied. The conversion process of surface energy and kinetic energy during the formation and fall stage of liquid droplets is analyzed. The results show that the negative and positive excitation voltage pulse width ratio of the MHD pump has a significant effect on the droplet velocity, breakup time, size, and sphericity. The amplitude of the excitation current and Hartmann number has a significant impact on the generation of stable droplets. The results show that the single droplet ejection state can be achieved within the Ha number between 319.5 and 391.1. As the Ha number increases, the volume, length, kinetic energy and surface energy of the droplets at breakup time also increase. The size of droplets can be adjusted by changing the amplitude of excitation waveform
Thermochemical kinetic model for high altitude and low altitude high-speed flow and radiation prediction based on the State-to-State model
No full textThe reasonable thermochemical kinetic model is a key prerequisite for accurately predicting the non-equilibrium flow field and radiation of high-speed atmospheric reentry vehicles. A vibrational and electronic specific State-to-State kinetic model is first established to couple with post-shock flow equations to analyze the thermochemical non-equilibrium flow characteristics. It is found that the vibrational and electronic energy levels non-Boltzmann metric are large at the flight altitude higher than 50 km, which is thus considered a demarcation line for constructing the low- and high-altitude models. Therefore, in this study, two new physics-based thermochemical kinetic models are constructed from the State-to-State model using the multi-group maximum entropy method for low-altitude and high-altitude regions, respectively, across the entire flight velocity domains. By analyzing the differences in post-shock flow physical characteristics under various flight altitudes, single-group and multi-group functions are, respectively, adopted to reconstruct the internal energy levels distributions within the flow field for the low-altitude and high-altitude chemical models. Compared to the State-to-State model, the low-altitude and high-altitude models significantly reduce the number of solved species and chemical reactions, while maintaining computational accuracy of post-shock non-equilibrium flow, with calculated thermodynamic parameters error less than 5% and chemical parameters error below 10%. Finally, the low-altitude and high-altitude chemical models constructed in this study exhibit better predictive capability in reproducing ground experimentally measured electron number density and predicting reentry flight heat flux and radiation compared with the classical Park's and Gupta's models, demonstrating the promising applicability of developed models. This study provides a new, reasonable chemical model for the entire flight altitude and velocity domain that can be used in computational fluid dynamics simulations to predict non-equilibrium flow and radiation in high-speed reentry vehicles
FIGURE 1 in Molecular identification of common hard ticks (Acari: Ixodidae) in Xinjiang, China
No full textFIGURE 1. Phylogenetic tree of 8 common species of hard ticks in Xinjiang based on the CO1 gene with the neighbor-joining method (bootstrap replicates: 1000).Published as part of Wang, Qiguo, Zhang, Yujiang, Sun, Surong, Luo, Tao, Mou, Wenting, Li, Bo, Dong, Xiao, Zhang, Xiaobing, Baokaixi, Guliayi & Cui, Yan, 2021, Molecular identification of common hard ticks (Acari: Ixodidae) in Xinjiang, China, pp. 46-60 in Zootaxa 4950 (1) on page 50, DOI: 10.11646/zootaxa.4950.1.2, http://zenodo.org/record/464336
FIGURE 3 in Molecular identification of common hard ticks (Acari: Ixodidae) in Xinjiang, China
No full textFIGURE 3. Phylogenetic tree of 8 common species of hard ticks in Xinjiang based on the 16S rDNA gene with the neighborjoining method (bootstrap replicates: 1000).Published as part of Wang, Qiguo, Zhang, Yujiang, Sun, Surong, Luo, Tao, Mou, Wenting, Li, Bo, Dong, Xiao, Zhang, Xiaobing, Baokaixi, Guliayi & Cui, Yan, 2021, Molecular identification of common hard ticks (Acari: Ixodidae) in Xinjiang, China, pp. 46-60 in Zootaxa 4950 (1) on page 52, DOI: 10.11646/zootaxa.4950.1.2, http://zenodo.org/record/464336
A novel anode structure for diffuse arc anode attachment
No full textAbstractA novel method for adjusting the direct current arc anode attachment mode by changing the anode surface structure is proposed. A transferred arc device is used to investigate the effect on the arc anode attachment state of the electrode separation and the presence and dimensions of an annular boss, or embossing, on the anode. The experimental results show the diffuse arc anode attachment mode is more likely to be formed in the presence of an annular boss structure on the anode, compared to the standard planar structure. In the case of argon working gas, as the distance between the cathode and the anode increases from 15 mm to 30 mm, the arc maintains the diffuse arc attachment on the anode with the annular boss, while for a planar anode, the arc anode attachment mode changes from diffuse to constricted. Comparison of the measured temperature distribution by the relative intensity method and the emission intensity of the arc attachment region verifies that the annular boss anode can indeed promote diffuse attachment. Analysis of the electric field strength distribution between the electrodes shows that the introduction of the annular boss doubles the electric field strength near the anode surface due to the boss edge effect, which drives the arc to be evenly dispersed on the boss, resulting in the formation of diffuse arc attachment. The enlarged attachment area reduces the current density and heat flux on the anode surface, which is important for the stabilization of diffuse arc attachment. No obvious ablation is found on the surface of the annular boss anode after 1 h operation, while there significant ablation is evident on the surface of the planar anode.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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