Small Arc Research Articles

Arc Ignition Methods and Combustion Characteristics of Small-Current Arc Faults in High-Voltage Cables

High-voltage cables will continue to operate for a period of time in the event of a small current arc fault, which poses a risk of fire. Two simulated ignition methods, moving electrode and melting fuses, are proposed to analyze the ignition characteristics of low-current arcs. The ignition test was carried out, and the combustion effect was compared. The results indicate that the moving electrode ignition method can achieve long-distance arc ignition test when the current is small and is suitable for simulating the arc ignition situation of cable outer protective layer damage. By controlling the movement speed, it can be ensured that the arc will not be interrupted during the electrode movement process. However, the arc is difficult to sustain using the fuse melting method when the current is small and the distance is long. The fuse melting method is suitable for simulating insulation breakdown situations. The results show that the critical arc duration for cable ignition under five different current conditions of 2–10 A is 28 s, 21 s, 14 s, 9 s, and 4 s, respectively. The maximum height of the cable flame under 2–10 A arc current is 9–52 cm and 16–63 cm, respectively, when the arc duration is 50 s and 100 s. The self-ignition time of the cable after the arc extinguishing is 8–95 s and 14–261 s, respectively. The maximum temperature of the cable flame is positively correlated with arc current, and the maximum flame temperature of the cable under 2–10 A arc current is 540–980 °C. Based on the actual current monitoring data in cable tunnels, the research results can provide reference for the risk assessment and protection of cable tunnel fires.

Variability in the Electrodynamics of the Small Scale Auroral Arc

Variability in the Electrodynamics of the Small Scale Auroral Arc

Finding small feedback arc sets on large graphs

The minimum feedback arc set problem (FASP), which seeks to remove a minimum set of arcs from a directed graph to make the remaining graph acyclic, is fundamental in graph algorithms with many applications in social network analysis, circuit testing, deadlock resolution, algorithmic games, and other fields. However, in theory, FASP is NP-Hard and cannot be approximated within any constant under the Unique-Games Conjecture. In practice, the performance of existing algorithms on large graphs is still unsatisfactory. To solve FASP on large graphs, we propose two novel methods in this paper. First, we systematically study the reduction rules for FASP that can quickly reduce the scale of input graphs without losing optimality. We integrate the reduction rules into an algorithm that can be used as a preprocessor for all existing FASP algorithms to simplify the input graphs. Second, we provide a scalable heuristic algorithm based on the divide-and-conquer method for better solution quality. Extensive experiments on a wide range of real-world graphs show that the reduction algorithm effectively reduces the size of input instances. Furthermore, for half of the circuit benchmark graphs, our final algorithm improves the quality of the existing heuristic solution by 24% to 40% within an acceptable running time.

Fatigue Life Prediction and Verification of Railway Fastener Clip Based on Critical Plane Method

Accurately predicting the fatigue life of fastener clips is crucial for improving material processing technology, enhancing the anti-fatigue design level, and guiding the maintenance and repair of track structures. Conventional methods that solely evaluate the fatigue life of fastener clips based on the uniaxial stress index under displacement loads may lead to significant errors. In this paper, the stress field of a type-III clip under displacement loading conditions was numerically simulated based on fatigue test standards, and the fatigue life of the clip was analyzed using the Fatemi–Socie (FS) multiaxial fatigue criterion based on the critical plane method. A comparison with standard fatigue test results revealed that, under non-resonance conditions, the predicted position of the fatigue critical plane of the fastener clip coincided with the fracture surface observed at the middle of the measured small arc, with a life prediction error of 7.3%. To further investigate the predictive capability of the FS multiaxial fatigue criterion for the fatigue life of the fastener clip under resonance conditions, the stress levels of the clip under non-resonance and resonance conditions were compared through on-site testing, and the effects of inertial loads caused by vertical and lateral vibration acceleration on the stress field of the clip were analyzed in numerical simulation according to the results of clip acceleration tests; the fastener clip’s resonance fracture position and fatigue life were also predicted based on the aforementioned multiaxial fatigue criterion. To verify the accuracy of the predicted results, a testing method was proposed that equates the high-frequency resonant inertial load of the fastener clip to a low-frequency additional preload under the premise of consistent stress fields. A comparison with the numerical simulation results shows that considering only vertical inertial loads would result in a discrepancy between the measured fracture location and the actual one. Considering both vertical and lateral inertial loads, the fracture location (at the heel of the small arc) under resonance conditions could be accurately determined, with a life prediction error of 13.8%. Compared to the non-resonant displacement loading condition, the inertial loads caused by acceleration under resonance conditions led to a reduction in fatigue life of approximately 77.8%.

Design of circular slots loaded MIMO antenna with DGS at 28 GHz for 5G wireless services

In this paper, a MIMO microstrip patch antenna with four radiating elements is designed and analyzed at 28 GHz. This paper addresses the problem of mutual coupling without adding a decoupling network. The decoupling method increases the complexity and volume of MIMO antennas. The CST Microwave simulator is used to simulate the MIMO antenna. The simulation and measurement results are compared to analyze the antenna's performance. The parameters of the MIMO patch antenna, including return loss, VSWR, gain, beam width, and radiation pattern, are evaluated at a center frequency of 28 GHz. The overall dimensions of the MIMO antenna are 60 × 42 × 1.6 mm3.An H-shaped slot is inserted in the middle of the ground plane to minimize mutual coupling among the radiating elements. The isolation amplitude between radiating elements is observed greater than 35 dB at 28 GHz frequency. A wide impedance bandwidth of 4 GHz (26.5 to 30.5) is achieved, by etching four small arcs into the patch’s corners. In this work, two circular slots are inserted on the radiating element to widen the bandwidth further by adjusting the surface current on each radiating patch. At the center frequency of 28 GHz, the Envelope Correlation Coefficient (ECC) is observed to be 0.0001, with a diversity gain of 10 dB. The antenna has a maximum radiation efficiency of 75% and a peak gain of 7.62 dB. This antenna can be used for 5G wireless services.

Rotational stability of a new hydrophobic acrylic intraocular lens platform.

To evaluate rotational stability for ease of rotation of a new intraocular lens (IOL) platform with 4 haptics in an ex vivo model and compare it with a control single-piece lens with 2 open loops. Intermountain Ocular Research Center, John A. Moran Eye Center, University of Utah, Salt Lake City, Utah. Experimental study. 10 human cadaver eyes were prepared as per the Miyake-Apple technique. After injection of the test or control lens, clockwise and counterclockwise rotations were attempted with a hook, with and without an ophthalmic viscosurgical device in place. Ease of rotation was scored as (1) very easy, (2) easy, (3) difficult, and (4) very difficult. Rotation of the entire eye containing test or control IOL was also performed with a multipurpose rotator (2 minutes; 220 revolutions per minute) to evaluate its effect on IOL alignment. There were statistically significant differences regarding ease of rotation between test and control lenses in all 4 scenarios, with rotation being more difficult with the test lens ( P < .05, Wilcoxon signed-rank test). No change in the alignment of test or control lenses was observed after eye rotation with the multipurpose rotator. The new IOL platform showed greater rotational stability than the control lens in this model, owing to design features such as 4 small arcs of contact between the haptics and the bag equator, a bulge at the distal end of each haptic, and arcuate haptics with curvatures oriented toward each other.

Nickel-doped microtubular CeVO4 inspired by wood powder structure for visible light photocatalytic degradation of methylene blue and bacterial inactivation

In this study, inspired by natural wood powder structure, nickel-doped microtubular cerium vanadate (Ni/T-CeVO4) was obtained using wood powder as a biological template. Photocatalytic experiments under visible light revealed that Ni/T-CeVO4-3wt possessed the highest photocatalytic activity, with a degradation efficiency of up to 99 % for methylene blue. The enhanced photocatalytic performance was not only attributed to the microtubule wood powder structure assigned the composite a larger specific surface area but also the nickel doping narrowed the band gap of the composites while introducing more oxygen vacancies. The rapidly generated current in transient photocurrent responses and small arc radius in electrochemical impedance spectra further indicated the higher photogenerated carrier separation and smaller photogenerated electron transfer resistance within the composite. ESR spin-trapping tests proved that O2− and OH dominated the photocatalytic process. Furthermore, owing to its unique structural characteristics, the composite showed excellent photocatalytic antibacterial activity against Staphylococcus aureus and Escherichia coli. The present study provides a theoretical basis for developing efficient dual-effect photocatalysts using visible light to remove organic dyes and pathogenic bacteria from the water environment.

Research on Quasi-isotropic Radiation of Small Circular Arc Antenna

The radiation characteristics of circular arc antennas are studied by applying the method of moments (MoM) to solve the electric field integral equation (EFIE). Based on the triangular current distribution of small circular arc antennas, the analytical expression of radiation fields of circular arc antennas is derived. It is found that the circular arc antenna is equivalent to a superposition of an electric dipole and a magnetic dipole, resulting in near isotropic radiation pattern. Finally, both MoM and CST simulations show that the small arc antenna can realize the near isotropic radiation pattern.

Artificial neural network analysis for classification of defected high voltage ceramic insulators

Partial discharge (PD) could lead to the formation of small arcs or sparks within the insulating material, which can cause damage and degradation to the insulator over time. In ceramic insulators, there are several factors that can cause PD including manufacturing defects, aging, and exposure to environmental conditions such as moisture and temperature extremes. As a result, detecting and monitoring PD in ceramic insulators is important for ensuring the reliability and safety of electrical systems that rely on these insulators. In this study, acoustic emission technique is introduced for PD detection and condition monitoring of defective ceramic insulators. A sequence of data processing techniques is performed on the captured signals to extract and select the most significant signatures for classification of defects in insulator strings. Artificial neural network (ANN) has been used to build an intelligent classifier for easily and accurately classification of defective insulators. The overall recognition rate of the classifier was obtained at 96.03% from discrete wavelet transform analysis and 88.65% from fast Fourier transform analysis. This obtained result indicates high accuracy and performance classification. The outcomes of ANN were verified by SVM and KNN algorithms.

Words are delicious

Words are delicious

Numerical analysis of arc physics and energy transfer under circumferential gas constraint effect

Energy dispersion and easy instability associated with arcs, the traditional metal processing heat source, restrict its development and application in the modern high-precision welding and additive manufacturing. This work aims to study the characteristics of a novel arc under circumferential gas constraint effect which can improve the arc stability and processing accuracy. A magnetohydrodynamics model was established to calculate the arc physics and heat transfer, considering the electron emission characteristics of tungsten and the effect of metal vapor. It indicates that the annular flexible constrained gas flow can significantly increase the physical characteristics such as arc temperature, plasma flow velocity and current density compared with traditional free arc which is named GTA. The arc heat generation increasement of the novel arc makes the heat transfer from arc to base metal higher than that of GTA. The additional annular gas flow inhibits the diffusion of metal vapor, stabilizing the arc and protecting the tungsten electrode from contamination. However, as the arc length decreases, eddy of arc plasma flow appears inside the arc, which can cause metal vapor to contaminate the tungsten. It's found that this novel gas flow constrained arc needs to be applied with a small current when welding with small arc length to avoid the eddy. Finally, the accuracy of the calculation model is verified by experimental detection of arc temperature.

Restudy of shoulder motion in the theropod dinosaur Mononykus olecranus (Alvarezsauridae)

Background Range of motion in the forelimb of the Upper Cretaceous theropod dinosaur Mononykus olecranus, a member of the family Alvarezsauridae, has previously been investigated. However, the method used to investigate range of motion at the shoulder in M. olecranus did not follow the standardized procedure used in subsequent studies. The latter procedure yields more reliable results, and its standardization provides that its results are directly comparable to the results of similar studies in other species. I therefore reinvestigated the range of motion at the shoulder in M. olecranus, using the latter procedure. Methods Casts of the left scapula and coracoid of M. olecranus were posed on a horizontal surface, supported from beneath with modeling clay, with the medial surface of the scapula facing toward the horizontal surface. A cast of the left humerus was posed at the limits of motion through the transverse and parasagittal planes. Photos of the poses in orthal views were superimposed and used to measure range of motion, which was measured as the angle between lines drawn down the long axis of the humerus in each position. Results Through the transverse plane, the humerus of M. olecranus could be elevated to a subhorizontal position and depressed to a subvertical position. It could move through the parasagittal plane from a subvertical position at full protraction to a position above the horizontal at full retraction. These results correct the previous mischaracterization of shoulder motion in M. olecranus as restricted to a small arc with the arms held in a permanent sprawl. The range of humeral motion in M. olecranus is much greater than that found by the previous method and allowed the animal to tuck its arms in at the sides, in addition to allowing them to sprawl so as to orient the palm downward. The wide range of humeral motion allowed M. olecranus to forage for insects by employing hook-and-pull digging at surfaces with a wider range of orientations than the previous study showed to be possible.

Robust one-pot solvothermal incorporation of InVO4 with polymeric-C3N4 nanosheets with improved charge carrier separation and transfer: A highly efficient and stable photocatalyst for solar fuel (H2) generation

Polymeric-C3N4 is a photocatalyst with desirable properties for efficient solar fuel (H2) generation. However, p- C3N4 exhibits a low H2 evolution rate. Herein, InVO4 is successfully incorporated on the surface of p- C3N4 nanosheets via a one-pot solvothermal method to generate solar fuel (H2) effectively. The optical gap energy of p- C3N4 was red-shifted to 2.23 eV after incorporating InVO4. A small arc radius of the Nyquist plot and substantial quenching of PL was observed when InVO4 was added to p- C3N4. The optimized catalyst loading (15 wt%) shows a maximum H2 production activity of 8980 µmol/g/h. This outstanding performance is a nearly 56-fold enhancement in comparison with bare p-C3N4. Furthermore, the STH conversion efficiency of 1.87% is achieved with the optimized photocatalysts, which is higher than many g- C3N4 - based photocatalysts. Moreover, the H2 generation activity achieved in the present work is higher than the reported one using the same InVO4-g- C3N4 photocatalysts.

Revealing the photophysics of N719 dye based dye-sensitized solar cell

Dye-sensitized solar cell (DSSC) has demonstrated promising photovoltaic performance with several photo-sensitizers. N719 dye, is a popular sensitizer used in DSSC due to its ability to absorb light in the visible region and its unique characteristics such as ultrafast electron injection and stable anchoring to the TiO2 surface. However, many of its intriguing optoelectronic properties and charge carrier relaxation at low frequency are contested. Here impedance and modulus spectroscopy were employed to extensively explore the charge carrier dynamics under both light-off and illumination conditions, and it was found that there is a significant change observed in the low-frequency regime in both cases. The fabricated N719 dye based DSSC exhibit the highest JSC of 10.89 mA/cm2, a highest VOC of 0.672 V, a fill-factor of 0.65 and photoconversion efficiency of 4.81%. The Nyquist plot of N719 DSSC under light-off and illumination conditions demonstrates that at higher frequency, a small arc is observed, and at a lower value, a large arc is observed. Moreover, the Nyquist plots exhibit depressed semicircles due to deviation from ideal Debye relaxation nature. The dielectric relaxation is found to follow the interfacial polarization of Maxwell-Wagner type probably attributed to the grain boundary effects. Furthermore, the comparative analysis of modulus and impedance spectra at low frequency reveals the localized carrier relaxation in this N719 DSSC which has been correlated with conductivity hopping process.

Strength characteristics and electrochemical impedance spectroscopy study of red mud-coal metakaolin geopolymer in a hydrochloric acid environment

In this study, the compressive strength and electrochemical impedance spectroscopy (EIS) of red mud - coal metakaolin geopolymer (referred to as RM-CMK geopolymer), soaked in a high concentration (pH value of 2) hydrochloric acid solution were tested. The compressive strength of the RM-CMK geopolymer increased first and then decreased with the increasing immersion time in a hydrochloric acid solution environment. When the immersion time was 14 d, the compressive strength reached a maximum of 39.3 MPa. The EIS results showed that the Nyquist diagrams were composed of a small capacitive arc in the high-frequency region and large capacitive arc in the medium-frequency region. The radius of the capacitive arc in the medium frequency region, the total impedance value and the phase angle increased first and then decreased with the increasing immersion time. The equivalent circuit model of the RM-CMK geopolymer in the hydrochloric acid solution environment was determined to be Rs(Q1(Rct1W))(Q2Rct2). The compressive strength and electrochemical parameters of the RM-CMK geopolymer in hydrochloric acid solution environment had a good linear correlation. In addition, combined with scanning electron microscopy (SEM), the reasons for the strength and EIS change of the RM-CMK geopolymer in the hydrochloric acid solution were explained from a microscopic point of view.

Efficient Combination of Carbon Quantum Dots and BiVO4 for Significantly Enhanced Photocatalytic Activities

The development of highly efficient and stable photocatalysts is of critical importance for the removal of environmental pollutants, such as paraben preservatives. In this work, carbon quantum dots (CQDs) were used to modify bismuth vanadate (BiVO4) through a hydrothermal reaction. Regarding the as-formed CQDs/BiVO4 composite, TEM, XPS, and Raman spectra analysis demonstrated the strong interaction between CQDs and BiVO4, possibly leading to the elevated energy level of the composite. As compared to pristine BiVO4, CQDs/BiVO4 showed an increase in light harvesting, and significantly enhanced visible-light activities in degrading the typical paraben pollutant—benzyl paraben (BzP)—where the maximum 85.4% of BzP was degraded in 150 min. After four cycle reactions, the optimum sample 0.6%CQDs/BiVO4 still degraded 78.2% of BzP, indicating the good stability and reusability of the composite. The notably higher photocurrent and smaller arc in Nyquist plot were measured by CQDs/BiVO4, unveiling the improved photocharge separation and lowered interfacial charge transfer resistance by CQDs modification. Meanwhile, due to the promoted energy level, CQDs/BiVO4 practically produced •O2− species and thereby contributed to the BzP degradation, while they had no ability to produce •OH. This was contrary to the BiVO4 system, where •OH and h+ played the dominant roles.

Experiment and analysis of self-centering semicircular corrugated steel plate shear walls with edge stiffeners

This study proposes a self-centering semicircular corrugated steel plate shear wall (SC-CSPSW) based on the conventional semicircular corrugated steel plate shear wall (CSPSW) with edge stiffeners. The restoring force model of SC-CSPSW and the key points affecting the recoverability are obtained by analyzing the mechanical properties of its components. In this study, two specimens with different diameters of SC-CSPSW are fabricated. Subsequently, low-cycle reciprocating loading tests are conducted on the two specimens to analyze their restoration, deformation, and energy dissipation properties. The experimental results show that the recentering performance of the SC-CSPSW with a large arc diameter is subpar than that of with a smaller arc diameter. The SC-CSPSW with a small arc diameter has a better energy dissipation performance than the large arc diameter of SC-CSPSW, and the main frame of the two specimens remain elastic. Additionally, it is observed that the CSPSWs are damaged with several “X" shapes. The refined finite element analysis (FEA) model of the two specimens is established within the ABAQUS environment, and the same loading system is used to analyze the specimens, thus laying a foundation for later analysis on the influence of various parameter changes on the structural performance of the SC-CSPSW. This study presents the results from the test program and compares the experimental results to the refined finite element model; further, theoretical formulas are verified via comparison at the same time.

On the application of MUSIC algorithm for identifying short sound-hard arcs in limited-view inverse acoustic problem

For proper application of the MUltiple SIgnal Classification (MUSIC) algorithm for imaging short, linear sound-hard arcs, one needs a priori information of the unit outward normal vector on each arc. Due to this reason, a set of directions was applied to estimate, which caused the imaging procedure’s slowness. Applying a unit vector instead of the estimation is natural to avoid this difficulty. However, no relevant mathematical theory has been developed to explain the various phenomena in simulation results. Here, we consider applying MUSIC without a priori information of the arcs. To this end, we introduce the imaging functions of MUSIC with and without information on the unit outward vector on the arcs. We analyze their mathematical structure by establishing an infinite series of Bessel functions and the range of incident/observation directions and discuss their properties. This is based on the physical factorization of the multi-static response (MSR) matrix that separates the incoming plane-wave information from the unknown density information. Numerical simulation results with noisy data are conducted for small and extended arcs to support the theoretical result.

Not sorcery after all: Roles of multiple charged residues in membrane insertion of gasdermin-A3.

Gasdermins execute programmatory cell death, known as pyroptosis, by forming medium-sized membrane pores. Recently, the molecular structure of those pores as well as the diversity in their shape and size have been revealed by cryoTEM and atomic force microscopy, respectively. Even though a growth of smaller to larger oligomers and reshaping from slits to rings could be documented, the initiation of the gasdermin pore formation remains a mystery. In one hypothesis, gasdermin monomers insert into membranes before associating into oligomeric pores. In the other hypothesis, gasdermin oligomers preassemble on the membrane surface prior to membrane insertion. Here, by studying the behavior of monomeric membrane-inserted gasdermin-A3 (GSDMA3), we unveil that a monomeric gasdermin prefers the membrane-adsorbed over the membrane-inserted state. Our results thus support the hypothesis of oligomers preassembling on the membrane surface before membrane penetration. At the same time, our simulations of small membrane-inserted arcs of GSDMA3 suggest that the inserting oligomer can be small and does not have to comprise a full ring of approximately 26–30 subunits. Moreover, our simulations have revealed an astonishingly large impact of salt-bridge formation and protein surroundings on the transmembrane passage of charged residues, reducing the energetic cost by up to 53% as compared to their free forms. The here observed free energy barrier of mere 5.6 kcal/mol for the membrane insertion of monomeric GSDMA3 explains the surprising ability of gasdermins to spontaneously self-insert into cellular membranes.

Stator Curvature Optimization and Analysis of Axial Hydraulic Vane Pumps

Aiming at the problem of large vibration of a high-subside stator inner cavity curve vane pump, the force analysis of the vane at the transition curve is carried out, and the functional relationship between the vane turning angle θ, the large arc radius R, the small arc radius r and the sliding friction is established. The particle swarm algorithm is used to optimize the solution of the objective function, and the optimized parameter values are brought into the MATLAB simulation program to obtain the optimized stator curve profile diagram. The dynamic performance of the vane pump before and after optimization is simulated using ADAMS. The results show that: the acceleration of the vane pump slide is significantly reduced; the friction between the slide and the slide groove is significantly reduced; the contact force between the slide and the stator is significantly reduced; the impact vibration of the optimized vane pump is significantly reduced; and the dynamic performance of the vane pump is improved.