Reverse Arc Research Articles

Cause Investigation of Fractures in the Anti-Arc Portion of the Gravity Dam’s Overflow and the Top of the Substation Tunnel

Clarifying the origins of fractures and adopting acceptable repair plans are crucial for the design, maintenance, and safe operation of concrete gravity dams. In this research, numerical simulation is largely utilized to investigate the reasons for fractures in the anti-arc portion of the concrete gravity dam and the top of a substation tunnel in Guangdong Province, China. The calculation parameters are chosen based on the design information and engineering expertise to model the temperature field and stress field distribution of the dam during both normal operation and severe weather. The study demonstrates that under the effect of severe structural restraints and high temperatures, the tensile stress at the top of the substation tunnel would be 2.64 MPa in the summer, which is more than the tensile strength by 1.5 MPa and causes deep cracks. The tensile stress reaches 3.0 MPa in the summer under the effect of severe weather near the top of the substation tunnel. When a cold wave strikes in the winter, the concrete’s tensile stress on the overflow dam surface rises from 1.6 MPa to 4.0 MPa, exceeding the tensile strength by 1.9 MPa, resulting in the formation of a connection fracture in the reverse arc section. Both the actual observed crack location and the monitoring findings of the crack opening, as determined by the crack gauge, agree with the modeling results. The technique to lessen the structural restrictions of a comparable powerhouse hydropower station is pointed out based on engineering expertise, and various and practical repair strategies are proposed to guarantee the structure’s safe operation.

On the Issue of Calculating the Reverse Arc Breakdown Voltage of a High-Voltage Thermionic Diode and Its Maximum Specific Electrical Power

The issues of creating powerful power propulsion systems (PPS) based on a thermionic reactor-converter (TRC) and electric rocket propulsion systems (ERPS) are related to the development of compact high-temperature radiation–resistant current conversion systems (CCS) using plasma electric power devices - grid key elements (GKE) and high-voltage plasma thermionic diodes (HVPTD). The main problem of the development of GCE and HVPTD is the determination of their operating voltage (or reverse arc breakdown voltage in the locked state), which together with the current density in the conductive state characterizes the electric power density of the valve and is its main parameter. Within the framework of this work, the authors, based on the study of the locked state, numerically and analytically obtained new dependences for calculating the reverse arc breakdown voltage and determined the limiting values of the electrical power density of the HVPTD.

Thermohydraulic performance of solar air heater having discrete double arc roughness elements on absorber plate

The creation of a laminar sub region near the absorber wall causes solar air heaters to have limited thermal performance. An experimental analysis indicated that artificial roughness is one of the best strategies for breaking this viscous sub layer and improving absorption efficiency. Artificial roughness stitched on the absorbent plate in manner of discrete double arc roughness elements is generated, generating turbulent flow inside the rectangular duct. The coefficient of heat transmission improves as the roughness element is developed. In the current study, developed a roughness element of the discrete double arc reverse arc manner is used to improve the THP of the solar collector. During testing, relative roughness pitch, p/e = 11.67, relative roughness height, e/ Dh = 0.027, and angle of arc, α = 30°, 45°, 60°, 75°, Reynolds Number, Re = 3000–14000 were utilised as fixed and variable parameters, respectively. After extensive testing, the outcomes have been compared to the above mentioned of a plain absorber plate under the same fluidity circumstances. Experimental investigation revealed that Nusselt number (Nu), and friction factor (f), are 2.59 & 1.96 contrast overhead plain (without roughness element) plates, respectively. At a p/e = 11.67 & α = 60°, overall THP was found to be 2.16.

Эффективная мощность сжатой сварочной дуги с разнополярными импульсами тока

The authors reviewed the research works on the effective power of direct and reverse polarity welding arcs with a non-consumable electrode in argon. The study shows that it is difficult to use the arc effective efficiency for effective power determination. It applies to the constricted arc more than to the free one. Based on data analysis for the effective power of polarities and the effective efficiency of a constricted arc burning toward the cooper heat flow calorimeter, the authors calculated the specific effective power of polarities and arc stresses. The maximum values are 23.2 W/A for the reverse polarity arc; and 14.2 W/A for the direct polarity arc. The study identified that the decrease in the specific effective power of polarities at the current increase within 100–150 A is well described by linear dependencies. With the current increase, there is a linear decrease in the direct polarity arc stress, while the reverse polarity arc stress remains constant. The spread of data for the specific effective power of polarities is about two times less than the spread for effective efficiency. Using a 2D mathematical model of the constricted arc column in a closed area, the authors calculated the power absorbed by plasma-forming argon and nozzle walls. As a result, the authors obtained the dependencies of the power transferred by argon on the nozzle channel length and the arc current. The specific effective power of argon flow for analyzed current densities and argon consumption shows poor dependence on the arc current and is equal to 5.5 W/A approximately. The power contribution of plasma-forming argon to the effective power of the constricted arc increases with the current increase.

Experimental investigation for pitch and angle of arc effect of discrete artificial roughness on Nusselt number and fluid flow characteristics of a solar air heater

Artificial roughness element with gap used to enhance the performance of solar air heater. Compared to the traditional smooth absorber plate and absorber plate with artificial roughness element without gap, the thermo-hydraulic performance (THP) of discrete artificial roughened solar air heater was found more. An experimental study of the heat transfer and fluid flow properties of the solar air heater was carried out using artificial roughness with an area in the absorbent plate. At present, discrete rib roughness in a double reverse arc manner has been used with variations in mass flow from 3000 to 14000 in the form of Reynolds number. The range of roughness parameters, such as the first used for the constant value of α of 600 and p/e from 6.67, 8.33, 10, 11.67 and the second used for the fixed value p/e of 8.33 along with the arc angle change, α of 300, 450, 600, 750 in the properties of heat transfer and fluid flow to achieve. These experimental results are important for applying an improved solar air heater.

Comparison of Modern Highly Interactive Flicker-Free Steady State Motion Visual Evoked Potentials for Practical Brain-Computer Interfaces.

Motion-based visual evoked potentials (mVEP) is a new emerging trend in the field of steady-state visual evoked potentials (SSVEP)-based brain–computer interfaces (BCI). In this paper, we introduce different movement-based stimulus patterns (steady-state motion visual evoked potentials—SSMVEP), without employing the typical flickering. The tested movement patterns for the visual stimuli included a pendulum-like movement, a flipping illusion, a checkerboard pulsation, checkerboard inverse arc pulsations, and reverse arc rotations, all with a spelling task consisting of 18 trials. In an online experiment with nine participants, the movement-based BCI systems were evaluated with an online four-target BCI-speller, in which each letter may be selected in three steps (three trials). For classification, the minimum energy combination and a filter bank approach were used. The following frequencies were utilized: 7.06 Hz, 7.50 Hz, 8.00 Hz, and 8.57 Hz, reaching an average accuracy between 97.22% and 100% and an average information transfer rate (ITR) between 15.42 bits/min and 33.92 bits/min. All participants successfully used the SSMVEP-based speller with all types of stimulation pattern. The most successful SSMVEP stimulus was the SSMVEP1 (pendulum-like movement), with the average results reaching 100% accuracy and 33.92 bits/min for the ITR.

Defect dipole polarization mechanism in low-dimensional europium substituted Al0.8La0.2TiO3 nanostructures

Abstract Low-dimensional Europium substituted Al0.8La0.2TiO3 (Al0.8EuyLa0.2-yTiO3 (y = 0.01–0.04))/AELTO nanostructures were prepared via hydrothermal method. The X-ray diffraction (XRD) patterns revealed the mixed phase (tetragonal and orthorhombic) structure of AELTO. Furthermore, the surface morphology evidenced the formation of AELTO nanostructures. The wide optical band gap (Eg) was achieved for y = 0.01–0.04 contents and found to be varying from 3.371 to 3.399 eV. The high dielectric constant (e′) values of 2.84 × 108 at 10 kHz and 101608.8 at 1 MHz were obtained for y = 0.02 at room temperature due to defect dipoles. In addition, the high ac-electrical conductivity (σac) of 15.78 S/cm (at 10 kHz) was observed at room temperature. The frequency dependence of dielectric modulus and impedance parameters was elucidated. The reverse arc present in the Cole-Cole plot of y = 0.02 content clearly suggested the presence of defect dipoles in AELTO.

Thermal efficiency decision of variable polarity aluminum arc welding through molten pool analysis

One of several solutions to enhance the weldability of aluminum alloy is removing the aluminum oxide layer on the surface by adopting variable polarity arc welding. The authors’ previous experimental research on the variable polarity arc welding of aluminum alloy showed that reverse arc polarity has larger heat input efficiency than a straight polarity. Furthermore, the authors have already developed a numerical analysis model and suggested a methodology of estimating the heat input efficiency through a comparison between three dimensional molten pool simulation and experiment with regard to the variable polarity GTA welding. This research is a follow-up of the previous study, and it reveals the heat input efficiency of reverse polarity arc in aluminum welding for the first time through the suggested method. As a result, the heat input efficiency of reverse polarity is 3.8 times larger than that of straight polarity in aluminum welding.

Guanidine derivative polymer coated microbubble resonator for high sensitivity detection of CO2 gas concentration.

A carbon dioxide (CO2) gas sensor based on a polyhexamethylene biguanide (PHMB)-coated whispering gallery mode (WGM) microbubble resonator is proposed and verified experimentally in this work. Microbubbles were fabricated using two reverse arc discharges focused on microcapillaries. The inner wall of the microbubble was coated with a layer of PHMB using a filling and sintering process. A significant WGM resonance was observed by coupling with a tapered fiber. The experimental results show that as the concentration of carbon dioxide increases, a blue shift appears in the spectrum. Addition, a high sensitivity (0.46 pm /ppm) and a good linear relationship were obtained in the measurement range of 200-700 ppm with a detection limit of 50 ppm. The sensor features include high sensitivity, simple structure, easy manufacture, and low cost.

Dosimetric analysis of tangent-based volumetric modulated arc therapy with deep inspiration breath-hold technique for left breast cancer patients

BackgroundTangent-based intensity modulated radiation therapy (TIMRT) is a common adjuvant radiotherapy strategy for breast cancer patients. This study compared the dosimetric characteristics of tangent-based volumetric modulated arc therapy (TVMAT) and TIMRT for left breast cancer patients during deep inspiration breath-hold (DIBH) and free breathing (FB) techniques.MethodsFourteen patients with left breast cancer after breast-conserving surgery were included. The first arc started at 331.8–353.6 degrees and stopped at 281.8–315.0 degrees. The third arc started at 123.2–149.1 degrees and stopped at 88.0–96.0 degrees. The second and fourth arcs were reverse arcs of first and third arcs. DIBH-TIMRT inversing plans were generated using opposing tangential fields. Wilcoxon signed rank test and Spearman correlation were used to examine the significance of dose difference.ResultsCompared with FB-TVMAT, the mean heart dose of DIBH-TVMAT plans was reduced from 7.9 Gy to 3.2 Gy (p < 0.001). The average left lung volume receiving 30 Gy or more (V30Gy) was reduced from 12.9 to 5.7% (p < 0.001). DIBH-TVAMT plans resulted in a lower mean dose to the contralateral breast and lung (2 Gy and 0.7 Gy vs 3.4 Gy and 1.5 Gy, respectively) as compared to FB-TVMAT plans. Compared with DIBH-TIMRT, the average left lung V30Gy of DIBH-TVMAT plans was reduced from 8.5 to 5.7% (p = 0.031). As for low-dose areas, exposure of the left lung, right breast, heart and right lung volume with 10 Gy or more was not significantly different between the IMRT- and VMAT-plans.ConclusionsDIBH-TVMAT for left breast cancer treatment retains treatment plan quality similar to the DIBH-IMRT technique without compromising dose restrictions to the heart, right breast and right lung. DIBH-TVMAT increased left lung protection but still had higher V5Gy to right breast and substantially higher V5Gy to heart. For left breast cancer patients receiving treatment with the DIBH technique, DIBH-TVMAT provides better treatment quality and is a safe and feasible treatment strategy.

Dependence of the melting rate of the electrode in CO2 welding on electrode extension

The data obtained for the variation of the melting rate and voltage in CO2 welding with the change of the electrode extension are analysed. The dependences of the mean resistance of the unit length of the extension, the increase of the melting factor and the arc voltage on the electrode wire diameter are determined. The appropriate approximating dependences are derived. The average value of the melting factor in the reverse polarity arc at zero extension is determined.

Numerical analysis of variable polarity arc weld pool

Aluminum alloys are the materials which face difficulties in weldability. One of solutions to increase the weldability of aluminum alloys is removing the oxide-layer on the surface of aluminum by adopting variable polarity arc welding. The authors’ previous experimental research about variable polarity arc welding of aluminum showed that reverse arc polarity has larger heat input efficiency than straight polarity. In this study, numerical analysis of molten pool in aluminum alloy by variable polarity GTAW has been introduced and developed. The arc heat source, arc pressure, electromagnetic force and Marangoni flow regarding the variable polarity GTAW have been applied as the boundary conditions and body force terms. Governing equations such as the conservation of the mass, momentum and energy are numerically solved to derive temperature and flow vector field. Additionally, volume of fluid method is adopted to track free surface of molten pool and it was implemented through using commercial package Flow-3D. Through the present analysis, mathematical model for variable polarity arc is newly suggested and following result successfully showed effect of different heat input efficiency for each straight and reverse polarity. The heat input efficiencies are arbitrarily decided here for feasibility but a methodology to numerically determine the exact value is suggested. The final goal of these research series is to determine the heat input efficiency of reverse polarity arc aluminum welding indirectly through simulation and experiment comparison.

Hermitian Adjacency Matrix of Digraphs and Mixed Graphs

AbstractThe article gives a thorough introduction to spectra of digraphs via its Hermitian adjacency matrix. This matrix is indexed by the vertices of the digraph, and the entry corresponding to an arc from x to y is equal to the complex unity i (and its symmetric entry is ) if the reverse arc is not present. We also allow arcs in both directions and unoriented edges, in which case we use 1 as the entry. This allows to use the definition also for mixed graphs. This matrix has many nice properties; it has real eigenvalues and the interlacing theorem holds for a digraph and its induced subdigraphs. Besides covering the basic properties, we discuss many differences from the properties of eigenvalues of undirected graphs and develop basic theory. The main novel results include the following. Several surprising facts are discovered about the spectral radius; some consequences of the interlacing property are obtained; operations that preserve the spectrum are discussed—they give rise to a large number of cospectral digraphs; for every , all digraphs whose spectrum is contained in the interval are determined.

Orthodontic-Surgical Management of a Skeletal Class II Patient with Reverse Smile Arc and Vertical Maxillary Excess

Orthodontic-Surgical Management of a Skeletal Class II Patient with Reverse Smile Arc and Vertical Maxillary Excess

Orthodontic-Surgical Management of a Skeletal Class II Patient with Reverse Smile Arc and Vertical Maxillary Excess

This is a case report of a 17-year-old female patient who presented with skeletal Class II malocclusion with excessive vertical growth of the maxilla and a reverse smile arc. Vertical maxillary excess, thin alveolar troughs, proclined upper and lower anterior teeth, excessive curve of Spee, crowding in the lower arch and excessive eruption of upper and lower incisors led to the decision of combination of orthodontic and surgical treatment. A combined orthodontic and surgical approach resulted in harmony in occlusion, function and esthetics in this patient.

The Independent Even Factor Problem

This paper deals with the independent even factor problem. For odd-cycle-symmetric digraphs, in which each arc in any odd dicycle has the reverse arc, a min-max formula is established as a common generalization of the Tutte–Berge formula for matchings and the min-max formula of Edmonds [Submodular functions, matroids, and certain polyhedra, in Combinatorial Structures and Their Applications, R. Guy et al., eds., Gordon and Breach, New York, 1970, pp. 69–87] for matroid intersection. We devise a combinatorial efficient algorithm to find a maximum independent even factor in an odd-cycle-symmetric digraph accompanied by general matroids, which commonly extends two of the alternating-path-type algorithms, the even factor algorithm of Pap [Math. Program., 110 (2007), pp. 57–69], and the matroid intersection algorithms. This algorithm gives a proof of the min-max formula and contains a new operation on matroids, which corresponds to shrinking factor-critical components in the matching algorithm of Edmonds [Canad. J. Math., 17 (1965), pp. 449–467]. The running time of the algorithm is $\mathrm{O}(n^4 Q)$, where n is the number of vertices and Q is the time for an independence test. The algorithm also gives a common generalization of the Edmonds–Gallai decomposition for matchings and the principal partition for matroid intersection.

Orthogonal Decompositions of Complete Digraphs

A family ? of isomorphic copies of a given digraph \(\) is said to be an orthogonal decomposition of the complete digraph \(\) by \(\), if every arc of \(\) belongs to exactly one member of ? and the union of any two different elements from ? contains precisely one pair of reverse arcs.

Magnet design and motor performances of a double-layer interior permanent magnet synchronous motor

In this paper we discuss the results of our investigation of the interior permanent magnet synchronous motor (IPM), with permanent magnets embedded in the rotor, and particularly the double-layer IPM synchronous motor, which has two layers of magnets embedded in the rotor, layered in the radial direction. For this investigation, we studied the arrangement of permanent magnets both through simulation and by experiments with a prototype. The results concerning the form of the magnets clearly show the advantages of the reverse arc configuration, which makes it possible to increase the surface area creating magnetic flux. We further determined that to maximize both the q-axis flux and the flux of the permanent magnets, the optimum width of the q-axis flux path between the magnets for the motor investigated here is 2 mm. The results also clearly show that chamfering the ends of magnets is effective in achieving better utilization of the q-axis flux.© 1999 Scripta Technica, Electr Eng Jpn, 128(1): 62–69, 1999

Asymptotic results on suborthogonal [formula omitted]-decompositions of complete digraphs

A G → -decomposition of a complete digraph D → n is a partition of D → n into isomorphic copies (called pages) of G → . A G → -decomposition is said to be suborthogonal if the union of any two distinct pages contains at most one pair of reverse arcs. Wilson (Proceedings of the fifth British Combinatorial Conference, 1975, pp. 647–659) proved in 1975 that a G → -decomposition exists for almost all integers n satisfying certain necessary conditions. In this paper we shall prove that under the same conditions there exists even a suborthogonal G → -decomposition.

Magnet Design and Motor Performances of a Double Layer Interior Permanent Magnet Synchronous Motor

In this paper we would like to discuss the results of our investigation of the Interior Permanent Magnet Synchronous Motor (IPM), which has permanent magnets embeded in the rotor, and in particular we are concerned with the Double Layer IPM Synchronous Motor, which has two layers of magnets embeded in the rotor layered in the direction of the radius. For this investigation, we studied the arrangement of permanent magnets both through simulation and experiments with a prototype. The results concerning the form of the magnets clearly show the superiority of the reverse arc form, which can increase the surface area creating magnetic flux. We further determined that to maximize both the qaxis flux and the flux of the permanent magnets, the optimum size for the q-axis flux path between the magnets for the motor studied on this occasion is 2 mm. In addition, the results clearly show that notching the ends of magnets is effective in further utilizing the q-axis flux.