Symmetric Plane Research Articles

Numerical investigation of the blocking effect of a short duct on propeller noise.

Electric vertical and takeoff/landing vehicles for urban aerial mobility have attracted considerable attention in recent years. Some of these vehicles are equipped with ducted propellers to improve power efficiency, but the duct may also affect propeller noise generation and radiation. This work presents thorough numerical investigations to assess the importance of a short duct on propeller noise radiation. An analytical model is employed to predict noise emission from an isolated propeller, and the boundary element method is adopted to account for acoustic scattering effects. Additionally, an efficient data-clustering method is proposed to accelerate the overall noise prediction process. Parametric studies concerning geometries and the propeller's installation location are performed to exploit the duct's feasibility for low-noise vehicle development. Results suggest that the blocking effect can significantly benefit noise control for different rotating speeds, and installing the propeller at the symmetric plane of the duct can achieve the most noise reduction.

Maximum Penetration Height and Intrusion Speed of Weak Symmetric Plane Fountains in Linearly Stratified Fluids

The flow behavior of weak symmetric plane fountains in linearly stratified fluids is studied numerically with three-dimensional simulations over a range of the Froude (Fr), Reynolds (Re), and stratification numbers (s). The two main parameters describing the fountain characterization are the dimensionless maximum fountain penetration height (zm) and intrusion velocity (uint), which differ significantly at different flow development stages. It was found that the stratification stabilizes the symmetry of the weak fountains, which makes the fountain become asymmetric at a larger Fr value, and zm at the fully developed stage continues to increase as a result of the intrusion, which continually changes the ambient fluid stratification features, thus the buoyant force. The evolution of intrusion experiences three distinct stages. Both Fr and s have effects on zm and uint, with the effect of Fr usually larger than that of s. The overall impacts of Fr and s can be quantified in terms of Frasb, with a and b varying for different parameters. With numerical results, empirical correlations are produced in terms of Frasb for each relevant parameter, which generally predict the results very well.

The Space-Time Properties of Three Static Black Holes

In the curved space-time, the neutral test particle is not affected by any other force except for the influence of the curved space-time. Similar to the free sub in the flat space, the Lagrangian of the test particle only contains the kinetic energy term—the kinetic energy term of the four-dimensional curved space-time. In the case of small space-time curvature, linear approximation can be made. That is, under the weak field approximation, the Lagrangian quantity degenerates into the Lagrangian quantity in the axisymmetric gravitational field in Newtonian mechanics. In this paper, the curved space-time composed of axisymmetric equidistant black holes is taken as a model. We study the geodesic motion of the test particles around three black holes with equal mass and static axisymmetric distribution, including time-like particles and photons. The three extreme Reissner–Nordstrom black holes are balanced by electrostatic and gravitational forces. We first give the geodesic motion equation of particles in Three black holes space-time, give the relativistic effective potential, discuss the possible motion state of particles, and classify their motion trajectories. Then, the particle motion of the special plane (equatorial plane) is studied. The circular orbits of the two types of particles in the symmetric plane are studied, respectively. The circular orbits outside the symmetric plane are also studied, and their stability is also discussed. We will show the influence of the separation distance of the three black holes on the geodesic motion and explore the change of the relativistic effective potential. Then, the relationship between the inherent quantity and the coordinate quantity in space-time is analyzed. Finally, the chaos of the test particle orbit is explored.

Ultrasensitive Strain Sensor Based on Core-Bending Long Period Fiber Grating

In this letter, a novel core-bending long period fiber grating (CB-LPFG) based on symmetrical polished fiber plane is designed and experimentally testified. By employing methods of CO2-laser polishing and oxyhydrogen flame heating, periodic bending cores are achieved on a symmetrical polished plane. Due to the reduction of the cladding and the bent core, the sensitivity of the structure is strongly enhanced. Experimental results present that the highest strain sensitivity of CB-LPFG with 7 periods reaches -0.846 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> . To the best of our knowledge, is firstly increasing the strain sensitivity of fiber sensor based on single-wavelength demodulation to nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> level. Meanwhile, the temperature sensitivity of CB-LPFG is 236 pm/°C with dynamic range of 30- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$130~^{\circ }\text{C}$ </tex-math></inline-formula> . Consequently, the proposed sensor is expected to offer significant potential to detect micro-deformation more precisely.

Unusual mechanical strengths of Ta2O5 stable phases: A first-principles calculation study

Tantalum, in its most stable Ta2O5 oxide form, has long been recognized as a superior coating material in orthopedic applications. In this study, the ideal mechanical strengths of I41/amd, Cmmm, C2/c, Pm, and Pbam phases of Ta2O5 are investigated from first-principles calculation, where the stress–strain curves under various deformation strains are obtained and the structural evolution in terms of atomic bonding is analyzed. The results reveal that these stable Ta2O5 polymorphs show unusual mechanical strengths on their high symmetric crystalline planes. Shear super-plasticity is found on the (001) crystalline plane of the I41/amd phase in any shear direction. Shear strain-stiffening exists on the (100) crystalline plane of the Pm phase in the shear direction within an angle of ±18° along the [001] direction. Both shear super-plasticity and shear strain-stiffening make these crystalline planes be able to sustain excessively large shear deformations. Large and isotropic shear strengths are predicted on the (010) crystalline planes of Pm and Pbam phases with nearly identical maximum and minimum peak shear stresses approaching 15 GPa. Much stronger compression and tensile strengths are obtained normal to the (010) crystalline plane of the C2/c phase due to its special spring-like bonding structure, which can endure the compression deformation up to 30%. These findings provide guidance for selecting suitable phases of Ta2O5 and growth directions with crystalline planes possessing excellent mechanical properties in applications of Ta2O5 as a coating material on Ti alloys for biomedical replacements of damaged human organs, such as hip joints, dental implants, and artificial hearts.

Evolution characteristics of streamwise vortex of crossing shock wave/turbulent boundary layer interaction

The streamwise vortex generated by the crossing shock wave/turbulent boundary layer interaction seriously affects the performance of the hypersonic inlet. The shock structure, vortex core, and vortex intensity in the flowfields of weak, moderate, and strong strength interaction are experimentally and numerically investigated at Mach 2.95. The evolution characteristics of the streamwise vortex are explored. The reflection and intersection of shock waves in the interaction flowfield divide the evolution process of the streamwise vortex into four stages. The typical conical vortex evolutes into two vortexes. The vortex close to the symmetric plane further evolutes into two vortexes in the weak and strong strength flowfields. A separated flow from the focus on the flat plate produces a new streamwise vortex in the strong strength flowfield. The streamwise vortex core trace is almost parallel to the symmetric plane after the pair of streamwise vortexes collide at the symmetric plane. The vorticity intensity of the streamwise vortex increases and then decreases along the flow direction, which is greatly influenced by the interaction strength.

Effect of a Short, Bio-Mimetic Control Device on Aerodynamic Drag of Ahmed Body

Abstract The effects of short automatic moving deflectors (AMD) on the aerodynamic characteristics of Ahmed body are considered in this study. AMDs, known as biomimetic control devices, were added to the leading edge of the slanted surface. Its position was automatically adjusted in a separation flow. The aerodynamic drag, the pressure, and the skin-friction distribution on the slanted surface were measured for the model with three deflectors with lengths of 9%, 18%, and 30% of the slant. Particle image velocimetry was also utilized to assess the flow on the vertical symmetric plane. The Reynolds number based on the height of the model is between 1.44 × 105 and 2.80 × 105. The results showed that at a low Reynolds number, a short deflector increases the drag of the model. The effectiveness of the deflector in reducing the drag arises at a high velocity, where a maximum drag reduction of 11% was observed. The deflectors also reduced the lift coefficient by as much as 89%. Global luminescent oil-film skin-friction measurements showed that in the low drag state, the structure of the longitudinal vortexes and the separation bubble disappear on the surface. A complex flow structure is classified for the baseline model and the model with deflectors. The relationship between the surface flow, pressure distribution, and flow on the symmetric vertical plane is discussed in detail.

GaN/AlInN/AlN/Safir HEMT Yapılar için Mozaik Kusur ve AFM Çalışması

In this study, three samples of GaN/AlInN/AlN/Al2O3 high electron mobility (HEMT) structures are investigated with high resolution X-ray diffraction (HR-XRD) technique. Peak positions and peak broadenings are used in calculations, gained from rocking curves. Structural quality is determined from symmetric and asymmetric peak planes. Mosaic defects such as treadening dilocations (TDs), tilt and twist angles, lateral and vertical crystallite lengths are determined by using Williamson Hall (WH) method. In addition to these, surface morphology is also investigated by atomic force microscopy (AFM). It is noticed that crystal quality of epitaxial layers decrease in the order of samples C, B and A. Al compositions for samples A, B and C are found as %87.4, %86.6 and %86.4, respectively by using Vegard’s law.

Dead Load Allocation in Triple-Cable Suspension Bridges by Adjusting the Unstrained Lengths of Hangers: A Novel Analytical Approach

Triple-cable design of suspension bridges with an ultrawide main girder can improve their mechanical properties, making it lucrative for numerous engineering scenarios. However, its realization requires assigning an appropriate share of the dead load of the main girder supported by three main cables to avoid the middle main cable overload by the main girder’s dead load since the latter would impair the mechanical behavior of the upper transverse beams in the towers and deteriorate the whole bridge’s torsional stiffness. Therefore, this study proposes an analytical approach for dead load allocation to the suspension bridge with three main cables, which adjusts the share of the main girder’s dead load supported by three main cables via changing the unstrained lengths of the hangers. The main advantage of the proposed approach is that it can consider both uniform and nonuniform allocations. The spatial model for the suspension bridge with three cable planes is first converted into a plane model. The relationship between unstrained lengths of the three hangers in the same cross section is determined via the deformation compatibility conditions and one of the following options: (1) equality of stiffness of the two side hangers in the case of a symmetrical plane model; or (2) energy conservation conditions in case of an asymmetrical one. The proposed method was applied to an example of a triple-cable suspension bridge with a main span of 2,100 m and a width of 75 m, and its analytical solutions were compared against finite-element method calculation results. An increase in the share of the main girder’s dead load supported by the two side main cables increased the torsional stiffness of the whole bridge and reduced the vertical load exerted by the middle main cable on the top transverse beam of each tower. Meanwhile, variation of the share of the main girder’s dead load supported by the side and middle main cables only slightly influenced the whole bridge’s vertical and lateral stiffness values. The aforementioned adjustment by the proposed method could be accomplished without increasing the steel consumption of the bridge cables. The results could provide references for the design, static, and dynamic response analysis of similar triple-cable ultrawide suspension bridges.

The uniqueness and monotonicity of incompressible jet with two fluids* *This work is supported by the National Natural Science Foundation of China Grants 11971331, 12125102, and Sichuan Youth Science and Technology Foundation 2021JDTD0024.

In the previous paper by Alt et al (1984 Indiana Univ. Math. J. 33 367–91), the existence of the symmetric plane flows of two fluids with two free boundaries has been established by variational approach. However, the uniqueness of the two-phase fluids with two free boundaries is an unsolved problem. In the present paper, we will deal with the uniqueness of the two-phase fluids. In addition, if we assume that the two nozzles both converge, we shall show the monotonicity of the two free boundaries of the incompressible two-phase fluids issuing from these two nozzles.

Nematic pinning of the superconducting state in the doped topological insulator SrxBi2Se3

The discovery of a rotational symmetry breaking, or nematic, state in the superconducting doped topological insulator MxBi2Se3 (M = Cu, Sr, Nb) indicates a multicomponent superconducting order parameter which is topological. Many questions remain in this family of materials. In particular, the nematic axis of twofold symmetry is always pinned along one of three rotationally equivalent directions in the threefold symmetric basal plane in the rhombohedral crystal. Crystallographic strain has been proposed as the origin of the choice of pinning axis. Here, we discuss nematic pinning of the superconducting state, summarizing our magnetotransport, magnetization, penetration depth, and calorimetry measurements, which support the theoretical picture of topological superconductivity. We discuss the impact of controlled disorder via proton irradiation on the nematic superconducting state and discuss results of our multimodal technique for searching for crystallographic strain below 1 K via simultaneous diffraction and magnetotransport measurements.

σh symmetry and electron-phonon interaction in two-dimensional crystalline systems

The coupling of electrons and phonons is governed wisely by the symmetry properties of the crystal structures. In particular, for two-dimensional (2D) systems, it has been suggested that the electrons do not couple to phonons with pure out-of-plane distortion, as long as there is a $\sigma_h$ symmetry. We show that such a statement is correct when constituents of the unit-cell layer are only located in the $\sigma_h$ symmetric plane; a prominent example of such a system is graphene. For those 2D crystals in which atoms are vertically located away from the horizontal symmetric plane (e.g., 1H transition metal dichalcogenides), acoustic flexural modes do not couple to the electrons up to linear order, while optical flexural phonons, which preserve $\sigma_h$ symmetry, do couple with the electrons. Our conclusions are supported by an analytic argument together with numerical calculations using density functional perturbation theory.

A Balanced Tri-Band Substrate Integrated Waveguide Bandpass Filter With High Selectivity

This paper proposed a balanced tri-band bandpass filter (BPF) with high selectivity based on substrate integrated waveguide (SIW) technology. The tri-band filtering response and multiple transmission zeros (TZs) are attained by elaborately merging cascaded quadruplet (CQ) topology and split topology. The proposed balanced tri-band bandpass filter is designed, which integrates high selectivity differential-mode (DM) transmission and good common-mode suppression by cleverly placing TE102-mode SIW cavity on the symmetric plane. To verify the proposed concept, a prototype of balanced tri-band BPF operating at 9.33, 9.67, and 10.02 GHz has been implemented. Measured results show eight TZs at out of DM passbands and more than 35 dB CM suppression within the DM passbands, which agree well with the simulated results.

Effect of Annulation Mode of Twistarene on the Physical Property and Self-Assembly Behavior of Functionalized Curved Aromatic Molecules.

Four novel curved polycyclic aromatic hydrocarbons 3 a, 5, 8, 15 a have been synthesized and characterized, where molecules 3 a and 15 a bear [5]carbohelicene units. X-ray single crystal analyses indicate that compound 3 a shows offset packing arrangements of (P5 )- and (M5 )-isomers, and 15 a has a symmetrical plane and looks like a butterfly. In comparison, 8 exhibits a slightly curved structure, in which the significant convex-to-convex π-overlap with the shortest distance of 3.42 Å occurs. In addition, the effect of annulation mode of twistarenes on the physical properties, self-assembly behaviors, and switchable photoconductivity of the as-prepared curved aromatic compounds were further examined in a comparative manner.

Analytical fuzzy space geometry II

In the present paper, we attempt to construct space fuzzy lines as well as fuzzy planes in R3. We construct a space fuzzy line as a bi-infinite extension of a space fuzzy line segment. A particular case of space fuzzy lines, namely, symmetric fuzzy lines, is also investigated. Importantly, the concept of skew fuzzy lines and the shortest distance between skew fuzzy lines are discussed in R3. In addition, the fuzzy planes are proposed in three different forms: a three-point form, an intercept form, and a fuzzy plane passing through an S-type space fuzzy point and perpendicular to a given crisp direction. The construction of all the different forms of fuzzy planes depends on the known details about the fuzzy planes, such as three S-type space fuzzy points, or its three intercepts, or an S-type space fuzzy point and a crisp direction. In the sequel, a symmetric fuzzy plane is investigated. The study and construction of all the proposed ideas are done with the help of the same and inverse points of S-type space fuzzy points. Geometric properties of the proposed space fuzzy lines and all the proposed forms of fuzzy planes are also explored. Numerical examples support all the formulations and studies. Notably, we also provide the algorithms to find the membership grade of a point in(i)the space fuzzy line passing through two continuous space fuzzy points,(ii)the shortest distance between symmetric skew fuzzy lines,(iii)the three-point form of the fuzzy plane,(iv)the intercept form of the fuzzy plane, and(v)the fuzzy plane passing through an S-type space fuzzy point and perpendicular to a given crisp direction.

Surface Tension-Driven Flow and Its Correlation with Mass Transfer during L-DED of Co-Based Powders

Laser direct energy deposition (L-DED) is one of the most promising additive manufacturing methods, which has been paid more and more attention in recent years. An improved heat and mass transfer model was developed here to analyze thermal behavior, driving force, surface tension-driven flow and its correlation with dilution during L-DED of Co-based powders to a 38MnVS substrate. Thermal behavior was firstly studied for its fundamental influence on fluid flow and mass transfer. Next, the roles of capillary force and thermal capillary force were characterized using both the dimensional analysis and simulation methods, and the mechanism of surface tension-driven flow was also qualitatively investigated. Finally, flow characteristics inside the melt pool were studied in detail and their correlation with the dilution phenomenon was analyzed based on the multi-component mass transfer model. The temperature gradient was found to be much larger at the front of the melt pool, and it took about 200 ms for the melt pool to reach a quasi-steady condition. Moreover, sharp changes in the curvature of the solid/liquid boundary were observed. Surface tension was demonstrated as the main driver for fluid flow and resulted in centrally outward Marangoni flow. Capillary force contributes to the reduction of the curvature of the free surface, and thermal capillary force (Marangoni force) dominated the Marangoni convection. Alloy elements from the powders, such as Co and Ni, were added to the front part of the melt pool and mainly diluted at the upper side of the rear region near the symmetric plane of the melt pool. Fundamental results in this work provide a valuable understanding of the surface tension-driven flow and its correlation with concentration dilution during the additive manufacturing process.

SO-SLAM: Semantic Object SLAM With Scale Proportional and Symmetrical Texture Constraints

Object SLAM introduces the concept of objects into Simultaneous Localization and Mapping (SLAM) and helps understand indoor scenes for mobile robots and object-level interactive applications. The state-of-art object SLAM systems face challenges such as partial observations, occlusions, unobservable problems, limiting the mapping accuracy and robustness. This letter proposes a novel monocular Semantic Object SLAM (SO-SLAM) system that addresses the introduction of object spatial constraints. We explore three representative spatial constraints, including scale proportional constraint, symmetrical texture constraint and plane supporting constraint. Based on these semantic constraints, we propose two new methods - a more robust object initialization method and an orientation fine optimization method. We have verified the performance of the algorithm on the public datasets and an author-recorded mobile robot dataset and achieved a significant improvement on mapping effects. We will release the code here. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup>

Reduced-Kernel Weighted Extreme Learning Machine Using Universum Data in Feature Space (RKWELM-UFS) to Handle Binary Class Imbalanced Dataset Classification

Class imbalance is a phenomenon of asymmetry that degrades the performance of traditional classification algorithms such as the Support Vector Machine (SVM) and Extreme Learning Machine (ELM). Various modifications of SVM and ELM have been proposed to handle the class imbalance problem, which focus on different aspects to resolve the class imbalance. The Universum Support Vector Machine (USVM) incorporates the prior information in the classification model by adding Universum data to the training data to handle the class imbalance problem. Various other modifications of SVM have been proposed which use Universum data in the classification model generation. Moreover, the existing ELM-based classification models intended to handle class imbalance do not consider the prior information about the data distribution for training. An ELM-based classification model creates two symmetry planes, one for each class. The Universum-based ELM classification model tries to create a third plane between the two symmetric planes using Universum data. This paper proposes a novel hybrid framework called Reduced-Kernel Weighted Extreme Learning Machine Using Universum Data in Feature Space (RKWELM-UFS) to handle the classification of binary class-imbalanced problems. The proposed RKWELM-UFS combines the Universum learning method with a Reduced-Kernelized Weighted Extreme Learning Machine (RKWELM) for the first time to inherit the advantages of both techniques. To generate efficient Universum samples in the feature space, this work uses the kernel trick. The performance of the proposed method is evaluated using 44 benchmark binary class-imbalanced datasets. The proposed method is compared with 10 state-of-the-art classifiers using AUC and G-mean. The statistical t-test and Wilcoxon signed-rank test are used to quantify the performance enhancement of the proposed RKWELM-UFS compared to other evaluated classifiers.

High-quality AlN nucleation layer on SiC substrate grown by MOVPE: Growth, structural and optical characteristics

Thin AlN epi-layers (∼100 nm) were grown on a SiC substrate by MOVPE (Metal Organic Vapor Phase Epitaxy). The effect of V/III ratio and growth rate on the surface morphology, quality (crystalline/interface), and stress of AlN epi-layer were studied. It was found that the quality of AlN epi-layer depends strongly upon the V/III ratio and growth rate. Crystalline quality improved significantly as reflected by very low X-ray rocking curves FWHM values of symmetric (004) and asymmetric (204) planes, which are ∼355 arc-sec and ∼840 arc-sec, respectively for a high V/III ratio and low growth rate. The AlN/SiC interface quality and surface morphology of AlN epi-layer were also improved remarkably. Raman spectroscopy results indicated that dislocation density influenced the biaxial stress (0.75 to 1.05 GPa). The blue shift in Fourier Transform Infra-Red spectroscopy of E1(TO) mode of AlN epi-layer as compared to stress-free value (i.e. 670 cm−1) is in close agreement with the Raman results.

Predicting damage evolution in panel paintings with machine learning

Understanding the mechanical behavior and properties of works of art, such as panel paintings, is helpful for evaluating the failure mechanisms in play, especially during exhibitions in confined spaces. A panel painting is typically formed by a wooden panel and by layers of gesso, followed by paints and varnishes on the top. Induced by environmental changes, the mismatch in the moisture response of a stiff gesso layer and of the underlying wood panel produces risk of fracture in the pictorial layer. This happens because the gesso layer experiences tension which leads to cracking if the mechanical strain exceeds a critical level. The proposed contribution aims to develop a 3D simplified model for paintings, to detect the environmental conditions which may lead to exceeding the critical strain levels. To this aim, a penny-shaped crack has been simulated inside the gesso layer, centered along the symmetrical planes. To establish if the crack is in critical conditions, the failure criterion of the strain energy density (SED) method has been used: when the critical SED value is reached, the crack is assumed to be in unsafe conditions, otherwise it is in safe conditions. Several combinations of the geometric parameters describing the model have been checked, allowing to define whether the different conditions are likely to lead to a further damage development. Finally, the obtained results have been used to train a preliminary extreme gradient boosting machine (XGBoost) that may be able to classify and predict the two possible outcomes: safe and unsafe. This way, by exploiting the capabilities of machine learning, it could be possible to limit the need of numerical simulations and to introduce new rationales in the framework of work of arts conservation.