Uniform Distortion Research Articles

A fisheye image correction method based on deep learning

Purpose Fisheye camera is a wide-angle camera with a large field of view, which can obtain more information than conventional cameras, but its own disadvantage of large distortion can lead to shape distortion of objects in the captured image. To correct lens distortion, most scholars use manual calibration methods. The traditional manual calibration method relies on complex data computation and specialized mathematical knowledge, but the method is complex and not universal. Considering the nonlinear features of neural networks can be used to fit the nonlinear distortion of distorted images, this paper aims to correct the distortion of a fisheye image based on convolutional neural networks. Design/methodology/approach By generating fisheye distortion images using readily available cityscape road data sets, this paper designs an effective correction model by taking advantage of the fact that the relationship between the pixel coordinates is basically stable after uniform distortion. In our training process, the corresponding distortion is firstly synthesized using the original image, the loss function is constructed using the geometric means of the Hough transform, the whole model is then trained with the help of the loss of the linear slope, and finally the predicted parameters are used to correct the fisheye image, which realizes the overall end-to-end framework. Findings Experimental results show that the method proposed in this paper outperforms similar methods in terms of correction performance. Originality/value This paper proposed a fisheye distortion correction algorithm based on convolutional neural network, which uses distortion-free images based on a generalized fisheye imaging model and maps to generate a fisheye distortion picture data set. It also builds a loss function training model based on line reconstruction error loss of Hough transforms.

Influence of tip air injection on the unsteady blade force under circumferential pressure distortion

In order to further understand the impact of tip air injection on compressor stability under circumferential pressure distortion, a series of experimental studies on tip air injection under uniform and circumferential distortion were conducted on a low-speed single rotor axial flow compressor. The unsteady measurements were carried out by use of microsensors and strain gauges bonded on the rotor blade surfaces, and a collection of dynamic pressure sensors installed on the casing wall. Results indicate that with the increase in the injected momentum ratio, the load at the leading edge near the rotor blade tip obviously decreases, thereby delaying the stall. By comparing the pressure distribution on the rotor blade surface under different injected momentum ratios, tip air injection can effectively suppress flow separation at the blade tip to enhance flow capability. In addition, it can also weaken the fluctuation of tip leakage flow and reduce the dynamic stress similar to natural vibration near the blade root both in stationary and rotating coordinate systems. Under the condition of inlet circumferential distortion, tip air injection can significantly reduce the load at the distorted region and suppress the low-frequency disturbances measured on the rotor blade surface caused by inlet distortion. In addition, the dynamic stress near the blade root can also be effectively reduced by tip air injection. It implies that tip air injection can both extend the stall margin and reduce blade vibration when suffering from circumferential distortion; thus, the compressor can safely operate.

A DFT study on half-metallicity of Ruddlesden–Popper layered perovskite Bi8Ba4Mn8O28

Half-metallic ferromagnet has attracted intense interest due to its unique electronic structure and potential applications in spintronic devices. The structural properties, electronic structure, and magnetism are systematically investigated for Ruddlesden-Popper layered Perovskite Bi8Ba4Mn8O28 by using the first-principles calculations. It is found that Bi8Ba4Mn8O28 is a half-metallic ferromagnet with a saturated magnetic moment of 31 μB f.u.−1 at its ground state with the orthorhombic Pbnm symmetry, which ground state is determined by the symmetry analysis, and the calculations of the total energy, the formation energy, and the magnetic exchange interaction. We demonstrate that the half-metallicity of Bi8Ba4Mn8O28 is fairly robust against large uniform and tetragonal distortions. Furthermore, the surface effect on half-metallic properties is also discussed. It is shown that all terminations but Mn1O can maintain their half-metallic properties and present good robustness of half-metallicity with rather wide half-metallic gap.

Numerical investigation of the effect of blade distortion laws on the corner flow separation of the axial-flow fan

To study the effect on performance of different blade distortion laws of axial flow fans, the radial distributions of blade stagger angle were fit as Bézier curves, and five distribution laws were established. Three-dimensional numerical simulations were carried out for the fan schemes. The results show that distortion near the blade root can effectively restrain the corner separation vortex from climbing along the blade suction surface, so that the low-energy fluid accumulates in the corner region. Tip distortion rises the pressure difference between the pressure and the suction surface, and the turbulence intensity of the tip leakage is increased. Root distortion inhibits the CV diffusion, resulting the decay of tip leakage vortex, thereby improving the stall margin. Relative to a uniform distortion blade, the blade-root distortion scheme increases the radial load of the blade, while the tip distortion scheme results in a decrease of the blade load coefficient. The maximum load position of the end-zone distorted blade moves to the root area, while the maximum load position of the middle distorted blade shifts to the tip area. The end-zone distortion improves the efficiency and total pressure of the fan without changing the efficient working range, and is considered to be the optimal scheme. The maximum pressure coefficient of the end-zone distortion scheme is increased by 4.97% and the maximum efficiency is increased by 1.28%.

Phonon softening and slowing-down of charge density wave fluctuations in BaNi2As2

BaNi$_2$As$_2$ is a nonmagnetic analogue of the iron pnictide superconductors, and in its tetragonal state exhibits an incommensurate charge-density-wave (IC-CDW) and a sizable elastoresistance. In this work, phonons in BaNi$_2$As$_2$ associated with the IC-CDW and uniform in-plane lattice distortions are investigated using high-resolution inelastic X-ray scattering. The in-plane transverse acoustic phonons reveal no softening at temperatures where the elastoresistance increases strongly, indicating the latter to be electronically driven. Systematic phonon measurements reveal the IC-CDW occurs in two stages upon cooling: underdamped phonons first soften to zero energy well above the IC-CDW ordering temperature, then the resulting quasielastic IC-CDW fluctuations gradually slow down and coalesce into the static IC-CDW order. A possible origin for our observations is the IC-CDW in tetragonal BaNi$_2$As$_2$ being uniaxial, which provides an additional Ising degree of freedom favorable for disordered IC-CDW modulations, and accounts for the elastoresistance through a weak coupling to the lattice.

Electromotive power generated by pressure gradient in metals with the band Jahn-Teller effect

In band Jahn-Teller (BJT) metals, some lattice distortions with their symmetries different from that of the bulk structure can linearly couple to the BJT electrons, so pressures to produce or enhance such distortions can affect the BJT electrons near the Fermi level. This pressure-electric effect in BJT metals is studied theoretically on the basis of the ${\mathrm{\ensuremath{\Gamma}}}_{12}$ subband model for the structural transition in A15 compounds. The applied pressure is assumed to consist of a spatially uniform pressure and a local pressure. The former induces or enhances a uniform distortion, which contributes to the redistribution of electrons between the ${\mathrm{\ensuremath{\Gamma}}}_{12}$ subbands, while the latter produces a local distortion with its gradient, which causes flows of band electrons between different regions in space. The steady electronic state under the uniform and local pressures is obtained by use of the Boltzmann equation and the relaxation-time approximation. It is clarified that the local pressure with its gradient can generate an electromotive power when the degeneracy of the BJT subbands is lifted spontaneously and/or by the external uniform pressure. The obtained pressure-gradient electric effect is predicted to be a probe into BJT effects which may work in some metals with structural transitions.

Study of structural, electronic, magnetic and vibrational properties of CoFeTiSi quaternary Heusler alloy

We have synthesized CoFeTiSi quaternary Heusler alloy and experimentally measured its structural and magnetic properties. Detailed ab-initio first principle calculations have been performed to investigate the half-metallic behavior of this quaternary Heusler alloy and the effect of disorder on its half-metallicity. The saturation magnetization and Curie temperature are obtained as 1.243 μB/f.u. and 583 K respectively. The spinwave-stiffness constant (D = 3.259 nm2-meV) is obtained from temperature dependence according to Bloch's law. Dynamical stability of the alloy is confirmed from the phonon dispersion curve of the alloy. The first principle calculations show that the alloy is 100% spin-polarized at the Fermi level and the spin-polarization is resistant to the uniform lattice distortion up to a large extent. The effect of anti-site disorder of atoms on the total magnetic moment and the electronic structure is also explored and the moment (and the half-metallicity) is found to be nearly independent (resistant) for the disorders due to Co–Fe and Ti–Si atomic swaps whereas it is affected in case of Co–Si and Fe–Ti atomic swaps. This study reveals that the alloy may be a viable candidate for spintronic applications at room temperature.

Characterization of Clustered Cracks at Weld Root Based on Uniform-Magnetic-Field Distortion Measurement

Girth welds in pipelines are critical links on which the pipeline system depends. After long-term operation, defects may appear at the weld root, which seriously threatens the safety of the system. Cracks are the most dangerous defect, especially multiple clustered cracks. Some closely spaced cracks are often misjudged as corrosion defects, leading to an error estimation of residual strength of pipelines and causing sudden accidents. The accurate characterization of closely spaced cracks is thus of great significance for subsequent hazard assessment. However, traditional nondestructive testing methods all have limitations because of the complex stress distribution and excess weld penetration at the weld root. To solve this problem, we propose to detect cracks using uniform magnetic field distortion (UMFD) method, which is highly sensitive to surface defects but insensitive to local variations in stress. This article proposes an analytical model of an isolated crack whose variables are merely the position and width of the crack. Furthermore, we provide a characterization algorithm based on this analytical model for evaluating the position and width of subcracks. Both the simulation and experimental results indicate that the proposed method accurately characterizes cracks. To assess the robustness of the proposed algorithm, additive white Gaussian noise with signal-to-noise ratios (SNRs) of 5 and 10 dB is superposed onto the raw data from the simulation. The results show that this method is robust against background noise.

Numerical simulation of S-shaped inlet under the intake total pressure distortion

During the development of the stealth fighter, the S-shaped inlet enters the designer’s vision because it has better stealth than bump inlet and straight inlet. During the use of the S-shaped inlet, due to its structural reasons, secondary flow is likely to occur in the curved section, which directly causes the flow state to be changeable and complicated. Therefore, this paper takes the S-shaped inlet as the research object to analyzes the steady flow field simulation under uniform inlet condition and distortion inlet condition and analyze the flow field of the airflow and the total pressure of each section under the S-shaped inlet by changing the intake distortion conditions with CFX software. The results show that although the S-shaped inlet will occur total pressure distortion under uniform intake. However, when the S-shaped inlet work under certain flight conditions, the level of total pressure distortion will be smaller than the uniform inlet condition, which can improve the air intake performance. Finally, it can be inferred that with use of the S-shaped intake port, the deterioration of distortion may be prevented under certain specific intake conditions.

Effect of Phase Transformations on Scanning Strategy in WAAM Fabrication.

Due to its high production rates and low cost as compared to other metal additive manufacturing processes, wire arc additive manufacturing (WAAM) has become an emerging technology in the manufacturing industry. However, the residual stress generation and part distortion hinder its widespread adoption because of the complex thermal build-histories of WAAM parts. One of the ways to alleviate this problem is to consider the effects of scan strategies as it directly influences the thermal history of the built part. Since WAAM itself is an evolved welding process and even though it is evident from welding studies that phase transformations directly affect the residual stresses in welded parts, it remains unclear how the consideration of phase transformations for different scan strategies will affect the residual stresses and distortions in the WAAMed parts. A FEM study has been performed to elucidate the effects of phase transformations on residual stresses and the distortion for different deposition patterns. The current findings highlight that for the fabrication of low-carbon martensitic steels: The consideration of phase transformations for line-type discontinuous patterns (alternate and raster) do not significantly affect the residual stresses. Consideration of phase transformations significantly affects residual stresses for continuous patterns (zigzag, in–out and out–in). To accurately simulate complex patterns, phase transformations should be considered because the patterns directly influence the temperature history of the built part and will thus affect the phase transformations, the residual stresses and the warpage. During the fabrication of WAAM parts, whenever possible, discontinuous line scanning patterns should be considered as they provide the part with uniform residual stress and distortion. The alternate line pattern has been found to be the most consistent overall pattern.

μ-distortion around stupendously large primordial black holes

In a variety of mechanisms generating primordial black holes, eachblack hole is expected to form along with a surrounding underdense region thatroughly compensates the black hole mass. This region will propagateoutwards and expand as a shell at the speed of sound in the homogeneous background. Dissipation of the shell due to Silk damping could lead todetectable μ-distortion in the CMB spectrum: if black holes are rare on the last scattering surface, the signal(s) would be pointlike; whereas if there are a sufficient number of them, we could have a uniform distortion in the CMB sky. While the currentbound on the average μ-distortion is |μ̅| ≲ 10-4,the standard ΛCDM model predicts |μ̅| ∼ 10-8,which could possibly be detected in future missions. It is shown inthis work that the non-observation of μ̅ beyond ΛCDMcan place a new upper bound on the density of supermassive primordialblack holes within the mass range 106 M ☉≲ M ≲ 1015 M ☉.Furthermore, black holes with initial mass M ≳ 1012 M ☉could leave a pointlike distortion with μ ≳10-8 at anangular scale ∼ 1° in CMB, and its non-observation wouldimpose an even more stringent bound on the population of these stupendously large primordialblack holes.

Uniform Mortgage Regulation and Distortion in Capital Allocation

Abstract The federal mortgage policy, the conforming loan limit (CLL), was spatially uniform before the 2008 crisis, despite remarkable heterogeneity across geography. I show that in areas that experienced a larger decline in the jumbo loan share following an increase in the CLL, lenders raised jumbo loan approval rates, lowered mortgage rates to defend short-term market share, extended credit to riskier borrowers, and incurred deteriorated asset quality in the long run. This result is not explained away by credit supply or demand changes, the bunching effect, or reverse causality. Instead, my evidence is consistent with a competition channel: the effect of CLL increases on jumbo loan credit expansion is significantly exaggerated in a more competitive jumbo-lending market. Overall, my findings suggest that the securitization policies of the government-sponsored enterprises can induce spillovers on the jumbo market segment and influence credit allocation.

Moving frames and compatibility conditions for three-dimensional director fields

The geometry and topology of the region in which a director field is embedded impose limitations on the kind of supported orientational order. These limitations manifest as compatibility conditions that relate the quantities describing the director field to the geometry of the embedding space. For example, in two dimensions the splay and bend fields suffice to determine a director uniquely (up to rigid motions) and must comply with one relation linear in the Gaussian curvature of the embedding manifold. In 3D there are additional local fields describing the director, i.e. fields available to a local observer residing within the material, and a number of distinct ways to yield geometric frustration. So far it was unknown how many such local fields are required to uniquely describe a 3D director field, nor what are the compatibility relations they must satisfy. In this work, we address these questions directly. We employ the method of moving frames to show that a director field is fully determined by five local fields. These fields are shown to be related to each other and to the curvature of the embedding space through six differential relations. As an application of our method, we characterize all uniform distortion director fields, i.e., directors for which all the local characterizing fields are constant in space, in manifolds of constant curvature. The classification of such phases has been recently provided for directors in Euclidean space, where the textures correspond to foliations of space by parallel congruent helices. For non-vanishing curvature, we show that the pure twist phase is the only solution in positively curved space, while in the hyperbolic space uniform distortion fields correspond to foliations of space by (non-necessarily parallel) congruent helices. Further analysis of the obtained compatibility fields is expected to allow to also construct new non-uniform director fields.

An AAC steganography scheme for adaptive embedding with distortion minimization model

Nowadays, most prevailing approaches to advanced audio coding (AAC) steganography are content non-adaptive which have low embedding capacity and poor security. In this paper, we construct a new distortion by integrating the uniform embedding distortion with the masking threshold, and propose an adaptive steganographic scheme for AAC audio by modifying quantized modified discrete cosine transform (QMDCT) coefficients. To hold the statistical distribution of QMDCT coefficients we introduce uniform embedding idea. Then the psychoacoustic model is used to avoid the declining of hearing quality. Finally, we minimize the overall embedding distortion by utilizing syndrome-trellis codes (STCs) technique and the defined distortion function. Comprehensive experimental results show that the proposed scheme achieves better performance than related works. The detection error of 128-kbps-AAC dataset is higher than 24.78% when the embedding payload reaches 3.70 kbps, which is significantly lower than the state-of-the-art AAC steganographic methods.

Notes on Ricci flows with collapsinginitial data (I): Distance distortion

In this note, we prove a uniform distance distortion estimate for Ricci flows with uniformly bounded scalar curvature, independent of the lower bound of the initial μ \boldsymbol {\mu } -entropy. Our basic principle tells us that once correctly renormalized, the metric-measure quantities obey similar estimates as in the noncollapsing case; especially, the lower bound of the renormalized heat kernel, observed on a scale comparable to the initial diameter, matches with the lower bound of the renormalized volume ratio, giving the desired distance distortion estimate.

Uniform distortions and generalized elasticity of liquid crystals.

Ordinary nematic liquid crystals are characterized by having a uniform director field as ground state. In such a state, the director is the same everywhere and no distortion is to be seen at all. We give a definition of uniform distortion which makes precise the intuitive notion of seeing everywhere the same director landscape. We characterize all such distortions and prove that they fall into two families, each described by two scalar parameters. Uniform distortions exhaust R. Meyer's heliconical structures, which, as it has recently been recognized, include the ground state of twist-bend nematics. The generalized elasticity of these new phases is treated with a simple free-energy density, which can be minimized by both uniform and nonuniform distortions, the latter injecting a germ of elastic frustration.

"Lattice Strain Matching"-Enabled Nanocomposite Design to Harness the Exceptional Mechanical Properties of Nanomaterials in Bulk Forms.

Nanosized materials are known to have the ability to withstand ultralarge elastic strains (4-10%) and to have ultrahigh strengths approaching their theoretical limits. However, it is a long-standing challenge to harnessing their exceptional intrinsic mechanical properties in bulk forms. This is commonly known as "the valley of death" in nanocomposite design. In 2013, a breakthrough was made to overcome this challenge by using a martensitic phase transforming matrix to create a composite in which ultralarge elastic lattice strains up to 6.7% are achieved in Nb nanoribbons embedded in it. This breakthrough was enabled by a novel concept of phase transformation assisted lattice strain matching between the uniform ultralarge elastic strains (4-10%) of nanomaterials and the uniform crystallographic lattice distortion strains (4-10%) of the martensitic phase transformation of the matrix. This novel concept has opened new opportunities for developing materials of exceptional mechanical properties or enhanced functional properties that are not possible before. The work in progress in this research over the past six years is reported.

Remote-Sensing Image Usability Assessment Based on ResNet by Combining Edge and Texture Maps

Authentic remote-sensing images suffer non-uniform complex distortions during acquisition, transmission, and storage. Clouds, light, and exposure also affect local quality. This paper constructs a usability-based subjective remote-sensing image dataset and gives a definition of usability for images with non-uniform distortion, where the image usability is determined by the weighted quality of image's blocks. It is difficult to extract the handcraft features from remote-sensing images with complex mixture distortion. Recently, convolutional neural network (CNN) has been introduced into blind quality assessment for images with uniform distortion, which includes feature learning and regression in one processing. In this paper, we first describe and systematically analyze the usability of remote-sensing images in detail. Then, we propose a remote-sensing image usability assessment (RSIUA) method based on a residual network by combining edge and texture maps. The score of remote-sensing image usability was obtained with the weighted averaging of the quality scores of all image blocks, and the weight of each image block was determined by its quality score. We compared the proposed method with three traditional image quality assessment methods, one CNN-based method for images with simulated distortion, and one scale-invariant feature transform-based RSIUA method. The linear correlation coefficient, Spearman's rank ordered correlation coefficient, and root-mean-squared error of experiments demonstrate that our method outperforms all five competitors. The experiments also reveal that the edge and texture maps can improve the performance.

Changes in the morphology of microgrooved stem tapers with differing assembly conditions

BackgroundFretting and corrosion at the head-stem taper junction has been cited as a potential clinical concern. Material loss measurement is a vital tool for quantifying changes due to in vitro, in vivo, and/or ex-vivo implant experience. Material loss measurement requires reconstruction of pre-implantation geometry to delineate damage. This is straightforward in principle for plain machined tapers, integrating between a fitted interpolated cone and the measured data. Mathematical filtration methods have been developed to remove this texture and facilitate measurement. The extent to which the assembly process could influence filtration accuracy is not currently known. MethodsAn engagement/ disengagement study was performed on 27 head/ stem pairs using 2, 4, and 8kN impact loads. Impact was delivered in three locations; axial, 10o anterior, and 10o anteroproximal. Pull-off force was measured, and stems were measured pre and post assembly using a Talyrond 365 roundness measurement machine. ResultsAn increase in the plastic deformation of microgrooves and pull-off force was noted with increasing assembly loads. Off-axis impaction resulted in reduced pull-off strength and reduced uniform microgroove distortion. Volumetric change between pre and post assembly was below the noise threshold on stem and head surfaces. DiscussionThe measurement method was shown to be capable of capturing linear microgroove deformation of 1 μm peak – peak and volume loss above 0.1mm3. Lower peak load was noted when impacting a seated head when compared with engagement of discrete heads and stems, under the same assembly conditions.

Robust Half-Metallicity in Quaternary Heusler Compounds KSrNZ (Z = O, S, and Se)

The first principle calculations based on density functional theory using full potential linearized augmented plane wave method was performed on the quaternary Heusler alloys KSrNZ (Z = O, S, and Se). Studies on structural properties showed that quaternary Heusler alloys KSrNZ (Z = O, S, and Se) were stable in YI-type structure. Furthermore, values of formation energies confirmed that these alloys may be synthesized experimentally. Verification of electronic properties resulted that KSrNO, KSrNS, and KSrNSe compounds were half-metals at equilibrium lattice constants with majority band gaps of 4.61, 3.82, and 3.51 eV, respectively. KSrNZ (Z = O, S, and Se) compounds maintained half-metallic behavior in relatively wide ranges of lattice constant under uniform strain distortion. This indicates that these compounds are promising materials for future spintronic applications. Furthermore, the origin of half-metallic characteristic was verified using electronic density of states. Calculations of magnetic properties showed that the total magnetic moments of KSrNZ (Z = O, S, and Se) were obtained equal to 2 μB satisfying the famous Slater-Pauling rule (Mtot= 12-Ztot).