Severely Distorted Research Articles

Fully automated measurement of intracranial CSF and brain parenchyma volumes in pediatric hydrocephalus by segmentation of clinical MRI studies.

Brain parenchyma (BP) and intracranial cerebrospinal fluid (iCSF) volumes measured by fully automated segmentation of clinical brain MRI studies may be useful for the diagnosis and follow-up of pediatric hydrocephalus. However, previously published segmentation techniques either rely on dedicated sequences, not routinely used in clinical practice, or on spatial normalization, which has limited accuracy when severe brain distortions, such as in hydrocephalic patients, are present. We developed a fully automated method to measure BP and iCSF volumes from clinical brain MRI studies of pediatric hydrocephalus patients, exploiting the complementary information contained in T2- and T1-weighted images commonly used in clinical practice. The proposed procedure, following skull-stripping of the combined volumes, performed using a multiparametric method to obtain a reliable definition of the inner skull profile, maximizes the CSF-to-parenchyma contrast by dividing the T2w- by the T1w- volume after full-scale dynamic rescaling, thus allowing separation of iCSF and BP through a simple thresholding routine. Validation against manual tracing on 23 studies (four controls and 19 hydrocephalic patients) showed excellent concordance (ICC>0.98) and spatial overlap (Dice coefficients ranging from 77.2% for iCSF to 96.8% for intracranial volume). Accuracy was comparable to the intra-operator reproducibility of manual segmentation, as measured in 14 studies processed twice by the same experienced neuroradiologist. Results of the application of the algorithm to a dataset of 63 controls and 57 hydrocephalic patients (19 with parenchymal damage), measuring volumes' changes with normal development and in hydrocephalic patients, are also reported for demonstration purposes. The proposed approach allows fully automated segmentation of BP and iCSF in clinical studies, also in severely distorted brains, enabling to assess age- and disease-related changes in intracranial tissue volume with an accuracy comparable to expert manual segmentation.

Meta-learning-based optical vector beam high-fidelity communication under high scattering.

While spatial structured light based free space optical communication provides high-bandwidth communication with broad application prospect, severe signal distortion caused by optical scattering from ambient microparticles in the atmosphere can lead to data degradation. A deep-learning-based adaptive demodulator has been demonstrated to resolve the information encoded in the severely distorted channel, but the high generalization ability for different scattering always requires prohibitive costs on data preparation and reiterative training. Here, we demonstrate a meta-learning-based auto-encoder demodulator, which learns from prior theoretical knowledge, and then training with only three realistic samples per class can rectify and recognize transmission distortion. By employing such a demodulator to hybrid vector beams, high fidelity communication can be established, and data costs are reduced when faced with different scattering channels. In a proof-of-principle experiment, an image with 256 gray values is transmitted under severe scattering with an error ratio of less than 0.05%. Our work opens the door to high-fidelity optical communication in random media environments.

Heterogeneous lattice strain strengthening in severely distorted crystalline solids

Multi-principal element alloys (MPEAs) exhibit outstanding mechanical properties because the core effect of severe atomic lattice distortion is distinctly different from that of traditional alloys. However, at the mesoscopic scale the underlying physics for the abundant dislocation activities responsible for strength-ductility synergy has not been uncovered. While the Eshelby mean-field approaches become insufficient to tackle yielding and plasticity in severely distorted crystalline solids, here we develop a three-dimensional discrete dislocation dynamics simulation approach by taking into account the experimentally measured lattice strain field from a model FeCoCrNiMn MPEA to explore the heterogeneous strain-induced strengthening mechanisms. Our results reveal that the heterogeneous lattice strain causes unusual dislocation behaviors (i.e., multiple kinks/jogs and bidirectional cross slips), resulting in the strengthening mechanisms that underpin the strength-ductility synergy. The outcome of our research sheds important insights into the design of strong yet ductile distorted crystalline solids, such as high-entropy alloys and high-entropy ceramics.

Severe distortion in the representation of foveal visual image locations in short-term memory

The foveal visual image region provides the human visual system with the highest acuity. However, it is unclear whether such a high fidelity representational advantage is maintained when foveal image locations are committed to short-term memory. Here, we describe a paradoxically large distortion in foveal target location recall by humans. We briefly presented small, but high contrast, points of light at eccentricities ranging from 0.1 to 12°, while subjects maintained their line of sight on a stable target. After a brief memory period, the subjects indicated the remembered target locations via computer controlled cursors. The biggest localization errors, in terms of both directional deviations and amplitude percentage overshoots or undershoots, occurred for the most foveal targets, and such distortions were still present, albeit with qualitatively different patterns, when subjects shifted their gaze to indicate the remembered target locations. Foveal visual images are severely distorted in short-term memory.

Enhanced strength and ductility synergy of a CoCrFeMnNi high entropy alloy with a hierarchical structure via severe distortion

Improvement on strength and ductility synergy has always been the unremitting pursuit for structural materials. In this study, the strengthen and ductility of CoCrFeMnNi HEA were improved simultaneously via a designed continuous driven friction process. The results show that a hierarchical structure, which consists of 3 zones: the homogenously distributed ultrafine grains in fusion zone, severely distorted grains in thermal mechanical effect zone and coarsening equiaxed grains with high dislocation density in base zone, was formed in CoCrFeMnNi HEA, leads to the tensile strength enhanced from 598 to 629 MPa with the ductility increased from 27% to 38%. The findings provide new insight into solution to strength and ductility trade-off for structural materials.

Study on Distortion Compensation of Underwater Archaeological Images Acquired through a Fisheye Lens and Practical Suggestions for Underwater Photography - A Case of Taean Mado Shipwreck No. 1 and No. 2 -

Underwater archaeology relies heavily on photography and video image recording during surveillances and excavations like ordinary archaeological studies on land. All underwater images suffer poor image quality and distortions due to poor visibility, low contrast and blur, caused by differences in refractive indices of water and air, properties of selected lenses and shapes of viewports. In the Yellow Sea (between mainland China and the Korean peninsula), the visibility underwater is far less than 1 m, typically in the range of 30 cm to 50 cm, on even a clear day, due to very high turbidity. For photographing 1 m x 1 m grids underwater, a very wide view angle (180o) fisheye lens with an 8 mm focal length is intentionally used despite unwanted severe barrel-shaped image distortion, even with a dome port camera housing. It is very difficult to map wide underwater archaeological excavation sites by combining severely distorted images. Development of practical compensation methods for distorted underwater images acquired through the fisheye lens is strongly desired. In this study, the source of image distortion in underwater photography is investigated. We have identified the source of image distortion as the mismatching, in optical axis and focal points, between dome port housing and fisheye lens. A practical image distortion compensation method, using customized image processing software, was explored and verified using archived underwater excavation images for effectiveness in underwater archaeological applications. To minimize unusable area due to severe distortion after distortion compensation, practical underwater photography guidelines are suggested.

Cepstral scanning transmission electron microscopy imaging of severe lattice distortions

The development of four-dimensional (4D) scanning transmission electron microscopy (STEM) using fast detectors has opened-up new avenues for addressing some of longstanding challenges in electron imaging. One of these challenges is how to image severely distorted crystal lattices, such as at a dislocation core. Here we develop a new 4D-STEM technique, called Cepstral STEM, for imaging disordered crystals using electron diffuse scattering. In contrast to analysis based on Bragg diffraction, which measures the average and periodic scattering potential, electron diffuse scattering can detect fluctuations caused by crystal disorder. Local fluctuations of diffuse scattering are captured by scanning electron nanodiffraction (SEND) using a coherent probe. The harmonic signals in electron diffuse scattering are detected through Cepstral analysis and used for imaging. By integrating Cepstral analysis with 4D-STEM, we demonstrate that information about the distortive part of electron scattering potential can be separated and imaged at nm spatial resolution. We apply the technique to the analysis of a dislocation core in SiGe and lattice distortions in a high entropy alloy.

A novel spatial pooling method for 3D mesh quality assessment based on percentile weighting strategy

Most of existing mesh quality assessment metrics consist of a similar two-stage computation process: first constructing a quality map by comparing the local regions between reference mesh and distorted mesh, then adopting a spatial pooling method to generate the overall quality score. In this paper, we propose a novel spatial pooling method for 3D mesh quality assessment based on percentile weighting strategy. We assign more weight to the severely distorted regions of the mesh at the pooling stage and extend the percentile weighting method by incorporating surface area at the pooling stage. Our analysis indicates that the percentile weighting method has a strong capability to emphasize the local regions with severe distortion of the mesh. We develop a mesh quality metric by pooling the local distances generated by the Tensor-based Perceptual Distance Measure metric with our spatial pooling method. We investigate the influence of the parameters of percentile weighting on the performance, and determine the optimal parameters and unified parameters through empirical tests on three publicly available databases. Experimental results demonstrate the effectiveness of our spatial pooling method and the superiority of our metric over state-of-the-art metrics.

Carrier-phase-estimation algorithm featuring fast trackability for high-speed coherent WDM PON based on RSOA.

There have been substantial efforts to implement high-speed (>10 Gb/s) upstream transmission using reflective semiconductor optical amplifiers (RSOAs) in a coherent wavelength-division-multiplexed (WDM) passive optical network (PON). In such a network, it is necessary to estimate the carrier phase of upstream optical signal to retrieve the phase-modulated information created by RSOA. However, due to the severe waveform distortions caused by the limited modulation bandwidth of RSOA (typically less than 3 GHz), previously reported carrier phase estimation (CPE) algorithms cannot accurately estimate the carrier phase of high-speed quadrature phase-shift keying (QPSK) signal generated from the RSOA seeded by a distributed-feedback (DFB) laser. We propose a novel CPE method capable of tracking the carrier phase rapidly by using a small number of symbols (e.g., 15 symbols) even when the waveforms are severely distorted by the limited modulation bandwidth of RSOA. The proposed CPE method utilizes the linear relationship between the intensity modulation and phase modulation indices inherent in the semiconductor opto-electronic device. By using the proposed method, we demonstrate the transmission of 25.78-Gb/s QPSK signal in a 20-km long loopback fiber link. In this experiment, a commercial DFB laser (linewidth: 3 MHz) is used as the seed light instead of an expensive narrow-linewidth laser. Also shown through the experiment is that the proposed CPE method is highly unsusceptible to variations of parameters required in the proposed method, such as the number of test phases, the accuracy of linewidth enhancement factor, and the accuracy of the normalized amplitude of DC component.

Imaging through strong turbulence with a light field approach

Under strong turbulence conditions, object's images can be severely distorted and become unrecognizable throughout the observing time. Conventional image restoring algorithms do not perform effectively in these circumstances due to the loss of good references on the object. We propose the use a plenoptic sensor as a light field camera to map a conventional camera image onto a cell image array in the image's sub-angular spaces. Accordingly, each cell image on the plenoptic sensor is equivalent to the image acquired by a sub-aperture of the imaging lens. The wavefront distortion over the lens aperture can be analyzed by comparing cell images in the plenoptic sensor. By using a modified "Laplacian" metric, we can identify a good cell image in a plenoptic image sequence. The good cell image corresponds with the time and sub-aperture area on the imaging lens where wavefront distortion becomes relatively and momentarily "flat". As a result, it will reveal the fundamental truths of the object that would be severely distorted on normal cameras. In this paper, we will introduce the underlying physics principles and mechanisms of our approach and experimentally demonstrate its effectiveness under strong turbulence conditions. In application, our approach can be used to provide a good reference for conventional image restoring approaches under strong turbulence conditions. This approach can also be used as an independent device to perform object recognition tasks through severe turbulence distortions.

NKCS, a Mutant of the NK-2 Peptide, Causes Severe Distortions and Perforations in Bacterial, But Not Human Model Lipid Membranes.

NKCS is an improved mutant of the bioactive peptide NK-2, which shows strong activity against Escherichia coli and low toxicity towards human cells. The different activity demonstrates the relevance of the physico-chemical nature of the target membrane for the biological effect of this peptide. We studied the effect of this potent antimicrobial peptide on model membranes by activity studies, differential scanning calorimetry, single molecule tracking and tracer efflux experiments. We found that NKCS severely distorted, penetrated and perforated model lipid membranes that resembled bacterial membranes, but not those that were similar to human cell membranes. The interactions of NKCS with phosphatidylethanolamine, which is abundant in bacterial membranes, were especially strong and are probably responsible for its antimicrobial activity.

Perforation of steel and aluminum targets using a modified Johnson–Cook material model

Numerical perforation studies involving finite element method (FEM) suffer from severe mesh distortion problem when subjected to large deformation in high velocity projectile impact cases. Severe element distortion causes negative volume problem and introduces numerical errors in the simulated results. Mesh free methods, such as smoothed particle hydrodynamics (SPH) method is capable of handling large deformation without any numerical problems, but at substantially high computational resources. To mitigate the problem, coupled smoothed particle hydrodynamics–finite element method (SFM) has been implemented to study the high velocity perforations of steel and aluminum target plates, where the SPH method is adopted only in severely distorted regions and the FEM further away. Strain rate and adiabatic heating have a considerable effect on material properties, especially at high velocity impact, and hence, a new material model with high strain rate and adiabatic temperature effects is adopted herein. Material properties for Weldox 460E steel and AA5083-H116 aluminum plates are determined and used to perform perforation of target plates with varying thicknesses and projectile nose geometries, such as blunt, conical and ogival noses. Numerical residual and ballistic limit velocities show good correlation with the published experimental results. The study demonstrates that the new material model is able to emulate failure characteristics of the steel and aluminum plates as observed in various experimental observations.

Blind Algorithms with Decision Feedback based on Zero-Error Probability for Constant Modulus Errors

The constant modulus algorithm (CMA) widely used in blind equalization applications minimizes the averaged power of constant modulus error (CME) defined as the difference between an instant output power and a constant modulus. In this paper, a decision feedback version of the linear blind algorithm based on maximization of the zero-error probability for CME is proposed. The Gaussian kernel of the maximum zero-error criterion is analyzed to have the property to cut out excessive CMEs that may be induced from severely distorted channel characteristics. Decision feedback approach to the maximum zero-error criterion for CME is developed based on the characteristic that the Gaussian kernel suppresses the outliers and this prevents error propagation to some extent. Compared to the linear algorithm based on maximum zero-error probability for CME in the simulation of blind equalization environments, the proposed decision feedback version has superior performance enhancement particularly in cases of severe channel distortions.

여성 얼굴의 불균형 개선을 위한 프로그램 구축

This study shows that the self-satisfaction individually is rising and social life is attracted effective and successful in image making field by structuring the facial image improvement program through experimental study in order to improve unbalance of women's face. Experiment is conducted by electing 3 samples for 12 weeks and analyzing the measurement and visual analysis, infrared thermography, and evaluation of experts in order to check the facial unbalance. Subject 1 had the effect at approximately in 4 weeks with the severely distorted chin line and mouth appendage. The facial outline became softer to turn entire image to be softer and more feminine. Subject 2 had the severe distortion of location and size of eyes and nose. But the skin was getting better at first, followed by eyes getting clearer with the location changed in left and right. Subject 3 had the twisted nose and lower chin, but after two weeks, the eye area and skin were better and the width of left and right chin was similarly changed. On the basis of the above research result, the program to effectively improve the image was structured and presented with the resolution of facial unbalance. Program is consist of the training of breathing method, face washing method, facial muscle exercise.

High Velocity Perforation Simulations of Lightweight Target Plates Using a Modified Johnson-Cook Model

Because of their superior ballistic and mechanical properties, lightweight materials like titanium alloy Ti-6Al-4V and aluminum alloy AA5083-H116 have been frequently used for aerospace and military applications. Tests of ballistic limit velocity are limited by expensive nature of the experimental setup, and indeed, that can be resolved by adopting numerical simulations. Numerical study involving the finite element method (FEM) suffers from severe element distortion problem when used for high velocity impact analysis. Therefore, the coupled smooth particle hydrodynamics — finite element method (SFM) has been adopted to study the perforation of Ti-6Al-4V and AA5083-H116 target plates with thicknesses of 26.72mm and 25mm, respectively. In the SFM, smooth particle hydrodynamics (SPH) method is incorporated in the severely distorted regions and the FEM otherwise. Effects of strain rate and adiabatic heating are significant for high velocity impact problems, and hence, a constitutive model incorporating effects of high strain rate and adiabatic temperature is proposed. The constitutive model is verified and finally adopted for perforation studies. Close correlation between the numerical and experimental ballistic limit velocities are accomplished. The study shows that the proposed method is able to emulate the failure mechanisms of the target plates without any numerical problem.

Registration Techniques for Using Imperfect and Par tially Calibrated Devices in Planar Multi-Projector Displays

Multi-projector displays today are automatically registered, both geometrically and photometrically, using cameras. Existing registration techniques assume pre-calibrated projectors and cameras that are devoid of imperfections such as lens distortion. In practice, however, these devices are usually imperfect and uncalibrated. Registration of each of these devices is often more challenging than the multi-projector display registration itself. To make tiled projection-based displays accessible to a layman user we should allow the use of uncalibrated inexpensive devices that are prone to imperfections. In this paper, we make two important advances in this direction. First, we present a new geometric registration technique that can achieve geometric alignment {\em in the presence of severe projector lens distortion} using a relatively inexpensive low-resolution camera. This is achieved via a closed-form model that relates the projectors to cameras, in planar multi-projector displays, using rational Bezier patches. This enables us to geometrically calibrate a 3000 x 2500 resolution planar multi-projector display made of 3 x 3 array of nine severely distorted projectors using a low resolution (640 x 480) VGA camera. Second, we present a photometric self-calibration technique for a projector-camera pair. This allows us to photometrically calibrate the same display made of nine projectors using a photometrically uncalibrated camera. To the best of our knowledge, this is the first work that allows geometrically imperfect projectors and photometrically uncalibrated cameras in calibrating multi-projector displays.

Analysis of distortion in the high range resolution profile from a perturbed target

Experimental results have demonstrated that even when a target possesses very small perturbed rotational motion, its high range resolution (HRR) radar image profile can be severely distorted. A numerical model has been developed and is able to accurately simulate the observed distorting effects. The well known range–Doppler coupling effect offers a partial explanation for the distortion of a target's HRR profile when the perturbing rotational motion is constant in time during radar interrogation. A more interesting and much more dramatic situation arises when the perturbing motion is time-varying; severe distortion in the target's HRR profile can occur due to the excitation of higher-order sidebands in the phase of the target echo.

Characterization of severe matrix distortions during phase separation from the redistribution of diffracted intensities

Severe matrix deformation has been examined at an early stage of age-hardening in a polycrystalline Brush 25 alloy containing Cu–11.50 at % Be–0.23 at % Co aged at 200°C. Simplified anisotropic elastic models for the atomic displacement field about coherent disc-shaped precipitates provide quantitative estimates of the atomic displacement field in the surrounding matrix. This requires a separation of diffracted intensity into Bragg peaks, static diffuse scattering, and quasilines. The latter originates from the severely distorted zone about the precipitates. Elastic models include single discs, and [1 0 1] stair-step pairs. Ageing at 200°C introduces larger changes in the diffraction profiles than at 315°C. This is observed mainly as large variations in quasiline intensities, as well as in their relative peak positions. Comparisons are made at about one-half the maximum hardness. These variations result from the response of the coherent anisotropic copper matrix to large tetragonal Bain strains in disc-shaped precipitates, and a strong preference for the largest deformations to be perpendicular to the free surface. Quasiline shifts are used along with Vegard's Law to extend the metastable Guinier-Preston (GP)-zone boundary to 200°C. This boundary extension is smooth and continuous with published data, and thereby relates the metastable GP boundary to a highly distorted matrix about disc-shaped precipitates. Disc diameters range from 4.8–6.4 nm with a thickness of 0.29 nm after 16–64 h at 200°C. The [1 0 1] stair-step pair model best fits the experimental results.

Linking of Lagrangian particle methods to standard finite element methods for high velocity impact computations

Abstract Lagrangian particle methods, such as smooth particle hydrodynamics, have been developed recently to include the effect of strength, and these techniques have been successfully applied to high velocity impact problems. These methods allow for variable nodal connectivity and can handle severe distortions in a manner comparable with Eulerian codes. The particle methods generally require more computer time than do standard finite element techniques, and are not accurate under some conditions. As a result, there are some advantages associated with linking the particle methods to standard finite elements. If the particle portion of the grid is restricted to those regions that are severely distorted, then the required computer time is reduced and the accuracy may be increased in the standard finite element grid. This paper describes and demonstrates techniques that include attachment, sliding and automatic generation of particles, which are linked to a standard finite element grid. Computed results show good agreement with test data.

Near-maximum-likelihood detectors for binary signals

The paper studies three developments of a class of near-maximum-likelihood detection processes derived from a conventional nonlinear (decision feedback) equaliser. The new detectors are suitable for binary signals transmitted over a linear baseband channel introducing severe amplitude distortion. The complexity of the processes is not excessive, and increases approximately linearly with the delay in detection. Thus, a sufficiently large delay in detection can be employed to achieve a near-optimum tolerance to noise when the received signal has been very severely distorted. The paper describes three novel detection processes, and presents the results of computer simulation tests, comparing the tolerances to additive white Gaussian noise of various arrangements of each detector with that of the optimum detector of the given class and that of a conventional nonlinear equaliser. Three different channels are used in the tests and binary signals are transmitted in every case.