Distortion Generation Research Articles

A frame level rate allocation algorithm based on temporal dependency model for AV1

Rate control is an essential module in video coding. Rate control strategies strive to deliver a stable playback experience as well as achieving high compression efficiency for modern video applications, constrained by restricted bandwidth and buffer limits. The difficulty of rate control often lies in the adaptation ability of the underlying algorithm to capture the variability of content and temporal correlation across frames. In this paper, we present a rate allocation algorithm to model the distortion propagation in the hierarchical coding structure premised on the temporal dependency model at frame level. Our experiments show that with the information collected from the temporal dependency model, the proposed rate allocation algorithm significantly improves the coding efficiency over the AV1 baseline on a set of variable user generated video clips.

Metal-to-metal communication during the spin state transition of a [2 × 2] Fe(II) metallogrid at equilibrium and out-of-equilibrium conditions.

Spin crossover (SCO) complexes are prototypes of materials with bi- or multi-stability in the solid state. The structural evolution during their spin transition is a key feature to establish the foundations of how to utilize this type of material. So far, ultrafast time-resolved structural investigations of SCO solids have been focused on monometallic complexes, though an increasing number of oligometallic SCO complexes showing cooperativity effects are being reported. Here, we used single crystal X-ray crystallography and time-resolved pink Laue photocrystallography to study the molecular reorganisation during the thermal and photoinduced SCO of a [2 × 2] tetranuclear metallogrid of the form [FeII4LMe4](BF4)4·2MeCN ([LMe]- = 4-methyl-3,5-bis{6-(2,2'-bipyridyl)}pyrazolate). A multitemperature crystallographic investigation on single crystals reveals an effective communication between the metal centres during thermal SCO, observed by the simultaneous transformation of the coordination polyhedra of both crystallographic-symmetry independent metal atoms accompanying the SCO in only one of them. Time-resolved photocrystallography results reveal the different molecular responses between mononuclear and oligonuclear complexes, after light irradiation with a picosecond laser pulse. While mononuclear SCO complexes reorganise once during the first nanosecond after excitation, the tetranuclear metallogrid exhibits a multiple structural rearrangement in the same span of time. Such behaviour is attributed to the elastic communication between metal atoms, which allows the propagation of a short-range elastic distortion over the entire Fe4 grid complex. The present study sheds light on the importance of strong elastic coupling of metal atoms during the correlated spin transition of oligometallic complexes.

State of the Art of Repetitive Control in Power Electronics and Drive Applications

Power electronic systems present a non-linear behavior mainly due to their switching nature. This is often combined with their interaction with non-linear systems, such as other switching converters, diode rectifiers, motor drives, etc. and with possible non linearities of the power grid in the case of grid connected systems. The major effect of these non-linear interactions is the generation of harmonic distortion on voltages and currents (both in DC and AC), which needs to be compensated to achieve high power quality systems. The use of passive filters is often the simplest and most immediate solution; however, this decreases converter efficiency and increases its weight and volume. Thus, the use of a control strategy capable of tracking periodic signals, rejecting periodic disturbance and largely improving steady state behavior and harmonic distortion with a limited bandwidth is a very desirable feature. Repetitive Control (RC) represents an extremely practical and efficient solution for the aforementioned issues, and it is widely employed in many different applications. This paper focuses on state of the art of RC used in power electronics and drives. RC basic concepts, different control structures, design methods, fixed and variable frequency operating conditions, etc. are investigated. Furthermore, many example applications and existing control approaches developed in recent years for power electronics and drive systems based on RC, have also been discussed in detail.

A Document Image Generation Scheme Based on Face Swapping and Distortion Generation

Nowadays, digital images are widely used in various services. The emergence of more and more image editing algorithms has made image forensic approaches to be severely challenged. Driven by the emergence of forged images, more and more image forensic methods are proposed to evaluate the authenticity of digital images. However, in some privacy-related image forensics areas, the scarcity of data affects their development. In this paper, we investigate a document image generation scheme based on face swapping and distortion generation to generate document image databases at a low cost. First, we propose an IDNet for editing face content and text content in digital document images. Second, we propose a Distortion Simulation Network (DSNet) for simulating print-and-scan distortion, and the generated data can be used to study a novel document attack type called recapture attack. Third, we use the database generated by our proposed method to assist in training document image recapture forensic networks. A qualitative comparison with existing methods illustrates that the image content generated by our proposed method maintains more complete semantic information and higher image quality. Quantitative results have confirmed that with the addition of the generated database, the performance of the model improves by about 8% measured in AUC.

Residual Stresses Control in Additive Manufacturing

Residual stresses are one of the primary causes for the failure of parts or systems in metal additive manufacturing (AM), since they easily induce crack propagation and structural distortion. Although the formation of residual stresses has been extensively studied, the core factors steering their development in AM have not been completely uncovered. To date, several strategies based on reducing the thermal gradients have been developed to mitigate the manifestation of residual stresses in AM; however, how to choose the optimal processing plan is still unclear for AM designers. In this regard, the concept of the yield temperature, related to the thermal deformation and the mechanical constraint, plays a crucial role for controlling the residual stresses, but it has not been duly investigated, and the corresponding approach to control stresses is also yet lacking. To undertake such study, a three-bar model is firstly used to illustrate the formation mechanism of the residual stress and its key causes. Next, an experimentally calibrated thermomechanical finite element model is used to analyze the sensitivity of the residual stresses to the scan pattern, preheating, energy density, and the part geometry and size, as well as the substrate constraints. Based on the numerical results obtained from this analysis, recommendations on how to minimize the residual stresses during the AM process are provided.

Intermodulation distortions from an array of active nonlinear oscillators.

Coupling is critical in nonlinear dynamical systems. It affects the stabilities of individual oscillators as well as the characteristics of their response to external forces. In the auditory system, the mechanical coupling between sensory hair cells has been proposed as a mechanism that enhances the inner ear's sensitivity and frequency discrimination. While extensive studies investigate the effects of coupling on the detection of a sinusoidal signal, the role of coupling underlying the response to a complex tone remains elusive. In this study, we measured the acoustic intermodulation distortions (IMDs) produced by the inner ears of two frog species stimulated simultaneously by two pure tones. The distortion intensity level displayed multiple peaks across stimulus frequencies, in contrast to the generic response from a single nonlinear oscillator. The multiple-peaked pattern was altered upon varying the stimulus intensity or an application of a perturbation tone near the distortion frequency. Numerical results of IMDs from a chain of coupled active nonlinear oscillators driven by two sinusoidal forces reveal the effects of coupling on the variation profile of the distortion amplitude. When the multiple-peaked pattern is observed, the chain's motion at the distortion frequency displays both a progressive wave and a standing wave. The latter arises due to coupling and is responsible for the multiple-peaked pattern. Our results illustrate the significance of mechanical coupling between active hair cells in the generation of auditory distortions, as a mechanism underlying the formation of in vivo standing waves of distortion signals.

2-D Deformed Half Fisheye Lens as Beamforming Network to Excite Planar Arrays of Antennas for Multibeam Radiations

Multibeam (MB) radiations of antenna arrays rely on effective beamforming networks (BFNs). A 2-D fisheye lens-based BFN (FL-BFN) was developed using a half 2-D lens realizable on metal parallel-plate sandwiched substrates to excite a planar antenna array. This FL-BFN implemented the beam and antenna excitation ports on its half-circular circumference and straight boundaries. An optimization scheme was developed to minimize the ray propagation distortion due to an incomplete half-lens propagation path for an offset beam, which results in an aperiodic array of antennas for MB radiations. Excitations for periodic arrays can also be implemented by considering an aperiodic output port establishment. The rule to determine the positions of antenna elements is also shown for easy design. This FL-BFN performance is demonstrated using its output amplitudes and phases to excite a Vivaldi antenna array for MB radiation. Numerical simulations and measurements over a prototype were performed to validate its feasibility with distinguished agreements.

Parametric Doppler correction analysis for wayside acoustic bearing fault diagnosis

Wayside acoustic system plays a crucial role in monitoring and diagnosing the status of train wheel bearings. However, due to the signal distortion caused by Doppler effect, the diagnosis accuracy will be seriously disturbed. In this manner, this paper proposes a model-driven Doppler distortion self-tuning method in theory, named as parametric Doppler correction analysis (PDCA). Different from traditional methods, such as instantaneous frequency tracking and Doppler distortion sparse representation, the proposed method aims to abstractly construct a physical model of acoustic signal distortion propagation based on Morse acoustic theory, where the acoustic forward propagation model and reverse reconstruction model are simultaneously built. The scheme consists of four basic steps. Firstly, the physical model with amplitude modulation operator and frequency shift operator is described for the distortion process. Secondly, the pseudo transition signal with the characteristics of energy accumulation and no distortion is obtained via a construction of frequency rearrangement operator and amplitude demodulation operator. Then, pseudo Doppler correction (PDC) is presented to solve the frequency distortion of the received signal, where a high energy accumulation for frequency distribution is designed as optimization function. Especially, quasi Newton algorithm L-BFGS is used to realize the adaptive learning for distortion parameters. Finally, through time-domain interpolation resampling (TIR) technique, the corrected signal can be analytically reconstructed with the optimal parameters. Applying the PDCA scheme to simulated signals and experimental signals, its validity is verified. The comparison with the instantaneous frequency ridge extraction approach further indicates the proposed model-driven method can reach a more accurate correction result in a faster and adaptive process.

Strain Response and Aerodynamic Damping of a Swirl Distortion Generator Using Computational Fluid Dynamics

Abstract Boundary layer ingestion (BLI) concepts have become a prominent topic in research and development due to their increase in fuel efficiency for aircraft. Virginia Tech has developed the StreamVane™, a secondary flow distortion generator, which can be used to efficiently test BLI and its aeromechanical effects on turbomachinery. To ensure the safety of this system, the complex vanes within StreamVanes must be further analyzed structurally and aerodynamically. In this paper, the induced strain of two common vane shapes at three different operating conditions is computationally determined. Along with these predictions, the aerodynamic damping of the vanes is calculated to predict flutter conditions at the same three operating points. To achieve this, steady computational fluid dynamics (CFD) calculations are done to acquire the aerodynamic pressure loading on the vanes. Finite element analysis (FEA) is performed to obtain the strain and modal response of the StreamVane structure. The mode shapes and steady CFD are used to initialize an unsteady CFD analysis, which acquires the aerodynamic damping results of the vanes. The testcase used for this evaluation was specifically designed to overstep the structural limits of a StreamVane, and the results provide an efficient computational method to observe flutter conditions of stationary systems.

Three-dimensional luminescence microscopy for quantitative plasma characterization in bulk semiconductors

Important challenges remain in the development of ultrafast laser writing inside semiconductor materials because the properties of narrow gap materials cause strong propagation distortions to intense infrared light. Here, we introduce a simple and robust imaging method for high-dynamic-range investigations of the laser–matter interactions in bulk semiconductors. Supported by measurements in gallium arsenide and silicon, we show how z-scan imaging of the band-to-band radiative recombination enables quantitative reconstruction of the three-dimensional distributions of free-carriers generated by nonlinear ionization with ultrashort pulses. The validity is confirmed by comparisons with ultrafast transmission microscopy (shadowgraphy) images. The superior sensitivity of the zero-background luminescence method allows the measurement of local carrier densities as low as ≈1016 cm−3 inside GaAs that is inaccessible by shadowgraphy. It provides the first direct evidence of the low density plasma generated far prior to the focus that causes the previously reported intensity clamping phenomenon. The potential of this non-coherent 3D imaging method to assess complex beam distortion features is also exemplified by real-time pre-compensation of aberration for an intense interacting beam.

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Thermo-mechanical analysis of laser welding of Grade 91 steel plates

Generation of residual stresses and distortion in weld component is a major concern in Grade 91 steel thin plates. In the present study, FEM based Laser welding analysis of Grade 91 steel is carried out for 3 thick plates using SYSWELD software. Heat input optimization has been carried out by bead-on-plate welding at different heat input. Optimized heat input with full depth of penetration is used for a square butt joint of Grade 91 steel laser welding. Experimentally measured residual stresses using X-ray diffraction technique are compared with predicted results. Residual stresses comparison shows that due to phase transformation effect the peak tensile stress values are observed next to heat affected zone. The predicted distortion in longitudinal and transverse directions is validated with experimental results.

Nanosized monometallic selenides heterostructures implanted into metal organic frameworks-derived carbon for efficient lithium storage

Two-phase heterostructure with rich phase boundaries holds great potential in engineering advanced electrode materials. However, current heterostructures are largely generated by introducing exotic cations or anions, complicating synthetic procedures and disturbing real insights into the intrinsic effect of heterostructure. Herein, nanosized monometallic selenides heterostructures are developed by precisely controlled selenylation of metal organic frameworks, which are implanted into in-situ formed carbon (NiSe/NiSe2@C, CoSe/CoSe2@C). The disordered atoms arrangement at two-phase boundary leads to the redistribution of interfacial charge and generation of lattice distortions, promoting easy adsorption and swift transfer of Li+, and providing extra active sites. As a proof of concept, the NiSe/NiSe2@C exhibits far surpassing lithium storage properties to single-phase counterparts (NiSe@C and NiSe2@C), including higher reversible capacity of 1015.5 mAh g−1, better rate capability (500.8 mAh g−1 at 4 A g−1), and superior cyclic performance. As expected, the NiSe/NiSe2@C manifests lower charge transfer resistance, higher Li+ diffusion coefficient, and accelerated capacitive kinetics. Ex-situ X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction combined with differential capacity versus voltage plots reveal multi-step redox mechanism of NiSe/NiSe2@C and the reason of conspicuous capacity enhancement. This work demonstrates the enormous potential of monometallic monoanionic heterostructure in energy-related field.

Experimental simulation methodology and spatial transition of complex distortion fields in a S-shaped inlet

The S-shaped inlet of the modern military aircraft propulsion system suffers from severe inlet distortion during flight maneuvering. The complex distorted flow field is generally decomposed into total pressure and swirl distortion, both of which could substantially degrade the performance and stability of an aero-engine. In the ground test of fans and low-pressure compressors, how to simulate the complex inlet distortion occurring in flight is non-trivial. In this paper, a subsonic S-shaped inlet test rig was constructed, and eight configurations of curved-edge plate-type distortion generators were installed in the intake channel to create a complex distorted flow field downstream. Results show that the distorted flow field is dependent on the circumferential position of the blocking plate due to the duct curvature. Prominent vortex structures caused by the pressure gradient and the cross secondary flow exist between the main flow and separated flow. Conventional distortion indices DC, CDI/RDI, and the SAE AIR1419/SAE AIR 5686 standard system are implemented to represent the total pressure distortion and swirl distortion and the effects of the size and location of the curved-edge plate on distortion intensity and distribution are investigated. Additionally, this paper also studied the spatial variation of the total pressure and swirl distortion between the duct circular exit section and the annular section, termed as spatial transition characteristics. This spatial transition process can be used in the future to specify a real inlet flow condition for stability assessment of a fan or low-pressure compressor. According to the experimental results, the circumferential total pressure distortion index is approximately unaltered along the contraction duct, while the radial index reduces by 62% on average. The spatial transition of the swirl distortion differs for bilaterally symmetrical and asymmetric swirling fields. The overall swirl intensity index decays by 37%∼70% only for bilaterally symmetrical modes, while being the same for bilaterally asymmetric approximately. At last, the generation and evolution mechanism of the above complex distorted flow field is analyzed theoretically.

On the Development of a Novel Contrast Pulse Sequence for Polymer-Shelled Microbubbles.

Contrast agents are routinely used in ultrasound examinations. Nonlinear ultrasound imaging techniques have been developed over decades to enhance the contrast between the tissue and the blood pool after the injection of ultrasound contrast agents (UCAs). In this study, we introduce a new contrast pulse sequence, CPS4. The CPS4 combines pulse inversion (PI), subharmonic (SH), and ultraharmonic (UH) techniques to remove propagation distortion while capturing the unique SH and UH responses from UCAs. The novel CPS4 and conventional PI, SH, and UH techniques were used to detect the presence of a research-grade, thick-shell, polymer microbubble in a tissue-mimicking flow phantom. The contrast-to-tissue ratios (CTRs) obtained from the applications of all techniques were compared. The results show that the highest CTR of approximately 16 dB was obtained using CPS4, which was superior to the individual reference techniques: PI, SH, and UH techniques, in all scenarios considered in this study.

Inverse Design of Flow Distortion Dominated by Shock Wave Interaction with Experimental Verification

With the development of supersonic/hypersonic vehicles, the influence of non-uniform flow has attracted increasing attention. Non-uniform flow exists everywhere in a scramjet, which is a potent engine for supersonic/hypersonic vehicles. Most flows entering the isolator, combustor, and nozzle exhibit high non-uniformity. Thus, several design methods for generating non-uniform flow have been proposed. However, these design methods cannot simulate flow distortion with high accuracy, especially the non-uniform flow caused by shock wave interaction. Thus, a design method for distortion generators, which can generate non-uniform flow associated with flow deflection angles, is proposed in this study to mimic the shock wave-dominated non-uniform flow with shock wave interaction. Numerical simulation and experiment are adopted to verify the effectiveness and reliability of the proposed method. The Mach number on the outlet and the surface pressure distribution on the upper wall of the distortion generator obtained in the experiment show a good agreement with the target one.

An Improved Design of a Swirl Distortion Generator

In order to study the effect of swirl distortion on the performance and stability of the compressor, this paper optimizes the design of the existing swirl distortion generator, and designs three different structures of pair swirl distortion generator. Using CFD technology, a comparative analysis of the standard pair swirl distortion flow fields and the pair swirl distortion flow fields produced by three newly designed swirl distortion generators and the existing pair swirl distortion generator is performed. The results show that the optimally designed distortion generator reproduces the standard pair swirl distortion flow field to a higher degree than existing distortion generators. On the three measurement rings, the average swirl angle error is reduced by 5.35%, 19.88%, and 8.22%. The total pressure recovery coefficient is increased by 2.2%, which proves that the design method in this paper is more reasonable and achieves the purpose of optimal design.

Experimental and numerical investigation on total pressure distortion generated by a rectangular movable flat baffle

A distortion generator equipped with a motor-activated movable flat baffle was installed just upstream of a rectangular plenum entrance to investigate the effects of inlet total pressure distortion on the stability and performance of an auxiliary power unit (APU). Experiments and numerical simulations on a direct connect scale inlet model of the APU were carried out to obtain a quantitative relationship between the insertion depth of the flat baffle in the flow stream and the total pressure distortion intensity and region. In the experiments, the blocking coefficient and total pressure distortion coefficient were controlled by adjusting the insertion depth of the flat baffle and the mass flow. In the simulations, detailed flow field was analyzed based on the detached-eddy simulation (DES) method. The results show that the pressure distribution of the distorted flow on the aerodynamic interface plane (AIP) can be divided into a high-pressure region, a transition region, and a low-pressure region. The area affected by the distorted flow was larger than the inserting area of the flat baffle. That area was more related to the relative blocking coefficient, and less affected by the mass flow. The total pressure distortion coefficient had a linear relationship with the mass flow rate and is positively correlated with the relative blocking coefficient. As the relative blocking coefficient increased to a certain value, an exponential growth in the total pressure distortion coefficient occurred, and consequently, the flow field distortion was intensified. In the flow field, a pair of corner vortices were formed at the corner between the flat baffle and the bottom wall of the inlet pipe, and a large separation zone was formed behind the flat baffle and exhibits certain unsteady characteristics.

Low-Complexity Error Resilient HEVC Video Coding: A Deep Learning Approach.

Intra/inter switching-based error resilient video coding effectively enhances the robustness of video streaming when transmitting over error-prone networks. But it has a high computation complexity, due to the detailed end-to-end distortion prediction and brute-force search for rate-distortion optimization. In this article, a Low Complexity Mode Switching based Error Resilient Encoding (LC-MSERE) method is proposed to reduce the complexity of the encoder through a deep learning approach. By designing and training multi-scale information fusion-based convolutional neural networks (CNN), intra and inter mode coding unit (CU) partitions can be predicted by the networks rapidly and accurately, instead of using brute-force search and a large number of end-to-end distortion estimations. In the intra CU partition prediction, we propose a spatial multi-scale information fusion based CNN (SMIF-Intra). In this network a shortcut convolution architecture is designed to learn the multi-scale and multi-grained image information, which is correlated with the CU partition. In the inter CU partition, we propose a spatial-temporal multi-scale information fusion-based CNN (STMIF-Inter), in which a two-stream convolution architecture is designed to learn the spatial-temporal image texture and the distortion propagation among frames. With information from the image, and coding and transmission parameters, the networks are able to accurately predict CU partitions for both intra and inter coding tree units (CTUs). Experiments show that our approach significantly reduces computation time for error resilient video encoding with acceptable quality decrement.

Stall inception prediction of axial compressors with radial inlet distortions

A stall inception prediction model considering radial inlet distortions is established in this paper in order to quickly and accurately predict the stall limit of a compressor at radially distorted inlet flow conditions. Furthermore, the quantitative effect of the radial inlet distortion on compressor stability is investigated on a low-speed single-stage axial-flow compressor which is named TA36 and located in Beijing University of Aeronautics and Astronautics. Two kinds of distortion intensities are achieved by two radial inlet distortion generators in experiments. By utilizing the developed stability model, the predicted stall limits of TA36 at clean, 10% and 20% radially distorted inlet flow conditions all agree well with the experimental data only with relative errors of −0.74%, 1.28%, and 0.53% respectively. These relative errors less than 1.50% validate the ability of the developed stability model to predict the stall onset of a compressor with clean inlet or radial inlet distortions. Moreover, the predicted results confirm that radial inlet distortions deteriorate the compressor stability, and the adverse effect becomes more severe with the increase of distortion intensity, which can also be concluded from the experimental data. After comparing the load distribution on the rotor blade at the three inlet conditions, the increase of the maximum load at the tip region at distorted inlet conditions is considered to be a critical factor contributing to the negative effect of radial inlet distortions on compressor stability.