As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding...As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding scenarios.This paper discusses interferogram modeling and phase distortion cor-rection techniques for spaceborne DASH interferometers.The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted,and the effectiveness of the analytical expression was verified through numerical simulation.The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms.In contrast,the phase distortion correction algorithm can achieve effective correction.This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer,providing a feasible solution to enhance its measurement accuracy.展开更多
The conversion of CO_(2)to dimethyl carbonate(DMC)offers a promising route for CO_(2)utilization.In this study,four CeO2 catalysts with distinct nanostructures were synthesized via a template-free hydrothermal method ...The conversion of CO_(2)to dimethyl carbonate(DMC)offers a promising route for CO_(2)utilization.In this study,four CeO2 catalysts with distinct nanostructures were synthesized via a template-free hydrothermal method by systematically varying the types and concentrations of precipitants as well as the hydrothermal reaction conditions,and they were employed for DMC synthesis from CO_(2)and methanol.The atomic arrangements of CeO_(2)varied significantly with its morphology,leading to differences in lattice distortion,which directly influenced the concentration of oxygen vacancies.Notably,the CeO_(2)nanospheres,which exhibited the highest lattice distortion and oxygen vacancy concentration,achieved a DMC yield(11.12 mmol/g)48 times greater than that of the nanocubes(0.23 mmol/g).The results indicated that oxygen vacancies played a pivotal role in the catalytic process by facilitating the adsorption and activation of CO_(2)to form bidentate carbonates,as well as activating methanol to generate methoxy species.These processes collectively promoted the formation of the key intermediate(*CH3OCOO).This study proposes a strategy to enhance the oxygen vacancy concentration by increasing lattice distortion,providing valuable insights for designing high-performance CeO_(2)catalysts for DMC synthesis.展开更多
The traditional orbit determination method based on pulsar profile distortion can determine the six elements of the orbit.However,the estimation accuracies of these methods are limited and the computational load of a ...The traditional orbit determination method based on pulsar profile distortion can determine the six elements of the orbit.However,the estimation accuracies of these methods are limited and the computational load of a six-dimensional search is huge.To solve this problem,the differential-geometry-based Multi-dimensional Joint Position-Velocity Estimation(MJPVE)using Crab pulsar profile distortion is proposed in this paper.Firstly,through theoretical analysis,it is found that the pulsar profile distortion caused by the initial state error in some joint positionvelocity directions is very small.In other words,the accuracies of estimation in these directions are very low.Namely,the search dimension can be reduced,which in turn greatly reduces the computational load.Then,we construct the chi-squared function of the pulsar profile with respect to the estimation error in joint position-velocity direction and use differential geometry to find the joint position-velocity directions corresponding to different degrees of distortion.Finally,we utilize the grid search based on directory folding in these joint position-velocity directions corresponding to large degrees of distortion to obtain the joint position-velocity estimation.The experimental results show that compared with the grouping bi-chi-squared inversion method,MJPVE has high precision and extensive navigation information.展开更多
The estimation of orientation parameters and correction of lens distortion are crucial problems in the field of Unmanned Aerial Vehicles(UAVs)photogrammetry.In recent years,the utilization of UAVs for aerial photogram...The estimation of orientation parameters and correction of lens distortion are crucial problems in the field of Unmanned Aerial Vehicles(UAVs)photogrammetry.In recent years,the utilization of UAVs for aerial photogrammetry has witnessed a surge in popularity.Typically,UAVs are equipped with low-cost non-metric cameras and a Position and Orientation System(POS).Unfortunately,the Interior Orientation Parameters(IOPs)of the non-metric cameras are not fixed.Whether the lens distortions are large or small,they effect the image coordinates accordingly.Additionally,Inertial Measurement Units(IMUs)often have observation errors.To address these challenges and improve parameter estimation for UAVs Light Detection and Ranging(LiDAR)and photogrammetry,this paper analyzes the accuracy of POS observations obtained from Global Navigation Satellite System Real Time Kinematic(GNSS-RTK)and IMU data.A method that incorporates additional known conditions for parameter estimation,a series of algorithms to simultaneously solve for IOPs,Exterior Orientation Parameters(EOPs),and camera lens distortion correction parameters are proposed.Extensive experiments demonstrate that the coordinates measured by GNSS-RTK can be directly used as linear EOPs;however,angular EOP measurements from IMUs exhibit relatively large errors compared to adjustment results and require correction during the adjustment process.The IOPs of non-metric cameras vary slightly between images but need to be treated as unknown parameters in high precision applications.Furthermore,it is found that the Ebner systematic error model is sensitive to the choice of the magnification parameter of the photographic baseline length in images,it should be set as less than or equal to one third of the photographic baseline to ensure stable solutions.展开更多
To eliminate distortion caused by vertical drift and illusory slopes in atomic force microscopy(AFM)imaging,a lifting-wavelet-based iterative thresholding correction method is proposed in this paper.This method achiev...To eliminate distortion caused by vertical drift and illusory slopes in atomic force microscopy(AFM)imaging,a lifting-wavelet-based iterative thresholding correction method is proposed in this paper.This method achieves high-quality AFM imaging via line-by-line corrections for each distorted profile along the fast axis.The key to this line-by-line correction is to accurately simulate the profile distortion of each scanning row.Therefore,a data preprocessing approach is first developed to roughly filter out most of the height data that impairs the accuracy of distortion modeling.This process is implemented through an internal double-screening mechanism.A line-fitting method is adopted to preliminarily screen out the obvious specimens.Lifting wavelet analysis is then carried out to identify the base parts that are mistakenly filtered out as specimens so as to preserve most of the base profiles and provide a good basis for further distortion modeling.Next,an iterative thresholding algorithm is developed to precisely simulate the profile distortion.By utilizing the roughly screened base profile,the optimal threshold,which is used to screen out the pure bases suitable for distortion modeling,is determined through iteration with a specified error rule.On this basis,the profile distortion is accurately modeled through line fitting on the finely screened base data,and the correction is implemented by subtracting the modeling result from the distorted profile.Finally,the effectiveness of the proposed method is verified through experiments and applications.展开更多
Jahn-Teller distortion(JTD)remains a fundamental bottleneck for transition metal oxides(TMOs)in electrochemical energy storage,where the e_(g)-orbital single-electron occupancy induces irreversible octahedral collapse...Jahn-Teller distortion(JTD)remains a fundamental bottleneck for transition metal oxides(TMOs)in electrochemical energy storage,where the e_(g)-orbital single-electron occupancy induces irreversible octahedral collapse and rapid capacity fading.Here,we pioneer an itinerant-electron-mediated dynamic suppression strategy that fundamentally reshapes the JTD evolution pathway throughπ-d orbital hybridization engineering.By constructing reduced graphene oxide/TMO heterointerfaces(rGO/MO_(x),M=Fe/Ni/Mn),localized 3d electrons are transformed into delocalized itinerant states,which(1)eliminate e_(g)-band degeneracy via orbital repopulation and(2)establish an electron density buffer layer to neutralize lattice strain.This electronic regulation enables ultrafast Na^(+)diffusion kinetics(508.3 F g^(−1)at 1 A g^(−1)→304.6 F g^(−1)at 20 A g^(−1))and near-zero lattice deformation(91.07%capacitance retention after 20,000 cycles).Synchrotron-based X-ray absorption spectroscopy and density functional theory calculations reveal that itinerant electron dynamics actively decouple the Mn^(3+)d^(4)electronic configuration from JTD triggering,leading to a dramatic suppression of octahedral distortion compared to the conventional MnO_(2).The proposed electron delocalization-to-lattice stabilization paradigm opens a universal route to design distortion-resistant electrodes for high-power energy storage systems.展开更多
In semiconductor quantum dot systems,pulse distortion is a significant source of coherent errors,which impedes qubit characterization and control.Here,we demonstrate two calibration methods using a two-qubit system as...In semiconductor quantum dot systems,pulse distortion is a significant source of coherent errors,which impedes qubit characterization and control.Here,we demonstrate two calibration methods using a two-qubit system as the detector to correct distortion and calibrate the transfer function of the control line.Both methods are straightforward to implement,robust against noise,and applicable to a wide range of qubit types.The two methods differ in correction accuracy and complexity.The first,coarse predistortion(CPD)method,partially mitigates distortion.The second,all predistortion(APD)method,measures the transfer function and significantly enhances exchange oscillation uniformity.Both methods use exchange oscillation homogeneity as the metric and are suitable for any qubit driven by a diabatic pulse.We believe these methods will enhance qubit characterization accuracy and operation quality in future applications.展开更多
To numerically study the impact of total temperature distortion on a transonic compressor with reduced computational costs,a Body-Force Model(BFM)is developed.Firstly,the interactions between the distorted flow and th...To numerically study the impact of total temperature distortion on a transonic compressor with reduced computational costs,a Body-Force Model(BFM)is developed.Firstly,the interactions between the distorted flow and the compressor are analyzed using full-annulus Unsteady Reynolds-Averaged Navier-Stokes(URANS)results and the orbit method.It is found that the induced swirl distortion and the mass flux nonuniformity are intensified in the compressor upstream flow field.A correction factor is thus added to the BFM to account for the effect of the induced swirl,which is crucial for the accurate representation of distortion transfer in the intake.Then,steady simulations with large-amplitude 180circumferential total temperature distortion are performed using the developed BFM.It is shown that the distorted compressor map simulated with the BFM matches well with URANS results.The circumferential phase shift of total temperature and the generation of the additional total pressure distortion across the rotor are in line with the time-averaged URANS flow field.The compressor upstream effects on the distorted inflow can also be exactly captured.All above-mentioned results demonstrate the BFM developed in this paper can effectively capture the distorted flow features inside the compressor,and significantly reduce the computational costs by five orders of magnitude compared with URANS.展开更多
The application of higher bypass ratios and lower pressure ratios significantly reduces specific fuel consumption with the development of turbofan engines.However,it also increases the risk of flow separation at the i...The application of higher bypass ratios and lower pressure ratios significantly reduces specific fuel consumption with the development of turbofan engines.However,it also increases the risk of flow separation at the intake,leading to severe circumferential non-uniform inlet conditions.This study aimed to present an experimental investigation on instability evolutions of the compressor under circumferential non-uniform inlet conditions.Two stall inceptions regarding the different spatial scales and initial locations were selected to investigate this issue.The experiments were carried out on one tested rig,which the stall inceptions verified with the rotational speeds.At 65%design rotational speed(X),the stall inception was the spike,which was triggered by disturbances within serval pitches scale at the tip.Consequently,the spike-type stall inception was sensitive to circumferential distortion and led to a shrunk stall margin of the compressor.With the rotational speed increasing to 88%X,the stall inception switched to partial surge,which was induced by the flow blockage in the hub region around the full-annular.The results indicated that the partial surge was insusceptible to the circumferential distortion,which caused an extended stall margin with a lower stalled mass flow rate.In summary,the influence of distortion on the stability of the target compressor was found to be determined by the stall inception.展开更多
The rhombohedralα-GeTe can be approximated as a slightly distorted rock-salt structure along its[111]direction and possesses superb thermoelectric performance.However,the role of such a ferroelectric-like structural ...The rhombohedralα-GeTe can be approximated as a slightly distorted rock-salt structure along its[111]direction and possesses superb thermoelectric performance.However,the role of such a ferroelectric-like structural distortion on its transport properties remains unclear.Herein,we performed a systematic study on the crystal structure and electronic band structure evolutions of Ge_(1-x)Sn_(x)Te alloys where the degree of ferroelectric distortion is continuously tuned.It is revealed that the band gap is maximized while multiple valence bands are converged at x=0.6,where the ferroelectric distortion is the least but still works.Once undistorted,the band gap is considerably reduced,and the valence bands are largely separated again.Moreover,near the ferro-to-paraelectric phase transition Curie temperature,the lattice thermal conductivity reaches its minima because of significant lattice softening enabled by ferroelectric instability.We predict a peak ZT value of 2.6 at 673 K inα-GeTe by use of proper dopants which are powerful in suppressing the excess hole concentrations but meanwhile exert little influence on the ferroelectric distortion.展开更多
The advent of laser powder bed fusion(LPBF)has provided an effective solution for fabricating lightweight structures with intricate designs that cannot be realized using other manufacturing methods.Lattice structures,...The advent of laser powder bed fusion(LPBF)has provided an effective solution for fabricating lightweight structures with intricate designs that cannot be realized using other manufacturing methods.Lattice structures,however,which feature unique characteristics,pose greater challenges in the LPBF process than solid structures and exhibit more significant distortion.The underlying mechanisms and influencing factors of this distortion remain unclear,presenting a significant research gap.This study investigates the generation mechanism of residual stress in Ti-6Al-4V lattice structures during LPBF and examines how process and geometric parameters influence residual distortion.Lattice-type cantilever structures with various arm thicknesses and strut diameters were fabricated using different laser powers and scan patterns.The residual distortion after removal from the building substrate was measured using a non-contact coordinate-measuring machine.The results suggest that increasing the arm thickness,reducing the strut diameter,and employing a scanning pattern with interlayer rotation effectively reduce residual distortion.Among these factors,the scanning pattern had the most distinct impact,differing significantly from those affecting solid structures.P2(45°)scanning pattern resulted in the greatest residual distortion,approximately twice that of the least distorted pattern.Meanwhile,the laser power exerted a minor influence on the distortion of the lattice structures.These findings provide insights and guidance for fabricating lattice structures using the LPBF process,broadening its applications in aerospace,automotive,and other weight-sensitive industries.展开更多
3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational acc...3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational accuracy and efficiency,the optimal choices of numerical parameters and algorithms in FE modelling were determined.The formation mechanisms of cross-section distortion and springback were revealed.The effects of pre-stretching,post-stretching,friction,and the addition of internal fillers on forming quality were investigated.The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress.The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile.As aluminum profile is gradually attached to bending die,the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape.After unloading the forming tools,cross-section distortion decreases obviously due to the stress relaxation,with a maximum distortion difference of 13%before and after unloading.As pre-stretching and post-stretching forces increase,cross-section distortion increases gradually,while springback first decreases and then remains unchanged.With increasing friction between bending die and profile,cross-section distortion slightly decreases,while springback increases.Cross-section distortion decreases by 83%with adding PVC fillers into the cavities of profile,while springback increases by 192.2%.展开更多
Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded aust...Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded austenitic stainless steel parts is limited owing to the micro bulging distortion that occurs on the back surface of the partial penetration side.In this paper,non-penetration lap laser welding experiments,were conducted on galvanized and SUS304 austenitic stainless steel plates using a fiber laser,to investigate the mechanism of bulging distortion.A comparative experiment of DC01 galvanized steel-Q235 carbon steel lap laser welding was carried out,and the deflection and distortion profile of partially penetrated side of the sheets were measured using a noncontact laser interferometer.In addition,the cold-rolled SUS304 was subjected to heat holding at different temperatures and water quenching after bending to characterize its microstructure under tensile and compressive stress.The results show that,during the heating stage of the thermal cycle of laser lap welding,the partial penetration side of the SUS304 steel sheet generates compressive stress,which extrudes the material in the heat-affected zone to the outside of the back of the SUS304 steel sheet,thereby forming a bulge.The findings of these experiments can be of great value for controlling the distortion of the partial penetrated side of austenitic stainless steel sheet during laser non-penetration lap welding.展开更多
Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and ...Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.展开更多
We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magne...We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.展开更多
A modified small perturbation stability prediction model for axial compressors with circumferential inlet distortions is established and applied to investigate the effect of fore/aft-loaded rotor on compressor stabili...A modified small perturbation stability prediction model for axial compressors with circumferential inlet distortions is established and applied to investigate the effect of fore/aft-loaded rotor on compressor stability under circumferentially distorted inlet conditions.The inlet total pressure distribution downstream of the distortion screen is measured in experiments and employed for simulations which are implemented via time-space spectral method.The stall inception prediction results via the stability model indicate that the compressor with aft-loaded rotor not only performs better in terms of stability under uniform inlet,but also maintains a larger stability margin under circumferentially distorted inlet.The experiments for compressors with fore-loaded and aft-loaded rotor are respectively carried out.The results validate the reliability of numerical simulations and the predicted conclusion that the aft-loaded rotor is beneficial for compressor stability.Besides,the ability of the developed theoretical model for compressor stability prediction under circumferential distortions is confirmed.In addition,dynamic pressure signals at rotor tip measured in experiments illustrate that the circumferential distortion has little effect on the compressor stall pattern.展开更多
For the ultimate strength model test evaluation of large ship structures, the distortion model with non-uniform ratio between the main size and the plate thickness size is usually adopted. It is the key to carry out s...For the ultimate strength model test evaluation of large ship structures, the distortion model with non-uniform ratio between the main size and the plate thickness size is usually adopted. It is the key to carry out scale model test to establish a distortion model similar to the real ship structure under combined load. A similarity criterion for ship distortion model under the combined action of bending moment and surface pressure was proposed, and the scale effect for the criterion was verified by a se ries of numerical analysis and model tests. The results show that the similarity criterion for ship distor tion model under combined loads has a certain scale effect. For the model tests of ship cabin struc tures, it is suggested that the scale range between the plate thickness scale and the main dimension scale should be controlled within 2:1, which can be used as a reference for distortion model design and ultimate strength test of large-scale ship structures.展开更多
To reduce the negative impact of the power amplifier(PA)nonlinear distortion caused by the orthogonal frequency division multiplexing(OFDM)waveform with high peak-to-average power ratio(PAPR)in integrated radar and co...To reduce the negative impact of the power amplifier(PA)nonlinear distortion caused by the orthogonal frequency division multiplexing(OFDM)waveform with high peak-to-average power ratio(PAPR)in integrated radar and communication(RadCom)systems is studied,the channel estimation in passive sensing scenarios.Adaptive channel estimation methods are proposed based on different pilot patterns,considering nonlinear distortion and channel sparsity.The proposed methods achieve sparse channel results by manipulating the least squares(LS)frequency-domain channel estimation results to preserve the most significant taps.The decision-aided method is used to optimize the sparse channel results to reduce the effect of nonlinear distortion.Numerical results show that the channel estimation performance of the proposed methods is better than that of the conventional methods under different pilot patterns.In addition,the bit error rate performance in communication and passive radar detection performance show that the proposed methods have good comprehensive performance.展开更多
Thin-walled aerostructural components frequently get distorted after the machining process.Reworking to correct distortions or eventually rejecting parts significantly increases the cost.This paper proposes a new appr...Thin-walled aerostructural components frequently get distorted after the machining process.Reworking to correct distortions or eventually rejecting parts significantly increases the cost.This paper proposes a new approach to correct distortions in thin-walled components by strategically applying hammer peening on target surfaces of a machined component.Aluminium alloy 7475-T7351 was chosen for this research.The study was divided in two stages.First,the residual stresses(RS)induced by four different pneumatic hammer peening conditions(modifying the stepover distance and initial offset)were characterised in a test coupon,and one of the conditions was selected for the next stage.In the second stage,a FEM model was used to predict distortions caused by machining in a representative workpiece.Then,the RS induced by hammer peening were included in an FEM model to define two hammer peening strategies(varying the coverage area)to analyse the capability to reduce distortions.Two workpieces were machined and then treated with the simulated hammer peening strategies for experimental validation.Results in the test coupon showed that pneumatic hammer peening can generate high compressive RS(-50 to350 MPa)up to 800 lm depth,with their magnitude increasing with a reduced stepover distance.Application of hammer peening over 4% of the surface of the representative workpiece reduced the machininginduced distortions by 37%,and a coverage area of 100% led to and overcorrection by a factor of five.This confirms that hammer peening can be strategically applied(in target areas and changing the percentage of coverage)to correct low or severe distortions.展开更多
Federated Learning(FL)is an emerging machine learning framework designed to preserve privacy.However,the continuous updating of model parameters over uplink channels with limited throughput leads to a huge communicati...Federated Learning(FL)is an emerging machine learning framework designed to preserve privacy.However,the continuous updating of model parameters over uplink channels with limited throughput leads to a huge communication overload,which is a major challenge for FL.To address this issue,we propose an adaptive gradient quantization approach that enhances communication efficiency.Aiming to minimize the total communication costs,we consider both the correlation of gradients between local clients and the correlation of gradients between communication rounds,namely,in the time and space dimensions.The compression strategy is based on rate distortion theory,which allows us to find an optimal quantization strategy for the gradients.To further reduce the computational complexity,we introduce the Kalman filter into the proposed approach.Finally,numerical results demonstrate the effectiveness and robustness of the proposed rate-distortion optimization adaptive gradient quantization approach in significantly reducing the communication costs when compared to other quantization methods.展开更多
文摘As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding scenarios.This paper discusses interferogram modeling and phase distortion cor-rection techniques for spaceborne DASH interferometers.The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted,and the effectiveness of the analytical expression was verified through numerical simulation.The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms.In contrast,the phase distortion correction algorithm can achieve effective correction.This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer,providing a feasible solution to enhance its measurement accuracy.
基金National Natural Science Foundation of China(22008166)Fundamental Research Program of Shanxi Province(202403021211029,201901D211047).
文摘The conversion of CO_(2)to dimethyl carbonate(DMC)offers a promising route for CO_(2)utilization.In this study,four CeO2 catalysts with distinct nanostructures were synthesized via a template-free hydrothermal method by systematically varying the types and concentrations of precipitants as well as the hydrothermal reaction conditions,and they were employed for DMC synthesis from CO_(2)and methanol.The atomic arrangements of CeO_(2)varied significantly with its morphology,leading to differences in lattice distortion,which directly influenced the concentration of oxygen vacancies.Notably,the CeO_(2)nanospheres,which exhibited the highest lattice distortion and oxygen vacancy concentration,achieved a DMC yield(11.12 mmol/g)48 times greater than that of the nanocubes(0.23 mmol/g).The results indicated that oxygen vacancies played a pivotal role in the catalytic process by facilitating the adsorption and activation of CO_(2)to form bidentate carbonates,as well as activating methanol to generate methoxy species.These processes collectively promoted the formation of the key intermediate(*CH3OCOO).This study proposes a strategy to enhance the oxygen vacancy concentration by increasing lattice distortion,providing valuable insights for designing high-performance CeO_(2)catalysts for DMC synthesis.
基金supported in part by the National Natural Science Foundation of China(Nos.61873196,62373030,61772187)the Innovation Program for Quantum Science and Technology(No.2021ZD0303400)。
文摘The traditional orbit determination method based on pulsar profile distortion can determine the six elements of the orbit.However,the estimation accuracies of these methods are limited and the computational load of a six-dimensional search is huge.To solve this problem,the differential-geometry-based Multi-dimensional Joint Position-Velocity Estimation(MJPVE)using Crab pulsar profile distortion is proposed in this paper.Firstly,through theoretical analysis,it is found that the pulsar profile distortion caused by the initial state error in some joint positionvelocity directions is very small.In other words,the accuracies of estimation in these directions are very low.Namely,the search dimension can be reduced,which in turn greatly reduces the computational load.Then,we construct the chi-squared function of the pulsar profile with respect to the estimation error in joint position-velocity direction and use differential geometry to find the joint position-velocity directions corresponding to different degrees of distortion.Finally,we utilize the grid search based on directory folding in these joint position-velocity directions corresponding to large degrees of distortion to obtain the joint position-velocity estimation.The experimental results show that compared with the grouping bi-chi-squared inversion method,MJPVE has high precision and extensive navigation information.
基金Natural Science Foundation of Hunan Province,China(No.2024JJ8335)Open Topic of Hunan Geospatial Information Engineering and Technology Research Center,China(No.HNGIET2023004).
文摘The estimation of orientation parameters and correction of lens distortion are crucial problems in the field of Unmanned Aerial Vehicles(UAVs)photogrammetry.In recent years,the utilization of UAVs for aerial photogrammetry has witnessed a surge in popularity.Typically,UAVs are equipped with low-cost non-metric cameras and a Position and Orientation System(POS).Unfortunately,the Interior Orientation Parameters(IOPs)of the non-metric cameras are not fixed.Whether the lens distortions are large or small,they effect the image coordinates accordingly.Additionally,Inertial Measurement Units(IMUs)often have observation errors.To address these challenges and improve parameter estimation for UAVs Light Detection and Ranging(LiDAR)and photogrammetry,this paper analyzes the accuracy of POS observations obtained from Global Navigation Satellite System Real Time Kinematic(GNSS-RTK)and IMU data.A method that incorporates additional known conditions for parameter estimation,a series of algorithms to simultaneously solve for IOPs,Exterior Orientation Parameters(EOPs),and camera lens distortion correction parameters are proposed.Extensive experiments demonstrate that the coordinates measured by GNSS-RTK can be directly used as linear EOPs;however,angular EOP measurements from IMUs exhibit relatively large errors compared to adjustment results and require correction during the adjustment process.The IOPs of non-metric cameras vary slightly between images but need to be treated as unknown parameters in high precision applications.Furthermore,it is found that the Ebner systematic error model is sensitive to the choice of the magnification parameter of the photographic baseline length in images,it should be set as less than or equal to one third of the photographic baseline to ensure stable solutions.
基金supported by the National Natural Science Foundation of China under Grant No.21933006.
文摘To eliminate distortion caused by vertical drift and illusory slopes in atomic force microscopy(AFM)imaging,a lifting-wavelet-based iterative thresholding correction method is proposed in this paper.This method achieves high-quality AFM imaging via line-by-line corrections for each distorted profile along the fast axis.The key to this line-by-line correction is to accurately simulate the profile distortion of each scanning row.Therefore,a data preprocessing approach is first developed to roughly filter out most of the height data that impairs the accuracy of distortion modeling.This process is implemented through an internal double-screening mechanism.A line-fitting method is adopted to preliminarily screen out the obvious specimens.Lifting wavelet analysis is then carried out to identify the base parts that are mistakenly filtered out as specimens so as to preserve most of the base profiles and provide a good basis for further distortion modeling.Next,an iterative thresholding algorithm is developed to precisely simulate the profile distortion.By utilizing the roughly screened base profile,the optimal threshold,which is used to screen out the pure bases suitable for distortion modeling,is determined through iteration with a specified error rule.On this basis,the profile distortion is accurately modeled through line fitting on the finely screened base data,and the correction is implemented by subtracting the modeling result from the distorted profile.Finally,the effectiveness of the proposed method is verified through experiments and applications.
基金Financial support from the National Natural Science Foundation of China(grant no.U20A20154,22279005,22379006,21575016)the National Program for Support of Top-notch Young Professionals is gratefully acknowledgedtechnical support from the Xi’an Advanced Computing Center
文摘Jahn-Teller distortion(JTD)remains a fundamental bottleneck for transition metal oxides(TMOs)in electrochemical energy storage,where the e_(g)-orbital single-electron occupancy induces irreversible octahedral collapse and rapid capacity fading.Here,we pioneer an itinerant-electron-mediated dynamic suppression strategy that fundamentally reshapes the JTD evolution pathway throughπ-d orbital hybridization engineering.By constructing reduced graphene oxide/TMO heterointerfaces(rGO/MO_(x),M=Fe/Ni/Mn),localized 3d electrons are transformed into delocalized itinerant states,which(1)eliminate e_(g)-band degeneracy via orbital repopulation and(2)establish an electron density buffer layer to neutralize lattice strain.This electronic regulation enables ultrafast Na^(+)diffusion kinetics(508.3 F g^(−1)at 1 A g^(−1)→304.6 F g^(−1)at 20 A g^(−1))and near-zero lattice deformation(91.07%capacitance retention after 20,000 cycles).Synchrotron-based X-ray absorption spectroscopy and density functional theory calculations reveal that itinerant electron dynamics actively decouple the Mn^(3+)d^(4)electronic configuration from JTD triggering,leading to a dramatic suppression of octahedral distortion compared to the conventional MnO_(2).The proposed electron delocalization-to-lattice stabilization paradigm opens a universal route to design distortion-resistant electrodes for high-power energy storage systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074368,92165207,12474490,12034018,and 92265113)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302300)+1 种基金the USTC Tang Scholarshippartially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication。
文摘In semiconductor quantum dot systems,pulse distortion is a significant source of coherent errors,which impedes qubit characterization and control.Here,we demonstrate two calibration methods using a two-qubit system as the detector to correct distortion and calibrate the transfer function of the control line.Both methods are straightforward to implement,robust against noise,and applicable to a wide range of qubit types.The two methods differ in correction accuracy and complexity.The first,coarse predistortion(CPD)method,partially mitigates distortion.The second,all predistortion(APD)method,measures the transfer function and significantly enhances exchange oscillation uniformity.Both methods use exchange oscillation homogeneity as the metric and are suitable for any qubit driven by a diabatic pulse.We believe these methods will enhance qubit characterization accuracy and operation quality in future applications.
基金the National Science and Technology Major Project,China(Nos.J2019-Ⅱ-0020-0041 and J2019-Ⅱ-0017-0038)the Science Center for Gas Turbine Project,China(No.P2022-A-Ⅱ-002-001)the National Natural Science Foundation of China(No.52206061).
文摘To numerically study the impact of total temperature distortion on a transonic compressor with reduced computational costs,a Body-Force Model(BFM)is developed.Firstly,the interactions between the distorted flow and the compressor are analyzed using full-annulus Unsteady Reynolds-Averaged Navier-Stokes(URANS)results and the orbit method.It is found that the induced swirl distortion and the mass flux nonuniformity are intensified in the compressor upstream flow field.A correction factor is thus added to the BFM to account for the effect of the induced swirl,which is crucial for the accurate representation of distortion transfer in the intake.Then,steady simulations with large-amplitude 180circumferential total temperature distortion are performed using the developed BFM.It is shown that the distorted compressor map simulated with the BFM matches well with URANS results.The circumferential phase shift of total temperature and the generation of the additional total pressure distortion across the rotor are in line with the time-averaged URANS flow field.The compressor upstream effects on the distorted inflow can also be exactly captured.All above-mentioned results demonstrate the BFM developed in this paper can effectively capture the distorted flow features inside the compressor,and significantly reduce the computational costs by five orders of magnitude compared with URANS.
基金support of the National Natural Science Foundation of China(Nos.52322603,51976005,52006002,and 51906005)the Science Center for Gas Turbine Project,China(No.P2022-B-II-004-001)+5 种基金the Advanced Jet Propulsion Creativity Center,AEAC,China(No.HKCX2020-02-013)the National Science and Technology Major Project,China(No.2017-Ⅱ-0005-0018)the Fundamental Research Funds for the Central Universities,China(No.501XTCX2023146001)the Beijing Nova Program,China(No.20220484074)the Beijing Municipal Natural Science Foundation,China(No.3242016)the Collaborative Innovation Center for Advanced Aero-Engines,China。
文摘The application of higher bypass ratios and lower pressure ratios significantly reduces specific fuel consumption with the development of turbofan engines.However,it also increases the risk of flow separation at the intake,leading to severe circumferential non-uniform inlet conditions.This study aimed to present an experimental investigation on instability evolutions of the compressor under circumferential non-uniform inlet conditions.Two stall inceptions regarding the different spatial scales and initial locations were selected to investigate this issue.The experiments were carried out on one tested rig,which the stall inceptions verified with the rotational speeds.At 65%design rotational speed(X),the stall inception was the spike,which was triggered by disturbances within serval pitches scale at the tip.Consequently,the spike-type stall inception was sensitive to circumferential distortion and led to a shrunk stall margin of the compressor.With the rotational speed increasing to 88%X,the stall inception switched to partial surge,which was induced by the flow blockage in the hub region around the full-annular.The results indicated that the partial surge was insusceptible to the circumferential distortion,which caused an extended stall margin with a lower stalled mass flow rate.In summary,the influence of distortion on the stability of the target compressor was found to be determined by the stall inception.
基金the financial support from the National Natural Science Foundation of China(Grant No.52171221)the National Key Research and Development Program of China(Grant No.2019YFA0704900)the support from the Core Facility of Wuhan University for their assistance with EPMA analysis
文摘The rhombohedralα-GeTe can be approximated as a slightly distorted rock-salt structure along its[111]direction and possesses superb thermoelectric performance.However,the role of such a ferroelectric-like structural distortion on its transport properties remains unclear.Herein,we performed a systematic study on the crystal structure and electronic band structure evolutions of Ge_(1-x)Sn_(x)Te alloys where the degree of ferroelectric distortion is continuously tuned.It is revealed that the band gap is maximized while multiple valence bands are converged at x=0.6,where the ferroelectric distortion is the least but still works.Once undistorted,the band gap is considerably reduced,and the valence bands are largely separated again.Moreover,near the ferro-to-paraelectric phase transition Curie temperature,the lattice thermal conductivity reaches its minima because of significant lattice softening enabled by ferroelectric instability.We predict a peak ZT value of 2.6 at 673 K inα-GeTe by use of proper dopants which are powerful in suppressing the excess hole concentrations but meanwhile exert little influence on the ferroelectric distortion.
基金supported by National Key Research and Development Program of China(Grant No.2021YFB1715400)National Natural Science Foundation of China(Grant No.52105261)High-level Special Funds at the Southern University of Science and Technology(Grant No.G03034K003).
文摘The advent of laser powder bed fusion(LPBF)has provided an effective solution for fabricating lightweight structures with intricate designs that cannot be realized using other manufacturing methods.Lattice structures,however,which feature unique characteristics,pose greater challenges in the LPBF process than solid structures and exhibit more significant distortion.The underlying mechanisms and influencing factors of this distortion remain unclear,presenting a significant research gap.This study investigates the generation mechanism of residual stress in Ti-6Al-4V lattice structures during LPBF and examines how process and geometric parameters influence residual distortion.Lattice-type cantilever structures with various arm thicknesses and strut diameters were fabricated using different laser powers and scan patterns.The residual distortion after removal from the building substrate was measured using a non-contact coordinate-measuring machine.The results suggest that increasing the arm thickness,reducing the strut diameter,and employing a scanning pattern with interlayer rotation effectively reduce residual distortion.Among these factors,the scanning pattern had the most distinct impact,differing significantly from those affecting solid structures.P2(45°)scanning pattern resulted in the greatest residual distortion,approximately twice that of the least distorted pattern.Meanwhile,the laser power exerted a minor influence on the distortion of the lattice structures.These findings provide insights and guidance for fabricating lattice structures using the LPBF process,broadening its applications in aerospace,automotive,and other weight-sensitive industries.
基金the National Natural Science Foundation of China(Nos.52005244,U20A20275)the Natural Science Foundation of Hunan Province,China(Nos.2021JJ30573,2023JJ60193)the Open Fund of State Key Laboratory of Advanced Design and Manufacture for Vehicle Body,China(No.31715011)。
文摘3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method.Considering the computational accuracy and efficiency,the optimal choices of numerical parameters and algorithms in FE modelling were determined.The formation mechanisms of cross-section distortion and springback were revealed.The effects of pre-stretching,post-stretching,friction,and the addition of internal fillers on forming quality were investigated.The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress.The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile.As aluminum profile is gradually attached to bending die,the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape.After unloading the forming tools,cross-section distortion decreases obviously due to the stress relaxation,with a maximum distortion difference of 13%before and after unloading.As pre-stretching and post-stretching forces increase,cross-section distortion increases gradually,while springback first decreases and then remains unchanged.With increasing friction between bending die and profile,cross-section distortion slightly decreases,while springback increases.Cross-section distortion decreases by 83%with adding PVC fillers into the cavities of profile,while springback increases by 192.2%.
文摘Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded austenitic stainless steel parts is limited owing to the micro bulging distortion that occurs on the back surface of the partial penetration side.In this paper,non-penetration lap laser welding experiments,were conducted on galvanized and SUS304 austenitic stainless steel plates using a fiber laser,to investigate the mechanism of bulging distortion.A comparative experiment of DC01 galvanized steel-Q235 carbon steel lap laser welding was carried out,and the deflection and distortion profile of partially penetrated side of the sheets were measured using a noncontact laser interferometer.In addition,the cold-rolled SUS304 was subjected to heat holding at different temperatures and water quenching after bending to characterize its microstructure under tensile and compressive stress.The results show that,during the heating stage of the thermal cycle of laser lap welding,the partial penetration side of the SUS304 steel sheet generates compressive stress,which extrudes the material in the heat-affected zone to the outside of the back of the SUS304 steel sheet,thereby forming a bulge.The findings of these experiments can be of great value for controlling the distortion of the partial penetrated side of austenitic stainless steel sheet during laser non-penetration lap welding.
基金supported by the National Natural Science Foundation of China (Grant No.22278123).
文摘Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2023YFA1607403,2021YFA1600201,and 2022YFA1602603)the Natural Science Foundation of China (Grant Nos.U19A2093,U2032214,and U2032163)+5 种基金the Collaborative Innovation Program of Hefei Science Center,CAS (Grant No.2019HSC-CIP 001)the Youth Innovation Promotion Association of CAS (Grant No.2021117)the Natural Science Foundation of Anhui Province (No.1908085QA15)the HFIPS Director’s Fund (Grant No.YZJJQY202304)the CASHIPS Director’s Fund (Grant No.YZJJ2022QN36)supported by the High Magnetic Field Laboratory of Anhui Province。
文摘We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.
基金The research presented here was supported by the National Natural Science Foundation of China(Nos.52306036 and 52325602)the Science Center for Gas Turbine Project,China(Nos.P2022-A-II-002-001 and P2022-C-II-003-001)+3 种基金the Project funded by China Postdoctoral Science Foundation(No.2022M720346)the National Science and Technology Major Projectc,China(Nos.Y2022-II-0003-0006 and Y2022-II-0002-0005)Also,the research is supported by the Key Laboratory of Pre-Research Management Centre,China(No.6142702200101)the Fundamental Research Funds for the Central Universities,China(Nos.YWF-23-Q-1009 and YWF-23-Q-1065).
文摘A modified small perturbation stability prediction model for axial compressors with circumferential inlet distortions is established and applied to investigate the effect of fore/aft-loaded rotor on compressor stability under circumferentially distorted inlet conditions.The inlet total pressure distribution downstream of the distortion screen is measured in experiments and employed for simulations which are implemented via time-space spectral method.The stall inception prediction results via the stability model indicate that the compressor with aft-loaded rotor not only performs better in terms of stability under uniform inlet,but also maintains a larger stability margin under circumferentially distorted inlet.The experiments for compressors with fore-loaded and aft-loaded rotor are respectively carried out.The results validate the reliability of numerical simulations and the predicted conclusion that the aft-loaded rotor is beneficial for compressor stability.Besides,the ability of the developed theoretical model for compressor stability prediction under circumferential distortions is confirmed.In addition,dynamic pressure signals at rotor tip measured in experiments illustrate that the circumferential distortion has little effect on the compressor stall pattern.
文摘For the ultimate strength model test evaluation of large ship structures, the distortion model with non-uniform ratio between the main size and the plate thickness size is usually adopted. It is the key to carry out scale model test to establish a distortion model similar to the real ship structure under combined load. A similarity criterion for ship distortion model under the combined action of bending moment and surface pressure was proposed, and the scale effect for the criterion was verified by a se ries of numerical analysis and model tests. The results show that the similarity criterion for ship distor tion model under combined loads has a certain scale effect. For the model tests of ship cabin struc tures, it is suggested that the scale range between the plate thickness scale and the main dimension scale should be controlled within 2:1, which can be used as a reference for distortion model design and ultimate strength test of large-scale ship structures.
基金supported by the National Natural Science Foundation of China(61931015,62071335,62250024)the Natural Science Foundation of Hubei Province of China(2021CFA002)+1 种基金the Fundamental Research Funds for the Central Universities of China(2042022dx0001)the Science and Technology Program of Shenzhen(JCYJ20170818112037398).
文摘To reduce the negative impact of the power amplifier(PA)nonlinear distortion caused by the orthogonal frequency division multiplexing(OFDM)waveform with high peak-to-average power ratio(PAPR)in integrated radar and communication(RadCom)systems is studied,the channel estimation in passive sensing scenarios.Adaptive channel estimation methods are proposed based on different pilot patterns,considering nonlinear distortion and channel sparsity.The proposed methods achieve sparse channel results by manipulating the least squares(LS)frequency-domain channel estimation results to preserve the most significant taps.The decision-aided method is used to optimize the sparse channel results to reduce the effect of nonlinear distortion.Numerical results show that the channel estimation performance of the proposed methods is better than that of the conventional methods under different pilot patterns.In addition,the bit error rate performance in communication and passive radar detection performance show that the proposed methods have good comprehensive performance.
基金the financial support given from Elkartek Program to the project FRONTIERS 2022-Superficies multifuncionales en la frontera del conocimiento(KK-2022/00109)LOFAMO grant given by EPSRC(EP/X023281/1).
文摘Thin-walled aerostructural components frequently get distorted after the machining process.Reworking to correct distortions or eventually rejecting parts significantly increases the cost.This paper proposes a new approach to correct distortions in thin-walled components by strategically applying hammer peening on target surfaces of a machined component.Aluminium alloy 7475-T7351 was chosen for this research.The study was divided in two stages.First,the residual stresses(RS)induced by four different pneumatic hammer peening conditions(modifying the stepover distance and initial offset)were characterised in a test coupon,and one of the conditions was selected for the next stage.In the second stage,a FEM model was used to predict distortions caused by machining in a representative workpiece.Then,the RS induced by hammer peening were included in an FEM model to define two hammer peening strategies(varying the coverage area)to analyse the capability to reduce distortions.Two workpieces were machined and then treated with the simulated hammer peening strategies for experimental validation.Results in the test coupon showed that pneumatic hammer peening can generate high compressive RS(-50 to350 MPa)up to 800 lm depth,with their magnitude increasing with a reduced stepover distance.Application of hammer peening over 4% of the surface of the representative workpiece reduced the machininginduced distortions by 37%,and a coverage area of 100% led to and overcorrection by a factor of five.This confirms that hammer peening can be strategically applied(in target areas and changing the percentage of coverage)to correct low or severe distortions.
基金supported in part by the Key Research and Development Program of Jiangsu Province(Grant No.BE2020084-2)in part by the National Key Research and Development Program of China(Grant No.2020YFB1600104)+4 种基金in part by the Key Research and Development Special Project of school and local cooperation in Lvliang(Grant No.2023XDHZ18)in part by Southeast University-China Mobile Research Institute Joint Innovation Centerin part by the National Natural Science Foundation of China(Grant No.62371119)in part by the Key Research and Development Program of Jiangsu Province(Grant No.BE2022059-3)in part by the Zhi Shan Young Scholar Program of Southeast University。
文摘Federated Learning(FL)is an emerging machine learning framework designed to preserve privacy.However,the continuous updating of model parameters over uplink channels with limited throughput leads to a huge communication overload,which is a major challenge for FL.To address this issue,we propose an adaptive gradient quantization approach that enhances communication efficiency.Aiming to minimize the total communication costs,we consider both the correlation of gradients between local clients and the correlation of gradients between communication rounds,namely,in the time and space dimensions.The compression strategy is based on rate distortion theory,which allows us to find an optimal quantization strategy for the gradients.To further reduce the computational complexity,we introduce the Kalman filter into the proposed approach.Finally,numerical results demonstrate the effectiveness and robustness of the proposed rate-distortion optimization adaptive gradient quantization approach in significantly reducing the communication costs when compared to other quantization methods.
