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COMPUTER OPTICS 2023年第6期47卷 901-+页

作者： Tsiplakova, E. G. Chopard, A. Balbekin, N. S. Smolyanskaya, O. A. Perraud, J. -B. Guillet, J. -P. Mounaix, P. Petrov, N. V. ITMO Univ Kronverksky Pr 49 St Petersburg 197101 Russia Univ Bordeaux IMS Lab UMR CNRS 5218 351 Cours Liberat Batiment A31 F-33405 Talence France Lytid SAS Rue Fontaine 8 F-92120 Montrouge France Optikan SAS Rue Permentade 64 F-33000 Bordeaux France

iterative phase retrieval algorithms from multiple diffraction patterns in the terahertz (THz) frequency range are a promising tool of computational imaging capable of providing high spatial resolution of reconstructed phase images. One of the commonly used algorithms is SBMIR, which employs multiple intensity distributions of the diffraction object wavefield as input data. Com -pared with single-frame methods, the multi-plane approach allows for a faster convergence, but requires time-consuming data acquisition from a receiver positioned at a variety of distances from the object. Previously, we proposed a method for THz data acquisition in a single scan mode, which allows one to quickly obtain an exhaustive set of diffraction distributions. In this paper we evaluate an up-to-date phase retrieval algorithm based on the SBMIR/R-SBMIR method (which utilizes stochastic wavefront propagation) on the experimental data captured by a single-scan technique. Unlike a number of conventional phase retrieval algorithms, which may require a series of numerical experiments for determining optimal intensity distributions from a large dataset, disordered propagation of the estimation wavefront guarantees the high-contrast and high-resolution image reconstruction without pre-setting the parameters. It is shown that the package use of the single-scan technique with the subsequent data processing using the R-SBMIR algorithm has ap-plication potential for automation of the multi-plane phase retrieval in the THz range.

关键词： phase retrieval terahertz radiation iterative algorithm stochastic optimization cascade laser

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Reconstruction of Two Functions in the Model of Vibrations of a String One End of Which Is Placed in a Moving Medium

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COMPUTATIONAL MATHEMATICS AND MATHEMATICAL PHYSICS 2023年第5期63卷 808-820页

作者： Andreyanova, O. A. Shcheglov, A. Yu. Lomonosov Moscow State Univ Moscow 119991 Russia MSU FPI Univ Shenzhen Shenzhen 518172 Guangdong Peoples R China

The paper considers an inverse problem of determining the coefficients in the model of small transverse vibrations of a homogeneous finite string one end of which is placed in a moving medium and the other is free. The vibrations are simulated by a hyperbolic equation on an interval. One boundary condition has a nonclassical form. Additional data for solving the inverse problem are the values of the solution of the forward problem with a known fixed value of the spatial argument. In the inverse problem, it is required to determine the function in the nonclassical boundary condition and a functional factor on the right-hand side of the equation. Uniqueness and existence theorems for the inverse problem are proved. For the forward problem, conditions for unique solvability are established in a form that simplifies the analysis of the inverse problem. For the numerical solution of the inverse problem, an algorithm is proposed for the stage-by-stage separate reconstruction of the sought-for functions using the method of successive approximations for integral equations.

关键词： iterative algorithm equation for vibrations inverse problem

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AN iterative algorithm FOR COMPUTING MEASURES OF GENERALIZED VORONOI REGIONS

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SIAM JOURNAL ON SCIENTIFIC COMPUTING 2014年第2期36卷 A792-A827页

作者： Larsson, Lisa J. Choksi, Rustum Nave, Jean-Christophe McGill Univ Dept Math & Stat Montreal PQ Canada

We present and analyze a fast algorithm for directly computing measures of generalized Voronoi regions associated with generators of arbitrary codimension. The algorithm consists of solving one eikonal equation to construct a kernel-based operator whose iteration accumulates mass along the closest generator. In particular, the algorithm does not require the computation of the Voronoi diagram or the gradient of the solution to the eikonal equation. The algorithm is shown to be first order and converge very quickly. By discretizing the distance to the generators on the grid (and not the generators themselves), very accurate geometric information is used even for coarse grids. Several examples are presented, including the computation of the population influence associated with the Los Angeles County highway system. The method is also one of the key ingredients for the fast computation of centroidal Voronoi tessellations (CVTs) of general rigid objects (e.g., rigid curves and surfaces) in higher dimensions. We present a few simple examples of these generalized CVTs.

关键词： iterative algorithm measures of generalized Voronoi regions eikonal equation Markov operator

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Reconstruction of the Time-Dependent Diffusion Coefficient in a Space-Fractional Parabolic Equation 10th

Reconstruction of the Time-Dependent Diffusion Coefficient i...

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10th International Conference New Trends in the Applications of Differential Equations in Sciences (NTADES)

作者： Koleva, Miglena N. Vulkov, Lubin G. Ruse Univ 8 Studentska St Ruse 7017 Bulgaria

ISBN: (纸本)9783031532122;9783031532115

We propose two algorithms for investigation the numerical reconstruction of the time-dependent diffusion coefficient in a space-fractional parabolic problem at integral and point measured outputs. In the first one, by implicit Euler method we perform a linearization of the quadratically nonlinear initial boundary value problem on each time level. Then, we apply a decomposition to this problem solution around the unknown diffusion coefficient. Finally, using the integral or point observations we express in exact form by the solutions of the new subproblems, the required diffusion coefficient. By the second one, on each time level, an iterative algorithm based on the secant method for the numerical identification of the diffusion coefficient, is proposed. We compare the two methods on computational test examples.

关键词： Space-fractional parabolic equation Coefficient inverse problem Decomposition Discretization iterative algorithm

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Gradient-based iterative algorithm for solving the generalized coupled Sylvester-transpose and conjugate matrix equations over reflexive (anti-reflexive) matrices

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TRANSACTIONS OF THE INSTITUTE OF MEASUREMENT AND CONTROL 2014年第1期36卷 99-110页

作者： Beik, Fatemeh Panjeh Ali Salkuyeh, Davod Khojasteh Moghadam, Mahmoud Mohseni Vali E Asr Univ Rafsanjan Dept Math Rafsanjan Iran Univ Guilan Fac Math Sci Rasht Iran Islamic Azad Univ Kerman Dept Math Kerman Iran

Linear matrix equations play an important role in many areas, such as control theory, system theory, stability theory and some other fields of pure and applied mathematics. In the present paper, we consider the generalized coupled Sylvester-transpose and conjugate matrix equations T-v(X) = F-v, v = 1, 2, ... , N, where X = (X-1,X-2, ... , X-p) is a group of unknown matrices and for v = 1,2, ... , N, T-v(X) = (p)Sigma(i=1) (s1)Sigma(mu=1) A(vi mu)X(i)B(vi mu) + (s2)Sigma(mu=1) (Cvi mu XiDvi mu)-D-T + (s3)Sigma(mu=1) M-vi mu(X) over bar N-i(vi mu) + (s4)Sigma(mu=1) H(vi mu)X(i)(H)G(vi mu,) in which A(vi mu), B-vi mu, C-vi mu, D-vi mu, M-vi mu, N-vi mu, H-vi mu, G(vi mu) and F-v are given matrices with suitable dimensions defined over complex number field. By using the hierarchical identification principle, an iterative algorithm is proposed for solving the above coupled linear matrix equations over the group of reflexive (anti-reflexive) matrices. Meanwhile, sufficient conditions are established which guarantee the convergence of the presented algorithm. Finally, some numerical examples are given to demonstrate the validity of our theoretical results and the efficiency of the algorithm for solving the mentioned coupled linear matrix equations.

关键词： Generalized Sylvester-transpose and conjugate matrix equation iterative algorithm reflexive (anti-reflexive) matrix

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Reconstructing Hypersonic Flow Over a Bluff Body from Experimental Background-Oriented Schlieren Data

Reconstructing Hypersonic Flow Over a Bluff Body from Experi...

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AIAA SciTech Forum

作者： Molnar, Joseph P. LaLonde, Elijah J. Combs, Christopher S. Grauer, Samuel J. Penn State Univ Dept Mech Engn University Pk PA 16802 USA Univ Texas San Antonio Dept Mech Engn San Antonio TX 78249 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

Background oriented schlieren (BOS) is a non-intrusive flow visualization technique that is used to characterize density in complex, high-speed flows. Hypersonic flows over bluff bodies are increasingly relevant to the design of next-generation air- and spacecraft, and BOS may help to study these devices. BOS measurements indicate 2D density gradients in the working fluid, which can be leveraged to render shock structures, quantify density ratios, and even reconstruct latent fields like velocity and pressure. High-speed tests require a fast camera exposure to freeze the flow, but increasing the shutter speed limits the signal strength, resulting in a low signal-to-noise ratio (SNR). Opening the aperture allows more light onto the sensor, increasing the SNR, but it also limits the camera's depth of field and leads to blurry deflections. To address this, we develop an accurate forward model of BOS imaging that accounts for depth-of-field effects. We employ this model to reconstruct the density field of a hypersonic flow over a spherical bluff body. The flow is well characterized in the literature and thus provides a suitable benchmark for our algorithm. Reconstructions are performed using the neural-implicit reconstruction technique, and we also report "physics-informed" estimates based on the compressible Euler equations. Our aperture sampling approach dramatically improves the accuracy of reconstructions: the sharp shock interface is well-resolved in all our tests, irrespective of the camera's aperture setting.

关键词： Compressible Flow Bluff Body Background Oriented Schlieren Sensors Euler Equations Chemiluminescence Free Stream Bow Shock iterative algorithm Laser Diagnostics

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Suppression of Aliasing Errors Introduced by Non-Ideal Mixers and Spectrum Partitioning Methods in the FI-DAC System

Suppression of Aliasing Errors Introduced by Non-Ideal Mixer...

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IEEE International Instrumentation and Measurement Technology Conference (I2MTC)

作者： Wang, Yixiao Liu, Shengjian Meng, Shengwei Liu, Liansheng Harbin Inst Technol Sch Elect & Informat Engn Harbin Peoples R China Harbin Inst Technol Zhengzhou Res Inst Sch Elect & Informat Engn Harbin Peoples R China

ISBN: (纸本)9798350380903;9798350380910

With the growing demands for increased bandwidth in arbitrary waveform generator, the Frequency-Interleaved Digital to Analog Converter (FI-DAC) technology plays a crucial role in enhancing the output bandwidth of individual DAC chips. Based on a dual-DAC chip and band interleaving techniques, the research addresses the issue of aliasing errors resulting from the non-ideal performance of practical analog circuits. By modeling the aliasing errors in the system and the non-ideal characteristics of the hardware, the article aims to minimize aliasing errors while achieving maximum bandwidth output, in compliance with the sampling theorem. The process includes filter selection, determination of sub-band division points for two signal paths, and the system's maximum output bandwidth. Finally, the local oscillator frequency for the mixer is determined. In a simulated environment accounting for actual hardware error components, this study employs a 7th-order elliptic filter with 50 dB aliasing suppression. With two DAC chips operating at a 5 GSa/s sampling rate, the system achieves 3.992 GHz signal output. Under the constraint of employing two 5 GSa/s DACs, this method results in a 59.68% increase in output bandwidth compared to a single DAC output.

关键词： FI-DAC analog filter aliasing suppression iterative algorithm

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A new sufficiently descent algorithm for pseudomonotone nonlinear operator equations and signal reconstruction

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NUMERICAL algorithmS 2023年第3期94卷 1125-1158页

作者： Awwal, Aliyu Muhammed Botmart, Thongchai Khon Kaen Univ Fac Sci Dept Math Khon Kaen 40002 Thailand Gombe State Univ Fac Sci Dept Math Gombe 760253 Nigeria

This paper presents a new sufficiently descent algorithm for system of nonlinear equations where the underlying operator is pseudomonotone. The conditions imposed on the proposed algorithm to achieve convergence are Lipschitz continuity and pseudomonotonicity which is weaker than monotonicity assumption forced upon many algorithms in this area found in the literature. Numerical experiments on selected test problems taken from the literature validate the efficiency of the new algorithm. Moreover, the new algorithm demonstrates superior performance in comparison with some existing algorithms. Furthermore, the proposed algorithm is applied to reconstruct some disturbed signals.

关键词： iterative algorithm Pseudomonotone Sufficiently descent Derivative-free method Nonlinear problem

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QoS Aware Task Offloading for Digital-Twin Enabled Connected Vehicular Network 25

QoS Aware Task Offloading for Digital-Twin Enabled Connected...

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IEEE Wireless Communications and Networking Conference (IEEE WCNC)

作者： Gupta, Akshita Diwani, Drishti Bohara, Vivek Ashok Srivastava, Anand Indraprastha Inst Informat Technol Delhi IIITD Dept Elect & Commun Engn Wirocomm Res Grp New Delhi 110020 India Visvesvaraya Natl Inst Technol VNIT Dept Elect & Commun Engn Nagpur 440010 Maharashtra India

ISBN: (纸本)9798350303582;9798350303599

Future autonomous driving would require a plethora of networking resources and high-quality vehicular communication links. As these mobile devices are resource-constrained, thus, offloading computer-intensive operations to the mobile edge servers has been a crucial strategy to meet the stringent quality of service (QoS) requirements. However, various types of smart vehicles with distinct capabilities, dynamic demands, and unpredictable topology pose significant challenges in realizing efficient edge computing services. To cope with these challenges, we incorporate a digital twin (DT)-enabled connected vehicular network which can facilitate automated resource management to enhance QoS of vehicular users. Specifically, we aim to allocate computation and spectrum resources for a DT-enabled vehicular network along with designing an optimal offloading policy. In addition, a problem to optimize the vehicular network's utility-cost ratio (UCR) is formulated in order to reduce the overall latency, energy consumption, and to improve the throughput. Further, to obtain an optimal resource allocation framework, we propose a three-step iterative algorithm to optimize the bandwidth, prices for latency, energy consumption, and offloading factor iteratively until convergence. The simulations demonstrate that the suggested approach efficiently reduces the task offloading latency as well as decreases the average energy usage for vehicular network, in addition to improving the throughput. Specifically, the utility-to-cost ratio decreases by 85% and 12.5% for sparse and dense traffic scenarios, respectively for a vehicle density of 0.137 vehicle/m.

关键词： Digital-twin Utility-to-Cost Ratio iterative algorithm Throughput Energy Consumption Latency

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Toward High-Performance Delta-Based iterative Processing with a Group-Based Approach

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Journal of Computer Science & Technology 2022年第4期37卷 797-813页

作者： Hui Yu Xin-Yu Jiang Jin Zhao Hao Qi Yu Zhang Xiao-Fei Liao Hai-Kun Liu Fu-Bing Mao Hai Jin National Engineering Research Center for Big Data Technology and System Huazhong University of Science and TechnologyWuhan 430074China Service Computing Technology and System Laboratory Huazhong University of Science and TechnologyWuhan 430074China Cluster and Grid Computing Laboratory Huazhong University of Science and TechnologyWuhan 430074China School of Computer Science and Technology Huazhong University of Science and TechnologyWuhan 430074China

Many systems have been built to employ the delta-based iterative execution model to support iterative algorithms on distributed platforms by exploiting the sparse computational dependencies between data items of these iterative algorithms in a synchronous or asynchronous approach. However, for large-scale iterative algorithms, existing synchronous solutions suffer from slow convergence speed and load imbalance, because of the strict barrier between iterations;while existing asynchronous approaches induce excessive redundant communication and computation cost as a result of being barrier-free. In view of the performance trade-off between these two approaches, this paper designs an efficient execution manager, called Aiter-R, which can be integrated into existing delta-based iterative processing systems to efficiently support the execution of delta-based iterative algorithms, by using our proposed group-based iterative execution approach. It can efficiently and correctly explore the middle ground of the two extremes. A heuristic scheduling algorithm is further proposed to allow an iterative algorithm to adaptively choose its trade-off point so as to achieve the maximum efficiency. Experimental results show that Aiter-R strikes a good balance between the synchronous and asynchronous policies and outperforms state-of-the-art solutions. It reduces the execution time by up to 54.1% and 84.6% in comparison with existing asynchronous and the synchronous models, respectively.

关键词： iterative algorithm delta-based execution model efficiency

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