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31st International Conference on Software, Telecommunications and computer Networks, SoftCOM 2023

作者： Mehnen, Lars Mandl, Thomas Pohn, Birgit Blaickner, Matthias Dregely, Isabel University of Applied Sciences Technikum Wien Faculty Computer Science and Applied Mathematics Department of Computer Science Austria

ISBN: (纸本)9798350301076

This paper presents a comprehensive analysis of student behaviour on Moodle, a widely used Learning Management System (LMS), in a large university setting with over 2000 students. The study investigates the distribution of student access to the LMS relative to the deadlines of quizzes (self-checked). Further, it explores the correlation between student engagement with course materials and their academic performance, finding that students with higher grades tend to access course materials earlier and more frequently before quiz deadlines. The paper also examines the distribution of two different student engagement with quizzes across different weekdays, highlighting distinct patterns between weekdays and weekends, and a unique trend on Saturdays due to lecture schedules for two study types-full-Time and part-Time. These findings provide valuable insights into student learning behaviours on large LMS, with potential implications for enhancing teaching strategies and improving student outcomes. The paper contributes to the growing body of research on learning analytics and offers a foundation for future studies in this area. © 2023 University of Split, FESB.

关键词： Students

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Entropy approach of hydromagnetic Williamson nanofluid flow with Joule heating

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International Journal of Ambient Energy 2023年第1期44卷 1106-1118页

作者： Yaseen Khan, Amir Oyelakin, Ibukun S. Mondal, Sabyasachi Dey, Sharadia Department of Mathematics Amity University Kolkata India School of Computer Science and Applied Mathematics University of the Witwatersrand Johannesburg South Africa Kolkata India

The current investigation, the flow of a hydromagnetic Nanofluid Williamson over an unsteady via a porous medium while stretching a sheet is being analysed along with the impact of thermal radiation and magnetic field on its flow properties. Slip condition between the nanofluid and stretching sheet is also considered. Appropriate similarity transformations are used for converting into a dimensionless form the governing equations with boundary conditions. The derived conventional differential equation was solved using the method of spectral local linearisation. After completing the numerical simulation, the outcomes are presented through different graphs and tables. The momentum conservation equation used in research papers on Williamson nanofluids, hitherto, was corrected. The effect of Joule heating has been considered in the temperature and entropy generation equations for Nanofluid flow over a stretched sheet by Williamson. The growth in the Weissenburg parameter (We) decreases the velocity profile. However, it increases the concentration and temperature distributions. Higher values of the temperature difference parameter ((Formula presented.)) are seen to decrease the entropy generated in the nanofluid system. The Reynolds number (Re) and the Brinkman number show the opposite tendency. The results have been validated with existing research and our results are found to be in great agreement. © 2022 Informa UK Limited, trading as Taylor & Francis Group.

关键词： Porous materials

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Hierarchical GraphCut Phase Unwrapping based on Invariance of Diffeomorphisms Framework

IEEE Open Journal of Signal Processing

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IEEE Open Journal of Signal Processing 2025年 6卷 546-554页

作者： Gao, Xiang Wang, Xinmu Zhao, Zhou Huang, Junqi Gu, Xianfeng David Department of Computer science Stony Brook University NY USA Deparment of Applied Mathematics and Statistics Stony Brook University NY USA

Recent years have witnessed rapid advancements in 3D scanning technologies, with diverse applications spanning VR/AR, digital human creation, and medical imaging. Structured-light scanning with phase-shifting techniques is preferred for its use of non-radiative, low-intensity visible light and high accuracy, making it well suited for human-centric applications such as capturing 4D facial dynamics. A key step in these systems is phase unwrapping, which recovers continuous phase values from measurements that are inherently wrapped modulo 2π. The goal is to estimate the unwrapped phase count k, an integer-valued variable in the equation Φ = ∅ + 2πk, where ∅ is the wrapped phase and Φ is the true phase. However, the presence of noise, occlusions, and piecewise continuous phase functions induced by complex 3D surface geometry makes the inverse reconstruction of the true phase extremely challenging. This is because phase unwrapping is an inherently ill-posed problem: measurements only provide modulo 2π values, and recovering the correct unwrapped phase count requires strong assumptions about the smoothness or continuity of the underlying 3D surface. Existing methods typically involve a trade-off between speed and accuracy: Fast approaches lack precision, while accurate algorithms are too slow for real-time use. To overcome these limitations, this work proposes a novel phase unwrapping framework that reformulates GraphCut-based unwrapping as a pixel-labeling problem. This framework helps significantly improve the estimation of the unwrapped phase count k through the invariance property of diffeomorphisms applied in image space via conformal and optimal transport (OT) maps. An odd number of diffeomorphisms are precomputed from the input phase data, and a hierarchical GraphCut algorithm is applied in each corresponding domain. The resulting label maps are fused via majority voting to efficiently and robustly estimate the unwrapped phase count k at each pixel, using an odd nu

关键词： Transillumination

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Towards end-to-end structure determination from x-ray diffraction data using deep learning

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npj Computational Materials 2024年第1期10卷 1048-1059页

作者： Gabe Guo Judah Goldfeder Ling Lan Aniv Ray Albert Hanming Yang Boyuan Chen Simon J.L.Billinge Hod Lipson Department of Computer Science Columbia UniversityNew YorkNY10027USA Department of Applied Physics and Applied Mathematics Columbia UniversityNew YorkNY10027USA Department of Mechanical Engineering and Materials Science Duke UniversityDurhamNC27708USA Department of Mechanical Engineering Columbia UniversityNew YorkNY10027USA

Powder crystallography is the experimental science of determining the structure of molecules provided in crystalline-powder form,by analyzing their x-ray diffraction(XRD)*** many materials are readily available as crystalline powder,powder crystallography is of growing usefulness to many ***,powder crystallography does not have an analytically known solution,and therefore the structural inference typically involves a laborious process of iterative design,structural refinement,and domain knowledge of skilled experts.A key obstacle to fully automating the inference process computationally has been formulating the problem in an end-to-end quantitative form that is suitable for machine learning,while capturing the ambiguities around molecule orientation,symmetries,and reconstruction *** we present an ML approach for structure determination from powder diffraction *** works by estimating the electron density in a unit cell using a variational coordinate-based deep neural *** demonstrate the approach on computed powder x-ray diffraction(PXRD),along with partial chemical composition information,as *** evaluated on theoretically simulated data for the cubic and trigonal crystal systems,the system achieves up to 93.4%average similarity(as measured by structural similarity index)with the ground truth on unseen materials,both with known and partially-known chemical composition information,showing great promise for successful structure solution even from degraded and incomplete input *** approach does not presuppose a crystalline structure and the approach are readily extended to other situations such as nanomaterials and textured samples,paving the way to reconstruction of yet unresolved nanostructures.

关键词： structure powder crystalline

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A Study on the Transmission Dynamics of the Omicron Variant of COVID-19 Using Nonlinear Mathematical Models

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computer Modeling in Engineering & sciences 2024年第6期139卷 2265-2287页

作者： S.Dickson S.Padmasekaran Pushpendra Kumar Kottakkaran Sooppy Nisar Hamidreza Marasi Department of Mathematics Periyar UniversitySalemTamilnadu636011India Faculty of Engineering and Natural Sciences Istanbul Okan UniversityIstanbulTurkey Department of Mathematics College of Science and Humanities in AlkharjPrince Sattam Bin Abdulaziz UniversityAlkharj11942Saudi Arabia Department of Applied Mathematics Faculty of MathematicsStatistics and Computer ScienceUniversity of TabrizTabrizIran

This research examines the transmission dynamics of the Omicron variant of COVID-19 using SEIQIcRVW and SQIRV models,considering the delay in converting susceptible individuals into infected *** significant delays eventually resulted in the pandemic’s *** ensure the safety of the host population,this concept integrates quarantine and the COVID-19 *** investigate the stability of the proposed *** fundamental reproduction number influences stability *** to our findings,asymptomatic cases considerably impact the prevalence of Omicron infection in the *** real data of the Omicron variant from Chennai,Tamil Nadu,India,is used to validate the outputs.

关键词： Omicron local stability reproduction number steady states global stability

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Comments on "relaxed Conditions for the Input-to-State Stability of Switched Nonlinear Time-Varying Systems"

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IEEE Transactions on Automatic Control 2025年第6期70卷 4233-4236页

作者： Şahan, Gökhan Trenn, Stephan Izmir Institute of Technology Department of Mathematics and Computational Science and Engineering Program Urla Izmir Turkey University of Groningen Bernoulli Institute for Mathematics Computer Science and Artificial Intelligence Groningen9722BA Netherlands

This study addresses the deficiencies in the assumptions of the results in Chen and Yang, 2017 [1] due to the lack of uniformity. We first show the missing hypothesis by presenting a counterexample. Then we prove why they are wrong in that form and show the errors in the proof of the main result of [1]. Next, we compare the assumptions and related results of [1] with similar works in the literature. Lastly, we give suggestions to complement the shortcomings of the hypotheses and thus correct them. © 1963-2012 IEEE.

关键词： Nonlinear simulations

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Retrial Queueing System of MAP/PH/N Type with a Finite Buffer and Group Service. The Process Describing the System Dynamics 22nd

Retrial Queueing System of MAP/PH/N Type with a Finite Buffe...

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22nd International Conference on Information Technologies and Mathematical Modelling, ITMM 2023 and 14th International Workshop on Retrial Queues and Related Topics, WRQ 2023

作者： Dudin, Alexander Dudina, Olga Department of Applied Mathematics and Computer Science Belarusian State University Minsk220030 Belarus

ISBN: (纸本)9783031653841

A queuing system with many identical servers, a finite buffer, and order retrials is under study. The order’s arrival is described by the Markov arrival process. Service is offered for orders in groups. The size of the group is bounded from above by the capacity of the buffer and from below by a fixed threshold. A group’s service time follows a phase-type distribution with the irreducible representation determined by group size. A classical retrial strategy is assumed. Retrying and waiting orders can renege from the service after a random time interval. The duration of this interval has an exponential distribution. We built a multidimensional continuous-time Markov chain that includes the number of retrying orders, the number of busy servers, the state of the underlying arrivals process, and an auxiliary multidimensional Markov chain that defines the number of servers providing service at all possible service phases. The infinitesimal generator of the constructed chain is written down and, and the explicit expressions for the matrix blocks of the generator are presented. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.

关键词： Markov chains

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Nonlinearity in Large-Cycle Cellular Automata

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Complex Systems 2025年第1期34卷 129-160页

作者： Mukherjee, Sukanya Adak, Sumit Department of Computer Science and Engineering Institute of Engineering and Management Kolkata University of Engineering and Management West Bengal Kolkata700091 India Department of Applied Mathematics and Computer Science DTU Compute Technical University of Denmark Kgs. Lyngby2800 Denmark

The class of maximal-length cellular automata (CAs) has gained significant attention over the last few years due to the fact that it can generate cycles with the longest possible lengths. For every l of the form l = 2n-1 where n ∈ , a cycle of length l can be generated by a cellular automaton (CA) of size ⌊log2 l⌋ + 1;this maximal-length CA is in fact the optimal (minimum-sized) CA to generate a cycle of length l. However, maximal-length CAs are, in general, linear and have some drawbacks. Moreover, it is nontrivial to address this problem for any l ∈ , that is, removing the constraint that l is of the form 2n-1. In this paper we therefore employ nonlinearity in the rules and aim to generate the near-optimal CA for any given cycle length l, meaning that the generated CAs will be of size n = (⌊log2 l⌋ + 1) + d, where the displacement d is as small as possible. We use a generic operator to concatenate a collection of component CAs of sizes n1, n2, …, nk by employing an evolutionary strategy. Here, n = n1 + n2 + ⋯ + nk and l ≥ lcm(1, 2, …, k ), where i (1 ≤ i ≤ k) is the maximum cycle length of a CA of size ni . An influencing factor in the design of component CAs is to achieve the near-optimal CA for a given cycle length. Here we consider nonlinear reversible large-cycle CAs as component CAs. We also measure the effectiveness of nonlinearity in large-cycle generation. © 2025, Complex Systems Publications, Inc. All rights reserved.

关键词： CAs cellular automata evolution large-cycle CA neighborhood dependent nonlinearity reversible CAs

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Approximate Analytical Solutions for a Heat Transfer in a Slab with Internal Heat Generation

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Defect and Diffusion Forum 2023年 424卷 45-57页

作者： Nkwanazana, Mpho Moitsheki, Raseelo Joel Department of Mathematics and Applied Mathematics Sefako Makgatho Health Science University Molotlegi Street Ga-Rankuwa0204 South Africa School of Computer Science and Applied Mathematics University of the Witwatersrand Private Bag 3 Braamfontien Johannesburg South Africa

In this article we consider heat transfer models prescribed by reaction-diffusion equations. The diffusivity term and internal heat generator are given by the power law. The differential transform method (DTM) is utilized to construct the approximate analytical solutions. These solutions are generated using one- and two-dimensional DTM for the steady state and the transient problem, respectively. The effects of parameters appearing in the our model are presented and explained. © 2023 Trans Tech Publications Ltd, Switzerland.

关键词： Heat transfer

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Matrix nearness problems with off-block-diagonal rank constraints

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Linear Algebra and Its Applications 2024年 721卷 635-673页

作者： Chen, Lujing Pedersen, Frederik H. Andersen, Martin S. Department of Applied Mathematics and Computer Science Technical University of Denmark Richard Petersens Plads Bldg. 324 Kgs. Lyngby2800 Denmark

This paper explores the problem of finding a rank-structured approximation to a given Hermitian positive definite matrix. We first study a fundamental matrix nearness problem which seeks an approximation whose off-diagonal block must have low rank. Our investigation focuses on three objective functions: the spectral norm, Frobenius divergence, and log-determinant divergence. We derive closed-form solutions for the fundamental nearness problem, extending our analysis to include problems with a range restriction on the off-diagonal block. Building upon these results, we propose a practical, scalable algorithm to compute a positive definite hierarchical off-diagonal low-rank approximation to a Hermitian positive definite matrix. Through numerical experiments, we explore the use of our approximation as a general-purpose preconditioner for the conjugate gradient method. Our results demonstrate that the log-determinant divergence-based approximation exhibits good performance across a diverse set of test problems. © 2024 The Author(s)

关键词： Conjugate gradient method

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