Article
Astronomy & Astrophysics
M. Koussour, N. Myrzakulov, Alnadhief H. A. Alfedeel, F. Awad, M. Bennai
Summary: In this paper, a cosmological model parametrized by a generalized variable deceleration parameter is investigated to understand the dynamics driving cosmic acceleration. The model's compatibility with observational data is assessed using constraints from the latest observational datasets. The present values of key parameters are estimated, and the stability of the model against small perturbations is confirmed.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Mechanics
David Yudin, Daniel Floryan, Tyler Van Buren
Summary: We used small-amplitude inviscid theory to study the swimming performance of a flexible flapping plate with time-varying flexibility. The results showed that the oscillating stiffness had a profound impact on thrust, with potential improvements of up to 35% compared to a constant-stiffness plate. However, large enough frequencies and amplitudes of the stiffness oscillation could lead to instabilities, which may enhance propulsive performance but require further verification through experiments or nonlinear simulations.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Automation & Control Systems
Hongjiu Yang, Hai Zhao, Yuanqing Xia, Jinhui Zhang
Summary: This paper investigates the application of nonlinear model predictive control with a time-varying terminal cost function in a nonlinear system, proposing an effective tracking control scheme. By introducing constraints and designing a time-varying weight matrix, the stability of the system is ensured, effectively solving the tracking problem of periodic references.
Article
Physics, Multidisciplinary
Parbati Sahoo, Avik De, Tee-How Loo, P. K. Sahoo
Summary: We study the periodic cosmic transit behavior of the accelerated universe in the framework of symmetric teleparallelism. The viability and physical reliability of the deceleration parameter are studied using observational constraints, and the dynamics of periodicity and singularity are discussed in detail.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2022)
Article
Engineering, Multidisciplinary
Lei YanFang, Li JunMin, Zhao AiLiang
Summary: This paper focuses on the problem of adaptive neural networks control for uncertain parabolic distributed parameter systems with nonlinear periodic time-varying parameter. The uncertain nonlinear dynamic and unknown periodic TVP are represented using neural networks and Fourier series expansion. Two control algorithms are designed to ensure the asymptotic stability of the system, and the conditions for the resulting closed-loop systems to be asymptotically stable are derived. Simulation results verify the effectiveness of the proposed algorithms.
SCIENCE CHINA-TECHNOLOGICAL SCIENCES
(2022)
Article
Engineering, Aerospace
Zhi Wang, Jun Wang, Jing Tian, Yu Liu
Summary: A method of parameter identification based on the block-pulse function is presented for periodic time-varying systems. The proposed method saves calculation time and provides highly accurate results. Experimental tests demonstrate its accuracy and effectiveness, making it valuable for various applications.
Article
Astronomy & Astrophysics
Priyanka Garg, Anirudh Pradhan, M. Zeyauddin
Summary: In this paper, the cosmic behavior of particle creation in FLRW models with time dependent gravitational constant and cosmological constant is investigated. The time-varying behavior of several quantities and their physical significance are discussed.
Article
Engineering, Marine
Yongcheng Li, Ziying Pan, Nan Zhang
Summary: This study introduces a new conceptual design of flexible oscillating wing with time-varying camber deformation and conducts a two-dimensional transient numerical simulation to compare its propulsive performance with that of conventional rigid oscillating wing. The results show that the flexible deformation motion greatly improves the propulsive efficiency of the oscillating wing, with optimum motion parameters leading to the highest efficiency. Additionally, the flexible deformation motion presents greater propulsive efficiency compared to the conventional rigid oscillating wing, with a maximum propulsive efficiency increase of 28.3%.
Article
Physics, Multidisciplinary
L. A. Devi, S. S. Singh, L. Kumrah
Summary: In this study, the spatially homogeneous and anisotropic Bianchi type-I space-time with perfect fluid is examined under the f(R, T) theory of gravity. By assuming a time-dependent function for the deceleration parameter, exact solutions to the field equations are found. The research reveals an anisotropic Universe in the early epoch that transitions to an isotropic state in the late epoch. Furthermore, the model establishes a phase of deceleration to acceleration, and evaluates the consistency of cosmological parameters with observations by examining the energy conditions.
INDIAN JOURNAL OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
Bhupendra Kumar Shukla, Rishi Kumaras Tiwari, Aroonkumaras Beesham
Summary: The current study investigates a modified theory of gravity called f(G,T) theory. It focuses on a Gauss-Bonnet cosmological model that integrates a non-linear Gauss-Bonnet term and a linear trace term. The optimal values of the model parameters are determined by aligning them with the latest observational datasets, and the physical behavior of the cosmographic parameters corresponding to the constrained values of the model parameters is analyzed.
ASTROPHYSICS AND SPACE SCIENCE
(2023)
Article
Automation & Control Systems
Ali Abdullah, Nirvana Borham
Summary: This paper investigates the problem of designing mixed H2/H infinity model reference control (MRC) systems for linear parameter-varying discrete-time systems. Two types of mixed H2/H infinity MRC systems, namely the state-feedback and dynamic output-feedback MRC systems, are considered and designed using a parameter-dependent Lyapunov function. The experimental results of the aeropendulum system are used to evaluate the proposed controllers and demonstrate their effectiveness in achieving satisfactory performances of the closed-loop systems.
INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL
(2022)
Article
Automation & Control Systems
Ning Xu, Feng Ding
Summary: This article focuses on the identification of time-varying systems. Unlike conventional polynomial approximation approaches, the changing laws of the time-varying parameters are taken into account to establish the identification model. The concept of the invariant matrix is introduced to characterize the time-varying parameters and establish the state-space model. Two state estimation algorithms, stacked and detached, are proposed to estimate the time-varying parameters and enhance computational efficiency. Numerical simulation examples are provided to demonstrate the effectiveness of the proposed algorithms.
INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL
(2023)
Article
Astronomy & Astrophysics
Giovanni Motta, Darlin Soto, Marcio Catelan
Summary: This paper introduces a new mathematical model for describing modulated light curves in periodic variable stars, which considers smoothly time-varying trends and harmonic components. The proposed method offers flexibility and avoids restrictive assumptions about the functional form of the trends and amplitudes. The authors develop a semi-parametric method for estimating the time-varying parameters and derive the mathematical definition of spectral density for unequally spaced time series to detect serial correlation in the residuals.
ASTROPHYSICAL JOURNAL
(2022)
Article
Economics
Joshua C. C. Chan
Summary: This study develops an efficient Bayesian sparsification method for a class of models called hybrid TVP-VARs, which automatically determines whether the parameters are time-varying. Using US datasets, it is found that some equations have time-varying parameters, and the large hybrid TVP-VAR model outperforms many standard benchmarks in terms of forecasting performance.
JOURNAL OF BUSINESS & ECONOMIC STATISTICS
(2023)
Article
Environmental Sciences
Chien-Chiang Lee, Godwin Olasehinde-Williams
Summary: The study found that gasoline consumption is not very responsive to price and income changes, with elasticity varying over time and increasing sensitivity during economic crises. Constant elasticity models tend to overestimate price and income elasticity, with income being more elastic than price.
ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH
(2021)
