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Solid-state impedance spectroscopy studies of dielectric properties and relaxation processes in Na_(2)O–V_(2)O_(5)–Nb_(2)O_(5)–P_(2)O_(5) glass

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International Journal of Minerals,Metallurgy and Materials 2024年第1期31卷 186-196页

作者： Sara Marijan Luka Pavic Division of Materials Chemistry Ruđer Boskovic InstituteBijenicka 54HR-10000 ZagrebCroatia

Solid-state impedance spectroscopy(SS-IS)was used to investigate the influence of structural modifications resulting from the addition of Nb2O5 on the dielectric properties and relaxation processes in the quaternary mixed glass former(MGF)system 35Na_(2)O–10V_(2)O_(5)–(55-x)P_(2)O_(5)–xNb_(2)O_(5)(x=0–40,mol%).The dielectric parameters,including the dielectric strength and dielectric loss,are determined from the frequency and temperature-dependent complex permittivity data,revealing a significant dependence on the Nb2O5 *** transition from a predominantly phosphate glass network(xrelaxation studies,analyzed through modulus formalism and complex impedance data,show that DC conductivity and relaxation processes are governed by the same mechanism,attributed to ionic *** contrast to glasses with a single peak in frequency dependence of imaginary part of electrical modulus,M″(ω),Nb-40 glass-ceramic exhibits two distinct contributions with similar relaxation *** high-frequency peak indicates bulk ionic conductivity,while the additional low-fre-quency peak is associated with the grain boundary effect,confirmed by the electrical equivalent circuit(EEC)*** scaling characteristics of permittivity and conductivity spectra,along with the electrical modulus,validate time-temperature superposition and demonstrate a

关键词： phosphate glasses glass-ceramics impedance spectroscopy dielectric properties relaxation processes permittivity scaling conductivity scaling modulus formalism

relaxation of Mechanical Stress in Poly(vinyl alcohol) Cryogels of Different Compositions

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Chinese Journal of Polymer Science 2023年第3期41卷 442-447,I0010页

作者： Vladimir N.Manzhai Maria S.Fufaeva Ekaterina S.Kashlach Institute of Petroleum Chemistry of the Siberian Branch of the Russian Academy of Sciences Tomsk 634055Russia

The study presents the experimental results of measurements of the relaxation time of cryogels formed from various colloid-dispersed systems based on a poly(vinyl alcohol) aqueous *** is shown that the value of relaxation time,which characterizes the relationship between the viscosity and elasticity of real bodies,describes the rheological properties of materials more objectively than the traditional assessment of their physical and mechanical characteristics only by the elasticity modulus of the samples.

关键词： Cryogel relaxation processes Viscoelasticity Rheological properties

Radar Cross-Section Measurement Using the Near-Field Single-Frequency Angular-Diversity Technique

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Journal of Systems Engineering and Electronics 2000年第1期11卷 1-7页

作者： Ye, Xiaodong Fang, Dagang Sheng, Weixing Nanjing Univ of Science and Technology Nanjing China

Radar cross-section (RCS) measurement with the near-field electromagnetic wave illumination of a target has been proved to be practical. The existing methods employ the multiplefrequency angular-diversity (MFAD) technique, whereas this paper considers the single-frequency angular-diversity (SFAD) technique. The paper takes into account the scattering center modeling and the limitation of higher sidelobes in reconstructing images in the SFAD technique compared to the MFAD technique. A method of combining the SFAD technique with the RELAX approach is presented for the high-resolution extraction of scattering centers on a target. The proposed method offers an excellent RCS recovery, which is validated by numerical results.

关键词： Electromagnetic wave scattering Image reconstruction Radar imaging Radar target recognition relaxation processes

NUMERICAL SIMULATION OF 1-D UNSTEADY TWO-PHASE FLOWS WITH SHOCKS

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Applied Mathematics and Mechanics(English Edition) 1992年第7期13卷 629-635页

作者：吴清松王柏懿 University of Science and Technology of China Hefei Institute of Mechanics Academia Sinica Beijing

In the present paper, random-choice method (RCM) and second-order GRP difference method, which are high resolution methods used for pure gas flows with shocks, are extended and employed to study the problem of one-dimensional unsteady two-phase flows. The two-phase shock wave and the flow field behind it in a dusty gas shock tube are calculated and the time-dependent change of the flow parameters for the gas and particle phase are obtained. The numerical results indicate that both the two methods can give the relaxation structure of the two-phase shocks with a sharp discontinuous front and that the GRP method has the advantages of less time-consuming and higher accuracy over the RCM method.

关键词： Gas dynamics Granular materials Mathematical models Numerical methods relaxation processes Shock tubes Shock waves Unsteady flow

Continuous-time System Identification with Nuclear Norm Minimization and GPMF-based Subspace Method

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IEEE/CAA Journal of Automatica Sinica 2016年第2期3卷 184-191页

作者： Mingxiang Dai Ying He Xinmin Yang the National Key Laboratory of Transient Physics Nanjing University of Science and Technology

To improve the accuracy and effectiveness of continuous-time (CT) system identification, this paper introduces a novel method that incorporates the nuclear norm minimization (NNM) with the generalized Poisson moment functional (GPMF) based subspace method. The GPMF algorithm provides a simple linear mapping for subspace identification without the timederivatives of the input and output measurements to avoid amplification of measurement noise, and the NNM is a heuristic convex relaxation of the rank minimization. The Hankel matrix with minimized nuclear norm is used to determine the model order and to avoid the over-parameterization in subspace identification method (SIM). Furthermore, the algorithm to solve the NNM problem in CT case is also deduced with alternating direction methods of multipliers (ADMM). Lastly, two numerical examples are presented to evaluate the performance of the proposed method and to show the advantages of the proposed method over the existing methods. © 2014 Chinese Association of Automation.

关键词： Identification (control systems) Matrix algebra Numerical methods relaxation processes Religious buildings

Evidence of a third kind of Johnscher’s like universal dielectric response

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Journal of Advanced Dielectrics 2018年第4期8卷 43-48页

作者： Maheswar Panda Department of Physics Dr.Harisingh Gour Vishwavidyalaya(A Central University)Sagar Madhya Pradesh 470003India

Polymer/metal composites(PMC)comprising of polyvinylidene fluoride/nanocrystalline nickel with varying volume fractions of nickel(fcon)prepared under cold press show an insulator to metal transition(IMT)at percolation threshold(f_(c)=f_(con)=0:27).The two kinds of generalized Johnscher’s universal dielectric response(UDR)laws on both sides of IMT hold good,while for the percolative sample,none of the two laws hold *** the concept of dipolar relaxation nor anomalous low frequency dispersion stands valid for f_(c)=0:27,while a completely different,neutral and competing electrical behavior is observed over the entire range of *** emerged third kind of Johnscher’s like UDR for fc is observed and the relaxation law has been formulated as the ratio of imaginary and real parts of dielectric constant remains constant over the entire range of frequency starting from dc to any higher *** value of the constant is attributed to depend on the PMC,the dielectric constant of the polymer,the differences of conductivity and fractions of the components of the PMC and also on their connectivity arising due to the difference of their process *** emerged unique dielectric relaxation consists of multiple relaxations arising due to the combination of other relaxations(arising due to the two different types of species)present in the sample,f_(con)=0:*** novel material may be suitable for certain specific applications in electrical and electronics engineering.

关键词： Dielectric losses dielectric materials dielectric measurements dielectric polarization frequency response image analysis impedance measurement polymers relaxation processes spectroscopy