المؤلفون: Ahmed Refaie Ali, Harun Or Roshid, Shariful Islam, Asma Khatun

المصدر: Scientific Reports, Vol 14, Iss 1, Pp 1-20 (2024)

مصطلحات موضوعية: Wave propagation, Electrical transmission lines, NPDEs, Travelling wave, Modified expansion, Jacobi elliptic, Medicine, Science

الوصف: Abstract This study presents a comprehensive analysis of a nonlinear telecommunications model, exploring bifurcation, stability, and wave solutions using Hamiltonian and Jacobian techniques. The investigation begins with a thorough examination of bifurcation behavior, identifying critical points and their stability characteristics, leading to the discovery of diverse bifurcation scenarios. The stability of critical points is further assessed through graphical and numerical methods, highlighting the sensitivity to parameter variations. The study delves into the derivation of both numerical and analytical wave solutions, aligning them with energy orbits depicted in phase portraits, revealing a spectrum of wave behaviors. Additionally, the analysis extends to traveling wave solutions, providing insights into wave propagation dynamics. Notably, the study underscores the efficacy of the planar dynamical approach in capturing system behavior in harmony with phase portrait orbits. The findings have significant implications for telecommunications engineers and researchers, offering insights into system behavior, stability, and signal propagation, ultimately advancing our understanding of complex nonlinear dynamics in telecommunications networks.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2045-2322Test

الوصول الحر: https://doaj.org/article/250450d6887d48119f9e78676223cf54Test

المؤلفون: Yihui Zhu, Wei Wu, Yang Song, Zhuangqing Fan, WeiLong Niu, Zhaoyu Wang, Yaoke Wen, Cheng Xu, Min Xia

المصدر: Journal of Materials Research and Technology, Vol 31, Iss , Pp 1483-1506 (2024)

مصطلحات موضوعية: Ceramics/UHMWPE laminate composite, Bulge hyperbolic profile, Blunt trauma assessment, Ballistic impact wave propagation, Energy transformation, Mining engineering. Metallurgy, TN1-997

الوصف: With increasing local conflicts worldwide, studying the impact response of body armor is crucial for enhancing soldier survival rates. However, there is still insufficient understanding of the back bulge expansion patterns, the impact waves transmission features, and blunt injury assessing method of body armor. To investigate these problems deeply, the three-dimensional digital image correlation method and numerical models were employed to reveal the ballistic response mechanism of ceramic/ultra-high-molecular-weight polyethylene (UHMWPE) composite body armor impacted by 7.62 mm rifle bullet. This study built theoretical function for the bulge expansion, revealed the wave transmission mechanism and fractures in both materials and their interaction. Firstly, the experiment revealed that the back-face bulge transverse expansion velocity exhibits a double exponential decrease. Secondly, the contour of back-face bulges consistently demonstrated excellent hyperbolic characteristics at various moments. Thirdly, the average Viscous Criterion (VC) and Blunt Criterion (BC) values were 5.37 and 0.95, corresponding to Abbreviated Injury Scale (AIS) values of 6 and 4. Fourthly, the simulation revealed that the ceramics transverse and radial cracks seems primarily induced by shear stress xy; ceramics conical cracks occurring at the boundaries of equivalent stress seems primarily induced by stress in x and y directions. Fifthly, numerical results revealed that the velocity of compression waves within the laminate increases over time in the impact direction and consistent with ceramic velocity impacted on the laminate. These findings lead to experimental and theoretical advances in the impact response mechanism of composite body armor and provide index for improving the protective performance.

وصف الملف: electronic resource

العلاقة: http://www.sciencedirect.com/science/article/pii/S2238785424014121Test; https://doaj.org/toc/2238-7854Test

الوصول الحر: https://doaj.org/article/4c7db1e4b91648ff973b82963da44a00Test

المؤلفون: V. V. Zakharenko, O. O. Kostenko, O. O. Konovalenko, D. M. Vavriv, S. L. Prosvirnin, Y. M. Yampolski

المصدر: Radio Physics and Radio Astronomy, Vol 29, Iss 2, Pp 137-169 (2024)

مصطلحات موضوعية: leonid m. lytvynenko (a.k.a. leonid n. litvinenko), national academy of sciences of ukraine, radio physics, radio astronomy, astrophysics, electromagnetic waves, difraction and wave propagation theory, "successive reonements" technique, Astronomy, QB1-991

الوصف: This paper is an attempt of paying tribute to the memory of Leonid Mykolayovych Lytvynenko (LML), an outstanding Ukrainian scientist, Full Member of the National Academy of Sciences who worked most fruitfully in the fields of radio science and radio astronomy. Starting of 1985, Dr. Lytvynenko was, over a 30-plus years period, at the head of the Institute of Radio Astronomy, Acad. Sci. of the Ukrainian SSR (currently the National Academy of Sciences of Ukraine) that had been established owing to his vigorous and direct participation in the process. In 1996 LML promoted foundation of a new scientific journal, namely the "Radio Physics and Radio Astronomy", which he devotedly served for, in the Editor-in-Chief capacity, during the 25 years that followed. Dr. L. Lytvynenko was one of the brightest representatives of the school of theoretical radio physics that had developed within the O. Usikov Institute for Radio Physics and Electronics in Kharkiv and further flourished within the Institute of Radio Astronomy. He is known as the founder of a new branch of radio science, specifically theory of electromagnetic wave diffraction and propagation through composite and multilayered periodic structures.

وصف الملف: electronic resource

العلاقة: http://rpra-journal.org.ua/index.php/ra/article/view/1443/pdfTest; https://doaj.org/toc/1027-9636Test; https://doaj.org/toc/2415-7007Test

الوصول الحر: https://doaj.org/article/b8793cf8fac24e179c75f0a58405a629Test

المؤلفون: Borisova T. D., Blagoveshchenskaya N. F., Kalishin A. S., Kovalev A. S.

المصدر: Solar-Terrestrial Physics, Vol 10, Iss 2, Pp 74-92 (2024)

مصطلحات موضوعية: radio wave propagation, small-scale artificial ionospheric irregularities, doppler observations, the eiscat heating facility, modeling, Astrophysics, QB460-466

الوصف: During experiments on the modification of the high-latitude ionosphere by high-power HF radio waves of ordinary or extraordinary polarization of the EISCAT/Heating facility (Tromsø, Norway) in 2013, 2016, and 2019, Doppler measurements of diagnostic HF radio signals over long radio paths were carried out by the bistatic scatter method. We studied characteristics of Doppler frequency variations in bistatic scattered radio signals, using the experimental results obtained along radio paths of different lengths (up to ~8500 km) and orientation. We examined numerical dependences of the Doppler frequency variations in a radio signal on the azimuth of the wave vector of a radio wave incident onto an artificially disturbed region, on the bistatic scattering angle, and on the azimuthal direction of irregularity motion in an artificially disturbed region of the ionosphere. From simultaneous measurements of the Doppler frequency fD of the radio signal along two diagnostic radio paths, we numerically estimated the velocity vector of irregularities in the artificially disturbed region of the ionosphere. The total vector velocity of artificial ionospheric irregularities can be calculated from measurements of the Doppler frequency shift along several long diagnostic radio paths after preliminary analysis of experimental observations with the results of trajectory modeling of diagnostic HF radio signals.

وصف الملف: electronic resource

العلاقة: https://naukaru.ru/en/nauka/article/71291/viewTest; https://doaj.org/toc/2500-0535Test

الوصول الحر: https://doaj.org/article/213971d755c2488db6c279cdbfff68d6Test

المؤلفون: Ponomarchuk S. N., Kurkin V. I., Ilyin N. V., Penzin M. S.

المصدر: Solar-Terrestrial Physics, Vol 10, Iss 2, Pp 93-101 (2024)

مصطلحات موضوعية: radio wave propagation, waveguide approach, radio path forecast, ionogram, radio channel diagnostics, Astrophysics, QB460-466

الوصف: We present a scheme for modeling HF radio signal characteristics along paths of different lengths, which is based on the waveguide approach — the normal mode method. We use a representation of the recorded signal field in the form of Green function products of the angular operator, excitation coefficients, and reception coefficients of individual normal modes. Algorithms have been developed for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals in large spatial regions through analysis and numerical summation of normal mode series. We have implemented a complex algorithm for simulating propagation conditions of HF radio signals, which includes a medium model, algorithms for calculating signal characteristics, and operational diagnostics of radio channel. We have compared the results of the HF signal propagation characteristic modeling and the experimental oblique sounding data obtained along paths of different lengths and orientation. To analyze experimental ionograms, determine the maximum usable frequencies for propagation modes along radio paths, we employ the method of automatic processing and interpretation of oblique sounding ionograms.

وصف الملف: electronic resource

العلاقة: https://naukaru.ru/en/nauka/article/75259/viewTest; https://doaj.org/toc/2500-0535Test

الوصول الحر: https://doaj.org/article/b1dd51683a4b4bf0b763b433c0a4e6b1Test

المؤلفون: Ponomarchuk S. N., Grozov V. P.

المصدر: Solar-Terrestrial Physics, Vol 10, Iss 2, Pp 102-110 (2024)

مصطلحات موضوعية: ionosphere, ionogram, radio wave propagation, oblique ionosphere sounding, Astrophysics, QB460-466

الوصف: The paper presents a method of interpreting data on oblique ionosphere sounding (OS) with a continuous chirp signal. Hybrid algorithms for automatic interpretation of ionograms by selected points with significant amplitude obtained during secondary data processing for various heliogeophysical conditions have been developed and implemented. For the conditions of the two-layer ionosphere, an interpretation method has been worked out which involves analyzing histograms for the distribution of points with significant amplitude, which fall into a model mask constructed from the results of modeling of the distance-frequency characteristic for propagation when it moves over the ionogram. For the multilayer ionosphere, the interpretation is based on the study of the ionogram amplitude relief. The algorithms for extracting tracks of signals reflected from sporadic layers are examined separately. We report the results of interpretation of ionograms obtained on the network of chirp sounding radio paths in the northeastern region of Russia.

وصف الملف: electronic resource

العلاقة: https://naukaru.ru/en/nauka/article/73915/viewTest; https://doaj.org/toc/2500-0535Test

الوصول الحر: https://doaj.org/article/67860f90272149a093754e39b55754eeTest

المؤلفون: Shang Fei, Wang Liangquan

المصدر: Scientific Reports, Vol 14, Iss 1, Pp 1-11 (2024)

مصطلحات موضوعية: Shock wave propagation, Pit, Shock wave diffraction, Numerical simulation, Medicine, Science

الوصف: Abstract To study the influence of pits on shock wave propagation and the propagation of shock waves within pits, numerical simulations were used to calculate the distribution of overpressure peak values at the bottom and rear of the pits at 5 depths and 5 explosion center distances. The results indicate that diffraction occurs when the explosion shock wave passes through the edge of the crater; The peak overpressure of the shock wave at the bottom of the pit exhibits a "spoon shaped" distribution, and the peak overpressure on the right side is significantly higher than that on the left side; There are two distinct boundary regions for the overpressure of the shock wave behind the crater due to the influence of the crater; The distance between the explosion centers has little effect on the distribution trend of the overpressure peak of the shock wave at the bottom and rear of the pit, mainly affecting the magnitude of the overpressure peak. The research results provide theoretical support for the analysis of the propagation law of explosion shock waves and guidance for the design of protective engineering structures, with significant engineering application value.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2045-2322Test

الوصول الحر: https://doaj.org/article/c97758dada8d4715b4a880886015db5eTest

المؤلفون: Dan Shi, Wanqing Li, Keyi Cui, Cheng Lian, Xiaoyong Liu, Zheng Qi, Hui Xu, Juejia Zhou, Zhao Liu, Hua Zhang

المصدر: IET Microwaves, Antennas & Propagation, Vol 18, Iss 6, Pp 391-401 (2024)

مصطلحات موضوعية: 5G mobile communication, electromagnetic fields, electromagnetic wave propagation, learning (artificial intelligence), Telecommunication, TK5101-6720, Electricity and magnetism, QC501-766

الوصف: Abstract A novel method based on machine learning is proposed to estimate the electromagnetic radiation level at the ground plane near fifth‐generation (5G) base stations. The machine learning model was trained using data from various 5G base stations, enabling it to estimate the electric field intensity at any arbitrary radiation point when the base station provides service to different numbers of 5G terminals which are in different service modes. The inputs required for the model include the transmit power of the antenna, the antenna gain, the distance between the 5G base station and 5G terminals, terminal service modes, the number of 5G terminals and the environmental complexity around the 5G base station. Experimental results demonstrate the feasibility and effectiveness of the estimation method, with the mean absolute percentage error of the machine learning model being approximately 5.98%. This level of accuracy showcases the reliability of the approach. Moreover, the proposed method offers low costs when compared with on‐site measurements. The estimated results can be utilised to reduce test costs and provide valuable guidance for optimal site selection, thereby facilitating radio wave coverage or electromagnetic radiation regulation of 5G base stations.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1751-8725Test; https://doaj.org/toc/1751-8733Test

الوصول الحر: https://doaj.org/article/81fcae9f2cba4ee3bbcd2cddce954b41Test

المؤلفون: David Alan Garren

المصدر: IET Radar, Sonar & Navigation, Vol 18, Iss 6, Pp 838-848 (2024)

مصطلحات موضوعية: antenna radiation patterns, antennas, bessel functions, conformal antennas, electromagnetic wave propagation, radar antennas, Telecommunication, TK5101-6720

الوصف: Abstract The author reveals that the power pattern for a particular selected rotating spherical electric current density profile exhibits the following two properties simultaneously: (a) fully omnidirectional in three dimensions (3‐D) and (b) invariant with regards to radio frequency (RF). Specifically, most known antenna designs exhibit either nodal lines or planes for at least some RF frequencies. In contrast, the primary innovation of the subject rotating electric current sphere is that it generates a power pattern that is characterised by no nodal lines nor nodal planes for any RF frequency. In the present analysis, the electro‐magnetic (EM) fields are calculated as an exact solution of Maxwell's equations for the subject electric current density that rotates azimuthally on a spherical surface. As expected, the spatial structure of the resulting EM fields also rotates azimuthally. More surprisingly, this rotating electric current density generates pure magnetic dipole radiation exactly, with the absence of any higher order multipole moments. This proposed antenna concept could offer utility in various applications, including communications beaconing and radar surveillance.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1751-8784Test; https://doaj.org/toc/1751-8792Test

الوصول الحر: https://doaj.org/article/89cf8c7c2a8e4023864685a0d67cf4a3Test

المؤلفون: Ya Yang, Xiangzhen Kong, Qin Fang

المصدر: Defence Technology, Vol 36, Iss , Pp 30-46 (2024)

مصطلحات موضوعية: Foam concrete, Blast wave propagation, Non-dimensional analysis, Stress enhancement, Military Science

الوصف: Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage. However, stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load. To investigate this interesting phenomenon, a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method. The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement. The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads, stress–strain relation and length of foam concrete are considered. In particular, the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed. Finally, non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data, which can provide a reference for the application of foam concrete in defense engineering.

وصف الملف: electronic resource

العلاقة: http://www.sciencedirect.com/science/article/pii/S2214914723003288Test; https://doaj.org/toc/2214-9147Test

الوصول الحر: https://doaj.org/article/3fcded0f614248e583cdc813a1a5c42eTest