partial reflection
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2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tania Tamoor ◽  
Nosherwan Shoaib ◽  
Fahad Ahmed ◽  
Tayyab Hassan ◽  
Abdul Quddious ◽  
...  

AbstractIn this paper, a flexible bianisotropic metasurface possessing omega-type coupling is presented. The designed metasurface behaves differently when excited from either forward (port 1) or back (port 2) sides. It provides an absorption of 99.46% at 15.1 Gigahertz (GHz), when illuminated from port 1, whereas, on simultaneous illumination from port 2, it behaves like a partially reflective surface (PRS). Furthermore, the presented metasurface not only acts as an in-band absorptive surface (port 1) and partially reflective surface (port 2), but it also provides 97% out-of-band transmission at 7.8 GHz. The response of the presented metasurface remains the same for both transverse Electric (TE) and transverse magnetic (TM) polarized wave or any arbitrary linearly polarized wave. Additionally, the response of the metasurface is angularly stable for any oblique incidence up to 45º. The proposed ultrathin flexible metasurface with absorption, partial reflection and out-of-band transmission properties can be used in the Fabry Perrot cavity antenna for gain enhancement with radar cross-section (RCS) reduction both for passband and stop-band filtering, and conformal antenna applications.


Author(s):  
Pavel Bulat ◽  
Anzhelika Melnikova ◽  
Konstantin Volkov ◽  
Vladimir Upyrev

Refraction of an oblique shock wave on a tangential discontinuity dividing two gas flows with different properties is considered. It is shown that its partial reflection occurs excepting of geometrical diffraction of an oblique shock. Another oblique shock, expansion wave or weak discontinuity that coincides with Mach line, can act as a reflected disturbance. This study focuses on relationships which define the type of reflected discontinuity and its parameters. Domains of existence of various shock-wave structures with reflected disturbances of two types and boundaries between them are defined. The domains of parameters with one or two solutions exist for the characteristic refraction. Conditions of the regular refraction and the Mach refraction are formulated, and boundaries between those two refraction types are defined for various types of gases. Refraction phenomena in various engineering problems (hydrocarbon gaseous fuel and its combustion products, diatomic gas, fuel mixture of oxygen and hydrogen etc.) are discussed.


2021 ◽  
Vol 46 (5) ◽  
pp. 957
Author(s):  
Jiancheng Deng ◽  
D. V. Churkin ◽  
Zuowei Xu ◽  
Xuewen Shu

2021 ◽  
Vol 4 ◽  
Author(s):  
Peter Richards

For much of the past two decades, the scientific and policy community has sought to reduce forest loss through well-targeted public policy and enforcement measures and private sector engagement. Unfortunately, recent increases in forest loss in the Amazon have raised new concerns over the drivers of deforestation in the region, and the durability of the policies designed to mitigate it. Here we argue that recent deforestation trends are a partial reflection of Brazil's economic trajectories. In this article we show that poor economic conditions, nationally, will increase micro-level incentives for forest clearing. Conversely, economic growth, nationally, will suppress prices and land clearing incentives. Ultimately, we argue that, at the national-scale, economic growth may be closely aligned with, and possibly a pre-condition to, the attainment of international or national-level environmental goals.


Author(s):  
L. M. Tereshchen ◽  
V. V. Khomicky ◽  
V. O. Tkachenko ◽  
I. A. Nikitin ◽  
A. G. Kharchenko ◽  
...  

This paper presents the results of mathematical and physical modeling of the interaction of waves with the wave chamber on cylindrical supports and the upper part in the form of a permeable waterfront. On the basis of the diffraction model the mathematical modeling of refraction and transformation of waves near the structure is carried out. In the presence of a structure, the transformation of waves is co-accompanied by the phenomena of wave destruction at the edges of the structure and the partial reflection of residual waves from the walls of the protective front. Reflection phenomena cause changes in wave heights along the front of the structure. The results of experimental data are given, which showed that the structure with such a construction is resistant to waves, large soil erosion was not observed.


2020 ◽  
Author(s):  
S.M. Cherniakov ◽  
◽  
V.A. Turyansky ◽  

The behavior of the ordinary radio wave amplitude at the frequency of 2.66 MHz of the partial reflection radar of the Polar Geophysical Institute (Tumanny observatory, Murmansk region, 69.0N, 35.7E) during the appearance of the polar mesospheric summer echoes on August 15, 2015 was considered. Using of radio physical method from the spectra of the amplitude at different heights the mesospheric temperature profile was calculated for the considered data. Significant reductionof temperature values near the heights of the mesopause corresponded to sharp changes in the amplitude spectra of the ordinary wave.


2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
A.I. Semenikhin ◽  
◽  
D.V. Semenikhin ◽  

The problem of arbitrary excitation of waves by a system of external sources near an anisotropic metasurface in the form of an elliptical cylinder with a surface homogenized impedance tensor of general form is solved. The solution to the problem is written as a superposition of E- and H-waves in elliptical coordinates. The partial reflection coefficients of waves were found from the boundary conditions using the orthogonality of the Mathieu angular functions. For these coefficients, four coupled infinite systems of linear algebraic equations of the second kind are obtained. The conditions under which the solution of the excitation problem by the method of eigenfunctions is obtained in an explicit form are found and analyzed. It is shown that for this, the surface impedance tensor of a uniform metasurface must belong to a class of deviators (have zero diagonal elements). In the particular case of a mutual (most easily realized) metasurface, its impedance tensor should only be reactance. In another special case, the impedance tensor of a set of deviators describes a class of anisotropic nonreciprocal metasurfaces with the so-called perfect electromagnetic conductivity (PEMC).


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