共查询到20条相似文献,搜索用时 0 毫秒
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The transmission properties of compound frequency selective structures with dielectric slab and air gaps were investigated by computation and experimentation.Mechanism analyses were also carried out.Results show that the air gaps have a distinct influence on the transmission properties.Resonant frequency of the structure would increase rapidly when the air gap appears.After the gap gets larger to a specific value,generally 1/5 wavelength corresponding to the resonant frequency,the transmission properties would change periodically with the gap thickness.The change of transmission properties in one period has a close relationship with the dielectric thickness.These results provide a new method for designing a bandpass radome of large incidence angle and low loss with the concept of stealth shield radome. 相似文献
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The generation and evolution of magnetic inhomogeneities of the stationary breather type, which appear in a flat layer with the magnetic anisotropy and exchange interaction parameters that are different from those in the bulk of an infinite ferromagnet after transmission through a 180° domain wall, have been investigated theoretically. The dependences of the amplitude and frequency of vibrations on the parameters of the defect have been constructed for the revealed magnetic inhomogeneities, and the ranges of the parameters determining the possibility of their existence have been found. 相似文献
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V. P. Kazantsev 《Russian Physics Journal》1980,23(12):1034-1037
It is shown that the effective conductivity tensor of an inhomogeneous sample of finite size is not determined uniquely. Boundary conditions corresponding to extremal values of this tensor are found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 58–61, December, 1980. 相似文献
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Long-range reverberation in a randomly inhomogeneous shallow water with the use of focused radiation
The low-frequency bottom reverberation in a randomly inhomogeneous shallow water is investigated within the framework of a numerical experiment using vertical transmitting arrays focusing the acoustic field at various distances from the sea bottom. It is assumed that the main source of sound velocity fluctuations in the medium is represented by background internal waves. To focus the field, a phase conjugation of acoustic waves from a probe source positioned at the focusing point is used. It is demonstrated that the reverberation level is mainly determined by the presence of internal waves and may vary by 5–20 dB as the distance from the focusing point to the sea bottom increases up to H/2, where H is the channel depth. 相似文献
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Erdal Panay?rc? Hakan Do?an Hakan A. ??rpan Alexander Kocian Bernard H. Fleury 《Physical Communication》2010,3(2):87-96
This paper is concerned with joint multiuser detection and multichannel estimation (JDE) for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency selective channels. The detection and estimation, implemented at the receiver, are based on a version of the expectation maximization (EM) algorithm and the space-alternating generalized expectation–maximization (SAGE) which are very suitable for multicarrier signal formats. The EM-JDE receiver updates the data bit sequences in parallel, while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithms have excellent BER end estimation performance. 相似文献
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《Infrared physics》1990,30(2):149-153
Because of the lack of theory and methods of measuring the ambient radiation in real situations, it is impossible to quantify the self-radiation properties of a target. Our earlier paper,(13) proposed a theory, “Equivalent Blackbody Radiation Theory,” and a design method for infrared systems that can measure quantitatively the ambient radiation and self-radiating properties of opaque targets. We now extend our treatment to the more general case which includes opaque, semi-transparent and transparent objects. As examples, the ambient radiation in different situations, the self-radiation properties of an opaque metal plate and a semi-transparent crystal, and the true temperature difference of human breath during inspiration and exhalation are measured quantitatively and successfully. 相似文献
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A. A. Snarskii K. V. Slipchenko I. V. Bezsudnov 《Journal of Experimental and Theoretical Physics》1998,86(4):811-814
An exact relation for the realization-averaged effective conductivities in the fractal region is found for two-dimensional
randomly inhomogeneous media. It has the form {σ
e
(τ,L)~× {1/σ
e
(−τ,L)~−1=σ
e
2
(τ=0, L≫ξ), where ξ is the correlation length (the self-averaging scale), L is the size of the system, τ=(p-p
c
)/p
c
, and p
c
is the percolation threshold. For L≫ ξ, the system is self-averaged, and the relation transforms into the Dykhne reciprocity relation, A. M. Dykhne, Zh. éksp. Teor.
Fiz. 59, 110 (1970) [Sov. Phys. JETP 32, 63 (1971)] σ
e
(τ)σ
e
(−τ])=σ
e
2
(τ=0)= σ
1
σ
2. A similar relation is obtained for media with an exponentially broad distribution of local conductivities, as well as for
individual realizations of some deterministic structures.
Zh. éksp. Teor. Fiz. 113, 1484–1490 (April 1998) 相似文献
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Radiophysics and Quantum Electronics - 相似文献
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Yu. N. Barabanenkov M. Yu. Barabanenkov 《Journal of Experimental and Theoretical Physics》1998,86(2):237-243
The propagation of a quasimonochromatic wave packet of acoustic radiation in a discrete randomly-inhomogeneous medium under
the condition that the carrier frequency of the packet is close to the resonance frequency of Mie scattering by an isolated
scatterer is studied. The two-frequency Bethe-Salpeter equation in the form of an exact kinetic equation that takes account
of the accumulation of the acoustic energy of the radiation inside the scatterers is taken as the initial equation. This kinetic
equation is simplified by using the model of resonant point scatterers, the approximation of low scatterer density, and the
Fraunhofer approximation in the theory of multiple scattering of waves. This leads to a new transport equation for nonstationary
radiation with three Lorentzian delay kernels. In contrast to the well-known Sobolev radiative transfer equation with one
Lorentzian delay kernel, the new transfer equation takes account of the accumulation of radiation energy inside the scatterers
and is consistent with the Poynting theorem for nonstationary acoustic radiation. The transfer equation obtained with three
Lorentzian delay kernels is used to study the Compton-Milne effect—trapping of a pulse of acoustic radiation diffusely reflected
from a semi-infinite resonant randomly-inhomogeneous medium, when the pulse can spend most of its propagation time in the
medium being “trapped” inside the scatterers. This specific albedo problem for the transfer equation obtained is solved by
applying a generalized nonstationary invariance principle. As a result, the function describing the scattering of a diffusely
reflected pulse can be expressed in terms of a generalized nonstationary Chandrasekhar H-function, satisfying a nonlinear integral equation. Simple analytical asymptotic expressions are found for the scattering
function for the leading and trailing edges of a diffusely reflected δ-pulse as functions of time, the reflection angle, the mean scattering time of the radiation, the elementary delay time, and
the parameter describing the accumulation of radiation energy inside the scatterers. These asymptotic expressions demonstrate
quantitatively the retardation of the growth of the leading edge and the retardation of the decay of the trailing edge of
a diffusely reflected δ-pulse when the conventional radiative transfer regime goes over to a regime of radiation trapping in a resonant randomly-inhomogeneous
medium.
Zh. éksp. Teor. Fiz. 113, 432–444 (February 1998) 相似文献
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A solution of the problem of ray diffusion in a randomly inhomogeneous medium is used to find the statistical properties of multiray fields. The longitudinal-coordinate dependence for the average ray number and the Lagrangian mean-square ray-tube divergence, which is related to the Eulerian mean of a quantity which is inversely proportional to intensity, is obtained.Nizhnii Novgorod Academy of Architecture and Civil Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 3, pp. 323–329, March, 1994. 相似文献
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G. Carbone B. Lorenz B. N. J. Persson A. Wohlers 《The European physical journal. E, Soft matter》2009,29(3):275-284
In this paper we extend the theory of contact mechanics and rubber friction developed by one of us (B.N.J. Persson, J. Chem.
Phys. 115, 3840 (2001)) to the case of surfaces with anisotropic surface roughness. As an application we calculate the viscoelastic
contribution to the rubber friction. We show that the friction coefficient may depend significantly on the sliding direction,
while the area of contact depends weakly on the sliding direction. We have carried out experiments for rubber blocks sliding
on unidirectionally polished steel surfaces. The experimental data are in a good qualitative agreement with the theory. 相似文献
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Acoustical Physics - A method for calculating the resulting field of an opaque radiator and the field scattered by an inhomogeneous inclusion in a planar layered waveguide is described. The... 相似文献