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The precursors that appear when geological disasters occur are geotechnical deformations. This paper studies the TDR (Time Domain Reflection) measurement technology for the distributed measurement of geotechnical deformation using parallel spiral wire as a sensor, which is used for monitoring and early warning detection of geological disasters. Based on the mechanism of the electromagnetic field distribution parameters of the parallel spiral sensing wire, the relationship between the stretching amount of the parallel spiral wire and the change in its characteristic impedance is analyzed. When the parallel spiral wire is buried in the soil, the geotechnical deformation causes the parallel spiral wire to be stretched, and according to its characteristic impedance change, the stretching position and the stretching degree can be obtained, thus realizing the distributed measurement of geotechnical deformation. Based on this principle, the TDR measurement system is developed, and a local single-point stretching amount and stretching positioning experiment are designed for the parallel spiral sensing line to verify the effectiveness of the sensing technology and the usability of the measurement system.

In this paper, a periodic array of Ag nanocones and Al2O3/Si nanopillars (AgNCs–Al2O3/SiNPs) deposited on a semiconductor substrate is designed, and their anti-reflection property is investigated systematically using the finite difference time domain method (FDTD). The obtained results show that the designed structure achieves a weighted reflectance as low as 1.99% over a broad spectral range of 400–1100 nm. The anti-reflection mechanism of the AgNC–Al2O3/SiNP array is elucidated through calculations of the scattering cross-section and electric field distribution of the AgNC array. The localized surface plasmon resonance (LSPR) effects of AgNC array, together with the multiple scattering and reflection effects of the SiNP array, can reduce the reflectance to some extent. Furthermore, the introduction of Al2O3 spacer layer leads to an additional decrease in reflectivity. In addition, the reflective properties of three alternative metal nanocones (Al, Cu, and Au), combined with the Al2O3/SiNP array on a Si substrate, are evaluated. Among these composite structures, the CuNC–Al2O3/SiNP array exhibits the lowest reflectivity of 1.66%. This study enriches the localized surface plasmon model and provides a theoretical foundation for the design of plasmonic solar cells and other optoelectronic devices requiring low reflectivity.

Terahertz time-domain spectroscopy (THz-TDS) allows broadband noninvasive measurement of the optical parameters of various materials in the THz domain. The measurement accuracy of these parameters is highly influenced by the difficulty in distinguishing THz signals from unwanted signals such as noise, signal fluctuation, and multiple echoes, which directly affects material identification and characterization efficiency. We introduce a novel method that provides effective extraction and separation of THz signals from such undesired effects. The proposed algorithm was assessed through experiments that presented enhancement in material parameter evaluation, such as the decomposition of the sample-induced echoes (SIEs) from the complex THz sample signal with near-zero extraction error. Improved precision ( ± 0.05 μ m) was achieved in the determination of the sample thickness compared to that of the mechanical method ( ± 10 μ m). Furthermore, we could infer from the component concentration measurement results of a compound sample (44.2 % decrease in the root mean square concentration error) that the material parameter calculation accuracy had improved, proposing a means to enhance the ultimate nondestructive material evaluation performance.

A mathematical model describing the processing of measurement information in the course of determining the reflection and transmission factors of radar-absorbing materials by means of sounding with the use of ultra-short electromagnetic pulses is proposed. The use of the method of kernel smoothing to eliminate the influence of the noise of the measurement equipment as well as a Fourier window transform for the purpose of realizing a transition to the frequency domain is evaluated. Estimation of the random and systematic measurements is carried out.

The deterministic Skorohod problem plays an important role in the construction and analysis of diffusion processes with reflection. In the form studied here, the multidimensional Skorohod problem was introduced, in time-independent domains, by H. Tanaka [61] and further investigated by P.-L. Lions and A.-S. Sznitman [42] in their celebrated article. Subsequent results of several researchers have resulted in a large literature on the Skorohod problem in time-independent domains. In this article we conduct a thorough study of the multidimensional Skorohod problem in time-dependent domains. In particular, we prove the existence of càdlàg solutions (x, λ) to the Skorohod problem, with oblique reflection, for (D, Γ, w) assuming, in particular, that D is a time-dependent domain (Theorem 1.2). In addition, we prove that if w is continuous, then x is continuous as well (Theorem 1.3). Subsequently, we use the established existence results to construct solutions to stochastic differential equations with oblique reflection (Theorem 1.9) in time-dependent domains. In the process of proving these results we establish a number of estimates for solutions to the Skorohod problem with bounded jumps and, in addition, several results concerning the convergence of sequences of solutions to Skorohod problems in the setting of time-dependent domains.

This paper presents a computational technique for mono-static and bi-static scattering from underwater objects of different shape such as submarines. The scatter has been computed using finite element time domain (FETD) method, based on the superposition of reflections, from the different elements reaching the receiver at a particular instant in time. The results calculated by this method has been verified with the published results based on ramp response technique. An in-depth parametric study has been carried out, by considering different pulse frequency, pulse length, pulse type (CW, LFM, SFM), sampling frequency, as well as different size, shape of the scattering body and grid size. It has been observed that increasing the pulse frequency, sampling frequency and number of elements leads to improved results. However, good amount of accuracy has been achieved with element size less than one third of wave length. The experimental result of the underwater object has been found very close to the 'simulated result. This technique is useful for computing forward scatter for inverse scattering applications and as well as to generate forward scatter of very narrow and wide band signals of any pulse type and shape of body.