Dielectric loss and electromagnetic absorption performance study of 1T/2H-MoS2/Mo2S3 nanocomposites with different ratios

High dielectric loss materials have an important application in electromagnetic (EM) absorption fields. In this paper, the ternary nanocomposites: 1T/2H-MoS₂/Mo₂S₃ with heterogeneous interfaces are synthesized by hydrothermal method. XRD, XPS, FTIR, SEM, and TEM measurements are applied to study the structure, morphology, and composition. The frequency spectra of complex permittivity (ε_r-f) are measured in 2–18 GHz by vector network analyzer. The results show that the nanocomposites have higher dielectric loss angle tangents than the reported 2H-MoS₂ absorbers. Based on the ε_r-f spectra, the reflection loss-frequency curves ($RL-f$) are simulated at given thicknesses. An effective absorption bandwidth of 5.2 GHz (12.8–18 GHz) and a $RL$ peak of −29.49 dB are achieved in a thin thickness of 1.62 mm, which are comparable to the reported 2H-MoS₂ absorbers with complex composition, showing that the 1T/2H-MoS₂/Mo₂S₃ nanocomposites have great application potential as an EM wave absorber in the K_u band.     

周期性管柱信道的声波通信技术研究综述

井下声波通信技术利用周期性管柱信道实时传输声波数据，相比于其他通信方式，具有适应性好、复杂度低、传输效率高等优点，在随钻地质导向、油水井监测等方面有广阔的应用前景，是发展智能油田的关键技术之一。本文主要综述上世纪90年代以来关于信道物理模型、信道容量、声信号调制与接收方法等关键问题的研究历程，并对通信系统的设计要点与国内外相关产品的现场应用进行梳理，为后续的技术改进提供依据。     

Periodic Solutions of the Duffing Differential Equation Revisited via the Averaging Theory

We use three different results of the averaging theory of first order for studying the existence of new periodic solutions in the two Duffing differential equations $\ddot y+ a \sin y= b \sin t$ and $\ddot y+a y-c y^3=b\sin t$, where $a$, $b$ and $c$ are real parameters.     

Human-to-metal electrostatic discharge current measurements – Notes on the ESD current waveform

The Electrostatic Discharge (ESD) phenomenon has been described through the IEC 61000-4-2. ESD current parameters' values, have been set in this Standard. The theoretical ESD current waveform defined in this standard, describing the conventional Contact discharge mode, needs to be re-evaluated on the basis of accurate experimental data. Even though the standard deals with commercial ESD generators, its goal is to simulate the natural phenomenon as good as possible. More and accurate data may contribute to the better simulation of the natural phenomenon. New values and better comprehension of the phenomenon demand new measurements based on high end measuring equipment. Such works and publications have been carried out the past years. Yet, the need to systematize and integrate this work remains. Larger and trust-worthy series of measurements need to be carried out and presented clearly.This paper deals with new ESD-current data, taken with broadband equipment. New and more detailed measurements like these, were never before taken at such a large number of individuals. The goal of this work is that the data acquired can serve as a basis for re-evaluating the conventional approach of the scientific community to the ESD event.In this paper, using a broadband measuring system, new parameters' values are measured and relations are presented, following standard statistical procedures. The results, which occur from measurements carried out on tenths of human individuals, are questioning the Standard in many points. A new way of approaching the standardization of the ESD current is proposed, as the excuse of the poor measuring equipment that sets barriers on the measuring accuracy, does not apply any more. The charging voltages of 500 V and 1000 V were also examined since such range of voltages are often met at ESD events and they are considered very harmful.