China
Africa
Explore chapters and articles related to this topic
Antennas or aerials
Published in Geoff Lewis, Communications Technology Handbook, 2013
300 kHz to 3 MHz (medium frequency, MF). This part of the frequency spectrum is used chiefly for the national medium wave broadcasting services. In general this requires an all-round coverage from any given transmitter. At these higher frequencies, a vertical antenna structure can meet this requirement. For a 1 MHz transmission, the λ/2 mast is now only 150 metres high and if fed as a dipole will provide all-round coverage. Alternatively a quarter-wave-high mast can be used to support conductors arranged as a folded dipole (see Half-wave dipoles, p. 31).
Effect of bedding angle on tunnel slate failure behavior under indirect tension
Published in Geomatics, Natural Hazards and Risk, 2020
Han Wang, Fuqiang Ren, Yuan Chang
The AE amplitude and peak frequency are the main parameters of AE characteristics. The peak frequency of AE signal can be obtained from the fast Fourier transform of AE waveform. In this study, the AE amplitude and peak frequency are presented together with the loading curve, as shown in Figure 13. During the Brazilian splitting tests, the maximum AE amplitude was less than 80 dB; the peak frequency ranged from 0 to 300 kHz. Three frequency bands were divided according to the range of peak frequency: low frequency (0–100 kHz), medium frequency (100–200 kHz), high frequency (200–300 kHz). Similarly, the amplitude was divided into four levels: low amplitude (40–50 dB), medium amplitude (50–60 dB), high amplitude (60–70 dB), and ultrahigh amplitude (70–80 dB).
The effect of MHD flow on hydrothermal characteristics of ferro-nano-fluid in circular pipe
Published in Experimental Heat Transfer, 2023
Edip Taşkesen, Mutlu Tekir, Hayati Kadir Pazarlıoğlu, Mehmet Gurdal, Engin Gedik, Kamil Arslan
As can be seen in the above-mentioned articles, the usage of MF on the thermal system applications increases the disruption of the thermal boundary layer and fluctuation of fluid flow inside the system with the help of magnetic force on NPs. Then, the usage of MF also significantly enhances the heat transfer rate compared to the absence of MF. Nonetheless, the use of MF in the system also increases pressure drop, which highly affects the performance evaluation criteria (PEC) and cost of operation. Hence, pressure drop should be monitored when the MF is used on the system. From the literature review, the usage of MF with different NFVC represents the minority, and data for constant MF with different NFVC in a circular pipe is extra limited. In this context, it is thought that the investigation of the MF effect with different NFVC will contribute to the literature. In this study, the effect of the MF (B= 0.3 T) on the convective heat transfer characteristics of Fe3O4/H2O flow with three different NFVC (1.0%, 2.0%, and 5.0% vol.) in a cylindrical cross-sectioned pipe has been investigated experimentally. The effect of different NFVC under MF on the thermal performance has been analyzed in detail to find the optimum value of NFVC of FNF, which will contribute to the literature. Besides, although there are studies on the MF effect for a more limited concentration range in the literature, a broad perspective analysis has not been done yet. Therefore, this study provides validation to researchers working at concentrations between 1% and 5%, and fills the gap in the literature. Moreover, the experimental nature of the study provides to researchers the opportunity to compare it with numerical studies under the same conditions. In this study, experimental analyses have been conducted under laminar regime (1000≤ Re≤2300). Finally, the main findings and recommendations of this study have been given in conclusion.