scholarly journals Experimental Study on the Measurement of Water Bottom Vibration Induced by Underwater Drilling Blasting

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Gu Wenbin ◽  
Chen Jianghai ◽  
Wang Zhenxiong ◽  
Wang Zhihua ◽  
Liu Jianqing ◽  
...  
Keyword(s):  
Experimental Study ◽  
Field Experiment ◽  
Frequency Band ◽  
Signal Analysis ◽  
Low Frequency ◽  
Ground Vibration ◽  
Frequency Component ◽  
Vibration Signals ◽  
Attenuation Laws ◽  
Water Bottom

Due to the lack of proper instrumentations and the difficulties in underwater measurements, the studies about water bottom vibration induced by underwater drilling blasting are seldom reported. In order to investigate the propagation and attenuation laws of blasting induced water bottom vibration, a water bottom vibration monitor was developed with consideration of the difficulties in underwater measurements. By means of this equipment, the actual water bottom vibration induced by underwater drilling blasting was measured in a field experiment. It shows that the water bottom vibration monitor could collect vibration signals quite effectively in underwater environments. The followed signal analysis shows that the characteristics of water bottom vibration and land ground vibration induced by the same underwater drilling blasting are quite different due to the different geological environments. The amplitude and frequency band of water bottom vibration both exceed those of land ground vibration. Water bottom vibration is mainly in low-frequency band that induced by blasting impact directly acts on rock. Besides the low-frequency component, land vibration contains another higher frequency band component that induced by followed water hammer wave acts on bank slope.

scholarly journals Comparison of Frequency Bands Using Spectral Entropy for Epileptic Seizure Prediction

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Susana Blanco ◽  
Arturo Garay ◽  
Diego Coulombie
Keyword(s):  
Frequency Band ◽  
Epileptic Seizure ◽  
Signal Analysis ◽  
Fourier Spectrum ◽  
Low Frequency ◽  
Eeg Signals ◽  
High Frequencies ◽  
Frequency Bands ◽  
Low Correlation ◽  
Rate Of Increase

Introduction. Under the hypothesis that the uncontrolled neuronal synchronization propagates recruiting more and more neurons, the aim is to detect its onset as early as possible by signal analysis. This synchronization is not noticeable just by looking at the EEG, so mathematical tools are needed for its identification. Objective. The aim of this study is to compare the results of spectral entropies calculated in different frequency bands of the EEG signals to decide which band may be a better tool to predict an epileptic seizure. Materials and Methods. Invasive ictal records were used. We measured the Fourier spectrum entropy of the electroencephalographic signals 4 to 32 minutes before the attack in low, medium and high frequencies. Results. The high-frequency band shows a markedly rate of increase of the entropy, with positive slopes and low correlation coefficient. The entropy rate of growth in the low-frequency band is practically zero, with a correlation around 0.2 and mostly positive slopes. The mid-frequency band showed both positive and negative slopes with low correlation. Conclusions. The entropy in the high frequencies could be predictor, because it shows changes in the previous moments of the attack. Its main problem is the variability, which makes it difficult to set the threshold that ensures an adequate prediction.

Contact Current Density Analysis Inside Human Body in Low-Frequency Band Using Geometric Multi-Grid Solver

2020 ◽  
Vol E103.C (11) ◽  
pp. 588-596
Author(s):  
Masamune NOMURA ◽  
Yuki NAKAMURA ◽  
Hiroo TARAO ◽  
Amane TAKEI
Keyword(s):  
Frequency Band ◽  
Current Density ◽  
Human Body ◽  
Low Frequency ◽  
Density Analysis

Low Frequency Noise from a Big Building Due to Oscillatory Forces of a Machine

1982 ◽  
Vol 1 (1) ◽  
pp. 22-27 ◽  
Author(s):  
Niichi Nishiwaki ◽  
Noboru Fujio ◽  
Takuji Mori
Keyword(s):  
Low Frequency ◽  
Ground Vibration ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Ground Acceleration ◽  
Building Frames ◽  
Acceleration Level ◽  
Residential District ◽  
Factory Building ◽  
Grinding Mill

People living in houses near a big factory complained about chattering of glass windows. At one of these houses, the SPL of low frequency noise was about 66 dB at 5.5 Hz and ground acceleration level was about 40 dB at 9 Hz in the horizontal direction. (0 dB acceleration = 10−5 m/s2). We found that the noise and ground vibration were caused by a big grinding mill in the factory, because both SPL and acceleration level at the residential district were considerably decreased when the mill was not in operation. We also confirmed that low frequency noise was not transmitted from the grinding mill directly, but was due to the resonant vibration of walls of the factory building. Two ideas are studied here to suppress the noise, one of which is to isolate the vibration of the grinding mill at its foundation, and the other is to improve the stiffness of the building frames to stop the wall vibration. As a result of the study, the latter method to increase the stiffness of the building was adopted. The SPL of low frequency noise near the wall was decreased.

scholarly journals Spillovers of Stock Markets among the BRICS: New Evidence in Time and Frequency Domains before the Outbreak of COVID-19 Pandemic

2021 ◽  
Vol 14 (3) ◽  
pp. 112
Author(s):  
Kai Shi
Keyword(s):  
Stock Market ◽  
Frequency Band ◽  
Stock Markets ◽  
Emerging Market ◽  
Low Frequency ◽  
Systematic Risk ◽  
Error Variance ◽  
Frequency Bands ◽  
Volatility Spillovers ◽  
Risk Sources

We attempted to comprehensively decode the connectedness among the abbreviation of five emerging market countries (BRICS) stock markets between 1 August 2002 and 31 December 2019 not only in time domain but also in frequency domain. A continuously varying spillover index based on forecasting error variance decomposition within a generalized abbreviation of vector-autoregression (VAR) framework was computed. With the help of spectral representation, heterogeneous frequency responses to shocks were separated into frequency-specific spillovers in five different frequency bands to reveal differentiated linkages among BRICS markets. Rolling sample analyses were introduced to allow for multiple changes during the sample period. It is found that return spillovers dominated by the high frequency band (within 1 week) part declined with the drop of frequencies, while volatility spillovers dominated by the low frequency band (above 1 quarter) part grew with the decline in frequencies; the dynamics of spillovers were influenced by crucial systematic risk events, and some similarities implied in the spillover dynamics in different frequency bands were found. From the perspective of identifying systematic risk sources, China’s stock market and Russia’s stock market, respectively, played an influential role for return spillover and volatility spillover across BRICS markets.

The Lightning Electromagnetic Pulse Coupling Effect Inside the Shielding Enclosure With Penetrating Wire

Frequenz ◽  
2017 ◽  
Vol 71 (11-12) ◽  
Author(s):  
Xue Jiao ◽  
Bo Yang
Keyword(s):  
Electromagnetic Pulse ◽  
Coupling Effect ◽  
Fdtd Method ◽  
Current Source ◽  
Low Frequency ◽  
Frequency Component ◽  
Lightning Current ◽  
Proper Size ◽  
Practical Engineering ◽  
Difference Time

AbstractTo study the lightning electromagnetic pulse (LEMP) coupling and protection problems of shielding enclosure with penetrating wire, we adopt the model with proper size which is close to the practical engineering and the two-step finite-difference time-domain (FDTD) method is used for calculation in this paper. It is shown that the coupling voltage on the circuit lead inside the enclosure increases about 34 dB, when add 1.0 m long penetrating wire at the aperture, comparing with the case without penetrating wire. Meanwhile, the waveform, has the same wave outline as the lightning current source, shows that the penetrating wire brings a large number of low frequency component into the enclosure. The coupling effect in the enclosure will reduce greatly when penetrating wire has electrical connection with the enclosure at the aperture and the coupling voltage increase only about 12 dB than the case without penetrating wire. Moreover, the results show that though the waveguide pipe can reduce the coupling effect brought by the penetrating wire, the exposing part of penetrating wire can increase the coupling when the penetrating wire outside the enclosure is longer than the waveguide pipe and the longer the exposing part is, the stronger the coupling is.

Locally resonant periodic structures with low-frequency band gaps

2013 ◽  
Vol 114 (3) ◽  
pp. 033532 ◽  
Author(s):  
Zhibao Cheng ◽  
Zhifei Shi ◽  
Y. L. Mo ◽  
Hongjun Xiang
Keyword(s):  
Frequency Band ◽  
Periodic Structures ◽  
Low Frequency ◽  
Band Gaps
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