3,972 research outputs found
Frequency resolution quantification of Brillouin distributed optical fibre sensors
No full textNoise analysis using Monte Carlo method is conducted in this paper to correct the relationship between the frequency resolution, the Q-factor, Signal-to-Noise Ratio (SNR), and frequency step in the Brillouin distributed optical fibre sensors. The quantification of the Brillouin gain spectrum is important in distributed Brillouin sensors in order to improve the Brillouin frequency resolution and the corresponding strain and temperature resolutions. Two analytical expressions are derived in order to estimate the error in the determination of the Brillouin central frequency with or without second order polynomialfitting
Dynamic strain measurement using small gain stimulated Brillouin scattering in STFT-BOTDR
No full textA distributed dynamic strain measurement is demonstrated using small gain stimulated Brillouin scattering (SBS) in Brillouin optical time domain reflectometry based on the short-time Fourier transform algorithm. The input power limits, frequency uncertainties for given pulse durations, fiber lengths, and the number of averaging are calculated. The output signal power and the signal-to-noise ratio of the system output are enhanced by SBS. It is found that the signal processing is faster and requires fewer averaging to achieve dynamic sensing performance along the fiber under test. A 60-Hz vibration on a 6-m fiber section at the end of a 935-m fiber is detected with the spatial resolution of 4 m with a sampling rate of 2.5 kS/s
Bai pin pu wang luo zhong de jing ji xue
No full textLuo, Yuan.Thesis Ph.D. Chinese University of Hong Kong 2015.Includes bibliographical references (leaves 273-283).Abstracts also in Chinese.Title from PDF title page (viewed on 01, November, 2016).Luo, Yuan
Frequency uncertainty improvement in a STFT-BOTDR using highly nonlinear optical fibers
No full textThe sensitivity of a sensor to strain or the temperature variations due to distributed Brillouin scattering are partially related to the type of fibers used and the Brillouin scattering induced effective index. In this paper, a highly nonlinear fiber that can generate a higher Brillouin scattering signal is compared to a standard single mode fiber in a short-time-Fourier-transform Brillouin optical time domain reflectometer (STFT-BOTDR). The results show that much higher signal to noise ratios of the Brillouin scattering spectrum and smaller frequency uncertainties in the sensing measurement can be achieved in the highly nonlinear fiber for comparable launched powers. With a measurement speed of 4 Hz, the frequency uncertainty can be 0.43 MHz, corresponding to 10 με in strain or 0.43°C in temperature uncertainty for the highly nonlinear fiber. In contrast, for the standard single mode fiber case, the value would increase to about 1.02 MHz (25 με or 1.02°C), demonstrating the advantage of the highly nonlinear fiber for distributed strain/temperature sensing.</p
Time and frequency localized pulse shape for resolution enhancement in STFT-BOTDR
No full textShort Time Fourier Transform-Brillouin Optical Time Domain Reflectometry (STFT-BOTDR) implements STFT over the full frequency spectrum to measure the distributed temperature and strain along the optic fiber, providing new research advances in dynamic distributed sensing. The spatial and frequency resolution of the dynamic sensing is limited by the Signal to Noise Ratio (SNR) and the Time-Frequency (T-F) localization of the input pulse shape. T-F localization is fundamentally important for the communication system, which suppresses interchannel interference (ICI) and intersymbol interference (ISI) to improve the transmission quality in multi-carrier modulation (MCM). This paper demonstrates that the T-F localized input pulse shape can enhance the SNR, the spatial and frequency resolution in STFT-BOTDR. Simulation and experiments of T-F localized different pulses shapes are conducted to compare the limitation of the system resolution. The result indicates that rectangular pulse should be selected to optimize the spatial resolution, Lorentzian pulse could be chosen to optimize the frequency resolution, while Gaussian shape pulse can be used in general applications for its balanced performance in both spatial and frequency resolution. Meanwhile, T-F localization is proved to be useful in the pulse shape selection for system resolution optimization
Research data supporting “Frequency uncertainty improvement in STFT-BOTDR using highly nonlinear optical fibers”
No full textThe data is for supporting the publication of a journal paper. It is based on experiment by using BOTDR to compare the performance of nonlinear fibre and normal single mode fibre. The date is collected in July 2016. The measurement are repeated 100 times and because of the size, 10 of them are uploaded. If you need more data, please feel free to contact me.</span
Esempio di rappresentazione del sé in Lu Ling 路翎, Luo Dadou de yisheng 罗大斗的一生 (La vita di Luo Dadou)
No full textIn the story Luo Dadou’s life (Luo Dadou de yisheng 罗大斗的一生), Lu Ling 路翎 (1923-1994) gives shape to the deepness of human psyche and stresses the suffering of the Self of his age by giving a brilliant emphasis to human individuality. The author succeeds in doing so by creating an amazing psychological characterization of the main character, both by means of words and by means of grammatical structures. By applying Denton’s categories for the study of the Self in modern Chinese literature, I analysed Lu Ling’s short story from the Freudian and Kleinian psychodynamic perspective, so to demonstrate how Lu Ling enters his characters’ minds and wonderfully recreates the psychological dynamics inside and between them
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