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Fiber-optic distributed acoustic sensing (DAS) has proven to be a revolutionary technology for the detection of seismic and acoustic waves with ultralarge scale and ultrahigh sensitivity, and is widely used in oil/gas industry and intrusion monitoring. Nowadays, the single-frequency laser source in DAS becomes one of the bottlenecks limiting its advance. Here, we report a dual-comb-based coherently parallel DAS concept, enabling linear superposition of sensing signals scaling with the comb-line number to result in unprecedented sensitivity enhancement, straightforward fading suppression, and high-power Brillouin-free transmission that can extend the detection distance considerably. Leveraging 10-line comb pairs, a world-class detection limit of 560 fε/√Hz@1 kHz with 5 m spatial resolution is achieved. Such a combination of dual-comb metrology and DAS technology may open an era of extremely sensitive DAS at the fε/√Hz level, leading to the creation of next-generation distributed geophones and sonars.

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OBJECTIVE: To study the differential metabolites in urine and the characteristics of metabolic pathway of middle school students with chronic fatigue syndrome (CFS) before and after exercise, and then explain the metabolic mechanism of CFS. METHODS: Eight male middle school students (age:17-19) with CFS were selectedas the CFS group according to CFS screening criteria of the U.S. centers.At the same time, 8 male health students of the same age from the same school were selected as the control group. They were administrated to do one-time exercise on the improved Harvard step (up and down steps 30 times/min for 3minutes). Their urinewascollected before and after exercise, and the differential metabolitesin urine were detected by liquid chromatography-mass spectrometry (LC-MS). The multidimensional statistical methods were used to analyze the metabolites by principal component analysis (PCA) and orthogonal projections to latent structures-discriminant analysis (OPLS-DA). Finally, MetPA database was used to analyze the metabolites and to construct the correlativemetabolic pathways. RESULTS: Compared with the control group, the creatine, indoleacetaldehyde, phytosphingosine and pyroglutamic acid were selected as differential metabolites and the contents of those were decreased significantly (P<0.05 or P<0.01) in CFS groupbefore the step movement. However, 11 differential metabolitesin CFS group were selected out after exercise, which were nonanedioic acid, methyladenosine, acetylcarnitine, capric acid, corticosterone, creatine, levonorgestrel, pantothenic acid, pyroglutamic acid, xanthosine and xanthurenic acid in sequence, the contents of methyladenosine and creatinewere significantly increased (P<0.05) and the contents of the other 9 differentialmetabolites were significantly decreased (P<0.05 or P<0.01)compared with the control group.The 15 differential metabolites mentioned above were input MetPA database in order to analyze the metabolic pathways weighted score.The results showed that the arginine-proline metabolism pathway disordersweredetected in theCFS group before exercise, the marker metabolite wascreatine. And 3 metabolic pathwaysdisorder weredetectedin the CFS groupafter exercise, which were arginine-proline metabolism, biosynthesis of pantothenic acid and CoA, steroid hormone biosynthesis, and the marker metabolites, in turn, werecreatine, pantothenic acid and corticosterone. CONCLUSIONS: The disorder of arginine-proline metabolic pathway is detected in CFS middle school students before exercise intervention. After exercise, it can be detected that the steroid hormone biosynthetic metabolic pathway, pantothenic acid and CoA metabolic pathways also have metabolic disorders.

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PURPOSE: Data about the association between serum uric acid and metabolic syndrome in healthy adolescents are sparse. This study examined this association and determined the optimal cutoffs for serum uric acid to predict metabolic syndrome among healthy adolescents. METHODS: During 2010-2011, we conducted a cross-sectional study of 927 adolescents (53.0% boys) aged 11-16 years from junior and senior high schools in northeast China. All participants received a physical examination and gave venous blood samples. RESULTS: Serum uric acid was positively associated with abdominal obesity, dyslipidemia and hypertension in boys and with abdominal obesity and dyslipidemia in girls. For those with hyperurecemia, the odds ratios (95% CI) for metabolic syndrome were 7.67 (95% CI, 2.58~22.78) for boys and 4.77 (95% CI, 1.01~22.60) for girls. SUA was a better predictor of metabolic syndrome than fasting glucose, though not as good as waist circumference. CONCLUSIONS: Among adolescents in China, serum uric acid level may be a useful predictor of metabolic syndrome.

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All-optical temporal integrator using phase-shifted distributed-feedback semiconductor optical amplifier (DFB-SOA) is investigated. The influences of system parameters on its energy transmittance and integration error are explored in detail. The numerical analysis shows that, enhanced energy transmittance and integration time window can be simultaneously achieved by increased injected current in the vicinity of lasing threshold. We find that the range of input pulse-width with lower integration error is highly sensitive to the injected optical power, due to gain saturation and induced detuning deviation mechanism. The initial frequency detuning should also be carefully chosen to suppress the integration deviation with ideal waveform output.

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A novel optical amplification configuration based on ultra-long fiber laser with a ring cavity was proposed and applied to Brillouin optical time-domain analysis (BOTDA) sensing system, in order to extend the measurement distance significantly. The parameters used in the experiment were optimized, considering the main limitations of the setup, such as depletion, self-phase modulation (SPM) and pump-signal relative intensity noise (RIN) transfer. Through analyzing Brillouin gain spectrum, we demonstrated distributed sensing over 94 km of standard single-mode fiber with 3 meter spatial resolution and strain/temperature accuracy of 28 /1. 4 degree C.

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An ultra-long phase-sensitive optical time domain reflectometry (Φ-OTDR) that can achieve high-sensitivity intrusion detection over 131.5km fiber with high spatial resolution of 8m is presented, which is the longest Φ-OTDR reported to date, to the best of our knowledge. It is found that the combination of distributed Raman amplification with heterodyne detection can extend the sensing distance and enhances the sensitivity substantially, leading to the realization of ultra-long Φ-OTDR with high sensitivity and spatial resolution. Furthermore, the feasibility of applying such an ultra-long Φ-OTDR to pipeline security monitoring is demonstrated and the features of intrusion signal can be extracted with improved SNR by using the wavelet detrending/denoising method proposed.

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A configuration of hybrid distributed Raman amplification (H-DRA), that is formed by incorporating a random fiber laser (RFL) based 2nd-order pump and a low-noise laser-diode (LD) based 1st-order pump, is proposed in this paper. In comparison to conventional bi-directional 1st-order DRA, the effective noise figure (ENF) is found to be lower by amount of 0 to 4 dB due to the RFL-based 2nd-order pump, depending on the on-off gain, while the low-noise 1st-order Raman pump is used for compensating the worsened signal-to-noise ratio (SNR) in the vicinity towards the far end of the fiber and avoiding the potential nonlinear impact induced by excess injection of pump power and suppressing the pump-signal relative intensity noise (RIN) transfer. As a result, the gain distribution can be optimized along ultra-long fiber link, due to combination of the 2nd-order RFL and low-noise 1st-order pumping, making the transmission distance be extended significantly. We utilized such a configuration to achieve ultra-long-distance distributed sensing based on Brillouin optical time-domain analysis (BOTDA). A repeater-less sensing distance record of up to 154.4 km with 5 m spatial resolution and ~ ± 1.4 °C temperature uncertainty is successfully demonstrated.

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Distributed Raman amplification (DRA) based on ultra-long fiber laser (UL-FL) pumping with a ring cavity is promising for repeaterless transmission and sensing. In this work, the characteristics (including gain, nonlinear impairment and noise figure) for forward and backward pumping of the ring-cavity based DRA scheme are fully investigated. Furthermore, as a typical application of the proposed configuration, ultra-long-distance distributed sensing with Brillouin optical time-domain analysis (BOTDA) over 142.2 km fiber with 5m spatial resolution and ± 1.5 °C temperature uncertainty is achieved, without any repeater. The key point for the significant performance improvement is the system could offer both of uniform gain distribution and considerably suppressed pump-probe relative intensity noise (RIN) transfer, by optimized design of system structure and parameters.

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The gain and noise characteristics of distributed Raman amplification (DRA) based on random fiber laser (RFL) (including forward and backward random laser pumping) have been experimentally investigated through comparison with conventional bi-directional 1st-order and 2nd-order pumping. The results show that, the forward random laser pumping exhibits larger averaged gain and gain fluctuation while the backward random laser pumping has lower averaged gain and nonlinear impairment under the same signal input power and on-off gain. The effective noise figure (ENF) of the forward random laser pumping is lower than that of the bi-directional 1st-order pumping by ~2.3 dB, and lower than that of bi-directional 2nd-order pumping by ~1.3 dB at transparency transmission, respectively. The results also show that the spectra and power of RFL are uniquely insensitive to environmental temperature variation, unlike all the other lasers. Therefore, random-lasing-based distributed fiber-optic amplification could offer low-noise and stable DRA for long-distance transmission.

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In this paper, we reported the realization of 2nd-order random lasing in a half-opened fiber cavity, which is formed by a FBG with central wavelength at the 1st-order Raman Stokes wavelength and a single-mode fiber (SMF) performing as a random distributed feedback mirror. Using this proposed method, the threshold of 1st-order (2nd-order) random lasing is reduced to 0.7 (2.0) W, which is nearly 2 times lower than that observed in a completely-opened cavity.

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