RESUMO
In this paper, we propose an optical module, consisting of an Erbium/Ytterbium co-doped fiber amplifier (EYDFA) and a cascaded periodically poled lithium niobate (cascaded-PPLN), to bridge the conventional telecommunication and the emerging underwater wireless optical communication (UWOC). Compared with using two discrete crystals to achieve the third harmonic generation (THG), using a cascaded crystal simplifies the optical system. Under a fundamental power of 5 W at 1550â nm, we have generated an optical power of 6.54â mW at 516â nm, corresponding to a conversion efficiency of 0.1308%. Furthermore, we added a 5-km single-mode fiber (SMF) before the EYDFA, and by adjusting the seed laser power, we successfully maintained the efficiency of the THG process and the output power of the green light. Afterwards, the nonlinearity of the THG process is analyzed, and a simplified nonlinear pre-compensation method has been proposed to tailor the 4-pulse amplitude modulation (PAM4) signals. In such case, the bit error rate (BER) of the modified PAM4 (m-PAM4) can reduce by 69.3% at a data rate of 12 Gbps. Finally, we demonstrate the practicality of our proposed system by achieving a 7-m UWOC transmission in a water tank at a data rate of 13.46 Gbps in an optical dark room. This result demonstrates the feasibility of the hybrid fiber/UWOC system, highlighting its potential for practical implementation.
RESUMO
The link alignment is a challenge in underwater wireless optical communication (UWOC). This paper proposes a UWOC system adopting a fisheye lens with a field of view (FOV) of ±90° at the receiver to alleviate alignment requirement, and a mobile scanning device (MSD) is exploited to track the variation of the imaging position generated by the fisheye lens due to different incidence angles. In a 7-m tap water channel, a transmission with a data rate of 400 Mbps and an FOV of ±90° is realized with 16-quadrature amplitude modulating-orthogonal frequency division multiplexing (16-QAM-OFDM) modulation and orthogonal matching pursuit (OMP) channel estimation algorithm.
RESUMO
In this paper, an omnidirectional underwater wireless optical communication (UWOC) system is proposed, including six lens-free transceivers. An omnidirectional communication with a data rate of 5 Mbps in a 7-m underwater channel is experimentally demonstrated. The optical communication system is integrated into a self-designed robotic fish, and the signal is processed real-time through an integrated micro-control unit (MCU). In addition, it is experimentally demonstrated that the proposed system could establish a stable communication link between two nodes, regardless of the nodes' locomotion and attitude, with a data rate of 2 Mbps and a communication range up to 7 m. In particular, the optical communication system features small footprint and low power consumption, which is suitable for integration in autonomous underwater vehicle (AUV) swarms to achieve an omnidirectional information transmission with low latency, high security, and high data rate compared with its acoustic counterpart.
RESUMO
OBJECTIVE: To evaluate the preventive effect of Zusanli (ST36) acupoint injections with various agents, for postoperative ileus (POI). METHODS: We searched electronic databases for randomized controlled trials from inception to 1st February 2015 evaluating ST36 acupoint injection for preventing POI. Revman 5.2.0 was used for data analysis with effect estimates presented as mean difference (MD) with 95% confidence interval (CI). Statistical heterogeneity was tested using I(2) (defined as significant if I(2)>75%). We used a random effects model (REM) for pooling data with significant heterogeneity. RESULTS: Thirty trials involving 2967 participants were included. All trials were assessed as high risk of bias (poor methodological quality). For time to first flatus, meta-analysis favored ST36 acupoint injection of neostigmine (MD -20.70h, 95% CI -25.53 to -15.87, 15 trials, I(2)=98%, REM), vitamin B1 (MD -11.22h, 95% CI -17.01 to -5.43, 5 trials, I(2)=98%, REM), and metoclopramide (MD -15.65h, 95% CI -24.77 to -6.53, 3 trials, I(2)=94%, REM) compared to usual care alone. Meta-analysis of vitamin B1 favored ST36 acupoint injection compared to intra-muscular injection (MD -17.21h, 95% CI -21.05 to -13.36, 4 trials, I(2)=89%, REM). Similarly, for time to bowel sounds recovery and first defecation, ST36 acupoint injection also showed positive effects. CONCLUSIONS: ST36 acupoint injections with various agents may have a preventive effect for POI. Safety is inconclusive as few of included trials reported adverse events. Due to the poor methodological quality and likely publication bias further robust clinical trials are required to arrive at a definitive conclusion.
