Experimental study of laser spot tracking for underwater optical wireless communication.

In this paper, a novel laser spot tracking algorithm that incorporates the Kalman filter with the continuously adaptive Meanshift algorithm (Cam-Kalm) is proposed and employed in an underwater optical wireless communication (UOWC) system. Since the Kalman filter has the advantage of predicting the state information of the target spot based on its spatial motion features, the proposed algorithm can improve the accuracy and stability of the moving laser spot tracking. A 2 m optical wireless communication experimental system with auto-tracking based on a green laser diode (LD) is built to evaluate the tracking performance of different algorithms. Experimental results verify that the proposed algorithm outperforms conventional tracking algorithms in aspects of tracking accuracy, interference resistance, and response time. With the proposed Cam-Kalm algorithm, the experimental system can establish an effective communication link, while the maximum tracking speed is 20 mm/s given the forward-error-correction (FEC) threshold.

Optimal design of integrated visible light communication and positioning system with energy harvesting.

In this paper, an optimization scheme that can simultaneously transmit communication information, positioning the information and energy in a visible light communication and positioning (VLCP) system with energy harvesting is proposed. The time switching-power splitting (TS-PS) method is applied, where the power and time allocation factors are defined as optimization variables, so that the system can maximize the harvested energy under the constraints of the information rate and positioning error. The multi-verse optimization (MVO) algorithm is introduced to obtain the optimal power and time allocation. In addition, the performance of the integrated system using the TS-PS method is investigated and compared with that using other conventional methods. The results show that a maximized harvested energy solution using the TS-PS method can harvest the most energy. Moreover, the effects of main external environment conditions, namely, the room height and field of view (FoV) of a photo diode (PD) on the system performance are also analyzed. The increase of the room height and FoV of the PD reduces the harvested energy, but does not change the information rate and positioning accuracy in the optimized system adopted in this paper.

The strategy of laparoscopic surgery for asymptomatic antenatally diagnosed choledochal cyst.

BACKGROUND: The aim was to investigate the characteristics, surgical management, and outcomes of asymptomatic patients with antenatally diagnosed choledochal cysts (ADCCs) and to justify the strategy of laparoscopic surgery (LS) for them in our hospital. METHODS: We developed our LS strategy for asymptomatic ADCCs. Patients with asymptomatic ADCCs who underwent LS or open surgery (OS) during January 2010 and January 2020 were included. Patients with recorded symptomatic ADCCs were exclude. All data of group LS and group OS were statistically compared and analyzed. RESULTS: Twenty-five patients received LS and 18 patients received OS were included. There was no significant difference in baseline characteristics between the groups. A total of 65.1% of biliary sludge formation was detected preoperatively by ultrasonography (US) (72.0% in group LS, 55.6% in group OS, P = 0.26). Compared to the OS group, the LS group had a longer operative time (313.4 ± 27.2 vs. 154.0 ± 11.9 min, P = 0.02), shorter postoperative fasting period (3.1 ± 1.2 vs. 6.2 ± 2.3 days, P = 0.03), and shorter postoperative hospital stay (5.1 ± 1.9 vs. 9.2 ± 1.1 days, P = 0.03). The incidence of late complications, such as reflux cholangitis, adhesive intestinal obstruction, and biliary enteric anastomotic stricture with stone formation, was not significantly different between the two groups. The liver function and liver stiffness of all patients in the two groups were normal. CONCLUSIONS: Based on the strategy for asymptomatic ADCCs in our hospital, the perioperative safety and midterm follow-up results after LS were satisfactory and comparable to those after OS.

Two-dimensional power allocation scheme for NOMA-based underwater visible light communication systems.

In this work, a two-dimensional power allocation scheme combining fractional transmit power allocation (FTPA) and the sine cosine algorithm (SCA) is proposed for non-orthogonal multiple access (NOMA)-based underwater visible light communication (UVLC) systems. Considering the proposed power allocation scheme, a downlink NOMA-based UVLC system using blue-light-emitting diodes in the deep-sea environment is set up to evaluate the influence of the FTPA coefficient and SCA on system communication performance. The simulation results demonstrate that the two-dimensional power allocation scheme can effectively reduce the impact of user pairing on system performance and improve the system transmission rate compared with the conventional power allocation scheme.

Integrated visible light communication and positioning CDMA system employing modified ZCZ and Walsh code.

In this paper, an integrated visible light communication and positioning (VLCP) code division multiple access (CDMA) system is proposed for recovering original user data and obtaining positioning information simultaneously. A generalized modification method for balanced bipolar code set is presented, which can be applied to VLCP-CDMA system with intensity modulation. Both modified bipolar code sets, zero correlation zone (ZCZ) code set and Walsh code set, are employed and evaluated in VLCP-CDMA systems. When considering synchronous and quasi-synchronous (QS) systems, it is demonstrated that the modified ZCZ code set with ideal zero correlation zone properties performs better communication and positioning performance than the modified Walsh code set by system simulations and experiments. As a result, a bit error rate (BER) of 1.8×10-3 and an average positioning error of 1.50 cm are successfully obtained by adopting modified ZCZ code set in a 4-user real-time VLCP-CDMA system. It will offer a promising solution to meet both communication and positioning requirements of future intelligent systems.

Adaptive feedback threshold based demodulation for mobile visible light communication and positioning integrated system.

In this paper, a novel adaptive feedback threshold (AFT) based demodulation for mobile visible light communication and positioning (VLCP) integrated system is proposed. The AFT can vary with the received signal without excessive fluctuation and support communication and positioning in mobile environment. For the VLCP integrated system with single light emitting diodes (LED) and multiple photodetectors (PDs), maximal ratio combining (MRC) and received optical power ratio (ROPR) based on the AFT is further achieved for communication and positioning with high performance, respectively. It is demonstrated that high credible communication and high accuracy positioning for the mobile integrated VLCP system can be realized by using the proposed AFT based demodulation. As a result, the implemented VLCP system with a moving speed of 1 m/s is evaluated experimentally. Average positioning error of 3.43 cm with 800 mA current and the bit error ratio (BER) with different currents are also obtained.

Performance-enhanced indoor MIMO-OFDM visible light communications using individual/joint CAZAC precoding techniques.

In this paper, efficient individual and joint constant amplitude zero auto-correlation (CAZAC) precoding schemes are proposed to improve the performance of an indoor multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM)-based visible light communication (VLC) system. By considering the proposed precoding scheme, a 3×3 MIMO-OFDM VLC system with symmetrical and asymmetrical structure is set up, whose peak-to-average-power ratio (PAPR) of transmitted signal, signal-to-noise ratio (SNR), and bit error rate performance are investigated. It is shown that both individual and joint CAZAC precoding schemes can reduce the PAPR of the transmitted signal and make the SNR uniform over data subcarriers, resulting in significant performance improvement compared to the system without precoding. It is demonstrated that there are similar performance improvements for the MIMO-OFDM VLC system using the individual CAZAC precoding and joint CAZAC precoding in a symmetric scenario. At the expense of higher implementation complexity, the joint CAZAC precoding has more performance benefits than the individual CAZAC precoding for the VLC system with asymmetrical MIMO.

Experimental demonstration of quasi-synchronous CDMA-VLC systems employing a new OZCZ code construction.

In this paper, we propose a new construction of optical zero correlation zone (OZCZ) code set for quasi-synchronous code division multiple access (QS-CDMA) visible light communication (VLC) system. The proposed code set includes a pair of unipolar and bipolar code sets, which is more suitable for intensity modulation and direct detection (IM/DD) and maintains dimming values at 50% regardless of user numbers for CDMA-VLC system. A QS-CDMA-VLC system adopting the proposed code set is investigated by numerical simulation and experimental verification. The system bit error rate (BER) performance is evaluated with different user numbers, sample rates, delay user numbers and transmission distances. In a 32-user CDMA-VLC system, the 250 MS/s transmission at a distance of 1.5 m can be achieved successfully with the BER less than the forward-error-correction (FEC) threshold. And the BER varies slightly taking account of small delay time. The results indicate that the new OZCZ code construction can effectively overcome non-perfect synchronous problem when the time delay among users does not exceed the zero correlation zone length.

An improved geomechanical model for the prediction of fracture generation and distribution in brittle reservoirs.

It is generally difficult to predict fractures of low-permeability reservoirs under high confining pressures by data statistical method and simplified strain energy density method. In order to establish a series of geomechanical models for the prediction of multi-scale fractures in brittle tight sandstones, firstly, through a series of rock mechanics experiments and CT scanning, we determined 0.85 σc as the key thresholds for mass release of elastic strain energy and bursting of micro-fractures. A correlation between fracture volume density and strain energy density under uniaxial stress state was developed based on the Theory of Geomechanics. Then using the combined Mohr-Coulomb criterion and Griffith's criterion and considering the effect of filling degree in fractures, we continued to modify and deduce the mechanical models of fracture parameters under complex stress states. Finally, all the geomechanical equations were loaded into the finite element (FE) platform to quantitatively simulate the present-day 3-D distributions of fracture density, aperture, porosity, permeability and occurrence based on paleostructure restoration of the Keshen anticline. Its predictions agreed well with in-situ core observations and formation micro-imaging (FMI) interpretations. The prediction results of permeability were basically consistent with the unobstructed flow distributions before and after the reservoir reformation.

Ag Nanoparticles-Modified 3D Graphene Foam for Binder-Free Electrodes of Electrochemical Sensors.

Ag nanoparticles-modified 3D graphene foam was synthesized through a one-step in-situ approach and then directly applied as the electrode of an electrochemical sensor. The composite foam electrode exhibited electrocatalytic activity towards Hg(II) oxidation with high limit of detection and sensitivity of 0.11 µM and 8.0 µA/µM, respectively. Moreover, the composite foam electrode for the sensor exhibited high cycling stability, long-term durability and reproducibility. These results were attributed to the unique porous structure of the composite foam electrode, which enabled the surface of Ag nanoparticles modified reduced graphene oxide (Ag NPs modified rGO) foam to become highly accessible to the metal ion and provided more void volume for the reaction with metal ion. This work not only proved that the composite foam has great potential application in heavy metal ions sensors, but also provided a facile method of gram scale synthesis 3D electrode materials based on rGO foam and other electrical active materials for various applications.

[Research progress on molecular ecology of Sciurus vulgaris].

Today, the main threats for Sciurus vulgaris are illegal hunting, deforestation, and subsequent population fragmentation, combined with interspecific competition from S. carolinensis in some regions of Europe, which has led to a sharp reduction in the number of population. S. vulgaris has been listed as Near Threatened IUCN Red List and included in key protected wild animals in Jilin Province, China. The molecular ecology of S. vulgaris is developing rapidly with the rapid development of molecular biology methods. In particular, the research of mtDNA fragments and the application squirrel study microsatellite loci has further promoted the molecular ecology of S. vulgaris. In this study, the molecular phylogeny, the genetic diversity and the molecular phylogeography involving the molecular ecology of S. vulgaris were reviewed. Four areas for the future development in molecular ecology of S. vulgaris were proposed: 1) to further explore the molecular phylogeny relationship between S. vulgaris and S. lis; 2) the comparative analysis of the genetic diversity of S. vulgaris for continuous populations, isolated populations and metapopulation; 3) the analysis of molecular phylogeography of S. vulgaris based on other markers of nuclear; 4) to explore whether there existed the quaternary glacial refuge in Asia.

[Diurnal activity rhythm of Clethrionomys rufocanus].

The diurnal activity rhythm of Clethrionomys rufocanus was studied under three different food conditions in a laboratory. The activity occurred both in the daytime and at night, but mainly at night (19:00-4:00). The mice fed with Mouse food exhibited six small peaks in their daily activity, and those fed with grass or hay exhibited seven, but the peak of the out-nest night activity was 2-3 hours earlier. The activity amount of out-nest was 30,518.0 +/- 3,694.9 s for those fed with grass, the next was 21,811.7 +/- 2,288.0 s for those fed with hay, and the least was 15,038.0 +/- 666.0 s for those fed with mouse food. The activity amount of feeding was 10,867.3 +/- 1,612.1 s for those fed with grass, much more than those fed with mouse food and hay. The activity amount for drinking was 988.5 +/- 79.1 s (fed with hay), 568.9 +/- 60.9 s (fed with mouse food) and 139.3 +/- 47.2 s (fed with grass).