Publications by authors named "Wenxi Cao"

Article Synopsis
  • The study addresses the challenge of accurately measuring particulate organic carbon (POC) in coastal waters due to the complex variability of marine particles.
  • A new method was created that uses the ratio of phytoplankton to detritus absorption coefficients to classify water types, leading to strong correlations between POC and specific optical measurements in certain water samples.
  • This method outperforms traditional algorithms and introduces a depth-resolved index for better representation of POC distribution, enhancing our understanding of its three-dimensional structure in ocean environments.
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Chlorophyll a (Chl-a) is a key indicator of marine ecosystems, and certain hydro-meteorological parameters (HMPs) are highly correlated with its fluctuations. Here, relevant and accessible HMPs were used as inputs, combined with machine learning (ML) algorithms for estimating 3D Chl-a in the South China Sea (SCS). With the inputs of temperature, salinity, depth, wind speed, wind direction, sea surface pressure, and relative humidity, the LightGBM-based model performed well, achieving high R values of 0.

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The vertical distribution of the diffuse attenuation coefficient K(z, λ) is critical for studies in bio-optics, ocean color remote sensing, underwater photovoltaic power, etc. It is a key apparent optical property (AOP) and is sensitive to the volume scattering function β(ψ, z, λ). Here, using three machine learning algorithms (MLAs) (categorical boosting (CatBoost), light gradient boosting machine (LightGBM), and random forest (RF)), we developed a new approach for estimating the vertical distribution of K(z, 650), K(z, 650), and K(z, 650) and applied it to the South China Sea (SCS).

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An instrument named as Volume Scattering and Attenuation Meter (VSAM) is presented. The VSAM can simultaneously measure the attenuation coefficient and the volume scattering function (VSF) from 10° to 170° with an interval of 10° at 659 nm. Using ultrapure water and NCRM-traceable polystyrene microsphere beads, the VSAM was calibrated, and the conversion factor χ for estimating the backscattering coefficient from the backward VSF was obtained based on Mie theory in the laboratory.

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Gold nanoparticles-modified silver nanorod (AuNPs@AgNR) arrays were fabricated as surface-enhanced Raman spectroscopy (SERS) substrates. The coffee ring effect of the AuNPs@AgNR was explored as a preconcentration method for enriching the target analytes and increasing the "hot spots." Furthermore, methyl viologen (MV) as a toxic herbicide used in agricultural production was successfully determined to investigate the application of the coffee ring effect on AuNPs@AgNR arrays and density functional theory (DFT) was employed to calculate its vibrational modes of corresponding characteristic peaks.

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Characterizing the vertical distribution of chlorophyll a in the water column in each oceanic region is crucial for accurate assessment of depth-integrated phytoplankton biomass. In this study, the characteristics of the subsurface chlorophyll maximum (SCM) in the South China Sea (SCS) during the boreal summer were investigated by using bio-optical and hydrological data collected during four cruises from 2008 to 2015. During the boreal summer, a well-developed SCM layer was found to be a prominent feature in the SCS, with the thickness, depth, and magnitude of the SCM exhibiting large spatial variability.

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A silver nano-tripod (AgNT) structure with a high-density "hot spots" distribution was fabricated by a tilting angle deposition technique. The electric field simulation distribution showed that the electric field enhancement of the AgNT structures is optimal when the tilting angle is 72°. Such AgNT substrates were successfully obtained experimentally when the included angle between the silver vapor and the normal of the sample platform was set to 86°.

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This study presents an innovative technique for the in situ analysis of aquatic biochemical elements detected through wet chemical processes. A new compact in situ phosphate analyzer based on sequential injection analysis, liquid waveguide capillary flow cell and spectrophotometry was developed, and a safe and modular electronics-chemical separation mechanical structure was designed. The sequential injection system of this analyzer was optimized, and the major functions of this analyzer were studied and estimated.

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Using large amounts of bio-optical data collected in the South China Sea (SCS) from 2003 to 2016, this study checks the consistency between well-known semi-analytical algorithms (SAAs)-the quasi-analytical algorithm (QAA) and the default generalized inherent optical property (GIOP-DC)-in retrieving the non-water absorption coefficient (a(λ)), phytoplankton absorption coefficient (a(λ)) and particulate backscattering coefficient (b(λ)) from remote-sensing reflectance (R(λ)) data at 412, 443, 490, 531, and 555 nm. The samples from the SCS are further separated into oligotrophic and mesotrophic water types for the comparison of the SAAs. Several findings are made: First, the values of an(λ) derived from the two SAAs deliver similar performance, with R values ranging from 0.

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An empirical algorithm is proposed to estimate suspended particulate matter (SPM) ranging from 0.675 to 25.7 mg L in the turbid Pearl River estuary (PRE).

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Article Synopsis
  • Phytoplankton cell size significantly influences ecological and biogeochemical processes, and analyzing their absorption and scattering spectra helps determine this size.
  • An inversion method was developed to extract quantitative data on phytoplankton cell size, requiring specific absorption and scattering spectra as inputs, with the average equivalent-volume spherical diameter (ESD) used for approximation.
  • The method's accuracy was evaluated using datasets from 12 phytoplankton species, showing close estimates of ESD with mean error rates between 5.8%-10.6% compared to traditional methods, indicating strong correlations with measured values.
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Pancreatic cancer (PC) is one of the most aggressive malignancies, with a high mortality. Distant metastasis and recurrence are the main causes of PC-related deaths. MicroRNAs (miRNAs) have been reported in the serum or tumor tissue of cancer patients, including PC, which makes them potential biomarkers.

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Article Synopsis
  • Phytoplankton size plays a crucial role in ocean ecosystems, but measuring it accurately is challenging due to existing methods.
  • A new approach has been developed that leverages the phytoplankton package effect to estimate the average size of different phytoplankton populations.
  • This new method has been validated with data from 13 species and shows improved efficiency and accuracy compared to traditional techniques, suggesting it could be used in real-time ocean instruments.
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Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products.

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Using a data set of 1333 samples, we assess the spectral absorption relationships of different wave bands for phytoplankton (ph) and particles. We find that a nonlinear model (second-order quadratic equations) delivers good performance in describing their spectral characteristics. Based on these spectral relationships, we develop a method for partitioning the total absorption coefficient into the contributions attributable to phytoplankton [a(ph)(λ)], colored dissolved organic material [CDOM; a(CDOM)(λ)], and nonalgal particles [NAP; a(NAP)(λ)].

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Article Synopsis
  • Colored dissolved organic matter (CDOM) is crucial for marine ecosystems, and measuring its absorption has faced challenges.
  • An automated onboard analyzer using liquid core waveguides was developed, featuring a flexible optical path, extensive measurement range, and high sensitivity.
  • Controlled by LabVIEW software, the analyzer can automate filtration and sample injection, while providing real-time data, proving to be reliable through various experiments.
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The spectral absorption and attenuation coefficients of 16 phytoplankton species were measured in the laboratory using acs instrument. Ancillary measurements included particle size distribution and chlorophyll a concentration (Chl a). The results indicated that both algal cell size and Chl a were the two major factors dominating the magnitudes of the spectral absorption and attenuation coefficients.

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The optical volume scattering function (VSF) of seawater is a fundamental property used in the calculation of radiative transfer for applications in the study of the upper-ocean heat balance, the photosynthetic productivity of the ocean, and the chemical transformation of photoreactive compounds. A new instrument to simultaneously measure the VSF in seven directions between 20° to 160°, the attenuation coefficient, and the depth of water is presented. The instrument is self-contained and can be automatically controlled by the depth under water.

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The scattering and backscattering coefficients of 15 phytoplankton species were determined in the laboratory using the acs and BB9 instruments. The spectral variability of scattering properties was investigated and the homogenous sphere model based on Mie theory was also evaluated. The scattering efficiencies at 510 nm varied from 1.

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Article Synopsis
  • The paper analyzes red tide water absorption data using Mie theory to extract the imaginary part of the index of refraction and evaluate absorption and backscattering efficiency factors.
  • It finds that Mie theory accurately predicts the absorption properties of the organism Chaetoceros socialis with an average error of 11%.
  • The study reveals that backscattering efficiency factors peak in the 400 to 700 nanometer wavelength range and fluctuate during the red tide event, while total scattering depends on cell size relative to wavelength.
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Teflon AF is chemically very inert, quite physically and optically stable, a highly vapor-permeable polymer with optical transparency through much of the UV-Vis region and with an RI lower than that of water, so Teflon AF LWCC/LCW (Long path-length liquid waveguide capillary cell/liquid core waveguides) has been used with a range of different detection techniques, including absorbance spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and gas sensor. The present article describes the properties and the aspects of Teflon AF LWCC/LCW instrumentation and applications. And finally,the future prospect and outlook of Teflon AF LWCC/LCW is also discussed.

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Water column correction has been a substantial challenge for remote sensing. In order to improve the accuracy of coastal ocean monitoring where optical properties are complex, optical property of shallow water at Sanya Bay and the suitable water column correction algorithms were studies in the present paper. The authors extracted the bottom reflectance without water column effects by using a water column correction algorithm which is based on the simulation of the underwater light field in idealized water.

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In this study, variations in the particulate organic carbon (POC) were monitored during a phytoplankton bloom event, and the corresponding changes in bio-optical properties were tracked at one station (114.29°E, 22.06°N) located in the Pearl River estuary.

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In the present study, the relationships between sea ice albedo and the bidirectional reflectance distribution in Liaodong Bay were investigated. The results indicate that: (1) sea ice albedo alpha(lambda) is closely related to the components of sea ice, the higher the particulate concentration in sea ice surface is, the lower the sea ice albedo alpha(lambda) is. On the contrary, the higher the bubble concentration in sea ice is, the higher sea ice albedo alpha(lambda) is.

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Sea ice plays an important role in the global climate systems. In the present article, a hyperspectral radiation system for the observation of optical properties of sea ice was designed. The system consists of three optical channels, which can operate simultaneously.

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