Chlorophyll-a concentrations inversion based on the modified Quasi-Analytical Algorithm and Sentinel-3 OLCI in Daihai Lake, China

The Quasi-Analytical Algorithm (QAA) is effective in retrieving water inherent optical properties (IOPs) from remote sensing spectral reflectance and has wider applications in studies of the open ocean and coastal waters than of inland waters. This research aimed to modify the QAA model based on measured field spectral reflectance and absorption coefficients to render it applicable to studies of Daihai Lake, China. The improvements mainly included the reference wavelength selection, the power index of the particle backscattering coefficient and the exponential slope of the absorption coefficient of the colored detrital matter estimation. The average relative error between the inversed and measured absorption coefficients was less than 20%. A linear model was established between the phytoplankton absorption coefficient at a wavelength of 674 nm (aph(674)) and the chlorophyll-a (Chl-a) concentration, with a determination coefficient of 0.88. Additionally, the modified Quasi-Analytical Algorithm (MQAA) model was applied to the Ocean and Land Color Instrument (OLCI) data aboard the Sentinel-3 satellite. Finally, a spatial distribution map for the Chl-a concentrations in Daihai Lake on August 10, 2017 was drawn and the mid-eutrophication area was found to occur in the north and border.

Design of Thin and Wideband Microwave Absorbers Using General Closed-Form Solutions

A new design method for RLC reactive absorbers is presented. This method is based on closed-form solutions to help realize the widest absorption bandwidth for an arbitrarily specified thickness. The solutions for the RLC values of the reactive screen are derived using an equivalent circuit in which the thickness of the substrate used, the permittivity and tangential loss of the substrate, and the frequency are all considered. A perfect match and maximum bandwidth at a design frequency can be achieved with the proposed method. Various aspects of the absorber characteristics, depending on the thickness and loss of the substrate, are analyzed using the presented solutions and electromagnetic (EM) simulations. To validate the proposed design method, an X-band microwave absorber with a crossed-dipole structure patterned on a silver nanowire resistive film is designed, fabricated, and measured. The substrate electrical thickness of the absorber is 70° at 10 GHz, with a permittivity of 2.2. The 90% absorption bandwidth is 8 GHz in the frequency range of 8.2–16.2 GHz. The measured absorption agrees well with the results obtained using circuit and EM simulations.

Superior tunable photocatalytic properties for water splitting in two dimensional GeC/SiC van der Waals heterobilayers

The photocatalytic characteristics of two-dimensional (2D) GeC-based van der Waals heterobilayers (vdW-HBL) are systematically investigated to determine the amount of hydrogen (H2) fuel generated by water splitting. We propose several vdW-HBL structures consisting of 2D-GeC and 2D-SiC with exceptional and tunable optoelectronic properties. The structures exhibit a negative interlayer binding energy and non-negative phonon frequencies, showing that the structures are dynamically stable. The electronic properties of the HBLs depend on the stacking configuration, where the HBLs exhibit direct bandgap values of 1.978 eV, 2.278 eV, and 2.686 eV. The measured absorption coefficients for the HBLs are over ~ 105 cm−1, surpassing the prevalent conversion efficiency of optoelectronic materials. In the absence of external strain, the absorption coefficient for the HBLs reaches around 1 × 106 cm−1. With applied strain, absorption peaks are increased to ~ 3.5 times greater in value than the unstrained HBLs. Furthermore, the HBLs exhibit dynamically controllable bandgaps via the application of biaxial strain. A decrease in the bandgap occurs for both the HBLs when applied biaxial strain changes from the compressive to tensile strain. For + 4% tensile strain, the structure I become unsuitable for photocatalytic water splitting. However, in the biaxial strain range of − 6% to + 6%, both structure II and structure III have a sufficiently higher kinetic potential for demonstrating photocatalytic water-splitting activity in the region of UV to the visible in the light spectrum. These promising properties obtained for the GeC/SiC vdW heterobilayers suggest an application of the structures could boost H2 fuel production via water splitting.

An optimization method for reverberation room design

The ISO 354:2003 standard relating to sound absorption measurements is currently under revision to improve the reproducibility of the procedure it describes. Round robin tests conducted across various reverberation rooms indeed revealed significant disparities between sound absorption measurements of the same sample. One of the reasons is that, at low frequencies, the sound field in a single laboratory cannot be considered fully diffuse. However, the average sound field across different laboratories may be considered diffuse if the interaction between the finite sample and the diffuse field is duly accounted for and the direct field close to the absorber is disregarded. In this work, a method is developed for optimizing reverberation room design such that measured absorption values are as close as possible to ensemble average diffuse values. The reverberation room is modelled using the finite element method and standardized measurements of an absorptive sample are simulated. The distance between resulting absorption coefficients and diffuse target values is minimized in an optimization procedure having the geometrical characteristics of the model as input parameters. The results are anticipated to participate to the revised ISO 354 as guidelines for the construction of new reverberation rooms or the improvement of existing ones.

Modeled source apportionment of black carbon particles coated with a light-scattering shell

The Aethalometer model has been used widely for estimating the contributions of fossil fuel emissions and biomass burning to equivalent black carbon (eBC). The calculation is based on measured absorption Ångström exponents (αabs). The interpretation of αabs is ambiguous since it is well known that it not only depends on the dominant absorber but also on the size and internal structure of the particles, core size, and shell thickness. In this work the uncertainties of the Aethalometer-model-derived apparent fractions of absorption by eBC from fossil fuel and biomass burning are evaluated with a core–shell Mie model. Biomass-burning fractions (BB(%)) were calculated for pure and coated single BC particles for lognormal unimodal and bimodal size distributions of BC cores coated with ammonium sulfate, a scattering-only material. BB(%) was very seldom 0 % even though BC was the only absorbing material in the simulations. The shape of size distribution plays an important role. Narrow size distributions result in higher αabs and BB(%) values than wide size distributions. The sensitivity of αabs and BB(%) to variations in shell volume fractions is the highest for accumulation-mode particles. This is important because that is where the largest aerosol mass is. For the interpretation of absorption Ångström exponents it would be very good to measure BC size distributions and shell thicknesses together with the wavelength dependency of absorption.

Acoustical Properties of Fiberglass Blankets Impregnated with Silica Aerogel

It is known that aerogel impregnated fibrous blankets offer high acoustic absorption and thermal insulation performance. These materials are becoming very popular in various industrial and building applications. Although the reasons for the high thermal insulation performance of these materials are well understood, it is still largely unclear what controls their acoustic performance. Additionally, only a small number of publications to date report on the acoustical properties of fibrous blankets impregnated with powder aerogels. There is a lack of studies that attempt to explain the measured absorption properties with a valid mathematical model. This paper contributes to this knowledge gap through a simulation that predicts the measured complex acoustic reflection coefficient of aerogel blankets with different filling ratios. It is shown that the acoustic performance of a fibrous blanket impregnated with aerogel is generally controlled by the effective pore size and porosity of the composite structure. It is shown that there is a need for refinement of a classical Biot-type model to take into account the sorption and pressure diffusion effects, which become important with the increased filling ratio.

Anisotropy of X-ray Absorption Cross Section in CeCoGe3 Single Crystal

Absorption spectra of two orthogonal linearly polarized x-rays in a single CeCoGe3 crystal were measured at the ID12 beamline of the ESRF for the energies near the K-edges of Ge, Co and near the L23 edges of Ce. The X-ray natural linear dichroism (XNLD) was revealed in the vicinity of all the absorption edges, which indicates a splitting of electronic states in a crystalline field. Mathematical modelling in comparison with experimental data allowed the isotropic and anisotropic parts of atomic absorption cross section in CeCoGe3 to be determined near all measured absorption edges. The calculations also show that the “average” anisotropy of the cross section close to the Ge K-edge revealed in the experiment is less than the partial anisotropic contributions corresponding to Ge atoms in two different Wyckoff positions.

ANTIOXIDANT ACTIVITY OF METHANOL EXTRACT NATUNA MARINE SPONGE (PORIFERA) WITH DPPH METHODE

Objective: Natuna sponge is a marine animal that contains a wide range of secondary metabolites that can be utilized in the field of pharmacy. The research aims to test the phytochemical content and antioxidant activity of the Natuna methanol marine sponge extract. Sample extraction is done by the maceration method with methanol solvent. Methods: Phytochemical tests include alkaloid testing, flavonoids, steroids, saponins, and tannins. Test antioxidant activity using the immersion DPPH method (1.1-diphenyl-2-picryl hydroxyl) measured absorption at a wavelength of 517 nm. Results: The phytochemical test results showing the sponge of Natuna contain secondary metabolites including alkaloids, flavonoids, steroids, saponins, and tannins. Conclusion: This Natuna sponge methanol extract has an antioxidant activity that is very strong with an IC50 value of 52.91 ppm, and the comparator used is Vitamin C with an IC50 value of 43,51 ppm.

Dual-Slope Diffuse Reflectance Instrument for Calibration-Free Broadband Spectroscopy

This work presents the design and validation of an instrument for dual-slope broadband diffuse reflectance spectroscopy. This instrument affords calibration-free, continuous-wave measurements of broadband absorbance of optically diffusive media, which may be translated into absolute absorption spectra by adding frequency-domain measurements of scattering at two wavelengths. An experiment on a strongly scattering liquid phantom (milk, water, dyes) confirms the instrument’s ability to correctly identify spectral features and measure absolute absorption. This is done by sequentially adding three dyes, each featuring a distinct spectral absorption, to the milk/water phantom. After each dye addition, the absorption spectrum is measured, and it is found to reproduce the spectral features of the added dye. Additionally, the absorption spectrum is compared to the absorption values measured with a commercial frequency-domain instrument at two wavelengths. The measured absorption of the milk/water phantom quantitatively agrees with the known water absorption spectrum (R2=0.98), and the measured absorption of the milk/water/dyes phantom quantitatively agrees with the absorption measured with the frequency-domain instrument in six of eight cases. Additionally, the measured absorption spectrum correctly recovers the concentration of one dye, black India ink, for which we could accurately determine the extinction spectrum (i.e., the specific absorption per unit concentration). The instrumental methods presented in this work can find applications in quantitative spectroscopy of optically diffusive media, and particularly in near-infrared spectroscopy of biological tissue.

High Hydrogen Ion Concentration Causes a Blue Shift in Gold Nanoparticles

In this research, our team used a rare electrochemical method to obtain gold nanoparticles (GNPs). The growth solution has been added with nitric acid in order to observe the effect of GNPs. The solution also included cetyltrimethylammonium bromide (CTAB) and acetone. All reactions involved the oxidation of acetone and chain polymerization. Therefore, the GNPs changed to a su pramolecular structure. In addition, our team measured absorption wavelength via ultraviolet/ visible spectrophotometer and found an obviously blue shift. This short absorption wavelength is obviously different from other GNPs.