Theoretical and experimental study on the radiative properties of Parachlorella kessleri: considering the effect of internal microstructure.

A microalgal cell model with multiple organelles considering both the irregular overall shape and internal microstructure was proposed. The radiative properties of Parachlorella kessleri during the normal phase, starch-rich phase, and lipid-rich phase were calculated by the discrete dipole approximation method in the visible wavelengths. The accuracy of the model is verified with experimental measurements. The results showed that the theoretical calculation of the established microalgal cell model is more accurate than those of the equal volume spheres, such as the homogeneous sphere and the coated sphere, with the errors of the scattering cross-section reduced by more than 10.7%. The calculated scattering phase function of the multi-component model is basically in good agreement with the experimental results. Compared to the normal growth phase, the lipid enrichment during the lipid-rich phase leads to a sharp increase in the scattering cross-section by three to four times, while the absorption cross-section remains stable. Remarkably, in the starch-rich phase, the abundant production of starch results in a reduction of two to three times in the absorption cross-section compared to the normal growth phase, while the scattering cross-section varies little. The results can provide basic data and theoretical support for the design and optimization of photobioreactors.

VO2 particle-based intelligent metasurface with perfect infrared emission for the spacecraft thermal control.

Thermochromism film can automatically adjust its emittance without additional energy consumption, which shows great prospect in the application of spacecraft thermal control. However, it is still challenging to achieve a large infrared emittance at a high temperature and emittance tunability of the thermochromism film. In this work, we propose a V O 2 particle-based intelligent metasurface for spacecraft thermal control, which consists of a square lattice array of hollow spheroidal V O 2 particles on Au substrate. The metasurface with a V O 2 particle having a large aspect ratio (∼10) displays perfect emission throughout the entire mid-infrared spectral range. The emittance tunability can exceed 0.63 with total normal emittance of 0.85. The underlying mechanisms involved in the metasurface are attributed to particle-dependent scattering, by which the infrared emittance is dramatically enhanced for the metallic state and restricted for the dielectric state. In addition, the infrared emittance at a high temperature and emittance tunability of the metasurface remain large for incident angles up to 60°. To the best of our knowledge, this work proposes the first thermochromism film structure with perfect infrared emission, which could accelerate the development and practical application of the thermochromic film in the field of spacecraft.

Optical properties of biochemical compositions of microalgae within the spectral range from 300 to 1700 nm.

The optical properties of biochemical compositions of microalgae are vital for the improvement of biosensor design, photobioreactor design, biofuel, and biophotonics techniques. A combination method using both the double optical pathlength transmission method (DOPTM) and the ellipsometry method (EM) is called DOPTM-EM, and it is used to acquire the optical constants of protein, lipid, and carbohydrate of Haematococcus pluvialis, Nannochloropsis sp., and Spirulina in both a solid state and a solution state within the visible and near-infrared spectral range. For different types of microalgae, the refractive indices of protein and carbohydrate in the solid state are similar to each other, but show an observed difference from lipid in the solid state. The refractive indices of protein and carbohydrate in the solution state presents a visible distinction in the researched spectral range. The absorption indices of protein, lipid, and carbohydrate in the solid state for these three types of microalgae are close to each other in the spectral range of 300-500 nm. However, an observed difference is shown in the spectral range of 500-1700 nm. For ease of application, the refractive index of biochemical composition of microalgae was fitted based on the Sellmeier equation. We believe this work can provide a reference to obtain the optical properties of biomaterial with high accuracy.

Dependent absorption property of nanoparticle clusters: an investigation of the competing effects in the near field.

Noble metal nanoparticle clusters show unique light absorption and catalysis properties, which have been widely used in the application of photocatalysis, optoelectronics, biomedical optics and so on. The absorption cross section of densely packed nanoparticle clusters, which can be enhanced or restricted due to the near field effects needs to be studied thoroughly. In this work, focusing on Au nanoparticle at the localized plasmon resonance wavelength, the effects of monomer diameter D, monomer number N, particle volume fraction Fv and complex refractive index m on the nondimensional absorption cross section η = Cabs,total/(N·Cabs) (normalized by N and the absorption cross section Cabs of a single particle) of densely packed nanoparticle clusters are studied by using the superposition T-matrix method. It is found that the enhancement (η > 1) and restriction (η < 1) mechanisms of the absorption cross section of nanoparticle clusters are determined by two competing factors (i.e. the multiple scattering and shielding effect), and the extent of these two mechanisms is mainly dependent on the monomer size parameter and the monomer number. The effect of the particle volume fraction on the nondimensional absorption cross section of nanoparticle clusters is totally different in different mechanisms. Specifically, the nondimensional absorption cross section peaks at the particle volume fraction of about 50% in the enhancement mechanism (in our calculation: D < 14 nm, N = 100), while in the restriction mechanism it decreases monotonously with increasing particle volume fraction. Moreover, the absorption efficiency of nanoparticle clusters with more absorptive monomer decreases more sharply with increasing particle volume fraction. The complex refractive index of particle shows significant effects on the nondimensional absorption cross section of nanoparticle clusters, and the largest nondimensional absorption cross section of nanoparticle clusters (N = 100) is larger than 8.

Performance matching of common pesticides in banana plantations on the surface of banana leaves at different growth stages.

BACKGROUND: The effective deposition of pesticide droplets on a target leaf surface is critical for decreasing pesticide application rates. The wettability between the target leaf surface and the pesticide spray liquid should be investigated in depth, with the aim of enhancing the adhesion of pesticide solutions. The wetting and deposition behavior of pesticides on target leaves depends on the properties of the liquid and the physical and chemical properties of the leaves. The physical and chemical properties of leaves vary with growth stage. This study aims to investigate the wetting behavior of banana leaf surfaces at different stages. RESULTS: The microstructures and chemical compositions of banana leaf surfaces at different stages were studied using modern methods. The surface structure of banana leaves exhibited a wide variety of characteristics at different growth stages, and the chemical composition changed marginally. The surface free energy (SFE) and polar and non-polar components of banana leaves at different growth stages were measured by examining the contact angles (CA) of different test solutions on the surface of banana leaves. Previous research has suggested that changes in the CA and SFE correlate with changes in leaf surface wettability. In general, the new upper leaves of banana trees are composed of polar components and exhibit hydrophobicity. Non-polar components become dominant as the leaf grows. The back surface of banana leaves was non-polar at all growth stages, with a trend that was opposite to that of the front surface. The critical surface tension of the banana leaf surface at different growth stages ranged from 7.83 to 24.22 mN m-1 , thus falling into the category of a low-energy surface. CONCLUSION: The surface roughness and chemical characteristics of banana leaves affected the wettability of the leaf surface. Differences in the free energy and the polar and non-polar components of the leaf surface at were seen at different growth stages. This study provides a favorable reference for the rational control of pesticide spraying parameters and the enhancement of wetting and adhesion of the solution on banana leaf surfaces. © 2023 Society of Chemical Industry.

Wetting and deposition characteristics of air-assisted spray droplet on large broad-leaved crop canopy.

Precision and efficient pesticide spraying is an important part of precision agriculture, banana is a large broad-leaved plant, with pests and diseases, has a high demand for spraying and pest control. The purpose of this study was to clarify the wettability of different pesticides on the banana leaf surface, and the effects of nozzle type and working parameters on the deposition distribution performance under air-assisted spray conditions. The wettability test results of different pesticides on banana leaf surfaces showed that the wettability of the adaxial side was always stronger than that of the abaxial side, the smaller the surface tension of the droplets, the better the wettability on the surface. The spray experiment was carried out on the previously developed air-assisted sprayer with the latest developed intelligent variable spray control system. Three types of nozzles were used to spray with different combinations of working parameters. The deposition distribution performance on the banana leaf surface was obtained by image processing using a self-compiled program. The experimental results show that the nozzle type, wind speed, and spray pressure have significant effects on the deposition distribution performance. Through the study of the interaction and coupling effect of nozzle type and working parameters on the spray droplet deposition distribution on both sides of banana leaves, the results show that under the conditions of hollow cone nozzle, 0.5Mpa spray pressure and 3-5 m/s wind speed, the spray coverage and droplet density are in the optimal state. This is mainly due to the low spray pressure and/or wind speed is not enough to make the banana leaves vibrate and improve the performance of pesticide deposition. excessive spray pressure and/or wind speed will cause large deformation of banana leaves and make them airfoil stable, which reduces the surface deposition performance. It is of great significance for promoting sustainable and intelligent phytoprotection.