Quantitative determination of microbial materials activity based on infrared extinction properties.

Microbial bacteria play an irreplaceable role in natural and human production and life; thus, determining their activities is an important issue. This study proposed a method to quantitatively determine the activity of microbial materials through extinction property calculation using infrared spectroscopy. Complex refractive indices of different active biomaterials were calculated based on their infrared spectra, and their extinction properties were determined using the discrete dipole approximation method. Using partial least squares (PLS), support vector regression (SVR), and extreme learning machine (ELM) regression, quantitative determination models of microbial materials based on infrared extinction properties were established to predict their activity. The results demonstrated that the model of least angle regression (LAR) combined with PLS exhibited better potential for the determination of biomaterial activity. The coefficient of determination (R2) values acquired by the optimal model for the three biomaterials were 0.9699, 0.9744, and 0.9621, respectively. These findings suggested that a rapid and accurate quantitative determination of microbial activity can be achieved based on extinction property.

Effects of relative humidity on the broadband extinction performance of bioaerosol.

Bioaerosol, a significant constituent of the atmosphere, exhibits excellent broadband extinction performance and has attracted increasing attentions in the fields of atmospheric science, environmental science and electromagnetic field, et al. Relative humidity of the atmosphere has obvious diurnal and seasonal variation characteristics, and the frequent variation of relative humidity has a significant impact on bioaerosol in the atmosphere. However, the influence of relative humidity on broadband extinction performance of bioaerosol is unclear. Herein, we present the humidity growth model of bioaerosol. And the variation law of broadband extinction performance of bioaerosol in different humidity conditions was obtained by simulation. The simulation results and experimental data from an aerosol chamber experiment show that as the relative humidity values above 70%, the broadband extinction performance of bioaerosol will be increased with humidity. As the relative humidity increases from 70% to 90%, the extinction performance of AN0913 spores increase about 30% in visible and mid-infrared bands, about 20% in ultraviolet and far-infrared bands. And the extinction performance of AO0907 spores increase about 23% in the all four bands.

Discrimination of viable and dead microbial materials with Fourier transform infrared spectroscopy in 3-5 micrometers.

We present a method to show that average mass extinction coefficient of microbes evaluated via Lorenz-Mie theory can be used to discriminate between viable and dead microbes. Reflectance of viable and dead self-cultured fungal spores and mycelia were measured by the Fourier transform infrared spectroscopy. Complex refractive indices and mass extinction coefficient of viable and dead fungal spores and mycelia were obtained in terms of Kramers-Kronig (KK) relation and Lorenz-Mie theory respectively. Smoke box experimental system was built to validate the effectiveness of the method. The results show that viable and dead fungal spores and mycelia via average mass extinction coefficients can be distinguished. The method can be used to discriminate the bioactivity of microbes and has potential applications in identification, detection, and optical characteristics of viable and dead microbial materials.

[Measurement and analysis on complex refraction indices of pear pollen in infrared band].

Pollen is an important part of bioaerosols, and its complex refractive index is a crucial parameter for study on optical characteristics and detection, identification of bioaerosols. The reflection spectra of pear pollen within the 2. 5 - 15µm waveband were measured by squash method. Based on the measured data, the complex refractive index of pear pollen within the wave-band of 2. 5 to 15 µm was calculated by using Kramers-Kroning (K-K) relation, and calculation deviation about incident angle and different reflectivities at high and low frequencies.were analyzed. The results indicate that 18 degrees angle of incidence and different reflectivities at high and low frequencies have little effect on the results, and it is practicable to calculate the complex refractive index of pollen based on its reflection spectral data. The data of complex refractive index of pollen have some reference value for optical characteristics of pollen, detection and identification of bioaerosols.

Analysis of factors influencing infrared extinction area of explosive smokescreen.

Objectives: Comparative studies of different smokescreen designs are essential to determine differences in extinction performance. This study aims to investigate the extinction performance of explosive smokescreen under different conditions, and to provide an evaluation method for the optimal design of its charge structure. Methods: The process of formation of the smokescreen with a cylindrical charge structure is described based on the smoothed particle hydrodynamics method. The blast radius and particle density distribution of the smokescreen were calculated for different charge structures and charge ratios through simulations. Lambert-Beer's law was combined to obtain the infrared extinction area. An analysis was then conducted to determine the influence of the number of baffles in the charge structure and charge ratio on the extinction performance of the smokescreen. Field tests were conducted to verify the simulation results. Results: Increasing the number of baffles in the projectile structure made the particle distribution of the smokescreen more uniform and resulted in a larger infrared extinction area. An increase in the explosive quantity, made the smokescreen more dispersed. However, too much of the explosives caused the smokescreen to be sparse, reducing the infrared extinction area.

Self-assembled CsPbBr3 quantum dots with wavelength-tunable photoluminescence for efficient active jamming.

CsPbBr3 perovskite quantum dots (QDs) show great potential in various applications due to their size-dependent and excellent optoelectronic properties. However, it is still challenging to synthesize size-tunable CsPbBr3 QDs with purple emission. Herein, CsPbBr3 nanospheres (NS) with purple emission (432 nm) and wavelength-tunable photoluminescence were synthesized using a two-step recrystallization method for the first time. A nanocube (NC) strategy resulting from CsPbBr3 nanosphere self-assembly via polar solvent-induced surface ligand mismatch was proposed. The self-assembly process endows the QDs with wavelength-tunable photoluminescence ranging from 432 to 518 nm. The significant reduction in defects during self-assembly was confirmed by transient optical spectroscopy measurements, photoluminescence quantum yields (PLQY), and the disappearance of tail bands in the long-wavelength region of the photoluminescence (PL) spectrum. This theory demonstrated that the decrease in high defect surfaces and increase in specific surface area were the reasons for the decline in defects. Most importantly, these QDs could be used for the active jamming of optical imaging systems based on charged-coupled devices (CCDs), including laser imaging radar and low light level (LLL) night vision systems. QDs significantly increase the mean square error (MSE) of the image, while the detection rate of the target by the artificial intelligence algorithm decreased by 95.17%. The wide wavelength tunable emission caused by structural changes makes it arduous for silicon-based detectors to avoid the interference of QDs by adding filters or by other means.

Infrared Extinction Performance of Randomly Oriented Microbial-Clustered Agglomerate Materials.

In this study, the spatial structure of randomly distributed clusters of fungi An0429 spores was simulated using a cluster aggregation (CCA) model, and the single scattering parameters of fungi An0429 spores were calculated using the discrete dipole approximation (DDA) method. The transmittance of 10.6 µm infrared (IR) light in the aggregated fungi An0429 spores swarm is simulated by using the Monte Carlo method. Several parameters that affect the transmittance of 10.6 µm IR light, such as the number and radius of original fungi An0429 spores, porosity of aggregated fungi An0429 spores, and density of aggregated fungi An0429 spores of the formation aerosol area were discussed. Finally, the transmittances of microbial materials with different qualities were measured in the dynamic test platform. The simulation results showed that the parameters analyzed were closely connected with the extinction performance of fungi An0429 spores. By controlling the value of the influencing factors, the transmittance could be lower than a certain threshold to meet the requirement of attenuation in application. In addition, the experimental results showed that the Monte Carlo method could well reflect the attenuation law of IR light in fungi An0429 spore agglomerates swarms.

Electromagnetic Attenuation Characteristics of Microbial Materials in the Infrared Band.

In this study, seven microbial materials (entomogenous fungi Bb3088 mycelia, entomogenous fungi Bb3088 spores, entomogenous fungi Ma2677 mycelia, entomogenous fungi Ma2677 spores, Bacillus subtilis 8204, Staphylococcus aureus 6725, and Saccharomyces cerevisiae 1025) were used to measure electromagnetic (EM) signal extinction. They were subjected to light absorption and reflection measurements in the range of 4000-400 cm(-1) (2.5-25 µm) using Fourier transform infrared spectroscopy. The specular reflection spectrum method was used to calculate the real (n) and imaginary (k) parts of the complex refractive index. The complex refractive index with real part n and imaginary part k in the infrared band satisfies the following conditions n ≥ 1 and k ≥ 0. The mass extinction coefficient was calculated based on Mie theory. Entomogenous fungi Ma2677 spores and entomogenous fungi Bb3088 spores were selected as EM signal extinction materials in the smoke box test. The transmittances of entomogenous fungi Bb3088 spores and entomogenous fungi Ma2677 spores were 11.63% and 5.42%, and the mass extinction coefficients were 1.8337 m(2)/g and 1.227 m(2)/g. These results showed that entomogenous fungi Bb3088 spores and entomogenous fungi Ma2677 spores have higher extinction characteristics than other microbial materials.