Light Loss Research Articles

Characterizing water-soluble brown carbon in fine particles in four typical cities in northwestern China during wintertime: integrating optical properties with chemical processes

Abstract. Brown carbon (BrC) aerosol could impact atmospheric radiative forcing and play a crucial role in atmospheric photochemistry. In this study, fine particulate matter (PM2.5) filter samples were collected synchronously in four major cities in northwestern China during the winter season (December 2019–January 2020): Lanzhou (LZ), Xining (XN), Yinchuan (YC), and Ürümqi (UR), which are represented as energy-producing and heavy manufacturing cities in China. The primary aim of the study is to explore the optical properties, sources, and chemical processes of water-soluble BrC (WS-BrC). The average mass absorption efficiency at 365 nm (MAE365) of WS-BrC at these four cities was 1.24 ± 0.19 m2 g−1 (XN), 1.19 ± 0.12 m2 g−1 (LZ), 1.07 ± 0.23 m2 g−1 (YC), and 0.78 ± 0.16 m2 g−1 (UR). The properties of WS-BrC were further investigated by an acid–base titration experiment. The results showed that the MAE365 values in all cities increased with higher pH values (2–11), while the fluorescence intensities of water extracts fluctuated with pH values, being stronger under both highly acidic and basic conditions. The sensitivity to pH variation was most pronounced in the WS-BrC samples from YC and LZ, indicating the important contribution of acid or base functional group compounds in these locations. Additionally, the study revealed significant photo-enhancement (LZ) or photo-bleaching (YC and UR) phenomena of WS-BrC in different cities. These results suggest that the sources and/or chemical processes of WS-BrC varied among the cities. The sources and chemical processes of WS-BrC were further explored by a combination of parallel factor analysis (PARAFAC) on excitation–emission matrix (EEM) spectra of WS-BrC and positive matrix factorization analysis (PMF) on high-resolution mass spectra of water-soluble organic aerosol (WSOA). Six PARAFAC components were identified, including three humic-like substances (HULIS; two less oxygenated (LO) HULIS and one highly oxygenated (HO) HULIS), two protein-like or phenol-like substances (PLS), and one undefined substance. Four PMF factors were identified, including a water-soluble primary OA (WS-POA), a less oxidized oxygenated OA associated with coal combustion-induced WSOA (LO-OOA), and two highly oxidized oxygenated OAs resulting from photochemical oxidation and aqueous-phase oxidation transformations (HO-OOA1 and HO-OOA2). WS-POA was determined to be the most significant source of light absorption, accounting for 30 %–60 % based on multiple linear regression models, and it showed a significant correlation with PLS and LO-HULIS components. The loss of light absorption of WS-POA was found to occur through its conversion to LO-OOA and HO-OOAs through photochemical or aqueous reactions, with HO-OOAs being significantly correlated with the HO-HULIS component. These processes can be clearly illustrated by integrating optical properties and chemical composition using a Van Krevelen diagram and an EEM plot.

Production of bioactive and functional frozen yogurt through easy-to-make microspheres incorporation.

In the food industry, the microencapsulation process is important to control the release of active encapsulated ingredients, mask unwanted flavors, colors, and unpleasant smells, increase shelf life, and protect encapsulated components from light, moisture, and nutritional loss. In this process, microspheres are formed using cross-linked polymer, which can incorporate aqueous or oily ingredients, using simple physicochemical methods of phase separation by coacervation, without the need for organic solvents. In this context, this study aimed to develop bioactive, functional frozen yogurt through the incorporation of microspheres loaded with ascorbic acid or omega 3. The process used resulted in small microspheres (15-80μm), imperceptible to the palate, and capable of swelling about 14 times, being suitable for incorporating omega 3, without altering the swelling, and extending the shelf life of the ascorbic acid for 6weeks, even in an acid medium. Also, the matrix does not affect the properties of frozen yogurt and acts as a stabilizer, contributing to reduce the melting rate. The sensory analysis proved that encapsulation was promising to mask the taste and odor of omega 3 and to protect the ascorbic acid, without altering the properties and quality of the frozen product.

Circularly polarized thermally activated delayed fluorescence OLEDs with nearly BT.2020 red emission

Thermally activated delayed fluorescence (TADF) materials with saturated red emission anda large x CIE coordinate hold significant potential for application in high-efficiency, high-contrast and wide-gamut display techniques. Recently, circularly polarized organic light-emitting diodes (CP-OLEDs) have attracted increasing attention for the enhancement of electroluminescence (EL) performance via minimizing the light loss caused by the integrated polarizer. However, the efficient red CP-OLEDs have been rarely reported by now. In this work, a simple approach to CP-OLEDs towards BT.2020 red emission was applied via the integration of polycyclic aromatic chromophore and chiral octahydrobinaphthol, which consequently resulted in the intense circularly polarized luminescence (CPL), long-wavelength emission and excellent photoluminescence quantum yields (PLQY). The CP-OLEDs based on (R)-OBN-3CN demonstrated the state-of-the-art EL performance with the maximum external quantum efficiencies (EQEmax) of 19.7 % at 646 nm and the dissymmetry factor (gEL) of −1.1 × 10−3. Furthermore, CP-OLEDs doped with 12 wt% (R/S)-OBN-3CN exhibited efficient red electroluminescence with the CIE coordinates of (0.70, 0.30), which was very close to the saturated red emission specified in BT.2020.

Integrating sphere port error in diffuse reflectance measurements.

The impact of a finite thickness integrating sphere port on the measurement of diffuse reflectance is addressed in a combined numerical and experimental study. It is shown that for a finite thickness port, additional light losses occur due to scattering between the sphere port wall and the test sample, causing the sample reflectance to be underestimated. Monte Carlo ray tracing is applied to obtain quantitative estimates of the resulting measurement error for the case of a diffusely reflecting sample. The effects of sample reflectance, port geometry, and illumination beam size on the measurement error are explored. Experimental data collected with a pair of integrating sphere reflectometers with different port geometries support the validity of the numerical results. It is argued that finite port thickness may be an important source of measurement error, even for a well-designed integrating sphere port, and a strategy for minimizing this error is discussed.

Fusing the Wireless Technique Optical Fiber Force Sensor for Remote Monitoring of Sleeping Posture

This article presents a novel three-dimensional-printable optical fiber force sensor used to guide the rehabilitation of patients with heart failure (HF), and builds the corresponding sleeping posture monitoring system. The designed sensing probe is mainly composed of a lamina emergent spring (LES), a prismatic-tip optical fiber, and a wireless-based signal collection module including WiFi and Bluetooth. A data and theoretical model-driven method has been proposed to derive the stiffness model of the LES with a small error of less than 10% compared with the experimental stiffness. To better obtain the sleeping posture characteristics, a herringbone sensing probe layout scheme with eight sensors has been proposed with consideration of the fiber bending-induced light loss. The calibration and performance experiments have been implemented to validate the reliability of the sensing probe including the wireless transmission function. A Sparrow Search Algorithm optimized back propagation neural network has been designed to distinguish the typical six sleeping postures with a high recognition accuracy of 98.1%. Several experiments have been carried out to verify the real-time performance, the feasibility of mutibed remote monitoring, and the long-term monitoring capability of the sleeping posture monitoring system. The monitoring results can be shared with the user's family member mobile phone or monitoring center to check their sleeping postures. Such merits indicate that fusing the wireless technique optical fiber force sensor has huge potential to guide the rehabilitation of HF patients

Low Blind Zone Atmospheric Lidar Based on Fiber Bundle Receiving

Atmospheric constituents feature a large vertical gradient in concentration, especially at the first few hundred meters over the earth’s surface. Atmospheric lidar usually cannot cover this range due to the incomplete overlap effect or the limited dynamic range of detectors. This drawback is well known as the blind zone effect, which hinders the application of atmospheric lidars in many aspects. In this work, a method based on an optical fiber bundle was proposed to mitigate the blind zone effect. An optical fiber head with several stages, installed at the focal plane of the telescope, is used to receive backscatter light from different range levels. The design of the optical fiber head is analyzed with the ray-tracing technique. The optical fiber installed at the highest stage of the fiber head can collect far-range light like a small aperture, and all the other optical fibers are bundled into a near-range detection channel to receive backscatter light from the first few hundred meters. This special design can avoid the near-range light loss in conventional lidar systems, usually equipped with a small aperture. Different optical attenuations are then applied to near-range and far-range channels to suppress the overall signal dynamic range. This light-receiving method was applied in a 1030 nm elastic lidar, in which a fiber bundle with a three-stage fiber head was fabricated and installed. A test experiment was performed to verify this approach. A good agreement between simulations and in-system results was found. Based on this design, the blind zone of the lidar system is less than 50 m, and the detectable range can be over 10 km along the lidar’s line of sight with a single telescope receiver. This approach brings a new way of designing atmospheric lidar with a low blind zone and can strengthen our ability to monitor urban pollution and promote land-atmosphere interaction research.

The synergistic regulation effect on the structure and electronic properties of graphene by methane plasma, Stone-Wales defect and equibiaxial strain

The synergistic regulation effects on the structure and electronic properties of graphene by methane plasma, Stone-Wales defect and equibiaxial strain has been investigated. It is found that the graphene containing Stone-Wales defect (SWG77) has metallicity, when surface adsorbing a CH3+ion, CH3+@SWG77 is a semiconductor with 0.339 eV indirect band gap. The stress-strain curve results indicate that adsorbing different plasma fragments in methane may influence to varying degrees on the ultimate strain of the SWG77 system. The hole mobility has an enhanced tendency as the tensile strain increases for the CH3+@SWG77 system. In addition, the hole mobilities seem to reach saturation when applied equibiaxial strain increase to 2 % or larger. Applying equibiaxial strain on the system substrate, the band gaps of CH3+@ SWG77 and 2CH3+@ SWG77 systems are almost unaffected. In addition, the concentration of CH3+ ion has a certain effect on the light absorption coefficient, reflectivity, and energy loss of the SWG77 system in the visible light region (1.62 eV–3.11 eV) and ultraviolet regions (3.11 eV–5.50 eV). Therefore, defect graphene with appropriate carrier mobility and band gap may be designed by adjusting the equiaxial strain and methyl concentration, which provides useful theoretical support for the development of optical electrical multifunctional electronic devices based on graphene, and is conducive to promoting the application of graphene materials in the field of band gap engineering.

Refractive index SPR sensor with high sensitivity and wide detection range using tapered silica fiber and photopolymer coating.

This paper introduces a surface plasmon resonance (SPR) sensor using tapered silica fiber and photopolymer coating for enhanced refractive index (RI) detection. Tapering the silica fiber to a diameter of 10 µm ensures the evanescent wave leaks into a 1.8-µm thick photopolymer film, which increases the average waveguide RI and broadens the RI detection range accordingly. A 50-nm thick single-side gold film is coated on the photopolymer film, exciting SPR and causing less light transmission loss than a double-side gold film. The method avoids the complex microfabrication processes of conventional polymer optical fiber SPR sensors, while the waveguide RI can be controlled by altering the curing time of the photopolymer during fabrication. The sensor has an overall sensitivity of 3686.25 nm/RIU, enabling RI detection of 1.333 - 1.493. Moreover, the sensor has an ultrahigh sensitivity of 6422.9 nm/RIU in the RI range of 1.423 - 1.493. The temperature response is about 1.43 nm/°C at 20 - 50 °C, which has little impact on RI detection. Finally, we demonstrate that the sensor can grade the severity of hepatic steatosis by measuring the RIs of cytoplasm/triglyceride emulsions with superior sensing performance.

TiO2 incorporated into a blend of biopolymeric matrices improves film properties and affects the postharvest conservation of papaya fruits under UV light

This work investigated the properties of chitosan-cassava starch biopolymeric films containing nanometric photoactive TiO2 particles for use in postharvest conservation of papaya fruits under UV light at a temperature of 15 ± 1 °C and a relative humidity of 90 ± 1 % for 24 days. Starch-chitosan blend films showed intermediate hydrophobicity and improved mechanical properties. The addition of 1 % TiO2 into the polymeric matrix of starch/chitosan (1:1) further improved the mechanical properties with solubility of 16.04 ± 0.41 %, visible transmittance of 31.76 ± 1.58 %, and reduced UV transmittance of more than 97 %. However, the addition of TiO2 exceeding 1 % led to the formation of agglomerates and excessive reduction in film transparency. UV exposure damaged the fruit peel and resulted in a higher weight loss. In contrast, the addition of 1 % TiO2 to the blend reduced the weight loss in light and dark by 7.12 ± 1.57 % and 5.27 ± 0.31 % respectively, and delayed fruit ripening.

Thermodynamic analysis and optimization of a novel system integrating with solid oxide fuel cell-gas turbine and parabolic trough collector for using in sports buildings

This study aims at sport buildings and discussing mathematical models' applications focused on energy problems, both on the thermal and electrical sides. Methanol is a type of alcohol that can be used as an alternative fuel option. Solid oxide fuel cells are a type of fuel cell that have advantages over other types of fuel cells such as high efficiency and low emissions. Researchers are exploring the use of methanol in solid oxide fuel cells, because it can be converted into synthetic gas at certain temperatures using catalysts. This study focuses on a system that uses solar energy for combined cooling, cooling, heating, and power generation. Solar energy is a renewable and environmentally friendly source of energy. Methanol is synthesized and then converted into gases for use in solid oxide fuel cells. This process is called reforming. A fuel cell and a gas turbine system can increase power generation and provide heat for cooling with a conversion efficiency exceeding 64%, but 15% of energy is lost due to light and heat losses.

(Invited) Photoelectrode Membrane Assemblies with Transparent Conductive Gas Diffusion Layers for Solar Fuel Production

Gas diffusion electrodes are essential components of common fuel and electrolysis cells that use gas phase reactants and products, but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance, and thus limit the development of photoelectrode membrane assemblies for gas-phase solar fuel production. In this presentation, the application of solar H2 production from humid air is motivated and the simple and scalable preparation of transparent gas-diffusion layers using F-doped SnO2 (FTO) coated SiO2 interconnected fiber felt substrates is introduced. The resulting substrates have a porosity of 90 %, a roughness factor of 15.8 and a Young’s Modulus of 0.2 GPa. A sheet resistivity of 20 ± 3 Ω sq−1 and a loss of incident light of 41% at an illumination wavelength of 550 nm is found with FTO coating. The application of various semiconductors on the substrates was established including Fe2O3 (chemical bath deposition), CuSCN and Cu2O (electrodeposition), and semiconducting polymers (dip coating) and the liquid-phase photoelectrochemical performance commensurate with flat FTO substrates was confirmed. Finally, gas phase H2 production was demonstrated with a polymer semiconductor photocathode membrane assembly at 1-Sun photocurrent density on the order of 1 mA cm–2 and Faradaic efficiency of 40%.

Towards real-world haze removal with uncorrelated graph model

The scene restoration effect of the dehazing algorithms usually suffers from double quality interference. First, the dehazing methods based on the atmospheric scattering model (ASM) lead to light loss. Second, the synthetic data used for supervised learning may produce apparent data deviation from the real hazy scene, which seriously weakens the generalization ability of the model. To address the above problems, we propose an uncorrelated graph dehazing model for real-world scenes. The process firstly eliminates the correlation in the representation space by establishing a directed acyclic graph with isolated points, thus enhancing the generalization performance of the model. Secondly, to suppress over-exposure that may occur on real-world data, the proposed model training is performed with a combination of light control. This work improves the ASM and constructs a new dataset applicable to natural haze scenes. Finally, the effectiveness of the proposed method can be verified through multiple experimental comparisons.

Flexible multi-layered coloring transparent electrode composed of AZO–based materials

Color implementation in flexible photovoltaics (PVs) is aesthetically important in modern vehicles and buildings. To implement color in flexible PVs using conventional distributed Bragg reflector (DBR) methods, it is necessary to reduce its brittleness and minimize the light loss due to refractive index differences (Δn). Here, color-implemented transparent front electrodes for flexible and transparent solar cells (FTSCs) have been proposed using an aluminum-doped zinc oxide (AZO)–based multilayer with periodic hydrogenation (AZO:H). The hydrogenation of AZO causes passivation in vacancies of oxygen and zinc and strengthening of the O–H bonds, resulting in improved of electrical and optical properties and a very low Δn of ∼5%. Using the AZO:H DBR–diffuser electrodes, we demonstrate three primary colors and colored FTSCs made of silicon thin film. The FTSCs show little change in power conversion efficiencies for the different colors owing to low return loss by the very low Δn. They are lightweight for their high specific power and exhibit excellent flexibility that enables them to endure the bending stress of 600 cycles at a 6 mm bending radius. The developed device can be used for vehicle and building-integrated PV applications, and the methodology can be used for other thin-film solar cells that require color and flexibility.

The Duration of Menstrual Blood Loss: Historical to Current Understanding

Most published research focuses on the amount of menstrual blood loss and, to a lesser extent, on cyclicity. Little attention has been paid to the duration of bleeding, the factors that enable its cessation within a ‘normal’ timeframe, or to patterns that entail interruption and resumption of blood loss. The definition of what constitutes normal remains arbitrary and there is no therapy specifically designed to shorten the duration of bleeding. Here, we critically review the literature that addresses the duration of bleeding and the factors that trigger endometrial breakdown and repair. Available reports used population averages which mask inter- and intra-individual variations. The duration of bleeding is not necessarily linked to the amount of loss but may be influenced by age, ethnicity, habitus, region and altitude of residence, dieting and stress. The onset of bleeding has been linked to declining steroid production by the corpus luteum. There remains considerable controversy around the extent of endometrial shedding at menstruation. This is likely to vary within and between women. The significance of a change from previous patterns, very short or prolonged bleeding, days of light loss or spotting before or after days of bleeding, or of bleed-free days that punctuate flow, remain poorly understood.

Effect of macroscopic defects on optical properties of fluorophosphate glasses

Fluorophosphate glass is the core of laser materials and also has an important reference value for an optical lens. According to Kirchhoff’s law, this paper focuses on the optical loss of incident light entering fluorophosphate glass. The transmittance and refractive index of optical glass were measured by an ultraviolet-visible spectrophotometer (Uv) and V-prism tester. With the sample thickness increasing from 10 mm to 50 mm, the transmittance of grade 4 fluorophosphate glass decreases from 85.32 % to 76.91 %, and the scattering rate increases from 8.4704 % to 17.0591 %. The microstructure and internal images of macroscopic defects were obtained by projective optical microscopy. In addition, an electron probe (EPMA) was used to analyze the defective components and identify the main components of the defects. The results show that the high content of P/Al/O element is the main cause of optical loss.

Development of thin film quarter-waveplate for polarization-independent liquid crystal on silicon phase modulators

Liquid crystal on silicon (LCoS) phase modulators spatially modulate the phase of light across the panel. The orientation order and elongated molecules of nematic liquid crystals (LCs) means that traditional LCoS phase modulators are inherently polarization-dependent, resulting in either complicated polarization manipulation systems or high optical power loss for unpolarized incident light. We propose a polarization-independent LCoS (PI-LCoS) device that combines existing technologies, which allows for cost-effective fabrication. Our PI-LCoS phase modulator is suitable for a wide variety of applications in telecommunication, adaptive optics, and display technologies. We have demonstrated the feasibility of the proposed PI-LCoS device by fabricating polarization-independent LC cells using a thin-film quarter-wave plate composed of a photoalignment layer and a layer of LC polymer. We show experimentally that the proposed design can efficiently modulate the phase of light with arbitrary input polarization.

Paper-Thin Al-Catalyzed Si Nanowire Solar Cells and Efficiency Enhancement by Hybrid Nanostructures with Mn-Doped Perovskite Nanocrystals

The use of thin silicon (Si) wafers and streamlined fabrication methods that can be scaled up without compromising device efficiency is a key strategy for realizing low-cost and flexible solar cells. Herein, aluminum (Al)-catalyzed Si nanowires (NWs) formed by vapor–liquid–solid growth on paper-thin polished and etched Si(111) wafers of 100 and 60 μm thickness with high proficiency for minimizing interfacial defects and light absorption loss have been accomplished. Successfully addressing the major challenge of rapid Al catalyst oxidation by ex situ and uncomplicated growth conditions allows for the potential to scale up the process while preventing the formation of deep-level traps resulting from catalyst contamination. The Si NWs formed on the nanowave surface of a thin etched Si wafer evidence comparable light absorbance and low interfacial defects to those grown on thin polished and traditional Si wafers. Fabrication of thin Si NW solar cells with a homojunction p+–p–n–n+ structure toward the enhanced power conversion efficiency (PCE) by hybrid nanostructures with manganese-doped cesium lead chloride (CsPb0.81Mn0.19Cl3) perovskite nanocrystals (NCs) using a simple drop-casting method has been explicitly explained. The precise tuning of the energy band and NC size enabled a significant radiative energy transfer by matching the light absorption range of NCs with a high Stokes shift in the luminescence spectrum and the spectral response range of underlying Si solar cells. The nonradiative energy transfer efficiency of NCs and an NC amount infiltration on homojunction Si NW solar cells for maximizing PCE enhancement were examined. The effective photon-harvesting architectures of NWs and NCs together with efficient energy transfers and surface passivation from NCs to the underlying homojunction Si NW solar cells could capably enhance PCE up to a 9% level. These results exhibited the potential for feasible low-cost and large-scale fabrication techniques with lower consumption of raw materials for future photovoltaic applications.

Configuration of the active region for the Ge-on-Si photodetector based on carrier mobility

The design of vertical and lateral PIN Ge-on-Si photodetectors was motivated by the disparity in electron and hole mobilities. In the case of vertical PIN junction detectors, configuring the slab region as n-type doping leads to a notable increase in the bandwidth of approximately 20 GHz compared to utilizing p-type doping for the slab. For lateral PIN junction detectors, we determined that setting the length of the n-type slab region to be 2.8 times that of the p-type slab region, based on the carrier saturation drift rate ratio, does not compromise the bandwidth. This configuration enhances the bandwidth while minimizing light absorption loss from the electrode. The proposed design in this study enhances the performance of Ge-on-Si photodetectors without adding complexity to the fabrication process. The principles applied in this study serve as instructive references for the conceptualization of other photonic or electronic devices, reinforcing the widespread applicability of these design strategies.

Antireflection and radiative cooling difunctional coating design for silicon solar cells.

Passive daytime radiative cooling (PDRC) as a zero-energy consumption cooling method has broad application potential. Common commercial crystalline silicon (c-Si) solar cell arrays suffer working efficiency loss due to the incident light loss and overheating. In this work, a radiative cooler with PDMS (polydimethylsiloxane) film and embedded SiO2 microparticles was proposed to use in silicon solar cells. Both anti-reflection and radiative cooling performance can be improved through numerical parametric study. For the best performing of PDMS/SiO2 radiative cooler, the thickness of PDMS layer, volume fraction and radius of the embedded SiO2 particles have been determined as 55 µm, 8% and 500 nm, respectively. 94% of emissivity in first atmospheric window band (8-13 µm) for radiative cooling and 93.4% of solar transmittance at the crystalline silicon absorption band (0.3-1.1 µm) were achieved. We estimated that the PDMS/SiO2 radiative cooler can lower the temperature of a bare c-Si solar cell by 9.5°C, which can avoid 4.28% of efficiency loss. More incident light can enter and be utilized by silicon layer to enhance the efficiency of the solar cells. The proposed difunctional radiative cooling coating may become guidance for next generation encapsulation of crystalline silicon solar cells.

Enhanced light extraction for red organic light emitting diodes via PDMS convex lens based on breath figure method

To inhibit the light loss of substrate mode at the substrate/air interface in organic light emitting diodes (OLEDs), regular porous polystyrene (PS) template was fabricated via the “Breath figure” method. The structure of porous mold was optimized by adjusting the PS solution concentration from 10 to 60 mg/ml and relative humidity from 60% to 80%. The optimal porous PS mold was achieved at 50 mg/ml PS solution under 70% relative humidity. Then, elastic micro-lens arrays based on transparent elastomer polydimethylsiloxane (PDMS) were obtained via a two-step transferring process from the porous PS mold. The projection experiment exhibits excellent focusing effect of the PDMS convex lens relative to the planar PDMS film. These PDMS micro-lens films were in situ fabricated onto the external face of the red OLED device to extract substrate mode light. By using the PDMS micro-lens array with a height of 1.2 μm and a diameter of 6.7 μm, the OLED device demonstrates an enhancement of 32.7%, 35.6%, 46.5%, and 27.6% for maximum luminance, current efficiency, power efficiency, and external quantum efficiency, respectively, without changing its color purity. The device with PDMS micro-lens exhibits a higher intensity than an ideal Lambertian emission pattern, especially at viewing angles from 30° to 60°. It suggests that the introduction of external micro-lens structure significantly improves the light outcoupling efficiency.