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Modeling of Radiative Properties of Polystyrene Foams Containing IR-Opacifiers
摘要： The addition of opacifiers in foams considerably reduces the radiative thermal conductivity and consequently enhances the insulation performance of the foams. In this work two different methods were developed to calculate the spectral specific extinction coefficient of opacified extruded polystyrene (XPS) foam material. Cell morphology and thermal conductivity of two identical XPS-foams, one opacified with 3 wt% carbon black as opacifier and one without opacifier, were thoroughly characterized. The experimental results were in a good agreement with the theoretical results obtained from two different computing techniques. These methods allow a good prediction of the specific extinction coefficient of arbitrary opacified foam material.
关键词： Radiative transfer,Radiative thermal conductivity,Complex refractive index,Extinction coefficient,Porous materials,Opacifiers
更新于2025-09-23 15:23:52
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Defects anomaly in cobalt-doped ZnO nanostructures using optical and charge transient analysis
摘要： The significant effect of electrically active defects present in the device, which limits the carrier mobility, generated due to cobalt doping via the co-precipitation technique in a ZnO matrix, has been investigated on the basis of its structural, optical and charge transient behaviours. The variations observed in the absorbance and extinction coefficients as a function of wave length reveal the presence of defect states, a range of localized states and structural disorder. The presence of a non-uniform trap centre density in the material has been measured on the basis of different operational modes in charge-deep level transient spectroscopic analysis. A disparity of such a kind in the structures at the nanoscale will provide for a remarkable approach to improve the performance and reliability of the smart electronic, optoelectronics, photonics and sensing devices.
关键词： absorption coefficient,ZnO,Defect density,Q-DLTS,Nano structures,extinction coefficient
更新于2025-09-23 15:22:29
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Synthesis, photophysical properties and DFT studies of the pyridine-imidazole (PyIm) Cu(I) complexes: Impact of the pyridine ring functionalized by different substituents
摘要： A series of the pyridine-imidazole (PyIm) Cu(I) complexes with different substituents (bromide (P1), methyl (P2), and phenyl (P3)) attached on the pyridine ring are synthesized and characterized. All the complexes show the typical metal-to-ligand charge transfer (MLCT) absorption in the visible region. Complex P1 with an electron-withdrawing substituent on the pyridine ring, e.g., a bromine group, shows a red shift of the emission wavelength. Conversely, an electron-donating substituent on the pyridine ring in complex P2, e.g., a methyl group, shifts the emission to longer wavelength. Similarly, complex P3 containing the extended π-conjugation system of the ligand also exhibits a red shift of the emission wavelength. All of the complexes exhibit efficient green-yellow emission in PMMA films at room temperature with emission wavelength of 547–569 nm and quantum yields of 24.8–53.0%. Meanwhile, DFT and TDDFT methods were employed to explain the photophysical properties.
关键词： Pyridine-imidazole,Copper (I) complex,Metal-to-ligand charge transfer,Molar extinction coefficient,Density functional theory
更新于2025-09-23 15:22:29
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High-throughput laser generation of Si-nanoparticle based surface coatings for antibacterial applications
摘要： High-productivity regime of nanosecond IR-laser ablative generation of silicon colloidal solutions in water for anti-bacterial applications was found in terms of GW/cm2-level laser intensity and scanning velocity by measuring multi-shot ablative mass loss and extinction coefficients of the colloids as sub-linear and third-power intensity functions, respectively. This advantageous regime implies sub-linear mass loss versus laser intensity at the simultaneous third-power yield of nanoparticles, resulting from the subcritical-density, opaque ablative plasma regulating the sample ablation rate and the related plasma-mediated dissociation (dispergation) of the ablation products. In contrast, at higher intensities, there is a drastic increase in mass loss with the corresponding increased yield of (sub) micrometer-sized particles owing to intense plasma-driven expulsion of micro-scale melt droplets and the corresponding saturation of the extinction coefficient of the colloidal solutions because of their dynamic local “self-limiting” effect during the high-rate ablation. The optimal low-intensity regime for Si nanoparticle production demonstrates the monotonous correlated increase of mass loss and extinction coefficient in terms of increasing laser scanning velocity, indicating the diminished cumulative effects. Surface coatings prepared from the generated Si nanoparticles exhibit minor surface oxidation, as acquired as their elemental composition via energy-dispersive X-ray spectroscopy, making their contact angle for water droplets (≈51°) close to that of bare Si wafer (≈58°) with its nanometer-thick native oxide layer. Owing to good wetting, the nanoparticle-based surface coatings show strong antibacterial response regarding Gram-negative Pseudomonas auereginosa bacteria even despite their minor oxidative passivation.
关键词： Silicon nanoparticles,Colloids,Surface oxidation,Extinction coefficient,Wetting,Antibacterial tests,Gram-negative bacteria Pseudomonas auereginosa,Sub-critical ablative plasma,Nanosecond laser ablation,Mass loss
更新于2025-09-23 15:21:21
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Surface and intrinsic contributions to extinction properties of ZnSe quantum dots
摘要： This work studies extinction properties of ZnSe quantum dots terminated with either Se-surface or Zn-surface (Se-ZnSe or Zn-ZnSe QDs). In addition to commonly observed photoluminescence quenching by anionic surface sites, Se-ZnSe QDs are found to show drastic signatures of Se-surface states in their UV–visible (Vis) absorption spectra. Similar to most QDs reported in literature, monodisperse Zn-ZnSe QDs show sharp absorption features and blue-shifted yet steep absorption edge respect to the bulk bandgap. However, for monodisperse Se-ZnSe QDs, all absorption features are smeared and a low-energy tail is identified to extend to an energy window below the bulk ZnSe bandgap. Along increasing their size, a cyclic growth of ZnSe QDs switches their surface from Zn-terminated to Se-terminated ones, which confirms that the specific absorption signatures are reproducibly repeated between those of two types of the QDs. Though the extinction coefficients per unit of Se-ZnSe QDs are always larger than those of Zn-ZnSe QDs with the same size, both of them approach the same bulk limit. In addition to contribution of the lattice, extinction coefficients per nanocrystal of Zn-ZnSe QDs show an exponential term against their sizes, which is expected for quantum-confinement enhancement of electron–hole wavefunction overlapping. For Se-ZnSe QDs, there is the third term identified for their extinction coefficients per nanocrystal, which is proportional to the square of size of the QDs and consistent with surface contribution.
关键词： ZnSe,quantum dots,surface state,extinction coefficient
更新于2025-09-23 15:21:01
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Solar Engineering of Thermal Processes, Photovoltaics and Wind || Radiation Transmission through Glazing
摘要： The transmission, reflection, and absorption of solar radiation by the various parts of a solar collector are important in determining collector performance. The transmittance, reflectance, and absorptance are functions of the incoming radiation, thickness, refractive index, and extinction coefficient of the material. Generally, the refractive index n and the extinction coefficient K of the cover material are functions of the wavelength of the radiation. However, in this chapter, all properties initially will be assumed to be independent of wavelength. This is an excellent assumption for glass, the most common solar collector cover material. Some cover materials have significant optical property variations with wavelength, and spectral dependence of properties is considered in Section 5.7. Incident solar radiation is unpolarized (or only slightly polarized). However, polarization considerations are important as radiation becomes partially polarized as it passes through collector covers.
关键词： absorptance,refractive index,solar radiation,transmittance,extinction coefficient,wavelength,reflectance,collector performance,polarization
更新于2025-09-16 10:30:52
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Seasonal aerosol variations over a coastal city, Zhoushan, China from CALIPSO observations
摘要： This paper presents the observed seasonal aerosol variations over Zhoushan, an eastern coastal Chinese city. Data were obtained from the Cloud – Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite from the period of June 2007 to May 2017. We compared the columnar Aerosol Optical Depth (AOD) data from the CALIPSO and MODerate resolution Imaging Spectroradiometer (MODIS). Results showed good consistency, but the former was systematically lower than the latter. The temporal distribution of columnar AOD showed significant variations with the highest in spring and lowest in summer. Similarly, the seasonal scatter plots suggested that the highest correlation coefficient was 0.56 in winter and summer, followed by the autumn (0.53), and spring (0.40) seasons. In addition, the results revealed that the polluted dust and polluted continental aerosols (38.9% and 30.5%, respectively) were dominant aerosol subtypes observed in winter, whereas, the polluted dust (47.2%) aerosol subtype was found dominant in spring. The polluted continental aerosol subtype appeared dominant during the summer and autumn seasons, with the frequencies of about 56.0% and 47.4%, respectively. These findings can be reasonably explained using the air mass cluster analysis computed for the obtained backward trajectories derived from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Furthermore, the aerosol vertical extinction coefficient measured at the wavelength of 532 nm was found to be highest near the surface (~0.2 km-1) in winter and autumn and decreased sharply as the altitude increased indicating that aerosols were present at an altitude <2 km. However, during spring, the values of extinction coefficient remained >0.15 km-1 at an altitude range of 0–3.5 km due to convection and strong vertical mixing lifting aerosols to slightly higher levels. Furthermore, during the spring, approximately 54% of the particulate depolarization ratio (PDR) values were ≤ 0.2, and the remaining 46% of the PDR were > 0.2, suggesting both spherical and irregular particles were present in the atmosphere.
关键词： MODIS,Aerosol Optical Depth,CALIPSO,Extinction Coefficient,East China,Aerosol subtype
更新于2025-09-10 09:29:36
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Influence of carbon nanofibers electric conductivity on infrared extinction capability
摘要： Using method of moment, the calculating model of electric current distributing and scattered electric field for carbon nanofibers is established in this paper. Based on it, the expression of absorption cross section, scattering cross section and extinction cross section are got. The relationship between infrared extinction cross section of carbon nanofiber and electrical conductivity is analyzed and calculated by using Matlab. The results show that the infrared extinction cross section increases with electrical conductivity increase and peak value appeares when wavelength is longer than the length of carbon nanofiber. The electrical conductivity on peak value is related to wavelength.
关键词： carbon nanofibers,infrared extinction,absorption,scattering,extinction coefficient
更新于2025-09-04 15:30:14