Evaluation methodology for light sources used to illuminate highly photosensitive artwork

Spectral energy radiated by light sources is the primary source of colour damage in highly photosensitive artworks (HPAs). However, spectral power distributions differ for different light sources, and the absorption and reflection characteristics of different materials, when irradiated by each narrow spectral energy band, also differ. This could result in large differences in the degree of radiation damage for materials under the same lighting intensity. In this paper, the suitability of different light sources used to illuminate HPAs was experimentally investigated over a long period of time by irradiating nine types of typical HPA materials with 10 different narrow-band light sources. By analysing the colour difference data of the illuminated material against the amount of exposure, a mathematical model relating the spectral composition and the damage to the colour of HPA materials was obtained. Based on this, a colour damage evaluation equation for light sources used for lighting HPAs was proposed. Finally, the equations were discussed using an example.

Reflection Characteristics of Airy Beams Impinging on Graphene-Substrate Surfaces

In this work, we analytically and numerically investigate the reflection characteristics of the airy beams impinging on graphene-substrate surfaces. The explicit analytical expressions for the electric and magnetic field components of the airy beams reflected from a graphene-substrate interface are derived. The local-field amplitude, Poynting vector, and spin and orbital angular momentum of the reflected airy beams with different graphene structure and beam parameters are presented and discussed. The results show that the reflection properties of the airy beams can be flexibly tuned by modulating the Fermi energy of the graphene and have a strong dependence on the incident angle and polarization state. These results may have potential applications in the modulation of airy beams and precise measurement of graphene structure parameters.

Polarization-insensitive broadband omni-directional anti-reflection in ZnO nanoneedle array for efficient solar energy harvesting

Broadband omni-directional anti-reflection characteristics have been an important issue because they can maximize the optical absorption in photovoltaic devices. Here, we investigate the optical properties of ZnO nanoneedle arrays to...

A three-dimensional broadband underwater acoustic concentrator

We propose a three-dimensional (3D) omnidirectional underwater acoustic concentrator based on the concept of acoustic prison, which can realize a substantial enhancement of underwater sound signals in broadband ranges. This device mainly employs the non-resonant multiple reflection characteristics of the semi-enclosed geometric space, so it has a wide working frequency bandwidth. Compared with the previous reported concentrators based on transform acoustics mechanism, the structure is more simple, and most importantly, it can realize omnidirectional signal enhancement in 3D space. Moreover, the working frequency band of this acoustic concentrator depends on the size of the concentrator, so it can be changed directly through a size scaling, which is convenient for engineering applications. In general, the designed underwater acoustic concentrator has the advantages of simple structure, scalability and large bandwidth of working frequency, and high signal gain. It has potential application values in underwater target detection and other aspects.

Spatial distribution prediction of pre-Sinian volcanic and metamorphic rocks in Xinhenan-Sandaoqiao area, Northern Tarim Basin

The main type of oil and gas reservoir in the Xinhenan-Sandaoqiao area is buried hills. The distribution pattern and scale of reservoirs are obviously controlled by pre-Sinian basement strata. However, the lithologic combination and spatial distribution pattern of pre-Sinian basement in this area are still unclear. In this paper, the spatial distribution of pre-Sinian basement volcanic and metamorphic rocks is studied by using the method of multifactor comprehensive analysis. Firstly, the lithology and lithologic combination of igneous and metamorphic rocks are determined according to cores and thin sections. Guided by the seismic reflection characteristics of different lithologic combinations, different lithologic combinations are identified on the profile by combining the seismic reflection characteristics of single well and multiwell. Secondly, using cluster analysis technology, three seismic attributes sensitive to lithology are selected from 10 attributes, crossplots of three seismic attribute values are constructed, and the distribution range of attribute values corresponding to different lithologic combinations is defined for plane lithologic identification. Finally, the plane lithology distribution of the surface layer of pre-Sinian basement is described by combining plane and profile. Six distribution types were identified: deep metamorphic bedrock area in Kuqu depression, dynamic mixed metamorphic rock and intermediate-acidic intrusive rock area, metamorphic bedrock in thrust napple slopes area, thermal contact metamorphic rock area, intermediate-acidic intrusive rock area, dynamic metamorphic rock area and gneiss area in faulted uplift core.

Vector-Field Visualization of the Total Reflection of the EM Wave by an SRR Structure at the Magnetic Resonance

Metamaterials are artificially structured composite media with a unique electromagnetic (EM) response that is absent from naturally occurring materials, which appears counterintuitive and aggravates traditional difficulties in perceiving the behavior of EM waves. The aim of this study was to better understand the interaction of EM waves with metamaterials by virtual visualizing the accompanying physical phenomena. Over the years, virtual visualization of EM wave interactions with metamaterials has proven to be a powerful tool for explaining many phenomena that occur in metamaterials. In this study, we performed virtual visualization of the interaction of an EM plane wave with a split-ring resonator (SRR) metamaterial structure, employing CST Studio software for modeling and comprehensive simulations of high-frequency EM fields of 3D objects. The SRR structure was designed to have its magnetic resonance at the frequency f = 23.69 GHz, which is of interest for antennas supporting wireless microwave point-to-point communication systems (e.g., in satellite systems). Our numerical calculations of the coefficients of absorption, reflection, and transmission of the EM plane wave incident on the SRR structure showed that the SRR structure totally reflected the plane EM wave at the magnetic resonance frequency. Therefore, we focused our research on checking whether the results of numerical calculations could be confirmed by visualizing the total reflection phenomenon on the SRR structure. The performed vector-field visualization resulted in 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period, which demonstrated the existence of characteristic features of the total reflection phenomenon when the EM plane interacted with the studied SRR, i.e., no EM field behind the SRR structure and the standing electric and magnetic waves before the SRR structure, thus, confirming the numerical calculations visually. For deeper understanding the interaction of the EM plane wave with the SRR structure of reflection characteristics at the magnetic resonance frequency f = 23.69 GH, we also visualized the SRR structure response at the frequency f = 21 GHz, i.e., at the so-called detuned frequency. As expected, at the detuned frequency, the SRR structure lost its metamaterial properties and the obtained 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period showed the transmitted EM wave behind the SRR structure and no EM (fully) standing waves before the SRR structure. The visualizations presented in this study are both unique educational presentations to help understand the interaction of EM plane waves with the SRR structure of reflection characteristics at the magnetic resonance and detuned frequencies.

A Composite Matching Layer with Anti-Reflection Characteristics for Broadband Acoustic Scattering Reduction

A composite matching layer composed of periodically arranged scatters with anti-reflection (AR) characteristics is proposed for broadband scattering reduction. The anti-reflection structure is composed of periodically arranged metal foam scatters, and it is the first attempt to be applied in the field of suppressing acoustic reflection. A complete theoretical model is developed to reveal the mechanism of scattering reduction and acoustic absorption based on effective medium theory and the transfer matrix method. The correctness and effectiveness of the theoretical model are verified by the finite element method (FEM), showing acoustic reflectance of less than 13.5% at broadband frequencies. The variation trends of reflectance are deeply investigated. The superior acoustic scattering reduction performance suggests that the matching layer possesses potential for acoustic imaging equipment and acoustic stealth.

Research on red and green porcelain sherd of Bayi Kiln using terahertz time-domain spectroscopy and imaging

Terahertz (THz) technology is particularly suitable for non-destructive detection of porcelain sherd due to the unique properties of non-ionizing, high penetration, and broad-spectrum. In this paper, we investigated the reflection characteristics of the pigments and sediments for red and green porcelain sherd of Bayi kiln made in Shanxi province during the Jin Dynasty by terahertz time-domain spectroscopy (THz-TDS), obtaining the spectral responses of different components. Furthermore, Raman spectroscopy was used as a complementary technique to complete the qualitative analysis of the pigments and sediments. In addition, the reflective THz imaging was performed to visualize the pigments and sediments in different regions of the porcelain sherd, realizing the visual detection of the pattern on the surface of porcelain sherd. These results show that THz-TDS and THz-imaging can serve as effective tools for the detection and analysis of ancient Chinese porcelain.