Measurements and Modelling of Aritificial Sky Brightness: Combining Remote Sensing from Satellites and Ground-Based Observations

In recent decades, considerable research has been carried out both in measuring and modelling the brightness of the sky. Modelling is highly complex, as the properties of light emission (spatial and spectral distribution) are generally unknown, and the physical state of the atmosphere cannot be determined independently. The existing radiation transfer models lack the focus on light pollution and model only a narrow spectral range or do not consider realistic atmospheric circumstances. In this paper, we introduce a new Monte Carlo simulation for modelling light pollution, including the optical density of the atmosphere and multiple photon scattering, then we attempt to combine the available information of satellite and ground-based measurements to check the extent to which it is possible to verify our model. It is demonstrated that we need all the separate pieces of information to interpret the observations adequately.

Unravelling the structural complexity of glycolipids with cryogenic infrared spectroscopy

Glycolipids are complex glycoconjugates composed of a glycan headgroup and a lipid moiety. Their modular biosynthesis creates a vast amount of diverse and often isomeric structures, which fulfill highly specific biological functions. To date, no gold-standard analytical technique can provide a comprehensive structural elucidation of complex glycolipids, and insufficient tools for isomer distinction can lead to wrong assignments. Herein we use cryogenic gas-phase infrared spectroscopy to systematically investigate different kinds of isomerism in immunologically relevant glycolipids. We show that all structural features, including isomeric glycan headgroups, anomeric configurations and different lipid moieties, can be unambiguously resolved by diagnostic spectroscopic fingerprints in a narrow spectral range. The results allow for the characterization of isomeric glycolipid mixtures and biological applications.

2D Perovskite Narrowband Photodetector Arrays

Narrowband photodetectors, which are capable of detecting light within a narrow spectral range, have important applications in the fields of digital cameras, biosensing and artificial vision. In particular, 2D layered...

The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

ABSTRACT A medium- and high-resolution spectroscopic survey of helium-rich hot subdwarfs is being carried out using the Southern African Large Telescope (SALT). Objectives include the discovery of exotic hot subdwarfs and of sequences connecting chemically peculiar subdwarfs of different types. The first phase consists of medium-resolution spectroscopy of over 100 stars selected from low-resolution surveys. This paper describes the selection criteria, and the observing, classification, and analysis methods. It presents 107 spectral classifications on the MK-like Drilling system and 106 coarse analyses (${T_{\rm eff}}, \log g, \log y$) based on a hybrid grid of zero-metal non-LTE and line-blanketed LTE model atmospheres. For 75 stars, atmospheric parameters have been derived for the first time. The sample may be divided into six distinct groups including the classical ‘helium-rich’ sdO stars with spectral types (Sp) sdO6.5–sdB1 (74) comprising carbon-rich (35) and carbon-weak (39) stars, very hot He-sdO’s with Sp ≲ sdO6 (13), extreme helium stars with luminosity class ≲5 (5), intermediate helium-rich subdwarfs with helium class 25–35 (8), and intermediate helium-rich subdwarfs with helium class 10–25 (6). The last covers a narrow spectral range (sdB0–sdB1) including two known and four candidate heavy-metal subdwarfs. Within other groups are several stars of individual interest, including an extremely metal-poor helium star, candidate double-helium subdwarf binaries, and a candidate low-gravity He-sdO star.

Controlling the plasmon resonance via epsilon-near-zero multilayer metamaterials

Localized plasmon resonance of a metal nanoantenna is determined by its size, shape and environment. Here, we diminish the size dependence by using multilayer metamaterials as epsilon-near-zero (ENZ) substrates. By means of the vanishing index of the substrate, we show that the spectral position of the plasmonic resonance becomes less sensitive to the characteristics of the plasmonic nanostructure and is controlled mostly by the substrate, and hence, it is pinned at a fixed narrow spectral range near the ENZ wavelength. Moreover, this plasmon wavelength can be adjusted by tuning the ENZ region of the substrate, for the same size nanodisk (ND) array. We also show that the difference in the phase of the scattered field by different size NDs at a certain distance is reduced when the substrate is changed to ENZ metamaterial. This provides effective control of the phase contribution of each nanostructure. Our results could be utilized to manipulate the resonance for advanced metasurfaces and plasmonic applications, especially when precise control of the plasmon resonance is required in flat optics designs. In addition, the pinning wavelength can be tuned optically, electrically and thermally by introducing active layers inside the hyperbolic metamaterial.

Efficiency enhancement of silicon solar cell using effective interface face method in antireflective coating layers

Carrier generation is one of the important processes in solar cell operations. The generation rate depends on the number of photons absorbed by solar cell. This absorption of photons is affected by the reflection losses. The light trapping technique is used to minimize the reflection loss. In this work, a theoretical design of Effective Interface Antireflective Coating (EI-ARC) in solar cell is proposed which is based on the theory of Fabry–Perot interference filters. This design is composed of a space index layer with two subsystems of multilayer, which allows multiple reflections within it. It is shown that the combination of this two systems yields high transmission values over a narrow spectral range. This EI-ARC model increases the Internal Quantum Efficiency (IQE) and carrier generation rate of solar cell. These parameters are significant to raise the efficiency of the solar cell.

UPT Chaos-Based Encryption Characteristic Analysis for Speech Signal

In chaotic speech signal encryption, masking is the most direct and convenient method. But the chaotic signals usually have a narrow spectral range in low frequency region. In order to overcome the disadvantage that the higher frequency signals can not be completely covered up, UPT is used to conduct a nonlinear transformation to chaotic signal. After UPT, chaotic types are increased, chaotic characteristics are improved and spectral range is widened. Simulation experiments are done respectively from frequency domain and spectrogram perspectives. The chaos before and after transformation are used to mask speech signal. Decoding experiment is taken on the speech encrypted by transformed chaos. Experiment results show that, after UPT, the encryption effect of speech signal is improved obviously. This method has a high security and a strong anti-attack ability.