Advances in radar systems have led to the emergence of low observability technologies that minimize target detectability. Among them, metasurfaces and metamaterials appear as promising solutions. In this paper, the analysis and design of a single-layer scattering metasurface with a thickness of lambda(s)/10 is presented for both monostatic and multistatic scenarios, simultaneously. The design achieves -12 dB of radar cross section reduction in the band 9.16 - 11.72 GHz, which means a reduction in the monostatic detection distance of 50%. Due to the symmetry and periodicity of the structure, the metasurface is infinitely replicable and the response has been validated for both polarizations. Moreover, the radar cross section reduction is applicable for an incidence range of theta=[-60,60](degrees) . Several prototypes have been fabricated and measured, and the results have been experimentally validated. For the measurement process, the vector background subtraction technique was used, as well as time gating and cylindrical mode expansion to transform from near-field to far-field.
Magnetohydrodynamic waves redistribute energy in magnetic structures of the lower solar atmosphere, yet constraints on how wave power and dominant frequencies are organized above sunspots remain limited, because most studies use only a few well-separated diagnostics. Here, we present multiline wave signatures in a sunspot from near-ultraviolet (near-UV) spectroscopy with the S unrise-iii UV Spectropolarimeter and Imager (SUSI). We analyse a 2 hr time series of repeated raster scans of a sunspot near disc center in the 327–329 nm spectral window (>100 lines). From these, we select 44 lines that radiative-transfer calculations suggest sample effective formation heights within the umbral core, from the deep photosphere toward the low chromosphere. For each line, we extract line-core intensity and line-of-sight velocity time series using a dedicated multiline fitting routine and compute Morlet wavelet power spectra. The refined global wavelet spectra show that most lines (in both intensity and velocity) are genuinely multifrequency, with a dominant peak and substantial statistically significant power up to 12 mHz. Unsupervised clustering of the normalized spectra groups lines into families with similar spectral shapes and reveals a progression of dominant frequencies from ∼2 to ∼10 mHz across the ensemble, for both intensity and velocity (not necessarily in the same lines). This behavior is not reproduced by a simple formation-height ranking, suggesting that uncertainties in the formation-height estimates and line-dependent diagnostic response together shape the ordering. These S unrise-iii /SUSI observations open a new regime for near-UV multiline wave studies and provide the first systematic characterization of frequency-structured sunspot wave behaviour in this spectral region.
Optimizing Raman spectrometer designs for use in extreme environments can enable acquisition of critical information that may not be accessible in situ by humans. Technology advancements currently being made for space exploration can be exploited in order for such spectrometers to be used in dangerous terrestrial environments.
The present study examines the influence of Li-Na-K molten carbonate corrosion at 700 degrees C for up to 1000 h on the microstructural evolution and mechanical behaviour of 347H Nb-stabilized austenitic stainless steel, a candidate material for Concentrated Solar Power (CSP) systems coupled with Thermal Energy Storage (TES). Corrosion exposure led to the formation of a similar to 130 mu m-thick oxide scale, composed of a poorly adherent outer LiMnO2/LiFeO2 layer and a complex multi-phased internal oxidation zone (IOZ). During the corrosion process under laboratory air conditions, extensive carburization was observed. This is consistent with carbon species generated by molten carbonate decomposition, subsequently reduced at the alloy surface and preferentially reacting with Cr-rich phases. Qualitative EDX line scans revealed carbon penetration depths of up to similar to 300 mu m, consistent with the spatial distribution of Cr-rich carbides and with pronounced hardness gradients, decreasing from the IOZ toward the specimen core. Complementary thermal ageing experiments conducted at 700 degrees C in N-2 for 1000 h confirmed that these microstructural changes could not be attributed to thermal exposure alone, but were driven by carbonate-induced carbon ingress. Tensile testing revealed severe degradation of mechanical properties after corrosion exposure, with crack initiation predominantly occurring in the brittle oxide scale and propagation through carburized regions exhibiting reduced toughness and localized strain leading to brittle fracture. In contrast, thermally aged specimens showed only limited mechanical degradation. This integrated corrosion-mechanical approach provides a framework for assessing synergistic chemical and mechanical degradation in molten salt environments and should be considered for CSP-TES design.
The deployment of electrolysis-based hydrogen technology requires identifying the advantages and disadvantages of scaling hydrogen production plants and determining the limits of the scaling-up process. Until now, experience has been demonstrated with electrolysers of tens and hundreds of kilowatts, but electrolysers in the tens of megawatts range are still closer to being prototypes than commercial products. Additionally, challenges such as maintenance, reliability, long-term operation, and investment recovery time arise in parallel as the scale increases. This raises the question of what is more suitable: installing a single high-power electrolyser or a modular plant composed of multiple smaller electrolysers? This paper addresses that question from both a technical and an economic perspective. Accordingly, it presents a study identifying the degree of modularisation that optimises the technical and economic performance of a large-scale hydrogen production plant. The results show that configurations with a higher degree of modularisation (based on multiple smaller electrolysers) exhibit a better technical performance and lower degradation. However, configurations with a lower degree of modularisation are more competitive in terms of costs. When combining technical and economic criteria, the results show that solutions based on a medium–low degree of modularisation are the most suitable. The advantages are lower replacement costs and uninterrupted hydrogen production. This study also recommends embracing modularisation to prevent a dependence on a single high-power electrolyser.
