Search Results (9)

The present work introduces a new solar selective absorber coating (SSAC) for the receiver tube of Concentrated Solar Power (CSP) systems, proposing silver as an infrared reflector for application at 550 °C. In the past, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) has developed SSACs suitable for applications at 550 °C, featuring solar absorbers based on graded multilayer cermet of WN-AlN and W-Al₂O₃ and an infrared reflector of tungsten. Although these coatings ensured properly stable photothermal performance at 550 °C, due to the low tungsten diffusivity, their hemispherical emittance could be reduced by using metals with higher reflectance in the infrared region, like silver. However, the high diffusivity of silver compromises its use at high temperatures. This last drawback has been addressed by foreseeing two stabilizing layers enclosing the Ag infrared reflector. One W stabilizing layer was placed between the substrate and the Ag infrared reflector, whereas a second stabilizing layer, selected among aluminum nitride deposited with a low and high nitrogen flow and aluminum oxide deposited at a low oxygen flow, was placed between the Ag infrared reflector and the solar absorber. Accelerated aging tests revealed a negligible (not detectable) degradation of the solar absorptance for the new SSACs. Furthermore, the hemispherical emittance at 550 °C increased by 0.75% and 0.42% for solar coatings with aluminum nitride stabilizing layers deposited through a high and low nitrogen flow, respectively. Differently, the increase was evaluated as being equal to 0.08% for the solar coating with an aluminum oxide stabilizing layer deposited through a low oxygen flow. The manufactured solar coating with a stabilizing layer of aluminum nitride deposited with a low nitrogen flow exhibited a solar absorptance of 95%, comparable to ENEA coatings incorporating a W infrared reflector for applications at 550 °C, whereas the estimated hemispherical emittance at 550 °C was 2% lower than that of the best ENEA coating with a W infrared reflector for the same temperature. Full article

Type 2 diabetes is a serious health problem worldwide. Metformin as the first-line drug in diabetes treatment mainly inhibits glucose production in the liver. Diabetes is often accompanied by other diseases, so patients may take many medications at the same time and have trouble controlling the therapy. This, in turn, may result in medications being stored in different, sometimes random places in the patient’s home where elevated temperatures or long-term exposure to solar radiation are possible. In this study, we aimed to analyze whether the total hemispherical reflectance and emittance values of metformin extended-release tablets would distinguish tablets stored correctly from those stored inconsistently with the manufacturer’s recommendations. Unexpired and expired extended-release tablets containing 750 mg metformin were tested. Unexpired tablets were analyzed in two ways i.e., 15 randomly selected tablets were stored as recommended (day 0), and the 15 next tablets in the blister were stored on a windowsill, where they were exposed to daylight for several hours during the day in mid-spring 2024 for 20 days (day 20). Total hemispherical reflectance (THR) was measured within seven spectral ranges from 335 nm to 2500 nm with a 410-Solar Reflectometer while emittance was analyzed within six spectral infrared ranges from 1500 nm to 21 microns with an ET 100 emissometer. The day 0 tablets showed the highest THR values in five spectral ranges from 400 to 1700 nm compared to expired and day 20 tablets. In the further infrared ranges, from 1.5 to 21 microns, unexpired tablets on day 0 had the lowest reflectance compared to day 20 tablets and expired tablets. This means that a greater amount of IR beam was absorbed by this type of tablet. Therefore, higher emittance was demonstrated by day 0 tablets than by other analyzed tablets. In addition, the emittance values for day 0 tablets decreased with increasing temperature. In conclusion, the storage of metformin extended-release tablets under unfavorable conditions may affect the physical structure of this drug form, which is manifested by changes in the reflectance and directional and hemispherical thermal emittance. Full article

High directional emission and high radiative quantum efficiency are strongly needed when moving a single optical nano-emitter (such as a quantum dot) into the practical realm. However, a typical optical nano-emitter struggles to meet the requirements above, which limits its practical applications in next-generation nano-photonic devices such as single-photon sources. Here, to achieve these features simultaneously, we propose and theoretically investigate a composite plasmonic antenna consisting of a hemispherical solid immersion lens (SIL) and a bowtie plasmonic nano-antenna, wherein a high directional emission of 10° and 2.5 × 10³ of Purcell factor have both been enabled. Moreover, we find that directionality and the Purcell factor can be manipulated independently in our antenna, which provides a novel platform for the optimization of single-photon sources. Full article

Transient terahertz time-domain spectroscopy (THz-TDS) imaging has emerged as a novel non-ionizing and noninvasive biomedical imaging modality, designed for the detection and characterization of a variety of tissue malignancies due to their high signal-to-noise ratio and submillimeter resolution. We report our design of a pair of aspheric focusing lenses using a commercially available lens-design software that resulted in about 200 × 200-μm² focal spot size corresponding to the 1-THz frequency. The lenses are made of high-density polyethylene (HDPE) obtained using a lathe fabrication and are integrated into a THz-TDS system that includes low-temperature GaAs photoconductive antennae as both a THz emitter and detector. The system is used to generate high-resolution, two-dimensional (2D) images of formalin-fixed, paraffin-embedded murine pancreas tissue blocks. The performance of these focusing lenses is compared to the older system based on a pair of short-focal-length, hemispherical polytetrafluoroethylene (Teflon^TM) lenses and is characterized using THz-domain measurements, resulting in 2D maps of the tissue refractive index and absorption coefficient as imaging markers. For a quantitative evaluation of the lens effect on the image resolution, we formulated a lateral resolution parameter, R₂₀₈₀, defined as the distance required for a 20–80% transition of the imaging marker from the bare paraffin region to the tissue region in the same image frame. The R₂₀₈₀ parameter clearly demonstrates the advantage of the HDPE lenses over Teflon^TM lenses. The lens-design approach presented here can be successfully implemented in other THz-TDS setups with known THz emitter and detector specifications. Full article

The hypothesis of this paper is that infiltration into drip irrigated soils can be described by simple spherical considerations as well as two dimensional (2D) numerical modeling. The major goal was to test a very simple model based on geometry of a sphere formulas, and compare it with elaborated numerical solutions and field experiments. Detailed analysis of soil–water infiltration under trickle regimes is shown to be pre-requisite in the search for the optimal design of system layout. Optimality and simplicity are sought by modeling a sphere for subsurface trickle/drip (SDI) and hemisphere (DI) pattern of moisture distributions during infiltration. Numerical simulations by MATLAB software were used to describe the distribution of soil water. The data produced by this simulation were successfully compared with analytical models and numerical results of Panoche clay loam. To simulate the four discharge rates (0.5, 1, 2, 3 $\frac{L}{h}$) under DI and SDI we used the input of Panoche soil properties, i.e., hydraulic conductivity function (K_θ) and soil water retention curve (ψ_θ). The resulting regression equation of numerical analysis (N) vs. spherical interpretation (S) was N = 0.97 × S − 19.1; r² = 0.98. This result exposes the novelty of the approach by showing that infiltration from a drip/trickle source can be described by simple spherical radial symmetry in addition to analytical or numerical simulations. An example of a design parameter for 3000 $\frac{{\mathrm{cm}}^3}{\mathrm{h}}$ suggested more emitters per meter laterals for SDI than for DI (100 vs. 77 unites, respectively) due to the shorter distance between SDI emitters that are required in order to maintain wetting continuity. At a discharge of around 500 $\frac{{\mathrm{cm}}^3}{\mathrm{h}}$ of three different soils’ SDI, positive pressure was detected near the orifice and it caused discharge reduction. This is a self-compensating property of SDI that regulates individual emitters according to the soil hydraulic properties. In conclusion SDI is associated with larger capital investment compared to DI, but it can be compensated by improving the water use efficiency due to increased productivity while reducing losses of water through evaporation, but this option should be investigated as part of specific research. Full article

In visual diffuse transmission density measurement, it is hard to measure optical density (OD) up to 6.0 because the signal to noise is more than 10E-06. Thus, there are only two methods to find the measurement. One is using a highly sensitive detector with low background noise, and the other is improving the incident light flux with a wide spectrum, including visual scope. A new diffuse optics emitter was designed to realize OD measurements up to 6.0. It uses 235 optical fibers on a hemisphere to collect and feed in the incident flux, then emits this flux by a diffuse opal. Thus, an incident light with a high diffuse coefficient and high incident flux was realized for high OD measurement. This emitter has been used in the new national reference of National Institute of Metrology, China (NIM) for diffuse transmission optical density. According to the measurement result in this reference, the OD can be measured up to 6.6. Full article

Active galactic nuclei are the dominant sources of gamma rays outside our galaxy and are also candidates for the source of ultra-high energy cosmic rays. In addition to being emitters of broad-band non-thermal radiation throughout the electromagnetic spectrum, their emission is highly variable on timescales from years to minutes. Hence, high-cadence monitoring observations are needed to understand their emission mechanisms. The Africa Millimetre Telescope is planned to be the first mm-wave radio telescope on the African continent and one of few in the southern hemisphere. Further to contributing to the global mm-VLBI observations with the Event Horizon Telescope, substantial amounts of observation time will be available for monitoring observations of active galactic nuclei. Here we review the scientific scope of the Africa Millimetre Telescope for monitoring of active galactic nuclei at mm-wavelengths. Full article

Regarding the fabrication of solar selective absorbers, the ability to create microstructures on top of metal surfaces is a promising technology. Typically, these materials are able to possess spectrally-selective absorption properties for high-temperature usage. Solar-selective absorbers that function at temperatures up to 700 °C and possess shallow honeycomb cylindrical microcavities coated with a metal-dielectric multi-layer have been investigated. Honeycomb array cylindrical microcavities were fabricated on W substrate with interference lithography and multi-layers consisting of Pt nano-film sandwiched by Al₂O₃ layers were created for a uniform coating via atomic layer deposition. The absorbance spectrum of fabricated samples reveals results consistent with a simulation based on a rigorous coupled-wave analysis method. A solar absorbance value of 0.92 and a hemispherical total emittance value of 0.18 at 700 °C was determined from the fabricated solar-selective absorber. Additionally, thermal stability of up to 700 °C was confirmed in vacuum. Full article

In this paper, a laboratory goniometer system for performing multi-angular measurements under controlled illumination conditions is described. A commercially available robotic arm enables the acquisition of a large number of measurements over the full hemisphere within a short time span making it much faster than other goniometers. In addition, the presented set-up enables assessment of anisotropic reflectance and emittance behaviour of soils, leaves and small canopies. Mounting a spectrometer enables acquisition of either hemispherical measurements or measurements in the horizontal plane. Mounting a thermal camera allows directional observations of the thermal emittance. This paper also presents three showcases of these different measurement set-ups in order to illustrate its possibilities. Finally, suggestions for applying this instrument and for future research directions are given, including linking the measured reflectance anisotropy with physically-based anisotropy models on the one hand and combining them with field goniometry measurements for joint analysis with remote sensing data on the other hand. The speed and flexibility of the system offer a large added value to the existing pool of laboratory goniometers. Full article