Characteristic parameters of photonic nanojets of single dielectric microspheres illuminated by focused broadband radiation

Herein, we report the theoretical investigation on the photonic nanojets (PNJs) of single dielectric microspheres illuminated by focused broadband radiation (polychromatic light) from a Halogen lamp, supercontinuum source, light-emitting diode, and Hg arc lamp. The role of incident beam waist, refractive index of the surrounding medium, and radius of the microsphere on the characteristic parameters such as the electric field intensity enhancement, effective width, and length of the PNJ is studied. Interestingly, the characteristic parameters of the PNJs of solid microspheres obtained for the above-mentioned broadband radiation sources are found close to those observed for the focused monochromatic radiation of wavelengths which are near to the central wavelengths of the sources. Moreover, the characteristic parameters of PNJs of the core–shell microspheres of different thicknesses (t) illuminated by polychromatic radiation from most commonly used sources such as Halogen and Hg arc lamps are studied. For each t value, a suitable wavelength of monochromatic radiation has been found to generate the PNJ with characteristic parameters which are close to those obtained in the case of polychromatic radiation. We believe that the analytical theory and the theoretical simulations reported here would be useful for researchers who work in the fields such as PNJ assisted photoacoustic spectroscopy, white light nanoscopy, low-coherence phase-shifting interference microscopy, and Mirau interferometry.

A method of measuring transmittance of radiation from the film of ice 0 in the IR wave band deposited on a dielectric plate

A method of measuring transmittance of radiation from the film of ice 0 in the infrared wave band is described. Ice 0 is formed from supercooled water at the temperature below –23°C. This ice is ferroelectric and forms a highly conductive layer of the nanometric order of thickness at the boundary with dielectric. The complexity of the experiment consisted in the necessity of using low intensities of the probing signal and considering radiation of the cooled parts of the installation. In order to obtain a thin film of ice, the method of depositing water vapor on a substrate cooled in nitrogen was used. The method rules out formation of condensate in cooling. Deposition of water vapor is possible only in heating, when delivery of cold nitrogen vapor into the chamber with the sample is excluded. To ensure exposure of the film to IR radiation, two sources of infrared radiation were considered: a halogen lamp with a broad radiation spectrum (on the surface of heated glass) and a CO2 laser with the radiation wavelength of 10.6 µm. In the first case, spectral measurements are possible when filters are used. In the installation based on a CO2 laser, an intense signal is emitted, requiring consideration of sample heating. Components of the installation have been elaborated and investigated, on which transmittance of radiation from the film of ice 0 is planned to be measured.

Lab-Controlled Experimental Evaluation of Heat-Reflective Coatings by Increasing Surface Albedo for Cool Pavements in Urban Areas

Many studies were conducted to find possible strategies for reducing the urban heat island (UHI) effect during the hot summer months. One of the largest contributors to UHI is the role that paved surfaces play in the warming of urban areas. Solar-reflective cool pavements stay cooler in the sun than traditional pavements. Pavement reflectance can be enhanced by using a reflective surface coating. The use of heat-reflective coatings to combat the effects of pavements on UHI was previously studied but no consistent conclusions were drawn. To find a conclusive solution, this work focuses on the abilities of heat-reflective pavement coatings to reduce UHI in varying weather conditions. Within this context, both concrete and asphalt samples were subject to a series of performance tests when applied to a heat-reflective coating, under the influence of normal, windy, and humid conditions. During these tests, the samples were heated with a halogen lamp and the surface temperature profile was measured using an infrared thermal camera. The air temperature was recorded with a thermometer, and the body temperature at multiple depths of the samples was measured using thermocouples. The results from these tests show that the effectiveness of the heat-reflective coating varies under different weather conditions. For instance, the coated samples were about 1 °C cooler for concrete and nearly 5 °C cooler for asphalt, on average. However, this temperature difference was reduced significantly under windy conditions. As such, the findings from this work conclude that the heat-reflective coatings can effectively cool down the pavement by increasing the surface albedo, and thus might be a viable solution to mitigate UHI impacts in the city/urban areas.

A Multi-Analytical Approach for Studying the Effect of New LED Lighting Systems on Modern Paints: Chemical Stability Investigations

This study aims to investigate the chemical stability of some modern paint samples exposed to a new Light Emitting Diode (LED)-lighting system and a halogen lamp by using micro-attenuated total reflectance of Fourier transform infrared spectroscopy (µ-ATR-FTIR), µ-Raman, pyrolysis—gas chromatography/mass spectrometry (Py-GC/MS), and thermally assisted hydrolysis and methylation of GC/MS (THM-GC/MS). Those investigations were performed before and after the exposure of the samples to lightings for 1250, 2400, 3300, and 5000 h. The results obtained with µ-Raman spectroscopy show the high stability of the selected inorganic pigments after the exposure to the lighting systems; while similar to the UV/Vis/NIR results reported in a previous study, µ-ATR-FTIR and THM-GC/MS results evidence greater chemical changes occurring principally on the linseed oil binder-based mock-ups among the acrylic and alkyd-based samples. Moreover, principal component analyses (PCA) and hierarchical cluster analyses (HCA) of THM-GC/MS results highlight that those changes were mostly dependent on the exposure time and on the type of pigment, while being independent of the lighting system used. Finally, semi-quantitative µ-ATR-FTIR results show slight pigment enrichment at the paint surface due to the auto and photo-oxidative degradation of the linseed oil binder.

Determination of the convective heat transfer constant (c and n) in a solar still

The geometry of a solar still determines the convection constants C and n, which in turn affect the convection heat transfer coefficient’s value and mass. A method for determining the value of convection heat transfer constants C and n has already been developed by the researchers. Therefore, this study aimed to use several methods and theories to find the value of convection heat transfer constants C and n. The results are then compared with the results of the study. The solar still used in this study has one slope. To reduce variables that cannot be controlled, the data collection was conducted indoors using a halogen lamp that can be regulated as a heat source for 24 hours nonstop. The sea surface height in the solar still was maintained at a height of 20 mm, using a height regulator. Temperature was measured using a data logger set to enter data every hour. The desalinised clean water was stored in bottles placed on scales that were recorded every one hour. Room temperature was maintained in the range of 35 to 36 oC. The data in this study were used to calculate the heat transfer constants C and n to obtain the value of the convection heat transfer coefficient and mass calculation. This study compares the calculation models of Tiwari, Dunkle and Power. The following calculation model results: Tiwari model, C = 0.082 and n = 0.612; Dunkle model, C = 0.075 and n = 1/3; Power model, C = 0.815 and n = 0.611. The C and n values obtained with these four approaches reveal that the results from the Power model calculation are the closest to the actual mass, showing a percentage deviation of 1.63%.

6 nm super-resolution optical transmission and scattering spectroscopic imaging of carbon nanotubes using a nanometer-scale white light source

Optical transmission and scattering spectroscopic microscopy at the visible and adjacent wavelengths denote one of the most informative and inclusive characterization methods in material research. Unfortunately, restricted by the diffraction limit of light, it cannot resolve the nanoscale variation in light absorption and scattering, diagnostics of the local inhomogeneity in material structure and properties. Moreover, a large quantity of nanomaterials has anisotropic optical properties that are appealing yet hard to characterize through conventional optical methods. There is an increasing demand to extend the optical hyperspectral imaging into the nanometer length scale. In this work, we report a super-resolution hyperspectral imaging technique that uses a nanoscale white light source generated by superfocusing the light from a tungsten-halogen lamp to simultaneously obtain optical transmission and scattering spectroscopic images. A 6-nm spatial resolution in the visible to near-infrared wavelength regime (415–980 nm) is demonstrated on an individual single-walled carbon nanotube (SW-CNT). Both the longitudinal and transverse optical electronic transitions are measured, and the SW-CNT chiral indices can be identified. The band structure modulation in a SW-CNT through strain engineering is mapped.

The effect of new LED lighting systems on the colour of modern paints

This research focuses on the investigation of the effect of a new light emitting diode (LED)-lighting system which reproduces indoor museum conditions, on some self-made art paint colours (acrylic-, alkyd-, and linseed oil-based paints) often used in modern-contemporary art. A halogen lamp representing a traditional light source for museum lighting was also considered. Lighting-set-up and lighting optimization parameters were considered while Ultraviolet/Visible/Near Infrared (UV/Vis/NIR) spectrophotometry was used for investigating the colour change of the paint samples. Univariate analyses allowed determining the highest effect of the lighting systems on the linseed oil binder and ultramarine blue PB29 mixture upon ageing, according to the highest total colour change ΔE*ab. In a more specific and detailed way, variance analyses not only demonstrated the strong correlation between the type of binder and pigment used for the paint samples with the colour variation, but also showed that the short-wavelength blue LEDs influenced the change along the yellow–blue b* axis of the yellow and blue samples, whereas the halogen lamp mostly had an impact towards the red–green a* axis of mostly the green specimens.

Removing MBD Using Fe2O3 NPs Modified by FeCl3 (0.1 M and 0.3 mM) With Myrtle Leaf Extract As Environmental Application

In this study, iron oxide nanoparticles were synthesized using FeCl3 (0.1 M and 0.3 M) with myrtle leaf extract for of methylene blue dye (MBD) degradation under visible light irradiation (100-watt halogen lamp) as environmental application. X-ray diffraction analysis showed the polycrystalline structure of Fe2O3 material with miller indices confirmed the presence of iron oxide with average crystalline sizes (15.59-16.8 nm) synthesized by (0.1M - 0.3mM) concentrations of FeCl3. Field emission-scanning electron microscopy revealed rods-like and spherical shapes of Fe2O3 nanoparticles, with an average particle size of 25 to 67 nm, covered the whole top surface of structure. Moreover, the change of the color of the iron oxide NPs from brown to dark brown enhances the transformation of the properties of the material obtained by adding the biomass which gives the absorbance peaks around 265-350 nm and energy band gaps (3 and 3.7 eV) using UV/VIS spectrometer. The methylene blue degradation efficiencies of Fe2O3 NPs prepared by plant extract and FeCl3 with concentrations (0.1 M and 0.3 mM) were 86.3% after 150 min and 90% after 120 min respectively.

Ag-TiO2 Nanocomposites: visible or solar light driven plasmonic photocatalysis?

Background: The demand for photocatalytic processes assisted by solar radiation has stimulated the upgrading of established systems, as the semiconductor modification with noble metals. Objective: the synthesis, characterization, and photocatalytic activity evaluation of the Ag-TiO2, against sulfamethoxazole molecule, and investigate the significance of the plasmonic phenomenon in Visible (450 - 1000nm) and UV-Vis (315-800 nm) radiation. Methods: Different nanocomposites Ag/TiO2 ratios were synthesized by the deposition of Ag nanoparticles on the TiO2 surface by in-situ photoreduction, and then calcinated at 400°C for 2 hr. The chemical-physical properties of the materials were examined by UV-Vis Diffuse Reflectance (UV-Vis DRS) Scanning Electronic Microscopy (SEM), Transmission Electronic Microscopy (TEM), X-Ray Energy Dispersive Spectroscopy (EDS). The experiments were conducted in a cooled photochemical reactor irradiated by halogen lamp (250W). The degradation of Sulfamethoxazole was monitored by HPLC-DAD. Results: Although the prepared photocatalysts show an intense plasmonic band centered at 500 nm, no photocatalytic activity was observed in the process assisted by artificial visible radiation ( ≥ 450 nm). In processes assisted by artificial UV-Vis radiation, the photolysis rate of the model compound (sulfamethoxazole) was higher than the photocatalytic rate, and in the absence of UV radiation, all the reactions were inhibited. The positive effect of the presence of silver nanoparticles onto the TiO2 surface was only evidenced in studies involving solar radiation. Conclusion: The results suggest the need for a balance between UV and Vis radiation to activate the nanocomposite and perform the sulfamethoxazole degradation.

Prospective study for commercial and low-cost hyperspectral imaging systems to evaluate thermal tissue effect on bovine liver samples

Thermal ablation modalities, for example radiofrequency ablation (RFA) and microwave ablation, are intended to prompt controlled tumour removal by raising tissue temperature. However, monitoring the size of the resulting tissue damage during the thermal removal procedures is a challenging task. The objective of this study was to evaluate the observation of RFA on an ex vivo liver sample with both a commercial and a low-cost system to distinguish between the normal and the ablated regions as well as the thermally affected regions. RFA trials were conducted on five different ex vivo normal bovine samples and monitored initially by a custom hyperspectral (HS) camera to measure the diffuse reflectance (Rd) utilising a polychromatic light source (tungsten halogen lamp) within the spectral range 348–950 nm. Next, the light source was replaced with monochromatic LEDs (415, 565 and 660 nm) and a commercial charge-coupled device (CCD) camera was used instead of the HS camera. The system algorithm comprises image enhancement (normalisation and moving average filter) and image segmentation with K-means clustering, combining spectral and spatial information to assess the variable responses to polychromatic light and monochromatic LEDs to highlight the differences in the Rd properties of thermally affected/normal tissue regions. The measured spectral signatures of the various regions, besides the calculation of the standard deviations (δ) between the generated six groups, guided us to select three optimal wavelengths (420, 540 and 660 nm) to discriminate between these various regions. Next, we selected six spectral images to apply the image processing to (at 450, 500, 550, 600, 650 and 700 nm). We noticed that the optimum image is the superimposed spectral images at 550, 600, 650 and 700 nm, which are capable of discriminating between the various regions. Later, we measured Rd with the CCD camera and commercially available monochromatic LED light sources at 415, 565 and 660 nm. Compared to the HS camera results, this system was more capable of identifying the ablated and the thermally affected regions of surface RFA than the side-penetration RFA of the investigated ex vivo liver samples. However, we succeeded in developing a low-cost system that provides satisfactory information to highlight the ablated and thermally affected region to improve the outcome of surgical tumour ablation with much shorter time for image capture and processing compared to the HS system.