Three dimensional (3D) Finite Time Lyapunov Exponents (FTLEs) are computed from numerical simulations of a freely evolving mixed layer (ML) front in a zonal channel undergoing baroclinic instability. The 3D FTLEs show a complex structure, with features that are less defined than the two-dimensional (2D) FTLEs, suggesting that stirring is not confined to the edges of vortices and along filaments and posing significant consequences on mixing. The magnitude of the FTLEs is observed to be strongly determined by the vertical shear. A scaling law relating the local FTLEs and the nonlocal density contrast used to initialize the ML front is derived assuming thermal wind balance. The scaling law only converges to the values found from the simulations within the pycnocline, while it displays differences within the ML, where the instabilities show a large ageostrophic component. The probability distribution functions of 2D and 3D FTLEs are found to be non Gaussian at all depths. In the ML, the FTLEs wavenumber spectra display -1 slopes, while in the pycnocline, the FTLEs wavenumber spectra display -2 slopes, corresponding to frontal dynamics. Close to the surface, the geodesic Lagrangian Coherent Structures (LCSs) reveal a complex stirring structure, with elliptic structures detaching from the frontal region. In the pycnocline, LCSs are able to detect filamentary structures that are not captured by the Eulerian fields.
This paper presents the spectral reflectance of thermally evaporated ZnS/Ag nanostructures. The coating of ZnS/Ag nanostructures was performed in two steps while varying the film thickness and deposition angle. Silver metal wire (99.99% purity) was heated under vacuum at a pressure of \(2.5 \times 10^{-5}\) mBars and deposited on glass slide substrates in the diffusion pump microprocessor vacuum coater (Edwards AUTO 306). Pieces of zinc sulphide (99.99% purity) were heated and deposited to the glass slides previously coated with silver to form the ZnS/Ag/glass composite. The optical reflectance of the samples was studied by the UV/Vis/NIR spectrometer (Perkin Elmer Lambda 19) with UV-WinLab software. The reflectance was measured at angles of incidence between \(15^o\) and \(75^o\). Spectrophotometric studies showed that reflectance decreased with decrease in film thickness and decreased with increase in deposition angle of silver nanoparticles. The reflectance of ZnS/Ag nanostructures decreased with increase in deposition angle of zinc sulphide.
The paper presents an analysis of spatial and temporal solar potential variations in Uganda. The solar radiation potential distribution was investigated based on measured data from 56 ground meteorological stations across Uganda from January 2015 to February 2022. The data were recorded after every 5-minute interval. The monthly average daily Global Horizontal Irradiance (GHI) was analysed using the spatial inverse distance weighting (IDW) interpolation technique in ArcGIS 10.7.1. The GHI distribution was found to have maxima at equinox and minimum between June and July. The average global horizontal irradiation is found to be 1680 KWh per year, with a daily variability below 10%. This is above the threshold for solar energy applications and with such low variability, large scale solar PV plants can be installed with minimum backup requirements. Northern Uganda receives the highest average daily global horizontal irradiation of 5.38 Whm–2 day–1, while Western Uganda receives 4.16 Whm–2 day–1, the lowest. The average AM/PM ratio depicted a value above 2 for all regions in Uganda and therefore, optimal solar energy exploitation for fixed systems favours eastern orientation. The central, eastern and northern Uganda which is 69.3% of the country has relief favourable for large scale solar PV power plants and CSP facilities. Keywords: GHI, IDW, Global solar radiation, Solar insolation, PV power plants, Uganda
This paper presents the optical transmittance properties of thermally evaporated coatings of ZnS/Ag nanostructures as a function of film thickness and deposition angle designed to mitigate the challenges of indoor heating and their effects on low temperature storage facilities. The nanostructures were deposited on glass by varying the film thickness and deposition angle of both silver and zinc sulphide nanofilms at a pressure of 2.5×10-5 mBars in the diffusion pump microprocessor vacuum coater (Edwards AUTO 306). The optical transmittance of the coatings was measured at normal incidence in the wavelength range of 250-2500 nm of the incident electromagnetic radiation. Spectral studies showed that the transmittance decreased with increase in the film thickness of the ZnS/Ag nanostructures and the optical transmittance increased with increase in deposition angle of zinc sulphide in the infrared region. The transmittance of (4 nm)ZnS/Ag, (7 nm)ZnS/Ag, (10 nm)ZnS/Ag and (15 nm)ZnS/Ag samples deposited at normal angle in the visible region had peaks at 61.7%, 66.3%, 54.9%, and 18.0% respectively. The transmittance of the nanostructures increased with the increase in deposition angle of silver nanoparticles. Thus optical transmittance measured at 1800 nm wavelengths for ZnS(0o)/Ag(0o), ZnS(0o)/Ag(30o) and ZnS(0o)/Ag(60o) were 2.8%, 21.7% and 22.1% respectively. The coating of ZnS at high deposition angle decreased transmittance in the visible wavelength. The transmittance peak values in the visible region measured up to 51.1%, 53.5%, and 45.1% for (4 nm)ZnS(0o)/Ag(0o) and (4 nm)ZnS(0o)/Ag(30o) and (4 nm)ZnS(0o)/Ag(60o) samples respectively. However, increase in deposition angle of (10nm)ZnS/Ag nanostructures measured at 1000 nm; ZnS(0o)/Ag(30o), ZnS(30o)/Ag(30o) and ZnS(60o)/Ag(30o) increased transmittance in the infrared wavelengths from 9% to 12% and 34% respectively. Therefore, to increase transmittance in the visible region, the Zinc sulphide nanoparticles should be coated on silver at low deposition angles.
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