Air pollution is affected by the atmospheric dynamics. This study aims to determine that air pollution concentration values in İstanbul increased significantly and reached peak values due to atmospheric blocking between the 30th of December 2022 and the 5th of January 2023. In this study, hourly pollutant data was obtained from 16 air quality monitoring stations (AQMS), the exact reanalysis data was extracted from ERA5 database, and inversion levels and meteorological and synoptic analyses were used to determine the effects of atmospheric blocking on air pollution. Also, cloud base heights and vertical visibility measurements were taken with a ceilometer. Statistical calculations and data visualizations were performed using the R and Grads program. Omega-type blocking, which started in İstanbul on December 30, 2022, had a significant impact on the 1st and 2nd of January 2023, and PM10 and PM2.5 concentration values reached their peak values at 572.8 and 254.20 µg/m3, respectively. In addition, it was found that the average concentration values in the examined period in almost all stations were higher than the averages for January and February. As a result, air quality in İstanbul was determined as \"poor\" between these calendar dates. It was found that the blocking did not affect the ozone (µg/m3) concentration. It was also found that the concentrations of particulate matter (PM) 10 µm or less in diameter (PM10) and PM 2.5 µm or less in diameter (PM2.5) were increased by the blocking effect in the İstanbul area. Finally, according to the data obtained using the ceilometer, cloud base heights decreased to 30 m and vertical visibility to 10 m.

This study explores the efficacy of dimples in influencing the aerodynamic performance of a straight rectangular wing. Computational Fluid Dynamics based numerical simulations were performed to model turbulent flow and quantify the forces exerted on the wing. The k-ω Shear-Stress Transport turbulence model was chosen to solve the underlying equations. To ascertain reliability, the results of numerical simulations were compared with both experimental and simulation results of the previous studies. The impact of various dimple configurations, placed at 15%, 50% and 85% of the chord length, on the aerodynamic performance of the wing was investigated. The evaluation involved analyzing the drag coefficient (CD), lift coefficient (CL), lift-to-drag (L/D) ratio, streamlines and the flow field around wing in both chordwise and spanwise directions. The findings indicated that a wing with a dimpled surface could yield a reduced drag coefficient of up to 6.6% compared to the unmodified wing. This reduction is attributed to the dimples ability to sustain attached airflow and delay flow separation. The results demonstrated negligible deviation in the lift coefficient with the incorporation of dimples. The incorporation of dimples on the wing surface has been demonstrated to enhance the aerodynamic performance of lifting surfaces.

In absence of the high-frequency measurements of wind components, sonic temperature and water vapour required by the eddy covariance (EC) method, Monin-Obukhov similarity theory (MOST) is often used to calculate heat fluxes. However, MOST requires assumptions of stability corrections and roughness lengths. In most environments and weather situations, roughness length and stability corrections have high uncertainty. Here, we revisit the modified Bowen-ratio method, which we call C-method, to calculate the latent heat flux over snow. In the absence of high-frequency water vapour measurements, we use sonic anemometer data, which have become much more standard. This method uses the exchange coefficient for sensible heat flux to estimate latent-heat flux. Theory predicts the two exchange coefficients to be equal and the method avoids assuming roughness lengths and stability corrections. We apply this method to two datasets from high mountain (Alps) and polar (Antarctica) environments and compare it with MOST and the three-layer model (3LM). We show that roughness length has a great impact on heat fluxes calculated using MOST and that different calculation methods over snow lead to very different results. Instead, the 3LM leads to good results, in part due to the fact that it avoids roughness length assumptions to calculate heat fluxes. The C-method presented performs overall better or comparable to established MOST with different stability corrections and provides results comparable to the direct EC method. An application of this method is provided for a new station installed in the Pamir mountains.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s10546-024-00864-y.

Susceptibility of airborne ultrasonic power to augment heat and mass transfer during hot air dehydration of peppermint leaves was investigated in the present study. To predict the moisture removal curves, a unique non-equilibrium mathematical model was developed. For the samples dried at temperatures of 40‒70 °C and the power intensities of 0‒104 kW m-3, the diffusion of moisture inside the leaves and coefficients for of mass and heat transfer varied from 0.601 × 10-4 to 5.937 × 10-4 s-1, 4.693 × 10-4 to 7.975 × 10-4 m s-1 and 49.2 to 78.1 W m-2 K-1, respectively. In general, at the process temperatures up to 60 °C, all the studied transfer parameters were augmented in the presence of ultrasonic power.

As a novel fluid of functional material, magnetohydrodynamic (MHD) micropolar fluid has the special properties of light, heat, magnetic and so on. It is of highly practical significance. The characteristics of flow, heat and mass transfer in MHD micropolar nanofluid boundary layer past a stretching plate are investigated based on the micropolar fluid theory in the present numerical work. In the presence of magnetic field, viscous dissipation and the cross-diffusion caused by Dufour effect and Soret effect are considered. First order slip velocity condition is employed. Mathematical models are built based on the assumptions. Collocation spectral method (CSM) via matrix multiplication is adopted to solve the two-dimensional dimensionless nonlinear partial governing equations. The program codes based on CSM is developed, validated and employed. The coupled effects of microrotation, Dufour effect, Soret effect, magnetic field as well as first order slip velocity boundary condition on the flow, heat and mass transfer are revealed. Besides, the variation trends of local Nusselt number and Sherwood number are analyzed in detail. The numerical results indicate that the fluid flow can be suppressed obviously in the consideration n of slip condition and magnetic field. As slip parameter δ and magnetic parameter M rise, the velocity in the boundary layer becomes lower gradually; further, both temperature and concentration increase. On the other hand, the opposite trend can be noticed with the effect of material parameter K. Moreover, Ec and Df augment the temperature; while, Sr leads to an upsurge in concentration. The temperature rises by about 79.73% with Dufour effect and Sh enlarges by a factor of about 38.15% with Soret effect. The concentration boundary layer decreases by about 37.50% is when K=5.0.

Despite the considerable potential of AlGaN-based ultraviolet-B light-emitting diodes (UV-B LEDs) in various applications such as phototherapy, UV curing, plant growth, and analytical technology, their development is still ongoing due to low luminescence efficiency. In this study, we introduced a novel epitaxial growth mechanism to effectively control the height and thickness of AlGaN multiple wells (MWs) on AlGaN nanorod structures using horizontal reactor-based metal-organic chemical vapor deposition (MOCVD). By adjusting the H2 carrier gas flow rate, we could control the growth boundary layer\'s thickness, successfully separating the AlGaN well and p-AlGaN layer from the substrate. Cathodoluminescence (CL) measurements confirmed the stability of the core-shell AlGaN quantum wells as a highly stable nonpolarized structure, with the wavelength peak remaining almost unchanged under various injection currents. Furthermore, transmission electron microscopy (TEM) provided clear evidence of differentiation, highlighting the distinct formation of the 275 nm AlGaN core and the 295 nm AlGaN shell structure. The developed AlGaN MW structure, characterized by these rectification features, not only demonstrated a significantly improved electroluminescence (EL) peak intensity but also exhibited a much lower leakage current compared to the conventional core-shell AlGaN structure. The newly proposed growth mechanism and advanced nonpolarized core-shell AlGaN structure are expected to serve as excellent alternatives for substantially enhancing the efficiency of the next generation of high-efficiency UV LEDs.

The three-year Black Carbon (BC) aerosol measurements made during 2020, 2021, and 2022 over a rural location, namely, Panchgaon, surrounded by Aravali hillocks (elevation of about 400-600 m) have been analyzed with an aim to determine their optical and radiative characteristics, seasonal and long-term variations in mass concentration. The affinity between these parameters and associated pollutants and planetary boundary layer height (PBLH), affected by the orography, to delineate their role in mass concentration changes with time have been investigated. The coincident OPAC (Optical Properties of Aerosols and Clouds) Model-derived aerosol optical depth (AOD), and single scattering albedo (SSA) have been compared with the observed BC mass concentration, and also with synchronous satellite measurements. The year-to-year variability analysis of the data reveals that the rate of increase of BC concentration is high. The variability was low due to the reasons explained. It implies that the year-to-year variability in BC concentration at the study site depends on the source strength modulated by the valley-driven meteorology. Added, the percentage departures of BC concentration show positive values (higher concentration) during morning and evening hours, which could be due to more anthropogenic activities while it shows negative values during afternoon hours and lower boundary layer heights. The force exerted by the radiation due to BC aerosols at the bottom of the atmosphere (BOA), and in the atmosphere (ATM) are almost equal in magnitude and negative, while that at the top-of-the-atmosphere (TOA) is smaller and positive, indicating that BC aerosols in the study region cools the atmosphere at the BOA and warms the ATM and TOA, which indirectly reveals the dominant role of long-range transport phenomenon at higher levels as compared to the surface level.

Barchans are dunes commonly found in dune fields on Earth, Mars and other celestial bodies, where they can interact with each other. This article concerns experimental data for the flow over subaqueous barchans that are either isolated or interacting with each other. The experiments were carried out in a transparent channel of rectangular cross section in which turbulent water flows were imposed over either one single or a pair of barchans. The instantaneous flow fields were measured by using a low-frequency PIV (particle image velocimetry) and high-frequency PTV (particle tracking velocimetry). From the PIV and PTV data, the mean flow, trajectories, and second-order moments were computed, which are included in the datasets described in this paper, together with raw data (images), instantaneous fields, and scripts to process them. The datasets can be reused for benchmarking or for processing new images generated by other research groups.

This work proposes a uniformly convergent numerical scheme to solve singularly perturbed parabolic problems of large time delay with two small parameters. The approach uses implicit Euler and the exponentially fitted extended cubic B-spline for time and space derivatives respectively. Extended cubic B-splines have advantages over classical B-splines. This is because for a given value of the free parameter [Formula: see text] the solution obtained by the extended B-spline is better than the solution obtained by the classical B-spline. To confirm the correspondence of the numerical methods with the theoretical results, numerical examples are presented. The present numerical technique converges uniformly, leading to the current study of being more efficient.

Electrodialysis desalination uses ion exchange membranes, membrane spacers, and conductors to remove salt from water. Membrane spacers, made of polymeric strands, reduce concentration polarization. These spacers have properties such as porosity and filament shape that affect their performance. One important property is the spacer-bulk attack angle. This study systematically reviews the characteristics of a 45° attack angle of spacers and its effects on concentration polarization and fluid dynamics. Membrane spacers in a channel create distinct flow fields and concentration profiles. When set at a 45° attack angle, spacers provide greater turbulence and mass-heat transfer than traditional spacers. This is because both the transverse and longitudinal filaments become diagonal in relation to the bulk flow direction. A lower attack angle (<45°) results in a lower pressure drop coupled with a decline in wakes and stream disruption because when the filaments are more parallel to the primary fluid direction, the poorer their affect. This research concludes that membrane spacers with a 45° spacer-bulk attack angle function optimally compared to other angles.