Fraction Of Surface Research Articles

Subgrid-scale horizontal and vertical variation of cloud water in stratocumulus clouds: a case study based on LES and comparisons with in situ observations

Abstract. Stratocumulus clouds in the marine boundary layer cover a large fraction of ocean surface and play an important role in the radiative energy balance of the Earth system. Simulating these clouds in Earth system models (ESMs) has proven to be extremely challenging, in part because cloud microphysical processes such as the autoconversion of cloud water into precipitation occur at scales much smaller than typical ESM grid sizes. An accurate autoconversion parameterization needs to account for not only the local microphysical process (e.g., the dependence on cloud water content qc and cloud droplet number concentration Nc) but also the subgrid-scale variability of the cloud properties that determine the process rate. Accounting for subgrid-scale variability is often achieved by the introduction of a so-called enhancement factor E. Previous studies of E for autoconversion have focused more on its dependence on cloud regime and ESM grid size, but they have largely overlooked the vertical dependence of E within the cloud. In this study, we use a large-eddy simulation (LES) model, initialized and constrained with in situ and surface-based measurements from a recent airborne field campaign, to characterize the vertical dependence of the horizontal variation of qc in stratocumulus clouds and the implications for E. Similar to our recent observational study (Zhang et al., 2021), we found that the inverse relative variance of qc, an index of horizontal homogeneity, generally increases from cloud base upward through the lower two-thirds of the cloud and then decreases in the uppermost one-third of the cloud. As a result, E decreases from cloud base upward and then increases towards the cloud top. We apply a decomposition analysis to the LES cloud water field to understand the relative roles of the mean and variances of qc in determining the vertical dependence of E. Our analysis reveals that the vertical dependence of the horizontal qc variability and enhancement factor E is a combined result of condensational growth throughout the lower portion of the cloud and entrainment mixing at cloud top. The findings of this study indicate that a vertically dependent E should be used in ESM autoconversion parameterizations.

Lack of vegetation exacerbates exposure to dangerous heat in dense settlements in a tropical African city

Both climate change and rapid urbanization accelerate exposure to heat in the city of Kampala, Uganda. From a network of low-cost temperature and humidity sensors, operational in 2018–2019, we derive the daily mean, minimum and maximum Humidex in order to quantify and explain intra-urban heat stress variation. This temperature-humidity index is shown to be heterogeneously distributed over the city, with a daily mean intra-urban Humidex Index deviation of 1.2 ∘C on average. The largest difference between the coolest and the warmest station occurs between 16:00 and 17:00 local time. Averaged over the whole observation period, this daily maximum difference is 6.4 ∘C between the warmest and coolest stations, and reaches 14.5 ∘C on the most extreme day. This heat stress heterogeneity also translates to the occurrence of extreme heat, shown in other parts of the world to put local populations at risk of great discomfort or health danger. One station in a dense settlement reports a daily maximum Humidex Index of 40 ∘C in 68% of the observation days, a level which was never reached at the nearby campus of the Makerere University, and only a few times at the city outskirts. Large intra-urban heat stress differences are explained by satellite earth observation products. Normalized Difference Vegetation Index has the highest (75%) power to predict the intra-urban variations in daily mean heat stress, but strong collinearity is found with other variables like impervious surface fraction and population density. Our results have implications for urban planning on the one hand, highlighting the importance of urban greening, and risk management on the other hand, recommending the use of a temperature-humidity index and accounting for large intra-urban heat stress variations and heat-prone districts in urban heat action plans for tropical humid cities.

Influence of surfactant on electrowetting-induced surface electrocoalescence of water droplets in hydrocarbon media

Electrocoalescence is a powerful technique for manipulating water-hydrocarbon media. This study is a detailed experimental investigation of the influence of surfactant on electrowetting-induced surface electrocoalescence of micron-scale water droplets in hexadecane. Surface electrocoalescence is studied over a vast parameter space comprising surfactant concentration, voltage, frequency and electrode geometry. We develop phase maps for various electrocoalescence possibilities and identify the parameter space for significant coalescence using three dimensionless parameters: i) modified electric capillary number (Cae*), ii) frequency (τ), and iii) surfactant concentration (C*). Electrocoalescence effectiveness is quantified using the parameter (δ/α): δ is the droplet density/area and α is the fraction of surface not covered by droplets. Strong coalescence (no surfactant) corresponds to δ/α < 10 droplets/mm2, with best-case δ/α = 1.6 droplets/mm2, with no droplets < 20 µm diameter and electrocoalesced droplets as large as 750 μm. With surfactant, electrocoalescence weakens; parameter space for strong electrocoalescence progressively reduces with concentration. Nonetheless, electrocoalescence at all concentrations results in substantial radius enhancement (after/before electrocoalescence); measured ratio ranges from 3.1 to 6.3 in the parameter space of Cae*: 3.3–4.9, and τ≤1.25*10−2. Surface electrocoalescence therefore promotes significant aggregation of water droplets over a wide range of interfacial energies. This study also characterizes droplet generation (via satellite droplet ejection (SDE)) of 2–10 µm radii droplets. SDE scales with voltage, frequency and concentration, and inversely with electrode spacing. Overall, we show that water droplets can be coalesced or generated using the same microfluidic device, and identify the parametric space to enable surface-electrocoalescence-based fluidic separation and droplet generation.

Surface tension of binary mixtures of benzene + propionic acid and butanoic acid between 298.15 K and 318.15 K: Measurement and modeling

Experimental measurement of the surface tension of benzene + propanoic acid and benzene + butanoic acid has been carried out in the temperature range of 298.15 K to 318.15 K and atmospheric pressure. 170 new experimental points of surface tension have been obtained. Three theoretical models, i.e., Linear gradient theory (LGT), Shereshefsky model (SM), and the extended Langmuir model (LM), were used to modeling the surface tension and adsorption phenomenon of these binary mixtures. The three models correlated the surface tension of the benzene + carboxylic acid mixtures, and the average percent deviation was, 0.04% for LGT, 0.08% for SM, and 0.05% for LM. The Helmholtz density term and the liquid and vapor densities required in computing density with LGT were obtained with perturbed chain-statistical associating fluid theory equation of state (PC-SAFT EOS). Based on SM, the standard Gibbs energy of adsorption and the free energy change in the surface region were calculated. The free energy change was used to obtain the excess number of molecular layers in the surface region. The required parameters of the LM were adjusted, the standard Gibbs energy of adsorption was calculated, and negative deviations from ideality were determined. Also mole fractions of solute 0at surface were calculated by using LM. Additionally, by using surface tensions at different temperatures, specific surface enthalpy and specific surface entropy were calculated for (benzene + carboxylic acid) mixtures.

Catalytic effects of activated-carbon particle size on the oxidative degradation mechanisms of a pharmaceutical

The effects of the size of activated carbon (AC) on the catalytic degradation of organic micropollutants was investigated by the removal of a pharmaceutical (acetaminophen, ACT) using persulfate (PS). The removal of ACT, either by adsorption or oxidative degradation, and PS decomposition were enhanced by decreasing the size of the AC. The smallest AC particle (AC1) showed higher specific surface area, pore volume, macropores, and fractions of sp2-C and CO, but lower ID/IG, I2D/IG, and fractions of sp3-C and of O-CO, compared with the largest AC particle (AC6). Electron paramagnetic spectroscopy revealed a strong SO4•− signal for AC1, but the signal for AC6 appeared weaker after 30 min of reaction time. Decomposition of PS and peroxymonosulfate (PMS) was significantly enhanced by increasing the concentration of the electron donor (ACT) when AC1 was used, but it was not affected when AC6 was used. In addition, degradation of micropollutants and PS decomposition were seriously affected by their ionization potential when AC1 was used, and less affected when AC6 was used. These results suggest that the degradation of organic pollutants by AC1 + PS and AC6 + PS can be attributed primarily to the non-radical and radical pathways, respectively. Meanwhile, the catalytic activity was decreased as AC1 and AC6 were reused because of deactivation process. This indicates that the size of AC is a powerful determinant of the characteristics and can be optimized for the catalytic degradation of organic micropollutants.

Arsenic in soils contaminated by arsenic-containing chemical weapons in a site of Jilin, China: fraction and bioaccessibility.

At the end of World War II, the Japanese abandoned arsenic (As)-containing chemical weapons (CWs) in China. During the long-term burial process, the As-containing agents leaked into the environment due to the corrosion of weapon shells. This study explored the surface distribution, fraction composition, and bioaccessibility of As in the soil contaminated by chemical weapons in a site of Jilin Province, China. Results showed that As was enriched in the soil of CWs buried and the maximum concentration of As in this area was 110mg/kg (dry weight). In terms of fraction, As primarily accumulated in amorphous Fe/Al-oxides bound and residual fractions. Moreover, from the perspective of fractions with potential environmental risks, As accounted for 45.6-82.0% and 61.0-80.7% of the fractions extracted by Wenzel and Shiowatana sequential extraction procedure (SEP), respectively. Bioaccessibility can also be used to assess environmental risks. The mean values of As bioaccessibility were as follows: gastric phase (15.0%) > colon phase (14.8%) > small intestinal phase (13.3%), and the As bioaccessibility was closely related to the Fe/Al oxide bound fraction. Compared with the surrounding farmland, the potential environmental risk of soil pollution was more significant in the CW burial areas. This study provided support for remediation of As-containing agent-contaminated soil in China.

Blue phosphorene on Au(111) as a decoupling layer for organic epitaxially grown films

Blue phosphorene (BlueP) is considered as a promising two-dimensional (2D) material for future-(opto)electronic applications. Monolayer BlueP is often fabricated on Au(111) single-crystal surfaces. It has been suggested that small P domains form a lateral network with Au adatoms. Previous studies attempting to use BlueP/Au(111) as a substrate for the deposition of fullerene indicated that the former is susceptible to structural deterioration, unlike most other 2D materials in this regard. Here, we investigate 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) monolayers and multilayer films deposited on BlueP/Au(111). We monitor the film growth in real time using in situ optical differential reflectance spectroscopy with the substrate kept either at room temperature or at $\ensuremath{\approx}120{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Furthermore, we examine the epitaxial alignment between PTCDA and BlueP by means of distortion-corrected low-energy electron diffraction and low-temperature scanning tunneling microscopy. Our data clearly reveal that PTCDA exhibits a highly ordered monolayer structure with a herringbone packing motif, whereas the domain orientations differ from all previously reported structures of PTCDA directly on Au(111). Importantly, we find no indications for adsorption-induced reordering or degradation of BlueP/Au(111). At elevated temperatures, PTCDA is observed to form multilayer islands covering only a fraction of the available PTCDA monolayer surface on BlueP/Au(111), and this Stranski-Krastanov growth mode bears similarities to literature results for PTCDA multilayers on pristine coinage metal surfaces.

The Simulation of L-Band Microwave Emission of Frozen Soil during the Thawing Period with the Community Microwave Emission Model (CMEM)

One-third of the Earth’s land surface experiences seasonal freezing and thawing. Freezing-thawing transitions strongly impact land-atmosphere interactions and, thus, also the lower atmosphere above such areas. Observations of two L-band satellites, the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) missions, provide flags that characterize surfaces as either frozen or not frozen. However, both state transitions—freezing and thawing (FT)—are continuous and complex processes in space and time. Especially in the L-band, which has penetration depths of up to tens of centimeters, the brightness temperature ( T B ) may be generated by a vertically-mixed profile of different FT states, which cannot be described by the current version of the Community Microwave Emission Model (CMEM). To model such complex state transitions, we extended CMEM in Fresnel mode with an FT component by allowing for (1) a varying fraction of an open water surface on top of the soil, and (2) by implementing a temporal FT phase transition delay based on the difference between the soil surface temperature and the soil temperature at 2.5 cm depth. The extended CMEM (CMEM-FT) can capture the T B progression from a completely frozen to a thawed state of the contributing layer as observed by the L-band microwave radiometer ELBARA-III installed at the Maqu station at the northeastern margin of the Tibetan Plateau. The extended model improves the correlation between the observations and CMEM simulations from 0.53/0.45 to 0.85/0.85 and its root-mean-square-error from 32/25 K to 20/15 K for H/V-polarization during thawing conditions. Yet, CMEM-FT does still not simulate the freezing transition sufficiently.

Water-gas shift reaction over supported Au nanoparticles

The water–gas shift (WGS) reaction rates per total mole of Au at 120 °C, 7% CO, 22% H2O, 8.5% CO2, 37% H2 decrease in the order Au/Anatase ∼ Au/Anatase001 (uniform anatase TiO2 single crystals with 64 per cent of the more {001} facets) ∼ Au/P25 ∼ Au/P25-WGC (obtained from the World Gold Council) ∼ Au/Rutile > Au/ZrO2 > Au/CeO2 > Au/ZnO when compared at the same number average Au particle size (d) and vary as ∼ d-3. From high resolution transmission electron microscopy images, the geometry of Au nanoparticles on these catalysts resembled truncated cubo-octahedra. A physical model of Au nanoparticles as truncated cubo-octahedra was used to calculate that the fractions of surface, perimeter and corner sites to the total Au sites vary as d-0.7, d-1.8 and d-2.9, respectively. Thus, the variation in the WGS reaction rate per total mole of Au (∼d-3) correlates well with the corner sites (d-2.9) allowing us to determine that the dominant active sites for these catalysts are the low coordinated metallic corner Au sites. In addition, as the apparent H2O order increases and the apparent activation energy decreases, the WGS reaction rate per total mole of Au systematically decreases for Au nanoparticles supported on anatase, anatase001, P25, rutile, ZrO2, CeO2, ZnO and Al2O3 at near 120 °C. Density functional theory calculations were carried out over Au nano-rods supported on rutile TiO2(100) and α-Al2O3(0001) surfaces to elucidate the differences in reactivity for the most reactive (Au/TiO2) and least reactive (Au/Al2O3) catalysts. Water preferentially adsorbs and dissociates at the Lewis acid- Lewis base Ti4+-Ob and Al3+-Ob site pairs at the Au/TiO2(110) and Au/α-Al2O3 interfaces with activation energies of 0.25 eV and 0.20 respectively. These barriers are significantly lower than those to activate water on the corner sites of unsupported Au nanoparticles (1.48 eV). The prediction that both the TiO2 and Al2O3 readily dissociate water supports the experimental findings that the support plays an important role in activating the water in the WGS reaction. The subsequent oxidation of CO appears to proceed at the Au/support interface via the reaction of CO adsorbed on Au with the OH on the support. DFT results indicate that OH binds 0.4 eV stronger to Al3+ sites at the Au/Al2O3 interface perimeter than to Ti4+ sites at the Au/TiO2 interface perimeter. As such, the barrier for OH to react with CO at an adjacent Au site is 0.52 eV higher for Au/Al2O3 (0.85 eV) than for Au/TiO2 (0.33 eV). The theoretical results suggest that the oxidation of CO is rate-limiting on Al2O3 whereas both the water dissociation as well as CO oxidation limit the rate on TiO2. This is consistent with the near first order CO dependence of the measured rates over both Au/TiO2 and Au/Al2O3 as well as the changes in the water reaction orders over Au/TiO2 (−0.2 to −0.5) and Au/Al2O3 (0.5 to 0.8).

The role of target strength on the ejection of martian meteorites

Our collection of meteorites recovered here on Earth contain over 200 samples believed to have originated on Mars. It is commonly accepted that these rocks were launched as ejecta during the formation of impact craters. The majority of the meteorites are young and basaltic representing only a small fraction of the martian surface. Previous studies have only examined impacts into basalt or other competent material, but the material bias remains unexplained. In this study we define fragmentation parameters for dry tuff, a proxy for the weakly cemented regolith and sedimentary material covering much of Mars. We simulate hypervelocity impacts into the martian surface using a joint Eulerian-Lagrangian shock physics code. A wide parameter search is conducted over impactor sizes ranging from 10 meter to 10 kilometers in radius. We find that dry tuff produces significantly smaller fragments than basalt for all impactor sizes. Maximum fragment size and amount of material ejected scale with impactor size. We also examine impacts into mixed targets, mainly simple layers and embedded boulders. We find that a layer of basalt overtop dry tuff inhibits ejection, while a layer of tuff overtop basalt enhances ejection and increases dry tuff fragment sizes. Boulders create a complex pressure field in the near-surface region, but fragment sizes are relatively unchanged.

Experimental investigation on effective thermal conductivity of powder-packed assembly gaps in heat pipe cooled reactor core

The heat pipe cooled reactor utilizes monolithic solid core inserted with fuel rods and heat pipes. There exist assembly gaps between fuel rods, heat pipes and the solid block to avoid contact stress resulted from heterogeneous thermal expansion. In order to reduce the additional thermal resistance caused by assembly gaps, thermal conductive powders can be filled into the gaps. For the sake of evaluation on the effects of powder packed gaps on the reactor safety margin of heat pipe cooled reactor, the effective thermal conductivity of stainless-steel powder packed beds with different particle sizes was measured using the one-dimensional steady-state hollow-cylinder method in both air and helium atmosphere under the heating temperature of 800–1000 K and the pressure of 1 bar. The Zehner-Schlünder model was calibrated by adjusting the particle deformation parameter and the flattened surface fraction based on the experimental data in air. The comparison of prediction results by the adjusted Zehner-Schlünder model with experimental results in helium and relevant experimental data from previous literature shows the relatively error within ± 20%. Finally, the performance of powder packed gaps on increasing the reactor safety margin was evaluated by analyzing the different heat transfer modes and initial assembly-gap sizes. Results show that the performance improves with the increase of initial assembly-gap size and the fuel temperature decreases by 19.19 K compared to the helium-filled gap even with a small initial assembly-gap size of 0.2 mm.

Fabrication of hierarchical structures on titanium alloy surfaces by nanosecond laser for wettability modification

Titanium alloy is widely used in aerospace industry due to its low density, high specific strength and high-temperature resistance. To broaden its application scope, superhydrophobicity of titanium alloy is required in certain situations, such as self-cleaning and anti-icing. In this study, direct nanosecond laser ablation was applied to fabricate distinct pits with hierarchical structures on titanium alloy substrates, followed with chemical treatment to modify the wettability of the surfaces. The effects of laser processing parameters on surface morphology and surface wettability were explored systematically. Results show that, increasing the number of scans improves the depth of the pits and the accumulation of the micro-nano structures around the craters. The scanning space mainly affects the overlap of the heat affected zones, and hence the distribution of the laser-induced hierarchical structures. The wettability of a laser processed surface is determined by both surface roughness and surface chemistry, and the solid fraction of the rough surface is regulated by the number of scans as well as the scanning space. Moreover, superhydrophobic surfaces are obtained on the laser processed titanium alloy after chemical treatment, which has great potential for the as-mentioned applications.

A particle digitization-based computational method for continuum percolation

A new theoretical model and its computational implementation in two dimensions (2D) for the study of continuum percolation phenomena is presented. The aim was the development of a model which has inherent similarity with lattice percolation. The physical medium is simulated as an (infinite) grid comprising of representative surface elements (RSEs). Assuming medium’s homogeneity the RSEs average propagation probability can be interpreted and generalized as the occupation probability for the infinite medium. The RSE’s resulting from a Monte Carlo iterative process involving the creation of the relative small samples and their propagation ability checked individually from their top to bottom. The propagation in the actual physical medium takes place when the calculated probability (p) is higher than the critical propagation probability (pc≈0.5927). The proposed method treats the low dimensional material system as a 2D infinite homogenized medium which can be further reduced leading to a mapping on a square lattice with site occupation. The proposed numerical algorithm considers the particles in the RSE as digitized using sites-pixels without contacts. Following the digitization procedure, traditional computational methods like Depth First Search are involved for the detection of possible propagation paths in the randomly selected square samples. For the confirmation of the theoretical model as well as the algorithm, problems known from the literature were used and it was found that regardless of microstructure at the critical concentration Φc the percolation probability on the RSE converges to the anticipated pc≈0.5927 value. In addition, the results obtained from the proposed methodology compare very well with available predictions in the literature. New results are reported covering a wide range of particle geometrical types (circular, elliptical, rectangular) and surface fractions in matrix-filler or matrix-fillers systems proving the robustness and applicability of the proposed methodology.

Formation and morphology of closed and porous films grown from grains seeded on substrates: Two-dimensional simulations

Two-dimensional simulations are used to explore topological transitions that occur during the formation of films grown from grains that are seeded on substrates. This is done for a relatively large range of the initial value Φs of the grain surface fraction Φ. The morphology of porous films is captured at the transition when grains connect to form a one-component network using newly developed raster-free algorithms that combine computational geometry and network theory. Further insight on the morphology of porous films and their suspended counterparts is obtained by studying the pore surface fraction Φp, the pore over grain ratio, the pore area distribution, and the contribution of pores of certain chosen areas to Φp. Pinhole survival is evaluated at the transition when film closure occurs using survival function estimates. The morphology of closed films (Φ=1) is also characterized and is quantified by measuring grain areas and perimeters. The majority of investigated quantities are found to depend sensitively on Φs and the long-time persistence of pinholes exhibits critical behavior as a function of Φs. In addition to providing guidelines for designing effective processes for manufacturing thin films and suspended porous films with tailored properties, this work may advance the understanding of continuum percolation theory.

Modelling the electrochemical transients during repassivation under open-circuit conditions in a neutral solution

The responses of the current and the coupled potential to rapid depassivation have been studied on a three-electrode system under open-circuit conditions. Passivated AISI 304 stainless steel in low- and high-conductivity solutions of Na2SO4 has been depassivated with a single, rapid scratch over the small fraction of surface of the working electrode (WE). Single- and dual-WE configurations have been implemented. Once the surface is scratched, the current and potential transients exhibit a delayed maximum and minimum, respectively, in contrast to the outcome of more common potentiostatic scratching experiments. A simple model based on the equivalent circuit has been developed to predict the observed transients and provides clear relations between the features of the transient and the parameters of the electrolyte and the electrodes. The interfacial capacitance of the electrodes’ passive surfaces proves crucial for the shapes of the observed potential and current transients. It is shown that this capacitance temporarily provides the majority of the charge for repassivation under open-circuit conditions. Possible sources of specific discrepancies between the model and the measured transients are indicated.

Numerical modeling of groundwater‐driven stream network evolution in low‐relief post‐glacial landscapes

AbstractIn the low‐relief post‐glacial landscapes of the Central Lowlands of the United States, fluvial networks formed and expanded following deglaciation despite the low slopes and large fraction of the land surface occupied by closed depressions. Low relief topography allows for subtle surface water divides and increases the likelihood that groundwater divides do not coincide with surface water divides. We investigate how groundwater transfer across subtle surface water divides facilitates channel network expansion using a numerical model built on the Landlab platform. Our model simulates surface and subsurface water routing and fluvial erosion. We consider two end‐member scenarios for surface water routing, one in which surface water in closed depressions is forced to connect to basin outlets (routing) and one in which surface water in closed depressions is lost to evapotranspiration (no routing). Groundwater is modeled as fully saturated flow within a confined aquifer. Groundwater emerges as surface water where the landscape has eroded to a specified depth. We held the total water flux constant and varied the fraction of water introduced as groundwater versus precipitation. Channel growth is significantly faster in routing cases than no‐routing cases given identical groundwater fractions. In both routing and no‐routing cases, channel expansion is fastest when ~30% of the total water enters the system as groundwater. Groundwater contributions also produce distinctive morphology including steepened channel profiles below groundwater seeps. Groundwater head gradients evolve with topography and groundwater‐fed channels can grow more quickly than channels with larger surface water catchments. We conclude that rates of channel network growth in low‐relief post‐glacial areas are sensitive to groundwater contributions. More broadly, our findings suggest that landscape evolution models may benefit from more detailed representation of hydrologic processes.

Understanding the effects of 2D/3D urban morphology on land surface temperature based on local climate zones

Summer increasingly gets hotter, which has become a common problem that threats human settlement environment and hinders urban sustainable development. The impacts of urban morphology on land surface temperature (LST) have been studied extensively, but the investigation from the local climate zones (LCZs) perspective is less concerned. We thus explored the relationship between 2D/3D urban morphology and spatial variation of LST across seasons based on LCZs by utilizing high-resolution remote sensing images and vector building data. The results showed that: (1) the spatial distributions of seasonal LSTs took a circle structure with three rings from the city center to the fringe area. In particular, the temperature showed a characteristic of “High-Low-High” in spring, autumn, and winter. However, the LSTs in the first ring were 1.4 °C and 2.2 °C higher than the second and third ring in summer, respectively. (2) The inter-LCZs differences of LST were consistent across seasons. In summer, the warmest zones were LCZ 2 and LCZ 3 with 2–3 °C higher than other built type LCZs, while the coldest zones were LCZ A and LCZ G with 4–6 °C lower than other land cover type LCZs. (3) The most influential 3D factor on LST was the mean building height with a significant cooling effect in LCZ 1, LCZ 3, and LCZ 4 in spring and autumn. Impervious surface fraction was the dominated 2D factor with a significant warming effect in all seven built type LCZs in summer.

Hydrogen embrittlement behaviors at different deformation temperatures in as-quenched low-carbon martensitic steel

The present study investigated hydrogen-related fractures at different deformation temperatures ranging from −100 °C to 100 °C in low-carbon martensitic steel. The sensitivity to hydrogen embrittlement increased as the temperature decreased from 100 °C to 0 °C, while it decreased as the temperature decreased further below 0 °C. We characterized the fracture surface types from the morphological and crystallographic aspects and found that the fraction of hydrogen-embrittled surfaces exhibited a similar temperature dependence on the sensitivity to hydrogen embrittlement. The qualitative discussion suggested that the degree of hydrogen accumulation exhibits a peak value in the medium temperature range, which has the same tendency as the sensitivity to hydrogen embrittlement confirmed experimentally. Thus, we proposed that the effect of deformation conditions on the sensitivity to hydrogen embrittlement could be explained on the basis of the hydrogen accumulation behavior.

Analysis of Spatio-temporal patterns and related factors of thermal comfort in subtropical coastal cities based on local climate zones

"Local Climate Zone" (LCZ) is a land classification scheme for urban thermal environment, combined with the "Universal Thermal Climate Index" (UTCI) indicator that characterizes human perception of the thermal environment, which can effectively reflect human perception of the thermal environment. In order to evaluate the thermal comfort of Shenzhen in 2020, the hourly data of 65 weather stations covering 11 LCZ types are used to calculate UTCI, which is used to analyze the temporal and spatial patterns of thermal comfort and related factors. The results show that the thermal comfort of 11 types of LCZ in Shenzhen all year round conforms to the characteristics of Shenzhen's subtropical monsoon climate. The 11 types of LCZ thermal comfort are higher at night than during the day. The thermal comfort of different LCZ types is statistically significantly different. The "Built type" LCZ has a higher thermal comfort value than the "Land cover type" LCZ, and the time in the thermal level is longer. Summer thermal comfort in Shenzhen was found to be positively correlated with building surface fraction, building height, street aspect ratio, and distance to the sea, and negatively correlated with sky view factor and pervious surface fraction. In addition, the summer sea breeze has a cooling effect on the thermal comfort of the entire Shenzhen area, and the barrier-free ventilation corridor can observe a better cooling effect. The research results of this paper can provide reference for improving the thermal comfort in Shenzhen.

Hall and ion slip effects on the MHD flow of Casson hybrid nanofluid past an infinite exponentially accelerated vertical porous surface

In the present investigation, the radiative MHD flow of an incompressible viscous electrically conducting non-Newtonian Casson hybrid nanofluidover an exponentially accelerated vertical porous surface has been considered. Under the influence of slip velocity in a rotating frame, it takes Hall and ion slip impacts into account. Water and ethylene glycol mixture is considered a base Casson fluid. A steady uniform magnetic field is applied under the postulation of a low magnetic Reynolds number. The ramped temperature and time-altering concentration at the surface are considered. First-order consistent chemical reaction and heat absorption are also regarded. Silver and Titania nanoparticles are disseminated in base fluid water and ethylene glycol combination should be formed by a hybrid nanofluid. The Laplace transformation technique is employed on the non-dimensional governing equations to ensure closed-form analytical solutions. The graphical representations scrutinize the effects of physical parameters on the significant flow characteristics. The expression for non-dimensional shear stress, heat transfer rate and mass transfer are also evaluated. They are tabulated with different variations in implanted parameters. For uniform and ramped wall temperatures, the resultant velocity grows by an increase in Hall and ion slip parameters. The resultant velocity increases by an increase in volume fractions of nanoparticles with uniform wall temperature, and a reverse effect is observed with ramped wall temperature. The temperature of Casson hybrid Ag-TiO2/WEG nanofluid is relatively superior to that of Casson Ag-WEG nanofluid. Species concentration of Casson hybrid Ag-TiO2/WEG nanofluid decreases with an increase in Schmidt number and chemical reaction parameters. The heat absorption increases the Nusselt number near the surface, while Ag and TiO2 nanoparticle volume fractions tend to lessen it.