Vertical Homogeneity Research Articles

Vertical Compositional Heterogeneity Induces Instability in All-Inorganic CsPbIBr2 Perovskites.

Understanding the vertical compositional homogeneity and defect distribution is of paramount importance in elucidating and maximizing the performance of halide-perovskite-based optoelectronic devices. This work reports the depth-dependent study of the chemical composition and metallic Pb0 content of all-inorganic CsPbIBr2 perovskite films undertaken using lab-based hard X-ray photoelectron spectroscopy and soft X-ray photoelectron spectroscopy. The presence of elemental or metallic Pb (Pb0), in the bulk and at the surface of the perovskite films highlights the formation of defect or recombination centers throughout the analyzed depth. The Pb0 content was found to be of higher concentration in the bulk of the CsPbIBr2 films compared to that at the surface. Engineering the CsPbIBr2 film growth using appropriate antisolvents resulted in the overall reduction and/or complete elimination of Pb0 at the surface and at the bulk of the perovskite films. However, the effect of antisolvent treatment was significantly pronounced in the bulk-like region as compared to that at the surface. Pb0 is synonymous with defect states/recombination centers in perovskite films and this reduction in defect density due to the antisolvent treatment corroborates the enhanced phase stability and improved solar cell performance of the corresponding CsPbIBr2 devices.

Deciphering Structure and Charge Carrier Behavior in Reduced‐Dimensional Perovskites

AbstractReduced‐dimensional perovskites (RDPs) have advanced perovskite optoelectronic devices due to their tunable energy landscape, structure, and orientation. However, the origin of structural and photophysical property changes when moving from low‐dimensional to high‐dimensional RDPs remains to be understood. This study systematically reveals structural and photophysical properties of slot‐die‐coated Dion‐Jacobson (DJ) and Ruddlesden‐Popper (RP) RDPs with different dimensionalities. RP RDPs with lower dimensionality (n = 2) exhibit a dominant n = 2 phase, preferential out‐of‐plane orientation, and longer charge carrier lifetime compared with DJ RDPs. In addition, the formation kinetics of RDPs with higher dimensionality (n = 4) are unraveled by in situ X‐ray scattering, showing the favorable formation of the lower‐n phase in RP RDPs. The formation of these lower‐n phases is thermodynamically and stoichiometrically favored, while these phases are likely in the form of an “intermediate phase” which bridges the 3D‐like and lower‐n phases in DJ RDPs. DJ RDPs with higher dimensionality demonstrate comparable phase purity, preferential orientation, spatially vertical phase homogeneity, and longer charge carrier lifetime. As such, DJ‐based perovskite solar cells (PSCs) (n = 4) demonstrate better photostability under operational conditions than RP‐based PSCs. Thus, the work paves the way for the utilization of RDPs to upscale PSCs.

Thermal regulation potential of urban green spaces in a changing climate: Winter insights

Global warming affects both summer and winter temperatures, altering the ecological and social dynamics of urban green spaces not only during the summer months but also during the winter. Strategies to mitigate climate change impacts often emphasize increasing urban vegetation cover, but the effectiveness of these green spaces in regulating the local microclimate depends on various factors, including the vegetation structure. These effects remain largely underexplored during the winter season. To investigate the thermal regulation capacity of urban green spaces we measured air temperature and humidity in 36 parks with different sizes and vegetation structures in Munich, Germany, in their non-green surroundings, as well as in a nearby forest during the 2022–23 winter. We then analyzed the relationship between the local microclimatic differences and the vegetation structure derived from mobile laser scans. In comparison with the nearby forest, we measured a winter urban heat island effect of 1.8 °C in Munich. The urban microclimates in winter were mainly influenced by the urban landscape of Munich, namely the distance to the city center with increasing air temperature closer to the center. Urban green spaces in Munich provided small but consistent local cooling and humidifying effects throughout the winter. These cooling effects largely depended on the green space size but partially also on the vegetation structure. We found a significant relationship between the microclimatic difference, the vegetation density, and the vertical homogeneity of vegetation. The canopy cover, however, could not significantly predict the cooling effect in winter. We conclude that increasing the structural complexity of urban green spaces through management decisions could improve their cooling effect and ecological value, even during winter months. To maximize the ecological and climatic benefits of urban green spaces, a nuanced understanding and management of urban microclimates is needed across all seasons.

Water stratification alters phytoplankton assemblages in scallop farming waters of the North Yellow Sea in China

As evaluation indicators of the primary productivity, the phytoplankton biomass and community structure are of great significance to the fishery industry, which can be driven by ocean currents, nutrients and water stratification. In the present study, the characteristics of phytoplankton assemblages in different water layers of a typical Yesso scallop farming area in Zhangzi Island, the North Yellow Sea were investigated from March 2021 to January 2022. According to the vertical distribution of temperature, water stratification was observed from June to August (stratification period), and disappeared in March, October and the following January with vertical homogeneity (mixing period). 18S rRNA gene sequencing results revealed that Pyrrophyta was the most dominant phylum during the sampling period, with high gene proportions in the stratification (63.36%) and mixing periods (77.35%). The gene proportion of Bacillariophyta in the stratification period was 5.44%, which was significantly lower than that in the mixing period of 8.93% (p < 0.05). Moreover, Pseudo-nitzschia, a toxin-producing taxon affiliated with Bacillariophyta, exhibited a significantly higher proportion in the stratification period than in the mixing period. During the stratification period, a number of toxin-producing taxa such as Pseudo-nitzschia and Karlodinium were enriched in the bottom layer, which was 1.29-fold and 1.37-fold of that in the surface layer, respectively. Redundancy analysis showed that phosphate and water temperature were major environmental factors driving the vertical distribution of phytoplankton assemblages. The phosphate (0.11 μM) and silicate (2.09 μM) concentrations in the surface layer approached the minimum threshold for phytoplankton growth, and the stoichiometric limitation of phosphate was detected in the surface and middle layers. Collectively, these results indicated that the decreased proportion ratio of Bacillariophyta to Pyrrophyta and unfavorable community composition of Bacillariophyta for scallops were observed during summer, which might result from the phosphate limitation driven by water stratification. The results will further our understanding of the dynamics of phytoplankton communities under the background of intensifying ocean stratification and provide ecological guidance for mollusc mariculture.

The Critical Role of Thermal Stratification Associated With the Yellow Sea Cold Water Mass in Modulating Winter Sea Surface Temperature

AbstractThe Yellow Sea Cold Water Mass (YSCWM), a seasonal bottom‐layer water mass in the Yellow Sea (YS) most prominent in summer, has always been overlooked in previous studies investigating variations in the winter Sea Surface Temperature. Here, using observations and high‐resolution numerical modeling, we reveal for the first time the significant contribution of thermal stratification associated with the YSCWM to the sea surface cooling and the formation of the westward‐shifted Yellow Sea Warm Water Tongue (YSWT) in early winter. Heat budget analyses indicated that the impact of the YSCWM to surface cooling manifests in two aspects. First, the upward mixing of bottom cold water from the remnant YSCWM triggers cooling in the mixed layer. Second, the shallower local mixed layer above the YSCWM facilitates more pronounced cooling processes compared to the YSWT region under similar heat flux. The formation of the westward‐shifted YSWT is the result of intensified surface cooling in both the coastal shallow waters and the YSCWM region in the central YS. During the formation process of the YSWT, its main axis aligns with the western boundary of the YSCWM. As the YSCWM dissipates, the YSWT shows an eastward apparent displacement and eventually stabilizes near approximately 123°E. This study enriches our understanding of the transition from stratification to vertical homogeneity in the water temperature structure of the YS during early winter.

Vertical homogeneity study of Bridgman-grown Cd0.95Mn0.05Te0.98Se0.02 for radiation detection

This study investigates the potential of CdMnTeSe as a spectroscopic-grade semiconductor, focusing on the enhanced vertical homogeneity achieved through the incorporation of Mn and Se. The segregation coefficient of Mn in the CdTe matrix, approaching 1, indicates remarkable vertical homogeneity, promising high-yield and cost-effectiveness compared to zinc-based counterparts. Selenium addition synergistically reduces structural defects inside CdMnTeSe. The spectroscopic-grade Cd0.95Mn0.05Te0.98Se0.02′s exceptional vertical homogeneity was confirmed thorough characterizations, regardless of sample’s origination. This study guides for scale-up growth conditions by replacing Zn with Mn, offering superior homogeneity including high yield, cost-effectiveness, and the potential for large-volume CdTe-based single crystals.

Homogeneity Enhancement of Mixtures Containing Epoxy Polymer and 100% Reclaimed Asphalt Pavement.

The utilization of reclaimed asphalt pavement (RAP) could reduce the cost of pavements containing epoxy polymer (EP) materials. This study was aimed at improving the homogeneity of an EP-reclaimed asphalt mixtures (ERAMs) at both the micro- and meso-scale to provide a reference for an ERAM production process. At the microscale, nanoindentation tests were conducted to characterize the diffusion between the EP and aged asphalt mastic. At the mesoscale, computerized tomography (CT) X-ray scanning and MATLAB analysis were employed to investigate the distribution of the aggregate within the ERAM. The results revealed that mixing temperature played a significant role in the diffusion and distribution between the EP and the aged asphalt mastic, thus impacting the mechanical properties of the material. Heating at 180 °C (the recommended mixing temperature of EP) resulted in a wider blending zone between the EP and the aged asphalt mastic compared to heating at 160 °C (the usual mixing temperature of ordinary reclaimed asphalt mixtures). The overall dispersion of the aggregate in the ERAM exhibited greater homogeneity in the vertical direction than in the horizontal direction. Adjusting the gradation of the RAP was found to be effective in reducing horizontal variability in the distribution of the coarse aggregate, fine aggregate, and air voids in the ERAM. Adjusting the RAP gradation further enhanced the vertical homogeneity in the distribution of the fine aggregate, while its impact on the vertical distribution of the coarse aggregate was minimal. Short-term aging led to increased variability in the distribution of the coarse aggregate, fine aggregate, and air voids within the ERAM. However, adjusting the gradation was effective in mitigating the adverse effects of short-term aging on both horizontal and vertical homogeneity in the aggregate distribution.

Application of isotopic labels optimised for large scale plot experiments

AbstractIsotopic tracer methods using 15N or other isotopes provide insights into the sources and underlying N transformations leading to N2O emissions from agricultural soils. However, homogeneous labelling of naturally structured soil in the field is challenging since macropore flow must be avoided while the application must be performed in a limited timeframe. Therefore, we tested the infiltration pattern of several application methods and consequently developed drip application (DA) for larger scales using individual dropper bottles. We performed a proof of concept test, followed by an evaluation experiment in-situ with a manual sprinkler as control at an undisturbed grassland site using 15NH415NO3 (80 kg N ha-1, 10 at.%, 15 mm precipitation equiv.). 15N-NH4+ and 15N-NO3- recovery rates and corresponding correlation coefficients were calculated to examine horizontal and vertical homogeneity. The proof of concept test showed the negative effect of very dry topsoil on homogeneous infiltration. DA achieved significantly larger 15N recovery rates than sprinkler application and led to a more homogeneous horizontal label distribution. For DA, coefficients of variation of 15N recovery rates were smaller than with sprinklers for most depths, yet for both methods 15N recovery rates especially of 15N-NH4+ decreased vertically. Besides optimised label distribution, the DA method offers high flexibility in application patterns while offering reproducibility, feasibility and a reasonable application speed also at undisturbed sites at the plot scale. Moreover, DA causes no change in soil structure or soil diffusivity. Thus, the drip application method was found suitable for tracer application to field sites.

Localized layers of turbulence in stratified horizontally sheared Poiseuille flow

This paper presents a numerical analysis of the instability developing in horizontally sheared Poiseuille flow, when stratification extends along the vertical direction. Our study builds on the previous work that originally detected the linear instability of such a configuration, by means of experiments, theoretical analysis and numerical simulations (Le Gal et al., J. Fluid Mech., vol. 907, 2021, R1). We extend this investigation beyond linear theory, investigating nonlinear regimes with direct numerical simulations. We find that the flow loses its vertical homogeneity through a secondary bifurcation, due to harmonic resonances, and describe this symmetry-breaking mechanism in the vicinity of the instability threshold. When departing from this limit, we observe a series of bursting events that break down the flow into disordered motions driven by localized shear instabilities. This intermittent dynamics leads to the coexistence of horizontal localized layers of stratified turbulence surrounded by quiescent regions of meandering waves.

Strain Relaxation on Perovskite Surface via Light-Enhanced Ionic Homogeneity.

The efficiency and stability of perovskite solar cells (PSCs) can be either deteriorated or enhanced by strain at interfaces, which is sensitive to various external conditions, particularly light illumination. Here we investigated the vertical strain distribution in perovskite films synthesized under light illumination with various wavelengths. The films were formed by reacting formamidinium iodide (FAI)/methylammonium chloride (MACl) vapor with vapor-deposited PbI2 (CsBr) films. Strain in the films was evaluated with incident-angle-dependent grazing-incidence wide-angle X-ray scattering, which showed out-of-plane compressive and in-plane tensile strains, particularly on the surface. Short-wavelength light relaxed the strain on the perovskite surface via promotion of ionic diffusion, including FA, MA, Cs, and I, to reach vertical ionic homogeneity. With the charge trap concentration being reduced, both the efficiency and stability were greatly improved. This finding provides deep insight into the effect of light on strain in PSCs.

Analysis of MONARC and ACTIVATE Airborne Aerosol Data for Aerosol-Cloud Interaction Investigations: Efficacy of Stairstepping Flight Legs for Airborne In Situ Sampling

A challenging aspect of conducting airborne in situ observations of the atmosphere is how to optimize flight plans for specific objectives and constraints associated with weather and flight restrictions. For aerosol-cloud interaction research, two recent campaigns utilized a “stairstepping” approach whereby an aircraft conducts level legs at various altitudes while moving forward with each subsequent leg: the 2019 MONterey Aerosol Research Campaign (MONARC) over the northeast Pacific and the 2020–2022 Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) over the northwest Atlantic. We examine the homogeneity of several atmospheric variables both vertically and horizontally in the marine boundary layer with a focus on the sub-cloud environment. In well-mixed boundary layers, there was generally good horizontal and vertical homogeneity in potential temperature, winds, water vapor mixing ratio, various trace gases, and many aerosol variables. Selected aerosol variables exhibited the most variability owing to sensitivity to humidity and near-cloud conditions (supermicrometer aerosol concentrations), coastal pollution gradients (e.g., organic aerosol mass), and small spatial scale phenomena such as new particle formation (aerosol number concentration for particles with diameter &gt;3 nm). Illustrative cases are described when stairstepping can pose issues requiring extra caution for data analysis: (i) poor vertical mixing and layers decoupled from those below; (ii) multiple cloud layers; (iii) fluctuating cloud base/top and boundary layer top heights; and (iv) horizontal variability across specific features leading to sharp gradients such as right near coastlines and over the Gulf Stream with strong sea surface temperature changes. Results from this study provide a guide both for future studies aiming to examine these mission datasets and for designing new airborne campaigns.

A study of the vertical homogeneity of trace gases in East Asian continental outflow

East Asian continental outflows containing with pollutants may deteriorate air quality in the downwind region via long-range transport (LRT). In particular, cold fronts with high wind speeds generally promote the LRT of air pollutants to further downwind areas, including Taiwan. To gain an insightful understanding of the characteristics and vertical homogeneity of trace gases in East Asian continental outflows, as well as their relation with atmospheric meteorological conditions, whole air samples were collected above a cape at the northern tip of the island of Taiwan during frontal passages. Aerial samples were collected at multiple altitudes from the surface to a maximum height of 700 m with a multicopter sounding platform carrying a robotic whole air sampling device. Simultaneously, aerial meteorological variables of temperature and wind vector from near the surface to a maximum height of 1000 m were also measured during the whole air sampling periods. An array of 106 volatile organic compounds (VOCs) as well as CO, CO2, and CH4 were analyzed to characterize the air composition and vertical homogeneity of trace gases. The results revealed rather homogeneous vertical distributions of most VOCs, CO, CO2, and CH4 in the frontal passages, indicating well-mixed conditions of trace gases in the East Asian continental outflows. The strong wind shear and minimal temperature inversion associated with the frontal passage likely induced turbulence and increased vertical mixing. Furthermore, higher levels of species characteristic of the East Asian continent were observed from the surface up to hundreds of meters above the cape, revealing a strong inflow of polluted air masses from the East Asian continent brought by cold frontal passages.

Chemical Vapor Deposition of Cobalt and Nickel Ferrite Thin Films: Investigation of Structure and Pseudocapacitive Properties

AbstractTransition metal ferrites, such as CoFe2O4 (CFO) and NiFe2O4 (NFO), have gained increasing attention as potential materials for supercapacitors. Since chemical vapor deposition (CVD) offers advantages like interface quality to the underlying substrates and the possibility for coverage of 3D substrates, two CVD processes are reported for CFO and NFO. Growth rates amount to 150 to 200 nm h−1 and yield uniform, dense, and phase pure spinel ferrite films according to X‐ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectrometry and nuclear reaction analysis (RBS/NRA) and scanning electron microscopy (SEM). Atom probe tomography (APT) and synchrotron X‐ray photoelectron spectroscopy (XPS) give insights into the vertical homogeneity and oxidation states in the CFO films. Cation disorder of CFO is analyzed for the first time from synchrotron‐based XPS. NFO is analyzed via lab‐based XPS. Depositions on conducting Ni and Ti substrates result in electrodes with pseudocapacitive behavior, as evidenced by cyclovoltammetry (CV) experiments. The interfacial capacitances of the electrodes are up to 185 µF cm−2.

CALIOP retrieval of droplet effective radius accounting for cloud vertical homogeneity.

Monitoring cloud droplet effective radius (re) is of great significance for studying aerosol-cloud interactions (ACI). Passive satellite retrieval, e.g., MODIS (Moderate Resolution Imaging Spectroradiometer), requires sunlight. This requirement prompted developing re retrieval using active sensors, e.g., CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization). Given the highest sensitivity of vertically homogeneous clouds to aerosols that feed to cloud base, here CALIOP profile measurements were used for the first time to quantify cloud vertical homogeneity and estimate cloud re during both day and night. Comparison using simultaneous Aqua-MODIS measurements demonstrates that CALIOP retrieval has the highest accuracy for vertically homogeneous clouds, with R2 (MAE, RMSE) of 0.72 (1.75 µm, 2.25 µm), while the accuracy is lowest for non-homogeneous clouds, with R2 (MAE, RMSE) of 0.60 (2.90 µm, 3.70 µm). The improved re retrieval in vertically homogeneous clouds provides a basis for possible breakthrough insights in ACI by CALIOP since re in such clouds reflects most directly aerosol effects on cloud properties. Global day-night maps of cloud vertical homogeneity and respective re are presented.

Temporal variability of the physical and chemical environment, chlorophyll and diatom biomass in the euphotic zone of the Beagle Channel (Argentina): Evidence of nutrient limitation

Coastal, semi-enclosed aquatic ecosystems of sub-polar regions surrounded by continental glaciers are among the most sensitive environments to climate change. The Beagle Channel (Argentina-Chile, ~55°S, 71°-66°W), which is part of the Patagonian Cold Estuarine System of austral South America, receives fresh water input from rivers, glaciers and mountain ice sheets. Like in most fjord systems, its productivity relies on the input of nutrients from marine and terrestrial sources. Bathymetry and circulation patterns in the western (inner) sector of the Beagle Channel are known to differ from those of the eastern (outer) sector. Physical and chemical conditions of the water column and climatic trends in the area have been understudied, as all previous surveys were strongly limited in time, spatial coverage and water depth (especially in wintertime). For the first time and during a 2.5-year period (2012–2014) this study covers the spatial and temporal variation of hydrographic and meteorological conditions, total chlorophyll concentration and diatom biomass at three different sites within the Argentine sector of the Beagle Channel. An overall vertical homogeneity and silicate limitation for diatom growth were observed in the euphotic zone of both the inner and outer sectors. These two sectors, however, differed in other ways: salinity was always higher in the outer sector occasionally showing a west-east gradient. Conversely, total chlorophyll and diatom biomass were higher in the inner sector at every sampling date. In both sectors, biotic and abiotic variables showed a seasonal pattern with clear differences between summer and winter. Nevertheless, interannual differences may cast shadow over seasonal patterns: The warmer summer and milder winter of year 2013, together with a delay in spring stratification, led to higher nutrient concentrations, lower total chlorophyll and lower diatom biomass during that year as compared to years 2012 and 2014. Inorganic nutrients and chlorophyll levels found in this study were compared with all available literature on the Beagle Channel. The present results represent a base line to encourage further time-sustained investigation relating biogeochemical, oceanographic and phytoplanktonic processes involving mainly silicate-dependent organisms. In turn, they will allow tracking changes and responses of the Beagle Channel ecosystem to climatic-oceanographic phenomena (e.g., ENSO, SAM) and climate change.

Direct Measure of Electrode Spatial Heterogeneity: Influence of Processing Conditions on Anode Architecture and Performance.

In this work, the spatial (in)homogeneity of aqueous processed silicon electrodes using standard poly(acrylic acid)-based binders and slurry preparation conditions is demonstrated. X-ray nanotomography shows segregation of materials into submicron-thick layers depending on the mixing method and starting binder molecular weights. Using a dispersant, or in situ production of dispersant from the cleavage of the binder into smaller molecular weight species, increases the resulting lateral homogeneity while drastically decreasing the vertical homogeneity as a result of sedimentation and separation due to gravitational forces. This data explains some of the variability in the literature with respect to silicon electrode performance and demonstrates two potential ways to improve slurry-based electrode fabrications.

Wireless sensor network to identify the reduction of meteorological gradients in greenhouse in subtropical conditions

Spatial and temporal monitoring of temperature and relative humidity is essential for greenhouse management, therefore, wireless sensor networks (WSN) can offer crucial advantages. The objective of this work was to use a WSN to characterize and map the horizontal and vertical variability of air temperature and relative humidity inside a greenhouse using five different configurations. The configurations were based on combinations between the following actuating mechanisms: i) mechanical ventilation (by two exhaust fans); ii) natural ventilation (through the roof vent openings); iii) shading through the use of thermo-reflective screen. The WSN was designed with 45 spatially distributed measuring points, and the air temperature and relative humidity were recorded automatically every 30 seconds, for ten consecutive days, for each configuration. Our results show that the horizontal and vertical homogeneity of the meteorological elements depends on the actuating mechanism used in the greenhouse. Mechanical ventilation approximated the temperature and relative humidity of the indoor and outdoor air, with a homogeneous horizontal distribution throughout the environment. Opening the roof vent reduced vertical gradients of temperature and relative humidity. Our observations also showed that the combination of the use of roof vent openings with mechanical ventilation is an effective way to achieve horizontal homogeneity of meteorological elements.

Mathematical modeling of thermal processes during "cassette" crystallization of chalcogenides

A new, relatively simple and highly efficient modification of the directional melt crystallization method in the form of a multi-cassette process has been considered. This study is based on Russian Patents and technological studies conducted at National Research and Technological University MISiS. As a result, mathematical models of a multi-cassette method have been developed for 3D radiation and conduction analysis of thermal processes in the entire volume of the heating unit and 2D analysis of convection and conduction heat exchange in a separate cassette. Parameters have been calculated on the basis of these mathematical models for clarifying the effect of heating unit component arrangement and dimensions on the formation of thermal fields in cassette units, the effect of vertical homogeneity of heat supply to the cassette unit and heating power reduction rate during crystallization on the shape of the crystallization front, as well as the effect of small asymmetry in cassette design and violation of cassette bottom cooling homogeneity on convection and asymmetrical heat transfer. Application of the conductive and radiative heat exchange model to the entire heating unit has allowed us to calculate process parameters on the basis of which we have analyzed the effect of heating unit components, their arrangement and temperature on the heat exchange conditions at the cassette unit boundaries. Application of the convective and conductive model to one growth cassette has shown that asymmetrical design and boundary thermal conditions as well as unstable vertical temperature gradient lead to the formation of convection vortices and substantial crystallization front deviation from planar shape. Calculations on the basis of the convective mass exchange model have shown that an increase in the crystallization rate by one order of magnitude greatly increases the tellurium flow into the crystal thus substantially altering the melt composition in the vicinity of the crystallization front and hence serving as a potential origin of dendrite growth. The authenticity of the calculation results has been verified in a number of tests aimed at analyzing the effect of heat and mass transport on crystallization front shape for cassette cooling rates that are typical of polycrystalline bismuth telluride growth processes.

The Effect of Weighting Materials on Oil-Well Cement Properties While Drilling Deep Wells

In deep hydrocarbon development wells, cement slurry with high density is required to effectively balance the high-pressure formations. The increase in the slurry density could be achieved by adding different heavy materials. In this study, the effect of the weighting materials (barite, hematite, and ilmenite) on the properties of Saudi Class G cement matrix of vertical homogeneity, compressive strength, porosity, and permeability was evaluated. Three cement slurries were weighted with barite, hematite, and ilmenite, and cured at 294 °F and 3000 psi for 24 h. All slurries have the same concentration of the different additives except the weighting material. The amount of weighting material used in every slurry was determined based on the targeted density of 18 lbm/gal. The results of this study revealed that the most vertically homogenous cement matrix was the ilmenite-weighted sample with a vertical variation of 17.6% compared to 20.2 and 24.8% for hematite- and barite-weighted cement, respectively. This is attributed to the small particle size of the ilmenite. The medical computerized tomography (CT) scan confirmed that the ilmenite-weighted sample is the most homogeneous, with a narrow range of density variation vertically along the sample. Hematite-weighted cement showed the highest compressive strength of 55.3 MPa, and the barite- and ilmenite-weighted cement compressive strengths are each 18.4 and 36.7% less than the compressive strength of the hematite-weighted cement, respectively. Barite-weighted cement has the lowest porosity and permeability of 6.1% and 18.9 mD, respectively. The maximum particle size of ilmenite used in this study is less than 42 μm to ensure no abrasion effect on the drilling system, and it minimized the solids segregation while maintaining a compressive strength that is higher than the minimum acceptable strength, which is the recommended weighting material for Saudi Class G cement.

A numerical study of the thermal bar in shallow water during the autumn cooling

The article presents numerical simulation of the autumnal thermal bar dynamics on the example of the Selenga River shallow water in Lake Baikal. Hydrophysical and atmospheric conditions of the object under study in autumn are taken into account. The influence of river inflow (runoff current and water mineralization) and wind impact on the thermal bar behavior are evaluated. The numerical modeling analysis demonstrates that in the early stage of the thermal bar development, the most significant for convection is the momentum of the river inflow. However, with the distance increase between the thermal bar and the river mouth, the role of the river mineralization and wind stress also increases. Highly mineralized inflow waters have the largest impact on thermohydrodynamic processes in shallow waters under calm weather conditions. Wind action on the lake surface may lead to the deviation of the line of convergence of water masses from to the 4 °C isotherm. Moreover, prolonged wind activity may result in the destruction of the thermal bar front and vertical thermal homogeneity across the entire shallow water area.