Mixing Region Research Articles

Explorative characterization and taxonomy-aligned comparison of alterations in lipids and other biomolecules in Antarctic bacteria grown at different temperatures.

Temperature significantly impacts bacterial physiology, metabolism and cell chemistry. In this study, we analysed lipids and the total cellular biochemical profile of 74 fast-growing Antarctic bacteria grown at different temperatures. Fatty acid diversity and temperature-induced alterations aligned with bacterial classification-Gram-groups, phylum, genus and species. Total lipid content, varied from 4% to 19% of cell dry weight, was genus- and species-specific. Most bacteria increased lipid content at lower temperatures. The effect of temperature on the profile was complex and more species-specific, while some common for all bacteria responses were recorded. Gram-negative bacteria adjusted unsaturation and acyl chain length. Gram-positive bacteria adjusted methyl branching (anteiso-/iso-), chain length and unsaturation. Fourier transform infrared spectroscopy analysis revealed Gram-, genus- and species-specific changes in the total cellular biochemical profile triggered by temperature fluctuations. The most significant temperature-related alterations detected on all taxonomy levels were recorded for mixed region 1500-900 cm-1 , specifically the band at 1083 cm-1 related to phosphodiester groups mainly from phospholipids (for Gram-negative bacteria) and teichoic/lipoteichoic acids (for Gram-positive bacteria). Some changes in protein region were detected for a few genera, while the lipid region remained relatively stable despite the temperature fluctuations.

Numerical investigation of thermal-mixing characteristics at vertically oriented T-junction pipelines

When hot and cold fluids are mixed at pipeline tees, temperature fluctuations are generated and can lead to thermal fatigue damage in the piping materials. At the University of Stuttgart in Germany, experimental investigations have been performed for understanding the flow mixing mechanism causing thermal fatigue. It was found that the inlet flow rate is one of the decisive factors on the mixing behaviors at a horizontal T-junction.In this study, the influence of the inlet flow rate on the flow mixing behaviors at the vertical T-junction is investigated using the large-eddy simulation (LES) method. The simulations are validated with the previous experiments and provide a good overview of the mixing flow. The LES method shows the advantage of illustrating the collision of two flow streams at the T-junction, which leads to different behaviors of the mixing flow. Generally, the temperature fluctuation in the mixing flow as well as the stability of thermal stratification decreases along the flow direction due to the dissipation of the turbulent kinetic energy in the mixing flow. The decrease in the main flow rate shows the impact of the increase in thermal stratification stability and the reverse flow distance. The decrease in the branch flow leads to a slight increase of the thermal stratification stability downstream of the T-junction and significant turbulent penetration in the branch pipe. The maximum temperature fluctuation at the pipeline inner surface is located at the joint position of the pipelines with a value higher than 30 K. Moreover, the flow collision at the T-junction leads to significant secondary flow in the mixing region, which can be influenced by the variations in the inlet flow rate. In particular, the secondary flow due to cold fluid presents a phenomenon of counter-rotating vortex pair (CRVP), and generates a temperature fluctuation with a frequency of approximately 1.1 Hz, which is recorded by the monitor points at both horizontal sides of the pipeline. In comparison with the previous work at the horizontal T-junction, the complete flow collision at the vertical T-junction is the reason for the totally different mixing phenomenon.

Experimental observation and characterization of amorphous carbon generated in graphene on gold nanoparticles.

The interaction of graphene with gold nanoparticles is investigated using transmission electron microscopy. We observe gold-nanoparticle-mediated etching of graphene flakes, often leading to hole formation. Further, using a combination of high-angle annular dark field imaging and electron energy loss spectroscopy, we highlight that the catalytic effects of gold nanoparticles on graphene lead to the formation of amorphous carbon layers. From the extracted diffractograms, we observe regions with diffraction halos as well as some regions with a weak tetrahedral motif. Using independently performed Raman measurements, we confirm the presence of tetrahedral amorphous carbon as well as mixed graphitic-amorphous regions. For the amorphous carbon regions with mixed sp2-sp3 states, the Raman G peak is red-shifted to 1564 cm-1 and an I D/I G ratio of 0.63 indicates less than 20% sp3 content. For the tetrahedral amorphous carbon regions, we observe that the Raman G peak is at 1580 cm-1, close to that of monolayer graphene. However, there is no Raman D peak, i.e., I D/I G = 0, which indicates close to 100% sp3 content. The translation of the Raman G peak location and the I D/I G ratios is on par with the amorphization trajectory analysis of Ferrari and Robertson (Phys. Rev. B: Condens. Matter Mater. Phys., 2000, 61, 14095) and validates the conversion route of graphite to amorphous carbon to tetrahedral amorphous carbon. The presented method provides a promising pathway for creating defect-induced amorphous carbon at room temperature, which has a broader impact on the electronics and semiconductor industries.

The Vertical Structure of Internal Lee-Wave-Driven Benthic Mixing Hotspots

Abstract In global ocean circulation and climate models, bottom-enhanced turbulent mixing is often parameterized such that the vertical decay scale of the energy dissipation rate ζ is universally constant at 500 m. In this study, using a nonhydrostatic two-dimensional numerical model in the horizontal–vertical plane that incorporates a monochromatic sinusoidal seafloor topography and the Garrett–Munk (GM) background internal wave field, we find that ζ of the internal lee-wave-driven bottom-enhanced mixing is actually variable depending on the magnitude of the steady flow U0, the horizontal wavenumber kH, and the height hT of the seafloor topography. When the steepness parameter (Sp = NhT/U0 where N is the buoyancy frequency near the seafloor) is less than 0.3, internal lee waves propagate upward from the seafloor while interacting with the GM internal wave field to create a turbulent mixing region with ζ that extends farther upward from the seafloor as U0 increases, but is nearly independent of kH. In contrast, when Sp exceeds 0.3, inertial oscillations (IOs) not far above the seafloor are enhanced by the intermittent supply of internal lee-wave energy Doppler-shifted to the near-inertial frequency, which occurs depending on the sign and magnitude of the background IO shear. The composite flow, consisting of the superposition of U0 and the IOs, interacts with the seafloor topography to efficiently generate internal lee waves during the period centered on the time of the composite flow maximum, but their upward propagation is inhibited by the increased IO shear, creating a turbulent mixing region of small ζ.

Influence of fluid viscosity hierarchy on the reverse-circulation displacement efficiency

Reverse-circulation cementing is an alternative strategy for well cementing where the cementing fluids are injected directly into the annulus from the surface. This cementing strategy can reduce downhole circulation pressures compared to conventional circulation cementing and potentially eliminate the need for retarders in the cement slurry. In reverse-circulation operations, the fluid hierarchy will normally involve density-unstable combinations along the annulus. Since the annular geometry prevents the mechanical separation of fluids, reverse-circulation cementing is associated with a risk of slurry contamination and mixing during placement. Although reverse-circulation cementing has been known for several decades and is used for cementing of both onshore and offshore wells, it remains unclear whether conventional circulation job design guidelines apply to reverse-cementing or indeed how fluid properties should be optimized for such operations. The purpose of the current study is to contribute to the understanding of buoyant annular displacements, with a particular focus on the role of viscosity hierarchy on the annular displacement in vertical and near-vertical annuli.We present a combined experimental and numerical study of density-unstable downward displacements in a downscaled, narrow concentric annulus. A transparent annulus flow loop was used to conduct downward displacements. A high-speed camera and a mirror arrangement were used to track the displacement. Numerical simulations of the experiments and selected other cases were performed using the open-source OpenFOAM computation framework. We study Newtonian and mildly shear-thinning fluids, and our study aims to determine whether it is more efficient to use a displacing fluid with higher viscosity or lower viscosity than the displaced fluid while maintaining a constant average viscosity for the fluid pair. The experimental and numerical results, which are in good qualitative agreement, demonstrate that the viscosity hierarchy of the fluids significantly affects the displacement flow features. Our results show that a more viscous displaced fluid leads to faster growth of the instabilities and, as a result, less efficient displacement. Oppositely, we observe less tendency for finger growth and a more diffusive mixing region for more viscous displacing fluids. The effect of the viscosity hierarchy can get stronger by increasing the inclination of the annulus and the viscosity difference between the fluids from 0.006 to about 0.02 Pa⋅s. The findings can assist in the selection of fluid properties for future reverse-circulation displacement operations.

Identification of source contributions to fine particulate matter at Indian desert-urban mixed region

This study aims to identify the source contributions based on the chemical composition in a desert-urban location at Bikaner, Rajasthan, India. USEPA-PMF5.0 was run and the analysis resolved eight factors which represents eight sources identified by their chemical profiles together with tracer species. The sources resolved were: Secondary sulphate (25.2%), resuspended dust (23.6%), residential cookstove (13.4%), smelter and non-tail-pipe emissions (11.3%), vehicular emissions (10.8%), lake and sea salt (8.5%), secondary nitrate (4.8%), and brick kilns (2.2%). Winter and post-monsoon PM concentrations in the region were majorly regulated by secondary sulphate and residential cookstove emissions, contributing to 22% and 22–27%, respectively. Dust storms prevalent in the region during pre-monsoon and monsoon resulted in higher resuspended dust contribution (30–43%) from crustal sources during these seasons. Salt lakes in the region influenced the fine PM mass with its effect aggravated during the monsoon by the sea-salts from the Arabian Sea. The fine PM mass was impacted by salt lakes in the area, which is exacerbated during the monsoon by sea-salts from the Arabian Sea. Smelters, non-tailpipe emissions, and vehicular emissions were substantial contributors to moderately polluted to poor conditions (PM2.5 loadings >60 μg m−3). Furthermore, highest PM2.5 concentrations (>90 μg m−3) marking the very poor conditions in the region were attributed to residential cookstove emissions and secondary sulphate. While vehicular emissions were found to be primarily from local sources, numerous smelters from northern states had potential influence on PM mass. The prominent seasonality in the source contributions observed in this study is particularly suggestive of substantial influence of meteorology on PM concentrations in the region.

Shaping territorial solutions to the Cyprus conflict: the role of international organizations

ABSTRACT This article offers a comprehensive assessment of territorial solutions for ethnic conflicts, with a specific focus on Cyprus. Despite its prominence, scholarly study has not adequately explored the complexities of territoriality as exhibited in the Cyprus conflict. To address such a gap, this study tackles the territorial dimension of the Cyprus problem from a unique perspective: the potential effects of international organizations acting as agents of socialization on the two community leadership. Despite the acceptance of bizonal, bicommunal federal state, which have become permanent UN parameters as a basis for the settlement, the Greek Cypriot side insisted on ‘loose bizonality’ suggesting ethnically mixed regions, whereas the Turkish Cypriot side demanded a ‘monolithic bizonality’ amounted to ethnic segregation. There are indications, however, that the UN, the EU, and the international judiciary support‘ pluralistic bizonality’, as an alternative to ‘lose’ or ‘monolithic’ bizonality encouraging revisions in territorial approaches of the two sides.

Universal insertion of molecules in ionic compounds under pressure.

Using first-principles calculations and crystal structure search methods, we found that many covalently bonded molecules such as H2, N2, CO2, NH3, H2O and CH4 may react with NaCl, a prototype ionic solid, and form stable compounds under pressure while retaining their molecular structure. These molecules, despite whether they are homonuclear or heteronuclear, polar or non-polar, small or large, do not show strong chemical interactions with surrounding Na and Cl ions. In contrast, the most stable molecule among all examples, N2, is found to transform into cyclo-N5- anions while reacting with NaCl under high pressures. It provides a new route to synthesize pentazolates, which are promising green energy materials with high energy density. Our work demonstrates a unique and universal hybridization propensity of covalently bonded molecules and solid compounds under pressure. This surprising miscibility suggests possible mixing regions between the molecular and rock layers in the interiors of large planets.

A Model of Mass and Heat Transfer for Disc Temperature Prediction in Open Compressor Cavities

Abstract Accurate prediction of heat transfer in compressor cavities is crucial to the design of efficient and reliable aircraft engines. The heat transfer affects the thermal expansion of the compressor rotor and, in turn, the tip clearance of the compressor blades. This article presents a novel, physically based predictive theoretical model of heat transfer and flow structure in an open compressor cavity, which can be used to accurately calculate disc temperatures. The radially higher region of the cavity is dominated by buoyancy effects created by the temperature difference between the hot mainstream flow and the axial throughflow used to cool the turbine. Strong interaction between the air in the cavity and this throughflow creates a mixing region at low radius. For a given geometry, the heat transfer and flow physics are governed by four parameters: the rotational Reynolds number Reϕ, the buoyancy parameter βΔT, the compressibility parameter χ, and the Rossby number Ro. The model quantifies both the buoyancy- and throughflow-induced mass and heat transfer, producing a reliable prediction of the disc and air temperatures. The model takes into account a twofold effect of the throughflow: being entrained into the cold radial plumes directly and creating a toroidal vortex in the radially lower region of the cavity. The exchange of mass between the cavity and throughflow is related to the mass flowrate in the radial plumes in the buoyancy-induced region, considering the effect of flow reversal at low Ro. The model is validated using data collected in the Bath compressor cavity rig and can be incorporated in engine design codes to robustly compute the thermal stress and expansion of the compressor rotor, contributing to more efficient engine designs.

On the preferred flapping motion of round twin jets

Linear stability theory (LST) is often used to model the large-scale flow structures in the turbulent mixing region and near pressure field of high-speed jets. For perfectly expanded single round jets, these models predict the dominance of azimuthal wavenumbers $m=0$ and $m = 1$ helical modes for the lower frequency range, in agreement with empirical data. When LST is applied to twin-jet systems, four solution families appear following the odd/even behaviour of the pressure field about the symmetry planes. The interaction between the unsteady pressure fields of the two jets also results in their coupling. The individual modes of the different solution families no longer correspond to helical motions, but to flapping oscillations of the jet plumes. In the limit of large jet separations, when the jet coupling vanishes, the eigenvalues corresponding to the $m=1$ mode in each family are identical, and a linear combination of them recovers the helical motion. Conversely, as the jet separation decreases, the eigenvalues for the $m=1$ modes of each family diverge, thus favouring a particular flapping oscillation over the others and preventing the appearance of helical motions. The dominant mode of oscillation for a given jet Mach number $M_j$ and temperature ratio $T_R$ depends on the Strouhal number $St$ and jet separation $s$ . Increasing both $M_j$ and $T_R$ independently is found to augment the jet coupling and modify the $(St,s)$ map of the preferred oscillation mode. Present results predict the preference of two modes when the jet interaction is relevant, namely varicose and especially sinuous flapping oscillations on the nozzles’ plane.

Classical and quantum elliptical billiards: Mixed phase space and short-range correlations in singlets and doublets

Billiards are flat cavities where a particle is free to move between elastic collisions with the boundary. In chaos theory, these systems are simple prototypes. The conservative dynamics of a billiard may vary from regular to chaotic, depending only on the shape of the boundary. This work aims to shed light into the quantization of classically chaotic systems. We present numerical results on classical and quantum properties in two bi-parametric families of billiards, namely Elliptical Stadium Billiard (ESB) and Elliptical-C3 Billiards (E-C3B). Both families entail elliptical perturbations of chaotic billiards with originally circular sectors on their borders. Our numerical calculations provide evidence that these elliptical families may exhibit a mixed classical dynamics, identified by the chaotic fraction of the phase space, the parameter χc<1. We use this quantity to guide our analysis of quantum spectra. We explore the short-range correlations through nearest neighbor spacing distribution p(s), revealing that in the mixed region of the classical phase space, p(s) is well described by the Berry–Robnik–Brody (BRB) distributions for the ESB. In agreement with the expectation from the so-called ergodic parameter α=tH/tT, the ratio between the Heisenberg time and the classical diffusive-like transport time. Our findings indicate the possibility of quantum dynamical localization when α<1. For the E-C3B family, the eigenstates can be split into singlets and doublets. BRB successfully describes p(s) for singlets as the previous family in the mixed region. However, for doublets, new distributions recently introduced in the literature come into play, providing descriptions for p(s) with a focus on cases where χc=1. We observed that as χc decreases, the p(s) distributions simultaneously deviate from the Gaussian Orthogonal Ensemble (GOE) for singlets, and Gaussian Unitary Ensemble (GUE) for doublets.

An NEA/OECD benchmark-experiment for the validation of CFD for mixing and thermal fatigue in T-junction dead leg flows

The current screening criteria for thermal fatigue used in isolated branch lines at nuclear power plants are based on simplified approaches, which, on one hand, tend to be overly conservative, and on the other hand, appear to miss important physics. This is demonstrated by the fact that a number of affected pipes were missed by the current screening methods.The purpose of the present work is to produce novel and accurate experimental data, which can be used for a benchmark of Computational Fluid Dynamics (CFD) in order to advance the prediction capabilities of thermal mixing and fatigue in dead leg T-junctions and improve the accuracy of the screening criteria. The ultimate value creation is increased safety and availability at nuclear power plants. This is of great interest and utmost importance to the nuclear reactor safety community.A new pressurized experimental setup of a T-junction has been designed and constructed for the purpose. The experimental setup, with a temperature difference of 120 °C, more closely resembles plant conditions than in earlier experiments. The boundary conditions in terms of the flowrates and temperatures are controlled and stable within their measurement uncertainty – a prerequisite for CFD-grade experiments.The novelty of the present work is measurements of the temperature fluctuations both in the near wall fluid mixing region and throughout the solid pipe wall material.It has been shown that the interaction between the swirl penetration of hot water and the stratified layer in the cold dead leg has an intermittent character and that random clusters of bursts of hot water penetrate into the stratification and the stagnant cold water below. The average time scale of this process is of the order of hundreds of seconds.The stratification between the hot and the cold water in the dead leg has also shown to have a low frequency oscillation of the order of 0.1 Hz, which wiggles in the circumferential direction. After hot water has penetrated downward and excited the instability, the temperature falls back to the initial one in a manner similar to a damped oscillation.The vertical temperature profiles have shown to be self-similar, for moderate temperatures, when scaled with the temperature difference between the hot and the cold water and with the penetration length.The penetration length increases with the velocity in the hot leg confirming earlier reported correlations.A small (less than 0.1 % of the hot main flow) cold leakage flow into the T-junction is sufficient to suppress the swirl penetration and substantially reduces the penetration length. However, the temperature fluctuations have a larger amplitude and range across the whole mixing zone. The fluid temperature fluctuations are shifted towards a more high frequency content, however, the low frequency nature of the swirl penetration is still present.The obtained novel dataset will be provided for a blind CFD benchmark exercise as part of an OECD/NEA project in 2023 and 2024.

Improved Two-Fluid Model for Segregated Flow and Integrated Multiphase Flow Modeling for Downhole Pressure Predictions

This work presents an integrated multiphase flow model for downhole pressure predictions with the purpose of producing relatively more accurate predictions under wide-flowing conditions while maintaining a simple form. As a component of the integrated model, an improved two-fluid model for segregated flow is proposed. The new two-fluid model was developed by improving the modeling of the wetted perimeters and the liquid wall shear stress. It outperformed five other existing state-of-the-art models in predicting the liquid holdup and pressure gradient of 11 experimental datasets from the literature, with an average relative error of 37.6% for liquid holdup predictions and 24.0% for pressure gradient predictions. The model succeeds in capturing the effects of inclination angle, pressure or gas density, and liquid and gas superficial velocities on liquid holdup and pressure gradient. The integrated model incorporates the state-of-the-art onset of liquid loading predictive model and classifies the flow into two major categories based on the onset of liquid loading that are modeled by two different approaches, respectively. It outperformed the other multiphase flow models in predicting the downhole pressure of 313 field data points, especially the wells that have both segregated and intermittent (mixed) flows. The errors were reduced to 4.4% for the field cases with mixed flow regions and 5.1% for all the field data points.

Etiology of Primary Cerebellar Intracerebral Hemorrhage Based on Topographic Localization.

Cerebellar intracerebral hemorrhage (cICH) is often attributed to hypertension or cerebral amyloid angiopathy (CAA). However, deciphering the exact etiology can be challenging. A recent study reported a topographical etiologic relationship with superficial cICH secondary to CAA. We aimed to reexamine this relationship between topography and etiology in a separate cohort of patients and using the most recent Boston criteria version 2.0. We performed a retrospective analysis of consecutive patients with primary cICH admitted to a tertiary academic center between 2000 and 2022. cICH location on brain computed tomography/magnetic resonance imaging scan(s) was divided into strictly superficial (cortex, surrounding white matter, vermis) versus deep (cerebellar nuclei, deep white matter, peduncular region) or mixed (both regions). Magnetic resonance imaging was rated for markers of cerebral small vessel disease. We assigned possible/probable versus absent CAA using Boston criteria 2.0. We included 197 patients; 106 (53.8%) were females, median age was 74 (63-82) years. Fifty-six (28%) patients had superficial cICH and 141 (72%) deep/mixed cICH. Magnetic resonance imaging was available for 112 (57%) patients (30 [26.8%] with superficial and 82 [73.2%] with deep/mixed cICH). Patients with superficial cICH were more likely to have possible/probable CAA (48.3% versus 8.6%; odds ratio [OR], 11.43 [95% CI, 3.26-40.05]; P<0.001), strictly lobar cerebral microbleeds (51.7% versus 6.2%; OR, 14.18 [95% CI, 3.98-50.50]; P<0.001), and cortical superficial siderosis (13.8% versus 1.2%; OR, 7.70 [95% CI, 0.73-80.49]; P=0.08). Patients with deep/mixed cICH were more likely to have deep/mixed cerebral microbleeds (59.2% versus 3.4%; OR, 41.39 [95% CI, 5.01-341.68]; P=0.001), lacunes (54.9% versus 17.2%; OR, 6.14 [95% CI, 1.89-19.91]; P=0.002), severe basal ganglia enlarged perivascular spaces (36.6% versus 7.1%; OR, 7.63 [95% CI, 1.58-36.73]; P=0.01), hypertension (84.4% versus 62.5%; OR, 3.43 [95% CI, 1.61 to -7.30]; P=0.001), and higher admission systolic blood pressure (172 [146-200] versus 146 [124-158] mm Hg, P<0.001). Our results suggest that superficial cICH is strongly associated with CAA whereas deep/mixed cICH is strongly associated with hypertensive arteriopathy.

The Supervision of Schools and the Language of the Czechoslovak Administration. On the Example of School Committees in the Bilingual Moravia

Based primarily on printed sources this study examines the building process of educational sector in the first years of Czechoslovakia, with a special emphasis on the issue of the supervisory bodies. Especially primary schools were considered by the so-called nationalist activists, both before and after 1918, strategic for building of the national education. School boards and then school committees played besides others an important role in the school enrolment, a key factor in the rise or fall of individual schools and language communities. Therefore, the process of creation of the school committees in the year 1921 is researched in particular. After the dissolution of the monarchy, a new organization of the school authorities and schools went hand in hand with a new language of the Czechoslovak administration. New laws, role of school boards and later committees, communication between them and teachers from primary schools are researched as well. Through the stenographic records of the Czechoslovak National Assembly and through other sources, the aforementioned points are analysed, on the example of the ethnically or linguistically mixed area of the former Crown land Moravia. The interests of the Czech nationalist activists clashed there with interests of the German nationalist activists. The Czech and German district school boards, as the supervision authorities, were abolished and new school committees were to be established instead. In the linguistically mixed regions they remained separated, which brought political disputes. At the same time, the daily agenda of schools, teachers and pupils’ demands could not be hindered. Ministry of Education and National Enlightenment called for speeding up the administrative steps.

Paul Harry Roberts. 13 September 1929—17 November 2022

Paul Roberts was a physicist and applied mathematician. He made important and often pioneering contributions in diverse research areas, but mainly with a fluid dynamic theme, which include rotating fluids, geophysical and astrophysical flows and superfluids. The cornerstone was magnetohydrodynamics with particular application to the geodynamo. His most notable achievement was the first three-dimensional self-consistent numerical geodynamo model, which built on the equations he had derived previously governing the Earth's core dynamics. His considerations included the role of thermal and compositional convection, and the inner core boundary layer (a mixed phase region). In addition to his remarkable illustration of magnetic field reversals, he applied his model to core–mantle coupling and variations in the length of the day. Paul investigated superfluid liquid helium on two fronts. He had a lifelong interest in Bose–Einstein condensates on the microscale governed by the nonlinear Schrodinger equation. His early work on the robust derivation of the mean-field Hall–Vinen–Bekharevic–Khalatnikov equations was far ahead of its time. Their importance and relevance was not appreciated until much later.

Atomistic mechanism of AlCu thin film alloy growth on trenched Si substrate

Molecular dynamics simulation was employed to study the growth mechanisms of an AlCu thin film on a trenched Si(001) substrate. The atomic interactions between Al, Cu, and Si atoms were described by using the Modified Embedded Atom Method (MEAM). This investigation focused on examining the effect of both incident energy and trench heights on the structure, and the morphology of deposited AlCu thin film. The results reveal that the growth mode follows an island mode, and the AlCu film surface exhibits both non-flat and non-uniform texture. The increase in the trench height leads to a more pronounced change in surface morphology and roughness. However, a higher incident energy can significantly reduce the surface roughness due to the mobility of deposited atoms. In addition, a mixing region was observed at the interface between the film and substrate. It is revealed that increasing the incident energy leads to deeper penetration of Al and Cu atoms into the substrate. More importantly, Al atoms penetrate deeper than the Cu atoms. On the other hand, deposition on a trench with 15 monoatomic layers leads to the formation of voids in the film. However, these voids disappear with higher incident energy. The microstructural evolution during deposition film was also analyzed based on the radial distribution function. The results of this function indicate that changes in trench height and the energy of incident adatoms do not significantly influence the structure of the film.

Observation of a dramatic increase in the positive cloud-to-ground lightning in the Indian summer monsoon season

Lightning is known for its meteorological importance and associated hazard potential. It is known that the polarity of cloud-to-ground flash (CG) can act as a prognosis of the storm's characteristics. Ground-based observation of lightning over the Indian region suggests that during the break period in the summer monsoon seasons, CG lightning of positive polarity increases dramatically relative to the pre-monsoon days. Here we propose that for thunderstorms forming in the wet season, the non-inductive charge separation happens in the presence of larger mean cloud liquid water in the mixed phase region of the storms. This facilitates the positive charging of graupel particles, thereby producing a large amount of positive CG lightning on these days. This observation is found to be consistent with the laboratory results of Takahashi (1978). The implication of these results has been discussed from the perspective of hazard mitigation associated with positive lightning over India.

Seasonal and regional variability of model-based zooplankton biomass in the Salish Sea and evaluation against observations

We used a three-dimensional coupled biophysical model to examine zooplankton dynamics in the Salish Sea, NE Pacific. First, we evaluated the two zooplankton classes of the SalishSeaCast model using a transboundary zooplankton dataset comprised of observation data from the Canadian and United States waters of the Salish Sea from 2015 to 2019. Model zooplankton classes correspond to micro- and meso-zooplankton whose biomass is tightly coupled to phytoplankton through modelled food web dynamics (Z1) and mesozooplankton with life cycle-based seasonal grazing impacts (Z2). Overall, the model effectively captured seasonal patterns in observed biomass, although with slightly higher biomass estimates for both Z1 and Z2 (Bias = 0.10 and 0.08 g C m−2, respectively). Model fit varied regionally, with a weaker model fit being observed in nearshore regions. In addition, an autumn peak in Z2 was observed in the model, but not in the observations, suggesting some seasonal variations in model fit. Following the model evaluation, we used the model to determine seasonal and regional patterns of zooplankton grazing. Seasonally, the main peak in modelled zooplankton biomass increased in April or May in most of the regions defined within the Salish Sea and was driven by grazing on diatoms. Regionally, depth-integrated zooplankton biomass was consistently highest in areas adjacent to regions of strong tidal mixing. In addition, model-based zooplankton grazing was highest in the tidally mixed regions where phytoplankton biomass was high due to advection into the region despite low primary productivity. Our model-based results provide an opportunity to examine bottom-up food web processes at spatio-temporal scales not achievable with in situ sampling and help to elucidate key drivers of lower trophic level dynamics within the Salish Sea.

Assessing mixing uniformity in microreactors via in-line spectroscopy

Mixing behavior is critical for enhancing the selectivity of fast chemical reactions in microreactors. A high Reynolds number (Re) improves the mixing rate and selectivity of the reactions, but some exceptions of increasing side product yield with the higher Re have been reported. This study investigated the mixing uniformity in microreactors with in-line UV–vis spectroscopy to clarify the relationship between reaction selectivity and chaotic mixing with the higher Re. A colorization experiment of thymolphthalein in an acidic solution was conducted with an excess acid amount to the base to indicate a non-uniformly mixed region. Non-uniformity significantly increased with Re. At the same time, the degree of mixing, which was measured by a usual decolorization experiment, showed that the mixing rate increased with Re. The in-line analysis of the Villermaux–Dushman reaction during the mixing clarified that side product yield significantly increased with Re at around 300 and then decreased at around 1100. These results suggest the compensation effect between the mixing uniformity and mixing rate on the selectivity of the mixing-sensitive reactions. Faster mixing, characterized by a larger Re, can disturb mixing uniformity and, in some cases, decrease reaction selectivity.