Vertical Uniformity Research Articles

Versatile fitting approach for operando spectroscopic imaging ellipsometry of HfS2 oxidation

Facile mapping of 2D heterostructures and resolving anisotropic formation kinetics down to the monolayer level are critical to developing scalable interfacing solutions and unlocking their application potential in emerging nano-optoelectronics. We adapt a Kramers–Kronig constrained variational fitting algorithm for spectroscopic imaging ellipsometry (SIE) to facilitate multi-scale heterostructure analysis comprising films with unknown complex dielectric functions and demonstrate how this enables non-destructive, scalable mapping and operando capability for the model system of HfS2 oxidation. This methodology proves highly accurate for assessing the thickness of buried HfS2 layers, oxide quality, and lateral and vertical uniformity. We capture dynamic stack evolution during thermal oxidation up to 400 ∘C, providing insights into the temperature and time-dependent nature of self-limiting oxide growth and reaction kinetics that involve the localised trapping and release of sulphur reaction products. Our methodology is versatile in material and device horizons, and advantageously agnostic to the underlying substrate. Combined with the various modes of SIE operation, it unlocks fast, high-throughput, large-area capability to accelerate process development at the atomic scale.

Numerical simulation and optimization of the multi-stage air/gas supply system in a coke oven battery with 7.1 m coking chambers

ABSTRACT 3-D numerical simulations based on diffusion combustion technology were employed to optimize the multi-stage air/gas supply system in a coke oven battery with 7.1 m coking chambers. In the heating flues, the Eddy-Dissipation Concept (EDC) model and the ideal gas model were utilized to numerically investigate diffusion combustion. What is more, the radiation between the flue gas and the silicon brick was calculated using the Discrete Ordinates (DO) model. After validating the reliability of the model with field-measured data, insights into the temperature field and gas flow in the heating flue, and heat flux distribution over the heating wall were obtained. To characterize the vertical heating uniformity, an index of the standard deviation of the heat flux over the vertical heating walls was proposed. By optimizing the multi-stage air/gas supply design of heating flues, the vertical heating uniformity was improved by 60% according to the index values. The approach developed in this work can be a useful tool for the design of large-capacity coke oven batteries at different scales.

Evaluation criterion of cathode flow field in air-cooling proton exchange membrane fuel cells

In recent years, air-cooling proton exchange membrane fuel cells (PEMFCs) have become a priority choice for applications due to their lightweight and simple structure. In this work, the mechanism of cathode flow field characteristics on PEMFC performance is revealed, and the evaluation criterion of the cathode flow field is proposed. A 2 kW PEMFC stack of 100 cells is used, and the different uniformity and airflow rate of the cathode flow field are achieved by varying the position and number of cathode fans with a constant total parasitic fan power. The PEMFC power, cathode temperature distribution, and single-cell voltage consistency of different configurations are evaluated. The results show that the maximum difference in output power and maximum temperature of different PEMFC cathode flow field configurations reach 6.5% and 22.3%, respectively. Three key parameters are proposed to evaluate the PEMFC cathode flow field: total uniformity rate can evaluate the overall uniformity of the PEMFC cathode flow field, vertical uniformity rate can be used to predict and evaluate the single-cell voltage consistency of the PEMFC stack, and cathode airflow rate determines the continuous operating power of the PEMFC stack. The evaluation criterion can guide the design and optimization of air-cooling PEMFCs.

Lidar Research during the First Stage of the 89th Cruise of the R/V “Academic Mstislav Keldysh”

A lidar survey of the western part of the Kara Sea was carried out in September 2022. The shipborne radiometric (profiling) lidar PLD-1 was used. The lidar optical unit was located on the 8th deck of the R/V ‘Akademik Mstislav Keldysh’ at an altitude of 15 m above the water surface. Lidar sounding was carried out at stations and underway. The vessel route passed through water areas characterized by a wide range of changes in hydrooptical characteristics. Lidar measurements were accompanied by synchronized measurements of hydrooptical and hydrological characteristics. These measurements were carried out using submersible instruments at stations and using a flow-through measuring complex along the ship's route. The hydrooptical characteristics vertical distribution uniformity in the upper ten-meter layer was controlled remotely using underway lidar data.Good agreement between the spatial distributions of the lidar echo signals parameters, of the hydrooptical and of the hydrological characteristics (coincidence of the locations of various distribution features, local maxima, minima and frontal zones) was demonstrated. A large volume of measurement data has been obtained, which allows for further statistical processing in order to find relationships between the parameters of lidar echo signals and hydrooptical characteristics recorded by contact methods.

The establishment of design criteria for precision ventilation in open-plan offices

Precision ventilation is used in open-plan offices to establish micro-climate zones according to the metabolic requirements of its occupants. The aim of this study is to determine design criteria and highlight the opportunities and limitations for precision ventilation in large-scale offices. The simulations and experiments were conducted under steady state conditions with fixed airflow from all active chilled beams (ACBs) and constant room temperatures. A temperature difference of 3.5K was maintained between supply and room air in all cases with and without occupants. Results showed that precision ventilation can simultaneously establish low-level (<0.15 m/s), medium-level (<0.45 m/s), and high-level (<0.65 m/s) air velocity zones in the same shared office space such that occupants with different metabolic rates had Predicted Mean Vote (PMV) values maintained within the acceptable limit. The establishment of a single air velocity zone in an open-plan office layout without influencing air velocities of other zones was achieved by lowering the airflow rates of two ACBs by 35%. The vertical and horizontal temperature uniformity was maintained with this precision ventilation system with draught rates of less than 20% for occupants with normal metabolic rates. Comparative analysis using precision ventilation with and without occupants showed that targeted air velocity distribution in the room can be negatively influenced by the absence of any heat sources in any zone. An annual energy saving of up to 15% was achieved by raising the cooling setpoint temperature from 23 °C to 25 °C.

Revisit flame modulation towards low-NOx and uniform thermal field in heating flue of a coke oven

To alleviate the environmental issues from the coal coking process, many efforts have been conducted on air staging and flue gas recirculation to dilute oxygen content with only a modest success of a NO discharge between 500 and 1000 ppm. In this work, we have attempted to modulate the structure of the fuel inlet to dilute the fuel content for a further mitigation of NOx emission. By using the CFD technique, three key structural parameters were used to demonstrate the effect on NOx formation and thermal uniformity in the heating flue. A three-dimensional CFD model was established based on an industrial scale coke oven battery of 7.63 m in height, and its reliability was verified by validating the calculation against practical data collected on-site. Comparative simulations were carried out in terms of flue gas flow pattern, temperature profile, fuel species and NO concentration distribution. The results show that the benchmark battery has probably selected appropriate parameters for the internal recirculation, but falls short with respects to the size of fuel inlet and the space between the fuel and air inlets. Compared to the basic design, the modified one presents a 57.3% reduction in NO formation, and an improved vertical temperature uniformity.

The Spatial Distribution of Microbially Induced Carbonate Precipitation in Sand Column with Different Grouting Strategies

For ground improvement via microbially induced carbonate precipitation (MICP), the spatial distribution of biocementation considerably affects the mechanical performance of soil. This study systematically assessed the CaCO3 spatial distribution in sand columns with various grouting strategies. CaCO3 dispersion along the radial and vertical directions was quantitatively evaluated. Furthermore, a series of biochemical monitoring experiments was conducted to investigate the MICP process in sand. The results indicated that the reversed and downward chemical solution grouting and high rates of microbial grouting all promoted CaCO3 vertical uniformity. Moreover, the grouting strategy slightly affected the dispersion degree of radially distributed CaCO3. The variation coefficient basically ranged from 0.1 to 0.3. However, the variation coefficient for radially distributed CaCO3 along the vertical direction was significantly affected by the chemical grouting direction. The biochemical monitoring results indicated that 38% Ca2+ was even consumed near the chemical solution outlet in the chemical solution grouting process. The initial Ca2+ concentration during the intermittent period gradually decreased along the chemical solution grouting direction. The CaCO3 vertical distribution was controlled by a combination of the total MICP reaction time, biomass, and Ca2+ availability in the intermittent phase. Different CaCO3 distributions resulted in each grouting strategy exhibiting specific applicable engineering requirements. Furthermore, the carbon footprint was preliminarily evaluated. The results in this study provide references for the selection of grouting strategies for the MICP technique in engineering applications.

Hygrothermal conditions for the biological aging of sherry wine

The present work analyzed the hygrothermal environment of several prestigious warehouses where sherry wines of “Fino” and “Manzanilla” type are made. Through descriptive statistics, frequency histograms and psychrometric diagrams of temperature and relative humidity variations have been obtained. In addition, other factors such as the stability and uniformity of the interior environment have been quantified. The results showed significant temperature variations throughout the year (limit values of 5 °C and 31 °C), with a more stable relative humidity (between 60% and 90% for most of the year). Indoor conditions varied much more rapidly than in wineries for the aging of red wine, as a result of constant ventilation. Therefore, the annual average stability was 2.0 ± 0.8 °C per day and 0.14 ± 0.12 °C per hour. Vertical uniformity decreased in spring and summer, with stratification values close to 0.5 °C/m and 3% r.h./m. The monitored indoor environment is outside the comfort ranges described in the literature for extended periods of time (in the most extreme case, 96% of the time outside the recommended interval). For that reason, a reference psychrometric comfort diagram was proposed. Industrial relevanceFor the first time, the hygrothermal behavior of several wineries producing high quality wines (very high scores in the oenological guides) was extensively analyzed. The results of the study, which include monthly comfort intervals, should be a very useful tool for the sherry wine industry, in order to control and ensure optimal development of the flor yeast film. It should also be taken into account for the correct design of new wineries or the rehabilitation of abandoned warehouses.

3D Network‐Assisted Crystallization for Fully Printed Perovskite Solar Cells with Superior Irradiation Stability

AbstractMeniscus‐coating as a high‐throughput preparation process has significant advantages in the manufacture of large‐area perovskite solar cells (PSCs). However, the gradient crystallization during printing significantly affects the vertical uniformity of perovskite films, which greatly affects the carrier transport of perovskite films and the stability of PSCs. Here, a perovskite ink compatible with printing technology is reported to realize uniform printing of perovskite film on a 3D scale. The siloxane 3D network hinders the solute migration caused by capillary force and acts as a skeleton to promote the uniform crystallization of perovskite films. Consequently, the corresponding fully printed PSCs have reduced efficiency loss (from 37.4% to 17.0%). In addition, based on the improvement of crystal quality and reduction of defects in perovskite films, the siloxane‐optimized PSCs achieved a championship efficiency of 22.0%, which is one of the highest performance for fully printed devices. The optimized device retains 80% of the initial PCE after 800 h AM 1.5G one‐sun illumination, and only decreases 20% after 160 h of ultraviolet light (365 nm, 20 mW cm−2) irradiation.

Multi-scale analysis for transport of fine settling particles through an ice-covered channel in a laminar flow condition

The current research deals with the dispersion of fine settling particles in a fluid flowing through an ice-covered channel under the laminar flow condition. An analytical solution of the two-dimensional convection–diffusion equation, based on the multi-scale homogenization technique, is obtained. To validate the current study, analytical results for the dispersion coefficient are compared with the available earlier research work. Moreover, the proposed analytical solutions for mean concentration distributions of the tracers are compared with the numerical results obtained from the finite difference technique. From the industrial and environmental points of view, the vertical concentration distribution provides a very significant information. The downstream evolution of the concentration distribution also is shown for typical time periods at different values of the settling velocity. The approach to the vertical uniformity shows that it is too slow a process in comparison to that of longitudinal normality. It was found that settling velocities of particles disturb the vertical uniformity and the centroid of the solute cloud rises due to the increase in settling velocity. Results illustrate that in the downstream direction, the vertical concentration distribution increases near the bed surface and it decreases in the proximity of the ice-covered surface of the channel with the increase of settling velocity, but the mean concentration of the solute increases. The current study may play an important role to understand the mechanism of the sedimentation process in a closed channel system.

Study of horizontal and vertical uniformity of B-doped layer on mosaic single crystal diamond wafers by using hot-filament chemical vapor deposition

Aiming at developing inch-sized processing of diamond, B-doped layer was grown on mosaic single-crystallin diamond wafers by using hot-filament chemical vapor deposition (CVD), which is expected to have an advantage in terms of the deposition area compared with microwave plasma (MWP) CVD. Uniformity in horizontal and vertical directions is studied. It is found that the junctions of the monocrystalline diamond domains in the mosaic wafer and the direction of the crystal off-angles against to these junctions are less effective to the uniformity of the impurity concentrations. On the other hand, it is suggested that excess incorporation of W from the filament suppresses the growth and incorporation of B. It is shown that millimeter scale or more precise control of the arrangement of the wafer and the filament enables to obtain more uniform and efficient doping.

Effects of neighbourhood morphological characteristics on outdoor daylight and insights for sustainable urban design

ABSTRACT Urban daylight significantly affects the physical and mental health of urban residents. Many previous studies focused on how outdoor daylight conditions affect indoor daylighting of buildings, whereas the design of outdoor daylighting conditions, which also exerted an equally significant part, was relatively overlooked. There are also few studies empirically explored the outdoor daylight in various forms of mature urban neighbourhoods. Through investigating the outdoor pedestrian daylight performances of 11 representative open urban neighbourhood units in inner-city Shenzhen, this study aims to identify the influence of urban design factors. Through field investigation, mapping and on-site measurement, this study explored and analysed the horizontal illuminance level and site illuminance uniformity of 84 outdoor spaces. As the results revealed, urban morphological characteristics significantly affected the daytime pedestrian illumination. Specifically, the high-density mid-rise urban villages and the urban park demonstrated the best daytime outdoor visual comfort conditions. The multivariate regression test demonstrated that sky view factor exerted the greatest influence on the daytime outdoor illumination, followed by the mean building height, ground surface albedo and vertical uniformity. Hence, urban morphological patterns have great potential in optimizing urban design for outdoor daylighting behaviours and energy use, which is of great reference value in setting specific standards to achieve the goals of the initiatives of “Healthy Cities.”

A Centrosymmetric Array Comprising a Horizontal Uniform Circular Subarray and a Vertical Uniform Linear Subarray—Its Design in Reference to Its Direction-Finding Cramér–Rao Bound

Azimuthal centrosymmetry in an array grid is typically associated with arrays that are circular, concentric, cylindrical, spherical, or hemispherical. However, a recently proposed alternative combines an azimuthal circular array with a linear vertical array. For this elegantly simple new array grid's use in the direction-of-arrival estimation, this article advances array-design insights to meet a given estimation-precision threshold, by examining the tradeoff between the azimuth-angle Cramér-Rao bound vis-a-vis the polar-angle Cramér-Rao bound in a proposed two-step design procedure.

Precision Wet Etching of ZnO Using Buffer Solutions

Zinc oxide (ZnO) is a metal oxide semiconductor of interest for a wide range of electronic and optoelectronic device applications. Many devices require etching of ZnO structures and there have been many investigations of ZnO wet-etching processes. However, most reported etches have problems with reproducibility and especially control of vertical and lateral (or undercut) etching uniformity. In this work, we report new buffer solutions that provide controlled vertical and lateral etching of ZnO. We compare the ZnO etch characteristics of buffer etchants to a previously reported ammonium chloride etch. Using buffer etchants of suitable composition we find reaction-rate-limited, uniform, reproducible etching, and similar vertical and lateral etch rates.

Propagation, deposition, and suspension characteristics of constant-volume particle-driven gravity currents

In this laboratory study, propagation behaviour, particle deposition patterns, and suspension characteristics of non-cohesive particle-driven gravity currents formed under constant-volume release conditions were investigated. The experimental gravity currents were created in a two-dimensional lock exchange type tank using two different particles (silicon carbide and glass beads) with four different median diameters. Video imaging and image processing techniques were utilized to monitor the current propagation, laser diffraction size analysis and dry weighing techniques were utilized to examine the size and mass characteristics of the deposits and suspensions, and acoustic Doppler velocimetry was utilized for flow velocity measurements for turbulence analysis. Our observations showed that the experimental gravity currents experienced two different propagation phases based upon the particle settling regimes. The first propagation phase was named as the propagation with the turbulence-dominated settling (TDS) and the later propagation phase was named as the propagation with gravity-dominated settling (GDS). It is found that a critical turbulent Reynolds number value (estimated to be O(1)) delineates the settling regimes, hence determines the transition between the propagation phases. With increasing particle settling velocity, the observed propagation phases in our experimental currents showed increasing deviations from the slumping, inertia-buoyancy, and viscous–buoyancy propagation phases that have been reported for homogeneous constant-volume gravity currents with no or negligible settling in the literature. Propagation observations showed that the initial median particle diameters of the currents have negligible effect on the current propagation characteristics during the TDS phase, but become important during the GDS phase. The currents with smaller initial median particle diameters propagated faster and a longer distance in the GDS phase than their counterparts with larger median particle diameters. The deposited particle characteristics indicated that particles of different sizes settle at similar speeds during the TDS phase due to turbulent mixing and the settling speed becomes dependent on the particle size during the GDS phase. As a result, size sorting of the deposited particles became more pronounced during the GDS phase. At the earlier stages of propagation, the vertical profiles of suspended particle concentrations in the current head showed some extent of vertical uniformity due to turbulent mixing around the half height of the current head. On the other hand, at the later stages of propagation, suspended particle concentration profiles exhibited an exponential profile. Deposited and suspended particle characteristics showed that horizontal particle sorting, that is size grading of particles in the flow direction, was more pronounced than the vertical particle sorting, that is size grading of particles at different elevations within the current head.

Particle reflectivity and movements in cirrus clouds over Beijing from four years of Ka radar measurements

Cirrus clouds are ice clouds. Our understanding of the basic microscale physics of ice clouds is not yet adequate. In this study, interior physical properties of cirrus clouds over Beijing are investigated based on four years of continuous measurements of a Ka-band polar Doppler radar, which performs long-term observations with higher temporal resolution than the aircraft and the satellite. The probability distribution functions of radar reflectivity at various temperatures are presented and a positive correlation relationship between reflectivity and temperature is also found. In addition, the distributions of the particle Doppler velocity and particle movements in cirrus clouds are also revealed. According to the cloud-base temperature (CBT), all cirrus clouds are divided into three types [Cih: CBT < 273 K and CBH (cloud-base height) ≥ 258 K; Cim: CBT < 258 K and CBT > 235 K; Cil: CBT ≤ 235 K] in order to understand their formation mechanisms and possible differences. The results of investigation show that Cil has the lowest mean depth, the lowest mean and maximum reflectivity, and the lowest inhomogeneity among the three types of cirrus clouds, while Cih has the highest and Cim lies between the two. The reflectivity–temperature relationship is also different in the three types. In particular, for Cil, reflectivity varies little with the variation in temperature. The significant difference in microphysical properties and interior structures between Cil and Cih proves their different formation mechanisms. Cil, illustrating higher vertical uniformity, is likely generated by radiation cooling, while the other cirrus cloud types are generated differently. The results presented and analyzed in this study provide new knowledge regarding cirrus clouds in Beijing, a mid-latitude region, and a reference for related parameterization in global climate models.

On the vertical uniformity of an ITER-like large beam

Abstract A beam uniformity higher than 90% is a crucial requirement for the ITER neutral beam injection (NBI) system, together with very low beam core divergence ( The ELISE test facility, equipped with an ITER-like multi-aperture 3-grid system, produces large ITER-like beams, with half the size in vertical direction. Due to the distance of the beam diagnostics from the grids, the overlapping of the beamlets is large, and information on divergence and uniformity can be retrieved in terms of beamlet groups or beam segments. In general, good symmetry in accelerated current density between beam segments is achieved. The vertical beam uniformity is determined by caesium distribution and by plasma parameters at the plasma grid, which are inhomogeneous due to the interplay of filter field and bias potential. In this work, the role of filter field and bias potential on the vertical beam uniformity (in intensity and divergence) between the two beam segments is identified: the filter field mainly affects the extracted current density and its distribution within and between the segments; the bias potential can be used to tune the beam divergence, differently between the beam segments.

An approach for retrieval of horizontal and vertical distribution of total suspended matter concentration from GOCI data over Lake Hongze

There are a few studies working on the vertical distribution of TSM, however, understanding the underwater profile of TSM is of great benefit to the study of biogeochemical processes in the water column that still require further research. In this study, three data-gathering expeditions were conducted in Lake Hongze (HZL), China, between 2016 and 2018. Based on the in situ optical and biological data, a multivariate linear stepwise regression method was applied for retrieval of the surface horizontal distribution of TSM (TSM0.2) using GOCI (Geostationary Ocean Color Imager) data. Then, the estimation model of vertical structure of underwater TSM was constructed using layer-by-layer recursion. This study drew several crucial findings: (1) the approach proposed in this paper generated very high goodness of fit results, with determination coefficients (R2) of 0.83 (p < 0.001, N = 54), and with smaller prediction errors (the mean absolute percentage error is determined to be 16.34%, the root mean square error is 9.01 mg l−1, and the mean ratio is 1.00, N = 26). (2) The monthly surface TSM and the column mass of suspended matter (CMSM) are affected by both wind speed and precipitation in HZL. In addition, the hourly variation of surface TSM and CMSM are driven by local wind, most especially in spring and winter. (3) Compared with the non-uniform hypothesis, the CMSM derived by conventional vertical uniformity hypothesis was underestimated by almost 10% in HZL during 2016. This should warrant the attention of lake managers and lake environmental evolution researchers.

Deposition and preservation of fluvio‐tidal shallow‐marine sandstones: A re‐evaluation of the Neoproterozoic Jura Quartzite (western Scotland)

AbstractThe 2 to 5 km thick, sandstone‐dominated (&gt;90%) Jura Quartzite is an extreme example of a mature Neoproterozoic sandstone, previously interpreted as a tide‐influenced shelf deposit and herein re‐interpreted within a fluvio‐tidal deltaic depositional model. Three issues are addressed: (i) evidence for the re‐interpretation from tidal shelf to tidal delta; (ii) reasons for vertical facies uniformity; and (iii) sand supply mechanisms to form thick tidal‐shelf sandstones. The predominant facies (compound cross‐bedded, coarse‐grained sandstones) represents the lower parts of metres to tens of metres high, transverse fluvio‐tidal bedforms with superimposed smaller bedforms. Ubiquitous erosional surfaces, some with granule–pebble lags, record erosion of the upper parts of those bedforms. There was selective preservation of the higher energy, topographically‐lower, parts of channel‐bar systems. Strongly asymmetrical, bimodal, palaeocurrents are interpreted as due to associated selective preservation of fluvially‐enhanced ebb tidal currents. Finer‐grained facies are scarce, due largely to suspended sediment bypass. They record deposition in lower‐energy environments, including channel mouth bars, between and down depositional‐dip of higher energy fluvio‐ebb tidal bars. The lack of wave‐formed sedimentary structures and low continuity of mudstone and sandstone interbeds, support deposition in a non‐shelf setting. Hence, a sand‐rich, fluvial–tidal, current‐dominated, largely sub‐tidal, delta setting is proposed. This new interpretation avoids the problem of transporting large amounts of coarse sand to a shelf. Facies uniformity and vertical stacking are likely due to sediment oversupply and bypass rather than balanced sediment supply and subsidence rates. However, facies evidence of relative sea level changes is difficult to recognise, which is attributed to: (i) the areally extensive and polygenetic nature of the preserved facies, and (ii) a large stored sediment buffer that dampened response to relative sea‐level and/or sediment supply changes. Consideration of preservation bias towards high‐energy deposits may be more generally relevant, especially to thick Neoproterozoic and Lower Palaeozoic marine sandstones.

Impact of the Shadowing Effect on the Crystal Structure of Patterned Self-Catalyzed GaAs Nanowires.

The growth of regular arrays of uniform III-V semiconductor nanowires is a crucial step on the route toward their application-relevant large-scale integration onto the Si platform. To this end, not only does optimal vertical yield, length, and diameter uniformity have to be engineered, but also, control over the nanowire crystal structure has to be achieved. Depending on the particular application, nanowire arrays with varying area density are required for optimal device efficiency. However, the nanowire area density substantially influences the nanowire growth and presents an additional challenge for nanowire device engineering. We report on the simultaneous in situ X-ray investigation of regular GaAs nanowire arrays with different area density during self-catalyzed vapor-liquid-solid growth on Si by molecular-beam epitaxy. Our results give novel insight into selective-area growth and demonstrate that shadowing of the Ga flux, occurring in dense nanowire arrays, has a crucial impact on the evolution of nanowire crystal structure. We observe that the onset of Ga flux shadowing, dependent on array pitch and nanowire length, is accompanied by an increase of the wurtzite formation rate. Our results moreover reveal the paramount role of the secondary reflected Ga flux for VLS NW growth (specifically, that flux that is reflected directly into the liquid Ga droplet).