Direct Rate Measurements Research Articles

Bayesian Calibration of Kinetic Parameters in the CH Chemistry Toward Accurate Prompt-NO Modelling

Abstract Significant efforts made by the gas turbine industry have helped reduce nitrogen oxides (NOx) emissions considerably. To meet and surpass the increasingly stringent regulations, accurate and robust thermochemical mechanisms are needed to help design future sub-10 ppm combustion systems. Uncertainty in kinetic modeling, however, can result in large prediction uncertainty and significant discrepancy between models that hinder the identification of promising combustors with confidence. Direct reaction rate measurements are seldom available for some reactions, especially when involving short-lived radicals such as methylidyne, CH. As the main precursor to the prompt-NO formation pathway, its large parametric uncertainty directly propagates through the nitrogen chemistry preventing accurate and precise emissions predictions. Recent independent CH concentration measurements obtained at various operating conditions are used as indirect rate measurements to perform statistical, or Bayesian, calibration. A subset of important reactions in the CH chemistry affecting peak-CH concentration is identified through uncertainty-weighted sensitivity analysis to first constrain the parametric space of this prompt-NO precursor. Spectral expansion provides the surrogate model used in the Markov-Chain Monte Carlo method to evaluate the posterior kinetic distribution. The resulting constrained CH-chemistry better captures experimental measurements while providing smaller prediction uncertainty of a similar order as the uncertainty of the measurements, which can increase the confidence in simulation results to identify promising future low-emissions configurations. For the quasi-steady-state species CH, fuel decomposition reactions leading to CH production are constrained while little impact is observed for intermediate reactions within the CH-chemistry. The reduction in prediction uncertainty results mainly from the constrained correlations between parameters which greatly limit the set of feasible reaction rate combinations. Additional independent direct and indirect measurements would be necessary to further constrain rate parameters in the CH chemistry, but this calibration demonstrates that predictions of radical species can be improved by assimilating enough data.

Strain Tracking of ‘Candidatus Liberibacter asiaticus’, the Citrus Greening Pathogen, by High-Resolution Microbiome Analysis of Asian Citrus Psyllids

The Asian citrus psyllid, Diaphorina citri, is an invasive insect and a vector of 'Candidatus Liberibacter asiaticus' (CLas), a bacterium whose growth in Citrus species results in huanglongbing (HLB), also known as citrus greening disease. Methods to enrich and sequence CLas from D. citri often rely on biased genome amplification and nevertheless contain significant quantities of host DNA. To overcome these hurdles, we developed a simple pretreatment DNase and filtration (PDF) protocol to remove host DNA and directly sequence CLas and the complete, primarily uncultivable microbiome from D. citri adults. The PDF protocol yielded CLas abundances upward of 60% and facilitated direct measurement of CLas and endosymbiont replication rates in psyllids. The PDF protocol confirmed our lab strains derived from a progenitor Florida CLas strain and accumulated 156 genetic variants, underscoring the utility of this method for bacterial strain tracking. CLas genetic polymorphisms arising in lab-reared psyllid populations included prophage-encoding regions with key functions in CLas pathogenesis, putative antibiotic resistance loci, and a single secreted effector. These variants suggest that laboratory propagation of CLas could result in different phenotypic trajectories among laboratories and could confound CLas physiology or therapeutic design and evaluation if these differences remain undocumented. Finally, we obtained genetic signatures affiliated with Citrus nuclear and organellar genomes, entomopathogenic fungal mitochondria, and commensal bacteria from laboratory-reared and field-collected D. citri adults. Hence, the PDF protocol can directly inform agricultural management strategies related to bacterial strain tracking, insect microbiome surveillance, and antibiotic resistance screening.

Metabolism in Micrathena gracilis, a stridulating orb-weaver (Araneae: Araneidae)

Metabolism powers all of life's processes, making it fundamental to understanding organisms in nature. For many arachnids, however, we do not have direct measurements of either metabolic rate or the relationship between metabolic rate and body size (i.e., allometric scaling, an important determinant of metabolic rate). Here, we present the first measurements of metabolic rate and allometric scaling in a stridulating spined micrathena spider, Micrathena gracilis (Walckenaer, 1805). Since intraspecific variation in metabolic rate may provide insights into variation in energetically costly behaviors, we additionally explore the link between stridulation and metabolism in M. gracilis. Our data suggests a link between stridulatory behavior and allometric scaling, such that increased stridulation is associated with a weaker connection between body mass and metabolic rate. We discuss how links between energetics, expression of behavior, and body size inform our understanding of trait variation in these spiders.

Aluminum Alloy Etching: New Insights By Element Resolved Electrochemical Analysis

Aluminum alloys are pickled and/or etched as a preliminary step prior to anodization or conversion coating. The chemistry of the etching/pickling process must be carefully engineered to avoid the enrichment of the alloying elements such metallic Cu which can interfere with subsequent treatments. Understanding and optimizing the etching process is therefore a major concern for the use of aluminum alloys, and especially, the Cu-rich high strength aluminum alloys.The etching reaction is a mixed potential process similar to other forms of aqueous corrosion. However, the dynamic nature of the interface makes it difficult to apply conventional electrochemistry to determine the rates and mechanisms of the different reactions and therefore, to predict how the etching process will vary with electrolyte composition. Among the many complicating factors, we can cite the very high dissolution rate of the alloy coupled with the formation of gas and the release of intermetallic particles. The dissolution of alloying elements such as Cu and Mg – the reactions of interest – occur at rates several orders of magnitude below that of Al dissolution. For example, Cu dissolution makes a negligible contribution to either electron exchange or mass loss. Finally, the rapid reaction rates and the short time scale of the process preclude the appearance of a true steady state, necessary for the interpretation of many electrochemical techniques.Therefore, to gain insight into the mechanism of the acid etching process, we have used an element-resolved electrochemical technique, atomic emission spectroelectrochemistry (AESEC) (Gharbi et al., 2016; Gharbi et al., 2017; Sultan et al., 2022). This permits the direct measurement of the elemental dissolution rates as a function of time, on an element-by-element basis.In this work, we illustrate the element-resolved electrochemical approach to surface treatment focusing on the acid etching of three alloys: a commercial high-strength AA7449 alloy (containing Zn, Cu, and Mg), and binary Al-Cu and Al-Mg alloys to represent the extremes of alloying element nobility. In sulfuric acid, the binary alloys also represent the extremes of selective versus congruent dissolution. The Al-Mg binary alloy undergoes a simultaneous, congruent dissolution mechanism with Mg dissolving simultaneously with Al. By contrast, the Al-Cu binary alloy exhibits a selective dissolution mechanism with Al dissolving to leave behind dealloyed metallic Cu on the surface of the material. This is ultimately followed by the release of Cu-rich particles due to anodic undermining.The electrolytes investigate in this work represent a range of oxidizing strengths from pure sulfuric acid to pure nitric acid and various mixtures of the two. The effect of Fe(III), an important component of many state-of-the-art etching solutions, was also investigated. Experimental elemental Evans diagrams were determined to clarify the electrochemical nature of the dissolution reactions, specifically how the elemental dissolution rates were related to one another and how they were coupled to the cathodic reactions.An example is shown in the Figure (right), based on the 2022 publication of Sultan et al. On the left, we show a cartoon representation of the dissolution process as determined for a high strength AA7449 alloy. On the right, we show the experimental element-resolved Evans diagram for the same alloy in sulfuric acid. It was found that Cu would not dissolve at the open circuit potential in sulfuric acid, but displayed active dissolution with a well-defined Tafel slope of 44 mV/decade at higher potential. The dissolution rate of Cu in the etching solutions was controlled by the redox potential of the electrolyte as determined by the addition of nitric acid and/or Fe(III). Based on our results, the Fe(III) additive in the presence of nitrate appears to serve a catalytic role, enhancing the rate of electron transfer between Cu and nitrate. The dissolution of Al and Mg were independent of potential suggesting simultaneous dissolution across an oxide film. The rates and mechanisms of Cu particle release will also be discussed.BBM Sultan, D Thierry, JM Torrescano-Alvarez, K Ogle, “Selective dissolution during acid pickling of aluminum alloys by element-resolved electrochemistry”, Electrochim. Acta, 404(2022)139737.O Gharbi, N Birbilis, K Ogle, “In-situ monitoring of alloy dissolution and residual film formation during the pretreatment of Al-alloy AA2024-T3”, J. Electrochem. Soc. 163 (2016)C240.O Gharbi, N Birbilis, K Ogle, “Li reactivity during the surface pretreatment of Al-Li alloy AA2050-T3”, Electrochim. Acta 243(2017)207-219. Figure 1

Simultaneous macroscale and microscale wave–ion interaction in near-earth space plasmas

Identifying how energy transfer proceeds from macroscales down to microscales in collisionless plasmas is at the forefront of astrophysics and space physics. It provides information on the evolution of involved plasma systems and the generation of high-energy particles in the universe. Here we report two cross-scale energy-transfer events observed by NASA’s Magnetospheric Multiscale spacecraft in Earth’s magnetosphere. In these events, hot ions simultaneously undergo interactions with macroscale (~{10}^{5} km) ultra-low-frequency waves and microscale (sim {10}^{3} km) electromagnetic-ion-cyclotron (EMIC) waves. The cross-scale interactions cause energy to directly transfer from macroscales to microscales, and finally dissipate at microscales via EMIC-wave-induced ion energization. The direct measurements of the energy transfer rate in the second event confirm the efficiency of this cross-scale transfer process, whose timescale is estimated to be roughly ten EMIC-wave periods about (1 min). Therefore, these observations experimentally demonstrate that simultaneous macroscale and microscale wave-ion interactions provide an efficient mechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas.

Online Monitoring of the Concentrations of Amorphous and Crystalline Mesoscopic Species Present in Solution.

Despite the growing evidence for the existence of amorphous mesoscopic species in a solution and their crucial roles in crystallization, there has been the lack of a suitable method to measure the time-resolved concentrations of amorphous and crystalline mesospecies in a lab-scale stirred reactor. This has limited experimental investigations to understand the kinetics of amorphous and crystalline mesospecies formation in stirred solutions and made it challenging to measure the crystal nucleation rate directly. Here, we used depolarized light sheet microscopy to achieve time-resolved measurements of amorphous and crystalline mesospecies concentrations in solutions at varying temperatures. After demonstrating that the concentration measurement method is reasonably accurate, precise, and sensitive, we utilized this method to examine mesospecies formation both in a mixture of two miscible liquids and in an undersaturated solution of dl-valine, thus revealing the importance of a temperature change in the formation of metastable and amorphous mesospecies as well as the reproducibility of the measurements. Moreover, we used the presented method to monitor both mesospecies formation and crystal nucleation in dl-valine solutions at four different levels of supersaturation, while achieving the direct measurement of the crystal nucleation rates in stirred solutions. Our results show that, as expected, the inherent variability in nucleation originating from its stochastic nature reduces with increasing supersaturation, and the dependence of the measured nucleation rate on supersaturation is in reasonable agreement with that predicted by the classical nucleation theory.

Measurements of Ion Transfer Kinetics for the Study of Electrocatalyst Corrosion in Gas Diffusion Electrode Microenvironments

Nanoparticulate Au, Ag, and Cu films with percolating ion-conducting polymers are common within devices for the electroreduction of carbon dioxide (CO2) to carbon monoxide, hydrocarbons, and alcohols. The kinetics of ion-transfer are influential on the rate of corrosion and catalyst sintering, but direct measurements of ion-transfer rates are challenging at bulk metal electrodes. We present data on the corrosion kinetics of metal nanoclusters and monolayers deposited via underpotential deposition on well-oriented and/or single-crystal metal surfaces within suspended ionomer electrolytes. Our results support the important role of nucleation and growth in corrosion processes as well as the influence of structural anions on reactive intermediates present during corrosion reactions. Figure 1

Nitrogenases in Oxygen Minimum Zone Waters

Biological dinitrogen (N2) fixation is the pathway making the large pool of atmospheric N2 available to marine life. Besides direct rate measurements, a common approach to explore the potential for N2 fixation in the ocean is a screening-based targeting the key functional marker gene nifH, coding for a subunit of the nitrogenase reductase. As novel sequencing techniques improved, our understanding of the diversity of marine N2 fixers grew exponentially. However, one aspect of N2 fixation in the ocean is often underexplored, which are the two alternative types of the key enzyme of N2 fixation, the nitrogenase. Altogether there are three isoenzymes, the most common Mo-Fe nitrogenase Nif, the Fe-Fe nitrogenase Anf, and the V-Fe nitrogenase Vnf, which differ regarding their genetic organization, as well as their metal co-enzymes. While Mo is only available in the presence of at least traces of oxygen (O2), V and Fe are available if O2 is absent. Therefore, low O2 and anoxic ocean environments could be an ideal place to explore the diversity of the different isotypes of the nitrogenases. Most phylogenetic studies, however, were only based on the functional marker gene nifH, encoding for a subunit of the Nif nitrogenase, and thus limited in representing the diversity of alternative nitrogenases. Here, we screened metagenomes and -transcriptomes from O2 minimum zones off Peru, from the Bay of Bengal, and the anoxic Saanich Inlet to explore the diversity of genes involved in N2 fixation. We identified genes related to all three nitrogenases, and a generally increased diversity as compared to our previous nifH based on studies from OMZ waters. While we could not confirm gene expression of alternative nitrogenases from our transcriptomic, we detected diazotrophs harboring the genetic potential for alternative nitrogenases. We suggest that alternative nitrogenases may not be used under conditions present in those waters, however, depending on trace metal availability they may become active under future ocean deoxygenation.

Simulation and validation of the gas flow in close-coupled gas atomisation process: Influence of the inlet gas pressure and the throat width of the supersonic gas nozzle

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29∙Lo, 0.5∙Lo, 0.77∙Lo and 2∙Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

High-throughput screening of soybean di-nitrogen fixation and seed nitrogen content using spectral sensing

Symbiotic di-nitrogen fixation of grain legumes has a substantial impact on crop performance, harvest product quality, and nitrogen (N) balance of crop rotations, particularly under organic management regimes. In soybean breeding, selection for increased nitrogen fixation is desirable for improving seed protein content and N balance of cropping systems. However, the lack of high-throughput screening methods for direct measurement of N2 fixation rates prohibits practical breeding efforts. Therefore, hyperspectral canopy reflectance measurement as a field-based phenotyping method was evaluated in three environments for indirect estimation of N fixation and uptake of soil nitrogen in a set of early maturity soybean genotypes exhibiting a wide range in seed protein content. Reflectance spectra were collected in repeated measurements during flowering and early seed filling stages. Subsequently, various spectral reflectance indices (SRIs) were calculated for characterizing nitrogen accumulation of individual genotypes. Moreover, prediction models for seed protein content as an end-of-season target trait were developed utilizing full spectral information in partial-least-square regression (PLSR) models. A number of N-related SRIs calculated from spectral reflectance data recorded at the beginning of the seed filling stage were significantly correlated to seed protein content. The best prediction of seed protein content, however, was achieved in PLSR models (validation R2 = 0.805 across all three environments). Environments lower in initial soil mineral N content appeared as more favorable selection sites in terms of prediction accuracy, because N fixation is not masked by soil N uptake in such environments. Hyperspectral reflectance data proved to be a valuable method for determining genetic variation in crop N accumulation, which might be implemented in high-throughput screening protocols for N fixation in plant breeding programs.

Correlation-Aware Flow Consolidation for Load Balancing and Beyond

Existing load balancing solutions rely on direct or indirect measurement of rates (or congestion) averaged over short periods of time. Sudden fluctuations in flow rates can lead to significant undershooting/ overshooting of target link loads. In this paper, we make the case for taking variations and correlations of flows into account in load balancing. We propose correlation-aware flow consolidation, i.e. aggregating inversely correlated (or uncorrelated) flows into superflows and using them as building blocks for load balancing. Superflows are smoother than individual flows, and thus are easier to estimate with a higher confidence, and can reduce overshooting/ undershooting of link capacities. We present heuristic methods combined with predictive models to consolidate flows and show they can lead to significant reductions in rate standard deviations compared to correlation-agnostic solutions (up to 33% and 12% improvements at the 50th and 99th percentiles respectively for 20 superflows based on real traffic traces).

Bottom-Up Control of the Groundwater Microbial Food-Web in an Alpine Aquifer

Groundwater ecosystems are typically poor in organic carbon and productivity sustaining a low standing stock of microbial biomass. In consequence, microbial food webs in oligotrophic groundwater are hypothesized to be bottom-up controlled. To date, quantitative information on groundwater microbial communities, food web interactions, and carbon flow is relatively lacking in comparison to that of surface waters. Studying a shallow, porous alpine aquifer we collected data on the numbers of prokaryotes, virus-like particles and heterotrophic nanoflagellates (HNFs), the concentration of dissolved (DOC) and assimilable organic carbon (AOC), bacterial carbon production (BCP), and physical-chemical conditions for a 1 year hydrological cycle. The potential effects of protozoan grazing and viral lysis onto the prokaryotic biomass was tested. Flow of organic carbon through the microbial food web was estimated based on data from the literature. The abundance of prokaryotes in groundwater was low with 6.1 ± 6.9 × 104 cells mL–1, seasonally influenced by the hydrological dynamics, with higher densities coinciding with a lower groundwater table. Overall, the variability in cell numbers was moderate, and so it was for HNFs (179 ± 103 HNFs mL–1) and virus-like particles (9.6 ± 5.7 × 105 VLPs mL–1). The virus to prokaryotes and prokaryote to HNF ratios ranged between 2–230 and 33–2,084, respectively. We found no evidence for a viral control of prokaryotic biomass, and the biomass of HNFs being bottom-up controlled. First estimations point at carbon use efficiencies of 0.2–4.2% with prokaryotic production, and carbon consumed and recycled by HNFs and phages to be of minor importance. This first groundwater microbial food web analysis strongly hints at a bottom-up control on productivity and standing stock in oligotrophic groundwater ecosystems. However, direct measurement of protozoan grazing and phage mediated lysis rates of prokaryotic cells are urgently needed to deepen our mechanistic understanding. The effect of microbial diversity on the population dynamics still needs to be addressed.

Development of a methodology to research the influence of liquid nitrogen exposure on carbon material

Recently, studies, which are dedicated to the effect of cryogenic substances on the structure of coal, are gaining popularity. The impact of liquid nitrogen on coal leads to micro- and macrostructural disturbances in the continuity of coal due to drastic cooling of the moisture in the microcracks and pore space of the coal, while the volume of ice microcrystals increases. This approach provides the opportunity to treat the massif without additional injection of liquid agents into seams to create pressure to disintegrate it, unlike traditional methods of increasing the filtration surface in coal. Research work, which are presented in this field, are aimed at studying the multiplicity of increase in porosity and fracturing of coal in the process of single or multiple exposure to portions of liquid nitrogen. A distinctive feature of the ongoing research is the evaluation of the results of cryotreatment of samples by non-destructive methods of measuring the pore space. Thus, the conclusion about the change in permeability is made without direct measurements of the gas filtration rates in the samples. Changes shown by CT scans show an increase in the total number of open pores and channels, however they do not illustrate the increase in gas permeability in general. As a part of this work, we carried out a number of studies on axial gas filtration in dense coal samples, which were under controlled all-round loading. Preparatory work was carried out to dry the samples and further saturate them with moisture to identical values in the entire batch. A scheme for conducting experiments to study the effect of cryotreatment on the internal structure of coal using the methods of stationary axial gas filtration and NMR relaxometry is proposed. The development of this technique contributes to obtaining reliable data on the increase in the gas permeability of coal samples. The data can be useful in designing methods and approaches to increase the degree of degassing by treating degassing wells at coal mining enterprises.

Data-Driven Methodology for the Prediction of Fluid Flow in Ultrasonic Production Logging Data Processing

A new method for the determination of oil and water flow rates in vertical upward oil-water two-phase pipe flows has been proposed. This method consists of an application of machine learning techniques on the probability density function (PDF) and the power spectral density (PSD) of the power spectrum output of an ultrasonic Doppler sensor in the pipe. The power spectrum characteristic parameters of the two-phase flow are first determined by the probability density function (PDF) method. Then, the transducer signal is preprocessed by distance correlation analysis (DCA), and independent features are extracted by principal component analysis (PCA). The extracted features are used as input to a least-squares fit, which gave the oil flow rates as output. In the same way, the transducer signal is also preprocessed by partial correlation analysis (PCA), and independent features were extracted using independent component analysis (ICA). The extracted features were used as inputs to multilayer back-propagation neural networks, which water cuts as output. The present method was used to calibrate an ultrasonic Doppler sensor to estimate the flow rates of both phases in oil–water flow in a vertical pipe of diameter 159 mm. Predictions of the present method were in good agreement with direct flow rate measurements. Compared to previously used methods of feature extraction from the ultrasonic Doppler power spectrum signals, the present method provides a theoretical basis for the interpretation of ultrasonic multiphase flow logging data. Ultrasonic multiphase flow logging has potential application value in the production profile logging and interpretation evaluation of production wells with low fluid production and high water cut.

True differential superconducting on-chip output amplifier *

The true-differential superconductor on-chip amplifier has complementary outputs that float with respect to chip ground. This improves signal integrity and compatibility with the receiving semiconductor stage. Both source-terminated and non-source-terminated designs producing 4 mV demonstrated rejection of a large common mode interference in the package. Measured margins are ±8.5% on the output bias, and ±28% on AC clock amplitude. Waveforms and eye diagrams are taken at 2.9–10 Gb . Direct measurement of bit-error rates are better than the resolution limit of at 2.9 Gb , and better than at 10 Gb .

Fast Changes in the Bioenergetic Balance of Krill in Response to Environmental Stress

A Dynamic Energy Budget (DEB) model is applied to predict rapid metabolic shifts in an ecologically important krill, Nyctiphanes australis, in response to temperature and ultraviolet radiation (UVR). Specifically, we predict changes in fatty acids, amino acids and respiration rate in response to several light and temperature treatments. Environmental variability can alter the metabolic equilibrium and the mechanisms marine ectotherms used to obtain energy, which is a topical point given the current level of environmental change. Environmental variability also includes multiple stressors, which can have additive, antagonistic or synergistic effects on metabolism. In consequence, disentangling and quantifying the effects of multiple stressors on metabolism and the energy balance of ecthothermal species, such as krill, can be challenging. Here we apply a DEB model to direct measurements of fatty acids, amino acids and respiration rate of krill experimentally exposed simultaneously to several doses of UVR and temperatures. We found that on average light escalates metabolic rates by a factor of two, and temperature has an effect 1.35 times greater than the effect of light over respiration rates at temperatures from 9 to 19°C. The DEB model predicted shifts in metabolic function and indicated that the combined effect of light and elevated temperatures decrease the total of fatty acid concentrations at a higher rate than amino acids when krill are exposed to environmentally relevant temperatures and light treatments. Our results demonstrate that, when krill experience warmer conditions and higher levels of solar radiation, the mobilization of energy-relevant metabolites from the reserves increases by up to 36% and increase the total energetic cost by up to 45%. These findings suggest that ectothermal species with a fast metabolism, such as krill, quickly deplete energy reserves to compensate for changes in the environment. This renders krill susceptible to the effects of climate variability if the current climatic trend for the region continues to show temperature increases, even if solar radiation levels remain unchanged.

Direct measurement of radiative decay rates in metal halide perovskites

A radiometric measurement of time-resolved photoluminescence that helps to identify unwanted photocarrier decay in hybrid perovskite thin-films for solar cell applications.

Исследование особенностей нанесения нанослоев Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- методом атомно-слоевого осаждения на структурированные пленки ITO

In this work, the antireflective nanostructured ITO/Al2O3 coatings that have a gradient of the effective refractive index in the direction perpendicular to the substrate plane have been studied. The coatings were obtained by the atomic layer deposition (ALD) of aluminum oxide on the structured ITO films. The transmission electron microscopy showed that the deposited nanosized aluminum oxide layer was of good quality and uniformly covered the ITO whiskers. As shown in experiments, the thickness of the resulting Al2O3 layer is affected by the thickness and, hence, by the degree of surface roughness of the initial ITO film. The resulting thicknesses can be several times lower than that planned in the experiment, based both on the calculations of the parameters of the ALD process and on the direct measurements of the aluminum oxide deposition rate for unstructured ITO films. A possible reason that affects the growth rate of Al2O3 layers in nanostructured ITO films is a strong increase in the surface area of the ITO film during its structuring. So, the transmission and scanning microscopy data for a 700-nm-thick structured ITO film have shown that its surface area is more than 20 times greater than that of a smooth film.

Study of Deposition of Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- Nanolayers by Atomic Layer Deposition on the Structured ITO Films

In this work, the antireflective nanostructured ITO/Al2O3 coatings that have a gradient of the effective refractive index in the direction perpendicular to the substrate plane have been studied. The coatings were obtained by the atomic layer deposition (ALD) of aluminum oxide on the structured ITO films. The transmission electron microscopy showed that the deposited nanosized aluminum oxide layer was of good quality and uniformly covered the ITO whiskers. As shown in experiments, the thickness of the resulting Al2O3 layer is affected by the thickness and, hence, by the degree of surface roughness of the initial ITO film. The resulting thicknesses can be several times lower than that planned in the experiment, based both on the calculations of the parameters of the ALD process and on the direct measurements of the aluminum oxide deposition rate for unstructured ITO films. A possible reason that affects the growth rate of A1O3 layers in nanostructured ITO films is a strong increase in the surface area of the ITO film during its structuring. So, the transmission and scanning microscopy data for a 700 nm-thick structured ITO film have shown that its surface area is more than 20 times greater than that of a smooth film. Keywords: Indium tin oxide, aluminum oxide, atomic layer deposition, antireflective coatings, deposition rate.

Performance measurement and evaluation of an ionic liquid electrospray thruster

As a novel micro-propulsion system for small satellites (from micro to nano), the ionic liquid electrospray propulsion system is a promising candidate. However, performance measurement and evaluation of the Ionic Liquid Electrospray Thruster (ILET) is one of the most challenging issues for practical application, due to the difficulties in the development of a prototype and direct measurements of micro-thrust and small flow rate. To address this issue, a Modular Ionic Liquid Electrospray Thruster (MILET) prototype is constructed, and a diagnostic system for thrust and mass flow rate is specially developed based on an analytical balance method. With the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate as the propellant, a series of experiments is carried out on the MILET prototype under a wide operating condition through changing the applied voltage to control the thrust. Under different applied voltages, the thrust and the mass flow rate of the propellant are directly measured. The propulsive performance parameters of the thruster, such as thrust, specific impulse, thrust-to-power ratio, thruster efficiency, etc., are comprehensively analyzed. Then, a performance comparison is made between the MILET and other representative ILETs. With a relatively low applied voltage ranging from 1550 V to 2000 V, the MILET achieves a quasi-constant specific impulse of 1263 s with the averaged thrust-to-power ratio of 65.2 μN/W and thruster efficiency of 40.7%. The performance of ILET is also compared with other typical electric propulsions. The results demonstrate that the ILET exhibits an excellent ability of minimalization with high specific impulse and thruster efficiency, which guarantees a great superiority in micro propulsions. Finally, the ways to further improve the performance of ILET are discussed, which further confirms the potential prospect of ILET. The present result helps to advance the development and application of ILET.