Medium-term Stability Research Articles

Clinical Observations of Soft Tissue Dimensions Around Teeth and Implants After Free Gingival Graft

Introduction and aimsThe histological and morphological differences in soft tissue between natural teeth and peri-implant may result in different clinical effectiveness to free gingival graft (FGG). This research aims to investigate the different efficacy of FGG in augmenting keratinized tissue width (KTW) between tooth and implant sites while evaluating its medium-term stability over a 2- to 5-year follow-up. MethodsIn this study, 29 patients underwent FGG to address insufficient clinical scenarios when KTW <2 mm at the buccal aspect, including 37 implant sites and 33 natural teeth sites both in posterior regions were included. The KTW and gingival margin position (GMP) of these sites was assessed by measuring the intra-oral photographs which were taken at 0 days (T0), 3-month (T1), 6-month (T2), 12-month post-surgery (T3), and 2 to 5 years follow-up (T4). ResultsThe results revealed that KTW increased significantly in both groups. However, the natural teeth group showed significantly less graft shrinkage (GS) than the implants group. (Teeth: 2.05 ± 0.51 mm and 25.42% ± 6.45%; Implants: 3.18 ± 0.65 mm and 38.92% ± 5.39%, P <.01). From T1 to T4. The gingival margin coronally advanced by 0.47 ± 0.51 mm and 0.18 ± 0.43 mm for the natural teeth and implants group, respectively (P<.05). ConclusionsA greater KTW reduction after FGG was observed at implants versus natural teeth. And, the graft surrounding implants after crown restoration was stable for up to 2 to 5 years. Clinical relevanceBy comparing the changes in KTW around natural teeth and implants following FGG to investigate whether there are differences between them and the degree of differences. Additionally, this allows us to explore whether the restorations impact the effect of FGG. This research can assist clinicians in selecting an appropriate amount of soft tissue during surgery to achieve treatment goals, reduce postoperative discomfort for patients, and enhance predictability in clinicians' ability to increase keratinized tissue. Furthermore, by observing changes in the position of GMP around natural teeth and implants, the effectiveness of FGG in root coverage can be understood, thus improving the predictability of FGG for root coverage.

IrO2 Oxygen Evolution Catalysts Prepared by an Optimized Photodeposition Process on TiO2 Substrates.

Preparing high-performance oxygen evolution reaction (OER) catalysts with low precious metal loadings for water electrolysis applications (e.g., for green hydrogen production) is challenging and requires electrically conductive, high-surface-area, and stable support materials. Combining the properties of stable TiO2 with those of active iridium oxide, we synthesized highly active electrodes for OER in acidic media. TiO2 powders (both commercially available Degussa P-25® and hydrothermally prepared in the laboratory from TiOSO4, either as received/prepared or following ammonolysis to be converted to titania black), were decorated with IrO2 by UV photodeposition from Ir(III) aqueous solutions of varied methanol scavenger concentrations. TEM, EDS, FESEM, XPS, and XRD measurements demonstrate that the optimized version of the photodeposition preparation method (i.e., with no added methanol) leads to direct deposition of well-dispersed IrO2 nanoparticles. The electroactive surface area and electrocatalytic performance towards OER of these catalysts have been evaluated by cyclic voltammetry (CV), Linear Sweep Voltammetry (LSV), and Electrochemical Impedance Spectroscopy (EIS) in 0.1 M HClO4 solutions. All TiO2-based catalysts exhibited better mass-specific (as well as intrinsic) OER activity than commercial unsupported IrO2, with the best of them (IrO2 on Degussa P-25® ΤiO2 and laboratory-made TiO2 black) showing 100 mAmgIr-1 at an overpotential of η = 243 mV. Chronoamperometry (CA) experiments also proved good medium-term stability of the optimum IrO2/TiO2 electrodes during OER.

Domestic Debt and Exchange Rate Stability in Nigeria (1980 - 2021)

This study investigated the relationship between domestic debt and exchange rate stability in Nigeria using data for the period 1981 to 2021. Domestic debt was disaggregated into treasury bills (TBILLS), treasury bonds (TBONDS) and Federal Government bonds (FGNB) as well as other sources of debt (OTHERS). Exchange rate stability was proxied by Nigerian naira/US dollar exchange rate. Data was collected from the Central Bank of Nigeria Statistical Bulletin 2021 and analyzed using a combination of Johansen cointegration, granger causality and co- integrating regression adopting the fully modified ordinary least square (FMOLS) technique. The findings showed that there is no long-run relationship between domestic debt and exchange rate stability. Also, TBILLS, TBONDS and OTHERS positively and significantly affect exchange stability in the short run at 5% level of significance while FGNB has a positive but insignificant short run relationship with exchange rate stability at 5% level of significance. It was also revealed that domestic debt variables (TBILLS, TBONDS and FGNB as well as OTHERS), does not granger cause exchange rate stability at the 5% level of significance. The study concluded that domestic debt significantly affects exchange rate stability in the short run but domestic debt has no long-run relationship with exchange rate stability, and there is no causal relationship between domestic debt and exchange rate stability. The study recommended among others that domestic debt variables are actually contracted using short term instruments. Thus, they should be used to maximally ensure short- and medium-term stability in exchanges.

H2S-sensing properties of flame-synthesized RuO2-decorated WO3 nanoparticulate spin-coated films

This work aimed to develop effective and reliable H2S gas sensors based on flame-synthesized RuO2-decorated WO3 spin-coated films. Inclusive material characterizations unveiled the decoration of 1–3 nm RuO2 nanoparticles on 10–25 nm WO3 nanoparticles with 0–1 wt% Ru. Sensing layers coated with 1–6 cycles were tested towards 0.25–10 ppm H2S at 200–400 °C under various humidity conditions (0–80 %RH). The sensors with four spin-coated layers and 0.2 wt% Ru presented a reproducibly optimum response of ∼71.0 with a fair response time of ∼ 15.1 s to 10 ppm H2S in dry ambient at 350 °C. Additionally, the optimal sensor exhibited high H2S selectivity with respect to CH3SH, CH3SCH3, C3H6O, C2H5OH, CH3OH, CH2O, C6H6, C8H10, NO2, NO, H2, CH4, CO2, C2H2, HCOOH, CH3COOH, and CH3CHOHCOOH. Furthermore, the sensors displayed decent repeatability and satisfactory medium-term stability of resistance and response. Therefore, flame-synthesized RuO2-loaded WO3 nanoparticles were promising for effective and practical H2S sensing.

Soil-phase immobilization of hexavalent chromium using L-ascorbic acid - kinetics, process optimization, and phytotoxicity studies

l-ascorbic acid is found to be an effective and environmentally friendly reagent for remediation of Cr(VI)-contaminated soil. Soil-phase batch kinetics experiments elucidated the effects of chromium(VI) and l-ascorbic acid dosing, pH, soil-to-water ratio, and temperature on Cr(VI) reduction. An extended reductive environment was observed at a lower pH range, possibly due to ligand oxidation of several reactive intermediates. The kinetic data were fitted into a second-order rate model, and the rate constant was evaluated. A reaction mechanism was proposed. Reduction was substantially complete within about 3 h at natural pH conditions at an appropriate dosing of the reagent, and any residual Cr(VI) is reduced by the remaining ascorbic acid during aging of the soil. The reagent worked much better than other organic reductants reported in the literature. The rate constant correlated linearly with the soil-to-water ratio, while its logarithm correlated linearly with pH within the specified range. The reduction was primarily attributed to the presence of carboxylic, hydroxyl, and carbonyl groups in the ascorbic acid molecule, as confirmed by FTIR and XRD analysis. Medium-term stability experiments suggest that treatment with l-ascorbic acid significantly decreased leaching concentrations of Cr(VI) and total Cr which remained stable for 75 d. Ecological studies have shown that remediated soil promotes plant growth and increases earthworm survival rates, thus negating the emergence of any secondary pollutants. Response surface methodology (RSM) was used to investigate the relationship between Cr(VI) reduction and experimental parameters and to determine the optimum values. About 98.8 % reduction was achieved, which was consistent with the calculated optimal value. The study provides new insights into the use of l-ascorbic acid for sustainable remediation of Cr(VI)-contaminated soil. The optimum process conditions and the rate data obtained in this study are expected to be useful for the process design of a remediation facility for Cr(VI)-contaminated soil.

Remediation and immobilization of Cr(VI)-contaminated soil using stabilized nanoscale iron sulfide and ecological impact

Soil contaminated with hexavalent chromium seriously threatens the environment and human health. The use of FeS, which has a high redox activity and excellent reduction capacity, limits its application in soil remediation due to its premature surface oxidation and massive aggregation. To prevent premature surface oxidation and agglomeration, cetyltrimethylammonium bromide-supported nano-ferrous sulfide (CTAB-nFeS) was chemically synthesized and used for immobilizing Cr(VI) in contaminated soil. In order to evaluate the role of CTAB stabilization of nFeS and interaction mechanisms were investigated by XPS, FTIR, XRD, and FESEM. Batch experiments showed a complete reduction of Cr(VI) within 3 h with only 235% excess of CTAB-nFeS at a soil pH of 8 compared to days as reported in the literature with alternative FeS forms. The reduction kinetic data could be satisfactorily fitted into the second-order rate model. The rate constant linearly depends on the soil-to-water ratio, but its logarithmic form is linear in the given pH range. The oxidation-reduction potential increases with decreasing initial pH, thus positively impacting the reduction process. XPS analysis revealed the reduction process as multi-steps (reduction, adsorption, and co-precipitation). Ecological studies showed improved plant growth and earthworm survival rate in the remediated soil. Medium-term stability experiments suggested a significant decrease in TCLP leachate concentration of Cr after CTAB-nFeS treatment and remained stable for 60 d. Overall results of our study suggested a sustainable, feasible, and effective strategy for in-situ remediation of Cr(VI)-contaminated soil using CTAB-nFeS at natural pH.

The Effect of Cryoprotectants and Storage Conditions on the Transfection Efficiency, Stability, and Safety of Lipid-Based Nanoparticles for mRNA and DNA Delivery.

Lipid-based nanoparticles have recently shown great promise, establishing themselves as the gold standard in delivering novel RNA therapeutics. However, research on the effects of storage on their efficacy, safety, and stability is still lacking. Herein, the impact of storage temperature on two types of lipid-based nanocarriers, lipid nanoparticles (LNPs) and receptor-targeted nanoparticles (RTNs), loaded with either DNA or messenger RNA (mRNA), is explored and the effects of different cryoprotectants on the stability and efficacy of the formulations are investigated. The medium-term stability of the nanoparticles was evaluated by monitoring their physicochemical characteristics, entrapment and transfection efficiency, every two weeks over one month. It is demonstrated, that the use of cryoprotectants protects nanoparticles against loss of function and degradation in all storage conditions. Moreover, it is shown that the addition of sucrose enables all nanoparticles to remain stable and maintain their efficacy for up to a month when stored at -80°C, regardless of cargo or type of nanoparticle. DNA-loaded nanoparticles also remain stable in a wider variety of storage conditions than mRNA-loaded ones. Importantly, these novel LNPs show increased GFP expression that can signify their future use in gene therapies, beyond the established role of LNPs in RNA therapeutics.

Clock Ensemble Algorithm Test in the Establishment of Space-Based Time Reference

A new concept of a space-based synchronized reference network is proposed with the development of an optical frequency reference and laser inter-satellite link. To build such time reference, three clock ensemble algorithms, namely the natural Kalman timescale (NKT) algorithm, the reduced Kalman timescale (RKT) algorithm, and the two-stage Kalman timescale (TKT) algorithm are considered. This study analyzes and compares the performance of these algorithms using BDS, GPS, and Galileo satellite clock data from the GFZ GNSS clock corrections, which will be used in constructing future space-based time references. The study shows that the NKT algorithm improves frequency stability by 0.1–0.2 orders of magnitude in the short and medium term. When the satellite clock is mostly a hydrogen clock, the RKT and NKT are close, and the short and medium-term frequency stability slightly increases. In contrast, the TKT algorithm produces a timescale that improves frequency stability by 1–3 orders of magnitude. A quadratic polynomial model predicts the three timescales, with the results indicating that the short-term prediction accuracy of the satellite clock is within 1ns, and the TKT algorithm’s prediction accuracy is 1–2 orders of magnitude higher than that of the NKT and RKT algorithms. With the deployment of next-generation Low Earth Orbit (LEO) satellites equipped with higher-precision clocks, the space-based time reference system will achieve improved accuracy and greater potential for practical applications.

A VMD-PE-SG denoising method based on K–L divergence for satellite atomic clock

The time scale of the global navigation satellite system (GNSS) is the core element for its position, navigation and timing services. A highly stable atomic clock is essential to ensure the reliability of the GNSS time scale. This study proposed a novel hybrid denoising model combining variational mode decomposition (VMD), K–L divergence, permutation entropy (PE), and Savitzky–Golay (SG) filter for satellite atomic clocks. Firstly, the key parameter of VMD is solved efficiently by taking the minimum sum of K–L divergence of decomposed modes as the constraint condition, and the optimised parameters are applied to the decomposition process. On this basis, the PE algorithm is used to determine the modes decomposed by VMD into signal-dominant and noise-dominant components by searching for the mutation of PE value at two adjacent points. Finally, the noise-dominant components are denoised by the SG filter and then reconstructed with the signal-dominant components to form the denoised signal. The analysis of the simulated signal shows that the method can effectively remove noise from the simulated signal, and the resulting denoised signal is similar to the pure signal. Compared with commonly used ensemble empirical mode decomposition and wavelet denoising methods, the signal-noise ratio of the proposed method is improved by 21.2% and 28.9%, and the root mean square error is improved by 24.1% and 29.8%, respectively. The results of experimental data testify that the K–L VMD-PE-SG-based denoising method can significantly reduce the dominant noise within one day, thus effectively improving the short to medium-term frequency stability. Compared with the original signal, the stability of the smoothing time within 76 800 s is generally improved, and the degree of improvement depends on the type of atomic clock and the smoothing time.

Manufacturing consent in Africa? Multinationals, NGOs and the (re)invention of resistance in the Niger Delta’s oilscapes

Does a proliferation of activist or advocacy non-governmental organisations (NGOs) indicate greater power to pressure multinationals to behave responsibly? This paper answers this question by exploring how multinational oil companies deploy corporate social responsibility (CSR) as a tool to shape the nature of resistance to their disruptive impacts on extractive contexts in Africa. It focusses in particular on their role in building NGO networks and uses evidence from the activities of Chevron in Nigeria’s Niger Delta to show how these networks have become new sites through which multinational corporations exercise hegemonic power over the resistance landscape in the region. It concludes that NGO density – in spite of its appearance of facilitating greater participation – has little impact on the power dynamics in extractive contexts, on the logics of extraction and on the medium-term stability of the sector. What it does achieve is the construction of a gentrified ‘resistance and engagement’ landscape that is bureaucratised and middle-class driven, that excludes key actors and that is inevitably sympathetic to the oil industry.

Hydrothermal Synthesis and Annealing Effect on the Properties of Gas-Sensitive Copper Oxide Nanowires

In this study, we report a straightforward and reproducible hydrothermal synthesis of copper oxide nanowires, their morphological and chemical characterization, and their application in gas sensing. Results show that the hydrothermal process is mainly influenced by the reaction time and the concentration of the reducing agent, demonstrating the synthesis of fine and long nanowires (diameter of 50–200 nm and length of 25 µm) after 10 h of reaction with 0.1 M of pyrrole. Two different annealing temperatures were tested (205 and 450 °C) and their effect on the morphology, chemical composition, and crystal size of the nanowires was analyzed by SEM, XPS, and XRD techniques, respectively. The analysis shows that the Cu2+ oxidation state is mainly obtained at the higher annealing temperature, and the nanowires’ shape suffers a transformation due to the formation of agglomerated crystallites. The gas sensing tests for acetone, ethanol, toluene, and carbon monoxide show preferential response and sensitivity to acetone and ethanol over the other analytes. The annealing temperature proves to have a higher influence on the stability of the nanowires than on their gas sensitivity and selectivity, showing better medium-term stability for the nanowires annealed at 450 °C.

Software-Defined Radio Implemented GPS Spoofing and Its Computationally Efficient Detection and Suppression

This article demonstrates global positioning system (GPS) spoofing with a commercial, off-the-shelf software-defined radio (SDR) emitter fitted with a local oscillator exhibiting a stability consistent with the medium-term (0.01-1 000 s) stability of atomic clocks on GPS satellite systems. Computationally efficient means of detecting spoofing is then addressed, namely codeless spoofing detection by phase-difference measurement of the signals received from a two-antenna array. We conclude by using a simple and effective method to suppress spoofing to restore positioning and time-transfer capabilities, and extend the demonstration to jamming cancellation. Experiment results demonstrate the performance of the proposed methods with an emphasis on computational efficiency for real-time execution on embedded single-board computers.

Performance of an extrapolation chamber in computed tomography standard beams

Among the medical uses of ionizing radiations, the computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. The dosimetry procedure in CT scanner beams makes use of pencil ionization chambers with sensitive volume lengths of 10 cm. The aim of its calibration is to compare the values that are obtained with the instrument to be calibrated and a standard reference system. However, there is no primary standard system for this kind of radiation beam. Therefore, an extrapolation ionization chamber, built at the Calibration Laboratory (LCI), was used to establish a CT primary standard. The objective of this work was to perform some characterization tests (short- and medium-term stabilities, saturation curve, polarity effect and ion collection efficiency) in the standard X-ray beams established for computed tomography at the LCI.

Stability issues of microcystins, anabaenopeptins, anatoxins, and cylindrospermopsin during short-term and long-term storage of surface water and drinking water samples

Reproducible analytical procedures and rigorous quality control are imperative for an accurate monitoring of cyanobacterial toxins in environmental water samples. In this study, the short-term and long-term storage stability of diverse cyanotoxins (anatoxins, cylindrospermopsin, anabaenopeptins, and 12 microcystins) was evaluated in water samples, under different scenarios. Transport controls were performed at three monitoring sites in spiked ultrapure water and lake water to investigate short-term stability issues. Medium-term storage stability was evaluated for up to 14–28 days in ultrapure water, chlorine-treated drinking water (amended with reductant), and surface water (filtered and unfiltered) stored at different temperatures (20 °C, 4 °C, and –20 °C). Substantial decreases of cylindrospermopsin and anabaenopeptins were observed in tap water (20 °C) and unfiltered surface water (20 °C or 4 °C). Regardless of matrix type, cyanotoxin recoveries generally remained within an 80–120% range when the water samples were kept frozen. After a prolonged storage duration of 365 days at –20 °C, most cyanotoxins experienced decreases in the range of 10–20%. The notable exception was for the tryptophan-containing MC-LW and MC-WR, with more substantial variations (30% to 50% decrease) and conversion to N-formylkynurenine analogs. Reanalysis of field-collected surface waters after long-term storage at –20 °C also indicated significantly decreasing trends of cyanotoxins (between 6% and 23% decrease). In view of the above, short sample hold times should be favored as recommended in EPA methods.

(Invited) High Performance La0.3Ca0.7Fe0.7Cr0.3O3-Δ-Based Cathodes for the Conversion of CO2 to CO in Solid Oxide Electrolysis Cells

Ni-based cathodes have been widely accepted as the state-of-the-art in terms of their superior catalytic activity for the CO2 reduction reaction (CO2RR) in solid oxide electrolysis cells (SOEC). However, they are prone to NiO formation and coking at high conversion rates, resulting in performance degradation and subsequent loss of activity (1, 2). For these reasons, numerous efforts have focused on investigating alternative electrocatalysts to replace Ni-based SOEC cathodes. Perovskite oxides, with a general formula ABO3, are a versatile class of materials that have very good catalytic properties that can be tailored by doping a variety of cations on the A- or B-site of the parent lattice. Extensive efforts in our group have been focussed on a very promising class of perovskite electrocatalysts, namely La0.3M0.7Fe0.7Cr0.3O3-δ (M = Sr, Ca) (LMFCr) that are not only highly active for oxygen reduction/evolution, but also for CO2 reduction (3-5). These materials are mixed ionic electronic conductors (MIEC) that also exhibit excellent compatibility with conventional electrolyte materials and hence can be employed directly as electrode layers without the need for composite electrodes that require mixing with ionic conductors, e.g., gadolinia-doped ceria (GDC) etc. Futhermore, the same electrocatalyst can be used as both the fuel and oxygen electrode which enables the cell to run reversibly (reversible solid oxide fuel cells, RSOFC). This is highly advantageous in terms of simplifying cell design and hence lowering cost, while also mitigating compatibility issues with neighboring cell components and generating long term stability (6), thus making the LMFCr electrocatalyst very promising for commercialization purposes. Of the two LMFCr analogues, La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr) exhibits superior catalytic activity for both the CO2RR and OER and therefore it is the focus of this work. Here, the stability of the LCFCr catalyst under high CO2 conversion to CO has been examined, determining whether these conditions lead to any deleterious effects, such as coke formation. We have answered this question by studying the stability and electrochemical performance of LCFCr in various CO2:CO environments. Furthermore, we have also employed Ni-doped LCFCr to decorate the perovskite surface with in situ exsolved metal nanoparticles (NP) to determine if this would further enhance its catalytic activity and stability. The LCFCr electrode ink was prepared by employing a 1:1 ratio of powder to ink vehicle. Symmetrical cells were prepared by tape casting the LCFCr ink over a ca. 0.50 cm2 area on both sides of 2.5 cm diameter SDC-buffered YSZ/SSZ substrates. Au paste was painted on as the current collector followed by sealing the cells on an alumina tube with a ceramic sealant. The fuel electrode was then exposed to various CO2:CO ratios (100:0, 90:10, 70:30, and 50:50), while air was supplied to the oxygen electrode at flow rates of 50 ml/min. The electrochemical performance of the cells was determined via electrochemical impedance spectroscopy (EIS) (at a 50 mV ac amplitude and over a range of 65000 – 0.01 Hz) and using cyclic voltammetry (CV at 5 mV/s). The short- and medium-term stability of the cells was determined by monitoring the current at various cell voltages of 1.0 – 1.6 V. The cells showed excellent performance for CO2RR in these gas mixtures, while the CO oxidation activity plateaued as the overpotential was increased. The CO2RR and CO oxidation activity was significantly enhanced when Ni-doped LCFCr with in situ exsolved Fe-Ni alloy NPs was employed as the electrode layers, also showing remarkably stable performance over several hours at 1.2 V without any evidence of coking or delamination up to 90% CO2 conversion, as revealed by postmortem SEM studies. The CO2/CO cells were also studied using synchrotron radiation at the Canadian Light Source in order to determine whether any changes occurred to the LMFCr surface or bulk properties and if any carbon could be detected, especially at very high conversion of CO2 to CO.References Yue and J. T. S. Irvine, Journal of The Electrochemical Society, 159, F442 (2012)Song, Z. Zhou, X. Zhang, Y. Zhou, H. Gong, H. Lv, Q. Liu, G. Wang and X. Bao, Journal of Materials Chemistry A, 6, 13661 (2018)K. Addo, B. Molero-Sanchez, M. Chen, S. Paulson and V. Birss, Fuel Cells, 15, 689 (2015)Molero-Sanchez, J. Prado-Gonjal, D. Avila-Brande, M. Chen, E. Moran and V. Birss, International Journal of Hydrogen Energy, 40, 1902 (2015)Haag, B. Madsen, S. Barnett and K. Poeppelmeier, Electrochemical and Solid State Letters, 11, B51 (2008)A. Hauch, S. D. Ebbesen, S. H. Jensen and M. Mogensen, Journal of Materials Chemistry, 18, 2331 (2008)

Clock tuning technique for a disciplined high medium–long-stability GNSS oscillator with precise clock drifts for LEO users

A crucial issue of low earth orbit (LEO) navigation augmentation satellite constellation is to obtain a satellite clock of high medium–long stability (i.e., averaging time of 10–10,000 s) using a disciplined oscillator to reduce satellite size, weight, power consumption and cost, instead of using a large, heavy and expensive space atomic clock. To resolve this difficulty, we propose a new global navigation satellite system (GNSS) clock discipline technique via a stand-alone GNSS receiver. Consequently, high medium–long stability can be attained with the disciplined receiver oscillator. Based on the Doppler measurements calculated from carrier phases, precise clock drifts of the receiver oscillator are derived. According to the motion state of the LEO GNSS receiver, a precise clock drift estimation model is chosen to have good adaptability to the receiver's high dynamic movement. Then, the receiver oscillator is properly tuned to its nominal frequency at each epoch without loss of lock. An automatic closed-loop frequency control system using a third-order frequency-locked loop filter is proposed to periodically compensate the instantaneous frequency offsets of the user clock with respect to its nominal frequency. A nonlinear frequency steering method is proposed to overcome the receiver lost lock problem during the oscillator discipline process. The correctness and effectiveness of the proposed clock tuning technique were numerically verified with MATLAB first. Then, the oscillator discipline performances were tested with a VCH-1008 passive hydrogen maser, a LEO GNSS receiver and a PicoTime clock stability analyzer. With static real GPS data of a static receiver as well as with hardware simulated data of a LEO receiver, both the medium-term and long-term frequency stabilities of the disciplined oscillator were confirmed. Finally, the proposed oscillator discipline technique was implemented in a self-developed LEO GNSS receiver. A high-quality voltage-controlled crystal oscillator mounted on an onboard LEO receiver was used for our test both in a static situation and in a LEO dynamic environment. The experiment results show that the overlapping Allan deviation of the disciplined GNSS oscillator could be less than 7E-12 over periods of 1 to 4,000 s in both the static situation and the LEO moving situation for a 1070 km orbit with 1 Hz epoch sampling rate at the testing stage.

Geochemical time series of hydrothermal fluids from the slow-spreading Mid-Atlantic Ridge: Implications of medium-term stability

Time series investigations of hydrothermal fluids from different geological settings at the slow-spreading Mid-Atlantic Ridge (MAR) indicate a surprising medium-term stability of their chemical composition over up to 20 years. This does not only apply to tectonically controlled systems with exposure of mantle rocks where magmatic activity is limited, such as the Logatchev-1 hydrothermal field at 14°45′N. We also found the 407 °C hot and extremely metal-rich fluids at the 5°S site Turtle Pits (2986 m water depth) to discharge at constant composition indicating supercritical phase separation for at least 4 years, which contrasts with rather dynamic volcanically driven hydrothermal systems at the fast-spreading East-Pacific Rise (EPR). Possibly, fluid pathways and pressure-temperature conditions are more stable in tectonically controlled settings at MAR than at the EPR where frequent volcanic activity affects permeability within the hydrothermal systems. Despite some spatial variability, hydrothermal fluids discharging at the shallower (ca. 810–870 m) Menez Gwen hydrothermal field at 37°50′N seem to represent a stable discharge of phase-separated vapor-type fluids over 16 years. This demonstrates that medium-term stability of hydrothermal fluid composition seems to be a general feature at slow-spreading ridges. As a consequence, hydrothermal vent organisms at the MAR may live in a more stable chemical environment compared to vent systems at fast-spreading ridges. Considering the fact that slow-spreading ridges account for more than half of the submarine ridge system, such a constant emanation of hydrothermal fluids makes hydrothermal vent systems on slow spreading ridges a medium-term stable source of Fe and other micronutrients into the ocean.

(Invited) High Performance La0.3Ca0.7Fe0.7Cr0.3O3-Δ-Based Cathodes for the Conversion of CO2 to CO in Solid Oxide Electrolysis Cells

Ni-based cathodes have been widely accepted as the state-of-the-art in terms of their superior catalytic activity for the CO2 reduction reaction (CO2RR) in solid oxide electrolysis cells (SOEC). However, they are prone to NiO formation and coking at high conversion rates, resulting in performance degradation and subsequent loss of activity (1, 2). For these reasons, numerous efforts have focused on investigating alternative electrocatalysts to replace Ni-based SOEC cathodes. Perovskite oxides, with a general formula ABO3, are a versatile class of materials that have very good catalytic properties that can be tailored by doping a variety of cations on the A- or B-site of the parent lattice.Extensive efforts in our group have been focussed on a very promising class of perovskite electrocatalysts, namely La0.3M0.7Fe0.7Cr0.3O3-δ (M = Sr, Ca) (LMFCr) that are not only highly active for oxygen reduction/evolution, but also for CO2 reduction (3-5). These materials are mixed ionic electronic conductors (MIEC) that also exhibit excellent compatibility with conventional electrolyte materials and hence can be employed directly as electrode layers without the need for composite electrodes that require mixing with ionic conductors, e.g., gadolinia-doped ceria (GDC) etc. Futhermore, the same electrocatalyst can be used as both the fuel and oxygen electrode which enables the cell to run reversibly (reversible solid oxide fuel cells, RSOFC). This is highly advantageous in terms of simplifying cell design and hence lowering cost, while also mitigating compatibility issues with neighboring cell components and generating long term stability (6), thus making the LMFCr electrocatalyst very promising for commercialization purposes.Of the two LMFCr analogues, La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr) exhibits superior catalytic activity for both the CO2RR and OER and therefore it is the focus of this work. Here, the stability of the LCFCr catalyst under high CO2 conversion to CO has been examined, determining whether these conditions lead to any deleterious effects, such as coke formation. We have answered this question by studying the stability and electrochemical performance of LCFCr in various CO2:CO environments. Furthermore, we have also employed Ni-doped LCFCr to decorate the perovskite surface with in situ exsolved metal nanoparticles (NP) to determine if this would further enhance its catalytic activity and stability. The LCFCr electrode ink was prepared by employing a 1:1 ratio of powder to ink vehicle. Symmetrical cells were prepared by tape casting the LCFCr ink over a ca. 0.50 cm2 area on both sides of 2.5 cm diameter SDC-buffered YSZ/SSZ substrates. Au paste was painted on as the current collector followed by mounting and sealing the cells on an alumina tube with a ceramic sealant. The fuel electrode was then exposed to various CO2:CO ratios (100:0, 90:10, 70:30, and 50:50), while air was supplied to the oxygen electrode at flow rates of 50 ml/min.The electrochemical performance of the cells was determined via electrochemical impedance spectroscopy (EIS) (at a 50 mV ac amplitude and over a range of 65000 – 0.01 Hz) and using cyclic voltammetry (CV at 5 mV/s). The short- and medium-term stability of the cells was determined by monitoring the current at various cell voltages of 1.0 – 1.6 V. The cells showed excellent performance for CO2RR in these gas mixtures, while the CO oxidation activity plateaued as the overpotential was increased. The CO2RR and CO oxidation activity was significantly enhanced when Ni-doped LCFCr with in situ exsolved FeNi alloy NPs was employed as the electrode layers, also showing remarkably stable performance over several hours at 1.2 V without any evidence of coking or delamination up to 90% CO2 conversion, as revealed by postmortem SEM studies. The CO2/CO cells were also studied using synchrotron radiation at the Canadian Light Source in order to determine whether any changes occurred to the LMFCr surface or bulk properties and if any carbon could be detected, especially at very high conversion of CO2 to CO.

Nigeria

This paper presents Nigeria’s Request for Purchase Under the Rapid Financing Instrument (RFI). The authorities’ immediate actions to respond to the crisis are welcome. The short-term focus on fiscal accommodation would allow for higher health spending and help alleviate the impact of the crisis on households and businesses. Steps taken toward a more unified and flexible exchange rate are also important and unification of the exchange rate should be expedited. Once the coronavirus disease 2019 crisis passes, the focus should remain on medium-term macroeconomic stability, with revenue-based fiscal consolidation essential to keep Nigeria’s debt sustainable and create fiscal space for priority spending. Implementation of the reform priorities under the Economic Recovery and Growth Plan, particularly on power and governance, remains crucial to boost growth over the medium term. The emergency financing under the RFI will provide much needed liquidity support to respond to the urgent balance of payments needs. Additional assistance from development partners will be required to support the government’s efforts and close the large financing gap.

Republic of Korea

The FSSA was prepared by a staff team of the IMF for the Executive Board’s consideration on Friday, March 27. The staff report reflects discussions with the Korean authorities in September and December 2019 and is based on the information available as of end June 2019. It focuses on Korea’s near and medium-term financial stability challenges and policy priorities and was prepared before COVID-19 became a global pandemic and resulted in unprecedented strains in global trade, commodity and financial markets. It, therefore, does not reflect the implications of these developments and related policy priorities. Staff is closely monitoring the situation and will continue to work on assessing its impact and the related policy response in Korea and globally.