This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by ...electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.
Nanocrystalline SnO2 fibers are fabricated by electrospinning using Pd as a grain growth inhibitor and a catalyst for enhancing oxidation reactions. Pd‐loaded or unloaded (pristine) SnO2 fibers can be used as gas sensors capable of detecting trace concentrations as low as several parts per billion (ppb) of H2 and NO2, respectively.
The development of gas sensors with innovative designs and advanced functional materials has attracted considerable scientific interest given their potential for addressing important technological ...challenges. This work presents new insight towards the development of high‐performance p‐type semiconductor gas sensors. Gas sensor test devices, based on copper (II) oxide (CuO) with innovative and unique designs (urchin‐like, fiber‐like, and nanorods), are prepared by a microwave‐assisted synthesis method. The crystalline composition, surface area, porosity, and morphological characteristics are studied by X‐ray powder diffraction, nitrogen adsorption isotherms, field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. Gas sensor measurements, performed simultaneously on multiple samples, show that morphology can have a substantial influence on gas sensor performance. An assembly of urchin‐like structures is found to be most effective for hydrogen detection in the range of parts‐per‐million at 200 °C with 300‐fold larger response than the previously best reported values for semiconducting CuO hydrogen gas sensors. These results show that morphology plays an important role in the gas sensing performance of CuO and can be effectively applied in the further development of gas sensors based on p‐type semiconductors.
High‐performance gas sensors based on CuO hierarchical morphologies with in situ gas sensor comparison are reported. Urchin‐like morphologies with high hydrogen sensitivity and selectivity that show chemical and thermal stability and low temperature operation are analyzed. The role of morphological influences in p‐type gas sensor materials is discussed.
Gait event detection is essential for controlling an orthosis and assessing the patient's gait. In this study, patients wearing an electromechanical (EM) knee-ankle-foot orthosis (KAFO) with a single ...IMU embedded in the thigh were subjected to gait event detection. The algorithm detected four essential gait events (initial contact (IC), toe off (TO), opposite initial contact (OIC), and opposite toe off (OTO)) and determined important temporal gait parameters such as stance/swing time, symmetry, and single/double limb support. These gait events were evaluated through gait experiments using four force plates on healthy adults and a hemiplegic patient who wore a one-way clutch KAFO and a pneumatic cylinder KAFO. Results showed that the smallest error in gait event detection was found at IC, and the largest error rate was observed at opposite toe off (OTO) with an error rate of -2.8 ± 1.5% in the patient group. Errors in OTO detection resulted in the largest error in determining the single limb support of the patient with an error of 5.0 ± 1.5%. The present study would be beneficial for the real-time continuous monitoring of gait events and temporal gait parameters for persons with an EM KAFO.
In this work, we report a remarkably improved toluene response and superior cross-sensitivity against H2S molecules by combining Pd catalysts and highly porous WO3 nanofibers (NFs). We functionalized ...Pd catalysts inside and/or outside of WO3 NFs synthesized by electrospinning, which is a facile and versatile process for producing webs of metal oxide NFs. Pd-embedded WO3 NFs were obtained by the electrospinning of a Pd and W composite precursor/poly(methyl methacrylate) (PMMA) solution followed by calcination at 700°C. Pd nanoparticles (NPs) (6–10nm) synthesized by a polyol method were decorated on the WO3 NFs (Pd-NPs/WO3 NFs) by the attachment of the Pd NPs on as-prepared WO3 NFs. The gas sensing characteristics of pure WO3, Pd-embedded WO3, Pd-NPs/WO3, and Pd-NPs/Pd-embedded WO3 NFs were tested using H2S and toluene gases in a highly humid atmosphere (RH 90%), which is similar to human exhaled breath. The results showed that the Pd-NPs/Pd-embedded WO3 NFs whose inner and outer layers were decorated by Pd catalysts, exhibited a high toluene response (Rair/Rgas=5.5 at 1ppm) and remarkable selectivity against H2S (Rair/Rgas=1.36 at 1ppm) at 350°C, whereas pristine WO3 NFs showed superior H2S response (Rair/Rgas=11.1 at 1ppm) along with a negligible response toward toluene (Rair/Rgas=1.27 at 1ppm). The highly porous WO3 NFs decorated with Pd catalysts, exhibited potential feasibility, i.e., a low limit of detection (LOD) of 20ppb (Rair/Rgas=1.32) at 350°C, for application in VOCs sensors, particularly for diagnoses of lung cancer.
The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The ...zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi0.5Sb1.5Te3 (bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved the zT to 1.86 ± 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices.
In accordance with South Korea’s recent 2030 Carbon Neutral Plan, an 8GW offshore wind farm is planned for construction in the South-west Sea. Therefore, it is expected that large-scale wind turbines ...will be installed, and these turbines must operate stably, even when there are instantaneous voltage fluctuations in the power system. The grid code is described for the low-voltage-ride-through (LVRT) and high-voltage-ride-through (HVRT) functions, and a test facility that can perform both LVRT and HVRT tests is essential. In the case of LVRT/HVRT test facilities developed by the existing RLC (impedance component) method, it may be difficult to test large-scale wind turbines due to problems such as power quality, frequent failures and narrow short-circuit capacity ranges. Therefore, to solve such problems, this paper proposes an LVRT/HVRT test facility of the autotransformer type, which is capable of outputting the desired voltage range by changing the wiring method and tap position. Specifically, in order to implement the test facility of the autotransformer type, which is able to output the desired voltage range by changing the wiring method and tap according to the LVRT/HVRT test status, this paper presents an impedance determination algorithm (two-step layer impedance determination algorithm) of auto-transformer based on the fault-current analysis and operation strategy at a real LVRT/HVRT testing evaluation facility.
In recent years, the energy industry has increased the proportion of renewable energy sources, which are sustainable and carbon-free. However, the increase in renewable energy sources has led to grid ...instability due to factors such as the intermittent power generation of renewable sources, forecasting inaccuracies, and the lack of metering for small-scale power sources. Various studies have been carried out to address these issues. Among these, research on Virtual Power Plants (VPP) has focused on integrating unmanaged renewable energy sources into a unified system to improve their visibility. This research is now being applied in the energy trading market. However, the purpose of VPP aggregators has been to maximize profits. As a result, they have not considered the impact on distribution networks and have bid all available distributed resources into the energy market. While this approach has increased the visibility of renewables, an additional method is needed to deal with the grid instability caused by the increase in renewables. Consequently, grid operators have tried to address these issues by diversifying the energy market. As regulatory method, they have introduced real-time energy markets, imbalance penalty fees, and limitations on the output of distributed energy resources (DERs), in addition to the existing day-ahead market. In response, this paper proposes an optimal scheduling method for VPP aggregators that adapts to the diversifying energy market and enhances the operational benefits of VPPs by using two Mixed-Integer Linear Programming (MILP) models. The validity of the proposed model and algorithm is verified through a case study analysis.
Films of tungsten-doped nickel oxide, denoted Ni1-xWx oxide as counter electrode in electrochromic devices were deposited onto indium tin oxide coated glass substrates by reactive dc magnetron ...sputtering using tungsten-doped nickel alloy target. Electrochromic properties of NixW1-x oxides were evaluated in lithium perchlorate in propylene carbonate. Enhanced cycle stability with moderate optical modulation was obtained for Ni1-xWx oxide film with x = 0.024. Significant degradation in pure NiO film during extended electrochemical cycling caused by microstructural deep trap sites was minimized by W doping. The EC device fabricated with WO3 thin film and Ni1-xWx oxide thin film with x = 0.024 showed stable optical modulation of about 2% reduction from 100 to 1000 cycles. Flexible EC device was also fabricated with WO3 thin film and Ni1-xWx oxide thin film with x = 0.024 deposited on c-ITO/graphene/PET electrode and showed stable cycling performance with maintaining optical modulation of ΔT ≈ 40%.
•W-doped Ni oxide as counter electrode in electrochromic devices were deposited onto ITO glass substrate by reactive DC magnetron sputtering.•Enhanced cycle stability with moderate optical modulation was obtained for Ni1-xWx oxide film with x = 0.024.•Flexible EC device fabricated with W-doped Ni oxide showed stable cyclability while maintaining high optical modulation.
In the last 100 years, agricultural developments have favoured selection for highly productive crops, a fact that has been commonly associated with loss of key traits for environmental stress ...tolerance. We argue here that this is not exactly the case. We reason that high yield under near optimal environments came along with
of plant stress perception and consequently
of stress avoidance mechanisms, such as slow growth, which were originally needed for survival over long evolutionary time periods. Therefore, mechanisms employed by plants to cope with a stressful environment during evolution were overwhelmingly geared to avoid detrimental effects so as to ensure survival and that plant stress "tolerance" is fundamentally and evolutionarily based on "avoidance" of injury and death which may be referred to as evolutionary avoidance (EVOL-Avoidance). As a consequence, slow growth results from being exposed to stress because genes and genetic programs to adjust growth rates to external circumstances have evolved as a survival but not productivity strategy that has allowed extant plants to avoid extinction. To improve productivity under moderate stressful conditions, the evolution-oriented plant stress response circuits must be changed from a survival mode to a continued productivity mode or to
the evolutionary avoidance response, as it were. This may be referred to as Agricultural (AGRI-Avoidance). Clearly, highly productive crops have kept the slow, reduced growth response to stress that they evolved to ensure survival. Breeding programs and genetic engineering have not succeeded to genetically remove these responses because they are polygenic and redundantly programmed. From the beginning of modern plant breeding, we have not fully appreciated that our crop plants react overly-cautiously to stress conditions. They over-reduce growth to be able to survive stresses for a period of time much longer than a cropping season. If we are able to remove this polygenic redundant survival safety net we may improve yield in moderately stressful environments, yet we will face the requirement to replace it with either an emergency slow or no growth (dormancy) response to extreme stress or use resource management to rescue crops under extreme stress (or both).
Myeloblastosis (MYB) transcription factors play central roles in plant developmental processes and in responses to nutrient deficiency. In this study, OsMYB5P, an R2R3-MYB transcription factor, was ...isolated and identified from rice (Oryza sativa L. 'Dongjin') under inorganic phosphate (Pi)-deficient conditions. OsMYB5P protein is localized to the nucleus and functions as a transcription activator in plant development. Overexpression of OsMYB5P in rice and Arabidopsis (Arabidopsis thaliana Col-0) increases tolerance to phosphate starvation, whereas OsMYB5P knock-out through RNA interference increases sensitivity to Pi depletion in rice. Furthermore, shoots and roots of transgenic rice plants overexpressing OsMYB5P were longer than those of wild plants under both normal and Pi-deficient conditions. These results indicate that OsMYB5P is associated with the regulation of shoot development and root- system architecture. Overexpression of OsMYB5P led to increased Pi accumulation in shoots and roots. Interestingly, OsMYB5P directly bound to MBS (MYB binding site) motifs on the OsPT5 promoter and induced transcription of OsPT5 in rice. In addition, overexpression of OsMYB5P in Arabidopsis triggered increased expression of AtPht1;3, an Arabidopsis Pi transporter, in shoots and roots under normal and Pi-deficient conditions. Together, these results demonstrate that overexpression of OsMYB5P increases tolerance to Pi deficiency in plants by modulating Pi transporters at the transcriptional level in monocots and dicots.
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