Enhanced Hydrogen Detection in ppb-Level by Electrospun SnO2-Loaded ZnO Nanofibers.

High-performance hydrogen sensors are important in many industries to effectively address safety concerns related to the production, delivering, storage and use of H2 gas. Herein, we present a highly sensitive hydrogen gas sensor based on SnO2-loaded ZnO nanofibers (NFs). The xSnO2-loaded (x = 0.05, 0.1 and 0.15) ZnO NFs were fabricated using an electrospinning technique followed by calcination at high temperature. Microscopic analyses demonstrated the formation of NFs with expected morphology and chemical composition. Hydrogen sensing studies were performed at various temperatures and the optimal working temperature was selected as 300 °C. The optimal gas sensor (0.1 SnO2 loaded ZnO NFs) not only showed a high response to 50 ppb hydrogen gas, but also showed an excellent selectivity to hydrogen gas. The excellent performance of the gas sensor to hydrogen gas was mainly related to the formation of SnO2-ZnO heterojunctions and the metallization effect of ZnO.

Gas Sensing Properties of Mg-Incorporated Metal-Organic Frameworks.

The gas sensing properties of two novel series of Mg-incorporated metal-organic frameworks (MOFs), termed Mg-MOFs-I and -II, were assessed. The synthesized iso-reticular type Mg-MOFs exhibited good crystallinity, high thermal stability, needle-shape morphology and high surface area (up to 2900 m2·g-1), which are promising for gas sensing applications. Gas-sensing studies of gas sensors fabricated from Mg-MOFs-II revealed better sensing performance, in terms of the sensor dynamics and sensor response, at an optimal operating temperature of 200 °C. The MOF gas sensor with a larger pore size and volume showed shorter response and recovery times, demonstrating the importance of the pore size and volume on the kinetic properties of MOF-based gas sensors. The gas-sensing results obtained in this study highlight the potential of Mg-MOFs gas sensors for the practical monitoring of toxic gases in a range of environments.

ppb-Level Selective Hydrogen Gas Detection of Pd-Functionalized In2O3-Loaded ZnO Nanofiber Gas Sensors.

Pd nanoparticle-functionalized, xIn2O3 (x = 0.05, 0.1, and 0.15)-loaded ZnO nanofibers were synthesized by an electrospinning and ultraviolet (UV) irradiation method and assessed for their hydrogen gas sensing properties. Morphological and chemical analyses revealed the desired morphology and chemical composition of the synthesized nanofibers. The optimal gas sensor namely Pd-functionalized, 0.1In2O3-loaded ZnO nanofibers showed a very strong response to 172-50 ppb hydrogen gas at 350 °C, which is regarded as the optimal sensing temperature. Furthermore, the gas sensors showed excellent selectivity to hydrogen gas due to the much lower response to CO and NO2 gases. The enhanced gas response was attributed to the excellent catalytic activity of Pd to hydrogen gas, and the formation of Pd/ZnO and In2O3/ZnO heterojunctions, ZnO-ZnO homojunction, as well as the formation of PdHx. Overall, highly sensitive and selective hydrogen gas sensors can be produced based on a simple methodology using a synergistic effect from Pd functionalization and In2O3 loading in ZnO nanofibers.

Sub-ppm Formaldehyde Detection by n-n TiO2@SnO2 Nanocomposites.

Formaldehyde (HCHO) is an important indicator of indoor air quality and one of the markers for detecting lung cancer. Both medical and air quality applications require the detection of formaldehyde in the sub-ppm range. Nanocomposites SnO2/TiO2 are promising candidates for HCHO detection, both in dark conditions and under UV illumination. Nanocomposites TiO2@SnO2 were synthesized by ALD method using nanocrystalline SnO2 powder as a substrate for TiO2 layer growth. The microstructure and composition of the samples were characterized by ICP-MS, TEM, XRD and Raman spectroscopy methods. The active surface sites were investigated using FTIR and TPR-H2 methods. The mechanism of formaldehyde oxidation on the surface of semiconductor oxides was studied by in situ DRIFTS method. The sensor properties of nanocrystalline SnO2 and TiO2@SnO2 nanocomposites toward formaldehyde (0.06-0.6 ppm) were studied by in situ electrical conductivity measurements in dark conditions and under periodic UV illumination at 50-300 °C. Nanocomposites TiO2@SnO2 exhibit a higher sensor signal than SnO2 and a decrease in the optimal measurement temperature by 50 °C. This result is explained based on the model considering the formation of n-n heterocontact at the SnO2/TiO2 interface. UV illumination leads to a decrease in sensor response compared with that obtained in dark conditions because of the photodesorption of oxygen involved in the oxidation of formaldehyde.

Effectiveness of neuromuscular electrical stimulation for management of shoulder subluxation post-stroke: a systematic review with meta-analysis.

OBJECTIVES: To examine the effectiveness of neuromuscular electrical stimulation (NMES) for the management of shoulder subluxation after stroke including assessment of short (1 hour or less) and long (more than one hour) daily treatment duration. DATA SOURCES: MEDLINE, CENTRAL, CINAHL, WOS, KoreaMed, RISS and reference lists from inception to January 2017 Review methods: We considered randomized controlled trials that reported neuromuscular electrical stimulation for the treatment of shoulder subluxation post-stroke. Two reviewers independently selected trials for inclusion, assessed trial quality, and extracted data. RESULTS: Eleven studies were included (432 participants); seven studies were good quality, four were fair. There was a significant treatment effect of neuromuscular electrical stimulation for reduction of subluxation for persons with acute and subacute stroke (SMD:-1.11; 95% CI:-1.53, -0.68) with either short (SMD:-0.91; 95% CI:-1.43, -0.40) or long (SMD:-1.49; 95% CI:-2.31, -0.67) daily treatment duration. The effect for patients with chronic stroke was not significant (SMD:-1.25; 95% CI:-2.60, 0.11). There was no significant effect of neuromuscular electrical stimulation on arm function or shoulder pain. CONCLUSION: This meta-analysis suggests a beneficial effect of neuromuscular electrical stimulation, with either short or long daily treatment duration, for reducing shoulder subluxation in persons with acute and subacute stroke. No significant benefits were observed for persons with chronic stroke or for improving arm function or reducing shoulder pain.

Experimental verification of methane-carbon dioxide replacement in natural gas hydrates using a differential scanning calorimeter.

The methane (CH4) - carbon dioxide (CO2) swapping phenomenon in naturally occurring gas hydrates is regarded as an attractive method of CO2 sequestration and CH4 recovery. In this study, a high pressure microdifferential scanning calorimeter (HP µ-DSC) was used to monitor and quantify the CH4 - CO2 replacement in the gas hydrate structure. The HP µ-DSC provided reliable measurements of the hydrate dissociation equilibrium and hydrate heat of dissociation for the pure and mixed gas hydrates. The hydrate dissociation equilibrium data obtained from the endothermic thermograms of the replaced gas hydrates indicate that at least 60% of CH4 is recoverable after reaction with CO2, which is consistent with the result obtained via direct dissociation of the replaced gas hydrates. The heat of dissociation values of the CH4 + CO2 hydrates were between that of the pure CH4 hydrate and that of the pure CO2 hydrate, and the values increased as the CO2 compositions in the hydrate phase increased. By monitoring the heat flows from the HP µ-DSC, it was found that the noticeable dissociation or formation of a gas hydrate was not detected during the CH4 - CO2 replacement process, which indicates that a substantial portion of CH4 hydrate does not dissociate into liquid water or ice and then forms the CH4 + CO2 hydrate. This study provides the first experimental evidence using a DSC to reveal that the conversion of the CH4 hydrate to the CH4 + CO2 hydrate occurs without significant hydrate dissociation.

Guest gas enclathration in semiclathrates of tetra-n-butylammonium bromide: stability condition and spectroscopic analysis.

In this study, guest gas enclathration behavior in semiclathrates of tetra-n-butylammonium bromide (TBAB) was closely investigated through phase equilibrium measurement and spectroscopic analysis. The three-phase equilibria of semiclathrate (H), liquid water (L(W)), and vapor (V) for the ternary CH(4) + TBAB + water and CO(2) + TBAB + water mixtures with various TBAB concentrations were experimentally measured to determine the stability conditions of the double TBAB semiclathrates. Equilibrium dissociation temperatures for pure TBAB semiclathrate were also measured at the same concentrations under atmospheric conditions. The dissociation temperature and dissociation enthalpy of pure TBAB semiclathrate were confirmed by differential scanning calorimetry. The experimental results showed that the double CH(4) (or CO(2)) + TBAB semiclathrates yielded greatly enhanced thermal stability when compared with pure CH(4) (or CO(2)) hydrate. The highest stabilization effect was observed at the stoichiometric concentration of pure TBAB semiclathrate, which is 3.7 mol%. From the NMR and Raman spectroscopic studies, it was found that the guest gases (CH(4) and CO(2)) were enclathrated in the double semiclathrates. In particular, from the cage-dependent (13)C NMR chemical shift, it was confirmed that CH(4) molecules were captured in the 5(12) cages of the double semiclathrates.

Functionalization of zirconium-based metal-organic frameworks for gas sensing applications.

The functionalization and incorporation of noble metals in metal-organic frameworks have been widely used as efficient methods to enhance their applicability. Herein, a sulfone-functionalized Zr-MOF framework labeled Zr-BPDC-SO2 (BPDC-SO2 =dibenzo[b,d]-thiophene-3,7-dicarboxylate 5,5-dioxide) and its Pd-embedded composite were efficiently synthesized by adjusting their functional groups. The obtained compounds were characterized to assess their potential for gas sensing applications. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, specific surface area measurements, and thermogravimetric analysis were employed to characterize the new sensor materials. The gas sensing properties of the novel functionalized sensor materials were systematically investigated under various temperature, concentration, and gas type conditions. Owing to the strong hydrogen bonds of the sulfonyl groups and Zr6 clusters in the framework with the hydroxyl groups of ethanol, Zr-BPDC-SO2 emerged as an effective sensor for ethanol detection. In addition, Pd@Zr-BPDC-SO2 exhibited efficient hydrogen sensing performance, in terms of sensor dynamics and response. More importantly, the material showed a higher sensing response to hydrogen than to other gases, highlighting the important role of Pd in the Zr-MOF-based hydrogen sensor. The results of the sensing tests carried out in this study highlight the promising potential of the present materials for practical gas monitoring applications.

Electrowetting-on-dielectric characteristics of ZnO nanorods.

Herein, we report the electrowetting-on-dielectric (EWOD) characteristics of ZnO nanorods (NRs) prepared via the hydrothermal method with different initial Zn2+ concentrations (0.03, 0.07, and 0.1 M). Diameter of the resultant ZnO NRs were 50, 70 and 85 nm, respectively. Contact angle (CA) measurements showed that the Teflon-coated ZnO NRs with diameters of 85 nm prepared from the 0.1 M solution had the highest CA (137°). During the EWOD studies, on the application of a voltage of 250 V, the water CA decreased to 78°, which demonstrates the potential application of this material in EWOD electronics. Furthermore, we explained the relationship between the applied voltage and CA based on the substrate nanostructures and our newly developed NR-on-film wetting model. In addition, we further validated our model by introducing the homo-composite dielectric structure, which is a composite of thin layered ZnO/Teflon and nano-roded ZnO/Teflon.

Effect of interlayer ions on methane hydrate formation in clay sediments.

Natural methane hydrates occurring in marine clay sediments exhibit heterogeneous phase behavior with high complexity, particularly in the negatively charged interlayer region. To date, the real clay interlayer effect on natural methane hydrate formation and stability remains still much unanswered, even though a few computer simulation and model studies are reported. We first examined the chemical shift difference of 27Al, 29Si, and 23Na between dry clay and clay containing intercalated methane hydrates (MH) in the interlayer. We also measured the solid-state 13C MAS NMR spectra of MH in Na-montmorillonite (MMT) and Ca-montmorillonite (MMT) to reveal abnormal methane popularity established in the course of intercalation and further performed cryo-TEM and XRD analyses to identify the morphology and layered structure of the intercalated methane hydrate. The present findings strongly suggest that the real methane amount contained in natural MH deposits should be reevaluated under consideration of the compositional, structural, and physical characteristics of clay-rich sediments. Furthermore, the intercalated methane hydrate structure should be seriously considered for developing the in situ production technologies of the deep-ocean methane hydrate.

Enhancement of CO and NO2 sensing in n-SnO2-p-Cu2O core-shell nanofibers by shell optimization.

SnO2-Cu2O core-shell nanofibers (C-S NFs) with various shell thicknesses (15-80 nm) were fabricated for gas (CO and NO2) sensing applications. SnO2 NFs were produced by electrospinning and then coated with Cu2O by atomic layer deposition, which allows control of the shell thickness. The role of the Cu2O shell thickness on the sensing characteristics was investigated systematically. The sensor responses to both CO and NO2 gases exhibited bell-shaped curves in the range of 15-80 nm, which was related to the radial modulation of the hole-accumulation layer (HAL) in the Cu2O and blocking of the expansion of the HAL because of the existence of the n-p heterojunction. In addition, the volume fraction of the shell relative to the total volume of C-S has a direct effect on the total degree of resistance modulation. Furthermore, the effects of SnO2 surface-Cu2O heterojunctions and Cu2O grain boundaries on the sensing behavior are explained. This study revealed an important aspect of C-S nanostructures for sensing studies, which is needed to optimize the shell thickness and obtain the strongest response towards specific hazardous gases.

Comparison of standard-setting methods for the Korea Radiological technologist Licensing Examination : Angoff, Ebel, Bookmark, and Hofstee.

PURPOSE: This study aims to compare the various standard setting methods for the Korean Radiological Technologist Licensing Examination with the fixed cut score and suggest the most appropriate method. METHODS: Six radiological technology professors, set the standards of 250 items for Korean Radiological Technologist Licensing examination that were conducted on December 2016 by using Angoff, Ebel, bookmark, and Hofstee methods. RESULTS: With the maximum percentile score of 100, the cut score for the examination was 71.27 in Angoff method, 62.2 in Ebel method, 64.49 in bookmark method, and 62 in Hofstee. Based on the Hofstee's acceptable cut score, the acceptable cut score for the examination was between 52.83 and 70, but the cut score was 71.27 in Angoff method. CONCLUSION: Above results suggested that the best standard setting methods to determine the cut score was panel discussion with the modified Angoff or Ebel methods, and verification of the rated results by Hofstee method. Because there was still no adoption of standard setting in the Korean Radiological Technologist Licensing Examination, this study will be able to provide the practical guideline to introduce the standard setting.

Significant Enhancement of Hydrogen-Sensing Properties of ZnO Nanofibers through NiO Loading.

Metal oxide p-n heterojunction nanofibers (NFs) are among the most promising approaches to enhancing the efficiency of gas sensors. In this paper, we report the preparation of a series of p-NiO-loaded n-ZnO NFs, namely (1-x)ZnO-xNiO (x = 0.03, 0.05, 0.7, 0.1, and 0.15 wt%), for hydrogen gas sensing experiments. Samples were prepared through the electrospinning technique followed by a calcination process. The sensing experiments showed that the sample with 0.05 wt% NiO loading resulted in the highest sensing performance at an optimal sensing temperature of 200 °C. The sensing mechanism is discussed in detail and contributions of the p-n heterojunctions, metallization of ZnO and catalytic effect of NiO on the sensing enhancements of an optimized gas sensor are analyzed. This study demonstrates the possibility of fabricating high-performance H2 sensors through the optimization of p-type metal oxide loading on the surfaces of n-type metal oxides.

High-Performance Nanowire Hydrogen Sensors by Exploiting the Synergistic Effect of Pd Nanoparticles and Metal-Organic Framework Membranes.

Herein, we report the fabrication of hydrogen gas sensors with enhanced sensitivity and excellent selectivity. The sensor device is based on the strategic combination of ZnO nanowires (NWs) decorated with palladium nanoparticles (Pd NPs) and a molecular sieve metal-organic framework (MOF) nanomembrane (ZIF-8). The Pd NPs permit the sensors to reach maximal signal responses, whereas the ZIF-8 overcoat enables for an excellent selectivity. Three steps were employed for the fabrication: (i) coating of a miniaturized sensor with vapor-grown ZnO NWs, (ii) decoration of these NWs with Pd NPs by atomic layer deposition, and (iii) partial solvothermal conversion of the tuned NWs surface to ZIF-8 nanomembrane. The microstructure and composition investigations of the ZIF-8/Pd/ZnO nanostructured materials confirmed the presence of both metallic Pd NPs and uniform ZIF-8 thin membrane layer. The integration of these nanomaterials within a miniaturized sensor device enabled the assessment of their performance for H2 detection at concentrations as low as 10 ppm in the presence of various gases such as C6H6, C7H8, C2H5OH, and CH3COCH3. Remarkably high-response signals of 3.2, 4.7, and 6.7 ( Ra/ Rg) have been measured for H2 detection at only 10, 30, and 50 ppm, whereas no noticeable response toward other tested gases was detected, thus confirming the excellent H2 selectivity obtained with such a sensor design. The results obtained showed that the performance of gas sensors toward H2 gas can be greatly increased by both the addition of Pd NPs and the use of ZIF-8 coating, acting as a molecular sieve membrane. Furthermore, the presented strategy could be extended toward the sensing of other species by a judicious choice of both the metallic NPs and MOF materials with tuned properties for specific molecule detection, thus opening a new avenue for the preparation of highly selective sensing devices.

Synthesis and gas sensing properties of membrane template-grown hollow ZnO nanowires.

One-dimensional, hollow nanostructured materials are among the most promising materials for sensing applications owing to their high surface area that facilitates the adsorption of target gases. Accordingly, for gas sensing studies, hollow ZnO nanowires (NWs) with different surface areas were successfully synthesized herein by using polycarbonate membranes with different pore sizes as templates, and deposition of ZnO via the atomic layer deposition technique. The sensing properties of the synthesized hollow ZnO NWs were examined for CO and NO2, revealing their comparative sensing performances with ZnO nanomaterials-based sensors reported in literature. This study highlights a novel way of synthesizing hollow ZnO NWs by using membrane template and their promising sensing properties as well.

Extraordinary improvement of gas-sensing performances in SnO2 nanofibers due to creation of local p-n heterojunctions by loading reduced graphene oxide nanosheets.

We propose a novel approach to improve the gas-sensing properties of n-type nanofibers (NFs) that involves creation of local p-n heterojunctions with p-type reduced graphene oxide (RGO) nanosheets (NSs). This work investigates the sensing behaviors of n-SnO2 NFs loaded with p-RGO NSs as a model system. n-SnO2 NFs demonstrated greatly improved gas-sensing performances when loaded with an optimized amount of p-RGO NSs. Loading an optimized amount of RGOs resulted in a 20-fold higher sensor response than that of pristine SnO2 NFs. The sensing mechanism of monolithic SnO2 NFs is based on the joint effects of modulation of the potential barrier at nanograin boundaries and radial modulation of the electron-depletion layer. In addition to the sensing mechanisms described above, enhanced sensing was obtained for p-RGO NS-loaded SnO2 NFs due to creation of local p-n heterojunctions, which not only provided a potential barrier, but also functioned as a local electron absorption reservoir. These mechanisms markedly increased the resistance of SnO2 NFs, and were the origin of intensified resistance modulation during interaction of analyte gases with preadsorbed oxygen species or with the surfaces and grain boundaries of NFs. The approach used in this work can be used to fabricate sensitive gas sensors based on n-type NFs.

A Case of Anaphylaxis Induced by Contact with Young Radish (Raphanus sativus L).

Young radish (Raphanus sativus L), a member of the mustard family (Cruciferae), is a common ingredient of Kimchi. Although few reports have described anaphylaxis to cruciferous vegetables, we report the case of anaphylaxis induced by contact with young radish. A 46-year-old female with a history of contact allergy to metal presented to our emergency room (ER) with dizziness, generalized eruption and gastrointestinal upset. Her symptoms developed after re-exposure to young radish while chopping it. Hypotensive blood pressures were noted. Three days prior, the patient had experienced generalized urticaria with pruritus immediately after chopping the fresh young radish, which resolved spontaneously. In the ER, her symptoms improved by the administration of epinephrine (0.3 mL), antihistamine (chlorpheniramine) and isotonic saline hydration. A skin prick test with young radish extract showed positive reactivity. The same skin test was negative in five adult controls. IgE-mediated hypersensitivity could be an important immunologic mechanism in the development of young radish-induced anaphylaxis.

Superoxide Dismutase Gene (SOD1, SOD2, and SOD3) Polymorphisms and Antituberculosis Drug-induced Hepatitis.

PURPOSE: Drug-induced liver injury (DILI) is a serious issue often leading to discontinuation of the proper regimen of antituberculosis drugs (ATD). Previous studies have suggested that antioxidant enzymes play an important role in DILI. METHODS: We explored whether polymorphisms in superoxide dismutase genes, including Cu/Zn superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2) and extracellular superoxide dismutase (SOD3) are associated with ATD-induced hepatitis. Genotype distributions of four single nucleotide polymorphisms (SNPs) in three genes (rs2070424, SOD1; rs4880, SOD2; rs2536512, and rs1799895, SOD3) were compared between 84 patients with ATD-induced hepatitis and 237 patients tolerant to ATD. RESULTS: Intron SNP rs2070424 of SOD1 showed a significant association with ATD-induced hepatitis. The frequency of genotypes carrying minor alleles (GA or GG) was significantly higher in the case group than that of controls (P=0.019, OR=2.26, 95% CI 1.14-4.49). For the other SNPs of SOD2 and SOD3, there were no differences in genotype frequencies between ATD-induced hepatitis and ATD-tolerant controls. CONCLUSIONS: These findings suggest that rs2070424 of SOD1 is significantly associated with ATD-induced hepatitis. This genetic variant may be a risk factor for ATD-induced hepatitis in individuals from Korea.

Suppression of Heme Oxygenase-1 by Prostaglandin E2-Protein Kinase A-A-Kinase Anchoring Protein Signaling Is Central for Augmented Cyclooxygenase-2 Expression in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages.

PURPOSE: Prostaglandin (PG) E2 is an immunomodulatory lipid mediator generated mainly via the cyclooxygenase-2 (COX-2) pathway from arachidonic acid at sites of infection and inflammation. A positive feedback loop of PGE2 on COX-2 expression is critical for homeostasis during toll-like receptor (TLR)-mediated inflammatory processes. The mechanism of PGE2-regulated COX-2 expression remains poorly understood. The low-molecular-weight stress protein heme oxygenase-1 (HO-1) contributes to the anti-inflammatory, anti-oxidant and anti-apoptotic response against environmental stress. METHODS: We explored the involvement of HO-1 on PGE2 regulation of LPS-induced COX-2 expression in RAW 264.7 macrophages. RESULTS: LPS-induced COX-2 expression in RAW 264.7 macrophages was enhanced by exogenous PGE2 or cyclic AMP (cAMP) analogue and was suppressed by a COX inhibitor (indomethacin), a protein kinase A (PKA) inhibitor (KT5720), and A kinase anchoring protein (AKAP) disruptors (Ht31 and RIAD). This result suggests that the stimulatory effects of endogenous and exogenous PGE2 on COX-2 expression are mediated by a cAMP-PKA-AKAP-dependent pathway. The induction of HO-1 was observed in LPS-stimulated RAW 264.7 macrophages. This induction was suppressed by exogenous PGE2 and enhanced by blockage of the endogenous PGE2 effect by the PKA inhibitor or AKAP disruptors. In addition, HO-1 induction by the HO activator copper protoporphyrin suppressed LPS-induced COX-2 expression, which was restored by the addition of exogenous PGE2. The induction of HO-1 inhibited LPS-induced NF-κB p-65 nuclear expression and translocation. CONCLUSIONS: AKAP plays an important role in PGE2 regulation of COX-2 expression, and the suppression of HO-1 by PGE2-cAMP-PKA-AKAP signaling helps potentiate the LPS-induced COX-2 expression through a positive feedback loop in RAW 264.7 macrophages.