The key bottleneck of applying Pd catalysts in fuel cells is their low activity and poor stability during the oxygen reduction reaction (ORR) although less precious Pd is still a promising ...alternative to Pt. Hence, new strategies to improve the performance of Pd in the ORR need to be developed. In this study, supported Pd (3.6 nm in average) catalysts on TiO2 with and without oxygen vacancies (VO) have been prepared via facile pyrolysis. Compared with commercial Pt/C (20 wt%) and Pd/TiO2 catalysts, Pd/TiO2-VO (10 wt%) demonstrated superior oxygen reduction activity, better durability, and higher methanol tolerance capability in alkaline solution. By means of experimental characterizations (ESR and XPS) and density functional theory (DFT) calculations, electron transfer from TiO2-VO to Pd nanoparticles (NPs) led to an electron-rich Pd surface and strong metal–support interactions (SMSIs). The electron-rich Pd NPs enhanced the adsorptions of key intermediates, lowered the Gibbs free energy of the ORR, and improved the ORR activity. SMSIs between Pd NPs and TiO2-VO endowed the catalyst with excellent stability and immunity to methanol poisoning. Therefore, the electron transfer from TiO2-VO to Pd NPs plays a crucial role in promoting the ORR performance of Pd-based electrocatalysts, which may be a new strategy to design high-performance ORR catalysts.
•A bond-slip model considering freeze-thaw damage effect of concrete is developed.•The proposed model incorporates most factors considered, including freeze-thaw damage level of concrete, concrete ...properties, rebar properties, and transverse confinements.•A steel stress-slip model is derived from the proposed model.•The steel model is implemented into a fiber beam-column model using the zero-length section element in OpenSees.•The seismic performance of the frozen-thawed reinforced concrete column is modeled by the proposed fiber model.
The bonding behavior between concrete and steel bar may be severely deteriorated due to freeze-thaw damage of concrete, which may significantly affect the seismic performance of the reinforced concrete structures. This paper presents a novel bond-slip model considering freeze-thaw damage effect of concrete and apply it into the fiber model. The proposed model is developed by modifying an existing bond-slip model to consider the freeze-thaw damage effect of the concrete. The freeze-thaw damage effect of the concrete on the bond behavior is considered to be caused by the deterioration of both material strength and cover confinement of the concrete. The reliability and accuracy of the proposed model in capturing the freeze-thaw damage effect of the concrete on the bond stress-slip relationship are verified by comparison with pull-out tests data and existing models. Then, the steel stress-slip model is derived from the proposed bond-slip model based on the infinitesimal procedure. The derived steel stress-slip model is implemented into a fiber model that considers the freeze-thaw induced uneven damage along the member section. The general framework for applying the proposed model to a fiber beam-column element model is established. The proposed fiber model is validated by the experimental results and existing fiber model without incorporating the bond-slip effect. Excellent accuracy is observed between the model results and the experimental results. The fiber model without incorporating the bond-slip effect may overestimate the seismic performance of the freeze-thaw damaged reinforced concrete column. The results confirm that the proposed fiber model can comprehensively incorporate the degradation of uneven material strength and the deterioration of the bond behavior due to freeze-thaw damage effect of concrete.
•A simple and efficient reinforcement model considering slip effect is developed.•The rebar strain is revised in tensile stage to consider the reinforcement slip.•The elastic modulus of the steel bar ...is reduced in model.•The model is implemented into a fiber beam-column element model using OpenSEES.•The effects of key parameters on the column slip displacement are investigated.
Reinforcement slip in the beam-column joint or column footing may significantly influence the lateral displacement of a reinforced concrete (RC) column. A simple and efficient reinforcement model to consider the reinforcement slip effect is presented in this study. The proposed model utilizes a bilinear stress-strain relationship which assumes the increase in rebar strain contributed by reinforcement slip in tensile stage. The slip is calculated by the assumption of stepped bond stress distribution along development length. Then the proposed model is simplified by an extensive parametric investigation. After that, the proposed model is implemented into a fiber beam-column element model. The results from the modified fiber model are compared with the test results of RC columns and compared with the results from the conventional fiber model and zero-length fiber model. The modified fiber model agrees well with the experimental results in the column stiffness, followed by the zero-length fiber model. However, the conventional fiber model may significantly overestimate the column stiffness. Moreover, the modified fiber model shows a good accuracy in simulating the total lateral displacement of the column and shows success in capturing the lateral displacement contributed by reinforcement slip deformation. The results confirm the reliability of the proposed model for both section and member level. Finally, a comprehensive parametric study is accomplished to evaluate the effects of concrete, rebar, section, and axial load properties on the lateral displacement response of an RC column contributed by reinforcement slip deformation.
The concept of using multiple models to cope with transients which arise in adaptive systems with large parametric uncertainties was introduced in the 1990s. Both switching between multiple fixed ...models, and switching and tuning between fixed and adaptive models was proposed, and the stability of the resulting schemes was established. In all cases, the number of models needed is generally large (c n where n is the dimension of the parameter vector and c an integer), and the models do not "cooperate" in any real sense. In this paper, a new approach is proposed which represents a significant departure from past methods. First, it requires ( n +1) models (in contrast to c n ) which is significantly smaller, when " n " is large. Second, while each of the ( n +1) models chosen generates an estimate of the plant parameter vector, the new approach provides an estimate which depends on the collective outputs of all the models, and can be viewed as a time-varying convex combination of the estimates. It is then shown that control based on such an estimate results in a stable overall system. Further, arguments are given as to why such a procedure should result in faster convergence of the estimate to the true value of the plant parameter as compared to conventional adaptive controllers, resulting in better performance. Simulation studies are included to practically verify the arguments presented, and demonstrate the improvement in performance.
•3D Ag2O–Ag/TiO2 composites have been synthesized through a facile method.•3D Ag2O–Ag/TiO2 composites exhibit large photocatalytic adsorption capacity, high selectivity, and excellent trace removal ...performance of I− under visible light.•3D Ag2O–Ag/TiO2 composites could be easily separated and regenerated.•The adsorption capacity of Ag2O for I− is enlarged 4.4 times by the photooxidation of Ag/TiO2.•The cooperative effects mechanism between Ag2O and Ag/TiO2 is proposed and verified.
Three-dimensional Ag2O and Ag co-loaded TiO2 (3D Ag2O–Ag/TiO2) composites have been synthesized through a facile method, characterized using SEM, EDX, TEM, XRD, XPS, UV–vis DRS, BET techniques, and applied to remove radioactive iodide ions (I−). The photocatalytic adsorption capacity (207.6mg/g) of the 3D Ag2O–Ag/TiO2 spheres under visible light is four times higher than that in the dark, which is barely affected by other ions, even in simulated salt lake water where the concentration of Cl− is up to 590 times that of I−. The capability of the composites to remove even trace amounts of I− from different types of water, e.g., deionized or salt lake water, is demonstrated. The composites also feature good reusability, as they were separated after photocatalytic adsorption and still performed well after a simple regeneration. Furthermore, a mechanism explaining the highly efficient removal of radioactive I− has been proposed according to characterization analyses of the composites after adsorption and subsequently been verified by adsorption and desorption experiments. The proposed cooperative effects mechanism considers the interplay of three different phenomena, namely, the adsorption performance of Ag2O for I−, the photocatalytic ability of Ag/TiO2 for oxidation of I−, and the readsorption performance of AgI for I2.
Recently, many approaches were applied for assembling graphene sheets into a three-dimensional structure. However, it is still a great challenge to obtain a three-dimensional macroporous graphene ...network with high mechanical strength after drying. Herein, an ammonia strengthened three-dimensional graphene aerogel was prepared. Based on graphene chemistry and ice physics, the mechanical strength of graphene aerogel was improved greatly when the graphene hydrogel was treated by ammonia solution at an ambient temperature. The results demonstrated that the three-dimensional structure of graphene aerogels was destroyed thoroughly without ammonia solution treatment; conversely, the three-dimensional structure was maintained and the compressive strength was improved to 152 kPa at the static load after it was treated by ammonia solution at 90 °C for only 1 h. This phenomenon is due to two reasons: (1) the low freezing point of ammonia solution, which effectively retarded its freezing and then kept the porous structure undestroyed; (2) the reaction between ammonia and graphene hydrogel, which brought some covalent bonds among graphene sheets. We believe our efforts may pave the way for the development and application of three-dimensional graphene based materials.
Abstract
Rare earth (RE
3+
)-doped phosphors generally suffer from thermal quenching, in which their photoluminescence (PL) intensities decrease at high temperatures. Herein, we report a class of ...unique two-dimensional negative-thermal-expansion phosphor of Sc
2
(MoO
4
)
3
:Yb/Er. By virtue of the reduced distances between sensitizers and emitters as well as confined energy migration with increasing the temperature, a 45-fold enhancement of green upconversion (UC) luminescence and a 450-fold enhancement of near-infrared downshifting (DS) luminescence of Er
3+
are achieved upon raising the temperature from 298 to 773 K. The thermally boosted UC and DS luminescence mechanism is systematically investigated through in situ temperature-dependent Raman spectroscopy, synchrotron X-ray diffraction and PL dynamics. Moreover, the luminescence lifetime of
4
I
13/2
of Er
3+
in Sc
2
(MoO
4
)
3
:Yb/Er displays a strong temperature dependence, enabling luminescence thermometry with the highest relative sensitivity of 12.3%/K at 298 K and low temperature uncertainty of 0.11 K at 623 K. These findings may gain a vital insight into the design of negative-thermal-expansion RE
3+
-doped phosphors for versatile applications.
A microarray‐based high‐throughput screening of human circulating circular RNA (circRNA) was applied with five patients newly diagnosed with hepatocellular carcinoma (HCC), five patients with ...HBV‐positive chronic hepatitis (CH) and five healthy controls (NC) enrolled. The plasma of HCC patients after hepatectomy was also collected. After multiple staged validation, we obtained five circRNAs as candidate. Based on the stratified risk score analysis, three increased circRNAs including circ_0009582, circ_0037120 and circ_0140117 were confirmed as candidate circulating fingerprints for distinguishing HCC from CH or NC group. With the combination of AFP, higher sensitivity and specificity were further guaranteed, suggesting that circ_0009582, circ_0037120 and circ_0140117 may serve as potential biomarkers for predicting the occurrence of HCC in patients with HBV infection.
Electrocatalytic Ammonia Synthesis Process on the Mo2TiC2 MXene.
Display omitted
•Nineteen different possible pathways (five association pathway and fourteen dissociation pathway) analyzed by DFT ...calculation and Gibbs free energy calculation.•Valid N2-philicity, N≡N triple bond of the N2 molecule (the optimal distance) is sufficiently activated, from 1.11 Å to 1.268Å•Mo2TiC2 MXene can reduce the overpotential by changing the reaction pathway.•Mo2TiC2 as an ordered, double transition metals carbides is an eligible electrocatalyst for the NRR
Electrocatalytic ammonia synthesis provides an energy-efficient alternative to the Haber−Bosch process. The aim is to find promising electrocatalysts which are able to change the reaction pathway and reduce the overpotential. Here, based on density functional theory, a comprehensive mechanism study of the N2 activation and NH3 synthesis on the Mo2TiC2 MXenes is presented. For catalytic reaction mechanism, nineteen different possible pathways are screened for the lowest overpotential, where the corresponding potential-determining step are compared by Gibbs free energy calculation. The result reveals Mo2TiC2 MXenes exhibit both valid N2-philicity and high catalytic activity for electrocatalytic ammonia synthesis through a dissociation mechanism with a low overpotential of 0.26 V. Further, the competing reaction of H2 evolution is simultaneously suppressed which shows a relatively high potentials of 0.74 V. This study shows a brand new material for catalyzing NH3 synthesis under ambient conditions and provides the theory background to reduce the overpotential by changing the reaction pathway.
Plants are known to respond to Ultraviolet-B radiation (UV-B: 280-320 nm) by generating phenolic metabolites which absorbs UV-B light. Phenolics are extraordinarily abundant in
leaves and are ...considered, together with pleasant volatile terpenoids, as primary flavor determinants in tea beverages. In this study, we focused on the effects of UV-B exposure (at 35 μW cm
for 0, 0.5, 2, and 8 h) on tea transcriptional and metabolic alterations, specifically related to tea flavor metabolite production. Out of 34,737 unigenes, a total of 18,081 differentially expressed genes (DEGs) due to UV-B treatments were identified. Additionally, the phenylpropanoid pathway was found as one of the most significantly UV-B affected top 20 KEGG pathways while flavonoid and monoterpenoid pathway-related genes were enhanced at 0.5 h. In the UVR8-signal transduction pathway,
was suppressed at both short and long exposure of UV-B with genes downstream differentially expressed. Divergent expression of
at different treatments could have differentially altered structural and regulatory genes upstream of flavonoid biosynthesis pathways. Suppression of
at 0.5 h could have led to the up-regulation of structural
, and
genes resulting in accumulation of specialized metabolites at a shorter duration of UV-B exposure. Specialized metabolite profiling revealed the correlated alterations in the abundances of catechins and some volatile terpenoids in all the treatments with significant accumulation of specialized metabolites at 0.5 h treatment. A significant increase in specialized metabolites at 0.5 h treatment and no significant alteration observed at longer UVB treatment suggested that shorter exposure to UV-B led to different display in gene expression and accumulation of specialized metabolites in tea shoots in response to UV-B stress. Taken together, our results indicated that the UV-B treatment applied in this study differentially altered the UVR8-signal transduction, flavonoid and terpenoid pathways at transcriptional and metabolic levels in tea plants. Our results show strong potential for UV-B application in flavor improvement in tea at the industrial level.
PDF
