Performance Analysis of Friction Stir Welded Lightweight Aluminum Alloy Sheet

The present research envisaged the performance analysis of a 1-mm thick 6061-T6 aluminum alloy sheet welded by the friction stir welding technique, using optical microscopy, micro-hardness measurement, a tensile test, a friction and wear test, and a salt spray corrosion test. It was found that the grain in the welded zone obtained was refined under each parameter. When the rotating speed of the tool was 15,000 rpm and the traveling speed of the tool was 300 mm·min-1, the tensile strength of the welded zone was highest, i.e. 74.8% of the base metal. Furthermore, the hardness distribution curve of the welded zone was of the 'W' type under each parameter, but the hardness value was lower than that of the base metal. The friction coefficient of the welded zone was lower than that of the base metal under each parameter, and the wear form was found to be mainly adhesive wear accompanied by abrasive wear. The welded zone and the base metal were subjected to salt spray corrosion after 12 hours under each parameter, which had a negative effect on the quality. However, after 12 hours of subsequent corrosion, the quality of each sample and the base material was not obvious

Route Redundancy-Based Network Topology Measure of Metro Networks

The metro system plays a very important role in the urban multimodal transportation system, yet it is susceptible to accidents. A well-designed metro system needs to provide alternative routes to travellers both in the disruptive events and the normal operating conditions for providing rerouting opportunities and balancing crowded lines. This paper provides a new dimension of assessing metro network performance—travellers’ route redundancy (or route diversity), which is defined as the number of behaviourally effective routes between each origin-destination (O-D) pair in the network. The route redundancy of metro network is evaluated by statistical indicators of the distribution of the O-D-level number of effective routes. Compared with the existing connectivity and accessibility measures of topology network performance, route redundancy is also based on the topology network, but it takes the travellers’ route choice into consideration. Specifically, the effective routes between each O-D pair would provide disaggregated information from the travellers’ perspective. Case studies in four metropolises in the world, i.e., Shanghai, Beijing, London, and Tokyo, are conducted to examine the predisaster preparedness of the four metro networks explicitly from the perspective of route redundancy. The results indicate that the London metro network has the best route redundancy performance in terms of the statistical indicators of the distribution of the O-D level number of effective routes. Furthermore, the results of route redundancy are compared with typical measures of topology network performance in terms of measuring connectivity and accessibility of metro networks. Their differences are attributed to the fact that the route redundancy measure considers the travellers’ O-D-level route choice beyond the pure network topology and the shortest path considerations of the existing measures. The route redundancy proposed in this paper could assist in evaluating the predisaster preparedness of current or planning metro networks from O-D level to network level. Document type: Articl

Influence of the Process Parameters on the Microhardness and the Wear Resistance of Friction Stir Processed H65 Copper Alloy

Friction stir processing (FSP) was used to modify a larger-size surface of H65 copper alloy. The influence of the traverse speed and the rotation speed on the microstructure, the microhardness and the wear resistance of the modified surface were analyzed. The wear mechanism of the modified H65 copper alloy was revealed. The results indicate that the grain size was greatly refined after FSP compared with the parent metal and that the grain size increased with the increment of the rotation speed. The average microhardness of the modified surface was higher than that of the parent metal. The average microhardness had a highest value of 174.13 HV when the traverse speed was 200 mm/min and the rotation speed was 200 rpm, i.e., 21% higher than that of the parent metal. The average microhardness decreased with the increase of the rotation speed. When the traverse speed was 200 mm/min and the rotation speed was 600 rpm, the average friction coefficient of the modified surface was the smallest (0.3213), which was lower than that of the parent metal (0.3810). The wear mechanism of the H65 copper alloy modified by FSP was mainly adhesive wear accompanied by local abrasive wear

Influence of the Process Parameters on the Microhardness and the Wear Resistance of Friction Stir Processed H65 Copper Alloy

Friction stir processing (FSP) was used to modify a larger-size surface of H65 copper alloy. The influence of the traverse speed and the rotation speed on the microstructure, the microhardness and the wear resistance of the modified surface were analyzed. The wear mechanism of the modified H65 copper alloy was revealed. The results indicate that the grain size was greatly refined after FSP compared with the parent metal and that the grain size increased with the increment of the rotation speed. The average microhardness of the modified surface was higher than that of the parent metal. The average microhardness had a highest value of 174.13 HV when the traverse speed was 200 mm/min and the rotation speed was 200 rpm, i.e., 21% higher than that of the parent metal. The average microhardness decreased with the increase of the rotation speed. When the traverse speed was 200 mm/min and the rotation speed was 600 rpm, the average friction coefficient of the modified surface was the smallest (0.3213), which was lower than that of the parent metal (0.3810). The wear mechanism of the H65 copper alloy modified by FSP was mainly adhesive wear accompanied by local abrasive wear

Reaction And Characterization Of Low-Temperature Effect Of Transition Nanostructure Metal Codoped Scr Catalyst

Typical p-type semiconductor MnO codoped with n-type semiconductors such as CeO2 and V2O5 was reported to achieve high efficiency in catalytic NO removal by NH3. In this paper, we present novel Mn-Ce codoped V2O5/TiO2 catalyst which exhibited an excellent NO conversion efficiency of 90% at 140°C. By using this codoped catalyst, the best low-temperature activity was greatly decreased when compared with single Mn- or Ce-doped catalyst. According to the characterization results from BET, XRD, and XPS, the codoped catalyst was composed of both CeO2 and amorphous Mn. The electron circulation formed between doping elements is believed to promote the electron transfer, which may be one of the reasons for excellent low-temperature denitration performance

Shape of the concentration–response association between fine particulate matter pollution and human mortality in Beijing, China, and its implications for health impact assessment, The

Includes bibliographical references (pages 107009-12-107009-14).Publisher version: https://doi.org/10.1289/EHP4464.Background: Studies found approximately linear short-term associations between particulate matter (PM) and mortality in Western communities. However, in China, where the urban PM levels are typically considerably higher than in Western communities, some studies suggest nonlinearity in this association. Health impact assessments (HIA) of PM in China have generally not incorporated nonlinearity in the concentration–response (C-R) association, which could result in large discrepancies in estimates of excess deaths if the true association is nonlinear. Objectives: We investigated nonlinearity in the C-R associations between with PM with aerodynamic diameter ≤2.5μm (PM2.5) and mortality in Beijing, China, and the sensitivity of HIA to linearity assumptions. Methods: We modeled the C-R association between PM2.5 and cause-specific mortality in Beijing, China (2009–2012), using generalized linear models (GLM). PM2.5 was included through either linear, piecewise-linear, or spline functions to investigate evidence of nonlinearity. To determine the sensitivity of HIA to linearity assumptions, we estimated PM2.5-attributable deaths using both linear- and nonlinear-based C-R associations between PM2.5 and mortality. Results: We found some evidence that, for nonaccidental and circulatory mortality, the shape of the C-R association was relatively flat at lower concentrations of PM2.5, but then had a positive slope at higher concentrations, indicating nonlinearity. Conversely, the shape for respiratory mortality was positive and linear at lower concentrations of PM2.5, but then leveled off at the higher concentrations. Estimates of excess deaths attributable to short-term PM2.5 exposure were, in some cases, very sensitive to the linearity assumption in the association, but in other cases robust to this assumption. Conclusions: Our results demonstrate some evidence of nonlinearity in PM2.5–mortality associations and that an assumption of linearity in this association can influence HIAs, highlighting the importance of understanding potential nonlinearity in the PM2.5–mortality association at the high concentrations of PM2.5 in developing megacities like Beijing. https://doi.org/10.1289/EHP446

Reaction and Characterization of Low-Temperature Effect of Transition Nanostructure Metal Codoped SCR Catalyst

Typical p-type semiconductor MnOx codoped with n-type semiconductors such as CeO2 and V2O5 was reported to achieve high efficiency in catalytic NOx removal by NH3. In this paper, we present novel Mn-Ce codoped V2O5/TiO2 catalyst which exhibited an excellent NO conversion efficiency of 90% at 140°C. By using this codoped catalyst, the best low-temperature activity was greatly decreased when compared with single Mn- or Ce-doped catalyst. According to the characterization results from BET, XRD, and XPS, the codoped catalyst was composed of both CeO2 and amorphous Mn. The electron circulation formed between doping elements is believed to promote the electron transfer, which may be one of the reasons for excellent low-temperature denitration performance

Metabolomic Analysis of Alfalfa (Medicago sativa L.) Root-Symbiotic Rhizobia Responses under Alkali Stress

Alkaline salts (e.g., NaHCO3 and Na2CO3) causes more severe morphological and physiological damage to plants than neutral salts (e.g., NaCl and Na2SO4) due to differences in pH. The mechanism by which plants respond to alkali stress is not fully understood, especially in plants having symbotic relationships such as alfalfa (Medicago sativa L.). Therefore, a study was designed to evaluate the metabolic response of the root-nodule symbiosis in alfalfa under alkali stress using comparative metabolomics. Rhizobium-nodulized (RI group) and non-nodulized (NI group) alfalfa roots were treated with 200 mmol/L NaHCO3 and, roots samples were analyzed for malondialdehydyde (MDA), proline, glutathione (GSH), superoxide dismutase (SOD), and peroxidase (POD) content. Additionally, metabolite profiling was conducted using gas chromatography combined with time-of-flight mass spectrometry (GC/TOF-MS). Phenotypically, the RI alfalfa exhibited a greater resistance to alkali stress than the NI plants examined. Physiological analysis and metabolic profiling revealed that RI plants accumulated more antioxidants (SOD, POD, GSH), osmolytes (sugar, glycols, proline), organic acids (succinic acid, fumaric acid, and alpha-ketoglutaric acid), and metabolites that are involved in nitrogen fixation. Our pairwise metabolomics comparisons revealed that RI alfalfa plants exhibited a distinct metabolic profile associated with alkali putative tolerance relative to NI alfalfa plants. Data provide new information about the relationship between non-nodulized, rhizobium-nodulized alfalfa and alkali resistance