496 research outputs found
N- and S-doped mesoporous carbon as metal-free cathode catalysts for direct biorenewable alcohol fuel cells
Nitrogen and sulfur were simultaneously doped into the framework of mesoporous CMK-3 as metal-free catalysts for direct biorenewable alcohol fuel cells. Glucose, NH3, and thiophene were used as carbon, nitrogen and sulfur precursors, respectively, to prepare mesoporous N-S-CMK-3 with uniform mesopores and extra macropores, resulting in good O2 diffusion both in half cell and alcohol fuel cell investigations. Among all investigated CMK-3 based catalysts, N-S-CMK-3 prepared at 800 °C exhibited the highest ORR activity with the onset potential of 0.92 V vs. RHE, Tafel slope of 68 mV decâ1, and 3.96 electron transfer number per oxygen molecule in 0.1 M KOH. The alkaline membrane-based direct alcohol fuel cell (DAFC) with N-S-CMK-3 cathode displayed 88.2 mW cmâ2 peak power density without obvious O2 diffusion issue, reaching 84% initial performance of that with a Pt/C cathode. The high catalyst durability and fuel-crossover tolerance led to stable performance of the N-S-CMK-3 cathode DAFC with 90.6 mW cmâ2 peak power density after 2 h operation, while the Pt/C cathode-based DAFC lost 36.9% of its peak power density. The high ORR activity of N-S-CMK-3 can be attributed to the synergistic effect between graphitic-N and S (CâSâC structure), suggesting great potential to use N-S-CMK-3 as an alternative to noble metal catalysts in the fuel cell cathode
Social Media in Dynamic Learning: Logistics and Influential Factors
Educators have been using social media to enrich learning activities and promote interactive and collaborative learning. Under the context of dynamic learning â the way that 21st centuryâs learners learn, the new challenges are: how educators design such a setting to effectively integrate certain social media tools to improve learning, and what the influential factors might be that educators need to focus during the design. In this article, we employ the concept âlogisticsâ to explain and redefine dynamic design, dynamic learning, and dynamic thinking, which furthermore formulate the framework of the study. This article presents a critical content review of current literature, and an analysis of 276 cases located from the literature on seven factors (Information Logistics, Technology Logistics, Overall Design Logistics, Collaborative Learning, Active Stimulation, Motivation, and Objective-Driven Activities) regarding their influence on the success of social medial supported learning experiences. All seven factors were found to be significant and included in a static predictive model. An in-depth comprehension of this static predictive model is provided, based on which a new dynamic model is proposed
Polybenzimidazole (PBI) Functionalized Nanographene as Highly Stable Catalyst Support for Polymer Electrolyte Membrane Fuel Cells (PEMFCs)
Nanoscale graphenes were used as cathode catalyst supports in proton exchange membrane fuel cells (PEMFCs). Surface-initiated polymerization that covalently bonds polybenzimidazole (PBI) polymer on the surface of graphene supports enables the uniform distribution of the Pt nanoparticles, as well as allows the sealing of the unterminated carbon bonds usually present on the edge of graphene from the chemical reduction of graphene oxide. The nanographene effectively shortens the length of channels and pores for O2 diffusion/water dissipation and significantly increases the primary pore volume. Further addition of p-phenyl sulfonic functional graphitic carbon particles as spacers, increases the specific volume of the secondary pores and greatly improves O2 mass transport within the catalyst layers. The developed composite cathode catalyst of Pt/PBI-nanographene (50 wt%) + SO3H-graphitic carbon black demonstrates a higher beginning of life (BOL) PEMFC performance as compared to both Pt/PBI-nanographene (50 wt%) and Pt/PBI-graphene (50 wt%) + SO3H-graphitic carbon black (GCB). Accelerated stress tests show excellent support durability compared to that of traditional Pt/Vulcan XC72 catalysts, when subjected to 10,000 cycles from 1.0 V to 1.5 V. This study suggests the promise of using PBI-nanographene + SO3H-GCB hybrid supports in fuel cells to achieve the 2020 DOE targets for transportation applications
Off-hour admission and mortality risk for 28 specific diseases: A systematic review and meta-analysis of 251 cohorts
Background: A considerable amount of studies have examined the relationship between off-hours (weekends and nights) admission and mortality risk for various diseases, but the results remain equivocal. Methods and Results: Through a search of EMBASE, PUBMED, Web of Science, and Cochrane Database of Systematic Reviews, we identified cohort studies that evaluated the association between off-hour admission and mortality risk for disease. In a random effects meta-analysis of 140 identified articles (251 cohorts), off-hour admission was strongly associated with increased mortality for aortic aneurysm (odds ratio [OR], 1.52; 95% confidence interval, 1.30-1.77), breast cancer (1.50, 1.21-1.86), leukemia (1.45, 1.17-1.79), respiratory neoplasm (1.32, 1.20-1.26), pancreatic cancer (1.32, 1.12-1.56), malignant neoplasm of genitourinary organs (1.27, 1.08-1.49), colorectal cancer (1.26, 1.07-1.49), pulmonary embolism (1.20, 1.13-1.28), arrhythmia and cardiac arrest (1.19, 1.09-1.29), and lymphoma (1.19, 1.06-1.34). Weaker (OR<1.19) but statistically significant association was noted for renal failure, traumatic brain injury, heart failure, intracerebral hemorrhage, subarachnoid hemorrhage, stroke, gastrointestinal bleeding, myocardial infarction, chronic obstructive pulmonary disease, and bloodstream infections. No association was found for hip fracture, pneumonia, intestinal obstruction, aspiration pneumonia, peptic ulcer, trauma, diverticulitis, and neonatal mortality. Overall, Off-hour admission was associated with increased mortality for 28 diseases combined (OR, 1.11; 95% confidence interval, 1.10-1.13).Conclusions: Off-hour admission is associated with increased mortality risk, and the associations varied substantially for different diseases. Specialists, nurses, as well as hospital administrators and health policy makers can take these findings into consideration to improve the quality and continuity of medical services
Sequential Algorithm Based on Number Theoretic Method for Statistical Tolerance Analysis and Synthesis
Heterostructured Bismuth Vanadate/Cobalt Phosphate Photoelectrodes Promote TEMPOâMediated Oxidation of 5âHydroxymethylfurfural
Motivated by replacing the kinetically unfavorable oxygen evolution reaction (OER) and producing valueâadded products in photoelectrochemical cells (PECs), we report that bismuth vanadate (BiVO4) photoelectrodes modified with a cobalt phosphate (CoPi) overlayer facilitate 2,2,6,6âtetramethylpiperidineâ1âoxyl (TEMPO)âmediated selective oxidation of 5âhydroxymethylfurfural (HMF). CoPi layers with sufficient thickness were found to reduce the potential required for TEMPO oxidation by 0.5â
V, as well as increase charge injection efficiency sevenfold compared to BiVO4 without CoPi. Furthermore, the undesired OER was completely suppressed when using the heterostructured photoanodes. Transient photocurrent measurements suggested that CoPi alleviates recombination losses resulting from the back reduction of oxidized TEMPO. The PECs with BiVO4/CoPi bilayer achieved 88â% yield to 2,5âfurandicarboxylic acid (FDCA) from HMF oxidation under mild conditions, whereas \u3c1â% FDCA was generated with BiVO4. These findings suggest that suppression of the back reduction process substantially improves the efficiency of the oxidation, giving a potential route to more efficient solar fuel/chemical production
Dynamic analysis of Th1/Th2 cytokine concentration during antiretroviral therapy of HIV-1/HCV co-infected Patients
<p>Abstract</p> <p>Background</p> <p>Co-infection with hepatitis C (HCV) is very common in human immunodeficiency virus 1 (HIV-1) infected patients. Although HIV co-infection clearly accelerates progression of HCV-related fibrosis and liver disease, controversy remains as to the impact of HCV on HIV disease progression in co-infected patients. HIV can cause immune dysfunction, in which the regulatory function of T helper (Th) cells is very essential. Moreover, cytokines derived from Th cells play a prominent role in viral infection. Investigating the functional changes of Th1 and Th2 cells in cytokine level can improve the understanding of the effect of co-infected HCV on HIV infection.</p> <p>Methods</p> <p>In this study, we measured the baseline Th1/Th2 cytokine concentration in sera by using flow cytometry in HIV/HCV co-infection, HIV mono-infection, HCV mono-infection, and healthy control group, as well as the dynamic changes of these cytokine levels after receiving highly active antiretroviral therapy (HAART).</p> <p>Results</p> <p>The ratio of Th1 and Th2 cytokine concentration in HIV/HCV co-infection was higher than HCV mono-infection and healthy control group, while lower than HIV mono-infection group. After HAART was initiated, the Th1/Th2 ratio of HIV/HCV co-infection group decreased to the same level of healthy control, while HIV mono-infection group was still higher than the control group.</p> <p>Conclusions</p> <p>There was no significant evidence showing co-infected with HCV had negative effect on HIV related diseases. However, co-infected with HCV can decrease Th1/Th2 ratio by affecting Th1 cytokine level, especially the secretion of IFN-Îł. With the initiation of HAART, Th1 and Th2 cytokine levels were progressively reduced. HIV was the main stimulating factor of T cells in HIV/HCV co-infection group.</p
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