Asymmetric oxygen vacancies : the intrinsic redox active sites in metal oxide catalysts

This work was financially supported by the Tianjin Municipal Natural Science Foundation (Grant 17JCYBJC22600), MOE Key Laboratory of Advanced Energy Materials Chemistry (IRT13R30), and the Fundamental Research Funds for the Central Universities.To identify the intrinsic active sites in oxides or oxide supported catalysts is a research frontier in the fields of heterogeneous catalysis and material science. In particular, the role of oxygen vacancies on the redox properties of oxide catalysts is still not fully understood. Herein, some relevant research dealing with M1–O–M2 or M1–□–M2 linkages as active sites in mixed oxides, in oxide supported single‐atom catalysts, and at metal/oxide interfaces of oxide supported nanometal catalysts for various reaction systems is reviewed. It is found that the catalytic activity of these oxides not only depends on the amounts of oxygen vacancies and metastable cations but also shows a significant influence from the local environment of the active sites, in particular, the symmetry of the oxygen vacancies. Based on the recent progress in the relevant fields, an “asymmetric oxygen vacancy site” is introduced, which indicates an oxygen vacancy with an asymmetric coordination of cations, making oxygen “easy come, easy go,” i.e., more reactive in redox reactions. The establishment of this new mechanism would shed light on the future investigation of the intrinsic active sites in oxide and oxide supported catalysts.Publisher PDFPeer reviewe

PC-SNN: Supervised Learning with Local Hebbian Synaptic Plasticity based on Predictive Coding in Spiking Neural Networks

Deemed as the third generation of neural networks, the event-driven Spiking Neural Networks(SNNs) combined with bio-plausible local learning rules make it promising to build low-power, neuromorphic hardware for SNNs. However, because of the non-linearity and discrete property of spiking neural networks, the training of SNN remains difficult and is still under discussion. Originating from gradient descent, backprop has achieved stunning success in multi-layer SNNs. Nevertheless, it is assumed to lack biological plausibility, while consuming relatively high computational resources. In this paper, we propose a novel learning algorithm inspired by predictive coding theory and show that it can perform supervised learning fully autonomously and successfully as the backprop, utilizing only local Hebbian plasticity. Furthermore, this method achieves a favorable performance compared to the state-of-the-art multi-layer SNNs: test accuracy of 99.25% for the Caltech Face/Motorbike dataset, 84.25% for the ETH-80 dataset, 98.1% for the MNIST dataset and 98.5% for the neuromorphic dataset: N-MNIST. Furthermore, our work provides a new perspective on how supervised learning algorithms are directly implemented in spiking neural circuitry, which may give some new insights into neuromorphological calculation in neuroscience.Comment: 15 pages, 11fig

A survey comparing the attitudes toward perinatal bereavement care of nurses from three Asian cities

Caring for parents whose infant has died is extremely demanding, difficult, and stressful. In some situations, nurses may experience personal failure, feel helpless, and need to distance themselves from bereaved parents because they are unable to deal with the enormity of the parental feelings of loss. The aim of the study was to describe and compare attitudes toward perinatal bereavement care across a sample of nurses working in five obstetrics and gynecology settings from three Asian cities, as well as the factors associated with these attitudes. A survey was conducted, and 573 nurses were recruited from 2006 to 2007. The data were collected using the perinatal bereavement attitudes scale, which involves an 11-item self-report questionnaire. Nurses’ attitudes were mainly positive, but differed across cities, with the attitude of Jinan nurses being significantly more positive than nurses from the other two cities, and the attitude of Hong Kong nurses being significantly the lowest. Positive attitudes were associated with position, and nurses who were well informed of hospital policy and received training for bereavement care were statistically significantly more likely to have a positive attitude toward perinatal bereavement care. Although nurses’ attitudes to prenatal bereavement care differ significantly across the three Asian cities, they are generally similar. The differences observed could be related to the wider social, cultural, and organizational circumstances of nursing practice

Big Data Analytics in Immunology: A Knowledge-Based Approach

With the vast amount of immunological data available, immunology research is entering the big data era. These data vary in granularity, quality, and complexity and are stored in various formats, including publications, technical reports, and databases. The challenge is to make the transition from data to actionable knowledge and wisdom and bridge the knowledge gap and application gap. We report a knowledge-based approach based on a framework called KB-builder that facilitates data mining by enabling fast development and deployment of web-accessible immunological data knowledge warehouses. Immunological knowledge discovery relies heavily on both the availability of accurate, up-to-date, and well-organized data and the proper analytics tools. We propose the use of knowledge-based approaches by developing knowledgebases combining well-annotated data with specialized analytical tools and integrating them into analytical workflow. A set of well-defined workflow types with rich summarization and visualization capacity facilitates the transformation from data to critical information and knowledge. By using KB-builder, we enabled streamlining of normally time-consuming processes of database development. The knowledgebases built using KB-builder will speed up rational vaccine design by providing accurate and well-annotated data coupled with tailored computational analysis tools and workflow

The active oxygen species promoted catalytic oxidation of 5-hydroxymethyl-2-furfural on facet-specific Pt nanocrystals

This work was supported by Natural Science Foundation of Tianjin (Grant No. 17JCYBJC22600) and the Fundamental Research Funds for the Central Universities.The aerobic oxidation of alcohols and aldehydes over noble metal catalysts is a critical reaction for the catalytic conversion of carbohydrates into value-added chemicals from biomass. However, to fully understand the reaction mechanism, in particular the role of O2 and the generated active oxygen species in these reactions is still a challenging target. In the present work, the sub-10 nm Pt nanocrystals with cubic (Pt-NCs), octahedral (Pt-NOs) and spherical (Pt-NSs) morphologies were synthesized and used as catalysts in aerobic oxidation of HMF. Through experimental and computational investigations, the facet-dependent O2 conversion pathway and catalytic oxidation performance were discussed. The molecular O2 tends to be dissoci-ated to generate •OH on Pt(100) surface, but prefers to be reduced to •O2- on Pt(111) surface. Moreover, Pt-NCs enclosed by the {100} facets exhibited significantly enhanced catalytic activity than Pt-NOs enclosed by the {111} facets and Pt-NSs, in particular for alcohol oxidation step. Based on the experimental data and density functional theory (DFT) calculations, an active oxygen species promoted dehydrogenation mechanism for aerobic oxidation of HMF was proposed. The dehydrogena-tion of alcohol group is more favourable on the Pt(100) surface with an assistance of •OH, which are the dominant active oxygen species on the Pt(100) surface. We anticipate that this work would provide a new insight into the role of active oxy-gen species in aerobic oxidation of alcohols and aldehydes over noble metal catalysts.PostprintPeer reviewe

Effect of oxygen coordination environment of Ca-Mn oxides on catalytic performance of Pd supported catalysts for aerobic oxidation of 5-hydroxymethyl-2-furfural

This work was supported by Natural Science Foundation of Tianjin (Grant No. 17JCYBJC22600) and the Fundamental Research Funds for the Central Universities. Computational support was provided by the Beijing Computing Center (BCC).Four types of Ca-Mn oxides, including CaMnO3, CaMn2O4, CaMn3O6 and Ca2Mn3O8, have been prepared and used as supports for Pd nanoparticles. The oxygen activation capacity of these oxides and the catalytic activity of the oxide supported Pd nanocatalysts have been investigated using the aerobic oxidation of 5-hydroxymethyl-2-furfural as a model reaction. It is found that the local coordination environment of lattice oxygen sites plays a crucial role on their redox property and charge transfer ability from Pd nanoparticles to the support. In particular, the Ca-Mn oxide with lower oxygen coordination number, weaker metal-oxygen bonds and tunnel crystal structure, e.g. CaMn2O4, exhibits promoted oxygen activation capacity, and stronger electron transfer ability. Consequently, Pd/CaMn2O4 exhibits the highest catalytic activity among these catalysts, providing a promising yield of 2,5-furandicarboxylic acid. This work may shed light on the future investigation on the design of local structure of active oxygen sites in oxides or oxide supported catalysts for redox reactions.PostprintPeer reviewe

Covalently immobilized lipase on a thermoresponsive polymer with an upper critical solution temperature as an efficient and recyclable asymmetric catalyst in aqueous media

This work was financially supported by the National Natural Science Foundation of China (Grant No. 21203102), the Tianjin Municipal Natural Science Foundation (Grant No. 14JCQNJC06000), China Scholarship Council (Grant No. 201606200087), MOE (IRT13R30) and 111 Project (B12015).A thermoresponsive lipase catalyst with an upper critical solution temperature (UCST) of about 26 °C was exploited by covalent immobilization of an enzyme, Pseudomonas cepacia lipase (PSL), onto poly(acrylamide-co-acrylonitrile) via glutaraldehyde coupling. The experimental conditions for the PSL immobilization were optimized. The immobilized PSL was much more stable for wide ranges of temperature and pH than the free PSL. The material was also evaluated as an asymmetric catalyst in the kinetic resolution of racemic α-methylbenzyl butyrate at 55 °C in an aqueous medium and exhibited high catalytic performance and stability. Up to 50% conversion and 99.5% product enantiomeric excess were achieved, thus providing highly pure enantiomers. More importantly, this biocatalyst could be easily recovered by simple decantation for reuse based on temperature-induced precipitation. It showed good reusability and retained 80.5% of its original activity with a well reserved enantioselectivity in the 6th cycle. This work would shed light on the future development of new UCST-type enzyme catalysts.PostprintPeer reviewe

The linear and nonlinear inverse Compton scattering between microwaves and electrons in a resonant cavity

In a free space, the Sunyaev-Zel'dovich (SZ) effect is a small spectral distortion of the cosmic microwave background (CMB) spectrum caused by inverse Compton scattering of microwave background photons from energetic electrons in the plasma. However, the microwave does not propagate with a plane waveform in a resonant cavity, the inverse Compton scattering process is a little different from that in a free space. By taking the Fourier expansion of the microwave field in the cavity, the coefficients of the first-order and the higher-order terms describe the local-space effect on the linear and nonlinear inverse Compton scattering respectively. With our theoretical results, the linear or nonlinear inverse Compton scattering cross section between microwave photons and electrons has important applications on the energy calibration of the extremely energetic electron beam, the sources of the terahertz waves, the extreme ultra-violet (EUV) waves or the mid-infrared beams.Comment: 8 pages, 5 figure

Comparative Genomic Analysis and Phenotypic Characterization of Bronchoscope-Associated Klebsiella aerogenes

Bronchoscopes have been linked to outbreaks of nosocomial infections. The phenotypic and genomic profiles of bronchoscope-associated Klebsiella aerogenes isolates are largely unknown. In this work, a total of 358 isolates and 13 isolates were recovered from samples after clinical procedures and samples after decontamination procedures, respectively, over the five months. Antimicrobial susceptibility testing found seven K. aerogenes isolates exhibiting a low-level resistance to antimicrobial agents. Among seven K. aerogenes isolates, we found five sequence types (STs) clustered into three main clades. Collectively, this study described for the first time the phenotypic and genomic characteristics of bronchoscope-associated K. aerogenes

M3+O(-Mn4+)2 clusters in doped MnOx catalysts as promoted active sites for aerobic oxidation of 5-hydroxymethylfurfural

This work was supported by Tianjin Municipal Natural Science Foundation (No. 17JCYBJC22600), China Scholarship Council (No. 201606200096), and the Fundamental Research Funds for the Central Universities. Computational support was provided by the Beijing Computing Center (BCC).Based on various experimental results, M3+O(-Mn4+)2 clusters in (Fe, Co, Ni)-doped MnOx catalysts were identified as principal active sites for aerobic oxidation of 5-hydroxymethylfurfural due to their special property that makes oxygen to be easy come, easy go.PostprintPeer reviewe