133 research outputs found
Synthesis, Characterization and Activity of Palladium Catalysts on the Dual Support of Cerium and Aluminum Oxides
The effects of sequence of impregnation (Pd on cerium oxides -alumina and cerium oxides on Pd-alumina) and calcination temperature (500 ℃ and 850 ℃) on the catalytic oxidation of methane under lean conditions were investigated. The catalysts were prepared by a combination of impregnation, slurry and vortexing methods. The catalysts had 4.7 wt.% Pd and 10.7 wt.% Ce based on inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. The catalysts were characterized by pulse chemisorption, temperature programmed reduction (TPD), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS). The activity of the catalysts for methane combustion was measured in a fixed-bed flow reactor by flowing a gas mix (0.98 vol % methane, 4.01 vol % and balance nitrogen) through a catalytic bed. The temperature of the catalytic bed was controlled by a temperature -controlled tube furnace. The % methane in the effluent gas mix was measured by a gas chromatograph fitted with a flame ionization detector and a ‘Carbon Plot’ column. Palladium was present as PdO and PdOx x\u3e2+ and cerium as CeOx (+3 and +4 oxidation states) as per XPS analysis. The activity of the Pd/cerium oxides-alumina500C catalyst was higher than the cerium oxides/Pd-alumina500C catalyst at 250-500 ℃. Similar trends in the activity were seen for the two catalysts calcined at 850 ℃. Higher dispersion and lower particle size, and the presence of small Pd particles on alumina accounted for the higher catalytic activities of the Pd/cerium oxides-alumina500C and 850C catalysts. The lower activities of cerium oxides/Pd-alumina500C and 850C were primarily due to the embedment of Pd onto ceria due to strong PdO-CeOx interactions. This research implies that the sequence of impregnation and calcination temperature could alter catalytic properties and activity for methane combustion through PdO/PdOx -support interactions
Emergence of new topological gapless phases in the modified square-lattice Kitaev model
We investigate emergent topological gapless phases in the square-lattice
Kitaev model with additional hopping terms. In the presence of nearest-neighbor
hopping only, the model is known to exhibit gapless phases with two topological
gapless points. When the strength of the newly added next-nearest-neighbor
hopping is smaller than a certain value, qualitatively the same phase diagram
persists. We find that further increase of the extra hopping results in a new
topological phase with four gapless points. We construct a phase diagram to
clarify the regions of emergent topological gapless phases as well as
topologically trivial ones in the space of the chemical potential and the
next-nearest-neighbor hopping strength. We examine the evolution of the gapless
phases in the energy dispersions of the bulk as the chemical potential varies.
The topological properties of the gapless phases are characterized by the
winding numbers of the present gapless points. We also consider the ribbon
geometry to examine the corresponding topological edge states. It is revealed
that Majorana-fermion edge modes exist as flat bands in topological gapless
phases. We also perform the analytical calculation as to Majorana-fermion
zero-energy modes and discuss its implications on the numerical results
Synthesis and characterization of integrated layered nanocomposites for lithium ion batteries
The series of Li[NixMxLi1/3-xMn2/3-x]O2 cathodes, where M is cobalt or chromium with a wide compositional range x from 0 to 0.33, were prepared by hydroxide coprecipitation method with subsequent quenching. The sample structures were investigated using X-ray diffraction results which were indexed completely on the basis of a trigonal structure of space group R3m¯ with monoclinic C2/m phase as expected. The morphologies and electrochemical properties of the samples obtained were compared as the value of x and substituted transition metal. The particle sizes of cobalt-substituted Li[NixCoxLi1/3-xMn2/3-x]O2 samples are much smaller than those of the Li[NixCrxLi1/3-xMn2/3-x]O2 system. The electrode containing Li[NixCoxLi1/3-xMn2/3-x]O2 with x = 0.10 delivered a discharge capacity of above 200 mAh/g after 10 cycles due to the activation of Li2MnO3
EXIT: Extrapolation and Interpolation-based Neural Controlled Differential Equations for Time-series Classification and Forecasting
Deep learning inspired by differential equations is a recent research trend
and has marked the state of the art performance for many machine learning
tasks. Among them, time-series modeling with neural controlled differential
equations (NCDEs) is considered as a breakthrough. In many cases, NCDE-based
models not only provide better accuracy than recurrent neural networks (RNNs)
but also make it possible to process irregular time-series. In this work, we
enhance NCDEs by redesigning their core part, i.e., generating a continuous
path from a discrete time-series input. NCDEs typically use interpolation
algorithms to convert discrete time-series samples to continuous paths.
However, we propose to i) generate another latent continuous path using an
encoder-decoder architecture, which corresponds to the interpolation process of
NCDEs, i.e., our neural network-based interpolation vs. the existing explicit
interpolation, and ii) exploit the generative characteristic of the decoder,
i.e., extrapolation beyond the time domain of original data if needed.
Therefore, our NCDE design can use both the interpolated and the extrapolated
information for downstream machine learning tasks. In our experiments with 5
real-world datasets and 12 baselines, our extrapolation and interpolation-based
NCDEs outperform existing baselines by non-trivial margins.Comment: main 8 page
Raoultella ornithinolytica in a healthy, young person: rapidly progressive sinusitis with orbital and intracranial involvement
Raoultella ornithinolytica is an encapsulated, Gram-negative, nonmotile, rod belonging to the Enterobacteriaceae family. Infections involving the gastrointestinal tract and the hepatopancreatobiliary system are most frequently reported, especially in immunocompromised patients. The authors present an unusual case of acute complicated sinusitis with orbital and intracranial involvement caused by R. ornithinolytica. The infection was rapidly progressive, even though the patient was a healthy, young person without any co-morbidities. The patient’s condition improved after antibiotic treatment and multiple ophthalmic and sinus surgeries
Stabilizing Pd-cerium oxide-aluminum oxide catalysts for methane oxidation by reduction pretreatments
Pd-CeO2 based catalysts are state-of-the-art for methane oxidation, but deactivate due to Pd nanoparticle growth at high temperature. While encapsulation by CeO2 shells was reported to increase the stability of Pd nanoparticles (NPs), the established synthesis methods are not easily scalable. Here, we report the synthesis of PdO/CeOx/Al2O3 and CeOx/PdO/Al2O3 catalysts with improved stability for methane oxidation by sequential impregnation of Pd and Ce precursors on an Al2O3 support followed by reduction. The reduced catalysts displayed higher methane oxidation activity, and a lowering of the light-off temperature compared to the fresh calcined catalysts. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) chemical imaging of the reduced catalysts indicated a redispersion of cerium oxide on the support surface and anchoring of Pd nanoparticles by cerium oxide. After aging at high temperature (850 °C), the activity of the reduced CeOx/PdO/Al2O3 catalysts remained high, while the activity of the calcined catalysts dropped significantly. The results showed that simple reduction pretreatments could improve the catalytic activity and stability of the catalysts at both low and high reaction temperatures through changing Pd-Ce interactions, restructuring of the surface and changes in the nature and types of adsorbed species, as shown by HRTEM, EDS and operando diffuse reflectance infrared Fourier transform spectroscopy. We believe that the proposed strategy can be used as a scalable alternative to embedding of Pd NPs by CeO2 in core-shell systems for enhanced thermal stability in exhaust after treatment applications
Web-based design and analysis tools for CRISPR base editing
Background: As a result of its simplicity and high efficiency, the CRISPR-Cas system has been widely used as a genome editing tool. Recently, CRISPR base editors, which consist of deactivated Cas9 (dCas9) or Cas9 nickase (nCas9) linked with a cytidine or a guanine deaminase, have been developed. Base editing tools will be very useful for gene correction because they can produce highly specific DNA substitutions without the introduction of any donor DNA, but dedicated web-based tools to facilitate the use of such tools have not yet been developed.
Results: We present two web tools for base editors, named BE-Designer and BE-Analyzer. BE-Designer provides all possible base editor target sequences in a given input DNA sequence with useful information including potential off-target sites. BE-Analyzer, a tool for assessing base editing outcomes from next generation sequencing (NGS) data, provides information about mutations in a table and interactive graphs. Furthermore, because the tool runs client-side, large amounts of targeted deep sequencing data (< 1 GB) do not need to be uploaded to a server, substantially reducing running time and increasing data security. BE-Designer and BE-Analyzer can be freely accessed at http://www.rgenome.net/be-designer/ and http://www.rgenome.net/be-analyzer /, respectively.
Conclusion: We develop two useful web tools to design target sequence (BE-Designer) and to analyze NGS data from experimental results (BE-Analyzer) for CRISPR base editors
Bio-inspired Molecular Redesign of a Multi-redox Catholyte for High-Energy Non-aqueous Organic Redox Flow Batteries
Redox-active organic materials (ROMs) have recently attracted significant attention for redox flow batteries (RFBs) to achieve green and cost-efficient energy storage. In particular, multi-redox ROMs have shown great promise, and further tailoring of these ROMs would yield RFB technologies with the highest possible energy density. Here, we present a phenazine-based catholyte material, 5,10-bis(2-methoxyethyl)-5,10-dihydrophenazine (BMEPZ), that undergoes two single-electron redox reactions at high redox potentials (-0.29 and 0.50 V versus Fc/Fc(+)) with enhanced solubility (0.5 M in acetonitrile), remarkable chemical stability, and fast kinetics. Moreover, an all-organic flow battery exhibits cell voltages of 1.2 and 2.0 V when coupled with 9-fluorenone (FL) as an anolyte. It shows capacity retention of 99.94% per cycle over 200 cycles and 99.3% per cycle with 0.1 M and 0.4 M BMEPZ catholyte, respectively. Notably, the BMEPZ/FL couple results in the highest energy density (similar to 17 Wh L-1) among the non-aqueous all- organic RFBs reported to date
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