Developing high‐performance, low‐cost, and robust bifunctional electrocatalysts for overall water splitting is extremely indispensable and challenging. It is a promising strategy to couple highly ...active precious metals with transition metals as efficient electrocatalysts, which can not only effectively reduce the cost of the preparation procedure, but also greatly improve the performance of catalysts through a synergistic effect. Herein, Ru and Ni nanoparticles embedded within nitrogen‐doped carbon nanofibers (RuNi‐NCNFs) are synthesized via a simple electrospinning technology with a subsequent carbonization process. The as‐formed RuNi‐NCNFs represent excellent Pt‐like electrocatalytic activity for the hydrogen evolution reaction (HER) in both alkaline and acidic conditions. Furthermore, the RuNi‐NCNFs also exhibit an outstanding oxygen evolution reaction (OER) activity with an overpotential of 290 mV to achieve a current density of 10 mA cm−2 in alkaline electrolyte. Strikingly, owing to both the HER and OER performance, an electrolyzer with RuNi‐NCNFs as both the anode and cathode catalysts requires only a cell voltage of 1.564 V to drive a current density of 10 mA cm−2 in an alkaline medium, which is lower than the benchmark of Pt/C||RuO2 electrodes. This study opens a novel avenue toward the exploration of high efficient but low‐cost electrocatalysts for overall water splitting.
A facile strategy based on electrospinning and a postcarbonization process is demonstrated to prepare carbon nanofibers incorporating Ru and Ni nanoparticles, which exhibits admirable Pt‐like hydrogen evolution reaction activity and superior oxygen evolution reaction performance. The electrolyzer with this hybrid as both anode and cathode displays a remarkable electrocatalytic activity and outstanding long‐term durability, which outperforms the commercial Pt/C||RuO2 electrocatalyst.
Clusters, filaments, sheets, and voids are the building blocks of the cosmic web. Forming dark matter halos respond to these different large-scale environments, and this in turn affects the ...properties of galaxies hosted by the halos. It is therefore important to understand the systematic correlations of halo properties with the morphology of the cosmic web, as this informs both about galaxy formation physics and possible systematics of weak lensing studies. In this study, we present and compare two distinct algorithms for finding cosmic filaments and sheets, a task which is far less well established than the identification of dark matter halos or voids. One method is based on the smoothed dark matter density field and the other uses the halo distributions directly. We apply both techniques to one high-resolution N-body simulation and reconstruct the filamentary/sheet like network of the dark matter density field. We focus on investigating the properties of the dark matter halos inside these structures, in particular, on the directions of their spins and the orientation of their shapes with respect to the directions of the filaments and sheets. We find that both the spin and the major axes of filament halos with masses 1013 h -1 M are preferentially aligned with the direction of the filaments. The spins and major axes of halos in sheets tend to lie parallel to the sheets. There is an opposite mass dependence of the alignment strength for the spin (negative) and major (positive) axes, i.e. with increasing halo mass the major axis tends to be more strongly aligned with the direction of the filament, whereas the alignment between halo spin and filament becomes weaker with increasing halo mass. The alignment strength as a function of the distance to the most massive node halo indicates that there is a transit large-scale environment impact: from the two-dimensional collapse phase of the filament to the three-dimensional collapse phase of the cluster/node halo at small separation. Overall, the two algorithms for filament/sheet identification investigated here agree well with each other. The method based on halos alone can be easily adapted for use with observational data sets.
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Superamphiphobic (both superhydrophobic and superoleophobic) surfaces have attracted great interests in the fundamental research and practical application. This research successfully ...fabricated the superamphiphobic surfaces by combining the nickel plating process and modification with perfluorocaprylic acid. The cooperation of hierarchical micro-nano structures and perfluorocaprylic acid with low surface energy plays an important role in the formation of superamphiphobic surfaces. The contact angles of water/oil have reached up to 160.2±1°/152.4±1°, respectively. Contrast with bare substrate, the electrochemical measurements of superamphiphobic surfaces, not only the EIS measurement, but also potentiodynamic polarization curves, all revealed that, the surface corrosion inhibition was improved significantly. Moreover, superamphiphobic surfaces exhibited superior stability in the solutions with a large pH range, also could maintain excellent performance after storing for a long time in the air. This method is easy, feasible and effective, and could be used to fabricate large-area mutli-functional surface. Such a technique will develop a new approach to fabricate superamphiphobic surfaces on different engineering materials.
•Constructed a new CRVI for red vegetation extraction.•Proposed an enhanced semi-automatic PVC algorithm.•The optimal PVIs reflected the phenological differences of vegetation.•The developed ...classification model had spatio-temporal stability and scalability.
Coastal salt marshes, as a globally significantintertidal ecosystem, are highly productive but extremely fragile and unstable. Mapping coastal salt marshes accurately is the basis of assessing global climate change, biological invasion, and coastal erosion. Using Landsat 8 images, this paper integrated the advantages of pixel- and phenology-based algorithms and vegetation indices in vegetation classification. An enhanced phenology-based vegetation index classification (PVC) algorithm is proposed to obtain the spatial distribution and community composition of coastal salt marshes in Bohai Sea of China accurately and quickly. The results showed that (1) the coastal redness vegetation index (CRVI) can be used to extract Suaeda spp. effectively, and the phenology-based vegetation indices (PVIs) dataset can alleviate the spatial variability of phenology in coastal salt marshes; (2) the crucial phenological periods for identifying coastal salt marshes are May, October, and November, and the optimal PVIs are consistent with the phenological characteristics of salt marshes; (3) during the year 2018–2019, the overall accuracy (OA) of the PVC algorithm in Yancheng coast of Jiangsu Province and Bohai Sea coast reached 80.49 % and 90.8 % respectively. A total of 14,763.39 ha of salt marshes were found in the coastal area of Bohai Sea, and Shandong Province had the most abundant types of salt marshes and the largest area; (4) the classification model based on the PVC algorithm is stable and scalable in 2016–2017 and 2020–2021, with the OA of 89.19% and 86.67% respectively. These results demonstrate the value of the PVC algorithm in vegetation classification, and this study can provide a referable semi-automatic vegetation classification method for other coastal areas.
PS16dtm was classified as a candidate tidal disruption event in a dwarf Seyfert 1 galaxy with a low-mass black hole ( ) and has presented various intriguing photometric and spectra characteristics. ...Using the archival Wide-field Infrared Survey Explorer and the newly released NEOWISE data, we found that PS16dtm is experiencing a mid-infrared (MIR) flare that started ∼11 days before the first optical detection. Interpreting the MIR flare as a dust echo requires close pre-existing dust with a high covering factor and suggests that the optical flare may have brightened slowly for some time before it became bright detectable from the ground. More evidence is given at the later epochs. At the peak of the optical light curve, the new inner radius of the dust torus has grown to a much larger size (i.e., a factor of seven of the initial radius) due to the strong radiation field. At ∼150 days after the first optical detection, the dust temperature has dropped well below the sublimation temperature. Other peculiar spectral features shown by PS16dtm are the transient, prominent Fe ii emission lines and outflows indicated by broad absorption lines detected during the optical flare. Our model explains the enhanced Fe ii emission from iron that is newly released from the evaporated dust. The observed broad absorption line outflow could be explained by accelerated gas in the dust torus due to the radiation pressure.
ABSTRACT We study how halo intrinsic dynamical properties are linked to their formation processes for halos in two mass ranges, and , and how both are correlated with the large-scale tidal field ...within which the halos reside at present. We identify infall halos that are about to merge with their hosts. We find that the tangential infall velocity increases significantly with the strength of the tidal field, but no strong correlation is found for the radial component. These results can be used to explain the environmental dependence of internal velocity anisotropy and spin of halos. The position vectors and velocities of infall halos are aligned with the principal axes of the tidal field, and the alignment depends on the strength of the tidal field. Opposite accretion patterns are found in weak and strong tidal fields, showing that in a weak field the accretion flow is dominated by radial motion within the local structure, while a large tangential component is present in a strong field. These findings can be used to understand the strong alignments we find between the principal axes of the internal velocity ellipsoids of halos and the tidal field, and their dependence on the strength of the tidal field. We further find that only in weak tidal fields does the spin-tidal field alignment follow the prediction of the tidal torque theory. We discuss how our results may be used to understand the spins of disk galaxies and velocity structures of elliptical galaxies and their correlations with large-scale structure.
Abstract
We extend the halo-based group finder developed by Yang et al. (2005c) to use data
simultaneously
with either photometric or spectroscopic redshifts. A mock galaxy redshift survey ...constructed from a high-resolution
N
-body simulation is used to evaluate the performance of this extended group finder. For galaxies with magnitude z ≤ 21 and redshift 0 <
z
≤ 1.0 in the DESI legacy imaging surveys (the Legacy Surveys), our group finder successfully identifies more than 60% of the members in about 90% of halos with mass ≳10
12.5
h
−1
M
⊙
. Detected groups with mass ≳10
12.0
h
−1
M
⊙
have a purity (the fraction of true groups) greater than 90%. The halo mass assigned to each group has an uncertainty of about 0.2 dex at the high-mass end ≳10
13.5
h
−1
M
⊙
and 0.45 dex at the low-mass end. Groups with more than 10 members have a redshift accuracy of ∼0.008. We apply this group finder to the Legacy Surveys DR8 and find 6.4 million groups with at least three members. About 500,000 of these groups have at least 10 members. The resulting catalog containing 3D coordinates, richness, halo masses, and total group luminosities is made publicly available.
The high performance gel polymer electrolytes (GPEs) based on remarkable heat-resistant composite nanofiber membrane composed of polyetherimide (PEI) and halloysite nanotubes (HNTs) were obtained ...through the activation of stacked membranes immersed into liquid electrolyte. The crystallization behavior, microstructure and thermal stability of nanofiber membranes were analyzed. The HNT/PEI composite nanofiber membranes showed the sufficient porosity and good affinity between the nanofibers and the electrolyte as well as the electrode, which led to a superb saturated electrolyte uptake and conservation rate. Thus, the GPEs involving the HNT/PEI composite nanofiber membranes displayed excellent electrochemical performances, such as high ionic conductivity, adequate lithium-ion transference number, good interfacial stability and cycle performance. In particular, the GPEs based on 1wt% HNT/PEI nanofiber membranes demonstrated high ionic conductivity of 5.30×10−3Scm−1 and low interfacial resistance of 180Ω. In addition, in contrast with the Li/GPE/LiCoO2 cells containing the commercial Celgard 2500, the assembled cells with the 1wt% HNT/PEI nanofiber membranes possessed outstanding initial discharge capacity, cycle performance and C-rate capability. Consequently, the GPEs involving HNT/PEI heat-resistant skeleton materials can satisfy the high-performance requirements of energy storage devices.
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•The halloysite nanotube (HNT)/polyetherimide (PEI) composite nanofiber membranes possessed the remarkable thermal stability.•The gel polymer electrolyte (GPEs) based on the HNT/PEI composite nanofiber membranes presented high ionic conductivity of 5.30×10−3Scm−1.•The GPEs with optimized HNT/PEI nanofiber membranes delivered high capacity retention of 94% after 50 cycles.•The GPEs involving superior heat-resistant materials can satisfy high-performance requirements of energy storage devices.
Our research objective in this paper is to reconstruct an initial linear density field, which follows the multivariate Gaussian distribution with variances given by the linear power spectrum of the ...current cold dark matter model and evolves through gravitational instabilities to the present-day density field in the local universe. For this purpose, we develop a Hamiltonian Markov Chain Monte Carlo method to obtain the linear density field from a posterior probability function that consists of two components: a prior of a Gaussian density field with a given linear spectrum and a likelihood term that is given by the current density field. The present-day density field can be reconstructed from galaxy groups using the method developed in Wang et al. Using a realistic mock Sloan Digital Sky Survey DR7, obtained by populating dark matter halos in the Millennium simulation (MS) with galaxies, we show that our method can effectively and accurately recover both the amplitudes and phases of the initial, linear density field. To examine the accuracy of our method, we use N-body simulations to evolve these reconstructed initial conditions to the present day. The resimulated density field thus obtained accurately matches the original density field of the MS in the density range 0.3 lap rho/rho lap 20 without any significant bias. In particular, the Fourier phases of the resimulated density fields are tightly correlated with those of the original simulation down to a scale corresponding to a wavenumber of ~1 h Mpc super(-1), much smaller than the translinear scale, which corresponds to a wavenumber of ~0.15 h Mpc super(-1).
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