4,743 research outputs found
Simulation of the Oxygen Reduction Reaction (ORR) Inside the Cathode Catalyst Layer (CCL) of Proton Exchange Membrane Fuel Cells Using the Kinetic Monte Carlo Method
In this paper, a numerical model of the kinetic Monte Carlo (KMC) method has been developed to study the oxygen reduction reaction (ORR) that occurs inside the cathode catalyst layer (CCL). Firstly, a 3-D model of the CCL that consists of Pt and carbon spheres is built using the sphere packing method; secondly, an efficient procedure of the proton-oxygen reaction process is developed and simulated. In the proton-oxygen reaction process, all of the continuous movements of protons and oxygen are considered. The maximum reaction distance is determined to be 8 Å. The input pressures of protons and oxygen are represented by the number of spheres of the species. The value of the current density is calculated based on the amount of reaction during the interval time. Indications are that the results of the present model match reasonably well with the published results. A new way to apply the KMC method in the proton exchange membrane fuel cell (PEMFC) research field is developed in this paper
How does the development of fintech affect financial efficiency? Evidence from China
The rapid development of fintech is transforming the global financial
system. However, how does fintech impact financial efficiency?
Based on the technology spillover theory, this study analysed the
theoretical mechanism of fintech’s impact on financial efficiency and
used the text mining method to construct a fintech level index for
each province in China. Using interprovincial panel data from 2008
to 2018, the study empirically tested the relationship between fintech
development and financial efficiency. The results show that
technology spillover theory can adequately explain the impact of
financial technology on financial efficiency and that there is a Ushaped
nonlinear relationship between fintech development and
financial efficiency. Further analysis shows that financial decentralisation
moderates the marginal effect of fintech on financial efficiency.
The effect of fintech on financial efficiency is more significant in
regions with greater financial decentralisation. Therefore, at this
stage, the study recommends that we actively embrace fintech, continuously
deepen the integration of technology and finance, promote
improvement in financial efficiency, and expand the positive
role of local governments in technological innovation
Dimensions of fractals related to languages defined by tagged strings in complete genomes
A representation of frequency of strings of length K in complete genomes of
many organisms in a square has led to seemingly self-similar patterns when K
increases. These patterns are caused by under-represented strings with a
certain "tag"-string and they define some fractals when K tends to infinite.
The Box and Hausdorff dimensions of the limit set are discussed. Although the
method proposed by Mauldin and Williams to calculate Box and Hausdorff
dimension is valid in our case, a different and simpler method is proposed in
this paper.Comment: 9 pages with two figure
Hypersonic Vehicles Profile-Following Based on LQR Design Using Time-Varying Weighting Matrices
In the process of applying linear quadratic regulator (LQR) to solve aerial vehicle reentry reference trajectory guidance, to obtain better profile-following performance, the parameters of the aerial vehicle system can be used to calculate weighting matrices according to the Bryson principle. However, the traditional method is not applicable to various disturbances in hypersonic vehicles (HSV) which have particular dynamic characteristics. By calculating the weighting matrices constructed based on Bryson principle using time-varying parameters, a novel time-varying LQR design method is proposed to deal with the various disturbances in HSV reentry profile-following. Different from the previous approaches, the current states of the flight system are employed to calculate the parameters in weighting matrices. Simulation results are given to demonstrate that using the proposed approach in this chapter, performance of HSV profile-following can be improved significantly, and stronger robustness against different disturbances can be obtained
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Cryo-EM structure of a fungal mitochondrial calcium uniporter.
The mitochondrial calcium uniporter (MCU) is a highly selective calcium channel localized to the inner mitochondrial membrane. Here, we describe the structure of an MCU orthologue from the fungus Neosartorya fischeri (NfMCU) determined to 3.8 Å resolution by phase-plate cryo-electron microscopy. The channel is a homotetramer with two-fold symmetry in its amino-terminal domain (NTD) that adopts a similar structure to that of human MCU. The NTD assembles as a dimer of dimers to form a tetrameric ring that connects to the transmembrane domain through an elongated coiled-coil domain. The ion-conducting pore domain maintains four-fold symmetry, with the selectivity filter positioned at the start of the pore-forming TM2 helix. The aspartate and glutamate sidechains of the conserved DIME motif are oriented towards the central axis and separated by one helical turn. The structure of NfMCU offers insights into channel assembly, selective calcium permeation, and inhibitor binding
Pressure induced superconductivity bordering a charge-density-wave state in NbTe4 with strong spinorbit coupling
Transition-metal chalcogenides host various phases of matter, such as
charge-density wave (CDW), superconductors, and topological insulators or
semimetals. Superconductivity and its competition with CDW in low-dimensional
compounds have attracted much interest and stimulated considerable research.
Here we report pressure induced superconductivity in a strong spin-orbit (SO)
coupled quasi-one-dimensional (1D) transition-metal chalcogenide NbTe,
which is a CDW material under ambient pressure. With increasing pressure, the
CDW transition temperature is gradually suppressed, and superconducting
transition, which is fingerprinted by a steep resistivity drop, emerges at
pressures above 12.4 GPa. Under pressure = 69 GPa, zero resistance is
detected with a transition temperature = 2.2 K and an upper critical
field = 2 T. We also find large magnetoresistance (MR) up to 102\% at
low temperatures, which is a distinct feature differentiating NbTe from
other conventional CDW materials.Comment: https://rdcu.be/LX8
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