Reducing Pt in proton exchange membrane fuel cells is the subject of intense research and development. Recently, researchers have observed significant performance loss due to a transport limitation ...at the Pt surface. This is investigated here with loading studies that fix electrode thickness and bulk properties. Within these layers, the impact of Pt dispersion is probed by varying the wt% of Pt/C while holding Pt loading and electrode thickness constant by diluting with carbon, effectively varying the average distance between Pt particles while maintaining gas phase loss in the catalyst layer. Results elucidate how the electrode structure impacts local transport loss. It is demonstrated that local transport loss is not fully captured with a normalized Pt area. Additional geometric considerations that account for ionomer surface area relative to the Pt particles are required to resolve performance loss at low Pt loading as electrode structure varies. Furthermore, within this ionomer layer an interfacial resistance at both the gas and Pt interfaces are necessary to account for performance trends observed. These results demonstrate that residual performance loss associated with low cathode Pt loading can be mitigated by electrode design, where oxygen flux through the gas/ionomer interface to the Pt surface is minimized.
Extensive real-data indicate that human motion exhibits novel patterns and has a significant impact on the epidemic spreading process. The research on the influence of human motion patterns on ...epidemic spreading dynamics still lacks a systematic study in network science. Based on an agent-based model, this paper simulates the spread of the disease in the gathered population by combining the susceptible-infected-susceptible epidemic process with human motion patterns, described by moving speed and gathering preference. Our simulation results show that the emergence of a hysteresis loop is observed in the system when the moving speed is slow, particularly when humans prefer to gather; that is, the epidemic prevalence of the systems depends on the fraction of initial seeds. Regardless of the gathering preference, the hysteresis loop disappears when the population moves fast. In addition, our study demonstrates that there is an optimal moving speed for the gathered population, at which the epidemic prevalence reaches its maximum value.
Polymer-electrolyte fuel cells are a promising energy-conversion technology. Over the last several decades significant progress has been made in increasing their performance and durability, of which ...continuum-level modeling of the transport processes has played an integral part. In this review, we examine the state-of-the-art modeling approaches, with a goal of elucidating the knowledge gaps and needs going forward in the field. In particular, the focus is on multiphase flow, especially in terms of understanding interactions at interfaces, and catalyst layers with a focus on the impacts of ionomer thin-films and multiscale phenomena. Overall, we highlight where there is consensus in terms of modeling approaches as well as opportunities for further improvement and clarification, including identification of several critical areas for future research.
The flow shop scheduling problem has been widely studied in recent years, but the research on multi-objective flow shop scheduling with green indicators is still relatively limited. It is urgent to ...strengthen the research on effective methods to solve such interesting problems. To consider the economic and environmental factors simultaneously, the paper investigates the multi-objective permutation flow shop scheduling problems (MOPFSP) which minimizes the makespan and total carbon emissions. Since MOPFSP is proved to be a NP-hard problem for more than two machines. A hybrid cuckoo search algorithm (HCSA) is proposed to solve the problems. Firstly, a largest-order-value method is proposed to enhance the performance of HCS algorithm in the solution space of MOPFSP. Then, an adaptive factor of step size is designed to control the search scopes in the evolution phases. Finally, a multi-neighborhood local search rule is addressed in order to find the optimal sub-regions obtained by the HCSA. Numerical experiments show that HCSA can solve MOPFSP efficiently.
Abstract
Acquired resistance to glucocorticoids (GCs) is an obstacle to the effective treatment of leukemia, but the molecular mechanisms of steroid insensitivity have not been fully elucidated. In ...this study, we established an acquired GC-resistant leukemia cell model and found a long noncoding RNA, HOTAIRM1, was overexpressed in the resistant cells by transcriptional profiling, and was higher expressed in patients with poor prognosis. The whole-genome-binding sites of HOTAIRM1 were determined by ChIRP-seq (chromatin isolation by RNA purification combined with sequencing) analysis. Further study determined that HOTAIRM1 bound to the transcriptional inhibitory region of ARHGAP18 and repressed the expression of ARHGAP18, which led to the increase of RHOA/ROCK1 signaling pathway and promoted GC resistance through antiapoptosis of leukemia cells. The inhibition of ROCK1 in GC-resistant cells could restore GCs responsiveness. In addition, HOTAIRM1 could also act as a protein sequester to prevent transcription factor AML1(acute myeloid leukemia 1) from binding to the regulatory region of ARHGAP18 by interacting with AML1. At last, we also proved AML1 could directly activate the expression of HOTAIRM1 through binding to the promoter of HOTAIRM1, which enriched the knowledge on the regulation of lncRNAs. This study revealed epigenetic causes of glucocorticoid resistance from the perspective of lncRNA, and laid a foundation for the optimization of glucocorticoid-based leukemia treatment strategy in clinic.
This study aimed to investigate the metabolic changes in globus pallidus (GP) and substantia nigra (SN) during the early stage of Parkinson disease (PD) using magnetic resonance spectroscopy (MRS). ...PubMed, Embase, Web of Science, and Chinese National Knowledge Infrastructure were searched till November 2018. Eligible trials comparing early metabolic changes in GP and SN in patients with PD vs. controls were included. The mean differences with 95% confidence intervals were estimated with either fixed- or random-effects models using Review Manager 5.3 software. Trial sequential analysis was performed using TSA 0.9.5.10 beta software. Finally, 16 studies were selected from the search. Overall, the
N
-acetyl aspartate-to-creatine ratio showed a significant difference between patients with early-stage PD and healthy controls. The overall heterogeneity was
P
< 0.00001,
I
2
= 94% in GP and
P
= 0.0002,
I
2
= 74% in SN. The results revealed that MRS could be a more sensitive imaging biomarker in the diagnosis of early-stage PD.
Systematic Review Registration
https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=125731
, registration number: CRD42019125731.
In this paper, the effect of repair welding heat input on microstructure, residual stresses, and stress corrosion cracking (SCC) sensitivity were investigated by simulation and experiment. The ...results show that heat input influences the microstructure, residual stresses, and SCC behavior. With the increase of heat input, both the
-ferrite in weld and the average grain width decrease slightly, while the austenite grain size in the heat affected zone (HAZ) is slightly increased. The predicted repair welding residual stresses by simulation have good agreement with that by X-ray diffraction (XRD). The transverse residual stresses in the weld and HAZ are gradually decreased as the increases of heat input. The higher heat input can enhance the tensile strength and elongation of repaired joint. When the heat input was increased by 33%, the SCC sensitivity index was decreased by more than 60%. The macroscopic cracks are easily generated in HAZ for the smaller heat input, leading to the smaller tensile strength and elongation. The larger heat input is recommended in the repair welding in 304 stainless steel.
The oxygen reduction reaction (ORR) kinetics of a high-surface-area carbon-supported platinum catalyst (Pt/C) were measured in an operating proton exchange membrane fuel cell (PEMFC). The ORR ...kinetics of Pt/C can be described over a wide range of temperature, pressure, and current density using four catalyst-specific parameters: transfer coefficient, exchange current density, reaction order with respect to oxygen partial pressure, and activation energy. These parameters were extracted using a combined kinetic and thermodynamic model, either referenced to the reversible cell potential (i.e., using exchange current density as activity parameter) or referenced to a constant ohmic-resistance-corrected (i.e., iR-free) cell voltage. The latter has the advantage of using an activity parameter (activity at 0.9 V iR-free cell voltage) which can be measured explicitly without extrapolation, in contrast to the exchange current density required in the former model. It was found that much of the variation in the published values for these catalyst-specific kinetic parameters derives from applying the same parameter name (e.g., activation energy) without specifying which of its many possible definitions is being used. The obviously significant numerical differences both for "oxygen reaction order" and for "activation energy" due to different definitions (often tacitly assumed and rarely explicitly stated in the literature) are illustrated by the kinetic ORR parameters which we determined for Pt/C: (i) at zero overpotential, where reaction order and activation energy are -0.5 and 67 kJ/mol, respectively, and (ii) at 0.9 V iR-free cell voltage, where reaction order and activation energy are -0.75 and 10 kJ/mol, respectively.
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