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Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene(pTFe)

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Friction 2024年第5期12卷 997-1015页

作者： pontus JOHANSSON p.MARKLUND M.BJORLING Y.SHI Division of Machine element LuleåUniversity of TechnologyLuleåSE-97187Sweden

Carbon fiber reinforced polytetrafluoroethylene (CF/pTFe) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/pTFe, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/pTFe sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/pTFe surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/pTFe surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm coul

关键词： polymer composite tribofilm tribochemistry atmosphere

Fuel cell stack design and modelling with a double-stage boost converter coupled to a single-phase inverter

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CLeAN eNeRGY 2024年第1期8卷 188-196页

作者： elnagi, Basem e. Ismaiel, Ahmed M. Mansour, Hany S. e. Abd-Alwahab, M. N. Suez Canal Univ Fac Engn Elect Engn Dept Ismailia 41522 Egypt

A comprehensive proton-exchange membrane fuel cell stack model was developed and integrated with a two-stage DC/DC boost converter. It was directly coupled to a single-phase (two levels-four pulses) inverter without a transformer. The pulse-width modulation signal was used to independently regulate every converter phase. The converter was modelled using a MATLAB (R)/Simulink (R) environment and an appropriate voltage control method. The analysis features of the suggested circuit were created and, through established experiments, the simulation results were verified. A single-phase (two levels-four pulses) inverter control circuit was tested and it produced a pure sinusoidal waveform with voltage control. It matches the voltage of the network in terms of amplitude and frequency. A sinusoidal pulse-width modulation approach was performed using a single-phase (two levels-four pulses) pulse-width modulation inverter. The results demonstrated an enhancement in the standard of the output wave and tuned the dead time with a reduction of 63 mu s compared with 180 mu s in conventional techniques. A comprehensive model of a proton-exchange membrane fuel cell stack is integrated with a single-phase (two levels-four pulses) inverter without a transformer. pulse-width modulation is used to independently regulate every converter phase. As a result, the dead time is reduced compared to conventional techniques. Graphical Abstract

关键词： peM fuel cell pulse-width modulation single-phase inverter and double-stage DC/DC boost converter peRFORMANCe SYSTeM

eco-toxicity and health risk assessment of polycyclic aromatic hydrocarbons in surface sediments of Burullus Lake in egypt

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China Geology 2024年第3期7卷 460-468页

作者： Hanan e Osman Mohamed H e el-Morsy Hazem T Abd el-Hamid Department of Biology Faculty of Applied ScienceUmm Al-Qura UniversityMecca 24382Saudi Arabia Deanship of Scientific Research Umm Al-Qura UniversityMakkah 24372Saudi Arabia National Institute of Oceanography and Fisheries(NIOF) Cairo 11865Egypt Botany and Microbiology Department Faculty of ScienceAl-Azhar UniversityCairo 11651Egypt

polycyclic aromatic hydrocarbons(pAHs)are ubiquitous environmental contaminants of growing concern due to their potential ecological and human health *** study presents a comprehensive assessment of pAHs contamination in the surface sediments of Burullus Lake,a vital and second largest delta lake in *** aim was to evaluate the eco-toxicity and potential health risks associated with the presence of these *** seven sediment samples were collected from various drains in the southern part of Burullus *** extraction method was employed to extract pAHs(16pAHs)from the sediment ***,target compounds were located using *** results showed that samples contained pAHs levels ranging from 0.038×10^(-6)to 0.459×10^(-6),which is considered heavily polluted by the european standard for pAHs ***,there was no apparent source of pAHs in the elKhashah drain or the Brinbal Canal,as HpLC found none of the *** most prevalent compound in sediment samples along the study area was *** diagnostic indices in the present study indicated that the hydrocarbons in the region originated from pyrolytic and man-made sources along the drains of Burullus *** principal component analysis(pCA)and diagnostic ratios revealed that coal combustion and pyrolytic sources were responsible for the pAHs contamination in the surface *** non-carcinogenic risk(HI),which is the product of the HQs for the adult and child populations,respectively,was *** values under 1,therefore,demonstrated that they had no carcinogenic effects on human *** and MeQs in the sediments of Burullus Lake do not have a cancer-causing impact on *** the safety of nearby wildlife,aquatic life,and people,all activities that raise petroleum hydrocarbon levels in Burullus Lake must be adequately regulated and *** to the ecological risk assessment,there is little chance that pAHs will be found

关键词： polycyclic aromatic hydrocarbons Diagnostic indices Toxicity Delta lake sediment Burullus Lake Human health risk Aquatic ecosystem HpLC Coal combustion

Biocompatible Biphasic Iontronics enable Neuron-Like Ionic Signal Transmission

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Research 2024年第3期2024卷 795-796页

作者： Xiaoyi Wang Aleksandar p.Ivanov Joshua B.edel Department of Chemistry Imperial College LondonMolecular Sciences Research HubLondon W12 OBZUK

Biocompatible connections between external artificial devices and living organisms show promise for future neuroprosthetics and *** study in Science by Zhao and colleagues introduces a cascade-heterogated biphasic gel(HBG)iontronic device,which facilitates electronic-to-multi-ionic signal transduction for abiotic–biotic *** by neuron signaling,the HBG device demonstrated its biocompatibility by regulating neural activity in biological tissue,paving the way for wearable and implantable devices,including brain–computer interfaces.

关键词： asi Signal Neuron

Jigsaw-Sketch: a fast and accurate algorithm for finding top-k elephant flows in high-speed networks

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Science China(Information Sciences) 2024年第4期67卷 113-130页

作者： Boyu ZHANG He HUANG Yu-e SUN Yang DU Dan WANG School of Computer Science and Technology Soochow University School of Rail Transportation Soochow University

Finding top-k elephant flows in high-speed networks is one of the most fundamental network measurement tasks. It is more challenging than per-flow size estimation since the IDs and sizes of top-k flows must be tracked simultaneously. Most existing studies only record the IDs of a small number of elephant flows to fit their estimators in the extremely limited high-speed on-chip memory. However, these solutions need too many memory accesses when a packet arrives to track the elephant flows with high accuracy, which limits their practicability. Therefore, this paper proposes Jigsaw-Sketch, a new algorithm to find the top-k elephant flows with much fewer memory accesses while achieving high memory efficiency and accuracy. In this design, we propose a novel two-stage jigsaw storage scheme, which can capture the candidate top-k flows from massive network steams efficiently, and further find the top-k elephant flows with high memory efficiency and only a few memory accesses for each packet. extensive experimental results based on real network traces show that Jigsaw-Sketch improves the packet processing throughput by at least 86%, while achieving smaller memory footprints and higher accuracy compared to the SOTA.

关键词： sketch top-$k$ network measurement elephant flow high-speed networks

2024 Wheelchair Compendium of physical Activities:An update of activity codes and energy expenditure values

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Journal of Sport and Health Science 2024年第1期13卷 18-23页

作者： Scott A.Conger Stephen D.Herrmann erik A.Willis Tom e.Nightingale Joseph R.Sherman Barbara e.Ainsworth Department of Kinesiology Boise State UniversityBoiseID 83725USA Kansas Center for Metabolism and Obesity Research The University of Kansas Medical CenterKansas CityKS 66160USA Center for Health promotion and Disease prevention University of North Carolina at Chapel HillChapel HillNC 27599USA School of Sport Exercise and Rehabilitation SciencesUniversity of BirminghamBirmingham AL B152TTUK Centre for Trauma Sciences Research University of BirminghamEdgbastonBirmingham AL B152TTUK College of Health Solutions Arizona State UniversityPhoenixAZ 85003USA School of exercise and Health Shanghai University of SportShanghai 200438China

purpose:This paper presents an update of the 2011 Wheelchair Compendium of physical Activities designed for wheelchair users and is referred to as the 2024 Wheelchair *** Wheelchair Compendium aims to curate existing knowledge of the energy expenditure for wheelchair physical activities(pAs).Methods:A systematic review of the published energy expenditure of pA for wheelchair users was completed between 2011 and May *** added these data to the 2011 Wheelchair Compendium data that was compiled previously in a systematic review through ***:A total of 47 studies were included,and 124 different wheelchair pA reported energy expenditure values ranging from 0.8 metabolic equivalents for wheelchair users(filing papers,light effort)to 11.8 metabolic equivalents for wheelchair users(Nordic sit skiing).Conclusion:In introducing the updated 2024 Wheelchair Compendium,we hope to bridge the resource gap and challenge the prevailing narratives that inadvertently exclude wheelchair users from physical fitness and health pAs.

关键词： Disability exercise MeT Mobility

New insights into the role of the endoplasmic reticulum in microglia

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Neural Regeneration Research 2024年第7期19卷 1397-1398页

作者： Veronika e.Neubrand M.Rosario Sepúlveda Department of Cell Biology Faculty of SciencesUniversity of GranadaGranadaSpain

Microglial cells are the only resident immune cells in the central nervous system and constitute its frontline *** are extremely reactive against infections,trauma,or toxins,but are also responsible for mediating inflammation,taking part in the pathogenic course of many neuropathologies(Sierra et al.,2019).Cell-specific staining,ultrastructural analysis by transmission electron microscopy(TeM),or two-photonmicroscopy imaging have been relevant for the characterization of microglia as well as their cell-cell interactions。

关键词： inflammation reticulum

HVOF-sprayed HAp/S53p4 BG composite coatings on an AZ31 alloy for potential applications in temporary implants

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Journal of Magnesium and Alloys 2024年第1期12卷 345-360页

作者： Carlos A.poblano-Salas John Henao Astrid L.Giraldo-Betancur paola Forero-Sossa Diego German espinosa-Arbelaez Jorge A.González-Sánchez Luis R.Dzib-pérez Susana T.estrada-Moo Idelfonso e.pech-pech CIATeQ A.C. Av.Manantiales 23-AParque Industrial Bernardo QuintanaEl MarquésQuerétaro 76246Mexico CONAHCYT-CIATeQ A.C. Av.Manantiales 23-AParque Industrial Bernardo QuintanaEl MarquésQuerétaro 76246Mexico CONAHCYT-Cinvestav Libramiento Norponiente#2000.Fraccionamiento Real de JuriquillaQuerétaro 76230Mexico Universidad Tecnológica de Querétaro Av.Pie de la Cuesta N°2501Querétaro 76148Mexico CIDeSI Av.Playa Pie de la Cuesta No 702Col.San PabloQuerétaro 76125Mexico Center for Corrosion Research Autonomous University of CampecheAv.Héroe de Nacozari No.480P.C.24070San Francisco de CampecheCam.Mexico

Bioactive thermal spray coatings produced via high-velocity oxygen fuel spray(HVOF)from hydroxyapatite(HAp)and bioactive glasses(BG)have the potential to be employed on temporary implants due to the ability of both HAp and BG to dissolve and promote osseointegration,considering that both phases have different reaction and dissolution rates under in-vitro *** the present work,75%***-25%wt.S53p4 bioactive glass powders were HVOF-sprayed to obtain HAp/S53p4 BG composite coatings on a bioresorbable AZ31 *** study is focused on exploring the effect of the stand-off distance and fuel/oxygen ratio variation as HVOF parameters to obtain stable structural coatings and to establish their effect on the phases and microstructure produced in those *** characterization techniques,such as scanning electron microscopy,X-ray diffraction,and Fourier transform infrared spectroscopy,were employed to characterize relevant structural and microstructural properties of the composite *** results showed that thermal gradients during coating deposition must be managed to avoid delamination due to the high temperature achieved(max 550℃)and the differences in coefficients of thermal *** was also found that both spraying distance and oxygen/fuel ratio allowed to keep the hydroxyapatite as the main phase in the *** addition,in-vitro electrochemical studies were performed on the obtained HAp/S53p4 BG composite coatings and compared against the uncoated AZ31 *** results showed a significant decrease in hydrogen evolution(at least 98%)when the bioactive coating was applied on the Mg alloy during evaluation in simulated body fluid(SBF).

关键词： Coatings Composites Thermal spray Temporary implants Hydrogen evolution

Mitochondrial recruitment in myelin:an anchor for myelin dynamics and plasticity?

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Neural Regeneration Research 2024年第7期19卷 1401-1402页

作者： Jean-David M.Gothié Timothy e.Kennedy Department of Neurology and Neurosurgery Montreal Neurological InstituteMcGill UniversityMontrealQCCanada

Optimal propagation of neuronal electrical impulses depends on the insulation of axons by myelin,produced in the central nervous system by *** is an extension of the oligodendrocyte plasma membrane,which wraps around an axon to form a compact multi-layered *** is composed of a substantially higher proportion of lipids compared to other biological membranes and enriched in a small number of specialized proteins.

关键词： plasticity insulation dynamics